JPH1180831A - Method for preventing coloring of sheet material passing through reducing atmospheric furnace and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suitably adjust the coloring of surface of a metallic material passing through a reduction atmospheric furnace and to reduce the running cost for adjusting the atmosphere. SOLUTION: A color difference meter 5 is arranged at the outlet side of a bright annealing furnace 2 passing a stainless steel sheet 1. A control device 6 adjusts the circulating quantity of a refining device 4 and the H2 concn. supplied from a reducing gas supplying device 3 so that a (b) valve showing the difference to a reference value with a Lab color specification system in the outlets detected with the color-difference meter 5 becomes a prescribed control range in the negative range. When the (b) value becomes less than the lower limit value in the control range, the circulating quantity of the refining device 4 rising the H2 concn., is increased. When the (b) value exceeds the upper limit value of the control range, the circulating quantity of the refining device 4 is lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reducing atmosphere furnace for passing a metal material such as stainless steel through a reducing atmosphere furnace for heat treatment or the like to prevent the surface of the metal material from being colored. The present invention relates to a method and an apparatus for preventing coloring of a plate material.

[0002]

2. Description of the Related Art Conventionally, for example, a stainless steel plate
A reducing atmosphere furnace is used for heat treatment such as bright annealing for obtaining material A. In a reducing atmosphere furnace, heating is performed while preventing oxidation of the metal material, heat treatment such as annealing is performed, and the metal material is cooled to around room temperature. In a reducing atmosphere furnace in which a metal material is continuously passed, the inlet and the outlet of the metal material cannot be completely hermetically sealed, and air containing oxygen and moisture enters from the surroundings. Since the oxygen component contained in oxygen or moisture oxidizes the heated metal material surface, a dry hydrogen gas is supplied as a reducing atmosphere, and the once formed reducing atmosphere is circulated to a refining device,
Oxygen and moisture are removed. In the reducing atmosphere, not only hydrogen gas but also nitrogen gas is mixed.

[0003] When an oxidation reaction occurs in a reducing atmosphere furnace, an oxide film is formed on the surface of the metal material, and coloring occurs.
If the reduction reaction proceeds excessively so as not to cause oxidation, the surface of the metal material is nitrided, and the details of the image on the surface become difficult to see, resulting in a reduction in resolution. Even when nitriding occurs to the extent that the resolution does not decrease, if the metal material is subjected to a chemical coloring process or the like later, the dissolution rate of the surface varies, and it is possible to obtain a chemically glossed steel plate with high gloss. become unable.

[0004]

The coloring caused by the oxidation of the surface of a metal material in a reducing atmosphere furnace varies depending on the components of the metal material and the state of the surface. As long as the state of coloring is visually determined, a delicate determination cannot be made, and the circulation amount of the refining device that lowers the moisture concentration that affects coloring always has the maximum capacity Max. It will drive in the state of. In order to remove water with a refining device, it is necessary to periodically supply a desiccant. Also, a power cost for circulating the reducing atmosphere is required. Therefore, the circulation amount of the refining device is always set to Max. If the vehicle is operated in the state described above, the running cost will increase. Moreover, in such a case, the surface condition of the metal material to be passed becomes excessive quality, and the processing cost increases.

In particular, when bright annealing is performed on the premise that the surface of a steel sheet is chemically treated to form a color, the resolution is important, and it is necessary to obtain a surface state with little variation in the color to be developed and high gloss. is there. It is very difficult to obtain such a surface condition only by visual control.

It is an object of the present invention to provide a method and an apparatus for preventing coloring of a passing plate material in a reducing atmosphere furnace, which can reduce the running cost by keeping the coloring state due to oxidation of the surface within a desired range.

[0007]

SUMMARY OF THE INVENTION According to the present invention, heating and cooling are performed while a metal material plate is passed through a reducing atmosphere containing hydrogen gas and nitrogen gas, and the reducing atmosphere is circulated through a refining device to reduce oxygen and oxygen. In a reducing atmosphere furnace for removing moisture, a method of preventing coloring of the passing material is provided, as a dye signal indicating a difference from a reference in the Lab color system on the exit side of the passing material from the reducing atmosphere furnace. Provide a color difference meter that derives an output including the b value, and adjust the refining device circulation amount and the hydrogen gas concentration so that the b value from the color difference meter falls within a predetermined negative value management range. This is a method for preventing coloring of a sheet material passed through a reducing atmosphere furnace.

