JP2005171294A - Method for adjusting dew point of atmospheric gas in continuous annealing furnace, and continuous annealing furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain the reducing atmosphere at early time, by adjusting the dew point of the atmospheric gas in a furnace for short period of time at the starting-up time of the continuous annealing furnace. <P>SOLUTION: In a method for adjusting the dew point of the atmospheric gas in the continuous annealing furnace, at the starting-up time of this furnace, the inert gas or the reducing gas is supplied into the furnace and also, a sacrificial oxidizing material is carried into a sacrificial oxidizing material station communicating with the inner part of the furnace, and when oxygen concentration in the furnace atmosphere becomes ≤1%, the sacrificial oxidizing material is brought into contact with the furnace atmosphere and then, the firing operation to the furnace is performed. As the sacrificial oxidizing material, a lathe turning waste of a carbon steel for structural use, a chromium-molybdenum steel containing one or more kinds of the elements having affinity with oxygen at stronger than that of the iron, is used. Then, the continuous annealing furnace is arranged with the sacrificial oxidizing material station communicating with the inner part of the furnace at the lower side wall part in the continuous annealing furnace, and this station is provided with a shut-off plate which can shut off the furnace atmosphere so as to be openable/closable, and a cylinder for performing the opening/closing of the shut-off plate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for adjusting the dew point of atmospheric gas at the time of startup of a continuous annealing furnace and a continuous annealing furnace, and in particular, at the time of startup, atmospheric oxygen and moisture are reacted with a sacrificial oxidant in an early manner to reduce quickly. The present invention relates to a method for adjusting the dew point of atmospheric gas as an atmosphere and a continuous annealing furnace apparatus therefor.

  Continuous annealing is employed to heat treat cold-rolled steel strips for use in automobiles, home appliances, and the like.

  FIG. 1 shows a configuration of a continuous annealing furnace forming the core of this continuous annealing and an outline of an atmospheric gas supply system. As shown in FIG. 1, the continuous annealing furnace is divided into a pre-tropical zone 1, a heating zone 2, a soaking zone 3, a primary cooling zone 4, an overaging zone 5, and a secondary cooling zone 6. Undergoes the desired heating and cooling by sequentially passing through each of these parts.

In such continuous annealing of a steel plate, it is necessary to make the furnace atmosphere during operation a reducing atmosphere in order to prevent oxidation of the surface of the steel plate to be passed. To obtain a reducing atmosphere, typically a gas mixture of H ₂ and N ₂ is used, it is supplied into the furnace through the ambient gas supply system. Gas mixture and the obtained by decomposing ammonia to obtain a mixed gas H ₂ and N _2, or by mixing N ₂ as necessary, or in obtaining of H ₂ alone gas, and N ₂ gas There are methods such as mixing. The gas in the reducing atmosphere is usually set to a dew point of −10 ° C. or lower.

Whether the furnace atmosphere is a reducing atmosphere or an oxidizing atmosphere is determined by the partial pressure of H ₂ : H ₂ O, which constitutes the steel strip to be annealed. The required limit value varies depending on the component elements to be processed. Eventually, an oxide film called a temper color is formed on the steel strip after annealing, and therefore the atmosphere is often determined based on whether the steel strip has an appearance or not based on the degree of coloring of the oxide film. In this case, even if a thin oxide film is present, it may be determined that it is practically harmless. For example, general low carbon Al killed steel and IF steel are operated at a dew point of about + 5 ° C. with respect to H ₂ : 3 to 5%. However, a material containing a large amount of strong oxidizing components such as Cr and Mn is required to be lower than general low carbon steel such as a dew point of −10 ° C. or less from the limit of temper color suppression.

  The furnace atmosphere is reduced and adjusted to a predetermined dew point for continuous annealing, but the furnace is opened to the atmosphere due to cases such as periodic repairs where the furnace is open to the atmosphere, and plate breakage in the furnace. It may be necessary to stop operations such as a case that becomes a state, a case where the radiant tube for combustion is broken, a case of deterioration due to leakage of cooling water for various in-core instruments, and the like.

