Surface quenching method for large diameter pole piece roller

Abstract

This invention discloses a method for surface quenching large-diameter pole piece rollers, belonging to the field of heat treatment. In actual production, the product passes through a power frequency inductor (50 Hz) and a medium frequency inductor (250 Hz) before being water-spray quenched. Depending on the material, the power frequency heating temperature is controlled between 830 and 870°C, the medium frequency heating temperature between 905 and 945°C (heating temperature varies with the material), and the cooling time is controlled between 0.5 and 1.0 hours. This invention replaces the traditional power frequency quenching method with dual-frequency quenching and optimizes the dual-frequency quenching parameters to enhance the automation control level of the surface quenching process, improving product quality and consistency.

Description

Technical Field

[0001] The present invention relates to the field of heat treatment, in particular to a surface quenching process for a pole piece roller. Background Art

[0002] At present, large-diameter pole piece rollers are quenched by industrial frequency. During the quenching process, the operator needs to manually control the entire process, such as edge temperature, water flow, power supply position, and machine stop position. The operation process is extremely cumbersome and difficult, and is greatly affected by the operator's skill level and operating habits. At the same time, it leads to low quality stability of large-diameter pole piece rollers, and is prone to some quality problems, such as edge collapse, excessive soft belt length, and low hardness of the soft belt area. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a surface quenching method for large-diameter pole piece rollers, adopt dual-frequency quenching to replace the original industrial frequency quenching method, and at the same time optimize the dual-frequency quenching parameters to improve the level of automation control of the surface quenching process and improve product quality and product quality consistency.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] The surface quenching method of the large-diameter pole piece roller is to undergo power frequency quenching and medium frequency quenching in sequence and then spray cooling. The power frequency quenching frequency is 50HZ, the medium frequency quenching frequency is 250HZ, the power frequency heating temperature is controlled at 830-870℃, the medium frequency heating temperature is controlled at 905-945℃, the cooling time is controlled at 0.5h~1.0h, and tempering is directly performed.

[0006] A further improvement of the technical solution of the present invention is that the moving speed of the pole piece roller is 0.7 mm / s.

[0007] A further improvement of the technical solution of the present invention is that: the industrial frequency quenching adopts a φ830mm inductor, the medium frequency quenching adopts a φ855mm inductor, and the water spray cooling adopts an annular sprinkler. The height of each inductor is 165mm, the distance between the two inductor coils is 65mm, the distance between the inductor coil and the annular sprinkler is 35mm, and the sprinkler height is 455mm.

[0008] A further improvement of the technical solution of the present invention is that the φ830mm sensor and the φ855mm sensor both include an induction coil and four independent heat dissipation tubes arranged outside the induction coil, and each heat dissipation tube has an independent water inlet and outlet.

[0009] A further improvement of the technical solution of the present invention is that each sensor is provided with five temperature measuring holes, and each temperature measuring hole is provided with temperature measuring points on both sides of each circle of heat dissipation pipes of the φ830mm sensor and the φ855mm sensor, which are T1, T2, T3...T10 in sequence, and points T5 and T10 are used as control points for the power frequency and medium frequency temperatures.

[0010] A further improvement of the technical solution of the present invention is that the overall height of the annular sprinkler is 455 mm, including an inclined water spraying area arranged at the upper part of the inner wall and a horizontal water spraying area at the lower part. The top row of the inclined water spraying area is provided with movable nozzles with a spraying angle of 24°.

[0011] Due to the adoption of the above technical solution, the technical advancements achieved by the present invention are:

[0012] The present invention studies a surface quenching method for large-diameter pole piece rollers, using dual-frequency quenching instead of the original industrial frequency quenching method, effectively solving the problems of unstable quality, easy edge collapse, poor controllability of soft strip length and hardness during the quenching process caused by the surface quenching method of large-diameter pole piece rollers; at the same time, the dual-frequency quenching parameters are optimized to improve the automatic control level of the surface quenching process and improve the consistency of product quality; at the same time, the existing tooling equipment is modified to meet the dual-frequency quenching needs of large-scale pole piece rollers.

[0013] After statistical analysis of pole piece rollers on the market, it was found that the working layer thickness of most pole piece rollers is no more than 10mm, and they are chrome-plated every time they are removed from the machine during use. Therefore, the requirements for the hardness drop of the roller body working layer are relatively low. However, due to the high hardness requirements and high stress of the roller body, there is a greater risk of edge collapse. Based on the above situation, it is necessary to reduce the power frequency control point temperature during process optimization to achieve the following goals:

[0014] 1) While ensuring a 10mm hardened layer thickness, the internal stress is reduced, thus lowering the risk of edge collapse. Since the quenching process was optimized, more than 120 large-diameter pole piece rollers have been quenched using dual-frequency technology, without a single edge collapse incident.

