JPH07185660A - Straightening method for rail roller - Google Patents

Abstract

PURPOSE:To provide a rail straightening method which improves the fatigue resistance and web brittle fracture resistance of a rail as straightening the rail in the longitudinal direction. CONSTITUTION:Four or more rollers 3 are arranged by holding between there the rail 1 to be straightened in zigzag shape, and an interval with an adjacent roller 3 is set at distance that the maximum contact bearing between the roller and the rail satisfies a value < 1200MPa and the bending stress of the rail exceeds the yield stress of the rail to be straightened, and straightening is performed as applying pure bending to the rail 1 repeatedly. In this way, since the straightening is performed by applying the repeat plastic deformation to the rail as setting the maximum contact bearing between the roller and the rail at a value < 1200MPa, the rail 1 can be straightened in the longitudinal direction, and also, residual stress in the longitudinal direction in the neighborhood of the head apex part and the center of bottom of the rail coming in contact with the roller 3 goes to nearly zero, which remarkably improves the fatigue resistance and web crack progressing characteristic resistance of the rail comparing with the conventional roller straightening method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rail roller straightening method for straightening the running rail in the longitudinal direction while improving fatigue resistance and web brittle fracture resistance.

[0002]

2. Description of the Related Art For straightening a rail, a roller straightening machine arranged in a zigzag pattern via rails running a plurality of rolls has been used since the 1950s, as shown in FIG. Roller straightening machines are used by most rail manufacturers around the world because of their features such as the ability to efficiently straighten the shape of rails, their productivity, and their straightness. Until now, it was necessary to correct the rail by taking into consideration only the straightness of the rail shape from the stable running of the train, but from the last ten years, speeding up and heavy loading of trains have been promoted year by year.

Under these circumstances, safety and longer life of rails have become important issues, and rails whose steel composition and manufacturing method are controlled are disclosed in Japanese Patent Publication No. 2-55488 and Japanese Patent Publication No. 5-30883. The material is being actively improved. Recently, it has been found that not only the material of the rail but also the residual stress existing in the rail has a great influence on the rail's use performance, and studies have been actively conducted to control the residual stress of the rail. When the rail is straightened with a roller straightening machine, there is no problem in the straightness of the rail shape, but there is a residual tensile stress of 200 MPa in the longitudinal direction of the rail near the center of the top and bottom of the rail that comes into contact with the roller. However, there is a problem that the fatigue resistance and the web brittle fracture resistance of the rail deteriorate. For example, the famous French rail maker "SACIL (SACIL
OR) ”in the document“ Second International Heavy Hau
l Railway Conference, Colorado Spring, Colorado,
USA September, 1982 ”, but instead of the roller straightening method that generates large tensile residual stress at the top and bottom of the rail, the rail is pulled in the longitudinal direction up to the plastic deformation region to reduce the tensile residual stress to almost zero. We are developing a stretch straightening method to improve rail fatigue resistance and other properties. However, the stretch straightening method has many problems such as there is room for improvement in the straightness of the rail shape, poor productivity, and inability to fully straighten the rail head to a hardened heat treated rail. Has not yet spread. Recently, for example, it is difficult to control residual stress with a conventional roller straightening machine.
As disclosed in Japanese Patent No. 17921, "the diameter is 50 to 3".
A straightening method for improving the fatigue resistance of rails has also been developed, in which the surface layer of the head and bottom of the rail is straightened with a small diameter roll of 00 mm to give compressive residual stress. However, this correction method also
There was a problem of expensive equipment costs. Therefore, regardless of the structure of the roller straightening machine, it is desired to develop a roller straightening method that does not generate tensile residual stress in the roller straightening itself.

[0004]

DISCLOSURE OF THE INVENTION The present invention aims at searching for a roller straightening method that does not generate tensile residual stress when straightening the shape of a rail. We investigated in detail and investigated whether tensile residual stress occurs only in the center of the bottom. As a result, it was clarified that tensile residual stress is generated in the surface layer of the roller straightening machine because plastic deformation occurs in the inner layer of the rail rather than the surface layer of the rail in contact with the roller. In other words, the tensile residual stress that occurs at the top and bottom of the rail is basically related to the contact pressure between the rail and the roller, the diameter of the roll, and the bending stress of the rail. In addition, if the roll diameter is small, compressive residual stress is generated on the rail surface that contacts the roller. Furthermore, the contact surface pressure between the rail and roller is smaller than that of the conventional straightening method of 1500 MPa or more.
It has been found that if the roll spacing is 0 MPa or less and the positions of the rollers arranged in a zigzag manner exceed the yield stress of the rail, a tensile residual stress is hardly generated in the rail surface layer.

[0005]

The present invention is constructed from these findings. The gist of the present invention is to arrange four staggered rails running in the longitudinal direction at roll intervals exceeding the yield stress of the rails. With the straightening roller composed of the above rolls, the rail is straightened while the rail contact surface of the roller is repeatedly subjected to bending plastic deformation of 1200 MPa or less,
This is a roller straightening method for rails to improve the fatigue resistance and web brittle fracture resistance by making the residual stress of the rail almost zero.

[0006]

The present invention will be described in detail below. FIG. 1 is a view presented to make the method of the present invention easy to understand. In the figure, 1 is a rail that is straightened while running, and 2 is a guide roll. The guide roll 2 is provided on the traveling path of the rail 1. That is, the rail 1 travels while being supported by the guide roll 2. 3 is a straightening roller. As shown in FIG. 2, the straightening rollers 3 are arranged in groups of four or more rolls arranged in a staggered manner through the rails running in the longitudinal direction at a roller interval (a) exceeding the yield stress of the rails 1. There is. That is, according to the present invention, the roller contact surface pressure of the rail 1 transported by the guide roll 2 is 1200.
Straightening processing is performed while giving plastic deformation by repeated processing of MPa or less. In this case, when the contact surface pressure between the rail 1 and the roll 2 exceeds 1200 MPa, plastic deformation occurs in the inner layer rather than the surface layer of the processed rail, and the tensile residual stress is generated in the surface layer due to the plastic deformation.

