JPH09111430A - Hot metal plating bath recycling method and equipment - Google Patents

Abstract

(57) Abstract: A method and apparatus for continuously reducing and regenerating dross in a continuous hot-dip metal plating bath are provided. SOLUTION: A recovery device for recovering dross on a molten metal plating bath, a transfer device for transporting the dross, a continuous reduction induction heating furnace, and a plating bath supply pipe are provided, and the dross is continuously heated by heating in a reducing atmosphere. Regenerate and supply to the plating bath. [Effect] According to the present invention, the dross consisting of oxides generated in the molten metal plating bath is continuously regenerated and effectively used, and at the same time, the dross floating on the bath surface is removed to produce a high-quality plated steel sheet. To enable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous hot-dip galvanizing method for steel sheets, and more particularly to a method for effectively reclaiming galvanized metal from dross of hot-dipped metal.

[0002]

2. Description of the Related Art As a method for continuously plating a steel sheet,
Methods such as hot dipping, electroplating and vapor deposition are known. Among them, the hot-dip plating method is capable of thickening the plating film, capable of high-speed plating, capable of low-cost plating, and, in principle, all metal plating is possible as compared with other methods. Due to these characteristics, the hot dipping method is widely used for corrosion-resistant plating of building materials and structural materials.

Of the hot-dip galvanizing methods, hot-dip zinc, hot-dip aluminum, or alloy plating methods of these metals are the mainstream, and CGL (Con
A continuous plating line called tinuous Galvanizing Line) is in practical use.

[0004] In CGL, a cold-rolled steel strip is introduced into an annealing furnace-cooling zone whose atmosphere is controlled to incinerate and activate the oil remaining on the surface and perform annealing heat treatment. Then, the plate is dipped in a molten metal plating bath while maintaining the atmosphere, and then the high-pressure air is blown while being pulled up into the air, the thickness of the plate is adjusted by so-called gas wiping, and then cooled to obtain a plated steel sheet. Since the bath surface of this plating bath is exposed to the atmosphere, the iron eluted from the steel sheet due to oxidation reacts with the zinc bath component to generate intermetallic compound particles (dross). There is a problem that these particles adhere to the plating layer of the steel sheet and deteriorate the appearance. In particular, dross adhesion of an alloyed zinc-plated steel sheet used for an outer panel of an automobile becomes a surface flaw at the time of molding. Further, the generation of such dross leads to consumption of zinc as a plating component. Currently, only the suspended top dross is regularly collected. As a method to make it easier to collect this dross and to prevent the consumption of zinc, Material and Process 128th (Autumn)
As described in CAMP-ISIJ Vol.7 (1994) -1531 at the lecture meeting, by adding 0.12% or more of Al in the bath, Fe-Al having a lower specific gravity than the zinc bath.
There is a method to generate dross. However, even if this method is used, the Fe-Zn dross can be reduced only by about 50%, and the zinc that has become dross cannot be recovered.

[0005]

As described above, the conventional continuous hot-dip metal plating method gives sufficient consideration to the corrosion resistance and high-speed productivity of plated steel sheets, but it is almost impossible to control the plated metal itself. It was not considered. That is, there is a problem in that the plating metal cannot be effectively used because the top dross that is inevitably generated during plating is not considered and regenerated. Even with the method of adding Al, the Fe-Zn dross can be reduced only by about 50%, the zinc that has become dross cannot be recovered, and this is not an essential solution.

The present invention solves the above-mentioned drawbacks of the prior art, and provides a method and equipment for continuously reducing top dross floating on the surface of a plating bath or in a bath near the surface to effectively use it as a plating metal. To do.

[0007]

[Means for Solving the Problems] As a means for continuously regenerating the top dross of a molten metal plating bath and effectively utilizing it as a plating metal, by heating in a dross reducing atmosphere floating on the bath surface to reduce the dross, It can be recovered by separating the zinc. By introducing a series of processes including recovery of dross, separation of dross, transportation, heat reduction dissolution, and supply of regenerated plated metal in this method, the plated metal can be effectively utilized continuously. That is, in order to collect the dross floating on the bath surface, an electromagnetic pump, a bath surface flow vane by a robot, or a combined device thereof is used to collect the floating dross at a predetermined place. The collected dross is entirely transferred to a heating reduction furnace by a transfer device composed of a mesh belt which is kept at a temperature equal to or higher than the melting point of the plating metal, and continuously charged.
At this time, excess molten zinc adhering to the dross is separated from the dross and returned to the molten zinc bath. In the heating reduction furnace, the molten metal is heated to a temperature equal to or higher than the melting point of the dross to be reduced to the original molten metal and continuously discharged from the lower part of the furnace. The reduced molten metal is returned to the plating bath again by a supply pipe whose internal atmosphere is kept at a temperature that is reducing and above the melting point, and is reused.

