This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP02/09252 filed Sep. 11, 2002.
The present invention relates to a method for cooling a steel plate, more specifically, a method for uniformly cooling a steel plate on a production line after hot rolling, and an apparatus therefor.
When performing on-line cooling of a hot rolled steel plate, it is difficult to uniformly cool upper and lower surfaces of the steel plate with the same cooling capability. Particularly, on the lower surface, after impingement of cooling water upon the steel plate, the cooling water is immediately moved away by the force of gravity from the steel plate. As such, no cooling beyond cooling only with impinging water jets can be accomplished, so that the cooling capability for the lower surface is lower than that for the upper surface of the steel plate. For this reason, conventionally, uniformity of cooling has been implemented by changing a volume of the cooling water that is applied to the upper and lower surfaces of the steel plate. However, depending on temperature, thickness, and the like factors of the steel plate, and temperature of the cooling water, an optimal volume of the cooling water on the upper and lower surfaces is different. This makes it difficult to implement uniform cooling therefore facilitating occurrence of cooling nonuniformity. As such, the steel plate after cooling can have problems of deformation, residual stress, and nonuniformity in properties, consequently leading to operational troubles and deterioration in production yield.
In order to solve these problems, various cooling apparatuses have been proposed, such as those for enhancing cooling capability for a lower surface of steel plate and those for uniformly cooling upper and lower surfaces of steel plate.
Japanese Examined Patent Publication No. 63-4604 discloses a cooling apparatus as shown in
This cooling apparatus has a water tank 2 provided with a predetermined spacing on a lower surface side of a steel plate 1; a round-tubular cooling nozzle 3 vertically fixed to a bottom portion of the water tank 2; and a conduit 4 that is vertically installed in an upper portion of the cooling nozzle 3 and that has a cross section substantially similar to a cross section of the cooling nozzle 3 and larger than the cross section of the cooling nozzle 3. A top portion of the cooling nozzle 3 and a bottom portion of the conduit 4 are positioned below the water surface, and a top portion of the conduit 4 is exposed above the water surface.
The cooling nozzle 3 having the conduit 4 is called an induced laminar flow nozzle (for water cooling) 6. The publication describes that the lower surface of the steel plate 1 can be stably and uniformly cooled by the nozzle, and the cooling capability can be controlled in a wide range.
Japanese Unexamined Patent Application Publication No. 10-166023 discloses a cooling apparatus as shown in
This cooling apparatus has cooling nozzles 3A installed on an upper surface side of a steel plate 1 and cooling nozzles 3B installed on a lower surface side of a steel plate 1 between individual sets of transfer rollers 7. The number of the cooling nozzles 3B on the lower surface side is larger than the number of the cooling nozzles 3A on the upper surface side. In addition, between the individual sets of the transfer rollers 7, the cooling nozzles 3A and 3B are disposed so that cooling starts synchronously for the upper and lower surfaces of the steel plate 1. The publication describes that the arrangement equalizes cooling capabilities for the upper and lower surfaces of the steel plate 1. The publication further describes that when the induced laminar flow nozzles of the type described above are used for the cooling nozzles 3B on the lower surface side of the steel plate, even more uniform cooling can be implemented for the upper and lower surfaces, occurrence of distortion is prevented, and in addition, nonuniformity in properties is reduced.
However, problems remain even in the case that the cooling apparatus described in Japanese Examined Patent Publication No. 63-4604 or Japanese Unexamined Patent Application Publication No. 10-166023 is used. In this case, in the top (front) portion of the steel plate, the temperature significantly drops after hot rolling, and in addition, the super cooling is liable to occur because of turbulent flows of the cooling water, consequently causing camber of the steel plate. Especially, when the induced laminar flow nozzles as described in Japanese Examined Patent Publication No. 63-4604 are used, since the cooling water once returned into the water tank after cooling of the steel plate is used to cool the center portion of the steel plate, the temperature of the water is high. This causes significant super cooling of the top portion of the steel plate, thereby further facilitating occurrence of camber.
Japanese Examined Patent Publication No. 5-61005 discloses a method proposed to prevent such super cooling in the top portion of the steel plate. According to the method, a shield plate movable downwardly of the steel plate is installed, and cooling water drawn up from the lower surface side is thereby prevented from going up to the upper surface of the steel plate.
According to the method, however, the top portion of the steel plate is not cooled at any time because of the shield plate, so that uniform cooling cannot be performed in the longitudinal direction of the steel plate.
An object of the present invention is to provide a method for uniformly cooling a steel plate and therefore preventing a top portion of the steel plate from being super cooled, when performing on-line cooling of the steel plate after hot rolling, and an apparatus therefor.
The object is achieved by a method for cooling a steel plate comprising the steps of: forming a water pool with jets of cooling water being injected to impinge on one another by using one slit nozzle and a plurality of induced laminar flow nozzles, the slit nozzle being provided in a position on an upper surface side of the steel plate, and the induced laminar flow nozzles being provided in a position on a lower surface side of the steel plate along a transfer direction and a direction perpendicular to the transfer direction; and passing the steel plate into the water pool, wherein when a top portion of the steel plate passes over the induced laminar flow nozzles located at least on the side of highest upstream, a volume of the cooling water to be injected from each of the induced laminar flow nozzles is reduced. It is particularly effective that the cooling method is repeatedly carried out a plurality of times.
