US2155394A - Method of and apparatus for making heat exchanging elements - Google Patents

Description

April 25, 1939. I A. J. ERG ET AL 2,155,394

METHOD OF AND APPARATUS FOR MAKING HEAT EXCHANGING ELEMENTS 3 Sheets-Sheet l Filed Feb. 14, 1936 INVENTOR.

J 55/? Jon/1v Q1/0515 BY ATTORNEYS.

April 25, 19 39. A. J. BERG ET AL 2,155,394

METHOD GI 5N3 APPARATUS FOR MAKING HEAT EXCHANGINQ T LSMENTS Filed Feb. 14, 1936 3 Sheets-Sheet 2 I ll! 2; 155,394 METHOD OF AND APPARATUS FOR MAKING HEAT EXCHANGING ELEMENTS April 25,1939.

A. J. BERG ET AL Filed Feb. 14, 1,936 3 Sheets-Sheet 5 INVENTOR. fluke-0 J 621% Jo/m' O. l/(ASE- ATTORNEYS.

Patented Apr. 25, 1939 METHOD OF AND APPARATUS FOR MAKING HEAT EXCHANGING ELEMENTS Alfred J. Berg, Portsmouth, N. H., and John 0. Huse, United States Navy Application February 14, 1935, Serial No. 63,895

7 Claims. (01. 29-1573) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) Our invention relates to a new and useful method of and apparatus for making heat or cold exchanging elements.

The objects of our invention are to provide a new and useful method of and apparatus for making heat or cold exchanging elements which will enable the production of such elements more rapidly and cheaply, of, very high capacity for exchanging heat or cold, and which produced elements will be very light, strong and long enduring under the conditions encountered in use.

Other objects and advantages of our invention will be readily understood by those skilled in this art from the following specification.

In the drawings, Figure 1 is a side elevation view partially in cross-section of a heat or cold exchanging element illustrating typical steps in the transition of the product from its commencement until it is finished; the left end illustrating the commencement, and the extremeright end illustrating the finish;

Fig.2 is a left end view of the parts shown in Fig. 1;

Fig. 3 is a view similar to Fig. 1 but including 5 the apparatus arranged to produce the requisite transitions from the commencement to the completion of the finished product in accordance with our invention;

Fig. 4 is a right end elevation view of the parts 30 shown in Fig. 3;

Fig. 5 is a left side view of a single typical one of the rows of bending and stretching tools, shown in Figs. 3 and 4;

Fig. 6 illustrates a detail of construction hereinafter described; and

Fig. 7 illustrates diagrammatically the front elevation view of a lathe or similar tool which may be employed in the practice of our method which may with substantially equal advantage be 40 practiced by a number of different kinds of machines than herein indicated as will be understood by those skilled in this art.

In the drawings, in which like characters of reference indicate the same part, It! represents 45 the body portion of the heat or cold exchanging element which may be a tube or other shaped hollow body.

Heretofore, the heat or cold exchanging ribs or fins have'been disposed edgewise upon the 50 body portion of the element with the rib or fin throughout the operation, regardless of whether the rib or fin be longitudinal, or formed in a ring, or wound helically, invariably maintained with one edge in contact with the surface of the 5;; element and the width of the rib or fin extending substantially at a right angle from the body of the element. In winding or ceiling the rib or fin edgewise about the body of the element and maintaining the rib or fin free from wrinkles and other objectionable surface irregularities 5 substantial lateral stress is required to be borne by the body portion of the element. This lateral stress was occasioned by longitudinal stress upon the straight portion Lu. the rib or fin as it was being advanced toward the stage of its edgewise 10 bending-or coiling about the body of the element, as well as further occasioned by the lateral stresses occasioned by the means for maintaining the ribs or fins at a right angle to the tube or body portion of the element. Despite the prior 5 teachings of the art to wind the fin edgewise about the body portion of the element our present invention, in its method aspect indicated in .Figs. 1 and 2 commences to wind or coil, helically or otherwise, the strip ll about with one of its 20 broad sides toward, the tube or body portion ID of the heat or cold exchanging element. A broad thin fiat ribbon of metal II is loosely advanced toward body portion l0, not under longitudinal or other stress, with one of its broad lateral faces substantially parallel with the outer surface of the tube or body portion l0. An end of said ribbon II is arranged in tangential contact with a surface of the tube or body portion III, and, for instance, a narrow strip [2 at its left corner is secured to the tube'or body portion III by solder or otherwise. Progressively with the coiling of said ribbon ll about the surface of tube or body portion III, a very narrow strip I! of said ribbon H is progressively secured to said tube or body 36 portion it). As the ribbon II is progressively coiled around or helically about the tube or body portion I0, free from longitudinal stress, the unsecured side of a previously bent or coiled portion of ribbon II is simultaneously bent and 40 stretched outwardly by progressive degrees until the main body of the rib or fin is formed at substantially right angles to its foot l2 which remains secured to the surface of the tube or body portion Ill. The initial fiat straight ribbon H, as it a'pproaches the tube or body portion [0, is

