EP3523085A1

EP3523085A1 - Corrosive flux cored wire and method of manufacture

Info

Publication number: EP3523085A1
Application number: EP18795850.9A
Authority: EP
Inventors: William DUFRAISSE; Franck Rousseau; Dean Wayne KICK; Ronald Joseph MCGUIRE
Original assignee: Lucas Milhaupt Inc
Current assignee: Lucas Milhaupt Inc
Priority date: 2017-10-03
Filing date: 2018-10-03
Publication date: 2019-08-14
Also published as: WO2019070779A1

Abstract

A brazing wire including a first metal alloy wrap defining an encasing perimeter around a core and having a longitudinal seam extending over a length of the first metal alloy wrap, and a second metal alloy wrap disposed within the core of the first metal alloy wrap. The second metal alloy wrap defines an encasing perimeter around a core and has a longitudinal seam extending over a length of the second metal alloy wrap. The brazing wire further includes a corrosive flux material disposed within the core of the second metal alloy wrap.

Description

CORROSIVE FLUX CORED WIRE AND METHOD OF MANUFACTURE

BACKGROUND

1. Field of the Disclosure

[0001] The present disclosure relates to a corrosive flux cored wire, wherein a corrosive flux forms the core of a wire having multiple wraps to protect the corrosive flux core from exposure.

2. Discussion of the Related Art

[0002] Brazing applications in the auto industry and HVAC industry include aluminum parts having higher percentages of magnesium, such as 5000 and 6000 series aluminum. Using a corrosive flux provides a better brazed joint than the use of a non-corrosive flux. In addition, a brazing wire having a non- corrosive flux is known to leave behind a cosmetic stain that is hard to remove from the finish parts. This stain can be the result of residue from the binder in the non-corrosive flux. However, any such corrosive flux is highly hygroscopic.

[0003] Previous attempts to create an aluminum brazing wire having a corrosive flux core have failed to properly prevent the corrosive flux from absorbing moisture and corroding the brazing wire while being stored. In addition, having the corrosive flux exposed on the exterior of the aluminum brazing wire would be dangerous to the user, since the corrosive flux is corrosive to skin as well as metal.

[0004] As a result, there is a need in the art for an aluminum brazing wire having a flux core that can properly shield the corrosive flux contained in a core of the brazing wire from moisture and the external environment to prevent absorption of moisture and corrosion of the product. In turn, such an aluminum brazing wire having a corrosive flux core would be preferred in the auto and HVAC industries, since their application would result in finished parts without the cosmetic stains associated with non-corrosive fluxes. SUMMARY OF THE DISCLOSURE

[0005] A corrosive flux cored wire is disclosed, wherein a corrosive flux forms the core of the wire and is surrounded by multiple alloy wraps to isolate the corrosive flux from the external environment.

[0006] In accordance with an aspect of the disclosure, a brazing wire includes a first metal alloy wrap defining an encasing perimeter around a core and having a longitudinal seam extending over a length of the first metal alloy wrap, and a second metal alloy wrap disposed within the core of the first metal alloy wrap. The second metal alloy wrap defines an encasing perimeter around a core and has a longitudinal seam extending over a length of the second metal alloy wrap. The brazing wire further includes a corrosive flux material disposed within the core of the second metal alloy wrap.

[0007] According to another aspect of the disclosure, the corrosive flux includes at least one of lithium chloride, zinc chloride, cesium chloride, stannous chloride, potassium fluoroaluminate, potassium tetrafluoroaluminate, cesium fluoroaluminate, and cesium tetrafluoroaluminate. In addition, the corrosive flux is 15% w/w of the brazing wire. In the context of the present disclosure, the abbreviation "w/w" means "weight for weight" and represents the proportion of the finished brazing wire by weight. As used above with reference to the corrosive flux, 15% w/w means that the corrosive flux makes up 15% by weight of the finished corrosive flux brazing wire. The weight proportion of the corrosive flux in the disclosed brazing wire is not limited to 15% w/w, and may vary between 7% w/w and 35% w/w.

