JPH0920927A - Method for partioning atmosphere in continuous annealing furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep gas quantity in each zone always to constant and to obtain a product having the stable quality by arranging plural contracted parts without contacting with a steel sheet at a boundary of the zones, forming an atmospheric buffering area having a gas exhaust hole between the contracted parts and specifying the gas exhaust quantity from this gas exhaust hole. SOLUTION: For example, in a continuous annealing furnace 1, a heating zone 2, soaking zone 3 and cooling zone 4 are arranged, and the buffering area 7 formed with the contracted parts 5, 6 is arranged between the soaking zone 3 and the cooling zone 4 and atmospheric gases of 65-70 deg.C and -20--30 deg.C are supplied from supplying devices 8, 9, respectively. The atmospheric gases in the heating zone 2 and the soaking zone 3 are exhausted from the gas exhaust hole 10 and the gas exhaust hole 11 having a flow rate adjusting device 13 to out of the furnace. Since the contracted parts do not develop the deterioration because of non-contact with the steel sheet, the gas flow in the furnace does not vary by keeping the gas flow rate of the gas exhaust hole 11 always to the constant. Further, the atmospheric gas from each zone adjoined to the buffering area 7 is passed through the contracted parts by a prescribed quantity and exhausted from the gas exhaust hole 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for partitioning an atmosphere in a continuous annealing furnace.

[0002]

2. Description of the Related Art For example, continuous strip annealing furnaces include those in which a heating zone, a soaking zone, and a cooling zone are continuously provided, and those in which a heating zone, a decarburizing zone, a reduction zone and a cooling zone are consecutively provided. is there. Continuous annealing or continuous decarburizing annealing is performed with a desired atmosphere gas in each zone.

In the case of continuously annealing strips whose surface properties need to be controlled strictly, those which need to be decarburized, and strips whose oxide layer on the surface of the steel sheet needs to be controlled, for example, a heating zone. , Decarburization zone, reduction zone each atmosphere in a predetermined atmosphere, for example, dew point is maintained in a specific range, and a specific component in the atmosphere gas composition is always kept at a constant concentration. There is a need to.

[0004] Therefore, it has been proposed to provide an atmosphere partition at the boundary of each zone in the continuous annealing furnace to prevent mixing of the atmosphere gas in the furnace. For example, in Japanese Unexamined Patent Application Publication No. 4-304322, a plurality of partitions are provided with a buffer zone sandwiched therebetween, and the gas flowing into each isolation chamber is discharged from the furnace through an exhaust hole provided in the buffer zone to create an atmosphere between the zones. Is disclosed to be completely separable.

As described above, since most of the atmosphere partitions currently used in the continuous annealing furnace are of the type in which they come into contact with the strip plate surface, the partitioning property changes with time due to wear of the contact surface. The reality is that the amount of atmospheric gas flowing into the buffer zone fluctuates. On the other hand, in order to keep the atmosphere in each zone at a desired composition, it is of course necessary to prevent a certain amount or more of gas from invading the adjacent zones, and to prevent the reaction between moisture and strip as in the case of decarburization annealing. When water is generated and consumed, a change in the gas amount in the zone immediately leads to a change in the atmosphere (dew point), which is a major impediment to the stabilization of the reaction in the furnace.

[0006]

DISCLOSURE OF THE INVENTION The present invention stably prevents the gas mixture between the zones below a certain amount, and always keeps the amount of gas withdrawn from each zone in order to secure partitioning at a constant level. And a partitioning method that can suppress the temporal and spatial fluctuations of the gas amount in each zone.

[0007]