in an unstressed condition which unstressed condition substantially continues in its portion bent about the tube or body portion I0 until the same commences to be bent, arched and stretched outwardly, Said outward bending, arching and stretching produces a very substantial longitudinal stress upon only the outwardly bent and stretched portion of the ribbon H. However, such longitudinalstress tends to produce no sub- 86 stantial lateral thrust upon the tube or body portion III for the reason that such stress is unidirectional about the tube or body portion III. Such longitudinal stress of the portion, other than the secured portion. I2, of the ribbon II, increases somewhat with the degree of outward bending or forming and stretching to which the same is progressively subjected until the main body of the ribbon II projects at substantially a right angle from the tube or body portion III, in which latter position the right angle portion of the ribbon II, which is of its normal thickness at its juncture with its foot I2, becomes progressively thinner as it extends beyond its foot I2. In this right angled or finished position of the main .width portion of ribbon II some longitudinal stress is maintained in the rib or fin so formed from the fiat unstressed ribbon II. Such longitudinal stress is so maintained by the foot I2 as well as by its securement at progressive intervals or continuously to the wall of tube or body portion ID. This longitudinal stress maintained in the finished rib or fin enables a very much thinner and wider ribbon II of metal to be employed in the production of the rib or fin, because the same maintains such thinner formed rib or fin in its initially fixed position by said longitudinalstress substantially increasing its resistance to deformation and distortion, accidental metal along one edge of ribbon II, which'strip forms the foot I2.

The various progressive transition stages of the foregoing method of making the heat or cold exchanging element, from the bending or coiling helically, or otherwise, of the flat ribbon II flatways about the tube or body portion I0, until the completion of the product with the rib or fin standing upon its own foot I2 and at the desired angle from the tube or body portion I0, may all be performed by hand, or by metal spinning or by a number of existing mechanisms, with or without substantial modification of such mechanisms, as may be understood by those skilled in this art after becoming familiar with our method as well as our provided apparatus.

Our methodiand the apparatus which we have provided for practicing the same are related and dependent inventions. The apparatus portion of our invention substantially demonstrates the utility as well as practical value of the method portion of our invention. The apparatus portion of our invention furthermore materially contributes to the understanding of our invention by those skilled in this art, more particularly with respect to the practice of the method portion of method.

In connection with the apparatus devised by us for the most economical, rapid and emcient practice of our method which we have thus far of ribbon II.

said tube or body portion II). A roller I5 having a central bearing portion I6 revoluble in bearing member I1 is attached in any desirable manner to the usual cross-slide He, or other member, of the lathe or like tool which bears the usual tool post and in such relation to tube or body portion III that the peripheral portion II of roller I5 engages the narrow edge I2 of the ribbon of metal H so as to hold such portion of such ribbon firmly against the outer surface oi the tube or body portion I0, with the adjacent face of shoulder IQ'of roller I5 bearing against the outer lateral edge of portion I2 of ribbon II.

