Hoisting Ore in Mining

Table of Contents

Auxiliaries Actuated by Oil under 135 lb. Pressure

When steam is used by the auxiliaries, which operate brakes, clutches, etc., it constitutes an important percentage of the total power used by the engine. The condensation is great and continuous, and since the controlling valves can have no lap, but must be set “line and line,” it is impossible to avoid leakage as well. The steam consumption by auxiliaries in a simple engine running at capacity is rarely less than 14 per cent, of the total. If the engine runs intermittently, the proportion used by the auxiliaries is correspondingly greater. In a more efficient engine, the steam for auxiliaries remains the same and is also a greater proportion of the whole.

In this engine, throttle, clutches, brakes and reverse are actuated by oil under a pressure of 135 lb. and controlled by poppet valves. The oil discharged from the auxiliaries is pumped back into an accumulator by a triplex pump, with plungers 2 7/16 in. in diameter by 4-in. stroke, which are driven by eccentrics on the valve-gear shaft. When the accumulator plunger is raised to its highest position, the oil is bypassed to a reservoir. When hoisting from the upper levels, the pump is too small and a relay steam pump which cuts in when the accumulator plunger is below a certain point runs most of the time. This method is entirely satisfactory, and the engine control is sensitive, positive, and efficient.

The operating levers arc arranged in a standard manner (Fig. 8) first used on the Frazer and Chalmers 20 by 48 in, engine at the Spray shaft. All the large hoists are controlled by levers on this plan. There is a great advantage in having all engine levers in relatively the same posi-

tion, acting by the same motion. Engineers can be transferred from one hoist to another without danger of confusion.

Pressure on Low-pressure Cylinder Automatically Regulated

A large steam-jacketed receiver is placed between the high- and low- pressure cylinders, in which pressure is maintained at 20 lb. by an automatic valve, through which steam is bypassed from the high-pressure main to the receiver, when the throttle is closed. Thus, the engine has pressure on all cylinders when starting, and picks up smoothly and quickly instead of needing a stroke or two to reach a working pressure in the low-pressure cylinders. When the throttle is opened, the bypass is shut off and the pressure in the receiver drops to that dependent on the load, speed, etc. When it is desired to hoist with great speed, quicker acceleration may be obtained by adjusting the reducing valve to raise the receiver
pressure.

Condenser Operates under Severe Conditions

The engine has Corliss valves, with automatic cutoff regulated by a governor. Severe conditions are imposed on the condenser by the irregular use of steam. During the first two or three strokes, while the engine is starting the load, steam is taken nearly full stroke, while at the end of the trip the cutoff maybe at 1/10 stroke. In order to condense this sudden rush of steam, a large reservoir of cold water is provided in the “Rain Type” Nordberg condenser cylinder, into which the steam is exhausted, by a series of shallow flat trays filled with water. Constant streams of water are poured into them which over-flow, rain down to the bottom of the cylinder and finally run off by gravity against the vacuum, to the cooling tower, from which it is re-pumped. A 900-gal. rotary pump is used for circulating the water and a 19 by 18 in. vacuum pump, both belted to 20-h.p. 220-volt alternating-current motors which run at constant speed. The temperature of the water at present (June, 1915), is 84° F. when entering and 96° F. when leaving the condenser. The barometer stands at approximately 25 in. The vacuum drops to 16½ or 17 in. at the beginning of a trip, but rises to 20 or 20½ in. The man engine also runs condensing and exhausts into the same system, which was increased in capacity by large pumps and a second condenser when the man engine was added.

Hoisting Speed 1,300 to 1,600 ft. per Minute

In order to insure continuity of operation under all conditions, the low-pressure cylinders are built to stand high-pressure steam. The receiver pressure can be built up to 150 lb. and the engine operated as a simple engine with cylinders 28 by 48 in. stroke. This makes it an engine of great power for emergency use, as for instance, hoisting unbalanced, but at a sacrifice of efficiency.

The engine governor is set for a rope speed of 1,300 ft. per minute when hoisting from the 1000 level or a level above, but by shifting the governor belt to another pulley, a speed of 1,600 ft. is used for greater depths. When production is increased, both speeds are raised. It is preferred to run the hoist at as regular and slow a rate as will conveniently hoist the ore.