The gist of the present invention is to provide a continuous annealing furnace in which a plurality of zones having different atmospheric gas compositions or dew points of the atmospheric gas are provided, and a diaphragm having no contact with the steel sheet at the zone boundary. A plurality of portions are provided at intervals, an atmosphere buffer zone having an exhaust port is formed between the throttle zones, and the atmosphere gas from each zone adjacent to the buffer zone passes through the throttle zone with a gas amount Q satisfying the following equation. A method for partitioning an atmosphere in a continuous annealing furnace, characterized by exhausting from the exhaust port. Gas amount Q ₁ to flow from the steel plate entry side adjacent zone atmosphere buffer zone to the buffer zone _{^{(m 3 / sec) Q 1}} ≧ 150D K (W S H / L) (1) D K: diffusion coefficient of the buffer zone ambient gas ( cm ² / sec),
W _S : Width of throttle portion (m) H: Space height of throttle portion (m), L: Length of throttle portion (m) Amount of gas flowing from the zone adjacent to the steel plate outlet side of the atmosphere buffer zone to the buffer zone Q ₂ (m ³ / _{sec) Q R ≧ C (A} -1) / (A · B-1) (2) A = W / W S · Q 2 / C B = exp [0.17 · W · L {1 / C-1 / (Q ₂ · W
_{/ W S)}] C =} W · V 2 {-V / 6H 2 · D) +1} / (D · H) D = 6Q 2 / (W S · H 3) + 3V / H 2 Q R: Atmosphere buffer Allowable amount of invading gas from the strip to the adjacent zone on the output side (m ³ / sec) W _S : Width of throttle portion (m), H: Height of throttle portion (m), L: Length of throttle portion (m) W: Sheet width (M), V: Line speed (m / sec)

The present invention will be described below in detail based on an embodiment with reference to the drawings. In FIG. 1, reference numeral 1 denotes a continuous annealing furnace, which is provided with a heating zone 2, a soaking zone 3, and a cooling zone 4 in this embodiment. Between the soaking zone 3 and the cooling zone 4, a buffer zone 7 formed by the narrowed portions 5 and 6 is provided.
Reference numeral 8 denotes an atmospheric gas supply device having a high dew point of 65 to 70 ° C., which is divided and supplied into the furnace of the heating zone 2 and the soaking zone 3. Reference numeral 9 denotes an atmospheric gas supply device having a low dew point of −20 to −30 ° C., which is supplied into the furnace in the cooling zone 4. Heating zone 2
The atmospheric gas in the soaking zone 3 is discharged from the exhaust port 10 and the exhaust port 11 to the outside of the furnace, and the atmospheric gas in the cooling zone 4 is discharged from the exhaust ports 11 and 12 to the outside of the furnace. Reference numeral 13 is a flow rate adjusting device for the exhaust port 11.

Since the throttle portion does not come into contact with the steel plate and is not deteriorated, the gas flow in the furnace does not fluctuate by always keeping the flow rate of the exhaust port 11 constant. On the other hand, the atmospheric gas in the buffer zone 7 is a mixture of the atmospheric gas in the heating zone, the soaking zone and the atmospheric gas in the cooling zone, and the mixed gas enters the adjacent zone (the soaking zone, cooling zone) in a certain amount or more. Then, the desired atmospheric gas composition (dew point) of each adjacent zone cannot be obtained, and the reaction of the steel sheet becomes abnormal. Despite the atmospheric gas flowing from each adjacent zone to the buffer zone, the mixed gas passes over the constricted portion and enters the adjacent zone due to the diffusion motion of the molecules of the mixed gas and the accompanying steel sheet. There is something. The present inventor considers the diffusion coefficient of the mixed gas and the passing speed of the steel sheet to determine the amount of gas that enters the adjacent zones of the mixed gas,
It was found that the amount of gas flowing into the buffer zone from each adjacent zone or the shape (length, width, space height) of 6 can be suppressed to a constant amount.

First, in the narrowed portion 5, the invasion of the gas from the buffer zone to the soaking zone is due to the diffusion motion of the gas.
Theoretical diffusion determined by the type of gas, temperature, and throttle shape The amount of gas that is proportional to the amount of invading gas can be prevented from flowing into the buffer zone from the soaking zone. Experiments were conducted by changing the conditions of the amount of gas and the gas temperature that flowed into the. As a result, as shown in FIG. 2, it has been found that it is possible to prevent the infiltration of the soaking zone 3 from the buffer zone by causing a gas quantity of ₅ or more satisfying the following equation (3) to flow from the soaking zone to the buffer zone. It was _{Q 5 ≧ 150D K (W S} H / L) (3) D K: diffusion coefficient of the buffer zone ambient gas (cm ² / sec),
W _S : Width of throttle portion (m) H: Space height of throttle portion (m), L: Length of throttle portion (m)

On the other hand, in the throttle portion 6, the diffusion of the buffer gas into the cooling zone is predominantly accompanied by the steel sheet due to the diffusion motion. Therefore, the shape of the throttle portion 6 and the steel sheet, which are factors that form the associated flow. It has been found that it can be represented by the width of the plate, the strip passing speed, and the amount of gas flowing into the buffer zone from the cooling zone. Hereinafter, a method for formulating the amount of gas invading from the buffer zone 7 to the cooling zone 4 accompanying the accompanying steel sheet as shown in FIG. 3 will be described.

