Performance and Failure Analysis of Injection Molded Carbon Reinforced Nylon Gears

Reinforced polymers offer superior strength and modulus required in many load-bearing applications. Reinforced thermoplastic polymer gears are used in motion as well as power transmission applications. The performance of reinforced polymer gears needs to be thoroughly understood for widening their application. This paper describes results of the ongoing research on polymer composite gear performance. Unreinforced and 20% short carbon fiber reinforced Nylon granules were used for the development of gears using injection-molding process. Gear tests were conducted in a power absorption type gear test rig. Gears were tested at a constant rotational speed of 1000 rpm and at various torque levels up to 3 Nm. Test results showed the superior fatigue strength of carbon reinforced Nylon gears compared with the unreinforced Nylon gears. Improved thermal resistance, high strength and modulus contributed to the superior fatigue performance of carbon reinforced Nylon gear. Failed and worn out surfaces were observed using optical and scanning electron microscope. Three major gear failure modes were observed; excessive wear, severe deformation and tooth fracture. Fiber orientation, presence of fiber particles between contact surfaces and poor surface finish affects the wear resistance of carbon-reinforced gear.