US2940737A

US2940737A - Heat exchanger

Info

Publication number: US2940737A
Application number: US500152A
Authority: US
Inventors: Ray A Sandberg
Original assignee: Houdaille Industries Inc
Current assignee: Houdaille Industries Inc
Priority date: 1955-04-08
Filing date: 1955-04-08
Publication date: 1960-06-14
Anticipated expiration: 1977-06-14

Description

R. A. SANDBERG I 2,940,737

HEAT EXCHANGER June 14, 1960 4 Sheets-Sheet 1 Z8 jg Z Filed April 8. 1955 122217. t UP @004. Smwamm June 14, 1960 I R. A. SANDBERG 2,940,737

HEAT EXCHANGER Filed April 8, 1955 4 Sheets-Sheet 2 47:22am /Q4 5/1/10552 June 14, 1960 R. A. SANDBERG 2,940,737

HEAT EX cccc ER AZW Al 5 1N055 g M4 4 7M zwx%zt June 14, 1960 R. A. SANDBERG 2,940,737

HEAT EXCHANGER Filed April 8, 1955 4 Sheets-Sheet 4 United States Patent HEAT EXCHANGER Ray A. Sandberg, Waukegan, 111., assignor to Houdaille Industries Inc., a corporation of Michigan Filed Apr. 8, 1955, Ser. No. 500,152

2 Claims. (Cl. 257-256) The present invention relates to a heat exchanger of the type having a tube secured to an elongated heat conductive member by deformation of the member.

In conventional plate and tube type heat exchangers, an elongated sinuous tube is generally secured to a backing plate of high thermal conductivity by brazing, soldering or welding. It has heretofore been proposed that the tube be secured in this manner within a shallow depression formed in the plate so that the heat transfer eificiency of the exchanger may be increased. Due to the necessary provision of means, such as Welding or brazing, to secure the tube to the backing plate, such heat exchangers have been expensive and complicated in manufacture and the efiiciency of heat transfer from the tubes to the plate has been low due to the necessarily small area of contact therebetween.

One form of the present invention comprises an improved type of tube and plate heat exchanger similar to that disclosed in my copending application Serial No. 36,598 filed July 2, 1948 now Patent No. 2,585,043 granted February 12, 1952, and assigned to the assignee of the instant application, in which the tube is firmly secured to the plate without the employment of external securing means, such as welding or brazing, and in which the area of contact between the tube and the plate is greatly increased to insure efficient heat exchange. In general, the heat exchanger of the present invention comprises an elongated heat conductive member and a tube secured to the member by deformation of the member into more than semi-peripheral contact with the tube. The present application is a continuation-in-part of Serial No. 332,693, filed January 22, 1953 now Patent No. 2,732,615 granted January 31, 1956, which in turn was a continuation of Serial No. 80,240 filed March 8, 1949 and Serial No. 124,179 filed October 28, 1949, Serial Nos. 80,240 and 124,179 now being abandoned.

The securing of the tube to the plate, as carried out by one embodiment of the method of the present invention, involves the forming of a groove or depression in the plate, the placing of a tube in the groove, the tube having a diameter less than the depth of the groove, and the formation of additional depressions or grooves in the plate by deforming portions of the plate immediately contiguous to the first formed depression. In this mannet, the plate is deformed into greater than semi-peripheral :surface contact with the tube to overlie a median diameter of the tube, thus anchoring the tube to the plate with the relatively great surface contact therebetween insuring eflicient heat transfer from the tube to the associated backing plate.

This method is satisfactory for use in the formation of heat exchangers employing tubes having relatively small outside diameters, e.g., on the order of one quarter inch or less, and it may also be used with larger diameter tubes if desired. However, it has been found that in the use of the method with tubes of outside diameters on the order of from to /2 inch or larger, the tube often does not have suflicient structural resistance to re- Patented June 14, 1960 ice tain its original circular cross-sectional shape without permanent distortion of the tube where the metal plate is folded or swaged back on the tube into interlocking engagement therewith. This deformation of the tube may prevent close gripping peripheral contact between the tube and the plate along the entire length of the tube and thus may seriously interfere with the heat transfer efficiency of the heat exchanger.

Of course, the tube wall thickness may be increased to prevent such tube distortion, but this is not economically feasible due to the increased cost of such tubing. Further, tubing of relatively thin Wall thicknesses, while of insufficient strength to resist distortion during forming of the exchanger, has sufiicient bursting strength and other structural characteristics for the actual operational demands imposed upon it in use, and also thin-walled tubing is desirable for reasons of heat transfer efficiency.

A further embodiment of the present invention now makes possible the employment of tubing of relatively large diameters and relatively thin wall thicknesses in the formation of plate and tube type heat exchangers by a method generally similar to that above outlined. This further embodiment contemplates the positioning of the tube within a groove formed in a backing plate of desired thermal conductivity, the distortion or swaging of the groove side walls and the plate portions immediately adjacent thereto into engagement with the tube, and the distortion of the tube radially outwardly into closely gripping engagement with the swaged portions of the plate to insure a snug fit between the plate and the tube and the efiicient transfer of heat between the tube and the plate.

