Method for controlling straightness of large-section turnout steel rail in vertical direction during online heat treatment

Abstract

Disclosed in the present invention is a method for controlling the straightness of a large-section turnout steel rail in a vertical direction during an online heat treatment. The method comprises the following steps: after a turnout steel rail is fed into a heat treatment unit, simultaneously performing accelerated cooling on a rail head and a rail base, with the cooling time being 80-110 s, the cooling speed of the rail head being 2-4°C / s and the cooling speed of the rail base being 1.5-2°C / s; when the accelerated cooling is finished, controlling the temperature of the rail head to be 510-530°C; performing accelerated cooling only on the rail base, with the cooling time being 5-10 s and the cooling speed being 1.0-1.5°C / s; and simultaneously performing accelerated cooling on the rail head and the rail base for 10-15 s, with the cooling speed of the rail head being 0.8-1.3°C / s and the cooling speed of the rail base being 0.6-1.0°C / s. The present invention can reduce the adverse effect caused by high temperature recovery of the large-section turnout steel rail, maintains good straightness in the vertical direction, and facilitates the continuity of the online heat treatment operation of the large-section turnout steel rail; moreover, the control method is convenient and efficient, has high operability, and is easy to apply and promote.

Description

Method for controlling vertical straightness of large-section turnout rail in on-line heat treatment TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgical heat treatment, in particular to a method for controlling vertical straightness of large-section turnout rail in on-line heat treatment. BACKGROUND

[0002] Turnout rails have the characteristics of strong integrity, large rigidity, good smoothness and high safety, and are widely used in the production of turnout points on lines. With the development of China's railway transportation towards high speed and heavy load, the performance requirements for turnout rails are becoming higher and higher, and the lines require that the turnout points are made of on-line heat treated turnout rails.

[0003] The on-line heat treatment production process of turnout rails is to utilize the residual heat of the rails after rolling to enter the heat treatment unit (which is essentially an accelerated cooling process), and after the rails leave the heat treatment unit, they are cooled on the cooling bed on the transportation roller way in an air cooling state. The entire temperature change of the rails is divided into three stages: in the first stage, the temperature of the rails continuously decreases during the accelerated cooling process; in the second stage, the temperature of the rails increases after the accelerated cooling is stopped; and in the third stage, the temperature of the rails gradually decreases to room temperature in the subsequent air cooling state after the temperature of the rails reaches a peak value.

[0004] During the heat treatment process of large-section turnout rails, due to the large specification section, especially the rail waist thickness reaching 44mm, which is increased by 175% compared to ordinary rails, the internal heat capacity of the rails is higher. When the rails stop accelerating cooling, the rail head return temperature is high. In the subsequent air cooling process, the rails are prone to upward bending in the vertical direction. In severe cases (the maximum bending amount reaches 4-5mm / m), the rails will run out of the roller way beyond the side baffle, causing the rails to fail to normally travel to the cooling bed, affecting the continuity of the production line operation. Moreover, the existing method is only applicable to the straightness control of ordinary rails and does not consider the adverse effects of high return temperature of large-section turnout rails on straightness control. SUMMARY

[0005] The purpose of the present application is to provide a method for controlling the vertical straightness of large-section turnout rails in on-line heat treatment, which reduces the adverse effects of high return temperature of large-section turnout rails, enables the turnout rails to maintain good straightness in the vertical direction after leaving the heat treatment unit and in the subsequent cooling process, and is beneficial to the continuity of on-line heat treatment of large-section turnout rails. Moreover, the control method is convenient, efficient, easy to operate and easy to popularize and apply.

