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).
Correspondence on the subject of insulation impregnation, copied from The Electrical Review.
| Identifier | ExFiles\Box 24\2\ Scan288 | |
| Date | 18th July 1928 | |
| X1109. CORRESPONDENCE ON THE SUBJECT OF INSULATION IMPREGNATION COPIED FROM THE ELECTRICAL REVIEW. "I was greatly interested in the article by Mr. A.C. Dunlap on "Insulation Impregnation" in your issue of February 17th. with much of which I am in entire agreement, but some statements in the article are a little misleading. Mr. Dunlap has not made it clear, in that article, that in the class of apparatus he wrote about the drying of the articles treated takes place under vacuum, and that it is pressure which causes the varnish or compound used to saturate the conductor coverings and penetrate between the windings of the wire. In the case of some apparatus, notably the early plants made in Germany and France, the pressure of the atmosphere was, and is, relied on to cause penetration, and that was often insufficient for the purpose. In other apparatus the pressure above atmosphere, in addition to atmospheric pressure, causes the varnish or compound to penetrate the windings and saturate the coverings. The writer was the originator of the process of "vacuum drying and pressure im-pregnation", designed the apparatus, and put in on the market. That business is now carried on by "Browns' Dryers, Limited" of Manchester. Many of the earlier plants were supplied on the Continent, where they and the system were largely copied after the original patents had expired. Since the first apparatus was put on the market many improvements have been made on it which have not yet been copied. There is, therefore, no need to go abroad for apparatus of this characterix, as the old style, and also the improved plants, can be obtained in England. The present electric-oil-heated apparatus is far in advance of the earlier impregnators, although a large number of those were sold, and are still in use; but they do not compare in convenience, economy, or safety with the present apparatus, in which temperatures up to 500 deg. or 550 deg. Fahr. can be readily attained without any pressure whatever on the heating medium, or any danger of fire, while the cost of operation is often considerably below the cost of steam heating. An incidental statement in the article mentioned, with reference to the penetration of wood, also needs a little explanation. The pressure required depends on the kind of wood treated and the thickness of the wood to be penetrated. | ||