The heat exchanger of this further embodiment thus comprises generally a backing plate of high thermal conductivity and a tube in interlocked engagement with the plate, both the tube and the plate being deformed from their configuration prior to assembly into tightly gripping, interlocked, thermally efiicient engagement.

In accordance with still another embodiment of the present invention, a tube and wire heat exchanger is manufactured by forming wires about more than a semiperiphery of each of a series of tubes. Tube and Wire heat exchangers at the present time involve a large num? ber of welds per assembly, for example as many as 2600, and fabrication of such assemblies involves extremely expensive and complicated machinery. Further, if the tube is burnt through in the welding operation at even a single one of the 2600 welds, the entire assembly must be discarded. By eliminating the welding as a fastening means, the costly equipment and danger of weld failure is avoided and important savings are effected.

It is therefore an important object of the present invention to provide an improved type heat exchanger in which a tube is secured to. a heat conductive member without the employment of external fastening means.

Another object of the present invention is to provide an improved method of making a heat exchanger by deforming a heat conductive member into greater than semiperipheral surface contact with the heat exchange tubing to maintain the components in assembled eilicient heat transfer relation.

It is a further important object of the present invention to provide a heat exchanger in which heat exchange tubing is secured within a groove or bend formed in a heat conductive member, with portions of the member extending into conforming contact with the tube above a median diameter thereof to securely lock the tube to the member.

A still further important object of this invention is to provide an improved method of forming a heat exchanger having a heat conductive member and heat exchange tubing.

" Still another obieet of the present invention is to proventiontorprovide animprovedmethod for themanufacture of :plate and .tube .type:heat exchangers, :in zwhichthe tubessof the heat exchanger are :of.relativ'elylarge' fam- V'eteri and of relatively thin wall thickness.

conforming contact with more than a semi-periphery of Another important additional object 'Of.the?pr6S611t.in

vention is to provide .an improved plate :and ztubeztype heatexchanger including a backing plate in-tightly 'gripping engagement witha tube deformed radially. outwardly into engagement' with the'splate. a

7 :Still another-important additional object ofthe present invention is to provide an'improvedmethod of making a tubeand plate type heatiexchanger including the steps of. positioning a tube in a groove formed in a backing plate, swaging adjacent portions ofthe plate into engage-' ment with the tube to'overlie a median diameter thereof,

and deforming the tube radially outwardly into snug fitting, interlocking engagement with swagcd portions .of

the plate. 7 V V c 7 LA furthermore specific object of the present ,inventioniis'toprovide an improved tube and wire type heat V exchangers 7 Other and :further important objects of the presentlinventionwill bezapparentfrom'the. disclosure in the-specification and initheiaccompanying drawings.

aOnthe'drawings:

.the tubing; 7

Figure 17 is an enla ged'cross-seetional view similar to Figure 16; 1

Figure 18 is a longitudinal sectional view taken generally along the line XVHL-XYIIIof Figure 17;

Figure 19 is a sectional View of the lower die used'in performing the method of Figures 14-18; and

Figure 20 illustrates a-sinuous wire configuration for providing a plurality or; parallel lengths on which the method of Figures 1 5 to :19 -may be practiced As shownonthe drawings? 7 is In Figure ,1, reference numeral -;10 ;.re fers' ;generally to a heat exchanger of the plate and tube type including a backing plate 11 =ancl-a continuous leng th' of tubing 12 of sinuous shape secured to the backing plate 11. It is to be noted that those portions of the serpentine or sinuvous length of tubing 12 extending across the width of backing plate -11 are substantially straight whilethebon- I-Figure 21 isa broken, plan view'of aheat exchanger10f.

c a firstembodiment ofthe present invention;

a "Figure'2sis a fragmentary, sectional view illustrating a step in the method of making the heat exchanger of Figure. l;"

Figure 3 is a fragmentary, sectional view illustrating further steps in the making of the :heat exchanger 20f Figure l; EFigure '4 is an enlarged fragmentary sectional view illustrating the final step in makingithe heat exchanger ofFigure 1;;

Figure 5 is a brokem-plan View of a heat exchanger 'of asecond embodiment of the present invention; Figure .6 is an.enlargedgiragmentary, sectional view illustrating a step in the method of making-the heat changer OfIFlglllfE 5;

' Figure 7*.is an :enlarged,:fragmentary,.sectional view illustrating a further-step in themaking of the heat exchanger of'Figure 5; V

FigureS is anenlarged, fragmentary, sectional view similartogFigure 7 and illustrating the final step in the makingof the. heat exchanger of Figure 5; A.