[0008] According to yet another aspect of the disclosure, the first metal alloy wrap and the second metal alloy wrap may comprise an aluminum alloy having 12% w/w silicon. The disclosed corrosive flux core brazing wire may be constructed with wraps comprising any alloy used to join 3000 series, 5000 series and 600 series aluminum base metals. Such alloys include, but are not limited to AISi12, AISi10, AISi7, AIMg5, AI822, and AI802. [0009] Further, in a disclosed embodiment the first (outer) metal alloy wrap has a diameter of 2.0 mm, and the second (inner) metal alloy wrap has a diameter of 1.6 mm. The disclosed corrosive flux core brazing wire is not limited to a single diameter and may be produced in a range of finished outside diameters and cross sectional shapes. Alternative round brazing wire sizes include a corrosive flux core brazing wire with a first (outer) metal alloy wrap with an outside diameter of 1 .6mm and a second (inner) metal alloy wrap with an outside diameter of 1 .2mm. An alternative non-round corrosive flux core brazing wire according to aspects of the disclosure may take the form of a flat band, with an inner metal alloy wrap having dimensions of 1 .4mm x 2.3mm. An outer metal alloy wrap surrounds the inner metal alloy wrap.

[0010] According to another aspect of the disclosure, the corrosive flux material has a melting temperature less than a melting temperature of the first metal alloy wrap; and less than a melting temperature of the second metal alloy wrap.

[0011] In according with another embodiment of the disclosure, a method of manufacturing a brazing wire includes providing a first metal sheet, disposing a corrosive flux on the first metal sheet, forming the first metal sheet into a first metal wrap with a core so that the corrosive flux is disposed within the core of the first metal wrap. In addition, the method includes providing a second metal sheet, disposing the first metal wrap on the second metal sheet, and forming a second metal sheet into a second metal wrap having a core so that the first metal wrap is disposed within the core of the second metal wrap.

[0012] According to yet another aspect of the disclosure, the first metal sheet and the second metal sheet may be an aluminum alloy having 12% w/w silicon (AISi12). In addition, the first (outer) metal wrap may be formed to a diameter of 2.0 mm, and the second (inner) metal wrap may be formed to a diameter of 1 .6 mm. The corrosive flux measures 15% w/w of the brazing wire, or alternatively between 7% w/w and 35% w/w of the brazing wire. [0013] The first and second metal sheets used to form the first and second metal alloy wraps are elongated strips having generally parallel longitudinal edges. According to an aspect of the disclosure, when forming the first metal wrap, a first longitudinal edge of first metal sheet overlaps a second longitudinal edge of the first metal sheet by 20°-30° of a circumference of the first metal wrap to form a seam. Similarly, when forming the second metal wrap, a first longitudinal edge of the second metal sheet and overlaps a second longitudinal edge of the second metal sheet by 20°-30° of a circumference of the second metal wrap to form a seam. An overlap of 20° to 30° has proven effective in isolating the corrosive flux core from the external environment, but the disclosed corrosive core brazing wire and methods of manufacture are not limited to this range of overlap. Overlaps of between 10° and 50° of the circumference of the first and second metal wraps may also be used, according to aspects of the disclosure. Embodiments of the disclosed corrosive core brazing wire are disclosed with the same overlap in the inner wrap and outer wrap, but the overlap of the inner wrap may be different from the overlap of the outer wrap.

[0014] In accordance with yet another aspect of the disclosure, a brazing wire includes a first (outer) wrap that surrounds a first core and has a first longitudinal edge overlapping a second longitudinal edge by 10° - 50° of a circumference of the first (outer) wrap to form a first seam. A second (inner) wrap surrounds a second core and has a first longitudinal edge overlapping a second longitudinal edge by 10° - 50° of a circumference of the second (inner) wrap to form a second seam. The second (inner) wrap is disposed within the core of the first (outer) wrap. A corrosive flux material is disposed within the core of the second (inner) wrap and is protected from the external environment by the first and second metal alloy wraps. Alternatively, the overlap of the longitudinal edges of the wraps may be expressed in terms of the thickness of the wraps. Specifically, the overlap of the longitudinal edges of the wraps is at least two times the thickness of the wrap, and preferably between 2 and 6 times the thickness of the wrap.