[0006] The technical solution adopted by the present application is as follows:

[0007] A method for controlling the vertical straightness of large-section turnout rails in on-line heat treatment, comprising the following steps in sequence:

[0008] Step 1, after the turnout rail enters the heat treatment unit, the rail head and the rail bottom of the turnout rail are simultaneously subjected to accelerated cooling, the cooling time is 80-110s, the cooling speed of the rail head is 2-4℃ / s, the cooling speed of the rail bottom is 1.5-2℃ / s, and the temperature of the rail head at the end of the accelerated cooling of Step 1 is controlled in the range of 510-530℃, and then Step 2 is performed;

[0009] Step 2, only the rail bottom is subjected to accelerated cooling, the cooling speed is 1.0-1.5℃ / s, and after 5-10s of cooling, Step 3 is performed;

[0010] Step 3, the rail head and the rail bottom are simultaneously subjected to accelerated cooling, the cooling speed of the rail head is 0.8-1.3℃ / s, the cooling speed of the rail bottom is 0.6-1.0℃ / s, and the cooling time is 10-15s, and then the turnout rail is discharged from the heat treatment unit.

[0011] Preferably, in Step 1, the temperature at which the rail begins to be accelerated cooled in the heat treatment unit is 740-800℃.

[0012] Preferably, in Step 2, the rail head stops being accelerated cooled and enters a re-heating stage, and the temperature of the rail head reaches a peak value within 5-10s. Therefore, the accelerated cooling time of the rail bottom in Step 2 is controlled to be 5-10s.

[0013] Preferably, after Step 3, the temperature of the rail head is 30-60℃ lower than the temperature of the rail bottom when the rail is discharged from the heat treatment unit, and the difference between the cooling speeds of the rail head and the rail bottom is reduced in the air cooling process after the rail is discharged from the heat treatment unit, so that the turnout rail maintains a good straightness in the vertical direction.

[0014] Preferably, the accelerated cooling medium for heat treatment of the heat treatment unit includes but is not limited to compressed air and water mist.

[0015] Preferably, in Step 1, the rail head and the rail bottom are simultaneously subjected to accelerated cooling for 85s, the cooling speed of the rail head is 2.8℃ / s, and the cooling speed of the rail bottom is 1.8℃ / s; and the temperature of the rail head at the end of the accelerated cooling in Step 1 is 522℃.

[0016] In Step 2, only the rail bottom is subjected to accelerated cooling for 8s, and the cooling speed is 1.2℃ / s; the temperature of the rail head increases by 26℃ in the re-heating stage;

[0017] In Step 3, the rail head and the rail bottom are simultaneously subjected to accelerated cooling for 10s, the cooling speed of the rail head is 1.2℃ / s, and the cooling speed of the rail bottom is 0.8℃ / s.

[0018] Preferably, in the step 1, the rail head and the rail bottom are simultaneously started to be accelerated cooling 91s, the cooling speed of the rail head is 3.0℃ / s, and the cooling speed of the rail bottom is 2.0℃ / s; when the accelerated cooling in the step 1 is finished, the temperature of the rail head is 517℃;

[0019] In the step 2, only the rail bottom is accelerated cooling 9s, the cooling speed is 1.5℃ / s, and the temperature increment of the rail head is 31℃;

[0020] In the step 3, the rail head and the rail bottom are simultaneously accelerated cooling 10s, the cooling speed of the rail head is 1.2℃ / s, and the cooling speed of the rail bottom is 0.8℃ / s.

[0021] Preferably, in the step 1, the rail head and the rail bottom are simultaneously started to be accelerated cooling 82s, the cooling speed of the rail head is 2.8℃ / s, and the cooling speed of the rail bottom is 1.9℃ / s; when the accelerated cooling is finished, the temperature of the rail head is 515℃;

[0022] In the step 2, only the rail bottom is accelerated cooling 6s, the cooling speed is 1.1℃ / s, and the temperature increment of the rail head is 23℃;

[0023] In the step 3, the rail head and the rail bottom are simultaneously accelerated cooling 12s, the cooling speed of the rail head is 0.8℃ / s, and the cooling speed of the rail bottom is 0.7℃ / s.

[0024] Further, after the step 3, the rail is out of the heat treatment unit and enters the air cooling stage. Since the turnout rail enters the heat treatment unit through the step 1 to the step 3, the cooling speed difference between the rail head and the rail bottom is reduced, so that the turnout rail can keep a good straight state in the vertical direction. Therefore, through the control method of the present application, the straightness of the turnout rail in the vertical direction is ≤0.35mm / m after the rail is out of the heat treatment unit and in the subsequent air cooling process, and the rail can smoothly pass through the transport roller and move to the cooling bed.

