ALTERNATING CURRENTS 



seen, the laminations are held together by means of bolts between 

 two sets of clamps, end grids being interposed between the clamps 

 and plates. These end grids are provided with teeth, which fit over 

 the teeth of the plates or laminations, and prevent them from spread- 

 ing outwards. The core-plates are, in the design of Fig. 63, provided 

 with key-way projections, which fit over keys screwed to the yoke- 



FIG. 64. Ventilating Space-block. 



ring. The end grids serve to ventilate the core, and additional 

 ventilation is secured by providing gaps, or ventilating ducts (see 

 Fig. 65), in the core, these gaps being formed by the interposition of 

 ventilating space-blocks. One of the simplest forms of space-block 

 is shown in Fig. 64. It consists of a steel plate, about -^ inch thick, 



VENTILATING DUCTS 

 FIG. 65. Armature Core Construction. 



shaped like one of the core-plates, and having semicircular pieces cut 

 and bent at right angles to the plane of the plate. These support 

 bent radial steel strips as shown, which act as distance-pieces between 

 the core-plates. The width of ventilating duct varies from about 

 inch to f inch. It is usual to provide a ventilating duct to every 

 5 inches or 6 inches of core length. 



