JP2010064122A - Stable manufacturing method of high-quality hot-rolled steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stable manufacturing method of a high-quality hot-rolled steel plate capable of preventing occurrence of any breakage, roll mark or the like in the finish rolling in advance by determining any perforation of a sheet bar before the sheet bar after the rough rolling enters a finish rolling machine. <P>SOLUTION: In the manufacturing method of the hot-rolled steel plate, the temperature distribution on the entire surface of a sheet bar 4 is measured by a width-direction thermometer 10 before a sheet bar after the rough rolling is subjected to the finish rolling, and a portion where the temperature deviation from the representative temperature exceeds a predetermined range is determined as a perforation. The entry into a finish rolling machine 5 of the shift bar which is determined as the perforation is prohibited to stop the rolling. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for stably producing a high-quality hot-rolled steel sheet, and more particularly, in a hot rolling line for steel, before the sheet bar after rough rolling enters the finish rolling mill, the hole of the sheet bar is determined. The present invention relates to a method for stably producing a high-quality hot-rolled steel sheet, in which a high-quality hot-rolled steel sheet is stably produced by preventing breakage and roll wrinkling in finish rolling.

For example, as shown in FIG. 1, in general, a hot-rolled steel strip 8 is heated to a few hundred hundred degrees in a heating furnace 2 after a slab 1 is heated to a sheet bar 4 with a plurality of rough rolling mills 3, and thereafter It is manufactured by a process of thinly rolling with a finish rolling mill 5 composed of a plurality of stands, subsequently cooling with a cooling table 6, and then winding with a coiler 7.
The sheet bar 4 rolled by the roughing mill 3 does not necessarily have a uniform thickness in the width direction and the longitudinal direction. For example, when rolling a wide roll of material after rolling a large width of the roll, a step wear is generated on the roll of the roughing mill, and the roll curve is not appropriate, and the sheet bar has holes. May occur. Further, when a large meandering occurs at the tail end of the sheet bar in rough rolling, the tail end may be folded against the side guide, and a hole may be generated around the folded portion by rolling.

  When finishing rolling a sheet bar with holes, there is no material in the holes, so there is insufficient material in the width direction and the rolling load per unit width increases, resulting in sheet breakage and rolling. Therefore, the steel sheet will not be a product and the yield will be greatly reduced. Moreover, when the local load of rolling increases remarkably, roll breakage is easy to occur, and unstable rolling is forced. Furthermore, even if the plate breakage or roll breakage does not occur, the stress around the hole may increase locally and cause roll wrinkles, which may be a problem.

  In order to solve the problem of finishing rolling problems caused by the opening of these sheet bars, it is known to detect holes by using a metal plate detection sensor that utilizes the presence or absence of light transmission for the opening of steel strips just before winding, not the sheet bars. (Patent Document 1). However, when the present inventors tried this method for punching a sheet bar, the hole detection can be effectively performed at the beginning of the installation of the metal plate, but as the number of rolled sheet bars increases, the projector and the receiver It was found that the tip was soiled and the detection ability was remarkably lowered, and the hole detection was not successful. This is because oxide scale powder scatters from the surface of the sheet bar during hot rolling from the roughing mill to the finishing rolling mill, or the refractory dust separated in the heating furnace rides on the slab and is rolled during rolling in the roughing mill. It was understood that it was scattered on the exit side of the machine, and it was caused by the contamination of the coolant water, scattered lubricating oil and grease, etc., adhering to the tip of the projector and receiver.

  Therefore, a method of measuring the temperature of the front end portion of the sheet bar has been proposed as a method that eliminates the above problems and is less susceptible to the effects of oxide scale and water vapor (Patent Document 2). This is a method of measuring the temperature of the leading end portion of the sheet bar and comparing the temperature of the intermediate portion with the deviation to determine the opening of the sheet bar. However, when this method is attempted according to the embodiment, the plate temperature is continuously measured in the longitudinal direction at a total of three positions offset by 300 mm to the center of the plate width and to the left and right. It is possible to detect that there is a hole in the hole, but if the hole is small or offset to the width end, the hole may pass by avoiding the temperature measurement position in the width direction, and the hole opening cannot be detected. In some cases, this causes problems such as plate breakage, roll wrinkles and roll breakage in finish rolling.

