RAIL RESTRAINING METHOD AND RAIL RESTRAINING DEVICE

FIELD

The present invention relates to a rail restraining method and a rail restraining device that restrain a hot-rolled rail in an upright position in a cooling process on the head portion and the foot portion of the rail.

BACKGROUND

There are cases in which a hot-rolled high-temperature rail in the austenitic region or higher temperature is subjected to forced cooling, more specifically, being cooled by a cooling medium jetted onto the rail as a heat treatment to ensure desired quality such as hardness required for the head portion of the rail. This forced cooling for the heat treatment (hereinafter, also referred to as heat treatment cooling) is normally performed until the composition of the head portion of the rail is fully transformed from austenite to pearlite or bainite, and the cooling stop temperature is about 400° C. to 500° C.

The above-described heat treatment cooling of the rail is normally performed from both sides of the head portion side and the foot portion side while the rail is in an upright state. However, a difference in temperature arises between the head portion and the foot portion thereof in the course of cooling, and due to the difference in temperature, a thermal stress to warp in a vertical direction occurs on the rail. For this reason, the heat treatment cooling of the rail is performed in a state of the displacement of the rail in the vertical direction being restrained by a restraining apparatus so that the curvature (warp) in the vertical direction after the heat treatment cooling falls within tolerance. For example, Patent Literature 1 discloses a rail-foot portion supporting and restraining apparatus that clamps both sides of the foot portion of a rail by openable and closeable claws to restrain the rail.

CITATION LIST
Patent Literature

Patent Literature 1: Japanese Laid-open Patent Publication No. 05-033057

SUMMARY
Technical Problem

To appropriately restrain the displacement of a rail in the vertical direction that occurs during the heat treatment cooling, however, it is important at which position of the rail to restrain and to what extent the restraining force is applied. In other words, when the position to restrain is not appropriate or the restraining force thereof is not sufficient, the warp that occurs on the rail cannot be adequately suppressed and a situation of the rail coming off from the restraining apparatus may arise. Cooling devices are placed above and below the rail in the vicinity along the longitudinal direction of the rail. Consequently, when a large warp occurs on the rail, there have been cases of being unable to uniformly cool the rail because the rate of cooling varies between the warped portion and a not-warped portion. In some cases, the rail contacted the cooling device, causing malfunction. Meanwhile, an increase in the number of the positions to restrain or an increase in the restraining force leads to an increase in cost to that extent.

In view of the above-described situations, the present invention aims to provide a rail restraining method and a rail restraining device that are capable of appropriately restraining the displacement of a hot-rolled high-temperature rail in the vertical direction at the time of performing forced cooling on the head portion and the foot portion of the rail.

Solution to Problem

To solve the above-described problem and achieve the object, a rail restraining method according to the present invention restrains a hot-rolled rail in an upright position at a time of forced cooling of a head portion and a foot portion of the rail, and includes: defining a predetermined position within 2 meters from each of both end faces of the rail along a longitudinal direction of the rail as a first restraining position; defining a predetermined position 3 to 10 meters from the first restraining position in a direction toward center of the rail along the longitudinal direction of the rail as a second restraining position at the time of forced cooling; and restraining displacement of the rail in a vertical direction at the first restraining position and the second restraining position by a restraining force F (kN) that satisfies following Expression (1):

F≧100/L2 (1)

where L2 (m) is a distance between the first restraining position and the second restraining position.

Moreover, a rail restraining device according to the present invention restrains a hot-rolled rail in an upright position at a time of heat treatment of a head portion and a foot portion of the rail, includes: a first restraining device that restrains displacement of the rail in a vertical direction at the first restraining position which is defined as a predetermined position within 2 meters from each of both end faces of the rail along a longitudinal direction of the rail; and a second restraining device that restrains the displacement of the rail in the vertical direction at the second restraining position which is defined as a predetermined position 3 to 10 meters from the first restraining position in a direction toward center of the rail along the longitudinal direction of the rail, and a restraining force F (kN) of each of the first restraining device and the second restraining device satisfies following Expression (1):

F≧100/L2 (1)

where L2 (m) is a distance between the first restraining position and the second restraining position.

