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).
Investigation report into the failure of standard Sintercorund sparking plugs and suggested modifications.
Identifier | ExFiles\Box 27\3\ Scan255 | |
Date | 10th October 1939 | |
Lr{Mr Ellor}/Wst.23/WJ.10.10.39. REPORT ON THE INVESTIGATION OF RECENT FAILURE OF STANDARD SINTERCORUND SPARKING PLUGS AND SUGGESTED MODIFICATIONS TO OVERCOME THE DISCREPANCIES BETWEEN SIMILAR TYPES OF PLUGS. TEST PROCEDURE AND RESULTS. Since the general introduction of Sintercorund plugs into use on Rolls-Royce engines it has been noted that there appears to be a considerable amount of discrepancy between batches of plugs of similar type and heat factor. In order to ascertain if possible the cause of these inconsistencies various modifications have been introduced and investigations have been made from time to time on plugs which have exhibited overheating characteristics. Primarily, consideration was given to the effect of earth points, it being maintained that poor thermal conductivity between the electrodes and earth retaining ring and plug body was the cause of plugs overheating. Whilst this factor had no doubt influenced the plugs in a number of cases it was felt that the true cause of overheating had not yet been clearly established. In view of this therefore further investigations have been made particularly with regard to the behaviour of the central electrode. It has been known for some time that with the A.C. type of Sintercorund plug greater insulator nose lengths have been possible for high duty plugs then it was possible to achieve with the K.L.G. and Lodge plugs. This feature was in the first place attributed to a greater heat conductivity of the insulator material. Tests at the research Laboratory on all three materials proved however that this theory was fallacious and that the thermal conductivities of all three materials was very similar. (See report SP.{Mr Spinney}40/JW.) Further investigation of the A.C. plug elicited the information that a silver central electrode was introduced into the plug thereby greatly increasing the thermal conductivity of the insulator as a whole. A further point of major importance has however since been established by investigation of a series of sparking plugs picked at random from batches | ||