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).
Technical comparison of various insulating materials, including Fabric Base, Tufnol, and Asbestos types.
| Identifier | ExFiles\Box 61\1\ scan0243 | |
| Date | 4th September 1935 guessed | |
| SYM. A.{Mr Adams} Fabric Base Material. Fabric Base material although having good insulating properties was not designed as an electrical insulator but are used for this purpose. Standard Fabric Sheets do not fulfil B.S.S.547 requirements but we are always willing to prepare something to meet a special purpose. SYM. B. Water Absorption. Based on B.S.S.test methods the comparative ratio of weight absorption is in the order of Swan type, Kite, Fabrice 1;2;5, 1/4" thick and over, but about 1; 2.2; 1.5 on thin material. The percentage curve given in B.S.S.547 represents Swan type but Kite is slightly higher for thick sheet. The percentage absorbed by weight depends on size and thickness and test piece. SYM. C. Tensile Strength. With regard to working tensile strength this to a certain degree depends on safety required. The ultimate tensile has a testing machine error of as much as 12% and the strength depends on whether the material is tested lengthwise or crosswise. The figures given exceed B.S.S.547 and are averages given for comparison between our types. As far as tubes are concerned the electrical and mechanical strength is similar to equivalent sheet material but in moulding tubes a weakness is produced at the lengthwise fin marks. The electric strength is lower, there is a reduction in mechanical strength and the moisture absorption is a little higher along these two lines. We take 70% value on tubes in normal practice to allow for this irregular amount of weakness. Asbestos Tufnol. There is not great demand for this class of material because its only advantage is where constant working temperatures over 130°C and below 220°C prevail. Its electrical properties are very moderate and paper base Tufnol meets all purposes except for the high working temperatures. | ||