AGMA 21FTM02 PDF

The load capacity of worm gears strongly depends on the size of the contact pattern. Worm wheels are often manufactured by using an oversized hob, which results in a relatively small initial contact pattern. Wear on the worm wheel with a softer material during the running-in process increases the contact pattern and thereby the load capacity. For the investigation of the continuous change of friction in the tooth contact during that process, a tribological simulation program is used. With a simplified model of the EHL-tooth contact, boundary as well as fluid friction are calculated locally, and the tooth efficiency is evaluated. The included wear model associates abrasive wear with solid friction energy occurring in the tooth contact and allows a time-dependent simulation by considering the wear-modified tooth flank in the tribological calculation.

The simulative results are compared with experimental wear studies on the running-in of worm gears. Since various values are determined in the simulation model, the comparison covers different aspects to verify the model. However, for measurement reasons a comparison is taking place on the macro scale. The tooth friction is reflected by the measured efficiency of the gearbox on the test bench. Wear is on one hand a directly measured value, on the other hand it changes the geometry of the tooth flank and influences thereby the unloaded kinematics of the gears. Both aspects are considered for a verification of the wear calculation.