US3839975A

US3839975A - Method of reshaping passageways in metal strip-type tubing

Info

Publication number: US3839975A
Application number: US00247606A
Authority: US
Inventors: L Tranel
Original assignee: Olin Corp
Current assignee: Olin Corp
Priority date: 1971-03-01
Filing date: 1972-04-26
Publication date: 1974-10-08
Anticipated expiration: 1991-10-08

Abstract

A method and apparatus for producing a metal strip-type tubing having a first surface and an opposing surface of the tubular passageways flattened. The flattened surfaces are obtained by passing the tubing through a deforming means such as spaced apart rolls. It is essential that the edges of the strip-type tubing be restrained during the flattening operation. The apparatus includes means for deforming the flats on the strip-type tubing and means for restraining the edges of the flats during the deforming operation. The resulting tubular passageways have a polyhedral cross section which is adapted to be bonded to the flat type fin stock. The resultant tubing and heat exchangers formed of the tubing is also part of the invention.

Description

Unlted States Patent 1 1 1 1 5 Tranel 1 *Oct. 8, 1974 METHOD OF RESHAPING PASSAGEWAYS 2,998,639 9/1961 Forst a 211....v 29/1573 v [N METAL STRHLTYPE TUBING 2,999,304 9/1961 Pauls 3,067,491 12/1962 Neel et a1. Inventor: Lester J- Tranel, is, o 3,196,657 7/1965 Fromson 29/1573 R x Assignfiez Olin corporafion, New Haven, 3,735,720 5/1970 Tranel 29/1573 D Conn. FOREIGN PATENTS OR APPLICATIONS 1 Notice; The portion of the term of this 702,086 1/1965 Canada 29/1573 V patent subsequent to May 29, 1990, has been disclaimed. Primary Examiner-Charles W. Lanham Assistant Examiner-D. C. Reiley, III [22] 1972 Attorney, Agent, or Firm-Robert H. Bachman [21] Appl. No.: 247,606

Related US. Application Data 1 ABSTRACT [62] Division of Ser. No. 122,607, March 1, 1971, A method and apparatus for producing a metal stripabandonedtype tubing having a first surface and an opposing surface of the tubular passageways flattened. The flat- 1 1 118 -3 9/ 7-3 V tened surfaces are obtained by passing the tubing [51 Int. Cl BZld 53/02, 323p 15/26 through a deforming means such as spaced apart rolls, 1 Field of Search It is essential that the edges of the strip-type tubing be /1 157-3 .3 D; 113/118 R, restrained during the flattening operation. The appara- 113 1 18 V tus includes means for deforming the flats on the striptype tubing and means for restraining the edges of the 1 1 References Cited flats during the deforming operation. The resulting tu- UNITED STATES PATENTS bular passageways have a polyhedral cross section L394 3/1934 which is adapted to be bonded to the flat type fin 190,494 M940 stock. The resultant tubing and heat exchangers 2341 95 3 1953 formed of the tubing is also part of the invention. 2,848,200 8/1958 5 Cl 13 D 2,920,380 l/l960 W1lliams et a1. 29/1573 v rawmg gums METHOD OF RESHAPING PASSAGEWAYS IN METAL STRIP-TYPE TUBING This is a division, of application Ser. No. 122,607, filed Mar. 1, 1971, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for forming metal strip-type tubing and, preferably, sheet metal tubing suitable for use in applications, such as condensers for automobile air conditioners. The tubing produced by this method is also part of this invention.

Condensers for automobile applications generally comprise a plurality of passes of tubing wound in a serpentine configuration with flat type fin stock bonded to the tubing surfaces of adjacent passes. In order to have sufficient contact between the tube surfaces and the flat fin stock extrusions have generally been used which have a comparatively flat surface.

SUMMARY OF THE INVENTION In accordance with this invention, metal tubing in the form of strip, preferably, sheet metal tubing having a plurality of inflated longitudinally extending tubular passageways is employed; however, the surface of this tubing is not sufficiently flat to obtain the necessary contact area between the fin stock and the tubing. Therefore, in accordance with this invention, a first surface and an opposing surface of the tubular passageways in the metal strip-type tubing are flattened to create more contact area between flat type fin stock and these surfaces. The flattening is accomplished by passing the metal strip-type tubing between a deforming means, such as rolls which are spaced apart an amount less than the diameter of the tubular passageways while simultaneously restraining the edges of the strip in order to provide adequate tube heights.