[0025] The large-section turnout rail in the present application is a turnout rail with a single weight greater than 70kg / m.

[0026] The working principle of the present application is: after the turnout rail enters the heat treatment unit, the accelerated cooling process is carried out in three steps, the first step is to start accelerated cooling of the rail head and the rail bottom at the same time for 80-110s, the cooling speed of the rail head is 2-4℃ / s, and the cooling speed of the rail bottom is 1.5-2.0℃ / s, at the end of the accelerated cooling, the temperature of the rail head is controlled at 510-530℃, at this time, the rail head part has completed the pearlite transformation and obtained fine pearlite structure; the second step is to only accelerate the cooling of the rail bottom to gradually reduce the overall temperature of the rail bottom, the cooling speed time is 5-10s, and the cooling speed is 1.0-1.5℃ / s; the rail head stops accelerated cooling and starts to enter the reheat stage in the heat treatment unit in advance, in 5-10s, the rail head reheat reaches the peak, and the temperature increases by 20-40℃; the third step is to simultaneously accelerate the cooling of the rail head and the rail bottom for 10-15s, the cooling speed of the rail head is 0.8-1.3℃ / s, a large amount of heat brought out by the rail head reheat is taken away, the cooling speed of the rail bottom is 0.6-1.0℃ / s, and when the rail exits the heat treatment unit, the temperature of the rail head is 30-60℃ lower than the temperature of the rail bottom, so that the difference between the cooling speeds of the rail head and the rail bottom in the air cooling process after the rail exits the heat treatment unit is reduced, and the turnout rail maintains good straightness in the vertical direction.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] The present application controls the cooling of the rail head and the rail bottom by a reasonable process, advances the reheat stage of the large-section turnout rail to be completed in the heat treatment unit, reduces the adverse effects caused by high reheat of the large-section turnout rail, maintains good straightness in the vertical direction of the turnout rail after the rail exits the heat treatment unit and in the subsequent cooling process, and enables the rail to normally travel to the cooling bed, the straightness of the obtained turnout rail in the vertical direction after the rail exits the heat treatment unit and in the subsequent air cooling process is ≤0.35mm / m, which is beneficial to the continuity of the online heat treatment operation of the large-section turnout rail, and the control method is convenient, efficient, and easy to operate and apply. BRIEF DESCRIPTION OF DRAWINGS

[0029] Fig. 1 is a flow chart of the control method of the vertical straightness of the large-section turnout rail in the online heat treatment according to the embodiment of the present application. Embodiment of the present application

[0030] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0031] In order to solve the problem of serious bending in the vertical direction of the large-section turnout rail in the on-line heat treatment, the application provides a control method for the vertical flatness of the large-section turnout rail in the on-line heat treatment, and the flatness of the vertical direction of the turnout rail is ≤0.35mm / m through a reasonable cooling process. The preferred mode of the application will be described in detail through specific embodiments.

[0032] The specification and model of the large-section turnout rail in the following embodiments is 60AT1, and the single weight is 82.23kg / m.

[0033] In example 1, the temperature of the turnout rail starts to accelerate cooling in the heat treatment unit is 760℃, the rail head and the rail bottom start to accelerate cooling at the same time for 85s, the cooling speed of the rail head is 2.8℃ / s, the cooling speed of the rail bottom is 1.8℃ / s, the temperature of the rail head is 522℃ when the acceleration cooling is finished, only the rail bottom starts to accelerate cooling for 8s, the cooling speed is 1.2℃ / s, the temperature increment of the rail head is 26℃, the rail head and the rail bottom start to accelerate cooling at the same time for 10s, the cooling speed of the rail head is 1.2℃ / s, and the cooling speed of the rail bottom is 0.8℃ / s. When the rail leaves the heat treatment unit, the temperature of the rail head is 53℃ lower than the temperature of the rail bottom. After the turnout rail leaves the heat treatment unit and in the subsequent air cooling process, the flatness in the vertical direction is 0.29mm / m, and the rail smoothly passes through the transportation roller and moves to the cooling bed.