In such a case, the continuous annealing furnace will be started up after repair, etc., but at the beginning of normal operation startup, an inert gas (inert gas) such as cheap N ₂ is blown into the annealing furnace, Purge O ₂ in the furnace with inert gas. The situation of gas replacement is performed by detecting the O ₂ concentration in the furnace. Thereafter, in order to finally obtain the necessary atmospheric gas conditions, the atmosphere is replaced by introducing H ₂ gas alone or a gas in which H ₂ gas and N ₂ gas are mixed in advance into the furnace.

  It is important in terms of improving the production capacity to shorten the time for replacement and obtain a necessary reducing atmosphere at an early stage, and various proposals have been made so far.

For example, a continuous annealing furnace that introduces a purge gas to each of a heating part, a soaking part, a slow cooling part, a first quenching part, a reheating part, an overaging part, and a second quenching part that constitute a continuous annealing furnace for steel sheets In the atmospheric gas replacement method, there is an atmospheric gas replacement method for a continuous annealing furnace characterized in that H ₂ is mixed into the purge gas in accordance with the O ₂ concentration in each part and introduced into each part to reduce the O ₂ concentration in the furnace. Yes (see, for example, Patent Document 1).

In this method, H ₂ is mixed into the purge gas and introduced into each part, H ₂ O is generated by a chemical reaction between H ₂ and O ₂ , and this is vaporized at the furnace temperature, thereby effectively reducing the O ₂ concentration. However, if the amount of H ₂ O produced is large and the dew point in the furnace is 0 ° C. or higher, scales are likely to be produced on the surface of the steel sheet, which deteriorates the appearance quality.

In addition, there is a technique for removing O ₂ and H ₂ O (moisture) in furnace gas as a preventive measure for temper color in box annealing different from continuous annealing.

  That is, there is a method (for example, Patent Document 2) in which pure copper is placed on a coil to be annealed and box annealing is performed. According to this method, in the initial stage of annealing, copper absorbs oxygen in the furnace gas by an oxidation reaction. However, since the affinity between copper and oxygen is weak, the produced copper oxide is reduced at a high temperature and oxygen is reduced. There is a problem of being discharged into the furnace again. In addition, the gas in the furnace is circulated, and the oxygen in the gas outside the circulation furnace is a strong deoxidized metal (Cr, Ti, V, Al, Si, Mn, Mg, etc.) that has a stronger affinity for oxygen than iron. ) And a catalyst that is a deoxidizer and removed, and moisture in the gas is removed with a desiccant that preferentially adsorbs water molecules (see, for example, Patent Document 3).

  However, since the capacity and structure in the furnace are completely different between continuous annealing and box annealing, the technique of the box annealing is applied to continuous annealing as it is, and the atmosphere gas in the furnace that becomes a problem at the start of continuous annealing It is difficult to adjust the dew point.

JP-A-8-109417 JP 54-102222 A JP 2000-104123 A

  An object of the present invention is to obtain a reducing atmosphere at an early stage by adjusting the dew point of the atmospheric gas in the furnace in a short time when the continuous annealing furnace is started up.

  The present inventor is not required to simply replace the gas in order to obtain the atmospheric condition in the furnace at the time of starting the continuous annealing furnace, but contains a large amount of Mn, Cr, Si, etc., and the temperature rise is also higher than that of the strip material. By using a sacrificial oxide material in a form that is fast and has a large reaction area, and actively reacting oxygen and moisture in the air with this sacrificial oxide material, a reducing atmosphere having a desired dew point can be obtained at an early stage. As a result, the present invention has been completed.

  The gist of the present invention is as follows.

  (1) At the time of startup of the continuous annealing furnace, an inert gas or a reducing gas is supplied into the furnace, and a sacrificial oxide material is carried into a sacrificial oxide material arrangement chamber communicating with the inside of the furnace, and oxygen and moisture in the atmospheric gas in the furnace A method for adjusting the dew point of a continuous annealing furnace atmosphere gas, characterized by reacting a gas with a sacrificial oxidizing material.

