JPH07316667A - Method for preventing meandering and slip of metal strip passing through continuous heat treatment furnace - Google Patents

Abstract

PURPOSE:To surely prevent the meandering and slip of a metal strip passing through a continuous heat treatment furnace by blowing the gaseous nitrogen of low viscosity against the biting part of the carrying roll in a heat treatment furnace at the metal strip. CONSTITUTION:Gaseous nitrogen of low viscosity is blown against a biting part of a carrying roll in a heat treatment furnace at a metal strip. This constitution allows the gas film entrapped and formed between the metal strip and the carrying roll to be thin, and the metal strip to be brought into contact with the projecting part of fine ruggedness of the surface of the carrying roll. As a result, the metal strip is correctly passed by the carrying roll to surely prevent the meandering and slip or the like. As the gas of low viscosity, the atmospheric gas in the furnace, e.g. the heat treatment furnace such as the continuous annealing furnace of the metal strip, is generally composed of about 95% gaseous nitrogen and the balance gaseous hydrogen, and the heat treatment is executed while reducing the oxide on the surface of the steel strip, and it is preferable to use a part of the gas in the furnace or the like, which does not largely change the composition of the atmospheric gas in the furnace.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal band meandering and slip prevention method in a continuous heat treatment furnace.

[0002]

2. Description of the Related Art In a heat treatment using a continuous heat treatment furnace such as a continuous annealing furnace, heat treatment such as heating, soaking and cooling is performed while moving (conveying) a steel strip by a conveying roll arranged in the furnace. However, when heat treatment is performed while continuously moving the steel strip by the transport rolls in this manner, a so-called meandering phenomenon may occur in which the steel strip moves to both ends in the width direction of the transport roll. Will be located outside the roll, and the end of the steel strip will break. In order to prevent such meandering of the steel strip and slip between the roll and the steel strip, for example, JP-A-55-55
As disclosed in Japanese Patent No. 100919 and Japanese Patent Publication No. 6-4894, it is known to prevent meandering, slipping, etc. by adjusting the roughness of the roll surface or improving the crown of the roll surface. There is.

[0003]

However, in the method of adjusting the roughness of the roll surface to prevent slippage and the like, the roughness (irregularities) formed on the roll surface may cause flaws on the surface of the metal strip. In addition, it is disadvantageous in terms of cost to change the roughness of the roll surface in various ways.Furthermore, in the method of improving the crown of the roll surface to prevent meandering, slipping, etc., increasing the amount of crown increases the metal band. In some cases, a so-called heat buckle that causes wrinkles in the longitudinal direction may be induced, and the cost increase due to the crown change cannot be avoided. In addition, when slips or the like occur during striping, flaws are generated on the surface of the metal strip, so it is necessary to reduce the stripping speed, and there is a problem that the average stripping speed decreases and productivity decreases. The present invention has been made to advantageously solve such problems,
It is an object of the present invention to provide a method for surely preventing meandering or the like of a metal strip in a continuous heat treatment furnace.

[0004]

Means for Solving the Problems A method for preventing meandering and slipping of a metal strip in a continuous heat treatment furnace according to the present invention, which solves the above-mentioned problems, is a biting portion between a carrier roll in a heat treatment furnace and a metal strip. It is characterized by spraying a low-viscosity gas onto the.

[0005]

According to such a method for preventing the meandering of the strip metal strip in the continuous heat treatment furnace, a low-viscosity gas is blown to the biting portion between the transport roll and the metal strip in the heat treatment furnace to intervene between the metal strip and the transport roll. The film thickness of the gas is reduced and the gas film is spread over the entire length of the contact length of the metal band between the transport roll and the metal band, thereby preventing the metal band from slipping. It is what It is known that one of the causes of the metal band meandering is the micro-slip of the carrier roll and the metal band, and the prevention of the slip and the meandering can be achieved at the same time. That is, as a result of various studies on the meandering and slipping of the metal strip in the continuous heat treatment furnace, the present inventors have found that the atmosphere gas in the furnace (about
(720-900 ℃) is rolled up to form a film of atmosphere gas in the furnace, and the thicker the film of the gas film, the lower the frictional force between the metal strip and the transfer roll, causing meandering or slipping. It became clear. In particular, as the strip running speed of the metal strip becomes high, the amount of atmospheric gas in the furnace wound between the metal strip and the transport roll also increases, so that the amount of increase in the film thickness of the gas coating becomes more remarkable and the occurrence of meandering and slippage occurs. It is easy to happen. Furthermore, it was also clarified that the film thickness of the gas film interposed between the metal strip and the transport roll is closely related to the viscosity of the gas.

[0006] Therefore, as a result of various experiments on whether or not the metal band meanders by spraying so that some gases having different viscosities are intervened on the biting portion between the transport roll and the metal band, a gas having a low viscosity is blown. It was confirmed that the metal band can be surely prevented from meandering by attaching it. That is, a low-viscosity gas is sprayed on the biting portion between the transport roll and the metal strip to reduce the atmosphere at the biting portion between the transport roll and the metal strip, so that the gas is transferred between the transport roll and the metal strip. The gas coating formed on the surface of the carrier roll becomes thin and the metal strip contacts the convex parts of the fine irregularities on the surface of the transport roll, and the metal strip is accurately threaded by the transport roll to reliably prevent meandering and slipping. I confirmed that I could do it.

