Method for obtaining hollow articles

The disclosure teaches a method for the manufacture of hollow articles useful as heat exchangers including the steps of rolling together two sheets of metal with at least one metal tube sandwiched therebetween to form a bonded assembly. The metal tube is subsequently expanded by the introduction of pressure therein to form an internal passageway.

BACKGROUND OF THE INVENTION 
The present invention relates to the preparation of expanded pressure 
welded passageway panels. More particularly, the present invention relates 
to the preparation of metal panels of the foregoing type having utility in 
heat exchange applications wherein the heat exchange medium is circulated 
through the passageways. 
A commonly used and efficient type of heat exchange unit for a variety of 
purposes is formed from a plurality of superimposed sheets of metal having 
internally disposed therebetween one or more conduits or tubes to carry a 
heat exchange medium. According to one known method of manufacture, as 
illustrated in U.S. Pat. No. 2,690,002, this type of heat exchange unit 
may be readily manufactured to provide if desired a great multiplicity of 
tubes in a metal panel in virtually any desired pattern. This method 
involves the application of a suitable predetermined pattern of weld 
inhibiting material corresponding to desired passageways in the final 
article between component sheets and pressure welding all adjoining areas 
except those separated by the weld inhibiting material. This forms a 
unified composite panel which is subsequently inflated along the unwelded 
areas to erect tubes integral with the resultant panel. 
The sheet-like structure having internal hollow passageways formed in 
accordance with the foregoing process is well adapted for use as a heat 
exchanger wherein a heat exchange medium can be circulated throughout the 
structure in the internal passageways. The panel may naturally be provided 
with the necessary connections for the circulation of the heat exchange 
medium. As can be appreciated, these connections can vary in number and 
displacement to suit the desired end use of the heat exchange panel. For 
example, U.S. Pat. No. 2,822,151, issued Feb. 4, 1958, discloses a 
plate-like heat exchanger of the foregoing type provided with a single 
connection for both entry and exit of fluid, and possesses particular 
utility for the circulation of refrigerants. Correspondingly, copending 
application Ser. No. 573,953, the disclosure of which is incorporated 
herein by reference, illustrates a heat exchange structure of the 
foregoing type provided with longitudinally opposed connections 
comprising, respectively, inlet and outlet portions provided to enable the 
continuous flow of heat exchange medium transporting absorbed energy. 
Heat exchanger panels of the foregoing type have found considerable utility 
in solar energy recovery systems. It is desirable, however, to provide 
improved panels similar to those discussed above and methods for obtaining 
same particularly for use in solar energy recovery systems. Thus, for 
example, panels formed by the foregoing process are frequently made of 
aluminum. Corrosion problems in these aluminum panels require the use of 
an inhibited heat transfer fluid to provide satisfactory life. Aluminum 
panels also require special connection procedures and special skills of 
installation. Panels made entirely of copper or copper alloys overcome 
these problems, but suffer from the disadvantage of considerably increased 
cost. 
Another process used to make satisfactory panels for solar energy recovery 
systems involves the use of copper tubing soldered to flat copper plates. 
The cost of both materials and fabrication is high for such panels. 
Accordingly, it is a principal object of the present invention to provide 
an improved method for the manufacture of hollow articles useful as heat 
exchangers, particularly in solar energy recovery systems, and also an 
improved panel obtained thereby. 
It is a further object of the present invention to provide an improved 
method and panel as aforesaid which is inexpensive to prepare and which 
may be readily used with a variety of different metals. 
Further objects and advantages of the present invention will appear 
hereinafter. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the foregoing objects and 
advantages may be readily obtained. The present invention comprises a 
method for the manufacture of hollow articles useful as heat exchangers 
which comprises: providing a first and second sheet of metal in superposed 
relationship; forming an assembly by placing at least one metal tube 
between said first and second sheets corresponding to a predetermined 
configuration of fluid passageways, said tube having a weld inhibiting 
material therein; pressure welding said assembly in the areas thereof not 
separated by weld inhibiting material; and expanding said assembly in the 
areas separated by weld inhibiting material by the introduction of fluid 
pressure therein. 
