GB2293786A

GB2293786A - Applying brazing flux material

Info

Publication number: GB2293786A
Application number: GB9420108A
Authority: GB
Inventors: Jeoffrey Stevens; Michael Andrew Kirk; Adrian Edward Griffiths
Original assignee: T&N Technology Ltd
Current assignee: Federal Mogul Technology Ltd
Priority date: 1994-10-05
Filing date: 1994-10-05
Publication date: 1996-04-10
Anticipated expiration: 2014-10-05
Also published as: GB2293786B; GB9420108D0

Abstract

Brazing flux material is applied to a workpiece by applying liquid adhesive to an area of the workpiece as a pattern of individual drops from nozzles (27) which project them on to predetermined locations within said area. Particles of the brazing flux material are then brought into contact with the adhesive and adhere thereto.

Description

APPLYING BRAZING FLUX MATERIAL This invention is concerned with applying brazing flux material, ie material consisting of brazing flux or brazing flux and filler material.

It is well-known to join two metal articles by a brazing process in which a brazing flux material is first applied to one or both articles. In some cases, the brazing flux material in powder form is formed into an aqueous slurry and sprayed or otherwise applied to the article (see eg US 3951328). Another possibility is to thermally spray the brazing material on to the workpiece (see EP 0 595 601 Al). These methods have cost advantages over cladding the article with a brazing alloy by cold pressure-bonding, eg by roll-bonding, and increase design flexibility, since it is only economically feasible to carry out such cladding operations on strip material which then needs to be fabricated into components. However, the material is not precisely located in precise quantities so that reliability problems may occur and the usage of material is usually greater than theoretically necessary.

It is an object of the present invention to provide a method of applying brazing flux material in which a precisely determined area of a workpiece is coated with a precise quantity of the material.

The invention provides a method of applying brazing flux material to a predetermined area of a workpiece, the method comprising applying liquid adhesive to said predetermined area, and bringing particles of the brazing material into contact with the liquid adhesive on said predetermined area so that the particles adhere to the adhesive, wherein the liquid adhesive is applied as a pattern of individual drops of adhesive each of which is projected on to a predetermined location within said predetermined area.

In a method in accordance with the invention, adhesive is applied separately from the brazing material as a pattern of drops. Each drop can be of a precisely known volume and be positioned in a precise location, and the flux material only adheres to the adhesive thereby being precisely located in precise quantities and only where required.

Preferably, in a method according to the invention, the drops of liquid adhesive are applied by bringing about relative movement between the workpiece and a plurality of nozzles, each nozzle being independently operable to project a drop of adhesive on to the workpiece when one of said predetermined locations is opposite said nozzle. For example, the workpiece may be moved linearly past a row of nozzles extending transversely to the direction of movement. Alternatively, the nozzles may be moved relate to the workpiece in two dimensions. The nozzles are preferably arranged to all produce drops of the same volume each time they are operated.

Preferably, the brazing material particles are brought into contact with the liquid adhesive by entraining said particles in a gas stream which is directed on to said predetermined area. The particles may be entrained in the gas stream by passing the gas stream through a venturi connected to a fluidised bed of the particles.

The particles of brazing material are preferably significantly smaller than the drops of adhesive, for example having a diameter between 1% and 10% of the diameter of the drops. This ensures that the particles efficiently cover the drops. The particles may comprise aluminium or an alloy thereof coated with a flux material such as potassium fluoride or aluminium fluoride. Another possibility is for the particles to be a mixture of flux particles and alloy particles.

The adhesive may be an acrylic resin dissolved in a solvent to liquify it. The solvent may contain methyl ethyl ketone.

The invention also provides an apparatus for use in applying brazing flux material to a predetermined area of a workpiece, the apparatus comprising a support for a workpiece, projecting means operable to project individual drops of liquid adhesive on to predetermined locations within said predetermined area so that liquid adhesive is applied as a pattern of individual drops on said predetermined area, and contacting means operable to bring particles of said material into contact with the liquid adhesive on said predetermined area so that the particles adhere to the adhesive.

