JP2006307296A - Method for continuously heat-treating metallic strip and horizontal continuous heat treating furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the winding of scale around a hearth roll of a horizontal continuous heat treating furnace. <P>SOLUTION: This furnace is the horizontal continuous heat treating furnace provided with the hearth rolls 5a, 5b and an indirect heating zone 2 having radiant tubes 3 which are arranged above and below the hearth rolls 5a, 5b. Heat insulating walls 11 for intercepting radiant heat from these radiant tubes 3 in the lower part between non-water-cooling hearth rolls 5b of the hearth rolls and radiant tubes 3 in the lower part. Gas nozzles 12 for blowing reducing gas for cooling onto the surface of the hearth rolls are provided below the non-water-cooling hearth rolls 5b. During the metallic strip is conveyed through the indirect heating zone 2, indirect heating is performed while blowing the reducing gas for cooling onto the surface of the non-water-cooling hearth rolls 5b as intercepting the radiant heat to the non-water-cooling heart rolls 5b. By this invention, the winding around the hearth rolls of the scale in the indirect heating zone is prevented without inflicting large heat loss on the inside of the furnace and the metallic strip. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for heat treatment while preventing winding of a scale around a hearth roll installed in a horizontal continuous heat treatment furnace used in continuous hot dipping plating equipment, etc., and a horizontal continuous heat treatment furnace for performing this method. .

  For example, a continuous annealing furnace used for continuous hot dipping equipment is a facility that heats and cools a steel sheet in a reducing atmosphere in order to give a predetermined mechanical property value to the steel sheet, and generally passes in a vertical direction. There are two types: vertical furnaces and horizontal furnaces that pass horizontally.

  Of these, the vertical furnace is heated and cooled while vertically passing between the hearth rolls installed on the top and bottom, and has a high productivity because a long annealing time is obtained with a short equipment length. For this reason, it is also possible to employ a fully indirect heating type reduction furnace (all radiant tube type heating furnace) with less steel plate oxidation in the furnace. Furthermore, since there are few hearth rolls which a steel plate contacts, the surface quality of a steel plate is also good, and it is mainly used for manufacture of high surface quality steel plates such as automobile outer plates and home appliances. On the other hand, since the height of the equipment is increased, the equipment cost and the construction cost of the building are increased.

  On the other hand, in a horizontal furnace, the furnace body is installed horizontally, and is heated and cooled while passing through a large number of small-diameter hearth rolls arranged. Become long. Therefore, in order to obtain a predetermined heating capacity while shortening the equipment length, there are many cases where a non-oxidizing furnace having a high heating capacity is arranged in the previous stage. Moreover, since the number of times the steel sheet contacts the hearth roll increases due to the horizontal passage, the surface quality of the steel sheet tends to be lower than that of the vertical furnace. However, since there is no bending or unbending of the steel plate by the hearth roll, it is possible to anneal the steel plate having a large thickness, and thus products such as building materials are often manufactured. In addition, since the equipment is simple and the height of the building can be lowered, the equipment cost is greatly reduced compared to the vertical furnace.

  By the way, in the non-oxidation furnace installed in the front stage of a horizontal furnace, the gas which mixed the fuel and the air required for combustion is burned with a burner, and a steel plate is rapidly heated to about 500-700 degreeC. At that time, generally, an operation method is adopted in which the ratio of fuel to air (air-fuel ratio) is set to 1.0 or less and incomplete combustion is performed so that oxygen is not left and the steel sheet is not oxidized as much as possible. It is done.

  In practice, however, the surface of the steel sheet is slightly oxidized, and a thin scale layer is formed. Since such a scale layer is reduced in a nitrogen-hydrogen atmosphere after the subsequent indirect heating zone, there is no influence of the product itself, but in a continuous hot dip galvanizing line, a hot dipping bath is provided at the rear end of the continuous annealing furnace. Since it is arranged and hot-dip plated, if the remaining amount of oxide scale increases, the plating does not adhere to cause a problem.

