From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Report page discussing leakage curves and the effects of temperature on electrical mouldings.
| Identifier | ExFiles\Box 61\1\ scan0128 | |
| Date | 12th September 1930 guessed | |
| -4- than A.{Mr Adams} While curve B is called a medium curve, the author would be inclined to recommend the rejection of all samples not conforming to at least this standard. The sharp bend in the leakage curves occurs in the case of most mouldings between the temperatures of 60 and 90°C. and it is unwise to use mouldings at temperatures on or beyond these bends owing to the danger of breakdown. If, however, the mouldings can be maintained for any length of time at temperatures above 70°C. but preferably in the region of 110°C. without subjecting them to any electrical stresses to cause breakdown, then a gradual improvement in the leakage figure is noted and the sample can be passed out finally as good i.e. equal to A and perhaps superior to it. This final baking operation has removed water from the moulding and probably completed the change in the resin from the B stage to the C, or final stage; a slight shrinkage will have taken place and the surface of the moulding will have become slightly wrinkled. Thus to produce good electrical mouldings with any powder is possible, although perhaps difficult; but to produce good electrical mouldings with an inferior powder and retain a good finish is impossible, owing to the shrinkage that will take place in the final curing. Table I shows the variation that may occur in the quality of powder obtained from the best suppliers; the four samples came from the same firm. The mouldings on which the tests were made were produced as follows: (1) A weighed quantity of powder put into a positive mould. (2) The mould (at 150°C.) immediately closed with 2 tons sq. in. pressure. (3) Five minutes cure. (4) Extraction without cooling. | ||