Ore Tramming in Mining

Ore Tramming in Mining

The ore deposits of the Warren district, in which the mines of the Copper Queen Consolidated Mining Co. are situated, have been described in a number of technical publications, and will not be discussed here in detail. Certain of their characteristics, however, control methods of underground transportation and hoisting of ore.

In the Copper Queen mine, the majority of the ore has occurred in a zone encircling the west boundary of the porphyry intrusion of Sacramento Hill. It has a width varying from 800 to 1,200 ft., and a thickness of about 400 ft. It reaches the surface in the older part of the mine to the northwest, but dips to the southeast, where it is reached at 1,400 ft. below the Czar collar, in its farthest extension at present developed on Copper Queen ground. There is one major extension from the northwest end of the zone toward the west along the Czar fault, and others of minor importance.

Individual orebodies are scattered through the zone in an eccentric manner, only matched by their own irregularities of form and size. Their most general characteristics are the softness of the ore and their great horizontal rather than vertical extent. It has been estimated that the average vertical thickness of ore in the Czar and Lowell divisions is between 30 and 35 ft. It is calculated by assuming it to be uniformly distributed over its horizontally projected area.

In this zone, and for some distance above it, the ground has been subjected to intense alteration and intense but irregular oxidation. It has resulted in an enormous quantity of earthy or clayey material, which may be either ore or waste, which when wet is both heavy and tenacious. Below alteration, the ground is fairly hard, and the limestones contain primary ores differing from those heretofore considered typical of the camp, and which have not yet been thoroughly exploited.

The mine production has been drawn from many orebodies spread over a great area. A diagram map (Fig. 1), of haulage drifts and loading stations, illustrates the situation in 1914. The effort to restrict the area of work and intensify production has not been particularly successful, for several reasons:

haulage drifts and chutes

First: The mine has been in continuous operation for more than 30 years. During the earlier period, the costs of mining and smelting were high, and ores which are now profitable could not be worked. Exploration was not carried far enough in advance of mining to explore orebodies as a whole, and they were attacked piecemeal. Much ore was, in consequence, left in and about the old stopes. When new ground was opened to supply the demand for greater production, the old areas were not yet exhausted, their output was merely reduced. In fact, more thorough exploration and the gradually decreasing cost of mining, etc., has actually increased the production and reserves of the Czar division, the oldest part of the mine.

Second: As all ore is smelted direct, a balanced production must be made to maintain a self-fluxing mixture. Since the oldest divisions, the Czar and Holbrook, have contained highly refractory ores, their output has been limited to what the smelter could handle, and their reserves have not been exhausted as rapidly as the economies of mining alone would suggest.

Third: While many of the orebodies are large when taken as a whole, they are small in section, complicated in form and mingled with waste. They cannot be mined rapidly.

The producing area has therefore increased rather than diminished. All the ore is not sticky or hard to handle, but some is extremely so.

To one not acquainted with it, it is hard to appreciate how seriously this quality interferes with every operation of handling, and forces complications into a general plan to insure certainty of action. There is not such a large proportion of sticky ores at present as in the past, except on the 400 level, but a successful method must be prepared to take care of it wherever it appears.

To summarize briefly: The three characteristics of the deposits which affect haulage are scattered operations, heavy ground in and near the ore, and clay ores.

Old Haulage System Unsatisfactory

Prior to the introduction of the system now in use, the ore was trammed by hand to one of several shafts, where it was hoisted on cages and loaded into railroad cars for shipment to the company’s smelter at Douglas. In most cases, it was dumped directly into the cars instead of loading from bins, since it was slow and hard work to get it out of storage once it was put in. An attempt was made to mix the ore when loading into the railroad cars, but without great success.. Each tenth mine car was loaded into a separate car as a sample for the smelter, but the returns were not beyond question.

An unusual number of shafts were required, since active production covered a wide area. Distances to the shafts were excessive for hand tramming, and it was impossible to maintain such great lengths of drifts and track in proper condition, although heavy repairs were continuous.

The defects of the system became more and more apparent as the mine grew, and tentative plans had been discussed from time to time, but the disadvantages of any new method were more apparent than the advantages, and nothing was done.

Attention was again and more forcibly drawn to the subject when the sudden loss of the Holbrook shaft in July, 1906, diverted more ore to the Czar and Spray than they could well handle. Tramming costs were raised by the increase in the distance trammed, and by congestion at junction-points or at the stations. This resulted in heavy expense, which lasted six months until the new 559-ft. shaft could be finished and equipped.

