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).
Analysis of Salamanite insulators, comparing their thermal conductivity to other materials and detailing test results in Champion plugs.
| Identifier | ExFiles\Box 35\3\ scan 174 | |
| Date | 15th September 1927 guessed | |
| contd :- -2- is said to be composed mainly of the the same material - Salamanite. It is claimed that 'Salamanite' although a good insulator electrically, is a comparatively good conductor of heat. This combination of a small section central electrode with a 'heat conducting' insulator is, we think, better than the B.G. arrangement, where a larger body of metal with a mica insulator tends to retain its heat, owing to the low thermal conductivity of the mica. Comparing thermal conductivities, we have :- (Kaye and Laby). Substance. Constant X 10-3 Porcelain. 2.5 Mica. 1.8 Gas carbon. 10.0 It is claimed that Salamanite has four times the thermal conductivity of porcelain - giving it the same value as gas carbon - above. Mica insulators tend to become impregnated with carbon, while the coating of carbon which the pot insulator received in time, can be readily scraped off. After about 30 hrs. total running on benzol with the R.12. plugs, we find they have depreciated sufficiently to cause the engine to cut out due to pre-ignition during any prolonged test. We think that this is due to the cement around the central electrode becoming dis-placed after lengthy running, affecting the heat transference to the Salamanite. Thus the Champion plugs have not a lasting quality and cracked and broken insulators would be liable to damage valve seats etc. (A new design of Champion plug is in hand, which may shew some improvement in these respects and also with regard to terminals, which are, at present, badly made and slacked off unless a spring washer is used). Hs{Lord Ernest Hives - Chair}/V.Halliwell. | ||