CHAPTER VIII 



PULLEYS 



THE life of and service rendered by belting is affected 

 in no little degree by the condition and arrangement of the 

 pulleys on which it runs. The notes on pulleys which follow 

 cover those features that have a direct influence on the belt 

 problem. In general it is advisable to use as large pulleys 

 as possible, providing that they are not so large as to give 

 a belt velocity in excess of 4700 ft. per minute. Small pulleys 

 running at high speed, however, will cost less when equipping 

 the mill than will large pulleys running at low speeds. 



Width of Pulleys. The face of the pulley should always 

 be wider than the belt that is to be used on it. Carl G. Earth 

 (American Machinist, February n, 1915) gives the following 

 formula for the relation of the width of pulley to that of the 

 belt, in which F and B are the widths of the pulley and belt 

 respectively, both in inches: 



The limits of design may make it impractical to use pulleys 

 as wide as those called for by the equation just given, in which 

 case the following may be substituted : 



Values of F by both formulae for various values of B are 

 given in Table VI on page no. 



Crowning of Pulleys. A belt on a pulley tends to climb 

 to the largest diameter of the pulley. Advantage may be 

 taken of this tendency to compel the belt to run in the center 

 of the pulley face by making the pulley of slightly larger 

 diameter at the center than it is at the edges, or " crowning " 

 it. The amount of crown that should be given to a pulley 



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