Round Rope on Grooved Drums Now Used

Round ropes, 1¼ in. in diameter, in two laps are used on reels, which are 7 ft. in diameter by 5 ft. face. The drums were made without grooving at first, as it was uncertain what ropes were best, a high-grade rope 1 1/8 in- in diameter or 1¼ in., rope of less tensile strength. The ropes began to cut into the drum in an irregular curve. They were grooved in April, 1914, to a depth of 5/16 in., leaving the diameter of the drums at the bottom of the grooves 83 3/8 in.

Fig. 9 shows the relative positions of drums and sheaves to shaft. The ground back of the shaft was cut out as far as practicable to get a reasonably long lead from the sheaves.

The fleet angles are unequal, and from the sheave line to the outside of the drum is 1° 33′. This would be considered excessive in certain districts, the copper country of Michigan for instance, but accepted practice in other places permits an angle of 1° 55′. The original attachments of the ropes were at the outside, or clutch side, of the drums. There was sufficient angularity in the pull from the sheave to draw the laps apart and leave openings into which the second layer of rope dropped. The winding was irregular and rough, and the wear excessive. Other sockets for rope attachment were cut on the inside of the drums, and the trouble ceased. The angular pull tends to hold the laps together instead of separating them. When the drums were grooved, the ropes were again attached at the outside, since the active part of the rope would be nearest the sheave line, and the fleet angle smaller. There is heavy side friction on the rope when the last laps of the second layer are wound on. If attached at the inside of the drum, the grooving would carry it to the outside without so much friction as if winding against a rope. On the second layer, the pull of the rope would again tend to separate the laps and reduce the side friction of rope against rope. Soft-steel wedge-shaped fillers lift the rope out of the inside groove, high enough to wind back on the first layer.

No difference has been noticed in the wear of the under or over wind. If there is a reasonable distance between sheave and drum, there should be none.

The sheaves are 7 ft. in diameter, and are lined with leather. Wood lining broke down rapidly. Cast-steel idlers support the ropes between sheaves and drums to reduce slapping. They are cast thin and the flanges machined to make them still thinner and lighter.

The ropes are attached to the skips by thimbles and six Crosby rope clamps. Once every four weeks, 6 or 8 ft. is cut off the end of each rope to change the points of maximum wear.

The shaft is usually dry. In the wet season, a little acid water seeps in, but no corrosion has been discovered.

A few years ago, Mr. Duncan, Agent of the Cleveland-Cliffs Iron Co., kindly furnished rope records from the Lake shaft hoist, which has 7-ft. drums, 9-ft. sheaves and uses 3½-ton skips, but with only one layer of rope on the drum.

The Copper Queen rope averages do not include those ropes which were obviously unsuited to the conditions.

The ratio of rope to drum diameter is 1:67.2. The experience of the Cleveland-Cliffs Iron Co. indicates that good service may be obtained with that ratio.

The rope cost on the Copper Queen ropes in the above comparison was 0.3 c. per dry ton. The ore contained about 11 per cent, moisture during the time covered by the records.

From the above comparison, the life of a rope is increased 75 per cent, by the use of one lap instead of two, and the cost for ropes at the Sacramento shaft would have been in consequence, 0.17 c. instead of 0.3 c. This would represent a saving in rope in an average year of about $1,000. In order to obtain this saving, the cost of the engine would have been approximately $15,000 greater, and it would be less efficient. A geared hoist would avoid some of these objections, but would introduce others.

The greatest tonnage, 549,324 dry tons, was hoisted by a pair of flattened strand ropes with Lang lay. The cost was 0.277 c. per dry ton. The increase in wearing surface provided by flattened strands is very noticeable. In winding on a smooth drum, the contact between two consecutive laps is made by a rubbing motion. In the ordinary lay, the outside wires which touch are parallel with the length of the rope at the point of contact, and the rough surfaces of the projecting strands bear against each other when the rope comes down against the last wrap. With the Lang lay, they are inclined to the line of the rope and each other, and the friction is reduced.

These conditions are of paramount importance when two layers are wound on a drum, since the bearing of the second lap is entirely rope against rope, and there is at the best a good deal of sliding of one rope on another. The external wear only need be considered, internal wear is of no consequence in comparison. Efficient lubrication on the outside of the rope is of great benefit.

This question is treated in some detail, because it was found very difficult to obtain information on the effect of small drums and two layers of rope on the cost of hoisting. It was of course recognized that the wear would be increased, but to what degree it would increase the cost could not be ascertained.

Underground Storage Bins Have Loading Hoppers

The storage bins at the haulage levels were at first made of standard design. The only attempt to avoid the difficulties formerly experienced with bins was to make them comparatively small to avoid pressure.

