path: root/67844-0.txt

*** START OF THE PROJECT GUTENBERG EBOOK 67844 ***

Transcriber’s Notes:

  Underscores “_” before and after a word or phrase indicate _italics_
    in the original text.
  Equal signs “=” before and after a word or phrase indicate =bold=
    in the original text.
  Small capitals have been converted to SOLID capitals.
  Illustrations have been moved so they do not break up paragraphs.
  Typographical and punctuation errors have been silently corrected.




                          Hoisting Appliances

                                  By
                             I.C.S. STAFF

                               HOISTING
                               Parts 3-4

                                  447
                             Published by
                    INTERNATIONAL TEXTBOOK COMPANY
                             SCRANTON, PA.




                       Hoisting, Parts 3 and 4:

                           Copyright, 1906,
                  by INTERNATIONAL TEXTBOOK COMPANY.

                  Entered at Stationers’ Hall, London

                          All rights reserved

                          Printed in U. S. A.

                     INTERNATIONAL TEXTBOOK PRESS
                             Scranton, Pa.




CONTENTS

      NOTE.--This book is made up of separate parts,
      or sections, as indicated by their titles, and the page
      numbers of each usually begin with 1. In this list of
      contents the titles of the parts are given in the order in
      which they appear in the book, and under each title is a
      full synopsis of the subjects treated.


                       HOISTING, PART 3
                                                           _Pages_
    Hoisting Appliances                                      1-43

    Hoist Indicators                                          1-5
    Column indicators; Dial indicators; Special indicators.

    Drums and Reels                                          6-20

    Cylindrical Drums                                         7-8

    Conical Drums                                            9-16
    Hoisting with cylindrical drums; Hoisting with conical
    drums; Comparison of cylindrical and conical drums.

    Flat Rope Reels                                         17-20

    Rope Wheels                                             21-26
    Koepe system; Whiting system; Modified Whiting system.

    Rope Fastenings                                            27

    Clutches                                                28-31
    Jaw clutch; Band friction clutches; Beekman friction
    clutch.

    Brakes                                                  32-43
       Block brake; Post brake; Strap brake; Differential
         brake; Power for brakes; Differential lever;
         Power brakes; Crank brake.

                       HOISTING, PART 4

    Hoisting Appliances                                      1-51

    Sheaves                                                   1-5
       Cast-iron sheave; Wood-lined sheaves; Diameter
          of sheave; Rollers and carrying sheaves.

    Cages for Vertical Shafts                                6-11
       Construction of cage; Safety catches;
          Multiple-deck cages.

    Automatic Dumping Cages                                 12-16
       Definition; Slope, or inclined shaft hoisting;
         Slope carriage.

    Skips, or Gunboats                                      17-22
       Definition; Method of loading skips; Method of
          dumping skips; Skip cage.

    Buckets                                                    23

    Car Locks                                               23-24

    Cage Guides                                                25

    Landing Fans, or Keeps                                  26-28
       Common forms of fans; Hydrostatic fans;
          Pneumatic fans; Cage chairs.

    Head-Frames                                             29-45
       Head-frames in general; Types of head-frames;
          Examples of various types; Head-frame
          specification.

    Detaching Hooks                                         46-47

    Signaling                                               48-51
       Hammer-and-plate signal; Electric bells;
          Speaking tubes; Pneumatic gong signal;
          Telephones.

                         HOISTING

    Serial 851C          (PART 3)          Edition 1




HOISTING APPLIANCES


HOIST INDICATORS

=1. The hoist indicator= is a mechanism attached to the drum shaft of a
hoisting engine to show the hoisting engineer the position of the cage
or skip in the shaft throughout the time of hoisting. The use of such
indicators is sometimes required by law, but there is a great diversity
of opinion as to the advisability of using them. The objections to them
are that they are liable to get out of order, and that in general the
use of any automatic device that tends to relieve the hoisting engineer
of responsibility and constant attention to his engine is not to be
commended. A hoisting engineer, however, depends for his stopping point
mainly on a mark made on the rope, or on the drum, or on both, and uses
an indicator mostly as a guide for the position of the cage during the
hoist.


TYPES OF INDICATORS

=2. Column Indicators.=--A very simple indicator, and one that was
formerly very commonly used, is made by inserting a pin into the
center of the end of the drum shaft and using this as a miniature
drum on which to wind and unwind a chain or cord, which corresponds
to the hoisting rope as the pin corresponds to the drum. This chain
or cord is led over a pulley placed at the top of a pair of guides,
representing the shaft, and carries at its end a weight, pointer, or
gong, representing the cage or car, as shown in Fig. 1.

[Illustration: FIG. 1]

[Illustration: FIG. 2] The different landings in the shaft are marked
on the guide; and as the pointer or gong rises and falls it indicates
the position of the cage in the shaft. If a gong is used, pointer
also may be added and the gong so arranged that it will ring at a
point some distance before the landing is reached and thus attract the
engineer’s attention. Indicators of this kind, though cheap and easily
constructed, are not reliable, for the cord and chain may stretch or
they may overlap in winding on the pin, or may bind in the pulley and
thus indicate a wrong position of the cage.

=3.= An indicator should have a positive motion and be driven by
gearing or by link belts. Fig. 2 shows a =column indicator= that
consists of a screw _a_ working inside of a slotted pipe _b_, which
may be of any length necessary. This screw is revolved by means of
the gears _c_, which are rotated by the sprocket wheel _d_. A nut _e_
travels up and down the screw _a_ and the pointer _f_ attached to the
nut indicates the position of the cage in the shaft. The pipe standard
_b_ is usually painted a dead black and the different levels may be
marked on it with chalk or white paint. Chalk marks are not safe, as
they may be tampered with and the engineer thus misled.

[Illustration: FIG. 3]

The pointer _a_, Fig. 3, is moved by the rotation of the screw shaft
_b_, which is revolved by the bevel gears _c_ and _d_. This indicator
also registers the number of hoists by means of the dials _e_, for
at each hoist the lower end of the pointer a engages a ratchet wheel
behind the two dial faces shown and thus registers on the dial.

[Illustration: FIG. 4]

=4. Dial Indicators.=--Fig. 4 shows a positive-motion indicator that is
operated as follows: A worm _a_ on the drum shaft _b_ engages with the
worm-wheel _c_ on the small shaft _d_ that is supported by the bearings
_e_. The pointer _f_ is rigidly attached to the shaft _d_ and revolves
in front of the properly marked dial _g_.

=5.= Fig. 5 shows a =dial indicator= attached to drum hoists where the
speed of rope is constant for each revolution. The wheel _a_ of this
indicator may be a worm-wheel working in a worm on the drum shaft, as
described in connection with the indicator shown in Fig. 4, or it may
be a sprocket wheel driven by a link belt from a sprocket wheel on a
drum, or it may be a gear-wheel driven directly from another gear-wheel
on the drum. The gear-wheels _b_ revolve a vertical shaft _c_ fitted
at the upper end with a worm _d_ that drives the worm-wheel _e_ placed
on the end of the pointer spindle. The different levels from which
hoisting is to be done may be painted on the dial, or better, they may
be placed on movable targets that are clamped to the dial and can thus
be moved as occasion requires.

[Illustration: FIG. 5]

    EXAMPLE.--An indicator is desired for a shaft 800
    feet deep at which the drum of the hoisting engine to be
    used is 10 feet in diameter; what ratio of gearing must be
    used so that the pointer will make one revolution during
    the hoist?

    SOLUTION.--The circumference of the drum is 31.42
    ft. (π_D_ = 10 × 3.1416 = 31.416 ft.); hence, the
    revolutions per hoist are 800 ÷ 31.42 = 25.46 revolutions.
    Then, if the pointer is to make one revolution per hoist,
    the ratio of the gearing will be 25.46 to 1. Ans.


=6. Special Indicators.=--One fault of nearly all indicators is that
they give a regular movement throughout the winding, and the space over
which the pointer travels is too small to enable the engineer to land
the cage accurately. Indicators have been made with a differential
motion to the pointer, the motion being greater at the time of landing
and less during the middle of the hoist. They are also made with two
pointers, one operating like the dial indicator above described and the
other remaining stationary during all the hoist but the last few feet,
when it moves around its circle.

[Illustration: (_a_) (_b_)

FIG. 6]

=7.= Where flat ropes are used or where round ropes wind on a conical
drum, the length of rope wound or unwound is different for each turn
of the drum. With all the indicators thus far described, while the
speed with which the indicator moves is proportional to the speed at
which the drum and the drum shaft revolve, it is not proportional to
the speed of the rope when winding and unwinding on a conical drum
or on a flat rope reel. Fig. 6 (_a_) and (_b_) shows two views of a
compensating dial indicator. By means of the spiral form of sheave
_c_, the hand _d_ is made to move equal distances around the disk _e_
for equal distances of cage movement in the shaft. The rope _f_ passes
about the spiral sheave and one end is attached at the small end _g_
of the spiral, while the other end is fastened to the periphery of the
sheave _h_, which takes its motion from the drum shaft or crank-shaft
of the hoisting engine by means of the bevel gear _i_. Consequently,
while the sheave _h_ has a regular motion dependent directly on the
revolution of the hoisting drum, the pointer _d_ moves irregularly,
depending on the position of the spiral sheave _c_; that is, whether
a small or large diameter of the spiral is presented to the rope. The
rope _j_ carrying the counterweight _k_ is attached to a small circular
drum _l_ that is on the same shaft as the spiral sheave. The purpose of
this cord and counterweight is to keep the indicator line _f_ taut and
to bring the indicator back to position as the cord _f_ unwinds from
the sheave _h_.

=8.= In order that the pointer may not stand at exactly the same point
on the dial when the cage is at the top and at the bottom, and so that
the engineer may be able to distinguish between the top and the bottom
positions of the cage by the pointer, the ratio of the gearing is
usually increased by allowing one or two extra teeth on the worm-wheel.
In the example in Art. =5=, assume a ratio of 27: 1; that is, if a
worm-gear is used, the worm-wheel will have 27 teeth.

If the pitch of the teeth is ¾ inch, the circumference of the pitch
circle will be ¾ × 27 = 20.25 inches and the diameter 6.44 inches.

The pitch of the worm will, of course, be the same as that of the
wheel, and its diameter will be whatever is necessary to give
sufficient strength outside of the shaft, since it bears no relation to
the ratio of the gearing.


DRUMS AND REELS

=9.= The =drum=, or =reel=, of a hoisting engine is the part on which
the rope winds. It is either keyed fast to the engine shaft or is
connected to the shaft by means of a clutch, the shaft being made extra
heavy to carry the strain due to the weight of the drum and the pull of
the rope.


CYLINDRICAL DRUMS

=10.= The outer part, or =shell=, of a drum _a_, Fig. 7, is supported
on rims _b_, and these rims are connected by arms or spiders _c_ with
the hubs _d_. The brake rings _e_ are for the band brakes, of which
there may be one or two. The part _a_ may be lagged with strips of wood
bolted to the rims _b_, the heads of the bolts being countersunk. Fig.
8 shows the detailed dimensions of a drum 8 feet in diameter having a
4-foot face designed to carry heavy loads and a large amount of rope.
The shell is of boiler plate and the spiders of cast-steel.

[Illustration: FIG. 7]

=11.= The shell may be cast in one piece for small drums or built up
in sections for large drums, as in Figs. 7 and 8. The shell may have a
smooth surface, Fig. 8, or it may have grooves, Fig. 7, for the rope
to lie in as it is wound on the drum. On an iron drum without grooves,
the rope will chafe sidewise; and furthermore if the rope winds on a
hard flat surface it bears here and there on a single wire and tends to
flatten, causing internal wear between the wires; while, in the case
of a rope winding in a groove, it is supported on about one-quarter
of its circumference, bringing many more wires to bear on the drum
and dividing the pressure between them. A wooden-lagged drum causes
less wear on a rope than an ungrooved iron-shell drum, as grooves are
gradually worn in the lagging, but is not so good as a grooved iron
drum. It is not good practice to allow a rope to wind on itself, and
the drum should be long enough to take the full length of the rope
required for the hoist. At least two turns of the rope should be on
the drum when the load is at the bottom, as the friction between the
rope and drum thus greatly lessens the strain coming on the rope at
the point where it is fastened to the drum. Allowance for two or three
additional turns of the rope should also be made so that the cage may
be hoisted above the landing.

[Illustration: FIG. 8]

The shell usually has a flange at each end, as shown in Figs. 7 and 8,
but it may have a flange at one end only, or may be without flanges
entirely. If, however, the flanges are not used, the drum must be extra
long to prevent the rope running off the end. If the drum is very long,
a third spider is added midway between the other two to stiffen it
against collapse.

      EXAMPLE.--Find the length of a drum 6 feet 3 inches in
      diameter necessary to hold 1,000 feet of 1¼-inch wire-rope.

      SOLUTION.--The diameter from center to center of the rope
      when wound on the drum is 6 ft. 3 in. plus 1¼ in., or 6
      ft. 4¼ in., which is equal to 19.96 ft. (approximately
      20 ft.) of circumference. Then, to wind 1,000 ft. will
      require ¹,⁰⁰⁰/₂₀ = 50 turns on the drum. Allowing two
      turns of the rope to protect the fastening and three
      turns in case of overwinding, gives fifty-five turns to
      be allowed for on the drum. If the drum is of iron with
      grooves turned in it, ¼ in. must be left between adjacent
      parts of the rope, or 1½ in. from the center of one turn
      to the center of the next. Then, 55 × 1½ = 82½ in. plus ¾
      in. at each end = 84 in., or 7 ft. for the length of the
      drum between the flanges. Ans.

      If the drum has wooden lagging, clearance need not be
      allowed between two adjacent coils of rope, as in this
      case the rope winds against itself and so takes up only 1¼
      in. It will then be 55 × 1¼ in. = 68¾ in., or 5 ft. 8¾ in.
      long (say 5 ft. 9 in.). Ans.


CONICAL DRUMS

=12.= In hoisting in balance from deep shafts with cylindrical drums,
if no tail-rope is used, or in hoisting from a single shaft with an
unbalanced cage, the hoisting engine is not loaded equally at different
points of the hoist owing to the gradually changing weight of the
unbalanced rope. The following illustrations will further explain this.

