US2740188A - Method of making a heat exchanger element - Google Patents

Description

April 3, 1956 E. c. SIMMONS 2,740,188

METHOD OF MAKING A HEAT EXCHANGER ELEMENT Filed May 24, 195?.

2 Sheets-Sheet l INVENTOR. Edward C. Simmons,

BY 36 6 WM,

F "hi April 3, 1956 E c, SIMMONS 2,740,188

METHOD OF MAKING A HEAT EXCHANGER ELEMENT Filed May 24, 1952 2 Sheets-Sheet 2 i-mwiikwm' I INVENTOR. 9 Bt;dword C. Simmons United States Patent METHOD OF MAKING A HEAT EXCHANGER ELEMENT Edward C. Simmons, Dayton, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware Application May 24, 1952, Serial No. 289,729 Claims. (Cl. 29-1573) This invention relates to heat exchangers and to the method of making the same. More particularly this invention relates to sheet metal heat exchangers of the type which are forge welded and then hydraulically dilated to form passages therein.

One of the primary objects of this invention is to provide a heat exchange design and a method of making heat exchangers which makes it possible to materially reduce the cost of the heat exchanger without in any way sacrificing quality.

'It has been found that there are definite cost advantages in forge welding sheet metal heat exchangers but there are also definite limitations in the amount of hydraulic dilation which can be done in a forge welded heat exchanger without excessively warping the main body of the plate and without weakening the walls of the passages of chambers thus formed and for that reason it is not practical to form the relatively large headers or boiler chambers in evaporators and the like by hydraulic expansion. It is an object of this invention to provide a heat exchanger design which makes it possible to mechanically form the relatively large header chamber and to hydraulically dilate the smaller fluid passages.

The pressures required for hydraulically dilating the smaller passages in a heat exchanger are so great that itis essential to limit the degree of expansion by means of heavy plates placed on opposite sides of the sheet metal during the process of dilating the passages. Due to the process used in forming the passages it is impractical, if not impossible, to use plates which have cutaway portions corresponding to the final shape of the passages to be formed and this complicates the problem of forming heat exchangers and the like wherein some of the internal passages are larger than others. I have discovered a method which makes it possible to manufacture sheet metal heat exchangers having both small and large chambers formed therein wherein the smaller chambers are hydraulically expanded and the larger chambers are mechanically expanded.

More particularly it is an object of this invention to provide an improved method of manufacturing heat exchangers and the like wherein the larger internal chambers are formed by a process which does not require the attenuation of the metal forming the Walls of the chamber and wherein the smaller passages are formed by both bending and attenuating the walls of the passages.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Figure 1 is a plan view of blank sheets of metal used in manufacturing a heat exchanger; Figure 2 is a perspective view passing between reducing rollers;

Figure 3 is a perspective view showing the blanks after having been reduced, but before having been dilated;

showing the blanks Patented Apr. 3, 1956 Figure 4 is a perspective view showing a fragmentary portion of the blanks just prior to dilation;

Figure 5 is a fragmentary view primarily showing the tool used for mechanically forming the header;

Figure 6 is a fragmentary plan view showing the header formation prior to the dilation of the refrigerant passages;

Figure 7 is a vertical sectional view showing the heat exchanger in place between 'the heavy steel blocks which are used to limit the extent of dilation;

Figure 8 is a fragmentary vertical sectional view taken at right angles to Figure 7; and

Figure 9 is a perspective view showing the final shape of a heat exchanger constructed in accordance with this invention.

The invention to be described is particularly intended to utilize a process wherein a pair of weldable metal sheets are used and wherein the one sheet is provided with a stop-weld coating in a definite pattern so as to prevent the weldingof the two sheets together throughout the area coated. The second sheet is laid over the first sheet and the two are forge welded at all other areas of contact by hot rolling the sheets so as to reduce the thickness thereof at least 40 per cent in a single pass through the rollers.

Referring now to the drawings wherein there is shown an illustrated embodiment of my invention, reference numerals 10 and 12 designate a pair of metallic sheets from which a heat exchanger is to be made. Reference numeral 33 designates these sheets after they have been forge welded into one composite sheet. The sheets are preferably made of .070 thick weldable bronze of the following specification:

Copper, 92-94% Iron, 2.l-2.6%

Zinc substantially all the remainder Iron/zinc minimum .30

Tensile strength 44,000'lbs. per square inch, minimum Elongation in'2", 31% minimum Hardness Rockwell H 96-103 Any other type of weldable material such as copper, brass or aluminum could be used in place of the bronze.

The sheets are cut to approximately the same width as the width of the final product, however slightly more than /3 the length of the final product desired. To the one sheet there is applied a stop-weld coating 14 which prevents the adjacent sheets from adhering to one another at those places where the coating is present. This stop-weld material may be applied by printing, rolling, painting or spraying the stop-weld material in fluid or solid form. In this example, the stop-weld material is in the form of a watersuspension of colloidal graphite and sodium silicate which serves as a binder.

