138 



Indiana University Studies 



be low and very massive on account of the great jar. The 

 machine should be low and the size of the jaws ample for the 

 amount of rock fed. Larger jaws will accommodate larger 

 lumps, and the power expended per ton crushed is the same 

 regardless of the size of the crusher. Larger crushers also cost 

 less for upkeep than smaller ones. The average rate of crushing 

 with a crusher of this type, working in hard limestone, is about 

 8 tons per horse-power per hour, with the output reduced to 1-inch 

 size. This amount increases rapidly as the output is turned out 

 in large sizes. Professor Richards, Textbook of Ore Dressing 

 (pp. 16, 17), gives the following amounts per horse-power per 

 hour : 



13 tons to 1 3^-ineh size. 

 16 tons to 2-inch size. 

 19 tons to 23^-inch size. 

 213^ tons to 3-ineh size. 

 283^ tons to 33^ inch size. 



The estimated cost of preliminary breaking with a Blake type 

 jaw crusher can be best obtained from the following table taken 

 with slight modification from Richard's Textbook of Ore Dressing 

 (p. 22): 



Size of moutli in inches 



10x4 



10x7 



15x9 



20x10 



30x13 



Tons per 24 hrs. to 2-inch size. . . 



92 



5 



$275 . 



120 



8 



$500 



192 

 12 

 $750 



360 

 20 

 $1,050 



600 

 40 

 $2,250 



Operating cost (in cents) per ton 



Oil 



0.020 

 0.097 



0.020 

 0.135 



0.020 

 0.127 



0.020 

 0.095 



0.020 

 0.122 



Interest and depreciation 





Power 



^0.705 

 .4.348; 

 .0-815^ 

 ^0.462* 



0.865 

 i3.333 

 4O.8I5 



0.462 



0.811 

 2.083 

 0.815 

 0.462 



0.721 

 1.111 

 0.815 

 0.462 



0.865 

 0.667 

 0.815 

 0.462 



Labor 



Wear 



Repairs 



Total cost (in cents) per^ton 

 of rock crushed 



6.447 



5.630 



4.318 



3.224 



2.951 



