Quantitative tests on finished mouldings

Moulded materials made from a given base by heat and pressure differ appreciably according to the type of mould and the moulding technique used. To avoid anomalies from this cause when comparing alternative materials, manufacturers of electrical equipment have adopted a standard test and test-specimen for each of the salient properties. The values obtained in this manner are, by common consent, deemed to be those of the material. It is recognized that these values may be higher or lower than those manifested by commercial mouldings other than standard test-specimens, and that it is sometimes necessary to know the actual values. Since it is usually not possible to apply the standard tests to nonstandard test-specimens, a new set of tests and test-specimens is required, the latter being cut from commercial mouldings. At the request of the British Standards Institution an investigation was put in hand by the Electrical Research Association to explore how this might be done. The paper surveys the problem and the steps taken over a period of live years to solve it. A metrical examination of typical mouldings is followed by practical advice on the preparation of specimens and suggestions for their use in the determination of resistance to impact and slow bend; resistance to crushing; electric strength; surface resistivity; plastic yield; effect of heat; specific gravity; and water absorption. The results are summarized in a Table showing the degree of correlation with standard tests.