Attention was particularly directed toward giving the loader as much time as possible to poke the chute. This was done by putting measuring hoppers holding one skip load each below the bins, which could be loaded at any time while the skip was in motion and tripped into the skip when it reached the loading position. When hoisting in balance at the maximum rate expected, a skip per minute, and allowing 15 sec. for tripping the hopper and ringing off the skip, each loader has 1¾ min. to load the hopper.

When starting the plant, it was found at once that the customary bin was not satisfactory. Not more than half the requisite speed could be attained. The 800-level bin was altered to one of the present type, but of small size, 40 tons capacity. As soon as it was found successful, the 400 and 600 bins were rebuilt but on a larger scale. Their capacity is 90 and 100 tons. The three lower bins are about the same size.

The bin as reconstructed consists of two parts, an upper chamber for storage and a lower part open in front which acts as a slide to the gates. The horizontal opening at the bottom, of the storage chamber is 4 by 8 ft., large enough to prevent arching, but small enough to carry the weight of the ore in storage without permitting it to exert much pressure on the ore resting against the gate. The front, immediately below the contraction, is open for an added relief against pressure as the ore is free to take its natural slope.

This principle has since been used in a 260-ton bin for the 400 level, which is shown in Figs. 10 and 11, together with a standard wooden bin. In this case, the excavation was made circular and lined with concrete lightly reinforced. The conical bottom is armored with rails set in the concrete. It has been found necessary to protect the concrete against erosion when hard ore is stored, but only where the ore strikes on rebounding from the inclined plane at the bottom of the chimney.

It was not known at first how large the hole in the bottom of the cone should be. It was accordingly made 6 ft. in diameter, with the expectation of enlarging it if necessary. It has since been cut out to 7 ft. 4 in., which appears to be the correct proportion to protect the ore below from excessive weight and still prevent arching. This storage bin, although much larger than the others, handles muddy ore equally well.

As finally constructed, the large bin was built on the opposite side of the shaft from that shown in the drawing.

Arc doors are generally used, 30 by 16 in. in size, with good results. The slight extra labor of operation is balanced against the higher cost for installation and maintenance of power doors, which are only used at the large concrete bin at the 400 level.

Below the doors are the loading hoppers (Fig. 12) which hold 58 cu. ft. each, or one skip load. The flat counter-weighted bottom is hinged at the rear and held shut by tension bars on each side extending up to a shaft which is turned by hand levers. It dumps quickly and locks positively, as the tension bars are turned past the center of the shaft. The chute beneath, which carries the ore to the skip, is very steep, to prevent sticking.

The operation of loading is very rapid under ordinary conditions.

The time required to dump the ore into the skip and ring it off rarely exceeds 12 sec., and frequently not more than 10 sec.

The best day’s record is 3,899 wet tons in three shifts, or 3,467 dry tons. An average has been maintained for several shifts at the rate of

433 skips per shift. When the 30 min. for lunch and the time estimated for changing levels are deducted, it makes a hoisting rate of 1.1 skip per minute. Two loaders are required. When there is much muddy ore, or when hoisting very rapidly, a third man is sometimes used. There are still occasions when, for short periods, not more than 20 or 30 skips per hour can be hoisted.

The construction of skips and loading mechanism is heavy and strong. There have been few delays and light repairs.

There has been trouble with the spillage of ore while loading. The chute through which the ore reaches the skip is so steep that the opening is 40 in. high. Even if the skip is held only 3 in. below the bottom of the chute when spotted for loading, there is an opportunity for the ore to spread in falling, and for some of it to fall on each side of the skip rather than in it.

A screen was attached to the side bars above the skip, composed of light plates, inclosing three sides but open on the loading and dumping side. It reached down to the top of the skip, but was spaced far enough outside, so that the skip could turn through it to dump. Since there was a certain amount of danger in adding this complication to the skip, and the spillage was not greatly reduced, it was removed.

The spilled ore falls into a pocket at the bottom of the shaft, from which it is loaded into cars and hoisted on the cage to the 16th level bin. It amounts to about 17 lb. per skip, or 0.21 per cent, of the ore hoisted. It results partly from ore falling outside the skip when loading, partly from the ore which hangs up in the slide below the loading hopper and which falls after the skip is hoisted and partly from overloading. If the skip does not dump clean, and it is not noticed, there may be enough remaining to make an overload when the next charge is tripped into it. As a result of the spill, there has been heavy wear on the timber in the hoisting compartments.