Plans were begun on a general system for tramming and hoisting, which were later extended to include a power plant, and thus began a centralization of the surface plant and work, which has only recently been completed by the construction of a central timber-framing mill and a drill-and tool-sharpening shop.

Formerly, ore was hoisted through five shafts. Beginning with the oldest and shallowest, and passing to the southeast, they were as follows:

tramming-and-hoisting-shaft

The Holbrook has since been sunk to the 600 level and the Lowell to the 1,600.

Of these, the Holbrook, Spray, and Lowell shafts were either in the ore zone or so near stoped areas that there was continual movement in them, and some little danger of a repetition of the Holbrook collapse.

Plumbings were made regularly to ascertain the extent and rapidity of movement in the new Holbrook shaft. During the first two years, the collar moved to the northeast at the rate of an inch per month. It is now 6 ft. 2½ in. N. 45° E. of the stationary part below the third level.

Although the Spray shaft is in rather solid limestone, a crack developed, which passed through the shaft and split the engine foundation.

It may be noted in passing, that the engine foundations at these shafts now consist of two massive blocks of concrete, reinforced with old rails, each heavy enough in itself to hold the engine securely, and resist the rope pull. The ground beneath was levelled off by a layer of concrete, but the surface was separated from the foundation block, so that there could be no bond which would tear the concrete block apart in case of future movement. The fissure at the Spray shaft has since widened, but with no more effect than to tilt the foundation backward, engine and all. It runs smoothly on a slope of 3/8 in. in 1 ft.

The Czar, although in rather heavy ground, was stable, and the Gardner is outside the ore zone and will probably remain true.

Each shaft was an independent unit, with its own boiler plant, etc. The equipment was miscellaneous, having been added to from time to time, and some of it was very old. The operation of the several plants was inefficient, from the number and small size of the units. The use of power was unimportant aside from that for hoisting.

New Plan Included Electric Haulage and Central Hoisting

It was proposed to equip a shaft, located in some central and safe position, for economical hoisting, where the ore might be mixed and sampled. The ore was to be drawn to the shaft by electric locomotives.

The advantages to be expected may be stated as follows:

  1. The hand tram would be cut down to an average of 300 ft. or less.
  2. Repairs would be reduced by diminishing the number and length of tramming drifts in bad ground. Access to stopes may be by circuitous routes to avoid heavy ground, and need not be so well maintained as is necessary when large quantities of ore must be drawn through them, the main-haulage drifts being placed beneath the ore in solid ground.
  3. Fewer trammers would be required, and they could be distributed to avoid interference. There was often great congestion near the shafts, even when mining less ore than in recent years.
  4. Hoisting would be cheapened by the use of skips, a more efficient engine, and a better method of transporting the ore to the railroad cars.
  5. The unstable shafts would not be so essential to continuous production.
  6. Shaft and cage repairs would be diminished, particularly in the moving shafts, by slowing down the hoisting speed, as could be done if only men, timber, and waste were hoisted.
  7. Miscellaneous work about the shafts and auxiliary equipment might be cut down.
  8. Power distribution from a central plant would be simplified and the investment for hoisting machinery reduced.
  9. The ore could be thoroughly mixed and accurately sampled before shipment.

There were also certain disadvantages, aside from the cost of the improvements:

  1. Haulage drifts must be driven and maintained without abandoning a corresponding length of hand-tramming drifts.
  2. The ore would be transported underground a greater distance than before. A part of the saving in the length of the hand tram would be lost in the added operation of power haulage.
  3. The old shafts must still be maintained for men, timbers, and waste rock, while the main shaft is added to those in use. (The new State law restricting the time of underground labor to 8 hr. from collar to collar, has made it important to have shafts close to the stopes and active workings.)

The advantages were believed to outweigh the disadvantages, and the construction was authorized.

Electric Haulage on Alternate Levels Only

The cost of equipping each level for electric haulage was prohibitive. Instead, each alternate level was chosen, beginning with the 400, making seven in all to the 1,600. By collecting the ore from 15 producing levels to seven haulage levels, the traffic density is increased, although still far below that necessary for really cheap transportation.