If the tubular passageways are flattened by merely passing them between flattening rolls without restraining their edges, the tube heights are substantially decreased. The extent of tube height decrease is so great that the tubing may not be bent without a severe pressure drop occurring in the bend areas due to the collapsing of the tubes during bending. One manner of overcoming this problem is exemplified by the skip flattening technique described and claimed in applicants copending US. application Ser. No. 1 19,600, filed Mar. 1, 1971, now Pat. No. 3,712,372, and assigned to the assignee of the instant invention. In accordance with that technique the tubular passageways in the area of the bends are not flattened, thereby leaving sufficient tube height to avoid pressure drops.

In accordance with this invention, the edges of the metal strip-type tubing are restrained while it is being flattened. Thereby, it is possible to obtain tubular passageways having sufficient tube height to substantially reduce pressure drops in bend areas while providing flat surfaces for the attachment of fins. The process of the instant invention tends to square up the cross section of the tubular passageways although they retain a generally six sided polyhedral shape. The invention is also directed to the tubing heat exchanger produced by this process and the various apparatus embodiments which may be used to carry out the process.

It is accordingly an object of this invention to provide a process for flattening a first surface and an opposing surface of at least one tubular passageway in a metal strip-type tubing, preferably a sheet metal tubing.

It is a further object of this invention to apply this process to long lengths of such tubing.

It is a further object of this invention to provide a strip-type metal tubing and heat exchanger having a plurality of tubular passageways wherein each tubular passageway has a first deformed flat surface and an opposing deformed flat surface and a polyhedral cross section.

It is a further object of this invention to provide an apparatus for flattening a first surface and an opposing surface of the two tubular passageways in a metal striptype tubing while retaining sufficient tube height for use in heat exchange applications.

Other objects and advantages will become apparent to those skilled in the art as a detailed discussion of particular embodiments proceeds with reference to the drawings which form a part hereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a perspective view illustrating the process for forming the sheet metal strip-type tubing preferably employed with this invention.

FIG. 2 shows a perspective view of strip-type tubing having fully inflated tubular passageways.

FIG. 3 shows a perspective view of a strip-type tubing in accordance with this invention.

FIG. 4 is a perspective view of the typical condenser application of the tubing produced by the instant invention.

FIG. 5 is a perspective view illustrating the effect of roll flattening strip-type tubing without restraining the strip edges.

FIG. 6 is a perspective view illustrating the effect of roll flattening strip-type tubing while restraining the strip edges.

FIG. 7 is a front view of an apparatus employing the roll configuration of FIG. 6.

FIG. 8 is a perspective view of an alternative embodiment for an edge guide in accordance with this inventlon.

FIG. 9 are sectional views of alternative roll configurations useful with this invention.

FIG. 10 is a perspective view of a modular roll configuration useful with this invention.

FIG. 11 is a perspective sectional view of a modular disk useful in the roll configuration of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and especially to FIG. 1, there is illustrated a composite metal strip 1 which is used to form the preferred starting material for this invention. The strip 1 may be fabricated by the method disclosed in US. Pat. No. 2,690,002, granted to Grenell on Sept. 28, 1954. While this invention will be described with reference to sheet metal strip-type tubing, it is broadly applicable to most types of strip-type tubmg.

Referring to FIG. 1, a pattern of weld-inhibiting or stop-weld material 2 is applied to a clean surface of a first strip 3 of metal. A second strip of metal 4 having a clean surface is superimposed on the surface of the first strip 3 as shown and the two strips are secured together to prevent relative motion therebetween.

Thereafter, the two superimposed strips 3 and 4 are pressure welded together as by rolling so that the adjacent areas 5 of the strip 1 which are not separated by the stop-weld material become bonded together. The rolling of the strips 3 and 4 results in reducing their thickness and in elongating the resulting strip 1 in the direction of rolling while the width of the strip 1 re mains substantially the same as the initial width of the strips 3 and 4.

Following the rolling operation, the resultant strip 1 is usually softened, as by annealing, to make it more pliable. If desired, it may be further rolled to the final gage and again softened, as by annealing. The stop-weld material results in the retention of unwelded portions 6 corresponding to the stop-weld pattern 2 which are sandwiched between the outer surfaces of the strip 1.

After softening the strip 1, the unwelded portions 6 are usually expanded to obtain the inflated strip as shown in FIG. 2 having passageways 7. The expansion is obtained by injecting a fluid, such as air, water or oil under pressure of sufficient magnitude such as 500 to 4000 psi to permanently deform the strip 1 in the area of the unwelded portions 6 to form the desired passageways 7.

