RESEARCH ON THE WEAR FAILURE MECHANISM OF HIGH SPEED POSITIVE DISPLACEMENT MOTOR BEARINGS.

The bearing group is a key load-bearing structure of positive displacement motor (PDM), which experiences significant alternating heavy loads during the drilling process and causes failure accidents. In order to study the failure mechanism of the bearing group, the bearing group of the 165mm positive displacement motor was taken as the research object. Based on the structural characteristics of the drive shaft assembly and the point contact theory of the thrust ball bearing, the load of the thrust bearing was analyzed and calculated. A finite element model was established for the nonlinear contact problem between the steel ball, stator, and rotor, and numerical analysis was conducted for ball bearings with different degrees of wear. The research results indicate that: 1) it is easy to cause fatigue fracture of the inner and outer rings when the series bearing operates for a long time and under the special working conditions. In addition, the inner ring of the string bearing has problems such as unqualified surface roughness and local hardness, which exacerbates the damage of the string bearing. 2) As the wear increases, the contact area between the bearing stator, rotor, and ball gradually decreases, and the stress concentration at the contact area between the steel ball and the stator and rotor intensifies, resulting in a significant increase in contact stress. 3) The maximum Mises stress, contact force, and contact stress that bearings are subjected to are greatly affected by ball wear. Once the ball wears, the stress concentration phenomenon will lead to a rapid increase in the bearing capacity of the shaft, which will intensify with the increase of drilling pressure. 4) Under the same working conditions, the maximum stress of the ball after wear of 1.5mm increased by 7.3 times compared to that without wear, resulting in bearing failure. The research methods and results of this article provide theoretical guidance for reducing the failure accidents of positive displacement motor bearing groups. [ABSTRACT FROM AUTHOR]