JP4490804B2 - Method of cooling steel sheet in continuous annealing furnace - Google Patents

Description

The present invention relates to a cooling method of a steel sheet in the continuous annealing furnace in which a plurality arranged a cooling device in series of the gas jet.

For example, a continuous annealing line for steel plates (steel strips), for example, after passing steel strips from payoff reels through entrance equipment such as welding machines, cleaning equipment, entrance loopers, heating zones, soaking zones, slow cooling zones, After continuous annealing in a continuous annealing furnace having a primary cooling zone, an overaging zone, and a secondary cooling zone, after passing through the exit looper, continuously temper-rolled by a temper rolling mill, and then after inspection through an inspection looper, It is configured to be wound in a coil shape by a tension reel.
In the primary cooling zone of this continuous annealing furnace, a steel plate having a temperature of about 700 to 400 ° C. is cooled to a temperature of about 450 to 200 ° C. at a required cooling rate by, for example, a gas jet cooling type cooling device. In order to ensure the speed, a plurality of large-capacity gas jet cooling devices are generally arranged.
These gas jet cooling devices are conceptually arranged with blowing gas boxes having a number of protruding nozzles as disclosed in FIGS. 3 and 4 of Patent Document 1, with the protruding nozzles facing both sides of the steel plate. In addition, the non-oxidizing cooling gas (for example, H ₂ -enriched N ₂ ) is pumped by a blower and sprayed from the protruding nozzle onto the steel plate surface (both sides) to cool the steel plate, and the concentration of the cooling gas The cooling capacity can be adjusted by selecting (H ₂ concentration), temperature, flow rate, and flow rate.

As each of these cooling devices, those having the same level of cooling capacity are used, and the temperature controllability deteriorates (becomes coarser) as the size increases, and the exit side of the cooling zone, that is, the exit side of the final cooling device Thus, there is a problem that a large cooling error is likely to occur with respect to the cooling target temperature of the steel plate.
In general, when cooling with a gas jet type cooling device, the temperature of the blower is controlled by controlling the blower rotation speed. However, in the case of a large capacity cooling device at the current level, the blower rotation speed is changed by, for example, 1%. Theoretically, the temperature variation on the steel sheet side is about 5 ° C., for example, and temperature control can be performed at this temperature step, but even if control is performed to change the blower rotational speed by 1%, it actually fluctuates. Therefore, it is inevitable that a cooling error of about 10 to 15 ° C. occurs.
In this cooling zone, it is required to control the temperature so that the cooling error with respect to the cooling target temperature of the steel plate is finally about ± 0 to 5 ° C. However, since the fluctuation of the cooling error is large, it is not possible to sufficiently meet this requirement. There is.
JP-A-9-235626.

The present invention solves the above-mentioned conventional problem when the cooling zone of the continuous annealing furnace is configured by arranging a plurality of gas jet type cooling devices in series, and achieves the cooling target temperature of the steel plate on the cooling zone exit side. against it, it provides a steel plate cooling method of securely small as possible temperature control capable continuous annealing furnace cooling error.

In order to solve the above problems, the present invention is summarized as the following (1).
(1) cooling zone of a continuous annealing furnace of steel sheet is composed of a cooling apparatus of a plurality of gas jet arranged in series, as the final cooling device of this, the lower cooling device cooling capability than other cooling device In the cooling method of the steel sheet in the continuous annealing furnace to be cooled ,
For the other cooling except the final cooling device, the maximum value of the protruding flow velocity of the cooling gas to the steel plate is 70 Nm / sec or more, and the cooling device in the previous stage of the final cooling device is the target cooling temperature of the steel plate + Δt ° C. (10 ≦ Δt ≦ 50)
Steel cooling method in the continuous annealing furnace final cooling apparatus characterized by cooling the steel sheet from the cooling target temperature + △ t ° C. of the steel plate (10 ≦ △ t ≦ 50) to the cooling target temperature of the steel sheet.

