JPS62297418A - Control method for sheet temperature at outlet side of cooling apparatus for steel sheet in continuous annealing line - Google Patents

Abstract

PURPOSE:To stably control sheet temp. at outlet side without any influence of changing factors, such as passing rate of the steel sheet, cooling water temp., etc., by adjusting cooling water level in water cooling jacket in the cooling method using the water cooling jacket. CONSTITUTION:The cooling water is introduced into the water cooling jacket 1 from supplying hole at downstream side of running course of the steel sheet S and after flowing forcibly as straightening flow along the both side surface of the steel sheet toward reverse direction of the running course of the steel sheet, it is overflowed from the discharging port. In this cooling apparatus, an elevating plate 6 is arranged at the inlet side of the steel sheet for the straight flow plate 1a and elevated by an elevating device 10, composing of such as cylinder 7, rope 8, sheave 9, etc., to change the overflow level in the cooling apparatus 1. A computing element 16 calculates the overflow level in order to make to the aimed sheet temp. from each detecting signal of thermometer 12 for the steel sheet, level meter 13 for the overflow height and thermometers 14, 15 for cooling water and the aimed cooling temp. 17 of the steel sheet and the passing rate 18 of sheet after treatment. The calculating result is inputted into a controlling device 19 and the elevating plate 6 is controlled by the device 10 so as to affairs the prescribed level.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for controlling the plate temperature at the exit side of a steel strip cooling device in a continuous annealing line, and in particular to a method for controlling the plate temperature at the exit side of a steel strip cooling device in a continuous annealing line. The objective is to efficiently (controllably) cool the steel strip to a predetermined target temperature, regardless of changes in the supplied cooling water temperature due to seasonal factors.

(Prior art) In general, after cold rolling, raw sheets for surface treatment and steel parts for deep drawing are subjected to so-called continuous heat treatment such as heating, soaking, and cooling in order to impart predetermined contract properties. Annealing is performed.

Cooling methods employed in such continuous annealing include gas jet cooling, roll cooling, and immersion cooling. Of these, gas jet cooling involves blowing cooled atmospheric gas onto the steel strip, roll cooling involves wrapping the steel strip around a roll with a refrigerant passed through it, and immersion cooling involves using a cooling water tank. The steel strip is cooled by immersion, and the cooling rate increases in the order of gas jet cooling, roll cooling, and immersion cooling.

Therefore, in the cooling zone of a continuous annealing line, when cooling from the recrystallization temperature to a temperature that does not oxidize in the atmosphere, it is most efficient to use gas jet and/or roll cooling on the high temperature side, while immersion cooling on the low temperature side. It is thought that there is.

Regarding such immersion cooling, various methods have been proposed so far. For example, the method disclosed in Japanese Patent Publications No. 57-11931 and No. 57-11933 uses a plurality of cooling water tanks and controls water injection into each water tank, and also by combining spray cooling and mist cooling. In addition to efficiently cooling the steel strip, the water temperature after cooling is raised as much as possible to effectively utilize the water as hot water.

By the way, immersion cooling is usually applied to cooling from a temperature of about 250 to 300° C., at which the amount of change in the amount of saturated solid solute carbon in the steel strip is small, to a temperature at which temper color does not occur in the atmosphere. In the past, if the cooling rate due to such immersion treatment was too fast, there were concerns about aging problems due to solid solution carbon, but recently, non-aging materials such as Nb-added ultra-low carbon steel have been developed using solid solution with a third element in advance. Materials that fixed carbon began to be used. Therefore, from a metallurgical point of view, it is no longer a problem no matter how high the cooling rate is, and in fact, it is desired to further improve the cooling rate in the final cooling from the viewpoint of higher speed and higher production efficiency.

However, in response to the above-mentioned demands, conventional immersion cooling still has the following problems.

(1) In order to suppress the temperature rise of the cooling water, it is essential to replenish the cooling water into the cooling water tank, but in this case, the flow of water in the tank stops in the upper part, and the water does not move in the lower part. When a high-temperature steel strip is immersed in cooling water, a vapor film is generated on the surface of the steel strip, and the removal of this vapor film,
Because it was difficult to destroy, there was a limit to its cooling efficiency. Therefore, in order to increase the speed and efficiency of the cooling process, it is necessary to increase the size of the immersion cooling device, which is disadvantageous in terms of construction costs and installation space. Furthermore, it was almost impossible to increase speed by improving existing equipment.

(2) As mentioned above, the uneven movement of water in the immersion water tank causes temperature unevenness, which adversely affects the steel strip.

(3) When reusing the cooling water discharged from the immersion cooling water tank as hot water, cascade control must be performed using at least two immersion tirF tanks, which not only increases the size of the installation but also complicates it. Control is also required.

