Boric acid free flux

Abstract

The invention described herein pertains generally to boric acid free flux composition wherein in some embodiments, a phthalocyanine pigment is used to effect a color change at activation temperature.

Claims

1. A boric acid free paste flux composition which comprises the following components: TABLE-US-00005 water balance a wetting agent 0.25-0.50% potassium bifluoride (KHF.sub.2) 12.4-16.8% fumed silica (SiO.sub.2) 0.71-1.35% potassium tetraborate (K.sub.2B.sub.4O.sub.74H.sub.20) 29.5-34.8% potassium fluoroborate (KBF.sub.4) 29.5-34.8% pigment 0.50-0.98% wherein amounts of said components are on the basis of weight percentages with respect to a combined total of 100% by weight.

2. The paste flux composition of claim 1 wherein said pigment is a phthalocyanine pigment which changes from colored to colorless at a temperature of approximately 500-600 C.

3. A process of using a boric acid free paste flux of claim 1 which comprises the step of: adding a phthalocyanine pigment to said flux.

4. The process of claim 3 wherein said step of adding a phthalocyanine pigment effects a color change at an activation temperature of said flux.

5. The process of claim 4 wherein said color change is effected at an activation temperature of between approximately 500-600 C.

6. A boric acid free paste flux, comprising: a wetting agent in a weight percentage in the range of 0.25 to 0.50%; an etchant in a weight percentage in the range of 12.4 to 16.8%; an emulsifying agent in a weight percentage in the range of 0.71 to 1.35%; potassium tetraborate in a weight percentage in the range of 29.5 to 34.8%; potassium fluoroborate in a weight percentage in the range of 29.5 to 34.8%; and pigment in a weight percentage in the range of 0.50 to 0.98%; wherein the balance is water.

7. The boric acid free paste flux of claim 6, wherein said flux is green in color.

8. The boric acid free paste flux of claim 6, wherein said flux is fully active in the temperature range of 566 to 871 C.

9. The boric acid free paste flux of claim 6, wherein said etchant is potassium bifluoride.

10. The boric acid free paste flux of claim 6, wherein said emulsifying agent is fumed silica.

11. The boric acid free paste flux of claim 6, wherein said pigment is a phthalocyanine pigment.

12. The boric acid free paste flux of claim 6, wherein said flux changes color at a temperature within the range of approximately 500 to 600 C.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The best mode for carrying out the invention will now be described for the purposes of illustrating the best mode known to the applicant at the time of the filing of this invention. The examples are illustrative only and not meant to limit the invention, as measured by the scope and spirit of the claims.

(2) As used herein, the term approximately means within the stated ranges with a tolerance of 10%.

(3) 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.

(4) The invention will now be described in a series of non-limiting, but illustrative examples.

Example #1

(5) In one embodiment of the invention, a black high temperature paste flux is described, the composition of which includes a mixture of water, potassium bifluoride, boron, udylite and fumed silica in the following weight percentages.

(6) TABLE-US-00001 TABLE 1 High Temperature Boric Acid Free Paste Flux Component Weight Percentage Water balance Udylite (wetting agent 62) 0.25-0.50% wetting agent/surfactant Potassium bifluoride (KHF.sub.2) 12.4-16.8% etchant/clean base metal surface Fumed silica (SiO.sub.2) 0.71-1.35% emulsifying agent/plasticizer Potassium tetraborate (K.sub.2B.sub.4O.sub.74H.sub.2O) 29.5-34.8% dissolve metallic oxides and protect brazing surface from oxidation Potassium fluoroborate (KBF.sub.4) 29.5-34.8% dissolve metallic oxides and halides and protect brazing surface from oxidation Boron 0.50-0.98% protect surface from oxidation at high brazing temperatures

Example #2

(7) In another embodiment of the invention, a low temperature boric acid free paste flux will include a mixture of water, potassium bifluoride, potassium tetraborate, potassium fluoroborate, pigment, Udylite and fumed silica in the following weight percentages.

(8) TABLE-US-00002 TABLE 2 Low Temperature Boric Acid Free Paste Flux Component Weight Percentage Water balance Udylite (wetting agent 62) 0.25-0.50% wetting agent/surfactant Potassium bifluoride (KHF.sub.2) 12.4-16.8% etchant/clean base metal surface Fumed silica (SiO.sub.2) 0.71-1.35% emulsifying agent/plasticizer Potassium tetraborate (K.sub.2B.sub.4O.sub.74H.sub.2O) 29.5-34.8% dissolve metallic oxides and protect brazing surface from oxidation Potassium fluoroborate (KBF.sub.4) 29.5-34.8% dissolve metallic oxides and halides and protect brazing surface from oxidation Pigment (phthalocyanine) 0.25-0.98% active temperature indicator

Example #3

(9) In another embodiment of the invention, a high temperature boric acid free powder flux will include a mixture of potassium tetraborate, potassium fluorosilicate, potassium fluoroborate and boron in the following weight percentages.