  (2) The continuous annealing furnace as described in (1) above, wherein when the oxygen concentration in the furnace atmosphere becomes 1% or less, the sacrificial oxidant is brought into contact with the furnace atmosphere and the furnace is ignited. How to adjust the dew point of atmospheric gas.

  (3) The sacrificial oxide material is lathe grinding scraps of structural carbon steel or chromium molybdenum steel containing one or more elements having an affinity for oxygen stronger than iron (1) ) Or (2), the method for adjusting the dew point of the continuous annealing furnace atmosphere gas.

  (4) A continuous annealing furnace characterized in that a sacrificial oxide material arrangement chamber communicating with the inside of the furnace is provided on the lower side wall of the continuous annealing furnace, and the arrangement chamber is provided with an openable / closable shielding plate capable of shielding the atmosphere in the furnace. .

  (5) The continuous annealing furnace according to (4), further comprising a cylinder for opening and closing the shielding plate.

  (6) The continuous annealing furnace as described in (4) or (5) above, wherein a sacrificial oxidant transfer device for transferring the sacrificial oxidant from the supply side to the discharge side is provided in the sacrificial oxidant arrangement chamber.

  (7) The continuous annealing furnace according to (6), wherein a sacrificial oxide material supply chamber and a discharge port are provided in the sacrificial oxide material arrangement chamber.

  According to the present invention, when the continuous annealing furnace is started up, the atmosphere condition in the furnace can be obtained in a short time by using the sacrificial oxide material as compared with only gas replacement, and the production capacity can be improved. Moreover, lathe grinding scraps of structural carbon steel and chrome molybdenum steel can be used as sacrificial oxidation materials, and because they are grinding scraps, they have a large surface area that reacts with oxygen and moisture in the gas. Reusable as a raw material for steel. And since the collected grinding scraps are temporarily diverted on the way, the cost is only a transportation cost and no special sacrificial oxidizing material cost is required.

  Further, by providing a sacrificial oxide material disposition chamber communicating with the inside of the furnace at the lower portion of the side wall of the continuous annealing furnace, the sacrificial oxide material can be easily supplied and discharged.

  In a continuous annealing furnace, a reducing atmosphere is used to prevent oxidation of the material to be passed, but there are cases where the reducing atmosphere is hindered during operation. For example, the case where the furnace is opened to the atmosphere by periodic repairs, the case where the furnace is opened to the atmosphere by measures such as plate breakage in the furnace, or damage to the radiant tube for combustion, cooling for various in-core instruments It is a case of deterioration due to water leakage.

  In such a case, improvement of production capacity is attempted by starting up a continuous annealing furnace early after repair.

To get from the air release state to the reducing atmosphere, to start purging with N ₂ gas, to obtain the final required furnace atmosphere gas conditions, a mixed gas of H ₂ gas alone or N ₂ gas It is normal to do.

  The present inventor has eagerly studied to obtain the furnace atmosphere gas conditions at an early stage and does not seek to simply replace the gas, but contains one or more elements having an affinity for oxygen stronger than iron. In a furnace that has a desired dew point at an early stage by using lathe grinding scraps of structural carbon steel or chromium molybdenum steel to be used as sacrificial oxidant and reacting oxygen and moisture in the atmosphere with the sacrificial oxidant. It has been found that atmospheric gas conditions can be obtained.

  FIG. 2 is a graph showing the relationship between the metal oxidation-reduction equilibrium, the dew point, and the temperature.

  As shown in FIG. 2, for example, Cr, Mn, Ti, Al, etc. are stronger oxidizing elements than Fe, and if a sacrificial oxidizing material containing these strong oxidizing elements is used, the dew point of the reducing atmosphere gas is adjusted. It becomes possible.

  Although not shown in FIG. 2, Si, V, Mg, and the like are also known to be strong oxidizing elements, and these can also be used as sacrificial oxidizing materials.