=13. Hoisting With a Cylindrical Drum.=--Suppose that, from a
single-compartment vertical shaft 1,000 feet deep, it is required to
hoist each trip a load, including friction, of 11,000 pounds made up as
follows:

                            POUNDS
    Weight of material      4,000
    Weight of car           3,000
    Weight of cage          3,000
    Friction, 10 per cent.  1,000
                           ------
        Total              11,000

If a 1⅜-inch cast-steel rope weighing 3 pounds per foot is used,
winding about a drum 7 feet in diameter, the weight of rope is then 3 ×
1,000 = 3,000 pounds and the load on the rope, when the cage is at the
bottom, is 11,000 + 3,000 = 14,000 pounds, while at the top the load on
the rope is only 11,000 pounds. The moment of the load at the bottom
is then the load 14,000 multiplied by the radius 3½, or 14,000 × 3½ =
49,000 foot-pounds; and at the top, 11,000 × 3½ = 38,500 foot-pounds.
This shows that the load against the engine is much greater at the
beginning than at the end of the hoist.

=14.= Take now a double-compartment vertical shaft of the same depth
as in Art. _13_ and assume the same amount of material hoisted at a
trip, in the same mine car and on the same cage; but that an empty car
and cage are lowered in one compartment while the loaded car and cage
are hoisted in the other. The two cars and the two cages will balance
each other, and the loads will be as follows: At the beginning of the
hoist, when the loaded car and cage are at the bottom, the gross load
is 14,000 pounds, made up as follows:

                                     POUNDS
    Weight of material               4,000
    Weight of mine car               3,000
    Weight of cage                   3,000
    Friction, 10 per cent. of above  1,000
    Weight of rope                   3,000
                                    ------
        Total                       14,000

Multiplying this by the radius of the drum, the gross turning moment is
14,000 pounds × 3½ feet = 49,000 foot-pounds, as before, but there is a
counterbalancing load of 6,000 pounds, made up as follows:

                                     POUNDS
    Weight of mine car               3,000
    Weight of cage                   3,000
                                     -----
        Total                        6,000
        Less friction, 10 per cent.    600
                                     -----
                                     5,400

This means a counterbalancing load moment of 5,400 pounds × 3½ feet =
18,900 foot-pounds. The net load moment to be overcome by the engine
at the beginning of the hoist is, therefore, 49,000-18,900 = 30,100
foot-pounds.

At the end of the hoist there is a gross load on the loaded side of
11,000 pounds, made up as follows:

                                             POUNDS
    Weight of material                       4,000
    Weight of mine car                       3,000
    Weight of cage                           3,000
    Friction, 10 per cent.                   1,000
                                            ------
      Total                                 11,000

This is equal to a gross load moment of 11,000 pounds × 3½ feet =
38,500 foot-pounds, but there is a counterbalancing load of 8,100
pounds, made up as follows:

                                             POUNDS
    Weight of mine car                       3,000
    Weight of cage                           3,000
    Weight of rope                           3,000
                                             -----
      Total                                  9,000
      Less friction, 10 per cent. of 6,000     600
                                             -----
                                             8,400

This is equal to a counterbalancing load moment of 8,400 pounds × 3½
feet = 29,400 foot-pounds, and leaves a net load moment against the
engine of 38,500-29,400 = 9,100 foot-pounds. In other words, the load
moment that the engine has to overcome varies from 30,100 foot-pounds
at the beginning of the hoist to 9,100 foot-pounds at the end of the
hoist.

=15. Hoisting With Conical Drums.--Conical drums= are designed to
make the work of the engine as nearly uniform as possible throughout
the hoist. To accomplish this, when the cage is at the bottom of the
shaft, and the load is therefore heaviest, the rope winds on that part
of the drum having the smallest diameter. As hoisting continues, the
rope winds on a gradually increasing diameter of drum, and when the
cage is at the top of the hoist, and the load therefore least, the
rope is winding on that part of the drum having the greatest diameter;
in this way, the moment of the load at every point of the hoist is
approximately the same. The great difference in the loads at different
parts of the hoist is due mainly to the variation in the weight of the
rope hanging from the drum; hence, the less the weight of the rope in
proportion to the total load on the engine, the more nearly uniform is
the load on the engine.

[Illustration: FIG. 9]

=16.= Fig. 9 (_a_) shows the condition at the beginning of the hoist
when conical drums are used. Cage _a_ is at the bottom and carries a
loaded car; cage _b_ is at the top and carries an empty car. The net
moment that the engine must overcome is the sum of the weight of the
material to be hoisted, weight of the cage and car at _a_, and the
weight of the rope attached to _a_, multiplied by the small radius _r_
of the drum, minus the weight of the car and cage at _b_, multiplied by
the large radius _R_ of the drum.

Fig. 9 (_b_) shows the condition of things at the end of the hoist,
when the cage _a_ is at the top and cage _b_ at the bottom. The
loaded car and cage _a_, whose rope in Fig. 9 (_a_) was winding on
the smallest diameter of the drum, is now at the top and the rope is
winding on the largest diameter of the drum. The cage _b_ with the
empty car is now at the bottom and the rope is unwinding from the
smallest diameter of the drum. The net moment that the engine must
overcome in this position is equal to the sum of the weight of the
material hoisted, the weight of the cage _a_ and the car, multiplied by
the larger radius _R_ of the drum, minus the sum of the weights of the
cage _b_, the car, and the rope, multiplied by the small radius _r_ of
the drum.

=17.= If the moment of the load against the engine at the beginning of
the hoist is to equal that at the end of the hoist, it is possible to
determine what relative diameters of drum will produce such an effect,
as follows:

    Let  _Wₘ_ = weight of material hoisted;
         _Wₖ_ = weight of cage and car;
         _Wᵣ_ = weight of rope;
         _R_  = large radius of drum;
         _r_  = small radius of drum.

The load moment may be calculated by including friction as ⅒ of the
total weight hoisted, except the weight of the rope, as shown in Art.
=14=; or the friction may be disregarded without serious error. Then,
under the conditions shown in Fig. 9 (_a_), and disregarding friction,

      Load moment = (_Wₘ_+_Wₖ_+_Wᵣ_)_r_ - _Wₖ__R_          (=1=)

   and under the conditions shown in Fig. 9(_b_),

      Load moment = (_Wₘ_ + _Wₖ_)_R_ - (_Wₖ_ + _Wᵣ_)_r_    (=2=)

    Placing formula =1= = formula =2=,

      (_Wₘ_+_Wₖ_)_R_ - (_Wₖ_+_Wᵣ_)_r_ = (_Wₘ_+_Wₖ_+_Wᵣ_)_r_ - _Wₖ__R_,

    and
                (_Wₘ_+ 2_Wₖ_+ 2_Wᵣ_)
      _R_ = _r_ -------------------                        (=3=)
                   (_Wₘ_ + _2Wₖ_)

Since the diameter of a drum is generally given instead of the radius,
it follows that if _D_ = larger diameter, _d_ = smaller diameter, and
then, since _D_ = 2_R_ and _d_ = 2_r_, formula =3= may be written

              (_Wₘ_ + 2_Wₖ_ + 2_Wᵣ_)
    _D_ = _d_ ----------------------                       (=4=)
                  (_Wₘ_ + 2_Wₖ_)

Formula =4= gives only approximate results, which are, however,
sufficiently accurate for the mine superintendent’s use, and for this
reason friction has been omitted, as it would make the formula much
more complex. It may be expressed as a rule as follows:

=Rule.=--_To find the large diameter of a conical drum, multiply the
small diameter by the sum of the weight of the material to be hoisted,
twice the weight of the cage and car, and twice the weight of the rope;
divide this product by the sum of the weight of the material, and twice
the weight of the cage and car._

[Illustration: FIG. 10]

Applying this rule to the problem given in Art. =14= and omitting
friction,

          7(4,000 + 12,000 + 6,000)
    _D_ = ------------------------- = 9.6 feet
             (4,000 + 12,000)

The drum would then be 7 feet in diameter at the small end and 9 feet
7¼ inches at the larger end.

=18=. Fig. 10 shows a special form of combined conical and cylindrical
drum designed for hoisting a total balanced load of 25 tons through a
vertical height of 550 feet.

Fig. 11 shows a combined conical and cylindrical drum; an unusual
feature is the rope reel shown at each end of the drum, which permits
of properly storing a few hundred feet of extra rope, allowing the rope
to be lengthened, when needed, without splicing.

[Illustration: FIG. 11]

=19. Comparison of Cylindrical and Conical Drums.= The disadvantages
of the cylindrical drum lie entirely in the fact that the load on the
engines is variable, but it is possible to overcome this disadvantage
by adding a tail-rope to the cages to balance the weight of the rope.
This system gives its best results where hoisting is done from one
level only, but in deep hoisting it is impracticable because of the
extra weight added and because of possible excessive swaying of the
rope.

The conical drum has two strong points in its favor: first, the load
on the engine may be nearly equalized during the entire hoisting
period; and, second, the starting of the engines with the load requires
less power.

The disadvantages of the conical drum are as follows: To maintain a
certain average speed of hoisting, the speed toward the end of the
hoist is of necessity higher than the average and comes at a time
when a slowing up should be taking place, so that more care must be
exercised when making the landing. To prevent the rope from being
drawn out of the grooves, the latter must be made deep and with a
large pitch, thereby increasing the width of the face or length of
the drum. In making a landing, when the rope is on the conical face,
the rope must be kept taut, as any slackness will permit the rope to
leave the groove, with the result that all the rope will pile up in the
bottom grooves of the drum allowing the cage to drop into the mine,
unless it is resting on the chairs. If there are several levels to be
hoisted from, the equalizing of the load on the engines can only be
realized for one level; for all other levels this advantage will be
lost. For large depths, conical drums become very long and require
correspondingly long leads from head-frame to drum. To hold the same
amount of rope, conical drums are heavier than cylindrical ones, and as
a result, the power required in starting the load is somewhat increased
owing to the greater inertia of the rotating parts.

Some of these disadvantages have been overcome by making a combination
of cone and cylindrical drums. The drums are so designed that the
landing takes place only when the rope is on the cylindrical portion
of the drum. For deep hoisting, the greater diameter of the drum and
its length must be inconveniently large if the load is equalized.
The length and diameter can be reduced by making one-half of the
drum cylindrical and by having the rope from each end wind on the
same cylindrical portion of the drum. In all cases, however, these
modifications are made at the expense of the equalization of the load
on the engines, and it is not possible to obtain the latter without
including some serious disadvantage.

There are certain objections to both cylindrical and conical drums:
their great size and weight, for large hoists, make them very
expensive; their width necessitates placing the engines far apart,
which adds to the cost of the engines, foundations, and buildings; the
great weight of the drums is also objectionable, because it forms a
large part of the mass to be put in motion and brought to rest at each
hoist.


FLAT ROPE REELS

=20=. To overcome the objections to conical and cylindrical drums,
several other systems of hoisting have been tried, among them being one
that uses a reel, Fig. 12, and a flat rope. The hub _a_ is increased in
diameter, above what is necessary for strength, to such a size as is
suitable to wind the rope on. It is then cored out from the inside, so
as not to contain too great a mass of metal.

[Illustration: FIG. 12]

The arms _b_ of the reel extend radially from the hub to confine
the rope laterally when it is all wound on the drum. These arms are
connected at their outer ends by a continuous flange _c_, which flange
is flared out, as shown at _d_, so as to take in the rope easily, if it
is deflected at all sidewise.

In the larger-sized reels, the arms are bolted to the hub, and often
the outer rim connecting the arms is omitted. Hardwood lining was
formerly used on the arms under the impression that the wear on the
rope would be less than with bare iron arms, but sand and grit become
embedded in the wood and grind the rope. Polished iron arms with
rounded corners and lubricated with oil or tar are best. The end of the
rope is fastened in a pocket _e_ provided for it in the hub.

The rope winds on itself, so that the diameter of the reel increases
as the hoist is made and as the load due to the weight of the rope
decreases. This serves to equalize the load due to the rope in the same
manner as the conical drum. Two reels are generally put on the same
shaft, and while one is hoisting from one compartment of the shaft the
other is lowering into another compartment. The periphery of the hub
where the rope winds should not be round but of gradually increasing
radius, for if a flat rope be wrapped about a round hub the rope will
have to abruptly mount itself at the end of the first revolution and so
on for every revolution. The radius of the hub should increase at such
a rate as to raise the rope an amount equal to its thickness in the
first wrap, so that it will wind on itself without jar at the point of
attachment, as well as on succeeding wraps.

=21.= In America, it is customary to wind on reels of small diameter,
that is, starting at 3 or 5 feet and increasing to 8 or 12 feet; but
several large plants have been built with reels starting at 8 feet and
increasing to 19 feet. In England, reels have been made starting at 16
feet and increasing to 20 or 22 feet. Such large reels are easier on
the rope but require large engines, as hoisting in balance is used to
only a slight extent. The large reel is easy on the rope, both from the
fact that it bends the rope but little and also gives less pressure on
the bottom wraps, as each wrap adds to the pressure. These reels are
driven by means of plain jaw or friction clutches.

The wear of a flat rope is excessive and the rope itself costs more
than a round rope of the same strength, does not last as long, and
requires more care and attention.

=22. Calculating Size of Flat Rope and Reel.=--The calculation of
the size of a flat rope for given work is not so simple as that of a
round rope, as there is a variable factor in the width and thickness
of the rope that must be taken into account. To illustrate the method
of calculation, suppose that it is required to hoist 5,000 pounds of
material in a 3,000-pound skip from a vertical two-compartment shaft
2,000 feet deep under conditions requiring a factor of safety of about
9 for the rope.

The determination of the size of the rope and the small and large
diameters of the reels must proceed together. The latter calculations
are performed in much the same manner as for conical drums.

Referring to Table relating to flat wire ropes in _Hoisting_, Part
2, it is found that a flat steel rope 6 inches by ½ inch in size and
with a breaking strength of 150,000 pounds weighs 5.1 pounds per foot;
hence, 2,000 feet of it weighs 2,000 × 5.1 = 10,200 pounds. The total
load on the rope will then be 19,000 pounds, made up as follows:

                             POUNDS
    Weight of material       5,000
    Weight of skip           3,000
    Friction, 10 per cent.     800
    Weight of rope          10,200
                            ------
      Total                 19,000

This rope gives a factor of safety of 150,000/19,000 = 7.8, which is
not quite enough when figured from the dead load without that due to
acceleration.

