DIN 3996: A New Standard for Calculating the Load Capacity of Worm Gears


During the last years the load capacity of worm gears was raised about 30%. The reasons for this are the introduction of synthetic oils, optimization of the worm gear geometry and manufacturing improvements. The forthcoming new standard DIN 3996 “Calculation of load capacity of cylindrical worm gear pairs” takes into account these developments. This standard contains the following load capacity limits: wear, pitting, tooth breakage, temperature and worm deflection. Also, efficiency was taken into consideration. In most cases the calculation methods are based on results of recent investigations, which were performed on worm gear test rigs at the FZG. In the case of wear, pitting and tooth breakage test results and their influence on DIN 3996 are shown. The calculation method for wear resistance is based on the fact that the wear intensity of a material/lubricant combination is a function of the lubricant film thickness and the lubricant structure. The main influence parameter on pitting resistance is the Hertzian stress. For tooth root strength the calculation method is based on a nominal shear stress theory, in case of worm deflection on the deflection curve of a cylindrical shaft. The application of this new standard for gears in practice is discussed by recalculating some examples.
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