JPH02115320A - Continuous annealing furnace for thin band steel - Google Patents

Abstract

PURPOSE:To continuously anneal a thin band steel while preventing its meandering and heat buckling by spirally building the wall of the continuous annealing furnace for thin band steel in a vertical plane, providing the heating zone, soaking zone, primary cooling zone, overageing zone, and secondary cooling zone along the wall, and traveling the thin band steel through the zones by a group of rolls. CONSTITUTION:The wall 11 of the continuous annealing furnace 10 for thin band steel S is spirally built in a vertical plane, and plural partition walls 17 are provided between the openings 10A and 10B of the spiral passage to form the heating zone 12, soaking zone 13, primary cooling zone 14, overageing zone 15, and secondary cooling zone 16. Plural groups 18 of rolls consisting of a fixed roll 18A and a looper roll 18B for conveying the steel S are provided in the zones 12-16. A heater and a cooler are furnished in the zones 12-16, and the steel S is conveyed by the roll group 18 from the opening 10A to another opening 10B and continuously annealed. As a result, the meandering of the steel S in the furnace 10 and generation of longitudinal wrinkles called 'heat buckles' are prevented, and the steel is stably annealed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a continuous annealing furnace for thin steel strip.

[Conventional technology]

Continuous annealing can perform heat treatment in just over ten minutes, whereas batch annealing requires several tens of hours.

For this reason, continuous annealing is being used as an annealing method that will replace the batch method in the future. Generally, when performing annealing by this method, a vertical furnace 1 as shown in FIG. 4 is used. The vertical furnace 1 performs a batch-type heat treatment process over time. [This is a furnace arranged along the line direction along which the band S runs. Therefore, in the line direction, a heating zone 2, a soaking zone 3, a primary cooling zone 4, an overaging zone 5.2, and a tertiary cooling zone 6 are arranged in order from the furnace entry side according to the heat treatment order. Each zone is equipped with heating means or cooling means depending on the processing purpose.

For example, since rapid heating is performed in the heating zone 2, a radiant tube with a large heat capacity maintains the temperature heated by the heating zone 2 in the soaking zone 3, so an electric heater whose temperature can be easily controlled is generally used. In addition, liquid cooling means or gas jet cooling means with high cooling capacity are used in the primary cooling zone 4, electric heater 2 is used in the overaging zone 5, and gas cooling means is used in the tertiary cooling zone 6. Although it depends on the steel type and processing purpose, in normal annealing, the temperature is heated to 10 - 700 - 850 °C in the heating zone 2, maintained at that temperature for several seconds in the soaking zone 3, and then heated to 50 °C in the primary cooling zone 4. A heat pattern is used in which the temperature is rapidly cooled to ~b°C, then maintained at that temperature for several minutes in the overaging zone 5, and then cooled to 10~b°C in the 2.3 tertiary cooling zone 6.

If a series of these treatments were performed by running the thin steel strip S in a straight line, the furnace length would be 1000 m or more.

This causes inconvenience, so in the vertical furnace 1, several tens of busses of hearth rolls 7, ... are placed above and below the furnace, and the thin steel strip S is reciprocated by these hearth rolls 7, .... At the same time, the distance between the rolls is set to 20 m or more to shorten the length of the furnace. Furthermore, if the roll interval is wide, the thin steel strip S may meander between the rolls and collide with the furnace wall.

To deal with this, centering is performed by attaching crowns to the hearth mouth, -a, -lua, and so on.

[Problem to be solved by the invention]

Incidentally, the temperature of the atF4 band straightened by the crown is low on the entry side of the heating furnace, and therefore the yield value is high, but since it is heated to 700 to 850°C on the exit side, the yield value is significantly lowered. If centering is performed by the crown in such a state, waves due to buckling may occur in the width direction, and the tension of the thin steel strip may crush the surface of the hearth roll, resulting in vertical wrinkles called heat occlusions.

Once heat buckling occurs, it cannot be cured unless the tension in the thin steel strip is relaxed or the temperature of the furnace is lowered, resulting in a large amount of scrap. Therefore, in order to improve yield, it is desirable to prevent the occurrence of heat buckling, but it is difficult to take measures because it is necessary to take measures that conflict with meandering prevention measures. The crown is made larger on the heating furnace entry side, where the temperature is lower, and the crown is made smaller on the heating furnace exit side, where the temperature of the thin steel strip is higher, but this is not an effective countermeasure.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a continuous annealing furnace for thin steel strips that simultaneously solves the contradictory relationships of preventing meandering and preventing the occurrence of heat buckling.

[Means to solve the problem]

In order to achieve the above object, the present invention constructs a furnace wall in a spiral shape within a vertical plane, divides and arranges the heat treatment process necessary for continuous annealing along the furnace wall, and guides and runs a thin steel strip. It is characterized by a group of rolls arranged along the furnace wall.

In this case, openings are inevitably formed at the beginning and end of the spiral, but in carrying out the present invention, either opening may be used as the entry side. If the center of the furnace is set as the entrance side, there will be a heating zone, a soaking zone, and a
A secondary cooling zone, an overaging zone, and a 2nd and 3rd cooling zone are arranged. . Further, when it is not necessary to carry out treatment in succession with pickling, a large space may be provided in the center and an unwinding machine may be incorporated therein to simplify introduction to the entry side.

