JPS5930412A - Controlling method for cooling hot rolled steel strip - Google Patents

Abstract

PURPOSE:To reduce the degree of steep slope of a steel strip recoiled from a cooled coil, by controlling an intercepting width and an intercepting time by calculating the water injection cooling of the side edges of a hot rolled steel strip at the outlet side of a finish mill, basing on the temperature, dimension, and components, etc. of the strip. CONSTITUTION:Before coiling a hot rolled steel strip W rolled out from a finish mill 1 by a coiler 3, the strip W is cooled on a cooling table 2 to the prescribed temperature by pouring a cooling water from nozzles 6 of lower cooling headers 4, 5. Temperature detecting devices 9, 12 are respectively provided to the inlet side of a coiler 3 and to the outlet side of the mill 1 to output the detected temperature signal of the strip to an arithmetic device 10. At the device 10, the ratios of an intercepting width to the strip width and a cooling water intercepting time to the whole water cooling time are respectively calculated so as to obtain the optimum values for reducing the degree of steep slope of the strip W, basing on the informations about the dimensions and the components, etc. inputted from a computor 13 and the data of operating conditions; thereby controlling baffle plates 8A, B of cooling water, which reciprocate parallelly on rails 7 by a driving mechanism 14.

Description

[Detailed description of the invention]

The present invention relates to a method for controlling the cooling of a hot-rolled steel strip, and more particularly to a method for controlling the temperature distribution in the width direction of a copper strip during cooling by injecting water onto the surface of a hot-rolled steel strip. The hot rolled copper strip that has been rolled by a continuous hot rolling mill is cooled by water injection on a cooling table to cool it to a predetermined winding temperature before being wound up by a winding machine. In conventional cooling methods using cooling water, it is customary to spray the cooling water evenly over the entire width of the hot-rolled steel strip on the cooling table, both above and below. However, the temperature drop at each side edge part of the rolled copper strip during operations such as rough rolling and finish rolling is larger than that at the center part of the strip width, and the temperature difference on the exit side of the finishing mill is 3CPC to 80C. It is occurring. This temperature difference is further amplified during the cooling process. Due to the difference in temperature and cooling rate between the edges in the width direction and the center of the hot rolled steel strip, the flatness of the steel strip from the exit side of the finishing rolling mill to the winding machine and the cooling of the 1 ton coil after winding are The flatness is different from the flatness when the copper strip is rolled back at the entry side of the finishing line in the next process, and in the normal case, a lot of edge elongation is observed. The reason why this difference in flatness occurs is that due to the temperature difference between the ends of the copper strip in the width direction and the center before winding, a difference in heat shrinkage occurs in the copper strip that is cooled after winding. This is thought to be because the compressive stress generated in the copper strip exceeds the critical buckling stress of the copper strip. In order to prevent the uneven temperature distribution in the strip width direction that occurs in conventional steel strip cooling methods that use such cooling water, this copper strip cooling method shields the parts adjacent to the side edges of the steel strip from cooling water. was developed and published in Japanese Patent Application No. 56-47233. However, it has been found through experiments and actual operations that it is not always possible to obtain satisfactory results even if the area adjacent to the side edge of the steel strip is isolated from the cooling water. For example, if the invention of the above application is carried out without considering the range of the side edge portion of the steel strip that cuts off cooling water and the time to cut off the cooling water, the portion adjacent to the side edge becomes excessively hotter than the center portion. It is also conceivable that this may result in stretching. The present invention is useful for solving such problems that occur with the invention of the above application. An object of the present invention is to maintain the flatness of the copper strip at a desired value in the strip width direction after the coil is cooled by water injection on the exit side of the finishing rolling mill and wound up into the winding machine. The object of the present invention is to obtain a cooling control method that generates a temperature distribution of . According to the present invention, the first rolling mill removed from the finishing mill. A method for controlling cooling by injecting water onto the surface of a hot-rolled steel strip sent to a winding machine by blocking areas adjacent to each side edge of the steel strip from water injection, the method comprising controlling the dimensions and composition of the copper strip. Based on the conditions such as temperature and thermal conductivity at a given point, calculate the cut-off width and cut-off water cooling time. ・Calculate the thermal stress as a paranoter and calculate the ratio of the cut-off width to the plate width and the cut-off water cooling time to the total water cooling time. A method for cooling a hot-rolled steel strip is obtained, which is characterized in that the ratio of the steepness reduction of the copper strip is set to an optimum value. Embodiments of the present invention will now be described with reference to the accompanying drawings. 1 and 2 show an apparatus 15 used in the method of the present invention, in which a cooling table 2 is provided on the exit side (left side) of the finishing mill 1, and a cooling water is provided on the upper part of the cooling table 2. The header 4 is installed, and the lower part (* is separate α) (1) cooling water header 5 is installed. Arranged in the width direction of the band W2

