US20050016240A1

US20050016240A1 - Method and apparatus for forming a turbulizer

Info

Publication number: US20050016240A1
Application number: US10/865,691
Authority: US
Inventors: Peter Zurawel; Dan Stefanoiu; Alex Cheong; John Izard
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-06-11
Filing date: 2004-06-10
Publication date: 2005-01-27
Also published as: EP1635968A2; WO2004108320A2; CN1805805A; WO2004108320A3; KR20060018257A; CA2431732A1; JP2006527087A; AU2004244684A1

Abstract

A turbulizer is formed that has corrugations that each have side walls with openings and offset portions in them. A strip is rolled longitudinally to form a corrugated strip that has longitudinally extending corrugations. Openings and the above-mentioned offset portions are formed in the corrugated strip. An apparatus for forming a turbulizer has one or more pairs of roll dies that have cooperating corrugated profiles that advance strip stock that is engaged between them. These roll dies provide the strip with longitudinally extending corrugations. First and second forming dies receive the corrugated strip and move relative to one another to form pairs of spaced cuts that each define a wall portion between them. This wall portion is displaced transversely of an adjacent portion of the corrugated strip. A fin or turbulizer for a heat exchanger has a strip that has longitudinally extending side edges and longitudinally extending corrugations. There are openings through the corrugations in a region that is intermediate the side edges. An imperforate side edge portion extends between the side edge and the intermediate region. The corrugations extend in a general plane. The imperforate side edge portion inclines with respect to that general plane outwardly away from the intermediate region. The side edge portion may incline with respect to the general plane outwardly away from the intermediate portion and may have a distal portion extending inwardly generally toward the intermediate portion.

Description

This application claims priority to Canadian Patent Application No. 2,431,732 filed Jun. 11, 2003.
The present invention relates to methods and apparatus for forming an inner fin or turbulizer, for example for a heat exchanger. More especially the invention relates to forming turbulizers such as low pressure drop turbulizers that are elongate and have corrugations extending longitudinally of the turbulizer, and that may have openings and offset portions formed in side walls of the corrugations. Further, the invention relates to novel fin or turbulizer structures that may preferably be made using the above methods and apparatus.
It is known to form low pressure drop turbulizers by rolling or stamping strip stock to form it with transverse corrugations. Since there are limits on the widths of the strip stock that can be used, this places a limit on the length of the turbulizer that can be produced when it is desired to employ an elongate turbulizer with longitudinal corrugations as may be desired when the flow of fluid is parallel to the corrugations to achieve a low drop in pressure.
In a first aspect, the present invention is directed to a method of forming a turbulizer having corrugations each having side walls with openings and offset portions formed in said side walls, said method comprising:

- (a) rolling a strip longitudinally to form a corrugated strip having longitudinally extending corrugations; and
- (b) forming said openings and said offset portions in said corrugated strip.

The present invention is directed in a further aspect to an apparatus for forming a turbulizer having corrugations each having side walls with openings and offset portions formed in said side walls,
said apparatus comprising:

- at least one pair of roll dies having cooperating corrugated profiles adapted to advance strip stock engaged therebetween and to provide it with longitudinally extending corrugations;
- first and second forming dies adapted to receive said strip having said corrugations exiting said at least one pair of roll dies;
- and said first and second forming dies on movement relative to one another forming pairs of spaced cuts each defining a wall portion between them and displacing each wall portion transversely of an adjacent portion of said corrugated strip.

