A method of controlling the shape of a rail prior to heat treatment

Abstract

The application discloses a method for controlling rail shape of heat-treated rails before straightening, and belongs to the field of rail production in the metallurgical industry. The rail shape of the heat-treated rails before straightening is realized by controlling the rail shape of the tail of the rails at the heat treatment outlet. When the tail of the rails is in a raised state at the heat treatment outlet, the raised amount should be no more than 20 cm. When the tail of the rails is in a down-dropped state at the heat treatment outlet, the gap between the rail bottom at a distance of 5 meters from the tail and the roller is taken as the basis, and the gap amount should be no more than 1 cm. The rail shape of the tail of the rails at the heat treatment outlet is adjusted by controlling the cooling medium pressure of the rail bottom. The application has the beneficial effects that the rail shape of the head and the tail of the heat-treated rails before straightening is ensured by controlling the rail shape of the tail of the rails at the heat treatment outlet, the problem of batch rail shape defects before straightening is avoided, the straightening qualified rate is improved, the operation method is relatively simple, the practicability is strong, and no additional cost is needed.

Description

Technical Field

[0001] This invention relates to the field of rail production, and specifically to a method for controlling the rail shape before straightening heat-treated rails. Background Technology

[0002] Online residual heat treatment of rails is a common method to improve the strength and toughness of rails. After heat treatment, the rails are air-cooled to room temperature and then straightened. The straightness of the rails after straightening is a key indicator for evaluating the straightening effect. A key factor affecting the straightness of heat-treated rails after straightening is the rail shape before straightening, i.e., the rail shape after air cooling to room temperature following heat treatment. After straightening, the vertical upward deviation of the rail end should not exceed 0.6mm / 1.5m, while the vertical downward deviation should not exceed 0.2mm / 1.5m. The allowable range for the vertical downward deviation is much smaller than that for the vertical upward deviation. If the heat-treated rail ends are bent downwards before straightening, it is easy to cause the straightened rail end to be vertically downwards, exceeding the allowable range. Therefore, bending the ends of heat-treated rails downwards before straightening should be avoided. On the other hand, if the rail is bent upwards too much, the vertical upward straightness of the rail after straightening is likely to exceed the standard, and the rail may tip over during the process of being transported to the straightening machine with the walking beam cooling bed, affecting the production rhythm. Practice has shown that when the upward curvature of the head and tail of the rail before straightening does not exceed 35cm, it ensures that the rail straightness meets the requirements and also prevents the rail from tipping over during transport to the straightening machine via the walking beam cooling bed. Therefore, maintaining an upward curvature at the head and tail of the heat-treated rail before straightening, with the curvature controlled within 35cm, is a crucial guarantee for improving the straightening pass rate of heat-treated rails.

[0003] It takes approximately two hours from the completion of heat treatment to air cooling to room temperature for the rails. If the rail shape is defective before straightening under a certain heat treatment process, it will only be discovered about two hours after heat treatment when the rails are air-cooled to room temperature, resulting in a delay. Rails produced continuously during these two hours may all have rail shape defects, which significantly impacts the rail straightening pass rate.

[0004] To address the issue of rail shape in heat-treated steel rails, patent application number 201621086809.1 discloses "a device for preventing quenched steel rails from bending and warping." This device consists of two sets arranged opposite each other on both sides of the cooling module in a quenching production line, equipped with side guide rollers and vertical rollers. When the steel rail is conveyed on the roller conveyor of the cooling module, the vertical roller rotates, and its roller surface abuts against the side edge of the rail bottom. The side guide rollers rotate, and their roller surfaces abut against the connection between the rail web and the rail bottom. This patent does not address the cooling deformation of the steel rail during the air cooling process after heat treatment, and the rail may have poor rail shape after cooling to room temperature.

[0005] Patent application No. 201811093074.9 discloses a "method for controlling the straightness of rails during online heat treatment," which mainly includes bending treatment and heat treatment cooling control: after the rails are rolled, a bending machine is used to control the curvature of the hot rails to be 0.4-1.0 mm / 1.5 m towards the rail base; after heat treatment, the temperature of the rail head is controlled to be 60-120°C lower than the temperature of the rail base. This patent's control of the straightness of heat-treated rails involves coordinated cooling of the rail head and rail base, and the cooling of the rail head is closely related to the microstructure and properties. This method requires controlling the straightness of the rails while also considering the microstructure and properties, resulting in a small "window" for process adjustment and significant adjustment difficulties.

