Patent Grant
10086418
This application is the U.S. National Phase under 35 U.S.C. § 371 of International Patent Application No. PCT/KR2012/011542, filed on Dec. 27, 2012, which in turn claims the benefit of Korean Patent Application No. 10-2012-0150135, filed on Dec. 21, 2012, the disclosures of which Applications are incorporated by reference herein.
The present disclosure relates to a shape-correcting and rolling method and a shape-correcting device for high-strength steel, and more particularly, to a shape-correcting and rolling method and a shape-correcting device using heat pipe rollers for correcting the shape of high-strength steel within a warm working temperature range.
The strength of steel sheets used in the automobile industry has been constantly increased to allow automobiles satisfying environmental regulations and having high fuel efficiency to be manufactured. However, it is difficult to form high-strength steel strips into desired shapes, and the load required in processes for correcting the shapes of high-strength steel strips is high. In addition, even in the case that high-strength steel is processed using a shape-correcting process, the shape of the high-strength steel may not be easily corrected. Due to this reason, after increasing the temperature of a steel strip, the shape of the steel strip may be corrected. In this case, if the strip is corrected within a warm working temperature range without using a roll cooling device, work rolls may be heated by the strip and expanded to have a large crown shape known as a thermal crown, and thus, uncontrollable severe wave shapes may be formed in the center region of the strip, rendering the strip useless as a product.
Moreover, in a correcting process, a large amount of scale formed on a steel strip may be separated therefrom, and when cooling water is applied to cool rolls, the separated scale may scatter to cause secondary surface defects, thereby making it difficult to use cooling water.
In the related art, cooling is not performed due to this reason, and thus, a shape-correcting process is restrictively performed at a strip temperature of about 50° C. In this case, however, the effect of the shape-correcting process is low, and the number of steel strips that can be continuously rolled is limited. In addition, it is necessary to supply a warm-rolling workpiece immediately before rolls are changed and to change the rolls after warm rolling.
Patent Document 1 (please refer to
However, Patent Documents 1 and 2 only state the effects of a shape-correcting process or a skin pass milling process performed within a warm-working temperature range higher than room temperature but do not state how the shape-correcting process is practically performed within the warm-working temperature range. That is, Patent Documents 1 and 2 do not disclose the possibility of shape errors caused by deformation of rolls heated when a strip is merely corrected at a temperature higher than room temperature.
(Patent Document 1) KR10-1153732 B
(Patent Document 2) JPH10-005809 A
An aspect of the present disclosure may provide a shape-correcting and rolling method for effectively correcting the shape of high-strength steel.
An aspect of the present disclosure may also provide a shape-correcting device for high-strength steel. The shape-correcting device may optimally correct the shape of a strip of high-strength steel regardless of the temperature of the strip, the number of rolled coils, and the feeding order of workpieces.
An aspect of the present disclosure may also provide a shape-correcting and rolling method for high-strength steel and a shape-correcting device for high-strength steel, designed to reduce or remove a waiting period in a yard, which can last for three to five days in the related art and thus to directly connect a hot rolling and coiling process to a shape-correcting and rolling process.
To achieve the above-mentioned aspects of the present disclosure, a shape-correcting and rolling method and a shape-correcting device are provided.
According to an aspect of the present disclosure, a shape-correcting and rolling method for high-strength steel may include: performing a hot rolling to skin pass mill direct transfer process by transferring a hot-rolled coil to a pay-off reel; unwinding a strip from the coil of the pay-off reel; correcting a shape of the strip by using a heat pipe roller; and rewinding the strip as a coil.
According to another aspect of the present disclosure, a shape-correcting and rolling method for high-strength steel may include: performing a first transfer process by transferring a hot-rolled coil to a temperature adjusting unit; cooling the coil while monitoring a temperature of the coil; performing a second transfer process by transferring the coil cooled to a temperature of 150° C. or higher to a pay-off reel; unwinding a strip from the coil of the pay-off reel; correcting a shape of the strip by using a heat pipe roller; and rewinding the strip as a coil.
Prior to the correcting of the shape of the strip, the method may further include rolling the strip at a reduction ratio of 20% to 30%, and prior to the rolling of the strip, the method may further include removing scale from surfaces of the strip by shot blasting.
In the correcting of the shape of the strip, the strip may have a temperature equal to or higher than 150° C. but lower than a phase transformation temperature.
The method may further include warm-rolling the strip continuously after the rewinding of the strip.
