26 LEATHER BELTING 



belt velocity of 403.2 ft. per minute. Turning now to the 

 horsepower table on page 91 we find in the section headed 

 " 180 Degrees Arc of Contact " under machine belts, that 

 a belt of i sq. in. of cross-sectional area will transmit 1.05 

 horsepower at 250 ft. per minute and 2.27 horsepower at 

 500 ft. per minute. The horsepower that is transmitted 

 at speeds intermediate to those in the table increases very 

 nearly in proportion to the increase in speed. The difference 

 in speed between 250 and 403 ft. per minute is 153 ft. per 

 minute, and between 250 and 500 ft. per minute is 250 ft. per 

 minute. The difference in horsepower transmitted at 250 

 ft. and 500 ft. per minute is, according to the table, 1.22 

 horsepower. Therefore, at 403 ft. per minute the horsepower 

 transmitted would be 



H.P. = 1.05+ 1.22 X^ 



\ 250, 



= 1.05 + 1.22x0.612 



= 1.79. 



As it is desired that the belt shall be capable of trans- 

 mitting 3 horsepower, the cross-sectional area of the belt 

 will be 3^-1.79 = 1.676 sq. in. The width of belt that should 

 be used on a cone pulley of 5-in. face should not exceed 

 4! in. We therefore look in the table of relative areas on 

 page 108 opposite the width of 4^ in. for the figure most 

 nearly corresponding to 1.676. We find it to be 1.719 under 

 the thickness of f in. Therefore a belt 4^ X f in. will be ample 

 to transmit 3 horsepower under the conditions. It should 

 be put on the pulleys under a total initial tension (see col- 

 umn 3 of table) of 



i. 7 i 9 x 



|i83. 7 s- 



= 1.719X181.61 =312 Ib. approximately. 

 By the same sort of a calculation we find from column / 