[0015] 2) Reduce the heat storage of the product and shorten the cooling time of the product. Under normal circumstances, the cooling time of the product of the same specification is about 2.5 hours. By reducing the power frequency quenching temperature and reducing the heat storage, the cooling time can be shortened by 60%-80%;

[0016] 3) Reduce the residual austenite content. Under normal circumstances, due to the high power frequency heating temperature of the work roll, the internal austenite of the roll body is relatively sufficient. After quenching, a cold treatment process is required to reduce the residual austenite content. This situation can be avoided by reducing the power frequency control temperature, saving a deep cold treatment process compared with other products.

[0017] 4) Reduce quenching and tempering time. This process optimization can reduce the quenching microstructural stress in the hardened layer. Through on-site process optimization and subsequent process comparison, the residual stress and residual stress of the roller body after 48 hours of quenching and tempering in this case are basically consistent with the previous test results of 116 hours after power frequency quenching and tempering. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the positions of the sensor and the annular sprinkler of the present invention;

[0019] Figure 2 It is a schematic structural diagram of the annular sprinkler of the present invention;

[0020] Figure 3 is a cross-sectional view of the interior of an annular sprinkler;

[0021] Among them, 1. φ830mm sensor, 2. φ855mm sensor, 3. annular sprinkler, 4. heat dissipation pipe, 5. temperature measuring hole. DETAILED DESCRIPTION

[0022] The present invention is described in further detail below in conjunction with the embodiments:

[0023] The surface quenching method of large-diameter pole piece roller is to undergo power frequency quenching and medium frequency quenching in sequence and then spray cooling. The power frequency quenching frequency is 50HZ, the medium frequency quenching frequency is 250HZ, the power frequency heating temperature is controlled at 830-870℃, the medium frequency heating temperature is controlled at 905-945℃, the heating temperature varies with different materials, the cooling time is controlled at 0.5h-1.0h, the cold treatment process is skipped and tempering is directly performed, and the moving speed of the pole piece roller is 0.7mm / s.

[0024] Power frequency quenching uses a φ830mm inductor, while medium frequency quenching uses a φ855mm inductor. Each inductor is 165mm tall, with a 65mm distance between the two inductor coils. Water spray cooling uses an annular sprinkler with a height of 455mm and a 35mm distance between the inductor coil and the annular sprinkler. Experiments have shown that this distance ensures a certain level of thermal conductivity without causing a significant temperature drop that would affect the heating and cooling process.

[0025] like Figure 1 As shown, the φ830mm sensor and the φ855mm sensor both include an induction coil and four independent heat dissipation pipes arranged outside the induction coil, and each heat dissipation pipe has an independent water inlet and outlet.

[0026] φ830mm sensor and φ855mm sensor, each sensor is equipped with five temperature measuring holes 5, and temperature measuring holes are set on both sides of each circle of heat dissipation pipe as temperature measuring points, which are T1, T2, T3...T10. After on-site temperature measurement, it is found that the values ​​displayed at positions T5 and T10 are the highest temperature points within the position of the power frequency and medium frequency sensors. Therefore, the temperature of the above two points is controlled. At the same time, for better control, T3 and T9 are used as monitoring points during actual operation. Figure 1 shown.

[0027] The overall height of the annular sprinkler is 455mm, and different angles are used to achieve the best cooling effect. Therefore, the sprinkler has two parts of nozzles, such as Figure 2 、 3 As shown, the upper 144mm is an inclined spray area, while the lower 290mm is a horizontal spray area. To control the uniformity and angle of the spray, the top row of nozzles is equipped with movable nozzles. Repeated testing has found that a 24° spray angle is the optimal one, ensuring cooling effectiveness while effectively preventing backflow.

[0028] Process improvement

[0029] 1. Sort out the use conditions and technical requirements of large pole piece rollers.

[0030] After investigation, it was found that the hardness requirements for large-diameter pole piece rollers are generally 830-850LE, with a working layer depth typically no greater than 10mm. The material is typically low-alloy 86CrMoV7. An on-site investigation of roller usage revealed that these rollers operate with a rolling force no greater than 400 tons, are chrome-plated before each roll, and exhibit minimal wear. Typically, a pair of pole piece rollers has a service life exceeding 15 years, with ring cracking being the most common quality issue encountered during use.

