JPH06306485A - Heat treating device for metallic belt - Google Patents

Abstract

PURPOSE:To improve operational stability and quality of products improving reducible property and passability of a metallic belt by providing a shape correcting machine for the belt on the inlet side of a reduction heating furnace of direct heating system in a continuous treating line to reduce the strain amount of the metallic belt. CONSTITUTION:After the steel belt 1 is rewound by a pay-off reel 2 and degreased by cooling equipment 5, the oxidized surface film of steel belt is reduced in the direct heating reduction heating furnace 12. Then, after the steel belt 1 is treated by a radiant tube type heating furnace 13 and a soaking pit 14, the belt is cooled from both sides to 350 deg.C, for instance, by roll cooling equipment 20 through a gas jet cooling equipment 15. And then, after the steel belt 1 is overageing treated by heatable and coolable cooling equipment 21, the belt 1 is successively passed in a rapid cooling furnace 22, water cooling equipment 23 and drying equipment 24, etc. In the above annealing line, a tension leveler 8 is arranged on the inlet side of direct heating reduction heating furnace 12 so that the shape of steel belt is corrected. For instance, the strain amount of steel belt is preferably to be equal to or smaller than 30mm when the distance between upper and lower rolls of reduction heating furnace 12 is equal to or larger than 30mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment apparatus for metal strips installed in a continuous treatment line for metal strips such as steel strips.

[0002]

2. Description of the Related Art In recent years, continuous annealing furnaces for treating steel strips such as steel sheets for automobiles and household appliances have been required to have good ability to reduce and heat strips and good thermal response when changing the strip size. In addition, for the purpose of preventing meandering by rapidly heating the unstable part of the steel strip material, a direct-fired heating furnace has been adopted, and an equipment configuration combined with a roll quench cooling method has been proposed from the viewpoint of energy saving. ing. Japanese Unexamined Patent Publication No. 62-54033 proposes such a continuous annealing equipment for the steel strip 1. As shown in FIG. 9, a preheating furnace 11, a direct flame is provided behind the inlet side cleaning equipment 5 as its heating configuration. Type reduction heating furnace 12, radiant tube type heating furnace 13 and the same soaking furnace 14 are provided, and as its cooling structure, a gas jet cooling equipment 15 and a roll cooling equipment 20 are provided, and in addition, there is an excess temperature behind them. It has been proposed to provide a controlled cooling facility with heating / cooling functions such as the aging treatment furnaces 21a and 21b, a quenching furnace 22, and a temper rolling mill 26 behind the quenching furnace 22.

[0003]

Distortion of the shape has become a problem in the trend of thinning of steel strips. However, it may be difficult for a cold rolling mill to perform proper shape correction. is there. In the shape-controlled cold rolling mill, which has been increasingly introduced in recent years, it is difficult to correct the shape defect between the center of the plate width direction and the plate edge, which is called quarter elongation.

However, if the shape defect is left as it is, the direct heating type reduction heating furnace 12 has a problem of oxidation, the radiant tube type heating and soaking furnaces 13 and 14 have a problem of contact with a radiant tube, and a gas jet cooling facility. No. 15 causes a problem of throttling, further has a problem of non-uniform cooling in the roll cooling facility 20, and has a problem of contact with the gas jet nozzle in the quenching furnace 22, which is a serious problem in line operation and product quality. Was there.

The present invention was devised in view of the above problems of the prior art, and enables stable line operation.
In addition, the present invention aims to provide a heat treatment device for metal strips, which is excellent in terms of product quality.

[0006]

Therefore, the heat treatment equipment for the metal strip according to the present invention is a direct-fire reduction heating furnace, a radiant tube heating / soaking furnace, a gas jet cooling equipment,
It has a roll cooling facility that blows a refrigerant to the backside of the metal strip that comes into contact with the cooling rolls to perform roll cooling as well as backside cooling, a regulated cooling facility with a heating / cooling function, and a quenching furnace. The basic feature is that a metal band shape corrector is installed on the inlet side of the reduction furnace.

