Electric heating – Metal heating – By arc
Patent
1992-12-04
1994-07-05
Shaw, Clifford C.
Electric heating
Metal heating
By arc
219 74, 219 75, B23K 9167
Patent
active
053269578
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for and a method of welding surface-treated metallic work-pieces, and more particularly to an apparatus for and a method of welding zinc-plated steel plates according to a gas-shielded arc welding or plasma welding process.
BACKGROUND ART
Welding technology for welding overlapping steel plates is finding wide use primarily in the automobile industry. Steel plates used in the automobile are plated with zinc layers for corrosion resistance. Welding apparatuses for welding such zinc-plated steel plates include gas-shielded arc welding and plasma welding apparatuses.
In such a gas-shielded arc welding and plasma welding apparatus, an inert gas is ejected from around an electrode toward a molten pool on a base material, so that the base material is welded in a given gas atmosphere, or an arc column is constricted to obtain a high temperature.
When overlapping zinc-plated steel plates are welded, plated-zinc surface layers sandwiched between the steel plates are evaporated into a zinc gas because the plated zinc layers have a lower melting temperature than the steel plates. The zinc gas is highly pressurized as there is no space it can escape into. When the steel plates are then heated, they are melted, and the zinc gas under high pressure is released into the atmosphere, forcing aside the molten steel. Therefore, the welded joint contains blowholes as marks indicative of the release of the zinc gas, resulting in a reduction in the welding quality.
To avoid the above drawback, it has been customary in the welding of overlapping zinc-plated steel plates to space the zinc-plated steel plates from each other with a clearance therebetween, and a zinc vapor generated from plated-zinc surface layers sandwiched between the steel plates is allowed to escape through the clearance. It is necessary for such a clearance to be as small as possible from the standpoint of a good welding process. The clearance is created by placing a sheet between the steel plates or applying a coating material to the steel plates.
Controlling the clearance between the steel plates in an actual production site has required an extra procedure. Therefore, there has been a demand for a method of welding zinc-plated steel plates while they are being held in intimate contact with each other without any clearance therebetween.
DISCLOSURE OF THE INVENTION
In view of the aforesaid difficulties of the conventional welding apparatus, it is an object of the present invention to provide an apparatus for and a method of welding surface-treated metallic workpieces such as zinc-plated steel plates with high welding quality while they are being held in intimate contact with each other.
To achieve the above object, there is provided in accordance with the present invention an apparatus for welding surface-treated metallic workpieces that are composed of a base material coated with a material whose evaporation temperature is lower than the melting temperature of the base material, according to a gas-shielded arc welding or plasma welding process, the apparatus comprising supply means for supplying an auxiliary gas composed of an oxygen gas and other gases, and ejecting means for ejecting the auxiliary gas to a welding point on the surface-treated metallic workpieces.
According to the present invention, there is also provided a method of welding surface-treated metallic workpieces that are composed of a base material coated with a material whose evaporation temperature is lower than the melting temperature of the base material, according to a gas-shielded arc welding or plasma welding process, the method comprising the step of supplying an auxiliary gas composed of an oxygen gas and other gases to a welding point on the surface-treated metallic workpieces.
When the surface-treated metallic workpieces, such as zinc-plated steel plates, are welded in the atmosphere of the auxiliary gas which is ejected from the ejecting means, surface layers of zinc and oxygen react with each other, producing a so
REFERENCES:
patent: 3253113 (1966-05-01), Breymeier
patent: 3692973 (1972-09-01), Oku et al.
patent: 4904842 (1990-02-01), Yasuda et al.
Karube Norio
Mori Atsushi
Nakata Yoshinori
Yamazaki Etsuo
Fanuc Ltd.
Shaw Clifford C.
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