It will be noted that the pattern is such that a relatively large coated area 16 vis formed adjacent the one end of the plates and this coating extends throughout the entire width of the sheets. It will also be noted that another portion of the stop-weld material also extends to the outer edge of the plates at the point indicated by the reference numeral 18. After this coating has been placed on the one sheet and another sheet laid thereupon, with the coating then being disposed between the two sheets, the edges of the two sheets are inert gas weldedrtogether so as to'hold the sheets together in the desired relationship and so as to prevent the admission of air into the space between the sheets during the subsequent roll forging and welding operation.

As indicated in Figure 2 of the drawings, the sheets are passed between small diameter working rollers v20 so as to forge weld'the sheets together at all points except where covered .by the stop-weld material. This welding is accomplished by hot rolling the two sheets together at a sufficient temperature (for example 950 C.) for hot working and with at least a 55% to 65% reduction in a single pass through the rollers so as to forge weld the two sheets into a single unit.

The pattern of the stop-weld material illustrated in Figure l of the drawings elongates in the rolling process to the same extent of the elongation of the sheets as they are rolled into one composite sheet. Several cold rolling passes may follow the initial hot rolling pass to bring the final composite sheet to approximately the desired length. The final length in this example is about 2.92 times the original length. The thickness of the single composite sheet is allowed to vary between .045 and .048. The composite sheet which has been designated by the reference numeral 30 is then annealed. The cold rolling and the annealing causes the line of separation between the two sheets to disappear and recrystallization and grain growth extends across the former line of separation so that the two sheets have been completely forge welded into one except where the stop-weld material has been provided.

The inert gas welded edges of the sheets are preferably cut away so as to form a product having straight cleancut edges with the single outer dimensions of all of the evaporators thus formed being very uniform. By inspection of the trimmed edges of the composite plate 30 it is possible to determine the area where the stop-weld material 16 is located. Likewise, the point 18 may also be observed. In order to form a header 32 adjacent the one end of the composite strip without materially stretching or attenuating the metal, a die 34 is driven into the side of the composite sheet at the point where the stop-weld material 16 shows upon the edge of the sheet. The circumference of the die 36 is substantially equal to twice the width of the stop-weld material at 16 after completion of the forge welding operation. This die primarily serves to bend the material of the adjacent sheets into tubular form. The die 34 is then removed and end caps 36 and 38 respectively are inert gas welded or otherwise secured to the ends of the header portion 32 so as to completely seal the ends of the header. The one end cap 38 is provided with a connection 40 for supplying refrigerant or other medium to the header 32.

At that point where the stop-weld material extends to the end of the composite sheet 30 as indicated by the reference numeral 18 the sheets are mechanically forced apart so as to make it possible to introduce a conduit 44 which is inert gas welded or otherwise secured to the composite sheet 30 at the point 18. The composite plate or sheet 30 is then inserted between a pair of rigid blocks or punch press elements 50 and 52. As best shown in Figures '7 and 8 of the drawings the elements 50 and 52 clamp the edges of the sheet 30 so as to hold the same against displacement. The blocks 50 and 52 are cut away as indicated at 54 so as to form a recess therebetween which provides room for subsequent dilation of the smaller refrigerant passages to be formed in the plate 30. The blocks 50 and 52 are also cut away as indicated at 56 so as to provide room for the header 32. With the plate 30 firmly gripped between the blocks 50 and S2, fluid is introduced through the pipe 44 so as to hydraulically expand the smaller refrigerant passages. By using rigid flat surfaces to limit the expansion or dilation of the various passages, the rupturing of the walls of the passages is prevented and the assembly remains uniformly flat. Experience shows that the passages formed by hydraulically expanding the same between the fiat blocks have uniformly flat tops and bottoms as indicated by the reference numeral 60. Figure 7 best shows the final shape of the refrigerant passages. These flat surfaces provide excellent contact for ice trays and other vessels which may be placed on the surface of the heat exchanger. The bydraulic pressure required for properly expanding or dilating the passages is approximately 10,000 pounds per square inch or even higher.

By virtue of the fact that the passages are expanded between substantially flat blocks rather than complex dies having recesses exactly corresponding to the final outer contour of the entire evaporator, it is obvious that any unevenness in the location or length of the smaller refrig erant passages does not present any problem. The shape and size of the headers will always be uniform on each heat exchanger manufactured by this process as the header extends crosswise of the sheet as it passes between the rollers and therefore there is no variation in the length of the header since the width of the sheet is not appreciably altered by the rolling process. Furthermore the inner diameter and consequently the outer diameter of the header is determined by the tool used for mechanically forming the header chamber. The inlet tube 40 will, of course, be sealed and properly protected against rupture by the high pressure fluid during the process of dilating the smaller refrigerant passages.