[6] It consists of a tube body equipped with a large number of nozzles 6, and the large number of tube bodies are arranged in the traveling direction of the steel strip W in the second and lower parts of the steel strip. The above shows a typical cooling table and cooling water header. The device 15 used in the method of the present invention includes a
・Equipped with baffle plates 8A and 8B that are reciprocatably mounted on a horizontal track 7 that is attached to the lower part of the plate in the width direction of the plate. Steel strips W are placed at the entrance side of the winding machine 3 and the exit side of the finishing rolling machine 1, respectively.
A device 9, 12 is provided for measuring the temperature of. The arithmetic unit 10 located above the upper header 4 is connected to the lead 11.
Temperature measuring device 9. ]
Connected to 2. The drive mechanisms 1 and 1 for the baffle plates 8A and 8B are installed at positions adjacent to the upper header 4.
ing. This drive mechanism 14 is connected to the arithmetic unit 10 by a lead IIB. Further, this arithmetic unit 10 is connected to a host computer 13 via a lead 11D. The cooling control method of the present invention is as follows. First, the temperature measuring devices 9 and 12 send the temperature of the steel strip on the three-man side of the winding machine and the temperature of the steel strip on the exit side of the finishing mill 1 to the computing device 10. The host computer 13 also sends information regarding the properties of the copper strip, such as plate thickness, plate width, and composition, to the arithmetic unit 101C. Arithmetic device 1
0 is the plate thickness, plate width, component, and winding details of Jt et al.;7+,,
Based on the data regarding the temperature at the exit side of the finishing mill, the width ratio (
The plate width (ratio of cut-off to ζ) and time rate (ratio of cut-off water cooling time to total water cooling time) are determined and sent to the drive mechanism 14. The combination is the numerical value, and after cooling the coil wound in winding machine 3, ?l1Jl
It is also possible to select the optimum value to reduce the steepness to the required range when the XV is unwound. The drive mechanism 14 operates based on the command sent from the arithmetic unit 10.
j Determine the area of the copper strip that is shielded from water and the time that it is shielded. The above-mentioned values regarding the width ratio and time ratio output from the arithmetic unit 10 are determined by experiments and thermal stress calculations as shown below to maintain the steepness of the steel strip W unwound from the coil after cooling within a permissible range. It is something that can be done. Therefore, when the steel strip W that has been cooled and refined through the above process is unwound from the coil at the entry side of the finishing line, it is satisfactory as far as flatness is concerned. As mentioned above, the cause of poor flatness that occurs in the steel strip that has been unwound from the coil after cooling is the temperature distribution in the width direction immediately after finishing rolling and the unevenness in the width direction that remains during the cooling process. It is assumed that stress is generated and this stress exceeds the critical buckling stress of the steel plate. Therefore, if the compressive stress occurring at the side edge portion of the copper strip is reduced and the buckling stress is expressed as %, then the ratio of the two is considered to be 7-111 degrees and is an index for determining failure, and when this value approaches 1, Poor flatness occurs. Figure 3 shows an example of a method for calculating the compressive stress occurring at the side edge portion of a steel strip using a thermal stress calculation model. Find the average compressive stress S/b when cutting the width of this part.・5,
The ratio of this uniform compressive stress S/b and buckling stress can be used as the above-mentioned index. Figure 4 is a plot of the ratio A6 obtained by the above thermal stress division and the actually measured steepness of the side edge portion of the copper strip. Figure 5 shows that the time ratio (ratio of cut-off water cooling time to total water cooling time) is fixed at various values such as 20%, 60%, and 100%. In this state, the relationship between the steepness and the width (ratio of cut-off width to the strip width) of the copper strip unwound after cooling is calculated using a strip thickness of 2 to 3 mm, strip width of 1200'nlIn, (winding d of 171 degrees). 55 (fG
, Experiment on low carbon material with finish rolling temperature of 850″G, ν
The results are plotted and the thermal stress calculation results are shown as a solid line, where -L%9 on the XX axis [i indicates the steepness of the ear wave, and the lower part indicates the steepness of the belly wave. As a result of thermal stress calculation using the curve in FIG. 4, it is found that the steepness can be expressed by the ratio /cz, -. That is, the steepness is -01%. -(L2 and 7
';(7,. The solid line in Figure 4 is nothing but the one that shows this equation. It can be seen that the results of thermal stress calculation agree well with the experimental results. Also, the ear wave steepness is determined for each time rate. It draws an almost smooth curve with respect to the change in width.The same is true for the steepness of the abdomen.From these 2'L and other curves, the steepness of both the ear wave and the abdomen can be calculated as 1'd/j・The method for calculating the thermal stress is as follows.The thermal stress calculation can ignore the heat flow in the longitudinal direction of the copper strip. year,
Derive the two-dimensional Fourier heat conduction equation and convert it into IA
A special difference method called the D method is used to calculate the stress component ↑1
I'm calculating. FIG. 6 shows a flowchart of thermal stress calculation. If you change the middle handle here, change the distribution of the heat transfer coefficient during water cooling so that it is lower at the cutoff part J in Figure 7,
