Method for controlling residual stress of rail bottom of steel rail

Abstract

The invention discloses a method for controlling residual stress of a rail bottom of a steel rail. The method comprises a pre-bending procedure and a straightening procedure. The number of horizontal rollers adopted in the straightening process is from R1 to R9, and R2, R4, R6 and R8 are driving pressing rollers; the straightening force F2 of the R2 roller is equal to alpha * (Rm-400), Rm is the tensile strength of the steel rail, and alpha is a coefficient related to the meter weight of the steel rail and the maximum bending height of the steel rail before straightening; the straightening force F4 of the roller R4 is not greater than 1.2 times of that of the roller F2, and the straightening force F6 of the roller R6 is not greater than 0.8 times of that of the roller F2; wherein alpha = beta * M1 / 2; m is the weight per meter of the steel rail, and beta is set according to the maximum bending height of the steel rail before straightening. According to the method, by controlling the straightening force, the residual stress of the rail bottom of the steel rail is controlled to be below 220 Mpa on the basis of ensuring that the straightness of the straightened steel rail is qualified, the cost is not increased, implementation is convenient, and good practicability and a large application range are achieved.

Description

Technical Field

[0001] The invention relates to the field of rail rolling, in particular to a method for controlling residual stress at the bottom of a rail. Background Art

[0002] In the process of rail production, the straightening method currently commonly used at home and abroad is roller-type horizontal and vertical composite straightening machine straightening. Under the huge contact stress of the straightening roller, the rail undergoes elastic deformation and plastic deformation. After straightening, the rail head, rail waist and rail bottom retain plastic deformation after the elastic deformation is restored, and the degree of deformation is uneven. The straightened rail produces longitudinal tensile stress at the rail head and rail bottom, and longitudinal compressive stress at the rail waist. Reducing the uneven deformation of the rail is the main way to reduce the residual stress at the rail bottom. Practice has shown that reasonable control of the force of the straightening roller on the rail can reduce the uneven deformation of the rail.

[0003] In the currently disclosed technical solutions, most of them take the control of the straightening roller reduction as a technical measure. However, in actual production, the straightening roller reduction is affected by many factors such as straightening roller assembly, calibration, and straightening roller wear. There is a deviation between the nominal reduction and the actual reduction, and this deviation changes dynamically. The practicality of the technical solution needs to be improved. In addition, the deformation resistance of the rail and the weight per meter of the rail type have an important influence on the control of residual stress. The specific influence rules are rarely considered in the existing technology, resulting in poor applicability to rails of different steel grades and rail types.

[0004] For example, the patent application with application number 201110121768.0 discloses a “method for controlling residual stress of 100-meter rails”, the patent application with application number 201910682649.9 discloses a “method for controlling residual stress at the bottom of 100-meter rails”, and the patent application with application number 202311325310.6 discloses a “method for reducing residual stress of high-strength treated rails”, etc. All of them use the reduction amount of straightening rollers as the control parameter. There is a problem of deviation between the nominal reduction amount and the actual reduction amount, which may lead to the control not being consistent with expectations, and the practicality needs to be improved.

[0005] For example, the paper “The Influence of Steel Type, Rail Type and Production Process on Residual Stress after Rail Straightening” in “Metal Heat Treatment” Vol. 27 No. 9, 2002 points out that the residual stress value increases with the increase of rail strength and the increase of rail unit weight, but no specific and clear relationship is given. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for controlling the residual stress at the bottom of a rail, so as to effectively reduce the residual stress at the bottom of the rail.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: including pre-bending and straightening processes; the horizontal rollers used in the straightening process include 9 horizontal rollers from R1 to R9, among which R2, R4, R6 and R8 are active pressing rollers; the straightening force F2 of the R2 roller is F2 = α × (R m -400), where R m is the tensile strength of the rail, α is related to the rail weight per meter and the maximum bending height H of the rail before correction 弯 Related coefficients; the straightening force F4 of the R4 roller shall not be greater than 1.2 times of F2, and the straightening force F6 of the R6 roller shall not be greater than 0.8 times of F2;

[0008] Where α=β×M 1 / 2 ; M is the weight of the rail per meter, β is the maximum bending height H of the rail before correction 弯 Set; when the maximum bending height H of the rail before correction 弯 >0.6m, then 0.28<β≤0.30; when the maximum bending height of the rail before correction H 弯 is 0.3~0.6m, then 0.26≤β≤0.28; when the maximum bending height of the rail before correction H 弯 <0.3m, then β<0.26.

[0009] Furthermore, the difference P between the straightening force on the transmission side and the operating side of the horizontal rollers R2, R4, R6 and R8 is 差 Not more than 50KN.

[0010] Furthermore, the control of the straightening force is achieved by adjusting the pressing amount of the horizontal roller.

[0011] The design principle of the present invention is as follows: During the straightening process, the rail is deformed by the force of the straightening roller. It is more direct and accurate to describe the effect of the straightening roller on the rail with the straightening force. Theoretically, the greater the straightening force, the greater the residual stress of the rail. In order to reduce the residual stress, the straightening force needs to be reasonably set.

[0012] During the straightening process, the greater the curvature of the rail before straightening, the greater the straightening force required to coordinate the rail curvature to be consistent. In actual operation, the straightening force can be adjusted according to the maximum curvature height of the rail before straightening.