Also, when trying this method, when a hole was detected with the end of the sheet bar already biting into the finishing mill, it was necessary to stop the rolling mill rapidly so that the holed portion would not enter the finishing mill. Therefore, it took a lot of time to remove the material to be rolled that had already been bitten into the finish rolling mill, which was a big problem.
JP 2002-143927 A Japanese Patent Laid-Open No. 2004-141879

  As described above, in the production of a conventional hot-rolled steel sheet, when roll wrinkles or sheet breakage occurs during finish rolling due to punching of a sheet bar, the steel sheet does not become a product, and the yield decreases significantly. Cutting down and scrapping and replacing the rolls with folds into rolls without folds requires significant downtime. However, the conventional hole detection technology has a problem that a detection error of the sheet bar hole is likely to occur, a finish rolling trouble due to the hole is likely to occur, and a high-quality steel sheet cannot be manufactured stably. . Therefore, there has been a great demand for a method that can reliably detect a hole in a sheet bar and stably manufacture a high-quality steel plate having no defects. The present invention meets this need.

In view of such circumstances, the present inventor has eagerly studied a method for stably producing a high-quality material by reliably detecting a hole in a sheet bar in the production of a hot-rolled steel sheet and preventing a decrease in yield and downtime. The present invention has been made.
That is, the present invention is as follows.
[1] In a method for producing a hot-rolled steel sheet, the sheet bar obtained by roughly rolling a heated slab with a roughing mill to finish-roll the sheet bar with a finishing mill to form a hot-rolled steel strip. Before the bar is finish-rolled, the temperature distribution over the entire surface of the sheet bar is measured, and the part where the temperature deviation from the representative temperature exceeds the specified range is judged as a hole. A stable manufacturing method for rolled steel sheets.

[2] The width direction thermometer is installed between the rough rolling mill exit side and the finish rolling mill entrance side, and the temperature distribution of the entire sheet bar is measured using this. A method for stably producing a high-quality hot-rolled steel sheet as described in 1.
[3] The method for stably producing a high-quality hot-rolled steel sheet according to claim 1 or 2, wherein the sheet bar determined as the perforation is prohibited from entering a finish rolling mill and rolling is stopped. .

  According to the present invention, since the perforation of the sheet bar can be reliably detected, a finish rolling trouble can be prevented in advance, and a high-quality steel plate free from wrinkles can be manufactured stably.

Hereinafter, the method of the present invention will be described in detail.
Conventionally, in order to detect perforations in the sheet bar, a method that utilizes light combining a projector and a receiver, a thermometer for spot position detection that can measure continuously in the longitudinal direction although there are only three specific locations in the width direction The method using was performed. However, these have problems in applying to actual operation, and it has been difficult to reliably catch the hole in the seat bar.

In view of this, the inventor has intensively studied a method that can reliably detect the presence or absence of perforations over the entire sheet bar.
When a hole in the sheet bar is found during the finish rolling and the rolling is stopped, the material to be rolled remains between the narrow stands, so that the time required for the cutting process and the attachment / detachment of the peripheral devices associated therewith becomes enormous. Therefore, it is necessary to detect perforations over the entire surface of the sheet bar before the sheet bar is between the roughing mill and the finishing mill and finishing rolling is started.

It is difficult to eliminate the contamination of the instrument due to an oxide scale or the like by the conventional method using light transmission. Therefore, it is considered advantageous to use temperature measurement that is not easily affected by dirt, but in the past, it was a method of detecting by installing thermometers at several spot positions in the width direction, and in the longitudinal direction there were holes. Although it was possible to measure continuously, the entire width direction could not be detected.
Therefore, the present inventors examined a method of measuring the temperature distribution over the entire surface of the sheet bar in combination with continuous temperature measurement in the longitudinal direction by measuring the temperature distribution in the width direction. This includes a method of directly detecting the temperature distribution in the width direction as a line sensor, a method of installing four or more spot position detection thermometers in the width direction, preferably 10 or more, and dividing the sheet bar surface into a plurality of surfaces. There is a method in which the brightness for each surface is measured and converted into a two-dimensional temperature distribution for detection.

Note that it is advantageous to use a width direction thermometer utilizing continuous movement of the steel sheet in the longitudinal direction in order to reduce the equipment cost and reduce the operating part as much as possible to enable stable temperature measurement.
For example, as the hole detection of the seat bar, the average temperature of the entire surface of the seat bar is used as a representative temperature, and a temperature difference with the temperature of each position in the seat bar surface is calculated. The calculated temperature difference is a specific temperature difference (threshold). It is good to determine the exceeding part as a perforated part. Equipment such as a lower sheet passing table is exposed from the perforated portion of the seat bar, and these can be easily detected because the temperature difference from the hot seat bar is significant.