When changing the time rate, the thermal stress distribution (i.e. the third
Figure). Therefore, in order to obtain the chart as shown in Figure 5 by thermal stress calculation, the distribution of the thermal conductivity coefficient during water cooling corresponding to various widths is given at a cutoff water cooling time corresponding to a certain time rate (for example, time rate lo%). That's it 2
Find the ratio 0 of 1 and predict the steepness C. Then, a chart like the one shown in Figure 8 is obtained. Perform similar calculations. By repeating this, a chart like the one shown in Figure 5 can be obtained. However, this thermal stress calculation model requires too much time to perform convergence calculations, so it cannot be used online. Therefore, it cannot be used online. Calculations are performed using a simple model that has the characteristics of a thermal stress calculation model. In other words, each copper strip has unique values for data such as plate thickness, plate width, composition, coiling temperature, finishing temperature, etc. as shown in Figure 5. By creating a chart similar to , it is possible to obtain the combination of width and time rate that is optimal for reducing the steepness of each copper strip after unwinding. Based on the above data for the copper strip, the above chart is obtained using a simple thermal stress calculation model, and from this, the optimal combination of time rate and width is selected by computer. Figure 9 shows the plate thickness 1. 5 mvr, board width 1200mm, J
A curve similar to that shown in FIG. 5 was created for a low charcoal cake with a starting temperature of 60σG and a finish rolling temperature of 85σG, and the steepness of the belly roll and the steepness of the ear waves are minimized. That is, in this case, the combination of the smallest width between the curves of the steepness of the belly and the steepness of the ear wave and the width is 10 parts for the width part and 60 parts for the time ratio, This value is the optimum value. Example 1゜Plate thickness 1.6rmn, plate width 1200mm, winding temperature 60σ
G, low carbon material with finish rolling temperature of 85 d'G.
For the optimum time rate of 60 cm and width of 10%, which was determined by a simple thermal stress calculation model that creates a chart as shown in the figure,
Water cooling was performed using various time rates and widths different from the optimum values shown in Table 1, and the flatness of the rolled copper strip after unwinding was investigated. The results show that, as shown in FIG. 10, the case where the cut-off cooling is performed at the optimal time rate and width is the most effective in terms of flatness improvement. As described above, according to the present invention, a copper strip that has been taken out from a finishing rolling mill and cooled by water injection while being sent to a winding machine is unwinded from the coil after winding. Poor flatness due to stretching can be prevented. FIG. 1 is a side view of the apparatus used in the method of the present invention, FIG. 2 is a sectional view taken along the line U-t+ in FIG. 1, and FIG. 3 shows a steel strip processed by the apparatus of FIG. Figure 4 is a graph showing the relationship between the compressive stress shown in Figure 3 and the edge steepness of the copper strip. Figure 5 is a graph showing the relationship between the compressive stress shown in Figure 3 and the edge steepness of the copper strip. A curve showing the relationship between the width and the steepness of the copper strip. Figure 6 is a curve showing the change in steepness when changing the width while keeping the time rate constant. Figure 7 is the heat transfer coefficient in the width direction of the strip. Figure 8 is a flowchart showing the process of thermal stress calculation. - Figure 9 was created for W4 Emperor, which is different from the copper belt in Figure 5.
Figure 10 is a curve showing the relationship between the width and steepness of a steel strip water-cooled by the method of the present invention and a steel strip water-cooled not by the method of the present invention after unwinding. FIG. 3 is a diagram showing a comparison of steepness. 1 Finishing rolling mill 2 Cooling table 3 Winding machine 4 Cooling water header (upper part) 5
(Lower) 6 Nozzle 7 Track 8 Baffle plate 9 Temperature measuring device 10 Arithmetic device 11 Lead 1
2 Temperature measuring device 13 Computer 14 Drive mechanism 15 Equipment used in the present invention T-65
- No. 2 Hei-ei-71 Procedural Amendment 1/8/1982 Kazuo Wakasugi, Official of the Japan Patent Office 1, Indication of the Case Patent Application No. 137959/1982 2, Name of the Invention Cooling of Hot-Rolled Steel Strip Control method 3, relationship with the case of the person making the amendment Patent applicant address 1-1-28 Kitahonmachi-dori, Chuo-ku, Kobe, Hyogo Prefecture
Title 125 Kawasaki Steel Corporation 4, Agent 5 Date of amendment order November 12, 1980 6
Subject of amendment: Four layers, 1 honor and drawing 7, Contents of amendment: As shown in the attached document, the description and drawings of the application are corrected as follows (1) Lines 15 and 16 of page 11 of the specification. (Table 1 (1j) drawing with the following entry amended as shown in the attached sheet, Figure 10)

Claims (1)

[Claims] A method for controlling cooling by blocking areas adjacent to each side edge of the copper strip from water injection when cooling the surface of a hot rolled steel strip taken out from a finishing mill and sent to a winding machine, the method comprising: ,
Thermal stress calculations are performed using the cut-off width and cut-off water cooling time as parameters based on conditions such as steel strip dimensions, composition, temperature at a predetermined point, and thermal conductivity, and the ratio of cut-off width to strip width 1, A method for cooling a hot-rolled steel strip in which the fi-ed method is to set the ratio of the cut-off water cooling time to the water cooling time to an optimal value for reducing the steepness of the copper strip.