JPH07228926A - Vertical continuous annealing furnace for steel strip - Google Patents

Abstract

PURPOSE:To prevent the development of an edge extension and a center buckling of a steel strip by arranging heating means in an air cooling zone in a vertical continuous annealing furnace, detecting a steel strip temp. at the outlet side of a heating means and controlling the heating temp. CONSTITUTION:In the vertical continuous annealing furnace 1, a heating means 10 is added to the inner part of the air cooling zone 5. A first steel strip temp. detecting means 11 is arranged at the lower part of this heating means 10, i.e., the outlet side of the air cooling zone 5. Further, if necessary, a second steel strip temp. detecting means 12 is added to the upper part of the heating means 10. These means 10, 11, 12 are electrically connected with a heating control means 13. The heating means 10 is controlled based on the signals of the steel strip temp. detecting means 11, 12 to suitably heat the steel strip W to the temp., at which the development of the buckling is free from care. By this method, low speed strip passing can stably be executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical continuous annealing furnace suitable for heat treatment of stainless steel strip (steel strip).

[0002]

2. Description of the Related Art For example, rolled stainless steel becomes extremely hard due to work hardening. This is called a hard material, but since the hard material is too hard, it is generally annealed for the purpose of recrystallizing the structure to soften it and solidifying it. As an annealing furnace for this purpose, there are a horizontal furnace for horizontally flowing the strip and a vertical furnace for vertically flowing the strip. The annealing furnace generally heats the strip to a predetermined temperature in a heating zone, sufficiently soaks it in the soaking zone, and forcibly cools it in the cooling zone.

FIG. 4 is a perspective view showing a conventional defective steel strip edge shape. This steel strip 100 has left and right edges 10.
Edge expansions 102 ... (... indicates a plurality; the same applies to the following) occur at Nos. 1 and 101, and are treated as defective products.

FIG. 5 is a graph showing the temperature drop of the steel strip in the conventional air-cooled strip, where the horizontal axis shows the position of the steel strip and the vertical axis shows the temperature of the steel strip. The steel strip soaked to a constant temperature in the soaking zone is naturally cooled in the next air cooling zone. Since the temperature drop of the steel strip per unit time is almost constant, the temperature of the steel strip at the exit of the air cooling strip is still high when the strip running speed is increased, and conversely when the strip running speed is decreased, the steel strip at the outlet of the air cooling strip is decreased. Temperature will be lower.

As described above, the temperature gradient (cooling gradient) of the steel strip changes depending on the strip running speed. Further, at the refraction point of the temperature gradient (point A in FIG. 5), compressive stress in the width direction is generated in the width center portion. On the other hand, in the steel strip, the cooling rate is different between the central portion and the edge, and generally the edge is cooled faster. Then, a tensile stress in the longitudinal direction is generated due to the temperature difference between the central portion and the edge of the steel strip. When these stresses exceed the yield point, plastic deformation begins. The cooling rate difference becomes more remarkable as the temperature gradient becomes larger, and as a result, the edge elongation 102 described in FIG. 4 occurs due to the tensile stress, or the edge becomes relatively flat due to the compressive stress. Thus, a V-shaped wrinkle is formed in the center (this is called center buckling).

Therefore, as a technique for solving this problem, Japanese Patent Laid-Open No. 62-67125 (a steel strip cooling method in a continuous annealing furnace) and Japanese Patent Publication No. 5-64220 (a cooling control method for a metal strip) are disclosed. Proposed.

[0007] In cooling the steel strip, the gas cooling and the roll cooling are used in combination, and the cooling capacity is maintained by maintaining the cooling capacity by the gas cooling and the roll cooling. It is said that buckling is suppressed by reducing the temperature unevenness of the steel strip.

Has a width direction plate temperature control means and a plate width direction shape detector, and the width direction plate temperature control means is provided in accordance with the width direction shape of the steel strip detected by the plate width direction shape detector. Adjust,
This is to achieve uniform cooling in the plate width direction.

[0009]

Since the above is cooled by the gas and the roll, it is likely to be overcooled. If it becomes supercooled, edge extension or center buckling becomes more likely to occur as described above, and it is necessary to further increase the threading speed, for example. That is, since is not a technique for solving supercooling which is a direct cause of edge elongation and center buckling, it must be said that its effect is small although the equipment is complicated.

Also, for example, if a part of the steel strip is swollen, it is said that the part is detected and only that part is cooled to flatten the steel strip, but the steel strip runs at high speed. It is not easy to measure the shape of a steel strip in detail and to cool it locally, and the equipment must be extremely complicated. That is, since it is not a technique for solving the supercooling that is a direct cause of edge elongation and center buckling, it must be said that the equipment becomes extremely expensive.

