JPH02267232A - Continuous annealing method - Google Patents

Abstract

PURPOSE:To prevent exhaust gas from a direct fire heating furnace from flowing backward to an indirect heating furnace and exhaust gas from the indirect heating furnace from flowing into a soaking pit by installing an intermediate roll chamber between both the beating furnaces and controlling the degree of opening of a damper fitted to the inlet or outlet of the roll chamber. CONSTITUTION:An intermediate roll chamber 6 is installed between a direct fire heating furnace 2 and an indirect heating furnace 3 in a continuous annealing furnace 10 and a freely opening and closing damper 7 is fitted to at least one of the inlet and outlet of the roll chamber 6. A change of the internal pressure of the direct fire heating furnace 2 is detected with a pressure gauge 12 and the degree of opening of the damper 7 is controlled with a controller 11. Even when combustion in the heating furnace 2 undergoes a sudden change, a steel strip having satisfactory surface properties is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a continuous annealing method for thin steel strips in which a direct heating furnace and an indirect heating furnace are arranged.

(b) Conventional technology In recent years, thin copper strips have been developed. ! In continuous annealing furnaces for continuous annealing lines and hot-dip galvanizing lines, a direct-fire reduction heating method in which a flame is directly applied to the copper strip is being adopted.

Figure 2 shows a 6-continuous annealing furnace 10 showing a typical example of continuous annealing.
The furnace is comprised of a preheating furnace 1, a direct-fired furnace 2, an indirect heating furnace 3, a soaking furnace 4, and subsequent cooling equipment (not shown) from the entrance side.

The steel strip 5 is first preheated to a temperature of 100 to 400° C. in the preheating furnace 1 using the exhaust gas from the direct-fired furnace 2 .

Subsequently, in an indirect heating furnace 3, a 750~750~
It is heated to 800°C, and then soaked in the soaking furnace 4 in the above atmosphere.

The direct-fired reduction heating furnace 2 usually uses coke oven gas at an air ratio of 1.
．． This is a furnace in which W is ignited at a temperature of 0 or less, and the steel strip 5 is exposed to flame and reduced. The exhaust gas at that time was N20. It contains CO2 and has a highly oxidizing atmosphere.

On the other hand, the indirect heating furnace 3 uses N to prevent the steel strip 5 from oxidizing.
2 and 6 in an atmosphere of N2. Typically, gas flows from the preheating zone 1 to flow from the indirect heating furnace 3 to the direct heating furnace 2. However, in the direct-fired heating furnace 2, since the gas is directly combusted in the furnace, the amount of incoming gas is extremely large, and when changing the combustion amount, the exhaust gas from the direct-fired backflows into the indirect heating furnace 3. , there was an opening in which the steel strip 5 was oxidized in the indirect heating furnace 3.

For this reason, Japanese Patent Application Laid-open No. 17020/1983 discloses providing an intermediate chamber between a direct heating furnace and an indirect heating furnace, which maintains an internal pressure higher than that of both furnaces. However, it is impossible to prevent backflow of exhaust gas using only the intermediate chamber. Seal plates with a certain interval are not effective unless the spacing is narrow, but in reality, if the spacing is about 20 [1ffi], the welded part of the copper strip (the part where dimensions change) is poor in shape, so the seal is not effective. It comes into contact with the board and causes scratches. Similarly, the occurrence of scratches on seal rolls is unavoidable.In particular, direct-fired furnaces usually have a high dew point, and seal rolls on the side of direct-fired furnaces are more likely to pick up flaws.Also, exhaust gas may flow into the intermediate chamber. , Due to the high internal pressure, the exhaust gas flows into the indirect heating furnace.
Furthermore, by increasing the internal pressure of the intermediate chamber, the atmospheric gas flow is directed from the indirect heating furnace to the cooling zone, making it difficult to control cooling. Therefore, this method is not practical.

(c) Problems to be Solved by the Invention The problems to be solved by the present invention are to prevent the exhaust gas from flowing back into the indirect heating furnace after combustion in the direct heating furnace in a continuous annealing furnace, and to prevent the exhaust gas from flowing back into the indirect heating furnace. The object of the present invention is to obtain a method for preventing waste gas from being accumulated in a soaking furnace.

(d) Means for Solving the Problems The continuous annealing method of the present invention provides a continuous annealing furnace in which a direct heating furnace and an indirect heating furnace are arranged, an intermediate roll chamber is provided between the two furnaces, and the intermediate roll chamber is provided between the two furnaces. The above-mentioned problem can be solved by providing a damper that can be opened and closed at least one of the inlet and outlet of the chamber, and controlling the degree of opening of the damper in response to changes in the furnace pressure of the direct-fired heating furnace. has been resolved.

(E) Embodiment An embodiment of the continuous annealing method of the present invention will be described with reference to FIG. 1 and FIGS. 3 to 5.

