Research On PTFE-Based Friction Materials Of Ultrasonic Motors

An ultrasonic motor (USM) is a new of type of motors, which is different from traditionalelectromagnetic motor. By using the anti-piezoelectric effect, USM can make stator vibrate andtransform stator’s vibrating energy into rotor’s output torque. Compared with traditionalelectromagnetic motors, ultrasonic motors have a series of merits such as its simple structure, fastresponse, high precision, free of magnetic interference and so on.Friction materials are one of key elements of ultrasonic motor. The efficiency of energy transformand serving life of ultrasonic motors are obviously determined by properties of friction materials.Therefore, the effects of composition, process, organic and mineral materials filled effects on themechanical and tribological properties of PTFE-based friction materials, as well as the mechanicalproperties of ultrasonic motors were researched to develop high performance friction materials forultrasonic motors. The paper’s main research contents and results are as follows:1. PTFE-based friction materials of ultrasonic motors filled with potassium titanate whiskers (PTW)were developed. The effects of PTW content on the properties of PTFE-based friction materials havebeen investigated and the optimized content of potassium titanate whiskers is confirmed. The resultsshow that PTW could not only increase the hardness and elastic modulus of PTFE composites, butalso improve the friction coefficient and wear resistance of PTFE-based composites. On the whole,PTFE-based friction materials filled with5wt%PTW is the preferable friction materials of ultrasonicmotors.2. The effects of coupling agent (KH550) and rare earth (LaF3) on the properties of PTFE-basedfriction materials have been studied and the optimized contents of KH550and LaF3are confirmed.The results show that coupling agent and rare earth can improve the surface activity of potassiumtitanate whiskers, which strengthen the binding capacity between PTFE and PTW. When bearing theexternal loads, the matrix can transfer the loads effective to whiskers, so that whiskers support mainloads and improve the performances of friction materials. However, the contents of coupling agentand rare earth are too high or too low, the effect of which on friction materials is little. Therefore, theoptimized contents of KH550and LaF3are confirmed at3wt%and0.2wt%respectively.3. PTFE-based friction materials of ultrasonic motors filled with poly-p-oxybenzoyl (POB) weredeveloped. The effects of POB content on the properties of PTFE-based friction materials have beeninvestigated and the optimized content of POB is confirmed. The results show that POB could notonly increase the hardness and elastic modulus of PTFE composites, but also decrease the frictioncoefficient and wear mass loss of PTFE composites. On the whole, PTFE-based friction materialfilled with5wt%PTW is the preferable friction materials of ultrasonic motors.