The cooling of the coil may include: measuring the temperature of the coil; and comparing the measured temperature of the coil with a predetermined temperature range so as to determine whether the measured temperature of the coil is within the predetermined temperature range.
The cooling of the coil may be performed by placing the coil on a skid in a yard, and a thermocouple disposed in the skid may indirectly measure the temperature of the coil by measuring a temperature of the skid heated by the coil placed on the skid.
A heat insulating process may be performed on the coil during the unwinding of the coil, so as to prevent cooling of the coil.
Prior to the correcting of the shape of the strip, the method may further include heating the strip so that the strip may have a uniform temperature.
The correcting of the shape of the strip may be performed using a skin pass mill which includes a pair of heat pipe rollers making contact with the strip and backup rolls supporting the heat pipe rollers.
Each of the heat pipe rollers may include a plurality of first heat pipes extending in a length direction of the heat pipe roller from an end to a center region of the heat pipe roller and a plurality of second heat pipes extending from an opposite end to a center region, and the first and second heat pipes may be alternately arranged in a circumferential direction of the heat pipe roller.
The first and second heat pipes may overlap each other in the center region in the length direction of the heat pipe roller.
According to another aspect of the present disclosure, a shape-correcting device for high-strength steel may include: a pay-off reel from which a coil is unwound; a skin pass mill correcting a strip unwound from the coil of the pay-off reel; and a coiler rewinding the strip after the strip passes through the skin pass mill, wherein the skin pass mill may include a work roll that is a heat pipe roller in which heat pipes are installed.
The heat pipes may include a plurality of first heat pipes extending in a length direction of the work roll from an end to a center region of the work roll and a plurality of second heat pipes extending from an opposite end to a center region, and the first and second heat pipes may be alternately arranged in a circumferential direction of the work roll.
The heat pipes may be uniformly arranged in the circumferential direction of the work roll at a predetermined insertion depth.
A heating device may be disposed between the pay-off reel and the skin pass mill so as to heat the strip to a temperature equal to or higher than 150° C. but lower than a phase transformation temperature.
The first and second heat pipes may overlap each other in the center region in the length direction of the work roll.
The method may further include a shot blaster configured to shoot steel balls having a micrometer (μm) size toward the strip and a rolling mill disposed behind the shot blaster to roll the strip, wherein the shot blaster and the rolling mill may be disposed between the pay-off reel and the skin pass mill.
As described above, the present disclosure provides a shape-correcting device and a shape-correcting device for effectively correcting the shape of high-strength steel.
According to the shape-correcting and rolling method and the shape-correcting device of the present disclosure, the shape of a strip of high-strength steel may be optimally corrected regardless of the temperature of the strip, the number of rolled coils, and the feeding order of workpieces.
In addition, according to the shape-correcting and rolling method and the shape-correcting device of the present disclosure, a waiting period in a yard which normally lasts three to five days in the related art may be reduced or removed to directly connect a hot rolling and coiling process to a shape-correcting and rolling process. Therefore, yards may be efficiently used, and inventory may be reduced or storage thereof may be unnecessary.
Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.
Generally, the temperature of rolls increases during a shape-correcting process, and thus rolls are designed to have initial thermal crown shapes in consideration of thermal expansion. However, if the process temperature of a shape-correcting process is increased, the temperature of rolls is also varied as the shape-correcting process proceeds. In this case, a proper initial roll shape is also varied. In addition, since the temperature of strips supplied to a correcting device is not uniform, the shapes of rolls are varied each time a new strip is supplied or while a strip is being fed. Therefore, initial roll crown shapes have to be changed. Due to this reason, the method of providing an initial thermal crown shape to a roll is not practical.
Particularly, if the shape of high-strength steel is corrected merely after increasing the temperature of the high-strength steel, shape errors occur due to a thermal crown, and thus the method of giving an initial thermal crown shape to a roll is not used.
According to the present disclosure, thin, wide, high-strength steel strips may be manufactured using a shape-correcting device through a shape-correcting process including a correcting process using heat pipe rollers.
Referring to
In the shape-correcting line, the coil is unwound using a pay-off reel 30, and the strip unwounded from the coil undergoes a scale removing process in which scale is removed from the strip by using a shot blaster 31. Thereafter, the temperature of the strip is uniformized using a heating device 32, and then the strip is first rolled by a rolling mill 33 and is then shape-corrected by a skin pass mill 40. Next, the strip is rewound by a coiler 35.