[0006] Patent application number 202110037685.7 discloses "a production control method for improving the straightness of rails after online heat treatment and quenching." This method achieves this by rationally controlling the cooling intensity and temperature difference between the rail head and base, thus keeping the bending of the rail within an ideal range after heat treatment. However, this patent relies on coordinating the cooling rate and temperature of the rail head and base to control the straightness of the rail before straightening. The process parameters are complex to adjust, and the on-site operation is quite difficult. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for controlling the rail shape before straightening of heat-treated rails, which can determine the rail shape after the rails have cooled to room temperature as early as possible, effectively avoid the problem of poor rail shape in batches before straightening, and improve the straightening qualification rate.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] Controlling the rail shape before straightening after heat treatment is achieved by controlling the rail tail shape at the heat treatment exit. When the rail tail is upturned at the heat treatment exit, the upturn should not exceed 20cm. When the rail tail is downturned at the heat treatment exit, the gap between the rail bottom and the roller conveyor at a distance of 5 meters from the tail should not exceed 1cm. The rail shape at the rail tail at the heat treatment exit is adjusted by controlling the pressure of the cooling medium at the rail bottom.

[0010] When the upward tilt of the rail tail at the heat treatment exit exceeds 20cm, increase the pressure of the cooling medium at the rail base. Based on the weight per meter of the rail, increase the cooling pressure proportionally for every 1cm exceeding the tilt. When the gap between the rail base and the roller conveyor at 5 meters from the tail at the heat treatment exit exceeds 1cm, decrease the pressure of the cooling medium at the rail base. Based on the weight per meter of the rail, decrease the cooling pressure proportionally for every 0.1cm exceeding the gap.

[0011] When the rail tail curves upward at the heat treatment exit, for rails weighing 60 kg / m and below, the rail base cooling pressure increases by 5%-7.5% for every 1 cm increase in upward curve; for rails weighing over 60 kg / m, the rail base cooling pressure increases by 7.5%-10% for every 1 cm increase in upward curve. When the rail tail curves downward at the heat treatment exit, for rails weighing 60 kg / m and below, the rail base cooling pressure decreases by 5%-7.5% for every 0.1 cm increase in the gap between the rail base and the roller conveyor 5 meters from the end; for rails weighing over 60 kg / m, the cooling pressure decreases by 7.5%-10% for every 0.1 cm increase in the gap between the rail base and the roller conveyor 5 meters from the end.

[0012] The rail shape before straightening the heat-treated rail is the rail shape after heat treatment and air cooling to room temperature.

[0013] The principle of this invention: The rail shape state after heat treatment is essentially a comprehensive reflection of the relative cooling intensity of the rail head and rail base, including two processes: heat treatment and subsequent air cooling to room temperature. During heat treatment, the relative cooling intensity of the rail head and rail base varies depending on the cooling process, while during air cooling to room temperature, the relative cooling intensity remains constant. The rail shape state at the heat treatment exit follows a consistent pattern during the subsequent air cooling to room temperature process. Therefore, the rail shape state after air cooling to room temperature can be predicted in advance by observing the rail shape state at the heat treatment exit.

[0014] The rail shape at the tail end of the rail at the heat treatment exit is chosen as the basis for determining the rail shape after cooling to room temperature. This is because, on the one hand, the rail has already undergone heat treatment and is in a static state at the heat treatment exit roller conveyor, which makes it easier to measure the warping amplitude. On the other hand, the tail end has just cooled down, which can more accurately reflect the overall cooling intensity comparison between the rail head and rail bottom during the heat treatment process.

[0015] If the rail tail curves upwards at the heat treatment exit, it indicates that the cooling intensity of the rail base relative to the rail head was less during heat treatment. During subsequent air cooling, the shrinkage caused by cooling the rail base is greater than that of the rail head, causing the rail to bend towards the rail base as it cools to room temperature. Extensive production experience shows that when the upward curve of the rail tail at the heat treatment exit does not exceed 20cm, both the rail head and tail will curve upwards after air cooling to room temperature. However, when the upward curve of the rail tail at the heat treatment exit exceeds 20cm, both the rail head and tail tend to curve downwards after air cooling to room temperature. Therefore, when the upward curve of the rail tail at the heat treatment exit exceeds 20cm, the pressure of the cooling medium at the rail base needs to be increased to enhance the cooling intensity. Since a larger rail weight per meter results in a larger cross-sectional area and stronger resistance to deformation, the pressure variation required to adjust the rail shape also increases. Extensive practical data shows that when the tail of the rail curls up at the heat treatment exit, for rails weighing 60 kg / m and below, the rail bottom cooling pressure needs to be increased by 5%-7.5% for every 1 cm increase in curl, and for rails weighing more than 60 kg / m, the rail bottom cooling pressure needs to be increased by 7.5%-10% for every 1 cm increase in curl.