[0013] The control of the straightening force of the R2 roller is directly related to the deformation resistance of the rail and the weight per meter of the rail. As the deformation resistance and weight per meter increase, the straightening force that coordinates the curvature of the rail increases. The present invention combines actual measurements and undergoes certain simplifications. The straightening force F2 of the R2 roller is approximately linearly related to the tensile strength and exponentially related to the weight per meter of the rail.

[0014] Through numerical simulation and other means, it is analyzed that the horizontal straightening rollers R4 and R6 have the most significant influence on the residual stress at the rail bottom, and a certain upper limit needs to be set for the straightening force of the R4 and R6 rollers. At the same time, in order to leave a certain space for adjusting the straightness of the rail, this upper limit value cannot be too small. Taking all factors into consideration, the straightening force F4 shall not be greater than 1.2 times of F2, and the straightening force F6 of the R6 roller shall not be greater than 0.8 times of F2.

[0015] During the straightening process, if the difference in straightening force on both sides of the straightening roller is too large, it will cause uneven force on the bottom of the rail, uneven deformation of the rail bottom, and easily cause abnormal fluctuations in residual stress. Therefore, it is necessary to control the difference in straightening force on both sides of the straightening roller.

[0016] The beneficial effect of adopting the above technical scheme is that the present invention controls the straightening force to control the residual stress at the bottom of the rail to below 220Mpa on the basis of ensuring the qualified straightness of the rail after straightening, without increasing the cost, being easy to implement, having good practicality and a large scope of application. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below in conjunction with specific implementation modes.

[0018] Embodiment 1-7: The method for controlling the residual stress at the bottom of a rail is specifically described as follows.

[0019] (1) The rails are straightened after rolling and pre-bending, and the pre-bending adopts conventional technology. The straightening process is arranged in the form of horizontal and vertical composite straightening, with 9 horizontal rollers, namely R1 to R9, and 7 vertical rollers, of which the horizontal rollers R2, R4, R6 and R8 are press rollers, and the straightening force is adjusted by the straightening press amount. The straightening force F2 of the R2 roller is F2 = α × (R m -400); where R m is the tensile strength of the rail, MPa; α is the coefficient related to the rail weight per meter and the maximum bending height of the rail before correction, α=β×M 1 / 2 ; Where M is the weight of the rail per meter, kg / m; β is based on the maximum bending height H of the rail before correction 弯 Setting: When the maximum bending height H of the rail before correction 弯 >0.6m, then 0.28<β≤0.30; when the maximum bending height of the rail before correction is H 弯 =0.3~0.6m, then 0.26≤β≤0.28; when the maximum bending height of the rail before correction H 弯 <0.3m, then β<0.26. The straightening force F4 of the R4 roller is ≤1.2×F2, and the straightening force F6 of the R6 roller is ≤0.8×F2; the difference P between the straightening force of the transmission side and the operating side of the horizontal rollers R2, R4, R6 and R8 is 差 The process parameters of the straightening process of each embodiment are shown in Table 1.

[0020] Table 1: Straightening process control parameters of Examples 1-7

[0021]

[0022] The calculation process is described using Example 1 as an example:

[0023] α=β×M 1 / 2 =0.30×51.46 1 / 2 =0.30×7.17=2.15; F2=α×(R m -400)=2.15×(970-

[0024] 400)=1225.5KN.

[0025] (2) Examples 1-7 were tested for residual stress and straightness of the rail bottom according to the corresponding standards. The test results are shown in Table 2.

[0026] Table 2: Test results of various embodiments

[0027]

[0028]

[0029] It can be seen from Table 2 that the residual stress values ​​of each embodiment do not exceed 220 MPa, and the straightness after correction is qualified.

Claims

1. A method for controlling residual stress at the bottom of a rail, characterized in that: The method comprises pre-bending and straightening steps; the horizontal rollers used in the straightening step include 9 rollers from R1 to R9, of which R2, R4, R6 and R8 are active pressing rollers; the straightening force F2 of the R2 roller is F2 = α × (R m -400), where R m is the tensile strength of the rail, α is related to the rail weight per meter and the maximum bending height H of the rail before correction 弯 Related coefficients; the straightening force F4 of the R4 roller shall not be greater than 1.2 times of F2, and the straightening force F6 of the R6 roller shall not be greater than 0.8 times of F2; Where α=β×M 1 / 2 ; M is the weight of the rail per meter, β is the maximum bending height H of the rail before correction 弯 Set; when the maximum bending height H of the rail before correction 弯 >0.6m, then 0.28<β≤0.30; when the maximum bending height of the rail before correction H 弯 is 0.3~0.6m, then 0.26≤β≤0.28; when the maximum bending height of the rail before correction H 弯 <0.3m, then β<0.

26.

2. A method for controlling residual stress at the bottom of a rail according to claim 1, characterized in that: The difference P between the straightening force on the transmission side and the operating side of the horizontal rollers R2, R4, R6 and R8 差 Not more than 50KN.

3. A method for controlling residual stress at the bottom of a rail according to claim 1 or 2, characterized in that: The control of the straightening force is achieved by adjusting the pressing amount of the horizontal roller.

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