  On the other hand, if there is water on the sheet bar after rough rolling, the temperature of that portion will be significantly reduced, so it is easy to detect it as a hole by mistake, so it is better to measure the sheet bar temperature after draining after rough rolling . In addition, if a thick oxide scale remains on the surface of the seat bar, the portion is also blackened, the heat dissipation on the surface of the sheet bar is blocked, and the surface of the seat bar looks as if it is at a low temperature. Therefore, the sheet bar width direction temperature after descaling should be measured as much as possible.

  For the sheet bar that has been determined to be perforated, the rolling (passing) is stopped before entering the finish rolling, and an unloading device and a dedicated lifting tool for the sheet bar are installed on the intermediate table from the roughing mill to the finishing mill. If it is removed in a short time using a crane or the like, the production efficiency does not need to be reduced. A series of operations from detection of a hole opening to finishing rolling stop command and sheet bar unloading can be automated by a computer.

  Further, by detecting the load fluctuation in the roughing mill and using it together with the hole determination by measuring the temperature of the entire surface of the sheet bar, it is possible to detect the hole more effectively.

In the hot rolling line illustrated in FIG. 1, the slab 1 was sequentially taken out from the heating furnace 2 and a total of 100 rolled materials were rolled. As a result, punching occurred in the sheet bar after rough rolling. The sheet bar was processed according to the present invention example or the conventional example shown.
FIG. 2 is a schematic diagram showing an example of the measurement situation when the temperature distribution of the entire surface of the seat bar 4 is measured using the draining device 9 and the width direction thermometer 10 installed. The drainer 9 device may still be installed and used. A descaling facility (not shown) is disposed on the entry side of the roughing mill 3.

(Invention Example 1)
A draining device 9 and a width direction thermometer 10 utilizing the brightness measurement in the width direction are installed in advance on the exit side of the rough rolling mill 3, and automatic hole opening determination by a computer and sheet bar automatic unloading processing at the time of hole opening detection are performed. As possible, rough rolling was performed while descaling was performed, the sheet bar 4 immediately after the final pass exit side of the rough rolling mill 3 was sufficiently drained, and the temperature of the entire surface of the sheet bar was measured. Here, with respect to the average temperature of the entire surface of the sheet bar (this is the representative temperature), a temperature difference of 100 ° C. is used as a threshold value, and a hole is generated when a temperature difference equal to or greater than the threshold value is detected. Opening judgment was performed.

  As a result, it was possible to normally and stably roll up to the 94th of the 100 rolled materials, but during the 95th rolling, about 1/5 from the longitudinal tip of the sheet bar and about 150 mm from the center in the width direction to the drive side. A hole with a width of about 100 mm occurred at the position. Therefore, before the sheet bar 4 enters the finish rolling mill 5, the computer automatically stops the finish rolling, and the sheet bar is removed from the table by the automatic carry-out device. Thereafter, the rolling roll for the final pass of the rough rolling mill 3 was replaced. From the 96th roll, efficient and stable rolling was achieved with no holes and good quality.

(Invention Example 2)
The spot position detection thermometer is spaced 100 mm apart in the width direction in advance between the rough rolling mill 3 and the finish rolling mill 5 at a position where the temperature of the entire length of the sheet bar can be measured before the sheet bar is bitten into the finish rolling. At 16 locations, the temperature of the entire length of the seat bar 4 was continuously measured, and the temperature measurement result was visually observed to monitor the hole opening. Here, with respect to the average value of the center temperature in the sheet bar width direction (this is the representative temperature), a temperature difference of 200 ° C. is used as a threshold, and a hole is generated when a temperature difference equal to or greater than the threshold is detected. Bar hole opening judgment was performed.

  As a result, it was normal and stable rolling up to 54 out of 100 materials to be rolled, but the 55th was the meander of the sheet bar at the tail end in the longitudinal direction of the sheet bar, about 400mm from the center in the width direction to the operator side. As a result of the occurrence of perforations, finishing rolling was stopped before the seat bar 4 entered the finishing mill 5, and the seat bar was removed from the table by a crane having a dedicated lifting tool. After that, the load difference between the left and right in the width direction of the roughing mill 3 was adjusted, and the rolling was continued from the 56th, and the rolling was normal until the 89th, but the 90th was about 2 from the front end in the longitudinal direction of the sheet bar 4. / 3, there was a hole in the position about 100mm from the center in the width direction to the operator side.