In a further aspect, the invention provides a fin or turbulizer for a heat exchanger comprising a strip having longitudinally extending side edges and longitudinally extending corrugations, openings formed through said corrugations in a region intermediate said side edges, an imperforate side edge portion extending between said side edge and said intermediate region, said strip having said corrugations therein extending in a general plane, and said imperforate side edge portion inclining with respect to said general plane outwardly away from said intermediate region.
In a still further aspect, the invention provides an inner fin or turbulizer for a heat exchanger comprising a strip having longitudinally extending side edges and longitudinally extending corrugations, a side edge portion extending inwardly from a side edge of the strip toward an intermediate portion thereof, said strip having said corrugations therein extending in a general plane, and said side edge portion inclining with respect to said general plane outwardly away from said intermediate portion and having a distal portion extending inwardly generally toward said intermediate portion.
The present invention will now be more fully described, by way of example only, with reference to the accompanying drawings. In the accompanying drawings:
FIG. 1 is a partially schematic perspective view of one preferred form of apparatus for forming a turbulizer in accordance with the invention.
FIG. 2 is a side view of the apparatus of FIG. 1.
FIGS. 3 to 10 are end views of rolling die pairs taken on the correspondingly numbered section lines indicated in FIG. 1.
FIGS. 3 a to 10 a are cross-sectional views of the rolled strip profile achieved by the correspondingly numbered roll die pairs, respectively.
FIG. 11 is an end view taken from an end opposite to that of the view of FIG. 1.
FIG. 12 is a partially schematic and fragmentary perspective view of the apparatus of FIG. 1 adjacent the exit end.
FIG. 13 is an exploded end view of the forming die portion of the apparatus, and showing the dies in open position.
FIGS. 14 and 15 are plan and end views, respectively, of a corrugated strip.
FIGS. 16 and 17 are plan and end views of a corrugated strip after cutting and offsetting.
FIG. 18 is a partially fragmentary perspective view of a strip having a plain-corrugated portion and a cut and offset portion.
FIG. 19 is a partially schematic cross-section through the forming die, taken on the line 19-19 of FIG. 13, and showing the dies in closed position.
FIG. 20 is a somewhat schematic perspective view of a die assembly forming a portion of the forming die seen in FIG. 19.
FIGS. 21 to 23 are end views, similar to FIG. 17, of novel forms of turbulizer that may be made using the method and apparatus of the invention.
FIGS. 24 to 26 are cross sectional views through generally plate form heat exchangers incorporating the turbulizers of FIGS. 21 to 23, respectively.
Apparatus in accordance with the embodiment shown in the drawing comprises a rolling station 26 wherein strip stock 27 is rolled to form a corrugated strip 28, a forming station 29 wherein the corrugated strip is formed with spaced cuts and portions between the cuts are offset laterally, and, in the example illustrated, a cutter station 31 wherein the strip having openings and offset portions is cut into lengths. Stations 26, 29 and 31 may be supported on a common base 32.
The terms “transverse” and “laterally” have been used above, and it may be clarified that the terms, and their derivatives, are used herein throughout in their ordinary meanings. “Transverse” is used herein to refer to directions that extend generally at right angles to the longitudinal direction, and “lateral” to transverse directions that extend generally parallel to the plane of the strip or to the corrugated strip.
In the example shown, station 26 consists of a series or train of roll die pairs 33 through 40 shown in more detail in FIGS. 3 through 10. Each roll pair 33 through 40 comprises an upper roll designated by suffix “a” and a lower roll designated by suffix “b”. Each roll is connected on a respective axle 42 journalled through conventional structure, not shown, that permits adjustment of the position of the associated roll, and particularly with respect to the adjacent roll in its pair, to a pair of support walls 43 connected to base 32.