  As a sacrificial oxide material, a metal (for example, sponge-like titanium) or an alloy (for example, ferrochrome or ferrosilicon) containing a strong oxidation element or a steel material (for example, for structural use) containing a strong oxidation element. Carbon steel, chrome molybdenum steel) can be used, and the shape of the sacrificial oxidant is effective for increasing the contact area with the atmosphere gas in the furnace, thereby effectively reacting with oxygen and moisture in the atmosphere gas. Therefore, it is preferable to use a granular shape or a sponge shape.

  In particular, it is preferable to use steel lathe grinding scrap as a sacrificial oxide material. That is, the lathe grinding scrap has a large contact area with the atmospheric gas, has a small heat capacity, can be heated quickly, and is temporarily used as a sacrificial oxide during recovery as an iron source for reuse. It can be used, the cost is only a transportation fee, no special cost is required, and the ground scrap after reaction can be reused as an iron source.

  FIG. 3 is a diagram showing a three-dimensional view of a continuous annealing furnace facility and a sacrificial oxidizing material deployment position.

  As shown in FIG. 3, the continuous annealing furnace includes a pre-tropical zone 1, a heating zone 2, a soaking zone 3, a primary cooling zone 4, an overaging zone 5 and a secondary cooling zone 6, and the steel zone is the entry side. 9 is passed through the exit side 10. The furnace gas is discharged from the exhaust chimney 11.

  The sacrificial oxidant is disposed at the sacrificial oxidant placement location 12 provided on the lower side wall 17 of the continuous annealing furnace so as to react with oxygen and moisture in the furnace gas.

  4 is a view showing a state in which a sacrificial oxide material is disposed on the lower side wall portion of the continuous annealing furnace, and FIG. 5 is a cross-sectional view taken along line AA of FIG.

  As shown in FIGS. 4 and 5, a sacrificial oxide material placement chamber 13 is provided in communication with the inside of the lower side wall 17 part furnace of the continuous annealing furnace, and the inside of the sacrificial oxide material placement chamber 13 and the inside of the furnace are provided by a shield plate 15 that can be opened and closed. The atmosphere with 16 can be shut off or opened. The shielding plate 15 moves up and down by operating the shielding plate opening / closing cylinder 14 to shield or open the atmosphere. In order to secure the shielding of the atmosphere, it is preferable to provide a plurality of shielding plates (two plates are shown in the figure). The shielding plate can be opened and closed by an electric motor or a crank mechanism, but is preferably performed by a hydraulic or pneumatic cylinder.

  A belt conveyor 27 as a transfer device for the sacrificial oxide material 29 is installed in the lower part of the sacrificial oxide material arrangement chamber 13, and the support shaft of the belt conveyor is cooled by the bearing cooling pipe 19. The upper surface position of the belt conveyor is substantially the same as the upper surface of the lower lid 18 of the continuous annealing furnace.

  FIG. 6 is a schematic diagram showing supply and discharge of the sacrificial oxide material.

  The sacrificial oxide material placement chamber 13 is provided with a sacrificial oxide material supply port 20 at one upper end and a sacrificial oxide material discharge port 21 at the other lower end. The bucket 22 containing the sacrificial oxidant 29 such as steel grinding scraps is moved to the upper part of the supply port 20 in the sacrificial oxidant arrangement chamber, the supply port hatch opening / closing cylinder 23 is operated, and the supply port 20 is opened. A predetermined amount of the sacrificial oxidant 29 is charged onto the belt conveyor 27 in the sacrificial oxidant placement chamber 13. Since the lower portion of the bucket 22 is openable and closable, the sacrificial oxide material can be easily inserted by opening the lower portion. After charging, close the supply port.

Next, a purge gas such as N _{2 is} supplied from the purge gas supply pipe 28 into the sacrificial oxide material arrangement chamber, and the chamber is made an inert gas atmosphere. The indoor atmosphere is dissipated to the outside through a cooling tube. On the other hand, when the oxidation concentration in the furnace becomes 1% or less by the gas replacement operation in the continuous annealing furnace, the shielding plate opening / closing cylinder 14 is operated to open the shielding plate 15, and the inside of the furnace and the room are shared. The atmosphere is ignited in the furnace. The sacrificial oxidant has a low thermal inertia and thus is heated quickly and contains many components that are more strongly oxidized than Fe. Therefore, the sacrificial oxidant is oxidized and rapidly O ₂ , H ₂ O in the furnace atmosphere gas. Reduce. As a result, the time to reach the predetermined atmospheric gas condition in the furnace is shortened.

