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).
Report from F.I.M.A.C. Milano on spark plug performance, detailing conductivity, temperature, and material deformation.
| Identifier | ExFiles\Box 58\2\ Scan133 | |
| Date | 14th June 1934 guessed | |
| F.I.M.A.C. MILANO -6- connection with the contact pressure, clearly shows how the conductivity varies a proportional law to pressure, and hence to expansion of the pin, and this explains how pressure is established during the plug's operation, which gives the coefficient of transmission required so that the pin's temperature shall not increase, and hence its length. The foregoing also explains the automatism of accomodation of the plug to different motors and different conditions of outside cooling (no matter if the plug is operating in a current of air or not, or with a diaphragm or not, etc.). Study was in view to determine the temperature of the electrode at the different pressures, but this could not be done because we have not yet succeeded in finding the expansion coefficient for the copper. The fact remains however, that in the plugs fitted knowingly without any play between the copper pins, the play was always found after working, to the extent in size of 1/10th of a m.m. This shows that the compression that took place between the two heads, was such as to pass the limit of elasticity of the copper and therefore a permanent deformation took place. The results given above clearly show the reason for these qualities of accomodation to different motors and conditions, which the most widely different and strict tests on the C.F. plugs have shown for the last two years. Also the less wear and tear of the middle electrode can be clearly explained, it being due to the fact that the electrode | ||