JPH06299310A - Method of preventing adherence of alloy to zinc plating roll - Google Patents

Abstract

PURPOSE: To provide a method for preventing the adhesion of a zinc alloy to respective surfaces of a sink roll and a support roll in hot dip galvanizing equipment.

CONSTITUTION: The adhesion of zinc to a roll is effectively prevented by combining a method where the physical adhesion of zinc dross is prevented by elevating the surface temp. of a roll 1 so that it is higher by 1-10°C than the temp. of the surrounding molten zinc alloy with a method where the alloying of zinc is prevented by coating the surface of the roll with a dense protective film. The protective film can be provided by means of PVC, CVD, plating or thermal spraying.

COPYRIGHT: (C)1994,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of preventing zinc alloy from adhering to sink rolls, support rolls, etc., which are used by being immersed in a zinc or zinc-aluminum alloy plating bath in a galvanizing manufacturing facility. .

[0002]

2. Description of the Related Art In order to improve the quality of galvanized steel sheets and the operating rate of a plant, preventing zinc alloy from adhering to the surfaces of sink rolls and support rolls is a major issue. As a conventional method of preventing zinc from adhering to a zinc alloy plating roll, a method of coating a self-fluxing alloy and a method of forming a thermal spray coating on the surface of the roll are typical.
The common point of these methods is to prevent the chemical reaction and alloying between zinc and the roll surface material by changing the material of the roll or the roll surface. However, the zinc alloy adhering to the surface of the roll is not necessarily a chemical adhering substance due to the reaction with zinc, and most thick adhering substances are physically adhering due to solidification of the zinc alloy. . For example, if the sync roll is MoB or W
Examination of the deposit on the sink roll coated with C-Co and used for galvanization revealed that the coating film underneath was not substantially attacked by zinc after the deposit was mechanically peeled off. . In recent years, in order to prolong the service life of zinc plating sink rolls, the properties of the coating itself, such as the selection of materials for the thermal spray coating, the improvement of the adhesion of the coating, the improvement of the denseness of the coating, the control of the surface roughness of the coating, etc. Although improvements have been made, the above-mentioned method often does not solve the problem with respect to the adhesion of such thick solidified matter.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is, unlike the above-mentioned method for preventing the adhesion of a zinc alloy to the roll surface by improving the roll material or the roll surface sprayed coating, the surface of the zinc alloy is solidified by the solidification. It is to propose a new method for preventing the adherence of metal, especially the thick zinc alloy.

[0004]

As a result of various studies, the inventors of the present invention have found that the amount of zinc alloy deposited on a roll surface coated with a thermal spray coating is governed by the composition of the zinc alloy and the temperature of the roll surface. It has been found that when a small amount of iron is dissolved in molten zinc, the dross solidifies and easily adheres to the surface of the roll. Chemical analysis of the composition of dross adhering to the roll surface, identification of the adhering matter by X-ray diffraction, and consideration of solidification starting temperature and phase transformation process of the adhering matter based on the ternary alloy phase diagram As a result, a method of preventing solidification and adhesion of dross on the roll surface was found, and the present invention could be achieved.

[0005]

The present inventor first chemically analyzed the composition of the dross attached to the surface of the galvanizing sink roll after use. The composition is shown in Table 1. The numbers in the table indicate wt%.

[0006]

[Table 1]

The composition of the deposit is mainly composed of Fe ₂ Al ₅ and δ ₁ phase. Since crystallization starting temperature of the Fe @ 2 Al ₅ phase is 1000 ° C. or more, Fe traces of dissolved in the galvanizing bath, further, by a roll surface temperature of only slightly lower than the surrounding zinc alloy temperature or roll, The Fe ₂ Al ₅ phase preferentially crystallizes on the roll surface due to the roughness of the surface and the crystal structure of the film on the roll surface, and then easily grows to form a stable deposit on the surface of the roll. The amount of deposition (adhesion amount) is Fe near the roll.
It increases with an increase in the dissolution amount of s and a decrease in the roll surface temperature. If the temperature of the roll surface is kept slightly higher than that of the surrounding liquid phase zinc alloy, that is, Fe ₂ Al
_{If the} degree of supercooling of crystallization of ₅ phases is large on the liquid phase side, Fe ₂ Al
_{The 5} phase preferentially crystallizes on the liquid phase side rather than the roll surface. Further, if the temperature of the roll surface is higher than the temperature of the surrounding liquid-phase zinc alloy, that is, if a negative temperature gradient is formed from the roll surface toward the molten zinc, the Fe ₂ Al ₅ phase will be formed on the roll surface. Even if it crystallizes
As shown in Fig. 2, the growth was in the form of fine dendrites of primary crystals, and the crystallized high melting point δ ₁ and Fe ₂ Al ₅ phases were exfoliated and dropped by the mechanical movement of the roll, and adhered to the surface of the roll. It seems that you cannot do it. For the above reasons, a method of heating the surface of the sink roll has been invented.

In an actual machine, the roll temperature tends to be slightly lower than the bath temperature. The reason why the surface temperature of the roll is slightly lower than the temperature of the surrounding zinc alloy is that the drive side of the roll is connected to an external drive member, so that the roll surface radiates heat due to heat conduction to the outside, or galvanization Since the temperature of the steel sheet in the bath is generally lower than the bath temperature, it is considered that the heat transfer from the sink roll surface to the steel sheet cools the roll surface.

