Chapter II: Part 2

=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.

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.

=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.

=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.

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.

=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.

=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.

=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_.

=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.

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.

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.

=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.

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.

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.

=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.

=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.

FIG. 7]

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.

=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.

=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.

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.

=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.

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.

=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.

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.

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.

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.

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.

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.