Research On The PTFE-based Wear-resistant Coating For Ultrasonic Motors

Ultrasonic motors(USMs) are widely used in many front fields, like precision positioning, aerospace and defense military etc. for its excellent performance. The driving force of USMs is obtained by means of the frictional contact force between the stator and rotor. Thus the performance of the friction materials has a vital influence for mechanical properties and service life of USMs. And PTFE becomes the preferred friction material of USMs for its low friction coefficient, good chemical stability, temperature stability.This thesis selected Polytetrafluoroethylene(PTFE) composites single or mixed filled with poly-p-oxybenzoyl(POB), carbon fiber, nano-Al2O3 and Alumina fiber as the research object. It aimed at preparing friction material coating which was conformed to the requirements of the use of ultrasonic motor. Preparation technology, component design and the effect of the different and content filler on the mechanical, anti-sticking properties, tribological behaviors of the composite coatings were studied. By using scanning electron microscopy(SEM) to analyses the original surface morphology and worn surface morphology of coatings, the wear mechanisms of composite coatings were discussed. The main conclusions are shown as follows:1. The PTFE friction materials for ultrasonic motor filled with different content of POB were prepared. The results showed that the proper content of POB can not only improve the mechanical and anti-sticking properties of the PTFE composite coatings, but also significantly enhance wear resistance of the PTFE composite coatings. The 10 wt.% POB/PTFE coating had the lowest wear rate with 3.42×10-4 mm3/N·m and slightest worn surface. The main wear mechanism was fatigue wear. The best PTFE composite as friction material of ultrasonic motor was obtained when the content of POB was 10 wt.%.2. The POB/PTFE friction materials for ultrasonic motor filled with different content of carbon fiber were prepared. The results showed that mechanical, anti-sticking properties and wear resistance of the POB/PTFE composites modified by carbon fiber were better than unmodified POB/PTFE. The 10 wt.% POB/PTFE composite coating had the lowest wear rate at 3.35×10-4mm3/N·m, the best mechanical properties and wear resistance and its wear mechanism was adhesive. Ultrasonic motor had the better comprehensive performance.3. The POB/PTFE friction materials for ultrasonic motor respectively reinforced by nano-Al2O3 and alumina fiber were prepared. The results showed that the proper content of nano-Al2O3 or alumina fiber could effectively improve the mechanical, anti-sticking properties and wear resistance of the POB/PTFE composite coatings. The POB/PTFE composite coatings which respectively reinforced by 1wt.% nano-Al2O3 or 0.5wt.% alumina fiber had lowest wear rate. The value of the former was 2.88×10-3mm3/N·m. In addition, nano-Al2O3 reinforced POB/PTFE composites which had more excellent comprehensive performance compared with alumina fiber. Using this friction material, ultrasonic motor had the bigger no-load speed and stall torque.