According to the present invention, a color difference meter is provided on the exit side of the sheet passing material from the reducing atmosphere furnace to quantitatively detect the coloring state of the surface of the metal material. Of the refining device and the hydrogen gas concentration are adjusted so that the b value of the color difference signal indicating the difference between the two falls within a predetermined negative value management range. It is known that the b value becomes smaller, that is, the bluish color becomes stronger as the absolute value becomes larger. The circulation amount of the refining device or the hydrogen gas concentration is adjusted so that the b value is within a predetermined control range, so that the degree of coloring of the surface due to oxidation is prevented from becoming remarkable, and the resolution becomes poor due to nitriding. Can also be prevented.

Further, the present invention is characterized in that when the b value is less than the lower limit of the control range, the circulation amount of the refining device is increased or the hydrogen gas concentration is increased.

According to the present invention, when the value of b is less than the lower limit of the control range and the degree of coloring by oxidation becomes excessive,
Increases the amount of circulation to the refining device to remove oxygen gas and moisture from the reducing atmosphere by increasing the circulation amount of the refining device and reduces the content of oxygen and moisture to oxidize the surface of the metal material and reduces the metal material surface Can be controlled so that the b value falls within the control range.

Further, the present invention is characterized in that when the b value exceeds the upper limit of the management range, the circulation amount of the refining device is reduced.

According to the present invention, when the value of b exceeds the upper limit of the control range, the surface of the metal material is apt to be nitrided, so that the resolution is reduced and the variation in the state of chemical coloring and gloss in the subsequent process is increased. If the amount of circulation in the refining device is reduced, nitriding is suppressed, and the variation in the case where chemical coloring is performed in a subsequent step can be reduced without lowering the resolution of the metal material surface. When the b value exceeds the upper limit of the control range, it is possible to adjust the b value to be within the control range even if the hydrogen gas concentration is reduced. However, when the hydrogen gas concentration decreases, the nitrogen gas concentration increases, and the nitridation increases. Is more likely to occur. The running cost of the refining device can be reduced by reducing the circulation amount of the refining device and adjusting the b value to be within the management range.

Further, the present invention is directed to heating and cooling a metal material plate while passing it through a reducing atmosphere containing hydrogen gas and nitrogen gas, and circulating the reducing atmosphere to a refining device to remove oxygen and moisture. In a reducing atmosphere furnace,
An apparatus for preventing coloring of a sheet passing material, which is provided on the outlet side of the sheet passing material from a reducing atmosphere furnace and derives an output including a b value as a color difference signal indicating a difference from a reference in a Lab color system. A reducing atmosphere furnace, comprising: a control device for controlling a refining device circulation amount and a hydrogen gas concentration so that the b value from the color difference meter falls within a predetermined negative value management range. This is a device for preventing coloring of a passing plate material.

According to the present invention, heating in a reducing atmosphere furnace
A color difference meter is provided on the outlet side of the metal material to be cooled, and an output indicating a difference from a reference in the Lab color system is derived. The control device adjusts the refining device circulation amount or the hydrogen gas concentration so that the b value of the output color difference signal is a negative value and falls within a predetermined management range. B of the output of the color difference meter
By controlling the refining unit circulation amount and hydrogen gas concentration so that the value falls within the predetermined control range with a negative value, the coloring state of the surface is kept in an appropriate range and the running cost increase due to excessive quality is suppressed. can do.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic configuration of an apparatus for preventing coloring of a passing material in a reducing atmosphere furnace as one embodiment of the present invention. The stainless steel strip 1 is passed through a bright annealing furnace 2 as a cold-rolled strip in order to anneal while maintaining the surface gloss. In order to keep the atmosphere in the bright annealing furnace 2 reducible, a reducing gas mixture of hydrogen (H ₂ ) and nitrogen (N ₂ ) is supplied from a reducing gas supply device 3. Oxygen and moisture adsorbed on the surface of the stainless steel strip 1 to be passed are brought into the bright annealing furnace 2, and oxygen and moisture in the air enter from the entrance and exit. The refining device 4 removes oxygen and moisture from the furnace gas in the bright annealing furnace 2 for reuse.