[0015] An enhancement of the disclosed corrosive flux core brazing wire and manufacturing methods may include applying a coating to the corrosive flux core brazing wire to improve protection of the corrosive flux from the exterior environment. The coating may be applied by dipping and wiping, or spray coating, with the brazing wire then dried. The coating is selected to decompose into inert substances that do not contaminate the brazed joint. Suitable coatings may include a blend of Elvacite 2044 and 2045, or a polypropylene carbonate such as QPAC 40. These are acrylic polymers dissolved in acetone, dimethyl carbonate (DMC) or Entron for faster drying.

[0016] In a further enhancement of the disclosed corrosive flux core brazing wire and manufacturing method, the corrosive flux powder may be encapsulated with a coating that renders the coated flux non-hygroscopic.

[0017] According to another aspect of the disclosure, the first and second wraps may be an aluminum alloy having 12% w/w silicon. The corrosive flux has a melting temperature lower than the melting temperature of the first and second wraps.

[0018] According to yet another aspect of the disclosure, the corrosive flux measures between 7% w/w and 35% w/w of the brazing wire. The corrosive flux includes at least one of lithium chloride, zinc chloride, cesium chloride, and stannous chloride, and at least one of potassium fluoroaluminate, potassium tetrafluoroaluminate, cesium fluoroaluminate, and cesium tetrafluoroaluminate. The at least one of lithium chloride, zinc chloride, cesium chloride, and stannous chloride is between 10% w/w and 90% of the corrosive flux.

[0019] These and other aspects and objects of the disclosure will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. Further, although many methods and materials similar or equivalent to those described herein may be used in the practice of the present invention, a few such suitable methods and materials are described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] A clear conception of the advantages and features constituting the present invention, and of the construction and operation of typical mechanisms provided with the present invention, will become more readily apparent by referring to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings accompanying and forming a part of this specification, wherein like reference numerals designate the same elements in the several views, and in which:

[0021] FIG. 1 is a perspective view of a brazing ring formed from an embodiment of the disclosed corrosive flux cored wire, according to aspects of the disclosure;

[0022] FIG. 2 is a perspective view of the brazing ring of FIG. 1 having portions cut away to further depict the layers of the corrosive flux cored wire;

[0023] FIG. 3 is a cross-sectional view of the brazing ring of FIG. 1 taken along line 3-3;

[0024] FIG. 4 is a block diagram depicting the method of forming a corrosive flux cored wire, according to aspects of the disclosure;

[0025] FIG. 5 is a perspective view, partly in section, of a flared brazing washer constructed of the disclosed corrosive flux core brazing wire; and

[0026] FIGS. 6A-6D illustrate the method steps of FIG. 4 according to aspects of the disclosure.

[0027] In describing embodiments of the invention, which are illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. DETAILED DESCRIPTION

[0028] The present invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments described in detail in the following description.

[0029] FIG. 1 , is a perspective view of a brazing ring formed from the disclosed corrosive flux core brazing wire 10. In the representative embodiment of the invention, the brazing wire 10 is generally circular in cross section and is formed into the shape of a ring. The corrosive flux core brazing wire 10 may be manufactured in non-circular cross sectional shapes, or may be processed into non-circular cross sectional shapes. In other embodiments of the invention, the brazing wire 10 may be formed into linear, circular, quasi-circular (e.g., oval, elliptical, hexagonal, semi-circular, or "U"), coiled, conical, saddled, bowled, or other custom shapes. As will be described in further detail below, the brazing wire 10 includes an external wrap 12 surrounding an internal wrap 14, which surrounds a core 16. The core 16 of the brazing wire 10 includes a corrosive flux 18.

[0030] FIG. 1 illustrates the brazing wire 10 in a circular ring shape and having a first end 1 1 and a second end 13. The first and second ends 1 1 , 13 are disposed directly adjacent each other to form a butt seam 15. However, in alternative embodiments of the invention, the first and second ends 1 1 , 13 may disposed directly adjacent each other to form a butt seam 15 or spaced apart from each other.