If the temperature of the roll surface is higher than the temperature of molten zinc, the required amount of energy is large and the operation is difficult. On the contrary, if the temperature difference is too small, that is, F
If the e ₂ Al ₅ phase does not reach a degree of supercooling sufficient to preferentially crystallize in the liquid phase, the effect of preventing the zinc alloy from adhering is low. According to the calculation of the degree of supercooling required for nucleation, if the surface temperature of the roll is 1 to 10 ° C. higher than the temperature of the surrounding zinc alloy, the zinc alloy can be prevented from adhering to the roll surface. This will be described in detail below with reference to examples.

[0010]

EXAMPLES There are various methods for heating the surface of the roll, but the present invention proposes the following method. (A) An electric heating method, that is, a method in which a metal heating wire is wound around the surface of the roll as shown in FIG. 1 and an electric current is applied from the outside to heat the surface of the roll. (B) Liquid phase heating method, that is, a method in which molten zinc having a temperature higher than the ambient temperature of the roll is flown from one end of the roll to the inside of the roll to heat the surface of the roll, as shown in FIG. (C) Chemical reaction method, that is, a method in which a chemical reaction agent is put inside the roll or on the surface of the roll and the surface of the roll is heated by heat of the chemical reaction. (D) Electromagnetic induction method, that is, a method of heating the surface of the roll by electromagnetic induction.

As a prior art seemingly similar to the present invention, there is an invention disclosed in Japanese Patent Laid-Open No. 254561/1992. In this invention, in order to increase the efficiency of alloying after hot dip galvanizing,
In a sink roll for hot metal plating, a method has been proposed in which a heating means is provided inside the roll and the roll is heated from the inside to heat the metal material to be plated that comes into contact with the roll. Although the above publication does not clearly describe the range of heating temperature, if the purpose of heating in the disclosed invention is to increase the efficiency of alloying, considering from the diffusion rate of alloying. , Roll 1-10
Even if the temperature is raised to about ℃, its effect is very small. further,
Even if the temperature of the metal material that comes into contact with the surface of the roll is raised by about 10 ° C. from the temperature of the molten bath by the method disclosed in the above publication, the metal material is then sent to a direct-fired heating furnace. In addition, since there is a portion in contact with molten zinc, the temperature of the metal material actually sent to the direct-fired heating furnace drops to a temperature close to the bath temperature. Therefore, roll the roll at 10
Even if heated to a certain degree, the initial purpose cannot be achieved. That is, in order to achieve the object of the invention disclosed in the above-mentioned publication, unlike the case of the present invention, it is substantially several tens
It is necessary to heat the rolls above ℃. But,
From the theoretical calculation, it is sufficient to raise the surface temperature of the roll by 1 ° C. or more in order to achieve the purpose of the present invention, that is, the purpose of preventing nucleation and solidification. Although the object of the present invention can be achieved by further heating the roll surface, the effect is the same even if the temperature of the roll surface is raised above 10 ° C., and the heat energy is wasted. is there.

By the above-mentioned method, that is, by making the surface temperature of the roll higher than the temperature of the surrounding molten zinc alloy, physical adhesion can be prevented, but this alone does not always give a sufficient effect. Absent. In order to solve the above-mentioned problem, actually, on the surface of the steel roll,
The surface of the roll is coated by a method such as coating a ceramic simple substance of WB, MoB, WC and MoC which does not react with Zn and Al or at least one material selected from cermet materials containing a metal binder to form a protective film. It is necessary to prevent the reaction of Zn with Zn. As materials for the protective film of the roll, other than the above, Z
It is also possible to use the substances which do not react with n to achieve the object of the present invention. For example, metal silicides are known to have low wettability with zinc.

The high density of the protective film of the roll is an important factor for preventing the penetration of zinc into the roll surface.
PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), plating, and thermal spraying are used to form the protective coating. However, the present invention does not limit the method of forming the protective film, and methods other than the above can be applied.

[0014]

The present invention is configured as described above,
A method for preventing physical zinc dross from adhering by increasing the temperature of the surface of the galvanizing sink roll above the temperature of the molten zinc alloy around the roll, and by covering the surface of the roll with a highly dense protective film. By combining with a method for preventing zinc alloying, it has become possible to efficiently prevent zinc from adhering to the roll.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an electric heating method as an example of a mode of heating the surface of a sink roll in a galvanizing manufacturing facility according to the present invention.

FIG. 2 is a schematic diagram showing physical adhesion on the surface of a sink roll in a galvanizing manufacturing facility.

FIG. 3 is an explanatory view showing a liquid phase heating method as an example of a mode of heating the surface of a sink roll in a galvanizing manufacturing facility according to the present invention.

[Explanation of symbols]

 1 sink roll 2 molten zinc bath 3 heating device

Claims (3)

[Claims] 1. In a hot-dip galvanizing equipment for steel sheets, the surface temperature of the sink roll or the support roll is increased by 1 to 10 ° C. higher than the temperature of the molten zinc alloy around the roll,
A method for preventing the zinc alloy from adhering to the roll surface. 2. A WB or Mo that does not react with Zn and / or Al as the sink roll and the support roll.
2. The method according to claim 1, wherein the ceramics of B, WC and MoC are used alone, or those coated with a protective film made of at least one material selected from cermet materials containing them and a metal binder. 3. The method according to claim 2, wherein the protective film is provided by PVD (physical vapor deposition method), CVD (chemical vapor deposition method), plating or thermal spraying method.