By referring again to the haulage map, it will be seen that the 400 level draws ore from the whole of the shallow western end of the mine. It begins in the solid ground under the stopes, passes out to one side of the ore zone and then to the hoisting shaft. It was possible to select old drifts in stable ground for most of the main line. The only new drift of any length was from the Gardner to the Sacramento. Ore is dropped from the 100, 200 and 300 to this level, through-transfer chutes, under or near the stopes. In some cases, the haulage cars are collected by hand through short branch drifts to the stopes on the haulage level; in others, when the quantity warrants it, the trolley wire is carried to the stope chutes direct. Of the whole 5,600 ft. of main-line trolley drift on the 400, not more than 1,500 ft. was timbered, and of this only 450 ft. is particularly heavy.

In a similar manner, the 600 level was driven through from the Sacramento to the Gardner, old drifts were used to the Spray shaft, which were extended by new drifts, to reach the ore as it dipped below the 400 level. It underlaps the 400 haulage for some distance. Although this drift passed through the ore zone between the Gardner and Spray, some of the old drifts were in good ground, and the proportion of heavy ground to sound is not much greater than on the 400.

The same plan was carried out for the other levels, each one-collecting ore from an area deeper, and farther to the south and east, than that served by the level above. Not very many new drifts were driven particularly for this purpose, and the percentage of main drifts which require repairs is small.

A trolley line on the 200 level to the Uncle Sam shaft was not contemplated in the beginning, but was added afterward. The ore from that shaft and the Southwest country is hauled to a transfer chute near the Holbrook shaft, where it is dropped to the 400. Extending the 400 level to the Uncle Sam to avoid re-handling may be justified at some later date.

To begin with, 7,000 ft. of new drift was driven especially for power haulage, but other drifts have been driven since, and others equipped for the purpose, until at this date, 10.9 miles of track and trolley line are in use or are standing ready. The connecting drifts on the 1,200 and 1,400 levels were warranted as prospects, and many others now used for haulage were driven to find or develop ore. Probably not more than one-quarter of the whole should be charged to the haulage system.

Track is 20-in. Gauge

Twenty-five pound rails on 20-in. gauge are used for the track, with 4 by 6 by 42 in. ties. They have been heavy enough except in a few cases.

track-layout-at-loading-station

The maximum concentrated load is on the 400 level. Locomotives are there used weighing 14,000 lb. The weight of a loaded car rarely exceeds 6,000 lb., although it may be more when loaded with massive sulphide ore. Wet ground on this level caused very heavy track repairs; even when slag was used for ballast, it was churned out from under the ties. To improve this condition, 4,200 ft. of second-hand 40-lb. rails were laid to replace lighter rails. The stiffer rails distributed the load better, and repairs were much reduced.

As a rule, the train crew does not load the ore. The motorman brings empties to the stope or transfer chute, and takes out the full cars standing there, or returns when the others are filled.

In the larger stations, sufficient double track is laid for tail room to hold 20 cars. A standard track layout is shown in Fig. 2. Only one switch, at A, is thrown by hand; spring switches direct the locomotives without further attention. At unimportant chutes, less elaborate sidings for car storage are used, or the trains may be made up in the stope drift or on the main line.

At the Sacramento shaft, the tracks are looped to avoid switching.

Standard switches on curves of 40 to 80 ft. radius are used. Curves of 25-ft. radius are permitted only in exceptional cases.

Direct Current at 250 Volts Used Underground

Direct current is carried into the mine at 250 volts, through the Sacramento, Gardner, and Holbrook shafts. The feeder cables are cambric insulated, lead covered, and wire armored. The return cables have weather-proof insulation only. The voltage on the west end has been low, for lack of capacity in the power cables. A transformer set has been purchased to be set up at the Holbrook shaft to serve as a booster, but it is not yet in service.

The current underground is carried on 00 B & S American standard grooved trolley wire. The rails are bounded with No. 12064 Type E O. B. rail bonds, length 32 in. center to center, capacity B & S. No. 0, diameter of compression terminals 5/8 in.

Trolley wires are now required by law to be 7 ft. above the track. They are hung from the timbers in timbered drifts, or from 4 by 6 in. cross bars held by vertical bolts wedged into drill holes, when the ground is hard. The old lines were sometimes hung lower, and in such cases were protected by 1 by 6 in. battens placed parallel with, the wire, 8 in. apart and projecting 2 in. below the wire. On straight track, the wire is supported every 20 to 25 ft., as very little sag is permissible. Occasionally, the wires must be protected from acid water dripping from the roof. There is also more or less trouble with bonds in wet drifts.

There have been five fatal accidents in which the trolley current has been involved:

No. 1, September, 1908. Pipe-fitter at work on air line above wire. Received shock and fell to track 7 or 8 ft. below. Uncertain whether shock or fall was fatal.

