JPH02190459A - Method for controlling temperature of molten metal in pot made of iron for molten metal - Google Patents

Abstract

PURPOSE:To prevent both erosion of a pot according to lowering of a bath surface and unnecessary heat dissipation by dividing electric heaters into a plurality of systems to the depth direction of the pot and turning on only the electric heaters of the system existing under the bath surface by the signal of a bath surface level detector. CONSTITUTION:In a pot 2 made of iron for molten metal which is utilized for regulating the component of a plating bath of a hot dipping line, an electric heater 3 for heating molten metal 1 is divided into a plurality of systems in the depth direction. The heaters 31-36 of the respective steps are independently turned ON/OFF or made capable of electric power control. In this constitution, a controlling device 7 turns on only the heaters existing under the bath surface and turns off the other heaters in accordance with descending and ascending of the bath surface by the bath surface detecting signal of a bath surface level detector 8. The heaters being in a turned-ON state are controlled so that the temp. is held constant by the signal of a thermometer 6. Further a radient thermometer 9 fitted with an angle of depression controlling device 10 is equipped to the trestle of the detector 8. This radiant thermometer 9 is positioned at angle of depression (alpha) according to the bath surface level. The heaters existing just under the bath surface are controlled and the pot 2 in the upper part of the bath surface is prevented from being overheated.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is used for adjusting the composition of a plating bath in a molten metal plating line, and is used to control the temperature of molten metal in an iron pot for molten metal equipped with an electric heater as a heating means. Regarding the method.

<Prior Art> Generally, an iron pot equipped with an electric heater as a heating means, or a ceramic pot equipped with an induction heating device as a heating means is used in a plating bath of a hot-dip metal plating line.

Ceramic pots have a semi-permanent lifespan because they are not corroded by molten metal, but are expensive, whereas iron pots are corroded by molten metal and require periodic repair, but are inexpensive. Ceramic pots are often used in plating baths in recent hot-dip metal plating lines. However, with the diversification of products and higher quality in hot-dip metal plating, for example,
254, Japanese Patent Application No. 62-324717, etc., in addition to the in-line plating bath, there are many cases in which several sub-pots for component adjustment are provided, and inexpensive iron pots are sometimes used for these sub-pots. The number is increasing.

The configuration of the iron pot is, for example, as shown in Figure 3.
, electric heater 3, furnace wall (brick) 4, furnace shell (steel frame) 5
Consists of. The temperature of the molten metal 1 in the iron pot 2 is controlled by turning the electric heater 3 ON10F according to the signal from the thermometer 6.
This is done by F or power control. 7 is a control device.

<Problems to be Solved by the Invention> When an iron pot is used as a plating bath in a plating line, conventional temperature control methods are sufficient because there is almost no variation in the bath level.

However, in sub-pots for component adjustment, etc., the molten metal in the sub-pot is used gradually, so the bath level drops, and when the bath level drops to a certain level, molten metal or ingots are replenished and the bath level is raised. It is accompanied by fluctuations in the bath level as it returns to normal. If there is only one electric heater system in the depth direction as in the past, when the bath level drops, not only will the heat from the heater above the bath level be dissipated wastefully, but the temperature of the iron pot will become abnormally high. There were problems such as the iron pot being more likely to be eroded by the molten metal (dry-boiled condition).

In particular, the area directly above the bath surface suffers from severe wear and tear due to the corrosive effects of floating matter (scum, top dross), which adversely affects the life of the iron pot.

An object of the present invention is to provide a method for controlling the temperature of molten metal in an iron pot for molten metal, which eliminates the drawbacks of the prior art and prevents corrosion of the pot and wasteful heat dissipation due to a drop in the bath surface of the iron pot. There is.

<Means for Solving the Problems> In order to achieve the above object, according to the present invention, in an iron pot for molten metal equipped with an electric heater as a heating means, a plurality of electric heaters are installed in a plurality of systems in the depth direction of the pot. Provided is a method for controlling the temperature of molten metal in an iron pot for molten metal, which is characterized in that only the electric heater in the system below the bath surface is turned on and the others are turned off based on a signal from a bath surface level detection device. Ru.

It is preferable that the uppermost electric heater, which is controlled and turned on by the control method, is further controlled by the temperature of the inner surface of the iron pot just above the bath surface.

Preferably, the temperature of the inner surface of the iron pot just above the bath surface is measured with a thermometer linked to the bath surface detector.

The present invention will be explained in more detail below based on an embodiment shown in FIG.

The structure of the iron pot is the same as before, consisting of an iron pot 2, an electric heater 3, a furnace wall 4, and a furnace shell 5, but the electric heater 3 is divided in the depth direction (Fig. 1 shows the case of 6 divisions).
The heaters in each stage are turned ON10 F F independently.
Or power control is possible.