At this time, the skin pass mill 40 uses heat pipe rollers 100 to correct the shape of the strip. Thermal crowns of the heat pipe rollers 100 may be maintained at a constant level even in the case that the strip introduced between the heat pipe rollers 100 has a temperature of 150° C. or higher, and since the strip has a temperature of 150° C. or higher, the shape of the strip may be easily corrected even in the case that the strip is a high-strength steel strip.
The rewound coil is directly subjected to a rolling process in warm-working conditions, in which the strip is unwound from the coil using a pay-off reel 50 and is then rolled by six to eight rolling mills 51.
In the first embodiment, the hot rolling mills 1, the cooling device 2, and the coiler 3 are the same as those of the related art, and thus detailed descriptions thereof will be omitted.
In the present disclosure, since a strip having a temperature of 150° C. or higher is supplied to the shape-correcting line, a time necessary for a cooling process 20 may be reduced. Particularly, since the rate of cooling is relatively high at high temperature and relatively low at low temperature, the time necessary for the cooling process 20 may be markedly reduced to about one day, as compared to the related art, requiring three to five days.
Therefore, the flow of coils may be improved in the yard in which the cooling process 20 is performed, and thus the amount of inventory may be reduced. The cooling process 20 will be explained later in detail with reference to
In the present disclosure, while the strip unwound from the pay-off reel 30 passes through the shot blaster 31, scale is removed from the strip. Then, when the strip passes through the rolling mill 33, the strip may not be damaged due to scale. When electrical steel strips or stainless steel strips are produced, before a pickling process, shot blasters are generally used to remove scale from the surfaces of the steel strips by shooting steel balls having a diameter of several tens of micrometers (μm) toward a strip from the upper and lower sides of the strip using centrifugal force.
After scale is removed from the strip using the shot blaster 31, the strip passes through the heating device 32. As long as the heating device 32 uniformizes the temperature of the strip, the heating device 32 may not heat the strip to a constant temperature. The heating device 32 may be an induction heater. When the strip is rolled using the rolling mill 33, if a model defining the relationship between an initial roll gap and a roll speed is operated based on logic for compensating for roll gap variations caused by temperature variations, the heating device 32 may not be used.
The rolling mill 33 performs a one-step rolling process at a reduction ratio of about 20% to about 30%. If the reduction ratio is greater than about 30%, shape errors may be increased to a degree to which the shape errors may not be corrected by the skin pass mill 40. Since the strip having a high degree of strength is rolled by the rolling mill 33 at a temperature of 150° C. or higher, the effect of rolling may be relatively large, as compared to the case in which the strip is rolled in a later process. Therefore, a wide and thin final product may be obtained.
After passing though the rolling mill 33, the strip is introduced to the skin pass mill 40 including the heat pipe rollers 100. In the present disclosure, since the skin pass mill 40 includes the heat pipe rollers 100, the skin pass mill 40 may be operated free from the temperature of the strip introduced to the skin pass mill 40. That is, although the strip has a relatively high temperature, the skin pass mill 40 may properly correct the shape of the strip. In detail, the heat pipe rollers 100 uniformly increase the overall temperature of rolls, thereby uniformizing thermal crown shapes and completely performing a shape-correcting process regardless of the temperature of an introduced strip or the number of rolled strips. The heat pipe rollers 100 will be described later in detail with reference to
After passing through the rolling mill 33 and the skin pass mill 40, the strip is rewound as a coil by the coiler 35, and then transferred for a rolling process. In the present disclosure, the coil processed along the shape-correcting line is directly subjected to the rolling process. Therefore, the rolling process may be performed within a warm-working temperature range. However, after an additional cooling process, the rolling process may be performed as a cold rolling process.
According to the present disclosure, the heat pipes 110 are installed in the heat pipe roller 100. Referring to
That is, since evaporation occurs in the center region 113a and condensation from steam occurs in the end regions 113b, steam moves from the center region 113a to the end regions 113b, and pure water moves from the end regions 113b to the center region 113a. Owing to this circulation in the heat pipe 110, heat transferred from the heating unit may be uniformly distributed throughout the heat pipe 110.
As shown in the graph of
Referring to
Each of the heat pipes 110 may penetrate the rolling portion 102. However, for example, first heat pipes 105 may be inserted from one end of the rolling portion 102, and second heat pipes 106 may be inserted from the other end of the rolling portion 102.
