A method of controlling residual stresses in the rail foot of a steel rail

Abstract

The application discloses a method for controlling residual stress of rail bottom, which comprises pre-bending and straightening processes; the horizontal roller used in the straightening process comprises nine rollers, i.e., R1 to R9, wherein R2, R4, R6 and R8 are active pressure rollers; the straightening force F2 of the R2 roller is F2=α×(R m -400), wherein R m is the tensile strength of the rail, and α is a coefficient related to the rail weight per meter and the maximum bending height of the rail before straightening; the straightening force F4 of the R4 roller should not be greater than 1.2 times of F2, and the straightening force F6 of the R6 roller should not be greater than 0.8 times of F2; wherein, α=β×M 1 / 2 ; M is the weight per meter of the rail, and β is set according to the maximum bending height of the rail before straightening. The method can control the straightening force, control the residual stress of the rail bottom to be below 220 MPa on the basis of ensuring the straightness of the rail after straightening, does not increase the cost, is convenient to implement, has good practicability and a larger application range.

Description

Technical Field

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

[0002] In the rail production process, the most commonly used straightening method both domestically and internationally is roller-type horizontal and vertical composite straightening. Under the enormous contact stress of the straightening rollers, the rail undergoes both elastic and plastic deformation. After straightening, residual plastic deformation remains at the rail head, rail web, and rail base after the elastic deformation recovers, and the degree of deformation is uneven. The straightened rail generates longitudinal tensile stress at the rail head and rail base, while longitudinal compressive stress occurs at the rail web. Reducing uneven deformation of the rail is the main way to reduce residual stress at the rail base. Practice shows that properly controlling the force exerted by the straightening rollers on the rail can reduce uneven deformation.

[0003] Currently, most publicly available technical solutions rely on controlling the reduction amount of the straightening rollers. However, in actual production, the straightening reduction amount is affected by various factors such as the assembly, calibration, and wear of the straightening rollers. The nominal reduction amount deviates from the actual reduction amount, and this deviation is dynamic, thus the practicality of the technical solutions needs improvement. Furthermore, the rail deformation resistance and rail weight per meter have a significant impact on residual stress control, but existing technologies do not adequately consider their specific influence patterns, resulting in limited applicability to rails of different steel grades and rail types.

[0004] Patent applications such as 201110121768.0 (disclosing a "method for controlling residual stress in 100-meter rails"), 201910682649.9 (disclosing a "method for controlling residual stress at the bottom of 100-meter rails"), and 202311325310.6 (disclosing a "method for reducing residual stress in high-strength treated rails") all use the amount of straightening roller reduction as the control parameter. This results in a discrepancy between the nominal and actual reduction amounts, potentially leading to discrepancies between control and expectations, and thus requiring improvement in practicality.

[0005] For example, the paper "The Influence of Steel Grade, Rail Type and Production Process on Residual Stress after Rail Straightening" in Volume 27, Issue 9 of "Metal Heat Treatment" in 2002 points out that the residual stress value increases with the increase of rail strength and rail weight, but does not give a specific and clear relationship. 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 the rail, so as to effectively reduce the residual stress at the bottom of the rail.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: It includes pre-bending and straightening processes; the straightening process uses nine horizontal rollers, from R1 to R9, of which R2, R4, R6, and R8 are active pressing rollers; the straightening force F2 of roller R2 is α × (R m -400), where R m The tensile strength of the rail is α, which is related to the rail weight per meter and the maximum bending height H of the rail before straightening. 弯 Relevant coefficients; the straightening force F4 of the R4 roller shall not exceed 1.2 times that of F2, and the straightening force F6 of the R6 roller shall not exceed 0.8 times that of F2;

[0008] Where α=β×M 1 / 2 M represents the weight per meter of the rail, and β is based on the maximum bending height H of the rail before straightening. 弯 Set the parameters; when the maximum bending height H of the rail before straightening is reached... 弯 If the radius is greater than 0.6m, then 0.28 < β ≤ 0.30; when the maximum bending height H of the rail before straightening... 弯 If the value is 0.3–0.6 m, then 0.26 ≤ β ≤ 0.28; when the maximum bending height H of the rail before straightening is... 弯 If β < 0.3m, then β < 0.26.

[0009] Furthermore, the difference P between the straightening forces on the drive side and the operating side of the horizontal rollers R2, R4, R6, and R8 差 All are no greater than 50 kN.

[0010] Furthermore, the straightening force is controlled by adjusting the amount of pressure applied to the horizontal roller.

[0011] The design principle of this invention is as follows: During the straightening process, the rail deforms under the force of the straightening rollers. Describing the effect of the straightening rollers on the rail using the straightening force is more direct and accurate. Theoretically, the greater the straightening force, the greater the residual stress in the rail. To reduce residual stress, the straightening force needs to be set appropriately.