In this embodiment, the stainless steel strip 1 is made of BA
A color difference meter 5 is installed in a portion coming out of the bright annealing furnace 2 as a material, and based on a detection output of the color difference meter 5, the control device 6 controls a circulation amount of the refining device 4 and a hydrogen gas concentration in the reducing gas supply device 3. To adjust. The circulation amount of the in-furnace gas from which oxygen and moisture are removed by the refining device 4 is adjusted by the circulation amount control device 7. The hydrogen and nitrogen gas supplied to the reducing gas supply device 3 are supplied to the H ₂ tank 8
And N ₂ tank 9, respectively, and mixed in buffer tank 10.

The bright annealing furnace 2 has a heating zone 11 and a slow cooling zone 1.
2 and a cooling zone 13. The refining device 4 sucks in-furnace gas at the entrance side of the stainless steel strip 1 to the heating zone 11 via the in-furnace gas suction pipe 14, and sends the gas to the circulating gas supply pipe 15 via the circulating amount control device 7. Then, the furnace gas from which oxygen and moisture have been removed is circulated. The reducing gas supplied from the buffer tank 10 is mixed with the circulating gas circulating in the circulating gas supply pipe 15 and supplied from the reducing gas supply pipe 16 to the slow cooling zone 12 and the cooling zone 13 of the bright annealing furnace 2.

In the bright annealing furnace 2, a plurality of heaters 17 and a heat insulating layer 18 are provided in the heating zone 11 to heat the stainless steel strip 1 to a temperature required for annealing. In the slow cooling zone 12, the surface of the stainless steel strip 1 is gradually cooled by spraying the reducing gas supplied from the reducing gas supply pipe 16. In the cooling zone 13, the reducing gas supply pipe 1 is passed through a plurality of cooling units 19.
The reducing gas supplied from 6 is sprayed on the surface of the stainless steel strip 1 and cooled more rapidly than the slow cooling zone 12. The stainless steel strip 1 is discharged out of the bright annealing furnace 2 through a sealing device 20 provided on the exit side of the furnace. In the cooling zone 13, even if the stainless steel strip 1 is discharged out of the furnace, the stainless steel strip 1 is cooled to a temperature at which the stainless steel strip 1 is not newly oxidized by oxygen in the air.

The color difference meter 5 detects the color difference on the surface of the stainless steel strip 1, and the control device 6 controls the flow rate control valve 21 in the circulation amount control device 7 so that the color difference falls within a predetermined management range.
The circulation amount or the hydrogen gas concentration of the refining device 4 is adjusted by the flow control valves 22, 23, 24 in the reducing gas supply device 3. The amount of circulation of the refining device 4 is detected by the flow meter 25. The hydrogen gas concentration is detected by the H ₂ concentration meter 26. The control device 6 includes the flow meter 2
The circulation amount and the H ₂ concentration are adjusted in accordance with a program set in advance based on the detection output of the H ₂ concentration meter 5 and the H ₂ concentration meter 26. Whether or not the atmosphere in the bright annealing furnace 2 is properly maintained is also confirmed by periodically sampling the atmosphere and measuring the dew point using the Dew cup 27 or the like.

FIG. 2 shows a SUS3 using a spectrophotometer CM-2002 manufactured by Minolta Co., Ltd. as the color difference meter 5.
An example in which the stainless steel strip No. 04 is managed by the b value will be described. As described later, the b value is considered to indicate the degree of “blueness” in a negative value range, and the upper limit of b is set to bmax, the lower limit of b is set to bmin, and the management range from bmax to bmin is set to the control range. And the central value is controlled as the control target. If the b value exceeds the upper limit bmax, poor resolution occurs due to nitriding. When the b value is less than the lower limit bmin, coloring due to oxidation occurs. When the b value is within the control range, the product can be sampled.

