Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
  • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
  • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K33/00—Specially-profiled edge portions of workpieces for making soldering or welding connections; Filling the seams formed thereby
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
  • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
  • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
  • B23K35/025—Pastes, creams, slurries
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
  • B23K35/3601—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with inorganic compounds as principal constituents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
  • B23K35/3601—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with inorganic compounds as principal constituents
  • B23K35/3603—Halide salts
  • B23K35/3605—Fluorides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
  • B23K35/3601—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with inorganic compounds as principal constituents
  • B23K35/3606—Borates or B-oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
  • B23K35/3601—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with inorganic compounds as principal constituents
  • B23K35/3607—Silica or silicates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
  • B23K35/3612—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with organic compounds as principal constituents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
  • B23K35/3612—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with organic compounds as principal constituents
  • B23K35/3613—Polymers, e.g. resins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
  • B23K35/362—Selection of compositions of fluxes

Definitions

• the invention is related to a boric acid free paste flux composition according to claim 1 , to a low temperature boric acid free paste flux composition according to claim 6, to a high temperature boric acid free paste flux composition according to claim 7, to a boric acid free powder flux composition according to claim 8, to a high temperature boric acid free powder flux composition according to claim 11 , to a low temperature boric acid free powder flux composition according to claim 12, to a process of making a boric acid free flux according to claim 13 and to a process of making a boric acid free flux according to claim 15.
• the invention described herein pertains generally to boric acid free brazing flux compositions.
• brazing fluxes remove oxides and contaminants from base materials to ensure good quality brazed joints.
• the choice of flux depends on the base material to be used, in addition to the filler metal types, heat source, and application method.
• Brazing joins similar and dissimilar materials by heating them in the presence of filler metal having a liquidus above 425°C - 450°C ( ⁇ 800°F - 840°F) and below the solidus of the base material.
• filler metal flows between fitted surfaces of the joint by capillary action.
• the minimum temperature on the surface of the component to be brazed at which said process takes place undisturbed is the so-called working temperature. It is a characteristic quantity for the filler metal in question.
• Filler metals can be alloys or pure metals. In gen- eral, the heat from brazing is less damaging than the heat from welding. Additionally, brazed joints typically have higher strength than soft-soldered joints. The choice of flux plays an important role in most all brazing processes, and the use of an incorrect flux can compromise joint quality.
• the molten filler metal In order to be able to form a bond with the base metal, the molten filler metal must come into direct contact with the base metal. Oxide layers of the kind present on any engineering metal surface must thus be loosened first and removed. If brazing takes place in the air, this is achieved by covering the brazing site with fluxes in the melt flow in which the oxides dissolve, are reduced or decompose at and above the active temperature of the flux.
• fluxes When heated, fluxes dissolve surface oxides and protect the cleaned surfaces from re-oxidation, transfer heat from the heat source to the joint, and remove oxidation products, allowing filler metal to contact and wet the base materials.
• Brazing fluxes, pastes or powders activate at temperatures below those needed to melt filler metals. Because fluxes must be in close contact with the joint surfaces, they are liquid or gaseous at brazing temperatures. They remove only surface oxides and tarnish. Other contaminants must be removed either mechanically or chemically before brazing.
• Fluxes are typically classified by form (powder, liquid, or paste), base materials and filler metals they can be used with, heat source, application method, and active temperature range.
• Silver brazing fluxes conain boric acid and potassium borates, combined with complex potassium fluoborate and fluoride compounds. Fluorides, up to 40% in flux content, give these fluxes their characteristically low melting points and high capacity for dissolving metal oxides.
• the melting point and the effective temperature of the fluxes must be matched to the working temperature of the brazing filler metal used, whereby the flux should melt at about 50-100°C below the working temperature of the filler metal used and become fully effective from this temperature onwards. Moreover, the molten flux should form a dense, uniform coating on the workpiece which remains intact at the required brazing temperature and for the duration of the brazing period.
• the liquid filler metal is able to spread in a thin layer on the base metal surface, wetting it.
• the filler metal adheres to the base metal surface by a slight alloying of the base and filler metals.
• the filler metal spreads out over the joint surface and, after solidifying, forms a loadable joint with the base metal.
• Brazing fluxes are composed substantially of salt mixtures which, in the molten state, are capable of dissolving metal oxides.
• These fluxes are substantially inorganic boron compounds such as, in particular, alkali borates and fluoroborates, including boric acid, and halides such as, in particular, an alkali halide; e.g. alkali fluorides.