The skips had originally only 70 cu. ft. capacity, and not sufficient margin to prevent an occasional overload. They were rebuilt and made to hold 90 cu. ft.

The skip is of standard Kimberly type, but built heavily. The dumping guides on the surface are formed of angles and heavy steel castings. As the castings wear, thin lining plates are riveted on.

Ore Loaded into Railroad Cars by Belt Conveyors and Trippers

The ore is dumped into a small bin holding about 12 tons, from which it is carried to the railroad track below, and loaded into cars for shipment to the reduction works. The arrangement of the conveyor plant is shown in Figs. 13 and 14.

A 36-in. steel pan conveyor forms the bottom of the bin, and in transporting the ore to an inclined belt equalizes the load. The receiving bin was made small to avoid a great accumulation of ore and consequent packing. It is now apparent that a larger bin would have been permissible and desirable.

The ore falls from the pan conveyor into a belt loader which breaks its fall and feeds it to the belt in the direction of belt travel (Figs. 15 and 16).

The V-shaped opening at the bottom of the pan allows the fine material to reach the belt first and form a bed for the coarser. The sides of the “V”, are movable, and may be spread apart to widen the opening when sticky ore is hoisted.

Great difficulty was encountered in obtaining, a feeder which would not clog with clayey ores. Even as it is, a solid mass of clay has accumulated above the plunger, the full width of the feeder, and several feet high, with the plunger still running ineffectively behind.

When the conveyor plant was first built, the ore fell from the pan conveyor upon the unprotected belt, which travelled on a slope of 15°. Boulders of ore sometimes bounded down the incline before they came to rest on a bed of finer material. When the feeder was put in, the upper 18 ft. of the belt was depressed to a horizontal position, and the bed of ore is well settled before it reaches, the incline.

The inclined belt A. (Figs. 13 and 14) carries the ore down to the loading tracks, passing over a Blake-Dennison weighing machine on its way.

It is supported in a catenary curve to reduce the height of the trestle. This is now recognized as a mistake, as the maximum inclination is increased and the belt cannot be run taut without lifting it off the rollers when it is run empty, or with a light load.

The line of the incline belt crosses four railway tracks and delivers ore to conveyor C, the first of two conveyors parallel with them. The ore is discharged off the end of the belt and falls into a belt feeder similar to that at the shaft. When the ore is to be carried to belt B, the end pulley of the short belt D, the bearings of which are supported on slides, is screwed back by hand under the stream of ore discharged from A. It is then carried by the short conveyor to B and dumped into the third

belt feeder. The short belt thus takes the place of a tripper on a continuous belt and reduces the belt cost.

The loading belts B and C are each located between two tracks, and are long enough to load seven 50-ton cars and a sample car.

A tripper (Fig. 17) moves back and forth constantly, depositing layer after layer of ore in the cars below, until they are loaded to capacity as shown by the belt scales. At one end, it travels a few feet over the eighth car and this is taken as a sample of the lot. When the first lot is full, the sample car is switched to the other end of the loading shed and attached to a string of seven cars loading from the other conveyor,

and the sample of another 350 tons is dropped into its opposite end. Its sample therefore represents two lots of ore of 350 tons each.

The belt speeds may be varied from 240 to 360 ft. per minute, but rarely exceeds 300. The tripper speed is from 150 to 190 ft. per minute, but at the maximum speed of the belt would be 225. It travels back and forth from 36 to 40 times in filling a lot, depending on the weight of the ore; thus depositing from 72 to 80 layers of ore in the cars, and taking half as many samples while doing so. Although each lot may be of widely different composition, the ore in each car or in each linear foot of the car is the same as any other in the same lot. At the smeltering plant, the ore is dumped into pits, one lot directly on the other, until a bed of 10,000 tons is made up. It has been found that when loading by steam shovel from one end of this bed, the ore encountered in working through to the other end is sufficiently uniform in composition to secure good metallurgical results. The sampling is also sufficiently accurate.

In its travel, the stream of ore from the tripper crosses a spout 12 in. wide, which catches a sample, splits it, returning one-half to the car, and drops the remainder into a heap on the ground, which is quartered, down and assayed for quick returns. It is surprising how closely this extremely rough sample checks with the smelter returns. Although there is considerable variation in the sample of individual lots, the average for a month’s run is rarely more than 0.1 per cent.