The portion I8 of roller I5 is provided with a small narrow projecting head 20. This bead 20 is either continuous or provided with short interruptions and extends completely around the peripheral portion I8 of roller I5, and it projects therefrom at a point intermediate the width of said portion I 8 so as to engage a portion intermediate the width of portion I2 of ribbon II. In operation. the bead forms a' shallow indentation 2| in the outer surface ofiportion I2 In thus forming indentation. adjacent metal of said portion I2 is forced inwardly and below the adjacent exterior surface of the tube or body portion I0, thus forming an indentation 22 in the exterior surface of tube or body portion III. This secures portion l2 of ribbon II firmly to the tube or body portion I0 throughout the extent that a ribbon Il may be formed or coiled about the tube or body portion Ill. When the ribbon I l is arranged in a straight line upon or about the body portion ill, the axis of roller I5 is disposed at a right angleto said straight line; but when ribbon II is, for instance, disposed at an angle to a direction of the body portion III, for instance helically, the axisof roller I5 is disposed at a right angle to such angle, or to the course of the helix. A structure admitting of such variable mounting of roller I! is indicated in Fig. 6 in which the bearing member II comprises the outward end of the upper bend and of a standard I'Ia having a circular base no bearing in a recess in the upper surface of the cross-slide He, or like member, of a lathe or similar tool which usually bears a tool post. Said base III) is provided with a slot IIc through which, and a portion of cross-slide IIe, extends a bolt IId for maintaining base I lb and standard I'Ia with roller IS. in any of their desired angular positions. To counteract the lateral deflection of tube or body portion I 0 due to the thrust thereon of roller I5 one or more rollers 23 having bearings in member 23a a'djustably secured to projection 24 of, or attached to, crossslide He, by bolt 24a, facilitates the engagement of roller orrollers 23 with the tube or body portion II) at a point or points opposite to and aligned with the point of engagement therewith of roller I5. When the bead 20 is continuous,- the depressions 2| and 22 are continuous, but

when the bead 20 is interrupted the depressions 2I and 22 are correspondingly interrupted. In the latter case we have found that such brief interruptions do not impair the securement of portion I2 of ribbon II to the tube or body portion III.

A bar 25 extending preferablyparallel with, but spaced apart from, an adjacent surface of the tube or body portion I0, is also mounted upon and supported by the cross-slide He, or other portion, of the lathe or like tool which usually bears the tool post. Removably secured to bar 25 by bolts 260 or otherwise, are a plurality of separate tool shanks 21 which extend from bar 25 toward the tube or body portion I8. Upon the below the horizontal, such mostadjacent portion 28 extending inward and slightly downward from shank 21 and toward the roller I5, the edge portion-thereof nearest the tube or body portion I0 being provided with a beveled edge 29, Fig. 3,'to provide clearance between such edge 29 and the adjacent surface of tube or body portion III to accommodate the coiled portion of the ribbon II. The angle of each succeeding portion 28 of each succeeding shank 21 is, progressively increased until the portion 28 of the shank 21 most remote from roller I5 is at such angle that the surface of its portion 28 nearest to the roller I5 is at substantially a right angle, or such other angle relative to the tube or body portion I8 that the finished rib formed from ribbon II is desired .to stand relative to the tube or body portion III.

