Geometrical Analysis of Tooth Form Factor and Stress Correction Factor In Calculating Tooth Root Bending Stress on Internal Gear

One of the most critical disadvantages of plastics must be much lower strength than steel, which prevents plastic gears from having high load capacity. Internal gears have larger tooth root thickness and smaller tooth flank sliding than external ones. In addition, they have a concave tooth profile. These facts indicate that even plastic gears could realize relatively high load capacity. Although tooth root bending stresses greatly depend on fillet profile, failure of internal gears is generally not crucial in steel gear pairs, which has provoked few discussions on fillet profile. The present paper describes fillet profiles of internal gears, which the top land of the pinion cutter generates. Geometrical analyses defined the change in the profiles associated with the number of teeth and profile shift coefficient of pinion cutter with the possible maximum radius of top land. According to ISO 6336-3, which is the basic standard on the load capacity of gear pair, calculations of tooth form factors and stress correction factors determined the positions of the critical section for evaluating tooth root bending stress.