JPH0813041A - Method and device for preventing cooling buckle in continuous heat treatment furnace - Google Patents

Abstract

PURPOSE:To provide a method and a device for preventing the cooling buckle in a continuous heat treatment furnace, in which the development of the cooling buckle can surely be prevented by investigating the true developing cause of the buckling flaw. CONSTITUTION:In the cooling buckle preventing method in the continuous heat treatment furnace, in which a specific heat treatment is executed while carrying a strip S by many rolls 20 arranged in the furnace, the temp. of the strip at the inlet side of the roll 20 arranged in a zone having the function for cooling the strip S is obtd. by the actual measurement or the calculation. The roll temp. in this zone is controlled so as not to lower by >=50 deg.C than the obtd. strip temp. By this method, the compressive stress developed in the strip S is restrained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous heat treatment furnace such as a continuous annealing furnace for continuously heat treating a strip (hereinafter referred to as a strip) along a predetermined annealing pattern.

[0002]

2. Description of the Related Art FIG. 16 is a schematic view showing a layout of a general continuous annealing furnace. The continuous annealing furnace 1 includes a pre-tropical zone 2, a heating zone 3, a soaking zone 4, a GJ (gas jet) cooling zone 5 and an RQ (roll quench) cooling zone 6 following the soaking zone 4, and further continues to the cooling zone 6. It is composed of a reheating zone 7, an OA (overaging) zone 8 and a final cooling zone 9. An entrance looper 10 and a payoff reel 11 are arranged in the front part of the pre-tropical zone 2, and an exit looper 12, a skin pass mill 13 and a coiler 14 are arranged in the rear part of the final cooling zone 9, respectively. Has been done. Also, each of the above bands 2
A large number of transport rolls (not shown) are horizontally arranged in parallel within each other. A strip S is sequentially wound around each roll, and the strip S is attached to each strip 2
Heat treatment is performed along a predetermined annealing pattern while sequentially passing through 9 to 9.

By the way, there may be a case where the strip S has a cooling defect called a cooling buckle during cooling in the GJ cooling zone 5, the RQ cooling zone 6, the overaging zone 8 and the final cooling zone 9. This cooling buckle is liable to occur in extremely low-carbon steel with low rigidity and wide and thin strips, which have been in increasing demand in recent years, and have a problem of causing losses such as a decrease in yield and productivity.

The following points have been considered as causes of the above-mentioned cooling buckle. That is, a hollow roll or an internal water-cooled roll is used as the transport roll adopted in the cooling zone. Therefore, as a result of the hot strip wrapping around the relatively cold roll, the temperature at the center of the roll becomes higher than that at the end, resulting in temperature unevenness, resulting in a convex thermal crown at the center, which causes cooling. The buckle is generated.

In order to prevent such a cooling buckle, the hearth roll is conventionally locally heated, for example, in Japanese Utility Model Publication Nos. 3-41839, 3-59356 and 58-43454. Alternatively, it has been proposed to cool it to reduce the generation of convex thermal crowns. Further, JP-A-2-277727 proposes that the emissivity of the roll chamber is regulated to reduce the temperature difference in the axial direction of the roll, thereby suppressing the convex thermal crown.

[0006]

However, as a result of comparatively examining various methods of the cooling buckle prevention method according to each of the above-mentioned prior art publications and implementing them on a test basis, none of the methods has the expected effect. It has been found.

For example, FIG. 17 (a) shows a conventional example in which the central portion 15a of the hearth roll 15 with which the strip S is in contact is cooled by spraying a cooling gas, and FIG. 17 (b) shows roll cooling. It shows the experimental results of examining the change in the limit tension at which the diaphragm is generated with and without. As shown in the figure, it can be seen that when the hearth roll is cooled, the limit tension at which the throttling is generated decreases rather than when it is not cooled, and the heat buckle is more likely to occur. In addition,
The iris generation limit tension will be described later.

FIG. 18 (a) shows a conventional example in which the contact portion between the strip S and the hearth roll 15 is heated simultaneously by a heater, and FIG. 18 (b) shows a diaphragm with and without roll heating. The experimental result which investigated the change of generation | occurrence | production limit tension is shown. As shown in the figure, it can be seen that the plate strength decreases as the temperature of the strip S rises, and as a result, the limit tension for drawing reduction is almost the same as in the case without heating.

The present invention has been made in view of the above circumstances, and provides a cooling buckle prevention method and device in a continuous heat treatment furnace capable of investigating the true cause of a drawing defect and reliably preventing the generation of a cooling buckle. Is intended.