There now follows a detailed description, to be read with reference to the accompanying drawings, of an apparatus which is illustrative of the invention in its apparatus aspects and of the method of operation of the illustrative apparatus which is illustrative of the invention in its method aspects.

In the drawings: Figure 1 is a plan view of the illustrative apparatus; Figure 2 is a front-elevational view of the illustrative apparatus, the direction of view being indicated by the arrow II in Figure 1; Figure 3 is a side-elevational view of the illustrative apparatus taken in the direction of the arrow III in Figure 1; Figure 4 is a diagrammatic sectional view of a nozzle of the illustrative apparatus; Figure 5 is a sectional view taken on the line V-V in Figure 4; and Figure 6 is a diagrammatic view of entraining means of the illustrative apparatus.

The illustrative apparatus 10 is for use in applying brazing flux material to a predetermined area of a workpiece (not shown), the workpiece being a radiator component made from an alloy of aluminium. In this case, the brazing flux material is in the form of particles approximately O.lmm in diameter, with each particle having a core made of aluminium containing 20% by weight of silicon and an outer layer coating the core formed from brazing flux.

The apparatus 10 comprises a support 12 which is arranged to support the workpiece. The support 12 is movable by the operation of moving means of the apparatus provided by a piston and cylinder assembly 14 whose piston rod is connected to the support 12. The assembly 14 is operable to move the support 12 and a workpiece supported thereby along a linear track from a loading position 16 (in which the support 12 is shown in Figures 1 to 3), at one end of the apparatus 10, to an unloading position 18 at the opposite end of the apparatus 10. The assembly 14 is also operable to return the support 12 to the loading position 16.

In passing from the loading position 16 to the unloading position 18, the support 12 passes successively through, an adhesive application position 20, a material application position 22, and a drying position 24. In the operation of the apparatus 10, the support pauses at the loading position 16 to receive a workpiece and at the unloading position 18 for a workpiece to be removed. The support 12 normally passes through the positions 20 and 22 without stopping but is arranged to pause at the position 24 before moving to the unloading position 18.

At the adhesive application position 20, the apparatus 10 comprises projecting means in the form of three banks of nozzles 25. Further details of these banks 25 are given below with reference to Figures 4 and 5. The nozzles in each bank are arranged in a row and are operable independently to project an individual drop of liquid adhesive on to a predetermined location within the predetermined area of said workpiece. The banks of nozzles 25 are arranged one above the track of the support 12, one to the left thereof, and one to the right thereof.

The apparatus 10 comprises control means in the form of a computer 30 which is operable to coordinate the operations of the assembly 14 and of the banks of nozzles 25 to ensure that the liquid adhesive is applied as a pattern of individual drops on said predetermined area.

The drops are projected by the nozzles as the required locations in the predetermined area are brought opposite the nozzles by the operation of the assembly 14. To enable this to be achieved, the apparatus 10 comprises a linear encoder 32 positioned alongside the portion of the track of the support 12 which includes the positions 20 and 22. The encoder 32 feeds the exact position of the support 12 to the computer 30. Additionally, proximity switches 34 are arranged along the track of the support 12 to indicate the progress of the support 12 to the computer 30. The computer 30 controls the operation of the nozzles in the banks 25 so that, as each of said predetermined locations comes opposite one of the nozzles, that particular nozzle is operated thereby projecting a drop of liquid adhesive on to that location.

At the material application position 22, the apparatus 10 comprises contacting means operable to bring particles of said brazing flux material into contact with said drops of the liquid adhesive on said predetermined area of the workpiece so that the particles adhere to the adhesive.

The contacting means is provided by three spraying nozzles 40 contained in a booth 46. The nozzles 40 are not visible in Figures 1 to 3 but one of them is illustrated in Figure 6. The nozzles 40 are operable to spray said particles entrained in an air stream on to the workpiece. The particles are entrained in the air stream by means of a venturi 55 associated with a fluidised bed 54 (see Figure 6 and associated description below). The spraying nozzles 40 are arranged one above the track of the support 12, one to the left of this track, and one to the right thereof.