Therefore, as with the 55th, the finish rolling was stopped before the seat bar 4 entered the finish rolling mill 5, and the seat bar was removed from the table by a dedicated lifting tool. After that, the rolling rolls of the second stand and the third stand of the rough rolling mill 3 were exchanged, and from the 91st roll, efficient and stable rolling was achieved with no holes and good quality.
(Conventional example 1)
A draining device 9 and a spot position detection thermometer are installed in advance at three locations on the outlet side of the rough rolling mill 3 at a position offset by 300 mm to the left and right from the center position in the width direction and the center position in the width direction. The sheet bar 4 can be automatically unloaded at the time of opening judgment and hole opening detection, and the temperature of the entire length of the sheet bar 4 is continuously increased in the longitudinal direction while sufficiently draining the sheet bar immediately after the final pass exit side of the rough rolling mill 3. It was measured. Here, with respect to the temperature of the front end portion of the sheet bar, the temperature difference of 100 ° C. was used as a threshold value, and it was determined that a hole opening occurred when a temperature difference equal to or greater than the threshold value was detected.

  As a result, the rolling was normal and stable up to 92 out of 100 materials to be rolled. However, during the rolling of the 93rd roll, a hole with an estimated width of about 80 mm occurred at a position of about 400 mm from the center in the width direction to the drive side, but it could not be detected and the holed sheet bar was finished. Rolling caused sheet breakage, and it took a lot of time to remove the sheet from the finish rolling mill and to change the rolls of the multiple stands of the finishing mill, resulting in significant downtime and a significant drop in yield. Thereafter, the periphery of the finish rolling mill was washed with high-pressure water and the roll was changed, and rolling was continued from the 94th roll. However, minute fragments remaining at the time of the plate breakage were caught, and wrinkles were generated in the material to be rolled.

(Conventional example 2)
A hole detector combined with a projector and a light receiver is installed in advance between the rough rolling mill 3 and the finish rolling mill 5 at the position where the end of the sheet bar is bitten in the finish rolling. Measured continuously.
As a result, it was normal and stable rolling up to the 49th of the material to be rolled, and a hole due to meandering was detected at the 50th, but the end of the sheet bar 4 entered the finishing mill 5. Since the rolling was stopped later, it was necessary to cut out and carry out the sheet bar that had been bitten into the finish rolling mill prior to carrying out the sheet bar with the special lifting tool, which took a great deal of labor and time.

  After that, the load difference between the left and right in the width direction of the rough rolling mill 3 was adjusted, but the rolling detection was continued with the perforation detector as it was, and normal rolling was performed up to the 84th, but the 85th was centered during the rolling. Despite the occurrence of a hole that is estimated to be approximately 100 mm wide at a position approximately 300 mm from the operator side, dirt is attached to the tip of the hole detector and cannot be detected, and the holed sheet bar 4 is finished. Rolling caused plate breakage, and it took a lot of time to extract the plate and replace the roll, resulting in significant downtime and a significant drop in yield.

As described above, the conventional hole detection method cannot reliably determine the presence or absence of holes, resulting in plate breakage and a significant decrease in yield, as well as significant downtime due to processing of broken materials and roll replacement. In some cases, there was also a case where the remaining broken pieces were bitten and cracks were generated in the rolling after restoration.
Compared with this, since the method of the present invention can reliably determine the hole opening, it is possible to stably roll a high quality material without suppressing a decrease in yield and causing downtime, and the effect is remarkably good. I understand that.

Schematic diagram showing an example of a hot rolling line suitable for carrying out the method of the present invention Schematic diagram showing an example of the measurement status of the temperature distribution on the entire surface of the sheet bar by the width direction thermometer according to the present invention

Explanation of symbols

1 Slab
2 Heating furnace
3 Rough rolling mill
4 Seat bar
5 Finishing mill
6 Cooling table
7 Coiler
8 Hot-rolled steel strip
9 Drainer
10 Width direction thermometer

Claims (3)

  In a method of manufacturing a hot-rolled steel sheet including a step of forming a hot-rolled steel strip by finish-rolling a sheet bar obtained by roughly rolling a heated slab with a rough-rolling mill, a sheet bar after the rough rolling is finished. Before rolling, the temperature distribution on the entire surface of the sheet bar is measured, and the portion where the temperature deviation from the representative temperature exceeds the predetermined range is determined as perforated. Stable manufacturing method.   The width direction thermometer is installed between the rough rolling mill exit side and the finishing rolling mill entrance side, and the temperature distribution of the entire sheet bar is measured using the thermometer. A stable manufacturing method for high-quality hot-rolled steel sheets.   The method for stably producing a high-quality hot-rolled steel sheet according to claim 1 or 2, wherein the sheet bar determined as the perforation is prohibited from entering the finish rolling mill and rolling is stopped.

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