In the cooling method of steel plate in by that continuous annealing furnace of the present invention, is constructed from the cooling device of the plurality of gas jet cooling zone of a continuous annealing furnace of the plate are arranged in series, other cooling except the last cooling device The maximum value of the flow velocity of the cooling gas to the steel plate is 70 Nm / sec or more, and is the cooling device in the previous stage of the final cooling device, up to the target cooling temperature of the steel plate + Δt ° C. (10 ≦ Δt ≦ 50) The final cooling device cools the steel plate from the target cooling temperature of the steel plate + Δt ° C. (10 ≦ Δt ≦ 50) to the target cooling temperature of the steel plate. Therefore, for example, a sufficient cooling capacity is secured even for a steel plate having a temperature of about 700 to 400 ° C., and a cooling error with respect to the cooling target temperature is about ± 5 ° C. in the final stage of cooling to a cooling target temperature of 450 to 200 ° C., for example. Cooling control can be suppressed to a minimum.

Below, the cooling zone which applied this invention to the (primary) cooling zone of the continuous annealing furnace of a steel plate is demonstrated concretely based on FIGS.
As shown in FIGS. 1 and 2, the cooling zone 1 of the present invention includes a plurality of other large-capacity gas jet cooling devices (hereinafter referred to as “pre-cooling devices”) 2 a disposed on the front side. 2b and a gas jet type small capacity final cooling device (hereinafter referred to as "final cooling device") 2s are arranged in series.
The gas jet type cooling devices 2a, 2b, and 2s each include a cooling gas box 4 having a large number of protruding nozzles 3 with the protruding nozzles 3 facing both surfaces of a steel plate 5, and a non-oxidizing cooling gas. (For example, H ₂ enriched N ₂ ) is pumped by the blower 6 and sprayed from the protruding nozzle 3 to the steel plate surface (both sides) to cool the steel plate 5.
In this cooling zone 1, basically, for example, a steel plate 5 having a temperature of about 700 to 400 ° C. is moved from 450 to 200 ° C., which is a cooling target temperature of the steel plate in this cooling zone 1, with a plurality of pre-stage cooling devices 2 a and 2 b. Cool to a temperature as high as about 10 to 50 ° C., and cool in a final cooling device 2 s having a minute temperature control step so that the steel sheet has a temperature within an allowable cooling error range of about ± 5 ° C. or less with respect to the cooling target temperature. Is.

The final cooling device 2s used here has a cooling capacity from the cooling target temperature of the steel plate 5 in the cooling zone 1 + Δt ° C. (10 ° C. ≦ Δt ≦ 50 ° C.) to the cooling target temperature of the steel plate. For example, when Δt is 50 ° C., it has a minute temperature control step of about 0.5 ° C. by changing the rotational speed of the blower 6 by 1%, and the steel plate 5 in the final cooling stage in the cooling zone 1 Cooling adjustment with high accuracy is possible within the range of the target cooling temperature of the steel plate +10 to 50 ° C, and a stable cooling error of about ± 5 ° C or less with respect to the cooling target temperature of the steel plate 5 in this cooling zone 1 is ensured. It can be done.
Here, Δt ° C. is Δt ° C. on the (+) side of the cooling target temperature. Since the final cooling device 2s does not have a heating function, the steel plate 5 is supercooled by another cooling device in the previous stage. This is because it does not function when the temperature is equal to or lower than the cooling target temperature on the outlet side of the cooling zone 1.
FIG. 3 shows the relationship between the cooling capacity (° C.) of the cooling device and the temperature control step (° C.). When the cooling capacity is 50 ° C. or lower, the temperature control step can be reduced to 2 ° C. or lower. As the final cooling device 2s that is required to have a temperature control step, it is appropriate that the cooling capacity is about 50 ° C. or less and the cooling can be adjusted within the range.

Moreover, the cooling capacity which can cool the high-temperature steel plate 5 of about 700 degreeC, for example to the temperature of about 250 degreeC by the front stage cooling device 2a, 2b total may be required.
In order to satisfy this condition, it is necessary to set the maximum value of the cooling gas protrusion flow rate in the pre-stage cooling devices 2a and 2b to 70 Nm / sec or more.
FIG. 4 shows the relationship between the cooling gas protrusion flow rate (Nm / sec) and the cooling capacity (° C.). The maximum value of the cooling gas protrusion flow rate of 70 Nm / sec or more is not This corresponds to a cooling capacity of 100 ° C. or higher.
When the cooling capacity is 100 ° C. or higher, the temperature control step is as large as about 15 to 20 ° C. However, the cooling capacity of the pre-stage cooling devices 2a and 2b is about 100 ° C. to 300 ° C. If cooling adjustment can be made within that range, The cooling error with respect to the target cooling temperature of the steel plate 5 in the cooling zone 1 can be cooled to an allowable range of the target cooling temperature ± 5 ° C. of the steel plate 5 by the final cooling device 2s having a cooling capacity of about 50 ° C. .