Here, whether or not to use each heater is determined by a signal from a bath level detection device 8 that detects the bath level of the molten metal 1 in the iron pot 2. Turn off the heater that comes out above, and if the bath level rises, turn on the heater that is submerged below the bath surface (first
In the example shown in the figure, heaters 31 to 34 are turned on). O
The heater in the N state is controlled to ON10 F F or power by a signal from the thermometer 6 to keep the temperature constant.

In FIG. 1, the heater 3 is divided into six parts, and a laser level meter is shown as the bath level detection device 8, but the number of divisions of the heater 3 may be determined according to the depth of the pot.
The method of the bath level detection device 8 is also not limited.

In addition, a radiation thermometer 9 with a depression angle control device 10 is installed on the mount of the bath level detection device 8, and is positioned at a preset depression angle α corresponding to the bath surface level. Measure the surface temperature of the inner surface of lid 2. Based on this measured value, only 34 heaters among the heaters 31 to 34 in use are controlled in addition to the control based on the bath temperature to prevent overheating of the iron lid 2 above the bath surface.

Type of bath level detection device 8 and iron lid 2 directly above the bath surface
The arrangement and control method of the thermometer 9 for measuring the inner surface temperature are not limited to those described above, and may take other known forms.

<Example> The present invention will be specifically explained below based on Examples.

(Example 1) The temperature of the molten metal in an iron pot for molten Zn was controlled under the following conditions using the equipment shown in FIG.

Pot internal dimensions: 1000mm x lO00mm x 150100O depth) Bath level fluctuation range near 00 to 1400mm (based on the bottom of the pot) Number of heater divisions = 6 stages (lowest stage: 40kW, others 15K)
W) In the above iron pot, the bath level is 1400mm.
The bath temperature was measured when the temperature decreased from 1,100 mm to 1,100 mm, and the temperature of the bath was measured, and the temperature on the inner surface of the iron lid at a height of 1,150 mm from the bottom of the iron lid was measured.

Here, the iron lid temperature was measured by welding a thermocouple to the bath side of the iron lid. Figure 2a shows the variation in heater position and bath level. The results are shown in Figure 2b.

For comparison, the inner surface temperature of the iron lid at a height of 1150 mm was measured in the same manner as in Example 1 under the same conditions as in Example 1 except that the heater was placed in one system in the depth direction as in the past.
Shown in Figure b.

In the conventional case, when the bath level lowered and the iron lid was exposed to the air, the temperature of the iron lid rose abnormally and corrosion by molten Zn progressed significantly. However, in Example 1, even if the bath level fluctuates, the iron It can be seen that the temperature change of the lid is small. As a result, not only electricity costs were reduced, but the lifespan of the iron lid was also significantly extended.

<Effects of the Invention> Since the present invention is configured as described above, even if there is a fluctuation in the bath level, it is possible to prevent the iron pot from drying out, which not only reduces power costs but also prevents abnormalities in the iron pot. Since temperature rise can be prevented, corrosion of the iron pot by molten metal is significantly reduced, and the life of the iron lid is also extended.

FIG. 2b is a graph of the iron lid temperature corresponding to the bath level variation in FIG. 2a.

FIG. 3 is an explanatory diagram showing the structure of a conventional iron pot.

Explanation of symbols 1... Molten metal, 2... Iron lid, 3...
Electric heater 4...furnace wall, 5...furnace shell,
6... Thermometer, 7... Control device, 8... Bath level detection device, 9... Thermometer, 10... Depression angle control device

[Brief explanation of the drawing]

FIG. 1 is a schematic side sectional view showing an example of the configuration of equipment for carrying out the present invention. Figure 2a is a graph showing variations in heater position and bath level. FIG, 1 Temperature (°C) Creepage level (mm) 1~-t LJ'I0 Number of heaters used FI G, 3

Claims (3)

[Claims] (1) In an iron pot for molten metal equipped with an electric heater as a heating means, the electric heater is divided into a plurality of systems in the depth direction of the pot, and a signal from a bath level detection device is used to control the system below the bath surface. A method for controlling the temperature of molten metal in an iron pot for molten metal, characterized by turning on only an electric heater and turning off the others. (2) Controlled by the control method according to claim 1 and turned on.
A method for controlling the temperature of molten metal in an iron pot for molten metal, wherein the electric heater at the top is further controlled by the temperature of the inner surface of the iron pot just above the bath surface. (3) The method for controlling the temperature of molten metal in an iron pot for molten metal according to claim 2, wherein the temperature of the inner surface of the iron pot just above the bath surface is measured by a thermometer linked to the bath surface detector.