JPH07173545A - Continuous heat treatment apparatus for metal strip and continuous heat treatment method - Google Patents

Abstract

(57) [Summary] [Objective] To provide means for realizing full-scale induction heating in a vertical furnace. [Constitution] Cleaning equipment 30, tension leveler 40 installed after the cleaning equipment, looper 50 installed after the tension leveler, and vertical heating using an induction heating device as a main heating means installed after the looper. A continuous heat treatment apparatus for metal strips, which comprises furnaces 60 and 70. Furthermore, a guide belt or pressure pad for guiding the metal strip is installed at one or a plurality of locations between the induction coils of the induction heating apparatus installed in the vertical heating furnace. The metal strip after cleaning is adjusted to have a shape distortion of 30 mm or less by a tension leveler, and then a vertical heating furnace is heated at a heating rate of 200 ° C. or less per second to a temperature of 70% or more of the entire heating temperature of the metal strip. A continuous heat treatment method for a metal strip, characterized by performing induction heating with an installed induction heating device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous heat treatment apparatus for a metal strip and a continuous heat treatment method.

[0002]

2. Description of the Related Art As a heating device for metal strips, a vertical furnace is widely used in order to make the installation space of the device compact. A vertical furnace is a type of furnace in which furnace rolls are installed above and below the furnace, and metal bands are wound around these rolls to heat the metal bands with a heating device.

As a heating device, a radiant tube that burns gas inside a heat-resistant steel tube is generally used, which is called a radiant tube type heating furnace. Further, in recent years, in order to improve the heating rate, a direct flame heating method using a direct flame burner,
An induction heating method of heating by electromagnetic induction is also used.

For example, in the "annealing furnace for steel strip galvanizing" disclosed in Japanese Patent Laid-Open No. 4-154947, "an induction heating furnace is continuously connected to the inlet side of the heating zone through an atmosphere gas seal device,
A technique has been proposed in which a degreasing device for removing rolling oil from a steel strip is installed on the inlet side of the induction heating furnace. By adopting the induction heating furnace, it is possible to eliminate the generation of an oxide layer on the surface of the steel strip due to the disturbance of the direct-burning burner flame, which is seen in the direct-fired non-oxidizing heating furnace.

[0005]

The radiation tube type heating furnace has a long line length because the heating rate is low. In particular, in a high-speed line for improving production efficiency, the line length becomes very long, and accordingly, the number of metal bands folded back by the in-furnace rolls, that is, the number of passes increases. As the number of passes increases, the number of rolls in the furnace also increases, so that the deviation of the metal strip from the normal position due to a slight deviation in the installation of the rolls in the furnace is likely to be amplified.

As described above, in the radiant tube type heating furnace, since the number of passes is large, not only when the shape of the metal strip is poor, but also when the metal strip is relatively good, the metal strip extends in the plate width direction. A so-called meandering phenomenon that reciprocates is likely to occur.
When the metal band causes a meandering phenomenon, it often comes into contact with the side wall of the furnace, etc., and both the edge part of the metal band and the side wall of the furnace may be damaged, or even the metal band may break, leading to stable operation. It's a big problem to do.

On the other hand, in a direct-fired heating furnace, since the number of passes is greatly reduced, it is difficult for the metal strip to meander. However, actually, even in a direct-fired heating furnace, meandering still occurs, and so-called squeezing in which the metal band is wrinkled and folded in a streak shape, and flapping of the metal band are likely to occur. The reason for this is that due to improper combustion adjustment of the burner, a part of the metal strip, especially the plate edge, is partially directly heated from the flame, etc., and the temperature distribution of the metal strip becomes uneven and the shape deteriorates. It is thought to occur.

Further, since the heating temperature of the direct-fired heating furnace is high, there is a problem that if the line is stopped for some reason, the metal strip overheats, and particularly a thin metal strip is easily broken. For example, when a can material having a plate thickness of about 0.15 to 0.5 mm is heated in a direct-fired heating furnace, the temperature inside the furnace is as high as 1200 to 1400 ° C., so that it is melted and damaged when the line speed decreases. . Therefore, a direct-fired heating furnace for treating such a thin material has not been put into practical use.