In the cooling zone 1, cooling is performed by the pre-stage cooling devices 2a and 2b so that the temperature is within the range of the cooling capacity of the final cooling device 2s. In some cases, the apparatus 2s cannot make the cooling error with respect to the cooling target temperature of the steel plate 5 on the exit side of the cooling zone 1 within an allowable range, and it is effective to have the following control system.
That is, a plate thermometer 7 is provided on the exit side of the final cooling device 2s, that is, the exit side of the cooling zone 1, and the temperature measurement information from the plate thermometer 7 is calculated by the control device 8 as shown in FIG. When the deviation Δt ° C. between the measured value of the plate thermometer and the cooling target temperature of the steel plate 5 on the outlet side of the cooling zone 1 is in the range of, for example, + 10 ° C. to + 50 ° C., the cooling capacity is 50 ° C. The final cooling device 2s having a temperature control accuracy of less than about is immediately cooled to bring the steel plate 5 to the target cooling temperature ± 5 ° C. or lower.

Here, the deviation Δt ° C. between the measured value of the plate thermometer 7 and the cooling target steel temperature of the steel plate 5 may be 50 ° C. or more, which may exceed the cooling capacity of the final cooling device 2s. Is immediately adjusted by the control device 8 in the pre-stage cooling devices 2a and 2b, for example, by changing the opening (blowing) conditions of the cooling gas by changing the opening of the flow rate adjusting valve 9 and the rotational speed of the blower 6. The cooling is performed by the final cooling device 2 s so that the cooling target temperature of the steel plate 5 on the outlet side of the cooling zone 1 is ± 5 ° C. or lower.
If the plate thermometer 7a is also arranged on the outlet side of the preceding cooling devices 2a and 2b and the cooling capacity of the final cooling device 2s is exceeded, immediately in the preceding cooling devices 2a and 2b, for example, the flow rate adjusting valve 9 It is possible to speed up the cooling adjustment by changing the opening degree and the rotation speed of the blower 6 and changing the cooling gas projection (blowing) conditions. In the final cooling device 2s, the cooling capacity is within a range of about 50 ° C. or less. Cooling adjustment can also be performed.

The relationship between the cooling capacity α (W / m ² K) that determines the cooling capacity of the cooling device used here and the steel sheet temperature ° C. is expressed as follows as a theoretical formula.
α = 2 · (ρC _P tV) / Le · 1n {(Ti−Tg) / (To−Tg)} (1)
Where ρ: Steel plate density C _P : Steel plate specific heat t: Steel plate thickness V: Steel plate passing speed Le: Effective cooling length Ti: Steel plate temperature before cooling To: Steel plate temperature after cooling Tg: Cooling gas temperature The required cooling capacity α of each cooling device is determined from the conditions. Further, since there is a relationship between the cooling capacity α and the cooling gas protruding flow rate (Nm / sec), the required protruding flow rate of each cooling device is determined. By these, the specifications as equipment can be determined.
FIG. 5 shows the relationship between the cooling flow velocity (Nm / sec) of the cooling gas and the cooling capacity α in the actual cooling device, and the hatched area is usually the practical area.
Since the cooling flow velocity of the cooling gas in the final cooling device 2s is about 50 Nm / sec, there is a cooling capacity α of 200 to 400 (W / m ² K), and the cooling flow velocity of the cooling gas in the preceding cooling devices 2a and 2b is Since it is 70 Nm / sec or more, it has a cooling capacity α of 300 (W / m ² K) or more.
As means for changing the cooling capacity α, in addition to the rotational speed of the blower, there are a change in the temperature of the cooling gas, a change in the distance between the cooling device and the steel plate, and the cooling adjustment can be performed.