Figure 9 .is a diagrammatic cross-sectional view of a plate-and tube typeheat-exchanger indicating. certain sections'which were. cut in .a'fini shed assembly to observe the clinching exerted by thelower portion. of the plate on the tube; 1

Figure 10 represents a plot iof strain measured at the lower portion of a plate;groove as a function of load;

the data .beingobtainedduring-the formation of-a .tube and plateheat exchangerasshown in Figures 11, 12and 13,; I

Figuresll, Hand 13 represent diagrammaticallysthe snccessivewstress: conditions in =arplatesgrooveportion duringthezfonnation-of a" tube and :plate .type assembly in themannenillnstrated;

' :Eigure -14.1illustrates-3the'=' 'tialncondition-rof :a wire' a which isa-io be. assembled intciga-tube andwvire heat cex changer accordingtotheipresent invention;

Figure 15 illustrates the condition of the wire-after the grooves' or -bends have; been formed: therein in preparafor receiving i,theheet-exchanger tubing; li igure 'lfi' illustrates the 'fo'rmation :of the wire into tions of the tubing extending beyond the plate 11. ".It is 'necting curved portions of the tubing 1-2 extend beyond.

the backing-plate 11. In this manner, it is not-necessary to-deform'the backing plate llint o a serpentine or sinuous path to receive the tube 12-but rather, it. is only necessary to's'ecnre the straight portions of the tubing 12 to the backing plate 11. 'T he method ofsecuring the serpentineor sinuous length of "tubing 12 to the plate 11 as herein described insures the efiicient transfer of heat'from the-tubing12 to the relativelylargeheat transfer surface 'of plate 11;

The plate 11 is initially deformed to provide a plurality of parallel, space-d depressions 'or grooves 1340 receive each 'of the substantially straight portions ofthe tubing 12. Each *ofxthe depressions -or grooves =-13,' as best shown in Figure 2, is provided with a closed areuate bottom 14 and'upstanding side walls '15 extendingupwardly from'the closed bottom 14. The depth of groove 13 is preferably greater than the external diameter of -the tubing 12 for reasons which will be hereinafter more fully described. 7 V v After the grooves have been formed in thelplate, each side of'the plate is placed in turn between the trimming and forming dies'25gand 26; The lower die'26 is provided with a pair of elongated. grooves 27 receiving the grooved portions 13 of the plateadjacenta side edge thereofso as to accurately index the plate inthedie. An'edge'portion indicated at '28 of the plate -is then removed by means of a shear blade 19. -It will be 'observed'that simultaneous with the trimming operation, theside edge portion 11a of the plate 'is displaced downwardlyby meansof cooperating'portions 25a and 26a of the dies. A portion 11b of the side edge 311a may be formed to slope at .an angle of approximately 30 to the major plane of the plate and to join with the groove upstanding side wall l5 on a"%; inch radius bend 110, The purposeof offset portions such as 11a at the side edges of the plate is to insure proper action of the forming dies "of Figures 3 and 4 in wrapping the plate about the tube length in the laterally outermost. groove in the plate as will hereinafter be more fully discussed. 7 V c As the next step of ,the method the tubing 12 is posi tioned within the grooves or depressions 13. In1the rrianu:

facture of a heat exchanger such a'sc that illustratedin Figure 1, only the straight portions of the serpentine tub: ing arecplaced withinthegrooves .13 with the curvedpoiito .be noted that when the tube 12 is bottomed within the depression or grooves '13, peripheral contact between tube and groove is established, the ,outer periphery of the tube having vapproximately the sameradius of. curvature. as the inner periphery of the arcuate ,groove bottom 14, so that the ltube .12 :fits ;snugly --.w ithin lihe groove =13.

' 1 fIhe securing of lhetube withinsthe platecdepressions liliis carried cut ea-pair ofrcooperating;dies16tand 17.

S The dies 16 and 17 are preferably of such size as to receive the entire exchanger unit shown in Figure l. The backing die 16 is recessed as at 18 to provide support for the bottom 14 of the groove 13. The backing die '16 is also recessed, as at 19, immediately adjacent each side of the recess 18. The recess 19 is preferably contiguous with the entire length of the recess 18 an with the width of the backing plate 11.

A movable forming die 17, adapted for cooperation with the backing die 16, is provided with a pair of arcuate protuberances 20 separated by an arcuate depression or groove 21'. As shown in Figure 4, one of the protuberances 20 is adapted to extend into each of the grooves 19 of backing die 16 and arcuate recess 21 is adapted to receive the tubing 12 as the upper die 17 completes its work stroke. Figure 3 indicates the position of the dies 16 and 17 prior to forming the plate about the straight lengths of tubing 12. As the die 17 moves downwardly, the protuberances 20 engage the plate laterally outwardly of bends 11d formed between the plate lands L and the upstanding side walls of the grooves. Further down-' ward movement of the upper die 17 results in a deflection of the land portions L as indicated by the dash lines so that a central portion of each land L is bottomed against the surface 16a of the lower die 16. It has been found" to be very important to limit the downward deflection of the lands L of the plate in the manner illustrated in Figure 3 in order to obtain the uniform and symmetrical wrapping of the plate about the tube on both sides of the tube as indicated in Figure 4. In one embodiment, the; bottoming of the deflected portions of the lands L oc curredrin the first .020 to .030 inch of downward travel; of the upper die from the position indicated in Figure 3." It is believed that the bottoming of'the lands .L as shown in dash outline in Figure 3- serves to.prevent the bends; 11d. between the groove side walls. and the lands, from moving laterally outwardly out of proper engagement with the respective protuberances 20. In the deflected condition of the lands L shown in dash outline in Fig-. ure 3, the protuberances progressively lock aroundthe' bends 11d between the .lands L and groove side wal1s-.; In one embodiment, the protuberances 20 were found to be locked about the bends 11d between the lands and the groove side walls after a total punch travel of approximately .050 to .060 inch. r p The upper die 17 causes the lands to lie fiatagainst the lower die surfaces 16a and the side wallstobe formed. around the tube substantially as in the final product after. a total downward travel of the upper die 17 of approxi-' mately .100 to .110 inch, this stage in the operation being. completed before the upper die 17 reaches bottom or. the limit of its total travel.

