JP3362443B2 - Continuous annealing line operation method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for continuously treating steel strip.
And a method of operating a continuous annealing line . 2. Description of the Related Art In recent years, continuous annealing furnaces for treating steel strips such as steel sheets for automobiles and household electric appliances have been required to have good ability to reduce and heat the steel strips and good thermal responsiveness when the steel strip size is changed. Direct heating furnaces have been adopted for the purpose of preventing meandering by rapidly heating the unstable part of the steel strip material, and the equipment configuration combined with the roll quench cooling system from the viewpoint of energy saving. Has been proposed. Japanese Patent Application Laid-Open No. Sho 62-54033 proposes such a continuous annealing equipment for steel strip 1, and as shown in FIG. A reduction heating furnace 12, a radiant tube heating furnace 13, and a uniform heating furnace 14 are provided, and a gas jet cooling facility 15 and a roll cooling facility 20 are provided as cooling configurations thereof. There has been proposed a configuration in which the aging zones 21a and 21b, the quenching furnace 22, and a temper rolling mill 26 are further provided behind the aging zones 21a and 21b. [0003] On the other hand, high tensile strength of general materials has been progressing mainly in automotive steel sheets and thinning of steel strips has been progressing. However, such steel sheet materials contain elements such as Mn, Si, and P. However, even in the case of a steel sheet annealed in a batch box annealing furnace, there is a problem in phosphatability, and in the case of continuous annealing equipment, there is a problem that the phosphatability is further deteriorated. . Therefore, in Japanese Patent Publication No. 58-37391, a metal salt, mainly Ni or Ni-P
A configuration is provided in which an electroplating facility for improving phosphatability by performing electroplating in an aqueous solution containing is provided. [0004] On the other hand, the shape disorder has become a problem as the steel strip has been made thinner. In the continuous annealing line equipped with the equipment, if the shape of the original plate is poor, the direct-fired reduction heating furnace causes the problem of oxidation due to the flapping of the steel strip, and if it is severe, even after the subsequent Ni, Ni-P plating treatment. The effect will remain. In some cases, it is difficult to perform appropriate shape correction with a cold rolling mill. [0005] Further, although the defective shape of the original plate can be considerably improved by the soaking furnace, the shape of the quarter portion between the center in the width direction of the plate and the end of the plate is not so much improved. This has caused a serious problem in the material and the sheet passing property, for example, inducing the drawing of the steel strip in the cooling equipment and the unevenness of the cooling in the roll cooling equipment. Furthermore, when such a shape defect occurs,
Even in the subsequent electroplating equipment for performing electroplating in an aqueous solution containing Ni and Ni-P, the steel strip came into contact with the electrodes, which led to a line stoppage, which caused a serious problem in operation. In order to solve this problem, it is conceivable to increase the distance between the steel strip and the electrode, but it has been industrially difficult in terms of cost and technology. [0007] The present invention has been made in view of the above problems of the prior art, and can perform a stable line operation,
It is an object of the present invention to provide a method for operating a continuous annealing line in a steel strip heat treatment apparatus capable of obtaining a product excellent in phosphatability and excellent in quality in which there is no defective shape of a steel strip and generation of oxidized portions. [0008] Therefore, the continuous annealing line operating method in the steel strip heat treatment equipment according to the present invention is a straightforward method.
Heat of steel strip with fire-type reduction heating furnace and roll cooling equipment
A method of operating a continuous annealing line in a processing apparatus,
Equipped with a steel strip shape straightening machine on the entrance side of the direct fire type reduction heating furnace
And a back cooling means in the roll cooling equipment.
The upper and lower rows installed in the direct-fired reduction heating furnace.
If the distance between the tools is 20 m or more,
After correcting the strain of the steel strip to 30 mm or less,
Pass the plate through a fired reduction heating furnace and cool the roll
When the equipment is passed through, the cooling system is
Coolant is sprayed on the back of the steel strip in contact with the
The basic feature is that the cooling of the back is performed at the same time as the cooling . The structure of the present invention described above was created based on the inference of the present inventors and the results of experiments based on the inference, and the inference and the background of the experiments will be described below. First, the present inventors have considered the mechanism of the occurrence of oxidation in a direct-fired reduction heating furnace as follows.
