JP2003027200A - Snout in continuous hot-dipping device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a snout in a continuous hot-dipping coating line, in particular, to restrain and prevent sticking and deposit of floated material generated on hot-dipping bath surface in the snout onto the inner surface of the snout (causing to damage to the surface quality of the hot-dip coated product). SOLUTION: The snout is formed with a thermal-sprayed film of ceramic having low wettability and reactivity to molten metal on an inner wall surface at the lower end part dipped into the hot-dipping bath. The ceramic film is desirably formed from CaO-SiO2 system or ZrO2 -SiO2 -CaO system ceramic. Further, it is desirable to form a laminated film by using as an under coat the thermal-sprayed film of alloy containing metallic component of one or more kinds among Co, Cr, Ni, W, Mo. The clean hot-dipping bath surface state having little floated material can stably be kept by performing the discharge of the floated material to the outer part with a snout pump in the hot-dipping coating operation at the suitable time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a snout of a continuous hot-dip galvanizing apparatus, and in particular, the plating bath surface in the snout is maintained in a good bath surface state with a small amount of floating matters, which results from the floating matters. It is intended to effectively suppress and prevent surface defects of plated products.

[0002]

2. Description of the Related Art In a hot-dip galvanizing line such as continuous hot-dip aluminum plating and hot-dip galvanizing, a strip of cold-rolled steel strip or the like, which is a material to be plated, is introduced from an annealing furnace into a plating bath through a snout. In FIG. 3, 1
Is an annealing furnace, 2 is a snout, and 3 is a molten metal plating bath. The snout (2) is installed so as to be inclined between the annealing furnace (1) and the plating bath (3), and the lower end portion is immersed in the plating bath (3). The material to be plated (strip) (W) is introduced into the plating bath (3) through the snout (2) and is plated by passing through the bath through the sink roll (4). The snout (2) is a member (cylindrical body made of heat-resistant alloy cast steel, etc.) for blocking atmospheric contact of the strip (W) and preventing oxidative contamination (which causes plating defects) on the strip surface, The inner space is kept in an inert atmosphere such as nitrogen gas.

On the surface of the molten metal plating bath, a suspended substance (F) is inevitably formed as shown in FIG. The suspended matter (F) is a molten or semi-molten fluid mainly composed of an oxide and is generally called a dross. The suspended matter (F) existing on the bath surface (3 ₁ ) in the snout (2) easily adheres to the surface of the strip (W) introduced into the bath, causing non-plating on the plated product, and dross. It is a cause of inducing surface defects called "pulling" and "bugs".

As a preventive measure, a method of sucking and discharging the suspended matter (F) by a pump (snout pump) to the outside is adopted. As shown in FIG. 2, this is because the suction duct is provided on one of the bath surface portions (a) and (b) near both ends of the strip (W), and the discharge duct (the molten metal sucked together with the suspended matter is drawn on the other side of the strip). Each time the pump is driven according to the condition of the bath surface monitored through the viewing window (not shown) of the snout, the amount of suspended solids is managed so as not to stay on the plating bath surface.

[0005]

In the hot dip galvanizing operation, the amount of suspended matter in the snout may temporarily increase rapidly, and the occurrence rate of surface defects of the plated product may increase. This phenomenon is caused by the fact that the suspended matter adheres and deposits on the inner wall surface of the snout, and the adhered deposit then remelts. As shown in FIG. 4, as the plating bath surface (3 ₁ ) descends from the position (a) of the chain line (the plating bath is gradually consumed as the plating operation progresses), the suspended matter on the bath surface snouts. It adheres (D) to the inner wall surface of (2).

After the plating bath surface level is lowered as described above, when the plating bath surface is raised (replenishment of the molten metal bath), the plating bath comes into contact with the deposit (D) and the deposit (D) is redissolved. Therefore, the amount of suspended solids in the snout increases rapidly. This rapid increase in suspended solids (F) cannot be dealt with by a snout pump alone,
The frequency of contamination (adhesion) of the material to be plated by the suspended matter (F) increases, and as a result, the occurrence rate of surface defects in the plated product increases. The present invention provides an improved snout to overcome the above problems in continuous hot metal plating operations.

[0007]

The snout of the continuous hot-dip galvanizing apparatus according to the present invention is capable of preventing the adherence of suspended matter on the inner wall surface of the lower end portion which is immersed in the hot-dip galvanizing bath in contact with the plating bath. As a protective film, a ceramic film having low wettability and reactivity with molten metal is provided and covered.

