312 



ARMATURE CONSTRUCTION 



FIG. 377. Methods of securing 

 Rotor Coils. 



against centrifugal force, and in the rotor shown in Fig. 374 this 

 is effected by binding them on to an iron ring with cord or tape 

 in the manner of Fig. 377. 



Another method is to embrace the coils with straps of sheet 

 metal bolted together through the inside of the rotor, or screwed on 

 to the rotor end flanges in the way shown in Fig. 378. 



The second method of wind- 

 ing with wire in semi-closed slots 

 consists in slipping the wires one 

 at a time through the mouth of 

 the slot, as in Figs. 379 and 380. 

 The slot opening must be suffici- 

 ently wide to admit the covered 

 wire without damaging the insula- 

 tion, which is closed over as in 

 Fig. 381. 



When the wire is small, the 

 end portions of the coils when 

 wound in this way are not 

 usually formed over a block ; but 

 the wire is fed direct off a shuttle 

 into the slot, and the coils shaped by hand. 



This method also adapts itself to form winding, as the coils may 

 be wound on formers ; and if they are not taped or bound up, the 

 wires can be slipped into the slot one at a time and the end parts 

 of the coils assembled into shape when the slot is filled with wires. 

 Messrs Siemens Bros, have taken out a patent (No. 2196 

 of 1903) on this method, of which Figs. 382 and 383 show the 

 principle. Here the coil is first wound on a former, and one 

 side bound round temporarily with a piece of tape or a clip of lead 

 to keep the coil intact, while the conductors on the other side are 

 being slipped into the slots as in Fig. 383. Windings' of this sort 

 have, however, been extensively used years ago. 



A patent was taken out by W. B. Sayers in 1904 (No. 12,801), 

 by which form-wound coils may be employed with semi-closed 

 slots, the substance of which is illustrated in Fig. 384. As shown, 

 alternate teeth, 1, are made detachable from the body of the 

 armature core, with which the other alternate teeth, 3, are made 

 in one piece. The detachable teeth are retained to the core in 

 channels 4. Fig. 384 shows one method of securing these teeth, 

 the stampings on each side of the ventilating duct, 10, being spaced 

 by brass plates, 11, 13, and with distance pieces, 14, between them. 



