JPH07216455A - Heat treatment of rail - Google Patents

Abstract

PURPOSE:To make uniform the hardness of rail in its longitudinal direction by adjusting the air discharge volume for cooling a specified range from the end part of rail to a specified ratio to the air discharge volume for the center part in the rail longitudinal direction. CONSTITUTION:The head part of a hot rolled rail 11 is directly heat-treated by a cooling device 10 which is provided with cooling headers 12-14 and by which approximately all length of the rail head part is encircled with a cooling medium of air. In this method, among all cooling headers 12-14, the average air discharge volume per unit time of the cooling headers 12-14 to cool the range of approximate <=3m from the rail end is made to 50-80% of the average air discharge volume per unit time of the center part in the rail longitudinal direction. By this method, the air movement in the rail longitudinal direction is corrected and the rail is uniformly heat-treated, thus the hardness of the rail head part is made uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rail heat treatment method, and more particularly to a heat treatment method for obtaining uniform hardness in the rail length direction.

[0002]

2. Description of the Related Art As a heat treatment method for a hot-rolled rail, Japanese Patent Publication No. 2-6810 and Japanese Patent Publication No. 2-737 are known.
Japanese Patent Laid-Open No. 1-1990 proposes a method of heat-treating a rail head located above a heated austenite region by blowing air from a cooling header arranged so as to surround the head to cool the rail head. In order to obtain a desired hardness, the above-mentioned publication uses a cooling header having a crown portion and both head side portions to improve cooling efficiency, and injects air toward the rail crown surface, the head side surface, and the jaw lower surface. The necessary cooling conditions of are shown.

[0003]

However, in the rail heat treatment method described in the above publication, as shown in FIG. 6, the hardness of the top of the rail in the vicinity of the end of the rail slightly rises relative to that in the center of the rail. There is a tendency. In other words, heat treated rails are mainly used for railroad tracks that are frequently passed by trains and have a large freight car weight, and their wear resistance is higher than that of non-heat treated rails. On the contrary, it is expensive. Therefore, the increase in hardness near the end of the rail means that the progress of wear during use of the rail differs between the center and the end, and the flatness of the rail head is impaired. This induces the vertical acceleration when the train is running, and gives an abnormal impact force to the rail head. Therefore, if the rail head is left unattended, the rail may be damaged. From this, now
There is a problem that rail heads are regularly trimmed by customers, but this causes an increase in track maintenance costs.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a rail heat treatment method for uniformizing the hardness in the length direction when heat treating the rail.

[0005]

A method according to the above-mentioned object.
The rail heat treatment method described above is a rail heat treatment method in which a hot-rolled rail is directly heat-treated by a cooling device that includes a cooling header and surrounds substantially the entire length of the rail head with air as a cooling medium. In, the average air discharge amount per unit time is compared by comparing the average air discharge amount per unit time of the cooling header that cools a range within about 3 m from the rail end portion with the same length in the center portion in the rail length direction. Of 50% to 80%. Here, the control of the air discharge amount within approximately 3 m from the rail end portion may be performed on average, or the air discharge amount may be sequentially or stepwise reduced toward the rail end portion.

[0006]

In order to solve the above problems, the inventor has
The air flow during cooling was investigated to find the cause of the increase in hardness near the rail ends. As a result, even though the direction of air discharged from each part of the cooling header is perpendicular to the rail surface, air flow occurs in the rail length direction on the rail surface near the rail end. I found out that Moreover, the range is within about 3 m from the rail end, and this air flow in the rail length direction increases the cooling efficiency of the rail surface near the rail end with respect to that at the center of the rail. It was estimated that the hardness near the rail ends increased compared to that at the center.