• boric acid a component of most brazing fluxes
• At least one aspect of the invention resides in the superior ability to achieve desirable flux characteristics without the presence of boric acid (H 3 B0 3 ) or borax (NaB 4 0 5 (OH) 4 H 2 0) in the flux.
• a boric acid free paste flux composition according to claim 1 is described and a low temperature boric acid free paste flux composition according to claim 6, a high temperature boric acid free paste flux composition according to claim 7, a boric acid free powder flux composition according to claim 8, a high temperature boric acid free powder flux composition according to claim 11 , a low temperature boric acid free powder flux composition according to claim 12, a process of making a boric acid free flux according to claim 13 and to a process of making a boric acid free flux according to claim 15.
• Preferred embodiments of the invention are subject of the subclaims.
• the invention describes various flux compositions which do not contain boric acid, and which optionally include a color change pigment at activation temperature, e.g., a phthalocyanine pigment.
• a boric acid free paste flux composition which comprises: water;
• KHF 2 potassium bifluoride
• wetting agent 0.1-1%
• potassium fluoroborate (KBF 4 ) 26-35%; and boron 0.1-2%.
• a boric acid free powder flux composition which comprises: potassium tetraborate (K 2 B 4 0 7 -4H 2 0);
• a boric acid free paste flux composition which contains: water; potassium bifluoride (KHF 2 ); fumed silica (Si0 2 ); potassium tetraborate (K 2 B 4 0 7 « 4H 2 0); and potassium fluoroborate (KBF 4 ).
• KHF 2 potassium bifluoride
• Si0 2 fumed silica
• K 2 B 4 0 7 « 4H 2 0 potassium tetraborate
• K 2 B 4 0 7 « 4H 2 0 potassium fluoroborate
• KF 4 potassium fluoroborate
• one embodiment of the boric acid free paste flux composition contains on a weight percent basis: water (balance to total 100%); a wetting agent, preferably UDYLITE 62 (0.1-1%); potassium bifluoride (KHF 2 ) (12-16%); fumed silica (Si0 2 ) (0.1-4%); potassium tetraborate tetrahydrate ( ⁇ 2 ⁇ 4 0 7 ⁇ 4 ⁇ 2 0) (26-35%); potassium fluoroborate (KBF 4 ) (26-35%); and pigment (phthalocyanine) (0.1-2%).
• a wetting agent preferably UDYLITE 62 (0.1-1%)
• KHF 2 potassium bifluoride
• fumed silica Si0 2
• potassium tetraborate tetrahydrate ⁇ 2 ⁇ 4 0 7 ⁇ 4 ⁇ 2 0
• potassium fluoroborate KF 4
• pigment phthalocyanine
• boric acid free paste flux composition contains on a weight percent basis: water (balance to total 100%); wetting agent, preferably UDYLITE 62 (0.1-1%); potassium bifluoride (KHF 2 ) (12-16%); fumed silica (Si0 2 ) (0.1-4%); potassium tetraborate tetrahydrate ( ⁇ 2 ⁇ 4 0 7 ⁇ 4 ⁇ 2 0) (26-35%); potassium fluoroborate (KBF 4 ) (26-35%); and boron (0.1-2%).
• wetting agent preferably UDYLITE 62 (0.1-1%
• KHF 2 potassium bifluoride
• fumed silica Si0 2
• potassium tetraborate tetrahydrate ⁇ 2 ⁇ 4 0 7 ⁇ 4 ⁇ 2 0
• potassium fluoroborate KF 4
• boron 0.1-2%
• the boric acid free powder flux composition includes: potassium tetraborate (K 2 B 4 0 7 *4H 2 0); potassium fluorosilicate (K 2 SiF 6 ); and potassium fluoroborate (KBF 4 ).
• the boric acid free powder flux will contain boron.
• one embodiment of the boric acid free powder flux composition will include on a weight basis: potassium tetraborate tetrahydrate ( ⁇ 2 ⁇ 4 0 7 ⁇ 4 ⁇ 2 0) (44-54%); potassium fluorosilicate (K 2 SiF 6 ) (1-3%); potassium fluoroborate (KBF 4 ) (44-54%); and boron (0.1-2%).
• boric acid free powder flux composition will include on a weight basis: potassium tetraborate tetrahydrate ( ⁇ 2 ⁇ 4 ⁇ 7 ⁇ 4 ⁇ 2 0) (44-54%); potassium fluorosilicate (K 2 SiF 6 ) (1-3%); potassium fluoroborate (KBF 4 ) (44-54%); and pigment (phthalocyanine) (0.1 -2%).