[0007]

The above-described structure of the present invention was created from the inferences made by the present inventors and the results of experiments based on the inferences, and the reasoning behind the inferences and experiments will be described below.

First, the present inventors considered the mechanism of oxidation generation in a direct-fire reduction heating furnace as follows.
That is, the burner flame formed in the direct-fire reduction heating furnace has a limited range suitable for the reduction heating of the metal band, and if it does not come into contact with the metal band in the specific range, it is oxidized rather than being reduced. On the other hand, in order to achieve direct-fire reduction in one or two passes in a direct-firing reduction heating furnace, the distance between the upper and lower rolls provided in the furnace must be at least 20 m or more, and thus the furnace length is long. And the metal strip that passes there will flap between the rolls. In addition, the shape of the metal strip may have unevenness or middle stretch at the center thereof, and shape defects such as ear waves may occur at the ends thereof. When the steepness a / w indicated by the ratio of the metal band width w becomes large, this shape defect becomes remarkable. In that case, if the distance between the upper and lower rolls provided in the furnace is at least 20 m or more, the metal band is greatly undulated on the flap due to the burner pressure during combustion as described above. If there is such a waviness of the metal strip, the metal strip will not come into contact with the burner flame within the proper range of the burner flame, thereby causing a problem of local oxidation. Therefore, in the conventional direct-fired reduction heating furnace, it is necessary to increase the concentration of H ₂ gas in the atmosphere gas in order to enhance the reduction burner and improve the reducibility in the radiant tube type heating furnace after the direct-fired furnace. However, the equipment cost and the amount of H ₂ gas used must be increased.

On the other hand, the inventors of the present invention have considered that the problem of generation of throttling in the gas jet cooling equipment and the problem of non-uniform cooling in the roll cooling equipment are also caused by the defective shape of the metal strip. It is generally known that some shape defects of metal strips are improved by uniform heating in a furnace under a constant tension. However, regarding the quarter elongation, it is difficult to fix it, and when it is passed through the gas jet cooling equipment as it is, it causes throttling, and when it is carried to the roll cooling equipment, the elongation part does not sufficiently contact the roll surface, or It is presumed that the non-contact state makes it difficult to uniformize the temperature distribution in the plate width direction after the final cooling, resulting in variations in the material in the plate width direction and the occurrence of throttling and meandering.

Further, the problem of contact with the radiant tube in the radiant tube type heating / soaking furnace and the problem of contact with the gas jet nozzle in the quenching furnace are also caused by the defective shape of the metal strip. It is considered that the defective shape promoted by the restriction generated in the gas jet cooling equipment or the roll cooling equipment was the trigger.

If the above-mentioned problems are caused by the above reasons, a shape-correcting machine for the metal strip is provided immediately before these heat treatment equipments, and the shape-corrected metal is thereby provided. The present inventors considered that these problems would be solved by heat-treating each strip. Then, as a result of actual implementation, it was further clarified that once the shape of the metal strip was corrected immediately before the direct-fired reduction heating furnace, the following problems would not occur in the subsequent equipment. However, in the roll cooling facility, it is difficult to achieve uniform temperature distribution in the width direction of the metal strip only by performing such shape correction once. Backside cooling, in which the refrigerant is blown from the backside of the strip, is also decided to be carried out together with roll cooling. Even when performing this back cooling, when spraying the refrigerant,
Usually, the spray nozzle is sufficiently brought close to the back surface of the metal strip wound around the cooling roll, and since the shape of the metal strip has been corrected before, there is no fear of contact with the nozzle.

