Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2002-01-24
2004-06-22
LaVilla, Michael (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S457000, C428S461000, C428S696000, C428S650000, C428S332000, C228S262900, C228S262500, C427S201000, C427S180000, C427S196000
Reexamination Certificate
active
06753094
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a composite sheet material for brazing, to the use of several components in such a composite sheet material, and further to a brazed assembly manufactured from such a composite sheet material and to a method a manufacturing such brazed assemblies.
DESCRIPTION OF THE PRIOR ART
A brazing technique which has become widely accepted involves an inert/controlled atmosphere furnace operation (CAB). To destroy and remove the aluminium oxide layer on the aluminium alloy and to protect it during brazing, a flux mixture is often being used to enhance the brazeability of the brazing alloy prior to brazing. A well known brazing process is the NOCOLOC (trade name) brazing process, developed by Alcan International Ltd, and for example as disclosed in U.S. Pat. No. 3,971,501 and U.S. Pat. No. 3,951,328. This process includes the steps of forming an assembly, cleaning the surfaces to be brazed to remove oil and grease to eliminate stopoff effects, applying a brazing slurry to the assembly, blowing off the excess slurry, drying the slurry onto the assembly, and then passing the assembly through a brazing furnace. The flux does not need to be removed at the end of the brazing cycle. The brazing slurry generally includes a brazing alloy and a flux material, but may include additional materials.
A disadvantage of this process are the many processing steps involved with the manufacturer of the assembly due to the use of such a brazing slurry.
Another disadvantage encountered with the mentioned brazing process is that more flux material is often required at the junction between for example the tubes and headers of a heat exchanger assembly than between the tubes and fins. To overcome this disadvantage, many manufacturers currently manually apply a paste-like substance between the tubes and headers prior to brazing. The paste-like substances provides additional filler metal between the tubes and headers and may add additional mechanical strength to the filet. However, such materials are expensive and occasionally interfere with the brazing process through the action of silicon erosion of the underlying aluminium tubes and headers. Also other methods of dealing with this disadvantage are known in the art.
A further disadvantage of the mentioned CAB brazing process is that only aluminium alloys with a limited magnesium level may be used at standard levels of this brazing flux application, typically up to about 5 gram flux/m
2
. If the magnesium level in the aluminium alloy is above 0.3 weight percent, the flux material gets poisoned due to the formation of MgO. This disadvantage can only be partly be overcome by applying higher loads of flux material.
A further disadvantage of the mentioned brazing process is that if the fluxing material also contains silicon or zinc an uneven distribution of the silicon and zinc after brazing causes preferential corrosion sites in the assembly.
Many heat exchangers have alternating rows of tubes or plates with convoluted fins made of aluminium or an aluminium alloy. Many of these heat exchangers have turbulators disposed within the tubes that require internal brazing. Also, CAB furnace brazing suffers from the disadvantages that the internal tube surfaces and the heat exchanger require individual fluxing before assembly and an overall fluxing of the completed assembly before brazing. Further, CAB furnace brazing suffers from the disadvantage that the individual fluxing of the components of the heat exchanger is costly and time consuming.
SUMMARY OF THE INVENTION
An object of this invention is to provide a composite sheet material for brazing in an inert atmosphere furnace (CAB) operation, as a result of said composite sheet material less processing steps at the side of the manufacturer of the brazed assembly are required.
A further object of this invention is to provide a composite sheet material for brazing in an inert atmosphere furnace (CAB) operation, which avoids the need for individual fluxing of internal and external surfaces of the assembly prior to brazing.
A further object of this invention is to provide a composite sheet material which requires less lubrication means, and preferably no lubrication, in a forming operation prior to assembly of the individual components of an assembly for brazing.
A further object of this invention is to provide a method of manufacturing composite brazing sheet material in accordance with the invention.
In accordance with the invention in one aspect there is provided a self-brazing composite sheet material, wherein the composite sheet material having a structure comprising aluminium or aluminium alloy substrate on at least one side coupled to a layer comprising an olefin-acrylic acid copolymer as a carrier filled with a brazing flux material in an amount sufficient to achieve brazing.
In an embodiment of the invention the composite sheet material having a structure comprising an aluminium or aluminium alloy substrate on at least one side coupled to a layer comprising an olefin-acrylic copolymer as a carrier filled with both a brazing flux material and a metal powder, in an amount sufficient to achieve brazing.
Films made out of this type of copolymer are extensively used for the production of packaging material for food. Applying this type of copolymer on a metal substrate and using it as a carrier by filling it with one or more selected from the group comprising brazing flux material and metal powder, in an amount to achieve brazing, achieves several unexpected advantages with respect to brazing technology.
By the invention we can provide a self-brazing composite sheet material suitable for use in brazing applications, which overcomes several processing steps at the side of the manufacturer of a brazed assembly, such as individual fluxing of surfaces by applying the brazing flux by means of dipping or spraying, drying the applied brazing flux, etc. and all further disadvantages related to these steps.
By the invention we can provide a self-brazing composite sheet material for utilisation in brazing operations which no longer requires the step of individual internal fluxing of surfaces of assemblies prior to brazing.
The copolymer used is inexpensive and is characterised by excellent adhesion characteristics on a metal substrate, such that the copolymer used as a carrier may be applied on the substrate in the form as coil. Coils of the composite sheet material as such may be supplied to the manufacturer of brazed assemblies, which overcomes all necessary processing steps related to applying and removing of the brazing flux at this side.
The brazing flux material and/or metal powder are arranged essentially homogeneously throughout the copolymer carrier, where the copolymer carrier has a thickness in the range of up to 150 &mgr;m, and preferably up to 50 &mgr;m, and more preferably up to 10 &mgr;m, and most preferably of not more than 5 &mgr;m, and covers essentially the whole surface area of at least one side of the metal substrate. The thickness of the filled copolymer carrier is essentially the same over the whole surface area covered.
The type of copolymer used as carrier will decompose during heating up for the brazing cycle and leaves only the brazing materials, namely the fillings of the carrier, on the articles for clean and efficient brazing. By using a copolymer carrier as indicated a very uniform distribution of the brazing flux material and/or metal powder is obtained, allowing for a very good brazing process. The amounts of carbon residue on the brazed assembly obtained are extremely low and do not affect the final corrosion behaviour of the brazed assembly.
A further advantage of the composite sheet material is that it may contain dedicated amounts of brazing flux material and/or metal powder. Depending on the circumstances of the case the copolymer as a carrier may be filled with less or even more than standard amount. For example in the case where the metal substrate is an aluminium alloy containing more than 0.3 wt. % of Mg more brazing flux material than standar
Corus Aluminium Walzprodukte GmbH
LaVilla Michael
Stevens Davis Miller & Mosher LLP
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