The dies are designed so as to travel a further and final of an inch downwardly, and this final movement stretches the metal of the lands and swages the. metal around the tubes, placing this metal under com-. pression so that it will not spring away from the tube. after removal from the die. In fact it has been found that the plate is actually under a tensile stress at the portions thereof wrapping the tube after removal from the forming dies. This'is indicated by constriction of the per-1 tion of plate wrapping the tube if the tube is removed therefrom. The plate land portions remain flat and in substantially a single plane with an apparent stiffness after removal of the assembly from the dies as a result of this swaging operation and stretchingof .rnetal-between the grooves. In the illustrated embodiment, the tubemay have a .4: inch outside diameter and'a wallthickness of about .028 inch while the plate maybe of 22 gaug'e steel having'a thickness of about .030 inch. 1 The dies shown in Figure 4l.show-- the exact proper tions 'of the protuberances 20 arid "recesses-1 9" in was tion to the tube diameter for the embodiment illustrated. l'

t 6 V The edge portion 11a of the plate adjacent the outermost groove is ofiset in such a manner as to bottom against the portion 16a of the lower die 16 to tend to resist lateral outward displacement of the bend portion 110 and thus to promote locking of a corresponding protuberance 20 about the bend 110 in the plate between the sloping plate portion 11b and the groove side wall portion 15. Further the formation of the sloping portion 11b adjacent the bend 11c provides a shoulder facing laterally outwardly against which the associated protuberance 20 of the upper die may engage as the die 17 moves downwardly to prevent laterally outward movement of the edge portion 11a which is not constrained between a pair of plate groove portions as are the land portions L of the plate.

It may be noted that the portions 17a of the upper die can be still further recessed as indicated in dotted outline at 17b in Figure 4 so as to avoid contact between the upper die and the land portions L of the plate without adversely affecting the final product. No compression of the land portion L by the upper die is necessary to the rigid planar plate configuration achieved by the method of Figures 1 to 4.

The land portions L of the plate may be uniformly perforated with circular holes or made of integral ex panded metal portions over the entire area thereof with the plate having imperforate solidly continuous main and auxiliary groove portions, as disclosed in my copending application Serial No. 88,342. In Figure 5, holes such as shown at 9 would be uniformly distributed along the planar portions of the plate 31.

It will be understood from the drawings that the slop-- ing die faces such as 20a in Figure 4 engage with portions of the plate laterally outwardly of the bends 22a in Figure 4 and force said plate portions inwardly by a wedging action as the upper die descends. The lower faces 20b of the protuberances cause what may be termed a peeling action as they move downwardly, that is, the metal of the plate forms a bend at.

successively lower portions of the side wall 1521s the upper die descends, until the bend has shifted from the position shown at 11a' in Figure 3 to the position indicated at 22a in Figure 4. As a result of the v converging configuration of die faces 20a, portions of the plate are formed inwardly into overlapping relation to the tube 12 without any need for holding the edges of the plate against laterally outward movement.

As will be apparent from Figure 4, the protuberances.

2 0 in the preferred embodiment cause acute angle folds" of metal 22 to be formed at each side of the tube at the junction between the main groove 13 and adjacent auxiliary grooves 23 and 24, respectively. The opposed pairs of such metal folds 22 overlie each tube length 12 and The forces employed in reshaping the metal of the plate around lock the tube length in the main groove.

the tube 12 are of such magnitude as to cause the plate material 11 to conform to the tube in spite of any commercial variations in the tube diameter or any lack of roundness of the tube, thereby insuring a consistent metal to-metal contact between the tube and the plate at all Further, the portion of the plate wrapping the times. tube is preferably under a tensile stress which tends to cause the plate to tightly and positively grip the tube with a resiliently tensioned gripping force to insure optinrum heattrans'fer contact between the tube and plate.

By way'of example, a pressure of the order of 2 to 3 5 tons per lineal inch on an assembly having a M; inch" 0.D. tube with a wall thickness of .028 inch and a plate of .030 inch thi ckness was required to set the metal so that upon release of such pressure and removal of the panel'assembly from the die, the panel as a whole'ie mained in a relatively fiat condition.