By the way, in order to advantageously solve the above-mentioned problems, the inventors disclosed in Japanese Patent Application No. 162909/1982 that, when final cooling a steel strip passed through a cooling zone of a continuous annealing line, As shown in Figure 3, a steel strip is covered with a water-cooling jacket that has flow regulating plates placed opposite each other across the cooling water flow path from the front and back sides of the steel strip. We have proposed a cooling method for a steel strip in continuous annealing treatment, which consists of forcing cooling water to flow in a rectifying direction along the front and back surfaces of the steel strip, and a cooling device suitable for carrying out the method.

The development of the new cooling technology described above has made it possible to cool the steel strip with much higher efficiency than before, and the processing capacity in continuous annealing treatment has been greatly improved.

(Problem to be solved by the invention) However, the above-mentioned cooling technology has problems when the cooling water supply temperature changes due to seasonal factors, or the amount of steel strip threaded changes. The problem remained that the temperature of the steel strip fluctuated and deviated from the target temperature.

Figure 4 shows the results of an investigation into the relationship between the threading amount of the steel strip and the steel strip temperature after cooling when the cooling water temperature is 40°C.As the threading amount increases, the temperature of the steel strip also increases. The temperature may become high and out of the target temperature range.

In the cooling method using the above-mentioned water-cooling jacket, this invention constantly and stably cools the steel strip temperature to a predetermined target temperature without being influenced by normally considered fluctuation factors such as the amount of steel strip passing through or the cooling water temperature. The purpose of this study is to propose a method for controlling the plate temperature at the exit side of a steel strip cooling device.

(Means for Solving the Problems) This invention provides for a steel strip that has passed through a cooling zone of a continuous annealing line to be placed inside a water-cooled jacket that is provided with rectifying plates that are disposed opposite to each other across a cooling water flow path from the front and back surfaces of the steel strip. In the method of cooling the steel strip by forcing the cooling water to flow in the water cooling jacket in the opposite direction to the running direction of the steel strip and along the front and back surfaces of the steel strip when conducting final cooling. , a method for controlling outlet side plate temperature of a steel strip cooling device in a continuous annealing line, characterized in that the temperature at the outlet side of the water cooling jacket of the steel strip is controlled to a predetermined target temperature by controlling the cooling water level in the water cooling jacket. It is.

This invention will be specifically explained below.

FIG. 1 schematically shows a control system according to the present invention together with a water-cooled jacket type cooling device. Number 1a in the figure.

1b are rectifying plates for forcibly guiding cooling water along the front and back surfaces of the steel strip as rectifiers, and these rectifying plates 1a and lb form a water cooling jacket 1 having a vertical U-shaped tubular structure. Configure. 2 is a deflector roll, 3 is a cooling water supply pipe, 4 is a pump, and 5 is a storage tank for cooling waste water.

Now, in the cooling device configured as described above, cooling water is introduced into the water cooling jacket 1 from the supply port provided on the downstream side of the running path of the steel strip S, and the cooling water is introduced into the water cooling jacket 1 in the running direction of the steel strip S. The steel strip is efficiently cooled while being forced to flow in the opposite direction, and then overflows from the discharge port.In this invention, the level of cooling water in the water cooling jacket is adjusted as follows. By doing this, the temperature of the steel plate on the exit side is controlled.

Reference numeral 6 denotes a lifting device installed on the steel strip entry side of the rectifying plate 1a, which can be freely raised and lowered by a lifting device 10 comprising, for example, a cylinder 7, a lobe 8, a sheave 9, and the like. That is, by raising and lowering this lifting plate 6, the overflow level of the cooling device 1 can be changed.

FIG. 2 shows a preferred bonding state between the elevating plate 6 and the rectifying plate 1a.

In addition, 11 is a thermometer for draining the steel strip after cooling treatment, 12 is a thermometer for measuring the temperature of the steel strip after cooling treatment, and 13 is a level meter for measuring the overflow height. Further, 14 is a thermometer for measuring the temperature of the cooling water, 15 is a thermometer for detecting the temperature of the cooling water at the outlet side of the cooling device 1, and 16 is a calculation device, including the thermometer 12, the level meter 13, and the cooling water temperature. Water thermometer 14. 15 detection words, the cooling target temperature 17 of the steel strip S, and the steel strip threading amount 18 are input manually, and the overflow level for achieving the target strip temperature is calculated. The calculation result is output to the control device 19, and the lifting device 10 controls the lifting plate 6 to reach a predetermined level.

(for production) Next, the contents of the calculation in the calculation device 16 will be explained.

Now, the cooling length of the steel strip S in the water-cooling jacket 1 (the length of contact between the cooling water and the steel strip) is directly m〉, and the threading amount of the steel strip is!
+I (kg/h), the steel strip temperature before and after cooling is TSI (t
), Ts5 (t), and strip width B (m
), the specific heat of the strip is CP (kcal/l ・kg)
, heat (if the transfer coefficient is α (kcal/m2·h·°C)), the amount of heat transfer Q (kcal/h) from the steel strip to the cooling water in the cooling device is expressed by the following equation.