Therefore, in the present invention, in order to generate compressive residual stress in the surface layer of the rail and improve the characteristics required for the rail such as fatigue resistance, the contact surface pressure between the rail 1 and the roll 2 is 1200 MPa or less. Need to Moreover, in the present invention, in order to prevent the residual tensile stress generated in the surface layer of the rail, each roller 3 that straightens the rail 1 is used.
(A) must be located at a position where the three-point bending stress of the roller exceeds the yield stress of the rail. This roller interval (a) is for straightening the rail 1 while giving repeated plastic deformation of pure bending by each roller, and if it is too large, not only a wide space is required for equipment layout but also rail If the straightness is also low, on the contrary, if it is too small, the roller contact surface pressure of the rail exceeds 1200 MPa, and excessive tensile residual stress is generated at the top and bottom central portions of the rail. Therefore, the proper position (roller interval) of each roller may be determined as follows.

The relationship between the maximum contact surface pressure (σ _max ) between the rail and the roller and the straightening load (P) is expressed by the following equation (1): σ _max = 610 × {P / (L × r)} ^1/2 …………………… (1) where, l: contact width between rail and roller (cm) r: radius of roller (cm), roller spacing (a) and straightening load The relationship of (P) is obtained from the following equation (2). σ _b = M / Z ……………………………………………… (2) where σ _b : Bending stress M: Bending moment Z: Rail section modulus Furthermore, rail yield From the relationship of the point (σ _y ), the straightening load (P), and the roller interval (a), in order to plastically deform the rail, σ _y = (P × a) / (2 × Z) ∴P ≧ (2 × _{Z × σ y) / a ..........................................} (3) However, (3) at a ≧ (2 × Z × σ y) / P becomes equation from the equation, the roller spacing ( a) is required.

The rail manufactured by the method of the present invention as described above is excellent in fatigue resistance and web brittle fracture resistance because the rail has good shape characteristics and almost no tensile residual stress is generated in the rail surface layer. Is obtained.

[0010]

EXAMPLES Next, examples of the present invention will be described. In order to confirm the effectiveness of the rail straightening method according to the present invention, rail straightening was carried out using a JIS 60k rail 12 m of ordinary carbon steel rail, and rail surface residual stress measurement and actual rail rolling fatigue damage test under water lubrication were conducted. . Comparing the correction conditions and the respective results by the method of the present invention and the comparison method,
It shows in Table 1.

From Table 1, in the rail straightening method of the present invention, the residual stress near the top of the rail and the center of the bottom in contact with the roller was almost zero, and rolling fatigue damage resistance and web brittle crack growth length were compared. Significantly improved compared to the roller straightening method. That is, when the rail is straightened with a comparative roller straightening machine, a tensile residual stress of about 200 to 245 MPa is generated in the rail longitudinal direction in the vicinity of the top and bottom centers of the rail, and the real rail under water lubrication In the rolling fatigue damage test, a crack was generated from the top surface of the rail where tensile residual stress exists at a tonnage of 79.5 million tons. The brittle crack growth length of the web at room temperature is 380 mm.
The rail web progressed straight. On the other hand, in the rail straightened by the roller straightening method of the present invention, the residual stress in the longitudinal direction of the surface of the rail top is compressed to about 20 MPa, and the tensile residual stress of about 10 MPa in the longitudinal direction near the center of the bottom of the rail causes residual stress. The stress was almost zero on the contact surface with the roller, and the tonnage until damage occurred was about 200 million tons in the actual rail rolling fatigue damage test under water lubrication, and the rolling fatigue damage resistance was remarkable. In addition, the web brittle crack growth characteristics are greatly improved with the crack growth length being as small as 170 mm.

As described above, the reason why the rail subjected to the rail straightening according to the present invention has improved rolling fatigue damage resistance and web brittleness crack propagation resistance is that the rail top portion where rolling fatigue damage occurs is compared with the straightening. Although a large tensile residual stress was generated in the method, it is almost zero in the method of the present invention, and the tensile residual stress of the rail head and the bottom surface, which is the driving force for the web brittle crack propagation, is almost zero. It is believed that this is because the brittle crack growth length of the web also became smaller as it became zero.

Further, in the roller straightening method of the present invention, the straightness of the rail is almost the same as that of the comparative roller straightening method.

[0014]

[Table 1]

[0015]

As described above, the method of the present invention provides a rail straightening method capable of significantly improving the use performance of rails at low cost and efficiently while securing the productivity as in the conventional roller straightening method. is there.

[Brief description of drawings]

FIG. 1 is a view presented to make the method of the present invention easier to understand.

FIG. 2 is a diagram presented to make the method of the present invention easier to understand.

[Explanation of symbols]

 1 Straightened rail 2 Guide roll 3 Straightening roller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Teruyuki Wakatsuki 1-1 No. 1 Tobita-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Co., Ltd. Yawata Works

Claims (1)

[Claims] 1. A staggered arrangement of 4 rails running in the longitudinal direction at roll intervals exceeding the yield stress of the rails.
With a straightening roller consisting of more than one roll, the rail is straightened while the rail contact surface of the roller is subjected to repeated bending plastic deformation of 1200 MPa or less, and the residual stress of the rail is almost zero and fatigue resistance and web brittleness fracture A roller straightening method for rails, which is characterized by improving characteristics.