That is, the burner flame formed in the direct-fired reduction heating furnace has a limited range suitable for the reduction heating of the steel strip, and oxidation is performed in the specific range, in addition to reducing the steel strip unless it comes into contact with the steel strip. On the other hand, in order to achieve direct-fire reduction in one or two passes in a direct-fired reduction heating furnace, the interval 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 steel strip passing through it rolls between the rolls. Also, in the shape of the steel strip,
Shape irregularities such as irregularities and middle elongation at the center and ear waves and the like may occur at the end, and the ratio of the steel strip width w to the steel strip strain amount a, which indicates the degree of lifting of the steel strip cross-section center, is shown. As the steepness a / w increases, the shape defect becomes remarkable. In this case, if the interval between the upper and lower rolls provided in the furnace is at least 20 m or more, the steel strip is greatly undulated due to the burner pressure on the batt during combustion as described above. Such undulation of the steel strip causes the steel strip to be out of contact with the burner flame within the above-mentioned appropriate range of the burner flame, causing local oxidation problems. 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 increase the reduction burner and to improve the reducibility in the radiant tube-type heating furnace after the direct-fired furnace. In addition, an increase in equipment costs and an increase in the amount of H ₂ gas used have been forced. On the other hand, the present inventors have considered that the problem of the occurrence of drawing in the gas jet cooling equipment and the problem of uneven cooling in the roll cooling equipment are also caused by the defective shape of the steel strip. In general, it is known that a slight shape defect of a steel strip is improved when the steel strip is uniformly heated in a furnace under a certain tension. However, the shape defect of the quarter part is not easily corrected, and when the sheet is passed through the gas jet cooling equipment as it is, a narrowing occurs there. No contact or no contact,
It is presumed that it became difficult to equalize the temperature distribution in the plate width direction after the final cooling, and that the material was uneven in the plate width direction and that the drawing and meandering occurred. Further, the problem of contact with the electrodes in the electroplating equipment for electroplating in a solution containing Ni or Ni-P is also caused by the defective shape of the steel strip, in which case the gas jet cooling equipment or roll cooling is used. It is considered that the shape defect promoted by drawing or the like generated in the equipment triggered the trigger. If the above-mentioned problem is caused by the above, a straightening machine for the steel strip is provided immediately before these heat treatment equipment, and the steel straightened by the straightening is provided. The present inventors have considered that these problems can be solved by heat-treating each of the belts. In practice, it was further clarified that once the shape of the steel strip was corrected immediately before the direct-fired reduction heating furnace, the following problems would not occur in subsequent equipment. However, it is difficult to achieve a uniform temperature distribution in the width direction of the steel strip by performing such a shape correction only once in the roll cooling equipment. The backside cooling, in which the refrigerant is blown from the backside of the belt, is also performed together with the roll cooling. Thereby, the drawing and meandering of the steel strip 1 are greatly improved, and the contact accident with the electrode in the subsequent electroplating equipment is completely prevented.
Also in the case of performing this backside cooling, the blowing of the refrigerant is usually performed by sufficiently bringing the spray nozzle close to the vicinity of the backside of the steel strip wound around the cooling roll, and the shape correction of the steel strip has been performed before. Therefore, there is no fear of contact with the nozzle. Further, since the present inventors have made a major element of the oxidation of the steel strip in the direct-fired type reducing furnace condition affects the quality of the product was investigated how you can prevent this with higher efficiency. First, the state of the oxide film on the exit side of the non-reducing burner of the open fire furnace was examined, and it was found that there was a correlation between the defective shape of the steel strip and the maximum thickness of the oxide film. That is, when the steel strip 1 in the open fire furnace 12 has a shape distortion as shown in FIG. 5, as shown in FIG. 6, the distance h between the steel strip and the burner is:
The oxide film thickness b becomes thicker at a certain point (h1) even if it becomes smaller or larger than that. Therefore, in the reduction heating of the steel strip by the reduction burner, when the proper distance was determined based on the assumption that the distance h between the steel strip and the burner would further influence the reduction effect, the result was 150 to 350 mm. It was found that if it was not within the range, a sufficient reduction effect could not be obtained. This means that the steel strip cannot come into contact with the burner flame within the range of the burner flame suitable for the reduction heating unless the separation distance is maintained. Among the steepness a / w, the steel strip strain amount a indicating the degree of lifting at the center of the steel strip cross section and the steel strip / burner distance h shown in FIG. 7 (a) and 7 (b). That is, FIG. 7A shows the relationship between the upper and lower rolls provided in the direct fired heating furnace when the distance between the upper and lower rolls is 18 m. According to this, the steel strip shape distortion amount a becomes close to 80 mm. Also, the distance h between the steel 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 steel strip). On the other hand, FIG. 8B shows the relationship between the upper and lower rolls when the distance between the upper and lower rolls is 25 m. In this case, the distance h between the steel strip and the burner is required unless the steel strip shape distortion amount a is 30 mm or less. are those Tsu see that does not fit within the range of 150~350mm. The configuration of the present invention is therefore based on this new finding, correction in the case of direct-fired type reducing furnace distance between the upper and lower rolls have more than 20 m, the straightening machine in immediately before the original plate shape distortion amount a to 30mm or less To do . Hereinafter, specific embodiments of the present invention will be described in detail. FIG. 1 is a schematic view showing a continuous annealing furnace line configuration of a steel strip 1 provided with a configuration of an embodiment of a heat treatment apparatus of the present invention. In this embodiment, the steel strip 1 is rewound by the pay-off reel 2 and is sheared by the entry shear 3, and the leading coil and the trailing coil are connected by the welding machine 4. Next, after being electrolytically degreased by the inlet cleaning equipment 5, it is supplied to the preheating furnace 11 and the direct-fired reduction heating furnace 12 via the inlet looper 10, and is heated to 600 to 750 ° C. After heating to a predetermined temperature in the furnace 13 and the radiant tube type soaking furnace 14, it is soaked as it is.