Therefore, an object of the present invention is to provide a vertical continuous annealing furnace capable of preventing edge extension and center buckling with a relatively simple structure.

[0012]

In order to achieve the above object, the present invention provides a heating means in the air cooling zone and a first steel strip temperature detecting means on the outlet side of the heating means. Heating control means for controlling the heating means based on a temperature signal from the zone temperature detection means is provided.

A second steel strip temperature detecting means is attached to the inlet side of the heating means.

Further, a seal mechanism for preventing outside air from entering is attached to the outlet side of the air cooling zone.

[0015]

If the temperature of the steel strip detected by the first steel strip temperature detecting means is below the steel strip temperature target value, buckling may occur, so the steel strip is heated by the heating means.

When the second steel strip temperature detecting means is attached, the detection signal of the second steel strip temperature detecting means is input to the heating control means.

A seal mechanism is attached to the cooling zone to prevent outside air from entering.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a configuration diagram of a vertical continuous annealing furnace according to the present invention. The vertical continuous annealing furnace 1 includes a preheating zone 2, a heating zone 3, a soaking zone 4, an air cooling zone 5, a bend floater device 6 and a cooling zone 7.
Are arranged in series in the flow direction of the steel strip W, a heating means 10 is further added inside the air cooling zone 5, and the first steel is provided below the heating means 10, that is, on the outlet side of the air cooling zone 5. A band temperature detecting means 11 and a second steel band temperature detecting means 12 are added above the heating means 11 and 12.
It is electrically connected to.

The bend floater device 6 is a device for changing the direction of the steel strip W traveling vertically from top to bottom while floating it with air pressure. At the exit of the air cooling zone 5, the steel strip W
The temperature is still high, and if you try to change the direction of the steel strip with a metal roll at this point, for example, the metal roll needs to be water-cooled, and since the steel strip W is slightly soft, it is prone to flaws. . However, if the bend floater device 6 is adopted as in this example, it is non-contact, and the above problems are eliminated, which is preferable.

The heating means 10 may be a gas burner, an induction heater, a resistance heater or the like. Also,
As the first and second steel strip temperature detecting means 11 and 12, suitable are optical temperature detecting means such as a radiation thermometer and a dichroic thermometer, or proximity type temperature detecting means such as a platinum rhodium thermocouple.

FIG. 2 is a view showing an example of the seal mechanism according to the present invention, and it is preferable to attach the seal mechanism 20 to the outlet side of the air cooling zone 5. The seal mechanism 20 includes, for example, a pair of seal rolls 21 and 21 and seal covers 22 and 22, the seal roll 21 rotates at a peripheral speed equal to that of the steel strip W in principle, and the seal cover 22 rotates behind the seal roll 21. It is a kind of baffle that prevents outside air from entering the air cooling zone 5. Alternatively, the seal mechanism 20 may be a non-rotating sliding plate type seal plate which is slidably contacted with the steel strip W. The point is that it is a mechanism that allows the penetration of the steel strip W but prevents the outside air from entering the air cooling zone 5. Good.

When the outside air enters the air cooling zone 5 by the draft action without the sealing mechanism 20, the heating means 10 has to warm not only the steel strip W but also the cold outside air, which is a loss of energy and a disturbance caused by the outside air. Because of this, temperature control will not work properly. Therefore, the seal mechanism 10 that prevents the invasion of outside air is useful.

The operation of the vertical continuous annealing furnace having the above construction will be described below. In FIG. 1, the steel strip W is charged upward to the pre-heat zone 2 and preheated, inverted by the top roll 15, and the steel strip W is charged downward to the heating zone 3 to heat the steel strip W. It is charged into the soaking zone 4, soaked, and then naturally cooled in the air cooling zone 5. After that, the orientation is changed horizontally by the bend floater device 6, and the cooling zone 7 is forcibly cooled sufficiently.

