JPH10121152A - Method for restraining contamination in continuous heat treatment furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the flowing of atmospheric gas containing CO into a cooling furnace and to prevent the contamination caused by sticking of soot on an inner wall by blowing inert gas faced to the front and the back surfaces of the steel strip in the strip passing direction in a throat part between a heating furnace and a soaking furnace. SOLUTION: In the throat part 7 between the heating furnace 1 and the soaking furnace 2 in a continuous heat treatment furnace 6, the inert gas of nitrogen, etc., is blown so as to face to the front and the back surfaces of the steel strip 10 during passing in the steel strip passing direction. This inert gas blowing is desirable to execute by arranging the introduction pipe 8 provided with gas nozzles 9, 9a in the heating furnace 1 to heat the inert gas to >=200 deg.C with the heat exchange. Further, this blowing angle at about 30-60 deg., the flowing rate at about 10-300Nm<3> /h, the distance between the nozzle and the steel strip at about 70-120mm and the blowing pressure at about 0.1-0.5MPa, are desirable to apply. By this method, CO concn. in the atmospheric gas in the cooling furnace 5 is made to be <=300ppm and the deposition of the developed carbides (soots) is restrained to prevent the lowering of the productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for suppressing contamination in a continuous heat treatment furnace.

[0002]

2. Description of the Related Art As is well known, a steel strip after cold rolling is led to a continuous heat treatment furnace comprising a heating furnace, a soaking furnace and a cooling furnace, where the steel strip is heat-treated (annealed) to be softened. It imparts processability.

[0003]

As described above, in the continuous heat treatment of the steel strip, the rolling oil during cold rolling adheres to the surface of the steel strip, and the adhered rolling oil is almost completely removed under the high temperature of the heating furnace. The decomposed CO gas is contained in the atmosphere gas of the heating furnace, and flows into the soaking furnace accompanying the steel strip passing through the strip, and further, some rolling oil remaining in the steel strip in the soaking furnace becomes CO
It is gasified to become a CO gas-containing atmosphere gas. In particular, when high-speed sheet passing is performed to improve the productivity of steel strip heat treatment, the amount of rolling oil brought into the furnace increases, and the CO gas concentration in the atmosphere gas in the heating furnace or the like becomes higher. Such a C
The atmosphere gas containing O gas flows into the soaking furnace along with the strip steel strip, and further flows into the cooling furnace. The CO gas in the atmosphere gas cooled by the cooling furnace becomes carbide, and the inner wall of the cooling furnace is cooled. The soot adheres to the steel strip and forms dirt, which gradually accumulates, peels off and falls off, and adheres to the steel strip in the passing of the sheet (during heat treatment) to deteriorate the quality. In order to avoid such difficulties, the operation is periodically stopped to remove soot that has adhered and accumulated in the cooling furnace, and the operation rate due to the operation stop is reduced (productivity is reduced). There is. The method of the present invention has been made to solve such a problem advantageously, and an inert gas is sprayed on the front and back surfaces of a steel strip during sheet passing in a throat portion between a heating furnace and a soaking furnace of a continuous heat treatment furnace. Accordingly, it is an object of the present invention to provide a method of suppressing the flow of the CO gas-containing atmosphere gas into the cooling furnace and suppressing the contamination due to the adhesion of soot (carbide) to the inner wall of the cooling furnace.

[0004]

