JPS6267122A - Method for preventing meandering of metal strip - Google Patents

Abstract

PURPOSE:To prevent meandering of a metal strip at the first half of heating zone in annealing furnace, by previously leveling the metal strip at inlet side of vertical continuous annealing furnace, at annealing the metal strip at a specified line speed in the furnace. CONSTITUTION:In vertical continuous annealing furnace, the metal strip 1 is passed by 350m/min line speed in a heating zone 2, a soaking zone 3, a slow cooling zone 4, a rapidly cooling zone 5 through hearth rolls 6 and continuously annealed. Thereat, shape straightening apparatus, e.g. a leveler 8 is provided at inlet side of the zone 2 to straighter flatly the strip and pass it. Shape of the strip 1 is straightened so that the relation between a max. heating capacity A (T/H) and a steepness (lambda) of the zone 2 becomes lambda4h86.4/A. The steepness (lambda) is defined as lambda=(H/P).100 in case wavelength of the strip 1 and wave height are denoted as P and H respectively. In this way, meandering of the strip is prevented at the first half of the zone 2, and stable operation is carried out without causing decrease of yield.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a continuous annealing furnace for processing metal strips such as tin plates, automobile steel plates, stainless steel plates, etc. It relates to the field of preventing strips from meandering.

(Prior Art) Generally, a continuous heat treatment furnace for metal strip uses a large number of hearth rolls for conveying the metal strip. For example, as shown in FIG. 2, in a vertical continuous annealing furnace, a large number of hearth rolls 6 are provided in each of the heating zone 2, soaking zone 3, slow cooling zone 4, and rapid cooling zone 5. The material is sequentially wound around this hearth roll 6 and passed through an annealing furnace in the direction of arrow A to arrow B to perform a predetermined heat treatment. In the first half of the heating zone of this annealing furnace, the low-temperature metal strip comes into contact with the hearth roll 6, so the temperature distribution of the hearth roll 6 (hereinafter referred to as thermal crown) is as shown by the solid line in Figure 3. ing. and,
As the line speed increases, the temperature distribution of the hearth roll 6 becomes more concave as shown by the dotted line in FIG. In a roll with such a concave profile,
If the shape of the metal strap is stretched at the edges or at the sides, the tension will immediately become unbalanced and the metal strip will meander significantly. Therefore, as shown in Figure 4, it is necessary to reduce the line speed and reduce the temperature difference between the roll edge and the roll center, in other words, to reduce the thermal crown, which improves efficiency. It will drop. Additionally, if the initial crown of the roll is made larger to deal with this, the crown becomes convex as the line speed becomes slower, causing heat buckling.

Therefore, many attempts have been made to transport the metal strip in a stable state by controlling the crown amount of the hearth roll. For example, Japanese Unexamined Patent Application Publication No. 57-177930 and Japanese Utility Model Application No. 58-10546 disclose that the amount of crown is controlled by heating and cooling the hearth roll.
Further, Japanese Utility Model Application Publication No. 55-172359 discloses that a bending device is provided to adjust the crown amount.

(Problems to be Solved by the Invention) However, in order to apply the above-mentioned techniques and techniques to actual operations, it is necessary to provide a means for measuring the amount of crown and a means for controlling the crown amount for each hearth roll, which reduces costs. Many problems remain.

An object of the present invention is to prevent meandering of a metal strip caused by the influence of thermal crown in the front half of a heating zone without providing a means for measuring the amount of crown and a means for controlling it for each hearth roll as in the conventional method. Our goal is to provide the following.

(Means for Solving the Problems) As shown in FIG. 1, the present invention aims at flattening the metal strip by using a shape straightening device, for example, a leveler 8, on the entry side of the heating zone 2 of a vertical continuous annealing furnace. The purpose of this plate is to prevent the metal strip from meandering in the front half of the heating zone of a vertical continuous annealing furnace operating at a line speed of 35 pm or higher.

Furthermore, by correcting the maximum heating capacity AT/H of the heating zone 2 and the shape of the steepness hub, meandering of the metal strip can be prevented.

This steepness λ is defined as λ=2×100, where P is the wavelength of the metal strip 1 and H is the height of the wave as shown in FIG.

(Function) The present invention is directed to a vertical continuous annealing furnace that operates at a line speed of 350 mpm or more, and the reason for this is that the line speed and the number of occurrences of meandering of 200+ mm or more have a relationship as shown in Figure 7. , line speed is 350m
This is because when operating at less than pm, there is no need to flatten the metal strip.

Further, the relationship between the maximum heating capacity AT/H and the steepness λ is as shown in FIG. 8 by taking data on the relationship between the shape of the metal strip on the entrance side of the furnace and the number of passing cars.

As can be seen from this figure, the steepness λ and the number of vehicles passing the plate are inversely proportional, and a multiple regression analysis of this data revealed that
The following relationship was obtained: number of passing trucks (T/H) x steepness (λ) = 86.4. Therefore, by correcting the shape of the metal strip on the entrance side so as to satisfy this relationship, the heating ability of the heating zone can be maximized.

(Example) FIG. 5 shows the results of threading a heavily meandering interposed metal strip with varying steepness λ, ie, straightening rate, in the first half of the heating zone of a continuous annealing furnace. As can be seen from this figure, the flatter the metal strip on the entrance side of the continuous annealing furnace, the more stable the operation at a high line speed with less meandering. For example, when continuously annealing a metal strip with a thickness of 0.311 ns and a width of 700 ++ m in the case of a tin plate, by keeping the steepness at the entrance of the continuous annealing furnace to about 1%, the conventional average line speed can be reduced to about 400 mpm. However, according to the method of the present invention, the speed could be increased to 550IIlpI11.

(Effects of the Invention) As explained above, according to the present invention, by flattening the metal strip on the entry side of the continuous annealing furnace, meandering of the metal strip in the front half of the heating zone of the continuous annealing furnace can be prevented and the yield can be improved. It is possible to operate stably without causing a decline in productivity, improve productivity, and improve quality.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the apparatus used when carrying out the method of the present invention, FIG. 2 is a diagram showing an overview of a continuous annealing furnace, and FIG. 3 is a diagram showing the temperature distribution of the hearth roll. It is. Figure 4 is a diagram showing the relationship between line speed, hearth roll center temperature and roll edge temperature, Figure 5 is a diagram showing the relationship between steepness and line speed, and Figure 6 is a diagram to define steepness. This is a diagram. Moreover, FIG. 7 is a diagram showing the relationship between line speed and the number of occurrences of meandering, and FIG. 8 is a diagram showing the relationship between steepness and the number of vehicles passing.

Claims (1)

[Claims] 1. When continuously annealing a metal strip at a line speed of 350 mpm or more in a vertical continuous annealing furnace, a metal strip that has been flattened in advance on the entrance side of the furnace is introduced into the furnace and passed through it. A method for preventing meandering of metal strips. 2. The relationship between maximum heating capacity A T/H and steepness λ is λ≦8
A method for preventing meandering of a metal strip according to claim 1, characterized in that the metal strip is straightened so that the angle becomes 6.4/A.