JPH0762512A - Method for decreasing amount of zinc vapor in snout for zinc-aluminum alloy plating - Google Patents

Abstract

PURPOSE:To prevent the evaporation of excess Zn from a hot dip Zn-Al alloy coating bath by floating a ball-shaped material made of ceramics on the surface of the coating bath in a snout at the time of plating a steel strip by immersing this steel strip into the coating bath via the snout. CONSTITUTION:The steel strip W got out of a continuous annealing furnace 11 is passed through the inside of a down chute 21 and the snout 31 and is introduced into the hot dip Zn-Al alloy coating bath A in a pot 41, by which the surfaces of the steel strip W are hot dip coated with the Zn-Al alloy. The steel strip is then pulled up from the coating bath A by a sink roll 61. The Zn in the Zn-Al alloy coating bath is lower in melting temp. than Al and evaporates in a larger amt. The vapor thereof flows back into the down chute 21 and the annealing furnace 11 and sticks and deposits on their inside surfaces. There is thus a defect that this vapor partly sticks to the steel strip W and generates a coating defect. The ball-shaped material 51 made of the ceramics is floated on the surface of the coating bath A in the snout 31 in order to prevent such defect. The exposed surface of the coating bath surface in the snout is thus decreased and the excess evaporation of the Zn is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing the amount of zinc vapor inside a snout in zinc-aluminum alloy plating. The continuously annealed metal strip is subsequently immersed in a plating bath to plate its surface. For example, when applying zinc-aluminum alloy plating to the surface of a steel strip, the extraction port of the continuous annealing furnace,
Steel extracted from a continuous annealing furnace by connecting a plating facility including a down chute, a snout attached to the lower end of the down chute, a pot arranged in association with the snout and a sink roll attached to the pot, and the like. The manufactured strip is immersed in a molten zinc-aluminum alloy plating bath stored in a pot through a down chute and a snout, and then taken out from the alloy plating bath through a sink roll. The present invention relates to a method for reducing the amount of zinc vapor inside a snout during the above zinc-aluminum alloy plating.

[0002]

2. Description of the Related Art Conventionally, zinc plating equipment has been diverted to zinc-aluminum alloy plating (Japanese Patent Laid-Open No. 4-24).
7858). The snout used here has a width, that is, an inner diameter in the thickness direction of the metal strip of 250 to
It has a rectangular cross section of about 350 mm and has a wide cross section structure with a considerable margin for the metal strip. By the way, when galvanizing a metal strip, the molten zinc in the pot is heated and held at about 460 ° C. in relation to the melting point of zinc. On the other hand, when the metal strip is plated with zinc-aluminum alloy, the molten zinc-aluminum alloy in the pot has a melting point of 600 to 600.
It is heated and held at about ℃. When zinc-aluminum alloy plating is applied, the amount of zinc vapor generated is necessarily larger than when zinc plating is applied to the metal strip.

Whether the metal strip is galvanized or zinc-aluminum alloy plated,
The outlet end of the snout is immersed in the plating bath. Since the snout has the wide sectional structure as described above, the surface area of the plating bath surrounded by the snout is correspondingly large. As described above, when zinc-aluminum alloy plating is applied to the metal strip, the amount of zinc vapor generated is necessarily larger than when zinc plating is performed, but the amount of zinc vapor generated inside the snout is the above. It is proportional to the surface area, and thus a large amount of zinc vapor is generated inside the snout when the metal strip is plated with a zinc-aluminum alloy as compared to when the metal strip is plated.

The zinc vapor as described above flows back into the downshoot, and further into the furnace, so to speak, adheres and deposits on the inner wall surfaces thereof, and a part thereof adheres to the metal strip, resulting in defective plating. . Even if the down chute or the inside of the furnace is cleaned, the defective plating cannot be sufficiently prevented in reality, and the cleaning itself is very troublesome in itself, and the productivity is remarkably reduced.

[0005]

The problem to be solved by the present invention is that when zinc plating equipment is diverted and a metal strip is plated with a zinc-aluminum alloy, a large amount of zinc vapor is generated inside the snout. That is the point.

