JPS61104032A - Method for cooling steel strip - Google Patents

Abstract

PURPOSE:To recover high-temp. treating water from the front water vessel by supplying water into the rear water vessel of a cooling water vessel in accordance with the temp. of the treating water in the vessel, injecting treating water from the rear water vessel into the front water vessel by overflow, and controlling the inlet side temp. of a steel strip in accordance with the treating temp. of the rear water vessel and the specified relation. CONSTITUTION:A cooler 7 is provided in the cooling zone 6 of a steel strip 3 positioned directly before a cooling vessel consisting of a front water vessel 1 and a rear water vessel 2, and the steel strip 3 is precooled. Besides, water is supplied into the rear water vessel 2 by a pump 10 for supplying cooling water in accordance with the temp. of the treating water detected by a temp. detector 8, and overflown water is injected into the front water vessel 1. At this time, the inlet side temp. Ts( deg.C) of the steel strip 3 and the temp. T2( deg.C) of the treating water in the rear water vessel are controlled in accordance with the relational equation, and high-temp. treating water is recovered from the front water vessel 1 through a treating water recovery pipe 13. In the equation, Tw is the temp. ( deg.C) of the cooling water.

Description

Detailed Description of the Invention (Industrial Field of Application) This specification relates to an improved method for cooling a steel strip in which the steel strip is passed through a cooling water tank for final cooling in a continuous heat treatment or similar line. The technical content described in the book is particularly the significant reduction in the amount of water treated in the cooling water tank used for the final cooling of the strip, and the improvement in the amount of treated water used to cool the steel strip! The purpose of this project is to propose the development results of an effective final cooling method for steel strips while making effective use of the amount of heat in one strip.

(Prior art) Regarding final cooling in a continuous heat treatment line for steel strips,
For example, Japanese Patent Publication No. 11931/1983 describes a cooling water tank in which the steel strip is continuously immersed, divided into a front water tank and a rear water tank, and each tank is equipped with a water temperature detector and a temperature control device. Based on the rise in the temperature of treated water in each water tank, which is set in the temperature control device in advance, as the steel strip passes through the immersion, cooling water is supplied to the subsequent water tanks by the temperature control device through the operation of the water temperature detector. It is disclosed that cooling water is supplied by a pump, and for the former water tank, treated water from the latter water tank is poured into the water tank by a water supply pump provided between the respective water tanks, and temperature adjustment 3 is performed for each tank.

In this case, generally the treated water in the latter stage water tank is kept at a temperature of 30 to 50°C in order to keep the temperature of the final cooling steel strip below 50°C, and the treated water in the earlier stage water tank is kept at a temperature of 80°C so that it can be reused as high temperature water. Each temperature is set to approximately 100°F.

The cooling water supplied to the second stage water tank is useful for adjusting the temperature of the treated water in the second stage water tank, and also occupies the portion of pouring into the first stage water tank and is used to adjust the temperature of the treated water, but the generation of surplus water is unavoidable. However, this had the disadvantage of wasteful discharge from the drain pipe installed in the rear water tank.

Since this wastewater has a low temperature of 50° C. or less, it is difficult to recover and reuse it as a heat source, and as the amount of steel strip processed increases, the amount of wastewater discharged also increases, making disposal time-consuming.

Points to be solved by the invention C) Eliminate the generation of low-temperature wastewater as described above, and direct the entire amount of water supplied to the rear-stage water tank to the front-stage water tank as high-temperature treated water where thermal energy can be easily recovered through heat exchange. It is an object of the present invention to achieve appropriate final cooling of the 'rrwj zone while making effective use of it.

Means for Solving Problem C) This invention provides a cooling method in which the steel strip is sequentially passed through a cooling water tank divided into several stages along a continuous heat treatment ridge or similar line for final cooling. The steel strip is cooled by a cooling device installed in the cooling zone of the cooling line, and water is supplied to the downstream water tank of the cooling water tank according to the temperature of the treated water in that tank. During this time, the steel strip is poured at gJU temperature T.
8 and the temperature T of the treated water in the downstream water tank are controlled in accordance with the relationship of the following formula, and high temperature treated water is recovered from the upstream water tank.