[0034] In example 2, the temperature of the turnout rail starts to accelerate cooling in the heat treatment unit is 790℃, the rail head and the rail bottom start to accelerate cooling at the same time for 91s, the cooling speed of the rail head is 3.0℃ / s, the cooling speed of the rail bottom is 2.0℃ / s, the temperature of the rail head is 517℃ when the acceleration cooling is finished, only the rail bottom starts to accelerate cooling for 9s, the cooling speed is 1.5℃ / s, the temperature increment of the rail head is 31℃, the rail head and the rail bottom start to accelerate cooling at the same time for 10s, the cooling speed of the rail head is 1.2℃ / s, and the cooling speed of the rail bottom is 0.8℃ / s. When the rail leaves the heat treatment unit, the temperature of the rail head is 51℃ lower than the temperature of the rail bottom. After the turnout rail leaves the heat treatment unit and in the subsequent air cooling process, the flatness in the vertical direction is 0.23mm / m, and the rail smoothly passes through the transportation roller and moves to the cooling bed.

[0035] Example 3: The switch rail starts accelerated cooling in the heat treatment unit at a temperature of 745℃, the rail head and the rail bottom start accelerated cooling at the same time for 82s, the cooling speed of the rail head is 2.8℃ / s, the cooling speed of the rail bottom is 1.9℃ / s, at the end of the accelerated cooling, the temperature of the rail head is 515℃; the accelerated cooling is started only for the rail bottom for 6s, the cooling speed is 1.1℃ / s, the temperature increment of the rail head is 23℃; the accelerated cooling is started for the rail head and the rail bottom at the same time for 12s, the cooling speed of the rail head is 0.8℃ / s, the cooling speed of the rail bottom is 0.7℃ / s. When the rail leaves the heat treatment unit, the temperature of the rail head is 45℃ lower than the temperature of the rail bottom. After the switch rail leaves the heat treatment unit and during the subsequent air cooling process, the straightness in the vertical direction is 0.21mm / m, and the rail smoothly passes through the transportation roller and moves to the cooling bed.

[0036] Example 4: The switch rail starts accelerated cooling in the heat treatment unit at a temperature of 750℃, the rail head and the rail bottom start accelerated cooling at the same time for 92s, the cooling speed of the rail head is 2.6℃ / s, the cooling speed of the rail bottom is 1.6℃ / s, at the end of the accelerated cooling, the temperature of the rail head is 511℃; the accelerated cooling is started only for the rail bottom for 9s, the cooling speed is 1.3℃ / s, the temperature increment of the rail head is 25℃; the accelerated cooling is started for the rail head and the rail bottom at the same time for 13s, the cooling speed of the rail head is 1.1℃ / s, the cooling speed of the rail bottom is 0.9℃ / s. When the rail leaves the heat treatment unit, the temperature of the rail head is 58℃ lower than the temperature of the rail bottom. After the switch rail leaves the heat treatment unit and during the subsequent air cooling process, the straightness in the vertical direction is 0.34mm / m, and the rail smoothly passes through the transportation roller and moves to the cooling bed.

[0037] Example 5: The switch rail starts accelerated cooling in the heat treatment unit at a temperature of 795℃, the rail head and the rail bottom start accelerated cooling at the same time for 81s, the cooling speed of the rail head is 3.3℃ / s, the cooling speed of the rail bottom is 2.0℃ / s, at the end of the accelerated cooling, the temperature of the rail head is 528℃; the accelerated cooling is started only for the rail bottom for 10s, the cooling speed is 1.5℃ / s, the temperature increment of the rail head is 37℃; the accelerated cooling is started for the rail head and the rail bottom at the same time for 14s, the cooling speed of the rail head is 0.9℃ / s, the cooling speed of the rail bottom is 1.0℃ / s. When the rail leaves the heat treatment unit, the temperature of the rail head is 52℃ lower than the temperature of the rail bottom. After the switch rail leaves the heat treatment unit and during the subsequent air cooling process, the straightness in the vertical direction is 0.35mm / m, and the rail smoothly passes through the transportation roller and moves to the cooling bed.