The operation of the mechanism thus far described will now be explained with relation to the helical coiling of the ribbon II about the tube or body portion II) which latter is inserted in the lathe adjacent the tip ends of portions 28 and between rollers I5 and 23 and mounted between centers 58, 52 and mounted in any usual manner to be rotated by the lathe. The cross slide He is moved, with the parts Ho, 24, 25 and their attachments mounted thereon, adjacent center 5|. As is usual with lathe work which may be performed only within an area between centers 58, 52 in which the required tools will not be interfered with, the ribbon II may be wound or helically coiled upon tube Ill within such area. In this case such area commences under roller I5 when the cross slide He is in said moved position and may continue toward center 52 and terminate at such point on tube III that roller I5 and portions 28 and their associated parts may have clearance between center 52 and the terminal coil of ribbon I0 after the last of portions 28 have acted upon the terminal portion of the coiled ribbon lIa which the uncoiled ribbon is severed from the coiled portion thereof. The length of the tube In employed being such as willsafford the required length of the coils of ribbon II thereon. as well as said clearance spaces at both ends of the tube III. The angularity required for such desired helical coiling is fixed by the adjustment and securement of base I") to I16. This likewise correspondingly adjusts the guide for ribbon II in its approach to roller I5. Said guide may be conveniently formed of a projecting arm I1f extending from bearing'member I1 and having a slot I19 in its outer end through which the ribbon I I loosely extends toward the roller I5. Ribbon II is led from a convenient roll or other source of supply loosely through slot Hg and thence without longitudinal or other stress to the roller I5. The loose end of ribbon II is placed between tube or body portion I8 and surface I8 of roller I5 with its adjacent edge against shoulder I9 of roller I5, the remaining portion of ribbon II resting upon a portion of the outer surface of hollow conical portion 28 of the most adjacent shank 21. The rotation of tube or body portion I8 between the centers of the lathe or like tool will cause the helical coils about tube or body portion III of the ribbon I I when the end of ribbon I I is forced between the tube and roller I5 in the position before stated. It will be understood by those skilled in the art that the lathe or like tool will also be set to longitudinally move the cross-slide I1e relative to the rotating tube or body portion I 0 at the rate corresponding to the required angle at which the ribbon I I is to be helically coiled about the tube or body portion II). In such helical coiling of the ribbon II about the tube III its portion I2 will be firmly and continuously secured to the tube or body portion II] by the interlocking metal comprising the depression 22, as well as further by the fact that the ribbon I I extends repeatedly around the tube or body II). This securement of the portion I2 of ribbon II also forms a slight bend in the ribbon II at-a point between its portions II and I2 due to the securing pressure of roller I5 upon portion I2 of ribbon II while the portion II thereof is resting upon the outward conical surface of portion 28 of shank 21 nearest to roller I5. In the progression of this coiling of ribbon II about the tube or body portion III the engagement of the inner surface of ribbon II with the exterior surface of said hollow conical segmental portions 28, as the end of the original ribbon II starts to be so coiled, tends to slightly outwardly bend as well as stretch the coiled portion of ribbon II by and throughout the extent the angularity of the engagement of the initial hollow conical segmental portions 28 of shanks 21. This engagement also exerts a spinning action upon the coiled portion of the ribbon II which progressively bends as well as stretches the metal of ribbon II, and which stretching occurs most at the unsecured edge of ribbon II and least or practically nothing at the point between the portions III and II of the ribbon. As the ribbon continues its coiling beyond the point where it engages with the initial segmental portion of the hollow cone 28 of shank 21 nearest roller I5, the end of the coiled ribbon II extends about the tube or body III, under and free from the inner surface of the before mentioned portion 28, thence again completely around the tube or body portion I8 until the same engages the exterior surface of a similar portion of the next succeeding hollow cone 28 having a similar shank 21 but slightly more inclined than the first portion 28. This second portion 28 further bends and stretches the coiled ribbon progressively at a further angle from the tube or body portion ID. From this pointonward the coiled portion of ribbon II at every alternate coil is engaged by a further separate portion 28, each of progressively greater inclination, and each separately supported by its own shank 21, and each further progressively outwardly bending and stretching the wound ribbon III, by reason of said portions 28 being each outwardly inclined on their outer surfaces at a progressively increasing angle, until the coiled ribbon II is finally finished and projects from the tube or body portion III at the desired angle, which is usually a right angle. The outward bending and stretching of the ribbon II, while it is being formed aboutthe tube or body portion In by the separate slight progressive changes due to the successive and progressive action on such ribbon by each of the successively spaced and positioned portions 28 of,fdifierent angularities ribbon IIfthe outer edge of the formed ribbon of metal being the thinnestQiand the intermediate of' theformed ribbon beingsubstantially progressively thicker at intermediate points throughout the width, and thickest (being of the normal thickness of ribbon II at the point of juncture of the formed ribbon I I with its substantially right angled foot I2. This bending and stretching of the outer portion, as distinguished from portion I2, of the ribbon II while it is being formed is caused by the frictional engagement of the portions" progressively'with the same under surface of the ribbon I I, while being formed. The temperature resulting from such engagement, coincident with the longitudinal stress created in the ribbon :I I while being bent outwardly concurrently contribute to the stretching action of the metal; The longitudinal stress, and therefore-the stretching, is greater at the outer edge of the ribbon IIwhile being formed,

; II to be employed than was heretofore possible,

which greatly increased the lightness, cost, number of coils of ribbon II per unit of length, in-

' creased the heat or cold exchanging rate and consequently reduced the size, space and weight requirements for such exchange unit to attain a given exchange capacity;

(b) Such wider, thinner coils of ribbon II in greater number-per unit of length of the tube or body portion II'I, which would otherwise be less stable and more'readily deformed and laterally bent together or of unequal spacing apart are by our method and apparatus provided with a substantial longitudinal stress which is uni-directional about and exerts no lateral deflecting influence upon the tube or body portion In notwithstanding the magnitude of such longitudinal stress; thatvthe ribbon II is devoid of such stress as it approaches the point of being wound about the tube'or body portion III; that said stressprogressively stretches the metal of the ribbon II while being formed about the tube or bodyportion I and such stress continues in the finished product to a degree less than that required to further stretch the metal of the finished formed ribbon I I. Suchpermanent stress of the metal i of the finished formed ribbon II gives greater stability and resistance to deformation-and lateral bending of each of the finished formed portions of the ribbon II, as well 'as' increases the rate of conductivity of heat or cold of the metal of such formed and stressed portions of ribbon I I due not only to the cold working of theribbon II in forming the same, but to the stretching as well as the permanent stress in the formed ribbon II and (c) The greater rapidityof the production of the finished heat exchanger element in accordance with our invention increases thecheapness of the same without detracting from but increasing the quality, efllciency, and durability of the finished product; the freedom from complex-, ity of required production mechanism and the direction of roller I5.