FIG. 3 shows the relationship between the chromaticity index including the b value in FIG. 2 and the color. As the chromaticity index, there is an a value together with a b value, and hue and saturation are represented by an a value and a b value. Hue is represented by tan ^-1 (b / a),
Saturation is represented by √ (a ² + b ² ). The b value indicates the degree of yellow when positive and the degree of blue when negative. Such a and b values represent a difference from a standard according to the Hunter's Lab color system, for example, JIS.
It is also adopted in standards such as the color difference display method of Z 8730-1980. By adjusting the atmosphere using such a chromaticity index, the atmosphere can be adjusted more accurately and reproducibly than visually, and the running cost can be reduced by avoiding excessive quality.

FIG. 4 shows that the surface of the stainless steel strip 1 of SUS304 is nitrided when the circulation amount of the refining device 4 of FIG. 1 is changed in the range of 0 to 350 Nm ³ / H by the circulation amount control device 7. An example of an experimental result as to whether or not is shown is shown. Upper limit b
If it exceeds max, rejection due to nitridation occurs and the upper limit bm
If it is less than or equal to ax, it passes. The H ₂ concentration is 80%. When the b value exceeds the upper limit bmax, it is understood that rejection due to nitriding is eliminated by reducing the refining device circulation amount. Varying lowering the concentration of H ₂ is considered the oxidation proceeds, for lowering the concentration of H ₂ N ₂ partial pressure is high, so further nitride advances H ₂
The concentration should not be reduced. Even if the H ₂ concentration is less than 75%, the problem of nitriding occurs, so it has been found that the concentration should be controlled within the range of 75% or more.

In FIG. 4, when the passing material is a stainless steel strip 1 of SUS304, the H ₂ concentration is 80%, and the circulating amount of the refining device is 350 Nm ³ / H, the b value is the upper limit bmax.
Has been found to exceed. When the circulation amount of the refining device is gradually reduced to 50 Nm ³ / H, the b value becomes smaller than the upper limit bmax, and the nitrided structure disappears.

FIG. 5 shows a stainless steel strip 1 of SUS304.
(A) shows a state where the refining device circulation amount is increased from 0 in a state where the H ₂ concentration is set to 75% with respect to the sample A, and the refining device circulation amount with respect to the sample B. Is 350Nm ³ / H and the H ₂ concentration is 75% to 100%
The change at the time of ascending is shown by (b). In sample A, as shown in FIG.
When the refining device circulation amount is increased to 200 Nm ³ / H or more even if the refining device circulation amount is
The value becomes bmin or more, and the coloring is eliminated. In addition, when the refining device circulation amount is 0 as in Sample B,
Further, when the value of the b value is small, the maximum circulation amount is 350 Nm.
^{Even if the} refining device circulation amount is increased to ³ / H, b
The value is less than the lower limit bmin, and the state of rejection due to coloring is not improved. As shown in (b), when the H ₂ concentration is further increased, the lower limit value bmin is exceeded at 90% or more, and the sample passes.

FIG. 6 shows the relationship between the H ₂ concentration and the nitriding when the circulating amount of the refining device is set to zero. H ₂ concentration of 75
%, The b value exceeds the upper limit bmax, and the state is rejected due to nitriding. It has been found that when the H ₂ concentration reaches 75%, no nitrided structure is generated. Table 1 below shows the effects of the present embodiment based on the state before the implementation.

[0026]

[Table 1]

According to the present embodiment, the b value is set to the lower limit value bmi.
By setting n or more, the number of occurrences of quality abnormalities due to coloring is reduced by 80%. By setting the b value to be equal to or less than the upper limit value bmax, poor resolution due to nitriding and abnormal quality during chemical coloring are reduced by 96% and 72%, respectively. In addition, by reducing the amount of circulating refining equipment,
44% lower than before implementation, which is always near maximum capacity
Running cost can be reduced.

