JP2603339B2 - Method for preventing thermal deformation of helper roll in vertical continuous heat treatment furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention has a group of helper rolls in a furnace, and strips are sequentially wound around an upper helper roll group and a lower helper roll group to form a path, The present invention relates to a method for preventing thermal deformation of a helper roll that occurs when a line is stopped in a vertical continuous heat treatment furnace in which a heating device is arranged on the way.

<Prior Art> FIG. 3 shows a schematic view of a heating zone of a vertical continuous heat treatment furnace.
A strip 2 is sequentially wound around an upper helper roll group 1 _U consisting of an upper roll 1 _Ui and a lower helper roll group 1 _L consisting of a lower roll 1 _Li to form a path, and a heating device 3 (radiant tube) is provided on the way. Is common) is located. In such equipment, heat is transferred between the helper roll and a heated strip, a heating device, a furnace wall, and the like, and as a result, the roll is deformed due to an uneven temperature distribution called a thermal crown. Due to the thermal crown, the centering force applied to the strip by the roll may be inappropriate, and meandering or buckling of the strip in the width direction, which is called a heat buckle, may be caused. Therefore, many techniques for preventing or controlling the thermal crown have been proposed.

For example, JP-A-49-98308 discloses that a shield plate is provided between a roll and a heating device to reduce the influence of heat radiation from the heating device, and that the roll surface is heated to a plate temperature by a heat source unrelated to the strip. A method of heating to a near temperature is shown. Japanese Patent Laid-Open No. 55-100919, Japanese Utility Model Application No. 58-65360
Japanese Patent Application Laid-Open Publication No. 58-105546 and Japanese Utility Model Application Laid-Open Publication No. Sho 58-105464 show a method of controlling the temperature distribution in the width direction of a roll by blowing cooling gas.

However, it should be noted here that all the conventional technologies aim at equalizing or controlling the temperature distribution in the width direction of the roll during the line operation. It is not mentioned at all. This is because during operation of the continuous heat treatment furnace, the helper roll in the furnace is rotating, and even if there are uneven thermal boundary conditions in the circumferential direction of the roll, they are periodically repeated, and as a result, This is because there is no uneven temperature distribution in the circumferential direction.However, this is true only when the rotation speed of the roll is sufficiently high compared to the temperature change speed of the roll, and when the line is stopped, Such an effect cannot be expected. That is, an effective technique for making the roll temperature distribution uniform while the line is stopped has not been proposed.

On the other hand, it is well known that in a vertical continuous heat treatment furnace, a heat buckle is likely to occur when the line is stopped from normal operation and restarted. One of the causes of this heat buckle is a fluctuation in tension after the start of operation.
FIG. 4 shows the state of the tension fluctuation. As can be seen from this, a periodic tension fluctuation corresponding to one rotation of the roll occurs. This is caused by the roll being deformed into a banana shape as shown in FIG. 5 by the heat from the heating device while the line is stopped. Such deformation not only causes a change in tension, but also easily causes cracks on the roll surface and shortens the life of the roll.

The reason why such thermal deformation of the roll occurs is considered as follows. That is, while the line is stopped, the supply of fuel or electric power to the heating device 3 is naturally stopped. However, since the heat capacity of the heating device is large, heat radiation and particularly the furnace inside the upper roll 1 _Ui shown in FIG. The convection of the atmosphere gas raises the temperature of the part of the roll facing the heating device, and if there is a shielding plate 4 between the heating device and the roll, there is a slight temperature rise prevention effect. Since the heat removal action to the outside is not large, the result is that the temperature distribution is also generated in the roll.

<Problem to be Solved by the Invention> An object of the present invention is to propose a method for preventing thermal deformation of a helper roll that occurs during a line stop of a vertical continuous heat treatment furnace.

<Means for Solving the Problems> The present invention is directed to a vertical continuous heat treatment furnace having loopers on an inlet side and an outlet side, one side being a high-temperature portion which is a heating device, and the other side being a low-temperature portion. A method for preventing thermal deformation of helper rolls disposed opposite to each other, wherein the helper rolls stopped with a metal strip are alternately defined in the forward and reverse directions by the following formula (1). A method of preventing thermal deformation of a helper roll of a vertical continuous heat treatment furnace, characterized in that a rotation amount L to be rotated is set to a minimum rotation amount, and a stripper is absorbed by the looper.

L = 0.5πD (1) where D indicates the maximum helper roll diameter in the section equipped with the strip heating device.

