GB1590695A

GB1590695A - Method of brazing

Info

Publication number: GB1590695A
Application number: GB33141/77A
Authority: GB
Original assignee: Rubbermaid Health Care Products Inc
Current assignee: Rubbermaid Health Care Products Inc
Priority date: 1977-08-08
Filing date: 1977-08-08
Publication date: 1981-06-10

Description

(54) METHOD OF BRAZING (71) We, FUSION, INCORPORATED, a corporation organised under the laws of the State of Ohio, United States of America, of 4658 East 355 Street, Willoughby, Ohio 44094, United States of America, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of brazing which provides, in use, ajoint clearance control.

One of the principal considerations in the brazing together of two components is the joint clearance to be established between the component faces to be brazed. Interface tolerances are of prime importance when selecting the proper filler metal to be used in a brazing composition, with regard to both flow characteristics and desired joint strength. Control of such joint clearance is most difficult when the parts to be brazed are brought together rapidly, usually with some force, as in certain automated brazing operations. Maintenance of a fine interface tolerance by physical control of the separate parts is very difficult. Therefore, one of the objects of this invention is to provide a new type of method of brazing with a built-in joint clearance control which is effective with any type of brazing operation, including automated brazing machines.

When the components to be brazed together are of dissimilar material, the difference in the thermal expansion and contraction characteristics of such materials not only may tend to increase or decrease joint clearance, depending on the relative positions and configurations of the joint components, but stresses caused by this difference also may introduce the additional problem of strain in the hazard joint.

Consequently, it is a further object of this invention to provide a method of brazing which not only gives an intemal control of joint clearance, but which also provides a measure of ductibility in the resulting brazed joint to relieve the strain induced by the stress caused by different rates of thermal expansion and contraction for dissimilar materials being brazed together and after being brazed together.

A previous commercial solution for this type of problem in brazing large carbide tool inserts has been the use of a three layer composite metal sandwich consisting of a ductile copper layer faced on each side with a filler metal alloy. This product is used as a preplaced shim at the interface of the parts being joined. The strain normally set up in the carbide, by the stress of differential contraction between the carbide and tool shank during cooling, is relieved by the yeilding of the copper core. This type of three layer composite has also been used to braze aluminium-bronze to steel where the copper core acts as a barrier layer to prevent aluminium from the aluminium-bronze migrating to the steel surface and adversely affecting the wetting of the steel by the filler metal.

The present invention provides a method of brazing wherein a composition is used comprising a flux and/or a vehicle and a filler metal and containing dispersed therein particles composed of a material which substantially maintains its shape during the brazing operation, any more than 0.5 weight percent of said particles based on the weight of said composition being wettable by said filler metal during the brazing operation, no more than 30 weight percent of any particles of said material having a minimum effective lineal dimension of less than 0.003 inch and substantially no particles of said material having a maximum effective lineal dimension greater than 0.010 inch.

The invention is applicable to presently known compositions made up of flux and/or vehicle and filler metal. When the composition are pastes, they generally have viscosities at room temperature in the range of about 100,000 to 1,000,000 centipoises.

The choice of a proper flux for a given brazing composition for brazing a given base metal is well within the skill of the art. Typical brazing fluxes are disclosed in U.S. Patent Nos.

2299 168;2403 110; 2 493 372;2 507 346; 2552 1052914435 and 3 149007, the dis- closures of these patents being hereby incorporated by this reference. Fluxes are generally categorized as neutral or non-corrosive fluxes to be used primarily where residue removal is impossible, intermediate fluxes to be used where the service environment may permit the presence of a residue which is corrosive in some environments but not in others, and corrosive fluxes to be used only where the residue can be removed. Fluxes are also particularly designed for varying flow characteristics and activities at different temperatures and are usually recommended for brazing specific materials such as aluminium, cadmium oxide, nickel-chrome, copper, brass, copper-zinc, malleable iron, and steel. These fluxes are generally mixtures of alkali metal chlorides fluorides with or without other metal chlorides and flourides, said other metals usually being alkaline earth metals although rare earth metals are also readily usable, but metal chlorides and fluorides which can react with each other or with the filler metal must be avoided. Obviously, the flux should be molten at the temperature of brazing.

Similarly, the vehicles which can be employed in the subject brazing compositions are also well known in the art as described, for example, in the over-cited patents. These vehicles are non-aqueous and substantially inert to the other components of the brazing composition. The vehicles must have ajelly- or cream-like consistency sufficient to carry the other brazing past components without significant separation on standing. Such consistency appears to be commensurate with viscosities in the range of 10,000 to 200,000 centipoises and preferably should not change so signifcantly with increasing temperature as to permit significant settling or separation of the other paste components until after application of the brazing paste to the surfaces of the pieces to be brazed.

The vehicles must volatilize or decompose at brazing temperatures without leaving a residue but otherwise are a matter of choice.

A vehicle can be a single compound or a mixture of compounds. Typical compounds for use as all or part of said vehicle include ethylene oxide polymers, polyacrylate polymers, polymethacrylate polymers, polyacrylonitrile polymers, paraffins, olefins and olefinic copolymers, polyethylene glycols and methyl ethers thereof.