A sprocket gear 44 is connected to each axle 42 and is engaged by a serpentine chain 46. The chain 46 is driven by a drive gear 47, and passes over an idler gear 48. The chain 46 drives each roll in counter-rotation to the other roll in its pair. In use, the strip 27, drawn from a supply reel 51 and passing over an idler roll 52 is engaged between successive roll pairs 33 through 40 and is drawn therethrough. Adjacent its longitudinal median, each roll in the pairs 33 through 40 has a peripherally continuous profile that imparts a corrugation or corrugations to the strip 27 and provides the strip with a progressively increasing number of corrugations transversely outwardly from its longitudinal median. FIGS. 3 a to 10 a show the progressively more complex configurations, respectively, of the corrugated strip 28. Fewer or greater numbers of corrugations may be imparted by adding or removing roll pairs. FIG. 1 shows eight roll pairs, and a roll pair has been omitted between pairs 39 and 40. The corrugated strip 28 passes freely through the space between axles 42 in this region. Transversely outwardly from the corrugating profile, each roll has a cylindrical surface that may lightly grip transversely outer margins of the corrugated strip 28. The arrangement of the roll pair profiles is such that alternate roll pairs 33, 35, 37 and 39 have a corrugating profile comprising a peripherally continuous recess within this surface on one side (in the example shown the upper side) of the strip 28, and a rib or ribs extending beyond this surface on the opposite or lower side. Each other roll pair (34, 36, 38 and 40) has the opposite configuration, with ribs on the said one (upper) side and a recess on the other, or lower, side. With each pass through a roll pair, this arrangement achieves a gentle bending of the material transversely outwardly from and in a direction opposite to the bending achieved in the pass through the preceding roll pair. The invention may subject the strip to less severe forming conditions than known methods, and relatively thin strip stock can be corrugated without tearing of the material. For example, the strip stock, which may for example comprise stainless steel or aluminum, may be about 0.05 to 2 mm thick, more preferably 0.1 to 0.5 mm thick.
In accordance with a preferred aspect of the present invention, multiple corrugations are formed in strip stock by rolling in station 26. Portions of the corrugated strip are cut and offset at a subsequent station 29 that in a preferred form comprises reciprocating stamping dies. Significant advantages accrue from this arrangement. The corrugating rolls entrain the strip stock and a separate strip stock feeder is not required. Whereas stamping dies need to be large, massive and relatively expensive in order to withstand the forces to which they are subjected, the invention avoids use of large numbers of stamping dies and uses corrugating rolls that are of reduced size, cost and footprint as compared with stamping dies.
In the preferred form as shown, chain drive gear 47 is rotated by a servo motor controlled by a controller operating the servo motor in a continuously repeated cycle of operation, wherein firstly the motor turns the gear 47 through a predetermined angular rotation followed by a predetermined interval during which the gear 47 and chain 46 are stationary, following which the cycle of operation repeats by commencement of turning of the motor and gear 47. As a result, the roll pairs rotate synchronously for intermittent periods during each of which the strip stock advances a predetermined length and a corresponding length of corrugated strip stock 28 exits from between the last roll pair 40. Intermediate these intermittent periods there are roll stationary times of predetermined length during which the roll pairs and strip 28 are stationary. During these roll stationary times, the forming station 29 operates to provide cuts and offset portions in the corrugated strip 28, to form an elongate turbulizer product.
FIGS. 14 and 15, for example, show a corrugated strip 28 having seven raised corrugations 56. FIGS. 16, 17 and 18 illustrate a lanced and offset strip 57 wherein cuts 58 have been made through substantially the full height of each side wall of each corrugation and portions 59 disposed between alternate adjacent pairs of cuts 58 have been offset transversely of the original corrugations 56. The spaced cuts 58 in each pair defining an offset portion 59 between them may be spaced uniformly longitudinally apart in the product. At least over an extended portion of the length of the product, the pairs of spaced cuts may be spaced uniformly longitudinally apart. In FIGS. 16, 17 and 18, the spacing between adjacent cut pairs and offset portions 59 is substantially the same as the spacing between cuts 58 in each pair.
While, as noted above, FIGS. 1 to 10 and 14 to 18 show by way of example forming a corrugated strip 28 having seven raised corrugations, it will be appreciated that a strip having more or fewer corrugations may be formed employing a rolling station 26 having more or fewer roll die pairs 33 to 40. For greater clarity of illustration, the following description of the operation of the forming station will refer to FIGS. 12, 13, 19 and 20 that illustrate, merely by way of example, forming operations conducted on a corrugated strip 28 having four raised corrugations. Similar apparatus to that illustrated, with minor modifications that will be readily apparent to those skilled in the art, may be used for corrugated strips having more or fewer corrugations and for providing them with spaced cuts and offset portions as generally described below.
