JPH03188250A - Molten metal dipping vessel used for continuous hot-dipping - Google Patents

Abstract

PURPOSE:To suppress the occurrence of surface flaws by dividing a molten metal vessel into feeding and dipping parts so that a molten metal can flow from the feeding part into the dipping part and separately controlling the temp. of the molten metal in the feeding part and that in the dipping part. CONSTITUTION:When a steel sheet 1 is dipped in a molten metal dipping vessel 3 by continuous passing through the vessel 3 to carry out hot-dipping, the vessel 3 is divided with a partition weir 9 into a feeding part 3 into which a solid metal 6 as the starting material of the molten metal is fed and a dipping part 3b in which the steel sheet 1 is dipped so that the molten metal can flow from the feeding part 3a into the dipping part 3b. The temp. of the molten metal in the part 3a and that in the part 3b are separately controlled with heaters 8a, 8b. Deviation of coating weight is reduced and equipment can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plating bath used for continuous hot-dip metal plating of steel strips.

[Prior Art] A conventional plating bath used for continuous hot-dip metal plating of steel strips will be described with reference to a vertical cross-sectional view shown in FIG.

The steel strip 1 passes through a pretreatment furnace 2, is immersed in a plating bath 3, is turned upward by a zinc roll 4, and is immersed in a plating bath 3.
When the molten metal comes out, the weight of the molten metal is controlled by the gas restricting nozzle 5, and the molten metal is sent to the next step.

The molten metal in the plating bath 3 adheres to the steel strip l and is taken out of the bath, so in order to replenish the amount, a solid metal 6 (for example, an ingot), which is a raw material for the molten metal, is transferred to the solid metal charging device 7. It is charged into the plating bath 3.

A molten metal heating device 8 is installed in the plating bath 3 in order to melt the solid metal 6 and control the temperature of the molten metal to a predetermined temperature, and the heating source of this heating device is an electric heater or induction heating. is common.

By the way, controlling the temperature of molten metal is very important for the following two reasons.

(1) When controlling the basis weight of the molten metal with the gas throttling nozzle 5, changes in the viscosity of the molten metal become a major disturbance to the basis weight control, and as the temperature of the molten metal changes, the viscosity also changes.

(2) Iron is constantly leached into the molten metal from the steel strip I in the plating tank 3, but when the temperature of the molten metal drops, the equilibrium state is disrupted and a compound of molten metal and iron called dross is precipitated. However, if this adheres to the surface of the steel strip 1, it will cause surface defects such as scratches.

However, in the conventional plating bath 3 shown in FIG. 4, no matter how much the heating device 8 attempts to control the temperature of the molten metal, for example, in the area where the solid metal 6 is melted, the temperature is in principle lower than that of the solid metal. Since the temperature drops to the melting point of the molten metal in the plating bath 3, a temperature difference will always occur in the molten metal in the plating bath 3.
The two problems mentioned above cannot be completely solved.

On the other hand, in Japanese Patent Application Laid-Open No. 1-165753, a bath dedicated to melting solid metal is installed separate from the plating bath 3,
A method has been proposed in which the molten metal melted in the bath is supplied to the plating bath using a pump, but this method complicates the equipment, increases equipment costs, and increases maintenance costs as the pump is corroded by the molten metal.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned drawbacks of the prior art, makes it easy to control the area weight of the steel strip, does not cause surface defects such as scratches, and has simple equipment and low equipment costs. Another object of the present invention is to provide a plating bath for use in continuous hot-dip metal plating, which has low maintenance costs.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a plating bath in which hot-dip metal plating is performed by continuously immersing a steel strip in the plating bath, in which there are two or more plating baths. The chamber is divided into two chambers, one of which is a supply section for the solid metal that is the raw material for molten metal, and the other is an immersion section for the steel strip, allowing molten metal to flow from the supply section to the immersion section. The present invention provides a plating bathtub used for continuous molten metal plating, characterized in that it is equipped with a heating device capable of independently controlling the temperature of molten metal in each divided room.

[Function] The plating bath of the present invention will be explained using FIG. 1, which shows a vertical cross-sectional view thereof.

A partition weir 9 whose height is slightly higher than the bath surface of the steel strip immersion section 3b is installed in the plating bath 3, and the plating bath 3 is divided into a solid metal supply section 3a and a steel strip immersion section 3b by this weir 9. Heating devices 8a and 8b are separately installed in the supply section 3a and the dipping section 3b, respectively.

Since the plating bath 3 is configured in this way, the solid metal 6 is melted by the supply section heating device 8a, and the temperature of the molten metal in the immersion section 3b is controlled by the immersion section heating device 8b.

In the supply section 3a, the bath level rises by the amount of solid metal 6 introduced, while in the immersion section 3b, the bath level decreases by the amount of basis weight applied to the steel strip 1. Therefore, the molten metal overflows the partition weir 9 from the supply section 3a to the immersion section 3b.

In the supply section 3a, temperature distribution of the molten metal occurs in the same manner as the above-mentioned problem, but by measuring the temperature of the molten metal near the overflow part of the weir 9,
The above-mentioned problem can be solved by controlling the supply section heating device 8a so that the temperature of the molten metal flowing out is equal to the temperature of the molten metal in the immersion section 3b.

Further, the elution of iron from the steel strip l occurs mostly in the immersion section 3b, and the molten metal from which the iron has eluted does not flow back toward the supply section 3a, so the molten metal in the supply section 3a does not contain iron. As described above, even if a temperature difference occurs within the supply section 3a, no dross is generated.