Upon completion of the dilating process the composite plate may be removed from between the heavy plates 50 and 52 and then bent into any desired shape such as that shown in Figure 9, wherein an evaporator for the frozen food compartment of a refrigerator has been shown. In this type of evaporator construction the ends of the sheet 30 would be inert gas welded or otherwise attached to one another at 62 (see Figure 9).

Although one specific example has been given, it should be understood that other types of materials which lend themselves to the forge welding process could be used and it is also apparent that certain aspects of this invention are applicable to the formation of evaporators from stainless and other types of steel sheets which may be secured to one another by electric welding or any other well known processes rather than by forge welding. By virtue of the method used in manufacturing the heat exchanger it is obvious that the wall thickness of the header will be greater than the Wall thickness of the smaller passages. This constitutes a definite advantage in that there is otherwise a much greater tendency for the larger chambers to rupture or distort in response to the high pressures than smaller chambers and passages.

Insofar as certain aspects of this invention are con cerned, one could dilate the smaller passages before mechanically expanding the header.

While the form ofembodiment of the invention as herein disclosed constitutes a preferred form, it is tobe understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. The method of producing a sheet metal element having relatively large and small internal passages which comprise superposing a stop-weld material on one side of a sheet of metal with a first portion thereof extending from edge to edge to form a large passage and a second portion extending from said first portion to form a smaller passage, placing a second sheet of metal in superposed relationship to said stop-weld material whereby said stopweld material is arranged between the sheets, forge weldv ing the two sheets into a single composite sheet of greater length and less thickness, forming said relatively large passage by expanding said sheets adjacent said first portion of stop-weld material by inserting a tool of such dimension that it separates said sheets at said first portion without appreciably stretching the metal, protecting the area thus expanded from further expansion by inserting the composite sheet within a die having portions engaging the outer walls of said large passage and having other portions,

spaced from said composite sheet opposite said second portion of stop-weld material, and expanding said smaller passage under a fluid pressure which stretches the metal in the walls of the smaller passage. 1

2. The method of expanding the header and connecting passages in a roll forged composite metal sheet having:

non-welded areas defining a relatively large header-and smaller connecting passages, which comprises expandingsaid header by inserting a tool into the header area of such a dimension that it does not stretch the metal, protecting the walls of the header thus expanded from further expansion by placing the composite sheet within a die having portions spaced from said composite sheet opposite said smaller connecting passages, and expanding said smaller passages under fluid pressure which stretches the metal of the smaller passages.

3. The process of forming a single sheet of metal having within its interior a relatively large chamber and communicating relatively small passages of predetermined configuration which consists in, superimposing one upon the other two sheets of metal having therebetween stopweld material arranged with a first area extending across the sheet to form said relatively large chamber and having a second area arranged to form said relatively small passages, forge welding the two sheets into one single sheet, separating the sheets throughout said first area by insert ing a tool of such dimension that it does not appreciably stretch the metal, clamping the sheets between die elements for preventing further expansion of said relatively large chamber, and expanding the smaller passages by applying an internal fiuid pressure which stretches the metal of said smaller passages.

4. The process of forming a single sheet of metal having within its interior a relatively large chamber and communicating relatively small passages of predetermined configuration which consists in, superimposing one upon the other two sheets of metal having therebetween stopweld material arranged with a first area extending across the sheet to form said relatively large chamber and having a second area arranged to form said smaller passages, forge welding the two sheets into one single sheet, forming said large chamber by separating the sheets throughout said first area by inserting a tool of such dimension that it does not appreciably stretch the metal, clamping the sheets between dies which prevent further expansion of said relatively large chamber but allow expansion of said small passages forming said smaller passages by applying an internal fluid pressure which stretches the metal 40 of the smaller passages, and limiting the extent of dilation of said smaller passages by means of said dies so as to prevent rupture of the walls of said smaller passages during the formation of said smaller passages.

5. The method of producing a sheet metal heat exchanger which consists in superposing a stop-weld material on one side of a sheet with one portion thereof extending from edge to edge, placing a second sheet in superposed relationship to said stop-weld material whereby said stop-weld material is arranged between said sheets, forge welding the two sheets by hot rolling the same into a single compo-site sheet of greater length and less thickness, mechanically expanding the composite sheet throughout said one portion of the area covered by said stopweld material by inserting a tool of such a dimension that it does not stretch the metal, capping the ends of said mechanically expanded portion, hydraulically expanding the composite sheet throughout other portions of the area covered by said stop-weld material at a pressure which stretches the metal adjacent said other portions, and protecting the metal of the mechanically expanded portion against stretching while hydraulically expanding said other portions.

References Cited in the file of this patent UNITED STATES PATENTS

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