106 



ARMATURE CONSTRUCTION 



generally used, wide open slots being very rarely employed for 

 squirrel cage motors. 



If the slots are totally closed, it is necessary for the iron bridge 

 over the mouth of the slot to be very thin ; and this necessitates 

 die-work, so that the slot mouths shall not break open in places 

 when the rotor core is turned or ground up. 



FIG 117. Grinding Surface of Induction Motor Rotor. 



Fig. 118 shows a group of typical slots for squirrel cage rotors ; 

 types a, b, c, and d are quite common. The slot shown in sketch e 



FIG. 118. Types of Slots used in Induction Motors. 



has been used to obviate the trouble just referred to ; in this case 

 the bridge across the slot mouth is filed down to a very narrow 

 thickness, from the inside of the slot, after the core is assembled 

 and machined. 



Some notes on the punching of slots and core plates for in- 

 duction motors will be found on pp. 42-46, Chap. II. 