In the snout of the present invention, the surface of a required region is covered with a ceramic film (which blocks the contact between the snout base material and the molten metal), so that the floating substances accompanying the vertical movement of the plating bath surface are removed. Sudden increase (caused by re-dissolution of suspended solids on the inner wall surface) is suppressed and prevented. Thus in the plating operation, by timely implementing the eject operation of the suspended solids in the snout (F), and held plating bath surface (3 ₁₎ in a small clean state of suspended solids, resulting from suspended solids (F) Surface defects of plated products can be suppressed and prevented.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The snout of the present invention is produced by forming a ceramic film on a required area (a portion in contact with a molten metal plating bath) on the inner surface of a cylindrical body (snout base) made of a heat-resistant alloy. . FIG. 1 schematically shows the lower end portion of the snout (the portion immersed in the plating bath). (2 ₁ ) is a snout base, and (2 ₂ ) is a ceramic film that covers the inner wall surface of its lower end.

Preferred examples of materials for forming a ceramic film include CaO-SiO ₂ system and ZrO ₂ -SiO ₂ -C.
Examples include aO type. In CaO-SiO ₂ system, Ca
O: 40 to 70 mass%, SiO ₂ : 60 to 30 mass%,
In the ZrO ₂ —SiO ₂ —CaO system, ZrO ₂ : 6 to 30
_{mass%, SiO 2: 30~40mass%} , CaO: 30~5
It is preferably adjusted to a composition range of 5 mass%. In any case, in order to ensure low wettability and resistance to molten metal necessary to prevent adherence of suspended solids, inevitable impurities (TiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , MgO, HfO, etc.) )
Is preferably regulated to 15 mass% or less (total amount).

The thickness of the ceramic film is about 150-5.
A range of 00 μm is suitable. If it is thinner than this, the life of the coating is poor, and if it is too thick, peeling is likely to occur due to the difference in thermal expansion coefficient from the snout base (heat-resistant cast steel), and stability is impaired.

It is desirable to provide an undercoat and laminate the ceramic coating as a topcoat so that the adhesion of the ceramic coating to the snout substrate is enhanced and the function of preventing the adherence of suspended solids is stably maintained. The undercoat can be formed as a thermal spray coating containing one or more metal components selected from Co, Cr, Ni, W, Mo and the like. The thickness of the undercoat is about 10
It may be about 0 to 200 μm.

The thermal spraying of the undercoat and the ceramic coating is performed as a pretreatment in accordance with a conventional method by subjecting the target area of the surface of the snout substrate to surface cleaning (such as degreasing) and roughening (such as shot blasting). Appropriate thermal spraying techniques (oxygen / acetylene flame spraying, arc spraying, plasma spraying, etc.) may be used.

The ceramic coating applied by thermal spraying has poor surface smoothness as it is. Finishing the surface of the film to be smooth is effective in increasing the effect of preventing the adherence of suspended solids, and it is preferable to finish the surface roughness to Ra of about 6 μm or less and Rmax of about 18 μm or less.

The snout substrate of the present invention (2 ₁ )
In the same manner as the conventional one, the heat-resistant cast steel cylinders may be connected by a plurality of cylinders, and the undercoat and the ceramic coating formed by the thermal spraying may be formed at the bottom of the snout base that contacts the plating bath. The region including the vertical fluctuation range (for example, ± 100 mm) of the bath surface with respect to the inner wall surface of (2 ₁ ) may be targeted.

[0016]

[Example] The inner surface of the lower end side of a snout base (heat-resistant cast steel, equivalent to SCH12) was pretreated (cleaning and roughening),
A test snout is prepared through undercoating by plasma spraying and lamination of ceramics film and finish machining of the surface of the ceramics film, and is used for a test of actual use of a continuous hot dip aluminum plating line.

(1) Preparation of Snout (1.1) Sample Snout 1 Undercoat (alloy film) Composition (mass%): Cr 25%, Ni 5%, W 10%, C
o Remaining film thickness: 150 μm Top coat (CaO-SiO ₂ system ceramic film) Composition (mass%): CaO 44%, SiO ₂ 54% (impurity 2%) Film thickness: 250 μm Surface roughness: Ra 3 μm, Rmax 18 μm

(1.2) Test Snout 2 Undercoat (alloy film) Composition (mass%): Cr 8.5%, Mo 29%, Co balance film thickness: 150 μm Topcoat (ZrO ₂ —SiO ₂ —CaO ceramic film) Composition (mass%): ZrO ₂ 25%, SiO ₂ 30%, C
aO 43%, (impurity 2%) Film thickness: 200 μm Surface roughness: Ra 4 μm, Rmax 18 μm

(2) Actual machine test plating bath composition: Al-9% Si bath temperature 650 ± 20 ° C material to be plated: cold rolled carbon steel plate (plate width 800 x plate thickness 0.8, mm) The bath surface inside the snout The suspended matter (F) generated in (1) was discharged by a snout pump (suction ducts and discharge ducts were placed at positions a and b in FIG. 2) at appropriate times.

