144 



Indiana University Studies 



types of screen can for present purposes be considered simply 

 as modifications of those already mentioned, and therefore need 

 no detailed description. 



Elevating the product is necessary in practically every plant, 

 unless the location selected is such that every movement of the 

 product from one machine to the next can be controlled by gravity. 

 Plants where this condition prevails are very few for the reason 

 that such a favorable location would in most cases make the 

 switching of the stone to the plant and its removal from bins to 

 cars a serious problem. The most common type of apparatus 

 used in carrying the crushed material from one point to another 

 is the belt conveyor. In this apparatus a belt is run over wheels 

 arranged to cause the upper surface of the belt to be concave so 

 that the product will remain on the belt. Rough belts or belts 

 with elects are sometimes used. The capacity of a belt conveyor 

 is determined by its velocity and width. They are in operation 

 up to 40 inches in width with a speed of 650 feet per minute. 

 Such a belt will handle about 1,220 tons per hour. As the eleva- 

 tion increases an elevator becomes necessary, and the bucket 

 elevator is the only one giving satisfaction in this kind of work. 

 This consists of an endless belt running over two pullej^s, one 

 above and one below and having buckets riveted to it. The 

 buckets act as scoops as they pass thru the material and carry 

 a quantity along the belt in each bucket. Bucket conveyors are 

 run at speeds up to 400 feet per minute, but slower speeds give 

 longer life and fewer repairs. 



Bins are the one problem that needs to be figured on closely 

 by any company about to start a plant, because the capacity 

 of the storage bins limits the running time in case of a dull market. 

 Bins are expensive at the best, and if extra large ones are put up 

 the first cost of the plant is so high as to seriously interfere with 

 the profits of the new venture. 



Bins are usually of wood construction and elevated so that 

 the material may be delivered from them by chutes. They 

 must be roofed and must not be leaky. 



The following letter received from one of the leading firms 

 handling crushing machinery in reply to a letter asking the cost 

 of crushing in plants of a certain size shows that even the large 

 manufacturing companies dealing in crushing machinery will not 

 give any but approximate figures: 

 Dear Sir: 



The necessary equipment of your plant would include a crusher, set of 

 rolls, screens, elevators, transmission machinery and power, but we can give 