In the example shown, a forming station 29 comprises a lower bolster 61 mounted on base 32, and an upper bolster 62 reciprocating relative to lower bolster 61 in a direction indicated by arrow 60 transversely of the longitudinal path followed by strip stock 27 and by corrugated strip 28. In the example illustrated, bolster 62 is connected to bushings 63 sliding on dowels 64 connected to lower bolster 61. Support structure 66 carries a fluid operated cylinder 67 having a piston working within it and connected to a piston rod 68. Rod 68 pivots at 69 to pivot structure 71 pivoted to support structure 66 at 72. Link 73 is connected pivotally at 74 and 76 to pivot structure 71 and to upper bolster 62, respectively. On extension of rod 68 from an “open” position shown in solid lines in FIG. 12, structure 71 rocks to a position moving link 73 to a position in which upper bolster 62 is moved downwardly to a “closed” position shown in broken lines in FIG. 12. As will be appreciated by those skilled in the art, other means for moving the elements between open and closed positions may of course be adopted, such as air pressure operations, or a servomotor with an operating cam, and the like.
Lower and upper bolsters 61 and 62 carry first and second dies 77 and 78 respectively. First die 77 comprises an assembly of a plurality of longitudinal rows 79 of punches 81. In the example illustrated, each row 79 includes a first series of punches 81 a that are aligned along a first longitudinal axis and a second series 81 b that are aligned along a second longitudinal axis that is offset laterally from the first axis. The punches 81 a are longitudinally spaced and alternate with punches 81 b. Longitudinally opposing end faces 82 (see FIG. 20) of adjacent punches in series 81 a and 81 b are in close proximity. The second die assembly 78 has an arrangement of punches similar to and complementary to the arrangement of the first die 77, so that when the dies 77 and 78 close together, the punches 81 of the first die 77 inter engage snugly between the punches 83 of the second die 78. It will be noted that, in the example shown in FIG. 19, the first die 77 comprises four rows of punches 81 a and 81 b. The second die 78 comprises five rows of punches 83 cooperating with the punches 81 and 81 b of the lower die. In the example illustrated, the punches 83 in the second die 78 include punches 83 a that cooperate with, for example, punches 81 a of the first die 77, as seen in FIG. 19, and punches 83 b that cooperate with the punches 81 b of the first die 77 and include a fifth row of punches 83 b seen at the upper left hand side in FIG. 19 that cooperate with a laterally outermost punch 81 b and form the adjacent outer side of a corrugation. For clarity of illustration, not all of the punches 81 a, 81 b, 83 a and 83 b are shown in FIG. 19. As will be appreciated, die configurations having more or fewer rows of punches may be adapted for differing configurations of corrugated strip.
In use, after each intermittent roll rotation period during which a predetermined length of the corrugated strip 28 has advanced from the exit end of the roll pairs, and while the rolls and strip 28 are stationary relative to the base 32, the controller actuates the cylinder 62 to extend the piston rod 68 and close the dies 77 and 78 together on the corrugated strip 28. As will be best appreciated from FIG. 19, a shearing action is exerted between opposing end faces 82 of adjacent punches 81 of the first series 81 a and of the second series 81 b offset therefrom, thereby forming cuts through the side walls of the corrugations 56, while reaction between the punches 81 and 81 b of the first die 77 with the complementary punches 83 a and 83 b of the second die 78 cause portions 59 between adjacent pairs of cuts to be displaced or offset laterally.
The controller then operates to retract the rod 68 and disengage the dies 77 and 78 from the strip 57, and to commence rotation of the servo motor driving the drive gear 47. The cycle of operation then re-commences.
In one mode of operation the length by which the strip 28 is advanced in each intermittent roll rotation is substantially equal to the longitudinal length of the dies 77 and 78 so that the product is formed with cuts or openings and offset portions along substantially its entire length. However, other modes of operation are possible, as discussed later.
