Electric heating – Metal heating – By arc
Reexamination Certificate
1999-06-07
2001-03-06
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121450, C219S121590, C219S076160
Reexamination Certificate
active
06198068
ABSTRACT:
It is also known to braze such joints using a copper-rich alloy of bronze filler wire. Performed correctly such brazed joints also offer structural enhancement.
Conventional brazing practice in these situations is to use either gas or GMA-brazing techniques. Gas brazing is comparatively slow due to the low temperature of the gas flame. As a consequence of slow brazing speeds, heat input to the joint area is high with a distinct propensity for joint and panel distortion. Furthermore, to activate joint metal and achieve good wetting of the base metal, an aggressive flux is necessary. Moreover, gas brazing causes problems due to the corrosive flux residue and the need for its subsequent removal. Consequently, for reasons of higher brazing speeds and the avoidance of corrosive fluxes, GMA-brazing has been adopted by many car manufacturers. Whilst offering the aforementioned advantages, this process, however, causes other problems. These include a rapid freezing rate which tends to cause microporosity, spatter adhesion to zinc panels with resultant localized damage to the panels and humped braze beads requiring excessive dressing.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a new brazing method by which a braze seam of cosmetic appearance may be obtained. Moreover, the brazing method should permit a high brazing speed.
This object is obtained by means of the method defined in claim
1
. By supplying a first gas comprising a principal inert component including at least argon and in a minor amount an active component, it is possible to reduce the number of spatter particles in the area of the braze seam. Moreover, the addition of an active component improves the wetting, resulting in a braze seam having a smooth and uniform shape and demonstrating a low microporosity. Consequently, the braze seam produced requires a minimum of finishing work, and such work required may be performed by means of soft methods, such as fine grinding, polishing etc. A good wetting also enables a high deposition rate and thus a high productivity. Furthermore, due to the relatively low temperature, in comparison with MIG-welding, the brazing process will not negatively affect the material of the work piece. A thin surface layer will be maintained.
The object is also obtained by the method defined in claim
4
. In a corresponding manner, by supplying a shielding gas comprising a principal inert component including at least argon and in a minor amount an active component, wetting properties may be improved and the amount of spatter reduced.
According to an embodiment of the present invention, said principal inert component includes a gas mixture of argon and helium. By adding helium the heat transfer is improved, resulting in a higher brazing speed. Preferably, said gas mixture comprises 30 to 90% by volume of helium and 10 to 70% by volume of argon. According to a further example said gas mixture may comprise 55 to 65% by volume of helium and 35 to 45% by volume of argon.
According to a further embodiment of the present invention, said active component includes at least one gas having an oxidizing effect. Such an active component stabilizes the arc, which is an important precondition for a uniform braze seam having a smooth and cosmetic appearance. Thereby, said active component may include at least one of NO, CO
2
, CO, O
2
, N
2
O, H
2
and N
2
. Moreover, the concentration of said active component may at most be 1% by volume, preferably 0.001% by volume to 0.5% by volume. In the case that the active component includes NO, the concentration of NO may be 0.001% by volume to 0.05% by volume.
According to a further embodiment of the present invention, said braze material comprises as the principal component Cu and a minor amount of Al, Si, Sn or mixtures thereof.
According to a further embodiment of the present invention, the work piece comprises at least two parts to be joined together by the material from the electrode. The work piece may comprise a metal substrate having a thin coating surface layer comprising at least one of the elements zinc and aluminium. Such coating surface layer may comprise a primer containing zinc or aluminium. By means of the inventive method such primer layer need not to be removed before brazing. It is also possible to keep the development of fume and dense fume on a low level, even if such surface layer has not been removed. Moreover, the inventive method reduces the build-up of dirt on the arc-forming device. Alternatively, the thin surface layer may be a metallic layer having a thickness of less than 30 &mgr;m, in particular less than 10 &mgr;m. The inventive method reduces the zinc loss in the proximity of the braze seam. Due to the low number of spatter particles localized damage to the surface layer of the work pieces may be avoided.
REFERENCES:
patent: 4058698 (1977-11-01), Bykhovsky et al.
patent: 4081656 (1978-03-01), Brown
patent: 4152571 (1979-05-01), Shimada et al.
patent: 4921157 (1990-05-01), Dishon et al.
patent: 5820939 (1998-10-01), Popoola et al.
patent: 417 595 A1 (1990-09-01), None
AGA AB
Paschall Mark
Pearne & Gordon LLP
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