No. 2, December, 1908. Miner repairing drift stood on a truck and fell off. Neck was broken. Thought that shock from trolley wire caused the fall.

No. 3, November, 1909. Loader carried chute bar when switching cars and struck wire beyond protection.

No. 4, May, 1912. Miner climbed over couplings of standing train. Tilted steel on shoulder and touched trolley wire.

No. 5, July, 1914. Miner repairing drift. Ground fell, carrying-down trolley wire and pinned him down with wire against his back. May have been killed by the fall. Current was left on trolley wife to light the drift, contrary to rules.

The first two cases were doubtful, as the shocks may not have been sufficiently severe in themselves to cause death. The danger of a current of 250 volts was not realized at once, as it is the lowest in common use, and other mines have not found it so. Other men also in this mine have received shocks without injury. It was supposed to be due to unusual susceptibility on the part of the individuals. It now appears most probable that when shoes are wet, as often happens, with acidulated water, and there is moisture on the hands or body, an unusually good contact may be made, with fatal results.

When this condition was recognized, special precautions were taken to prevent accidental contacts. The wires are high enough to avoid being touched ordinarily. Any reasonable increase in height would not entirely prevent contact when carrying tools, etc., on the shoulder, which is also contrary to rules.

The greatest danger is in repairing drifts or loading ore. No repairs are now permitted in the vicinity of live wires, and the system has-been divided to facilitate cutting out the current in sections under repairs, without interfering with ore haulage. At loading stations, the wires were at first protected by boards on each side of the wire. The current is now switched off the wire on each side of the chutes for such a distance that the loader cannot receive a shock while loading, or when switching cars, even in case he should carry a chute bar with him when doing so. When the loading station is on a main line, the current is carried past on an insulated cable, and is only turned on the trolley wire when the train passes and after warning the loader. Current in the wire is indicated by a light.

There are a number of loading stations on each level, and as it takes as long or longer to load, than to make the trip to the shaft, dump, and return, the locomotive usually draws from more than one station. On the 400 level, where the ore is most difficult to handle, and there are many loading stations, they are connected by wire to a signal box containing an annunciator similar to that used in hotels. The loader can thus signal to the motorman when his train is nearly full, and save a trip to a station where the train is not loaded.

Red lights are used in a crude hand-operated block system when there is danger of interference with timber or waste handling, or when there is a second locomotive at work on the same level.

Colored lights are also used to indicate the position in which switches are set, or the location of a place of refuge from passing trains.

Factors Affecting the Choice of Cars

So many of the old drifts were to be used when the system was planned, that it seemed impossible to use large cars.

The first cars bought held 21 cu. ft. They had gable bottoms, with hinged sides, and were equipped with M. C. B. Midget couplers, spring-draft rigging and roller-bearing axles. The latches were to be sprung for dumping at the shaft bins, by a block between the rails.

This type of car was not satisfactory. A large proportion of the ore is too sticky to slide out of the cars, even when the doors are held open. It was customary on the 400 for two men to rock them from side to side on the rails, in order to clear them of ore. The frictional resistance to dumping increases as the size diminishes.

Another disadvantage was their tendency to leak fine ore, particularly if wet.

After using them for some months, a few rocker dump cars were designed and built, of about the same capacity. Spring-draft rigging, automatic couplers and roller bearings were used, as they had been found advantageous. The rollers in the first, bearings were solid. For the new cars, an axle was designed to use Hyatt rollers, with special care to make them dirt-proof. They dumped freely, and were otherwise satisfactory.

Since it was necessary to secure a complete new equipment of cars, the question of size was re-opened, and a car of 33 cu. ft. capacity was adopted.

The cost per cubic-foot capacity decreases as cars increase in size. They should cost less for repairs also, in proportion to the ore carried, as the details of latches, etc., are heavier and stronger. Larger net loads can be carried in large cars, as the weight does not increase in proportion to the capacity. The cost of loading and particularly unloading is generally less. For these reasons, the largest car possible should be used.

The size of the cars in this case was limited by the cost of enlarging the drifts, and by the weight which can be conveniently handled by one man.

A large sum of money was spent in widening drifts for the 33-ft. cars. A car enough larger to be of appreciable benefit would have incurred prohibitive expense in widening the 4½ miles of drift then in use, and an added expense for all haulage drifts to be driven in the future.