[0031] In the representative embodiment of the invention, the external wrap 12 and the internal wrap 14 both comprise an aluminum alloy for brazing aluminum parts. For example, in instances where the aluminum parts contain a high level of magnesium (such as 5000 series or 6000 series aluminum, which contain at least 1 .2% w/w of magnesium), the external wrap 12 and the inter wrap 14 may comprise an aluminum alloy having 12% w/w of silicon. In embodiments of the invention wherein the brazing wire 10 is used to braze together non-aluminum parts, the external and internal wraps 12, 14 may comprise the appropriate alloy known in the art for brazing such parts.

[0032] In some embodiments of the invention, the external wrap 12 and the internal wrap 14 may comprise the same alloy. Meanwhile, in other embodiments of the invention, the external wrap 12 and the internal wrap 14 may comprise different alloys. For example, while the external wrap 12 and the internal wrap 14 may both be aluminum alloys, the % w/w of silicon and/or zinc in the external wrap 12 may be higher or lower than that of the internal wrap 12%.

[0033] . The disclosed corrosive flux core brazing wire may be constructed with wraps comprising any alloy used to join 3000 series, 5000 series and 6000 series aluminum base metals. Such alloys include, but are not limited to AISi12, AISi10, AISi7, AIMg5, AI822, and AI802.

[0034] According to aspects of the disclosure, the flux 18 is a corrosive flux. A corrosive flux is a water soluble flux containing both chloride and fluoride salts. In some embodiments, the corrosive flux 18 includes at least one of potassium fluoroaluminate, lithium chloride, zinc chloride, cesium tetrafluoroaluminate, potassium tetrafluoroaluminate, and cesium fluoroaluminate. In other embodiments, the corrosive flux includes at least one of sodium chloride, cesium chloride, zinc chloride, zinc fluoride, potassium fluoride, stannous chloride, lithium fluoride, cesium hexafluorosilicate, sodium hexafluorosilicate, stannous fluoride, sodium fluoride, sodium fluoroaluminate, potassium fluoroaluminate, and zinc oxide. In the representative embodiment of the invention, the flux 18 contains between 10% w/w and 90% w/w of lithium chloride, zinc chloride, cesium chloride and/or stannous chloride. That is, if lithium chloride, zinc chloride, cesium chloride, and stannous chloride are included , they would combine to be between 10% w/w and 90% w/w of the flux 18. On the other hand, if only one of the lithium chloride, zinc chloride, cesium chloride, or stannous chloride is included, it would be between 10% w/w and 90% w/w of the flux 18. [0035] In one embodiment of the invention, the addition of at least one of potassium fluoroaluminate, cesium tetrafluoroaluminate, potassium tetrafluoroaluminate, and cesium fluoroaluminate to at least one of lithium chloride and zinc chloride assists with limiting the corrosiveness of the corrosive flux 18 and may prevent the corrosive flux 18 from absorbing too much moisture.

[0036] According to an embodiment of the invention, a melting temperature of the flux 18 is lower than a melting temperature of the external and internal wraps 12, 14. In further embodiments of the invention, the internal wrap 14 may have a higher melting temperature than the external wrap 12, a lower melting temperature than the external wrap 12, or the same melting temperature of the external wrap 12. In one embodiment of the invention, the melting temperature of the flux 18 may be between 540°C and 560°C.

[0037] Next, FIG. 2 illustrates another perspective view of the brazing wire 10 with portions of the external wrap 12, portions of the internal wrap 14, and portions of the flux 18 cut away to further illustrate the elements of the brazing wire 10. FIG. 3 is a sectional view through the brazing wire 10, taken along line 3-3 of Figure 1 . As shown in FIGS. 2 and 3, the flux 18 is disposed within a core 20 of the internal wrap 14, while the internal wrap 14 is disposed within a core 22 of the external wrap 12. The alignment of the elements of the brazing wire 10 is further shown in FIG. 3.