It is preferred that the invention be carried out under tension in accordance with the teachings of US. Pat. No. 3,538,577, granted Nov. 10, 1970, to M.P.OMalley, and assigned to assignee of the instant invention.

The pattern of weld-inhibiting material may be formed by any desired technique. It is preferred to use the process disclosed in US. application Ser. No. 723,055, filed Apr. 22, 1968, by N. A. Keith, now abandoned and assigned to the assignee of the instant invention.

The weld-inhibiting material itself may be any of the various conventionally used materials such as graphite or titanium dioxide based stop-weld compositions.

The process disclosed in US. application Ser. No. 7,729, filed Feb. 2, 1970, by N. A. Keith, now abandoned, and assigned to the assignee of the instant invention is further illustrative of the processes which may be used to obtain the sheet metal strip for inflation into the tubing useful with this invention. As disclosed therein, the strip may be initially formed as part of a wide sheet which is later slit into strip-like material which may be coiled for further use.

It is to be understood that the above described methods of forming the sheet metal strip-type tubing useful with this invention are only exemplary and that other methods may be employed in the manufacture of the strip. The strip material made by the processes disclosed above or other suitable processes is usually employed in very long lengths. Further, the strip-type tubing may contain any desired number of tubular passageways of any desired diameter, as may be required for achieving given flow and heat transfer rates.

In accordance with the instant invention a strip-type tubing 1 as shown in FIG. 3 is produced preferably in the form of very long lengths. As shown therein, the tubular passageways 7 have flattened surfaces 8 to which may be affixed flat type fin stock.

In FIG. 4, there is illustrated the application of the tubing 1 produced in accordance with this invention. As shown therein, the tubing 1 has been bent in a serpentine configuration and flat fin stock 10 has been affixed to the tubing 1 between adjacent passes II. The

flat fin stock 10 is commonly affixed by means of brazing or soldering so that a bond having good heat transfer qualities is obtained. The fin stock 10 is therefore bonded to the flattened surfaces 8 of adjacent passes 1 1.

If the strip-type tubing 1 of FIG. 2 were employed in the configuration of FIG. 4, there would be unsufficient contact between the tubing 1 and the fin stock 10 to obtain adequate heat transfer properties. Therefore, it is necessary to increase the contact area between the fin stock 10 and the tubing 1 as by roll flattening in accordance with this invention.

When the strip 1 of FIG. 1 is inflated to form the metal strip-type tubing 1 of FIG. 2, the width of the strip decreases as the height of the tubular passageways 7 increases. If the tubing 1 of FIG. 2 is flattened between rolls R, as shown in FIG. 5 or otherwise, without restraining the edges 12 of the strip, there is a severe reduction in tube height 7. If the edges 12 are not restrained, the width of the strip 1 tends to increase as the first and opposing surfaces of the tubular passageways 7 are flattened. Such a procedure does provide metal strip-type tubing with flattened tubular passageways, however, the tube heights are substantially reduced. Upon bending the strip into a serpentine configuration as in FIG. 4, there is a further intolerable reduction in the tube height in the bend areas. The collapsing of the tubes in the bend areas increases the pressure drop substantially over that of the original tubing.

In accordance with this invention, as shown in FIG. 6, the edges 12 of the metal strip-type tubing 1 are restrained during the flattening operation so that the width of the strip 1 cannot increase. By adopting this approach, there is considerably less reduction in the tube heights 7 as compared to carrying out the process without restraining the edges as in FIG. 5.

The tubing 1 as shown in FIG. 3 obtained by the method and apparatus of this invention has the desired flattened surfaces 8 with a small but generally acceptable reduction in tube height 7 The cross section of the tube 1' as shown in FIG. 3 reveals that the tubular passageways 7 have been substantially squared up. The passageways generally have what may be described as a polyhedral cross section. The polyhedron usually appears as a six sided figure with the sides 8 which contact the fin stock being wider than the adjoining sides S.

The diameter of the tubular passageways 7' in the metal strip may be as desired to meet a given application. However, for condenser applications, it has been found that a diameter between about 0.175 and 0.250 inch is most useful with a preferred range between about 0.200 and 0.230 inch. Generally, there is a reduction of between 0.020 and 0.060 inch in the tube height following roll flattening in accordance with this invention. Preferably, the reduction in tube height is between 0.040 and 0.050 inch. The width of the flat formed on the tube varies with the tube diameter and the amount of reduction in tube height. For the preferred tube diameter of 0.230 inch, a reduction in tube height of 0.020 inch and 0.060 inch will generally yield a flat having a width between 0.075 inch and 0.125 inch. Preferably, for this size tubing, the flat is around 0.100 inch.