The first spout tripper was not positive in operation, and a man was needed to ride on it to keep it clear when loading mud. A special tripper was built, in which the ore is discharged upon a short 36-in. belt running at right angles to the main belt. It is driven by a small reversible motor carried on the tripper, which, collects its power from a trolley wire, and may load into either of the string of cars spotted below. The spout tripper was built so high, to secure a steep incline for the spout, that it was unsteady and it was impossible to prevent the main belt from running out of line and cutting the edges. The belt tripper is low and steady and the’main belt runs more truly and with less wear.

The tripper belts cost 0.266 c. per ton of ore handled. Now that there is a smaller proportion of muddy, ore, a low heavy spout tripper might be better. Less attention than before, would be needed to keep the spouts clear.

The inclined belt A is driven by a 30-h.p. direct-current variable-speed motor at the lower end. The belt travel can be varied between 240 and 360 ft. per minute. The pan conveyor at the shaft is driven from the upper pulley by a sprocket chain, as is the belt feeder also. Belt D is also driven from this motor, through a friction clutch. Very little power is required, except to start, about 10½ h.p. with, and 8 h.p. without belt D. When loaded and in motion, it will drift so far that it is equipped with a brake in order to stop it quickly when necessary. The two loading belts B and C are driven by a 30-h.p. variable-speed direct-current motor at the far end, through friction clutches. The tripper belts are driven by 5-h.p. motors.

The trippers are pulled back and forth by ½-in. steel cables driven through reversing clutches, geared to the drive shafts of the belt. Buttons on the rope throw the clutches over at points of reversal, by turning the three-way valve of a compressed-air cylinder, the piston of which acts on the clutch levers. The buttons and points of reversal may be changed quickly, but there is little alteration in the routine and it is rarely necessary. The operation is positive and very satisfactory since powerful clutches have replaced the lighter ones formerly used. The conveyor belt passes idly through the tripper, and there should be less wear than if it supplied the power to propel it.

The control of the whole plant is located on a platform between the loading belts and near the incline. Here are the starting switches for all motors, brake for the incline belt, and levers connected by cables with the clutches at the driving end of the belt conveyors. The belt speed is governed by the speed of hoisting. They are run faster when hoisting from the upper levels. They are stopped when the skips are delayed or stopped for any purpose. The conveyor man is stationed at this point, where he can see all the belts and everything that goes on. One Mexican helper oils up rollers, chains, pulleys, etc. Another is stationed at the shaft to look after the loading end. A mechanic on day shift has been found desirable to attend to current repairs, to re-lace belts, etc. Other men are required from time to time to make more extensive repairs, clean tracks, attend to sampling, etc.

Many changes have been made in the original installation. Belt feeders have been added. The incline belt has been cut in two to eliminate a tripper. The trippers have been rebuilt. The control of the driving mechanism has been centralized. A roof has also been added to protect it from the weather.
The ore is rough, uncrushed, and very hard on belts. The life of belts is gradually increasing, due to improvements in the plant and a better understanding of the conditions.

Recently, it has been desired to screen a certain class of ore for fettling in the reverberatory furnaces, and to supply a coarse sulphide for pyritic smelting. This has been done by raising the discharge end of belt D so that the ore falls against a screen above the belt feeder. The fine ore falls into cars directly below, the reject into the belt feeder and makes up a regular lot and sample of coarse screened ore. Sufficient for present needs can be screened out in this manner, but if more were required, more costly changes would be needed.

Increase in Underground Storage Capacity Contemplated

After the changes in the shaft storage bins, no others were necessary to reach the capacity desired or increase the certainty of operation. Alterations have been for purposes of economy or convenience. There have been few delays caused by accident, and none which stopped operations for more than a few hours.

As stated above, the most rapid hoisting in one day was 998 skips, containing 3,467 dry tons of ore, in three shifts of 7½ hours net working time each. There was not enough ore to fill out the third shift at the same rate as the other two. The rate for an hour or two has exceeded, this considerably. The maximum rate for any month was in February, 1914, when 65,901 dry tons were hoisted in 58 shifts, or 1,136 per shift. When hoisting at this rate, the shaft bins have not sufficient storage capacity. Time is wasted in changing frequently from level to level to avoid blocking the haulage motors. It is to prevent this that the 260-ton bin on the 400 was put in. Two others are in contemplation, which would increase the storage capacity to 1,350 tons. The hoisting capacity of the shaft would be increased, and there would be fewer delays to electric haulage.

