JP4466086B2 - Hot dip galvanizing equipment and control method thereof - Google Patents

Description

  The present invention relates to a hot dip galvanizing facility and a control method thereof.

  In a hot dip galvanizing facility having a direct-fired alloying furnace, a metal plate such as a steel plate (which also includes a metal strip, the same shall apply hereinafter) directly immersed in a molten zinc bath and adjusted in the amount of plating is directly applied. The metal component (iron in the case of a steel plate) in the metal plate is diffused into the galvanized layer by heating at a metal plate temperature of 400 to 600 ° C in a fire type alloying furnace (hereinafter referred to as an alloying furnace). Heat treatment is performed. A schematic diagram of the alloying process of the plating layer in this alloying furnace is shown in FIG.

  In the figure, 1 is a snout, 2 is a zinc plating bath, 3 is hot dip zinc, 4 is an adhesion amount control device, 5 is an alloying furnace, 10 is a hot dip galvanizing facility, and a metal plate on which S is plated (FIG. 1). In the example, a steel plate), the arrow in the figure is the conveying direction.

  By the way, when alloying is promoted and the content of metal components such as iron in the plating layer increases, a fragile plating layer having a Γ phase is generated, and when the metal plate is deformed by a press or the like, the powder is peeled off. Ring failure will occur. On the other hand, when the degree of alloying is insufficient, a color defect called “burn-out unevenness” occurs. In other words, the metal component content (degree of alloying) such as iron in the plating layer has an appropriate range, but the alloying speed varies depending on the material, plating thickness, zinc bath component, and the like. For this reason, in the hot dip galvanizing equipment (also referred to as a hot dip galvanizing line) 10, the alloying furnace 5 before and after the joint (stepped point) of the preceding metal plate and the succeeding metal plate whose materials, plating thickness, plate thickness, etc. are changed. It is necessary to change the temperature rising rate of the metal plate (S) inside. This is because the metal plate must be transported at the same transport speed before and after the joint between the preceding metal plate and the succeeding metal plate due to the characteristics of a continuous facility such as a hot dip galvanizing facility.

  In general, (1) direct furnace method, (2) induction heater method, and (3) induction heater + direct furnace method are used as heating means of the alloying furnace. In the method (1), as shown in FIG. 2, the furnace wall is heated by a direct flame of a short frame gas burner 52, and the metal plate (S) is heated by radiant heat transfer from the furnace wall. For this reason, the heating rate of the metal plate is linked to the furnace wall temperature, but in a direct-fired alloying furnace, the time required to change the furnace wall temperature is long, and it takes 1 to 2 minutes. Unfortunately, before and after the stepping point, there are many cases where defects due to the loss of alloying occur.

  On the other hand, the methods (2) and (3), although sufficient control responsiveness when changing the heating rate of the metal plate before and after the stepping point, are very expensive compared to the direct-fired alloying furnace. There is a problem to become.

  In order to solve this problem, the inventors previously installed a flame heating type burner 52 in the lower part of the alloying furnace 5 as shown in FIG. In addition, an inexpensive and highly responsive alloying control method was proposed even for direct-fired alloying furnaces.

Japanese Patent Application No. 2002-200781

  However, in the direct flame type alloying furnace using the conventional flame heating type burner, the alloy temperature is controlled by controlling the flow rate of fuel and air in the burner. There was a problem that stable control could not be performed, such as hunting of control.

  The present invention provides a hot-dip galvanizing facility and a control method thereof capable of controlling the temperature of a highly reliable and stable metal plate that solves the above-described problems, and the surface defects of the metal plate due to a poor degree of alloying are provided. It is an object to suppress the occurrence.

The present invention is directed to a direct-fired hot-dip galvanizing facility that performs alloying using only a direct-fired alloying furnace , by directly applying a flame generated by combustion to a metal plate at the lower part of the direct-fired alloying furnace. A frame heating type burner for jet heating the plate, a moving unit capable of approaching and separating the burner from the metal plate, and a control device for variably controlling the distance between the metal plate and the burner by the moving unit providing the door, a structure capable of changing the distance between the metal plate and the bar Na, is obtained by solving the above problems.

  The present invention also provides a control method for hot dip galvanizing equipment, wherein alloying control is performed by controlling the distance between the metal plate and the burner using the hot dip galvanizing equipment. Is.

  According to the present invention, in a hot dip galvanizing facility having a direct-fire type alloying furnace, a frame heating type burner is disposed at the lower part of the direct-fire type alloying furnace, and the distance between the metal plate and the burner is controlled. This makes it possible to control the temperature of the metal plate with high response and stability, thereby suppressing the occurrence of surface defects due to poor alloying.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The present embodiment schematically shows a hot-dip galvanizing equipment 10 having a direct-fire type alloying furnace 5 provided with a flame heating burner 52 schematically shown in FIG. 1 and FIG. The basic structure of the fire-type alloying furnace 5 is followed.