[0010]

Means for Solving the Problems The inventors of the present invention repeatedly conducted various experiments described below in order to elucidate the cause of the squeezing flaw, and as a result, found a completely new method for preventing a cooling buckle. Invented.

First, as shown in FIG. 15, when the tension is normally raised while the strip S is wound around the hearth roll 15 having a crown, the dimensions and material of the strip S and the crown of the hearth roll 15 are increased. Longitudinal wrinkles are generated on the strip S depending on the size, and drawing flaws are generated when a certain tension is reached. The tension that causes this drawing flaw is referred to as the drawing-generation limit tension.

1 to 4 are diagrams showing experimental results for explaining the formation process of the present invention. FIG. 1 shows an experimental value obtained by examining the limit tension ratio at which squeezing occurs with respect to the temperature difference between the strip temperature and the roll temperature. In this experiment, a strip of ultra-low carbon steel having a thickness of 0.3 mm and a plate width of 910 mm was heated to 350 ° C., while the roll generation limit was changed when the roll temperature was changed from 150 ° C. to 450 ° C. The tension was measured. The throttle generation limit tension ratio is a ratio between the throttle generation limit tension at each temperature difference and the throttle generation limit tension when the temperature difference is zero.

As shown in FIG. 1, when the roll temperature is higher than the strip temperature (+ area) as compared to when the temperature difference is zero, the throttle generation limit tension ratio is remarkably large in proportion to the temperature difference. You can see that it has become. On the contrary,
When the roll temperature is lower than the strip temperature (-region), the throttle generation limit tension ratio is small as described above.

The reason for this is considered to be the influence of thermal stress caused by the temperature difference between the strip temperature and the roll temperature. First, consider a case where there is almost no temperature difference between the two and only the roll crown changes.

FIG. 2 is a diagram showing the relationship between the roll crown amount (diameter difference between the roll central portion and the end portion) and the diaphragm generation limit tension. As is clear from the figure, it is found that the limit tension at which the squeeze occurs decreases rapidly as the crown amount increases. This is because the larger the amount of crown, the more unevenly the strip is pulled on the roll surface,
The amount of shear deformation of the strip becomes larger. as a result,
This is because a large vertical wrinkle is formed immediately before winding around the roll, and the larger the vertical wrinkle, the easier it is to get on the roll.

At this time, as shown in FIG. 3, compressive stress directed inward in the width direction acts on the strip width center portion just before being wound around the roll. The larger the compressive stress and the larger the area on which the compressive stress acts, the easier the vertical wrinkles formed on the roll entry side will ride on the roll.

Next, consider the case where the roll temperature TR is lower than the strip temperature TS. As shown in FIG. 4, the heat capacity of the strip having a small thickness is extremely small, so that the strip temperature sharply decreases when the strip comes into contact with the roll. Therefore, there is a temperature difference between the low temperature portion contacting the roll and the high temperature portion immediately before contacting the roll with the contact start point a between the roll and the strip as a boundary. As a result, a compressive force in the width direction acts on the high temperature portion due to the thermal contraction of the low temperature portion (see the left side of FIG. 4B). The region where this compressive force acts is substantially overlapped with the region where the compressive stress shown in FIG. 3 acts, and therefore acts in the direction in which it is easier to generate a squeezing flaw. Therefore, the limit tension at which the squeeze occurs is significantly reduced as compared with the case where there is no temperature difference.

On the other hand, when the roll temperature TR is higher than the strip temperature TS, the thermal stress is in the opposite tensile direction (see the right side of FIG. 4B). As a result, this tensile stress acts in the direction of canceling the compressive force, so that the occurrence of vertical wrinkles is suppressed and the draw flaws are less likely to occur.

From the above, the relationship between the strip temperature and the roll temperature is more important than the thermal crown of the roll, and by controlling the temperature difference between the two, it is possible to surely prevent the occurrence of drawing defects. The present invention has been made.

According to a first aspect of the present invention, in the cooling back prevention method in a continuous heat treatment furnace, the strip is cooled by transporting the strip by a number of rolls arranged in the furnace to perform a predetermined heat treatment. The temperature of the strip on the entrance side of the roll disposed in the zone having the function to obtain is obtained by actual measurement or calculation, and the roll temperature of the zone is controlled so as not to fall below the obtained strip temperature by 50 ° C. or more. It is characterized by that.

The invention of claim 2 is an apparatus for carrying out the prevention method of claim 1, wherein a predetermined heat treatment is carried out while the strip plate is conveyed by a large number of rolls arranged in the furnace. In a cooling back prevention device in a continuous heat treatment furnace, a plate temperature recognizing means for measuring or calculating the temperature of the strip plate on the entrance side of the roll arranged in the zone having a function of cooling the strip plate, Roll temperature control means for controlling the roll temperature so as not to fall below the obtained strip plate temperature by 50 ° C. or more are provided.