[0006]

DISCLOSURE OF THE INVENTION The present invention, however, provides a method of continuously dipping a continuously annealed metal strip in a plating bath through a down chute and a snout to apply a zinc-aluminum alloy plating to the surface thereof. The present invention relates to a method for reducing the amount of zinc vapor inside a snout in a zinc-aluminum alloy plating, characterized in that a plurality of ceramic balls are suspended inside the snout whose end on the outlet side is immersed in a plating bath.

In the present invention, the zinc-aluminum alloy plating is applied to the metal strip while the plurality of ceramic balls are suspended inside the snout whose end portion on the outlet side is immersed in the plating bath. The ceramic ball-like material floats in a molten zinc-aluminum alloy plating bath stored in a pot, has corrosion resistance to the alloy plating bath, and has poor wettability. Floating the ceramic balls inside the snout correspondingly reduces the surface area of the alloy plating bath surrounded by the snout, thus reducing the amount of zinc vapor inside the snout.

The ceramic balls are oxide-based such as alumina and zirconia, carbide-based such as silicon carbide and zirconium carbide, and nitride-based such as silicon nitride and zirconium nitride. Further, the material such as an oxynitride-based or boride-based material is not particularly limited, and the shape is not limited to a sphere, and may be a ball-shaped polyhedron as a whole. It is preferable that the ball-shaped material having an outer diameter of about 10 to 30 mm is suspended so as to form a multilayer of 2 to 4 layers. Further, by mixing and suspending such a ball-shaped material with a large-diameter one and a small-diameter one, the surface area of the alloy plating bath surrounded by the snout is further reduced, so that the amount of zinc vapor inside the snout is further reduced. It can be reduced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a longitudinal sectional view schematically showing an embodiment of the present invention, and FIG. 2 is a partially enlarged view thereof. A down chute 21 is attached obliquely downward to the extraction port of the continuous annealing furnace 11, and a snout 31 is attached to the lower end of the down chute 21 along the axial direction thereof. The outlet side end 32 of the snout 31 is immersed in the molten zinc-aluminum alloy plating bath A stored in the pot 41, and a plurality of ceramic ball-shaped objects 51 are suspended inside the snout 31. A sink roll 61 is attached to the pot 41. The metal strip W is a continuous annealing furnace 11
→ Down shoot 21 → Snout 31 (ceramic ball 51) → Molten zinc stored in pot 41-
The surface of the aluminum alloy plating bath A to the sink roll 61 is zinc-aluminum alloy plated.

According to one embodiment of FIG. 1, a metal strip was plated with a zinc-aluminum alloy under the following conditions. Conditions: metal strip; width 914 mm × thickness 0.5 mm steel strip; metal strip transport speed; 100 m /
Min, snout; rectangular cross section with inner diameter of 350 x 1700 mm, slant angle of snout; 30 degrees, ceramic balls; solid alumina balls with a diameter of 10 to 30 mm are mixed in size to be about 2 inside the snout. Alloy plating bath composition suspended in 4 layers: 43.4% by weight of zinc + 55% by weight of aluminum + 1.6% by weight of silicon, hot water temperature of the alloy plating bath: 600 ° C Zn vapor in the snout The generated amount was 95 g / hour. On the other hand, when the ceramic strip is not floated inside the snout and the metal strip is similarly plated with zinc-aluminum alloy,
The amount of Zn vapor generated inside the snout is 698 g /
It was time.

[0011]

As is apparent from the above, according to the present invention described above, the amount of zinc vapor generated inside the snout can be remarkably reduced when the continuously annealed metal strip is subsequently subjected to zinc-aluminum alloy plating. effective.

[Brief description of drawings]

FIG. 1 is a vertical sectional view schematically showing an embodiment of the present invention.

FIG. 2 is a partially enlarged view of FIG.

[Explanation of symbols]

11 ... Continuous annealing furnace, 21 ... Down shoot, 3
1 ... Snout, 32 ... Exit end, 41 ...
Pots, 51 ... Ceramic balls, 61.
..Sink rolls, A: molten zinc-aluminum alloy plating bath, W: metal strip

Claims (1)

[Claims] 1. When the continuously annealed metal strip is subsequently immersed in a plating bath through a down chute and a snout to subject the surface to zinc-aluminum alloy plating, the end portion on the outlet side is immersed in the plating bath. A method for reducing the amount of zinc vapor inside a snout in zinc-aluminum alloy plating, which comprises suspending a plurality of ceramic balls inside the snout.