The inventors of the present invention investigated a method of preventing this with higher efficiency because the state of oxidation of the metal strip in a direct-fired reduction heating furnace is a major factor that affects the quality of the product. First, the state of the oxide film on the outlet side of the non-reduction burner in a direct furnace was examined, and it was found that there was a correlation between the shape defect of the metal band and the maximum film thickness of the oxide film. That is, when the metal strip 1a in the direct furnace 12 has a shape distortion as shown in FIG. 6, the metal strip-burner distance h is around a certain point (h1) as shown in FIG. The oxide film thickness b becomes thicker even if it becomes smaller or larger. Therefore, in the reduction heating of the metal strip by the reduction burner, the proper distance was calculated based on the assumption that the metal strip-burner distance h further influences the reduction effect. It was found that a sufficient reduction effect could not be obtained unless it was within the range. This means that the metal strip cannot come into contact with the burner flame within the range of the burner flame suitable for reduction heating unless the distance is kept such.

Of the steepness a / w, between the metal band strain amount a indicating the degree of lift of the central portion of the metal band cross section and the metal band-burner distance h shown in FIG. 8 (a)
It was found that there is a relationship as shown in (b). That is, FIG. 4A shows the relationship between the two when the distance between the upper and lower rolls provided in the direct-fired heating furnace is 18 m, which shows that the metal strip shape strain amount a is close to 80 mm. Also, the distance h between the metal strip and the burner is within the range of 150 to 350 mm (the hatched portion in the figure indicates the flapping range of the metal strip). On the other hand, FIG. 6B shows the relationship between the two when the distance between the upper and lower rolls is 25 m, and in this case, the metal strip shape distortion amount a is 30 m.
If the distance is not less than m, the distance h between the metal strip and the burner is 150 to 3
It can be seen that it does not fit within the range of 50 mm. Therefore, in the configuration of the present invention, in the case of a direct-fired reduction heating furnace having a distance between upper and lower rolls of 20 m or more, it is corrected immediately before that by a shape correcting machine so that the original plate shape distortion amount a becomes 30 mm or less. Is desirable.

[0014]

EXAMPLES Specific examples of the present invention will be described in detail below. FIG. 1 is a schematic diagram showing the configuration of a continuous annealing furnace line for a steel strip 1 having a configuration of an embodiment of a heat treatment apparatus of the present invention.

In the structure of this embodiment, the steel strip 1 is rewound by the pay-off reel 2 and sheared by the entrance side shearing machine 3, and then the welding machine 4 connects the preceding coil and the following coil. Next, after being electrolytically degreased in the inlet side cleaning equipment 5, it is supplied to the preheating furnace 11 and the direct-firing type reduction heating furnace 12 through the inlet side looper 10 to be heated to 600 ° C. to 750 ° C. and radiant tube type heating. After being heated to a predetermined temperature in the furnace 13 and the radiant tube type soaking furnace 14, the soaking is carried out as it is, and the gas jet cooling facility 15 uses, for example, 600
It is cooled to ℃, and it is 350 ℃ in the roll cooling equipment 20.
Cool down. Subsequently, after passing through an overaging zone 21 and a quenching furnace 22 provided as a regulated cooling facility with a heating / cooling function, water cooling / drying is performed in a water cooling facility 23 and a drying facility 24,
After passing through the exit looper 25, the plate surface is tempered by a temper rolling mill 26, inspected and oiled by a surface defect meter 27 and an oil coating machine 28, and a predetermined length is given by an output shearing machine 29. After being cut into pieces, it is wound up by the tension reel 30. A tension leveler 8 as a plate shape corrector is installed in front of the direct-fire reduction heating furnace 12 with an entrance looper 10 and a preheating furnace 11 interposed therebetween. In addition, the distance between the upper and lower rolls provided in the direct heating type reduction heating furnace 12 is 25
m.