In the above embodiment, SUS304
Although the bright annealing of the stainless steel strip 1 described above is described, the same effect can be obtained with respect to the heat treatment of other metal materials. In particular, in the case of a steel sheet, although the coloring state of the oxide film easily changes depending on the composition of the material and the state of the surface, and it is difficult to perform visual management, in the present embodiment, appropriate management can be performed using a color difference meter.

[0029]

As described above, according to the present invention, the color of the surface of a metal material coming out of a reducing atmosphere furnace is measured by a color difference meter,
Since the refining device circulating amount and the hydrogen gas concentration are adjusted so that the b value of the measurement output is within a control range set in advance as a negative value, it is ensured to avoid variations as in the case of visual observation. A metal material having a uniform colored state can be obtained. Since it is not necessary to always operate the refining device at the maximum capacity, the running cost can be reduced.

According to the present invention, when the b value is less than the lower limit of the control range, the refining device circulation amount is increased, or the hydrogen gas concentration is increased to increase the reducing ability of the reducing atmosphere, and the b value is controlled. It can be adjusted to be within the range.

Further, according to the present invention, when the b value exceeds the upper limit of the control range, when the hydrogen gas concentration is decreased, the nitrogen gas concentration relatively increases, and nitridation easily occurs. Instead, it is possible to reduce the circulation amount of the refining device, suppress the excessive reducing action, and reduce the running cost while maintaining the quality of the metal material surface.

Further, according to the present invention, it is possible to reduce the occurrence of defective quality due to abnormal coloring of the surface of the metal material by the color difference meter, reduce the defective resolution due to nitriding and the abnormal quality during chemical coloring, and reduce the running cost. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a graph showing a management range of the embodiment of FIG.

FIG. 3 is a diagram illustrating a concept of a b value in FIG. 2;

FIG. 4 is a graph showing the influence of a change in the refining device circulation amount near the upper limit of the b value.

FIG. 5 is a graph showing the influence of the refining device circulation amount and the H ₂ concentration near the lower limit of the b value.

FIG. 6 is a graph showing the influence of the H ₂ concentration near the upper limit of the b value.

[Explanation of symbols]

1 stainless steel strip 2 bright annealing furnace 3 reduction gas supply device 4 Clarifying device 5 color difference meter 6 controller 7 circulation quantity control device 8 H ₂ tank 10 buffer tank 11 heating zone 12 Johiyatai 13 cooling zone 20 sealing device 21, 22, 23 and 24 flow rate control valve 25 flowmeter 26 H ₂ concentration meter

Claims (4)

[Claims] 1. Heating and cooling while passing a metal material plate into a reducing atmosphere containing hydrogen gas and nitrogen gas, and the reducing atmosphere is circulated through a refining device to remove oxygen and moisture. A method for preventing coloring of a passing material in a furnace, wherein an output including a b value as a dye signal indicating a difference from a reference in a Lab color system is derived on the exit side of the passing material from a reducing atmosphere furnace. A refining device circulation amount and a hydrogen gas concentration are adjusted so that a color difference meter is provided and a b value from the color difference meter is within a predetermined negative value control range. A method for preventing coloration of plate materials. 2. The reducing atmosphere furnace according to claim 1, wherein when the b value is less than the lower limit of the control range, the refining device circulation amount is increased or the hydrogen gas concentration is increased. A method for preventing coloration of plate materials. 3. The method according to claim 1, wherein when the b value exceeds the upper limit of the control range, the circulation amount of the refining device is reduced. 4. Heating and cooling while passing a metal material plate into a reducing atmosphere containing hydrogen gas and nitrogen gas, and the reducing atmosphere is circulated through a refining device to remove oxygen and moisture. An apparatus for preventing coloring of a passing material in a furnace, provided on an outlet side of the passing material from a reducing atmosphere furnace, and outputting an output including a b value as a color difference signal indicating a difference from a reference in a Lab color system. A color difference meter to be derived, and a control device for controlling the refining device circulation amount and the hydrogen gas concentration such that the b value from the color difference meter falls within a predetermined negative value management range. Prevention device for coloring of furnace plate material in reducing atmosphere.