The first and second heat pipes 105 and 106 may be alternately arranged in the circumferential direction of the rolling portion 102 for structural stability and benefits in manufacturing processes. That is, it may be advantageous to form insertion tubes of the first and second heat pipes 105 and 106 in such a manner that the insertion tubes do not meet each other, and in this case, the formation of cracks may be prevented even in the case that the load of a rolling process is repeatedly applied to the first and second heat pipes 105 and 106.
In addition, the first and second heat pipes 105 and 106 may overlap each other in a center region of the rolling portion 102. The temperature of a rolling roll is generally highest in a center region thereof. Therefore, if the first and second heat pipes 105 and 106 overlap each other in the center region of the rolling portion 102, the temperature of the center region of the rolling portion 102 may be effectively lowered, and thus the temperature difference between regions of the heat pipe roller 100 may be lowered.
According to the present disclosure, the shape of the heat pipe roller 100 may not be varied according to temperature. That is, the temperature difference between a center region and both end regions of the heat pipe roller 100 may be lowed. In other words, the temperature difference along the heat pipe roller 100 may be constantly maintained regardless of the temperature of a strip supplied to the heat pipe roller 100.
For example, when edges of the rolling portion 102 have a temperature of 50° C., the center region of the rolling portion 102 may be maintained at a temperature of about 65° C., and when the edges of the rolling portion 102 have a temperature of 70° C., the center region of the rolling portion 102 may be maintained at a temperature of about 85° C., so as to maintain the temperature difference between the center region and edges of the rolling portion 102 at a constant level. Therefore, a thermal crown shape caused by a temperature difference may be constantly maintained.
In the heat pipes 110 of the heat pipe roller 100, pure water evaporates into steam in a hot center region, and the steam moves to ends due to an increased pressure in the hot center region. Then, the steam condenses into pure water at the ends due to a low temperature, and the pure water moves back to the center region by the capillary action. As these actions are repeated, heat may be transferred from the center to edges of the heat pipe roller 100 by the evaporation and condensation of pure water, and thus the heat pipe roller 100 may have a uniform widthwise temperature distribution.
The temperature sensor 25 measures the temperature of the coil C and transmits the measured temperature to a monitoring unit (control unit) 28. The monitoring unit 28 compares the temperature of the coil C with a predetermined temperature range, and if the temperature of the coil C is within the temperature range, the coil C is transferred away from the yard and coupled to a pay-off reel.
The temperature range may be properly determined. For example, it may be preferable that the temperature range be set to equal to or higher than 150° C. in consideration of cooling of the coil C when the coil C is unwound from the pay-off reel.
Referring to
In the shape-correcting line, a plurality of coils coupled to a plurality of pay-off reels 30a and 30b are sequentially unwound. Since an amount of time necessary for unwinding a coil after unwinding a previous coil is relatively long compared to an amount of time necessary for coupling the coils to the pay-off reels 30a and 30b, heat insulation covers 34a and 34b are used to maintain the temperature of the coils coupled to the pay-off reels 30a and 30b until the coils are unwound from the pay-off reels 30a and 30b. In other words, a heat insulating process may be performed using the heat insulation covers 34a and 34b to maintain the temperature of the coils coupled to the pay-off reels 30a and 30b. As shown in
Each strip unwound from the coils of the pay-off reels 30a and 30b passes through a heating device 32 in which the temperature of the strip is uniformized, and the shape of the strip is corrected by a skin pass mill 40. Thereafter, the strip is rewound by a coiler 35.
At this time, like in the first embodiment, the skin pass mill 40 uses heat pipe rollers 100 to correct the shape of the strip. A thermal crown of the heat pipe rollers 100 may be maintained at a constant level even in the case that the strip introduced between the heat pipe rollers 100 has a temperature of 150° C. or higher, and since the strip has a temperature of 150° C. or higher, the shape of the strip may be easily corrected even in the case that the strip is a high-strength steel strip.
In the third embodiment, a coil wound by a coiler 3 in a hot rolling process is directly transferred to a shape-correcting device without a cooling process 20. That is, the coil is directly wound from a pay-off reel. In
In the third embodiment, a strip unwound from a coil as described above is directly fed into a skin pass mill 40 for correcting the shape of the strip, and then the strip is rewound by a coiler 35. In the present disclosure, as described above, the skin pass mill 40 includes heat pipe rollers 100. Therefore, the skin pass mill 40 is free from the temperature of the strip, and thus even in the case that the strip has a high temperature, the shape of the strip may be stably corrected. In addition, as shown in
Referring to
That is, the temperature difference along the width of the heat pipe roller of the present disclosure is low. In addition, the temperature difference along the width of the heat pipe roller of the present disclosure may be constantly maintained even in the case that the overall temperature of the heat pipe roller increases.
