Friction and wear behavior of PI and PTFE composites for ultrasonic motors

Abstract

High-performance polymer-based frictional materials have become increasingly important to improve the mechanical output properties of ultrasonic motors. This study discussed the friction and wear behavior of 2 dominating frictional materials of polymer composites for ultrasonic motors, polyimide (PI), and polytetrafluoroethylene (PTFE) filled by aramid fibers (AF) and molybdenum disulfide (MoS 2 ). To explore the wear mechanisms, the tribo-pair contact stress was theoretically characterized, and the interface temperature rise was numerically predicted. The predictions showed that the flash temperature on asperity tips could reach the glass transition temperature of the polymer materials. The experimental results indicated that the contact stress and sliding speed have a small effect on the friction of the PI composite but influence considerably the friction of the PTFE composite. A higher contact stress brings about a higher specific wear rate, but a higher sliding speed reduces the wear rate. Compared with AF/MoS 2 /PTFE, the AF/MoS 2 /PI has much better tribological performance under high loads and speeds. KEYWORDS friction and wear, polyimide, polytetrafluoroethylene, temperature, ultrasonic motors 1 | INTRODUCTION An ultrasonic motor (USM) is driven by the frictional force between its stator and rotor. Such motors have been extensively used in medical apparatus, precision positioning devices, and aerospace structures because of their fast response capacity, high torque at low speed, and self-locking without the application of external power. 1 However, there are also drawbacks which have hindered the development of USMs, including their low transfer efficiency, poor mechanical output stability, and short service life in harsh environments. To improve the performance of USMs, better frictional materials of ultralow wear rate and stable friction are required because their properties determine directly the output characteristics and service life of USMs in complex, harsh environments. Some frictional materials have been tested for USMs, 2-6 including rubber, resin, metal coatings, alloys, and ceramic composites. It was found that most of them cannot meet the requirements due to, eg, severe wear, short service life, and high noise. Polymer-based frictional materials, however, have been found to be applicable to travelling wave USMs for their excellent wear resistance, low noise, suitable hardness, and thermal stability. For instance, Rehhein and Wallaschek 7 studied the friction and wear behavior of PI composites and found that the inclusion of carbon fibers could improve the wear resistance of PI sliding against steel. Ishii et al 8 established a method to predict the service life of USMs with a carbon-fiber-reinforced polymer as the frictional material. Qu et al 3-5,9,10 investigated the tribological properties of polytetrafluoroethylene (PTFE), phenolic resin, and Ekonol composites in different environments and proposed a method for selecting frictional materials incorporating operation conditions. Ding et al ...

Tribological behavior prediction of friction materials for ultrasonic motors using Monte Carlo‐based artificial neural network

“…[1][2][3][4] Nevertheless, driving efficiency and service lifetime of USMs are limited by friction materials, the heart of the motors. [1][2][3][4] Nevertheless, driving efficiency and service lifetime of USMs are limited by friction materials, the heart of the motors.…”

“…Ultrasonic motors (USMs), new type microactuators, have received widespread attention in the field of aerospace, robotics, precision instruments, and various other applications due to high torque, exceptional start/stop feature, and fast response. [1][2][3][4] Nevertheless, driving efficiency and service lifetime of USMs are limited by friction materials, the heart of the motors. To enhance the properties of USMs, high-performance polymer-based friction materials still need to be optimized immediately.…”

A life test of ultrasonic motors under different torque loads and the analysis of the characteristics of wearing surfaces

“…Song et al 8 presented a USM with PTFE-based friction material, and investigated the friction coefficient, worn surfaces, and wear rate under different temperatures and vacuum levels. A similar comparative study on USM characteristics under atmosphere and vacuum conditions was completed by Qu et al 9 Zhao et al 10 investigated the wear properties of frictional materials of PTFE and PI with proper hardness and intensity and excellent wear resistance. Ishii provided a life prediction method based on the measured specific wear rate of fiction material.…”

“…9 Zhao et al. 10 investigated the wear properties of frictional materials of PTFE and PI with proper hardness and intensity and excellent wear resistance. Ishii et al.…”

Comparative study of tribological properties of insulated and conductive polyimide composites

“…Figure 4 shows the hardness (SD) of polyimide composites. Compared with PI-1, the hardness of PI-2 decreased slightly due to the addition of PTFE as it has a relatively lower modulus and hardness than PI [21]. That will affect the thermal and tribological properties of the composites.…”