  In addition, the scale is generated thicker as the temperature of the steel plate in the non-oxidizing furnace becomes higher, but the generated scale is wound around the hearth roll before the reduction and the steel plate is pressed, or the wound scale is peeled off. Re-adhered to the surface, and the surface quality is significantly degraded.

  Since it is impossible to continue operation in this state, the hearth roll must be maintained or replaced. In order to do so, it is necessary to stop the line and cool the furnace before starting work, which significantly impedes productivity.

  Therefore, for such a problem, a technology is used in which the inside of the hearth roll is water-cooled so that the scale does not wrap around using heat shrinkage, or peels off immediately even when wound. Yes.

For example, Patent Document 1 discloses a method of controlling the roll surface temperature to a predetermined temperature mainly by water cooling. In this patent document 1, by adjusting the amount of water passing through the inside of the roll so that the surface temperature of the roll becomes 750 to 800 ° C. in the heating zone where the furnace atmosphere temperature, which is the build-up formation region, is 800 ° C. or higher. It is stated that the objective is achieved. In addition, when two hearth rolls are installed side by side and one of them is in use, the other is in a standby state. If a problem such as the scale winding around the hearth roll in use occurs, The technique used is disclosed.
JP-A-9-241762

Patent Documents 2 and 3 disclose a hearth roll surface treatment technique for coating a material that does not wind the scale.
Japanese Patent Publication No.8-19535 Japanese Patent Publication No. 8-966

  The water-cooled roll as disclosed in Patent Document 1 is very effective, and the scale does not wind around the hearth roll. However, in order to reduce the surface temperature of the hearth roll, it is necessary to cool the inside with a large amount of cooling water, so that the cooling loss of the furnace becomes enormous, which is not economical. Even if the surface temperature of the hearth roll is controlled, a device such as a water amount adjusting valve or piping is required for that purpose. Also, the method of waiting one of the hearth rolls requires twice the number of hearth rolls and motors, so that the equipment cost increases and the waiting hearth roll is not bent or damaged by heat. It is necessary to keep rotating or cooling at all times, which is not economical.

  Further, according to the inventors' test, there is a surface treatment that has an effect in a state where the furnace temperature is low, but the surface treatment of the hearth roll as disclosed in Patent Document 2 and Patent Document 3 is not enough. When the furnace temperature becomes high, it is impossible to completely prevent the winding of the scale.

  The problem to be solved by the present invention is that, in the past, there was nothing that could prevent the scale from being wound around the hearth roll in the horizontal continuous heat treatment furnace with simple equipment while preventing energy loss. is there.

The continuous heat treatment method of the metal strip of the present invention is as follows:
To prevent the scale from being wound around the hearth roll in the horizontal continuous heat treatment furnace while preventing energy loss,
In a continuous heat treatment method for a metal strip, in which heat treatment is continuously performed in the process of conveying on a number of horizontally arranged hearth rolls,
While transporting the indirect heating zone where the radiant tube is placed above and below the hearth roll,
1) Indirect heating while blocking radiant heat from the radiant tube disposed below to the non-water cooled hearth roll,
2) Indirect heating while blowing a non-oxidizing or reducing gas for cooling on the surface of the non-water cooled hearth roll,
3) Implementing both 1 and 2 above,
One of the main features is to implement one of the following.

And the continuous heat treatment method of the metal strip of the present invention,
In a horizontal continuous heat treatment furnace having an indirect heating zone having a number of horizontally arranged hearth rolls and radiant tubes arranged above and below these hearth rolls,
1 ′) Between the non-water-cooled hearth rolls of the hearth rolls and a radiant tube disposed below, a heat insulating means for blocking radiant heat from the radiant tubes is provided.
2 ′) A gas spraying means for spraying a non-oxidizing or reducing gas for cooling on the surface of the hearth roll below the non-water cooled hearth roll of the hearth roll,
3 ′) including both 1 ′ and 2 ′,
A horizontal continuous heat treatment furnace can be used.

