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 description of cellulose-based insulators, including vulcanised fibre and nitro-cellulose.
| Identifier | ExFiles\Box 24\2\ Scan098 | |
| Date | 25th January 1921 guessed | |
| C H O 12 20 10 We have mentioned wood amongst the natural insulators. This consists mostly of cellulose, which has the chemical composition (C 12 H 20 O 10) x., and is therefore isomeric with starch and dextrine. Cellulose is the raw product of a large number of bodies which have become important as electric insulators. By the use of cellulose cotton wool, linen and hemp, which are all of the same composition, a number of fibrous materials, paper and textiles can be formed, which when impregnated with suitable insulating material may be used to cover wires and cables and to separate current-carrying conductors. They therefore act in a way as carriers of the insulating substances. Quite pure cellulose is obtained by treating wadding, i.e. cotton wool, successively with dilute caustic potash, dilute sulphuric acid water, alcohol and ether. It is a white amorphous substance that is produced by thus separating out all hardening impurities. Swedish filter-paper is nearly pure cellulose. In manufacturing paper it is necessary to distinguish between sulphite and sodium-cellulose. In the former pine woods are treated with solutions of sulphuric acid or potassium bisulphite in compression chambers which causes a sort of hydrolysis and separation of the resinous from the other components. In the soda process wood is treated with caustic soda or sodium sulphat Insulating materials of paper, cotton wool and linen are known under varied trade names, such as pertinax (Neirovsky) carts, papier mache, Henelit and Presspan, which are compressed papers which sometimes contain linen and cotton wool. The dielectric strength of presspan is 19,999 volts with a thickness of 1 mm. or greater if impregnated. With a rise of temperature is tends to carbonise. or spar If cellulose is treated with zinc chloride or strong sulphuric acid, the fibres assume a form which can be squirted and compressed into a solid mass under high pressure. This material is called vulcanised fibre. Its production is possible by the use of a pulping machine, by treating the paper with sulphuric acid before it is sized, and then washing it carefully and wrapping it on hot cylinders in layers, and thus amalgamating it into a solid. In order to facilitate the transformation of cellulose into Hydro-cellulose, the materials must be exposed to the action of the air for a long time after washing. Vulcanised fibre is an unreliable material in its electrical properties that is only an insulator when dry. It is very hydroscopic, swells in water and breaks up with a crackling noise if an open flame is suddenly supplied to it. It is a hard and pliable material and can be easily machined and its strength and toughness are particularly good. If nitric acid is used instead of sulphuric acid to act on cellulose then the so called nitro-cellulose are produced. The cellulose hexanitrate C 12 H 14 (O.N.O.) 04 is pyroxyline or gun cotton produced by the action of cold. This material is insoluable in alcohol and ether and together contd. | ||