First, as shown in FIG. 1, the continuous annealing method of the present invention is as follows:
Continuous annealing furnace 1 equipped with a direct heating furnace 2 and an indirect heating furnace 3
0, an intermediate roll chamber 6 is provided between the two furnaces 2.3,
A damper 7 which can be opened and closed is provided at at least one of the inlet and outlet of the intermediate roll chamber 6, and changes in the furnace pressure of the direct-fired heating furnace 2 are detected by a pressure gauge 12, and the opening degree of the damper 7 is controlled a.
It is characterized in that it is controlled by a ll device 11.

As shown in FIG. 3, at least one of the inlet and outlet (in the illustrated example, both the inlet and outlet) of the intermediate roll chamber 6 provided between the direct-fired heating furnace 2 and the indirect heating furnace 3 is provided with a damper that can be freely opened and closed. Install 7.

Each embodiment of the damper 7 is shown in FIG. 4. In FIG. 4, a slit 611 is provided in the furnace wall 61, a slide plate 71 is slidably inserted into the slit 611, and the damper 7 is driven by a drive unit 8 such as a screw shaft. Figure (B) shows a damper 7 having a structure for adjusting the opening degree 1, in which a rotary plate 72 is rotatably installed on the furnace wall 61, and the opening degree 1 is adjusted by a drive unit (not shown). The structure of the damper 7 is shown.

The figure (C) shows an example in which two rotating plates 72 are provided to form a negative space 721 that can absorb pressure fluctuations.

The figure (D) shows an example in which a plurality of rotating plates 72 are provided and a plurality of buffer spaces 721 are formed.

When combustion is being carried out steadily in the direct heating furnace 2, the damper 7 is left open to allow atmospheric gas to flow in from the indirect heating furnace. However, if rapid combustion occurs in the direct heating furnace 2, the exhaust gas damper control of the distant preheating furnace 1 cannot keep up, so the pressure inside the direct heating furnace 2 will rise suddenly.
The indirect heating furnace 3 and even the soaking furnace 4 are in an atmosphere with a high dew point, and the copper strip is oxidized. Conventionally, the above-mentioned phenomenon occurred because the damper part remained open or had a slightly constricted structure.

Therefore, if the opening degree 1 of the damper 7 is closed from the maximum of 600 mm to 2011 I1 m immediately before rapid combustion in the direct-fired heating furnace 2, the furnace pressure in the intermediate roll chamber 6 will hardly change, and the exhaust gas from the direct-fired The phenomenon of backflow to the indirect heating furnace 3 has disappeared.

An example of the test results conducted by the inventors is shown in Fig. 5, where the firing rate of the burner in the first half of the direct-fired heating furnace 2 was varied from Q% to 100%.
If the temperature increases rapidly, the furnace is installed at the bottom of the indirect heating furnace 3. The measured value of the CO2 analyzer 9 (FIG. 3) changed as shown in FIG. 5 according to the damper opening degree 1. therefore,
By reducing the opening degree 1 of the damper 7, the phenomenon in which the exhaust gas from the two direct-fired heating furnaces 2 flows backward is completely prevented. As a result, even in the case of rapid combustion change in the direct-fired heating furnace 2, the surface of the copper strip was not oxidized. Even when the damper opening degree O was set to 20 m, the #4 band surface was not oxidized during both steady heating and rapid heating.

During the continuous annealing operation, there are various disturbances such as changes in the plate speed and deterioration of the plate shape, so there is a risk that the steel strip 5 will come into contact with the damper 7 and surface flaws will occur. Therefore, as in the present invention, it is effective to reduce the damper opening 1 only when changing to rapid combustion with direct fire, and maximize the opening 1 during steady heating. Furthermore, if the damper 7 is released during maintenance, repairs can be made easily.

(f) Effects According to the method of the present invention, a steel strip with good surface properties can be obtained in a continuous annealing furnace even when combustion is rapidly changed in a direct-fired heating furnace.

[Brief explanation of drawings]

Fig. 1 is a schematic structural explanatory diagram of a continuous annealing furnace to which the method of the present invention is applied, and Fig. 2 is a schematic structural explanatory diagram of a conventional continuous annealing furnace.
FIG. 3 is a longitudinal sectional view of the intermediate roll chamber according to the present invention;
The figure is an explanatory diagram of various dampers used in the method of the present invention, and FIG. 5 is a graph showing the effects of the method of the present invention. 1: Preheating furnace 2: W, large heat furnace 3: Indirect heating furnace 4: Soaking furnace 5: Steel strip 6: Intermediate roll chamber 7: Dumper
8: Drive unit 9: CO2 analyzer 1
0 = Continuous heating furnace 12: Pressure gauge 71 = Slide plate 72: Rotating plate (4 people outside)

Claims (1)

[Claims] In a continuous annealing furnace having a direct-fired heating furnace and an indirect heating furnace, an intermediate roll chamber is provided between the two furnaces, and a damper that can be freely opened and closed is provided at at least one of the entrance and exit of the intermediate roll chamber, A continuous annealing method characterized in that the degree of opening of the damper is controlled in response to changes in the pressure inside the direct-fired heating furnace.