The dross recovery device collects metal oxides floating on the surface of the molten metal plating bath and its vicinity in a predetermined place,
It acts to load on the transfer conveyor. That is, the electromagnetic pump has a suction port of the pump installed near the surface of the molten metal, sucks the molten metal, and conveys the molten metal onto the mesh belt. This causes the plating metal near the bath surface to flow.
Due to the flow of the plating metal, at the same time, so-called dross floating in the vicinity of the surface is sucked together with the molten metal and conveyed on the mesh belt. The bath surface fluidizing blade mechanically moves on the bath surface to scrape floating dross and places it on a mesh belt. At this time, since the plating bath is made of high-temperature molten metal, the operation of the fluidized blade is preferably performed by a robot. The robot effectively follows the change in the flow state of the bath due to various factors such as the passing speed of the plated steel sheet and effectively operates the flow vanes to efficiently collect the dross and load it on the mesh belt.

The mesh belt of the transfer conveyor conveys the dross from the plating bath to the heating reduction furnace. The mesh belt has a function of separating the dross from the hot-dip plated metal in addition to transporting the dross. That is, the entire conveyor is maintained at a temperature equal to or higher than the melting point of the plating metal, the solidification of the plating metal is prevented, and the dross is conveyed by flowing out from the mesh belt. The material of the mesh belt may basically have a melting point equal to or higher than the melting point of the plated metal, but practically it is necessary to form no alloy or intermetallic compound with the plated metal.

The heating reduction furnace has a function of heating the dross in a reducing atmosphere to reduce oxides and regenerate the plated metal. In the heating reduction furnace, the bottom of the furnace is filled with coke, and the dross carried by the mesh belt is deposited on the coke, and is heated by electromagnetic induction by an induction coil wound around the furnace body. The heating is done in two steps. That is, the dross is heated and melted by electromagnetic induction, and the dross is further heated by the heat of the coke which is induction-heated, and the oxide of the dross is reduced by CO generated from the coke, and the plated metal is regenerated.
The regenerated metal is continuously taken out from the bottom of the furnace, and is supplied to the plating bath through a supply pipe whose inside is kept at the same reducing property as in the furnace and at a temperature equal to or higher than the melting point of the plating metal. The atmosphere in the heating reduction furnace may be other than coke, and the purpose can be achieved by introducing gas in the annealing furnace of the continuous hot dip galvanizing line (CGL), using hydrogen / nitrogen mixed gas, or ammonia decomposition gas.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings.

In the continuous hot-dip galvanizing equipment, as shown in FIG. 1, the steel strip 1 is annealed by being heated to a high temperature in an annealing furnace 2 having a reducing atmosphere, and rolling oil remaining on the surface is removed by burning. Then, the surface is activated. The steel strip 1 is cooled to near the plating temperature in the same atmosphere, then introduced into the snout 4 through the deflector roll 3, immersed in the molten zinc bath without being exposed to the atmosphere, and the sink roll 6
Plated while changing direction. After the plating, the steel strip 1 is sent to the next step after the amount of coating adhered is controlled by the air ejected from the gas wiping nozzle 7. In this plating step, molten zinc is oxidized by air injection, and a large amount of zinc oxide is produced. Since the specific gravity of zinc oxide is lighter than that of zinc, it floats on the surface of the plating bath. This causes a loss of zinc to be plated and causes a problem of mixing in the plated zinc adhered to the steel sheet and deteriorating the quality. The removal and regeneration of dross 8 solves this. The dross floating on the surface of the bath is collected at a certain place in the molten zinc bath by the dross recovery device as shown in FIGS. 2, 3 and 4. For example, as shown in FIG. 2, there is a method in which a partition plate is provided in a molten zinc bath, and molten zinc is caused to flow using an electromagnetic pump to collect dross in one location in the bath. Further, as shown in FIG. 3, while a flow is created in the bath using an electromagnetic pump, the dross is collected by the stirring blade at a certain location in the molten zinc bath. The stirring blade in this case operates between 90 degrees between A and B, the blade is immersed in molten zinc when moving from A to B, and the blade moves when moving from B to A. The structure is drawn out from within the layer. In this example, the moving speed of the blade was set to 10 cm / s. As another method, as shown in FIG. 4, there is also a method of sucking together with molten zinc by an electromagnetic pump 9 and discharging the molten zinc onto a conveyor 10 composed of a mesh belt. Here, the transfer device 10 is composed of a duct and a tantalum mesh belt that moves in the duct. Since the inside of the duct is maintained at a temperature of 500 ° C. or higher than the melting point of zinc, fluidity is not lost, and the dross passes through the mesh belt. And separated. The size of the mesh used was such that holes of 5 mm were opened at regular intervals. Of course, in the case of the method of FIGS. 2 and 3, the collected dross is carried to the mesh belt. In the dross recovery device shown in FIGS. 2 to 4, the galvanized portion of the steel plate is omitted. The separated molten zinc flows in the duct and returns to the plating bath again. Dross 8 left on the mesh belt
Is transported by a mesh belt conveyor and put into a reduction heating furnace 11 by induction heating as shown in FIG. The reduction heating furnace 11 by induction heating is filled with coke, and the dross 8 is electromagnetic induction heated by the induction coil installed on the coke and installed outside the furnace, and the heat of the coke heated by induction and above the melting point of the dross. It is heated to the temperature of and melts. Dross is dissolved in C by burning coke
It is carried out in an O gas atmosphere, the dross oxide is reduced,
CO becomes CO ₂ and is discharged outside the furnace by the fan. Heating is performed at 550 ° C, and the oxygen partial pressure in the furnace is 42 atm [-log
(PO ₂ )]. The reduced-melted molten zinc passes through the gap of the coke, is discharged from the lower part of the furnace, flows in the supply pipe 12, and is returned to the molten zinc plating bath 5 again. Since the inside of the supply pipe 12 is kept reducible by CO gas and is heated to a temperature equal to or higher than the melting point of zinc by electromagnetic induction heating by an induction coil wound outside the pipe, zinc solidifies in the pipe. There is no. The temperature of the supply pipe is 500 ° C,
The oxygen partial pressure in the tube was 46atm [-log (pO _2)]. The heating of the supply pipe may be performed by an electric heater or steam heating.