Further, since no solid metal is supplied to the immersion section 3, no low temperature areas are created in the molten metal, and therefore no dross is generated and no scratches are generated on the surface of the plated steel strip.

In order for the molten metal overflowing the weir 9 to enter the immersion section 3b with a small head, the supply amount of the solid metal 6 is made to match the consumption amount of molten metal in the immersion section. If the head is large, the atmosphere is likely to get caught up in the molten metal, and dross is likely to occur.

In the present invention, the plating bath 3 is constructed by using a partition box 10 as shown in FIG. , 9b, it can be divided into two or more parts.

The plating bath of the present invention is suitably used for continuous hot-dip galvanizing of steel strips.

[Example 1 Example 1 An example in which the present invention is applied to a hot-dip galvanized steel bathtub in which the galvanized bathtub is divided into two rooms by a partition, is shown in FIG. I will explain using

The operating conditions are that the size of the steel strip is 1mm thick x 1000mm.
The width and traveling speed are 100mpm, and the total basis weight on both sides is 20
0 g/rri''.

The steel strip 1 enters the immersion section 3b of the plating bath 3 at a temperature of 460.degree. C., and the molten zinc in the immersion section 3b is controlled by a heating device 8b to have a temperature of 460.degree.

On the other hand, in the supply section 3a of the plating bath, the heating device 8
a, while melting the zinc ingot 6, the immersion section 3b
The temperature of the molten zinc flowing out is controlled at 460°C.

Under such operating conditions, the amount of zinc attached to the steel strip l in the immersion section 3b and taken out is 1200 kg/h.
Corresponding to this amount, in the supply section 3 ail: 1000 kg of zinc ingot 6 is delivered every 50 minutes.
It is charged at an average of 1200 kg/h each time.

The required power for the heating devices 8a and 8b is 190kW for 8a,
8b was 90kW.

At this time, the temperature difference in the molten zinc in the supply section 3a was about 30.degree. C., but the temperature of the zinc flowing out toward the immersion section 3b was constant within the range of 460.+-.2.degree. Further, in the immersion section 3b, only the heating device 8b heated the immersion section by an amount corresponding to the amount of heat dissipated from the immersion section, and the temperature difference inside the molten zinc was within the range of 460±2°C.

In such a situation, iron elution into the molten zinc occurs only in the immersion section 3b, but since there is almost no temperature difference inside the molten zinc, the generation of dross is drastically reduced. Further, the molten zinc does not flow back from the immersed part 3b to the supply part 3, and the molten zinc does not flow back to the supply part 3a.
Since there was no iron leached out, no dross was generated even when the temperature difference was large as mentioned above. The above results are summarized in Table 1 in comparison with the case using the conventional device shown in FIG. Incidentally, the surface flaw occurrence rate was determined by visually observing the steel strip product, defining a steel strip with even one flaw as a "scarred steel strip", and determining the ratio to the total manufactured steel strip.

The amount of dross generated was reduced to 175, and as a result, the incidence of surface scratches was also halved. In addition, the variation in basis weight was also reduced, albeit slightly.

Table 1 Embodiment 2 FIG. 2 is a longitudinal cross-sectional view of another embodiment of the present invention, which is divided into a supply section 3a and a dipping section 3b by a partition box 10.

The partition box IO is provided with an opening II so that the temperature of the molten metal therein can be controlled by the heating device 8a.

Zinc flows out from the supply section 3a to the immersion section 3b through this opening 11.

When the operating conditions were the same as in Example 1, results similar to those in Example 1 were obtained in Example 2, and the object of the present invention could be achieved by simply modifying the conventional apparatus.

Embodiment 3 FIG. 3 is a longitudinal cross-sectional view of still another embodiment of the present invention, in which a buffer section 3C is provided between the supply section 3a and the dipping section 3b by partitions 9a and 9b, and a heating device is also installed here. 8c was installed. When operating under the same conditions as in Example 1, except that the power of the heating device 8c was 50 kW and the temperature of the buffer section 3C was 460 ° C., the temperature difference in the immersion section 3b was reduced due to the installation of the buffer section 3C, This improved the surface quality of the plated steel strip.

[Effects of the Invention] According to the present invention, (1) the amount of dross generated can be reduced and the occurrence of surface scratches can be significantly reduced; (2) the deviation in the basis weight can also be reduced; and 3) the equipment can be simplified.

[Brief explanation of drawings]

FIG. 1 is an explanatory longitudinal cross-sectional view of an embodiment of the present invention, FIG. 2 is an explanatory longitudinal cross-sectional view of another embodiment, and FIG. 3 is an explanatory longitudinal cross-sectional view and a cross-sectional explanatory diagram of still another embodiment. l...Steel strip 2...Pretreatment furnace 3...Plating bath 3a...Supply section 3b...Immersion section 3c...Buffer section 4...Zinchlor 5...For gas squeezing Nozzle 6...Solid metal 7...Solid metal charging device 8.8a, 8b, 8c =-Heating device 9.9a, 9b
... Partition weir 10 ... Partition box 11 ... Opening Figure 4 shows the vertical view of the conventional device.

Claims (1)

[Claims] 1. In a plating bath in which hot-dip metal plating is carried out by continuously immersing a steel strip in the plating bath, the plating bath has two
It is divided into two or more chambers, one of which is a supply section for the solid metal that is the raw material for molten metal, and the other is an immersion section for the steel strip, so that the molten metal can flow from the supply section to the immersion section. 1. A plating bathtub used for continuous molten metal plating, characterized in that it is equipped with a heating device that can independently control the temperature of molten metal in each divided room.