JPS6365030A - Method for cooling metallic strip - Google Patents

Abstract

PURPOSE:To adequately cool a metallic strip at a specified cooling rate in a prescribed temp. range by dividing a gas-water cooler for the high-temp. metallic strip to a plurality in the moving direction of the metallic strip and setting the number of the divisions to be used and the flow rates of water and gas according to treatment conditions. CONSTITUTION:The metallic strip heated in an annealing furnace, etc., is subjected to gas-water cooling by atomizing the water and adding and spraying the same into the cooling gas. The gas-water cooler constituted in the above- mentioned manner is divided to a plurality in the moving direction of the metallic strip and to the cooling zones which are respectively independently controllable in the flow rate. Any or all of the number of the divisions to be used, water flow rate and gas flow rate in the above-mentioned cooling zones are set and the cooling is executed. The metallic strip is thereby cooled at the specified temp. range rate in the prescribed temp. range and the use of the unnecessary driving power by over cooling is prevented even if the line speed changes. This method is easily adapted to cooling conditions over a wide range.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for cooling a metal strip, which is suitable for application to a continuous annealing furnace, a continuous normalizing furnace, etc.

<Prior Art> The heating section and cooling section of a conventional continuous annealing furnace are as shown in FIG. That is, the steel strip 1 to be heat treated is heated in the heating section 2.
is heated to a predetermined temperature. The heat source 3 is gas fuel such as coke oven gas or electricity, and the length of the heating section and the amount of heat of the heat source 3 are determined by metallurgical requirements such as the throughput of the steel strip 1 and the amount or rate of temperature rise. The steel strip 1 whose temperature has been raised is soaked at a predetermined temperature for a predetermined time as necessary.

A soaking zone 4 is provided to satisfy this condition. After soaking, the steel strip 1 is cooled down to a predetermined temperature at a predetermined rate in a cooling zone 5. Air-water cooling, which is the object of the present invention, is used as a cooling method. This is a method in which water 7 is atomized and added to cooling gas 6, and the hot steel strip 1 is sprayed to cool it.

<Problems to be Solved by the Invention> Air-water cooling, which is the object of the present invention, has the advantage that the cooling capacity can be changed greatly depending on the mixing ratio of the cooling gas and the atomized water. On the other hand, considering conventional cooling zones, the length of the cooling zone is determined as the product of the maximum line speed and the time required to cool a given temperature range. The conventional cooling zone determined in this way has the following problems.

In other words, if a predetermined cooling rate is achieved at the maximum line speed, when the line speed decreases due to a heating zone or production process request, the same predetermined temperature range as the maximum line speed can be cooled at the same rate. The required cooling zone length is reduced. Therefore, even after the cooling end temperature is reached, the cooling device is present and cooling continues, making it impossible to maintain a predetermined cooling end temperature at the outlet of the cooling zone. Further, in general, a minimum cooling rate is often specified from a metallurgical perspective. In such cases, set the minimum line speed (processing amount) and set the product S cooling length, which is the time required to cool the specified temperature range at the minimum cooling rate, and even at the maximum line speed, this cooling length is used. The cooling capacity (that is, the amount of gas and water) that can cool a predetermined temperature range was set. In such an apparatus, when the maximum line speed, that is, the apparatus is to be used most efficiently in terms of throughput, a large amount of power is used for cooling, exceeding the metallurgically required conditions.

The present invention has been made in view of the current situation, and even when the line speed changes, a predetermined temperature range can be cooled at a constant cooling rate, and an excessive cooling rate is not generated, thereby eliminating unnecessary cooling. It is an object of the present invention to provide a method for cooling metal strips that can be cooled in the same device without the use of power and for a very wide range of line speeds and different cooling patterns.

Means for Solving the Problems In order to achieve the above object, the present invention has a configuration in which an air-water cooling device is used to move the metal band when air-water cooling a high-temperature metal band heated in an annealing furnace or the like. The number of divisions, water flow rate, and gas flow rate to be used in the cooling zone consisting of the air-water cooling device can be adjusted depending on the throughput of the metal strip, plate thickness, metallurgical requirements, etc. The feature is that cooling is performed by setting any or all of the following.

<Function> With the above configuration, the cooling length determined by the maximum line speed, minimum cooling speed, and cooling temperature range is divided into multiple groups in the line movement direction, and the cooling gas supplied to each group is divided into multiple groups in the line movement direction. The volume and/or the amount of water can be controlled.

<Example> The following will explain based on FIG. 1, which is a principle diagram according to an example of the present invention, and FIG. 2, which is a graph showing the relationship between heat transfer coefficient and heat transfer surface collision speed.

