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Tham khảo tài liệu 'mechanical design an integrated approach part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 460 PART ỉi Applications Cast irons have low cost ease of casting good machinability high wear resistance and good noise abatement which make them one of the most commonly used gear materials. Cast-iron gears typically have greater surface-fatigue strength than bending fatigue strength. Nodular cast iron gears containing a material such as magnesium or cerium have higher bending strength and good surface durability. The combination of a steel pinion and cast iron gear represents a well-balanced design. Steels usually require heat treatment to produce a high surface endurance capacity. Heat-treated steel gears must be designed to resist distortion hence alloy steels and oil quenching are often preferred. Through-hardened gears usually have 0.35 to 0.6 carbon. Case-hardened gears are generally processed by flame hardening induction hardening carburizing or nitriding. When gear accuracy is required the gear must be ground. Nonferrous metals such as the copper alloys known as bronzes are most often used for gears. They are useful in situations where corrosion resistance is important. Owing to their ability to reduce friction and wear bronzes are generally employed for making worm wheel in a worm gearset. Aluminum zinc and titanium are also used to obtain alloys that are serviceable for gear materials. Plastics such as acetal polpropylene nylon and other nonmetallic materials have often been used to make gears. Teflon is sometimes added to these materials to lower the coefficient of friction. Plastic gears are generally quiet durable reasonably priced and can operate under light loads without lubrication. However they are limited in torque capacity by their low strength. Furthermore plastics have low heat conductivity resulting in heat distortion and weakening of the gear teeth. Reinforced thermoplastics formulated with fillers such as glass fiber are desirable gear materials owing to their versatility. For best wear resistance nonmetallic gears are often mated with .
