Technical requirements for gear shafts
One: the main technical requirements of cold processing
1. Since the oil pump shaft transfers torque by the friction force of the two conical surfaces, in order to ensure sufficient contact area to transfer torque, the process requires that the area of the two conical surfaces should not be less than 800 after grinding
2. The cone at both ends of the shaft is provided with a semicircular keyway, which is easy to produce stress concentration at the keyway gap. In order to effectively reduce the sensitivity of stress concentration and stress concentration coefficient, and improve the strength of the cone part, the process requires that the root of the semicircular keyway has a rounded corner r of 0.4 s.A. Z 2.
3. Smooth transition is required at the junction of cone and cylinder.
Two: heat treatment technical requirements
1. The material
According to the service conditions of the front gear shaft, the forces on the CAM part and the cone part of the shaft are different, so there are different hardness requirements after heat treatment. CAM parts require high wear resistance, so the part requires a high hardness, and in the cone part is to bear the role of cyclic torque and bending moment, so the part requires a good combination of strength and toughness, so the requirements of hardness. In order to meet the requirements of a variety of different parts of the same parts hardness, in mechanical design, often choose low carbon steel by surface treatment to meet the requirements, the camshaft is so material to 20 cr steel, the chemical composition of concrete meet the camshaft GB3077-880 with 20 cr steel can well satisfy the manufacturability, heat treatment, heat treatment after cold working technology to achieve the performance requirements. This is because 20Cr steel is on the basis of 20 steel, in order to improve its performance, add 0. 7-1. 00} Cr. 20Cr steel has good process performance, good machinability after forging normalizing, hardness of (156-207) HB after fire. Good cutting performance, high surface finish. Because of the addition of chromium, the hardenability of steel is improved, and chromium is the element of strengthening ferrite, dissolved in ferrite can also play a strengthening role, so the core strength of camshaft after carburizing is improved. Due to the improvement of hardenability, a more moderate coolant cooling (cooling medium for nitrate) can be used during quenching, so as to reduce the quenching deformation of gear shaft. The affinity between chromium and carbon is large, and the carbon content on the surface of carburizing layer tends to be saturated, and the gradient of carbon concentration is increased, so that the carburizing speed is increased, so that the gear shaft has higher hardness and better wear resistance after carburizing and quenching. It is because of the large affinity of carbon and chromium, this kind of steel in the carburizing layer is easy to form a network of carbides on the surface of the gear shaft, so the carbon potential in the atmosphere of the carburizing furnace should be strictly controlled. Although 20Cr steel is essentially fine grain steel, but in the carburizing temperature for a long time heating a carburizing, the grain will grow significantly, so the gear shaft can not be directly quenched after carburizing. In order to overcome the defects of carburizing, refine grain, further improve the strength and toughness of the core, and prepare for the subsequent heat treatment, so normalize after carburizing. It is then reheated and hardened.
2. Heat treatment process requirements
The whole heat treatment process of the gear shaft is: the gear shaft is carburized first, then normalized, then quenched and tempered, and then high-frequency annealing of the cone of the shaft. The purpose of carburizing is to increase the carbon content of the shaft surface, so that the gear shaft in the subsequent quenching treatment to obtain high surface hardness and wear resistance, to meet the technical requirements of the gear surface. The original low carbon content of 20Cr steel is still maintained in the center of the shaft, so that the center of the gear shaft still has high toughness after quenching. After carburizing, a normalizing process is to eliminate the network carbide formed after carburizing and other microstructure defects, refine grain, further improve the strength and toughness of the core, and make tissue reserve for quenching. The purpose of axial quenching is to improve the hardness, strength and wear resistance of the surface and obtain the appropriate structure. Axis after quenching, although has the very high hardness, but also brings a lot of quenching stress, gear shaft surface quenching after the formation of the high carbon acicular martensite also has the very high brittleness, therefore cannot be used directly, so you must eliminate the quenching stress by tempering, appropriate to reduce the intensity, reduce the brittleness, improve the toughness, and can also improve the dimensional stability, In this way, the surface of the gear can get high hardness and high wear resistance to meet the technical requirements of the gear part after carburizing and quenching. The cone part in high frequency annealing can be carburized after hardening of high hardness down, to meet the requirements of hardness.