A feature of the method of the present invention is that a throat portion between a heating furnace and a soaking furnace of a continuous heat treatment furnace is applied to a front and a back surface of a steel strip in the passing in the direction of the passing of the steel strip. A method for suppressing in-furnace contamination in a continuous heat treatment furnace, characterized by suppressing an inflow of an atmosphere gas in a heating furnace into a cooling furnace by spraying an inert gas in opposition. And a pair of partition walls are provided at the throat portion between the heating furnace and the soaking furnace of the continuous heat treatment furnace, and an inert gas is blown between the partition walls on the front and back surfaces of the steel strip during the passing in the steel strip passing direction, A method for suppressing in-furnace contamination of a continuous heat treatment furnace, characterized by suppressing inflow of atmospheric gas in a heating furnace into a cooling furnace. A pair of partition walls is provided at the throat between the heating furnace and the soaking furnace of the continuous heat treatment furnace, and from the vicinity of the front partition steel strip exit side between the partition walls to the steel strip passage gap of the partition wall, the steel strip table in the passing plate. This is a method for suppressing in-furnace contamination of a continuous heat treatment furnace, which comprises blowing an inert gas to a back surface of the continuous heat treatment furnace in such a manner as to oppose the steel strip in a sheet passing direction, thereby suppressing an atmospheric gas in the heating furnace from flowing into a cooling furnace.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, in the throat section between the heating furnace and the soaking furnace of the continuous heat treatment furnace, the atmosphere gas in the furnace is generally H
About ₂ % of the _two gases are composed of the remaining N ₂ gas. Therefore, it is preferable to use the N ₂ gas. The inert gas is blown at the height of the throat part generally provided (800 to 9).
00 mm), a spray angle of 30 to 60 ° and a flow rate of 10 to 300 N with respect to the traveling direction (passing direction) of the steel strip.
m ³ / h, distance between gas spray nozzle and steel strip 70-120
mm, with a spray pressure of 0.1 to 0.5 MPa, the CO gas-containing atmosphere gas in the heating furnace accompanied by the steel strip is reliably prevented from flowing into the soaking furnace, and the cooling provided in the soaking furnace is connected. It suppresses the inflow into the furnace, suppresses the generation of carbides due to cooling of the CO gas in the atmosphere gas in the cooling furnace, and suppresses the deposition on the inner wall of the cooling furnace.

Further, by blowing a high-temperature inert gas,
Prevents deterioration of the shape (heat buckle) due to rapid cooling of the steel strip and prevents meandering at the position of the transfer rolls in the furnace after that,
In order to prevent the occurrence of scratches at both ends in the width direction of the steel strip and to quickly perform soaking in the soaking furnace, the temperature of the spraying inert gas is 200 ° C. or more and the inlet temperature of the soaking furnace (about 6 ° C.).
(50 ° C.) or lower is preferred. As a method of adjusting to such an inert gas temperature, for example, a gas conduit is arranged in a heating furnace, an inert gas is supplied to a throat gas nozzle through the heating furnace, and heat exchange is performed with heat in the heating furnace. By adjusting the temperature to a high temperature, the temperature can be advantageously adjusted in terms of cost.

[0007] As described above, the inert gas is blown onto the steel strip being passed through the throat portion of the heating furnace and the soaking furnace, and the CO in the heating furnace is blown.
In addition to suppressing the flow of the gas-containing atmosphere gas into the heating furnace and suppressing the flow from the soaking furnace to the cooling furnace, for example, a pair of partition walls are provided in the throat portion, and an inert gas is provided between the partition walls as described above. To increase the gas pressure between the former partition (partition wall on the entrance side in the steel strip traveling direction) and the gas nozzle, to suppress the inflow of atmospheric gas in the furnace into the soaking furnace, and to flow into the cooling furnace installed continuously. Suppress.

In addition, as described above, the front partition wall between the pair of partition walls (from the vicinity of the steel strip exit side (inside of the partition wall) of the partition wall on the entrance side in the traveling direction of the steel strip) is directed toward the front and back surfaces of the steel strip in the steel strip passage gap of the partition wall. By blowing the active gas, the steel strip accompanies the heating furnace from the heating furnace to the throat part (especially accompanying the vicinity of the steel strip surface), that is, the atmosphere gas containing the CO gas, that is, the boundary layer flow flows from the steel strip passage gap of the partition wall to the heating furnace. It is possible to peel and diffuse and push back, thereby more surely suppressing the flow of the CO gas-containing atmosphere gas into the soaking furnace.