• the invention includes a process of making a boric acid free flux which comprises the step of replacing boric acid present in a boric acid containing flux with a substantially similar molar amount of potassium tetraborate tetrahydrate ( ⁇ 2 ⁇ 4 ⁇ 7 ⁇ 4 ⁇ 2 0).
• the process optionally also includes the step of adding a phthalocyanine pigment effects a color change at an activation temperature of said flux.
• the invention further includes a process of making a boric acid free flux which comprises the step of: replacing borax present in a borax containing flux with a substantially similar molar amount of potassium tetraborate tetrahydrate ( ⁇ 2 ⁇ 4 ⁇ 7 ⁇ 4 ⁇ 2 0).
• the process optionally also includes the step of adding a phthalocyanine pigment effects a color change at an activation temperature of said flux.
• the present brazing flux composition is boric acid free, provides good wetting characteristics and changes color from a color in the visible spectrum to clear at activation temperature.
• Boric acid has a melting temperature of approximately 336°F (169°C) and melts early during heating in the brazing process. This allows boric acid brazing fluxes to begin melting at low temperatures, well before brazing temperature is reached, thereby protecting the faying surfaces from further oxidation. Additionally, this low melting temperature, coupled a boiling/dehydration temperature of approximately 532°F (300°C) helps to create brazing fluxes that hot rod well, that is to say that the flux will melt, then subsequently freeze, adhering to heated brazing rod.
• boric acid By the time boric acid reaches 842°F (450°C) it completely dehydrates (or decomposes releasing H 2 0) leaving boron trioxide, which protects the base and filler metal surfaces throughout the remaining brazing process.
• Replacing boric acid in a brazing flux requires the substitution of the boric acid with one or more compounds that can approximately duplicate the above properties.
• Potassium carbonate offers protection at temperatures exceeding 1600°F (871 °C); and combining potassium carbonate with diammonium phosphate (DAP) would allow protection from oxidation above 302°F (150°C).
• DAP diammonium phosphate
• this combination was not practical for a dry powdered flux due to the deliquescence of potassium carbonate, the tendency of the flux to absorb moisture.
• the high dissociation partial pressure of ammonia from DAP require that the flux remain in a tightly sealed container when it is not in use, to preserve flux chemical and physical properties.
• ammonia fluoroborate and fluorosilicate The release of ammonia is also an issue with the ammonia fluoroborate and fluorosilicate; the release of ammonia is exacerbated when the paste flux is made due to the ready dissociation of ammonia from its anionic counterparts in an aqueous solution, though water gain is not an issue.
• these flux formulations yield an adequate performance, better alternatives were pursued based on at least two factors: (1 ) the unpleasant ammonia fume, from flux application to heating; and (2) the probable change in flux properties through hygroscopic update over time.
• Potassium tetraborate is also found in brazing fluxes. It readily dissolves metallic (not refractory) oxides at high temperature almost as well as potassium pentaborate (also another replacement option) at a fraction of the cost. It was selected as an option to consider in the replacement of boric acid.
• Anhydrous potassium tetraborate alone does not melt until 1500°F (816°C) and is hygroscopic, converting to the tetrahydrate with prolonged exposure to humidity. Hydration of powdered anhydrous potassium tetraborate fluxes causes an uncontrolled change in flux properties over time and imposes unnecessary conditions and/or processing during manufacture. Hydration is an exothermic process that causes manufacturing concerns.
• potassium tetraborate tetrahydrate was chosen as a preferred replacement over anhydrous potassium tetraborate as a boric acid substitute.
• a black high temperature paste flux is described, the composition of which includes a mixture of water, potassium tetraborate tetrahydrate, potassium bifluoride, boron, UDYLITE (Udylite 62 is a product of Enthone ® , 350 Frontage Road, West Haven, CT) and fumed silica in the following weight percentages.
• a low temperature boric acid free paste flux will include a mixture of water, potassium bifluoride, potassium tetraborate tetrahydrate, potassium fluoroborate, pigment, UDYLITE and fumed silica in the following weight percentages. Table II
• Copper Phthalocyanine Green No. 7 was employed in several compositions as a visual indicator of activation temperature. It decomposes in the range of temperature form 1022°F (550°C) to 1650°F (900°C), depending on the level of accessible oxidizing agents. Testing revealed reliable correlation between the color change of the low temperature (green) brazing fluxes from green to clear and brazing temperature, at the faying surfaces. Furthermore this color change did not appear to be dependent on the level of pigmentation.