Therefore, the present inventor reduces the air discharge amount per unit time from the cooling header in the vicinity of the rail end portion in advance with respect to that in the central portion so that the rail surface near the rail end portion during cooling is substantially reduced. We invented a technology to make the cooling efficiency equal to that of the rail central part. As a specific method, the cooling air flow rate per unit time near the rail end is set to 50% or more and 80% or less of that in the central part, and the cooling air flow control range is set to within about 3 m from the rail end. I found it suitable. Here, when the cooling air flow rate is less than 50%, the hardness of the end portion is lowered to the central portion, and when the cooling air flow rate exceeds 80%, the hardness difference between the end portion and the center portion is hardly improved. In addition, as shown in FIG. 5, the air volume suppression range of the cooling header is 3 from the rail end.
If the length is more than 5 m and exceeds 5 m, there will be a portion where the hardness is lowered between the rail central portion and the rail end portion.

[0008]

Embodiments of the present invention will now be described with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIG. 1 is a side view of a cooling device to which a heat treatment method for rails according to a first embodiment of the present invention is applied (note that the cooling device is reduced in the rail length direction for easy understanding), and FIG. Is a cross-sectional view of the cooling device, FIG. 3 is a plan view of the nozzle plate, FIG. 4 is a graph showing the top hardness of the rail processed by the method of the first embodiment, and FIG. 5 is the head of the rail according to the comparative example. It is a graph which shows a top hardness.

As shown in FIGS. 1 and 2, a cooling device 1 to which the rail heat treatment method according to the first embodiment of the present invention is applied.
0 is a cooling header 12 on the top of the rail 11 to be heat-treated and a cooling header 1 on the head side of the rail 11.
3 and 14.

The cooling headers 12 to 14 are divided in the rail length direction, and in the vicinity of the rail ends, as shown in FIG. And the divided cooling headers 12A to 12C, 13A to 13C, 14A
To air supply pipes 15A to 15 respectively connected to
C, 16A to 16C, 17A to 17C have a flow rate adjusting valve 1
8A to 18C, 19A to 19C, 20A to 20C are provided respectively, and each divided cooling header 12A to
The amount of cooling air discharged from 12C, 13A to 13C, and 14A to 14C can be adjusted independently.
Then, each of the divided cooling headers 12A to 12C, 1
A nozzle plate 22 having nozzles 22a formed of small holes as shown in FIG. 3 is provided on the surfaces of 3A to 13C and 14A to 14C, and cooling air is blown out substantially uniformly from the nozzle plate 22.

In this embodiment, although there is a gap between the adjacent cooling headers 12 and 13 and the cooling headers 12 and 14, in order to improve the cooling efficiency,
Adjacent cooling headers 12 and 13 and cooling header 1
It is also possible to block the gap between 2 and 14 with a blind plate to prevent the airflow from being blown out obliquely from above. Further, the cooling device 10 is provided with an elevating device (not shown) for elevating and lowering the cooling headers 12 to 14 simultaneously, and the rail 11
Only when the above heat treatment is performed, the rail 11 is lowered to cover the rail 11. In FIG. 1, reference numeral 21 indicates a chain conveyor that conveys the rail 11.

In such a cooling device, the flow rate adjusting valves 18A to 18C, 19A to 19C, 20A to 20C are used.
To control the divided cooling headers 12A to 12C, 13A to 13C, 14A to 1 at a position 3m from the end.
The air volume per unit time from 4C is calculated by the cooling header 1
Corresponding length of the middle part of 2, 13, 14 (ie 1m)
FIG. 4 shows the hardness of the crown when the heat treatment of the rail 11 is performed by reducing the air volume per hit as shown in Table 1. Since airflow is more likely to occur in the rail longitudinal direction toward the rail end, it is preferable that the cooling header located at the rail end has a smaller air volume per unit time than the rail center side.

[0013]

[Table 1]

Next, a second embodiment of the present invention will be described. As in the first embodiment, the cooling header 12
~ 14 are divided into many, and each cooling header 12-14
In some cases, it is difficult to provide a flow rate adjusting valve so that the amount of air discharged from the device can be independently controlled (for example, an existing device). In such a case, it is possible to obtain the same effect as that of the above embodiment by changing the shape and / or the arrangement of the nozzles 22a of the nozzle plate 22. Also in this case, by changing the shape and / or the arrangement of the nozzle within the range of 3 m from the rail end, the cooling header within the range of 3 m from the rail end has an air discharge amount per unit area / unit time of the cooling header. Unit area discharged from the center of
It is set to 50% or more and 80% or less of the discharge amount per unit time.

