Increase of wear resistance of gears by hardening applying pulsed electron beam

The hardening of gears to increase their wear resistance was investigated within the framework of a diploma thesis in close cooperation with the Institute of Production Technology of the University of Karlsruhe and the company "PuIsgetriebe W. & J. Puls GmbH & Co", Karlsruhe. In close cooperation with Pulsgetriebe a test facility was designed, allowing the simultaneous testing of gears modified by different methods under equivalent conditions. The surface of gears, made of 16MnCr5, were hardened by surface re-melting applying pulsed electron beams produced with the facilities GESA I and GESA II. The GESA I allows the variation of the electron energy between 50 and 150 keV with a maximum energy density of 2 MW/cm(2). The beam diameter can be chosen between 4 and 8cm and the pulse duration between 5 and 50 mu s. Steels can be re-melted to a depth of 30 pm with this facility. The electron energy of the GESA 11 facility can be varied between 200 and 400 keV. This results in an increase of the maximum energy density of up to 6 MW/cm(2). The beam diameter is 4 cm and the pulse length is similar to the one that can be achieved with the GESA I. Applying the GESA II facility melting depths in steel of up to 150 pm can be realized. Employing the GESA I facility the hardness of none case hardened steel could be increased to about 750 Vickers (HV) to a depth of about 30 pm. Case hardened steel could be hardened to about 1100 HV to the same depth with GESA 1. The higher electron energy of GESA 2 results in a hardened surface layer of about 140 pm with a maximum hardness of 1600 HV. The reduction in grain size due to rapid cooling has an additional positive effect on the wear resistance of the gears. The roughness of gears after GESA treatment was about a factor 2 to 4 above the tolerable values. The specified tolerances could be reached by manual rolling the treated gear against another gear. Case hardened gears with and without GESA - hardening were tested with a revolution of 1500 turns per minute for duration of 160h applying a load of about 8000 Nm that is double of the nominal load. The wear was evaluated by measuring the weight change and the variation in base tangent length before and after a test run. Case hardened gears with subsequent GESA-hardening exhibit a reduction in wear resistance by a factor of 6 to 8, only the roughness peaks formed during GESA-hardening are smoothed.