The rnethod of the present invention thus includes a the steps of rigidly and conformingly' backing the plate groove portions 14 by means of die grooves 18 and also inggroove wall portions, the hends lldyand contiguous inwardlyfinto. conforming relation to the tube 12.

It may thus be seen that the backing plate 11 isideformed into greater than semi-peripheral: contact with.

the tube, 12. Both side walls 15 of each groove 13 are thus deformed inwardly into contact with the outer periphcry of the tube to overlie a median diameter of the tub e and effectively prevent its removal from its position withmain groove 13, or that supplemental grooves'may be main groove.

The heat-exchanger, as shown in Figure 1, thus in formed only at spaced points along the length of the cludes the backing plate 11 and the continuous,.sinuous.

tube 12, the straight portions of which arersecured within recesses or grooves formed in the backing plate 11 by anemia hackiug theplate land portions L: by meansof sur- 7 face; 16a, while leaving effectively unbacked the upstanrlliortions li e of theplate] Thev unbacked portions' iare thenreshaped'to formfolds 22 and to move thefolds V walls 381:. 'Ifhe depth'of. thegro9ve-38is greater theexterior diameter of thetubing 32 and, determines. the amounbof wrap of themetalof theplate about thetube." As: will: hereinafter. become moreapparent, .the greater .thedepthIo f-thegroove; the greatenthe amount of wrap.

' about the periphery {Of the tube. 'It will be-note'd from deformation of the backing plate into greater than semiperipheral contact with the tubing. The immediately contiguous main groove 13' and the supplemental grooves 2 3 and. 24.1ie on the same side of the plate lL with the metal of the main groove in contact'with the tube to securely lockthe tube in the groove. It has been found thatthis relatively great surface contacting area between. the backing surface and the tube increases, the efficiency of heat transfer over those welded tube and plate type.

heat exchangers of the prior art.

InrEigure 5, reference numeral refers. generally-Jo the heat exchanger of the plate.and.tubetyp eincluding ar hacking plate Sland a continuous length of tubing 32 0f sinuous shape secured to the'backing plate .31.

It is to benoted'that' those'portions 32a of the serpen tinerorfsiuuous length of tubing 32'extending acrossthe leugthtof the. backing plate are substantially straight; with'theco'nnecting .curved'portions 32b of. the tubing.

32; extending beyondjthe backing plate 31. "lngthis manf ner hi't' is notjnecessary to deform 'the backing, K into a serpentine or sinuous path to receive the tube 32 I hutrather. .itis onlynecessaryz to secure the straight por-- 1 time of the tube .to the backing plate.

7 V V The. inethodof securing the serpentine length to,.theplate 31} as herein described, insures the elfic'ient transfer of heat from the tube 32 toithe. relatively large heattransfer surface of the plate '31; The plate 31 may beany desired sheet metal having a high heat transfen efliciency and suitably may be a mild, low carbon steel: having. a thickness on the order of No. 20 U.'S.S. gaugeg' Figure -7 that When-thetube 32 ispositioned'withinlthe groove 33, the tube" and the arcuategroove-bottom 38, are in close fitting peripheral contact, since the arcuate groove bottom 3S has approximately the same radius of curvature as the. outer periphery of the tube. Itlwill he.

understood that in the manufacture of. a heat exchanger such as that shown in Figure 5, only the straight portions 32aof the tube 32 are bottomedIwithin'thegrooves 33'- au'd that the curved portions 32b of the tube 32-jextendl. outwardly beyond the lateral edges of the'plate31.

' In the next step in the method of makingthe heat exchanger, the straight lengths of the tube are. interlocked, within the grooves 33 by means of a pair of cooperating; dies .39 and40. 'The dies 39 and 40 are preferably of. such size as to receive the entire exchanger unit3fl shown in Figure 4. The backing die 39 is recessed as at 41 to provide a conforming support for-the bottom 38 ofthe. groove 33. The.backing die 39 is also recessed, as at 42 immediately adjacent both lateral edges of the groove 38, the recesses 42 being preferably contiguous with the. entire length of'the-re'cess 41, i.e. with the full lengthof the backing plate 3 1 p V The second. forming die 49 is adapted for movement relative to the backing die into andout of cooperating" relationship with the backing die 39. r The movable'die 40 is provided with a pair of: spaced parallel; arcuate; protuberances-43 separated by an arcuate: depressionf'o'r deforiij themetal' of the backing platejlfinto the co? operatinggrooves 42-. Howeve'rgeverii after,full closing' ofg th e dies 39 and 41);. as 'shownin f re 8 'no'"contact' is jmade between the portions of .thef'pl te" contigousi to the groove' 38iandthe bottoms-of'thegrooves 42. This".