[0038] It can be seen that the straightness in the vertical direction of the large-section switch rail produced by the method of the present application after leaving the heat treatment unit and during the subsequent air cooling process is controlled below 0.35mm / m, and the rail smoothly passes through the transportation roller and moves to the cooling bed, which guarantees the safe and smooth operation of the online heat treatment of the large-section switch rail.

[0039] It is to be understood that all such modifications and variations that can occur to those skilled in the art in the light of the foregoing description are to be considered within the scope of the application as defined in the claims appended hereto.

Claims

1. A method for controlling the vertical flatness of a large cross-section turnout rail in an on-line heat treatment, characterized in that: The method comprises the following steps: Step 1, after the turnout rail enters the heat treatment unit, the head and the bottom of the turnout rail are simultaneously subjected to accelerated cooling, the cooling time is 80-110s, the cooling speed of the head is 2-4℃ / s, the cooling speed of the bottom is 1.5-2℃ / s, and the temperature of the head is controlled at 510-530℃ when the accelerated cooling is completed; Step 2, only the bottom is subjected to accelerated cooling, the cooling time is 5-10s, and the cooling speed is 1.0-1.5℃ / s; Step 3, the head and the bottom are simultaneously subjected to accelerated cooling for 10-15s, the cooling speed of the head is 0.8-1.3℃ / s, and the cooling speed of the bottom is 0.6-1.0℃ / s.

2. The method for controlling the vertical straightness of the heavy- section turnout rail on-line heat treatment according to claim 1, characterized in that: In the step 1, the temperature of the rail starts to be accelerated in the heat treatment unit is 740-800℃.

3. The method of controlling the vertical straightness of the heavy- section turnout rail on-line heat treatment according to claim 1, characterized in that: In the step 2, the head starts to enter the re-heating stage because the accelerated cooling of the head is stopped, and the head re-heating reaches the peak value within 5-10s.

4. The method of controlling the vertical straightness of the heavy- section turnout rail on-line heat treatment according to claim 1, characterized in that: After the step 3, the temperature of the head is 30-60℃ lower than the temperature of the bottom.

5. The method of controlling the vertical straightness of the heavy- rail turnout rails during on-line heat treatment according to claim 1, characterized in that: The accelerated cooling medium for heat treatment includes but is not limited to compressed air and water mist.

6. The method of controlling the vertical straightness of the heavy- rail turnout rails during on-line heat treatment according to claim 1, wherein: In the step 1, the head and the bottom are simultaneously subjected to accelerated cooling for 85s, the cooling speed of the head is 2.8℃ / s, and the cooling speed of the bottom is 1.8℃ / s; In the step 2, only the bottom is subjected to accelerated cooling for 8s, and the cooling speed is 1.2℃ / s; In the step 3, the head and the bottom are simultaneously subjected to accelerated cooling for 10s, the cooling speed of the head is 1.2℃ / s, and the cooling speed of the bottom is 0.8℃ / s.

7. The method of controlling the vertical straightness of the heavy- rail turnout rails during on-line heat treatment according to claim 1, characterized in that: In the step 1, the head and the bottom are simultaneously subjected to accelerated cooling for 91s, the cooling speed of the head is 3.0℃ / s, and the cooling speed of the bottom is 2.0℃ / s; In the step 2, only the bottom is subjected to accelerated cooling for 9s, the cooling speed is 1.5℃ / s, and the re-heating increment of the head is 31℃; In the step 3, the head and the bottom are simultaneously subjected to accelerated cooling for 10s, the cooling speed of the head is 1.2℃ / s, and the cooling speed of the bottom is 0.8℃ / s.

8. The method of controlling the vertical straightness of the heavy- rail turnout rails during on-line heat treatment according to claim 1, wherein: In the step 1, the head and the bottom are simultaneously subjected to accelerated cooling for 82s, the cooling speed of the head is 2.8℃ / s, and the cooling speed of the bottom is 1.9℃ / s; In the step 2, only the bottom is subjected to accelerated cooling for 6s, the cooling speed is 1.1℃ / s, and the re-heating increment of the head is 23℃; In the step 3, the head and the bottom are simultaneously subjected to accelerated cooling for 12s, the cooling speed of the head is 0.8℃ / s, and the cooling speed of the bottom is 0.7℃ / s.

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