In Table 2, the cooling header within 3 m from the rail end is divided into cooling zones of 1 m, and the diameter of the nozzle of the nozzle plate attached to each cooling zone is changed to change the cooling zone from each cooling zone per unit time. An example in which the average air discharge amount is changed with respect to the central portion of the cooling zone will be shown.
The results of heat-treating the rails using the cooling device having the cooling headers arranged at the top of the head and both sides of the head as described above were substantially the same as the results shown in FIG. this is,
Table 1 and Table 2 show the reduction rate of air within 3m from the rail end.
It is clear that and are almost equivalent.

[0016]

[Table 2]

Incidentally, FIG. 5 shows the hardness of the crown from the rail end when the air volume per unit time from the cooling header within a range of 5 m from the rail end is suppressed to about 60% substantially evenly. , The hardness distribution is not uniform as shown in the figure.
Therefore, it can be seen that it is sufficient to control the air volume of the cooling header 3 m from the rail end. Further, in the above-mentioned embodiment, since the distance between the rail end and the end of the cooling header is very small, the cooling header is improved by adding an improvement in the range of 3 m from the cooling header. When there is a distance between the end of the rail and the end of the rail, the air volume of the cooling header portion within a range of 3 m from the end of the rail is controlled.

[0018]

According to the rail heat treatment method of the present invention, the average air discharge amount per unit time of the cooling header for cooling a range within about 3 m from the rail end portion is defined as the central portion in the rail length direction. Since 50% or more and 80% or less of the average air discharge amount per unit time of the rail is corrected, the movement of air in the rail length direction is corrected and the rail is heat-treated evenly, whereby the hardness of the top of the rail is uniform. become. As a result, the wear caused by the use of rails was evened out, train travel was smooth, and track maintenance costs were reduced.

[Brief description of drawings]

FIG. 1 is a side view of a cooling device to which a rail heat treatment method according to a first embodiment of the present invention is applied.

FIG. 2 is a cross-sectional view of the cooling device.

FIG. 3 is a plan view of a nozzle plate.

FIG. 4 is a graph showing the hardness of the rail top from the rail end when the first embodiment of the present invention is applied.

FIG. 5 is a graph showing the hardness of the top of the rail head with the air volume per unit time from the cooling header within a range of 5 m from the rail end portion suppressed to 60%.

FIG. 6 is a graph showing the hardness of the rail crown from the rail end when the heat treatment method according to the conventional example is applied.

[Explanation of symbols]

 10 Cooling Device 11 Rail 12 Cooling Header 12A Split Cooling Header 12B Split Cooling Header 12C Split Cooling Header 13 Cooling Header 13A Split Cooling Header 13B Split Cooling Header 13C Split Cooling Header 14 Cooling Header 14A Split cooling header 14B Split cooling header 14C Split cooling header 15A Air supply pipe 15B Air supply pipe 15C Air supply pipe 16A Air supply pipe 16B Air supply pipe 16C Air supply pipe 17A Air supply pipe 17B Air supply pipe 17C Air supply pipe 18A Flow rate adjusting valve 18B Flow rate adjusting valve 18C Flow rate adjusting valve 19A Flow rate adjusting valve 19B Flow rate adjusting valve 19C Flow rate adjusting valve 20A Flow rate adjusting valve 20B Flow rate adjusting valve 20C Flow rate adjusting valve 21 Chain Conveyors 22 nozzle plate 22a nozzle

Claims (1)

[Claims] 1. A heat treatment method for a rail, wherein a hot-rolled rail is directly heat-treated by a cooling device having a cooling header and using air as a cooling medium to surround substantially the entire length of the rail head. The average air discharge amount per unit time of the cooling header for cooling a range within about 3 m from the rail end portion is set to 50% or more and 80% or less of the average air discharge amount per unit time of the rail length direction central portion. A heat treatment method for a rail, which is characterized in that