An 8" × ½" rope with a breaking strength of 200,000 pounds weighs 6.9
pounds per foot; hence, 2,000 feet of it weighs 2,000 × 6.9 = 13,800
pounds. The load on the rope will then be 22,600 pounds, made up as
follows:

                             POUNDS
    Weight of material       5,000
    Weight of skip           3,000
    Friction, 10 per cent.     800
    Weight of rope          13,800
                            ------
      Total                 22,600

                                           200,000
    This rope gives a factor of safety of -------- = 8.8.
                                           22,600

Substituting the foregoing weights of material, skip, and rope in
formula =4=, in Art. =17=, gives

              (5,000 + 6,000 + 27,600)
    _D_ = _d_ ------------------------ .
                   (5,000 + 6,000)

Hence, the equation of moments is _D_ = 3.5_d_. In other words, the
large diameter, or that of the last coil of rope, should be 3.5 times
the small diameter, or that of the reel hub.

=23.= Fig. 13 represents a coil of flat rope whose greater diameter
_D_ and smaller diameter _d_ are to be determined. The area of the hub
about which the rope is to coil is (¼)π_d_², while the area included
by the outer coil of rope is (¼)π_D_² hence, the area of annular space
occupied by the rope is

    (¼)π_D_² - (¼)π_d_² = (¼)π(_D_² - _d_²).

Such values for _D_ and _d_ must be chosen that the equation of
moments in Art. =22= is satisfied, while the area (¼)π(_D_²-_d_²) must
correspond to the space occupied by the given rope when rolled.

[Illustration: FIG. 13]

    ILLUSTRATION.--2,000 feet of rope ½ inch thick requires

           2,000 × 12
           ---------- = 12,000
                2

    square inches in which to be coiled. To satisfy the equation of
    moments, _D_ must equal 3.5 _d_; hence, to satisfy both
    these conditions

      (¼)π[(3.5_d_)² - _d_²] = 12,000;
      _d_ = 37 inches, or 3 feet 1 inch;
      _D_ = 37 × 3.5 = 129.5 inches, or 10 feet 9½ inches.

      The dimensions of the reel will then be: diameter of
      hub 3 feet 1 inch; width between flanges, 8½ inches,
      allowing ¼ inch on each side of the rope for clearance;
      diameter of the flanges where they flare, 10 feet 9½
      inches.


ROPE WHEELS

[Illustration: FIG. 14]

=24. Koepe System.=--In its lightest form, a drum requires a large
amount of power to set it in motion, which power is absorbed by the
brake and lost when it is brought to rest again. Furthermore, with deep
shafts requiring long drums, the fleet, or angle that the rope makes
with the head-sheave due to its traveling from one end of the drum to
the other, is not only a disadvantage and possible cause of accident,
but it is a source of wear. To overcome these objections and also the
great cost of large cylindrical or conical drums, the =Koepe system=
of hoisting, shown in Fig. 14, was devised by Mr. Frederick Koepe.
A single grooved driving sheave _a_ is used in place of a drum. The
winding rope _b_ passes from one cage _A_ up over a head-sheave, thence
around the sheave _a_ and back over another head-sheave, and down to
a second cage _B_; it encircles a little over half the periphery of
the driving sheave and is driven by the friction between the sheave
and rope. A balance rope _c_ beneath the cages and passing around the
sheave _d_ gives an endless-rope arrangement with the cages fixed at
the proper points. The driving sheave is stronger than an ordinary
carrying sheave, as it has to do the driving and is usually lined with
hardwood, which is grooved to receive the winding rope, the depth of
the groove being generally equal to twice the diameter of the rope.
Instead of being placed parallel, the head-sheaves are placed at an
angle with each other, each pointing to the groove in the driving
sheave, thus reducing the side friction of the rope on the sheaves.

The system has been in successful operation since 1877, and experiments
made on it have determined that, with a rope passing only one-half
turn around the drum sheave, the coefficient of adhesion with clean
ropes is about .3. If the ropes are oiled, the adhesion becomes less,
and sometimes slippage occurs, producing not only wear of the driving
sheave lining but giving an incorrect reading of the hoist indicator
and thus possibly producing overwinding, unless the position of the
cage is indicated by marks on the rope, or unless the engineer can see
the cage.

At the end of the hoist, if the upper cage is allowed to rest on the
keep, its weight and the weight of the tail-rope are taken from the
hoisting rope, and there is then not enough pull on the hoisting rope
to produce sufficient friction with the drum sheave to start the next
hoist. To prevent this trouble, the keeps are dispensed with, or the
rope is made continuous and independent of the cage. To do this,
crossheads are placed above and below each cage and connected by ropes
or chains outside of the cages. The bridle chains are then hung from
the top crosshead, and when the cage rests on the keeps, the weight of
the winding and tail-ropes remains on the driving sheaves.

=25. Advantages and Disadvantages of the Koepe System.=--With this
system, only one driving sheave is necessary for the operation of two
compartments, and it is light, inexpensive to build, and very narrow,
admitting of a short sheave shaft and small foundations. This system
permits a perfect balance of rope and cage, so that the work to be done
by the engine is uniform, except for the acceleration, and consists
only in lifting the material and overcoming the friction. There is no
fleeting of the rope between the driving sheaves and the head-sheaves.

The system has the following disadvantages, which prevent its being
used to any considerable extent: Liability to slippage of the rope
on the drum; if the rope breaks, both cages may fall to the bottom;
hoisting from different levels cannot be well done, for, since the
cages are at fixed distances from each other, the length of the rope
is such that when one cage _A_ is at the top, the other cage _B_ is
at the bottom. If hoisting is to be done from the bottom, this is
satisfactory, but if hoisting is to be done from some upper level, cage
_B_, which is at the bottom, must be hoisted to that level to be loaded
before it can go to the top. Then, when cage _B_ goes to the top with
its load, cage _A_ must go to the bottom, wait there while cage _B_ is
being unloaded, and then be hoisted to the upper level to receive its
load. For each trip, therefore, the time required for a cage to go from
the bottom to the upper level and be loaded is lost; and two movements
of the engines are necessary for a hoist instead of one.

=26. The Whiting System.=--This is a system of hoisting with
round ropes, in which two rope wheels placed tandem are used in
place of cylindrical or conical drums. As shown in Fig. 15, for a
two-compartment shaft the rope passes from one cage _a_ up over a
head-sheave _c_, down under a guide sheave _d_, and is then wound three
times about the rope wheels _e_ and _f_, to secure a good hold, then
around a fleet sheave _g_, and back under another guide sheave _h_, up
over another head-sheave _i_, and down to the other cage _b_. When the
system is to be used for a single-compartment shaft, one end of the
rope carries the cage and the other end carries a balance weight, which
is run up and down in a corner of the shaft. A balance rope below the
cages, as shown, is generally used, though it is not essential to the
working of the system, as it is in the Koepe system. When sinking a
shaft, a balance rope cannot be used as it interferes with the work at
the bottom of the shaft.

[Illustration: FIG. 15]

The drums or wheels _e_, _f_ are light, inexpensive, and narrow, thus
permitting short sheave shafts and small foundations. They are lined
with hardwood blocks, each lining having three rope grooves turned
in it. The main wheel _e_ is driven by a hoisting engine, which may
be either first or second motion. The following wheel _f_ is coupled
to the main wheel by a pair of parallel rods, one on each side, like
the drivers of a locomotive. As the rope wraps about the wheels _e_,
_f_ three times, there are six semi-circumferences of driving contact
with the rope, as compared with the one semi-circumference in the
Koepe system, and there is no slipping of the rope on the wheels. The
following wheel _f_ is best tilted or inclined from the vertical an
amount equal, in the diameter of the wheels, to the pitch of the rope
on the wheel, so that the rope may not run out of its groove and may
run straight from one wheel to the other without any chafing between
the ropes and the sides of the grooves.

The capacity of the wheels _e_, _f_ is unlimited, while grooved
cylindrical drums, conical drums, and reels will hold only the fixed
length of rope for which they are designed.

As shown by the dotted lines, the fleet sheave _g_ is arranged to
travel backwards and forwards, in order to change the working length of
the rope from time to time to provide for an increased depth of shaft,
and for the changes in the length of rope due to stretching and when
the ends are cut off to resocket the rope. The fleet sheave _g_ is
moved a distance equal to half the change in the length of rope.

=27=. Hoisting from intermediate levels can be readily done with the
Whiting system; for instance, if the cage _a_ is at the top and cage
_b_ at the bottom, and hoisting is to be done from some upper level, it
is only necessary to run the fleet sheave _g_ out, and thus shorten
the working length of the rope until cage _b_ comes up to the upper
level. It can then be loaded and go to the top. While cage _b_ goes to
the top, cage _a_ descends to the same level, where it can be loaded
while cage _b_ is being unloaded, and can then go directly to the top
without any of the lost time, as is the case in the Koepe system.

The system permits a perfect balance of rope and cage, so that the work
to be done by the engines is uniform, except for the acceleration, and
consists only in lifting the material and overcoming the friction.

There is no fleeting of the rope, so the rope wheels can be placed as
close to the shaft as may be desired.

=28.= This system was tried as early as 1862 in Eastern Pennsylvania,
but it was not used extensively because hoisting from great depths was
not necessary, since, for depths of less than 1,000 feet, cylindrical
and conical drums are quite satisfactory. In the Lake Superior copper
region, there are now three Whiting hoists, two of which are probably
the largest hoisting plants in the world. Each plant consists of a pair
of triple-expansion, vertical, inverted-beam engines, driving direct
a pair of 19-foot drums. The high-pressure cylinders are 20 inches in
diameter, the intermediate cylinders 32 inches, and the low-pressure
cylinders 50 inches, and all six of them have a 72-inch stroke. The
rope used is a 2¼-inch plow-steel rope and hoists 10 tons of material
at a trip, in one case from a depth of 4,980 feet, the deepest shaft
in the world. Several plants on the Whiting system have been built in
England, and two or more are working in South Africa.

=29. Modified Whiting System.=--A modification of the Whiting system
is sometimes used in which a large drum keyed to the crank-shaft
replaces the small tandem drums, and even the slight probability of
the rope slipping in the Whiting system is thus obviated. One rope is
fastened to one end of the drum, and the other rope to the other end
in such a way that while one is winding on the other will be winding
off the drum. One rope passes directly to the head-sheave while the
other passes first around a fleet sheave, similar to that used for the
Whiting system, but preferably placed horizontal, and thence to the
head-sheave. This system possesses the same advantages as the Whiting
system except that the depth of hoist is limited by the size of the
drum, and that there is a fleet of the rope. Up to the limiting depth,
as determined by the size of the drum, this system can be used with
equal economy for any depth. This hoist, as well as the Whiting, is
therefore especially suitable for a place where one mining company
operates several mines, for it enables the company to select one size
for all their permanent work, with all the advantages that come from
duplicate machinery.


ROPE FASTENINGS

[Illustration: FIG. 16]

=30.= A common method of fastening a rope to a drum, Fig. 16 (_a_),
is to pass the rope through a hole in the drum rim and then around
the shaft, clamping the end to the rope between the shaft and shell,
as shown. Care should be taken to make the radius of curvature of the
hole at _a_ as large as possible so that the rope will not be bent any
sharper than is necessary. When an iron drum is used, the thickness of
the rim does not afford enough depth in which to bend the rope and it
is necessary to build in a pocket for the purpose, as shown at Fig. 16
(_b_). It is well to make both sides of this pocket with a long radius
to avoid damaging the rope in case all the rope is accidentally unwound
and the drum backed so as to bring the rope against the other side of
the pocket.


CLUTCHES

=31.= It is often desired to have the drum of a hoisting engine run
loosely on the engine shaft, so that it may run independently of the
engine. With such loose-running drums, the engine generally runs only
in the direction required to hoist the load, while the cage is lowered
entirely by means of the brake. In this way, one engine provided with
several drums may be used for hoisting from several shafts or from
several levels in the same shaft at the same time. Such a loose-running
drum is connected to the engine shaft when a load is to be hoisted
by means of a clutch, of which there are two forms commonly used for
hoisting machinery: _jaw_ or _piston clutches_ and _friction clutches_.

[Illustration: FIG. 17]

=32. Jaw Clutch.=--Fig. 17 shows a =jaw clutch=, one-half _a_ of which
is shown ready to be bolted to a drum or flat rope reel, which is loose
on the shaft _b_. The other half _c_ of the clutch is moved back so
that the jaws _d_ are not in contact with the jaws _e_ on the part
_a_. The half _c_ slides freely on a feather key _f_, which is driven
tightly into a deep key seat in the shaft _b_; a collar _g_, fitting
loosely in a groove in the hub of _c_, is provided with trunnions _h_
on each side; levers _i_ connect these trunnions with the lever _j_
attached to a suitable handle, by means of which the clutch is made to
slide endwise on the shaft so that the jaws _d_ engage or disengage
the jaws _e_ and thus connect or disconnect the drum or reel from the
clutch. There are generally four or six jaws _d_ that engage the same
number of jaws _e_ on the drum, and it is necessary to have little or
no play between _d_ and _e_ when the clutch is connected or there will
be too much shock. The clutch is about 2 feet in diameter, and the jaws
are 3 or 4 inches deep for the average 20" × 48" first-motion hoisting
engine. Instead of the clutch being fastened to the shaft by feather
keys, the shaft may be hexagonal where the clutch slides on it and the
clutch is machined to match. Jaw clutches are made of either cast-iron
or cast-steel, and should be in halves, for convenience of repair, and
securely bolted together.

[Illustration: FIG. 18]

=33. Band Friction Clutches.=--Fig. 18 shows a =band friction clutch=
that is attached to and revolves with the shaft _a_. The winding
drum runs loosely on the same shaft and has a driving-band ring or
seat _b_ on one end; when the ring _c_ of the clutch is tightened by
means of the mechanism shown, the clutch and driving band become
practically one piece and the drum revolves with the clutch. The clutch
is constructed as follows: The driving disk _d_ keyed to the driving
shaft _a_ is connected to one end of the ring _c_ by a fixed arm _e_,
which is bolted firmly to the disk _d_ and revolves with it; a movable
arm _f_ that connects with the other end of the band _c_ turns on the
pin _g_. When the band _c_ is loose, it can revolve about the seat _b_
without touching it, but the band can be tightened and made to clamp
_b_ either when revolving or standing still, as follows: The sliding
sleeve _h_ may be caused to slide about 6 inches along the hub of the
disk _d_ by levers (not shown) that take hold of trunnions _i_ on a
ring on the sliding sleeve; this sleeve is connected to the movable arm
_f_ by a link _j_, and when the sleeve is on the end of the hub the
link stands at an angle of about 60° with the shaft; by sliding the
sleeve toward the disk _d_, the link is made to move the arm _f_ about
1½ inches at its outer end and to thus tighten the driving-band _c_, so
that it grips the ring _b_. The adjusting nuts _k_ take up the wear of
the wooden blocks with which the ring _c_ is lined. Band lifters _l_
hold the band clear of the ring when it is loose. The clutch shown is
built to run in the direction indicated by the arrow, but such clutches
may be built to run in either direction; they should always be run in
the direction for which they are designed, so that the load may always
come on the fixed arm. If the band be tightened slowly, there will
be no sudden start or jerk on the rope, as the slip of the band will
prevent the entire force of the grip taking effect at once; and after
the drum reaches full speed, there is little or no slipping of the
driving-band. It is best to keep the band only just tight enough to do
the work, for should the car get off the track, or be overwound, or
should a cage stick in the shaft for any reason, the band will slip and
thus become a safety appliance, and not strain or break the rope, shaft
timbering, or machinery, as would be the case if a positive clutch,
Fig. 17, were used.