[0038] As shown in FIG. 3, the external or outer wrap 12 is rolled to create a core 22 disposed within the external wrap 12. The core 22 is encased by a perimeter 23 formed by the external wrap 12. In the embodiment of the invention shown in FIGS. 1 -3, the external wrap 12 has a diameter of 2.0 mm, but other embodiments of the invention may have an external wrap 12 with a larger or smaller diameter than 2.0 mm. The disclosed corrosive flux core brazing wire is not limited to a single diameter and may be produced in a range of finished outside diameters and cross sectional shapes. Alternative round brazing wire sizes include a corrosive flux core brazing wire with a first (outer) metal alloy wrap with an outside diameter of 1 .6mm and a second (inner) metal alloy wrap with an outside diameter of 1 .2mm. An alternative non-round corrosive flux core brazing wire according to aspects of the disclosure may take the form of a flat band, with an inner metal alloy wrap having dimensions of 1 .4mm x 2.3mm. An outer metal alloy wrap surrounds the inner metal alloy wrap.

[0039] A first longitudinal edge 24 of the external wrap 12 is configured to overlap a second longitudinal edge 26 of the external wrap 12 to limit exposure of the core 22 to the external environment. In the embodiment of the invention shown in FIGS. 1 -3, the first longitudinal edge 24 of the external wrap 12 overlaps the second longitudinal edge 26 of the external wrap 12 by an angle β of approximately 10° - 50° of a circumference of the external wrap 12. However, other embodiments of the invention may include a larger or smaller overlap, such as an overlap of 20° - 30° of a circumference of the external wrap. A seam 32 is created along the overlap of the first and second longitudinal edges 24, 26.

[0040] Similar to the external wrap 12, the internal or inner wrap 14 is also rolled to create a core 20 within the internal wrap 14. The core 20 is encased by a perimeter 21 formed by the internal wrap 14. FIG. 3 further illustrates that the internal wrap 14 is smaller than and disposed within the core 22 of the external wrap 12. In the representative embodiment of the invention, the internal wrap 14 has a diameter of 1 .6 mm. While the diameter of the internal wrap 14 may be greater or smaller than 1 .6 mm in varying embodiments of the invention, the diameter of the internal wrap 14 is always smaller than the diameter of the external wrap 12. In the representative embodiment of the invention, a first longitudinal edge 28 of the internal wrap 14 overlaps a second longitudinal edge 30 of the internal wrap 14 by an angle a approximately 10° - 50° of a circumference of the inner wrap 14to limit the exposure of the core 20 to the external environment. In other embodiments of the invention, the first end 28 of the internal wrap 14 may overlap the second end 30 of the internal wrap by 20°- 30° of a circumference of the inner wrap 14. A seam 34 is created along the overlap of the first and second longitudinal edges 28, 30. The overlap of the longitudinal edges 24, 26 of the external wrap 12 may be the same, greater than, or less than the overlap of the longitudinal edges 28, 30 of the internal wrap 14. [0041] While FIG. 3 illustrates the seam 32 of the external wrap 12 being positioned opposite the seam 34 of the internal wrap 14, it is contemplated that the seams 32, 34 may be positioned anywhere with respect to each other. The relative position of seam 32 with respect to seam 34 may vary along the length of the disclosed corrosive flux core brazing wire 10.

[0042] As shown in FIG. 3, the core 16 of the brazing wire 10 aligns with the core 20 of the internal wrap 14, and the flux 18 is disposed within the core 20 of the internal wrap 14. In some embodiments, the corrosive flux 18 includes at least one of potassium fluoroaluminate, lithium chloride, zinc chloride, cesium tetrafluoroaluminate, potassium tetrafluoroaluminate, and cesium fluoroaluminate. In other embodiments, the corrosive flux includes at least one of sodium chloride, cesium chloride, zinc chloride, zinc fluoride, potassium fluoride, stannous chloride, lithium fluoride, cesium hexafluorosilicate, sodium hexafluorosilicate, stannous fluoride, sodium fluoride, sodium fluoroaluminate, potassium fluoroaluminate, and zinc oxide. In accordance with one embodiment of the invention, the flux 18 may be 15% w/w of the brazing wire 10. In other embodiments of the invention, the flux 18 may be more or less than 15% w/w of the brazing wire 10. Several variables may impact the proportion of the finished corrosive core brazing wire represented by the flux 18, including the density of the metal alloys selected for the wraps 12, 14, the diameter of the finished diameter and cross sectional shape of the corrosive core brazing wire 10, and variation in the dispensing of the flux during manufacture. The weight proportion of the corrosive flux in the disclosed brazing wire is not limited to 15% w/w, and may vary between 7% w/w and 35% w/w.