In order to assist in disengaging the punches 81 from the corrugated and lanced and offset strip 57, the laterally facing sides of the punches 81 and 83 may have slight draft angles so that the punches 81 taper slightly toward their tip. Preferably, stripper plate arrangements are used to further assist in disengaging the punches of the dies 77 and 78 from the strip 57. For example, a first stripper plate 86 has slots 87 each of width and length sufficient to receive through it the longitudinal rows 79 of the punches 81 of the first die 77. The plate 86 forms part of an inverted tray-like structure 88 having downwardly depending side walls and within which are received compression springs 89 normally biasing the plate 86 upwardly to a position above the lower bolster 61 and the punches 81 of the first die 77. The structure 88 is guided for vertical movement and limited in upward travel by guide structure (not shown). A second stripper plate 91 that has slots 92 to accommodate the rows of punches 83 in the second die 78 is connected or yoked to the first plate 86 by downwardly depending portions 93 secured to the plate 86. A recess 94 formed longitudinally through the portions 93 is of dimensions sufficient to receive the width and depth of the corrugated strip 28 and provides a guide through which the strip 28 intermittently advances, and limits vertical or transverse deviation of the strip 28 laterally of its normal path of movement. At the limit of upward travel of the plate 77, the recess 94 is aligned approximately with the line along which the rolls 40 a and 40 b of the final roll pair 40 engage with the work piece or corrugated strip 28. Normally, the plates 86 and 91 are spaced from the dies 77 and 78 in the open position. In operation, the punches 83 of the second die 78 penetrate the slots 92 as the die 78 moves to the closed position. The die 78 engages the plate 91 and urges the plates 86 and 91 against the action of the springs 89 to the fully closed position seen in FIG. 19 wherein the punches 81 of the lower first die 77 penetrate the slots 87. On opening of the dies, the plate 86 moving upwardly under the action of springs 89 disengages the lanced and offset strip 57 from the first die 77 and secondly the plate 91 disengages the strip 57 from the second die 78 following retraction of the latter beyond the upper limit of motion of the connected plates 86 and 91.
The compression of the corrugated strip 28 between the punches 81 and 83 and the inner surfaces of the stripper plates 86 and 91 form the lanced and offset strip 57 to a desired size, and, in particular to a desired height dimension defined between a crest of a corrugation on one face of the strip 57 and a crest of a corrugation on an opposite face. As a result the corrugated strips 57 can be manufactured using a relatively small number of roll die pairs as compared with methods that rely on rolling for control of the height dimension of the product.
The lanced and offset strip 57 exiting the forming station 29 may pass through a conventional cutter device at station 31, for example a guillotine cutter or traversing cutter, that preferably operates under the control of the controller to cut the strip into discrete lengths during roll stationary times As an alternative, the cutter may be incorporated in the dies 77 and/or 78, with a separate activation mode. By varying the timing of operation of the cutter, product of varying lengths can be obtained.
A further advantage of the present method is that it provides considerable flexibility in the range of designs of fins or turbulizers that can be produced.
For example, the procedure described above with reference to the drawings may be easily modified to provide corrugations that vary in wavelength across the width of the corrugated strip 28, by adopting roll die pairs of appropriate profile. In this manner it is possible to achieve a turbulizer having approximately planar portions, or portions at least of relatively broadened channel width, that may be uninterrupted by lanced and offset corrugations, extending along longitudinal zones of the product. Such zones provide so-called “neutral channels” described together with their advantages in commonly-assigned U.S. Pat. No. 6,273,183 (So et al) the disclosures of which are incorporated herein by reference.
While the example shown in the drawings has pairs of cuts spaced uniformly apart, with the cuts in each pair also spaced generally uniformly, by simple modification of the arrangement of the punches 81 and 83 these spacings can readily be varied as desired, and punches may be omitted from portions of the dies corresponding to the above mentioned “neutral channel” zones, where desired.
Turbulizer strip comprising alternating lengths of fully formed regions, having spaced cuts and offset portions, and partially formed regions, that are corrugated only, can readily be achieved either by interrupting operation of the forming station 29 periodically, or by overfeeding the strip 28 by adopting a mode of operation in which the strip 28 is advanced in each intermittent roll rotation a distance greater than the length of the dies 77 and 78. The partially formed sections may be useful with heat exchanger structures as pressure control zones. Moreover, it is often desired to cut holes through a turbulizer to accommodate a heat exchanger design, especially at manifold locations. The partially formed portions facilitate hole cutting. Alternatively, a hole may be cut through a corrugated strip 28 before the strip 28 is provided with spaced cuts and offset portions by passing it through the forming station 29, for example using hole punch operations at a location between stations 26 and 29. A further preferred procedure for providing holes is to pre-form holes in the starting material strip, such as a hole 96 indicated in broken lines in strip 27 in FIG. 1.