  Here, the flame heating type burner 52 is installed below the refractory partition wall 51 of the direct-fired alloying furnace 5 and overcomes a large amount of air entering from the lower part of the furnace due to the chimney effect. The fuel gas is mixed with the air discharged at 100 m / s or more and burned so that the jet heating with the S frame (hot gas) is possible.

  In the present invention, the additionally installed portion is a portion surrounded by a broken line. 54 is a moving means such as a hydraulic cylinder that can move the burner 52 closer to and away from the steel sheet S, 56 is a control device that variably controls the distance between the steel sheet S and the burner 52 by each moving means, and 58 is a process computer. is there. The moving means 54 is not limited to a hydraulic cylinder, and may be anything such as a servo motor or an electric motor as long as the position can be controlled intermittently or continuously, and may be other than those listed here.

  3A and 3B are enlarged views of the frame heating type burner 52. FIG. 3A is a perspective view and FIG. 3B is a cross-sectional view of the frame heating type burner 52. As shown in FIG. ”Is a mechanism for injecting air from the shadow-colored holes labeled“, ”and fuel gas from the white holes labeled“ fuel ”. As shown in FIG. Air that is marked “Air” and fuel gas that is marked “fuel” are supplied from a separate piping system, and the flame F generated by combustion is applied to the steel sheet S to heat the steel sheet S by jet heating. It is a mechanism.

  FIG. 4 shows a change in the heating capacity of the steel plate when the flow rate of the burner fuel and air is changed in the hot dip galvanizing equipment 10 having the direct flame type alloying furnace 5 in which the flame heating type burner 52 is installed. Show. When the fuel flow rate is reduced, the method of shortening the length of the frame F is abrupt. Therefore, the reduction rate of the steel sheet heating capacity is larger than the reduction rate of the fuel flow rate, and the fuel flow rate (the length of the frame F is set by the air flow rate). It can be said that it is very difficult to control the alloying by controlling the air flow rate because the air flow rate may be changed. The cause is that the flame F (hot gas) speed decreases due to a decrease in the flow rate of fuel or air, the temperature of the frame F decreases, and the lower part of the direct-fire type alloying furnace 5 that is suppressed by the frame curtain. Increase of intrusion air.

  Thus, as a result of intensive studies, the inventors have realized that good alloying control can be achieved by controlling the distance between the steel plate and the burner, leading to the present invention. FIG. 5 shows a change in the heating capacity of the steel plate when the distance between the steel plate and the burner is changed. By controlling the distance between the steel plate and the burner to, for example, 100 to 400 mm, preferably 200 to 400 mm, the steel plate heating capacity can be controlled gently and almost linearly, and the flow rate of fuel or air is kept constant. Thus, since only the controllable object such as the mechanical distance is changed, problems such as hunting are hardly caused, and the stability of control can be ensured.

  An embodiment of the present invention is shown in FIG. A comparison of the operating conditions when a preceding material (0.6 t × 1000 w) is passed at a plate speed of 60 mpm and a succeeding material (1.2 t × 1000 w) is passed is shown. In addition, a rapid heating zone of 3.5 m is installed at the bottom of the alloying furnace. Appropriate operating conditions are input to the process computer, and the operating conditions are automatically changed when the coil stepping point passes through the alloying furnace. When the flow rate of the fuel or air is controlled as in the conventional case indicated by the broken line, the controllability is greatly deteriorated after passing through the stepped point and the alloying failure (burn-out unevenness) occurs. However, as shown by the solid line, the present invention Thus, it can be seen that the temperature of the highly responsive steel sheet S can be controlled, and a steel sheet having an appropriate degree of alloying can be obtained.

  The object of application of the present invention is not limited to steel plates, and can be applied to metal plates in general.

Schematic cross-sectional view schematically showing a hot-dip galvanizing facility with a direct-fired alloying furnace Sectional drawing which expands and shows the alloying furnace part of FIG. (A) perspective view and (b) cross-sectional view showing an enlarged frame heating type burner. The figure which shows the mode of the change of the heating capability of the steel plate at the time of changing the flow rate of the fuel and air of the burner The figure which shows the mode of the change of the heating capacity of a steel plate when the distance between a steel plate and a burner is changed The figure which shows the Example of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Snout 2 ... Zinc bath 3 ... Zinc 4 ... Adhesion amount control apparatus 5 ... Alloying furnace 10 ... Hot-dip galvanization equipment 52 ... Flame heating type burner 54 ... Moving means 56 ... Control apparatus 58 ... Process computer S ... Steel plate F …flame

Claims (2)

In direct-fired furnace galvanizing equipment that performs alloying only with direct-fired alloying furnaces,
In the lower part of the direct-fired alloying furnace , by placing a flame generated by combustion directly on the metal plate, a flame heating type burner for jet-heating the metal plate is disposed,
Moving means capable of approaching and separating the burner from the metal plate;
A controller for variably controlling the distance between the metal plate and the burner by the moving means;
Galvanizing, characterized in that it has a structure capable of changing the distance between the metal plate and the bar burner.   A control method for a hot dip galvanizing facility, wherein alloying control is performed by controlling the distance between the metal plate and the burner using the hot dip galvanizing facility according to claim 1.

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