greater useful life of the required production mechanism, due to the absence of the substantial longitudinal stress upon the ribbon II at the point where it commences to be wound about the tube or body portion III; the pleasing uniform high polished appearance of the finished product; the ability to employ a very wide much thinner ribbon II than was possible to heretofore use without precoiling edgewise to a diameter larger than the tube or body portion I 0 before coiling the same upon each tube or body portion; the requirement that the tube or body portion III may have a thin wall no more than necessary to resist the pressure and corrosion or other deteriorating action thereon in normaluse because such Wall requires no grooving or other working, which may lessen itsresistance, requisite to the winding and securing of the ribbon thereabout, but instead thereof the ribbon II is coiled about the virgin unworked wall of the tube or body portion I0 andthe strength and resistance of the wall of the tube or body portion I0 is increased by the flat winding thereabout of the foot I2 under no initial longitudinal stress but whose bent side is subjected to inward and/or longitudinal stress resulting from the bending and stretching of the metal of the ribbon II extending outwardly from such side of the foot I2, as well as by the continuous or slightly interrupted row comprising thedepression 2I in the foot I2 resulting in the slight depression 22 in the outer wall of the tube or body portion II) with metal of foot I2 interlocked in such depression 22, which depression and the cold working of the metal resulting in their formation, tend substantially to reinforce the strength and resistance of the substantially thinner wall of the tube or body portion Ill.

' One of the bending and stretching portions 28 acting upon ribbon II while it is beingcoiled, bent and stretched about the tube or body portion I 0 is illustrated in Fig. 5 which shows an end elevation view thereof looking toward it from the Instead of the portions 28, ordinary spinning tools or, rods or sticks may be employed to progressively bend and stretch the ribbon II about the tube or body portion Ill.

It will be'noted from Fig. 3 that in the form of the apparatus therein disclosed the forming-bybending-and-stretching portions 28 engage the wound ribbon I! at but one point in at least every other coil of the ribbon II about the tube orbody'portion III. This afiords a substantial area of the ribbon II to transmit the heat engendered by auch cold working operations as said bending and stretching, tothe metal of the tube or body portion ID by conductivity through the metal of the ribbon II as well as very large surface areas of the metalof ribbon II exposed to the atmosphere throughout points thereof which are contacted bysaid portions 28, and which conduction to the atmosphere of such surplus heat of the ribbon I I in its successive forming stages is very substantial and results in a very eflicient, cheap, durable and highly finished product being very rapidly made from the metal comprising the ribbon 'II which may be most advantageous for the employment 'of.the apparatus shownin Fig. 3. Such heat exchange to the atmosphere throughout the area of ribbon II engaged by successive portions 28 is very substantial for the further reason that the rotation of tube orbody portion I0 with the wound portion of the ribbon is very rapid and this, together with the progressive outward bending and tions.

stretching of the metal of ribbon ll creates a substantially increased circulation of air around and between the coils of ribbon ll.

Any number of bars 25 supported by cross-slide He may be employed each with its row of shanks 21, with their respective portions 28 at diiferent radial points about the tube or body portion Ill. Fig. 4 illustrates such an arrangement in which three bars 25 are employed each with attachment similar to those shown and described relative to Fig. 3, each bar 25 being substantially equally spaced about the tube or body portion III. In such arrangement the segmental hollow conical portion 28 of each shank '21 are of such segmental dimensions that ample space is afforded between the adjacent portions 28 to not only enable their insertion and removal, but also to afford a substantial area of ribbon ll exposed to the atmosphere and the afi'ordance of substantial heat conductivity from such exposed portions of ribbon H to the atmosphere.