It is desirable to correct the shape of the steel strip 1 immediately after the oil content adhering to the surface is washed off by the inlet side cleaning facility 5. Therefore, in this embodiment, the inlet side cleaning facility 5 and the preheating are carried out. The tension leveler 8 is installed between the furnace 11 (in the actual equipment configuration, a two roll type steering roll 6 is disposed immediately before the tension leveler 8, and 7 and 9 are on the inlet side of the tension leveler 8 and The bridle roll on the exit side). On the other hand, from the viewpoint of preventing meandering in the entrance side looper 10, it is better to correct the shape of the steel strip 1 immediately before that, and in consideration of the complexity of roll replacement in the looper 10, this tension leveler 8 is The entrance looper 10
I decided to install it just before. The entrance-side cleaning equipment 5 does not have to be installed directly above the tension leveler 5. As a similar equipment arrangement configuration, there is a configuration shown in FIG.

The structure of the roll cooling equipment 20 used in the structure of this embodiment has at least one cooling roll that contacts the steel strip 1 while rotating and continuously cools it. The roll has a body length at least equal to the plate width of the steel strip 1, and the cooling liquid flows inside the roll to cool it continuously and moves in a direction substantially orthogonal to the moving direction of the steel strip 1. The contact area can be controlled (that is, the cooling length can be controlled).

The structure of the roll cooling equipment 20 is shown in FIG.
As shown in FIG. 3, a tension adjuster including at least two rolls 16a to 16d is installed on each of the entrance side and the exit side. Further, gas spray headers 18a to 18e for spraying a cooling gas from the back surface of the steel strip 1 which is in contact with the cooling rolls 17a to 17e are provided. By blowing the cooling gas, the steel strip 1 can be prevented from being lifted up and uniformly cooled in the plate width direction. However, as described above, the cooling roll 17a
To 17e are for adjusting the contact length with the steel strip 1,
Of the gas spray headers 18a to 18e.
Can move in the same direction at the same time. On the other hand, on the outlet side of the present roll cooling equipment 20, a latter stage gas cooling header 19 is installed at a predetermined distance from both surfaces of the steel strip 1. As shown in FIG. 4, these headers 19 are installed in a state of being divided into three parts in each plate width direction (three of 19a to 19c are shown on one surface, and only 19d is shown on the other side). By separately controlling the flow rate and / or the flow velocity of the cooling gas blown from these to the surface of the steel strip 1, the temperature distribution in the width direction of the steel strip 1 after the final cooling becomes uniform. I am able to do it.

In the continuous annealing line of this embodiment having the above construction, the tension leveler 8 is connected to the direct-fire reduction heating furnace 12
By arranging the steel strip 1 on the upstream side of the heating furnace 12, the strip passing property of the steel strip 1 in the heating furnace 12 is improved, and as will be apparent from the experiments described later, the reduction heating characteristics in the direct-fire reduction heating furnace 12 are also improved. It will be stable.

Further, the steel strip 1 is made by the tension leveler 8.
It becomes possible to correct the shape of the portion where the quarter elongation occurs, and the occurrence of throttling in the gas jet cooling equipment 15 is eliminated, and the occurrence of throttling and non-uniform cooling in the roll cooling equipment 20 is greatly improved. As a result, the steel in the line is The meandering of the strip 1 was eliminated, and the quality of the obtained product was improved. Further, the radiant tube type heating furnace 13 comes into contact with the tubes in the same soaking furnace 14, the gas jet nozzles in the gas jet cooling equipment 15, the back side gas blowing headers 18a to 18e in the roll cooling equipment 20 and the latter stage gas cooling header 1.
9 and the problem of contact with the gas jet nozzle in the rapid heating furnace 22 disappeared.

FIG. 5 shows the correlation between the steel strip strain amount a and the steel strip-burner distance h obtained from the experimental results when the tension leveler 8 is not installed as in this embodiment. In the figure, the min value indicates the minimum value of the strain amount a measured in the steel strip 1 having a constant length, and the max value indicates the maximum value on the contrary, and according to this figure, , Steel strip 1
If the minimum strain amount a exceeds 30 mm and there is a shape defect, the distance h between the steel strip and the burner will be less than 150 mm, so it will not be suitable for reduction heating (the above strain amount critical value is converted to steepness). Then it will be 1.8%).