=34. The Beekman Friction Clutch.=--A simple friction clutch is
shown in Fig. 19, in which _a_ is a section of the drum shell. The
wooden blocks _b_ bolted to the side of the gear-wheel _c_ are made
of suitable shape to conform to the =V=-shaped groove _d_ in the side
of the drum. The steel spring _e_ between the two steel washers _f_,
_f_ disengages the clutch, as soon as the pressure is relieved, by
reversing the motion of the lever _g_ and screw _h_ from the opposite
end of the drum. When the lever _g_ is turned, the screw _h_ is forced
against the end of the pin _i_, which, in turn, presses the cross-key
_j_ against the collar _k_, forcing the drum against the blocks _b_ and
frictionally engaging the gear-wheel _c_. This drum shaft is prevented
from moving endwise by means of the collar _l_ and the grooves _m_ in
the babbitted pillow-block. The wide bearings of the drum on its shaft
are lubricated by means of the pipes _n_.

[Illustration: FIG. 19]

A clutch is often used to change the length of the hoisting rope when
hoisting from two or more lifts or levels. In this case the shaft
carries two drums, one of which is fixed to the shaft, while the other
is provided with a friction clutch. When it is desired to change the
length of the rope, the cage attached to the loose drum is brought
to, say, the upper landing. The cages both resting on the wings, the
clutch is loosened and the other cage attached to the fixed drum is now
brought to the desired level, when the clutch is again tightened and
hoisting proceeds. The change is made in 2 or 3 minutes.


BRAKES

=35=. A =brake= is a device by means of which the motion of a hoisting
drum may be retarded or stopped. This is accomplished by friction of
the brake against the circumference of the brake wheel. There are three
types of brakes, known as _block brakes_, _post brakes_, and _strap
brakes_.

[Illustration: FIG. 20]

=36. The Block Brake.=--The =block brake=, Fig. 20, consists of one or
more wooden blocks or shoes _b_ attached to a lever having a fulcrum at
_d_, and connected by a rod to the lever _c_. Block brakes are objected
to mainly because they throw a great load on the journals of the drum
when they are applied; they cannot be relied on when there is a heavy
load on the drum, and they require the application of great force to
the lever _c_ for a given braking power. They are, however, cheap and
easily applied to a drum, and the shoe is readily replaced when worn.

=37. The Post Brake.=--The =post brake=, Fig. 21, is composed
practically of two block brakes applied at two places on the drum
diametrically opposite each other, thus equalizing the pressure on the
journals. The blocks are generally somewhat longer than in the block
brake, or about one-quarter of the circumference of the drum on each
side. In Fig. 21, _a_ is the drum; _b_ are wooden brake blocks; _c_
are the posts which in the brake shown are of massive, built-up, steel
construction; _d_ are the fulcrums on the plates _e_, which plates
are adjustable by means of the nuts _f_; by means of these nuts, the
fulcrums may be brought closer together as the wooden blocks _b_ wear
away; _g_ is a tension rod generally furnished with a turnbuckle to
adjust its length as the wooden blocks wear away. Power is applied at
the end of the bent lever _h_, as shown by the arrow.

[Illustration: FIG. 21]

The stops _i_ are adjusted so that the blocks _b_ on each side are
equally distant from the drum when the brake is off. The fulcrums _d_
should be some distance below the drum and brake ring, for if they are
too near the drum it will be difficult to swing the lower end of the
wooden blocks far enough to clear the drum.

[Illustration: FIG. 22]

=38. Improved Post Brake.=--In order to have an equal clearance at
top and bottom, and to have a more powerful leverage than in the
ordinary post brake, the posts may be made movable at both top and
bottom, Fig. 22. The tops of the posts _a a′_ are moved, as in Fig. 21,
by the tension rod _b_ and the lever _c_, the latter being connected
by rod _d_ to lever _e_. This lever is pivoted at _f_ and motion is
transmitted to the fulcrums _j_ by the link _g_, the lever _h_, and
the tension rod _i_. The back post _a_ is supported by the uprights
_k_, which are pivoted at _l_ and swing backwards and forwards like a
parallel ruler. The front post _a′_ is supported by the single upright
_m_, pivoted at _n_. The setscrews _o_ regulate the motion of the
bottom of the posts so as to give equal clearance to the bottom and top
of the posts.

An objection to both the block and the post brake is the fact that, if
the drum surface to which the brake is applied is not perfectly round,
the resistance of the brake will not be uniform when applied while the
drum is in motion.

=39. The Strap Brake.=--A =strap brake= consists of a wrought-iron
band or strap that partly encircles the drum and is connected at its
free ends to levers with which the band may be tightened on the brake
wheel and the drum thus firmly held. The iron or steel band either lies
directly against the wooden lagging of the drum or on wooden blocks
bolted to the drum; or else it has bolted to it a lining of wooden
blocks that bear on the drum when the band is tightened.

The most efficient forms of strap brakes are those in which the strap
or straps are in contact with 270° or more of the circumference of the
drum. The greater the arc of contact, the more securely is the drum
held by the brake. A single strap is sometimes used, but this is only
satisfactory with small drums, say 8 feet or less in diameter; on large
drums two straps are generally used, each extending half way around
the drum. The levers for transmitting the power from the hand lever or
treadle to the brake strap are variously arranged. In some cases, the
force is multiplied by several short levers; in others, by one long
lever. The treadle or foot-lever, however, has been replaced almost
entirely by the hand lever.

[Illustration: FIG. 23]

=40.= The simplest form of strap brake, Fig. 23, consists of a single
strap _a_, with one end anchored at _b_ and the free end attached to
the brake lever _c_. This brake acts on the same principle as the block
brake and is open to the objection that it brings an undue load on the
journals, but it is more efficient and holds the drum more firmly under
a heavy load than a block brake.

[Illustration: (_a_) (_b_) (_c_)

FIG. 24]

Block brakes are usually run dry, but in band brakes and post brakes
with ample surfaces and proper leverage the wood may be occasionally
slightly oiled with black oil, which greatly adds to the durability of
the blocks without unduly lessening the power of the brake.

=41.= A two-strap brake is shown in Fig. 24. One end of each strap _a_,
_b_ is fastened to the pedestal _c_ by either of the methods shown in
Fig. 24 (_a_), (_b_), and (_c_). In the method shown in Fig. 24 (_a_)
and (_b_), the forgings _d_, _d′_, drawn out to the form of bolts, are
riveted to the ends of the straps and passed through a casting _c_ that
is secured to the foundation. The object in giving one bolt to one
strap and two bolts to the other strap is to allow the straps to pass
each other and yet have their lines of action intersect. The bolts are
fastened to _c_ by four nuts on each bolt, i. e., two principal nuts
and two locknuts. This gives a means of adjustment in the length of the
strap to take up the wear.

A second method of securing or anchoring the back ends of the straps is
shown at (_c_). In this case, a wrought-iron angular piece is riveted
to each strap, and these pieces are passed over the bolt _e_ that takes
the place of the casting of the former arrangement. Nuts are used, as
shown, to adjust the straps for wear. The bolt should be short and
stiff, so as to be well able to stand up to its work when the drum is
moving or tending to move in the direction shown by the arrow.

When the brake is applied, the friction between the brake strap and
the circumference of the brake wheel produces a great strain on the
pedestal _c_, which must be securely anchored.

The front ends of the straps are worked into eyes, as shown at _f_,
and by these eyes and suitable pins passing through them the ends are
fastened to the brake lever _g_. This lever is supported on and rotates
about a pin _h_, so that when the braking force is applied at _i_, in
the direction of the arrow, the brake lever rotates, pulling down on
strap _a_ and up on strap _b_; and, if the straps are held firmly at
the back end, the more force that is applied at _i_ the tighter will
the drum be gripped by _a_ and _b_.

The ends of the straps should be brought in as close to the drum as is
practicable, both front and back, so as to give the greatest amount of
contact between the drum and the straps and to get the best effect from
the force applied. The springs _j_ are used with straps that are not
stiff enough to clear the drum when the brake is released.

=42.= The rotation of the drum may assist or retard the action of the
lever in applying the drop brake. For instance, if, in Fig. 23, the
drum revolves in the direction indicated by the arrow, the pull of
the drum at the brake strap is in the same direction as the pull of
the lever when applying the brake and the action of the lever is then
assisted by the motion of the drum. On the other hand, if the drum
is revolving in the opposite direction, it opposes the action of the
lever and a greater force must be applied to the lever to overcome
this opposing pull of the drum. Hence, in the case of strap brakes, if
possible, that end should be anchored which will cause the revolution
of the drum to assist the lever in applying the brake and throw the
strain on the anchor bolt instead of on the lever.

[Illustration: FIG. 25]

=43.= If a brake is required to work with the drum running in either
direction, there are several ways of bringing the strain due to the
load on the anchorage in whichever way the drum runs. One of the
simplest of these is shown in Fig. 25, where _a_ is a drum with a strap
brake _b_ embracing nearly the entire circumference; _c_ is a lever
bar that is attached to the ends of the brake strap by pins _d_ and
_e_, which work in the slots _f_ in the iron anchor plates _g_. One
anchor plate is on each side of the lever, and both are bolted to the
foundation. If the band is kept of the proper length, then, no matter
which way the drum is turning, the pull of the drum will come on the
anchorage, and the pull on the lever need be only sufficient to take
up the slack end of the band. To illustrate: If the drum is turning in
the direction indicated by the arrow, the pin _e_ holding the lower end
of the band will be on the bottom of its slot and the pin _d_ will be
free in its slot and engaged in tightening the slack end of the band
through the motion of the lever _c_. Were the drum running the other
way, the pin _d_ connected with the upper half of the band would move
to the upper end of its slot and take the main load, while the pin _e_
at the lower end of the band would only have to take up the slack.
The outer, or long, end of the lever moves downwards in all cases to
tighten the band. Provision must be made to lift the band clear of the
drum when slack, but no anchorage other than at _g_ should be attempted.

[Illustration: FIG. 26]

=44. The Differential Brake.=--The differential brake has both ends
of the brake strap attached to short lever arms operated by the brake
lever, but these arms are of different lengths and are so arranged that
as the longer arm tightens the brake strap the shorter arm yields and
loosens the strap. The tightening, however, is more than the loosening
or yielding and, as a result, the brake band is tightened about the
brake wheel. The form of the lever arm is immaterial so long as the
differential principle is retained, that is, that the shorter arm
yields when the longer pulls, when the brake is thrown into action.
This principle is illustrated in Fig. 26. In this brake, no provision
is made for anchoring either end of the brake strap, but the entire
load is thrown on the lever arms _a_ and _b_. These lever arms are
connected with the arm _c_, which revolves on the same shaft _d_ and
is operated by the reach rod _e_. The revolution of the drum is thus
resisted by the shaft _d_.

This brake is self-acting when the drum revolves so as to pull on the
shorter arm, as indicated by the arrows; that is, the motion of the
drum helps to set the brake when the latter is once applied. When,
however, the drum revolves in the opposite direction, the action of
the brake is opposed, instead of being assisted, by the motion of the
drum. As a consequence, this particular form of brake is not adapted to
hoisting drums that revolve in opposite directions at each alternate
hoist. Differential brakes are not generally used.

[Illustration: FIG. 27]

=45. Power for Brakes.=--For small drums and light loads, the brakes
are usually applied by hand power through suitable lever connections.
The force that a man can exert can be multiplied indefinitely by
levers and combinations of levers; but while the force is multiplied,
the distance through which it can act is divided in the same ratio. A
certain amount of motion is required to free the brake band from the
drum, when the brake is off; this, then, limits the leverage that a
man can use. Suppose, for instance, that with a strap brake the band
moves from the drum ½ inch, thus increasing the diameter 1 inch, or the
circumference about 3 inches. Then, supposing that a man can exert his
force to advantage through 3 feet, or 36 inches, the available leverage
is ³⁶/₃ = 12. That is, if a man can pull 50 pounds on his hand lever,
he can exert 50 × 12 = 600 pounds circumferentially on the brake band,
with simple levers. If any form of differential levers is used, the
ratio by which the force applied at the hand lever can be increased
will be considerably larger. A diagram will explain this more clearly.

=46.= In Fig. 27, _a_ is the hand lever, with a fulcrum at _b_ and a
pin at _c_ by which it takes hold of a reach rod or connection _d_.
This rod is connected to the end _h_ of the brake lever _e_, which is
connected by pins at _f_, _g_ to the brake bands. If the leverage of
the hand lever _a_ is made 6 to 1, that is, if

    _ab_     6
    ----- = --- ,
    _cb_     1

and a force of 50 pounds is applied at _a_, a pull of 300 pounds will
be exerted at the pin _c_ and, consequently, along the rod _d_ to the
end of the brake lever _e_. Then, if the brake lever is made with a
ratio of 4 to 1, that is, if

    _eh_     4    _eh_
    ----- = --- = ---- ,
    _eg_     1    _ef_

a pull of 300 pounds × 4 = 1,200 pounds will be exerted at the pin _f_
or _g_. This total pull must be divided equally between the arms _eg_
and _ef_, giving 600 pounds pull on each. According to the principle of
the lever, the distances through which these forces act are inversely
proportional to the forces acting. It is assumed that the brakeman can
exert the force of 50 pounds through 36 inches; if this is the motion
of the end of the hand lever _a_, one-sixth of this, or 6 inches, will
be the motion at _c_ and, therefore, at _h_; one-fourth of 6 inches or
1½ inches will be the motion at _f_ and _g_; that is, _f_ will increase
its half of the brake band 1½ inches in circumference, and _g_ will do
likewise with its half, making the total circumference 3 inches more,
or the diameter 1 inch more, and thereby moving the band away from the
drum ½ inch radially. The levers are all shown in mid-position to make
the figure more simple, but the relative leverages remain the same at
all points in the motion.