At important loading stations, the track is laid on a grade to favor the loader in assembling cars. In many cases, the quantity produced will not warrant special sidings, and the cars must be loaded and pushed by hand to the point of assemblage. The 33-cu. ft. car weighs 1,700 lb. Loaded with dry, oxidized ore it weighs about 4,250 lb. When loaded with sulphide, it may weigh as much as 7,500 lb. This car with roller-bearing axles can be readily moved by one man at all transfer chutes, and through branch drifts in most cases, unless the grades are unfavorable. A larger car would quite frequently need two men. The use of cars larger than one man can move would increase the expense of switching by hand, until a car twice as large is used, while that of loading would be practically doubled, since there is only room for one man to work conveniently at a chute.

The rolling-dump type was selected for its ease of dumping sticky ore, and simplicity of construction. Tipples were not seriously considered, as seven would have been required.

The advantages of such refinements as spring-draft rigging and automatic couplers may be open to argument, but a few fingers have probably been saved by the latter.

The roller-bearing axles have been a most unqualified success. They are made in two sizes, and are of as great advantage on small cars as large. The axles on the motor cars are filled with grease once a month; on the hand or mule cars once in two months. It is probable that this time is shorter than necessary, and experiments are being made to determine how long the charge will last. There has been an economy in lubricants accompanied by a very low depreciation charge. A few of the first Hyatt bearing axles, in use since January, 1909, have begun to fail. The cage goes first which allows the rollers to become displaced and injured. These axles are 1¾ in. in diameter and are used on 22-cu. ft. cars. They are rather light for the service. The larger cars have 2¾- in. axles, which appear to be amply large for the load, and a longer life is expected.

The friction load is very light. Unfortunately, the average mileage per car cannot be known.

wear-of-car-wheels

The roller bearings on which the above tests were made were manufactured either five or six years ago. The Hyatt Roller Bearing Co. advises that the rollers are now made of chrome-nickel alloy steel, which has a very much higher elastic limit than the steel used in bearings formerly.

The limits of accuracy in finishing are now approximately 0.002 in. instead of 0.005 in. It is very probable that better results would be obtained with the rollers as they are now made.

Several Types of Cars Used

Several types of cars have been used, and a summary of their characteristics may be of interest.

The original car had a capacity of 12 cu. ft., and was of an ordinary type, dumping forward and also, by, swivelling, to the side. It is not worth serious consideration, as it was both light and weak. The older shafts were small, and a car of greater capacity of this construction could not be put on the cages.

Two cars of 16- and 20-ft. capacity each (Fig. 3), dumping only to the side, were recently designed after a car developed by the Old Dominion Copper Mining & Smelting Co. The 16-ft. car will go on the cages in the smaller shafts. The 20-ft. car can only be used in the Gardner,

square-side-dump-car

Sacramento, Spray, and the newer prospect shafts. These cars have great capacity for their over-all dimensions. They are of heavy construction. They can be dumped without uncoupling when used in trains. This is an important advantage, as they are frequently hauled in short trains by mules or motor to transfer chutes, or in carrying waste from development work. It is a disadvantage that it can only dump to one side, and care must be taken to see that it comes to the dumping place faced the proper way. It is proposed to replace the 12-ft. cars with these as fast as they wear out. It is unfortunate that two sizes need to be used, but it is believed that the added capacity of the large car makes it worth while.

Rolling-dump cars of extremely simple construction were designed for use at the North Star Mines, in Grass Valley, Cal., and were introduced at the Copper Queen for surface work. Afterward, they were taken underground, and have proved satisfactory for hand and mule tramming. They are cars reduced to then lowest terms, consisting as they do of a pair of axles with wheels, two beams of “I” or channel section tied together at the ends by two cast-steel supports for the body, which also form bumpers and attachments for connecting in trains. In small sizes, they may be locked by a pin through trunnion and support, if necessary. When properly balanced, they dump with great ease, and do well with sticky ore. As the body forms a tight box, ore is not spilled, even if it is a thin mud. As they dump more easily when well filled, the tendency is to heap them up rather than load them to only a part of their capacity.

They are bulky for their capacity, however, and while this is not important when used exclusively on levels, it is an objection for cage work. They are also high and not so convenient to shovel into. In order to prevent a multiplicity of types, it is probable that the square-bodied side-dump car will eventually supersede these also, as they can only pass through the newest shafts.

