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).
The performance and test results of 'Maconite' insulated cable under various temperature, chemical, and oil exposure conditions.
| Identifier | ExFiles\Box 168\1\ img005 | |
| Date | 29th January 1926 guessed | |
| the present state of the art, maximum strength and elasticity are not compatible with maximum insulation resistance or dielectric strength. He states that this is especially true as regards the former, and gives quantitative illustrations, besides drawing attention to the way in which hardened vulcanised rubber is affected by immersion in water. It is well known that even the softer insulating qualities of vulcanised rubbers are hygroscopic to some degree. Now, whilst the measurable insulation of “Maconite” is comparable with that of a good quality vulcanised rubber, this insulation resistance is constant and is unaffected by prolonged immersion in water or in a saturated solution of caustic soda. Furthermore, its dielectric strength, i.e., resistance to breakdown pressure, is high under ordinary, and many extraordinary, conditions of use, and it is becoming recognised that it is by dielectric strength and resistance to physical change over a long life that insulating materials must be judged. Its resistance to the action of a wide range of chemical reagents must appear to be remarkable to anyone familiar with ordinary rubbers. Some details of the tests to which “Maconite” has been satisfactorily subjected will perhaps better indicate the degree of success which has been obtained. It must be understood that, except where specifically mentioned, no tests of less duration than some thousands of hours have been considered. Extremes of Temperature. 1. Freezing “Maconite” cable in a block of ice for several days, and testing at 1,000 volts. A.C. for 30 minutes. Then thawing out in running water and again testing at 1,000 volts. A.C. 2. Boiling in water and for three hours in a weak solution of caustic soda. 3. Exposure for several months in temperature of 100 deg. F.{Mr Friese} above boilers and brass furnaces. N.B.—In all these cases, not only did the cable withstand the tests, but its flexibility was found to be absolutely unimpaired at the end. Exposure to Chemical Action. 1. Immersion in dilute uric acid. 2. " " copper pickling acid. 3. " " 5% solution of sulphuric acid. 4. " " 5% solution of nitric acid. 5. " " 50% solution of hydrochloric acid. 6. Immersion in slaked slag water. 7. " " two samples of corrosive pit waters. 8. " " saturated solution of caustic soda. 9. " " common soda. 10. " " 10% solution of ammonia. 11. " " saturated solution of common salt. 12. " " sea water. 13. " " rust (dry and moist). 14. " " saturated solution caustic potash. N.B.—In all these cases the cables were carrying direct current at 250 volts, two cables being on test in each solution, and being connected to the positive and negative poles of the system respectively. This was done in order to be certain that the material would withstand osmotic action. OILS. 15. Immersion in Rape Oil. (a) 16. " " Machine Oil. (b) 17. " " Crude Oil. (c) 18. " " Fuel Oil. (d) 19. " " Paraffin. (e) 20. " " Petrol. (f) 21. " " Benzol. (a) The Cable swelled about 10 per cent after 3 years' immersion, with no apparent destructive effects. (b) The Cable swelled 20 to 40 per cent., with no apparent destructive effect. (c) The Cable swelled about 40 per cent., with no apparent destructive effect. After a few hours exposure to air, the Cable gained its normal size. These tests, and others too numerous to mention here, serve to indicate that a remarkable material has been produced. By those responsible for the installation of cables in such places as Chemical Works, Steel Works, Dye Works, long Railway Tunnels, etc., etc., where corrosive fumes or liquids are always present, “Maconite” has been found to be the most satisfactory solution. It is obvious that a substance such as this, in addition to forming a valuable dielectric covering for cables to take the place of V.I.R. and other types in bad or difficult situations, possesses great advantages as a sheath for other classes of cables in the place of lead alloys or bitumen. It is being largely used for a surface wiring system which requires no bonding or earthing. | ||