Coating processes – Direct application of electrical – magnetic – wave – or... – Induction or dielectric heating
Patent
1996-07-26
1997-09-02
Pianalto, Bernard
Coating processes
Direct application of electrical, magnetic, wave, or...
Induction or dielectric heating
118405, 118419, 118423, 118429, 118500, 118600, 118623, 118665, 118667, 118693, 118712, 427 8, 427318, 427320, 427321, 427349, 4273983, 4274342, 427436, 427543, 427549, 427598, H05B 602
Patent
active
056629699
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention pertains to a method and apparatus for coating a workpiece, such as in the process of galvanising, and more particularly, to an in-line galvanising process utilising a coreless induction furnace which develops a meniscus of liquid metal. In particular, the invention relates to the selection of desirable parameters to consequently control the meniscus.
BACKGROUND OF THE INVENTION
Galvanisation of steel sheet, strip, wire or odd shaped steel members is a well known process. There are several known methods, particularly in relation to continuous rigid members in the galvanising industry for in-line processing. However, a difficulty associated with the prior art methods is the requirement of one or more pumping devices for transporting the liquid metal coating from a melting vessel to a galvanising chamber, either directly or indirectly through a holding vessel. Further, with regard to in-line galvanising processes where material is introduced into the galvanising chamber continuously, there needs to be means for preventing molten metal from leaking outside the galvanising chamber. These means are known to take the form of either electromagnetic seals or secondary chambers which house the galvanising chamber so that molten metal is collected in the secondary chamber for eventual return to the holding vessel or melting vessel. Another common prior art method is the trough method, where rigid material is required to be bent or deflected down into a galvanising pot and then slanted upwards thereafter.
Whilst these prior art approaches attempt to improve the operational efficiency and are space saving, they are far from an adequate and economical solution. Recent prior art has considered the use of an induction heating coil to pre-heat the work before entering the galvanising chamber, and the use of electro-magnetic seal rings to prevent the liquid escaping from the galvanising chamber. However, auxiliary equipment is still required, including, a vessel for the purposes of melting zinc or aluminium ingot, a mechanical or electro-magnetic pump to pump the molten zinc/aluminium to the galvanising chamber, and a heating element to maintain galvanising temperature.
As will be appreciated, therefore, there have been various attempts to achieve a successful in-line galvanising of straight products without subjecting them to bending.
SUMMARY OF THE INVENTION
The present invention seeks to provide an apparatus and method for coating a workpiece, such as in galvanising, which apparatus and method substantially ameliorates the disadvantages associated with prior art methods and devices.
In one broad form, the present invention provides a coating apparatus, for applying a coating to a workpiece, comprising:
a vessel to contain a molten metal; and,
an induction coil disposed about said vessel;
wherein, in use, said induction coil induces a magnetic field within said vessel such that a meniscus of molten metal is formed above said vessel, through which said workpiece is passed for coating.
In a further broad form, the present invention provides a method for applying a coating to a workpiece, comprising the steps of:
forming a meniscus above a vessel containing molten metal by creating a magnetic field to effect said molten metal; and
passing said workpiece through said meniscus such that a coating is formed on said workpiece.
Preferably, the present invention enables the power, current, voltage and/or frequency within said induction coil to be controlled to produce a predetermined magnetic field in said molten metal and to consequently create a meniscus of predetermined height.
Also preferably, the composition, temperature and/or density of the molten metal is chosen to create a meniscus of predetermined height.
In preferred forms, said workpiece is formed of ferrous or non-ferrous material.
Also in preferred forms, said workpiece is commercial grade, low carbon steel.
Perhaps most preferably, said molten metal comprises zinc or an aluminium zinc mixture.
In a preferred embodiment, s
REFERENCES:
Derwent Abstract Accession No. 90-13104/17, Class X25, SU,A, 149253, Hardware Ind. Res, Jul. 15, 1989.
Patent Abstracts of Japan, C45, p. 158, JP, A, 54-32135, Asahi Glass KK, Sep. 3, 1979.
Derwent Abstract Acession No. 44118C/25, Class M 13, JP, A,. 55-062153, Nippon Steel Corp, 10 May 1980.
Derwent Abstract Acession No. 79927B/44, Class M13, JP, A, 54-122640; Kube Steel KK, 22 Sep. 1979.
Patent Abstract of Japan, C61, p. 52, JP, A, 54-102247; Kobe Seikosho KK; 8 Nov. 1979.
Patent Abstract of Japan, C66, p. 49, JP, A, 54-124836; Asahi Glass KKO; 28 Sep. 1979.
Derwent Abstract Accession No. 32425E/16, Class M13, JP, A, 82-015664; Mitsubishi Heavy Ind KK; 31 Mar. 1982.
Graham Group
Pianalto Bernard
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