Compressed-Air Hoists for Men and Timber at Most Shafts

The engine for men and timbers at the Sacramento shaft is a compound, two-cylinder engine, made by the Nordberg Manufacturing Co., but drives through Wuest herringbone gears. The cylinders are 18 in. and 30 in. by 42 in. stroke, the gears are 32 in. and 73 in. in diameter, with drums 9 ft. in diameter by 48-in. face, grooved for 1¼-in. rope. The brakes, clutches, etc. are actuated by oil under pressure from the same accumulator which the ore hoist uses, and in a similar manner. The two triplex pumps to supply pressure for the auxiliaries have plungers 2 13/16 in. in diameter by 6 in. stroke, but the oil used when landing several decks is more than it can supply. Three-deck cages in balance are used.

When ore hoisting was transferred to the Sacramento shaft, the Holbrook, Spray and Lowell steam hoists were connected up to drive by compressed air from the central power plant.

The Gardner hoist was at first driven lay steam from the power house, delivered through a 5-in. main, 920 ft. long. Upon making tests on the efficiency of hoisting by compressed air, the latter was found to be more economical, and it is now driven by air also.

No changes were made in the engines when using compressed air. The cylinders for brakes, clutches, etc. use cold air. The leakage has been less than when hot air was used and there has been less trouble with packing.

The air for the cylinders is heated to a temperature of 225° to 275° F. The cylinder of the heater is filled with heavy high-test oil, which flashes at about 700° F., and is inclosed in a brick setting like a small boiler. It is heated by a small coke fire under the front part, which is covered by a brick arch to protect the oil from overheating. The gases return to the stack in front through fire tubes in the lower third of the cylinder.

The air makes three passes through the cylinder in small tubes. An open pipe from the dome carries off any products of distillation. The temperature of the oil ranges from 250° F. to 275° F., although it may be carried higher without undue loss of its lighter elements.

The reheater supplies a reservoir of heat for the heavy drain on the system when the engine is starting, and does not over-heat if the engine is idle for a short time.

At the Lowell shaft, the air is heated to an average temperature of 250°. The air consumption there is estimated to be 30,000,000 cu. ft. of free air per month, at a gauge pressure of 92 lb. In the past five months, the consumption of coke has been 3.8 tons per month.

The oil grows slowly thicker by the gradual loss of its volatile constituents. At a temperature of 275° F. it has been used for two years before getting too thick to circulate freely enough to keep the temperature of the whole quantity uniform, and avoid overheating a part of it. The usual life is 9 to 12 months. When too thick for further use, it makes an excellent rope compound. It preserves a rubbery consistency without hardening in cold weather, and does not melt. In fact, it has to be thinned somewhat before the rope takes it well.

Air Stored in Six Cylinders

An air-storage system, composed of six cylinders of 2,500 cu. ft. capacity each, is connected by a 24-in. pipe to a reservoir above. The reservoir holds 4 ft. of water; and is set at such a height that it exerts 93 to 91 lb. pressure on the tanks as it is full or empty. A drop in pressure from 93 lb. to 91 lb. will empty the reservoir and fill the air tanks with water, forcing 15,000 cu. ft. of air at 91 lb. or approximately 100,000 cu. ft. of free air back into the system. This eases the variable hoisting engine load.

Electric Hoist at Czar Shaft

The Czar engine was an old steam hoist for single-deck cages, built by the Union Iron Works, in San Francisco, about 30 years ago. The gear shaft was lifted out of its bearings, and replaced by another, geared to a 112-h.p. alternating-current motor. It has since been replaced by an electric hoist driven by a 225-h.p. alternating-current motor. It hoists a double-deck cage at 800 ft. per minute, but it is usually operated in balance. It is driven through a direct line from the power house, where there is sufficient power in reserve to obviate the necessity of a fly-wheel set or other method of cutting down the peak load. It is started, however, by a General Electric automatic magnetic controller, to prevent too heavy a drag at the time of acceleration.

Brakes are operated by hand, the clutches by air pressure. Power for the latter was added after it was found that the method of throwing them by hand was too slow, when making many changes, as in cage hoisting it is necessary to do.

Several of the shafts are most inconveniently situated for waste disposal. At the Czar, Holbrook, and Lowell, the waste is dumped from the mine cars at the shaft into large cars holding 75 to 100 cu. ft., which are pulled out to the waste pile, by small hoists, and dumped automatically. One of them is pulled up an incline and returns by gravity, and one runs away by gravity and the empty car is pulled back by an engine.