Ts: Temperature at the entrance of the steel strip into the front water tank C) T: Temperature of the treated water in the rear water tank C″C) TW: Cooling water temperature (°C) In Figure 1, 1 is the front water tank and 2 is the rear water tank. , 8 is a steel strip, 4 is a temperature detector for the steel strip, 5 is a strength control device for the steel strip, 6 is a cooling zone that cools the steel strip at the end of the heat treatment line, and 7 is the cooling device. 8 is a temperature detector for the second stage water tank 2, 9 is a temperature control device for the second stage water tank 2, 10 is a cooling water supply pump, 11 is a cooling water supply pipe, 12 is a cooling water temperature detector, and 13 is a high temperature treatment This is a water recovery pipe.

The temperature of the strip 3 is detected by the temperature sensor 4 of the steel strip, and the operation of the cooling device 7 in the cooling strip 6 is controlled according to the temperature TF3 on the inlet side of the strip 3 toward the cooling water tank, which is set in the temperature control device 5. Control.

The steel strip a is subsequently introduced into the front water tank 1, and the thermal energy of the steel strip 8 is transferred to the treated water, and 7M of the treated water from the front water tank 1 is heated to 71°C.

The steel strip 8 advances from the front-stage water tank 1 to the rear-stage water tank 2 to achieve the final cooling temperature, so the temperature of the treated water is detected by the temperature detector 8 installed in the rear-stage water tank 2, and the temperature is controlled according to the temperature rise. Cooling water with a temperature Tw''C is supplied by the cooling water supply pump 10 so that the treated water temperature T, ``C'' set in the device 9 is reached. By supplying the treated water, the temperature T□ of the treated water in the front water tank 1 can be guided to a heat exchanger or the like through the treated water recovery pipe 18 at a temperature that can be reused.

During the final cooling of the strip as explained in FIG. 1, the control of the temperature T8 on the inlet side of the steel strip and the temperature T2 of the treated water in the downstream water tank 2 is carried out by a computing device as roughly shown in FIGS. 2 and 3. The operation of the computing device in FIG. 2 is controlled by the operation of 14. The operation of the arithmetic unit in FIG.
According to the temperature change of the treated water in the second stage water tank 2, the input (IIi degree Ts) of the steel strip that should match the preset treated water temperature T□ of the first stage water tank 1 is calculated by the calculation unit [14] The temperature control device 6 compares the temperature at the entrance side of the steel strip with the temperature T at the entrance side of the steel strip detected by the temperature sensor 4', and controls the temperature at the entrance side of the steel strip to be Ts.

At this time, the temperature T2 of the treated water in the latter water tank 2 is controlled by detecting the temperature of the treated water with a temperature detector 8 installed in the water tank.
In response to the temperature rise, the cooling water supply pump 10 supplies cooling water at a temperature TW° C. so that the treated water temperature T, “C” set in the temperature control device 9 is reached.

The operation of the arithmetic unit 14 in FIG. 8 is based on the temperature Tw°C of the cooling water supplied to the rear water tank 2 and the temperature Ts''C of the steel strip, which is set in advance for the treated water in the front water tank 1. The temperature T of the treated water in the rear water tank 2 that should match the temperature T1 is calculated by the arithmetic unit 14, and the calculated result and the temperature T of the treated water in the rear water tank 2 detected by the temperature detector 9 are used.
2' by the temperature control device 9, and the temperature T of the treated water in the downstream water tank 2 is determined.

Perform the control that should be achieved.

At this time, the inlet temperature Ts of the steel strip is controlled by detecting the inlet temperature Ts/ of the steel strip by the temperature detector 4 installed on the outlet side of the cooling zone 7, and according to the temperature rise, a temperature control device is operated. The steel strip is controlled so that the temperature at which it enters the steel strip is T8, which was set at T5.

(effect) From the latter water tank 2 during the final cooling process of the steel strip.

The supply amount W0 of treated water supplied to the front water tank 1 and the supply amount W2 of cooling water supplied to the rear water tank 2 can be expressed as the following formula.

Here, Wo: supply amount of treated water supplied from the second stage water tank 2 to the first stage water tank 1 c tons/h) W, supply amount of cooling water supplied to the second stage water tank 2 - (tons/hl) W8: steel strip treatment Amount (tons/h) Ts: Temperature at the entrance of the steel strip (Cl T1: Temperature of the treated water in the front water tank 1 ('C) T,: Temperature of the treated water in the rear water tank 2 (C) T1: Cooling water temperature ('C) C) Ratio of ap:fll band @ (kca4%9℃l (Op=
0.121 The amount of cooling water and treated water supplied to the second stage water tank 2 and the first stage water tank 1 is calculated as follows from formulas (1) and (2): W□=
W, and is expressed by the following formula.