[0012] During the straightening process, the greater the curvature of the rail before straightening, the greater the straightening force required to bring the rail curvature into a uniform state. In practice, the straightening force can be adjusted according to the maximum curvature height of the rail before straightening.

[0013] The control of the R2 roller straightening force is directly related to the rail deformation resistance and the rail weight per meter. As the deformation resistance and weight per meter increase, the straightening force required to coordinate the rail curvature increases. Based on actual measurements and with certain simplifications, this invention shows that the R2 roller straightening force F2 has an approximately linear relationship with the tensile strength and an exponential relationship with the rail weight per meter.

[0014] Numerical simulations and other methods revealed that the horizontal straightening rollers R4 and R6 have the most significant impact on the residual stress at the rail base, necessitating an upper limit on the straightening force of R4 and R6 rollers. Simultaneously, to allow sufficient leeway for adjusting rail straightness, this upper limit cannot be too small. Taking all factors into consideration, the straightening force F4 should not exceed 1.2 times F2, and the straightening force F6 of the R6 roller should not exceed 0.8 times F2.

[0015] During the straightening process, if the difference in straightening force between the two sides of the straightening roller is too large, it will lead to uneven stress on the rail base, resulting in uneven deformation of the rail base and easy to cause abnormal fluctuations in residual stress. Therefore, it is necessary to control the difference in straightening force between the two sides of the straightening roller.

[0016] The beneficial effects of adopting the above technical solution are as follows: By controlling the straightening force, the present invention ensures that the straightness of the straightened rail is qualified, and controls the residual stress at the bottom of the rail to below 220 MPa, without increasing the cost, making it easy to implement, and having good practicality and a wide range of applications. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to specific embodiments.

[0018] Examples 1-7: The specific methods for controlling residual stress at the bottom of the rail are as follows.

[0019] (1) After rolling and pre-bending, the rails are straightened. The pre-bending process uses conventional technology. The straightening process is arranged as a horizontal-vertical composite straightening system, with nine horizontal rollers (R1 to R9) and seven vertical rollers. Horizontal rollers R2, R4, R6, and R8 are pressure rollers, and the straightening force is adjusted by the straightening pressure amount. The straightening force F2 of roller R2 is α × (R m -400); where R m α is the tensile strength of the rail, MPa; α is a coefficient related to the rail weight per meter and the maximum bending height of the rail before straightening, α=β×M 1 / 2 Where M is the weight per meter of the rail, kg / m; β is based on the maximum bending height H of the rail before straightening. 弯 Set the following: When the maximum bending height H of the rail before straightening is reached... 弯 If the bending height is greater than 0.6m, then 0.28 < β ≤ 0.30; when the maximum bending height of the rail before straightening is H 弯 =0.3~0.6m, then 0.26≤β≤0.28; when the maximum bending height H of the rail before straightening is... 弯 If the straightening force is less than 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 forces on the drive side and the operating side of the horizontal rollers R2, R4, R6, and R8. 差 All are no greater than 50 kN. The process parameters for the straightening process in each embodiment are shown in Table 1.

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

[0021]

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

[0023] α=β×M 1 / 2 =0.30 × 51.46 1 / 2 =0.30 × 7.17 = 2.15;

[0024] F2=α×(R m -400)=2.15×(970-400)=1225.5KN.

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

[0026] Table 2: Detection results of each embodiment

[0027]

[0028]

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

Claims

1. A method for controlling residual stress at the bottom of a rail, characterized in that: The process includes pre-bending and straightening; the straightening process uses nine horizontal rollers, R1 to R9, of which R2, R4, R6, and R8 are active pressing rollers; the straightening force F2 of roller R2 is α × (R m -400), where R m The tensile strength of the rail is α, which is related to the rail weight per meter and the maximum bending height H of the rail before straightening. 弯 Relevant coefficients; the straightening force F4 of the R4 roller shall not exceed 1.2 times that of F2, and the straightening force F6 of the R6 roller shall not exceed 0.8 times that of F2; Where α=β×M 1 / 2 M represents the weight per meter of the rail, and β is based on the maximum bending height H of the rail before straightening. 弯 Set the parameters; when the maximum bending height H of the rail before straightening is reached... 弯 If the radius is greater than 0.6m, then 0.28 < β ≤ 0.30; when the maximum bending height H of the rail before straightening... 弯 If the value is 0.3–0.6 m, then 0.26 ≤ β ≤ 0.28; when the maximum bending height H of the rail before straightening is... 弯 If β < 0.3m, then β < 0.

26.

2. The method for controlling residual stress at the bottom of a rail according to claim 1, characterized in that: The difference P between the straightening forces on the drive side and the operating side of the horizontal rollers R2, R4, R6, and R8 差 All are no greater than 50 kN.

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

Images