40 LEATHER BELTING 



to= minimum initial tension in the belt at rest on its pulleys, 

 pounds per square inch. This is the tension to which 

 the belt can be allowed to fall before retightening. 



t m = maximum initial tension in the belt at rest upon its 

 pulleys, pounds per square inch. This is the tension 

 to which the belt is retightened. 



t c = centrifugal tension in belt, or loss in effective tension 

 due to centrifugal force, pounds per square inch. 



p = effective pull in belt, pounds per square inch. 



a = arc of contact of the belt on the smaller pulley, in radians 

 = (7r/i8o) Xarc in degrees. 



/= coefficient of friction between the belt and the pulleys. 



F = velocity of belt, feet per minute. 



e=basis of Naperian system of logarithms = 2. 7 1828. 



A =a constant; whose values range from 160 to 320 as ex- 

 plained below. 



The problem is to find a formula which will express the 

 relation of the initial tensions to and t m to the tensions t\ and fa 

 in the tight and slack strands of the belt, in order to ascertain 

 what value must be given to to to obtain a predetermined 

 value of p in the formula (4) : 



P = h-t2 (4) 



Bearing in mind the conditions under which the intervals at 

 which the belts should be retightened will be made equal as 

 explained in a previous paragraph, we can express this rela- 

 tion algebraically as 



/i+ife-4 (5) 



For machine belts A = 240 and 320, depending upon whether 

 values of to or t m respectively are being sought, as explained 

 later; for countershaft belts A = i6o and 240 respectively 

 for finding values of to and t m . 



The passage of the belt around the pulleys develops 

 in it centrifugal force whose effect is to decrease the tension 



