Damping characteristics of unreinforced, glass and carbon fiber reinforced nylon 6/6 spur gears

Polymer based gears replace metal gears in many light duty power and/or motion transmission applications due to their noiseless operation even under unlubricated conditions. Visco elastic behaviour of the polymer, which is mainly responsible for the sound absorption, is altered by the addition of short fibers. Addition of high modulus fibers to the base polymer matrix reduces the damping characteristics of the composite. Material damping affects the hysteresis heating as well as the ability to absorb vibration during service. Dynamic mechanical analysis carried out on unreinforced Nylon 6/6, 20% short glass and 20% carbon fiber reinforced Nylon 6/6 gear materials indicates the reduction of damping factor due to the incorporation of fibers. Injection molded spur gears made of unreinforced and reinforced materials were tested for durability in a power absorption type gear test rig. Surface temperature of the test gears and noise generated near the gear mesh region were continuously measured and monitored using a personal computer based data acquisition system. Test results indicate that the reinforced gears generate more gear mesh noise than unreinforced gears.