18 LEATHER BELTING 



impractical to weigh the tension of a belt in tightening it, 

 d safe rule is to shorten a double belt one-half inch for every 

 10 ft. of length if it requires tightening when working under 

 a load of 1 1 1 Ib. per inch of width. If working under a total 

 load of 54 Ib. per inch of width, the belt may be shortened 

 one inch for every 10 ft. of length when re tightened. 



6. The total life of belting, cost of maintenance and re- 

 pairs and the interruptions to manufacture caused by belts, 

 are dependent upon the total load to which the belts are 

 subjected more than upon any other condition. The method 

 of fastening and the speed are the other chief considerations 

 affecting their life. Double belts treated with care and 

 running night and day at a moderate speed, should last for 

 seven years when under a total average load of in Ib. per 

 inch of width. They should last for eighteen years when 

 under an average total load of 54 Ib. per inch of width. The 

 speed at which belting runs has comparatively little effect 

 on its life until it is in excess of from 2500 to 3000 ft. per 

 minute. The belt speed for maximum economy should be 

 from 4000 to 4500 ft. per minute. 



7. In the machine shop in which the experiments were 

 made, the average cost per double belt per year of service, 

 including the first cost and the cost of maintenance and 

 repairs, proved to be $6.72 for belts used under a total load 

 of in Ib. per inch of width. For belts under a total load of 

 54 Ib. per inch of width the cost was found to be less than 

 $5.70. The cost of all labor and materials used in the main- 

 tenance and repairs of double belts plus the cost of renewals 

 as belts give out through a term of years, will amount to an 

 average of 37 per cent per year of the original cost of the belts 

 if belts are tightened accurately so that they will work under 

 an average total load of in Ib. per inch. If, however, 

 they are worked under a total load of 54 Ib. per inch of width, 

 the annual cost of maintenance, repairs and renewals amounts 

 to not more than 14 per cent of the first cost and probably 