  In order to discharge the sacrificial oxidant from the sacrificial oxidant arrangement chamber 13, the shielding plate opening / closing cylinder 14 is operated to operate the shielding plate opening / closing cylinder 14 to close the shielding plate 15, and then the outlet hatch opening / closing cylinder 24 is opened. The discharge port 21 is opened by operating, and the belt conveyor is operated by the motor 25 with speed reduction, and the sacrificial oxidized material placed on the belt conveyor is discharged from the discharge port 21. The discharge port 21 is opened and closed by a discharge port hatch opening / closing cylinder 24. The sacrificial oxidant discharged in the bucket 26 provided at the lower part of the discharge port 21 is stored.

  The charging and discharging of the sacrificial oxidizing material may be performed a plurality of times as necessary until the atmospheric gas in the furnace reaches a predetermined condition. When the oxygen concentration in the furnace atmosphere becomes 1% or less, it is desirable that the sacrificial oxidant and the furnace atmosphere are brought into contact with each other in order to accelerate the start-up of the operation. When ignition and heating are performed in a high state, equipment and facilities in a continuous annealing furnace such as a roll are oxidized and deteriorated. Therefore, it is usually necessary to ignite with an oxygen concentration of 1% or less (several hundred ppm or less).

  Thus, by matching the ignition timing in the state in which the oxidation of the in-furnace equipment is prevented and the contact timing of the sacrificial oxidant and the atmosphere in the furnace, the temperature rise of the sacrificial oxidant with low thermal inertia is accelerated, and the oxidation proceeds effectively. Because it will be.

  In other words, the oxygen concentration is 1% or less in order to match the ignition timing.

  According to the method for adjusting the dew point of the atmospheric gas in the furnace according to the present invention, the dew point of the atmospheric gas in the furnace necessary for annealing the low carbon aluminum killed steel (equivalent to JIS G 3141), which is a general steel, when the continuous annealing furnace is started up. The shortening effect was shortened by about 2 hours to reach + 5 ° C., and the shortening effect by about 6.5 hours was achieved by reducing the dew point to −10 ° C. or less necessary for 5% Cr-added steel.

  Hereinafter, the present invention will be described in detail based on examples.

  The start-up test of the continuous annealing furnace includes a conventional method of replacing the gas in the furnace by supplying a replacement gas, and a method of removing oxygen and moisture in the gas in the furnace using a sacrificial oxidizing material during the gas replacement of the present invention. And went in two ways.

In this test, a relatively small-scale continuous annealing furnace having a furnace volume of 1600 m ³ was used.

Conventional method (gas replacement method)
The dew point (DP) is -40 ℃ below the level of the N ₂ gas and HNX gas _{(5% H 2 -95% N} 2 gas) was supplied at 2400 m ³ / Hr, the O ₂ concentration in the furnace atmosphere gas 1% The dew point corresponding to the elapsed time (minutes) was measured.

Method of the present invention (use of sacrificial oxide material)
As the sacrificial oxide material, chromium molybdenum steel grinding scraps having a bulk specific gravity of 2.5 ton / m ³ were used. As shown in FIGS. 4 to 6, 1.5 ton of grinding waste is carried into the furnace, and gas replacement is performed in the same manner as in the conventional method. After the O ₂ concentration in the furnace atmosphere gas becomes 1% or less, The sacrificial oxidant and the furnace gas were brought into contact with each other, and the dew point was measured according to the elapsed time (minutes).

  The relationship between each elapsed time (minutes) and dew point DP (° C.) is shown in FIG.

