THE DESIGN OF ELECTROMAGNETS 



Let R = mean radius, in feet. 



A = area of all North, or of all South, polar surfaces in 



contact (square inches). 



P = pressure in pounds per square inch of contact surface. 

 N = revolutions per minute. 



c = coefficient of friction, the meaning of which is that 

 c X PA is the tangential force which will just produce 

 slipping. 



then 



hp. 



PAX c X 2irR XN 

 33,000 



(32) 



T 





FIG. 19. Magnetic clutch. 



which gives the horsepower that the clutch will transmit just 

 before slipping occurs. If k is the safety factor, and (hp.) is 

 the horsepower which has to be transmitted, the value of hp. 

 to insert in formula (32) should be (hp.) X k. Note also that 

 p = _J?!_ and different values of B can be tried; these 





1,730,000' 



