Ultra-light and ultra-light bearing rings (the ratio of outer diameter to inner diameter ≤1.143) are prone to distortion during processing, especially during heat treatment. The final heat treatment process generally adopts martensite grading quenching, die quenching, and sometimes medium carbon steel after quenching and tempering for gas nitriding treatment. On the one hand, the above traditional heat treatment process takes a long time, especially the gas nitriding treatment, to obtain the nitriding layer of 0.8mm needs to spend more than 100h, the overall quenching distortion is large, the need for shaping treatment, so the energy consumption is very high; On the other hand, quenching will appear soot, saltpeter residue and so on, easy to cause environmental pollution, but also there is a certain degree of safety hazards.
The rolling bearing parts are hardened by induction heating, and the service life of the bearing is increased by 10%~20% compared with that of heating, quenching, and tempering in the furnace. Meanwhile, induction quenching equipment covers a small area, saves energy, has good working conditions, and is convenient for mechanization, and axial scanning induction quenching has the advantages of small part distortion, no soft belt, less oxidation and decarbonization, and high production efficiency. This paper mainly introduces the soft belt – free induction quenching technology and its application of extra-large extra-light bearing ring.
1. Technical requirements for the heat treatment of parts
The material of extra large and extra light bearing ring used in a certain type of wind power increasing box is 42CrMo, the pretreatment is tempered, the hardness is about 300HBW. The dimensions and specifications of the parts are shown in Figure 1. The ratio of the outside diameter to the inside meridian of the parts is 1.042.
FIG. 1 Bearing ring diagram
The process is medium-frequency induction quenching, and the quenching part is the position of the internal hole of the part, as shown in Figure 1. The hardness is 52~58HRC, the effective hardening depth is 3~5mm (the effective hardening depth is determined according to ISO3754), the metallographic structure is required to meet the requirements of JB/T9204. Distortion requirements: the runout of phase point should be controlled within 0.5mm and the runout of the end face circle should be controlled within 0.1mm.
2. Induction hardening process
(1) Quenching heating equipment
The heating power is IGBT all-solid state transistor intermediate frequency heating power JIGC-500-10, the maximum heating power is 500kW, the adjustable frequency is 1~10kHz.Ф 1500 mm x 5000 mm vertical quenching machine tool.
The inductor is composed of the induction heating part, the quenching spray part, and the fixing device. The gap between the inductor and the workpiece is controlled within 4~6mm. The method of delayed heating quenching is adopted.
FIG. 2 Schematic diagram of the induction heating device
1. Sensor heating part 2. Sensor spraying part 3
(2) Induction quenching process parameters
The heating is carried out by scanning and quenching along the axial direction of the ring, the inductor is fixed, and the ring is continuously heated with the rotation of the working plate. By adjusting the input power of the heating power, that is, by adjusting the current and voltage to control the specific power of the workpiece during induction heating, so as to control the induction heating speed. The process parameters of induction heating are shown in Table 1.After quenching, the workpiece was tempered at a low temperature of 200℃.
Table 1 Technological parameters of bearing ring induction heating
3. Test results and analysis
The sample is intercepted in the middle of the parts’ induction hardening zone, and the test results are shown in Table 2.
Table 2 Test results of sample interception
Note: 1. The depth of the effective hardening layer is determined according to ISO3754.
2. The metallographic structure was assessed according to JB/T9204.
The measured microhardness value and hardness gradient curve are shown in FIG. 3.
FIG. 3 Hardness gradient curve
From the above test results, the surface hardened layer depth, hardness, metallographic structure, and other heat treatment technical indicators are better in line with the technical requirements. There is no soft belt in the quenched area because of the induction quenching technique of scanning quenching along the axial direction. A portable Richter hardness tester was used to detect the hardness of the physical quenching area, which was all 54~56HRC with uniform hardness.
Deformation measurement: the runout of the contact point is 0.30mm and the runout of the end face is 0.05mm, which meets the technical requirements.
Measurement of power consumption: calculate the actual power consumption of the heat treatment process within a cycle according to GB/T17358.After calculation, in one production cycle, the actual process power consumption of the induction quenching process is about 0.120kW•h/kg, the actual process power consumption of overall quenching is about 0.306kW•h/kg, and the actual process power consumption of gas nitriding is about 0.844kW•h/kg. Thus it can be seen that the actual process of the bearing ring using induction hardening technology saves energy of 60.8% over overall quenching and energy of 85.8% over gas nitriding.
In terms of production efficiency, the induction quenching ring is about 3 times more efficient than the overall quenching, and 30 times more efficient than the gas nitriding.
(1) With reasonable inductor design and appropriate process parameters, the adoption of soft band-free induction quenching technology for extra-large and extra-light bearing rings can meet the design requirements. This soft-band-free induction quenching technology for bearing rings has been successfully applied to mass production, with a stable process and reliable quality.
(2) Axial scanning induction quenching technology solves the common defect of induction heating soft belt in the large bearing ring, and the hardness of parts quenching area is uniform and consistent.
(3) The use of soft-band-free induction hardening technology for extra-large and extra-light bearing rings not only saves a lot of energy but also greatly improves production efficiency, shorts manufacturing cycle, and reduces manufacturing cost.
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