Coating apparatus – Immersion or work-confined pool type – With means for moving work through – into or out of pool
Reexamination Certificate
1999-05-11
2001-11-13
Lamb, Brenda A. (Department: 1734)
Coating apparatus
Immersion or work-confined pool type
With means for moving work through, into or out of pool
C428S641000, C428S681000, C428S937000
Reexamination Certificate
active
06315830
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the priority of Japanese patent document 10-127668, filed May 11, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a molten metal plating apparatus in which an object is plated by immersing it in a molten metal, and particularly to a molten metal plating apparatus composed of components having good corrosion resistance and wear resistance to the molten metal.
Metals such as casting iron, stainless steel, high chromium steel and the like having corrosion resistance have been used for components of a molten metal plating apparatus, which are disposed in a molten metal. However, sinking rollers, supporting rollers and the like which are made of these materials cannot be used for long periods of time because the molten metals are strongly corrosive. Further, when a roller bearing or the like is corroded or worn, a plated film cannot be formed uniformly because of occurrence of vibration in a steel plate, which sometimes deteriorates the plating quality.
When an iron component used in a molten metal is corroded by the molten metal, an impurity in the form of a chemical compound of iron and the molten metal (called “dross”) is formed in the molten metal. This not only degrades the plating film quality, but also shortens the lifetime of the molten metal itself. For these reasons, the rollers in a molten metal plating apparatus must be exchanged frequently, and the productivity of plated products is poor due to interruption of the operation for exchange of the roller.
In order to solve these problems, one known technique is to cover the components used in the molten metal with a cermet or a ceramic which is resistant to corrosion by the molten metal. Alternatively, the whole component used in the molten metal can be made of the cermet or the ceramic material. For example, Japanese Patent Application Laid-Open No. 61-37955 discloses a method of manufacturing a roller for use in a molten metal bath, having good corrosion resistance, heat resistance and wear resistance, by plasma spraying a ceramic onto a surface of a steel body. Japanese Patent Application Laid-Open No. 4-124254 discloses a bearing made entirely of a cermet or a ceramic, while Japanese Patent Application Laid-Open No. 5-44002 discloses a shaft of a roller made of cermet and a bearing totally made of a ceramic.
However, in known technology for surface treatment by the plasma spray method, pin holes are formed in the melt-sprayed film, and the molten metal can penetrate through the pin holes to corrode the body material, therefore, the melt-sprayed film is easily peeled off from the body material, and accordingly the reliability is low. On the other hand, since the component which is to be placed in the molten metal is generally quite large , it is technically and economically difficult to make the whole component using a cermet or a ceramic.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a molten metal plating apparatus which can be operated for a long time, has good productivity of plated products, and can perform plating with good quality.
This and other objects and advantages are achieved by the molten metal plating apparatus according to the invention, which comprises a component made of iron having an iron silicide surface film (preferably Fe
3
Si, or FeSi). The inventors have studied the corrosion resistance of various kinds of materials in a molten Zn-Al alloy, and have found that iron silicides have particularly good corrosion resistance.
As the iron suicides, there are Fe
3
Si, Fe
5
Si
3
, FeSi, FeSi
2
and so on. An Fe
3
Si film can be formed through silicon penetration methods by which silicon is penetrated into a surface of a steel plate. As an example of silicon penetration methods, a steel member and silicon powder or silicon carbide powder are placed in a container and heated to a temperature of 930 to 1000° C. while chlorine gas is introduced (Metal Progress, 33 (1938) 367). In another method, a steel member is heated at 1200° C. for approximately 20 minutes in a flow of a mixed gas of 10% SiCl
4
+90% N
2
(Journal of Metallurgical Association of Japan, 26 (1962) 157). Finally, a steel member can be immersed in a molten Mg-Si alloy bath, and heated to 800 to 900° C. for several minutes (Iron and Steel, 83 (1997) 25).
Since an iron silicide film made of Fe
5
Si
3
, FeSi or FeSi
2
cannot be formed by silicon penetration, it is formed instead by a plasma spray method. However, when the iron silicides Fe
5
Si
3
and FeSi
2
are used in the form of powder, they decompose at temperatures of 1193° C. and 1204° C., respectively, to produce Si. Therefore, Fe
5
Si
3
and FeSi
2
in powder form are not suitable for use as raw materials for forming the iron silicide film. On the other hand, since FeSi powder has a melting point of 1410° C. and is unstable, it is preferable to form the iron silicide film by forming an FeSi spray film through a plasma spray method, using FeSi powder.
In the present invention, the Fe
3
Si film is formed by the Si penetration method, using an Mg-Si alloy bath, and the FeSi film is formed through the plasma spray method using FeSi powder as the raw material. By these methods, a closed compact film of iron silicide can be comparatively easily formed, and the formed iron silicide film has good adhesive property to the body material of iron. Therefore, since components made of iron and having an iron silicide surface film have a long lifetime without being corroded, even in a molten metal, molten metal plating apparatus employing such components can be operated for a long time and accordingly the productivity of the plated products can be improved.
Further, an intermediate film made of iron, silicon and cobalt, for example, an FeSi-12Co film may be interposed between the iron body and the iron silicide film. By interposing the intermediate film made of iron, silicon and cobalt between the iron body and the iron silicide film, it is possible to prevent the iron silicide film from being peeled off from the iron body, even if a thermal shock is applied to it.
Another feature of the present invention is that an iron rotating body disposed in the molten metal has an iron silicide film on its surface. A molten metal plating apparatus which includes rotating bodies such as a sinking roller, a supporting roller and so on having an iron silicide film on their surfaces can be operated for a long time. Accordingly the productivity of the plated products can be improved because the sinking roller and the supporting roller exhibit good corrosion and wear resistance. In addition, since less dross is produced, the occurrence of plating defects can be reduced, the quality of the plating can be improved and the lifetime of the molten metal itself can be lengthened.
A further feature of the present invention is that a bearing for supporting a rotating shaft of the rotating body comprises a member made of carbon fiber which is brought in contact with the rotating shaft having an iron silicide film on its surface. In a molten metal plating apparatus which uses a component which combines a rotating shaft with an Fe
3
Si surface film on the iron body and a bearing made of a carbon fiber such as a carbon-carbon fiber complex material, vibration does not occur in a steel plate even if the apparatus is operated for a long time. Accordingly, the plating quality can be maintained for a long time since corrosion and wear of the rotating shaft are very small.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
REFERENCES:
patent: 5137375 (1992-08-01), Murakami et al.
patent: 5736198 (1998-04-01), Yasutomi et al.
patent: 61-37955 (1986-02-01), None
patent: 62-297454 (1987-12-01), None
patent: 4-124254 (1992-04-01), None
patent: 5-44002 (1993-02-01), None
Kimura Takehisa
Nakagawa Mitsuo
Saito Yukio
Sakai Junji
Shimogama Hironori
Crowell & Moring LLP
Hitachi , Ltd.
Lamb Brenda A.
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