The 33-ft. car of this type, which is used for haulage, is too large for general hand or mule tramming, and has most of the advantages and disadvantages of a small car of the same type. It dumps muddy ore more readily than any car which has been tried, but if the ore does not all slide out together, what remains is in the bottom and it is hard to hold in position to dump. The point of support is placed below the center of gravity in order to dump easily, and a lock on the bottom prevents its over-turning in transit. A larger-sized rolling-dump car is not to be recommended. The force necessary to revolver weight of 2 to 3 tons may be excessive.

In larger sizes also, the objections to the saddle-back car disappear. They dump ore well when they hold 75 to 100 cu. ft. The doors are the only moving parts, the ore is merely permitted to fall out, and, if it does, nothing better can be desired.

Three to 7-Ton Electric Locomotives in Use

There was difficulty at first in securing standard locomotives small enough to go through the drifts; 3-ton Goodman locomotives were selected, their type No. 1600-K. They were small and compact, and were driven by a single motor of 20 to 25 h.p. on one-hour rating. Since, under ordinary conditions, the train crew does no loading, the locomotives were in continuous motion. It gave the motors no time to cool off, armatures burned out, and electric repairs in general were very heavy. About this time, it was decided to use larger cars, the drifts were widened and larger locomotives could be used. Two 6-ton locomotives (6 N-0-2) were then purchased. They were driven by two 8-A Goodman motors of 22 h.p. each on one-hour rating, and have been satisfactory.

The haul on the 400 level is long, with adverse grades for a third of the distance. A still larger locomotive was thought desirable for this level, and two 7-ton machines were designed and built in the mine shop. They are extremely small for their weight and power. The frame is of cast steel. The two Westinghouse No. 79 mining motors, of 30 h.p. each on one-hour rating, were taken second-hand from stock. In the design, everything was sacrificed to compactness and power, and it is not to be recommended for general purposes. The unusually rugged electric equipment has fulfilled every expectation in the elimination of delays and repairs. The tire expense is rather heavy, since the clearance below gears is so small, the tires can only be worn down 1 in. in diameter before replacement.

The small locomotives replaced by the heavy machines have been used to good advantage on light work, either on levels where the ore production is not heavy, or in hauling waste or timber. They were well constructed, serviceable machines when used with the load for which they were designed. Since then, repairs have been general and not confined to any particular feature. Gears and tires make up most of the operating cost. The gears are cut out of special steel blanks on a milling machine at the mine shops. The tires are of forged steel shrunk on a cast-iron center. The treads are re-faced when necessary, and are worn down to a thickness of ¼-in. at times. Manganese-steel tires were tried, but were found to wear very rapidly.

Odometers have only recently been attached, accurate mileage figures therefore cannot be given.

In narrow drifts, it is sometimes impossible to turn the trolley pole, and many were broken in backing up. A trolley pole with a knuckle in the center, which is easier to turn and which can be turned anywhere, has reduced the breakage.

In selecting a locomotive, it should be seen that the motor equipment is large enough for the work to be done; it will save endless trouble, delays and expense.

power-ratings-of-locomotives

Storage-Battery Locomotive Tried

One of the 3-ton locomotives was used for a time in 1910 and 1911 with an Edison storage battery. The results of the running test were presented in a paper by Charles Legrand. The battery was composed, of 150 A-6 cells carried in two separate trailing cars.

Moisture from the air accumulated on the cells, to which was added a small proportion of electrolyte as a result of spillage or gassing while being charged, and a number of cells were lost by short circuiting.

In 14 months, 21 cells were burned out. The whole battery was then returned to the factory, and replaced by another with different crating to provide better insulation. A new battery car provided with springs

underground-motor-storage-battery-car

(Fig. 4) was built large enough to contain them all. It weighed 2,400 lb., and the battery 3,000 lb. The cells were occasionaly wiped dry, painted and coated with vaseline. The nickel cell walls of only two cells were burned through in the 7½ months of its service. The cells at the ends of the cars were those usually lost.

If the batteries could have been kept perfectly dry, or if the voltage had been lower, there should have been little or no difficulty from short circuiting.

When idle and fully charged, the voltage was 213, after travelling about 8 miles, one-half under load, the voltage dropped to about 200. When the voltage dropped still lower; the speed of the locomotive decreased and the work went slowly.

Ore was drawn during the day and the battery was charged at night, by current from a 20-h.p. motor-generator set taking power from the alternating-current circuit. It was automatically cut out when charging was complete.

The production from the area served by this locomotive gradually increased until its capacity was exceeded. It was then thought better to lay a wire than to get another battery, and the use of the storage battery was discontinued. The cost of the locomotive was approximately $1,300, that of the battery about $3,000.