• Example #3
• a high temperature boric acid free powder flux will include a mixture of potassium tetraborate tetrahydrate, potassium fluorosilicate, potassium fluoroborate and boron in the following weight percentages.
• a low temperature boric acid free powder flux will include a mixture of potassium tetraborate tetrahydrate, potassium fluorosilicate, potassium fluoroborate and a pigment in the following weight percentages. Table IV
• the phthalocyanine pigment is an aromatic macrocvclic compound that forms coordination complexes with many elements of the periodic table. These complexes are intensely colored which facilitates the color transformation at temperatures employed in the reaction. As described above, the phthalocyanine pigment is an aromatic macrocvclic compound that forms coordination complexes with many elements of the periodic table. These complexes are intensely colored which facilitates the color transformation at temperatures employed in the reaction from colored in the visible spectrum to essentially colorless at temperature.
• the phthalocyanine macrocyclic compound is illustrated below, and wherein a metallic ion would be coordination bonded to the nitrogen atoms, typically within the 5-membered rings.
• compositions are useful for the brazing of metallic materials based on copper, silver, nickel and iron based alloys.
• the flux is used to remove the oxide layer and enable the wetting of the base materials.
• the activated flux creates a layer on the workpiece and removes any surface oxides.
• the color change at activation temperature is a distinct characteristic not seen when compared to fluxes commercially available for purchase.
• compositions and combinations of the above fluxes were tested and met all AWS A5.31 M/A5.31 :2012 testing standards for water content, particle, adhesion, fluidity, fluxing action, flow, life and viscosity.
• boric acid free fluxes described in Tables l-IV deliver excellent performance, standing on their own as brazing fluxes. As discussed below, the boric acid free fluxes deliver results often superior to commercially available standard fluxes that are not boric acid free.
• boric acid free fluxes are fully active, removing oxides, throughout the range of 1050°F - 1600 (566°C - 871°C) and 1050°F - 1800°F (566°C - 982°C), for the low temperature (green) flux and the high temperature flux (black) respectively.
• Hot Rodding is the coating of a piece of brazing rod (filler metal) by dipping a hot end into a powdered flux. This is applicable to powder fluxes only. Both powder fluxes "hot rodded” extremely well.
• a flowability test was performed per AWS A5.31 M/A5.31 :2012. Flowability was good for both the boric acid free powders and the pastes.
• Hot Rod The ability of a powder brazing flux to adhere to a hot brazing rod/wire.
• (2) Flux Flow How well the molten flux spreads, or “wets out", across the heated surface of the base-metal(s) - more specifically, how well the molten flux flows along the brazing joint capillary and the immediately adjacent faying surfaces;
• Metal Flow - Metal flow is an arbitrary measure of the brazing flux's ability to lower the surface tension of the molten filler metal at the base-metal surface - it is in general measured by how well the molten filler metal spreads, or "wets out", across the heated surface of the base-metal(s) - more specifically, how well the molten filler metal flows along the brazing joint capillary and the immediately adjacent faying surfaces;
• Hot Clean The ease with which flux residue is removed using hot water alone.
• Each criterion is evaluated for the flux formulation as having a subjective value between one and five, where 1 (one) is “not desirable” and 5 (five) is “desirable”.
• Potassium tetraborate is a common component in brazing fluxes. It readily dissolves metallic (not refractory) oxides at high temperature; this makes it a natural consideration for replacement of boric acid; for these reasons it was actually the chemical of first choice.
• Anhydrous potassium tetraborate alone does not melt until 1500°F (816°C) and is hygroscopic, converting to the tetrahydrate with prolonged exposure to humidity. Hydration of powdered anhydrous potassium tetraborate fluxes causes an uncontrolled change in flux properties over time and imposes unnecessary conditions and/or processing during manufacture. Hydration is an exothermic process that causes manufacturing concerns.
• potassium tetraborate tetrahydrate was chosen as a preferred embodiment over anhydrous potassium tetraborate.
• Boric acid in both the powder and paste fluxes was replaced with potassium tetraborate tetrahydrate. This replacement was approximately a 1:1 molar ratio of borate content for both fluxes initially, and then adjusted against the wetting agent(s) to achieve the optimal performance.

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