THE DESIGN OF ELECTROMAGNETS 53 



NUMERICAL EXAMPLES 



16. Horseshoe Lifting Magnet. Assume the specified condi- 

 tions to be as follows: 

 Initial pull = 200 Ib. 



Travel of armature (being the length of the single air gap) = 

 0.35 in. 



D.C. voltage = 110. 

 Allowable temperature rise = 40C. 



Pole Face 2 Square 



FIG. 20. Horseshoe magnet. 



The temperature to be taken on the outside surface of the 

 exciting coils, after a sufficient time has elapsed for the final tem- 

 perature to be reached. 



The required magnet might be generally as shown in Fig. 20, 

 where the iron limbs are of circular section with square pole pieces. 

 These limbs may be steel castings, or they can be turned down 

 from square bar iron. Cast iron would not be a suitable material, 