[0013]

According to the present invention, since the molten metal plating bath can be continuously recycled and at the same time dross floating on the bath surface can be continuously removed, high quality melting without the inclusion of dross in the plating layer is achieved. The effect that metal plating can be performed is exhibited.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a method for regenerating a molten metal plating bath according to the present invention.

FIG. 2 is a side view and a top view of the dross recovery device according to the embodiment of the present invention.

FIG. 3 is a side view and a top view of the dross recovery device according to the embodiment of the present invention.

FIG. 4 is a side view and a top view of the dross recovery device according to an embodiment of the present invention.

FIG. 5 is a conceptual diagram of a reduction heating furnace.

[Explanation of symbols]

1 ... Steel strip, 2 ... Annealing furnace, 3 ... Deflector roll, 4 ... Snout, 5 ... Hot dip galvanizing bath, 6 ... Sink roll,
7 ... Gas wiping nozzle, 8 ... Dross, 9 ... Electromagnetic pump, 10 ... Conveying device, 11 ... Reduction heating furnace, 12 ... Supply pipe, 13 ... Molten zinc, 14 ... Iron core, 15 ... Coil, 16
... stirring blades, 17 ... ducts, 18 ... mesh belts, 19
... Dross inlet, 20 ... Fan, 21 ... Induction coil, 2
2 ... coke, 23 ... tap, 24 ... refractory material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsumi Mabuchi 7-1-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (7)

[Claims] 1. A molten metal plating bath regeneration method for continuously plating a metal in a plating bath, wherein dross floating on the surface of the plating bath is heated in a reducing atmosphere to be continuously regenerated and supplied to the plating bath. A method for regenerating a molten metal plating bath, comprising: 2. A method for regenerating a molten metal plating bath in which a metal is continuously plated in a plating bath, in which dross is recovered, the dipped metal and the dross are separated and conveyed, and then the dross is internally fed with coke. A method for regenerating a molten metal plating bath, which comprises reducing and melting in a filled heating furnace and supplying to the plating bath. 3. A molten metal plating facility for continuously plating a metal in a plating bath, a device for collecting dross floating on the surface of the plating bath, a device for separating and transporting the plating bath and the dross, and the dross. Hot-dip metal plating equipment provided with a device for heating and reducing the above, and a device for supplying regenerated hot-dip metal to the plating bath. 4. The hot-dip galvanizing facility according to claim 3, wherein the device for collecting dross comprises an electromagnetic pump or a dross recovery robot having a plating bath surface stirring blade. 5. An apparatus for separating and transporting comprises a metal mesh belt that does not form an alloy or an intermetallic compound with a plated metal, and a duct provided with a heating device capable of driving the mesh belt in a reducing atmosphere. The hot dip metal plating equipment according to claim 3 or 4. 6. The hot-dip galvanizing equipment according to any one of claims 3 to 5, wherein the apparatus for heating and reducing comprises an electromagnetic induction heating furnace having coke filled therein. 7. The hot-dip metal plating according to claim 3, wherein the device for supplying the regenerated hot-dip metal plating metal is composed of a supply pipe with a heating device, the inside of which is kept in a reducing atmosphere. Facility.