[0043] When the external and internal wraps 12, 14 of the brazing wire begin to melt during the brazing operation, it is contemplated that the first longitudinal edges 24, 28, respectively, and the second longitudinal edges 26, 30, respectively, will begin to open and separate from each other along the seams 32, 34 and expose their respective cores 22, 20. In turn, the flux 18, which will have already melted, will flow out of at least one of the ends 1 1 , 13 of the brazing wire 10 and the opening of the external and internal wraps 12, 14. In some embodiments of the invention, the melting points of the external wrap 12, internal wrap 14, and flux 18 are so close together that flux 18 flows from the ends 1 1 , 13 of the brazing wire 10 as it does not have the time to flow out of the openings at seams 32, 34.

[0044] FIG. 4 is a block diagram of a method 36 for manufacturing the disclosed corrosive flux core brazing wire 10. FIGS. 6A - 6D illustrate some of the steps set forth in FIG. 4. In the first step 38 of the method 36, an elongated metal sheet is shaped into a U-shaped channel by a first die to partially form the core 20 of the internal wrap 14. FIG. 6A illustrates the U-shaped channel of the elongated metal sheet, which may be described as a strip, and includes generally parallel longitudinal edges 28, 30. In step 40, the resulting U-shaped channel is then passed through a trough, and the flux 18 is conveyed from a dispenser to the trough and fills the partially formed core 20. FIG. 6A shows the flux 18 within the U-shaped channel of the internal wrap 14. A vibrating apparatus is typically employed to vibrate the trough in order to fill the strip. Optionally, lasers may be employed to ensure that the amount of flux 18 is sufficient to form an adequate braze joint. In step 42, the filled U-shaped channel is passed out of the trough and through at least one die to close the U-shaped channel and form the internal wrap 14 having the flux 18 disposed in its core 20 and its seam 34, as described above and shown in FIG. 6B. In step 44, the internal wrap 14 is formed to its final diameter via at least one die.

[0045] In step 46, another elongated metal sheet is shaped into a U-shaped channel by a first die to partially form the core 22 of the external wrap 12. FIG. 6C illustrates the elongated metal sheet, which may be described as a strip, formed into the U-shaped channel and including generally parallel longitudinal edges 24, 26. In step 48, the internal wrap 14 having the flux 18 disposed in its core 20 is disposed in the U-shaped channel, as shown in FIG. 6C. In step 50, the filled U-shaped channel is passed through at least one die to close the U- shaped channel and form the external wrap 12 having the internal wrap 14 disposed in its core 22 and its seam 32 as shown in FIG. 6D. In step 52, the external wrap 12 is formed to its final diameter via at least one die. [0046] FIG. 5 illustrates a flared, or conical brazing washer 60 formed from the disclosed corrosive core brazing wire 10, with part of the brazing washer removed to show a cross section. This configuration of a brazing member may be formed from brazing wire having a round cross section by first flattening the brazing wire and then cutting and forming the flattened brazing wire into a conical washer 60. Alternatively, the conical brazing washer may be formed from a brazing wire in the form of a flat band. In the conical brazing washer 60, the corrosive flux core 18 is surrounded by an internal wrap 14 and an external wrap 12. The ends of the segment of corrosive flux core brazing wire 10 from which the brazing washer 60 is formed may be against each other to form a butt joint in the finished product, or may be spaced apart from each other. As shown in FIG. 5, the internal wrap 14 has a thickness 62, and the overlap of the longitudinal edges 28, 30 of the internal wrap 14 may be expressed in terms of the thickness 62 of the wrap 14. Specifically, the overlap 64 of the longitudinal edges 28, 30 of the internal wrap 14 is at least two times the thickness 62 of the wrap 14, and preferably between 2 and 6 times the thickness 62 of the wrap 14. The external wrap 12 has a thickness 66, and the overlap 68 of the longitudinal edges 24, 26 of the external wrap is at least two times the thickness 66 of the wrap 12, and preferably between 2 and 6 times the thickness 66 of the wrap 12.