  In this example, a cooling zone of a steel sheet continuous annealing furnace as shown in FIG. 2 is a cold thin steel plate (steel strip) having a temperature of 700 to 400 ° C., a thickness of 0.6 to 3.2 mm, and a width of 600 to 1800 mm. Assuming the case where it is applied to the (primary, secondary) cooling zone of a continuous annealing furnace that is cooled to 450 to 200 ° C. on the exit side of the cooling zone during conveyance at 150 m / min. , Simulation of cooling capacity distribution (including unfavorable distribution) of the cooling capacity of the pre-stage cooling devices 2a and 2b and the cooling capacity of the final cooling device 2s (including unfavorable distribution) and temperature deviation (cooling error) with respect to the cooling target temperature on the outlet side of the final cooling device It is. The results are shown in Table 1.

"Result Evaluation"
From Table 1, for example, the following can be said.
When the cooling capacity of the final cooling device 2s is 40 ° C to 60 ° C,
Pre-cooling device 2a: 100 ° C to 250 ° C
Previous stage cooling device 2b: 100 ° C. to 200 ° C.
In this case, the steel plate can be cooled with a cooling error of 10 ° C. or less with respect to the cooling target temperature of the steel plate on the outlet side of the cooling zone 1, and particularly when the cooling capacity of the final cooling device 2s is 50 ° C. or 40 ° C. ,
Pre-cooling device 2a: 100 ° C to 150 ° C
Pre-cooling device 2b: 100 ° C to 150 ° C
In this case, the cooling can be performed with a minute cooling error of 2 ° C. or less with respect to the cooling target temperature of the steel plate on the outlet side of the cooling zone 1.
In addition, although Example 1 showed the case where the cooling device with a cooling capacity of 100-250 degreeC was used on the premise that two sets of 2a and 2b are used for the pre-stage cooling apparatus, the temperature of the steel plate 5 is 700 degreeC, for example. In the temperature range, when the target cooling temperature is about 200 ° C. and the cooling temperature range is wide, for example, the cooling capacity of the front cooling device 2a is increased to 250 ° C. or more, or three or four front cooling devices are arranged. It is also possible to consider reducing the cooling capacity of each pre-stage cooling device to about 100 ° C., for example.
Also, when the temperature of the steel plate is low, or when it is used for a cooling zone where the steel plate temperature and the target cooling temperature are close and the cooling temperature range is narrow, a single pre-stage cooling device is arranged or a cooling capacity of about 100 ° C. It is also possible to consider using an apparatus.

  In Example 2, a cooling zone of a continuous annealing furnace for steel plates as shown in FIG. 2 is used. A cold thin steel plate (steel having a temperature of 700 to 400 ° C., a thickness of 0.6 to 3.2 mm, and a width of 600 to 1850 mm). Assuming the case of applying to various cooling zones of a continuous annealing furnace that is cooled to 450 to 200 ° C. on the exit side of the cooling zone during conveyance at 150 m / min. In consideration of the result, the cooling capacity of the pre-stage cooling devices 2a and 2b and the cooling capacity of the final cooling device 2s are distributed (including an unfavorable distribution example), and the cooling zone 1 output when cooling is shared by each cooling device The temperature deviation (cooling error) with respect to the cooling target temperature on the side is simulated. The results are shown in Table 2.