It can be apppreciated that the process of the present invention is quite 
versatile and that a variety of materials may be utilized for either the 
sheet components or the tube components. In the preferred embodiment, the 
sheet components are formed of an aluminum or aluminum alloy material and 
the tube components are formed of a copper or copper alloy material in 
order to provide the advantages of both of these materials. In the 
preferred embodiment a plurality of metal tubes are placed between the 
sheets spaced from each other in a predetermined, spaced relationship, 
with each of said tubes being subsequently expanded by the introduction of 
pressure therein. A panel of this type is particularly useful as a solar 
panel in solar energy recovery systems. In the expansion step the trailing 
end of said tubes are clamped shut and pressure is introduced into the 
tubes at the leading edge. Headers may be connected to said tubes at the 
leading and trailing edges thereof as by soldering.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to the drawings, FIG. 1 schematically depicts the formation of 
the bonded assembly of the present invention. In accordance with FIG. 1 a 
first sheet of metal 10 and a second sheet of metal 11 are provided. At 
least one metal tube 12 is placed between the first and second sheets 
corresponding to a predetermined configuration of fluid passageways to 
form an assembly 14. The tube 12 has a weld inhibiting material 13 therein 
substantially throughout the extent thereof. The assembly 14 is pressure 
welded as by feeding the assembly through rolls 15 and 16 to reduce the 
thickness thereof and to form a bonded assembly or pressure welded article 
17 wherein the components thereof are pressure welded in the areas thereof 
not separated by weld inhibiting material. Naturally, if desired, a 
plurality of sheets 10 and/or 11 may be employed based on the 
characteristics desired in the final product wherein the sheets may be of 
similar or dissimilar compatible metals. In the preferred embodiment 
indefinite length strip is utilized which is subsequently sheared to 
desired length. Naturally, the process may be conducted as a batch-type 
procedure where sheets are used generally corresponding to final panel 
length. 
FIG. 1 schematically shows the formation of the bonded panel by feeding the 
components thereof simultaneously between rolls 15 and 16. As is apparent, 
the present invention contemplates such simultaneous feeding of components 
or other variants thereof that will be obvious to one skilled in the art. 
Thus, tube 12 may be preliminarily spot welded to the surface of the first 
sheet of metal 10 in a predetermined configuration. Alternatively, tube 12 
may simply be superimposed on the surface of sheet 10 and held thereon by 
means of tension. In the preferred embodiment, a plurality of tubes are 
utilized, such as, for example, three tubes shown in FIG. 2. Naturally, 
any number of tubes may be used spaced from each other in a predetermined 
spaced relationship such as exemplified in FIG. 2. In the preferred 
embodiment, the metal sheets are aluminum or aluminum alloys and the tubes 
are copper or copper alloys. Also, the procedure schematically depicted in 
FIG. 1 may be employed on an indefinite length of material or on discrete 
sections corresponding to the desired panel length, as indicated above. 
The preferred embodiment utilizes an indefinite length of material, 
although one can also use discrete sections since this avoids subsequent 
trimming operations. 
In the preferred embodiment, the panel has a leading edge 20 and a trailing 
edge 21, see FIGS. 4 and 5. Preferably, additional weld inhibiting 
material 22 is placed between the first and second sheets of metal prior 
to bonding at the leading edge thereof so that welding of the sheets is 
precluded at this point. Hence, sheets 10 and 11 may be peeled back after 
the pressure welding step as shown in FIG. 2 to expose the tubes for 
subsequent expansion. The peeled back portion may be subsequently trimmed. 
The same procedure is preferably employed on the trailing edge to expose 
both ends of the tubes. Alternatively, the tube length may be greater than 
the sheet length taking care to insure that the longer tubes are clearly 
exposed after bonding. 
The expansion step is shown schematically in FIG. 3 wherein the trailing 
edge 21 of said panel 17 is clamped shut by any desired means, as by clamp 
23 and pressure is introduced into tubes 12 by means of fluid pressure 
inflation needle 24 which expands the copper tubes to form expanded 
passageways 25 clearly shown in FIG. 6. In a preferred embodiment, all 
tubes are expanded simultaneously by the use of an inflation apparatus 
having a plurality of nozzle attachments (not shown). Naturally, the tubes 
may be inflated one at a time, if desired. 
After the formation of bonded panel 17 and expanded tubes 25, one may 
conveniently attach headers 26 and 27 to both ends of the panel to form 
completed heat exchanger 28 shown in FIG. 5. 
