174 



HANDBOOK OF MECHANICAL DESIGN 



FLAT- AND V-BELT HORSEPOWER CHARTS 



1098 7 6 5 



Sin is the half angle of the V groove for V-type belt. 

 For a flat belt, the angle is equal to 90 deg. and sin /3 is 

 equal to 1. 



The working value of Ti can be determined from the 

 breaking strength of the material and the factor of safety 



to be used. The value of e^'" ^ can be obtained from the 

 accompanying chart if v, the coefficient of friction, and 

 the angle 8 of the arc of contacts are known. The rela- 

 tion between Ti, the tight side tension, and Ts, the slack 

 side tension, can be found from the accompanying chart. 



Example. — A flat belt operating on a 20-in. diameter 

 puUev is making 600 r.p.m., the arc of contact is 165 deg. 

 Assume Ti equal to 120 lb. per in. of width, the belt 

 weighs 0.150 lb. per ft. per in. of width and has a coeffi- 

 cient of friction equal to 0.25. Find the horsepower the 

 belt can transmit. _ _■ 



From the speed-horsepower chart on page 171, it is 

 found that v, the velocity of the belt, equals 3,160 ft.per 

 min. The quantity ww-Zff may be calculated or determined 

 from a chart on page 172. 



To find e''*, enter this chart at the horizontal line which 

 represents the value of angle of arc of contact equal to 

 165 deg. Trace right to the diagonal representing a 

 value of V equal to 0.25, and then upward to the diagonal 

 labeled 90 deg., which represents a flat belt, then right 

 to the curve and then down to the scale where we read 

 ef^ equal to 2.1. 



By substituting this value of e sin /3 or, as in this 

 example, e*** in the preceding equation, the value of 

 Ti — T- may be calculated. With this quantity known, 

 and the use of the chart on page 171, the horsepower per 

 inch of width of belt may readily be obtained. 



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