Advantageous Effects of Invention

The rail restraining method and the rail restraining device of the invention have an effect in that the displacement of a hot-rolled rail in the vertical direction can be appropriately restrained at the time of performing forced cooling on the head portion and the foot portion of the rail.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of a relevant portion of a rail production line.

FIG. 2 is a schematic cross-sectional view for explaining the configuration of a forced-cooling device.

FIG. 3 is a diagram illustrating first clamping devices and second clamping devices placed on one end portion of a rail.

FIG. 4 is a diagram for explaining the amount of warp of the rail.

FIG. 5 is a diagram for explaining a warp that occurs at the end portion of the rail by forced cooling (heat treatment cooling).

FIG. 6 is a chart illustrating the relation between a first distance and a maximum amount of warp that occurs at the end portion of the rail.

FIG. 7 is a diagram for explaining a warp that occurs between first and second restraining positions on the end portion of the rail by forced cooling (heat treatment cooling).

FIG. 8 is a chart illustrating the relation between a second distance and a maximum amount of warp that occurs at the end portion of the rail.

FIG. 9 is a chart illustrating the relation between the second distance and a maximum restraint reaction force that occurs at the first restraining position.

DESCRIPTION OF EMBODIMENT

With reference to the accompanying drawings, the following describes an exemplary embodiment of a rail restraining method and a rail restraining device of the invention. The invention, however, is not intended to be limited by the embodiment. Furthermore, in the description of the drawings, the same constituents are illustrated with the same reference signs.

Embodiment

FIG. 1 is a diagram illustrating the configuration of a relevant portion of a rail production line 1 to which a rail restraining method and a rail restraining device according to an embodiment is applied. As illustrated in FIG. 1, the rail production line 1 includes a finishing mill 2, a hot saw (hot sawing machine) 3, a forced-cooling device 4 (hereinafter, also referred to as a heat treatment device 4), a cooling bed 5, and others, and performs manufacturing of rails (railroad rails). In the rail production line 1, a rail for which the process at an upstream stage is finished is conveyed to the finishing mill 2, and the rail is rolled by the finishing mill 2, to obtain a cross-sectional shape of a product. After the rail is cut to a predetermined length by cutting off the crops at the leading and trailing ends thereof by the hot saw 3, the rail is conveyed to the heat treatment device 4. The heat treatment device 4 is a device that performs a heat treatment (forced cooling: also referred to simply as cooling, hereinafter) on the hot-rolled rail corresponding to desired quality. After the heat treatment cooling is performed on the rail by the heat treatment device 4, the rail is conveyed to the cooling bed 5 and is cooled down to almost ambient temperature.

FIG. 2 is a schematic cross-sectional view for explaining the configuration of the heat treatment device 4. In the heat treatment device 4, a rail 10 after hot-rolling is conveyed in an upright position to a processing position by conveying rollers 49 (see FIG. 3) laid at appropriate places, and the heat treatment device 4 individually cools down a head portion 11 and a foot portion 13 of the rail 10. As illustrated in FIG. 2, the heat treatment device 4 includes a head-top cooling header 41 and head-side cooling headers 43 to cool the head portion 11 of the rail 10, and a foot-portion cooling header 45 to cool the foot portion 13 of the rail 10. The heat treatment device 4 further includes a pair of clamping devices 47 at the positions to face each other on both sides of the foot portion 13 of the rail 10 conveyed to the processing position.

The head-top cooling header 41, the head-side cooling headers 43, and the foot-portion cooling header 45 are connected to a cooling media source via respective pipe arrangements, and from a plurality of nozzles not depicted, a cooling medium such as air is jetted out. Specifically, the head-top cooling header 41 is placed along the longitudinal direction of the rail 10 above the head portion 11 of the rail 10 at the processing position, and as indicated by arrows A11 in FIG. 2, cools down the head portion 11 by jetting out the cooling medium toward the surface of the head top of the head portion 11. The head-side cooling headers 43 are placed along the longitudinal direction of the rail 10 on both sides of the head portion 11 of the rail 10 at the processing position, and as indicated by arrows A13 in FIG. 2, cool down the head portion 11 by jetting out the cooling medium toward both side surfaces of the head portion 11. Furthermore, the foot-portion cooling header 45 is placed along the longitudinal direction of the rail 10 below the foot portion 13 of the rail 10 at the processing position, and as indicated by arrows A15 in FIG. 2, cools down the foot portion 13 by jetting out the cooling medium toward a bottom surface of the foot portion 13.