Therefore, in this embodiment, the strain amount is 30 mm.
As described below, the shape of the original plate was corrected by the tension leveler 8 and then the steel strip 1 was introduced into the preheating furnace 11 and the direct-fire reduction heating furnace 12. As a result, stable reduction heating was performed in the direct-fire reduction heating furnace 12, and the problem of local surface oxidation was eliminated.

In this embodiment, between the direct heating type reduction heating furnace 12 and the radiant tube type soaking furnace 14 behind it,
A radiant tube type heating furnace 13 is arranged, which is provided because the soaking furnace 14 has a low heat following property. That is, since the heating method of the soaking furnace 14 is a radiant tube method (the same applies to the electric heater heating method), the temperature rising rate and the temperature lowering rate at the time of temperature change are slower than those of the direct-firing reduction heating furnace 12 in front of it. When changing the heating end temperature (soaking temperature), it is preferable to provide the radiant tube type heating furnace 13 between the heating end temperatures from the viewpoint of followability. Therefore, by providing the radiant tube type heating furnace 13 between them as in the present embodiment, the rapid thermal response of the direct-fire reduction heating furnace 12 can be effectively utilized.

In this embodiment, the tension leveler 8 is used as a shape straightening machine for the steel strip 1, but the same effect can be obtained by using a skin pass mill. Further, in the present embodiment, the overaging zone 2 is used as the adjustment cooling equipment with heating / cooling function.
Although No. 1 is used, a tempering furnace and a slow cooling zone (IF steel, ultra low carbon steel, etc.) may be used instead.

[0025]

According to the heat treatment equipment for metal strips according to the present invention described in detail above, stable line operation can be carried out, and there is no occurrence of quarter elongation or throttling and uniform cooling is possible during cooling. In terms of product quality, excellent products can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a continuous annealing furnace line for a steel strip provided with an example configuration of a heat treatment apparatus according to the present invention.

FIG. 2 is a schematic view showing another continuous annealing furnace line configuration having a facility arrangement configuration similar to that of the above-described embodiment.

FIG. 3 is an explanatory diagram showing a configuration of roll cooling equipment in the present embodiment.

FIG. 4 is a perspective view showing a configuration of a post-stage gas cooling header in the present embodiment.

FIG. 5 is a graph showing a correlation between a steel strip strain amount obtained from an experimental result when a tension leveler is not installed and a steel strip-burner distance.

FIG. 6 is a cross-sectional view of a direct furnace showing an example of shape distortion generated in a metal band in the direct furnace.

FIG. 7 is a graph showing a correlation between a shape defect of a metal band on the outlet side of a direct-fired furnace non-reduction burner and a maximum film thickness of the oxide film.

FIG. 8 is a graph showing a correlation between a metal strip strain amount and a metal strip-burner distance when the distance between upper and lower rolls in a direct-fired heating furnace is different.

FIG. 9 is a schematic line diagram showing a conventional configuration example of a continuous annealing equipment for steel strips.

[Explanation of symbols]

 1 Steel strip 8 Tension leveler 12 Direct-fire reduction heating furnace 15 Gas jet cooling equipment 20 Roll cooling equipment 22 Quenching furnace

Claims (2)

[Claims] 1. A direct-firing reduction heating furnace, a radiant tube heating / soaking furnace, a gas jet cooling facility, and a cooling medium that is blown with a refrigerant to the back surface of a metal strip that is in contact with a cooling roll to cool the roll and the back surface. Roll cooling equipment
A heat treatment apparatus for a metal strip, comprising a controlled cooling facility with a heating / cooling function and a quenching furnace, wherein a metal strip shape corrector is provided on the inlet side of the direct-firing reduction heating furnace. 2. The heat treatment apparatus for a metal strip according to claim 1, wherein when the distance between the upper and lower rolls installed in the direct-heating reduction heating furnace is 20 m or more, distortion of the metal strip is caused by the shape straightening machine. The heat treatment apparatus for a metal strip according to claim 1, wherein a material whose amount can be set to 30 mm or less is used.