JPH0229732B2 - RENZOKUSHODONRAINNIOKERUKOTAINOREIKYAKUSOCHISHUTSUGAWAITAONSEIGYOHOHO - Google Patents

Description

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

(Conventional technology) In general, original sheets for surface treatment and steel sheets for deep drawing are
After cold rolling, so-called continuous annealing is performed in which heat treatments such as heating, soaking, and cooling are sequentially performed in order to impart predetermined mechanical properties.

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 through which a refrigerant is passed, and immersion cooling involves The steel strip is cooled by immersing it in a cooling water tank, 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, special public relations
The methods disclosed in Publications No. 11931 and No. 57-11933 use multiple cooling water tanks to control water injection into each tank, and in combination with spray cooling and mist cooling. In addition to efficiently cooling the belt, the temperature of the water after cooling is raised as much as possible so that it can be used effectively 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 by 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 perspective, it is becoming less of a problem no matter how high the cooling rate is.In fact, from the standpoint of increasing speed and production efficiency,
Further improvement of the cooling rate in final cooling is desired.

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 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 at the upper part, and the water does not move at the lower part. As a result, when a high-temperature steel strip is immersed in cooling water, a vapor film is generated on the surface of the steel strip, and this vapor film is difficult to remove or destroy, so cooling efficiency has its own limits. .
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 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 tanks.
Therefore, not only the device becomes larger but also requires complicated control.

By the way, in order to advantageously solve the above-mentioned problems, the inventors disclosed in Japanese Patent Application No. 162909/1987 that, when final cooling a steel strip passed through a cooling zone of a continuous annealing line, As shown in Figure 4, a steel strip is covered with a water-cooling jacket that has rectifier plates placed opposite each other across the cooling water flow path from the front and back sides of the steel strip, and a water cooling jacket is passed through the water-cooling jacket in the opposite direction to the running direction 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 5 shows the relationship between the cooling water supply temperature and the steel strip temperature after cooling when the steel strip passing rate is 40T/h.As is clear from the figure, the cooling water supply temperature is If it is too high or too low, the steel strip temperature will be out of the target temperature range.

Figure 6 also shows two cooling water temperatures of 40°C and 30°C.
The results of an investigation into the relationship between the threading amount of the steel strip and the temperature of the steel strip after cooling for each level are shown, but as the threading amount increases, the temperature of the steel strip also rises and may deviate from the target temperature range. There is.

In the cooling method using the water-cooled jacket described above, this invention is capable of constantly and stably cooling the steel strip temperature to a predetermined target temperature without being affected by normally considered fluctuation factors such as the amount of steel strip threaded 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) The present invention provides for a steel strip that has passed through a cooling zone of a continuous annealing line to be placed in a water-cooled jacket equipped with rectifying plates arranged oppositely across a cooling water flow path from the front and back surfaces of the steel strip. In a method of cooling a steel strip by forcing 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. , As the cooling water, a part of the cooling waste water on the outlet side of the water cooling jacket is circulated and mixed with fresh water supplied on the inlet side, and this mixture ratio is adjusted to control the temperature of the cooling water. , a method for controlling the temperature at the exit side of a cooling device for steel strip in a continuous annealing line, characterized in that the temperature at the exit side of the water cooling jacket of the steel strip is controlled to a predetermined target temperature.

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 1 in the diagram
Reference numerals a and 1b are current plates for forcibly guiding the cooling water as rectification along the front and back surfaces of the steel strip, respectively, and these current plates 1a and 1b constitute the water cooling jacket 1. 2 is a deflector roll, 3 is a cooling water supply pipe, 4 is a storage tank for cooling wastewater, and 5 is a pump.

Now, in the cooling system constructed as described above, the 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 flows through the jacket 1 in the running direction of the steel strip S. While the steel strip is forced to flow in the opposite direction, it is efficiently cooled and then discharged from the discharge port.
In this invention, a part of the cooling waste water is recycled and recycled for temperature adjustment of the cooling water.

6 is a return pipe for circulating cooling waste water, 7
Reference numeral 8 indicates a thermometer for detecting the temperature of circulating water, 8 indicates a flow rate control valve for circulating water, and 9 indicates a flow meter for circulating water. Also 1
0 is the piping for supplying fresh cooling water, and 11, 12,
13 is a thermometer, a flow rate control valve, and a flow meter for fresh cooling water, and 14 is a thermometer for detecting the outlet side plate temperature of the steel strip.

Furthermore, 15 is a computing unit, which calculates the amount of circulating water and fresh water based on the detected values from each detector so that the supplied cooling water temperature becomes a predetermined temperature. The obtained calculation results are output to the flow rate controllers 16 and 17,
The opening degrees of the flow control valves 8 and 12 are adjusted according to the output. The circulating water and fresh water, each adjusted to a predetermined amount, are mixed in the mixer 18 to form cooling water at a predetermined temperature, which is then supplied to the water cooling jacket 1 via the supply pipe 3.

Note that 19 is a ringer roll for draining the steel strip S after cooling treatment.

(Function) Next, the contents of the calculation in the calculation device 15 will be explained.

The allowable temperature range for the target cooling temperature T _SO of the steel strip is now
As shown in equation (1).

T _SO1 ≦T _SO ≦T _SO2 ...(1) When the amount of circulating water is Q _C and the amount of new water is Q _N , the amount Q of cooling water supplied is expressed by the following equation (2).