[0016] If the rail tail curves downwards at the heat treatment exit, it indicates that the cooling intensity of the rail base relative to the rail head was greater during heat treatment. During subsequent air cooling, the shrinkage caused by the cooling of the rail base is less than that of the rail head, causing the rail to bend towards the rail head during air cooling to room temperature. Since the rail tail remains above 450°C after heat treatment, the amount of downward curvature is inconvenient to measure using conventional rulers and feeler gauges. To clearly quantify the rail head curvature, the gap between the rail base and the roller conveyor at a distance of 5 meters from the tail is chosen as the basis. Extensive production practice has shown that at the heat treatment exit, when the gap between the rail base and the roller conveyor at a distance of 5 meters from the tail does not exceed 1 cm, the upward curvature at both ends of the rail does not exceed 35 cm after air cooling to room temperature. Conversely, at the heat treatment exit, when the gap between the rail base and the roller conveyor at a distance of 5 meters from the tail exceeds 1 cm, the upward curvature at both the rail head and tail is likely to exceed 35 cm after air cooling to room temperature. Therefore, when the gap between the rail base and the roller conveyor at 5 meters from the tail exceeds 1 cm, it is necessary to reduce the rail base cooling pressure and intensity. Since the greater the rail weight per meter, the larger the cross-sectional area and the stronger the resistance to deformation, the greater the pressure variation required to adjust the rail shape. Extensive practical data shows that when the rail head is bent downwards at the heat treatment exit, for rails weighing 60 kg / m and below, for every 0.1 cm increase in the gap between the rail base and the roller conveyor at 5 meters from the tail, the rail base cooling pressure should be reduced by 5%-7.5%; for rails weighing over 60 kg / m, for every 0.1 cm increase in the gap, the cooling pressure should be reduced by 7.5%-10%.

[0017] The beneficial effects of this invention are as follows: By controlling the rail shape at the tail of the rail at the heat treatment exit, this invention ensures the rail shape of the head and tail of the heat-treated rail before straightening, avoids the problem of poor rail shape in batches before straightening, improves the straightening qualification rate, and the operation method is relatively simple, highly practical, and does not require additional costs. Detailed Implementation

[0018] The preferred embodiments of the present invention are described below to make the technical solution clearer and easier to understand.

[0019] A method for controlling the rail shape before straightening of heat-treated rails is provided. The control of the rail shape before straightening is achieved by controlling the rail tail at the heat treatment exit. When the rail tail is in an upward state at the heat treatment exit, its upward movement should not exceed 20cm. When the rail tail is in a downward state at the heat treatment exit, the gap between the rail bottom and the roller conveyor at a distance of 5 meters from the tail should not exceed 1cm.

[0020] When the upward tilt of the rail tail at the heat treatment exit exceeds 20cm, the pressure of the cooling medium at the rail bottom needs to be increased. Based on the weight per meter of the rail, the cooling pressure should be increased proportionally for every 1cm exceeding the tilt. When the gap between the rail bottom and the roller conveyor at 5 meters from the tail at the heat treatment exit exceeds 1cm, the pressure of the cooling medium at the rail bottom needs to be reduced. Based on the weight per meter of the rail, the cooling pressure should be reduced proportionally for every 0.1cm exceeding the gap.

[0021] When the tail of the rail curves upward at the heat treatment exit, for rails weighing 60 kg / m and below, the cooling pressure at the rail base increases by 5%-7.5% for every 1 cm increase in upward curve; for rails weighing over 60 kg / m, the cooling pressure at the rail base increases by 7.5%-10% for every 1 cm increase in upward curve. When the tail of the rail curves downward at the heat treatment exit, for rails weighing 60 kg / m and below, the cooling pressure at the rail base decreases by 5%-7.5% for every 0.1 cm increase in the gap between the rail base and the roller conveyor 5 meters from the tail; for rails weighing over 60 kg / m, the cooling pressure decreases by 7.5%-10% for every 0.1 cm increase in the gap between the rail base and the roller conveyor 5 meters from the tail.

[0022] The rail shape before straightening the heat-treated rail is the rail shape after heat treatment and air cooling to room temperature. Example 1

[0023] A method for controlling the rail shape before straightening of heat-treated steel rails, the steel rails being U71Mn with a specification of 50kg / m and a weight per meter of 51.65kg / m. Water is used as the cooling medium for heat treatment. After heat treatment, the steel rails are air-cooled to room temperature before straightening. Table 1 shows a comparison of the specific conditions before and after using this invention.

