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If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: Hoisting Appliances - -Author: Various - -Release Date: April 15, 2022 [eBook #67844] - -Language: English - -Produced by: deaurider and the Online Distributed Proofreading Team at - https://www.pgdp.net (This file was produced from images - generously made available by The Internet Archive) - -*** START OF THE PROJECT GUTENBERG EBOOK HOISTING APPLIANCES *** - - - - - -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 HOISTING APPLIANCES *** - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the -United States without permission and without paying copyright -royalties. Special rules, set forth in the General Terms of Use part -of this license, apply to copying and distributing Project -Gutenberg-tm electronic works to protect the PROJECT GUTENBERG-tm -concept and trademark. 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