Belting. 543 



have gotten out of line with the shaft, (G) the collar or 

 pulley may bear too hard against the end of the box. 



BELTING. 



The use of belting, ropes and cables, in transmitting 

 power from a motor to the machine being driven, is a prac- 

 tical utilization of friction. 



685. Action of Belting. When machinery is being 

 driven by a belt its two sides are not under equal tension 

 and the efficiency of the belt depends upon the difference 

 in tension between the two sides and the rate at which the 

 belt is traveling. Suppose the effective tension of the belt 

 is 66 Ibs. and that the belt is traveling with a velocity of 

 1,000 feet per minute, then the energy it is transmitting, 

 or its activity, is equal to 



66 X 1000 = 66,000 foot pounds per minute. 

 or 66,000 



It is clear from this that the more rapidly the belt is 

 driven the larger is the horse-power transmitted when the 

 effective tension of the belt is the same. 



686. Efficiency of Belting. The highest efficiency is at- 

 tained from belting when there is least stretching and. least 

 slipping of the belt and when there is the least unnecessary 

 pressure developed by it on the shafts of the driving pul- 

 leys. 



Good leather belts usually give a higher efficiency than 

 rubber or other types and when they are used where they 

 can always be kept dry are most satisfactory. To get the 

 highest service from a leather belt it should be run with 

 the hair side next to the pulley and over a pulley faced 

 with leather with the hair side out. Under these condi- 

 tions there is the least slipping of the belt and the strain 

 on the belt in bending around the pulley is least, so that it 

 wears more slowly when being bent and straightened. 