In this manner, the CO gas-containing atmosphere gas in the heating furnace is prevented from flowing into the soaking furnace, and the CO gas-containing atmosphere gas is prevented from flowing into the cooling furnace connected to the soaking furnace. By this, it is possible to suppress the rise of the CO gas concentration in the atmosphere gas in the cooling furnace, and to suppress the contamination due to the adhesion of the carbide to the inner wall of the cooling furnace. However, as the CO gas concentration in the atmosphere gas in the cooling furnace, Although it varies slightly depending on the cooling furnace temperature, etc., when the cooling furnace temperature of a generally used continuous heat treatment furnace is 600 to 150 ° C., by setting the CO gas concentration in the atmosphere gas in the cooling furnace to 300 PPm or less, Contamination due to the adhesion and deposition of carbides on the inner wall of the cooling furnace can be remarkably suppressed, and the method of the present invention as described above reliably reduces the CO gas concentration in the atmosphere gas in the cooling furnace to 3%.
It can be less than 00 PPm.

Next, an example of the method of the present invention will be described with reference to the drawings. In FIG. 1, an inert gas is supplied to a throat portion 7 between a heating furnace 1 and a soaking furnace 2 of a continuous heat treatment furnace 6 in which a cooling furnace 5 comprising a heating furnace 1, a soaking furnace 2 and an annealing furnace 3 and a quenching furnace 4 are connected. A conduit 8 is disposed inside the heating furnace 1, and gas nozzles 9 and 9 a are provided at the tip of the inert gas conduit 8 so as to be opposed to the traveling direction of the steel strip 10 so as to be directed to the front and back surfaces of the steel strip. An inert gas is blown onto the steel strip 10 to seal the CO-containing atmosphere gas in the heating furnace 1 accompanying the steel strip 10 to suppress the inflow into the soaking furnace 2, and to connect to the soaking furnace 2. This suppresses the inflow into the provided cooling furnace 5 and suppresses the adhesion of the generated carbide (soot) 11 due to the CO gas cooling in the cooling furnace 5 to the inner wall of the cooling furnace 5. When the inert gas sprayed on the steel strip 10 passes through the inert gas conduit 8 of the heating furnace 1, the inert gas is heated by the internal heat of the heating furnace 1 to a high temperature and sprayed from the gas nozzles 9 and 9 a onto the steel strip 10, By preventing the deterioration of the shape due to rapid cooling of the steel strip 10 and the meandering at the position of the transport roll 12 thereafter, it is possible to prevent the generation of flaws at both ends in the width direction of the steel strip 10 and to quickly perform the soaking treatment in the soaking furnace 2. Apply to

As described above, a specific example of suppressing the inflow of the CO gas-containing atmosphere gas from the heating furnace by blowing the inert gas at the throat portion between the heating furnace and the soaking furnace will be described. As shown in FIG. 2 (a), the steel strip 1 is connected to the gas nozzles 9 and 9a.
0 Inert gas is blown against the steel strip 10
Seals the atmosphere gas containing CO gas in the heating furnace 1 accompanied by the gas. Further, as shown in FIG. 2B, a pair of a partition wall 14 composed of the partition walls 13 and 13a and a partition wall 14a composed of the partition walls 13b and 13c are disposed in the throat portion 7, and a subsequent stage between the partition walls 14 and 14a. An inert gas is injected from gas nozzles 9 and 9a from the entrance side of the steel strip 10 from the entrance side of the steel strip 10 of the partition wall 14a (the exit side partition wall 14a in the traveling direction of the steel strip 10). The gas pressure during the heating is increased to seal the CO gas-containing atmosphere gas from the inside of the heating furnace 1 in the throat section 7 to suppress the flow into the soaking furnace 2. Further, as shown in FIG. 2C, the gas nozzles 9 and 9a face the steel strip 10 in the advancing direction in the vicinity of the steel strip 10 exit side of the former partition wall 14 and are not directed toward the steel strip 10 passage gap of the partition wall 14. Activated gas is blown, and steel strip 10 accompanying steel strip 10
The CO gas-containing atmosphere gas from the vicinity of the heating furnace 1, that is, the boundary layer flow is separated and diffused and pushed back, thereby sealing and suppressing the inflow into the soaking furnace 2.

[0012]

Next, examples of the method of the present invention will be described together with comparative examples.