The invention of claims 3 to 5 is a specific example of the roll temperature control means, and the invention of claim 3 is provided with a fluid heat medium and a heater in the roll, and the fluid heat medium is provided by the heater. The roll surface is controlled to be heated via a medium, and the invention of claim 4 is characterized in that a heat medium supply device for forcibly circulating the fluid heat medium is provided in the roll. Furthermore, the invention of claim 5 is characterized by comprising an electromagnetic induction heater, a resistance electric heater, or an infrared heater.

In the present invention, to keep the roll temperature below 50 ° C. below the strip temperature means to make the roll temperature one side strip inlet temperature higher than −50 ° C., preferably −50 ° C. C to + 100 ° C.

[0024]

According to the cooling buckle prevention method and apparatus in the continuous heat treatment furnace of the present invention, since the roll temperature one side strip inlet side temperature is set higher than -50 ° C, the compressive direction force acting on the strip is higher than that in the conventional method. The compressive stress generated in the strip can be suppressed by making it small or by applying thermal stress in the tensile direction to the strip. As a result, it is possible to avoid the occurrence of drawing defects due to vertical wrinkles, which in turn improves yield and productivity.

In the inventions of claims 3 to 5, heating is performed by the heater via the fluid heat medium, and the fluid heat medium is forcedly circulated for heating, and further, the electromagnetic induction heater, the resistance electric heater, Alternatively, since it is heated by the infrared heater, the roll temperature can be controlled without increasing the cost so much.

[0026]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 5 and 6 are views for explaining a cooling buckle prevention method and device in a continuous annealing furnace according to an embodiment of the inventions of claims 1 to 3.

In the continuous annealing furnace 1 of this embodiment, as shown in FIG. 16, pre-tropical zone 2, heating zone 3, soaking zone 4, GJ cooling zone 5, RQ cooling zone 6, reheating zone 7, OA zone 8 , And the final cooling zone 9, and the basic structure is the same as the conventional one.

In the cooling zone, a carrying roll 20 characterizing this embodiment is arranged, and the carrying roll 20 is rotatably installed between the left and right furnace walls 21a and 21b. In this transport roll 20, the inner pipe 20 b is inserted into the shaft core of a cylindrical roll outer shell 20 a via a bearing 22, and the inner pipe 2
Both ends of 0b are fixed to the outside of the furnace walls 21a and 21b.

Silicon oil 23 as a heating medium is filled in a space 24 between the outer shell 20a of the roll and the inner tube 20b, and the bearing 22 is protected from leakage of the silicon oil 23. Is equipped with an oil seal 25. A heater 26 is provided on the outer peripheral surface of the inner tube 20b, and thermocouples 27 for detecting the temperature of the silicon oil 23 are attached to the center and both ends of the heater 26, respectively.

The transport roll 20 has a strip S on it.
Is wound around, and the transport roll 2 for the strip S
A thermometer 28 as a plate temperature recognizing means for detecting the temperature of the strip S is arranged at the entry side of 0.

Reference numeral 29 denotes an ECU as roll temperature control means.
The ECU 29 is configured so that the detected temperatures from the thermocouples 27 and the thermometer 28 are input to the ECU 29, and the heater 26 is heated and controlled according to the detected values.
That is, if the surface temperature of the roll outer shell 20a is the strip S
Control so that the temperature does not drop below 50 ° C.

[0032]

[Table 1]

Table 1 shows the results of experiments conducted to confirm the effects of this embodiment. In this experiment, the crown amount is 1m
m of the carrier roll 20 and a strip S of ultra-low carbon steel having a thickness of 0.3 mm and a plate width of 910 mm are wound around the roll, and the surface temperature of the roll outer shell 20a is 150 to 450 ° C.
The limit tension at which squeeze occurs when the range was changed was examined.

The roll temperature was set as follows. 1. Prior to the strip S, a roll temperature adjusting material having a thickness substantially equal to the roll width is passed at a low speed to intentionally raise the roll temperature.

2. The thermocouple 27 built into the roll is used to monitor the roll temperature, and the plate passing speed, cooling device, and furnace temperature are adjusted so that the desired roll temperature can be maintained.

3. When the roll temperature stabilizes at a desired temperature, the strip S is connected, and the strip S is wound around the transport roll 20 while adjusting the threading speed so that the strip temperature becomes equal to the roll temperature adjusting material.

4. The tension is changed variously within the time when the roll temperature does not change, and the limit tension at which the squeeze occurs is obtained.