[0047] An enhancement of the disclosed corrosive flux core brazing wire and manufacturing methods may include applying a coating to the corrosive flux core brazing wire to improve protection of the corrosive flux from the exterior environment. The coating may be applied by dipping and wiping, or spray coating, with the brazing wire then dried. The coating is selected to decompose into inert substances that do not contaminate the brazed joint. Suitable coatings may include a blend of Elvacite 2044 and 2045, or a polypropylene carbonate such as QPAC 40. These are acrylic polymers dissolved in acetone, dimethyl carbonate (DMC) or Entron for faster drying.

[0048] In a further enhancement of the disclosed corrosive flux core brazing wire and manufacturing method, the corrosive flux powder may be encapsulated with a coating that renders the coated flux non-hygroscopic. [0049] Other objects, features and advantages of the present invention will be apparent to those skilled in the art. The invention described herein is not limited in any manner by the descriptions, definitions or characteristics of any brazing material or the metals or alloys or ceramics that may be joined thereby, of any flux composition. Any brazing flux or brazing material may be used for the purposes of the invention.

[0050] It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but includes modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.

Claims

CLAIMS What is claimed is:

1 . A brazing wire comprising:

a first metal alloy wrap defining an encasing perimeter around a core and having a first seam extending over a length of the first metal alloy wrap;

a second metal alloy wrap disposed within the core of the first metal alloy wrap, the second metal alloy wrap defining an encasing perimeter around a core and having a second seam extending over a length of the second metal alloy wrap;

a corrosive flux material disposed within the core of the second metal alloy wrap.

2. The brazing wire of claim 1 , wherein the corrosive flux is water soluble and comprises both chloride and fluoride salts.

3. The brazing wire of claim 1 , wherein the corrosive flux comprises a material selected from the group consisting of potassium fluoroaluminate, lithium chloride, zinc chloride, cesium tetrafluoroaluminate, potassium tetrafluoroaluminate, cesium fluoroaluminate, sodium chloride, cesium chloride, zinc fluoride, potassium fluoride, stannous chloride, lithium fluoride, cesium hexafluorosilicate, sodium hexafluorosilicate, stannous fluoride, sodium fluoride, sodium fluoroaluminate, potassium fluoroaluminate, and zinc oxide.

4. The brazing wire of claim 1 , wherein the corrosive flux comprises between 10% w/w and 90% w/w of at least one of lithium chloride, zinc chloride cesium chloride, and stannous chloride combined.

5. The brazing wire of claim 1 , wherein the corrosive flux material has a melting temperature less than a melting temperature of the first metal alloy wrap; and

wherein the corrosive flux material has a melting temperature less than a melting temperature of the second metal alloy wrap.

6. The brazing wire of claim 1 , wherein the first metal alloy wrap and the second metal alloy wrap are an aluminum alloy independently selected from the group consisting of: AISM 2, AISM O, AISi7, AIMg5, AI822, and AI802.

7. The brazing wire of claim 1 , wherein the corrosive flux is between 7% w/w and 35% w/w of the brazing wire.

8. The brazing wire of claim 1 , formed into a ring.

9. The brazing wire of claim 1 , formed into a flared conical washer.

10. The brazing wire of claim 1 , wherein the first metal alloy wrap includes longitudinal edges that overlap to form said first seam, said overlap extending over 10° to 50° of a circumference of said first metal alloy wrap, and said second metal alloy wrap includes longitudinal edges that overlap to form said second seam, said overlap extending over 10° to 50° of a circumference of said second metal alloy wrap.