The pair of clamping devices 47 clamps the foot portion 13 on both sides of the rail 10 at the processing position to restrain the displacement of the rail 10 such that the rail 10 in heat treatment cooling does not move in the vertical direction. Each of the clamping devices 47 includes a support 471 that supports the foot portion 13 of the rail 10 and a pressing member 473 that presses the foot portion 13 from above the support 471, and by adjusting the pressing force of the pressing member 473 as indicated by arrows A17, the pressing member 473 clamps the foot portion 13 by a predetermined clamping force (restraining force).

Two pairs each of the clamping devices 47 are placed, at both end portions of the rail 10 at the processing position, with a predetermined distance in the longitudinal direction of the rail 10. FIG. 3 is a diagram illustrating two pairs of clamping devices 47-1 and 47-2 as a first restraining device and a second restraining device placed on one end portion of the rail 10, and illustrating the positional relation of the two pairs of clamping devices 47-1 and 47-2 viewed from the side of the rail 10. These two pairs of clamping devices 47-1 and 47-2 are hereinafter referred to, from the one closer to the end face, as first clamping devices 47-1 and second clamping devices 47-2. While the other end portion of the rail 10 is not depicted, two pairs of the first clamping devices 47-1 and the second clamping devices 47-2 are placed at respective positions (a first restraining position and a second restraining position described later) in which the distances from the other end face are the same as those described for the one end portion in the following.

As illustrated in FIG. 3, the first clamping devices 47-1 are placed such that the restraining position of the foot portion 13 (hereinafter, referred to as the first restraining position) is positioned away from the one end portion of the rail 10 along the longitudinal direction of the rail 10 by a predetermined length L1. Furthermore, the second clamping devices 47-2 are placed such that the restraining position of the foot portion 13 (hereinafter, referred to as the second restraining position) is positioned away from the first restraining position in the direction toward the center (inward) of the rail 10 along the longitudinal direction of the rail 10 by a predetermined length L2.

While it is not depicted in FIG. 3, conveying rollers may be placed between the first clamping devices 47-1 and the second clamping devices 47-2. Furthermore, a third and subsequent pairs of clamping devices may be placed as necessary on the center side in the longitudinal direction of the rail than the second clamping devices 47-2. The third and subsequent clamping devices may not produce a significant effect on the restraint in the vertical direction because a force to restrain the displacement in upward direction by the own weight of the rail becomes greater toward the center side in the longitudinal direction of the rail 10. However, when the curvature of the rail in the horizontal direction is large, the effect to correct and restrain it can be expected.

In the forced-cooling process of the rail 10, the curvature (warp) in the vertical direction of the rail 10 may occur in the heat treatment cooling, and in particular, the warp tends to occur at both end portions of the rail 10, causing trouble. As for the central portion of the rail 10, it is not likely to deform from a state of being horizontally supported on the conveying rollers 49 due to its own weight. FIG. 4 is a diagram for explaining the amount of warp δ in the final product of the rail 10. In the embodiment, a maximum amount of rise or a maximum amount of fall of the head-top surface of the rail 10 from a straight line connecting the surfaces of the head top on both ends of the rail 10 indicated by the dashed line in FIG. 4, or a maximum amount of rise or a maximum amount of fall of the bottom surface of the rail 10 from a straight line (omitted to illustrate) connecting the bottom surfaces on both ends of the rail 10 is defined as the amount of warp δ of the rail 10, and the amount of rise is represented by a negative value and the amount of fall is represented by a positive value.