Careful tests of the efficiency of different methods of hoisting were made, the conditions governing the tests being shown in the following paragraphs. Comparative results of the tests are shown in Table IV.

Conditions of Hoisting Tests

Test. No. 1

Double-drum engine, reels 7 ft. diameter by 5 ft. face, 1¼-in. rope. Driven by duplex, tandem compound, condensing steam engine, with Corliss valves. Dimensions, 18 and 28 in. by 48 in. Cut-off by governor. Brakes, etc., actuated by hydraulic pressure, condenser and circulation pump by electricity Hoisting 3½-ton skips in balance.
Average depth of hoisting 825 ft.; maximum depth- 1,580 ft.
Boilers isolated for test and feed water weighed.
Steam main 5 in. by 619 ft.
Condensation in main 625 lb. per hour.
Ore weighed on conveyor at shaft, on Blake-Dennison scales.
Work done in changing levels calculated from weight of skip.

Test No. 2

Double-reel flirt-rope engine, ropes ½ by 5½ in.
Driven by a 20 by 60 in. simple, duplex, non-condensing engine, with Corliss valves. Cut-off by governor. Brakes, etc. actuated by steam. Boilers close to hoisting engine.
Hoisting triple-deck cages in balance from a maximum depth of 1,000 ft.
Boilers isolated for test and feed water measured.
Ore or waste weighed on scales at collar of shaft.
Work done in changing levels calculated from weight of cages, etc.
Steam for auxiliaries was generated in another boiler, and amounted to 16.1 lb. per shaft horsepower hour, making a total consumption of 111.6 lb.

Test No. 3

Double-reel flat-rope engine, ropes ½ by 5½ in.
Same engine as No. 2, and same hoisting conditions, but engine driven by compressed air.
Air measured by displacement of compressor run especially for this engine. Allowance is made for volumetric efficiency. Transmission losses are practically all leakage, not included since the proportion chargeable to hoisting depends on the quantity of air passing through the main.
Air heated by coke heater.
Auxiliaries for brakes, etc., driven by cold air.
Ore or waste weighed on scales at collar of shaft.

Test No. 4

Double-reel flat-rope engine, ropes ½ by 5½ in.
Driven by a 21 by 60 in. simple, duplex, compressed-air engine, with Corliss valves. Cut-off by governor.
Hoisting triple-deck cages in balance from a maximum depth of 1,032 ft.
Air measured by displacement of compressor run especially for this engine, allowance being made for volumetric efficiency and line leakage, which was measured.
Air heated by coke heater.
Auxiliaries for brakes, etc., driven by cold air.
Ore or waste weighed on scales at collar of shaft.

Test No. 5

Double-reel flat-rope engine, ropes 3/8 by 5½ in.
Engine driven by a 20 by 48 in. simple, duplex, compressed-air engine, with Corliss valves, with cut-off by governor.
Hoisting triple-deck cages in balance from a maximum depth of 943 ft. Air measured by displacement of compressor run especially for this engine, allowance being made for volumetric efficiency and line leakage, which was measured. Air heated by coke heater.
Auxiliaries for brakes, etc., driven by cold air.
Ore or waste weighed on scales at collar of shaft.

Test No. 6

Double-reel flat-rope engine, ropes 3/8 by 4 in.
Engine driven by a 16 by 42 in. simple, duplex, compressed-air engine with Corliss valves; cut-off by governor.
Hoisting double-deck cages in balance from a maximum depth of hoisting 645 ft. Air measured by displacement of compressor run especially for this engine, allowance being made for volumetric efficiency and line leakage, which was measured.
Air heated by coke heater.
Auxiliaries for brakes, etc., driven by cold air.
Ore or waste weighed on scales at collar of shaft.

Test No. 7

Double-drum geared engine driven by 225-h.p. induction motor. Current three phase, 2,200 v.
Started by automatic magnetic control.
Hoisting double-deck cages in balance from a maximum depth of 417 ft.
Power measured by wattmeters at power house, and includes line losses.
Every fifth car of ore or waste was weighed on scales at the collar of the shaft.
Equivalent pounds of steam and cost of power at power house per shaft horse-power hour are high, due to inefficient turbines at power house and also low load factor.

Test No. 8

Conditions similar to Test No. 7.

The double- and triple-deck cage hoists are at a disadvantage compared to skip hoisting, since two or three lifts of 6 to 8 ft. must be made to land the decks. This only appears as so many feet of hoisting in work done, but it means getting the load in motion, which is the least efficient part of the work, twice or thrice instead of once.