The method described above can be implemented using a cooling apparatus comprising: one slit nozzle provided in a position on an upper surface side of the steel plate; and a plurality of induced laminar flow nozzles provided in a position on a lower surface side of the steel plate along a transfer direction and a direction perpendicular to the transfer direction, wherein a plurality of cooling zones are provided for cooling the steel plate by forming a water pool with cooling water being injected from the slit nozzle and the induced laminar flow nozzles, and a cooling water control means is provided in the cooling zone located on the side of highest upstream among the plurality of cooling zones to control a volume of the cooling water to be injected from each of the induced laminar flow nozzles located at least on the side of highest upstream.
The first feature of the cooling method of the present invention lies in that to uniformly cool a steel plate by equalizing cooling capabilities for the upper and lower surfaces of the steel plate, cooling water is injected from one slit nozzle provided on the upper surface side of the steel plate and a plurality of induced laminar flow nozzles provided on the lower surface side of the steel plate so that jets of the cooling water impinge upon each other in such a manner as to form a water pool, and then the steel plate is passed into the water pool.
The present method avoids a phenomenon, as is observed in a conventional method, that the cooling water is injected from the cooling nozzles toward the upper and lower surfaces of the steel plate, water-volume densities are therefore increased in portions where the cooling water are brought into contact with the steel plate, and the portions are super cooled as compared with peripheral portions, thereby causing cooling nonuniformity.
The steel plate is cooled in a water pool formed by one slit nozzle provided on the upper surface side of the steel plate and a plurality of induced laminar flow nozzles provided on the lower surface side of the steel plate. Thereby, the steel plate and the cooling water can be brought into secure contact with each other, and the cooling capabilities for the lower surface of the steel plate can be enhanced. Consequently, uniform cooling can be implemented.
In comparison,
Compared with
The second feature of the cooling method according to the present invention lies in that to prevent the top (front) portion of the steel plate from being super cooled, the volume of cooling water injected from each of induced laminar flow nozzles is reduced when the top portion of the steel plate passes over the induced laminar flow nozzles on the side of highest upstream.
As shown in
As shown in
As described above, in order to prevent such camber in the top portion, when the top portion of the steel plate passes at least over the induced laminar flow nozzles located on the side of highest upstream, the volume of the cooling water injected from each of the induced laminar flow nozzles may preferably be reduced to prevent the top portion of the steel plate from being super cooled.
Shown in
As shown in
When the cooling water is completely blocked by using the shield plate 8, distortion can generate in the steel plate because of a difference in the first contact positions with the cooling water between the upper and lower surfaces of the steel plate in the transfer direction. For this reason, it is preferable that the half of an opening of each of the induced laminar flow nozzles 6A be closed to reduce the volume of the cooling water to about ½ of the normal volume of the cooling water.
Ordinarily, the shield plate 8 is positioned where the openings of the induced laminar flow nozzles 6A are each fully opened. However, when the top portion of the steel plate is detected by sensors (not shown) located between sets of transfer rollers 7, the shield plate 8 horizontally moves to close the half of the opening of each of the induced laminar flow nozzles 6A. After the top portion of, the steel plate passes over the induced laminar flow nozzles 6A, the shield plate 8 is horizontally moved to fully open the openings of the individual induced laminar flow nozzles 6A. Thereby, cooling capabilities for the upper and lower surfaces of the steel plate are equalized.
The induced laminar flow nozzles 6 to be closed by the shield plate 8 are not always limited to one line of nozzles on the side of highest upstream, but may be provided in a plurality of lines of nozzles.
By repeating the operations described above in the subsequent cooling zones, the top portion of the steel plate can be prevented substantially completely from being super cooled. These operations should only be conducted until uniform temperature distribution is attained on the upper and lower surfaces of the steel plate; that is, the operations need not be performed in all the cooling zones.
When the steel plate is cooled by repeating the above described operations in a plurality of cooling zones, if the steel plate is air cooled in at least two of the cooling zones, water cooling and air cooling can be alternately performed, which allows to control the properties of the steel plate in a wider range.
Provision of a flow regulating valve in each of the cooling zones enables finer cooling control of the steel plate. In the case that water cooling and air cooling are alternately performed, the flow regulating valve may be replaced with an on/off valve.
When the top portion of the steel plate passes in each of the cooling zones, if not only the volume of the cooling water to be injected from induced laminar flow nozzles but also the volume of the cooling water to be injected from a slit nozzle is reduced, temperature drop in the top portion of the steel plate can be prevented.
In the present invention, it is effective to dispose a rectifying means on an entrant side of the cooling zone located on the side of highest upstream, whereby the steel plate is rectified and then cooled. This enables uniform cooling and prevention of distortion during cooling. The rectifying means is used to rectify hot steel plates having a thickness of 50 mm or less, so that it may be of the type having a simple construction as compared with an ordinary hot rectifying machine.
Using the individual cooling methods as shown in
The result is shown in Table 1.
In the cases of the examples 1 to 3 cooled by using the method shown in
However, although the method shown in
Number | Date | Country | Kind |
---|---|---|---|
2001-290004 | Sep 2001 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP02/09252 | 9/11/2002 | WO | 00 | 4/30/2004 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO03/026813 | 4/3/2003 | WO | A |
Number | Date | Country |
---|---|---|
0 080 932 | Jun 1983 | EP |
358157517 | Sep 1983 | JP |
60-43435 | Mar 1985 | JP |
60070126 | Apr 1985 | JP |
361229414 | Oct 1986 | JP |
62021413 | Jan 1987 | JP |
63-168215 | Jul 1988 | JP |
2-179828 | Jul 1990 | JP |
2000-1719 | Jun 1998 | JP |
10166023 | Jun 1998 | JP |
410291019 | Nov 1998 | JP |
11-347629 | Dec 1999 | JP |
Number | Date | Country | |
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20040244886 A1 | Dec 2004 | US |