Generally, viscosity control is simpler with multiple-component vehicles.

The filler metals which can be employed in the subject brazing compositions are also well known in the art. The choice of filler metal depends primarily on the base materials to be brazed because the filler metal must at least wet the base materials and preferably alloys with them. Four typical classes of filler metal are silver and the silver alloys, such as those designated as BAg; the nickel, such as those designated BNi; the gold alloys, such as that designated BAu; and cooper and the copper alloys, such as those designated BCu, BCuP and RBCuZn-D, said designations being under AWS specification A5. 8-62 and ASTM specifiction B260-62.

The filler metal can be employed in such form as the aforementioned three layer composite metal sandwich, but preferably the filler metal is used in particulate form, the size of the particles being a matter of choice. For commerical use, especially with automated brazing equipment, it is preferable that the filler metal particles be fine enough, i.e. less than 250 microns, to pass through a 60 mesh screen, (U.S. Sieve Series) in order to make possible a smooth brazing paste. It is also preferable that the particles be such that no more than 40 to 60 percent of the filler metal particles pass through a 200 mesh screen (U.S.

Sieve Series) and no more than about 25 percent pass through a 325 mesh screen (U.S.

Sieve Series).

The relative proportions of vehicle, flux, and filler metal can vary considerably with some compositions lacking vehicle or flux. In the normal three component brazing compositions from 20 to 50 weight percent of combined flux and vehicle is normally used with the weight ratio of flux to vehicle usually in the range of 1:1 to 3:1. Filler metals usually form from 50 to 80 weight percent of the brazing compositions of this invention.

Thus, the invention discloses a brazing method using a brazing compositions containing particles which substantially maintain their shape at brazing temperature, thereby providing in use ajoint clearance commensurate with the maximum effective size of the particles. The particles can have any shape so long as they are oriented to give a minimum effective dimension of 0.003 inch and a maximum effective dimension of 0.010 inch. Thus, cylindrical particles 0.004 inch in diameter and 0.020 inch long can be used if they are oriented so that the effective joint clearance control dimension is the cylindrical diameter of the particles. The particles are preferably substantially spherical and preferably have diameters no greater than about 0.008 inch. Up to 30 weight percent of said particles can be smaller than the defined minimum dimension, but substantially, none should be effectively larger than defined maximum dimension.

The term "effective", as used in this specification in relation to particle dimensions, relates to the dimensions of the particles in the direction of the joint clearance, and relates to their effect in maintaining the joint clearance.

The defined particles can be used in amounts up to 10 weight percent or more based on the weight of the brazing composition so long as the strength of the brazed joint is not significantly reduced, but generally no more than 5 weight percent is needed. There need be only enough of said particles to provide in use the joint clearance control, but generally there should be at least 0.05 weight percent of said particles to make possible adequate dispersion of the particles in the brazing composition.

The joint clearance control particles are preferably wettable by the filler metal of the brazing composition at the brazing tempera ture. No more than about 0.5 weight percent of said particles based on the brazing composition can be non-wettable by the filler metal at brazing temperature. Some of said particles can even alloy to some degree with said filler metal. This is particularly true for metallic particles. Spherical nickel particles have been found to be particularly useful.

In addition, up to 40 weight percent of the filler metal can be replaced by a different metal which is ductile, only partially soluble in said filler metal at the brazing temperature. Copper has been found to be very satisfactory as the substitute metal. The copper particles are generally used in a particle size similar to the size of the filler metal particles, but preferably no copper particles less than 325 mesh (U.S.

Sieve Series) or greater than the nickel particles should be used.

The following examples illustrate two of the best modes for practicing this invention but are not intended to limit its scope which is properly delineated in the claims.

EXAMPLES Two typical brazing pastes were prepared by mixing together the following ingredients: Ingredients Weight % I Liquid flux-binder (1 :1 25 weight ratio with a room temperature viscosity of about 40,000 cps.

A silver-rich filler metal 70.9 AWS BAg-3 (passing 100 mesh U.S. Sieve Series) Nickel alloy spheres (AWS 4.1 BNi-3) having diameters in the range of 0.003 to 0.004 inch II Liquid flux-binder of 25.1 paste I Filler metal of paste I 56.5 Nickel alloy spheres (AWS 3 BNi-3) having diameters in the range of 0.006 to 0.007 inch Copper spheres greater than 15 325 mesh (U.S. Sieve Series) but smaller in diameter than 0.006 inch Both pastes were used in brazing tungsten carbide and steel components while pressed together, and satisfactory joints were obtained with desired joint clearance. When similar pastes without the nickel alloy spheres are substituted, the desired joint clearance is not maintained, and the resulting joints are weaker.

WHAT WE CLAIM IS: 1. A method of brazing wherein a composition is used comprising a flux and/or a vehicle and a filler metal and containing dispersed therein particles composed of a material which substantially maintains its shape during the brazing operation, any more than 0.5 weight percent of said particles based on the weight of said composition being wettable by said filler metal during the brazing operation, no more than 30 weight percent of any particles of said material having a minimum effective lineal dimension of less than 0.003 inch and substantially no particles of said material having a maximum effective lineal dimension greater than 0.010 inch.