This is exaggerated in the case of the Czar hoist by the shallow depth of hoisting. It will be noted that the decrease in power per shaft horsepower hour in test No. 8 as compared to No. 7 is due to a greater percentage of the material to be hoisted coming from the 400 level. When hoisting from that level, the current consumption per shaft horsepower hour was 2.29 kw.hr.; from the 200 level it was 2.92 and from the 100 level 4.6 kw.-hr. per shaft horsepower hour. The record of this test is not representative of electric hoisting, and is included as a matter of interest only. Another hoist of the same type will shortly be erected at a 900-ft. shaft, and further tests will be made.

The simple steam hoist is inefficient at best, and particular so in intermittent service, which does not, however, particularly affect either the compressed-air hoist or an electric hoist without fly-wheel motor generator.

It was a great economy to be able to use the hoisting engines as they stood, even if they were not quite so efficient as those especially designed for air.

The average distance trammed per car in 1914 was 2,939 ft., returning empty.

Car repairs are rather higher than normal, since the equipment is growing old. Most of the cars have been in service for five years.

The charge for labor indicates that one man takes care of three to four miles of main trolley line, as well as bonding, and a proportion of the transmission line in the shaft. Trolley lines in heavy ground require much attention.

Track maintenance includes renewals and all other repairs. One man cares for 1½ miles of track. Track and trolley extensions are not included. In 1914, this amounted to 5.3 c. per ton.

In 1914, 1.2 c. per ton were spent in transfer-chute construction, and an equal amount in 1915. Much permanent work has been done, and future costs are expected to be lower.

The cost of hand and mule tramming is so intermingled that it is impossible to separate them. Ore is trammed 194 ft. by hand and 708 ft. by mule. All new light track is charged to this account, whether for new drifts or replacements. In 1914, 47,800 ft. of drift were driven.

The cost of hoisting is divided into two classes, that of ore hoisting at the Sacramento shaft, and that of handling men, timbers, and waste rack at that and other shafts.

The rope cost includes that of some defective ropes on which a credit is expected.

Belts are usually charged off more rapidly than they wear out. A better idea of the cost is given by the records of the last belts on each conveyor.

Cage riders were not customarily employed before the change in the hoisting arrangement. They were found to reduce the danger of shaft accidents.

It will be noted in Table X that the costs at the shafts handling on ore are much more in the aggregate than those at the Sacramento shaft. They are necessary evils, to be held down to the lowest terms.

In 1907, the usual equipment for a producing shaft was: First-motion double-reel engine; double- or triple-deck cages; single-drum man engine; single-deck cage; boiler plant; blacksmith shop; drill- and tool-sharpening shop; timber-framing mill; drill repair shop.

In 1915, the plant is reduced to the first-motion hoist, to which an air heater has been added. The drill- and tool-sharpening shop, framing mill and drill repair shop were not eliminated by the change in hoisting- methods, but followed the tendency toward centralization. The expense for surface labor has been reduced in proportion, although it appears principally as a credit to mechanical labor and other surface accounts. The fuel consumption has been approximately cut in two, although the change rooms at each shaft must be heated by independent plants instead of by exhaust steam from the engines.

As a whole, the costs of tramming and hoisting have not been reduced as much below the costs of 1906 as expected. A reduction in costs due to an improvement in method has been counteracted by the gradually increasing area of operation and necessary equipment. If a comparison might be made with former methods, developed and extended to cover the present work, it would be all that was claimed for it and more.

Although a saving in repairs was counted upon in the original estimates, it was not specified. In 1914, underground repairs cost 51.2 c. per ton and in the first four months of 1915, 40 c. During the last three months of 1905, they cost 59.8 c. for labor alone, and for the first six months of 1906 the cost was 62 c. for labor and supplies.

Individual shafts are not so vitally essential as before. In 1911, the gases from a mine fire rendered the Lowell shaft impassable to men between the 800 level and the surface, for about five months. For two months, timber and supplies were lowered and waste was hoisted through the gas, but since no repairs could be made, a guide finally broke loose and jammed one of the cages. During this period, workmen were lowered through neighboring shafts and- ore was hoisted as usual. . Both production and costs for the year were normal.

The writer wishes to express his indebtedness to members of the mine department staff for assistance in collecting data used in this paper; W. Saben, Chief Clerk, Charles Legrand, Consulting Mechanical Engineer, R. E. Cameron, a member of his staff, and George Mieyr, Master Mechanic.