This is an example of simple levers, but the force applied at the hand
lever may be increased in a much greater ratio by the use of a device
known as a _differential lever_.

[Illustration: FIG. 28]

=47. The Differential Lever.=--The principle of the operation of the
=differential lever= with which a constantly increasing force can
be applied to the brake strap is illustrated in Fig. 28. Let _a o_
represent a straight lever whose fulcrum is at _o_; and let the reach
rod be attached at _e_. In this position, if

    _a o_     6
    ------ = --- ,
    _e o_     1

the effective lever is 6 to 1. If, now, the lever is moved through
30° to the position _b o_, the force applied at _a_ moves through the
distance _a b_, and the reach rod through the horizontal distance _k
f_, so that the effective leverage is increased a small amount _e k_
and the ratio of the arms becomes

     _a o_
    ------- .
     _k o_

When the lever is moved another 30° to the position _c o_, the reach
rod moves a distance _i g_, which is less than _k f_, so that the
effective leverage is increased by the amount _k l_ and the ratio of
the arms becomes

    _a o_
    ------ .
    _l o_

Again, moving the lever 30° more to the position _d o_, the reach rod
moves through the still shorter distance _j h_, which is less than
_i g_, and the effective leverage becomes very great. It is evident
from this that the farther the lever is moved toward _d_ the greater
becomes the effective leverage. In practice, it would be impossible
to move the lever through the entire quadrant to advantage, and there
would also be more movement of the reach rod at the beginning of the
stroke and less at the end than is needed to produce the desired effect.

[Illustration: FIG. 29]

From the principle just given, it is plain that, if _p o_, Fig. 28,
represents a brake lever with the reach rod attached at _q_, a smaller
pull will be exerted on the brake band if the lever is moved to the
position _b o_ than would be exerted if a lever were moved through the
same angle from _b o_ to _d o_. The movement from _p o_ to _b o_ is a
convenient and easy one for the engineer to make, while the movement
from _b o_ to _d o_ is inconvenient. To overcome the inconvenience and
still to obtain the advantage of this latter movement, the differential
lever shown in Fig. 29 is used. By means of an arm placed on the lever,
the point of attaching the reach rod is at _l_ instead of _p_; hence,
when the handle _r b_ is moved to the position _s b_, the point _l_
moves to _m_, thus securing a greater and gradually increasing pull
with the easier movement of the handle.

A differential lever may be advantageously used in connection with any
band or post brake and on a drum running in either direction. Such
levers are considered by many preferable to the differential brake.

=48. Power Brakes.=--Large drums and heavily loaded drums cannot be
controlled by hand-power brakes, and in such a case some other form of
power, such as steam, compressed air, or water, must be used.

[Illustration: FIG. 30]

Fig. 30 shows, in outline, how such power is applied. The movements
of the hand lever _A_, instead of being directly communicated to the
lever operating the brake, merely control the valve _v_ connected
with the cylinder _a_. By means of this valve, steam, compressed air,
or water is admitted to either end of the cylinder and this moves
the piston in the direction necessary to apply or release the brake.
There are a number of varieties of such power brakes, differing in
structural details, but the action of all is essentially the same.
With steam or air power, the brake would be applied with its full
force almost instantaneously, thus subjecting the various parts of the
mechanism to very severe and objectionable strains, unless the valves
were modified so as to regulate the admission of the steam or air. One
method of controlling this action is the use of a valve that requires
a long travel to give it a full opening. Such a valve can be opened a
little, so as to allow the steam to leak through and thereby increase
the pressure in the cylinder gradually. As the motion is difficult to
regulate, a better method is by means of a floating valve, described in
_Hoisting_, Part 1.

=49. Crank Brake.=--In addition to the brake applied to the drum and
intended for use mainly in emergencies, many hoisting engines are also
fitted with a strap brake applied to the crank-disk. In some states,
crank-brakes are required by law. In order to give a large bearing
surface, the crank-disk is made very large.

                   HOISTING
                   (PART 4)

    Serial 851D                  Edition 1




HOISTING APPLIANCES


SHEAVES

=1. Sheaves= are grooved iron or steel wheels used to carry or guide
a rope. The general method of mounting them on a frame for hoisting
light loads is shown in Fig. 1. The journal boxes are so constructed as
to be easily taken apart for inspection or repair. For hoisting heavy
loads, the timbers must be braced, as is explained under the heading
Head-Frames in this Section. Sheaves are of two styles--those composed
entirely of cast-iron and those with cast-iron hubs and rims and
wrought-iron or soft-steel arms or spokes.

[Illustration: FIG. 1]

=2.= The =cast-iron sheave=, Fig. 2, has arms with a cross-section, as
shown at _a b_, and with the flanges of the arms tapering from the hub
to the rim; that is, _d_ is greater than _c_ and _f_ is greater than
_e_. The bottom of the groove _g_ in the rim should be a circular arc,
whose radius is a little larger than that of the rope used over the
sheave, to allow for the angling of the rope due to its fleeting on the
drum. The flanges _h_ are made quite deep to prevent the rope jumping
off.

This sheave is cheaper than a combined cast-iron and wrought-iron or
steel sheave, and for many purposes it is entirely satisfactory. Its
great weight is an objection, because it adds to the weight on the
journals and also offers considerable resistance to being set in motion
and stopped.

[Illustration: FIG. 2]

If a sheave is merely used to carry the rope or to deflect it only a
little, the contact and pressure between the rope and the sheave is
small; consequently, the power of the rope to turn the sheave will be
slight. In such a case, when the rope starts or stops quickly, as it
usually does in modern hoisting plants, the heavier the sheave the more
will it lag behind the rope and the greater will be the wear on the
rope due to slipping.

=3.= The sheave with a cast-iron hub and rim and wrought-iron or
soft-steel spokes, Fig. 3, is an excellent and extensively used
sheave, especially the larger diameters. The spokes are screwed
into the hub and rim and are carried to the right and to the left of
the hub alternately, as shown in Fig. 3 (_b_), so as to take hold of
the opposite ends of the hub, thereby giving stiffness to the sheave
against any side stress.

[Illustration: FIG. 3]

With a sheave having cast-iron arms, the load from the rope is
transmitted to the shaft by a compressive stress through the arms
directly under the load; that is, if a rope runs over the sheave, Fig.
2, putting a load on it from _j_ to _k_, this load will be transmitted
as a compressive stress through the arms _l_ and _m_ to the hub and
the shaft. Of course, a part of this load is carried around the rim to
the lower arms and is supported by them in tension, but these lower
arms are not considered in designing the sheave because cast-iron is
of comparatively little value in tension, whereas it is of great value
in compression. In the case of the sheave with wrought-iron arms, or
spokes, Fig. 3, the load is transmitted around the rim to the side
opposite its point of application and is carried from there to the hub
and shaft by the tension of the spokes; in fact, from the method of
construction, the spokes in this sheave act only by tension. The sheave
is strong and rigid, and much lighter than a cast-iron sheave of the
same strength, so that there is less wear between it and the rope due
to any slipping action when it is started or stopped.

[Illustration: FIG. 4]

[Illustration: FIG. 5]

=4.= Sometimes, the spokes, instead of being radial as in Fig. 3,
are made tangent at the center of the wheel, Fig. 4, to an imaginary
circle, which is about 2 inches in diameter for a 10-foot sheave.
Alternate pairs of spokes are made tangent to the opposite sides of
the circle, so that they pull against each other, and this makes the
sheave rigid in both directions. That is, spoke _A_ is tangent to the
right side of the tangent circle and _A′_ to the left side, while spoke
_B_ is tangent to the right side of the circle and _B′_ to the left
side. The pair _B B′_ is joined to one end of the hub, while the pair
_A A′_ is joined to the other end, thus giving lateral stiffness to the
sheave. This arranges the spokes in groups of four, so that the total
number must be some multiple of four. The tangential direction of the
spokes is often necessary in very large sheaves carrying heavy loads,
because with such a sheave it requires considerable force to turn the
shaft in its bearings, and while radial spokes act only as long levers
in turning the shaft, with tangential spokes there is also a direct
pull to do it.

=5. Wood-Lined Sheaves.=--The rims of all sheaves are made either
solid or with wooden lining, as shown in section in Fig. 5. One flange
_a_ of the rim is a separate piece that is held on by bolts _b_. The
wooden lining is in the form of blocks placed with the grain of the
wood running radially and held securely by clamping together the two
flanges with bolts, as shown. With such a sheave, there is much less
wear on the rope than there is with one that has a plain cast-iron rim.
The wear of the sheave proper is also avoided, because as the blocks
wear down they are taken out and replaced by new ones.

=6. Diameter of Sheave.=--The size of a sheave about which a rope
bends is determined generally by the size of the rope to be used, as
explained under Wire Ropes in _Hoisting_, Part 2; but, if the rope is
simply to be supported in a straight line, the space available for
setting the sheave and its cost and weight usually determine the size
used. The minimum allowable diameter of sheave should not be used
unless it is necessary to do so, for the larger the sheave the less
will be the wear of the rope due to the bending, and the longer the
life of the rope, but the cost of the sheave, which increases with the
size, puts a limit in the other direction.

=7. Rollers and Carrying Sheaves.=--Wooden or iron rollers are
sometimes used for rope carriers or guides, instead of light sheaves,
when the rope has merely to be supported and there is no bending of
the rope, excepting the slight amount due to the sagging between the
rollers. The diameter of the rollers is of little importance in such
cases so far as the rope is concerned. If they are for use on a slope
to keep the rope from dragging on the ground, they must be small,
because the cars must run over them, and mine cars are usually made
low because of restricted headroom in the mine. Rollers and carrying
sheaves are fully described and illustrated in _Haulage_.

If a hoisting rope changes its course from a straight line, even if
the deflection is only a small amount, a roller is not advisable and a
sheave should be used, if possible.


CAGES


CAGES FOR VERTICAL SHAFTS

=8.= A =cage= is a carriage used for hoisting mine cars and their
contents, men, timber, etc., in both vertical and inclined shafts.
Cages are built of wood strengthened with iron or steel, or entirely of
iron or steel.

[Illustration: FIG. 6]

=9.= The cage shown in Fig. 6 is much used in the anthracite region of
Pennsylvania. It is made largely of oak strengthened with iron and the
size varies to suit the shaft, being sometimes as large as 6 feet wide
by 12 feet long. The general construction of the cage is evident from
the figure, but several appliances that should be common to all cages
in some form or other require detailed explanation.

A covering _a_, called a =bonnet=, protects persons on the cage from
objects falling down the shaft, and is required by law in some States.
This bonnet is made of steel plate with flanges or angle irons to
stiffen it, and is usually inclined. To prevent objects of moderate
size from wedging between the edge of the bonnet and the shaft lining,
the former is sometimes made shorter than the cage, so that a space of
about a foot is left between its lower edge and the shaft lining. A
short bonnet of this character does not, however, fully protect persons
on the cage. The upper part of the bonnet is fastened to the upper
cross-bar of the cage by two hinges and is held up by rods _b_ that are
attached to the bonnet and have sockets at their lower ends, which fit
over pins bolted to the uprights of the cage. By raising the rods from
the pins the bonnet can be lowered so that pipes or long timbers may be
lowered on the cage.

=10. Safety catches= are intended to prevent a cage falling in case
the hoisting rope breaks. A common form, shown at _c_, Fig. 6, and
in detail in Fig. 7, consists of a pair of toothed cams _j_, Fig. 7,
fastened on each side of the cage near the shaft guides. The drawbar
_b_ to which the rope is attached extends through the top cross-piece
of the cage and through the cylinder _d_, at the bottom of which is
a plate _c_ supplied with lugs for the rods _f_ that connect it with
the levers _g_. Inside the cylinder are three powerful rubber springs,
which are in compression so long as the cage hangs from the rope, but
are extended if the rope breaks, drawing the rods _f_ down and with
them the ends of the levers _g_ to which they are attached; and, since
the levers are pivoted, their other ends are moved upwards and with
them the rods _k_. The cams _j_ are each attached to one end of the
rods _k_ in such a manner that as the rods move upwards they rotate the
cams inwards until they come in contact with the shaft guides. The
teeth of the cams grasp the wooden shaft guides and stop the descent
of the cage. The cams are provided with projections _a_ and _l_ that
strike the guide and thus prevent the cams turning entirely around.
Fig. 7 (_a_) shows the springs extended and the dogs _j_ just about
to grasp the shaft guides, while Fig. 7 (_c_) shows the position of
the dogs when the springs are compressed as they are when hoisting.
At _e_ in cylinder _d_, Fig. 7 (_b_), there are slots for the lugs of
plate _c_ to move up and down as the spring is compressed or extended.
Instead of rubber springs, helical steel springs are sometimes used,
and with a somewhat different design flat steel springs are used.

[Illustration: (_a_) (_b_) (_c_)

FIG. 7]

[Illustration: FIG. 8]

The cams, or dogs, may be placed at any point along the upright post
of the cage, and in some cases two sets of cams are used on each side,
one set at the top and another in the middle, both sets being connected
by rods so that they work together. Practical tests of these catches,
made by allowing the cage to drop, show that they are, as a rule,
very efficient devices. The cams usually take hold at once, the cage
dropping only a few inches, or, at most, a few feet if the guides are
dry and free from oil. When the guides are very greasy or wet, the
cage may drop several feet before the cams take a firm hold and stop
it, and with ice-covered guides, instances are given where the cage
has fallen 15 feet before the cams ploughed their way through the ice
and took firm hold of the guides; but in so doing the momentum the
cage acquired was so great that the guides were destroyed. Fortunately
for the utility of safety catches, ropes are usually broken while a
loaded cage is being raised, and the cage has an upward momentum; if
a rope breaks when the cage is descending at a speed of 30 or 40 feet
a second, its momentum is so great that either the catches or guides
break. The catches generally hold and either the guides or cage suffer
more or less injury under such circumstances. Instead of being placed
near the top of the cage the dogs are frequently placed near the
center, or near the bottom; in some cases two sets of dogs have been
used, one set being at the top and the other at the bottom. Instead of
being cam-shaped with a number of small teeth on the rim of the cam, as
shown in Fig. 7, the dogs are now frequently made consisting of one or
more strong straight teeth on each side of the guide. These teeth are
operated similarly to those shown in Fig. 7, and are driven into the
guides if the rope breaks, thus holding the cage more firmly than the
cam-shaped guides, particularly where the guides are wet.