'is-fbecausefthe protuberauces 43 are shallower than"the; rem e? N i F i The metal immediately acted uponflby thep u ances 43, as the upper die 40 is moved tbwar'dthe' lower 7 die-39,15 that of the" unbacked -po rtions 31a. crime plate (0.0359, inch), and the tubeis preferably formed oi cop-j perof-an outside diameter on the order of /5 ;to /2} inch and a. wall thickness of about 0.0359 inch. Other metals than copper, such as iron or steel, or aluminum, may

be used for the tube, and larger diameters.thanindicated may be. employed inthe'method of my invention. The tube is suitably seamless but may bea welded tube;-

laterally contiguous to thealso' :unmkes-n nsnaingwall portions;3811' of'the groove 33. The laterally contiguous portions 31aarefirstdeflected downwardly into arconfiguration similar-to that shown in dotted outline in Figure 3. Thereaftenas the dies -40 and 39continue to move relatively toward each other', the--metal' of the unbacked portions 31a is moved inwardly aboutthe-tu be as. a'mandr'elto form nearly closed'folds 48 extending into the clearance on. either side; of the punch bar 46;

' tube and thusi'locksthe-tube in 'its .gr oove:38.

trated inFigure 6 by 'the cooperationof aEp airt -rolls 34. and'35. The roll 34-is'provided with auc entral,

radially outwardly extending annularembossment' 36',

while the roll 35 is provided with a peripheral annulanj 1 'ggoove 37 for re'ceiving the embossmentfifi and that; portipn of. the. plate 31 confined;betweenqtherolls. ltr will be seen that when the plate. 31 is passed betweenthe rolls 7 34, an d 35. that the groove .33 is formed thereimto extend thereacross. Dies may be usedv in placeof the r0115 34.

a Each of the gr. Yes, 33 is. provided with an arcuate bot-tom' portion, 3.8. and parallelv upstandingilstraight side;

By the: coactiomof the forming; dies; thefplate is provided. wtihga pair: of parallel shallowsiupplem'enta r grooves. 49; laterally co'ntiguouslto and'coextensiv each maingro'ov'ei33v'i 7 rAlsloyirLthetlatter lstages; ofgtheLclosing'movementof' thecooperating. dies and 4tl,::the lower-i face 47 oft-he? insert: contacts :the: exposed surface of the tube-132 jbetween the folds;48' to deform such. surface-inwardlyfand I portionsAS. of theplate -j3l. 'I'heforming dies-39 and 40 with? p asters? are moved together under relatively heavy forces of such magnitude as to deform both the plate and the tube into interlocking engagement to insure at all times an extended metal-to-metal surface contact between the tube 32 and the plate 31.

As previously indicated, the extent to which the metal of the plate is wrapped about the tube can be varied by varying the depth of the groove 33. Regardless, however, of the extent of the wrap of plate metal about the tube, it is preferable, for a given depth of the groove 33, to so arrange and dimension the profiles of the cooperating dies 39 and 40 as to effect a cold working of the metal that is deformed by the dies. Such cold working is effected not only by the deformation of the metal but by an actual stretching of the metal due to the fact that there is not initially at the stage of the operation illustrated in Figure 7 a sufficient length of unsupported metal to form the supplemental grooves 49 and the folds 48 and to lap said folds about the tube. In addition, there is a slight stretching of the metal in the lands L between adjacent grooves 38 due to the action of protuberances 43, which stretching occurs during the final closing movement of the dies 39 and 40. The lands are not tightly clamped between the flat die faces even after the deformation of the unsupported metal has occurred.

Thus, as a result of the cold working of the metal during the swaging or deforming operations, and the pressure subsequentially applied, the metal takes a permannet set under a tension tending to contract the loop of metal lapped about the tube. This contracting tendency maintains good mechanical and thermal contact between the plate and the tube.

The tube thus serves as a mandrel about which the plate is swaged or deformed, and the deformation of the tube with the resulting radial expansion of confined portions thereof produces positive and permannet peripheral contact between the tube and the inner wall of the main groove 33 and of the deformed plate folds 48. This expansion of the tube accommodates any slight irregularities or distortions of either the plate or the tube so that virtually perfect, continuous metallic contact is obtained therebetween.

As a result of the deformation of both the tube and the plate, the members are in extended surface engagement over a tube area greater than its semi-periphery. If desired, the deformation of either the plate or the tube, or both the plate and the tube, into interlocking engagement may be either coextensive with the length of the plate 31 or for spaced distances along the length of the plate. The deformation of the tube obviates the diflficulties heretofore caused by the attempted deformation of a plate into extended plate engagement with a tube of relatively large external diameter where the thickness was disproportionately thin.

The heat exchanger, as shown in Figure 5, thus includes the backing plate 31 and the continuous, sinuous tube 32, the straight portions of which are secured within the surface in grooves formed in the backing plate 31 by deformation of the backing plate into greater than semiperipheral contact with the tubing and the deformation of the tubing radially outwardly into interlocking contact with the plate. The convex portions of the main grooves 33 and of the supplemental grooves 43 and 44 lie on the same side of the plate 31. Therefore, since the deformed portions 48 of the plate terminate approximately in the mean plane of the plate 31, a finished heat exchanger construction is provided having one substantially plane surface, as is desirable in many installations.