While the above ranges are specific to tubing especially adapted for use in condenser applications, the invention is broadly applicable to any type of metal striptype tubing having any given diameter of tubular passageways.

FIG. 6 is exemplary of a roll configuration suitable for carrying out this invention. The configuration 20 comprises flattening rolls 21 which are spaced apart a distance less than the diameter of the inflated tubular passageways 7 in the metal strip-type tubing 1 which is the starting material of this invention. The configuration 20 also includes edge guide rolls 22 which restrain the edges 12 of the strip 1 to keep it from spreading during the flattening operation.

The roll configuration 20 of FIG. 6 may be employed using an apparatus similar to that shown in FIG. 7. The apparatus 30 comprises a frame 31. One of the flattening rolls 32 is rotatably mounted to the frame 31, the shaft extension at 33 being connected to a suitable gear drive (not shown) which are known in the art. A second flattening roll 34 is rotatably mounted within a movable carriage 35 which has shafts 36 which pass through the frame 31. The carriage is spring biased at 37 with respect to the frame 31 so that sufficient pressure is applied to the roll 34 to do the flattening. The height of the roll 34 and, thereby, the distance between flattened rolls 32 and 34 is adjusted by means of nuts 38 which may be tightened or loosened about the threaded shafts 36. As with the other flattening roll 32, this flattening roll 34 has a shaft 39 extending out from the frame 31 which is connected to a suitable gear drive mechanism (not shown). The hole 40 in the frame 31 through which this shaft 39 passes is elongated to provide for travel of the roll 34.

The edge guides 42 in the apparatus of FIG. 7 comprises

rolls

42 and 43. The edge guide roll 42 is rotatably mounted to the frame 31. The roll 43 is held within a movable carriage 44 which moves within a hole in the frame 31. The carriage 44 has flanges 45 with holes which pass about threaded shafts 46 mounted to the frame 31. Spring biasing 47 and nuts 48 are used to provide adjustment of the distance between the edge guide rolls 42 and 43.

In using the apparatus 30 of FIG. 7, the distance between the edge guides 42 and 43 is adjusted to substantially equal the width of the starting metal strip-type tubing 1. The distance between the flattened rolls 32 and 34 is adjusted to give the desired amount of flattening. Then the strip 1 of the type shown in FIG. 2 is fed into the apparatus. The emerging strip 1' from the apparatus 30 is of the type shown in FIG. 3.

The apparatus 30 shown in FIG. 7 is but one configuration that may be used. The specific design of the mill itself, other than the roll configuration and means for restraining the strip edges 12 is conventional and forms no part of the invention herein. The way in which the rolls 32 and 34 are mounted and the adjustments provided for them may be done in any conventional manner and FIG. 7 is merely illustrative of one apparatus which could be used.

Thus far, the edge guides 42 and 43 have been described in the form of rolls. It is also possible to use edge guides as shown in FIG. 8. This edge guide 50 is not rotatable but rather the strip 1 engages it by sliding within the slot 51. The body 52 of the guide is shaped similar to the edge guide carriage 44 in FIG. 7. The operative surface of the guide contains a slot 51 which engages the edge 12 of the strip 1. A similar type of edge guide 50 could be used in place of the edge guide roll 42 on the other side of the apparatus 30.

In the apparatus of FIG. 7, the flattening rolls 32 and 34 were of a simple cylindrical shape and, therefore, edge guides 42 and 43 were required as aforenoted to restrain the strip 1 edges to maintain adequate tube heights. Other roll shapes could be used which would eliminate the need for edge guides. i

In FIG. 9A, there is shown a roll configuration wherein the upper flattening roll has deep flanges6l between which the metal strip-type tubing 1' rides. These flanges 61 act in the same manner as the edge guides 42 and 43 in the apparatus of FIG. 7. The bottom flattening roll 62 has a width which is adapted to fit between the flanges 61 of the upper flattening roll 60. In operation, the flanges 61 of the upperflattening roll 60 restrain the edges of the metal strip-type tubing 1 while the hub surface 63 of the upper flattening roll 60 coacts with the surface 64 of the lower flattening roll 62 to provide the flattening action.