                               TABLE I

    ==================+=========================+=========+========
         Platform     |         Guides          |         |
    -----------+------+--------+----------------+Safe Load| Weight
       Width   |Length|  Size  |Distance Between|  Pounds | Pounds
    ----+------+ Feet | Inches +------+---------+         |
    Feet|Inches|      |        | Feet | Inches  |         |
    ----+------+------+--------+------+---------+---------+--------
      4 |  3   |   6  | 6 ×  6 |   4  |   6     |  5,000  |  2,000
      6 |      |  10  | 6 × 10 |   6  |   3     |  8,000  |  3,800
    ====+======+======+========+======+=========+=========+========

=11. The Heavy Steel Cage.=--The cage that is shown in Fig. 8 is made
of iron and steel except the wood flooring, which is laid in two
courses, one lengthwise and one diagonal. The joints should not be
driven too tightly, as the wood is likely to swell. The track is bolted
to the floor, or =deck=, of the cage. The cast-steel safety dogs are
operated by steel springs _a_, coiled about the bars _b_, which are
connected to the drawbar _c_ by chains, as shown. The drawbar drops if
the rope breaks and thus assists the action of the springs _a_. This
cage is in use at both coal and iron mines, and is built to suit any
size of shaft and guides. Standard sizes are given in Table I.

=12. The Light Steel Cage.=--Fig. 9 shows a light steel cage much used
at gold and silver mines. It has a spring drawbar and steel safety
dogs, operated by steel springs, as in Fig. 8, but the floor is of
steel grating in order to give as little air pressure as possible
against the cage. The openings _a_ in the side frames are provided so
that through them the nuts can be tightened on the bolts that hold the
shaft guides. The cage is provided with bails _b_ that swing down over
each end of a car to hold it on the cage.

[Illustration: FIG. 9]

=13. Multiple-Deck Cages.=--Cages are sometimes built that have two
or more decks or platforms one above the other, thus giving greater
hoisting capacity to a shaft. A two-deck, safety, hoisting cage is
shown in Fig. 10. The upper deck is heavier than in a single-deck
cage of similar construction. The lower deck is suspended from the
upper deck by means of pins so that it may be removed at any time. A
double-deck cage may be used by first changing the car on the upper
deck and then bringing the lower deck to the track level and changing
the other car. Time can be saved by having two track levels, both at
the loading and landing stations, enabling both decks to be loaded and
unloaded at the same time.

[Illustration: FIG. 10]

=Multiple-deck cages= have been mainly used at ore mines in America and
very few coal mines have been equipped with them. Cages are also built
to accommodate two cars placed either side by side or end to end.

[Illustration: FIG. 11]


AUTOMATIC DUMPING CAGES

=14.= A =dumping cage= is a cage so constructed that at the proper
place it can be automatically tipped sufficiently to dump the contents
of a car that is on it and will then right itself for the down trip,
thus avoiding the necessity of removing the car from the cage, and
saving time at the head. The construction of the cage is such that
the car is held firmly in place while dumping. The principle of the
self-dumping cage is illustrated in Fig. 11, the cage being shown in
its highest and lowest positions. The cage is made in two parts _a_ and
_b_. The fixed frames _b_ slide on the guides _k_ and have attached
to them the safety catches and hoisting gear. The movable part _a_ is
united to the frame _b_ by the hinge _c_. The platform _d_, on which
the car rests, is fastened to the movable part _a_ by the support _e_
and further secured by the braces _f_. At the top of _a_ is attached
the wheel _g_ that runs along the rail _h_, keeping _a_ in an upright
position until it reaches the dumping place _i_. Here the rail _h_
is bent as shown and the wheel _g_ is made to follow it by means of
the guide _j_. This throws the top of _a_ over so as to incline the
platform and dump the car that is on it. On lowering, the cage rights
itself when _g_ passes below the point _i_. The part _b_ is kept in a
vertical position by means of shoes that slide on the main guides _k_.

It is possible to dispense with the guide rail _h_ by attaching a
flange to the top of _a_ at the back, to slide on the main guide _k_.
This flange should be shorter than the shoe on _b_. The main guide
is cut away at the point where this flange comes when the wheel _g_
enters the curved guide _j_, leaving an opening just large enough to
allow the flange on _a_ to pass through. The shoe on _b_, being longer,
completely spans the space and cannot pass through, but makes _b_ move
straight up on the main guides.

The bottom of the cage in Fig. 11 has an interrupted track, and at the
bottom of the shaft the track is also interrupted, as shown in the
plan at the bottom of the figure, but in such a way that when the cage
is resting at the bottom this portion of the track _n_ projects up
through the bottom of the cage and makes a continuous track. When the
cage is raised the wheels of the car drop into the spaces _n_ in the
cage bottom, thus preventing the car from running off the cage during
hoisting or dumping.

=15. Slope, or Inclined-Shaft, Hoisting.=--In a slope, or inclined
shaft, the mine cars are attached directly to the hoisting rope and
hoisted singly or in trains for inclinations less than 35°, at which
inclination the material will begin to fall from the top of the car.
For steeper slopes, it is customary to use a slope cage or carriage on
which the mine car is hoisted, or else to dump one or more cars of the
material into a gunboat, or skip, at the bottom of the slope or at some
landing along the slope, and to then hoist the gunboat, or skip.

Fig. 12 shows a cage for use in a slope or steeply inclined shaft. It
is made of steel with timber platform and differs from a vertical shaft
cage mainly in having its upper frame inclined and in running on four
wheels _a, b_. These wheels usually run on timber guides, so that the
safety dogs _c_ will take hold of the guide in case the rope breaks.
For slopes of variable inclination, the platform _d_ may be made
adjustable by means of a hand lever so as to be always level.

[Illustration: FIG. 12]

=16.= A =slope carriage= is a frame so constructed that when rails
are placed on the top and a mine car run on them the car will be
practically horizontal. The carriage is mounted on wheels and axles in
order to follow the slope tracks, and is supplied with a drawbar, or
with hooks, as shown in Fig. 13, for attachment to the hoisting rope.

These carriages are sometimes built to run on a slope track of the same
gauge as the mine cars, but to insure stability they have generally a
broader gauge. The headroom necessary is governed not so much by the
form of the carriage as by the length of the car and the inclination
of the seam. This height is less when the cars are placed on the
carriage with their length across the slope than when they are run on
lengthwise; but this arrangement increases the width of the slope. When
the inclination is very steep, the wheels are sometimes placed on the
sides of the carriage and above its center of gravity and run between
two tracks or guides, on each side of the slope.

[Illustration: FIG. 13]

The carriage, Fig. 13, is for use on slopes of a uniform inclination.
It is made almost entirely of heavy timber, is stiff and simple of
construction, and is easy to repair. Its details will be readily
understood from the illustrations, except perhaps, the device for
locking the car to prevent its running off during the hoist. The middle
portion of the platform _a_ having a piece of the car track on it,
may move vertically up or down. As shown in the side elevation, it is
resting on the horizontal timbers _b_ of the carriage in a position
ready for hoisting. At the end of the hoist, when the cage settles on
the keeps _c_, shown in the end elevation, this platform reaches them
first and is supported by them while the rest of the carriage descends
still farther until the timbers _d_ rest on the keeps also. The track
on the platform _a_ is then at the same level as that on _d_, and the
car can be run off and replaced by another. When the empty car is on,
the carriage is lifted from the keeps, but the platform _a_ remains
until the timbers _b_ pick it up, when the keeps are swung back out of
the way and the carriage is lowered.

Slope carriages usually have the tracks running crosswise so that the
car is pushed on from the side instead of from the end.


SKIPS, OR GUNBOATS

=17. Skips= are self-dumping cars used for hoisting material from
shafts or slopes. In a vertical shaft, they run in guide tracks; but
in a slope they have wheels and run on a track like a car. In the
anthracite region of Pennsylvania, skips are called =gunboats=.

As the skip is not detached from the hoisting rope, time is saved at
the top over that needed to unhook and hook the cars to the rope or to
remove and place the cars on the cage. But since dumping the material
into the skip and again on the surface produces considerable fine
material, skips, or gunboats, are seldom used for any material, such
as coal, that is often lessened in value by being broken. The skip, or
gunboat, shown in Fig. 14 is closed along the top _a_ and open at the
end _b_, which is cut at about the angle of the slope in which it is
to be used, so as to remain practically level during the hoist. It is
made of sheet iron, the bottom, sides, and top being stiffened by angle
or =T= irons, and the back stiffened and protected by 3-inch planks,
backed by 3" × 6" timbers. The wheels of a skip are fixed on the axles,
which run in journal boxes, thus insuring smoother running than is
obtained with loose wheels. The details of the journal bearings, as
shown in Fig. 15, consist of three castings, the bracket _a_, which is
bolted or riveted to the gunboat, a pivot casting _b_, and the bearing
proper _c_. The bearing _c_ rests on the axle and carries, by means of
trunnions _d_, the pivot casting _b_, on the top of which is placed a
rubber cushion _e_ to lessen the shocks between the casting and the
bracket.

[Illustration: FIG. 14]

[Illustration: FIG. 15]

=18. Method of Loading Skips.=--In Fig. 16, a skip _a_ is shown in
a slope standing immediately below a level where a car _b_ is ready
to have its load dumped into the skip. Instead of dumping the mine
car directly into the skip, a bin is frequently provided at the level
station, or landing, into which the mine cars are dumped and from which
the material is loaded into the skip through suitable chutes. The
use of such bins makes the hoisting of material largely independent
of the working conditions on the levels and the hoisting can be more
systematically and satisfactorily carried on.

[Illustration: FIG. 16]

[Illustration: FIG. 17]

If the material comes to the slope as shown in Fig. 17, it is necessary
to let down a bridge _a_, on which the car runs, in order to reach the
skip. After the car is dumped, the bridge is lifted out of the way into
the dotted position, so as to leave the slope unobstructed.

=19. Method of Dumping Skips.= To dump a skip at the surface, the
tracks are extended above the slope mouth, as shown in Figs. 18 and 19,
and are arranged so that the material may be dumped directly into a bin
or into cars as desired.

In the arrangement shown in Fig. 18, the front wheel of the skip
strikes a stop _a_ and, since the bail of the skip is pivoted far down
toward the lower end, as the rope continues to pull, the rear of the
skip is raised and the material is dumped. The objection to this method
is that if the rope is slightly overwound the skip is pulled off the
track and does not then right itself on the track when the rope is
released.

[Illustration: FIG. 18]

In the Lake Superior iron and copper region, many of the dumps are
built as shown in Fig. 19. In this dump, the rails of the main track
_a_ are curved as shown at _b_; a short distance back of the beginning
of this curve, another track _c_ begins outside the track _a_ and runs
in a straight line parallel to the inclination of the hoist. The track
_c_ is of a wider gauge than _a_, and the rear wheels of the skip have
a wider tread than the front, so that they will run on _c_ while the
front wheels take the curved track until they strike the stop _d_. The
rear of the skip will thus be raised and the material dumped. There are
but two tracks in the main part of the slope.

[Illustration: FIG. 19]

[Illustration: FIG. 20]

[Illustration: FIG. 21]

In the method illustrated in Fig. 20, the rear and front wheels have
the same tread, but the rear axle is longer than the front and has
rollers _a_ on each side. These strike the track _b_, and while the
front wheels follow the curved track _c_ these rollers run on the track
_b_ and thus raise the rear end of the skip.

=20. Skip Cage.=--Where a self-dumping skip is to be used in a vertical
or highly inclined shaft and it is desired to use safety catches, the
skip _a_ is mounted in a cage or frame _b_, Fig. 21, similar to the
self-dumping cage, Fig. 11. The skip being pivoted at _c_ one side
of the center, and resting on the frame of the cage, tends to remain
upright until it reaches the dump; but for safety it is sometimes
locked in place by the latch _d_, which hooks over the pin _e_. When
near the top, the roller _f_ on the end of the latch _d_ comes in
contact with a bar that depresses the roller and thus unhooks the
latch. The roller _g_ enters and travels along the guide rails _h_,
tipping the skip. There are two rollers _g_, one on either side of
the skip. The nose _i_ is temporarily caught on the roller _j_, thus
stopping the movement of the skip sidewise and away from the upright
guide.


BUCKETS

=21. Buckets=, such as are used for hoisting material during shaft
sinking, are continued in use after mining begins when the amount of
material to be hoisted is small.


CAR LOCKS

=22.= Several methods of keeping the car on the cage have already
been illustrated: by chains, Fig. 8; by bails, Figs. 9, 10, and 12;
by omitting sections of the rail under the car wheels, Fig. 11; and
by dropping a portion of the platform, Fig. 13. A very common way is
merely to put a pin through the hole in the drawbar and into the floor
of the cage. Another common device consists of a brake block that fits
between the wheels and can be thrown in from the side by a lever when
the car is in place. Another device consists of a yoke, which, by
means of a lever, is raised when the car is in place so that it passes
about the axle and thus holds the car. A device frequently used on
self-dumping cages is shown in Fig. 22.

[Illustration: FIG. 22]

The curved bars _a_ of iron, which just fit around the car wheels as
shown, are attached to the loose bars _b_, on the ends of which are the
weights _c_. When the cage is at the bottom, these weights strike on a
cross-piece and are raised to the position shown by the dotted lines,
throwing out the bars _b_, as shown by the dotted line, thus releasing
the wheels. The devices shown in Figs. 11, 13, and 22 do not come into
action until the cage leaves the landing and the cars must, therefore,
be watched until that time.


CAGE GUIDES

=23. Guides= are used in all vertical shafts of any considerable depth
and in many highly inclined shafts to keep the cage from swinging
about and striking the sides of the shaft. They are made of wooden
rails, iron rails, or wire ropes. In American mines, timber guides
predominate, although some iron ones are used, and for small shafts
at ore mines wire-rope guides are common. In English mines, wire
ropes, called _conductors_, are very largely used. This difference
in practice is probably due to the fact that in English mines the
shafts are usually round and the cages are rectangular. In such a
shaft, the wire-rope conductors hang from the head-frame without any
cross-bracing, but they require a strong support, as both the weight
of the ropes and the strain to give the necessary tension come on the
head-frame. When both the shaft and the cage are rectangular, as in
most American mines, timber guides are easily put in and they offer a
good surface for the safety catches to grip.