And cooled to 350 ° C in the roll cooling equipment 20.
Cool down to Subsequently, the overaging treatment zone 21 and the quenching furnace 22
After, in the electroplating equipment 23, the electroplating is performed in an aqueous solution containing Ni (or Ni-P) for improving the chemical conversion property and pressability, dried in the drying equipment 24, passed through the outlet looper 25, The surface of the sheet is subjected to a temper treatment by a temper rolling mill 26, inspected and lubricated by a surface defect meter 27 and an oiling machine 28, and cut into a predetermined length by an output shearing machine 29. Wound by 30. In front of the direct heating type reduction heating furnace 12, the entrance looper 10 and the preheating furnace 11 are provided.
And a tension leveler 8 serving as a plate shape correcting machine is provided therebetween. In addition, this direct fire type reduction heating furnace 1
The distance between the upper and lower rolls provided in 2 is 25 m. It is desirable to correct the shape of the steel strip 1 immediately after the oil adhering to the surface of the steel strip 1 is washed off by the inlet cleaning equipment 5, and therefore, in this embodiment, the inlet cleaning equipment 5 and the preheating are performed. The above-mentioned tension leveler 8 was installed between the furnace and 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 the entrance side of the tension leveler 8 and Outgoing bridle roll). On the other hand, from the viewpoint of preventing meandering in the entrance-side looper 10, it is better to perform the shape correction of the steel strip 1 immediately before that, and in consideration of the complexity of changing the rolls in the looper 10, the tension leveler 8 is The entrance looper 10
I decided to install just before. Note that the entrance-side cleaning equipment 5 does not have to be installed immediately above the tension leveler 5. The structure of the roll cooling equipment 20 used in the present embodiment has at least one cooling roll for rotating and contacting the steel strip 1 while rotating and continuously cooling the steel strip 1. The roll has a body length at least equal to the plate width of the steel strip 1, and a cooling liquid continuously flows through the inside of the roll to cool the roll, and moves in a direction substantially perpendicular to the moving direction of the steel strip 1. The contact area can be controlled (that is, the cooling length can be controlled). The configuration of the roll cooling equipment 20 is shown in FIG.
As shown in (1), 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 blowing headers 18a to 18e for blowing 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 uniformly cooled in the sheet width direction while preventing the steel strip 1 from rising. However, as described above, the cooling roll 17a
17e to 17e, for adjusting the contact length with the steel strip 1,
The gas blowing headers 18a to 18e can be moved in a direction substantially perpendicular to the moving direction of the gas blowing headers 18a to 18e.
Can also move in the same direction at the same time. On the other hand, on the exit side of the roll cooling equipment 20, a post-stage gas cooling header 19 is installed at a predetermined interval from both surfaces of the steel strip 1. As shown in FIG. 3, these headers 19 are installed in a state of being divided into three in each plate width direction (three surfaces 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 rate of the cooling gas blown out onto the surface of the steel strip 1 from these, the temperature distribution in the width direction of the steel strip 1 after the final cooling is made uniform. I can do it. In the continuous annealing line of the present embodiment having the above-described structure, the tension leveler 8 is connected to the direct-fired reduction heating furnace 12.
Is arranged on the upstream side of the heating furnace 12, the sheet-passing property of the steel strip 1 in the heating furnace 12 is improved, and the reduction heating characteristics of the direct-fired reduction heating furnace 12 are also improved, as is apparent from an experiment described later. It can be obtained stably. Therefore, when the subsequent plating process of the electroplating equipment 23 is performed,
The phosphatability of the steel strip 1 is improved. Further, the steel strip 1 is controlled by the tension leveler 8.
