Mance: Quarry Industry of Southern Indiana 139 



Machines of this type are more widely used for crushing stone 

 for road metal than in regular crushing plants because they pro- 

 duce less fine material then is produced by the gyratory crushers 

 of the larger sizes. A jaw breaker uses more power per unit of 

 output than the gyratory crushers on account of the large weight 

 of the reciprocating parts and the fact that they are in the act of 

 crushing only half the time, while the action in the gyratory 

 crusher is continuous. The cost list given m the above table was 

 calculated as follows by Professor Richards (op. cit., p. 21): 



1. Sizes, capacities, power, and original costs are taken from catalog 

 figures [of the different companies putting out these machines]. 



2. Oil, costing 35 cents per gallon, is estimated to be used at the rate of 

 one quart per 24 hours, on a 30xl3-inch breaker breaking 600 tons in 24 

 hours to a maximum size of 2 inches. The cost per ton is 35 x 3^ 600 = 

 0.015 cent. The cost per ton for a 10x4-inch breaker, estimated to use 

 one-half pint per 24 hours, breaking 92 tons to 2 -inches is 35xyV -f- 92 = 

 0.024 cent. The average of these two figures is about 0.020 cent. 



3. Interest and depreciation at 10 per cent per annum. For a 10x4- 

 inch breaker this would be $27.50 per year. On a basis of 308 operating 

 days per year 92 tons being crushed pe. day, the cost would be 

 $27 . 50 



■ - 0.097 cent. Other sizes can be calculated in the same way. 



308x92 



4. Power is estimated to <^ost $40 per horse-power year of 308 operating 

 days or $0.1298 per day. For a 10x4-inch breaker using 5 horse-power and 



0 . 1298x5 



breaking 92 tons per day, the cost per ton would be — = 0.705 cent. 



92 



Other sizes arc figured in like manner. 



5. Labor. It is assumed that the breaker is fed by a sloping chute and 

 can therefore be fed by one man at a cost of $2 per 12-hour shift, or $4 per 



$4.00 



24 hours. The cost per ton for the 10x4-inch breaker would be = 4.348 



92 



cents. Other sizes can be figured in a similar manner. 



6. Wear is estimated at 0.815 cent per ton, which is the average of the 

 gross cost per ton at 18 mills. 



Repairs other than wearing parts. The maximum figure recalled by 

 the author was $155 per year. These repairs were required by a breaker 

 breaking 109 tons per day or 33,572 tons per year of 308 days, making the 

 $155.00 



cost per ton or 0.462 cent. 



33 , 572 



Altho this table is taken from average conditions and average 

 hardness of rock, it can be considered as a conservative set of 

 figures for the conditions that exist in the limestone belt of South- 