The furnace temperature was set to 150 ° C. and the strip temperature was set to 350 ° C. The strip temperature was measured using both a radiation thermometer and a contact thermometer.

As is clear from Table 1, when the roll temperature is 150 ° C. and 200 ° C. (refer to the conventional method 1.2 in the table), the limit tension for drawing is 2.0, 2.5 Kg / mm ² It is low and it is easy for ring buckles to occur. On the other hand, when the roll temperature is 300 to 450 ° C. (in the table,
Inventive methods 1 to 3), and the limit tension for drawing is 3.5 to
It is as high as 5.0 kg / mm ² , and it can be seen that the occurrence of cooling buckles can be suppressed.

Here, when the roll temperature is controlled between 200 ° C. and 300 ° C., it is clear from the above description that the smaller the temperature difference between the two is, the higher the drawing tension limit tension becomes. However, it is difficult at present to limit the numerical values according to the material, size, or temperature condition of the strip. Therefore, in order to obtain a reliable effect, it is desirable that the roll temperature does not fall below 50 ° C. above the strip temperature.

FIG. 9 shows the results of an experiment in which the limit tension at which the squeeze occurs was examined when the strip temperature was 200 ° C. and the roll temperature was 400 ° C. in the final cooling zone. As can be seen from the figure, the limit tension for drawing is 6 kg / m compared to the conventional method.
It can be seen that it is almost doubled to m ² .

As described above, according to the present embodiment, by making the temperature of the transport roll 20 equal to or higher than the roll-entry temperature of the strip S, the strip S is given a tensile stress in the direction opposite to the conventional compression direction. Will work,
Therefore, the generation of vertical wrinkles can be suppressed and the generation of cooling buckles can be prevented. As a result, it becomes possible to continuously pass ultra-low carbon steel and wide and thin strips, thus improving yield and productivity.

FIGS. 7 and 8 are views for explaining a cooling buckle prevention device according to an embodiment of the present invention.

In the transport roll 30 of this embodiment, an air supply pipe 32 and an exhaust pipe 33 are connected to both ends of a hollow roll main body 30a via rotary joints 31, and steam as a fluid heat medium is connected to the air supply pipe 32. A passage 34 is connected, and a heating device 35a and a supply amount adjusting device 35b are provided in the middle of the steam passage 34. As the fluid heat medium, in-furnace atmosphere gas, air, non-combustible oil, etc. can be adopted in addition to factory steam.

Further, thermocouples 37 are provided on the inner surface of the roll body 30a via slip rings 36, respectively, and a thermometer 38 is provided at the entrance side of the strip S carrying roll 30. There is.

The ECU 39 reads the detected temperature from each of the thermocouples 37 and the thermometer 38 and supplies the heating device 35a and the supply device so that the surface temperature of the roll body 30a does not fall below 50 ° C. more than the detected temperature. Quantity adjustment device 35
It is configured to control b.

FIG. 10 shows the experimental results for confirming the effect of this embodiment. For this, the limit tension for drawing was examined when the strip temperature was 350 ° C. and the roll temperature was 450 ° C. in the gas jet cooling zone at the exit of the overaging zone. As can be seen from the figure, the limit tension for drawing generated is 5 Kg / mm ² , which is more than double that of the conventional method, and it can be seen that substantially the same effect as the above is obtained.

11 and 12 are views for explaining a cooling buckle prevention device according to an embodiment of the invention of claim 5, respectively.

11 (a) and 11 (b) show a transport roll 40.
This is an example in which an electromagnetic induction heater 41 is disposed in a portion of the outer surface of the sheet which is not touched by the strip S, and heating of the roll is controlled by the heater 41.

Since the induction heater 41 heats the shell itself of the transport roll 40, it can be efficiently heated. As a result, the roll surface temperature is reduced to strip S
5 to 20 ° C. lower than the strip temperature and, if necessary, the roll surface temperature is 0 to below the strip temperature.
It can also be maintained at a high temperature of 15 ° C.

12 (a) and 12 (b) show the transport roll 45.
In this example, the resistance electric heating heater 46 is arranged so as to cover the exposed portion of the. Thereby, heat transfer between the atmospheric gas and the transfer roll 45 can be suppressed, and the surface of the transfer roll 45 can be efficiently heated.
C can be lowered.

FIG. 13 is a diagram showing the relationship between the temperature difference between the roll and the strip and the iris generation limit tension ratio in this embodiment. In this figure, the temperature difference is shown in the form of strip temperature TS-roll temperature TR. FIG. 13 above
Also, by keeping the temperature difference between the two at -30 to 50 ° C, that is, the roll temperature is 50 ° C higher than the strip temperature.
It can be seen that the diaphragm tension limit tension ratio can be improved by not lowering the above.

