Pressing and clamping laminated cores

Tests were carried out on laminated cores to determine the relationship of the axial deflection ¿ to the applied axial pressure p. These showed that increase in tightness decreases substantially with increase in p beyond 401b/in2. A controlled penknife test demonstrated that a core is tight at this pressure. It is thus assumed that a core in which a pressure of 401b/in2 is maintained at all points, throughout its life, is tight. A theoretical investigation shows that the ¿/p characteristics can be calculated by determining the incidence of microscopic peaks of various heights on the lamination surface. It is shown that this incidence is in accordance with the Gaussian probability integral and that the resulting ¿/p characteristic shows the same change in shape at p=401b/in2. Further experiments yielded equations from which the distribution of pressure throughout a core and the factors governing the fatigue failure of teeth may be calculated. Practical investigations show that slack cores may originate in shrinkage of the core varnish and mechanical vibration, and a method is developed by which a factor of safety can be included to cover these phenomena. Methods of clamping cores are reviewed with reference to differential expansion, stored energy and cost. A worked example relating to a large hydroelectric generator is included.