A cooling device according to the present invention is shown in FIG. 11 is steel strip 1
2 is a cooling zone. The length 1 of this cooling zone 12 is determined by the maximum line speed Vmax and the cooling start temperature T3. The cooling end temperature is T2, and the metallurgically required minimum cooling rate is Cs.
1 n, it is determined as follows. In the example of the present invention described below, V, Il, -30m/1oin, T, -850°C
, T, −400°C.

C, 1, -25°C/sec, l = 15m.

13 is a cooling gas supply pipe, 14 is a cooling water supply pipe, 15
and 1B are flow control valves provided in each of the cooling gas supply pipe 13 and the cooling water supply pipe 14. The total length of the cooling zone 12 +5a+ is divided into six sub-divided cooling zone zones a to f in units of 2.5 m in the line longitudinal direction.

The lower part of Figure 1 is the cooling curve of the steel strip 11, where β is the setting condition of the cooling zone, the maximum line speed is 50 m/win, the temperature range is 850°C → 400°C, and the minimum cooling rate is 25°C/sec.
This is the cooling curve when cooling at . Similar 850℃ → 4
When cooling 00℃ at 25'C/sec, the cooling curve when the line speed is 25m/min is α, and a to C
The three zones up to dNf are used for cooling, and the three downstream zones of dNf are not used with the flow control valves 15 and 16 closed. In addition, γ and δ are the line speeds that are lower than the maximum line speed, and due to metallurgical or heat transfer requirements, cooling is slowed down during cooling, and a cooling zone is created when a predetermined temperature is reached (γ).
, or in the case (δ) where cooling is terminated at a predetermined temperature.

Concerning gas jet and water droplet cooling, the relationship between the heat transfer coefficient α and the heat transfer surface collision velocity V is shown in FIG. 4, and the relationship between α and the water volume density is shown in FIG. Conditions other than V in FIG. 4 and water volume density are fixed in FIG. 5. Both figures are shown in logarithms.

Here, the relationship between α and V is α=C, vC2, that is, togc = C2 (logv+K), however, C,,C
2 is a constant. Here, conditions other than V, such as water density,
This value is determined by the heat transfer surface temperature, etc.

■The heat transfer coefficient when m, X and 1.8 is α, 111
1K, logαwaax −C2(logV 11111X
+llaM) Therefore, if this is represented in a graph, it will be as shown in FIG.

In the above embodiment, the circular hole two-fluid nozzle is
300m each on the top and bottom of the copper strip in a staggered pattern of 50 pitches.
At the maximum line speed, cooling is performed with 250fl/ll1in of cooling air from one nozzle and 200cc/min of cooling water from one nozzle. The heat transfer surface collision speed V is controlled by the injection air pressure, and the relationship in the example is shown in FIG.

<Effects of the Invention> As described above, according to the present invention, even when the line speed changes, a predetermined temperature range can be cooled at a constant cooling rate, and unnecessary cooling is performed to avoid excessive cooling speed. Also a very wide range of line speeds, without the use of power
Appropriate cooling processing can be performed for various cooling patterns by performing simple operations on the same device.

[Brief explanation of the drawing]

Figures 1 and 2 are related to one embodiment of the present invention, where Figure 1 is a principle diagram, Figure 2.4 is a graph showing the relationship between heat transfer coefficient and heat transfer surface collision speed, and Figure 3 is a graph showing the relationship between heat transfer coefficient and heat transfer surface collision speed. The figure shows the principle of the conventional example, and Figure 5 shows the relationship between heat transfer coefficient and water density.
FIG. 6 is a diagram showing the relationship between heat transfer surface collision speed and ejection air pressure. Also, in the figures, 11 is a steel strip, 12 is a cooling zone, 13 is a cooling gas supply pipe, 14 is a cooling water supply pipe, 15, 16
is the flow control valve. Patent applicant: Mitsubishi Heavy Industries, Ltd. (1 person in charge of chemistry) Sub-agent patent attorney Shibe Mitsuishi (1 person in charge of chemistry) Figure 2 Q 50
to.

Claims (1)

[Claims] When cooling a high-temperature metal strip heated in an annealing furnace or the like, the air-water cooling device is divided into multiple sections in the direction of movement of the metal strip to control the flow rate, thereby controlling the throughput of the metal strip, the plate thickness, and the like. A method for cooling a metal band, characterized by performing cooling by setting either or all of the number of divisions of a cooling zone consisting of an air-water cooling device and the flow rate of water and gas according to metallurgical requirements.