(1). Low speed: speed 2m/s, unit pressure 350-600n /mm^2.
(2). Medium speed: rotation speed 2-6m/s, unit pressure 100-1000n /mm^2, small impact load.
(3) high speed: rotating speed 4-12m/s, large bending torque, unit pressure 200-700n /mm^2.
2. Gear materials and heat treatment commonly used in machine tools:
(1)45 quenching, high temperature tempering, hb200-250, for circular speed < 1m/s medium pressure, high frequency quenching, surface hardness hrc52-58, for gear with high surface hardness requirements and small deformation.
(2)20Cr carburizing, quenching, low temperature tempering hrc56-62, for high-speed, pressure, medium, and impact gear.
(3)40Cr quenching and tempering, hb220-250, for gear with small circumference speed and medium unit pressure, quenching and tempering, hrc40-50, for gear with medium circumference speed and small impact load.
(4) in addition to the above conditions, high frequency quenching and hardness hrc52-58 should be used if the deformation during heat treatment is required to be small.
3. The working condition of automobile and tractor gear is more onerous than machine gear, wear resistance, fatigue strength, core strength and impact toughness is higher than machine gear. As a result, the weight and impact load is generally used more low carbon alloy steel (in addition to the list of brands, there are 20 mnmob, 20 simnvb, 30 crmnti, 30 mntib, 20 mntib, etc.), by carburizing, quenching and low temperature tempering processing. Tractor final drive gears of transmission torque is bigger, tooth surface unit pressure is higher, sealing is not good, sandy soil, lime soil is easy to go, with poor working conditions, is often used20CrNi3A isocarburization.
4. The most commonly used materials of general mechanical gear are 45 and 40Cr, and the heat treatment method is selected as follows:
(1) overall quenching;The strength and hardness (hrc50-55) are improved, the bearing capacity is increased, but the toughness is reduced, and the deformation is large. After quenching, the teeth must be grinded or grinded.
(2) tempering: due to low hardness, toughness is not too high, can not be used for large impact load work, only for low speed, medium load gear, a pair of tempering gear pinion surface hardness is higher than the large tooth surface hardness hb25-40.
(3) normalizing: it is not suitable for large diameter gear for quenching and tempering due to conditions.
(4) surface quenching :45, 40Cr high-frequency quenching machine gear is widely used, the diameter is larger than the flame surface quenching. However, due to the high impact load of the gear is not tough enough, the use of low carbon steel (impact, small and medium load) or low carbon alloy steel (impact, heavy load) carburizing.