AU686185B2 – A method of galvanising
– Google Patents
AU686185B2 – A method of galvanising
– Google Patents
A method of galvanising
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Publication number
AU686185B2
AU686185B2
AU70379/94A
AU7037994A
AU686185B2
AU 686185 B2
AU686185 B2
AU 686185B2
AU 70379/94 A
AU70379/94 A
AU 70379/94A
AU 7037994 A
AU7037994 A
AU 7037994A
AU 686185 B2
AU686185 B2
AU 686185B2
Authority
AU
Australia
Prior art keywords
gas
molten metal
reducing
article
wire
Prior art date
1993-08-27
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
AU70379/94A
Other versions
AU7037994A
(en
Inventor
Robert David Chapman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BOC Group Ltd
Original Assignee
BOC Group Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1993-08-27
Filing date
1994-08-19
Publication date
1998-02-05
1994-08-19
Application filed by BOC Group Ltd
filed
Critical
BOC Group Ltd
1995-03-09
Publication of AU7037994A
publication
Critical
patent/AU7037994A/en
1998-02-05
Application granted
granted
Critical
1998-02-05
Publication of AU686185B2
publication
Critical
patent/AU686185B2/en
2014-08-19
Anticipated expiration
legal-status
Critical
Status
Ceased
legal-status
Critical
Current
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Classifications
C—CHEMISTRY; METALLURGY
C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
C23C2/14—Removing excess of molten coatings; Controlling or regulating the coating thickness
C23C2/22—Removing excess of molten coatings; Controlling or regulating the coating thickness by rubbing, e.g. using knives, e.g. rubbing solids
C—CHEMISTRY; METALLURGY
C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
C23C2/26—After-treatment
C23C2/261—After-treatment in a gas atmosphere, e.g. inert or reducing atmosphere
Description
1-
AUSTRALIA
PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT
ORIGINAL
r Name of Applicant: Actual Inventor: Address for Service: Invention Title: THE BOC GROUP plc Robert David CHAPMAN SHELSTON WATERS Clarence Street SYDNEY NSW 2000 «A METHOD OF GRt-VA1S~% G» The following statement is a full description of this invention, including the best method of performing it known to us:-
C,
I-
A METHOD OF GALVANISING The present invention relates to the treatment of articles and relates particularly, but not exclusively, to the treatment of metallic wire or strip by passing it through a bath of oxidisable metal. One example of such a treatment is the galvanising of ferrous metal wire or strip.
Galvanising of wire is carried out commercially by passing the wire through a bath of molten zinc. The freshly galvanised wire is particularly susceptible to oxidation at the location where it breaks the surface of the molten zinc. In addition, there tends to be a build-up of zinc oxide particles on the surface, which particles tend to adhere to the wire.
It is accordingly common practice to employ a layer of charcoal impregnated with oil at the location where the wire breaks the surface on leaving the molten zinc. This practice helps to clean the wire of any particles of zinc oxide «ash» loosely adhering to it and also helps to protect the freshly galvanised surface of the wire from oxidation. This practice does however have the drawbacks that the charcoal needs regular replenishment and that erosion of the charcoal tends to take place rendering less effective the protection given I against pick-up of zinc oxide and against oxidation.
One alternative method of protecting the emerging freshly galvanised wire from oxidation is to form a shroud around the location where the wire leaves the surface of the .go molten zinc and to pass into the shroud a stream of nitrogen or argon, or other gas that 20 does not react with the zinc to form zinc oxide, so as to maintain around the emerging galvanised wire an atmosphere which in comparison with air is relatively free of oxygen.
Our experiments with such shrouds using nitrogen as the protective gas hav .;’Aown that better quality wire can be produced for a short period of time. It has been found \T i I -3however that over prolonged periods of operation there is nonetheless still a build-up of zinc oxide around the surface of the emerging galvanised wire which has a deleterious effect on the quality of the wire giving rise to coating weight variations and a rough surface finish.
The build-up of zinc oxide may arise partly as a result of reaction between the molten zinc and what oxygen there is in the shrouding atmosphere and partly as a result of reaction between zinc and any fluxing agent which is used to pre-treat the wire so as to facilitate the formation of a good bond between the zinc coating and the ferrous metal.
Accordingly, we believe that the mere maintenance of a relatively non-oxidising atmosphere in the vicinity of the location where the wire leaves the surface of the molten zinc is inadequate to obtain the highest quality of finish to the galvanised wire.
There therefore exists a requirement for a method and apparatus for treating articles which avoids the build-up of oxide around the surface of the molten metal.
«It is an object of the present invention to overcome at least some of the 15 disadvantages of the prior art or at least provide a commercial alternative to the prior art.
i Accordingly, in a first broad aspect, the present invention provides a method of treating an article by passing said article through a bath of molten metal, comprising a •step of directing a gas of a reducing or non-oxidising nature at the surface of the molten metal at a location where the article leaves the surface thereby to shroud the article in a S 20 reducing or non-oxidising atmosphere thereby to reduce or prevent oxidisation of the Smolten metal at said surface, wherein the gas is preheated by passing it through tle molten metal prior to the directing of said gas at the surface of the molten metal and -t Li) ‘lr O