In Fig. 7 is shown a diagrammatic view of a lathe or other tool in which the tube or body portion I is mounted between the conical centers 50 of tail-stock i and 52 of head-stock 53. The conical center 52 oi head-stock 53 being rotated by power pulley or motor 54, which correspondingly drives a pulley 55 belted by belt 56 to pulley 51 upon a shaft 58 mounted in bearings 59 on base plate 60, said shaft 58 being provided with screw threads 6| engaging a suitable nut mounted upon the cross-slide Me for imparting longitudinalmotion to said slide lle along base plate 60 at the rate required to obtain the desired pitch of the helical coils of ribbon ll about the tube or body portion Ill. To vary such rate any one of different sized pulleys 55 or equivalent means may be employed. In conventional view, Fig. 7, the details indicated in Fig. 6 are not disclosed for clearness.

To increase the rate of conductivity of the surplus working heat from the portions of the ribbon being bent and stretched and from the portions 28 which perform such functions, each shank 21 may be provided with a longitudinal opening I0 opening to the atmosphere at its end adjacent portion 28 and having its upper end connected to a pipe 12. Air or other fluid under any desired pressure may be passed through pipe 12 and opening to and around adjacent surfaces of the ribbon H and portions 28 to further increase the rate of heat conductivity occasioned by the cold working of the portions of the ribbon H formed about the tube or body portion It. The rate of such heat transfer may be controlled by varying the pressure of the fluid conveyed to each opening 10.

Our invention in each of its related and dependent aspects of method and of apparatus will be readily understood and usable by those skilled in this art from the foregoing speciflca- This invention may be made and used by or for the Government of the- United States of America for governmental purposes without the payment of any royalty thereon or therefor.

Having now so fully described our invention that others may therefrom be enabled to prac-.

tice, construct and usethe same, what we claim is: I

l. The method of making a heat exchange device including a heat exchange element provided with a heat exchange fin secured thereto, comprising the steps of securing a portion of a metal strip to a heat exchange element to form at least one convolution thereabout and then progressively bending the unsecured portion of the strip outwardly of the heat exchange element and angularly with respect to its secured portion to directly form by the bending operation a heat exchange fin circumferentially secured to a heat exchange element.

2. The method of making a heat exchange device including a heat exchange element provided with a helical heat exchange fin secured thereto, comprising the steps of helically securing a portion of a metal strip to a heat exchange element and then progressively bending the unsecured portion of the strip outwardly of the heat exchange element and angularly with respect to its secured portion to directly form by the bending operation a helical heat exchange fin secured to a heat exchange element.

3. The method of making a heat exchange device including a heat exchange element provided with a helical heat exchange fin secured thereto, comprising the steps of helically securing a portion of a metal strip to a heat exchange element with adjacent convolutions of the unsecured portion of the strip in overlapping relation and then progressively bending the unsecured portion of the strip outwardly of the heat exchange element and angularly with respect to its secured portion to directly form by the bending operation a helical heat exchange fin secured to a heat exchange element.

4. The method of making a heat exchange .device including a heat exchange element provided with a' helical heat exchange fin secured thereto, comprising the steps of helically securing a portion of a metal strip to a heat exchange element with adjacent convolutions of the unsecured portion of the strip in overlapping relation, then progressively bending the unsecured portion of the strip outwardly of the heat exchange eleso v ment and angularly with respect to its secured ment and means for progressively bending theunsecured portion of the strip outwardly of the heat'exchange element and angularly with respect to its secured portion to directly form by the bending operation the helical heat exchange fin, said last mentioned means including a plurality of spaced members of varying and progressive angulation with respect to the element tobe finned and arranged lengthwise thereof.

6. An apparatus for making a heat exchange device including a heat exchange element provided with a helical heat exchange fin secured thereto, comprising means for helically securing a portion of a metal strip to a heat exchange element and means for progressively bending the unsecured portion of the strip outwardly of the heat exchange element and angularly with respect to its secured portion to directly form by the bending operation the helical heat exchange fin, said last mentioned means including a row' of spaced overlapping members having a varying and progressive angulation with respect to the element to be finned and arranged lengthwise thereof.

7. An apparatus for making a heat exchange device including a heat exchange element provided with a helical heat exchange fin secured thereto, comprising means for helically securing a portion of a metal-strip to a heat exchange ale- 5 ment and means for progressively bending the unsecured portion ofthe strip outwardly of the heat exchange element and angularlywith respect to its secured portion to directly form by the bending operation the helical heat exchange fln,

tinned and arranged lengthwise thereof, at least one of said members being apertured for the ln- 5 troduction of a cooling fluid.

ALFRED J. BERG. JOHN o. HUSE.

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