A still further advantage of the present method is that it readily allows formation of fins or turbulizers having advantageously novel edge profiles, examples of which are illustrated in FIGS. 21 to 26.
FIGS. 21 to 23 show turbulizers 101 to 103, respectively, that each have main or intermediate portions provided with corrugations 104 provided with longitudinally spaced cuts and laterally offset portions 106.
It may be noted that the crests or channel bottoms of the corrugations 104 are flattened. This may desirably be achieved by compression of the corrugated strip with correspondingly profiled punches during a sizing or compression step performed within a recess such as recess 94 as described above with reference to FIG. 19.
Each turbulizer 101 to 103 has a side edge portion 107 that inclines outwardly away from the corrugated intermediate region, at an angle with respect to the general plane of the latter. Desirably, each edge portion 107 is imperforate and is not provided with cuts or offset portions.
The side edge portions 107 of turbulizers 101 and 102 have distal portions 108 that extend inwardly generally toward the intermediate, corrugated portion, and that preferably curve smoothly from the main portion of the edge portion 107 to its distal portion.
The side edge portions 107 of turbulizers 101 and 103 extend a distance less than the height dimension of the turbulizer, i.e. the distance between a crest of a corrugation such a corrugation 104 on one face of the strip constituting the turbulizer, and a crest of a corrugation (or channel base) such as corrugation 104a on an opposite face.
As will be readily understood by those skilled in the art, turbulizers having profiles such as those shown for turbulizers 101 to 103 can be easily manufactured employing conventional forming techniques to provide the edges of the corrugated strip 28 with the desired profiles, preferably by modified roll forming in the rolling station 26 before the forming station 29 and the modifications to the procedure described above with reference to FIGS. 1 to 20 do not need to be described in detail to allow one of ordinary skill in the art to carry out the modified process. For example, the inclining or inturned edges 107 and 108 may be formed using profiled rollers engaging the edges of the strip 28, the axes of the rollers inclining with respect to the general plane of the strip 28. It is also possible to form the edges of the corrugated strip to the desired profiles in a forming die for example in the forming station 29. The recess 94 may be dimensioned to provide a spacing between the side walls of the recess 24 and the laterally outermost punches 81 or 83 to accommodate and lightly engage the edge portions 107.
FIGS. 24 to 26 show the turbulizers 101 to 103 disposed within brazed together generally channel section plate pairs 111 providing a fluid channel in a heat exchanger component 112. The side edge portions 107 accommodate tolerances in the gauge or width of the starting material strip 27 while avoiding defects or leaks in the assembled heat exchanger component. With known turbulizers, in the event that the product is wider than nominal or as designed, the edges may ride up the inner surfaces of the component 112 and interfere with assembly by insertion between the surfaces 113 to be brazed together or may prop the portions apart. In the example of FIG. 24, an increase in the width of the turbulizer 101 results in increased width of the inturned distal portion 108, without this increased width interfering with assembly or brazing. Similarly with the turbulizer 102, with the added advantage that the distal portion 108, whether of nominal or increased width, can bond to the adjacent inner surface of the plate 111, resulting in increased efficiency of heat exchange. Likewise, the portion 107 of the turbulizer 103 can accommodate increased width without risking an assembly defect or leak.
Further, increased efficiency is achieved as compared with structures in which there is a gap between the edge of the turbulizer and the plate pair channel. The structure extending into this gap avoids loss of efficiency that results from the existence of a fluid bypass channel in this gap, and provides for heat transfer augmentation. Moreover, fluid that would otherwise bypass the intermediate portion of the turbulizer tends to be deflected by the side edge portions 107 and 108 toward the intermediate portion that is provided with the heat exchange promoting spaced offset portions. Heat exchange efficiency is also increased as a result of the increased surface area of the turbulizer.