(10) TABLE-US-00003 TABLE 3 High Temperature Boric Acid Free Powder Flux Component Weight Percentage Potassium tetraborate (K.sub.2B.sub.4O.sub.74H.sub.2O) 46.2-51.6% dissolve metallic oxides and protect brazing surface from oxidation Potassium fluorosilicate (K.sub.2SiF.sub.6) 1.20-1.99% wetting agent/surfactant Potassium Fluoroborate (KBF.sub.4) 46.2-51.6% dissolve metallic oxides and halides and protect brazing surface from oxidation Boron 0.85-1.02% protect surface from oxidation at high brazing temperatures

Example #4

(11) In another embodiment of the invention, a low temperature boric acid free powder flux will include a mixture of potassium tetraborate, potassium fluorosilicate, potassium fluoroborate and a pigment in the following weight percentages.

(12) TABLE-US-00004 TABLE 4 Low Temperature Boric Acid Free Powder Flux Component Weight Percentage Potassium tetraborate (K.sub.2B.sub.4O.sub.74H.sub.2O) 46.2-51.6% dissolve metallic oxides and protect brazing surface from oxidation Potassium fluorosilicate (K.sub.2SiF.sub.6) 1.20-1.99% wetting agent/surfactant Potassium Fluoroborate (KBF.sub.4) 46.2-51.6% dissolve metallic oxides and halides and protect brazing surface from oxidation Pigment (phthalocyanine 500-600 C.) 0.50-0.98% active temperature indicator

(13) As described above, the phthalocyanine pigment is an aromatic macrocyclic 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 macrocyclic 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.

(14) ##STR00001##

(15) The above compositions are useful for the brazing of metallic materials based on copper, silver, nickel and iron based alloys. Without being held to any one theory or mechanism of operation, 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.

(16) The four classes of fluxes were tested and met all AWS A5.31M/A5.31:2012 testing standards for water content, particle, adhesion, fluidity, fluxing action, flow, life and viscosity.

(17) The boric acid free fluxes described in Tables 1-4 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. The following tests were performed.

(18) Oxide Removal

(19) All of the boric acid free fluxes in Tables 1-4 dissolved all oxides from the base metal surface. The paste fluxes outperformed commercially available EASY-FLO flux, which contains boric acid, having a registered office at Johnson Matthey Plc., 5th Floor 25 Farringdon Street, London EC4A 4AB, United Kingdom.

(20) Activation Range

(21) All of the boric acid free fluxes in Tables 1-4 are fully active, removing oxides, throughout the range of 1050 F.-1600 F. (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.

(22) The powder fluxes outperformed commercially available EASY-FLO flux, which contains boric acid, commercially available from Johnson Matthey Plc. and having a registered office at 5th Floor 25 Farringdon Street, London EC4A 4AB, United Kingdom, as well as BRAZETEC flux, commercially available from Umicore AG & Co. KG, Business Line BrazeTec, Rodenbacher Chaussee 4, 63457 Hanau Wolfgang, Germany.

(23) Hot Rodding

(24) Hot Rodding is the coating of a piece of brazing rod (filler metal) by dipping a hot end into a powdered flux. The boric acid free fluxes in Tables 1-4 coated 22% better than a commercially available powder flux, STTS Flux IT 340 M, available from STTS Brazing Solutions, Z.A.E. la Neuvillette 60240 Fleury (France).

(25) Flux Flowability in Activation Range

(26) A flowability test, AWS FB3-K, was performed per AWS A5.31M/A5.31:2012. Flowability was good for both the powder and the paste fluxes for the boric acid free fluxes in Tables 1-4. The paste flux flowabilty was superior, outperforming commercially available EASY-FLO flux, which contains boric acid, commercially available from Johnson Matthey Plc., having a registered office at 5th Floor 25 Farringdon Street, London EC4A 4AB, United Kingdom.

(27) Brazing Odor and Fumes

(28) There was very little objectionable odor and fumes throughout the brazing process for all of the boric acid free fluxes in Tables 1-4. The powder flux had significantly less odor than that of the Castolin boric acid containing flux, which was tested, commercially available from Castolin Eutectic International.

(29) Activation Indicator

(30) The pigmented fluxes of Tables 2 & 4 were the only fluxes that has a visual indicator of activation temperature.

(31) The invention has been described with reference to preferred and alternate embodiments. Obviously, modifications and alterations will occur to others upon the reading and understanding of the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.