THE ARMATURE FRAME 



67 



large holes. This assists the ventilation and also effects a saving 

 in weight. 



In Fig. 69 the armature laminations are not held together to 

 the frame by bolts connecting the two end plates, but they are 

 secured by a number of short keys (K) driven in circumferentially 

 between the loose end flange and a circular rib on the frame. 

 This construction has obtained considerable use recently, and it 



FIG. 64. Armature of 750 k.w. 1500 r.p.m. Generator, showing 

 Ventilating Arrangements. 



dispenses with bolts passing through the stampings or connecting 

 the end flanges. 



Fig. 70 shows a section through a large frame of the box 

 type, which is common practice for very large frames. Here the 

 core is clamped up between two end flanges neither of which is a 

 part of the frame, the bolts being just outside the circumference 

 of the laminations. The laminations are secured to the frame by 

 dovetail keys. In some cases the frame is made in two exactly 

 similar halves, bolted together by bolts usually inside the box part 

 of the frame, as shown in Fig. 71. In this frame the armature 