On the other hand, if the end of winding in the furnace is to be the entry side, the above steps are reversed.

The roll group consists of fixed rolls and louver rolls because it is necessary to stably run the thin steel strip between the furnace walls.

In this case, the fixed rolls and louver rolls are arranged alternately, but since it is necessary for these rolls to guide the 8114 belt along the curved surface of the furnace wall, the roll spacing is
narrowed. Further, each roll is provided with a crown to prevent meandering, but in the case of the present invention, the distance between the rolls is narrow, and therefore the amount of movement in the roll axis direction due to meandering is also small, so the crown is made small. Further, in the case of the present invention, since the furnace is spiral-shaped, sheet threading becomes a problem, but this can be solved by allowing the louver rolls to be released outward.

Furthermore, if each roll not only simply guides the thin steel strip but also has heating and cooling capabilities, the furnace can be made more compact.

[Effect]

In a vertical furnace, in order to make the furnace length as short as possible, it is necessary to have a wide distance between the rolls, but in the case of the present invention, since the furnace is also spiral-shaped, the distance between the rolls can be narrowed. Therefore, if the inclination angle of the 1 m band with respect to the roll axis is the same, the amount of movement due to meandering is smaller in the present invention, so the amount of crown attached to the roll can be reduced.

Further, when the thin steel strip is wound around a roll and run, tension is applied to the thin steel strip, so a frictional force is generated in the axial direction of the roll. If the tension is the same, this frictional force increases as the contact angle with the roll increases. In a vertical furnace, the contact angle is 180°C because the thin steel strip is run back and forth by rolls, but in the case of the present invention, the contact angle is 180°C because the thin steel strip is run curved along the furnace wall. can be lowered to 180°C or less. Therefore, in the present invention, the frictional force in the roll axis direction is smaller, and even if movement in the roll axis direction is forced by the crown, it is easy to move smoothly, so that the occurrence of heat buckling can be suppressed as much as possible.

〔Example〕

A detailed description will be given below with reference to the drawings.

In a vertical furnace, the furnace is generally formed in a rectangular shape,
In the present invention, the furnace 10 is constructed in a spiral shape in a vertical plane, as shown in FIG. In such a furnace 10, the outer diameter of the furnace corresponds to the furnace length. Therefore, whether the furnace becomes larger or not depends on the outer diameter of the furnace, so how to determine the outer diameter will be explained below. That is, the outer diameter of the furnace is D,
If the inner diameter of the furnace is d, and the number of turns of the passage through which the thin copper strip passes through the furnace is N, then the length of the line formed in the furnace is π L-N (1) + d)... ...(1
).

In addition, the width W between the furnace walls (assuming no wall thickness) is N, and the line length L0 actually required for annealing is 1.0, where V is the line speed and t is the time required for heat treatment. =v
t......(3).

In this case, the width W between the furnace walls is determined by the size of the auxiliary equipment installed inside the furnace, and the inner diameter d of the furnace is determined by the auxiliary equipment installed at the center of the furnace. Therefore, since W and d can be determined in advance, by substituting equations (2) and (3) into equation (1), the outer diameter of the furnace is as follows.

Normally, the line length required for annealing is 1000 m, and if the outer diameter of the furnace is set to 50 m, the above-mentioned line length can be secured. Since the length of a vertical furnace is generally 100 m or more, the length of the furnace can be shortened by forming the furnace into a spiral shape. In addition, by making the furnace into a spiral shape, it becomes possible to simultaneously solve the problems of heat buckling and meandering, which could not be solved with vertical furnaces. Since there is a relationship, I will explain this when explaining the role group.

Next, the internal configuration of the furnace 10 will be explained.

Large openings 10A and 10B are formed in the furnace 10 at the beginning and end of the vortex, respectively; in this case, one of the openings is used as the inlet side of the furnace and the other opening is used as the outlet side of the furnace. . In the embodiment, since the beginning of the vortex is set as the entry side, the heating zone 12, the soaking zone 13, the primary cooling zone 14, the overaging zone 15, and the secondary cooling zone 16 gradually expand from the beginning of the vortex. It is arranged along the wall 11. Each band 12~
16, the line length is ensured according to the processing time, and partition walls 17,...
It is classified by

In order to guide the thin steel strip S along the furnace wall 11, a group of rolls 18. ... are arranged along the curved furnace wall 11. Each roll group 18 is composed of a fixed roll 18A and a louver roll to facilitate sheet threading.

These rolls 18A, 18B are arranged alternately, and the louver roll 18B is expanded outward in the radial direction of the furnace IO. As the expanding mechanism, although not shown, a mechanism for expanding louver rolls installed between rolling mills can be used.

Further, each zone 12 to 16 is provided with heating/cooling means necessary for heat treatment, similar to the vertical furnace. In this case, radiant tubes and electric heaters used in vertical furnaces, as well as gas jet cooling, can be used; however, in the present invention, the furnace 10 is constructed in a spiral shape, and rolls for guiding the thin steel strip Since the groups 18 are closely spaced, the roll groups 18 can be used for heating and cooling in addition to the above. In the embodiment, the latter measure is taken.