Q=Q _C +Q _N ...(2) Also, T _W is the set temperature of the cooling water, and T W is the temperature of the circulating water.
When T _WC is the new water temperature and T _WN is the new water temperature, the following equation (3) holds true.

Q _C :Q _N =T _W −T _WN /T _WC −T _WN :T _WC −T _W /T _WC −T _WN, that is, (T _W −T _WN )Q _N = (T _WC −T _W )Q _C … …(3) Therefore, from equations (2) and (3), Q _C =T _W −T _WN /T _WC −T _WN Q …(4) Q _N =T _WC −T _W /T _WC −T _WN Q...(5) is calculated.

First, the temperature of the steel strip detected by thermometer 14 is
Determine whether T _SO ′ is within the range of equation (1).
If equation (1) is satisfied, the detected temperatures T _WN and T _WC
Based on this, calculate Q _C and Q _N from equations (4) and (5).

On the other hand, if the upper limit is exceeded, the set water temperature T _W is lowered by a certain value.

T _W = T _W −a (6) Conversely, if the water temperature is below the lower limit, increase the set water temperature T _W by a certain value.

T _W = T _W +a ... (7) Next, based on the newly set water temperature T _W , the circulating water amount Q _C and the new water amount Q _N are calculated from equations (4) and (5).
Here, the detected values of the thermometers 7 and 11 are used for each water temperature T _WC and T _WN .

To summarize the above, the flow is as shown in Figure 2.

FIG. 3 schematically shows the relationship between the sheet temperature on the outlet side of the steel strip and the threading amount when the cooling water supply temperature is controlled by the procedure described above.

(Example) A steel strip was cooled under the following conditions using the cooling device and control system shown in FIG. 1 above.

●Steel strip dimensions: thickness 1mm, width 1000mm ●Cooling water amount: 13.2T/h (new water amount: 3.3T/h, circulating water amount: 9.9T/h) ●Cooling water amount: 40℃ (new water temperature: 10℃, circulating Water temperature: 50℃) ●Target temperature after cooling treatment: 50 to 60℃ ●Initial threading rate: 20T/h When the threading rate was gradually increased under the above conditions, the threading rate reached 40T/h. At one time, the temperature at the outlet of the steel strip cooling system was about to exceed the upper limit of the target temperature of 60℃, so the mixing ratio of fresh water and circulating water was changed to 7.1T/h and 6.1T/h, respectively. The cooling water temperature was reduced to 30℃. As a result, the steel strip temperature dropped to 50℃, so we continued the cooling process, and when the throughput reached 65T/h, the steel strip temperature tended to exceed 60℃ again. , the mixing ratio of fresh water and recycled water, respectively.
The cooling water temperature was lowered to 20℃ by adjusting to 11T/h and 2.2T/h.

As a result, the steel strip temperature decreased to 50°C, and thereafter, even when the throughput was increased to 80T/h, the steel strip temperature did not exceed 60°C. As shown in Fig. 7, the operating results are summarized and shown, even when the throughput rate changes from 20T/h to 80T/h, the temperature at the outlet of the steel strip cooling device is always kept at the target temperature of 50~80T/h. 60℃
was able to fit within the range.

(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 drawings]

FIG. 1 is a schematic diagram showing a control system according to the present invention together with a water-cooled jacket type cooling device, and FIG.
A flowchart showing the control procedure according to the present invention,
FIG. 3 is a graph showing the relationship between the amount of sheet passing and the temperature of the steel strip at the exit side of the water-cooled jacket when performing sheet temperature control according to the present invention. FIG. Figure 5 is a graph showing the relationship between the cooling water inlet temperature and the water-cooled jacket outlet steel strip temperature when the threading amount is constant. A graph showing the relationship between the amount and the temperature of the steel strip at the exit side of the water-cooled jacket.
FIG. 7 is a graph showing the relationship between the throughput amount and the temperature of the steel strip at the exit side of the water-cooled jacket when the present invention is applied to actual operation. 1... Water cooling jacket, 1a, 1b... Current plate, 2... Deflector roll, 3... Cooling water supply pipe, 4... Cooling wastewater storage tank, 5... Pump, 6... Return piping , 7, 11, 14... Thermometer, 8, 12... Flow rate control valve, 9, 13... Flow meter, 15... Arithmetic unit, 16, 17... Flow rate controller, 18... Mixer, 19 ...Ringer roll.

Claims (1)

[Scope of Claims] 1. A steel strip passed through a cooling zone of a continuous annealing line is guided from its front and back surfaces into a water-cooled jacket equipped with baffle plates placed opposite each other across a cooling water flow path for final cooling. In this method, the steel strip is cooled by forcing the cooling water to flow in the water-cooling jacket in a direction opposite to the running direction of the steel strip and along the front and back surfaces of the steel strip, in which the water-cooling jacket is used as the cooling water. A part of the outlet cooling waste water is circulated and mixed with the fresh water supplied to the inlet side, and by adjusting this mixing ratio and controlling the temperature of the cooling water, the water cooling jacket outlet of the steel strip can be cooled. 1. A method for controlling outlet side plate temperature of a steel strip cooling device in a continuous annealing line, the method comprising controlling the side temperature to a predetermined target temperature.