[Table 1]

[0013]

[Table 2] (Continuation of Table 1)

[0014]

[Table 3] (Continuation of Table 2)

Note 1: The continuous heat treatment furnace is composed of generally used heating furnace, soaking furnace and cooling furnace (slow cooling furnace and quenching furnace), and the atmosphere gas in each furnace is 8% H ₂ gas and the remaining N ₂ gas. Using gas, plate width 700 to 1000 mm, plate thickness 0.15
The ultra-low carbon steel strip rolled to a thickness of about 0.4 mm by cold rolling using palm-based rolling oil was heat-treated. Note 2: In-furnace time in each furnace is the time in heat treatment of steel strip. Note 3: throat blowing gas, using N ₂ gas. Note 4: The gas spraying angle is the angle facing the steel strip traveling direction. Note 5: The gas spray distance is the distance between the gas spray nozzle and the steel strip. Note 6: In the gas spraying position A, gas was sprayed on the front and back surfaces of the steel strip at the throat portion between the heating furnace and the soaking furnace as shown in FIG. B denotes a rear partition wall 14 as shown in FIG.
Gas was blown from the inlet side of the steel strip to the front and back of the steel strip. C
As shown in FIG. 2C, gas was blown toward the front and back surfaces of the steel strip toward the gap of the steel strip 10 of the partition wall 14 near the exit side of the steel strip of the former partition wall 14 as shown in FIG. Note 7: The gas spray nozzle has a hole diameter of 3 mm at a pitch of 50 mm in the width direction of the steel strip. Note 8: As shown in FIGS. 2 (b) and (c), the partition wall is 340m high at the throat (height: 820mm).
m, partition walls consisting of a lower partition wall height of 310 mm and an interval of 1
A pair of partition walls was provided at 70 mm. Note 9: The soot removal interval is the interval (period) during which soot adhered and accumulated on the inner wall of the cooling furnace and was removed.

[0016]

According to the method of the present invention, fouling due to the accumulation of carbides (soot) on the inner wall of the cooling furnace of the continuous heat treatment furnace can be remarkably suppressed, and the operation rate of the continuous heat treatment furnace by removing the carbides can be improved to improve the production efficiency. Can be enhanced. In addition, since the intervals of carbide removal are long, excellent effects such as reduction of the cost of removing carbides (manually) can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view showing an example of the method of the present invention.

FIG. 2 is a side view showing an example of a gas seal.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kazuo Manbu 5-3 Tokai-cho, Tokai-shi, Aichi Prefecture Nippon Steel Corporation Nagoya Works

Claims (5)

[Claims] An inert gas is blown at a throat portion between a heating furnace and a soaking furnace of a continuous heat treatment furnace in a direction opposite to a direction in which a steel strip is passed through a steel strip in a sheet passing direction. A method for suppressing in-furnace contamination of a continuous heat treatment furnace, characterized by suppressing inflow of water into a cooling furnace. 2. A pair of partition walls are provided in a throat portion between a heating furnace and a soaking furnace of a continuous heat treatment furnace, and between the partition walls, the front and back surfaces of a steel strip being passed are opposed to each other in a steel strip passing direction and are inactive. A method for suppressing in-furnace contamination in a continuous heat treatment furnace, which comprises blowing gas to suppress inflow of atmospheric gas in the heating furnace into a cooling furnace. 3. A pair of partition walls is provided at a throat portion between a heating furnace and a soaking furnace of a continuous heat treatment furnace, and a portion between the partition walls near the exit side of a steel strip of a former partition wall is directed toward a steel strip passage gap of the partition walls. A method for suppressing in-furnace contamination in a continuous heat treatment furnace, characterized in that an inert gas is blown against the front and back surfaces of the steel strip in the direction of passing the steel strip, thereby suppressing the flow of atmospheric gas in the heating furnace into the cooling furnace. 4. The method according to claim 1, wherein an inert gas having a temperature of 200 ° C. or higher is blown. 5. The furnace of the continuous heat treatment furnace according to claim 1, wherein the CO gas concentration in the atmosphere gas in the cooling furnace is set to 300 PPm or less. Dirt control method.