In this case, the furnace IO can be made more compact.

Although not shown, combustion gas for heating and heat retention is passed through each roll 18A, 18B arranged in the heating zone 12, soaking zone 13, and overaging zone 15, and the primary cooling zone 14 and
Cooling water for rapid cooling or gradual cooling is passed through each of the rolls 18A and 18B arranged in the secondary cooling zone 16.

Particularly in the heating zone 12 and the primary cooling zone 14, the heating and cooling rates are high, so the roll spacing is close to obtain a folding angle of 150 degrees or more, and in other zones, heat retention and gradual cooling are also performed, so the roll interval is 1006 or less. They are arranged roughly to obtain a winding angle of . In such heating/cooling means, the second
As shown in the figure, sensitivity is better if the position of the louver roll 18B is changed to change the winding angle θ. Therefore, although the louver rolls 18B, . . . in the embodiment are not shown, their positions can be freely changed by a servo actuator.

By the way, just because the furnace 10 is constructed in a spiral shape as shown in the illustrated example, it does not mean that the thin steel strip S will not meander within the furnace 10. Therefore, each roll 18A, 18B has
A crown is attached to prevent meandering, but in the case of the present invention, unlike a vertical furnace, the crown can be made small to the extent that heat buckling does not substantially occur. This point will be explained in detail below. Generally, when a thin steel strip is wound around a roll to change its direction, there is friction between the roll and the thin copper strip, so a difference in tension is created between the roll entry side and the roll exit side. The thin steel strip stretches in the longitudinal direction due to this tension difference, but since the Young's modulus in the longitudinal direction is not uniform, there is a difference in elongation. This difference causes the left and right balance to collapse, causing the 3174 band to meander left and right. In this case, since the tension difference increases in proportion to the winding angle, the larger the winding angle, the higher the incidence of meandering.

In the vertical furnace, since the direction is changed by 180 degrees by the hearth roll, the winding angle is large, and therefore the incidence of meandering is high. Further, since the interval between the upper and lower hearth rolls is wide, even if the inclination due to meandering is slight, the amount of movement in the roll axis direction is large. Naturally, the amount of correction becomes larger, so in a vertical furnace, it is necessary to make the crown for correcting meandering larger.

In the present invention, it is sufficient to run the '3w4 belt S in a curved manner along the furnace wall 11, and there is no need to run it back, so the winding angle θ around the rolls 18A and 18B can be made small, and the roll interval 18A , Since narrowing 18B has no effect on the furnace length, the roll spacing is 18A.

18B can be made narrower. Therefore, compared to a vertical furnace,
Since the incidence of meandering is low and the amount of movement in the roll axis direction is small, the crown can be made smaller. In the vertical furnace,
In order to correct meandering, a crown of 0.2 or more was attached, but in the present invention, the crown amount is reduced to 0. I Ilm. When the amount of crown reaches this level, heat puncture is substantially less likely to occur, so in the present invention, meandering and heat buckling can be solved at the same time.

The furnace 10 is equipped with two rolls 19 and 20 at the center and outside of the furnace 10 in order to introduce the thin steel strip S from an unwinding machine or a pickling line. 4 (to the refining line), two rolls 21, 22++ (also placed on the outlet side of the furnace 10).

In the furnace 10 configured in this manner, the louver rolls 18B, . After threading, each louver roll 18B is moved to a predetermined position so as to obtain a winding angle determined for each zone, and heat treatment is performed according to the heat pattern shown in FIG. 3.

In this case, in order to obtain the optimum characteristic value depending on the steel type, and so that heat treatment can be performed with a heat pattern other than that shown in Fig. 3, the heating zone 12 should be made to have a selection of 20 to b, and the heating zone 14 should be selectable from 50 to b. is desirable. Further, when the target is off in each band, adjustment is made by changing the position of the looper roll 18B for each band.

〔Effect of the invention〕

As described above, according to the present invention, meandering and heat buckling, which could not be solved with a vertical furnace, can be solved at the same time. Further, since the roll group arranged in each zone can be used as a heating/cooling means, the furnace can be made more compact.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view showing one embodiment of the present invention, Fig. 2 is an explanatory view showing the relationship between the looper roll and the winding angle, and Fig. 3 is an explanatory view showing the relationship between the looper roll and the winding angle.
The figure is an explanatory diagram showing the relationship between the heat pattern and the heating/cooling means, and FIG. 4 is a schematic diagram of the vertical furnace. 10...furnace, 11...furnace wall, 12-16...heat treatment! L18... Roll R118A... Fixed roll, 18B... Looper roll, S... Thin steel strip.

Claims (1)

[Claims] (1) The furnace wall is constructed in a spiral shape in a vertical plane, and the heat treatment process necessary for continuous annealing is divided and arranged along the furnace wall, while a group of rolls that guide and run the thin steel strip are placed along the furnace wall. A continuous annealing furnace for thin steel strip characterized by the following arrangement.