As shown in the relationship between the elapsed time (minutes) and the dew point DP (° C) when the O ₂ concentration in the furnace atmosphere gas in Fig. 7 is 1% or less, ordinary steel (equivalent to low carbon aluminum killed steel JIS G3141) is used. The upper limit of dew point required for continuous annealing + 5 ° C. requires about 250 minutes in the conventional method, but is about 100 minutes in the method of the present invention, and the startup time is about 2 hours according to the method of the present invention. Was shortened. In addition, it took about 700 minutes in the conventional method to set the upper limit of the dew point of −10 ° C. necessary for continuous annealing of the specific material (5% Cr-added steel), but it is about 250 minutes in the method of the present invention. The startup time was shortened by about 6.5 hours according to the method of the present invention.

  Therefore, according to the start-up test of this continuous annealing furnace, it was confirmed that the start-up time of the present invention can be greatly reduced as compared with the conventional method.

It is a figure which shows the structure of the continuous annealing furnace which makes the core of continuous annealing, and the outline | summary of an atmospheric gas supply system. It is a figure which shows the relationship between the equilibrium of metal oxidation-reduction, a dew point, and temperature. It is a figure which shows a continuous annealing furnace equipment three-dimensional view and a sacrificial oxidation material deployment position. It is a figure which shows the state which arrange | positions a sacrificial oxide material in the lower side wall part of a continuous annealing furnace. It is sectional drawing in the AA line of FIG. It is a schematic diagram which shows supply and discharge | emission of a sacrificial oxidation material. O ₂ concentration in the furnace atmosphere gas is a graph showing the relationship between the elapsed time from less than 1 percent (min) and the dew point DP (° C.).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pre-tropical zone 2 Heating zone 3 Soaking zone 4 Primary cooling zone 5 Overaging zone 6 Secondary cooling zone 7 Steel zone 8 Atmospheric gas 9 Incoming side 10 Outlet 11 Waste chimney 12 Sacrificial oxidant arrangement place 13 Sacrificial oxidant arrangement room DESCRIPTION OF SYMBOLS 14 Shielding plate opening and closing cylinder 15 Shielding plate 16 Furnace 17 Continuous annealing furnace lower side wall 18 Lower lid 19 Bearing cooling pipe 20 Supply port 21 Discharge port 22 Bucket 23 Supply port hatch opening / closing cylinder 24 Discharge port hatch opening / closing cylinder 25 Motor with speed reduction 26 Bucket 27 Belt Conveyor 28 Purge Gas Supply Pipe 29 Sacrificial Oxidizing Material

Claims (7)

  When the continuous annealing furnace is started up, inert gas or reducing gas is supplied into the furnace, and the sacrificial oxide material is loaded into the sacrificial oxide material placement chamber that communicates with the inside of the furnace, and oxygen and moisture in the atmosphere gas in the furnace are sacrificial oxidized. A method for adjusting a dew point of a continuous annealing furnace atmosphere gas characterized by reacting with a material.   2. The dew point of the continuous annealing furnace atmosphere gas according to claim 1, wherein when the oxygen concentration in the furnace atmosphere becomes 1% or less, the sacrificial oxidant is brought into contact with the furnace atmosphere and the furnace is ignited. Adjustment method.   The sacrificial oxidizing material is lathe grinding scraps of structural carbon steel or chromium molybdenum steel containing one or more elements having an affinity for oxygen stronger than iron. Of adjusting the dew point of the continuous annealing furnace atmosphere gas.   A continuous annealing furnace characterized in that a sacrificial oxidant arrangement chamber communicating with the inside of the furnace is provided on the lower side wall portion of the continuous annealing furnace, and the arrangement chamber includes an openable / closable shielding plate capable of shielding the atmosphere in the furnace.   The continuous annealing furnace according to claim 4, further comprising a cylinder for opening and closing the shielding plate.   6. The continuous annealing furnace according to claim 4, further comprising a sacrificial oxidant transfer device for transferring the sacrificial oxidant from the supply side to the discharge side in the sacrificial oxidant arrangement chamber.   The continuous annealing furnace according to claim 6, wherein a supply port and a discharge port for the sacrificial oxide material are provided in the sacrificial oxide material disposition chamber.

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