[0024] Table 1 Control status of Comparative Example 1 and Example 1

[0025]

[0026] Example 2

[0027] A method for controlling the rail shape before straightening of heat-treated steel rails is disclosed. The steel rails are U71Mn with a specification of 50 kg / m and a weight per meter of 51.65 kg / m. Water is used as the cooling medium for heat treatment. After heat treatment, the steel rails are air-cooled to room temperature and then straightened. The specific comparison before and after using the method of this invention is shown in Table 2.

[0028] Table 2 Control status of Comparative Example 2 and Example 2

[0029]

[0030] Example 3

[0031] A method for controlling the rail shape before straightening of heat-treated steel rails, the steel rails being 60kg / m specification U75V with a weight per meter of 60.80kg / m. Water is used as the cooling medium for heat treatment. After heat treatment, the steel rails are air-cooled to room temperature before straightening. Table 3 shows a comparison of the specific situations before and after using this invention.

[0032] Table 3 Control status of Comparative Example 3 and Example 3

[0033]

[0034] Example 4

[0035] A method for controlling the rail shape before straightening of heat-treated steel rails, the steel rails being 60kg / m specification U75V with a weight per meter of 60.80kg / m. Water is used as the cooling medium for heat treatment. After heat treatment, the steel rails are air-cooled to room temperature before straightening. Table 4 shows a comparison of the specific situations before and after using this invention.

[0036] Table 4 Control status of Comparative Example 4 and Example 4

[0037]

[0038] Example 5

[0039] A method for controlling the rail shape before straightening of heat-treated steel rails, the steel rails being 75kg / m specification U75V with a weight per meter of 74.60kg / m. Water is used as the cooling medium for heat treatment. After heat treatment, the steel rails are air-cooled to room temperature before straightening. Table 5 shows a comparison of the specific situations before and after using this invention.

[0040] Table 5 Control status of Comparative Example 5 and Example 5

[0041]

[0042] Example 6

[0043] A method for controlling the rail shape before straightening of heat-treated steel rails, the steel rails being 75kg / m specification U75V with a weight per meter of 74.60kg / m. Water is used as the cooling medium for heat treatment. After heat treatment, the steel rails are air-cooled to room temperature before straightening. Table 6 shows a comparison of the specific conditions before and after using this invention.

[0044] Table 6 Control status of Comparative Example 6 and Example 6

[0045] .

Claims

1. A method for controlling the rail shape before straightening of heat-treated rails, characterized in that: Controlling the rail shape before straightening after heat treatment is achieved by controlling the shape of the rail tail at the heat treatment exit. When the rail tail is upturned at the heat treatment exit, the upturn should not exceed 20cm; when the rail tail is downturned at the heat treatment exit, the gap between the rail bottom and the roller conveyor at a distance of 5 meters from the tail should not exceed 1cm. Controlling the rail shape at the heat treatment exit is achieved by adjusting the pressure of the cooling medium at the rail bottom. When the upturn at the rail tail at the heat treatment exit exceeds 20cm, the pressure of the cooling medium at the rail bottom needs to be increased. Based on the rail weight per meter, the cooling pressure is increased proportionally for every 1cm exceeding the limit. When the gap between the rail bottom and the roller conveyor at a distance of 5 meters from the tail at the heat treatment exit exceeds 1cm, the pressure of the cooling medium at the rail bottom needs to be decreased. Based on the rail weight per meter, the cooling pressure is decreased proportionally for every 0.1cm exceeding the limit.

2. The method for controlling the rail shape before straightening of heat-treated rails according to claim 1, characterized in that: When the tail of the rail curves upward at the heat treatment exit, for rails weighing 60 kg / m and below, the cooling pressure at the rail base increases by 5%-7.5% for every 1 cm increase in upward curve; for rails weighing over 60 kg / m, the cooling pressure at the rail base increases by 7.5%-10% for every 1 cm increase in upward curve. When the tail of the rail curves downward at the heat treatment exit, for rails weighing 60 kg / m and below, the cooling pressure at the rail base decreases by 5%-7.5% for every 0.1 cm increase in the gap between the rail base and the roller conveyor 5 meters from the tail; for rails weighing over 60 kg / m, the cooling pressure decreases by 7.5%-10% for every 0.1 cm increase in the gap between the rail base and the roller conveyor 5 meters from the tail.

3. A method for controlling the rail shape before straightening of heat-treated rails according to claim 1 or 2, characterized in that: The rail shape before straightening the heat-treated rail is the rail shape after heat treatment and air cooling to room temperature.

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