JPH0144784B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vapor deposition furnace that has a fast response to a vapor deposition rate and has good plating performance, in a continuous vacuum vapor deposition apparatus for galvanizing steel strips, for example.

As a method for continuously forming a galvanized film on a steel strip, in addition to the conventional molten zinc bath method and electroplating method, the vacuum evaporation plating method is attracting attention because of its advantage over plating only on one side. As shown in FIG. 1, a conventional vapor deposition furnace is one in which heating is performed from the bottom of the furnace.

In FIG. 1, 1 is a furnace housed in a vacuum atmosphere, and molten zinc 7 is held inside this furnace body. There is an opening 6 in a part of the ceiling 3, which is covered with a shutter 4 which is rotatably driven around a hinge 5. A heater 8 as a heating source is installed below the furnace, and both the furnace body 1 and the heater 8 are covered with a heat insulating material 9.

During deposition, the shutter 4 is open, and the molten zinc 7 is heated by the heater 8 through the bottom plate of the furnace body 1, evaporated, and plated onto the steel strip 10 running above the deposition furnace through the opening 6. . Molten zinc is continuously supplied from the supply duct 2 in an amount equal to the amount of evaporation.

Such a conventional vapor deposition section has the following drawbacks.

(1) In the plating process line, for example, when the thickness of the supplied steel strip changes, it may be necessary to instantaneously change the amount to be plated on the steel strip, that is, the amount of coating per unit area. In the vapor deposition furnace, the heat capacity of the molten zinc in the vapor deposition furnace and the furnace body itself is large, so even if the heating amount of the heating source is changed instantaneously, the response of the evaporation rate of zinc is slow.
The disadvantage is that a large amount of products with a non-standard basis weight are produced before the process is settled. For example, in a deposition furnace planned for a line with a line speed of 30 m/min and a basis weight of 70 g/ ^m2 , it will take 6
It is expected that it will take about a minute, and during this time the 180m product will be out of specification.

(2) Since the zinc bath is heated from the bottom, bubbles are generated due to boiling at the bottom of the zinc bath, which rise upward through the liquid and exit from the liquid surface. At this time, a so-called splash occurs in which the liquid scatters. In addition, an oxide film is easily formed on the liquid surface, and if a film is formed,
If air bubbles accumulate below and reach a certain size, they will instantly destroy the film, resulting in a larger splash. When splash occurs, droplets may form on the steel strip, resulting in product defects.

The present invention has been made to solve the above-mentioned drawbacks and realize a heating method with a fast response speed. This is a vapor deposition furnace characterized by having carbon blocks suspended therein, and it is possible to realize a vapor deposition furnace that has quick response and prevents splash.

Hereinafter, the embodiments of the present invention shown in FIGS. 2 to 6 will be described in detail.

Embodiment FIG. 2 shows an embodiment of the vapor deposition furnace of the present invention. In FIG. 2, a heater 8 serving as a heating source is installed above molten zinc 7 in a furnace, and carbon blocks 11 are suspended in the zinc bath. The rest of the structure is the same as the conventional structure shown in FIG. 1, so a description thereof will be omitted.

In FIG. 2, when the shutter 4 is open and the steel strip 10 is running above the vapor deposition furnace, for example to the right in the figure, the molten zinc 7 is directly heated by the heater 8 above or by the carbon block 11. The steel strip 10 is heated and evaporated through the opening 6.
It is marked by.

With such a configuration, the following effects are achieved.

If simply heated from above, the heat absorption rate of the surface of molten zinc is very small, approximately 0.1, so direct radiation heating from above is difficult to achieve because the heater temperature becomes too high. When suspended in carbon, the heat absorption rate of the surface of carbon is as high as approximately 1.0, so the overall heat absorption rate can be improved, making it possible to heat the carbon from above.

According to the present invention, zinc is heated from above and evaporates from the surface layer, so it quickly responds to changes in the amount of heat from the heating source. In other words, the time required for stabilization becomes extremely short, and the occurrence of non-standard products is reduced.

At the same time, since the carbon block has reducing power, it suppresses the formation of an oxide film on the surface of the zinc liquid, making splash less likely to occur and preventing droplets from adhering to the product.

