Metal treatment – Compositions – Fluxing
Reexamination Certificate
2000-06-24
2001-08-21
Jenkins, Daniel (Department: 1742)
Metal treatment
Compositions
Fluxing
C148S023000
Reexamination Certificate
active
06277210
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of silver brazing and, in particular, to a silver brazing flux that is non-corrosive and non-hygroscopic in nature.
BACKGROUND OF THE INVENTION
For many years, metal parts have been joined using silver-based brazing compounds. As is well known in the art, it is necessary to prepare the surfaces to be joined prior to applying the brazing compounds in order to provide adhesion of the brazing compound to the surfaces to be joined. This preparation is typically performed by a flux material, which is applied to the joint and activated by the application of heat to the joint. Once activated, the flux thoroughly cleans the surfaces to the joined and removes any oxides that will degrade the strength of the brazed joint.
As they must aggressively clean the surfaces to be joined, fluxes have typically been highly corrosive and hygroscopic in nature. Accordingly, it is necessary in many applications to remove any residual flux or flux residue from the joined parts in order to prevent corrosion of the parts. This removal increases the overall costs of the parts, due to the additional process steps and the cost of waste disposal from the cleaning process. In addition, the waste generated by this cleaning is hazardous to humans and harmful to the environment.
Finally, because of their corrosiveness and affinity for absorbing water, many typical fluxes have not been adapted for use in flux cored wires. As this is the case, the use of these fluxes has necessitated the additional step of applying the flux in a paste form prior to heating and joining the parts. As was the case with the cleaning step described above, the need to perform this additional step increases the overall cost of the joined parts.
Accordingly, there is a need for a flux for use with silver brazing compositions that effectively prepares the surfaces to be joined, is non-corrosive and non-hygroscopic and, accordingly, does not need to be cleaned from joined surfaces after they are joined, and may be formed into a powder for disposal within a flux cored wire.
SUMMARY OF THE INVENTION
The present invention is a silver brazing flux that is non-corrosive and non-hygroscopic in nature, and a method of making this flux. In it most basic form, the flux includes the following compounds in the following percentages by weight:
TABLE 1
Composition of Basic Flux Compound
COMPOUND
PERCENTAGE BY WEIGHT
Potassium Fluoroborate
21%-31%
Boric Acid
21%-31%
Potassium Bifluoride
19%-29%
Potassium Tetraborate
15%-25%
Potassium Carbonate
2.5%-4.5%
In some embodiments, the flux is combined with de-ionized water, or other suitable binder materials, to form a flux paste. In other embodiments, the flux is mixed and dried into a powder and dispensed within a sheath of silver based filler material, using the process described in U.S. Pat. No. 5,781,846, which is incorporated herein by reference, to form a flux cored brazing composition.
The preferred flux includes the same compounds in the following percentages by weight:
TABLE 2
Composition of Preferred Flux Compound
COMPOUND
PERCENTAGE BY WEIGHT
Potassium Fluoroborate
26.3%
Boric Acid
26.3%
Potassium Bifluoride
23.8%
Potassium Tetraborate
20.2%
Potassium Carbonate
3.5%
The basic method of making the flux includes the following steps:
Weighing all ingredients such that desired percentages are identified.
Adding boric acid on top of potassium bifluoride.
Mixing the boric acid and potassium bifluoride at medium-low speed until a completely smooth wet paste is formed.
Adding potassium tetraborate and mixing at medium low speed.
Adding potassium carbonate to the paste and mixing until it is completely dissolved
Adding de-ionized water to each step of the mixture as it begins to stiffen in order to keep a loose, smooth consistency, similar to that of cake frosting, and scraping the sides and bottom of the mixing bowl as needed to keep the mix even
Mixing the paste at medium speed.
Stopping the mixer and pouring the mixture into a pan.
Placing the pan into a pre-heated oven at approximately 560 degrees Fahrenheit for a period of four hours such that substantially all de-ionized water is dried from the mixture.
Removing the dried flux, milling to a powder and screening to a desired particle size.
The resulting flux powder is non-corrosive and non-hygroscopic, and is readily adapted for suspension within a paste or disposition within a sheath of brazing alloy to form a flux cored brazing composition.
Therefore, it is an aspect of the invention to provide a silver brazing flux that is non-corrosive.
It is a further aspect of the invention to provide a silver brazing flux that is non-hygroscopic.
It is a further aspect of the invention to provide a silver brazing flux that does not leave a residue that must be cleaned from surfaces after they are joined.
It is a further aspect of the invention to provide a silver brazing flux that effectively prepares surfaces for joining.
It is a further aspect of the invention to provide a silver brazing flux that may be formed into a powder.
It is a further aspect of the invention to provide a silver brazing flux that may be combined with a silver brazing alloy to form flux cored brazing composition.
It is a still further aspect of the invention to provide a silver brazing flux that may be combined with a binder material to form a flux paste.
REFERENCES:
patent: 4482607 (1984-11-01), Neelameggham et al.
patent: 5781846 (1998-07-01), Jossick
patent: 5984161 (1999-11-01), Koch et al.
Jenkins Daniel
Lawson, Philpot & Persson P.C.
Omni Technologies Corporation
Persson Michael J.
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