In the induction heating method, the temperature distribution of the metal strip becomes relatively uniform as compared with the direct fire method, and therefore the meandering and throttling of the metal strip are less likely to occur. Also, since the furnace temperature is low, the metal strip will not overheat when the line is stopped.

However, since the cross section of the metal strip is extremely flat, there is a problem that the efficiency of conversion into heat energy in electromagnetic induction is very poor. This is because the metal strip occupies a smaller volume of material in the induction coil than a pipe or a square bar, and thus has a large amount of magnetic flux leakage. As a result, the power factor of the electric power applied to the induction coil becomes low, and the reactive power increases. Therefore, in the induction heating of the metal strip, there is a problem in that both the coil capacity and the power supply capacity require a device having a much larger capacity than that corresponding to active power.

In order to increase the efficiency of conversion of the induction coil into heat energy, the coil winding and the metal strip may be brought closer to each other. In a vertical furnace, the metal strip vibrates in the plate thickness direction. There is also a limit because it exists.

Further, even in the induction heating, there is a problem that it is promoted if there is a defective shape due to thermal stress due to rapid heating, though not so much as in the case of the direct flame method. This is because a part of the metal band approaches the winding of the induction coil due to the defective shape, and the part is locally heated and further deformed by thermal stress.

When the metal strip is meandered, it often breaks as described above, but even if it does not reach that point, it will hinder rapid cooling after heating. A roll cooling method in which contact cooling is performed by contacting a cooling roll is widely used for rapid cooling of the metal strip. When the meandering occurs in the heating furnace, the meandering naturally occurs even in the quenching zone, and the contact pressure of the metal strip with the roll partially changes. Generally, in the contact cooling of the metal strip, the non-uniform contact condition causes the non-uniform temperature, and the non-uniform contact condition results in a vicious cycle. As a result, there is a problem that the material is deteriorated due to the non-uniform temperature, and further, the deformation due to the thermal stress occurs.

In the "annealing furnace for steel strip galvanizing" disclosed in Japanese Patent Laid-Open No. 4-154947, which uses induction heating, the furnace type is not a vertical furnace, but a steel strip is simply placed on a furnace roll. Since it is a horizontal furnace of the type to be transported, the problems as in the vertical furnace described above do not occur so much, and in particular, the flapping phenomenon peculiar to the vertical furnace cannot occur.

The induction heating method has many advantages over the radiation tube method and the direct fire method, but has not been put to practical use. Even if it was put to practical use, there were many horizontal furnaces, and its application to vertical furnaces was limited to partial use in the alloying treatment section of zinc plating lines and the reflow section of tin plating lines. The present invention provides means for realizing full-scale induction heating in a vertical furnace.

[0016]

A first aspect of the present invention provides a cleaning equipment, a tension leveler installed after the cleaning equipment, a looper installed after the tension leveler, and an induction heating device installed after the looper. It is a continuous heat treatment apparatus for metal strips, which includes a vertical heating furnace as a main heating means.

According to a second aspect of the present invention, guide rolls or pressure pads for guiding the metal strip are further installed at one or a plurality of positions between the induction coils of the induction heating device installed in the vertical heating furnace. It is a continuous heat treatment device for metal strips.

According to a third aspect of the present invention, the metal strip after cleaning is adjusted to have a shape distortion of 30 mm or less by a tension leveler, and then at a heating rate of 200 ° C./sec or less, 70% or more of the entire heating temperature of the metal strip. The method for continuous heat treatment of a metal strip is characterized in that induction heating is performed by an induction heating device installed in a vertical heating furnace up to the temperature.

[0019]

First, the arrangement and function of the equipment used in the present invention will be described. First of all, the cleaning equipment is not just for cleaning the surface of the metal strip. To exert the function of the tension leveler, such as facilitating tension adjustment by removing foreign matter and oil adhering to the surface of the metal strip, and preventing scratches on the surface of the metal strip due to adhesion and transfer of these deposits to the roll. Is essential to.