The distance from the end face of the rail 10 to the first restraining position (hereinafter, referred tows a first distance) L1 will be described first. FIG. 5 is a diagram for explaining a warp that occurs at one end portion of the rail 10 by heat treatment cooling. As in the foregoing, the head-top cooling header 41 is placed above the head portion 11 of the rail 10. Thus, when a warp as illustrated in FIG. 5 occurs, the distance between the head portion 11 and the head-top cooling header 41 at the end portion of the rail 10 is closer as compared with that at the central portion of the rail 10. As a result, the cooling rate of the head portion 11 may differ between the end portion and the central portion of the rail 10, and a situation of being unable to uniformly cool the rail 10 may arise.

Furthermore, the head-top cooling header 41 is placed above the head portion 11 of the rail 10 relatively close to the head-top surface (generally, at a position approximately 20 millimeters away from the head-top surface, for example: the distance from the head-top surface to the head-top cooling header 41 is referred to as a head-top to header distance, hereinafter). Consequently, when the amount of warp δ that occurs at the end portion of the rail 10 is large, the end portion of the rail 10 may contact the head-top cooling header 41, and a situation such as damaging the device may arise.

Thus, the heat treatment cooling was performed by varying the first distance L1 to acquire the relation between the first distance L1 and a maximum amount of warp δ1, and the first distance L1 that renders the amount of warp δ1 to be smaller than the head-top to header distance was examined. In addition, the strength of the rail 10 after the heat treatment cooling was compared between a warped portion (i.e., the end portion) and a not-warped portion, and the first distance L1 that renders the difference in strength to be within a tolerable range was also examined. FIG. 6 is a chart of the acquired values plotted with the first distance L1 (m) as the abscissa axis and the maximum amount of warp δ1 (mm) as the ordinate axis. As illustrated in FIG. 6, the maximum amount of warp δ1 that occurs at the end portion of the rail 10 increases as the first distance L1 becomes longer. In the embodiment, based on the relation between the first distance L1 and the maximum amount of warp δ1 acquired and the head-top to header distance, and with the difference in strength by the first distance L1 taken into consideration, the first distance L1 was determined to be within two meters as an appropriate value.

Determining the first distance L1 in this manner can resolve the foregoing troubles attributable to the warp that occurs at both end portions of the rail 10. In other words, because the warp that occurs at both end portions of the rail 10 can be sufficiently suppressed, the difference in cooling rate, which arises between the end portion and the central portion of the rail 10, is settled within a tolerable range, then the non-uniformity in heat treatment cooling (unevenness in cooling) can be reduced, and at the same time a situation of damaging the head-top cooling header 41 as the end portion of the rail 10 contacts the head-top cooling header 41 can be prevented.

Next, the distance from the first restraining position to the second restraining position (hereinafter, referred to as a second distance) L2 will be described. FIG. 7 is a diagram for explaining a warp that occurs at one end portion of the rail between the first and the second restraining positions by heat treatment cooling. During the heat treatment cooling, there is a time period in which the rail is to warp in a downward direction due to a temperature state of the head portion and the foot portion. At this time, because the first clamping devices 47-1 and the second clamping devices 47-2 restrain the deformation in the vertical direction as in the foregoing, the displacement at the clamped positions is approximately zero. However, between the first clamping devices 47-1 and the second clamping devices 47-2, an upward lifting of the rail 10 arises as illustrated in FIG. 7. A maximum value of the amount of lift here is defined as δ2 (hereinafter, also referred to as a maximum amount of warp δ2).

The heat treatment cooling was performed by varying the second distance L2 to acquire the relation between the second distance L2 and the maximum amount of warp δ2 that occurs between the first and the second restraining positions of the rail 10. In addition, the hardness of the head-top surface of the rail 10 after the heat treatment cooling was compared between a warped portion (i.e., between the first and the second restraining positions) and a not-warped portion, and the second distance L2 that renders the difference in the hardness to be within tolerance was also examined. FIG. 8 is a chart of the acquired values plotted with the second distance L2 (m) as the abscissa axis and the maximum amount of warp δ2 (mm) as the ordinate axis. As illustrated in FIG. 8, the maximum amount of warp 82 that occurs between the first and the second restraining positions increases as the second distance L2 becomes longer, which is similar to the case for the first distance L1.

