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).
Comparison of properties for Synthetic, Rubbers, and Fibres, with details on synthetic moulding powder.
| Identifier | ExFiles\Box 39\3\ Scan256 | |
| Date | 1st November 1925 guessed | |
| -2- Contd. SYNTHETIC. Brinell 30 or more Heating Blisters at 250°C. Moisture absorption 1%. Acid No effect. Breakdown 500-600 RUBBERS. About 20. Soften at 75°C. 1% No effect. 1000 FIBRES. About 20. Blister at 250°C 50% (by weight) Rot away (dilute sulph 250 (volts per mil) The synthetic material is only inferior to rubber in its breakdown voltage, which is, however, ample for all ordinary purposes. It may sometimes possess a higher dielectric loss than the rubbers and thus be unsuitable for high frequency insulation. But if a good grade of material be employed and the article well "cured" in the die, this defect is avoided. Another limitation is that if a spark passes across the surface of a synthetic moulding it is liable to form a carbon track which thereby destroys its property as an insulator. Owing to this danger it cannot be used for distributors for magnetos, etc. of the carbon brush type. Where this danger does not exist however, it may be freely employed for high voltage apparatus of large or small scale. Sp.{Mr Spinney}Gr.{George Ratcliffe} The cost of the moulding powder is two or three shillings per pound, its density being about 1.4 taking water as unity. The time occupied in moulding one article may be from a few minutes for small nuts, etc. to an hour or so for large articles. The cost of the moulds is high, but they last well and even improve their polish with use, so that for large outputs, the cost of the mouldings is quite small. Synthetic insulation is unaffected by oil; retains its polish and colour in all weathers; has a very small coefficient of expansion on heating; its dielectric conductance is negligible and it is mechanically much stronger than ebonite; when overstressed it snaps. Pleasing mottled effects may be obtained, and the flow of the material in the moulds may be shown, by mixing the black and red powders when moulding. Electrical contacts may safely be made which are dependent on pressure upon the surface of moulded parts. Bolt holes require no metal inserts, brass chip fillings are used for friction surfaces; asbestos fillings for high temperatures etc. Transverse parts are avoided as much as is conveniently possible in the moulds, but they may be quite successfully incorporated. | ||