  In the present invention, in the horizontal continuous heat treatment furnace, roll cooling by water cooling that gives large heat loss to the furnace and the metal strip is reduced as much as possible to effectively wind the scale around the hearth roll in the indirect heating zone. Can be prevented, and productivity can be improved and quality deterioration can be suppressed.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings, together with the process up to the establishment of the present invention.
FIG. 1 is a schematic view of a horizontal continuous heat treatment furnace targeted by the present invention. As shown in FIG. 1, a heating device called a radiant tube 3 is provided in an indirect heating zone 2 arranged at the rear stage of a non-oxidizing furnace 1. However, it is installed above and below the conveyance line of the steel plate 4, for example.

  In this radiant tube 3, the burner is burned inside the tube, so that the combustion gas does not flow out into the furnace, and the atmosphere in the furnace can maintain a reducing atmosphere of nitrogen and hydrogen. Then, for example, the steel plate 4 and the inside of the furnace are heated by radiant heat from the tube. Further, the furnace itself and the atmosphere in the furnace are also heated to generate radiant heat to heat the steel plate 4.

  In the non-oxidizing furnace 1 in the preceding stage of the indirect heating zone 2, the surface of the steel plate 4 is weakly oxidized, so that the steel plate 4 is gradually reduced while moving in the indirect heating zone 2. Therefore, since the steel plate 4 in the initial zone 2a of the indirect heating zone 2 has not yet been reduced, the hearth roll 5a installed in the initial zone 2a is installed in the second and third zones 2b and 2c. Compared with the made hearth roll 5b, the winding of the scale is likely to occur.

  Therefore, a water-cooled roll is normally used for the hearth roll 5a in the initial zone 2a of the indirect heating zone 2, and no winding of the scale occurs on the hearth roll 5a without any surface treatment.

  However, in the second zone 2b and the third zone 2c subsequent to the initial zone 2a, from the viewpoint of preventing heat loss, the hearth roll 5b that is non-cooled and ceramics sprayed on the surface is used, so the furnace temperature is high. Indeed, troubles due to winding of the scale occur.

  Therefore, conventionally, as shown in Table 1 below, there is only a method to deal with by reducing the furnace temperature in the second and third zones 2b and 2c. As is clear from Table 1 below, even with the same furnace temperature, the occurrence of troubles due to scale winding was greater in the second zone 2b than in the third zone 2c.

  As can be seen from Table 1, if the furnace temperature is lowered, the frequency of troubles due to scale winding will decrease, but reducing the furnace temperature will reduce the ignition time of the burner in the radiant tube 3. In other words, the time during which the burner is extinguished has become longer, resulting in a decrease in the heating capacity of the furnace and a decrease in productivity.

  In Table 1, when there was no trouble due to scale winding, the effect was confirmed for 3 months or more. In the case of occurrence, trouble occurred within a few days. The same applies to Tables 2 and 4 described later.

  From the results shown in Table 1, it is effective to reduce the surface temperature of the hearth roll because there is no trouble caused by the winding of the scale in the water-cooled roll and the winding of the scale is difficult to occur when the furnace temperature is lowered. It turned out to be.

  Therefore, the inventors estimated that in the second and third zones 2b and 2c, this effect can be obtained by blocking the radiant heat from the radiant tube 3 to the hearth roll 5b. And in the horizontal furnace which this invention makes object, since the radiant heat of the upper radiant tube 3 is interrupted by the steel plate 4 among the radiant tubes 3 installed so that the steel plate 4 may be pinched | interposed from the upper and lower sides, it is not a problem. It was estimated that the radiant heat from the lower radiant tube 3 that would directly irradiate the roll 5b was a problem.

  From the above estimation, the inventors manufactured the heat insulating wall 11 with heat-resistant bricks and installed it at a position where the radiant heat from the lower hearth roll 5b is blocked as shown in FIG. As shown in FIG. 2, the heat insulating wall 11 has a U-shape, as shown in FIG. 2, in order to more effectively block the radiant heat from the radiant tube 3 to the hearth roll 5b.

  The upper end shape of the U-shape is ideally 100% in the radial direction of the hearth roll 5b and the shape covering the hearth roll 5b is ideal. You will be wearing a bag. According to the investigation by the inventors, the effect was exhibited if the shape was made to cover 1/6 or more of the roll diameter.

