Cause of Failure Beyond Conjugate Theory of Gear Meshing

Abstract

It is obvious that the basics of gear technology is the theory of geometry for conjugate action of mating gears for transmission of motion through contacting tooth flanks. Teeth of actual gears though contact not only on tooth flank to tooth flank, but also at edges of tooth tip and of tooth sides. Such edge contact is usually out of the conjugate meshing theory of gearing. Many causes of failure of highly loaded gear teeth are initiated due to the contact at such tooth edges. Contact of tooth edge produces considerable amount of wear debris. Meshing teeth crush intruded wear debris and damage themselves. With run of gear operation, gear failure develops as a phenomenon of such a positive feedback system.

Appendix

* Wording: “Rag-wear”

For convenience of discussion, I defined here the concept of following gear tooth flank damage as “Rag-wear”:

Under very high surface temperature, the thickness of lub.oil film becomes very thin and granular falling-off of surface material occurs, adhesive wear occurs, pitting occurs, crush of wear debris occurs, plastic deformation of that tooth flank occurs simultaneously. Such complex situation of gear tooth flank wear develops itself with run of operating time as positive feedback system of failure development. During the damage development, tooth flank wear and plastic deformation often covers pitted area and eliminates pitting.

Fig. 44

One typical mode of tooth flank failure that depends on run of operational time

The expression “Rag wear” indicates such state of gear tooth flank wear with one word(Fig. 44).