[Illustration: FIG. 23]

Wooden guides are always rectangular in cross-section and in the United
States are usually made of yellow pine or other long-grained wood that
does not splinter easily; in some localities, oak or some of the other
harder woods are used. There is no fixed size for cage guides, but 4" ×
4", 6" × 8", 8" × 10", and 4¼" × 11" timbers are frequently used.

The guides are firmly fastened to the shaft buntons with lagscrews or
with bolts countersunk into the guide so as to be clear of the shoes,
and, to secure safety with speed in hoisting, the ends of the guides
must be put together with joints that are not liable to displacement
and that offer no projections to the shoes in passing. The buntons
to which the guides are secured must be so firmly fastened that they
cannot get out of place, and the guides must be set as nearly as
possible in a straight line, because if they are crooked the cage
is thrown back and forth as it travels along them and this not only
increases the strain on the hoisting rope and engine, but sooner or
later loosens and misplaces the guide. Fig. 23 shows a plan of a cage
with the bunton _A_, guides _B_, and cage shoes _C_ in their normal
positions.


LANDING FANS OR KEEPS

=24.= In order to take the strain off the hoisting rope while a cage
or skip is being loaded or unloaded, a mechanism to support the cage
is placed at the top and at any level of the mine where loading is
done, excepting at the bottom level where all that is usually required
are the cross-timbers for the cage to rest on. These supports have
different names in various localities, being known as _fans_, _keeps_,
_cage rests_, _landing dogs_, _landing chairs_, _wings_, etc. Their use
increases the safety of caging.

=25.= A common form of keeps is shown in Fig. 24. The cage _a_ rests on
four square bars of iron _b_, one under each corner of the cage. These
bars have an eye or hub at the lower end and are keyed to the shafts
_d_, which rest in cast-steel boxes. The levers _e_ and _f_, which are
also keyed to the ends of the shafts _d_, are connected by a rod _g_.
Chains _h_ prevent the fans from moving too far under the cage. When
the cage is to be lowered, it is first lifted clear of the fans and the
lever _e_ is moved into the dotted position, thus moving the fans _b_
out of the way and permitting the cage to be lowered. The inside of the
fans have no projections, and the operating mechanism is such that no
harm would come if they were left in the shaft and a hoist were made,
as the cage would open out the fans and pass through them without any
trouble. If, however, the fans are not drawn back at all the headings
in the shaft when the cage is lowered, great damage results when the
cage strikes the projecting fans. To avoid the possibility of such
an accident, fans have been devised that fall back out of line of the
shaft as soon as the weight of the cage is removed from them.

[Illustration: FIG. 24]

=26. Hydrostatic Fans.=--Most fans in use are built on the same
principle as those just described, although the details of their
construction may vary. An objection that can be raised against them is
that, with large cages and heavy loads, the jar caused by letting the
cage down on such a rigid support is very hard on the cage. All cages,
particularly heavy ones, suffer much more wear from being landed too
suddenly than from the strains of hoisting. For this reason, it is
advisable to make the upper parts as light as compatible with strength
and the side pieces stronger than needed for the actual strains to
which they are subjected. Hydraulic fans, Fig. 25, have successfully
overcome this trouble. The cylinder shown is one of four on which the
cage rests. The eye at the lower end fits on a bar by means of which
the cylinders are moved backwards and forwards similar to the motion
of the fans _b_, Fig. 24. In Fig. 25 (_a_), the cage is shown as about
to rest on the jaw _a_. As the cage settles, it pushes the plunger
_b_ downwards, but this action is resisted by oil in the cylinder at
_c_. At first, this resistance is very slight, because the =V=-shaped
grooves _d_ in the plunger, which are of considerable size at the end
of the plunger, allow the oil to escape freely into the upper chamber
_e_. These grooves, however, taper down to nothing, so that the flow of
oil through them decreases until none can pass except by leakage around
the plunger. This allows the plunger with its load to settle slowly to
the bottom, as shown in Fig. 25 (_b_).

[Illustration: (_a_) (_b_)

FIG. 25]

If now the cage is lifted and the weight thus removed from the jaw _a_,
the spring _g_ pushes the plunger _b_ outwards and allows the oil to
run from _e_ back into _c_.

=27. Pneumatic Fans.=--A pneumatic fan, shown in section in Fig. 26,
is one in which the shock of the landing is partially relieved by a
cushion of compressed air. The fan is keyed at the bottom to the
shaft _a_ that rotates it, as in Fig. 24. The cylinder _b_ contains
the plunger _c_, which is kept at the top limit of its motion by the
spring _d_. When the cage lands in the jaw _e_, the plunger descends,
compressing the air in the cylinder _b_. The air escapes slowly through
the ¹/₁₆-inch hole _f_, thus allowing the cage to settle into place
with very little shock. These fans should be made of wrought-iron or
cast-steel so as not to be easily broken.

[Illustration: FIG. 26]

=28. Cage Chairs.=--In the case of a cage required to stop at a large
number of levels, it is expensive to provide fans at each level, and to
obviate this a strong steel bar or dog may be used under each corner
of the cage, all four bars being connected to a lever on the cage, by
means of which they can be thrown out at will so as to rest on supports
provided at each level. Fig. 27 shows Gray’s patent cage chair, which
operates on this principle. The sliding bars _a_ are connected by the
cross-bars _b_, which are pivoted at the center and operated by the bar
_c_ through the links _d_. By moving the lever _e_ into the position
shown, the bars _a_ are thrown out so as to rest in notches or on wall
plates in the shaft. The springs _f_, through the cross-bars _b_, force
the sliding bars _a_ back under the cage when the lever _e_ is released.


HEAD-FRAMES

=29.= A =head-frame= of wood, iron, or steel is built over a shaft or
slope mouth to carry the sheaves over which the hoisting ropes are
conducted from the mine to the drum of the hoisting engine; it also
usually carries the upper portion of the cage guides or, in the case of
a slope, the tracks for cars.

[Illustration]

[Illustration: FIG. 27]

A head-frame must be strong enough to bear the strain brought on it due
to the total load hoisted and the pull of the engine in hoisting this
load; it must also be rigid in construction to withstand the severe
vibration and shock to which it is subjected on account of the rapid
hoisting and the jar due to the landing of the cages.

[Illustration: FIG. 28]

The amount and direction of stresses that a head-frame must resist
are usually determined by applying the parallelogram of forces as
follows: Fig. 28 is a simple head-frame at a slope; _a_ is the drum
of the hoisting engine with the rope coming from its upper side and
running over the head-sheave _b_ down to the slope cage _c_. Assuming
that the angles _e_, _f_ made by the two portions of the rope with the
horizontal are equal, and that the pull on each part of the rope is
20,000 pounds, to determine the amount and direction of the resultant
of the two rope pulls, proceed as follows: Extend the rope lines to the
point of intersection _g_ and from there lay off the two lines _g h_
and _g k_, to some definite scale, representing the pull of the rope.
If a scale of 2,000 pounds to ⅒ inch is taken (⅒ inch = 2,000 pounds),
_g h_ and _g k_ will each be 1 inch long. Complete the parallelogram
by drawing _h l_ parallel to _g k_ and _k l_ parallel to _g h_. The
diagonal _g l_ represents the direction and amount of the force acting
on the head-frame due to the pull of the two portions of the rope.
The diagonal, by measurement, is 1½ inches or ¹⁵/₁₀ inches long, and
since each tenth inch equals 2,000 pounds, the stress on the head-frame
in the line of the diagonal _g l_ is 2,000 × 15 = 30,000 pounds. The
figure also shows that the direction of this force is vertical, hence
there is no tendency for the frame to be pulled over to either side
and, theoretically, side bracing is not needed.

[Illustration: FIG. 29]

=30.= Consider now the case of a vertical shaft, Fig. 29, in which, as
before, _a_ is the drum, _b_ the head-sheave, _c_ the cage, and _d_ the
head-frame, and assume the same pull of 20,000 pounds on each part of
the rope. As before, extend the lines of the rope, which are the lines
of force along which the pulls due to the engine and the load act,
until they intersect at _g_. From this point lay off on these lines
distances representing the stresses in the rope to any scale. Using the
same scale as before, ⅒ inch = 2,000 pounds, the lines _g h_ and _g k_
representing the two forces will be each 1 inch long. Completing the
parallelogram by drawing _h l_ parallel to _g k_, and _k l_ parallel to
_g h_, and drawing the diagonal _g l_ through _g_, the resultant, _g
l_ = ¹⁹/₁₀ inches, represents a stress of 38,000 pounds. The direction
of the resultant is also determined, being in the line of the diagonal
_g l_. If the head-frame shown in Fig. 28 were used for this case,
it would be overturned by this resultant force, unless the leg on the
opposite side of the shaft from the engine were securely anchored, so
an inclined brace _m_ is added to resist this overturning action. The
resultant of all forces acting on the head-frame should generally fall
within the structure if the greatest stability is to be secured, but
when this cannot be done it is necessary to resist the overturning pull
by anchoring the head-frame to its foundations much more securely than
is the case where the resultant falls within the structure.

The direction of the resultant force may be obtained by drawing a line
through the intersection of the lines of action of the forces at _g_
and the center of the head-sheave _b_, as may be seen in Figs. 28 and
29.

[Illustration: FIG. 30]

=31.= In Figs. 28 and 29, the pull of one hoisting rope running from
the top of the drum was considered, but in most cases it is necessary
to consider the pull from two hoisting ropes, one running from the top
and one from the bottom of the drum _f_, as shown in Fig. 30. _a b_ and
_a′ b′_ represent the directions of action of the two forces acting
on the hoisting ropes, while the two vertical forces _a c_ and _a′ c_
acting down the shaft are approximately equal to the two forces acting
toward the drum. There are, therefore, two resultants _a d_ and _a′
d′_, the directions of which are determined by lines from _a_ and _a′_
through the center of the sheave _e_. The amounts of these resultant
forces can be determined by the parallelogram of forces as shown in
Figs. 28 and 29. A resultant that is a mean between _a d_ and _a′ d′_,
both in position and amount, is sometimes taken, or the greater value
as determined from _a d_ or _a′ d′_ and the greatest inclination as
given by _a′ d′_ may be used, as being the worst theoretical conditions
to which the frame may be subjected. A head-frame usually has a
vertical post approximately parallel to the vertical pull of the rope
in the shaft, and an inclined member _g h_ approximately parallel to
the resultant determined by the parallelogram of forces. If _g h_, Fig.
30, is parallel to the resultant, the vertical leg _h i_ is under no
strain and merely supports the end of _g h_. If the resultant falls
between _g h_ and _h i_, both of these legs will be under compression.
If the resultant falls outside of _g h_, the leg _g h_ will be under
compression and _h i_ will be under tension. The head frame will be
most stable when the resultant falls between _g h_ and _h i_, but this
cannot always be accomplished in building the frame on account of the
conditions at the head of the shaft; nor is it always advisable to do
so from structural considerations.

=32.= Since wood is much better adapted to withstand compressive than
tensile stresses and since steel is adapted to withstand either tensile
or compressive stresses, it is much more important that the members of
timber frame conform as closely as possible to the theoretical line
worked out in Figs. 28, 29, and 30 than in the case of a steel frame.
Take, for instance, the case shown in Fig. 31, where for some local
reason it is impossible to put an inclined strut in or near the line
of the resultant stress to withstand the pull that tends to overturn
the head-frame. In a steel structure, _a_ can very easily be made a
tension member by anchoring its lower end to a heavy foundation. This
resists the tendency to overturn and makes a very stable structure.
In practice, braces can generally be located parallel to the line of
resultant strain, Fig. 29, or outside this line, as shown in Fig. 30,
so that the strain due to the pull of the rope will come mainly on the
inclined brace and not on the upright. To distribute the stress on the
foot of the different parts of the frame, an inclined brace is usually
set farther from the shaft than the parallelogram of forces locates it,
and so placed that about two-thirds of the strain due to the pull of
the rope comes on the brace and one-third on the upright parts of the
frame. In order to give the frame a more stable base and because the
base must be larger than the top of the frame to bring the foundations
back from the shaft mouth, usually the members _h i_ are also slightly
inclined.

[Illustration: FIG. 31]

Wherever permanency of head-frames is required, if steel is obtainable
at a price at all comparable with wood, steel structures are being
used, as timber frames rot.


TYPES OF HEAD-FRAMES

=33.= There are three types of head-frame construction--_the_ =A=
_type_, the _square type without an inclined brace_, and the _square
type with an inclined brace_.

=34. A Type of Head-Frame=.--Fig. 32 shows the construction of a
triangular, or =A=-shaped, head-frame of which (_a_) is a side
elevation and (_b_) an end view. This particular frame is largely
used at anthracite mines, but the type is one quite commonly used for
timber frames, though the details of construction vary in different
localities. The height of the frame is from 30 to 50 feet, and with
direct-acting engines this height should be sufficient to allow a play
of at least two-thirds of a revolution between the cage landing and the
overwinding point. The posts _a_ are parallel to the hoisting rope _b_
as it hangs down the shaft and the inclined brace _c_, which resists
any thrust that would tend to rotate the head-frame, is parallel to the
resultant pull of the two parts of this rope _b_; the inclined braces
_d_ stiffen the frame and help support the cross-timbers _m_ that
support the cage guides _e_. The sills _f_ are made of three pieces of
timber 8 inches by 14 inches in cross-section. The posts _a_ rest in
cast-iron shoes _g_ that are firmly bolted to the posts and sills. The
inclined braces _c_, _d_ are fitted with cast-iron shoes _h_, _i_. The
post _a_ and the two braces _c_, _d_ are held in place at the top of
the frame by the casting _j_, which also supports the pillow-block _k_.

The posts _a_ and the brace _c_ are made up of two pieces of timber
each 8 inches by 14 inches in cross-section. The brace _d_ consists
of one piece of timber 8 inches by 14 inches in cross-section. The
transverse braces _l_ consist of two pieces of timber 6 inches by 14
inches in cross-section, bolted through the timbers _a_ and _c_. The
supports _m_ for the guides are single pieces of 8" × 8" timber. The
center post, as shown in Fig. 32 (_b_), is braced by the two pieces
_n_, _o_, which are supported by two timbers _p_, _q_ bolted to the two
outside posts. The posts _a_ and the inclined braces _c_ are further
braced by the tie-rods _r_, _s_, _t_, and _u_, all of which are fitted
with turnbuckles, as shown at _v_. The different posts are firmly
bolted together, the bolts being fitted with cast-iron washers.