Table 1 shows the operation results of the above hot dip aluminum plating. The comparative example is the operation result using the conventional snout (the same as the invention example except that it does not have a ceramic film) (the operation of discharging the suspended matter by the snout pump is performed under the same conditions as the invention example).

[0021]

[Table 1]

As shown in the table, in the comparative example, the amount of suspended solids in the snout increased rapidly when the bath surface was raised, whereas in the inventive examples, the suspended solid amount hardly changed, and the good bath surface with few suspended solids was obtained. The condition is kept stable. This difference is due to the fact that in the comparative example, the suspended matter adheres to the inner wall surface of the snout, whereas in the inventive example, the phenomenon of adherence of the suspended matter is suppressed and prevented as an effect of the ceramic film. The effect of preventing adherence of suspended solids in the invention examples is also clearly shown in the difference in the surface state of the inner wall surface of the snout after use. As described above, in the invention example, as an effect of preventing the adherence of the suspended matter on the inner wall surface of the snout and maintaining the plating bath surface with less suspended matter, the occurrence rate of the surface defects of the product-plated steel sheet was significantly reduced to half of the comparative example. ing.

[0023]

INDUSTRIAL APPLICABILITY The snout of the present invention suppresses and prevents the adherence of suspended solids to the inner wall surface, which causes a rapid increase in the amount of suspended solids on the plating bath surface (the suspended solids adhered to the inner wall surface are regenerated as the bath surface rises). (Caused by dissolution) is prevented in advance. Therefore, in the molten metal plating operation performed using the snout of the present invention, by appropriately discharging the suspended matter to the outside by a pump or the like, the plating bath surface in the snout is stably maintained in a state in which the suspended matter is small, It is possible to suppress and prevent the surface defects of the plated product due to the suspended matter.
Further, as an effect of preventing adherence of suspended solids, the frequency of repairing the snout is reduced and the service life is improved, so that effects such as reduced maintenance and improved efficiency of the molten metal plating line can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a main part of a snout of the present invention.

FIG. 2 is a perspective view schematically showing the vicinity of the plating bath surface inside the snout.

FIG. 3 is a front view schematically showing a plating apparatus section of a continuous hot-dip metal plating line.

FIG. 4 is a cross-sectional explanatory view showing vertical movement of a plating bath surface in a snout and a state of adhered suspended matter on an inner wall surface of the snout.

[Explanation of symbols]

1: Annealing furnace 2: Snout 2 ₁ : Ceramics film 3: Molten metal plating bath (plating bath) 3 ₁ : Bath surface 4: Sink roll F: Floating matter (dross) D: Adhesion W: Plated material (strip) a, b: Duct opening position of the snout pump (suction port, discharge port)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yukihiko Hirooka             4-13-4 Fukaekita-cho, Higashinada-ku, Kobe-shi, Hyogo             No. Tokaro Corporation F term (reference) 4K027 AA05 AD10                 4K031 AA04 AB03 CB22 CB23 CB24                       CB48 DA01 DA03 DA04

Claims (4)

[Claims] 1. In a snout whose lower end is immersed in a molten metal plating bath, a ceramic sprayed coating having low wettability and reactivity with the molten metal is formed in a region of the inner wall surface which comes into contact with the molten metal. Snout for continuous hot dip metal plating equipment. 2. The ceramic sprayed coating is CaO: 4.
The snout of the continuous molten metal plating apparatus according to claim 1, which contains 0 to 70 mass% and SiO ₂ : 30 to 60 mass% and inevitable impurities are 15 mass% or less. 3. The ceramic sprayed coating is ZrO ₂ :
_{6~30mass%, SiO 2: 30~40mass%} , Ca
O: contains 30 to 55 mass% and inevitable impurities are 15 ma
The snout of the continuous hot-dip metal plating apparatus according to claim 1, which has a ss% or less. 4. A thermal spray coating comprising at least one metal component selected from Co, Cr, Ni, W and Mo is used as an undercoat, and a ceramic thermal spray coating is laminated thereon as a top coat. Snout of the continuous hot-dip metal plating apparatus as described in 2 or 3.