The operating costs were good in spite of light rails and sharp curves. No information on normal depreciation can be given.

Favorable conditions for motor and battery are opposed. In order to protect the battery, the motor must not be too large. And yet it has been found that motor repairs are reduced by making them powerful enough to slip the wheels of the locomotive readily. The added weight of the battery gives them good traction, and there is always a temptation to pile on the load. By incorporating the battery with the locomotive, they may be better suited to each other and the work to be done.

The capacity is not very great. The cost of battery, charging station, etc. is to be balanced against that of trolley wire and rail bonding. The charge for power is so small that the greater consumption of power-house current is of no particular consequence.

The battery is now set up in the power house to excite the fields of the alternating-current generators when starting. They replaced a small steam-generator set, and have been very useful.

Several Designs for Stope and Transfer Chutes

When the stopes are on a haulage level, only the regular stope chutes, are used, and the cars are brought to them by the locomotives, if the tonnage is of sufficient importance, or by hand from some nearby point where they may be re-assembled into a train to be hauled to the shaft. If the ore comes from the level above, it is dropped through a transfer chute to the haulage level. This may be an old stope chute or it may be a special raise into which the ore from a considerable area is collected.

For the larger bodies, a chute is usually provided close to the stopes, even if a special drift must be brought in from the main line. In a top slice, the main chute is brought up to the top floor and the ore is trammed from the working faces to the haulage chute direct. In the Dividend slice, the ore being too soft for raises to be maintained through it, they are placed in the country rock outside, and the ore will be trammed a longer distance on the working floor of the slice, instead of to a central raise within the ore.

In the Howell slice, the ore mined above the 600 is dropped to the 1,000, as it is economically impossible to maintain a trolley drift through the ore zone on the 800. In this case, the ore is trammed again on the 900, as there is not sufficient to justify a special raise clear through.

loading-cost-for-levels

The 400-level costs for loading are highest, since the greatest proportion of clay ore originates in the area tributary to that level. The ore in the Dividend stopes is a very tenacious clay, and a cost of 10c. per ton for loading has not been uncommon nor excessive. The difficulties of loading have directed particular attention to the development of a better chute than that formerly employed.

A rectangular vertical chute of small section, with a bottom sloping down to a door in the front, is the worst possible for sticky ores. The small section increases side friction and favors arching. The weight of the column of ore packs it tightly into the wedge-shaped section at the bottom, particularly when it falls as a mass after hanging up. Only a part of its weight acts as a force to push it horizontally through the door. By shortening and widening the column of ore, the weight per square foot on the bottom layer is lessened, and there is less possibility of arching. By putting the door underneath instead of at the side, the full weight of the ore acts to force it through. These principles were used in developing a chute which has been found to be of great advantage. The doors have been put underneath the bin in only one case, as it is seldom necessary.

From the sketch of a standard transfer chute (Fig. 5), it will be seen that the storage is all at the bottom. The ore falls through the chimney and strikes a baffle, its downward velocity is checked and it falls lightly on the heap below. The pile of ore is not allowed to extend up into the raise, which serves only as a passage way. The storage space is long enough to let it spread into a loose pile, there is little tendency to pack, and it cannot readily arch. Below, there are several doors. If, when loading, the ore hangs up over one door, the car is moved to the next, which will break the arch, or if that door does not, to the third. The bin itself is usually placed in solid ground and requires no timber except in the bottom. The narrow chute above is only lined in heavy ground, and then usually with concrete. Its small diameter, from 3 to 3½ ft-, brings this expense within reason.

Seven chutes have been lined with concrete. One which has been in use for 20 months, needs re-lining, due to wear by sharp ore. This

standard-haulage-chute

chute would have required heavy repairs if timbered, both to provide against outside pressure and to replace the lining. In re-lining, a thicker wall of concrete will be used. Other chutes are only slightly worn.

An elaborate storage bin, shown in Fig. 6, was built on the 400 level to serve a large aluminous orebody which has been developed, but not yet mined. It was described by Joseph P. Hodgson, Mine Superintendent of the Copper Queen mines, in a paper read at the Salt Lake meeting of the Institute. A large tonnage of ore is tributary to it which is so sticky that extreme measures were considered necessary.

This is the case in which the doors are put underneath the center of the pile of ore. There is an opening from one end to allow the loader to climb up on the pile, if necessary, for inspection, or to work the ore down. A ¾-in. pipe is laid in the concrete lining, to serve as a speaking-tube between the loader and the trammer above.

