Hardening Gradient Accuracy of Contact Surfaces of Gears

Abstract

Case-hardening of contact surfaces of teeth can increase durability and reliability of gears. In gears, chemical-thermal hardening by nitriding, carburizing and nitrocarburizing has become widespread. When performing design and verification calculations of gears, it is necessary to know the hardness gradient of the tooth hardened case, the accuracy of which determines the correctness of transmission calculations. The purpose of the article is to evaluate the accuracy of the existing functions of hardness gradient over the depth of the hardened case of gear contact surfaces based on known experimental data; the subject of research is the hardness gradient of carburized and nitrocarburized surfaces of gears. The analysis of the existing hardness gradient of carburized and nitrocarburized surfaces of gears used in verification calculations of gears for resistance to bending fatigue and tooth interior fatigue fracture is carried out. The article presents the hardness gradient proposed by Tesker E.I., Korotkin V.I., Mack Aldener M., Dang Van K., Thomas J. To estimate the accuracy of the considered hardness gradient, the approximation error was calculated. The approximating functions were the hardness gradient, and the actual values were the results of well-known experiments to determine the hardness by the depth of the hardened case of carburized and nitrocarburized rollers. The calculation was implemented using the MathCad package, in which the figure of the hardness gradient presented in the article were also built for all the experimental results used. As a result of the calculation, the most accurate hardness gradient of carburized and nitrocarburized cases were determined. The hardness gradient proposed by MackAldener M. gives the least error during carbonization (up to 1.1 %). The hardness function proposed by V. I. Korotkin for nitrocarburizing gives the least error (up to 2.3 %). The least accurate values were shown by the hardness gradient developed by Dang Van K. (up to 5 %). The work performed is part of the study aimed at improving the methodology for assessing the reliability of case-hardened cylindrical gears based on the use of numerical modeling methods and non-parametric statistics tools.