Patent Application
20150027599
The present invention relates to a rail cooling method and a rail cooling device for forcibly cooling, with a coolant such as air or water, a high-temperature rail immediately after hot rolling or a high-temperature rail heated to an austenitic temperature range for heat treatment after hot rolling so that a head part thereof has a fine pearlitic microstructure.
Conventionally, to cause a head part of a rail to have the fine pearlitic microstructure to improve wear resistance and toughness of the rail, forcible cooling with the coolant such as air or water has been performed on the head part (a head top part and a head side part) of a high-temperature rail immediately after hot rolling or a high-temperature rail heated to an austenitic temperature range for heat treatment after hot rolling. In this case, if only the head part of the rail is forcibly cooled, an asymmetrical temperature range is formed in the vertical direction of the rail, so that the rail may be largely bent due to a stress existing inside the rail after cooling. So an underside of the base of the rail is also forcibly cooled.
Patent Literature 1 discloses a porous plate having cooling nozzle holes for forcibly cooling a rail. Patent Literature 2 discloses a technique for preventing a rail after forcible cooling from bending by starting forcible cooling of an underside of the base of the rail earlier than forcible cooling of a head part of the rail to precool the underside of the base. Patent Literature 3 discloses a technique for uniformizing hardness of a rail in the longitudinal direction by controlling a discharge amount of air for forcible cooling toward the vicinity of an end of the rail.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2002-105538
Patent Literature 2: Japanese Laid-open Patent Publication No. 10-130730
Patent Literature 3: Japanese Laid-open Patent Publication No. 7-216455
Rail manufacturing facilities are required to increase cooling speed for a rail to increase a production capacity thereof. As a countermeasure against the above, the number of porous plates having cooling nozzle holes may be increased, for example. In addition, as described later, material uniformity should be taken into consideration.
Conventionally, as quality of a rail, only quality of a rail head part to be in contact with a wheel has attracted attention. However, in recent years, demands for quality of a base of the rail have been increasing with a situation in which high-strength rails are increasingly demanded with increasing speed and weight of a railroad vehicle. Accordingly, it is expected to uniformize mechanical characteristic values represented by hardness of the base of the rail. However, any of the Patent Literatures described above does not disclose a technique for uniformizing mechanical characteristic values in the width direction of the base of the rail.
The present invention is made in view of such a situation, and provides a rail cooling method and a rail cooling device that can uniformize the mechanical characteristic values in the width direction of the base of the rail.
To solve the above-described problem and achieve the object, a rail cooling method according to the present invention is a rail cooling method for forcibly cooling a rail by jetting a coolant and includes jetting the coolant to an underside of the base of the rail from a porous plate nozzle in which a nozzle hole at an end in a width direction is smaller than a nozzle hole at a central part in the width direction and causes a cooling capacity for the end in the width direction of the underside of the base of the rail to be lower than a cooling capacity for the central part in the width direction of the underside of the base of the rail.
Moreover, in the above-described rail cooling method according to the present invention, the nozzle holes have a circular shape, and a diameter of the nozzle hole at the end is 20% to 90% of a diameter of the nozzle hole at the central part.
Moreover, a rail cooling device according to the present invention is configured to forcibly cool a rail by jetting a coolant and includes a porous plate nozzle including a plurality of nozzle holes configured to jet the coolant that are opposed to an underside of the base of the rail to cool the underside of the base of the rail, wherein the nozzle hole at an end in a width direction is formed to be smaller than a nozzle hole at a central part to cause a cooling capacity for the end in the width direction of the underside of the base of the rail to be lower than a cooling capacity for the central part in the width direction of the underside of the base of the rail.
Moreover, in the above-described rail cooling device according to the present invention, the nozzle holes have a circular shape, and a diameter of the nozzle hole at the end is 20% to 90% of a diameter of the nozzle hole at the central part.
According to the present invention, a flow rate of the coolant with respect to the end in the width direction of the underside of the base of the rail is controlled, so that the mechanical characteristic values in the width direction of the base of the rail can become uniform.
The following describes an embodiment of the present invention in detail with reference to drawings. The present invention is not limited to the embodiment. Through the drawings, the same components are denoted by the same reference numerals.
First, the following describes a schematic configuration of a rail cooling device 1 according to the embodiment with reference to
The head top part cooling device 2 includes a head top part cooling nozzle header 2a and a head top part cooling nozzle 2b provided to the head top part cooling nozzle header 2a. The head side part cooling device 3 includes a head side part cooling nozzle header 3a and a head side part cooling nozzle 3b provided to the head side part cooling nozzle header 3a. The cooling device for the underside of the base 5 includes a cooling nozzle header for the underside of the base 5a and a porous plate nozzle 5b provided to the cooling nozzle header for the underside of the base 5a.
