CHAPTER VI 



CONSTRUCTION OF SQUIRREL CAGE ARMATURES 



THE design and construction of squirrel cage armatures is com- 

 paratively a simple problem, as these pieces of apparatus are by 

 far the least complicated types of armature occurring in any class 

 of dynamo-electric machinery. 



A squirrel cage armature, when completed, forms a very 

 hardy structure, and it is largely on account of this and of its 

 inherent simplicity that the squirrel cage induction motor 

 recommends itself for such a large field of work. 



So far as the spicier is concerned, this does not differ much 

 from the spiders used for ordinary continuous-current armatures, 

 many types of which have already been referred to in Chap. III. 

 As, however, with squirrel cage armatures there are no collector 

 rings or commutator present, the spider may be made exactly 

 symmetrical about the vertical axis of the machine. Thus a good 

 spider for supporting the laminations of a squirrel cage rotor 

 need only consist of a simple armed spicier, with a pair of similar 

 end flanges to clamp the laminations together. 



For small motors, where the internal diameter of the rotor 

 stampings is small, no spider is necessary, and the laminations are 

 mounted directly on the shaft. This plan is sometimes applicable 

 to rotors of larger diameter, where the laminations would have 

 apertures stamped in them for purposes of ventilation, as in the 

 illustrations in Figs. 64 and 84 on pages 67 and 81. 



Fig. 103 shows a typical rotor construction on this plan. In 

 this case the stampings are clamped up between two end flanges, 

 one of which fits up against a shoulder on the shaft, and the other 

 is screwed on to the shaft at the other end of the core ; or it may 

 be secured by a separate collar screwed on the shaft, and fixed by 

 a grub-screw or a lock-nut. A method sometimes adopted in very 

 small rotors is to make the end flanges with a small boss project- 



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