"Result Evaluation"
From Table 2, the following (1) to (3) can be said, for example.
(1) When the outlet side temperature of the pre-stage cooling device 2b is within the preferable cooling capacity of about 50 ° C. of the final cooling device 2s, all are small cooling errors of 2 ° C. or less with respect to the cooling target temperature of the steel plate. Can be cooled.
(2) When the outlet side temperature of the pre-stage cooling device 2b exceeds the preferable cooling capacity of about 50 ° C. of the final cooling device 2s, a cooling error of 10 ° C. or more is likely to occur with respect to the cooling target temperature of the steel plate 5.
(Note) As a measure to reduce this cooling error, for example, adjusting the cooling capacity of the pre-cooling devices 2a and 2b, that is, increasing the cooling capacity of the pre-cooling device and increasing the cooling capacity of the final cooling device 2s It is effective to allow cooling within the range.
(3) When the cooling capacity of the final cooling device 2 s is increased to 50 ° C. or more, a cooling error of 10 ° C. or more (supercooling) tends to occur on the − (minus) side with respect to the cooling target temperature of the steel plate 5. .
(Note) As a measure to reduce this cooling error, for example, the cooling capacity of the final cooling device 2s is lowered to about 50 ° C., and the cooling capacity of the front cooling devices 2a and 2b is increased to increase the cooling capacity of the front cooling devices 2a and 2b. It is effective to lower the delivery temperature.
In Table 2, there is a cooling example in which the cooling temperature by the pre-stage cooling devices 2a and 2b is as low as several tens of degrees Celsius. However, this pre-stage cooling device has a cooling capacity larger than the cooling capacity of the final cooling apparatus 2s. Then, the cooling is adjusted and suppressed.
In the present invention, according to the steel plate temperature on the inlet side of the cooling zone to be applied and the steel plate temperature on the outlet side of the cooling zone (cooling target temperature), the pre-stage cooling device and the final cooling device for cooling to the cooling target temperature ± 5 ° C. or less. In consideration of the optimum cooling capacity, the optimum arrangement is selected.
Conceptually, the cooling capacity of the final cooling device can be controlled, for example, by setting the cooling capacity of the final cooling device to about 50 ° C. or less, and the cooling capacity of the final cooling device can be controlled by a pre-stage cooling device having a cooling capacity larger than that of the final cooling device. It cools to the range which can be cooled.
If the cooling by the pre-cooling device is insufficient, exceeds the range of the cooling capacity of the final cooling device, and cooling cannot be performed at the target cooling temperature ± 5 ° C or less, the cooling capacity of the pre-cooling device is adjusted (cooling adjustment), It can cool to the range of the cooling capacity of the final cooling device.
The cooling capacity of the final cooling device can also be adjusted. For example, the cooling can be adjusted in a range of 50 ° C. or less.
When it is already cooled to the cooling target temperature of about ± 5 ° C. in the pre-cooling device of the final cooling device, it can be considered that the final cooling device passes without cooling.

The present invention is not limited to the contents of the above embodiments. Examples 1 and 2 show the case where the present invention is applied to a cooling zone of a continuous annealing furnace, but it can also be applied as a cooling zone of another heat treatment line (for example, a hot dipping line) of a steel plate in a similar temperature range. It is.
In addition, regarding the structure, cooling capacity, cooling capacity conditions (including cooling capacity allocation), arrangement conditions, and cooling operation (cooling temperature, cooling rate) conditions of each cooling device, the steel strip conditions to be processed (steel type, size, temperature) Depending on the basic conditions (including the conveyance speed) of the equipment (processing line), the operation schedule, etc., there are changes within a range that satisfies the scope of the claims.

Side surface explanatory drawing which shows the example of arrangement | positioning of each cooling device at the time of arrange | positioning the cooling zone of this invention as a cooling zone of a continuous pure annealing furnace. Side surface explanatory drawing at the time of providing the control system of each cooling device in the cooling zone of FIG. Explanatory drawing which shows the relationship between the cooling capability of the cooling device of a gas jet type cooling device used by this invention, and a temperature control step. Explanatory drawing which shows the relationship between the protrusion flow velocity of the cooling gas of the cooling device of the gas jet system used by this invention, and cooling capacity. Explanatory drawing which shows the relationship between the cooling gas protrusion flow velocity and cooling capacity in the actual gas jet type cooling device used in the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cooling zone 2a, 2b Previous stage cooling device 2s Final cooling device 3 Protruding nozzle 4 Cooling gas box 5 Steel plate (steel strip)
6 Blower 7, 7a Plate thermometer 8 Controller 9 Flow control valve

Claims (1)

The cooling zone of the steel sheet continuous annealing furnace is composed of a plurality of gas jet type cooling devices arranged in series, and the final cooling device is cooled by a cooling device having a lower cooling capacity than other cooling devices. In the method for cooling a steel plate in a continuous annealing furnace ,
For the other cooling except the final cooling device, the maximum value of the protruding flow velocity of the cooling gas to the steel plate is 70 Nm / sec or more, and the cooling device in the previous stage of the final cooling device is the target cooling temperature of the steel plate + Δt ° C. (10 ≦ Δt ≦ 50)
Steel cooling method in the continuous annealing furnace final cooling apparatus characterized by cooling the steel sheet from the cooling target temperature + △ t ° C. of the steel plate (10 ≦ △ t ≦ 50) to the cooling target temperature of the steel sheet.

Images