FIG. 3 is a diagram showing an example of a control flow relating to the heating means, the temperature detecting means and the temperature controlling means of the present invention,
In ST01 (step No. 1, the same applies hereinafter), the initial conditions such as the width, thickness, and steel type of the steel strip are taken in, and in ST02, T2 (the second steel strip temperature detecting means signal or the soaking zone temperature signal) is taken in. The soaking temperature outlet temperature signal is the output of a thermometer for monitoring the temperature inside the furnace which is permanently installed in the soaking zone. In ST03, the temperature control means calculates Tc (steel strip temperature target value) from the above initial condition and T2. This is a critical temperature at which the temperature on the outlet side of the air-cooling zone 5 is monitored and accumulated from the viewpoint of whether harmful buckling has occurred in trial operation or normal operation, and buckling does not occur at a certain temperature Tc. Means

In ST04, the temperature signal of the first steel strip temperature detecting means 11 set on the outlet side of the heating means 10 is fetched, and S
At T05, it is determined whether T1 is equal to or greater than (Tc + a). Here, a is a raised value for preventing hunting, which is a value of about several tens of degrees. T1
If is not smaller than (Tc + a), there is no fear of buckling.
If T1 is smaller than (Tc + a), there is a risk of buckling.
At 07, the heating means is controlled so that T1 (variation value) = Tc (target value). When there is no concern about buckling due to T1 exceeding (Tc + a), ST05 is reached through ST05, the heating means is turned off at ST08, and control is returned to the start.

The above control flow is one example, and the present invention is not limited to this, as long as the heating means appropriately heats the steel strip to a place where there is no fear of buckling. Further, as described above, the second steel strip temperature detecting means 12 can be omitted by using the thermometer for monitoring the temperature inside the furnace which is always provided in the soaking zone 4.

[0027]

Since the present invention is constructed as described above, it has the following effects. According to the present invention, heating means is provided in the air cooling zone of the vertical continuous annealing furnace, and the first side is provided on the outlet side of the heating means.
Since the steel strip temperature detecting means is provided, and the heating control means for controlling the heating means based on the temperature signal from the first steel strip temperature detecting means is provided, the steel strip is removed when there is a risk of buckling. It can be heated to avoid the danger. Therefore, it is not necessary to intentionally increase the strip running speed as a countermeasure against buckling, and low-speed strip running can be performed without anxiety.

According to a second aspect of the present invention, the second steel strip temperature detecting means is provided on the inlet side of the heating means, and the detection signal of the second steel strip temperature detecting means is input to the heating control means. This is preferable because it can be calculated.

According to a third aspect of the present invention, a sealing mechanism is provided on the outlet side of the air cooling zone to prevent outside air from entering, and the outside air is prevented from entering the air cooling zone. Moreover, the loss of heat energy can be prevented.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a vertical continuous annealing furnace according to the present invention.

FIG. 2 is a diagram showing an example of a sealing mechanism according to the present invention.

FIG. 3 is a diagram showing an example of a control flow relating to a heating means, a temperature detection means, and a temperature control means of the present invention.

FIG. 4 is a perspective view showing a conventional steel strip edge shape defective product.

FIG. 5 is a graph showing the temperature drop of the steel strip in the conventional air-cooled strip.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vertical continuous annealing furnace, 2 ... Pre-tropical zone, 3 ... Heating zone, 4 ... Soaking zone, 5 ... Air cooling zone, 6 ... Bend floater device, 7 ... Cooling zone, 10 ... Heating means, 11 ... 1st steel Zone temperature detection means,
12 ... Second steel strip temperature detecting means, 13 ... Heating control means,
15 ... Top roll, 20 ... Sealing mechanism, 21 ... Seal roll, W ... Steel strip.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Kojima, 3rd Oita, Kashima-cho, Kashima-cho, Kashima-gun, Ibaraki Sumitomo Metal Industries, Ltd. Kashima Steel Works (72) Inventor Yukio Hyugaji, 3 Oita, Kashima-cho, Kashima-gun, Ibaraki Address Sumitomo Metal Industries Co., Ltd. Kashima Steel Works

Claims (3)

[Claims] 1. A vertical type of steel strip in which a heating zone, a soaking zone, an air cooling zone for naturally cooling the steel strip, and a bend floater device for changing the plate direction while floating the steel strip by air pressure are arranged in order from top to bottom. In the continuous annealing furnace, the vertical continuous annealing furnace includes a heating means provided in the air cooling zone, a first steel strip temperature detecting means provided on an outlet side of the heating means, and a first steel strip temperature detecting means. A vertical continuous annealing furnace for a steel strip, comprising: a heating control unit that controls the heating unit based on a temperature signal from the unit. 2. The vertical continuous annealing furnace for steel strip according to claim 1, wherein a second steel strip temperature detecting means is additionally provided on the inlet side of the heating means. 3. The vertical continuous annealing furnace for a steel strip according to claim 1, further comprising a sealing mechanism attached to the outlet side of the air-cooling zone to prevent outside air from entering.