Improvement of Machining Process of ZSY450 Hard Tooth Surface Reducer High Speed ​​Gear Shaft

The ZSY450 hard-tooth surface reducer used with the belt conveyor of the horse spine coal washing plant has a high-speed gear shaft fracture during use. The material used for the shaft is 20CrMnMo. The heat treatment technical requirements are: carburizing and quenching of the tooth. The carbon layer depth is 0.8~1.3mm, the tooth surface hardness is HRC58~62, the core hardness is HRC30-40, and its structure is 20CrMnMo advanced carburized steel. It has high flexural strength and wear resistance after carburizing and quenching. It has good low temperature impact toughness and is suitable for the manufacture of carburized parts with high surface hardness and good wear resistance. Therefore, the material selection is reasonable.
1.2 Strength check The gear shaft is mainly affected by two aspects during the operation. One is the force moment M transmitted through the coupling; the other is the meshing force acting on the gear, and the meshing force can be decomposed into radial Force Pr and circumferential force P, see (a) The circular force P is simplified to the axis to obtain the lateral force P and the force moment PD/2 acting on the axis. See (b) From the equilibrium condition 2Mx=0, it is known that PD/2= M0 force moments M and PD/2 cause torsional deformation of the gear shaft; and lateral force P and radial force Pr cause bending deformation of the shaft in the horizontal plane. According to the calculation diagram of the axis, the vertical plane of the torque Mn diagram of the shaft is respectively made. The bending moment Mz diagram inside and the bending moment My diagram in the horizontal plane, see (c) In the AE section, the torques on each section are equal, but both My and å°¬ on the section e are maxima, so the section E (ie both sides of the gear) are dangerous sections on the dangerous section Li Runlian (1968-), female, Shanxi Datong, engaged in mechanical teaching and research work, 037003 Datong City, Shanxi Province, the internal moment is: vertical plane The bending moment Mzmax=Prab/L. The bending moment Mymax=Pab/L in the horizontal plane and the coupling end only bears the twist The strength check is as follows: f 1.3 original process analysis 4 carburizing; 5 quenching, low temperature tempering; 6 grinding teeth; 7 assembly analysis of the original processing process, the main reason for the fracture is that the manufacturer did not take the non-carburizing part Effective anti-seepage carbon protection, resulting in excessive carbon content, reduced toughness, such parts generally use integral carburizing, carbon in 20CrMnMo material is easy to saturate when carburizing in this carbon-free atmosphere carburizing atmosphere Therefore, the carbon content of the surface layer of the part is often quite high, generally 1.2%~1.4, and a large amount of large carbides are formed in the grain boundary, and even become a closed network. The presence of coarse carbides in the surface layer reduces the toughness of the parts after quenching, and the brittleness is increased. In order to remove the layer containing coarse carbides after carburizing, it is generally necessary to increase the machining allowance or implement anti-seepage protection.
Based on the above analysis, the reason why the high-speed gear shaft is broken is that the original process is defective, so the process is mainly improved (the gear part is machined to the size, and the remaining part has a margin of 5 mm including the total length); 4 coarse hobbing ( Single tooth single-sided residual allowance 1mm); 5 carburizing; 6 high temperature tempering; 7 machining (tooth surface correction, take the total length and re-drill the top hole, remove the carburized layer, the outer diameter is 4mm, the length direction is not 8) hobbing (single-tooth unilateral residual allowance 0.15~0l18mm, good tooth depth rolling); 9 quenching; low temperature tempering; 1 turning and milling keyway (correcting the top hole with tooth surface correction, each Roughness Ra1.6, leaving a margin. 5mm, other parts processed to size); 2 grinding outer circle, grinding teeth; 3 assembly 2 improved process analysis, high temperature tempering after carburizing, is to make carburized oil The cold-derived acicular martensite and retained austenite can be converted into uniform fine-grained or point-like sorbite, which is easy to machine and prepare for the next quenching.
The time is about 5h. If the residence time is insufficient, only the outermost part of the carburized layer can be decomposed into troostite, but the middle part of the carburized layer is too late to decompose, and after cooling, it will be transformed into martensite, which is liable to cause cracking and heating temperature of quenching. For 850 ° C, the cooling time in oil is 4~15min (the purpose is to avoid the carburization of the carburized crystals), the workpiece is cooled to 100~130 °C oil cooling air quenching is mainly to prevent quenching crack The low temperature tempering temperature is 200 ° C, and the air is cooled for about 5 h.
3 After the new technology is adopted, the gear surface has high hardness, good wear resistance, high contact fatigue strength, and the core has certain toughness and sufficient strength and hardness. The non-toothed part can maintain the original material. Some characteristics. Practice has proved that the improved new process effect is good

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