Claims

1. Method of forming a turbulizer having corrugations each having side walls with openings and offset portions formed in said side walls, said method comprising:

(a) rolling a strip longitudinally to form a corrugated strip having longitudinally extending corrugations; and

(b) forming said openings and said offset portions in said corrugated strip.

2. Method according to claim 1 wherein said step of forming said openings and said offset portions in said corrugated strip comprises forming pairs of spaced cuts extending transversely of said corrugated strip, each pair of spaced cuts defining a wall portion between them, and having each said wall portion displaced transversely of an adjacent portion of said corrugated strip.

3. Method according to claim 2 wherein the spaced cuts in each pair are spaced uniformly longitudinally apart.

4. Method according to claim 2 wherein the pairs of spaced cuts are spaced uniformly longitudinally apart.

5. Method according to claim 1 wherein said openings and said offset portions are distributed uniformly continuously along said corrugated strip.

6. Method according to claim 1 wherein said openings and said offset portions are at differing spacings along said corrugated strip.

7. Method according to claim 1 including a step of severing said corrugated strip transversely into discrete lengths after said step of forming said openings and said offset portions.

8. Method according to claim 1 including providing first and second forming dies moving between an open position and a closed position wherein the forming dies engage the corrugated strip between them, said forming dies when moving to said closed position cooperating to form said openings and said offset portions in said corrugated strip.

9. Method according to claim 8 including providing at least one pair of roll dies having cooperating corrugated profiles, said roll dies rotatingly driven during intermittent periods and having said strip engaged between said roll dies and said roll dies advancing said strip and providing it with corrugations by its passage between said roll dies, and including passing said strip having said corrugations between said forming dies, and said forming dies moving intermittently to said closed position at roll stationary times intermediate said intermittent periods.

10. Method according to claim 8 including providing a train of pairs of roll dies, each of said roll die pairs driven rotatingly synchronously for intermittent periods that are intermediate roll stationary times and having said strip engaged and advanced successively between pairs of roll dies of said train, said roll dies in each pair having cooperating corrugated profiles such that successive pairs of roll dies form said strip with a progressively increasing number of said corrugations, and including exiting said strip from said train between said forming dies, and wherein said forming dies move intermittently to said closed positions at said roll stationary times.

11. Method according to claim 1 wherein said strip has a thickness of 0.05 mm to 2 mm.

12. Method according to claim 11 wherein said thickness is 0.1 to 0.5 mm.

13. Apparatus for forming a turbulizer having corrugations each having side walls with openings and offset portions formed in said side walls,

said apparatus comprising:

at least one pair of roll dies having cooperating corrugated profiles adapted to advance strip stock engaged therebetween and to provide it with longitudinally extending corrugations;

first and second forming dies adapted to receive said strip having said corrugations exiting said at least one pair of roll dies;

and said first and second forming dies on movement relative to one another forming pairs of spaced cuts each defining a wall portion between them and displacing each wall portion transversely of an adjacent portion of said corrugated strip.

