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).
Test report on an Acme thread oil seal for a Bentley 50 rear axle.
| Identifier | ExFiles\Box 111\4\ scan0110 | |
| Date | 1st June 1939 | |
| 802 To Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} from HPS{Horace Percy Smith - Experimental Factory Mgr}/B1. c. Da.{Bernard Day - Chassis Design} c. Hdy.{William Hardy} c. By.{R.W. Bailey - Chief Engineer} HPS{Horace Percy Smith - Experimental Factory Mgr}/B1.1/BA.1.6.39. BENTLEY 50 REAR AXLE OIL SEAL. Acme Thread Test. It was proposed that in addition to the existing "Perfect" Oil Seal on the B.50 rear axle shaft ( see GCD.839) an Acme type of thread be formed in the bore of the housing to retain any oil leaking past the seal. In order to investigate the efficiency of the Acme thread as a seal, a special housing, BL.1029 was made, which would accommodate bushes,BL.980, of various bores and having an Acme thread in the bore, provision for supplying oil, either under pressure, or gravity feed, to the thread being also included. For the particular test carried out, a diametral clearance of .004" between the shaft and the bore of the bush was used. Using the standard gear oil Castrol XL.30, under a pressure of 30 lbs/sq in", the shaft was run in the appropriate direction at various speeds up to 3500 r.p.m., the temperature of the oil at the shaft being kept constant at 50° C. The amount of leakage past the thread was measured at each speed; it was observed that with the shaft revolving the leakage increased up to a critical speed between 200-300 r.p.m. beyond which the leakage decreased with increased speed. The test was repeated with oil pressures of 40 lbs/sq in", 20 lbs/sq in", 10 lbs/sq in", 2 lbs/sq in", and lastly with a head of 1ft of oil. In each case the same general characteristic was obtained, with a head of 1' of oil, however, there was a slight leakage of about .05 pints per hour with the shaft stationary but this stopped completely as soon as the shaft commenced to rotate. The behaviour of the "Acme" thread under these conditions is illustrated in BL.2336, Sheets 1 & 2. The higher pressures are not probable under normal running conditions but were tested to obtain corroborative evidence of the critical speed at which maximum leakage occurred and to provide information for future reference. In order to see exactly what pumping effect the thread had, the shaft was rotated in the opposite direction, the oil being under a pressure of 30 lbs/sq in" and at a temperature of 50° C. Under these conditions the leakage of oil increased rapidly with increased speed up to about 3000 r.p.m. then the curve continued. | ||