  In addition, although it is realistic and economical to manufacture the material of the heat insulating wall 11, it goes without saying that the same effect can be obtained even if manufactured using ceramics or heat-resistant cast steel.

  By installing the heat barrier 11, the temperature of the hearth roll 5 b is reduced by about 100 ° C., and the third zone 2 c where the scale winding is small is caused by the winding of the scale even if the furnace temperature is increased as shown in Table 2 below. Trouble occurred. However, the installation of the heat barrier 11 only caused the trouble to occur due to the winding of the scale. In the second zone 2b, as the furnace temperature was raised, the winding became smaller, but there was still nothing.

Therefore, the inventors remove the above-described heat barrier 11 and reduce the surface temperature of the hearth roll 5b, as shown in FIG. 3, the nozzle 12 for injecting nitrogen gas in the width direction of the hearth roll 5b, Two nozzle headers 13 attached in large numbers under the conditions shown in Table 3 below were attached to the lower part on the upstream side of the hearth roll 5, and nitrogen gas at 50 ° C. was blown at a flow rate of 16 Nm ³ / m · hr per unit width.

  The results are shown in the following Table 4. Although the temperature drop of the hearth roll 5b was about 50 ° C. and the effect as that of the heat barrier 11 was not obtained, improvement was recognized in both the second zone 2b and the third zone 2c. It was.

  In the experiments by the inventors, the nitrogen gas sprayed from the nozzle 12 was used at room temperature, but in this case, it is possible to use a branched and distributed one from the amount originally purged as the reducing gas in the furnace body. Like cooling by water cooling, it does not cause a decrease in furnace temperature or heat loss.

  From the above results, the inventors provided a number of nozzles 12 for injecting nitrogen gas in the width direction of the hearth roll 5b in addition to the above-described heat barrier 11 in order to further reduce the surface temperature of the hearth roll 5b. As shown in FIG. 4, two nozzle headers 13 were attached to the inside of the U shape of the heat barrier 11.

  The results are shown in Table 5 below. In this case, the hearth roll 5b has a temperature of about 150 ° C., and even if it operates at 950 ° C. which is the maximum furnace temperature, both the second zone 2b and the third zone 2c Troubles due to winding of scale did not occur.

The present invention has been made based on the above experimental results of the inventors.
That is, the horizontal continuous heat treatment furnace of the present invention is, for example, as shown in FIG. 4, between the hearth rolls 5b of the second and third zones 2b and 2c and the radiant tube 3 disposed below the horizontal continuous heat treatment furnace. And a nozzle header 13 provided with a heat insulating wall 11 for blocking radiant heat from the radiant tube 3 and having a nozzle 12 for blowing a reducing gas for cooling on the surface of the hearth roll 5b below the hearth roll 5b. It is provided.

  The continuous heat treatment method of the present invention uses the horizontal continuous heat treatment furnace of the present invention to block the radiant heat from the lower radiant tube 3 to the hearth roll 5b while conveying the indirect heating zone 2, while Indirect heating is performed while spraying a reducing gas for cooling on the surface of the roll 5b.

  The present invention is not limited to the above example, and it goes without saying that the embodiment may be appropriately changed within the scope of the technical idea described in each claim.

  For example, when injecting the cooling gas to the hearth roll 5b, the gas to be injected may contain not only nitrogen gas but also 5-70% hydrogen gas. Moreover, although it is desirable to install two or more nozzle headers 13, even a single nozzle header 13 can achieve a certain degree of effect. In addition, the cooling gas injection is preferably performed by attaching the nozzle 12 to the nozzle header 13 as in the above example, but the nozzle header may be provided with a slit. Furthermore, the injection position is not limited to the upstream side of the roll with respect to the traveling direction of the steel sheet, and may be the downstream side.

  Further, the shape, the structure, and the installation position of the heat insulating wall 11 are not limited to the above examples as long as they can block the radiant heat from the radiant tube 3 disposed below to the hearth roll 5b. The hearth roll 5b is preferably made of heat-resistant cast steel, and the roll surface is preferably subjected to surface treatment such as ceramic spraying, but a certain degree of effect can be obtained without surface treatment. Further, when the surface treatment is not performed, the roll body may be made of ceramics.

