The effect of the gear wear for the contact ratio

The contact ratio is such a parameter of a gear, that is very important because of the noise of the drive and the quality of the mesh. In general condition, the contact ratio can be considered constant during the whole lifetime. Although there are applications where the gears are working without any lubrication and the only criteria of the lifetime. Among these conditions the measure of the wear can be so extensive, that has a significant influence on the contact ratio in a quite long period of the lifetime. In these cases, the contact ratio decreases, which leads to the increase of the dynamic loads. The pressure line can be move, which results the modification of the tooth bending force's arm. It is easy to understand that this phenomenon depends on geometrical parameters, the initial conditions, relative movements and the loads. This means, not only the measure of the wear can be restricted by the strength, but the new geometry. In these conditions, the operational characteristics can be significantly different from the original, which was determined by calculation. Because of that, it is expedient to suppose more conditions as a basis in case of non-lubricated gear drives. It is recommended to calculate in every condition the safety factors. If we know the measure of the wear, we can determine when will be the gear pair inoperable with the use of known calculations. This paper shows an iterative process, in which the suspected measure of the wear is used as tolerance, the possible consequences were determined.