As described above, if general rolls are used, since large thermal crowns having a dimension of 150 μm are formed in center regions of the rolls, a large wave shape may be formed on a center region of a strip, thereby making the strip useless as a product.
However, if the heat pipe rollers of the present disclosure are used, almost no thermal crown grows, and thus the shape of a strip may not be affected.
Referring to
However, after the strip of
If the shape of a strip is corrected as described above, the load of a later process may be reduced, and the strip may be less cut in the later process, thereby improving overall process efficiency.
Table 1 illustrates samples prepared using shape-correcting devices and methods of the related art and the present disclosure.
As illustrated in Table 1, fifteen coils of 1180CP steel were tested using a shape-correcting device of the related art and the shape-correcting device of the present disclosure. When the shape-correcting device of the present disclosure was used, cutting was not necessary. However, when the shape-correcting device of the related art was used, the average amount of cutting was 37.1 m.
In addition, when thirty three coils of steel 980DP were shape-corrected using the shape-correcting device of the related, the average amount of cutting was 63.5 m. However, in the case of the present disclosure (heat pipe rollers+150° C.), the average amount of cutting was only 2.8 m when one hundred coils were shape-corrected.
As described above, the shape-correcting and rolling method or the shape-correcting device of the present disclosure has remarkable effects on high-strength steel compared to methods or devices of the related art. Particularly, cutting lengths may be markedly reduced, and high-strength steel may be formed into wide and thin sheets.
While exemplary embodiments have been shown and described above mainly based on the first to third embodiments, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2012-0150135 | Dec 2012 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2012/011542 | 12/27/2012 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2014/098297 | 6/26/2014 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4793172 | Eibe | Dec 1988 | A |
| 5119886 | Fletcher et al. | Jun 1992 | A |
| 5823037 | Kim et al. | Oct 1998 | A |
| 5832985 | Pleschiutschnigg | Nov 1998 | A |
| 5984848 | Hyllberg et al. | Nov 1999 | A |
| 6240617 | Nitoh | Jun 2001 | B1 |
| 6327883 | Noe et al. | Dec 2001 | B1 |
| 6776857 | Lee | Aug 2004 | B2 |
| 20040239013 | Bodin | Dec 2004 | A1 |
| 20100175452 | Ohlert et al. | Jul 2010 | A1 |
| 20110097973 | Jin et al. | Apr 2011 | A1 |
| 20130337282 | Oishi et al. | Dec 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 1004066 | Jan 1977 | CA |
| 101670372 | Mar 2010 | CN |
| 101755058 | Jun 2010 | CN |
| 1 452 247 | Sep 2004 | EP |
| 57-009501 | Jan 1982 | JP |
| 61-269901 | Nov 1986 | JP |
| 04-188585 | Jul 1992 | JP |
| 07-204704 | Aug 1995 | JP |
| 10-005809 | Jan 1998 | JP |
| 10-192915 | Jul 1998 | JP |
| 2000-054098 | Feb 2000 | JP |
| 2001-105006 | Apr 2001 | JP |
| 2007-044751 | Feb 2007 | JP |
| 2008-213015 | Sep 2008 | JP |
| 2010-530807 | Sep 2010 | JP |
| 2010-240691 | Oct 2010 | JP |
| 2011-167736 | Sep 2011 | JP |
| 2011-526543 | Oct 2011 | JP |
| 2012-172254 | Sep 2012 | JP |
| 2000-0010065 | Jun 2000 | KR |
| 10-2004-0049855 | Jun 2004 | KR |
| 10-2010-0007940 | Jan 2010 | KR |
| Entry |
|---|
| Extended European Search Report issued in corresponding European Patent Application No. 12890177.4, dated Apr. 5, 2016. |
| Notice of Office Action issued in corresponding Japanese Patent Application No. 2015-549232, dated May 24, 2016; with English translation. |
| International Search Report issued in corresponding International Patent Application No. PCT/KR2012/011542, dated Jun. 21, 2013; 4 pages with English translation. |
| Office Action issued in corresponding Chinese Patent Application No. 201280077682.5, dated Jan. 4, 2016. |
| Number | Date | Country | |
|---|---|---|---|
| 20150306645 A1 | Oct 2015 | US |