2. A method according to Claim 1, wherein said particles are substantially spherical and said material is substantially metallic.

3. A method according to Claim 1 or Claim 2, wherein said brazing composition is a paste comprising at least 50 weight percent of a powdered filler metal and at least 20 weight percent of combined flux and vehicle, said flux and vehicle being present in a weight ratio of from 1:1 to 3:1.

4. A method according to any one of Claims 1 to 3, wherein said particles are present in an amount ranging from 0.05 to 10 weight percent based on the weight of said composition.

5. A method according to any one of Claims 1 to 4, wherein all of said particles are wettable by said filler metal during the brazing operation.

6. A method according to any one of Claims 1 to 5, wherein up to 40 weight percent of said filler metal is replaced by a different powdered metal which is ductile, and which is only partially soluble in said filler metal at the brazing temperature said different powdered metal being present at particles having a maximum effective lineal dimension less than the maximum effective lineal dimension of substantially all of said particlles of said material.

7. A method according to Claim 6, wherein said particles of said material are present in an amount ranging from 0.05 to 10 weight percent based on the weight of said composition.

8. A method according to Claim 7, wherein all of said particles of said material are wettable by said filler metal during the brazing operation.

9. A method of brazing substantially as hereinbefore described.

10. An article produced by a method according to any one of Claims 1 to 9.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

ture. No more than about 0.5 weight percent of said particles based on the brazing composition can be non-wettable by the filler metal at brazing temperature. Some of said particles can even alloy to some degree with said filler metal. This is particularly true for metallic particles. Spherical nickel particles have been found to be particularly useful.

In addition, up to 40 weight percent of the filler metal can be replaced by a different metal which is ductile, only partially soluble in said filler metal at the brazing temperature. Copper has been found to be very satisfactory as the substitute metal. The copper particles are generally used in a particle size similar to the size of the filler metal particles, but preferably no copper particles less than 325 mesh (U.S.

Sieve Series) or greater than the nickel particles should be used.

The following examples illustrate two of the best modes for practicing this invention but are not intended to limit its scope which is properly delineated in the claims.

EXAMPLES Two typical brazing pastes were prepared by mixing together the following ingredients: Ingredients Weight % I Liquid flux-binder (1 :1 25 weight ratio with a room temperature viscosity of about 40,000 cps.

A silver-rich filler metal 70.9 AWS BAg-3 (passing

100 mesh U.S. Sieve Series) Nickel alloy spheres (AWS 4.1 BNi-3) having diameters in the range of 0.003 to 0.004 inch II Liquid flux-binder of 25.1 paste I Filler metal of paste I 56.5 Nickel alloy spheres (AWS 3 BNi-3) having diameters in the range of 0.006 to 0.007 inch Copper spheres greater than 15

325 mesh (U.S. Sieve Series) but smaller in diameter than 0.006 inch Both pastes were used in brazing tungsten carbide and steel components while pressed together, and satisfactory joints were obtained with desired joint clearance. When similar pastes without the nickel alloy spheres are substituted, the desired joint clearance is not maintained, and the resulting joints are weaker.

WHAT WE CLAIM IS: 1. A method of brazing wherein a composition is used comprising a flux and/or a vehicle and a filler metal and containing dispersed therein particles composed of a material which substantially maintains its shape during the brazing operation, any more than 0.5 weight percent of said particles based on the weight of said composition being wettable by said filler metal during the brazing operation, no more than 30 weight percent of any particles of said material having a minimum effective lineal dimension of less than 0.003 inch and substantially no particles of said material having a maximum effective lineal dimension greater than 0.010 inch.
2. A method according to Claim 1, wherein said particles are substantially spherical and said material is substantially metallic.
3. A method according to Claim 1 or Claim 2, wherein said brazing composition is a paste comprising at least 50 weight percent of a powdered filler metal and at least 20 weight percent of combined flux and vehicle, said flux and vehicle being present in a weight ratio of from 1:1 to 3:1.
4. A method according to any one of Claims 1 to 3, wherein said particles are present in an amount ranging from 0.05 to 10 weight percent based on the weight of said composition.
5. A method according to any one of Claims 1 to 4, wherein all of said particles are wettable by said filler metal during the brazing operation.
6. A method according to any one of Claims 1 to 5, wherein up to 40 weight percent of said filler metal is replaced by a different powdered metal which is ductile, and which is only partially soluble in said filler metal at the brazing temperature said different powdered metal being present at particles having a maximum effective lineal dimension less than the maximum effective lineal dimension of substantially all of said particlles of said material.
7. A method according to Claim 6, wherein said particles of said material are present in an amount ranging from 0.05 to 10 weight percent based on the weight of said composition.
8. A method according to Claim 7, wherein all of said particles of said material are wettable by said filler metal during the brazing operation.
9. A method of brazing substantially as hereinbefore described.
10. An article produced by a method according to any one of Claims 1 to 9.