Particle Size Effect on Abrasive Wear Behavior of All-Metal Positive Displacement Motor and Abrasive Particles Control

Abstract

Downhole drilling operations expose all-metal positive displacement motors (AMPDM) to abrasives of different sizes, causing serious abrasive wear behavior. Controlling the entry of large particles into the motor by installing a filter can effectively reduce wear conditions and improve its lifespan. This study investigated the particle size effect on abrasive wear to seek an appropriate filter size for AMPDM. The multi-function tribo-tester was modified according to the actual working conditions of the stator and rotor. The tribological properties of stator material (nitrided 38CrMoAl steel) against rotor material (YL10.2 cemented carbide) were conducted using SiO2 particles with 1–500 μm sizes in the range on a pin-on-disc tribo-tester under wet sliding-vibration conditions. The results showed more complicated friction coefficient evolution characteristics for small particles, existing two stable stages. Two critical-size values of average wear-rate and wear mechanism transformation are determined. The wear products of the tribochemical reaction were determined. The filter porosity of about 200 μm may be an optimal selection to decrease wear. This work has developed new insights into how AMPDM responds to changing abrasive sizes and provides a proposal for controlling the entry size of abrasive particles.