However, when the second distance L2 is simply shortened, another problem arises. FIG. 9 is a chart of the values plotted with the second distance L2 (m) as the abscissa axis and a maximum restraint reaction force (kN) that occurs at the first restraining position as the ordinate axis. The relation between the second distance L2 and the maximum restraint reaction force illustrated in FIG. 9 was acquired by attaching a load detector to the first clamping devices 47-1, performing heat treatment cooling while varying the second distance L2, and measuring the restraint reaction force at the first restraining position during the heat treatment cooling. As illustrated in FIG. 9, a considerable degree of restraint reaction force is required when the second distance L2 is shorter. While the restraint reaction force at the second restraining position is not depicted, a greater restraint reaction force is required when the second distance L2 is shorter, which is similar to the case for the first restraining position.

In other words, when the second distance L2 is short and thus the first restraining position and the second restraining position are close, the clamping force of the first clamping devices 47-1 and that of the second clamping devices 47-2 necessary to restrain the warp of the rail 10 increase. Specifically, the clamping force of the first clamping devices 47-1 and that of the second clamping devices 47-2 necessary to restrain the downward displacement of the rail 10 that arises as the end portion of the rail 10 tries to return downward and to restrain the upward displacement (lifting) of the rail 10 that arises between the first and the second restraining positions increase, as described with reference to FIG. 7.

Consequently, when the clamping forces of the first and the second clamping devices 47-1 and 47-2 are insufficient, a trouble of the rail 10 coming off from the first clamping devices 47-1 and the second clamping devices 47-2 may arise.

In contrast, when the second distance L2 is set too long, the warp that occurs between the first and the second restraining positions increases as illustrated in FIG. 8. When the warp increases, a situation to cause the unevenness in cooling and the damage to the head-top cooling header 41 may arise, which is similar to the case for the first distance L1. Furthermore, setting the clamping forces of the first and the second clamping devices 47-1 and 47-2 greater or increasing the number of clamping devices to be placed leads to an increase in cost to that extent.

Thus, in the present embodiment, the second distance L2 and the clamping force of the first and the second clamping devices 47-1 and 47-2 that can appropriately restrain the displacement of the rail 10 in the vertical direction while moderating the increase in the clamping force were examined based on the relation between the first distance L1 and the maximum amount of warp δ1 and the relation between the second distance L2 and the maximum amount of restraint reaction force acquired, and with the difference in hardness of the head surface of the rail acquired by the second distance L2 taken into consideration. The second distance L2 was then determined to be 3 to 10 meters as an appropriate value. Furthermore, the clamping force of the first and the second clamping devices 47-1 and 47-2 was determined that a minimum of 100/L2 (kN) is necessary, from the relation between the distance L2 between the first and the second restraining positions and the maximum amount of restraint reaction force illustrated in FIG. 9. More specifically, the clamping force (restraining force F (kN)) of the first and the second clamping devices 47-1 and 47-2 needs to satisfy the following Expression (1):

F≧100/L2 (1)

where L2 (m) is the distance between the first and the second restraining positions.

Defining the second distance L2 and defining the clamping forces of the first and the second clamping devices 47-1 and 47-2 in this manner can appropriately restrain the displacement of the rail 10 in the vertical direction while moderating a significant increase in cost, and can substantially reduce the warp that occurs at both end portions of the rail 10. As a consequence, the unevenness in cooling of the head portion 11 and the damage to the head-top cooling header 41 at the time of heat treatment cooling can be prevented.

EXAMPLES

An applied example that conforms to the clamping condition of the first distance L1, the second distance L2, and the clamping force in the foregoing, and first to third comparative examples that do not conform thereto were verified using rail material of 100 meters long (136 pounds per yard). The condition of forced cooling of the rail material here was set as the surface temperature of the head portion 11 at the start of cooling to be 720° C. and the surface temperature of the head portion 11 at the end of cooling to be 420° C.