Q=2・α・L-B-4JT ・・・・・・ (1
)-C3・W・(Ts+'rs:)...
... (2) Here, 4T (t) is cooling water and IJ
It is the logarithmic average temperature difference of the whelk, and is calculated by the following formula.

Note that TI+TwO(t) are the cooling water supply temperature and overflow water temperature, respectively.

Therefore, the cooling length is calculated from equations (1) and (2). For example, when the steel strip passing amount changes from W to W', the steel strip exit temperature becomes T.
Assuming that T's'' changes from s'o to T's''0, the following equation holds true since the cooling length is not changed at this point.

In addition, the steel strip entrance temperature T,! is constant due to the heat treatment in the annealing furnace in the front stage of the water-cooled jacket, and as the steel strip exit temperature changes, the overflow water temperature also changes, and therefore the average logarithmic temperature difference 7jT also changes to AT'. do.

Therefore, the steel strip outlet temperature T's? The cooling length L' required to return i to Ts; is determined by the following equation.

That is, by changing the current cooling length by 71L=L'-L (1), the steel strip outlet temperature can be maintained at Tsm.

Although the above description has been made regarding the case where the sheet passing amount changes, calculations can be made in the same way when the cooling water supply temperature changes.

(Practical Example) Using the cooling device and control system shown in FIG. 1 above, a steel strip was cooled under the following conditions.

・Steel strip dimensions: Thickness 1mm, width 1000mm ・Cooling water temperature:
40℃ ・Cooling water amount: 14 T/h ・Steel strip cooling start temperature = 150℃ ・Target temperature after cooling treatment: 50 to 60℃ ・Initial threading amount:
30T/h ・Cooling water overflow height = 0.6m Cooling treatment was started under the above conditions and the throughput was gradually increased, and the temperature at the outlet of the cooling device for the steel strip also gradually increased accordingly. The overflow height was raised to 0.8 m when the throughput reached 40 T/h. As a result, the temperature on the exit side of the steel strip decreased to 53°C, so we continued the cooling process, and when the throughput reached 50T/h, the temperature on the exit side of the steel strip tended to rise again. The overflow height was raised to 1.2m.

As a result, the steel strip temperature decreased to 51°C, and thereafter, even if the threading rate was increased to 60 T/h, the steel strip temperature did not exceed 60°C. As shown in Fig. 5, the operating results are summarized and shown, even when the throughput rate changes from 30T/h to 60T/h, the temperature at the outlet of the steel strip cooling device is always kept at the target temperature of 50T/h. It was possible to keep the temperature within the range of ~60°C.

(Effects of the Invention) Thus, according to the present invention, even if the threading amount etc. fluctuates in the cooling process in the continuous annealing line, the steel strip temperature is always kept within the predetermined target temperature range without being influenced by such fluctuation factors. can be accommodated in

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a control system according to the present invention together with a water-cooled jacket type cooling device, Fig. 2 is a diagram showing a preferred state of connection between the elevating plate and the rectifying plate, and Fig. 3 is a water-cooled jacket type cooling device. Fig. 4 is a schematic diagram of the cooling device, and Fig. 4 is a graph showing the relationship between the sheet passing amount and the steel strip temperature on the outlet side of the water-cooled jacket when the temperature on the cooling side is constant. It is a graph showing the relationship between the throughput amount and the temperature of the steel strip on the exit side of the water-cooled jacket when this application is applied. 1...water cooling jacket) la, lb...straightening plate 2
... Deflection crawl 3 ... Cooling water supply pipe 4 ... Pump 5 ... Cooling wastewater storage tank 6 ... Elevating plate 7 ... Cylinder 8 ...
Rope 9... Sheave 10... Lifting device
11... Ringer roll 12... Thermometer
13... Level meter 14, 15... Thermometer
16... Arithmetic device 17... Cooling target temperature 18
...Steel strip threading amount 19...Control device Fig. 2 Fig. 3 Fig. 4 Threading amount (T/h) Fig. 5 Appropriate reaction amount c t/h)

Claims (1)

[Claims] 1. A steel strip passed through a cooling zone of a continuous annealing line,
When conducting final cooling by guiding the cooling water from the front and back surfaces into a water-cooling jacket equipped with rectifying plates arranged oppositely across the cooling water flow path, the cooling water is directed in the direction opposite to the running direction of the steel strip within the water-cooling jacket. Moreover, in the method of cooling the steel strip through forced flow as rectification along the front and back surfaces of the steel strip, by controlling the level of cooling water in the water cooling jacket, the temperature at the exit side of the water cooling jacket of the steel strip can be adjusted to a predetermined target temperature. 1. A method for controlling the plate temperature at the exit side of a steel strip cooling device in a continuous annealing line.