In the tension leveler, bridle rolls are installed in front of and behind the leveler for applying tension to the metal strip. The bridle roll is in contact with the metal strip at a large contact angle (180 degrees or more), and tension is applied to the metal strip by the frictional force with the metal strip. Therefore, in order to secure this frictional force, it is necessary to remove a substance that reduces the frictional force such as oil on the surface of the metal strip, and for that purpose, it is necessary to install a cleaning facility before the tension leveler.

Next, the tension leveler should be placed before the looper. This is because by placing the tension leveler in front of the looper, the tension of the metal strip in the tension leveler can be appropriately set independently of the tensions of the looper and the heating furnace. Furthermore, by adjusting the shape of the metal strip before the looper with the tension leveler, there is an effect that the flap of the metal strip in the looper and the meandering due to it can be prevented.

After the looper, a vertical heating furnace having an induction heating device as a main heating means is installed. Here, the vertical heating furnace having an induction heating device as a main heating means is a vertical heating furnace having only an induction heating device or an auxiliary furnace such as a preheating furnace before the induction heating device. Say

In the induction heating device of the present invention, since the fluttering of the metal strip is small as described above, the distance between the winding of the induction coil and the metal strip may be small. FIG. 7 is a diagram showing the relationship between the shape distortion of the metal strip and the flapping of the metal strip. The distance between the upper and lower furnace rolls is 25 m. Here, the shape distortion of the metal band is represented by the height a of the crest caused by the distortion of the metal band when the metal band is placed on a surface plate or the like without applying tension. It can be seen that as the shape strain a of the metal strip increases, the flapping of the metal strip sharply increases. This tendency is not so remarkable when the distance between the upper and lower furnace rolls is about 15 m, but is not negligible in a vertical furnace having a length of more than 20 m as in the case of this figure.

From this figure, when the shape distortion a is 20 mm, the fluttering is ± 60 mm at the reference position, and similarly, when a is 30 mm and the fluttering is about ± 90 mm, the fluttering becomes ± 150 mm or more when a becomes 50 mm. From this, it is understood that when it is desired to set the distance between the winding of the induction heating coil and the metal strip to about 100 mm, the shape strain a of the metal strip is set to 30 mm or less.

In the induction heating furnace, the metal strip is heated to preferably 70% or more of the entire heating temperature, but if it is about 60%, it is necessary to heat the remaining 40% in the subsequent furnace. This is because a heating rate equivalent to that of induction heating is required. Although there is only a direct fire method such as heating rate other than induction heating, when using a direct fire method of about 40%,
The problems of the direct fire method mentioned above come out.

The upper limit of heating in the induction heating furnace may be the entire heating temperature as long as the temperature control by the induction heating can be accurately performed, but in practice, it may be set to a slightly lower temperature at which the induction heating does not overheat. When the metal strip is a steel strip, when it exceeds 700 ° C., it approaches the magnetic transformation point, and the efficiency of induction heating is lowered due to the decrease in magnetic permeability, so the temperature around this becomes the upper limit temperature. If the heating rate is too large, the shape disorder of the metal strip becomes large, so the upper limit is set to 200 ° C./sec, where the shape disorder of the metal strip is relatively small.

[0027]

EXAMPLE FIG. 1 is a view showing an example in which the present invention is applied to continuous annealing equipment for cold rolled steel strip. Here, 1 is a steel strip, 1
0 is a pay-off reel, 20 is a metal strip connection facility, 30 is a cleaning facility, 40 is a tension leveler, 41 and 4
2 is a bridle roll, 50 is a looper, 60 is an induction heating furnace, 70 is a radiant tube heating furnace, 80 is a soaking furnace, 90 is a quenching zone, 100 is an overaging furnace, 110 is a cooling zone, 120 is an exit side looper, 130 is a temper rolling mill, 140 is an oil coating / inspection facility, and 150 is a tension reel.