<Operation> While the line is stopped, a part of the surface of the roll is opposed to a high-temperature part such as a heating device, and a part of the roll is stationary while facing the low-temperature part such as a furnace wall. Thermal deformation occurs. Therefore, the surface of the roll may be evenly opposed to the high-temperature part and the low-temperature part even when the line is stopped. In the present invention, since the target is during the line stop when the strips are connected in the furnace, the helper roll cannot be continuously rotated. Therefore, the roll temperature is made uniform by moving the strip back and forth, that is, by alternately rotating the helper roll forward and backward. As the amount of rotation, L = 0.5πD (D is the largest helper roll diameter in the section equipped with the strip heating device) is required at a minimum. This is because, in a normal vertical continuous heat treatment furnace, a result that does not hinder practical use can be obtained only by roughly dividing the ambient temperature condition of the roll into a high temperature portion and a low temperature portion. The rotation of the rolls may be alternately performed when the furnace temperature is 300 ° C. or higher. This is because when the temperature in the furnace is lower than 300 ° C., the temperature difference between the heating device and the furnace wall is almost eliminated, and the inside of the furnace can be regarded as having a substantially uniform temperature.

<Example> Fig. 1 shows an example of a specific example of the present invention. This is a continuous annealing line of a vertical furnace, which consists of a heating zone, a soaking zone, and a cooling zone. 1 is helper roll, 5 is on,
The exit looper, 6 is a tension meter roll, 7 is a bridle roll, and 8 is a speed controller (Automatic Spee
d Regulator: ASR), 9 is a tension controller (Automatic Tensi
on Regulator: ATR). In the above configuration, when a speed command described later is input to each ASR 8, each helper roll 1 and bridle roll 7 are driven according to the speed command value. At this time, feedback control is performed based on a detection value from a speed detector (not shown). In the illustrated example, the bridle roll 7 is used as a speed master, and the helper rolls 1... This is feedback-controlled by the detected value of each tension meter roll 6. Let D be the diameter of the in-furnace helper roll. In this case, when the roll diameter is different in each band, the largest helper roll diameter in the section provided with the strip heating device is used.

In such a line, after stopping the line due to a trouble or the like from the normal operation, a speed command as shown in FIG. 2 is given. Here, + indicates the forward rotation side and-indicates the reverse rotation side, and the strip feed amount L (the area of the hatched portion) is set to L = πD. At this time, the feed amount of the strip is absorbed by the looper 5 on the furnace entrance side and the exit side. Not particularly necessary to define the maximum value V ₀ which is the speed command but, 10～30Mpm is preferable from the viewpoint of controllability of the strip feed amount L. With this speed, a sufficiently high roll rotation speed can be obtained as compared with the change in the roll temperature. Or it may be provided with the appropriate pause time t ₀ during the transition from forward to reverse. However, if the t ₀ too long deformation of the roll is likely to guide the less than 10 seconds because there is to be progress.

It is better to start the forward and reverse rotation patterns of the roll as soon as possible after the line stops. Also, as mentioned above, if the temperature of the heating zone and the soaking zone falls below 300 ° C,
Turn off this speed command. When the line is operated again at a furnace temperature of 300 ° C. or higher, the line operation is started immediately after stopping the normal rotation and reverse rotation patterns. This interval should be within 10 seconds.

When the operation was carried out under the above-described operating conditions, the thermal deformation of the helper roll during the stop of the line could be almost prevented, and the heat buckle and breakage of the strip could be prevented when the line was restarted.

<Effects of the Invention> According to the method of the present invention, it is possible to prevent a strip heat buckle which occurs when the operation is restarted after the line is stopped, which is a problem in the conventional vertical continuous heat treatment furnace, and the yield is improved. Achieved. Also, since secondary troubles such as breakage due to heat buckle can be prevented,
The operation rate of the line was also improved.

Furthermore, since the occurrence of cracks due to the thermal deformation of the roll can be prevented, the roll life can be prolonged.

[Brief description of the drawings]

FIG. 1 is a diagram showing a specific configuration when the method of the present invention is carried out, FIG. 2 is an explanatory diagram showing a speed command according to the present invention, FIG. 3 is a schematic diagram of a heating zone of a vertical continuous heat treatment furnace, FIG. The figure is an explanatory view showing an example of a tension fluctuation after the start of the line operation, and FIG. 5 is a schematic view of the roll deformation during the stop of the line. 1 ... Furnace helper roll, 1 _Ui ... Upper roll, 1 _U ...
Upper helper roll group, 1 _Li ...... Lower roll, 1 _L ... Lower helper roll group, 2 ... Strip, 3 ... Strip heating device, 4 ... Shield plate, 5 ... Looper.

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuhisa Nakajima 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (56) References JP-A-60-255931 (JP, A)

Claims (1)

(57) [Claims] 1. A helper roll which is disposed in a furnace of a vertical continuous heat treatment furnace having loopers on an inlet side and an outlet side, one side being disposed at a high temperature portion as a heating device, and the other side being disposed at a low temperature portion. Wherein the helper roll, which is stopped with the metal strip, is rotated alternately in a forward direction and a reverse direction by a minimum rotation amount L defined by the following equation (1). A method for preventing thermal deformation of a helper roll in a vertical continuous heat treatment furnace, characterized in that the helper roll is rotated as an amount and the feed amount of the strip is absorbed by the looper. Note: L = 0.5πD (1) where D indicates the maximum helper roll diameter in the section provided with the strip heating device.