The ore from this stope had formerly been dropped from the 200 to the 400 through a standard, timbered chute. No attempt was made

czar ore pocket

to use the chute for storage, and the door at the 400 was kept open by the loader, but other men were required above to keep the chute clear and the ore moving.

It was found that the whole capacity of the storage bin could not be used, the weight of the ore packing it too hard; but if the quantity does not exceed 50 or 60 tons, the loading is rapid, and there has been no accumulation of ore in the concrete chimney at any time. In rebuilding it, the storage chamber would not be made so high.

The timbered chute shown in Fig. 7 is sometimes used successfully for stopes. The half bulkheads partly support the ore, and it does not pack so badly in the bottom. It was used by the Cananea Consolidated Copper Co.

timbered chute

Sacramento Selected for Hoisting Shaft

The greatest month’s production prior to July, 1907, had been, 55,347 dry tons, in January, 1906, or 1,910 tons per working day. It was not exceeded until March, 1912. The desired capacity of the plant was assumed to be 60,000 tons per month, or about 2,150 tons per working day, with a reasonable margin for emergencies. At that time, the mine worked alternate Sundays, and three shifts were run in tramming and hoisting.

The Sacramento shaft had been sunk for general development purposes, and had been located within the porphyry intrusion, to avoid the ore zone and its possible movement. It was selected for the hoisting shaft since it was in a central position and convenient to the main line of the railroad.

It was 928 ft. deep to the 1,000 level, and had three compartments 4 ft. 6 in. by 5 ft., and a half compartment for air pipes, etc. Since then, it has been sunk to the 1,700 level and widened to five compartments, making two for skips, two for cages and a large one 5 ft. by 5 ft. for pipes and cables.

It was at once decided to use skips.

The size of the compartments restricted the cross-section of the skip to 4 ft. 2 in. by 3 ft. 3 in. inside. The effective capacity fixed upon was 60 cu. ft. It was thought that one of large capacity would be too long, and that the bottom layer of ore might be packed so hard by the fall into the skip and the weight of a high column of ore upon it, that it might stick. This has sometimes been the case with the size adopted. The average skip load in April, 1915, was 8,117 lb. of wet, or 7,459 lb. of dry ore. The moisture, 8.11 per cent., is the lowest in years, the average would be nearer 12 per cent.

There would be no difficulty in raising much more than the quantity of ore assumed, when it runs freely, even with small skips. When it does not, large skips are of no particular advantage.

The uncertain factor was the rate at which ore could be drawn from the storage bins, which are necessary when skips are used. The experience with bins had not been particularly successful. Attention was therefore concentrated upon providing facilities for rapid loading, and to give loaders the maximum time for work at the loading door.

The size of the skips, power and efficiency of the hoist and economy of rope wear are interdependent. Conditions favorable to one are usually opposed to efficiency in the other.

A larger skip requires a more powerful and expensive engine, the efficiency of which is less, due to less continuous hoisting for the assumed tonnage, and greater condensation. There might be a small saving in rope expense, as the skips would make fewer trips.

Maximum efficiency in ropes would be obtained by larger drums, or drums long enough to avoid two layers. Larger drums require larger cylinders and again an engine more costly and less efficient. There is no great advantage in the use of larger drums unless they are large enough to hold the rope in one layer.

The capacity of the skips, the proportions of the engine, and diameter of the ropes were arrived at by one of those compromises, which must be so frequently made in balancing an advantage against its complementary disadvantage.

Reports of the steam economy of compound engines operating in South Africa had been received, and after thorough investigation by John Langton, Consulting Mechanical Engineer for the company, a duplex, tandem-compound, condensing, first-motion engine was purchased from the Nordberg Manufacturing Co. The conditions were not the most favorable for a compound condensing engine, as the depth of the center of gravity of production in 1906 was only 570 ft., but it was expected that the depth of hoisting would increase. The center of gravity of production is now 970 ft. below the collar.

The plant is driven by steam at 150 lb. power-house pressure, transmitted 619 ft. through a 5-in. main. The steam leaves the power house with 75° F. of superheat. The engine can lift an unbalanced load of 17,000 lb. Its speed is rated at 2,000 ft. per minute. The reels hold 2,100 ft. of 1¼-in. rope in two layers. The cylinders are 18 in. and 28 in. in diameter by 48-in. stroke.

Most of the details are of standard Nordberg design, but there are three unusual features:

The operation of the auxiliaries.
The regulation of pressure on the low-pressure cylinders.
The condensing system.