34 



LEATHER BELTING 



PERCENTAGE OF BELT CREEP FOR VARIOUS VALUES OF p AND E 



for common leather belt under ordinary working conditions 

 the creep should be not over i per cent. While this is some- 

 times called legitimate slip, it is an actual loss of power and 

 cannot be avoided by belt tighteners and patent pulley 

 coverings. 



A study of the experiments of Messrs. Lewis and Bird 

 by Mr. Earth led to the development of an equation for the 

 coefficient of friction / as follows : 



/=o.6 



in which v is the total average sliding velocity of the belt in 

 feet per minute, it being based on belts in active service and 

 tested without the application of belt dressing. The equa- 

 tion covers in a satisfactory manner results obtained with 

 belts in service. 



To be of practical use, however, the velocity of sliding of 

 the belt should in some way be connected with its pulling 

 power at a given actual velocity of belt. This is accomplished 

 through the medium of the ratio of the effective tensions 



expressed in formula (i), namely ^=e /0 , which ratio will 



later be used in determining a value for p. It is quite evident 

 that an average coefficient of friction for all velocities of belt, 

 such as was assumed in the rule of thumb formulae, and even 

 in more pretentious ones, would be incorrect, in view of the 

 work of Messrs. Lewis and Bird. Mr. Barth further main- 

 tains that basing the coefficient of friction on an average 