1 1 . The brazing wire of claim 1 , wherein the first metal alloy wrap has a first thickness and includes longitudinal edges that overlap to form said first seam, said longitudinal edges overlapping by at least twice said first thickness, and the second metal alloy wrap has a second thickness and includes longitudinal edges that overlap to form said second seam, said longitudinal edges overlapping by at least twice said second thickness.

12. A method of manufacturing a brazing wire comprising:

providing a first metal sheet;

disposing a corrosive flux on the first metal sheet;

forming the first metal sheet into a first metal wrap, the first metal wrap having a core with the corrosive flux disposed within the core;

providing a second metal sheet;

disposing the first metal wrap on the second metal sheet; and

forming a second metal sheet into a second metal wrap, the second metal wrap having a core with the first metal wrap disposed within the core.

13. The method of claim 12, wherein the first metal sheet and the second metal sheet are an aluminum alloy independently selected from the group consisting of: AISi12, AISi10, AISi7, AIMg5, AI822, and AI802.

14. The method of claim 12, wherein the corrosive flux measures between 7% w/w and 35% w/w of the brazing wire.

15. The method of claim 12, comprising: cutting a segment of said brazing wire; and forming the segment of brazing wire into a ring.

16. The method of claim 12, comprising: cutting a segment of brazing wire; and forming the segment of brazing wire into a flared conical washer.

17. The method of claim 12, wherein said first metal sheet includes longitudinal edges and said forming a first metal sheet into a first metal wrap comprises overlapping said longitudinal edges of said first metal sheet by 10° to 50° of a circumference of said first metal wrap to form a seam.

18. The method of claim 12, wherein said second metal sheet includes longitudinal edges and said forming a second metal sheet into a second metal wrap comprises overlapping said longitudinal edges of the second metal sheet by 10° to 50° of a circumference of said second metal wrap to form a seam.

19. The method of claim 12, wherein the corrosive flux comprises at least one of lithium chloride, zinc chloride, cesium chloride, stannous chloride, potassium fluoroaluminate, potassium tetrafluoroaluminate, cesium fluoroaluminate, and cesium tetrafluoroaluminate, with said lithium chloride, zinc chloride, cesium chloride, and stannous chloride combined comprising between 10% and 90% w/w of said corrosive flux.

20. A brazing wire comprising:

a first wrap surrounding a first core, the first wrap having a first longitudinal edge overlapping a second longitudinal edge by10° to 50° of a circumference of said first wrap to form a seam;

a second wrap surrounding a second core, the second wrap having a first longitudinal edge overlapping a second longitudinal edge by 10° to 50° of a circumference of said second wrap to form a seam, and wherein the second wrap is disposed within the core of the first wrap; and

a corrosive flux material disposed within the core of the second wrap.

21 . The brazing wire of claim 20, wherein the first and second wraps comprise an aluminum alloy selected independently from the group consisting of: AISi12, AISi10, AISi7, AIMg5, AI822, and AI802.

22. The brazing wire of claim 20, wherein the corrosive flux measures between 7% w/w and 35% w/w of the brazing wire.

23. The brazing wire of claim 20, wherein the corrosive flux comprises:

at least one of lithium chloride, zinc chloride, cesium chloride and stannous chloride, wherein the at least one of lithium chloride, zinc chloride, cesium chloride and stannous chloride is between 10% and 90% w/w of the corrosive flux; and

at least one of a material selected from the group consisting of potassium fluoroaluminate, cesium tetrafluoroaluminate, potassium tetrafluoroaluminate, cesium fluoroaluminate, zinc fluoride, potassium fluoride, lithium fluoride, cesium hexafluorosilicate, sodium hexafluorosilicate, stannous fluoride, sodium fluoride, sodium fluoroaluminate, potassium fluoroaluminate, and zinc oxide.

24. The brazing wire of claim 20, wherein the corrosive flux has a melting temperature lower less than a melting temperature of the first and second wraps.