In practicing the method of Figures 1 to 4, it has been found that there is a definite ratio of plate thickness to tube diameter which is required if the plate is to exert a contractive force on the tube after the forming pressures have been moved. A one-quarter inch O.D. steel tube having a wall thickness of .028 to .031 inch will maintain a visually perfect roundness after assembly if to a plate of low carbon steel of about .029 inch is formed around the tube. The proportions have been found to be ideal for almost perfect end results mechanically and economically, and provide the desired inward contracting force of the plate on the tube without any need for deforming the tube. Heavier gages of tube and plate produce equally good mechanical results without the need for deforming the tube if the above ratio of plate thickness to tube thickness is maintained. For example, a one inch O.D. tube with .120 to .125 inch wall thickness and a plate of the same thickness produce an almost perfect product without the need for tube distortion. With these dimensions a two inch length of tube is clinched so tightly by a corresponding section of plate that a free end of the tube cannot be manually rotated out of its original position relative to the plate.

It has been found that if the plate thickness is reduced to .014 inch and a one-quarter inch O.D. tube is employed having a thickness of about .028 inch, the quality as to the roundness of the tube and the plate surrounding the tube is substantially as good as with a plate thickness of .030 inch; however, the loop of plate surrounding the tube fails' to exert an inward contractive pressure on the tube.

Figure 9 illustrates a test which was performed wherein successive sections of 'a single groove heat exchanger construction (made by the method of Figures 11, 12 and 13) wereremoved by means of a surface grinder with a inch rubber cut-off wheel. In the test, a 1 inch O.D. steel tube having a wall thickness of .125 inch and a plate having a thicknessof 0.120 inch were utilized. Care was taken during the grinding operations to keep the speci men cool so that no thermal stresses would be set up. It'- was found that the residual stresses introduced in the plate at the lower portion 50a thereof causedthe plate to positively clinch the tubing. This fact was 'qualitatively demonstrated by the successive dissections which are represented by the section lines 1-1, 2--2, 3-3 and 4'4 in Figure 9. It was found that even after all of the plate located above the center line 4--4 of the strain as measured with the post-yield strain gauge (in-- dicated at 52 in Figure 10) located on the outside surface of the plate at the bottom portion 50a thereof as a function of load applied during formation of the tube and plate assembly indicated in Figure 9. The curve indicates that the material yields in compression (as in-' dicated at 51a) before any buckling of the sides of the plate takes place. In this first stage of the'clinching process the material follows the conventional stress-strain curve for ductile materials. However, as the sides of" the plate groove buckle and begin to fold'in, it is ap parent that the load on the lower section of the plate' becomes tensile. Thus, at a load of approximately 30,000

pounds, the curve actually reverses itself and as indicated at 51b, the tensile loading on the lower portion of the plate shows up as a relief of the compressive strains present. As soon as the metal is formed completely around the tubing any continued loading results in further compressive yielding as indicated by the portion 510 of the curve.

a plurality of lengths of tubing as in Figures 1 to 4, the material of each land between adjacent grooves in the plate is restrained from movement toward'either' groove, and there is a tendency to stretch the part l'of the plate being wrapped about each length of tubing Thus there would be a considerably higher tensile loading on the lower part of the plate below the horizontal fFigures .11, .12 and 13 represent diagrammatically the condition of theplate at stages in the forming opera- ..tion.,.represented. by portions 51a, 51b and Y510 of curve 5.1 ,in .Figure respectively. The plate is preferably preformed-with .its lateral edges 53 ofiset downwardly for the same reasons discussed in'connection with 'edge ll i liigu l r 'Referring now'to Figures .14 to 19 of the drawings, a

' method of forming 'a tube and wire heat exchanger is illustrated. in thisnrethod, a straight leng h of wire such as indicated at 60 is first provided with a plurality of grooves orbends .61, which grooves extend trans- V -versely to the lengthof the wire and have semi-circular portionsfilaldefiningthe bottoms of the grooves of sub- 7 stantially the same inside diameter as the outsidediarnetcr of the tubing 6210 be inserted therein. The grooves also include generally straight upstanding parallel portions of the wire 61b defining the sides of the groove andrising above thetubing when the tubingis bottomed in the grooves. The ends of the wire may be offset as indicated at 61 as'disclosed inconnection with the ofiset 11a infigure 2. V a f a During the forming operation as illustrated in Figure 15, the semi-circular portions 61a of the wire are rigidly. and conformingly :backed by means of a lower die 64. The lower die -64 as indicated in Figure 19 is provided with ya transverse groove 65 having a semi-cylindrical bottom portion 65a of diameter to exactly receive the extern l d et r o the u ing. The die furth r s recessed portions: spaced therealong as indicated at 65b. 7 for receiving :the groove portions of successive wires,