First, the gas flow in the throttle portion 6 can be expressed by the equation of motion (4). -(Dτ / dy) = ΔPg _c / L (4) y: Height from plate, τ: Shearing force in the horizontal plate passing direction ΔP: Differential pressure before and after the throttle, g _c : Gravity conversion coefficient formula (4) Can be expressed as in equation (5). _{τ = -ΔPg c y / L +} C 1 = -μ (du / dy) (5) u: horizontal passage plate direction velocity in y, mu: viscosity coefficient,
C ₁ : constant

Boundary condition y = 0, u = V, y
= H / 2 and u = 0 and the gas flow rate mass balance equation (6) in the throttle portion are taken into consideration, the gas flow rate associated with the steel sheet can be expressed as in equation (7).

[Equation 1] C = W · V ² {−V / (6H ² · D) +1} / (D · H) (7) where D = 6Q ₆ / (W _S · H ³ ) + 3V / H ² Q ₆ : each band Amount of atmospheric gas (m
³ / sec) Q _R: allowable penetration gas amount to the delivery side adjacent bands from atmosphere buffer zone _{^{(m 3 / sec) W S}} : throttle section width (m), H: diaphragm portion space height (m),
L: Drawing length (m) W: Plate width (m), V: Line speed (m / sec)

The gas composition in the accompanying flow is the composition of the buffer zone gas immediately after the buffer zone 7, but is gradually diluted with the gas in the cooling zone 4 while passing through the throttle section 6. Considering the driving force of this dilution phenomenon as the buffer zone gas concentration difference contained in the associated gas and the gas that passes from the cooling zone 4 to the buffer zone, the dilution amount per unit time in the minute section dL of the throttle portion is calculated by the formula ( It can be represented by 8). k · X · WdL = 2 { 1 / C-1 / (Q 6 · W / W S)} dX (8) X: buffer zone gas concentration difference in the minute section dL (accompanying flow -
Cooling zone → Buffer zone flow) k: Coefficient Equation (8) can be expressed as Equation (9) by integrating in the section of the throttle unit 6. X7 / X4 = exp [2k · W · L {1 / C-1 / (Q 6 · W / W S)}] (9) X4: density difference at the boundary of the cooling zone 4 and the throttle portion 6 X7: buffer strips 7 and the density difference at the boundary between the diaphragm 6

Here, the buffer zone gas concentration in the accompanying flow at the boundary between the buffer zone 7 and the throttle section 6 is close to 1, and
Since the buffer zone gas concentration in the accompanying flow at the boundary between the cooling zone 4 and the throttle section 6 is close to X4, considering the mass balance of the buffer zone gas in the throttle section 6, the cooling zone 4 is calculated from the equation (9). Gas concentration R (approximately X4
Equal to) can be represented by equation (10). R = (A-1) / (A · B-1) (10) A = W / W S · Q 6 / C B = exp [2k · W · L {1 / C-1 / (Q · W /
W _S )}] Therefore, from the equations (7) and (10), the buffer zone 7 to the cooling zone 4
The amount Q ₇₄ of gas that enters the space can be expressed by equation (11). Q ₇₄ = R ・ C (11)

