Material and manufacturing optimisation for worm wheels

Tests on worm gears with a case-hardened steel worm and a worm wheel made of bronze as well as testing of materials show the influences of alloying elements and structural constitution on the wear characteristics of worm wheel bronze and lead to a wear-optimised bronze. Long term tests examine the pitting resistance of this bronze. The optimised bronze GZ-CuSn12Ni with a nickel content of 4 % and a middle grain size of 100 mu m achieves a wear life factor of more than 7 and at the same time an improved pitting load capacity in comparison to frequently used worm wheel bronze. Wrong adjusted casting parameters on a bronze of identical chemical composition however may cause a much lower load capacity. The program "TBV" enables the design of worm wheel hobs and the calculation of milling machine adjustments to get an optimal initial contact pattern. Measured deviations of the tooth flank topography can be analysed to find incorrect milling process parameters or to determine correction values of the milling machine adjustments for a best possible initial contact pattern.