It is possible to correct the shape of the portion where the defective shape of the quarter portion occurs, eliminating the occurrence of squeezing in the gas jet cooling facility 15 and greatly reducing the squeezing and non-uniform cooling in the roll cooling facility 20. The meandering of the band 1 was eliminated, and the quality of the obtained product was improved. Therefore, the problem of contact with the electrode in the electroplating equipment 23 was eliminated. Further, there was no problem of contact with the gas jet nozzle in the gas jet cooling facility 15 and contact with the back gas spray headers 18a to 18e and the subsequent gas cooling header 19 in the roll cooling facility 20, and stable operation became possible. FIG. 4 shows the correlation between the strain a of the steel strip obtained from the experimental results when the tension leveler 8 was not installed as in this embodiment and the distance h between the steel strip and the burner. 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 opposite thereto. , Steel strip 1
If the minimum strain amount a exceeds 30 mm, the distance h between the steel strip and the burner is less than 150 mm, which is not suitable for the reduction heating. Then it becomes 1.8%). Therefore, in the present embodiment, the amount of distortion is 30 mm
The steel strip 1 was introduced into the preheating furnace 11 and the direct-fired reduction heating furnace 12 after the shape of the original sheet was corrected by the tension leveler 8 as described below. As a result, stable reduction heating is performed in the direct fire type reduction heating furnace 12, and the problem of occurrence of local surface oxidation is eliminated. In this embodiment, between the direct fire type reduction heating furnace 12 and the radiant tube type soaking furnace 14 behind it.
Although the radiant tube type heating furnace 13 is provided, this is provided because the heat equalizing furnace 14 has low heat followability. 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 heating rate and the cooling rate at the time of temperature change are slower than that of the direct-fired reduction heating furnace 12 before the heating method. When the heating end temperature (soaking temperature) is changed, it is desirable to provide the radiant tube heating furnace 13 between them in terms of followability. Therefore, by providing the radiant tube type heating furnace 13 between them as in this embodiment, the speed of the thermal response of the direct fire type reduction heating furnace 12 can be effectively utilized. The installation position of the electroplating equipment 23 in the present embodiment is located after the quenching furnace 22 in consideration of the improvement of press formability, and is installed before the drying equipment 24 because it is necessary to dry after plating. Since there is no fluctuation or stoppage of the line speed, it is necessary to provide it before the exit looper 25. Further, 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. According to the continuous annealing line operation method definitive in heat treatment equipment of the strip according to the present invention as described above in detail, it can be performed stable line operation, the oxidation in direct-fired type reducing furnace problems Therefore, the phosphatability of the steel strip after electroplating in an aqueous solution containing Ni or Ni-P is improved. In addition, since there is no shape defect or drawing of the steel strip quarter portion and uniform cooling can be performed at the time of cooling, a product excellent in quality can be obtained, and the problem of contact with the electrode at the time of the electroplating is also eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a line configuration of a continuous annealing furnace for a steel strip provided with an embodiment of a heat treatment apparatus for performing a method according to the present invention. FIG. 2 is an explanatory diagram illustrating a configuration of a roll cooling facility in the present embodiment. FIG. 3 is a perspective view showing a configuration of a post-stage gas cooling header in the present embodiment. FIG. 4 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. 5 is a cross-sectional view of an open fire furnace showing an example of shape distortion generated in a steel strip in the open fire furnace. FIG. 6 is a graph showing a correlation between a shape defect of a steel strip at an outlet side of a non-reducing burner of a direct-fired furnace and a maximum thickness of the oxide film. FIG. 7 is a graph showing a correlation between a steel strip strain and a steel strip / burner distance when the distance between upper and lower rolls in the direct heating furnace is different. FIG. 8 is a schematic line diagram showing a conventional configuration example of continuous annealing equipment for steel strip. [Description of Signs] 1 Steel strip 8 Tension leveler 12 Direct fire reduction heating furnace 15 Gas jet cooling equipment 20 Roll cooling equipment 22 Quenching furnace 23 Electroplating equipment

Continuation of the front page (56) References JP-A-63-69924 (JP, A) JP-A-61-99633 (JP, A) JP-A-50-90567 (JP, A) JP-A-57-67134 (JP) JP-A-62-54035 (JP, A) JP-B-58-37391 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9/56 101 C21D 1/00 125

Claims (1)

(57) [Claims] (1)Direct fire type reduction heating furnace and roll cooling equipment
Operation of continuous annealing line in heat treatment equipment for steel strip with cracks
The method A steel strip shape straightening machine is provided on the entrance side of the direct-fired reduction heating furnace.
Back cooling means in the roll cooling equipment.
Equipped with The interval between the upper and lower rolls installed in the direct-fired reduction heating furnace is
If it is 20 m or more, the shape straightening machine
After correcting the strain amount to 30 mm or less, the steel strip
Letting it pass through a heating furnace, When passing through the roll cooling equipment, the back cooling means
Blows refrigerant to the back of the steel strip in contact with the cooling roll
The back cooling is performed simultaneously with the roll cooling.
Operation method of continuous annealing line.