Part 2 (1/2)

The labor cost of erecting bins and installing a 916 jaw crusher, elevator, etc., averages about $75, including hauling the plant two or three miles, and dismantling the plant when work is finished.

The following is a record of the cost of crus.h.i.+ng stone and cobbles on four jobs at Newton, Ma.s.s., in 1891. On jobs A and B the stone was quarried and crushed; on jobs C and D cobblestones were crushed. A 915-in. Farrel-Marsondon crusher was used, stone being fed in by two laborers. A rotary screen having , 1 and 2-in. openings delivered the stone into bins having four compartments, the last receiving the ”tailings” which had failed to pa.s.s through the screen. The broken stone was measured in carts as they left the bin, but several cart loads were weighed, giving the following weights per cubic foot of broken stone:

-----------Size.--------------

-in. 1-in. 2-ins. Tailings.

lbs. lbs. lbs. lbs.

Greenish trap rock, ”A” 95.8 84.3 88.3 91.0 Conglomerate, ”B” 101.0 87.7 94.4 ....

Cobblestones, ”C” and ”D” 102.5 98.0 99.6 ....

A one-horse cart held 26 to 28 cu. ft. (average 1 cu. yd.) of broken stone; a two-horse cart, 40 to 42 cu. ft., at the crusher.

---------------------Job.-------------

A. B. C. D.

Hours run 412 144 101 198 Short tons per hour 9.0 11.2 15.7 12.1 Cu. yds. per hour 7.7 8.9 11.8 9.0 Per cent of tailings 31.8 29.3 17.5 20.5 Per cent of 2-in. stone 51.3 51.9 57.0 55.1 Per cent of 1-in. stone 10.2 .... .... ....

Per cent of -in. stone or dust 6.7 18.8 25.5 23.4

---------------------Job.-------------

A. B. C. D.

Explosives, coal for drill and repairs $0.084 $0.018 .... ....

Labor steam drilling 0.092 .... .... ....

Labor hand drilling .... 0.249 .... ....

Sharpening tools 0.069 0.023 .... ....

Sledging stone for crusher 0.279 0.420 .... ....

Loading carts 0.098 0.127 .... $0.144 Carting to crusher 0.072 0.062 $0.314 0.098 Feeding crusher 0.053 0.053 0.033 0.065 Engineer of crusher 0.031 0.038 0.029 0.036 Coal for crusher 0.079 0.050 0.047 0.044 Repairs to crusher 0.041 .... .... 0.011 Moving portable crusher .... 0.023 .... 0.019 Watchman ($1.75 a day) .... 0.053 0.022 0.030 ------ ------ ------ ------ Total cost per cu. yd. $0.898 $1.116 $0.445 $0.447 Total cost per short ton 0.745 0.885 0.330 0.372

Note.--”A” was trap rock; ”B” was conglomerate rock; ”C” and ”D” were trap and granite cobblestones. Common laborers on jobs ”A” and ”D” were paid $1.75 per 9-hr. day; on jobs ”B” and ”C,”

$1.50 per 9-hr. day; two-horse cart and driver, $5 per day; blacksmith, $2.50; engineer on crusher, $2 on job ”A,” $2.25 on ”B,” $2.00 on ”C,” $2.50 on ”D”; steam driller received $3, and helper $1.75 a day; foreman, $3 a day. Coal was $5.25 per short ton. Forcite powder, 11-1/3 cts. per lb.

For a full discussion of quarrying and crus.h.i.+ng methods and costs and for descriptions of crus.h.i.+ng machinery and plants the reader is referred to ”Rock Excavation; Methods and Cost,” by Halbert P. Gillette.

~SCREENING AND WAs.h.i.+NG GRAVEL.~--Handwork is resorted to in screening gravel only when the amount to be screened is small and when it is simply required to separate the fine sand without sorting the coa.r.s.er material into sizes. The gravel is shoveled against a portable inclined screen through which the sand drops while the pebbles slide down and acc.u.mulate at the bottom. The cost of screening by hand is the cost of shoveling the gravel against the screen divided by the number of cubic yards of saved material. In screening gravel for sand the richer the gravel is in fine material the cheaper will be the cost per cubic yard for screening; on the contrary in screening gravel for the pebbles the less sand there is in the gravel the cheaper will be the cost per cubic yard for screening. The cost of shoveling divided by the number of cubic yards shoveled is the cost of screening only when both the sand and the coa.r.s.er material are saved. Tests made in the pit will enable the contractor to estimate how many cubic yards of gravel must be shoveled to get a cubic yard of sand or pebbles. An energetic man will shovel about 25 cu. yds. of gravel against a screen per 10-hour day and keep the screened material cleared away, providing no carrying is necessary.

A mechanical arrangement capable of handling a considerably larger yardage of material is shown by Fig. 8. Two men and a team are required.

The team is attached to the sc.r.a.per by means of the rope pa.s.sing through the pulley at the top of the incline. The sc.r.a.per is loaded in the usual manner, hauled up the incline until its wheels are stopped by blocks and then the team is backed up to slacken the rope and permit the sc.r.a.per to tip and dump its load. The trip holding the sc.r.a.per while dumping is operated from the ground. The sc.r.a.per load falls onto an inclined screen which takes out the sand and delivers the pebbles into the wagon.

By erecting bins to catch the sand and pebbles this same arrangement could be made continuous in operation.

[Ill.u.s.tration: Fig. 8.--Device for Excavating and Screening Gravel and Loading Wagons.]

[Ill.u.s.tration: Fig. 9.--Gravel Was.h.i.+ng Plant of 120 to 130 Cu. Yds., Per Hour Capacity.]

In commercial gravel mining, the gravel is usually sorted into several sizes and generally it is washed as well as screened. Where the pebbles run into larger sizes a crus.h.i.+ng plant is also usually installed to reduce the large stones. Works producing several hundred cubic yards of screened and washed gravel per day require a plant of larger size and greater cost than even a very large piece of concrete work will warrant, so that only general mention will be made here of such plants. The commercial sizes of gravel are usually 2-in., 1-in., -in. and -in., down to sand. No very detailed costs of producing gravel by these commercial plants are available. At the plant of the Lake Sh.o.r.e & Michigan Southern Ry., where gravel is screened and washed for ballast, the gravel is pa.s.sed over a 2-in., a -in., a -in. and a 1/8-in. screen in turn and the fine sand is saved. About 2,000 tons are handled per day; the washed gravel, 2-in. to 1/8-in. sizes, represents from 40 to 65 per cent. of the raw gravel and costs from 23 to 30 cts. per cu. yd., for excavation, screening and was.h.i.+ng. The drawings of Fig. 9 show a gravel was.h.i.+ng plant having a capacity of 120 to 130 cu. yds. per hour, operated by the Stewart-Peck Sand Co., of Kansas City, Mo. Where was.h.i.+ng alone is necessary a plant of one or two washer units like those here shown could be installed without excessive cost by a contractor at any point where water is available. Each washer unit consists of two hexagonal troughs 18 ins. in diameter and 18 ft. long. A shaft carrying blades set spirally is rotated in each trough to agitate the gravel and force it along; each trough also has a fall of 6 ins. toward its receiving end. The two troughs are inclosed in a tank or box and above and between them is a 5-in. pipe having -in. holes 3 ins. apart so arranged that the streams are directed into the troughs. The water and dirt pa.s.s off at the lower end of the troughs while the gravel is fed by the screws into a chute discharging into a bucket elevator, which in turn feeds into a storage bin. The gravel to be washed runs from 2 ins.