[Illustration: (_a_) (_b_)

FIG. 32]

[Illustration: FIG. 33]

Fig. 33 shows the construction of the ordinary timber gallows frame
used at many ore mines.

Fig. 34 shows a steel =A= frame, of which the principal dimensions are
as follows: height to sheave center 48 feet; base 33 feet 10 inches by
56 feet. Legs _a_ and _b_ are made of laced channels, as are also the
central upright posts and cross-braces. The forward inclined legs are
made of =I= beams. The weight of the frame is 98,000 pounds without the
sheaves. The advantages claimed for this type of design are that it
gives a very strongly braced frame while using a minimum of material.
Also, in cases of overwinding, the cage goes over the top of the frame
without injury to the frame, and should men be overwound they would
fall only the height of the frame instead of being crushed against the
top.

=35. Square Type Without Inclined Brace.=--Fig. 35 shows a steel frame
in which the tendency to be overturned by the pull of the rope is
resisted by a nearly vertical tension leg as explained in =Art. 32=.
Each leg of the frame is built of channel bars connected by lattice
bracing, as shown, and the legs are stiffened by horizontal channel
cross-bars similarly braced and also by diagonal tie-rods, provided
with turnbuckles.

[Illustration: FIG. 35]

[Illustration: FIG. 34]

Springs are sometimes placed under the journals of the head-sheaves
to lessen the strain on the rope while starting the load; the 15-foot
head-sheaves of the Robinson deep mine at Johannesburg have locomotive
springs under the journal boxes, the actual load on each spring due to
the weight of the sheave, rope, skip, and rock being equal to about
20,000 pounds; it was estimated that the sheave would thus be lowered
by the load on it, about 3 inches, which would be equal to an action
of a spring giving motion of 6 inches at the cage. Springs can often
be used both on the rope and under the sheave in the same plant to
advantage.

[Illustration: FIG. 36]

=36. Square Type With Inclined Brace.=--Fig. 36 shows a very
substantial frame with square tower and inclined brace.

[Illustration: FIG. 37]

Its principal dimensions are as follows: height to sheave center 59
feet 6 inches; base of tower 15 feet 8 inches by 14 feet; distance of
bottom of inclined leg from vertical post 48 feet. Each end post _a_ is
composed of two channels, double-latticed. The horizontal members _b_
are =I= beams and each inclined member _c_ is made up of two angles.
The inclined leg _d_ is trussed as shown and built of channel and
angle beams, the main member being made of two channels, the incline
and base members of the truss being made up of two angles, and the
short vertical member of two channels. The center post of the tower
is similar to the end posts, except that the uprights are =I= beams
instead of channels. The frame is designed for a static weight of
16,000 pounds and for a maximum strain on the cable of 32,000 pounds.

Fig. 37 shows a frame of similar form, but in which the landing
platform is placed at a height above the surface, so that the cars
hoisted can be run off on a trestle and thus be delivered at the top of
a car, breaker, tipple, or ore house. Its principal dimensions are as
follows: height to sheave center 75 feet; base 40 feet 11¾ inches by 21
feet 8½ inches. The leg _a_ is made of two angles. The bracing leg _b_
is built of two angles. The diagonal braces _c_ are single angles. The
horizontal braces are angles or channels of various sizes depending on
the stresses.

=37.= The =head-sheave= is supported directly on top of the main frame,
as shown in Figs. 32, 34, 36, and 37, or a small superstructure _a_ is
built on top of the main frame, as shown in Fig. 38, so that the base
of the sheave journals is perpendicular to the resultant pull on the
frame, that is, to the theoretical direction of the inclined leg of the
frame if one is used.

=38.= Timber frames are usually built by the mining company from its
own designs. Steel frames are generally built by the structural steel
companies from detailed plans and designs furnished by the mining
company, or from a skeleton diagram furnished by the mining company,
giving the loads on the rope and the general conditions about the shaft
to which the frame must conform, the frame being then designed and
erected in detail by the steel company.

=39. Enclosing Head-Frames.=--Head-frames are sometimes wholly or
partially enclosed to protect them and the men from the weather. A
covering of boards is warmest. All woodwork should be painted with
fireproof paint and ample means for extinguishing fire should be
provided. A covering of corrugated sheet iron well painted on both
sides to prevent rusting is often used instead of wood and lessens the
danger of fire, but is not as warm a covering as wood.

[Illustration: FIG. 38]

=40.= In many states, it is required by law that the top of the shaft
be protected by a fence or by gates to prevent persons falling down the
shaft. This protection is secured at the sides of head-frames by extra
timbers or beams forming part of the frame, or by means of a fence
placed near the sides of the frame. The ends of the shaft are protected
by a bar placed across uprights, by gates that swing like an ordinary
door, or more generally by vertical sliding gates that are raised by
the cage when it comes to the surface and drop into place when the cage
descends. Similar gates, doors, or bars should be used at all landings
below the surface.


HEAD-FRAME SPECIFICATIONS

=41.= The following is a sample set of specifications for a steel
head-frame to be built from detailed plans furnished by the mining
company.

This head-frame to be made from drawings to be furnished by the----
Coal Company, and placed on foundations furnished by said company.

=Material.=--Structure to be built throughout of soft structural steel,
net strength 55,000 to 62,000 pounds per square inch; elastic limit
not less than 30,000 pounds per square inch; elongation, 25 per cent.;
bending test, bend flat on itself without fracture.

Builder agrees to guarantee structure to withstand strains specified
on drawings with factor of safety of 10, to provide for possible
overwinding or sticking in shaft.

No steel shall be used less than ¼ inch thick except for lining or
filling vacant places.

=Workmanship.=--The tower to be built in a neat and workman-like
manner. The pitch of the rivets (distance between centers) shall not
exceed 6 inches or sixteen times the thinnest plate, nor be less than
three diameters of the rivets.

The rivets used shall generally be ½ inch, ¾ inch, and ⅞ inch in
diameter.

The distance between edges of any piece and the center of rivet hole
shall not be less than 1¼ inches, except for bars less than 2½ inches
wide; when practicable it shall be at least two diameters of the
rivet. All rivet holes shall be spaced and punched, so that when the
several parts are assembled together a rivet of ¹/₁₆ inch less diameter
than the hole can be entered hot into any hole, without reaming or
drifting. The rivets when driven should fill the holes. The heads must
be rounded; they must be full and neatly made, and be concentric to
the rivet hole, and thoroughly pinch the connecting pieces together.
Field riveting must be reduced to a minimum. All joints and connections
shall be neatly made, the several parts to be brought together without
twists, bends, or open joints.

=Inspection.=--All facilities for inspecting the material and
workmanship shall be given by the builders during the erection of the
head-frame. The company reserves the right to reject any or all parts
not built in accordance with the plans or these specifications. Final
inspection of work 1 month after being in actual service.

=Painting.=--All work, before leaving the shops, shall be thoroughly
cleaned from all loose rust and scale, and be given one good coat of
paint well worked into all joints and open spaces. In riveted ironwork,
the surfaces coming in contact shall each be painted before being
riveted together. Bottoms of bearing plates and any parts that are not
accessible for painting after erection shall have two coats of paint.
After the structure is erected in place, it shall be given one coat of
paint. All recesses that will retain water, or through which water can
enter, must be filled with thick paint or some waterproof cement before
receiving the final painting. The paint shall be a lampblack paint,
mixed with pure linseed oil, or of red lead mixed with raw linseed oil
containing Japan dryer.

=General Clauses.=--The specifications and drawings are intended to
cooperate and to indicate the principal dimensions and requirements
necessary to the complete structure. It being understood that
while some work may be shown in the plans and not described in the
specifications, or vice versa, and some minor details and fastenings
are omitted from both plans and specifications, the work is to be
executed without extra charge therefor, the same as if the minutest
details were set forth in full in both drawings and specifications.
The contractor is to make good any defects of material or workmanship
developing within 1 year after final acceptance.

The contractor shall furnish a location plan and also two copies of the
detail shop drawings for convenience in making future alterations and
repairs.

=Erection.=--The head-frame is to be erected complete, secured to
foundations provided by the---- Company.

Contractor shall furnish all foundation bolts and washers. Iron
stairway with hand rails beside main back bracers and platform with
wooden floor under sheaves, also iron stairs from platform under
sheaves to back sheave pedestal for oiling. Wood furnished by the----
Company.

Price includes all material for completion of work delivered, erected,
and riveted in place and painted.

The---- Company will furnish and place in position the sheaves, with
the shafts and boxes belonging to the same, also the wooden guides.

=Delivery.=--The head-frame to be erected, complete, and secured to
foundations in---- weeks from date of order.


DETACHING HOOKS

[Illustration: FIG. 39]

=42.= In hoisting, there is more or less danger of overwinding or
lifting the cage too far, and dashing it against the top of the
head-frame, or if the top is open the cage may be pulled entirely
over the top. =Detaching hooks= are intended to prevent this. Several
varieties of such hooks are made, which differ from each other only
in their smaller details. In all of them, detachment is effected by
passing the rope through a circular hole in an iron plate or through an
iron cylinder, the diameter of which is sufficient to allow the upper
portion of the hooks to pass through when passing upwards, but the
lower portion is made larger and so arranged that when this larger part
strikes the plate the upper portion is forced open and the hoisting
rope released. After the upper part has been thus opened, it is too
large to pass back through the opening and the plate and the cage is
therefore held suspended. Fig. 39 shows such a hook. It consists of two
outside fixed plates slightly narrower at the top than the diameter
of the hole in the disengaging plate _h_. Between the frame plates
_a_ are two inner plates _b_ that move about a strong pin _c_ passing
through both plates _a_ and _b_, but near the bottoms there are two
projections _d_ to prevent the hook from passing entirely through the
hole. The winding rope is attached to the top shackle _e_ and the cage
to the lower shackle _f_. When the two movable plates _b_ are closed as
tightly as possible at the top about the pin of the shackle _e_, they
are secured by a copper pin _g_. In case of overwinding, when the hook
passes into the hole of the disengaging plate _h_, the two projections
_k_ on plates _b_ are pressed inwards, shearing off the copper pin _g_
and allowing the plates _b_ to turn about the central bolt _c_, thus
releasing the shackle _e_. The plates _b_ are then in such a position
that the projections _l_ on them cannot pass down through the hole.
The cage then hangs by the hooks from the disengaging plate, and the
rope passes on. An objection raised against this hook is that, being
constructed of plates, there is considerable surface in contact between
the moving parts, and unless they are regularly taken apart and oiled,
there is danger of their rusting firmly together.

In England, detaching hooks are used quite commonly, and also in
certain parts of the Central Basin in the United States, but they have
not yet been generally adopted throughout the United States.

=43.= It is claimed by many that such devices inspire the engineer
with a misleading feeling of security; that they are more or less
complicated in construction and so need care, and destroy the
simplicity of the plant; that they may be the direct cause of accident
by introducing new elements of danger; that they add to the cost; and
that they are not thoroughly reliable. Again, it is held that the
surest prevention of overwinding is obtained by the employment of
a sober, reliable, and competent engineer, who is held personally
responsible for overwinding accidents; by having a good brake and an
engine thoroughly under the control of the engineer; by a reliable
method of indicating the position of the cage; by sufficient height
to head-sheaves to allow of considerable hoisting over and above that
necessary for landing.


SIGNALING

=44.= Some method must be provided for communicating between the bottom
or any level of a shaft and the top landing or the engine room, also
between the top landing and the engine room, so that the hoisting
engineer may be notified when both the head-man and foot-man are ready
for him to hoist. A common method of signaling is by means of a gong,
bell, or triangle placed in the engine room and connected by a wire
or small wire-rope with the point from which it is desired to signal.
Attempts have been made in different localities and by different
associations to adopt a standard code of hoisting signals, and while it
would be advantageous if this could be done, none of the attempts made
have been entirely successful. Although there is no uniform system of
signals, one bell generally means stop, two bells lower, three bells
hoist, and four bells hoist men.

[Illustration: FIG. 40]

=45. Hammer-and-Plate Signal.=--Fig. 40 shows a hammer-and-plate
signal, the plate being a piece of boiler iron or steel. The hammer is
often located beneath the plate instead of above, as shown. Another
style of hammer-and-plate is shown in Fig. 41. The hammer is made of
2-inch square iron and heavy enough to balance the weight of wire
hanging in the shaft and to take the sag out of the horizontal wire
connecting the top of the shaft with the lever _a_. A simple dial
turned by a ratchet motion attached to the lever _a_ is sometimes used
to show the number of strokes, and thus check the number counted by the
engineer. The dial is reset by the engineer as soon as he understands
the signal.

[Illustration: FIG. 41]

[Illustration: FIG. 42]

=46. Electric Bells.=--Electric bells operated by push buttons are
rapidly coming into use for mine signaling on account of the ease and
completeness with which such a system can be installed. Electric flash
lights are also extensively used for signaling purposes. The principle
of action and details of the wiring for electric signals and flash
lights have been described in _Transmission, Signaling, and Lighting_.

=47. Speaking Tubes.=--The laws of certain states require speaking
tubes, in addition to the ordinary means of signaling. These speaking
tubes are generally made of 2-inch iron pipe and are from 300 to 1,500
feet long, and are often provided with whistles at the end of the pipe
and at each level of the mine, by which the attention of persons at any
level can be attracted or the whistle may be omitted and the attention
of persons attracted merely by rapping on the pipe with a piece of iron.

[Illustration: FIG. 43]

=48. Pneumatic Gong Signal.=--Fig. 42 shows an attachment that can be
connected to a speaking tube and that is widely used for signaling. It
consists of a brass cylinder _a_ fitted with a piston _b_ containing
valves _c_. The gong _d_ is attached to the cylinder _e_ inside of
which the clapper _f_ fits loosely. When the piston is pushed inwards,
as shown by the arrow, by means of the handle, the air in the cylinder
and in the pipe _h_ is compressed and forces the clapper _f_ upwards
against the gong _d_. The arrangement of these gongs in the mine is
shown in Fig. 43. A cylinder and whistle are usually placed at each
landing and a gong and whistle in the engine room, though, if desired,
a cylinder, whistle, and gong may be placed at each landing and in the
engine room.

=49. Telephones.=--Telephones connecting the different levels with the
top and the engine room are now frequently used in connection with
other signal systems, but they are not as well adapted as bells or
gongs for rapid-hoisting signaling.

*** END OF THE PROJECT GUTENBERG EBOOK 67844 ***