The porous plate nozzle 5b of the cooling device for the underside of the base 5 is arranged in a manner opposed to the underside of the base 13a of the rail 10. The porous plate nozzle 5b includes a plurality of nozzle holes arranged therein for jetting a coolant in the width direction of the rail 10 and the longitudinal direction of the rail 10.
An opening shape of each nozzle hole 51 may be an ellipse or a polygon. However, to facilitate processing of the nozzle hole, the opening shape of each nozzle hole 51 is preferably a circle. In this case, a diameter of each of the nozzle holes 51a at both ends of each column is preferably 20% or more and 90% or less of a diameter of each of the nozzle holes 51b at the central part, and more preferably, 50% or more and 85% or less thereof. In the embodiment, the diameter of each of the nozzle holes 51a at both ends of each column is formed to be 20% or more and 90% or less of the diameter of each of the nozzle holes 51b at the central part other than both ends.
To further optimize the size of the nozzle holes 51 (for example, a nozzle diameter) at the central part and at both ends, the following method may be employed. Among three main factors in cooling behavior on a surface of the underside of the base 13a of the rail 10, that is, a distance between the surface of the underside of the base 13a and the nozzle hole 51 (hereinafter, referred to as a jet distance), an interval between the nozzle holes 51 in the width direction (hereinafter, also simply referred to as a nozzle interval), and a size of the nozzle hole 51 (hereinafter, represented by the nozzle diameter for description), the jet distance that is largely affected by restrictions on a device is assumed to be a constant value. In addition, influence of the nozzle diameter and the nozzle interval on a distribution of the cooling behaviors (for example, a heat transfer coefficient on the surface of the underside of the base 13a) in the width direction is examined to determine the nozzle diameter and the nozzle interval so that the cooling speed is substantially the same at a central part 13c and at both ends 13b of the base 13 while taking a thickness distribution of the base 13 into consideration.
The maximum value of the distance between the centers of the nozzle holes 51a at both ends of each column is preferably 30% or more of the width of the underside of the base 13a of the rail 10. As an arrangement of the nozzle holes 51, a staggered arrangement may be employed as illustrated in
The porous plate nozzle 5 is arranged so that a center line in the width direction thereof coincides with a center line in the width direction of the rail 10. The cooling device for the underside of the base 5 of the rail cooling device 1 then jets the coolant from the porous plate nozzle 5b to forcibly cool the entire length of the underside of the base 13a of the rail 10.
With the porous plate nozzle 5b configured as described above, the flow rate of the coolant to the underside of the base 13a of the thin end 13b in the width direction of the base 13 of the rail 10 is controlled to be smaller than that to the central part in the width direction of the underside of the base 13a, so that a cooling capacity for the end in the width direction of the underside of the base 13a of the rail is lowered compared to a cooling capacity for the central part in the width direction of the underside of the base 13a. Accordingly, the temperature lowering speed is controlled at the end 13b in the width direction of the base 13, and a difference between the cooling speed for the end 13b and the cooling speed for the central part 13c in the width direction of the base 13 is reduced, so that variation in the mechanical characteristic values in the width direction of the base 13 of the rail 10 can be suppressed.
Conventionally, a ratio of the maximum value of the distance between the centers of the nozzle holes 51a at both ends in the width direction of the porous plate nozzle 5a to the width of the underside of the base 13a of the rail 10 has been normally about 15 to 25%. When the ratio is increased to 30% or more, the flow rate of the coolant to the entire underside of the base 13a of the rail 10 is increased, so that time required for cooling can be shortened.
Regarding the arrangement of the nozzle holes 51 in the porous plate nozzle 5b, by reducing a density of the nozzle holes at the end in the width direction with respect to that at the central part in the width direction, that is, by reducing the number of nozzle holes 51 per unit length in the longitudinal direction at the end in the width direction with respect to that at the central part in the width direction, the cooling capacity for the end in the width direction of the underside of the base 13a is set to be lower than the cooling capacity for the central part of the underside of the base 13a, so that it is possible to reduce a difference between average cooling speed at the end 13b and average cooling speed at the central part 13c in the width direction of the base 13. However, in this case, the mechanical characteristic values of the base 13 of the rail 10 cannot become uniform in the width direction due to the following reason. As described above, the rail cooling device 1 forcibly cools the rail 10 while oscillating (reciprocating) the supporting and restraining device for the rail 10 and various cooling devices in the longitudinal direction of the rail 10. That is, a jet of the coolant is prevented from concentrating on a specific position in the longitudinal direction by reciprocating the nozzle holes 51 in the longitudinal direction of the rail 10. The coolant from the nozzle hole 51a intermittently strikes a certain position in the longitudinal direction of the rail 10 by performing the oscillation, so that cooling and non-cooling are alternatively repeated. When the density of the nozzle holes 51a in the porous plate nozzle 5b is set to be smaller at the end in the width direction than the density of the nozzle holes 51b at the central part in the width direction, the interval between the nozzle holes 51a adjacent to each other in the longitudinal direction increases at the end in the width direction. In this case, time during which the coolant strikes the end in the width direction of the underside of the base 13a of the rail 10 while the nozzle hole 51a reciprocates once is shortened, so that a recuperative process occurs during the non-cooling operation. Accordingly, even if the average cooling speed at the end 13b in the width direction of the base 13 may be equal to the average cooling speed at the central part 13c from cooling start to cooling end, it is not possible to reduce variation in the mechanical characteristic values in the width direction or in the longitudinal direction of the base 13.