FIG. 14 is a diagram showing the effect of this embodiment, and as is clear from the figure, it can be seen that the thin-walled and wide-sized sheet passing limit, which was difficult in the prior art, can be greatly expanded.

[0054]

As described above, according to the cooling buckle prevention method and apparatus in the continuous heat treatment furnace according to the inventions of claims 1 and 2, the temperature of the roll is prevented from falling below the strip plate temperature by 50 ° C. or more. There is an effect that the generation of vertical wrinkles can be suppressed by suppressing the compressive stress generated in the strip and that the occurrence of cooling buckles can be avoided, and as a result, the yield and the productivity can be improved.

According to the third to fifth aspects of the invention, as the roll temperature control means, a fluid heat medium, a heater, a fluid supply device,
Further, since the electromagnetic induction heater, the resistance electric heater, and the infrared heater are provided, there is an effect that the roll temperature can be controlled at low cost.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a temperature difference and a diaphragm generation limit tension ratio for explaining a formation process of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a crown amount and a diaphragm generation limit tension for explaining a formation process of the present invention.

FIG. 3 is a diagram showing a contact portion between a strip and a roll for explaining a formation process of the present invention.

FIG. 4 is a diagram for explaining a formation process of the present invention.

FIG. 5 is a cross-sectional view of a conveyance roll for explaining a cooling buckle prevention device according to an embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of the apparatus of the above embodiment.

FIG. 7 is a sectional view of a transport roll for explaining a cooling buckle prevention device according to an embodiment of the invention of claim 4;

FIG. 8 is a schematic configuration diagram of the apparatus of the above embodiment.

FIG. 9 is a diagram showing an effect of the above embodiment.

FIG. 10 is a diagram showing an effect of the above embodiment.

FIG. 11 is a view for explaining a cooling buckle prevention device according to an embodiment of the invention of claim 5;

FIG. 12 is a view showing a prevention device according to another example of the above embodiment.

FIG. 13 is a diagram for explaining the effect of the above embodiment.

FIG. 14 is a diagram for explaining the effect of the above embodiment.

FIG. 15 is a diagram for explaining the cause of occurrence of aperture flaws.

FIG. 16 is a schematic configuration diagram showing a general continuous annealing furnace.

FIG. 17 is a diagram for explaining a conventional problem.

FIG. 18 is a diagram for explaining a conventional problem.

[Explanation of symbols]

20, 30, 40, 45 Transport roll 23 Silicon oil (fluid heat medium) 26 Heater 28, 38 Thermometer (plate temperature recognition means) 29, 39 ECU (roll temperature control means) 34 Steam passage (heat medium supply device) 41 Electromagnetic Induction Heater 46 Resistance Electric Heater S Strip (Bandboard)

Claims (5)

[Claims] 1. A cooling back prevention method in a continuous heat treatment furnace, wherein a predetermined heat treatment is carried out while a strip plate is conveyed by a number of rolls arranged in the furnace, and a zone having a function of cooling the strip plate. It is characterized in that the temperature of the strip plate on the entrance side of the roll disposed in the above is obtained by actual measurement or calculation, and the roll temperature of the zone is controlled so as not to fall below the obtained strip plate temperature by 50 ° C. or more. Cooling buckle prevention method in continuous heat treatment furnace. 2. A cooling back prevention device in a continuous heat treatment furnace, wherein a predetermined heat treatment is carried out while transporting the strip plate by a large number of rolls arranged in the furnace, a zone having a function of cooling the strip plate. And a plate temperature recognition means for obtaining the temperature of the strip on the entrance side of the roll by actual measurement or calculation, and controlling the roll temperature of the zone not to fall below the obtained strip temperature by 50 ° C. or more. A cooling buckle prevention device in a continuous heat treatment furnace, comprising: a roll temperature control means. 3. The roll temperature control means according to claim 2, wherein the roll temperature control means includes a fluid heat medium and a heater in the roll, and the roll surface is heated and controlled by the heater via the fluid heat medium. Cooling buckle prevention device for continuous heat treatment furnace. 4. The roll temperature control means according to claim 2, further comprising a heat medium supply device for forcibly circulating a fluid heat medium in the transport roll, and the heating device controls heating of the roll surface. Cooling buckle prevention device for continuous heat treatment furnace. 5. The roll temperature control means according to claim 2, wherein the roll temperature control means comprises an electromagnetic induction heater, a resistance electric heater, or an infrared heater, and the roll surface is heated and controlled by the heater. Cooling buckle prevention device for continuous heat treatment furnace.