the-spacing'of the wires along each tube being indicated in Figure 18. The upper die 66 is provided :with protuberancesgsuch as 67 for exertinga reshaping pressure against unbacked, upstanding-portions 61b of each groove and contiguous portions 61dof the wireon' each side of thewgroove ;to;form a fold. The folds Von eachside of r the groove are moved toward each other {and reshaped into conforming contact withthe-tubingn A punch bar 68 carried with theupper die fifid iorms the tubing 62 into .a non-circular cross section :including a flat portion 62a. This flattening operation also :drives portions,.-of the tube 62 against the adjacent portions-of 1 ires to wraplhe tube partially about the wiresvas' ndicated t 9 in Figure 18. 'The pr0tuberances .7 imultaneously drive the portionsfilc-of the wires;against.

h PQ i n=69 of :thetnbing. Thus the wireis :ac llally indented into the tube to form a series of transverse: ridges snch as 70in Figure 18 which will cause turbulence: in .the' 'flow -of heat exchange fluid through the. tubing;

The dies may also be so proportioned .as to-flatten the wires at-61e between thesuccessive lengthsof tubin inorder to increasethe radiating area.

According to a further feature of the present inven- 1 tion, instead of separate straight lengths ,of .wire suchas 60-Figure l4,"the method of this embodiment may,

be;prac,ticed on a sinuous, wire60' as showniniFigure, '20...v Since 120 or more wire lengths may beutilizedzper:

assembly, it willbe appreciated-that the use-of a-sinuous wire, cut off to the desired length, .will-etfect Fgreat .-si1n-v plification the; method-Jot :this embodiment. ,1 :In practicing the :Incthod on :the sinuous wire .60, :it will be understood thatspa'ced grooves or bends areformed in each shiaightlcngth .portionsuc'h :as 60''. of :the;"wire.

of Figure 20 is thus identicalto that disclosed in Figures l5.to 19; a V

The assembly may be finished by hot galvanizing, or

a black enamel paint finish maybe applied. 1f desired,

the assembly may be welded'in several places'to increase its rigidity without unduly sacrificing the manufacturing advantages ofthe present invention. 7

, I, The term groove as'used in the claims is intended to :be-descriptive of both an elongated U-shaped bend in a plate and a U,-shaped'bend in awire. 1 V

The plate or wireis considered .as, being backed in the description and claims if movement is substantial ly restrained at some time during the forming operation whether or not the plate or wire is initially supported by a stationary die surface, for example, and is considered as being opera tively or effectively unbackedf -if no such restraint is applied during the forming operation;

It will beapparent .thatmodifications and variations mayabe efiected without departing from the scope-of the novel concepts of the present invention.

I claim as my invention: r

l. A tube and plate assembly comprising a generally fiat sheet metal backing plate having a plurality of main grooves and a P r llel contiguous shallower auxiliary groove on each side of'each of said main grooves and extending continuously for the entire length of the main grooves, all of said grooves being concave cross-sec tion and offset from and lying on the same side of the general plane of said backing plate, and a length of metal tube in each of said main grooves, there being an acute angle fold of metal integral with said plate metal formed at the junction between closely spaced oppositely concave portions of each main groove'and each of the corresponding auxiliary grooves, an. opposed pair of such metal folds overlying the tube in the main groove and holding the wall of said main groove in greater than semi-pe-' ripheral conforming surface contact with said tube.

2. 'A tube and plate assembly comprising a generally flat sheet metal backing plate havinga plurality of main grooves and a parallel contiguous shallower auxiliary groove on each side of each of said main grooves, all of said grooves being concave in cross-section and olfset from and lying on the same'side of the general plane of said backing plate, a length of metal tube in-each of said main grooves, there being an acute angle fold of metal integral with said .plate metal formed at the junction between closely spaced oppositely concave portions of each main groove and each of the corresponding auxiliary grooves, an opposed. pairof such, metal folds overlying the tube in thernain grooveandholding the wall of said metal groove. in greater .than serniperipheral conforming surface contact with said tube, the exposed portion of said tube between said folds being non-circular and holding remaining portions of saidtube engaged by the plate in tight metal-to-metal peripheral surface engagement with the inner wall of said groove.

V References Cited in the file of thispatent V i UNITED STATES PATENTS Junkers Jan. '19, 1915' 1,971,723 QDell Aug. 28, 1934 1,982,075 Smith Nov. 27, 1934 2,091,584 Brown Aug. 31, 1937' 2,092,170 Kritzer et al. 'Sept.' 7,1937 2,245,069 Clarke June :10, 1941 2,281,299 'Steenstrup Apr. 28, 1942 2,382,340 Smith Aug. 14, 1945 2,585,043 'Sandberg Feb. 12, 1952 2,602,649 Goldberg 'July 8, 1952 2,620,170 Briclutnan- Dec. 2, 1952 2," 6463 71 Raskin July 28, 1953 2,666;-98l Sandbe rg Jan. 26,1954} 2,688,794

Mulutich' Sept. 14,1954