Discussion on the deformation of carbon material in looped bevel gear
Improved furnace loading method After analyzing the spiral bevel gear structure and heat treatment process, it is believed that due to the non-uniformity of heat conduction and the different time of tissue transformation, the spiral bevel gear will produce plane warp and inner hole ellipse after carburizing and quenching. Deformation, which is mainly plane warping. In order to reduce and control the heat treatment deformation, press hardening is often used. However, there is no quenching press in our factory, and we consider reducing the deformation by improving the furnace loading method. That is, two spiral bevel gears are back-to-back to the spiral bevel gears numbered 1 to 4, and the screw holes of the parts themselves are used to fasten them with three bolts, and the process measures of mounting the furnace are performed, and the carburizing is performed twice. Quenching, so that the two parts inhibit each other during carburizing and quenching, the specific way is shown in Figure 1. Results The plane warpage of the four spiral bevel gears was above 0.60mm, as shown in 1.
Due to the fact that the plane warpage of the above four spiral bevel gears did not meet the technical requirements, we further improved the process measures and designed a special tooling [1], and the other 4 pieces were numbered 5-8. The spiral bevel gear is heat treated. That is, before the carburizing, the tooling is clamped, and the original three bolts are fastened to 12 bolts (GB5781-86, M16×60) and symmetrically fastened, as shown in Figure 2.
20Cr2Ni4A steel usually uses secondary quenching after carburizing, but it is heated and quenched again, which will cause more deformation. Therefore, it was decided to directly quenching after carburizing [2], that is, carburizing at (930±10) °C, after reaching the depth requirement of the layer, the furnace was cooled to 790 °C and cooled to room temperature. After quenching directly after carburizing, the hardness meets the technical requirements. The plane warpage of the four spiral bevel gears after heat treatment is ≤0.2mm, which satisfies the technical requirements of the spiral bevel gear.
Analysis of experimental results (1) Spiral bevel gears numbered 1 to 4 We tried to adopt an improved furnace loading method. A pair of gears are back-to-back, and the two gears are fastened by the three screw holes inherent in the parts themselves, and the two gears resist each other. Restricted to reduce deformation, but the bolt material creeps at 930 ° C high temperature, so that the bolt is loose, does not play a fastening role; at the same time, secondary quenching after carburizing will also cause greater deformation; the main reason is The thickness of C is thin [3], and the microstructure transformation speed is faster when quenching. The quenched martensite is formed first, and the structural stress at A is suppressed, thereby forming a plane warp. In addition, the large plane of the part hinders cooling and heating due to back-to-back, while the other side is normally heated and cooled. The difference in tissue stress and thermal stress between the two sides is also an important cause of deformation.
(2) In view of the fact that the bolt will be loosened at high temperature, the creep will be loose and the fastening will not be achieved. For the spiral bevel gears numbered 5-8, 12 screw holes are designed on the tooling, and 12 bolts are simultaneously Fasten. In the process of controlling deformation, the special tooling not only increases the wall thickness around the bolt, but also controls the phenomenon that the bolt is smoldering and creeping at high temperature, and the effect of fastening 12 bolts at the same time is obvious, even if the bolt creeps slightly at high temperature, You can also rely on the weight of the tooling to reduce the deformation. In addition, the special tooling can also reduce the cooling rate of the C-plane, and the A-side is first transformed into martensite, and then the C-plane is transformed to ensure the accuracy of the A-plane.
(3) From the structure of the spiral bevel gear, it can be found that the main cause of the deformation of the spiral bevel gear is the result of the combined action of the thermal stress and the different structural stresses of the A and C surface transitions [4]. Therefore, by adjusting the heat treatment process specification, the secondary quenching after carburizing is changed to direct quenching and the quenching heating temperature is appropriately reduced, and the deformation of the spiral bevel gear can also be effectively controlled.
At the end of the experiment, the deformation law of the spiral bevel gear was mastered, and the measures to control the deformation of the spiral bevel gear were found. Design special tooling, adjust heat treatment process specification to control deformation, not only easy to operate, mechanical properties and deformation after heat treatment can meet the technical requirements of drawings, and save a lot of correction man-hours, and avoid waste caused by improper correction, significantly improve The productivity, the cost reduction, and the obvious economic benefits.
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