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).
Results of tests conducted on vee belts from various manufacturers.
| Identifier | ExFiles\Box 135\1\ scan0240 | |
| Date | 8th November 1938 | |
| 8th November, 1938. REPORT OF TESTS ON VEE BELTS OF VARIOUS MANUFACTURES. A 36 H.P. D.C. motor drives an intermediate shaft through a flat belt and a step up of 3.404 to 1. Mounted on this intermediate shaft is the driving vee belt pulley. The driven vee pulley of the same diameter as the driver carries a five bladed Rolls Royce fan assembly and is mounted on a pedestal, adjustable to allow the vee belt centres to be altered to suit the conditions of the moment. On the suction side of the fan is mounted a Rolls Royce radiator through which passes the fan air. The whole of the vee belt section of the test is cased in and sand-bagged. The main conditions of the test are as follows. The vee belt slip must not be allowed to rise above 4%. If this happens the vee centres are to be increased by a small amount. The amount of increase is to be decided by the feel and tightness of the belt, and subsequently checked by stroboscope readings. The fan speed must not be allowed to fall below 4,000 R.P.M.. This condition was adhered to, but in some cases the fan speed came very near to the minimum figure. This was due to a high slip figure on either of the belts, or the low-cold speed of the D.C.driving motor. The speeds of the driving and driven vee pulleys are measured with a stroboscope, and from these figures the slip is obtained. Shortly before the end of the Gates Vulco test the original Ashdown stroboscope (spring driven) was replaced by a neon tube type. Another factor found difficult to solve was the flat belt slip. Due to the high speed of the belt and the reduced arc of contact on the intermediate pulley the slip became very high and a periodic speed variation was introduced due to flat belt pulsations. Eventually this was overcome by the fitting of a jockey pulley which allows the flat belt to run at a much lower tension and increases the arc of contact on the intermediate flat pulley to 180°. Another source of trouble was also experienced prior to the fitting of the jockey pulley. It took the form of overheating ballraces in the intermediate shaft and eventually necessitated the renewal of these. This was put down to the excessive bearing pressure due to high belt tension, combined with the high speed of revolution (4,400 R.P.M. approx.). No trouble has been experienced since the jockey pulley was fitted and the bearings now run cool over long periods. Due to the relatively short lives of the fans and the subsequent replacement by a fan not completely identical, the power absorbed varies. In the first of the fan bursts the fracture was across the base of one of the legs of the steel spider. From the appearance of the fracture a fault in the metal was suspected. All the subsequent fractures have been on the riveted blades, and in all cases the fracture has passed through the last rivet at the tip of the spider leg. - continued - | ||