14. Apparatus according to claim 13 including an operator device operated to move said first and second dies between an open position and a closed position engaging said strip;

and including a drive rotating said roll dies during intermittent periods that are intermediate roll stationary times;

and wherein said operator device moves said first and second dies to said closed position during a roll stationary time, and said first and second dies on moving to the closed position are effective to form said pairs of spaced cuts and to displace each said wall portion transversely of an adjacent corrugation portion.

15. Apparatus according to claim 14 wherein said first and second dies each have a longitudinal length and said drive is effective to advance said strip stock a distance equal to said longitudinal length in successive intermittent periods.

16. Apparatus according to claim 14 wherein said first and second dies each have a longitudinal length and said drive is effective to advance said strip stock a distance greater than said longitudinal length in successive intermittent periods.

17. Apparatus according to claim 14 wherein said first and second dies each comprise at least one longitudinal row of punches each comprising a first series of longitudinally spaced punches aligned to a first longitudinal axis, and a second series of longitudinally spaced punches that are disposed alternately between the punches of the first series, said punches in said second series aligned to a second longitudinal axis offset transversely from said first longitudinal axis, said punches of said first die generally opposing and disposed complementarily with respect to said punches of said second die.

18. Apparatus according to claim 17 wherein each of said first and second dies is provided with a respective stripper plate normally maintained spaced from the die and having an elongated slot that is penetrated by said at least one longitudinal row of punches in said closed position, and wherein said at least one pair of roll dies has a line of engagement of the rolls constituting said at least one pair, and said line of engagement is aligned with a region disposed between said stripper plates in an open position.

19. Apparatus according to claim 18 including yoke structure yoking said stripper plates together.

20. Apparatus according to claim 19 including a biasing device biasing said stripper plates normally a distance laterally away from each of said first and second dies.

21. Apparatus according to claim 19 wherein said yoke structure provides laterally disposed guide surfaces adapted to guide said corrugated strip in its passage between said stripper plates.

22. Apparatus according to claim 13 comprising a train of said pairs of roll dies, said roll dies in each pair having cooperating corrugated profiles such that successive pairs form said strip with a progressively increasing number of said corrugations.

23. Apparatus according to claim 13 including a cutter adapted to cut said strip exiting said forming dies into lengths.

24. A fin or turbulizer for a heat exchanger comprising a strip having longitudinally extending side edges and longitudinally extending corrugations, openings formed through said corrugations in a region intermediate said side edges, an imperforate side edge portion extending between said side edge and said intermediate region, said strip having said corrugations therein extending in a general plane, and said imperforate side edge portion inclining with respect to said general plane outwardly away from said intermediate region.

25. A fin or turbulizer according to claim 24 wherein said strip having said corrugations therein has a height dimension defined between a crest of a corrugation on a face of said strip and a crest of a corrugation on an opposite face of said strip, and wherein said side edge portion extends a distance less than said height dimensions.

26. An inner fin or turbulizer for a heat exchanger comprising a strip having longitudinally extending side edges and longitudinally extending corrugations, a side edge portion extending inwardly from a side edge of the strip toward an intermediate portion thereof, said strip having said corrugations therein extending in a general plane, and said side edge portion inclining with respect to said general plane outwardly away from said intermediate portion and having a distal portion extending inwardly generally toward said intermediate portion.

27. A fin or turbulizer according to claim 26 wherein said side edge portion curves smoothly toward said distal portion.

28. A fin or turbulizer according to claim 26 wherein said strip having said corrugations therein has a height dimension defined between a crest of a corrugation on a face of said strip and a crest of a corrugation on an opposite face of said strip, and wherein said side edge portion extends a distance less than said height dimensions.