In FIG. 9B, a still more preferred embodiment is shown. In this embodiment, both flattening rolls are identical and each has flange portions 71. Opposing flange portions 71 clamp the edge of the sheet metal strip-type tubing 1' as it is being flattened between the hub portions 72. The engagement. between the flanged portions 71 of the flattening rolls 70 and the edges of the strip-type tubing 1 provides the restraining action required in accordance with this invention. However, because only the outer edges of the strip-type tubing 1 are clamped, there tends to be a greater squaring up of the outer tubes 73 as compared to the inner ones 74. To overcome this effect, the rolls of FIG. 9C were designed.

In the configuration of FIG. 9C, both rolls are identical and each roll has flange portions 81 which clampingly engage each of the welded portions 82 of the composite metal strip-type tubing 1. In this manner, each of the tubular passageways is squared up substantially the same amount.

The alternative embodiments for the roll configuration shown in FIGS. 9A to 9C could be made in one piece as is common in the art, or they could be assembled from a plurality of pieces in a manner similar to the assembly in slitting knives used in the slitting art. In accordance with this aspect of the invention, the flattening rolls are assembled from a plurality of disks on a shaft 91 having a key way 92 as shown in FIG. 10. Each disk 90 as shown in FIG. 11 is cylindrical in nature and has a hole 93 of a diameter adapted to fit about the shaft 91. Each disk 90 further has a key-type protrusion 94 extending into the hole and adapted to engage the key way 92 of the shaft 91.

As shown in FIG. 10, taking the configuration of FIG. 98 as an example, the flange portions 71 could comprise disks 90 of a different diameter than the hub portion 72. The width W of the hub portion 72 could be varied by increasing or decreasing; the number of disks 90 present in it. One could obtain the configuration of FIG. 9C to merely inserting further disks 90 of larger diameter at the appropriate positions alongthe hub portions 72. This approach of using cylindrical disks 90 to form the desired roll configuration is preferred because of the flexibility it gives in. changing from one width of strip 1 to another and from one diameter tubing to another, and in changing between strip having different numbers of passageways.

In the embodiment discussed thus far, the flattening of the metal strip-type tubing was obtained by means of roll deforming. However, the flats could be obtained by other methods of deforming the surface as, for example, by compressing the strip in a press or by swaging the strip or hammering the flats. The essential element, however, is that some means must be included in any apparatus for restraining the edges of the strip so that the strip width cannot increase as the tubular surfaces are flattened. The embodiments discussed employing roll deforming, however, are the most preferred and economical approach toward carrying out the instant invention.

Sheet metal strip-type tubing shown in FIG. 2 is preferred as the starting material of this invention. The invention, however, is broadly applicable to any type tubing including extruded type tubing having a shape similar to that of the tubing of FIG. 2.

The tubing is generally formed of steel, copper, copper alloys and, preferably, aluminum and aluminum alloys.

It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are suitable of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within the spirit and scope as defined by the claims.

What is claimed is: l. A process of reshaping passageways in a metal strip-type tubing adapted to be used in a heat exchanger comprising:

providing a metal strip-type tubing having at least one previously inflated tubular passageway;

flattening a first surface and an opposing surface of said at least one tubular passageway, and simultaneously restraining the edges of said metal striptype tubing to prevent the tubing from increasing in width whereby the shape of the passageway is modified but the length of the tubing is substantially unchanged.

2. A process as in claim 1 wherein said strip-type tubing has a plurality of tubular passageways.

3. A process as in claim 2 wherein said strip-type tubing is formed of at least two strips of metal pressure welded together in parts.

4. A process as in claim 3 wherein said flattening is performed by deforming said strip between a pair of spaced apart rolls.

5. A process as in claim 2 wherein the strip-type tubing has a thickness between passageways which is substantially twice the thickness of the passageway walls. =I =l

Claims

1. A process of reshaping passageways in a metal strip-type tubing adapted to be used in a heat exchanger comprising: providing a metal strip-type tubing having at least one previously inflated tubular passageway; flattening a first surface and an opposing surface of said at least one tubular passageway, and simultaneously restraining the edges of said metal strip-type tubing to prevent the tubing from iNcreasing in width whereby the shape of the passageway is modified but the length of the tubing is substantially unchanged.

5. A process as in claim 2 wherein the strip-type tubing has a thickness between passageways which is substantially twice the thickness of the passageway walls.