In formula (3), in order to recover the treated water in the front water tank 1 as high-temperature water, the temperature range of the treated water to be obtained in that water tank is set, and the inlet temperature T8 of the steel strip and the treated water in the rear water tank 2 are set. The temperature T may be controlled to suit the temperature range.

Therefore, the temperature range of the treated water temperature T in the front water tank 1 is set to the conditions described below.

If the inlet temperature Ts of the steel strip introduced into the front water tank L is high and a large amount of water vapor is generated due to boiling of the treated water as it passes through the water tank, the operation for cooling the steel strip will become difficult. There is no risk of oxidation of the steel strip due to water vapor.
The temperature T0 of the treated water in the front water tank 1 is set to 100°C or less.

According to formula (3), the temperature of the treated water in the front water tank 1 is 100°C.
In order to satisfy
It is necessary for the treated water temperature T2 and the cooling water temperature TV to satisfy the relationship of the following formula.

In addition, the minimum temperature at which the treated water in the pre-stage water tank 1 can be used is 1. For example, when replenishing a cleaning tank installed in a continuous annealing line, it is usually set at 70 to 90°C, so the minimum temperature of the treated water in that tank is 1. The temperature shall be 70°C or higher. formula(
In order to make the treated water temperature T0 of the front stage water tank 1 70°C or higher in 3), the temperature T8 of the steel strip, the treated water temperature T2 of the rear stage water tank 2, and the cooling water temperature TW are determined according to the relationship of the following formula. need to be satisfied.

Regarding the temperature range of the inlet side temperature Ts of the steel strip and the treated water temperature T3 of the downstream water tank 2 in equation (4>1 (5)), the following conditions are set.

Regarding the temperature T2 of the treated water in the second stage water tank 2, the final cooling temperature of the steel strip is usually set to 50' (or less), so the temperature of the treated water is 30'.
Set to ~50°C.

Regarding the inlet temperature T6 of the steel strip, if the steel strip is cooled more than necessary before being introduced into the pre-stage water tank 1, not only will the treated water in the water tank not be recovered as high-temperature water, but the temperature will rise to 350' as shown in FIG. When the steel strip C is cooled down to 110℃ using a gas jet cooling device, the temperature of the steel strip is 110℃.
If the temperature drops below 50'C, the amount of electricity required becomes very large, causing problems such as increased cooling costs.Furthermore, if the temperature of the steel strip exceeds aOO'C and the final cooling is completed, the steel strip will be oxidized. The film becomes thicker and a defect called temper color occurs.

Therefore, the lower limit of the steel strip entrance temperature Ts is set to 15t)''C1 and the upper limit is set to 250''C.

5th FgJ is a graph showing the relationship between the inlet temperature Ts of the steel strip and the temperature of the treated water in the rear water tank 2 using the treated water temperature TI of the front water tank 1 as a parameter.

This figure shows the case where the temperature Tw of the cooling water supplied to the rear water tank 2 is 25°C, and as described above, 1.
=@ Set the inlet temperature Ts of the band and the temperature T of the treated water in the second water tank 2, and cool the steel strip to reduce the temperature T of the treated water in the first water tank.
0 is stable at a certain temperature.

Moreover, the shaded area shown in the figure indicates each condition 2 under which the temperature T8 on the inlet side of the steel strip, the temperature T0 of the treated water in the front water tank 1, and the temperature T of the treated water in the rear water tank 2 are set.

Therefore, the final cooling of the steel strip can be performed by setting conditions that satisfy the following equations obtained from equations (4) and (5).

It is.

! Example) Regarding the example according to the present invention, the steel strip processing amount Ws==1
00) n/h, temperature of front water tank 1? , = 85°C and the temperature of the cooling water supplied to the subsequent water tank 2° = 25°C, and the steel strip was cooled.

(Specific heat Op of the steel strip here = 0.12 kca/ /
kg°C] Example 1 During the final cooling of the steel strip according to the present invention, the temperature T of the treated water in the downstream water tank 2 was set to ==40'', and the temperature of the cooling water Tw =
This temperature was input to the calculation device 14 together with 25°C, and the entrance temperature T6 of the steel strip was calculated based on equation (6), which was 220'C.