  The present invention can be applied not only to a horizontal continuous heat treatment furnace used in continuous hot dipping equipment, but also to any horizontal continuous heat treatment furnace having a transport roll that generates similar scale winding.

It is the schematic of the horizontal type continuous heat processing furnace which this invention makes object. It is principal part explanatory drawing explaining the 1st example of the horizontal type continuous heat processing furnace of this invention, (a) is the figure seen from the side surface, (b) is BB sectional drawing of (a). It is principal part explanatory drawing explaining the 2nd example of the horizontal type continuous heat treatment furnace of this invention, (a) is the figure seen from the upstream of the advancing direction, (b) is BB sectional drawing of (a). . It is principal part explanatory drawing seen from the side surface explaining the 3rd example of the horizontal type continuous heat treatment furnace of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Non-oxidizing furnace 2 Indirect heating zone 2a Initial zone 2b 2nd zone 2c 3rd zone 3 Radiant tube 4 Steel plate 5a, 5b Hearth roll 11 Thermal barrier 12 Nozzle 13 Nozzle header

Claims (7)

In a continuous heat treatment method for a metal strip, in which heat treatment is continuously performed in the process of conveying on a number of horizontally arranged hearth rolls,
While transporting the indirect heating zone where the radiant tube is located above and below the transport line,
A continuous heat treatment method for a metal strip, characterized in that indirect heating is performed while shielding radiant heat from a radiant tube disposed below to a non-water cooled hearth roll. In a continuous heat treatment method for a metal strip, in which heat treatment is continuously performed in the process of conveying on a number of horizontally arranged hearth rolls,
While transporting the indirect heating zone where the radiant tube is located above and below the transport line,
A continuous heat treatment method for a metal strip, characterized by indirect heating while spraying a non-oxidizing or reducing gas for cooling on the surface of a non-water cooled hearth roll. In a continuous heat treatment method for a metal strip, in which heat treatment is continuously performed in the process of conveying on a number of horizontally arranged hearth rolls,
While transporting the indirect heating zone where the radiant tube is located above and below the transport line,
Indirect heating while spraying a non-oxidizing or reducing gas for cooling on the surface of the non-water cooled hearth roll while blocking radiant heat from the radiant tube disposed below to the non-water cooled hearth roll. A continuous heat treatment method for a metal strip.   4. The continuous heat treatment method for a metal strip according to claim 2, wherein the cooling non-oxidizing or reducing gas sprayed on the surface of the non-water-cooled hearth roll is an atmosphere gas in an indirect heating zone. 5. . In a horizontal continuous heat treatment furnace having an indirect heating zone having a number of horizontally arranged hearth rolls and radiant tubes arranged above and below these hearth rolls,
2. The continuous heat treatment method according to claim 1, further comprising a heat-proof means for blocking radiant heat from the radiant tube between the non-water-cooled hearth roll of the hearth roll and the radiant tube disposed below. Horizontal continuous heat treatment furnace to be implemented. In a horizontal continuous heat treatment furnace having an indirect heating zone having a number of horizontally arranged hearth rolls and radiant tubes arranged above and below these hearth rolls,
The gas blowing means for blowing a non-oxidizing or reducing gas for cooling on the surface of the hearth roll is provided below the non-water-cooled hearth roll of the hearth roll. Horizontal continuous heat treatment furnace for performing the continuous heat treatment method. In a horizontal continuous heat treatment furnace having an indirect heating zone having a number of horizontally arranged hearth rolls and radiant tubes arranged above and below these hearth rolls,
Between the non-water-cooled hearth roll of the hearth roll and the radiant tube disposed below, a heat insulating means for blocking radiant heat from the radiant tube,
4. The continuous gas generator according to claim 3, further comprising a gas spraying unit that sprays a non-oxidizing or reducing gas for cooling on a surface of the hearth roll below the non-water cooled hearth roll. A horizontal continuous heat treatment furnace for carrying out heat treatment methods.

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