The operation of the spraying nozzles 40 blankets the workpiece in particles so that everywhere that there is adhesive receives particles. Those particles which impinge on adhesive stick thereto while the remainder of the particles either fall to the bottom of the booth 46 where they are collected in a hopper 48 or are drawn out of the booth 46 by operation of a fan 50 which draws air through a filter 52 at the back of the booth. The booth 46 has a small entrance 53 (Figure 3) and a small exit (not shown) to allow passage of the support 12 and a workpiece.

At the drying position 24, the apparatus 10 comprises drying means operable to dry the liquid adhesive after the particles have been brought into contact therewith. The drying means comprises a fan 60 which is operable to blow air into a booth 62 surrounding the position 24 through a tunnel 64. The tunnel 64 contains electrical coil heaters (not shown) which are operable to raise the temperature of the air entering the booth 64 to approximately 1000c. Air is extracted from the top of the booth 62 through a pipe 66. The booth 62 has a small entrance and a small exit similar to those of the booth 46.

Figures 4 and 5 illustrate one of the banks of nozzles 25. The bank comprises an elongated manifold 26 on which a plurality of nozzles 27 are mounted. The manifold 26 contains air under pressure which is supplied from a pipe 26a. The three manifolds 26 are mounted on a gantry 28 at the position 20. Each manifold 26 is adjacent to the track of the support 12 and has its nozzles 27 directed towards said track. Each manifold 26 extends horizontally parallel to said track, one being directly above said track, and the others being to the left and right thereof.

The nozzles 27 mounted on each manifold 26 are arranged in a row along the manifold 26, the row being inclined transversely relative to a longitudinal direction of the manifold. This inclination of the row means that the nozzles 27 each have a different alignment relative to the track, ie the nozzles 27 of the upper manifold 26 are arranged to left and right of the centre-line of the track.

Each nozzle 27 has a hollow cylindrical body 27a which is supplied with liquid adhesive from a container 29 through pipes (not shown). In this case, the adhesive is an acrylic polymer dissolved in methyl ethyl ketone. At one end thereof, the interior of the body 27a is connected to the interior of the manifold 26 through a pipe 27b and, at the other end, has an outlet opening 27c directed towards the track of the support 12. The body 27a contains a piston 27d which is movable between a closing position (in which it is shown in Figure 4) and an opening position nearer to the pipe 27b. When the piston 27d is in its closing position, a seal 27e carried thereby seals the opening 27c against the passage of adhesive, and, when the piston is removed from its closing position, adhesive can exit through the opening 27c being driven by air pressure from the manifold 26.The piston 27d has longitudinal grooves 27f in its outer surface (see also Figure 5) to allow the adhesive to reach the opening 27c past the piston 27d. The piston 27d is urged into its closing position by a spring 27g and is movable away from its closing position by operation of an electrical solenoid coil 27h which surrounds the body 27a.

Each nozzle 27 is independently-operable to allow a single drop to be projected out of the opening 27c and on to the workpiece. The size of the drop is determined by the duration of the operation of the coil 27h.

Figure 6 illustrates the operation of the fluidised bed 54. The bed 54 comprises a plenum chamber 54a to which fluidising air is supplied through a pipe 54b. The air passes upwardly through a porous plate 54c to fluidise particles of flux material in a chamber 54d. Three pipes 54e (only one shown) lead from the chamber 54d and each supplies fluidised particles to the venturi 55. Air under pressure is supplied to the venturi 55 through a pipe 55a so that the air picks up the fluidised particles and then passes along a pipe 55b (not shown in Figures 1 to 3) to one of the spraying nozzles 40.

In the operation of the apparatus 10, brazing flux material is applied to a predetermined area of a workpiece which is loaded on to the support 12 at the loading position 16. The assembly 14 is then operated to move the support 12 to the positions 20, 22, 24 and 18 in turn.

As the support 12 approaches the adhesive application position 20, the support 12 operates one of the proximity switches 34. The computer 30 then begins to count pulses produced by the encoder 32 as the support 12 passes through the positions 20 and 22. The computer 30 causes operation of applicable nozzles 27 in the banks of nozzles 25, each such nozzle 27 being operated at a particular count of the pulses from the encoder 32. These particular counts represent positions of the support 12 when said predetermined locations are opposite the nozzles 27. Any particular nozzle 27 may be operated many times as the support 12 passes through the position 20 whereas other nozzles may not be operated at all depending where the predetermined locations come in relation to the nozzles.