As described above, according to the present invention, a low-viscosity gas is blown to the biting portion between the transport roll and the metal strip to prevent the metal strip from meandering and slipping. , Heat treatment is performed while moving (passing) the metal band by the cooling band and the sequential transfer rolls.
By applying to a portion where the meandering and slipping are likely to occur, for example, the front stage of the heating zone, the meandering and slipping can be surely prevented.

Next, as the low-viscosity gas, for example, in a heat treatment furnace such as a continuous annealing furnace for steel strip, nitrogen gas is generally about 95%, and the residual hydrogen gas constitutes the atmosphere gas in the furnace. Since the heat treatment is carried out while reducing the oxides on the surface of the steel strip as the nitrogen-based gas in the atmosphere gas, for example, a part of the gas in the furnace is taken out and the viscosity of this is reduced to allow the transport roll and the steel strip to be caught as described above. It is preferable that the composition of the atmosphere gas in the furnace is not greatly changed, such as by spraying onto the site.

Further, the low-viscosity gas as described above is 2.5 ×
By setting the pressure to 10 ^-5 Pa · S or less, the meandering of the metal strip can be particularly reliably prevented. Also, like this 2.
In order to obtain a low-viscosity gas of 5 × 10 ⁻⁵ Pa · S or less, it is possible to easily secure the temperature by setting the nitrogen gas temperature to about 200 ° C. or less.

Next, an example of the method of the present invention will be described with reference to the drawings. In FIG. 1, 1 is a continuous heat treatment furnace, 2 and 2a.
.. is a transport roll arranged in the continuous heat treatment furnace 1, 3 is a steel strip transported by the transport rolls 2, 2a ...
Designated by 4a are blowing nozzles which are oriented at the biting portion of the width of the steel strip 3 in the width direction.
The low-viscosity nitrogen gas is blown to the part where the transport rolls 2, 2a ... And the steel strip 3 are caught by 4a.

Incidentally, such transport rolls 2, 2a ...
・ The arrangement of the spray nozzles 4, 4a, 4b, and 4c against is effectively used for all the conveying rolls in all continuous heat treatment furnaces such as continuous annealing furnaces for steel strips and steel strip pretreatment furnaces for continuous galvanizing equipment. be able to.

[0012]

[Example] Next, a continuous firing casting furnace (heating zone, soaking 720 ℃,
Conveyor rolls with a roll roughness (Ra) of 3.5 μm and a roll diameter of 750 mm placed above and below the heating zone of the cooling zone (100 ℃), and a plate thickness of 0.25 conveyed by this conveyor roll with a threading tension of 2.0 kg / mm ^2. mm, width 850 mm steel strip (C: 0.03% low carbon steel plate)
Atmosphere composition is N ₂ 95
%, The results of heat-treating the steel strip while blowing a low-viscosity gas of H ₂ are shown as Examples 1 to 4, and the case where the low-viscosity gas is not blown to the biting part is shown in Table 1 as a comparative example. .
According to this table, in each of the examples, there was almost no meandering of the steel strip, and high-speed conveyance with an average sheet passing speed of 800 m / min was possible and production efficiency could be improved, while low-viscosity gas was added to the biting part. In the comparative example without spraying, since the meandering occurs, the conveying speed is suppressed to an average plate passing speed of 550 m / min to prevent the meandering, and the productivity is lowered. Next, examples of the method of the present invention will be given together with comparative examples.

[0013]

[Table 1]

[0014]

As is apparent from the above description, the present invention is as follows.
By blowing a low-viscosity gas to the part where the transport roll in the heat treatment furnace and the metal strip are caught, it is possible to reliably prevent meandering and slipping of the metal strip on the transport roll, and to improve the strip running speed of the metal strip. Since the heat treatment can be performed without lowering the productivity, the productivity can be remarkably improved. Moreover, since it is not necessary to adjust the surface roughness and crown of the transport rolls, excellent effects such as cost reduction can be obtained. Therefore, the present invention has a very great effect on the industry as a method for preventing the metal strip from meandering and slipping in the continuous heat treatment furnace, which can prevent the metal strip from meandering the transport rolls accurately and easily.

[Brief description of drawings]

FIG. 1 is a side view illustrating an embodiment of the method of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hayato Kazeoka 5-3 Tokai-cho, Tokai-shi, Aichi Nippon Steel Co., Ltd. Inside the Nagoya Works

Claims (2)

[Claims] 1. A method for preventing the meandering and slipping of a metal strip in a continuous heat treatment furnace, which comprises spraying a low-viscosity nitrogen gas onto a portion where a carrier roll in the heat treatment furnace and a metal strip are caught. 2. The method of preventing meandering and slipping of a strip of metal in a continuous heat treatment furnace according to claim 1, wherein a low-viscosity gas of 2.5 × 10 ⁻⁵ Pa · S or less is sprayed.