The inventor of the present invention used the coefficient k, which is an unknown number in the equation (11), by changing the conditions such as the sheet passing speed, the width, the shape of the narrowed portion, and the amount of gas flowing from the cooling zone to the buffer zone. Asked by doing. The relationship between the calculated value and the actual value by the equation (11) is shown in FIG. Therefore, the amount of gas Q ₆ satisfying the equation (12) by allowed to flow from the cooling zone to the buffer zone can be suppressed from entering the cooling zone below the allowable entry amount Q _R does not affect the quality of the buffer zone. _{Q R ≧ C (A-1} ) / (A · B-1) (12) A = W / W S · Q 6 / C B = exp [0.17 · W · L {1 / C-1 / ( Q ₆ · W
/ W _S )}] C = W · V ² {−V / 6H ² · D) +1} / (D · H) D = 6Q ₆ / (W _S · H ³ ) + 3V / H ² Q ₆ : each band Amount of atmospheric gas (m
³ / sec) Q _R: allowable penetration gas amount to the delivery side adjacent bands from atmosphere buffer zone _{^{(m 3 / sec) W S}} : throttle section width (m), H: diaphragm portion space height (m),
L: Drawing length (m) W: Plate width (m), V: Line speed (m / sec)

[0017]

[Examples] Table 1 shows changes with time in the soaking zone dew point and the reduction zone dew point when decarburization annealing was carried out by the method of the present invention and the conventional method.
From the table, in each of Examples 1 to 3 of the present invention, the dew point in the furnace is stable even after 10 months have passed from the start of the treatment, whereas in the conventional method, the dew point is 5 months or even 10 months later. It can be seen that fluctuates.

[0018]

[Table 1]

[0019]

As described above, according to the present invention, since the atmosphere flow in the furnace in the continuous annealing furnace is constant, the heating zone as a reactor and the dew point in the soaking zone are stable, and the temperature is always constant. It is possible to manufacture steel sheets with the decarburization and oxidation amounts of. This reduced yield loss due to poor quality of the final product.

[Brief description of drawings]

FIG. 1 is a diagram showing a furnace apparatus configuration in an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the speed of invasion from the buffer zone to the soaking zone by diffusion and the amount of inflow gas from the soaking zone to the buffer zone, which is necessary to prevent the intrusion.

FIG. 3 is a schematic diagram showing a gas flow and gas components in the throttle unit 6.

FIG. 4 shows the amount of gas flowing into the buffer zone from the cooling zone with respect to the amount of gas entering the cooling zone from the buffer zone, the strip passing speed, the strip width,
The figure which showed the relationship of a diaphragm part shape.

[Explanation of symbols]

 1 continuous annealing furnace 2 heating zone 3 soaking zone 4 cooling zone 5 inlet side throttle section 6 outlet side throttle section 7 buffer zone 8 atmosphere gas supply device 9 atmosphere gas supply device 10 atmosphere gas exhaust port 11 atmosphere gas exhaust port 12 atmosphere gas exhaust Mouth 13 Flow rate controller 14 Steel plate

Claims (1)

[Claims] 1. A method for partitioning an atmosphere in a continuous annealing furnace in which a plurality of zones having different atmospheric gas compositions or dew points of the atmospheric gas are provided, and a narrowed portion having no contact with a steel sheet is provided at the zone boundary. An atmosphere buffer zone having a plurality of exhaust ports is formed between the narrowed portions, and an atmospheric gas from each zone adjacent to the buffer zone is filled with a gas amount Q ₁ ,
A method for partitioning an atmosphere in a continuous annealing furnace, which comprises passing the throttle portion at Q ₂ and exhausting from the exhaust port. Gas amount Q ₁ to flow from the steel plate entry side adjacent zone atmosphere buffer zone to the buffer zone _{^{(m 3 / sec) Q 1}} ≧ 150D K (W S H / L) (1) D K: diffusion coefficient of the buffer zone ambient gas ( cm ² / sec),
W _S : Width of throttle portion (m) H: Space height of throttle portion (m), L: Length of throttle portion (m) Amount of gas flowing from the zone adjacent to the steel plate outlet side of the atmosphere buffer zone to the buffer zone Q ₂ (m ³ / _{sec) Q R ≧ C (A} -1) / (A · B-1) (2) A = W / W S · Q 2 / C B = exp [0.17 · W · L {1 / C-1 / (Q ₂ · W
_{/ W S)}] C =} W · V 2 {-V / 6H 2 · D) +1} / (D · H) D = 6Q 2 / (W S · H 3) + 3V / H 2 Q R: Atmosphere buffer Allowable amount of invading gas from the strip to the adjacent zone on the output side (m ³ / sec) W _S : Width of throttle portion (m), H: Height of throttle portion (m), L: Length of throttle portion (m) W: Sheet width (M), V: Line speed (m / sec)