FIG. 2 is a view showing the details of the heating furnaces 60 and 70. In this example, the first three passes are induction heating furnaces. In the figure, 61 is an induction coil and 71 is a guide roll. Following the induction heating furnace, although not shown in the figure, a heating furnace equipped with heating means such as a radiation tube system is installed. Here, instead of the radiant tube system, an electric heater, an open flame burner, an open flame reducing burner or the like may be used.

FIG. 3 is a plan view of the induction coil. In the figure, 62 and 63 are cooling water inlets and outlets for induction coils, 65 is a bus for supplying power, 66 is a coil support beam, and 6
Reference numeral 7 is an insulating material, 68 is a furnace shell, and 69 is a heat insulating material. The induction coil is insulated and supported in the furnace, and a bus 65 for supplying power, a cooling water inlet 62, a discharge port 63, and the like penetrate the furnace shell 68 and are connected to the outside.

FIG. 4 is a side view of another type of induction coil. This induction coil has four turns, but the number of turns of the induction coil may be appropriately determined according to the frequency of the power source and the like.
The guide roll shown in FIG. 2 is provided so that the metal strip does not come into contact with the induction coil, but in the present invention, the flap of the metal strip is small, so that it is essentially unnecessary when the operation is stable. However, in the connecting portion of the metal strip, the shape of the metal strip cannot be adjusted even if a tension leveler is used for a portion (connection portion) 10 to 20 m before and after the connection portion. As a result, when the connecting portion of the metal strip passes through, the fluttering of the metal strip may increase in some cases.
Therefore, it is desirable to install these guide rolls.

FIG. 5 is a mounting view of the guide roll. In the figure, 72 and 73 are insulating materials, 74 is a bellows, 75 is an electric motor, and 76 is an insulating coupling. The guide roll of the embodiment is brought into contact with the metal strip at a predetermined winding angle in order to avoid slipping between the metal strip and the roll. In particular,
It is desirable to drive in synchronization with the line speed in order to prevent the occurrence of scratches when the metal strip comes into contact with the guide roll.
Even if the guide roll is not a set of two rolls,
It may be a book or a set of three books.

The guide roll 71 is provided between the induction coils 61, but instead of the guide roll, a pressure pad for suppressing the fluttering of the metal band by the pressure of the gas jet may be used. FIG. 6 is a view showing the arrangement of the pressure pads, and 79 shows the pressure pads. In the figure,
Pressure pad 7 near the edge of the metal strip and in the center of the plate width
9 are installed.

Since the pressure pad is operated using the atmospheric gas of 600 to 900 ° C. for the gas jet, a blower for the high temperature gas is required. This is disadvantageous from the viewpoint of equipment cost, but it is also desirable to reduce the number of contact between the metal strip and the guide roll by using it together with the guide roll from the viewpoint of preventing the occurrence of scratches as much as possible.

These guide rolls and pressure pads may be used all the time, or may be used in accordance with the passage of the connecting portion of the metal strip. In that case, the guide roll 71 may be normally retracted from the metal band 1, and the pressure pad 79 may be operated by stopping the blowing of the gas jet.

The heat treatment method for the metal strip by this continuous heat treatment apparatus will be described. Steel strip 1 is a cleaning facility 30
The oil and fat on the surface of the steel strip and the adhered iron powder are removed with the steepness 1
The steel strip having a hardness of about 5% has a flatness of about 0.1 to 0.5% by the tension leveler 40. This reduces the shape distortion of the steel strip to 30 mm or less. Then, it is guided to the induction heating equipment 60 via the looper 50. With this induction heating equipment, the temperature of the steel strip is heated from room temperature to 600 ° C at a maximum heating rate of 150 ° C / sec. Then, it is heated to a predetermined heating temperature (for example, 700 ° C.) in the radiant tube heating furnace 70 or the like, and subjected to subsequent processing such as soaking and cooling.

