ARMATURE CORK VENTILATING PIECES 



75 



retrogressive manufacturers, and a good many manufacturers have 

 already arrived at the stage of employing many more ducts, each 

 duct having a width of some 10 to 15 mm. according to circum- 

 stances. The result is that, although of the gross core length, only 

 some 70 per cent., and often a lower percentage, is "effective" 

 iron, the improved ventilation thereby obtained permits of a con- 

 siderable decrease in 

 the weight of a 

 machine for a given 

 rating. Careful at- 

 tention is also very 

 often given to the 

 design and construc- 

 tion of the so-called 

 " ventilating pieces," 

 i.e. pieces of as skele- 

 ton a construction as 

 is consistent with the 

 necessary mechanical 

 strength, and serving 

 the purpose of pre- 

 serving the required 

 distance between the 

 neighbouring sections 

 of the core. 



An interesting ex- 

 ample is a ventilating 

 piece employed by the 

 Allmanria Svenska 

 Elektriska Aktiebo- 

 laget. This is shown 

 in Fig. 75. It will be 

 observed that this is 

 employed in a design 



in which the teeth are exceedingly thin ; and in order that the 

 " separating-fingers " shall not obstruct the space between the 

 armature coils, there is only provided one finger for every alter- 

 nate tooth. The authors have seen maiiy an armature in which 

 points of this sort have been utterly neglected, with the result 

 that the "ventilating ducts" are just so much lost space. In 

 some cases, only one "finger" for every third or even fourth 

 tooth could preferably be employed. 



FIG. 76. Cast Ventilating Distance-piece. 