If an oscillation cycle is shortened, the recuperative process during the non-cooling operation of the rail 10 is prevented from occurring even when the density of the nozzle holes 51 in the porous plate nozzle 5b is smaller at the end than that at the central part in the width direction. However, to shorten the oscillation cycle, it is necessary to move the supporting and restraining device for the rail 10 or the various cooling devices in the longitudinal direction of the rail 10 at high speed, which is not practical.
Instead, when the diameter of the nozzle hole 51 in the porous plate nozzle 5b is reduced and the number of nozzle holes 51 per unit length in the longitudinal direction is increased, the recuperative process during the non-cooling operation of the rail 10 is prevented from occurring even if the density of the nozzle holes 51 in the porous plate nozzle 5b is smaller at the end than that at the central part in the width direction. Herein, to prevent the nozzle hole 51 from being clogged with dust and dirt, the diameter of the nozzle hole 51 is preferably 1 mm or more. However, with the nozzle hole 51 having the diameter of 1 mm or more, even if the number thereof is increased, the mechanical characteristic values of the base 13 of the rail 10 cannot become uniform in the width direction when the present density thereof at the end is smaller than that at the central part in the width direction.
Based on the above reason, in the porous plate nozzle 5b according to the embodiment, the density of the nozzle holes 51 is the same at the end in the width direction and at the central part, and the nozzle hole 51a at the end in the width direction is formed to be smaller than the nozzle hole 51b at the central part.
As described above, with the rail cooling device 1 according to the embodiment, the flow rate of the coolant to the end in the width direction of the underside of the base 13a of the rail 10 is controlled, so that the difference between the cooling speed at the end 13b in the width direction and the cooling speed at the central part 13c of the base 13 is reduced and the mechanical characteristic values can become uniform in the width direction of the base 13 of the rail 10. The flow rate of the coolant to the entire underside of the base 13a of the rail 10 is increased, so that the time required for cooling can be shortened.
In the embodiment described above, it is assumed that the diameters of only the nozzle holes 51a at the ends in the width direction of the porous plate nozzle 5b are reduced. Alternatively, the diameter of the nozzle hole is formed to be smaller toward the end taking the diameter of the nozzle hole at the center in the width direction of the porous plate nozzle 5b as the maximum.
The embodiment described above is merely an example for implementing the present invention. The present invention is not limited thereto. Various modifications corresponding to a specification and the like are within the scope of the present invention. It is obvious from the above description that other various embodiments can be employed within the scope of the present invention.
In the present example, an experiment of the rail cooling processing was performed with the rail cooling device 1 according to the embodiment while changing the configuration of the porous plate nozzle 5b. A width of an underside of the base of a rail used for the experiment is 152 mm.
In the case of the models A3a, A3b, and A3c, variation in hardness in three examples are presented, where the method for reducing the number of the nozzle holes at the ends is modified. Any of numerical values thereof is smaller than that of the model A1 but larger than that of the model A2. This may be because, when the number of nozzle holes at the ends in the width direction is reduced, time during which the nozzle hole is not opposed to the end in the width direction of the underside of the base 13a is elongated during one oscillation (reciprocation), cooling is not sufficiently performed, and the recuperative process occurs, so that a difference between the hardness at the end 13b in the width direction of the base 13 and the hardness at the central part 13c is increased and the variation in hardness increases in the entire base 13. Even when the maximum speed of the oscillation is changed within a range of practical operation, the mechanical characteristic values of the base 13 of the rail 10 could not be equalized between the end 13b in the width direction and the central part 13c. Accordingly, it has been found that, when the density of the nozzle holes is set being equal between the end in the width direction and the central part as in the model A2 and the diameter of the nozzle holes at both ends of each column in the width direction is reduced, the variation in the mechanical characteristic values in the width direction of the base 13 of the rail 10 can be preferably suppressed.
The present invention can be applied to processing for forcibly cooling, with the coolant such as air or water, the high-temperature rail immediately after hot rolling or the high-temperature rail heated to the austenitic temperature range for heat treatment after hot rolling to cause the head part of the rail to have a fine pearlitic microstructure.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/JP2012/052345 | Feb 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/052355 | 2/1/2013 | WO | 00 |