The operation of the nozzles causes the liquid adhesive to be applied to the workpiece as a pattern of individual drops of adhesive each of which has been projected on to one of said predetermined locations. Thus, the drops of liquid adhesive are applied by moving the workpiece relative to the nozzles 27 which are operated as the workpiece moves past them.

When the predetermined area of the workpiece is within the booth 46 at the position 22, the computer 30 causes operation of one or more of the spraying nozzles 40 so that said predetermined area is blanketed with the particles.

Thus, the particles are brought into contact with the liquid adhesive so that the particles adhere thereto.

When the support 12 arrives in the booth 62 surrounding the position 24, the workpiece is subjected to a hot air stream which hastens drying of the adhesive.

The computer 30, which receives notice of the arrival of the support 12 in the booth 62 from one of the proximity switches 34, controls the time which the support spends in the booth 62.

When the support 12 arrives at the unloading position 18, the workpiece is unloaded therefrom, and the assembly 14 is operated to return the support to the loading position 16.

Claims

CLAINS

1A method of applying brazing flux material to a predetermined area of a workpiece, the method comprising applying liquid adhesive to said predetermined area, and bringing particles of the brazing material into contact with the liquid adhesive on said predetermined area so that the particles adhere to the adhesive, wherein the liquid adhesive is applied as a pattern of individual drops of adhesive each of which is projected on to a predetermined location within said predetermined area.
2 A method according to claim 1, wherein the drops of liquid adhesive are applied by bringing about relative movement between the workpiece and a plurality of nozzles, each nozzle being independently operable to project a drop of adhesive on to the workpiece when one of said predetermined locations is opposite said nozzle.
3 A method according to either one of claims 1 and 2, wherein said particles are brought into contact with the liquid adhesive by entraining said particles in a gas stream which is directed on to said predetermined area.
4 A method according to claim 3, wherein the particles are entrained in the gas stream by passing the gas stream through a venturi connected to a fluidised bed of the particles.
5 A method according to any one of claims 1 to 4, wherein the adhesive is dried by passing an air stream over said predetermined area after the particles have been projected on to the adhesive.
6 A method of coating a predetermined area of a workpiece with a brazing flux material substantially as hereinbefore described with reference to the accompanying drawings.
7 An apparatus for use in applying brazing flux material to a predetermined area of a workpiece, the apparatus comprising a support for a workpiece, projecting means operable to project individual drops of liquid adhesive on to predetermined locations within said predetermined area so that liquid adhesive is applied as a pattern of individual drops on said predetermined area, and contacting means operable to bring particles of said material into contact with the liquid adhesive on said predetermined area so that the particles adhere to the adhesive.
8 An apparatus according to claim 7, wherein the apparatus also comprises moving means operable to move said support and a workpiece supported thereby to an adhesive application position at which said drops can be projected on to the workpiece, and to a material application position at which said particles can be brought into contact with said drops on the workpiece.
9 An apparatus according to claim 8, wherein the apparatus comprises control means operable to coordinate the operations of said moving means and of said projecting means to ensure that the liquid adhesive is applied as said pattern of individual drops.
10 An apparatus according to claim 9, wherein said projecting means comprises a plurality of independently-operable nozzles arranged in a row.
11 An apparatus according to any one of claims 7 to 10, wherein said contacting means comprises at least one nozzle operable to spray said particles entrained in a gas stream on to said workpiece.
12 An apparatus according to claim 11, wherein the apparatus also comprises a venturi associated with a fluidised bed by means of which said particles are entrained in said gas stream.
13 An apparatus according to any one of claims 7 to 12, wherein the apparatus also comprises drying means operable to dry the liquid adhesive after the particles have been brought into contact with the liquid adhesive.
14 An apparatus for use in coating a predetermined area of a workpiece with brazing flux material substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.