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).
Page describing the properties, composition, and applications of vulcanite, particularly as an electrical insulator.
| Identifier | ExFiles\Box 24\2\ Scan096 | |
| Date | 25th January 1921 guessed | |
| - 9 - or caustic soda should be quite free from water before the sulphur is added, in order to prevent the production of bubbles and the troubles associated therewith. The material thus obtained withstands temperatures up to 70 degrees. Many kinds of vulcanite can stand temperatures exceeding 140 degrees without becoming soft. This depends completely on the nature of the materials that are mixed with it, which include zinc oxide, heavy spar, chalk, talc, lamp-black, cinnabar and other materials for adding weight. It may be assumed that the greater portion of the sulphur which may amount to 30% of the total volume of the vulcanite, is only a mechanical admixture and that only a very small portion has combined closely with the hydro-carbons. So called "patent rubber" is produced according to the process of Parkes by using compounds of sulphur such as sulphur chloride and carbonic sulphide instead of elementary sulphur. In order to remove excess of sulphur the rubber may be treated with solutions of potassium or soda-lye or with alkaline carbonatee, but the quality is likely to be impaired by such treatment. Vulcanite swells in volatile oils, benzine, carbonic sulphide and chloroform. Used pieces of rubber can be regenerated, that is to say may be recovered by removing the sulphur by mechanical or chemical means combined with cleansing processes. I must mention that Dr. Hofmann has succeeded in producing rubber synthetically from isoprene, and a number of experiments are being carried out in chemical factories that promise results of considerable commercial importance. The vulcanite products are to be regarded as having a most important use as electrical insulators for high tension purposes and for the construction of apparatus. An average quality has, after abrasion of the surface, an insulating resistance of several millions of megohms which is maintained after 30 hours immersion in water. It does not absorb water. If a vulcanite plate of 10 mm.thickness is placed for five days in a 25% solution of sulphuric acid there is no action by the acid, nor any increase of weight of the plate, and the surface insulation retains its previous value. The dielectric strength has a value of 40,000 volts with a thickness of 1 mm. Vulcanite is mechanically strong and tough, is able to be machined easily with moderate power. The tools are heated somewhat, but their wear is small. It may be moulded into any shape, and can be polished and threaded. If it is brought into contact with a flame it has the property of continuing to burn and after the combustion the components are softened and partly carbonised. Most varieties become elastic and pliable in boiling water. A very unpleasant quality of vulcanite is the separation out of sulphur, under the action of light. This gives rise to chemical action and blackening of metallic conductors mounted on it and the sulphuric acid that is formed produced a conducting surface. contd. | ||