With the rapid development of the coal industry, coal mining equipment is also developing in the direction of low-speed heavy-loading, and the requirements for its transmission components, such as gear shafts, are also increasing. The gear shaft, which is the main component of the transmission mechanism, transmits torque and changes speed by combining with the gear. In order to ensure that the heavy-duty gear shaft is often operated under a high load without early failure, the tooth surface must be hardened to provide good wear resistance, high contact fatigue strength and high bending strength. And the heart is strong enough and tough. At present, the developed industrialized countries in the world manufacture large-modulus heavy-duty gear shafts with alloy steel to temper and toughen the tooth surface. luoyang hongxin heavy machinery co.,ltd. produce a gear shaft with a modulus of 33.8 in the 2800XP electric shovel transmission mechanism. The chemical composition of 40CiNi2M is shown in Table 1, and the dimensions of the parts are as follows. Technical requirements Base hardness HB286~321, tooth surface hardness HRC>50, hardened layer depth; 48mm and evenly distributed along the tooth profile. The electric shovel large modulus gear shaft has been supplied by the PH company.
Table 1 PH112 steel chemical composition mandate received date: 1999 a table 2 tooth surface hardness range soft tooth surface medium hard tooth surface hard tooth surface HB20HB320 1 heavy duty gear shaft tooth surface hardening gear shaft according to its working conditions are divided into soft tooth surface Medium hard surface and hard tooth surface, the hardness range of the tooth surface is shown in Table 2. Due to the poor working conditions, the soft tooth surface and the medium hard tooth surface are far from the heavy-duty gear shaft. high performance. Therefore, large modulus heavy-duty gear shafts often use surface hardening and carburizing and quenching heat treatment methods to strengthen the tooth surface. Compared with induction heating surface quenching, carburizing and quenching can achieve high contact fatigue strength, high bending strength and good wear resistance of the tooth surface, but the heat treatment cycle is long and the quenching deformation is large, so the industrialized countries in the world The production of large modulus heavy duty gear shafts has gradually begun to use induction hardening. The quenching method and characteristics of the large modulus heavy-duty gear shaft are shown in Table 3. The medium-frequency quenching along the tooth surface only hardens the tooth surface, and the hardened layer is broken at the root of the tooth. Although the contact fatigue strength of the tooth surface is high, the root of the tooth The bending strength is very low, and it is easy to break the teeth at the root portion. The entire tooth profile is uniformly hardened along the intermediate frequency quenching of the tooth groove, and the tooth surface has both good contact fatigue strength and high bending strength. See the distribution along the tooth surface and the intermediate frequency quench hardened layer along the tooth groove. Therefore, medium frequency quenching along the groove is a good way to harden the tooth surface. Under the normal service conditions of ensuring the large modulus heavy-duty gear shaft, it is economical and reasonable to use the intermediate frequency quenching hardened tooth surface along the tooth groove.
Table 3: Large modulus heavy-duty gear shaft quenching method and characteristics Quenching method Contact fatigue strength Bending strength Quenching deformation period Quenching cost Deep carburizing high long high carbon nitrogen nitriding high Small longer high along the tooth surface intermediate frequency quenching high and low small short along Tooth groove intermediate frequency quenching high and small 2 process test 2.1 quenching equipment quenching equipment meter with a heavy group company from Germany Pedding-haus company introduced a 263/3000 type CNC gear quenching machine, the power is 120kW, the frequency is 8~1CkHz SCR inverter. The machine tool solves the problem that the uniform quenching machine causes the quenching temperature to be too low at the both ends of the tooth groove, or the quenching of the ordinary quenching machine due to the excessive heating temperature. It is designed to have a short stop section at the quenching start position and a fast section at the end of the quenching.
23 Process test piece Preparation Test piece steel is smelted by alkaline electric furnace, atmospheric casting, chemical composition is shown in Table 4. The mechanical properties of the test piece after forging and quenching and tempering are shown in Table 5. According to the modulus of 33.8 gear shaft meshing characteristics, the ratio is 1: 1 test piece.
2.2 Sensor design The level of sensor design and production level is critical to the impact of the tooth-to-tooth quenching quality along the groove. According to the introduced tooth shape calculation method, referring to the introduced structure and the design of the sensor introduced by the German Peddinghaus company and the chemical composition method of the test piece of Table 4, according to the effect of the gear shaft groove and the tooth surface heating and cooling, the induction is determined. The special inductor of the modulus of 33.8 is designed. The sprinkler is in the form of multiple rows of water jet holes, and has a quenching process of 2.4 quenching process and a result of ~20%, temperature 25~30C of PAG (polyethylene glycol) water-based quenching liquid produced by Houghton Company of the United States. The special inductor of the self-made modulus of 33.8 is used to perform the intermediate frequency quenching test on the gear shaft of the modulus of 33.8 on the 263/3000 type digital gear quenching machine to determine the optimum process parameters. After anatomical examination, the hardness of quenching and the depth of hardened layer reached the technical requirements of PSH, and the hardness fluctuation curve of hardened layer was found. 5 Results Analysis 2.5.1 Sensor and tooth profile gap In the induction heating, the heat transfer conditions of the gear teeth are different, the tooth top heat dissipation is slow, the tooth root heat dissipation is fast, that is, the tooth top heating effect is better than the tooth root and the cooling effect It is not as good as the root of the tooth, and the two toothed sides of the proximal root portion cause the magnetic flux of the root to disperse, while the top of the tooth causes the magnetic flux to concentrate. Therefore, the inductor should be used to increase the power distribution from the crest to the root. For this reason, the nose structure, the magnetism structure, the gap between the inductor and the gear tooth profile should be properly selected to ensure uniform heating of the tooth bottom, tooth surface and tooth tip, so that the hardness and hardened layer depth after quenching are uniformly stable. .
2.5.2 Quenching process parameters Induction heating quenching is characterized by a fast heating rate and almost no holding time (hardening immediately after heating to temperature). This makes the critical point of steel, especially Ac3, increase to a certain extent, making austenite difficult to achieve homogenization, and there is little chance of grain growth. For 40CrNi2Mo, the medium-carbon alloy structural steel contains more alloying elements. In order to make the alloying elements more soluble in austenite to ensure hardenability, the quenching temperature must be increased, but at the same time, care should be taken not to make the quenching temperature too high. . Therefore, adjusting the moving speed of the inductor to make the surface layer fully austenitized without coarsening the crystal grain is the key to ensure the quenching hardness. It is proved by experiments that the moving speed of the inductor is controlled to the right and the best quenching can be achieved. Ub fire effect. In addition, adding a preheating before quenching can not only increase the depth of heat penetration, but also effectively increase the depth of the hardened layer, reduce the temperature gradient of the cross section of the workpiece, and reduce the quenching stress. At the same time, due to the use of multiple rows of water sprayers, the tooth surface slow cooling time is prolonged, which promotes the transformation of retained austenite to martensite, thereby obtaining high quenching hardness.
Harden layer hardness fluctuation curve 25.3 Original organization According to the data, the carbide is a fine particle uniformly distributed in the microstructure of the ferrite, and can be transformed into austenite at a lower temperature and quickly at the induction temperature. Homogenize. However, the coarser spheroidized structure has an adverse effect on the induction heating surface quenching. In induction heating, in order to dissolve enough carbide into the austenite, a higher quenching temperature must be used, which will result in coarsening of the surface layer grains and formation of coarse martensite after quenching, and more The retained austenite causes the surface layer to be low in hardness and brittle. Therefore, in the preliminary heat treatment before the surface quenching, the base structure should be obtained to obtain a uniform and fine dolomite structure for surface quenching to prepare for sufficient organization.