Since thermoplastics are temperature-sensitive materials, heat generation in running spur gears is an important parameter. This paper presents two models for its evaluation, an exact one which considers all the parameters but needs a computer to solve the equations; then a simplified model. Both models take into account the contact outside the theoretical line of action which is the usual case with thermoplastic gears. Results for the simplified model are within reasonable agreement with the exact one.
An analytical method is presented for calculating real contact ratios for plastic/plastic or plastic/steel spur gear pairs. A comparison is made with published experimental data and the method is used to explain the importance of load sharing in thermoplastic gearing.
Tests have been made for use of a high‐density polyethylene of ultra‐high molecular weight as a gear material. The gears had a diametral pitch of 10 and 30 teeth. They were tested in mesh with a steel gear of the same size in two operating conditions: (1) in still air without lubrication, and (2) in oil with generous lubrication.The effects of speed, temperature, and initial lubrication on the load capacity of the gears were tested and an equation was developed to express the limits of these gears operating without lubrication. In the lubricated conditions, the influence of oil flow and its temperature on the gear teeth temperature were evaluated. The wear of the plastic gear was measured in both operating conditions and wear rate was calculated as a function of the load and gear life. Curves are presented suggesting design limits of the gears in the two operating conditions. There are also recommendations on the center distance setting and the backlash to use.
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