Coating apparatus – Immersion or work-confined pool type – With tank structure – liquid supply – control – and/or...
Patent
1997-07-28
2000-08-22
Lamb, Brenda A.
Coating apparatus
Immersion or work-confined pool type
With tank structure, liquid supply, control, and/or...
118419, B05C 1300
Patent
active
061066206
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the pots used to hold baths of molten metal for use in the continuous hot dip coating of metal strip with liquid metal coatings. It was developed for use in the continuous hot dip galvanising of steel strip, wherein the coating metal is essentially zinc. However, it will become apparent that it is applicable to any situation wherein the substrate strip is metal and the coating is a liquid metal, for example, hypereutectic aluminium-zinc alloys and other alloys.
More particularly the invention is directed to electromagnetic plugging means for preventing the leakage of bath liquid from the pot in those instances in which the pot has an opening in it that is below the surface level of the liquid during normal operation.
BACKGROUND ART
In conventional continuous galvanising processes, steel strip, after being cleaned and otherwise conditioned for the adherent acceptance of the coating, is fed from above into a bath of molten zinc or zinc based alloy. The strip passes around a so called "sink roll" submerged in the bath, then emerges from the bath, and passes between coating thickness control devices, which return surplus liquid coating to the bath. The coating is then allowed or caused to solidify and the coated strip is finally coiled for storage, further processing or sale.
The sink roll, being submerged in the bath, operates in a hostile environment and thus is a source of trouble and unreliability unless carefully maintained. Even when adequately maintained, unavoidable wear and tear requires its periodic replacement. Furthermore, dross is sometimes dragged from the surface of the bath by the strip and may become attached to the sink roll and rough alloy growths tend to form on the roll's surface. That dross and those growths damage the strip requiring frequent shut down of the line for removal and replacement of the sink roll with a new or renovated roll. Thus it would be desirable to eliminate the sink roll.
With that desirability in mind, it has been proposed to provide at least one inlet opening in the pot, positioned below the normal operating level of the bath liquid so that a strip to be coated may enter the pot, either horizontally or from below, and depart, either through a similar exit opening or through the mouth of the pot, without need for a change in direction of the strip's pass line within the bath.
It is of course necessary to prevent the outflow of bath liquid through the opening or openings and various electromagnetic plugging means have been proposed for that purpose.
For descriptive convenience the surface of the liquid metal that is supported or otherwise restrained by forces generated by the electro-magnetic plugging means rather than by a solid component of the pot is referred to hereinafter as the "bare" surface of the liquid metal.
Prior proposed electromagnetic plugging means have usually fallen into either of two categories, namely those utilising either poly-phase energising windings or multiple pole electromagnets and switching devices which provide moving magnetic fields passing through the liquid or within the space into which the liquid might otherwise leak, and those which are analogous to electric motors utilising either permanent magnets or DC or single phase electro-magnets in combination with a transverse electric current. All such electro-magnetic plugging devices rely on the interaction of electric currents and magnetic fields, either generated independently or induced one by the other, and the currents are either DC or power frequency and the fields are likewise either steady or oscillating at power frequencies. In both categories of plugging means, the magnetic field and/or the electric current passes through the bath liquid adjacent to the opening to generate restraining forces therein.
Prior proposed electro-magnetic plugging means of the kind discussed above require relatively complex assemblies of components in close association with the liquid metal, thus they all operate in a hot and frequently crowded environment
REFERENCES:
patent: 3701357 (1972-10-01), Granstrom et al.
patent: 4842170 (1989-06-01), Del Vecchio et al.
patent: 5681527 (1997-10-01), Aoi et al.
patent: 5765730 (1998-06-01), Richter
patent: 5827576 (1998-10-01), Carter et al.
Database WPI, Section CH, Week 8548, Derwent Publications Ltd, XP002086798 (1985).
Database WPI, Section CH, Week 9303, Derwent Publications Ltd, XP002086799 (1993).
Baharis Chris
Ellis Peter James
Jinks Damien
Morrison Bruce Robert
O'Neill James Arthur
BHP Steel (JLA) Pty Ltd.
Lamb Brenda A.
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