In the conventional method, the zinc bath surface is 550℃ and the furnace bottom plate is 600℃.
If a steel plate was used for the bottom of the furnace, the corrosion rate would be very high, and for industrial use it would have been necessary to use ceramic instead of steel.However, according to the present invention, the zinc bath surface can also be used. Since the temperature at the bottom of the furnace is almost the same at 550°C, steel plates can be used, which reduces the manufacturing cost of the furnace body.

Example FIG. 3 shows an example. In FIG. 3, a heater 8 serving as a heating source is installed above molten zinc 7 in the furnace, and a block 11 made of a material with a specific gravity smaller than zinc and whose surface is coated with carbon 12 is floating in the zinc bath. There is. The rest of the structure is the same as the conventional structure shown in FIG.

As a result, the same action and effect as in the example
has.

Example FIG. 4 shows an example. In FIG. 4, a heater 8 serving as a heating source is installed above molten zinc 7 in a furnace, and carbon pellets 11 are suspended in the zinc bath. The rest of the structure is the same as the conventional structure shown in FIG.

As a result, the same action and effect as in the example
Furthermore, there is a certain relationship between the evaporation rate per unit area and the bath temperature, so when the total evaporation amount is constant and a pellet is floated, the evaporation area decreases and the bath temperature increases. Using this relationship, the desired bath temperature can be easily obtained by controlling the number of pellets floating in the bath. be effective.

Example FIG. 5 shows an example. In FIG. 5A, a heater 8 serving as a heating source is installed above a bath of molten zinc in a furnace, and a carbon parallel cross 11 (FIG. 5B is a plan view of the parallel cross) is floating in the zinc bath. The rest of the structure is the same as the conventional structure shown in FIG.

As a result, in addition to the same functions and effects as those of the embodiment, since the surface area of the carbon parallel girder is large, the heat transfer between the carbon and the molten zinc is improved. be effective.

Example 1 Structure An example is shown in FIG. In FIG. 6, a heater 8 serving as a heating source is installed above molten zinc 7 in a furnace, and a honeycomb-shaped block 11 having a specific gravity smaller than that of zinc or having many holes is floating in the zinc bath. The rest of the structure is the same as the conventional structure shown in FIG.

7 and 8 show examples of the shape of the block 11, with A being a side view and B being a plan view. that's all,
The effects achieved by the configuration of the vacuum evaporation section of the present invention described above are summarized as follows.

If simply heated from above, the absorption rate of the surface of molten zinc is very small at approximately 0.1, so direct radiant heating from above is difficult to implement because the heater temperature becomes too high.
When a honeycomb-shaped or many-pored carbon block is suspended in a liquid, the apparent blackness (which is the same as the heat absorption rate) of the block surface increases due to the cavity effect, and the shape of the block increases. If you choose appropriately, you can increase the absorption rate to 1.0.
Since this can improve the overall heat absorption rate, a method of heating from above can be adopted.

According to the present invention, zinc is heated from above and evaporates from the surface layer, so it quickly responds to changes in the amount of heat from the heating source. For example, line speed 30m/min, area weight 70g/m ²
The settling time for this line is about 30 seconds to 1 minute. In other words, the time required for stabilization becomes extremely short, and the occurrence of non-standard products is reduced.

There is a certain relationship between the evaporation rate per unit area and the bath temperature, and if the block is floated when the total evaporation amount is constant, the evaporation area will decrease and the bath temperature will rise. The apparent absorption rate can be improved while maintaining the area and preventing the bath temperature from increasing more than necessary.

In the conventional method, the zinc bath surface is 550℃ and the furnace bottom plate is 600℃.
℃, so if a steel plate was used for the bottom of the furnace, the corrosion rate would be very high.For industrial use, it would have been necessary to use ceramic instead of steel plate.However, with the method of the present invention, the zinc bath surface can also be used. The temperature at the bottom of the furnace is almost the same at 550°C, so steel plates can be used and the cost is low.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a conventional vacuum evaporation section, FIGS. 2 to 6 are diagrams showing embodiments of the vacuum evaporation section of the present invention, and FIGS. 7 and 8 are diagrams shown in FIGS. FIG.

Claims (1)

[Claims] 1. A vacuum evaporation section characterized in that a heating source heater is installed above the furnace, and blocks of carbon are suspended in the bath.