[0031] 2. Heating temperature selection

[0032] Based on the above situation, the dual-frequency quenching process was primarily optimized by reducing the power frequency heating control temperature of the rolls. In previous power frequency quenching and dual-frequency quenching of other continuous rolling work rolls, the medium frequency and power frequency quenching temperatures were the same to ensure the product's working layer depth and hardness drop within the working layer. However, the technical requirements of large-diameter pole piece rolls differed significantly from those of the aforementioned products. Based on this situation, repeated testing determined that the power frequency heating temperature was controlled at 75°C lower than the medium frequency heating temperature (and higher than the austenitization temperature of the material). Repeated testing confirmed that the hardened layer depth at this temperature could reach 10-12mm, meeting the process requirements for over 98% of pole piece rolls.

[0033] 3. Shorten the product cooling time

[0034] By lowering the power frequency heating temperature, the product's heat storage can be reduced, shortening the product's cooling time. By measuring and statistically analyzing the roller temperature return under different cooling times, it was found that the roller surface temperature return after 0.5 hours of cooling was basically the same as the roller temperature return after 2.5 hours of power frequency quenching cooling (under normal circumstances, the cooling time for products of the same specifications is about 2.5 hours). This can shorten the cooling time by 60%-80%.

[0035] 4. Cancel the cold treatment process.

[0036] Under normal circumstances, the working roll is fully austenitized inside the roll body due to the high power frequency heating temperature. After quenching, a cold treatment process is required to reduce the martensite content. However, this roll can reduce the degree of austenitization in the working layer by reducing the power frequency control temperature, thereby achieving the purpose of reducing the martensite content. The martensite test after tempering found that the martensite content of the roll body was in the range of 10-15% after the cold treatment was cancelled, which met the company's technical requirement of a martensite content not exceeding 15%. It was significantly lower than the martensite content of 13-16% after the previous power frequency quenching (martensite is a structure derived from quenching, caused by the incomplete transformation of austenite into martensite. This structure is harmful and is prone to structural transformation during use, resulting in changes in grain volume and defects such as cracks). Through process optimization, one deep cold treatment process can be saved compared with other products.

[0037] 5. Reduce quenching and tempering time

[0038] By lowering the power frequency heating temperature of the product, the quenching structure stress in the hardened layer can be reduced. After quenching, the roller body was subjected to stress testing, and it was found that the tensile stress and compressive stress were reduced by about 30% compared with the power frequency quenched products. Subsequent tempering time comparison tests were conducted, and the residual stress and residual stress of the roller body after quenching and tempering for 48 hours in this case were basically consistent with the previous test results of tempering for 116 hours after power frequency quenching. Therefore, the quenching and tempering time can be shortened by about 60%.

Claims

1. A surface quenching method for a large diameter pole piece roller, characterized in that: After power frequency quenching and medium frequency quenching, water spray cooling is performed. The power frequency quenching frequency is 50HZ, the medium frequency quenching frequency is 250HZ, the power frequency heating temperature is controlled at 830-870℃, the medium frequency heating temperature is controlled at 905-945℃, the cooling time is controlled at 0.5h~1.0h, and tempering is performed directly. The power frequency quenching adopts a φ830mm inductor (1), the medium frequency quenching adopts a φ855mm inductor (2), and the water spray cooling adopts an annular water sprayer (3). The height of each inductor is 165mm, the distance between the two inductor coils is 65mm, the distance between the inductor coil and the annular water sprayer (3) is 35mm, and the water sprayer height is 455mm; the φ830mm inductor ( 1) and the φ855mm sensor (2) both include an induction coil and four independent heat pipes (4) arranged outside the induction coil, each heat pipe (4) having an independent water inlet and outlet; each sensor is provided with five temperature measuring holes (5), each temperature measuring hole (5) is provided with temperature measuring points on both sides of each heat pipe of the φ830mm sensor (1) and the φ855mm sensor (2), which are T1, T2, T3...T10 in sequence, and T5 and T10 are used as control points for the power frequency and medium frequency temperatures; the annular water sprayer (3) includes an inclined water spraying area arranged on the upper part of the inner wall and a horizontal water spraying area on the lower part, and the uppermost row of the inclined water spraying area is provided with movable nozzles, and the spraying angle is 24 degrees.

2. The surface quenching method for a large-diameter pole piece roller according to claim 1, characterized in that: The moving speed of the pole piece roller is 0.7 mm / s.

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