Metallurgical apparatus – Means treating a continuum of work – With heating means
Patent
1990-05-08
1991-06-04
Kastler, S.
Metallurgical apparatus
Means treating a continuum of work
With heating means
266200, 118429, B05C 1902
Patent
active
050207792
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for in hot-dip galvanizing in which the coating formed during the galvanizing process no longer undesirable impurities accompanying from the bath of molten zinc.
DESCRIPTION OF PRIOR ART
In the hot-dip galvanizing of an object, for example of iron, steel etc., the object is immersed in a bath of molten zinc, the iron and zinc forming alloys with one another. The alloys build up a coating of iron-zinc layers on the object, in which the layers have a decreasing iron content towards the coating surface. As a rule, the coating closest to the surface consists of substantially pure zinc which, on removal of the object from the bath, has adhered to the coating of iron-zinc already formed in the bath. A number of factors such as the solidifying process, the composition of the iron, the condition of the iron surface, the composition and temperature of the molten zinc, the immersion time, etc. determines the thickness and quality of the coating which is formed.
In order to attain fully adequate quality in the galvanizing, it is necessary that part of the surface of the zinc bath through which the article passes during its immersion and removal be free of impurities. Within this art, use is made of the expression "working surface" for that portion of the surface of the bath through which the article passes. As a rule, the zinc surface of the bath is covered by impurities which, primarily, consist of oxides and flux residues. These impurities must be removed from the working surface before the article passes therethrough, since such impurities would otherwise accompany the article and cause a deterioration in the quality of the coating which is formed on the article in the galvanizing process.
It is known in this art to employ different types of mechanical devices in order to remove mechanically the impurities from the working surface. In certain cases the mechanical devices move the impurities floating on the zinc surface towards the edges of the container (bath of "pot") in which the molten zinc is located, while in other physical applications, such removal is supplemented by means of frothing the impurities and raising them from the zinc bath. However, it is difficult to ensure that the working surface is completely exposed and free of impurities and, according to prior art technology, the time consumed for cleaning the working surface may be unacceptably high, whereby the capacity of the galvanizing plant is reduced and/or that the thickness of the coating will be undesirably large. In both cases, extra costs are incurred for the hot-dip galvanizing which is carried out. Because of the uncertainty which always prevails in respect of efficiency in the removal of impurities from the working surface, the technology currently employed requires continual monitoring of the galvanizing process in order to attain the contemplated quality of the coating on those articles which are hot-dip galvanized.
It is desirable within this art to be able, as far as is possible, to automize the hot-dip galvanizing process, but such desire is difficult to reconcile because of the inherent problems involved in exposing and freezing the working surface from impurities preparatory to the passage of the article through the working surface. Automation of the process is particularly desirable in view of the severe environment surrounding the hot-dip galvanizing bath.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and an apparatus which satisfy the requirements and objectives as set forth in the preceding paragraph. The present invention obviates essentially all requirements of manual monitoring of the hot-dip galvanizing process.
In one preferred embodiment of the present invention, the flow movement of molten and pure zinc is directed substantially from beneath towards the working surface in order thence to continue, in the surface region of the bath, in a direction away from the working surface. In such event, all pos
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Evensen Torstein
Lindblom Lars
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