The results obtained in the final cooling of the steel strip under the above conditions are that the temperature of the treated water in the front water tank 1 is T = 85°C, the cooling water is supplied iiw,
=aehn/h, obtained amount of treated water W, =86) n/h
Met.

Example 2 During the final cooling of the steel strip according to the present invention, the entrance side temperature of the steel strip is set to Ts=200'C, and the cooling water temperature is set to Ts.

225°C was input to the arithmetic unit 14, and the temperature T of the treated water in the rear water tank 2, = 41.5°C, was calculated based on equation (6).

The results obtained in the final cooling of the steel strip under the above conditions are as follows:
Treated water temperature T in front stage water tank 1, = 85°C1 Cooling water supply 1
! k W2 = 31.2) n/h, and the obtained amount of treated water W = 31.2) n/h.

Comparative example: By using the conventional cooling method, the entrance temperature of the steel strip is Ts=200°
The temperature of the treated water in C1 rear water tank 2 is set to T, = 40°C,
The supply amount for each water tank was calculated based on equations (1) and (2), and the final cooling of the steel strip was performed according to these conditions.

The obtained results show that the temperature of the treated water in the front water tank 1 is T□=86°
C1 Cooling water supply dragon W2 = 36) n/h% Treated water supply supplied to front stage water tank 1 W, = 31.2) n/h, amount of treated water discharged from rear stage water tank 2 (W, -w
, > = W, = 4.8) n/h.

Table 1 summarizes the above results.

Table 1 As shown in Table 1, in the final cooling of the steel strip according to the present invention, the cooling water supplied to the rear water tank 2 is poured into the front water tank 1 due to overflow. Even though the displacement amount W8 is 0, the conventional cooling method
Except for supplying treated water by the cooling water supply pump installed between the rear stage water tank 1 and the front stage water tank 2, the water is discharged from the drain pipe - in this case, the cooling water supply pipe W2 = 36) n/h. On the other hand, the amount of treated water recovered as treated water at 85°C was 81.2 tons/h, meaning that 4.8 tons/h of treated water was wasted.

Treated water W recovered by the method of cooling the belt according to the present invention
Compared to conventional cooling methods, the entire amount of cooling water supplied to the rear water tank 2 is reduced to a high level of drought.

It can be seen that this was a dramatic improvement.

(Effects of the invention) According to this invention, it is possible to greatly reduce the amount of water treated in the cooling water tank used for the final cooling of the strip, and to effectively utilize the heat of the steel strip obtained from the treated water. The hot water can be recovered and the steel strip can be appropriately cooled.

[Brief explanation of the drawing]

The first factor is the method for cooling a steel strip according to the present invention. Figure 4 is a graph showing the relationship between the steel strip inlet temperature Ts and the required power, and Figure 5 shows the relationship between the steel strip inlet temperature T0 and the treated water temperature T2 using the treated water temperature T□ as a parameter. This is a graph shown as . 1... Front water tank 2... Back water tank 3...
Steel strip 4...Temperature detector 5...Temperature control device 6...Cooling zone 7...Cooling device
8...Temperature detector 9...Humidity side wJ device 1
0... Cooling water supply pump 11... Cooling water supply pipe
12... Temperature detector 13... Treated water recovery pipe
14... Arithmetic device Figure 1 Figure 3 Figure 4 T5 (@C) Figure 5

Claims (1)

[Scope of Claims] 1. In a cooling method in which the steel strip is sequentially passed through cooling water tanks divided into multiple stages in a continuous processing or similar line for final cooling, the steel strip is installed in the cooling zone of the line located immediately before the cooling water tank. At the same time, water is supplied to the downstream tank of the cooling water tank according to the temperature of the treated water in that tank, and the treated water from the downstream tank is poured into the upstream tank of the cooling water tank by overflow. During this period, the temperature T_s on the inlet side of the steel strip and the temperature T_2 of the treated water in the downstream water tank are controlled in accordance with the relationship shown in the following equation, and the high temperature treated water is recovered from the downstream water tank. Method. Note [(70-T_2)^2]/(T_2-T_w)+70
≦T_s≦[(100-T_2)^2]/(T_2-T
_w) +100 where T_s: Temperature at the entrance of the steel strip to the front water tank (°C) T_2: Temperature of treated water in the rear water tank (°C) T_w: Cooling water temperature (°C)