In the applied example, the heat treatment cooling of the rail was performed while the first and the second clamping devices 47-1 and 47-2 were placed with the first distance L1=1 meter and the second distance L2=5 meters and the respective clamping forces thereof were set to 20 kilonewtons to restrain the foot portions of the rail. Furthermore, the amount of warp δ (see FIG. 4) at both end portions of the rail after the heat treatment cooling was measured. In the applied example, the rail did not deform greatly during the heat treatment cooling, and the displacement of the rail in the vertical direction was able to be restrained appropriately. As a result, the unevenness in cooling of the head portion of the rail was able to be reduced, and the amounts of warp δ at both end portions of the rail were good and within 10 millimeters.

The first comparative example is a situation of the first distance L1 not conforming to the clamping condition, and the heat treatment cooling of the rail was performed with the first distance L1=3 meters, the second distance L2=5 meters, and the respective clamping forces of the first and the second clamping devices 47-1 and 47-2 set to 20 kilonewtons, and then the amount of warp δ (see FIG. 4) of the rail after the heat treatment cooling was measured. In the first comparative example, large upward warps occurred at both end portions of the rail. As a result, the head portions at both end portions of the rail were excessively cooled, and thus overcooling resulted at the head top portions of both end portions of the rail after the heat treatment cooling, and the hardness of the surfaces of the head portion 11 at both end portions was abnormally high as compared with that of the surfaces of the head portion 11 at the other portions. Furthermore, during the heat treatment cooling, both end portions of the rail contacted the head-top cooling header 41.

The second comparative example is a situation of the second distance L2 not conforming to the clamping condition, and the heat treatment cooling of the rail was performed with the first distance L1=1 meter, the second distance L2=12 meters, and the respective clamping forces of the first and the second clamping devices 47-1 and 47-2 set to 20 kilonewtons, and then the amount of warp δ (see FIG. 4) of the rail after the heat treatment cooling was measured. In the second comparative example, during the heat treatment cooling, a large warp (lift) occurred between the first and the second restraining positions at both end portions of the rail. As a result, the head portions between the first and the second restraining positions at both end portions of the rail were excessively cooled, and thus overcooling resulted at the head top portions of both end portions of the rail after the heat treatment cooling, and the hardness of the surfaces of the head portion 11 at both end portions was abnormally high as compared with that of the surfaces of the head portion 11 at the other portions.

The third comparative example is a situation of the clamping force not conforming to the clamping condition, and the heat treatment cooling of the rail was performed with the first distance L1=1 meter, the second distance L2=5 meters, and the respective clamping forces of the first and the second clamping devices 47-1 and 47-2 set to 5 kilonewtons, and then the amount of warp δ (see FIG. 4) of the rail after the heat treatment cooling was measured. In the third comparative example, during the heat treatment cooling, the rail came off from the first and the second clamping devices 47-1 and 47-2 because the warps at both end portions of the rail were not able to be restrained, and thus large upward warps occurred at both end portions of the rail. As a result, the head portions were excessively cooled at both end portions of the rail, and thus overcooling resulted at the head top portions of both end portions of the rail after the heat treatment cooling, and the hardness of the surfaces of the head portion 11 at both end portions was abnormally high as compared with that of the surfaces of the head portion 11 at the other portions. Moreover, during the heat treatment cooling, both end portions of the rail contacted the head-top cooling header 41.

As in the foregoing, in accordance with the embodiment, at the time of performing the forced cooling of the head portion and the foot portion of a hot-rolled rail, the displacement of the rail in the vertical direction can be restrained at appropriate restraining positions by an appropriate clamping force.

REFERENCE SIGNS LIST

- 4 forced-cooling device (heat treatment device)
- 41 head-top cooling header
- 43 head-side cooling header
- 45 foot-portion cooling header
- 47-1 first clamping devices
- 47-2 second clamping devices
- 49 conveying roller
- L1 first distance
- L2 second distance
- δ amount of warp

RAIL RESTRAINING METHOD AND RAIL RESTRAINING DEVICE

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