FIG. 8 is a diagram showing the relationship between the steepness of the steel strip before heating and the shape disorder due to heating. The shape strain a was used as an index of the shape disorder of the steel strip. As the heating rate increases,
The shape disorder of the steel strip becomes large, but it depends on the steepness before heating. When the steepness λ is 2%, the shape disorder rapidly increases at a heating rate of 50 ° C./sec. However, when the steepness λ of the steel strip is set to 0.5% according to the present invention, a region where the shape disorder is small is small. Expanded to around 200 ° C / sec.

FIG. 9 is a diagram showing the relationship between the type of continuous heat treatment equipment and the operation results. In the figure, the horizontal axis represents the transport speed of the steel strip, that is, the line speed, and the vertical axis represents the frequency of so-called strip abnormalities such as deceleration due to meandering and line stop due to breakage of the steel strip, converted per month. In the figure, region A is the continuous heat treatment apparatus of the present invention described above, B is a continuous heat treatment apparatus using only the conventional radiation tube system, and C is a continuous heat treatment apparatus that combines a tension leveler and a conventional radiation tube type heating furnace. The operating results by

In the continuous heat treatment apparatus using only the radiant tube system (region B), the frequency of sheet passing abnormality increases as the line speed increases, and the line speed exceeds 500 times per month at 15 times. In the continuous heat treatment device (region C) that combines the tension leveler and the conventional radiant tube type heating furnace, the increase in the frequency of stripping abnormalities due to the increase in the line speed is slightly suppressed, but it exceeds 15 times a month at 900 mpm. Like On the other hand, in the device of the present invention (area A),
Even if the line speed increases, the frequency of strip passing abnormally does not increase so much, and it is less than 10 times a month up to around 1400 mpm.

[0039]

In the continuous heat treatment apparatus of the present invention, by appropriately disposing the tension leveler, the shape of the metal strip is adjusted within a predetermined range, and the flapping of the metal strip in the vertical furnace is suppressed. As a result, the induction heating system can be used in a vertical heating furnace in earnest. Further, the distance between the winding of the induction coil and the metal strip can be reduced, and the capacity of the induction coil and the power source can be reduced. Further, by using the continuous heat treatment apparatus of the present invention, operational troubles such as meandering and drawing of the metal strip due to defective shape of the metal strip can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an example in which the present invention is applied to continuous annealing equipment for cold rolled steel strip.

FIG. 2 is a diagram showing details of a heating furnace.

FIG. 3 is a plan view of an induction coil.

FIG. 4 is a side view of another type of induction coil.

FIG. 5 is a mounting view of a guide roll.

FIG. 6 is a view showing the arrangement of pressure pads.

FIG. 7 is a diagram showing the relationship between the shape distortion of the metal strip and the flapping of the metal strip.

FIG. 8 is a diagram showing a relationship between steepness of a steel strip before heating and shape distortion after heating.

FIG. 9 is a diagram showing the relationship between the type of continuous heat treatment apparatus and the operation results.

[Explanation of symbols]

 1 Metal Band 30 Cleaning Equipment 40 Tension Leveler 50 Looper 60 Induction Heating Furnace 61 Induction Coil 71 Guide Roll 79 Pressure Pad

Claims (3)

[Claims] 1. A vertical heating furnace having cleaning equipment, a tension leveler installed after the cleaning equipment, a looper installed after the tension leveler, and an induction heating device as a main heating means installed after the looper. And a continuous heat treatment device for metal strips. 2. The metal according to claim 1, wherein a guide roll or a pressure pad for guiding the metal strip is installed at one or a plurality of positions between the induction coils of the induction heating device installed in the vertical heating furnace. Belt continuous heat treatment equipment. 3. The metal strip after cleaning is adjusted to have a shape distortion of 30 mm or less by a tension leveler,
Then, a continuous heat treatment method for a metal strip, characterized by performing induction heating at a heating rate of 200 ° C. or less per second to a temperature of 70% or more of the entire heating temperature of the metal strip by an induction heating device installed in a vertical heating furnace. .