Naturally, the process of the present invention contemplates numerous 
variations therein. As indicated hereinabove, the preferred operation 
utilizes aluminum sheets 10 and 11 and copper tube 12. Naturally, a 
variety of other metals may be used depending upon particular end use. For 
example, one can conveniently utilize virtually any like metal sheet and 
tube, such as aluminum or aluminum alloy sheet and similar tube or copper 
or copper alloy sheet and similar tube. Other representative combinations 
include copper sheet or tube with ferrous sheet or tube and zinc sheet or 
tube with ferrous sheet or tube. 
The bonding rolling operation, which may if desired be performed hot or 
cold, normally produces an average area reduction in thickness of from 40 
to 70%, with naturally the aluminum strip being reduced a greater extent 
than the copper tube. For example, where an average 60% area reduction is 
utilized, the aluminum strip would be reduced about 70% and the copper 
tube would be reduced about 50%. Generally, the ratio of the reductions in 
the copper and aluminum components would be the inverse of the ratio of 
the ductility of the copper and aluminum components. At the exit of the 
mill, a metallurgical bond would exist at all metal interfaces not 
protected by weld inhibiting material. In order to help maintain flatness, 
foretension may be applied to the exiting strip to overcome the unequal 
reductions occurring at the width of the assembly. After bonding, a heat 
treatment operation, or additional cold reductions, may be given to the 
bonded assembly to adjust the mechanical properties of the composite to 
desired levels. If an indefinite length of material is prepared by the 
bonding operation, the bonded strip would then be sheared to the desired 
length to form panels. A plurality of strips of weld inhibiting material 
would preferably be applied so that the tubes may be exposed at a leading 
and trailing edges of the sheared panel in a manner similar to that shown 
in FIG. 2 
Any suitable aluminum or copper material may be employed in the process of 
the present invention. The aluminum alloy shown should preferably be high 
in thermal conductivity and sufficiently workable to facilitate bonding, 
such as aluminum alloys of the 1000, 3000 or 5000 series. If structural 
rigidity is an important factor in the final panel, age hardenable 
aluminum alloys, such as of the 6000 or 7000 series, can be used. These 
alloys should be bonded in the annealed condition. A subsequent solution 
heat treatment and aging operation is naturally required to take advantage 
of these type alloys. The chosen copper alloy should preferably be 
commercially available in tube form and workable enough to allow bonding. 
Solderability and corrosion resistance should also be high. Illustrative 
copper alloys that may be employed include the copper-nickel alloys and 
CDA Alloys 110 and 194. 
The gages of strip and tubing employed should naturally minimize the amount 
of the expensive copper component, but still maintain the desired 
characteristics of strength, corrosion resistance and solderability. 
Bonding reductions should naturally depend on the alloys chosen, but 
should not be less than 40% in order to insure a good bond. The upper 
limit is generally below 70% available reduction, but depends on the 
workability of the alloys employed and the desired mechanical properties 
of the finished product. 
Naturally, one may utilize first and second sheets of metal of the same or 
unequal thicknesses. Also, if desired, one may inflate the tubes into a 
die in order to obtain exact inflated dimensions. Alternatively, one may 
use profiled bonding rolls or profiled sheet or sheets to equalize 
reduction across the entire strip. One may, if desired, use composite 
sheets or tubes in order to achieve particularly advantageous 
characteristics. 
The process of the present invention may provide for the production of 
panels with corrosion resistance, strength and post bonding fabricability 
superior to conventional materials, such as pressure welded all aluminum 
panels, with cost and weight below that of pressure welded all copper 
panels. Panels produced by this process are more efficient and less 
expensive than panels produced by conventional bonding techniques and may 
be fabricated so that they can be readily interfaced into conventional 
plumbing systems without specialized techniques. Particularly, the present 
panels eliminate the problem of crevice corrosion which may be encountered 
in pressure welded panels. 
This invention may be embodied in other forms or carried out in other ways 
without departing from the spirit or essential characteristics thereof. 
The present embodiment is therefore to be considered as in all respects 
illustrative and not restrictive, the scope of the invention being 
indicated by the appended claims, and all changes which come within the 
meaning and range of equivalency are intended to be embraced therein.