GB2134430A - Method of securing and/or sealing an element relative to a support - Google Patents

Abstract

A hollow element 10 (such as a tube) is secured and/or sealed relative to a support 12 (such as a tubeplate of a heat exchanger) by first forming in the support 12 an aperture (11) having at least one channel 15 between its side wall and the element 10. After insertion into the aperture (11), the element 10 is expanded to bring its external surface 13 into close contact with the aperture side wall, except where the channels 15 are provided. A flowable securant/sealant is then applied to a side surface 12a of the support 12 onto which the channels 15 open, and is caused to flow into the channels 15 at least partly by capillary action. <IMAGE>

Description

SPECIFICATION Method of securing and/or sealing an element relative to a support This invention relates to a method of securing and/or sealing an element relative to a support, particularly (though not exclusively) for securing and/or sealing tubes to tubeplates in the manufacture of heat transfer apparatus.

In the production of heat exchangers, it is the customary practice to secure a tube to a tubeplate by initially forming in the plate an aperture which is substantially the same shape as, although slightly larger than, the external cross-section of the tube.

The tube is then inserted through the aperture and is expanded to bring its external surface into close contact with the aperture side wall, thereby removing excessive clearances. Finally, the tube is secured and/or sealed in the aperture by means of a material such as solder, brazing alloy or adhesive.

For tubes having a relatively small external diameter (usually less than 10.0mm), expansion is normally performed using suitable drifts or punches, the action of which not only removes excessive clearances but also anchors the tube within the aperture, thereby preventing the tube from becoming misplaced during the subsequent sealing operation. A particularly advantageous manner of utilising this technique is disclosed in UK Patent publication No. 2072554A. For larger diameter tubes, it is usual to achieve expansion by means of well-known roller expanders, the action of which is on many occasions sufficient to secure the tube sealingly within the aperture. Nevertheless, situations can arise where it is still desirable to enhance the sealing effect by soldering, brazing or adhesive.

The aforesaid material can be applied to either or both sides of the tubeplate, depending mainly upon accessibiiity. The resultant joint would be expected to exhibit a fillet of the material between the tube and the surface of the tubeplate, and to penetrate to a greater or lesser degree the interface between the tube exterior and the aperture side wall. The degree to which such penetration can be achieved depends upon many factor, such as the wetability of the tube and tubeplate material by the securing/sealing material, the action of any fluxes or primers used, the capillary attraction properties of the securing/sealing material, and the clearances (if any) remaining after expansion of the tube.

In the main, such joints are reasonably reliable but are found to be prone to premature failure if subjected to arduous operating conditions, especially prolonged cyclic high temperatures and/or pressures. Generally, the cause of such failure can be attributed to a lack of desirable penetration of the securing/sealing material within the joint, with the result that the loads are imposed on the fillet joint only, which is known to be of low strength. Improved penetration could in principle be obtained by, for example, pre-coating the tube or the aperture side wall with the securing/sealing material prior to insertion of the tube into the aperture, or by carefully controlling expansion of the tube such that a gap is left between the tube exterior and the aperture side wall which is of the correct size to draw in the subsequently applied material by capillary action.

However, these possibilities are often not practically or economically desirable.

It is an object of the present invention to provide a method by which penetration of the securing/sealing material can be achieved both practically and econo mically.

According to one aspect of the present invention, a method of securing and/or sealing an element relative to a support comprises the steps of: (a) forming in the support an aperture whose shape generally conforms to the external crosssectional shape of said element; (b) inserting said element through the aperture; (c) providing between the external surface of said element and a side wall of the aperture at least one channel of which opens onto a side surface of the support; (d) providing on said side surface of the support a flowable material capable of securing and/or sealing the element relative to the support; and (e) causing said material to flow into said at least one channel at least partly by capillary action.

Advantageously, said element is hollow (e.g.

tubular) and, prior to step (e), is expanded at least in the vicinity of the aperture to bring its external surface into close contact with the aperture side wall except where said at least one channel is provided: this will achieve initial mechanical securement of the element to the support, and will also maintain a dimensional control on the depth of said at least one channel. Alternatively, however, initial mechanical securement can be achieved by other fixing or locating devices, in which case it is possible to dispense with such expansion of the tubular element.

Preferably, said at least one channel is formed in the side wall of the aperture. However, in certain circumstances it may be cheaper and more convenient to provide said at least one channel in the external surface of said element, in which case the channel or channels can be formed by local embossment or impressment of said element.

Where said material is initially in a readily flowable form (which will be the case for solder and brazing alloy, for example), the dimensions of said at least one channel are chosen so that the material can penetrate the latter wholly by capillary action.

However, where the capillary attraction properties of the material are poor (e.g. in the case of an adhesive), the dimensions of said at least one channel can be enlarged accordingly to achieve the desired penetration.

The or each channel may extend axially of the aperture, or may be of any other convenient configuration, for example helical, spiral, sinuous or otherwise curved or cranked. Where more than one such channel is provided, these may be interconnected or crossed as desired.

Advantageously, a plurality of channels are provided in spaced relation around the aperture, these channels preferably being equi-angularly spaced about the major axis of the aperture. The or each channel may be of substantially constant depth across its width: alternatively, the or each channel can be of non-constant depth, and for example may be of generally triangular or part-circular crosssection. In either case, the corners of the or each channel in its cross-section transverse to the major axis of the aperture are preferably radiussed.

In one particular arrangement, the aperture and the external cross-section of the element are both generally circular in shape. In a different arrangement, the aperture is defined by a circle of radius R, and the channels are formed in the side wall of the aperture and are defined by the corners of a regular polygon whose apex-to-centre dimension is D1 and whose side-to-centre dimension is D2, wherein: D2 P < Di.

The aperture can be produced by a drilling or punching operation, while said at least one channel (when formed in the side wall of the aperture) can subsequently be formed by broaching. Where the aperture is produced by punching, the broach for forming said at least one channel can be provided on the punching tool behind the punch proper, in which case both of the punching and broaching operations are performed in a single pass of the tool. Where the aperture is produced by drilling, the broach can be provided on the drill, in which case rotation of the drill is arrested after the aperture has been produced and the drill is then advanced through the aperture to broach said at least one channel.

In an alternative arrangement, the support has an integral hollow spigot which surrounds the aperture, and said at least one channel extends along the internal surface of the spigot. In this case, the aperture can be produced byfirstforming an undersize opening in the support by a piercing operation, the opening subsequently being enlarged and the spigot and said at least one channel being produced by a single plunge-forming operation.

According to a second aspect of the present invention, a method of producing heat transfer apparatus comprises the steps of: (a) providing at least one tube and at least one tubeplate through which the or each tube is to be passed; (b) forming in the or each tubeplate an aperture for the or each tube, which aperture has a shape generally conforming to the external cross-section of said tube; (c) inserting the or each tube through the respective aperture in the or each tubeplate; (d) providing at least one channel between the external surface of the or each tube and a side wall of the aperture in the or each tubeplate through which the tube passes, said at least one channel opening onto a side surface of the or each said tubeplate;; (e) providing on said side surface of the or each said tubeplate a flowable material capable of securing and/or sealing the or each tube relative to said tubeplate; and (f) causing said material to flow into said at least one channel at least partly by capillary action.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure lisa longitudinal sectional view of part of a heat exchanger; Figure 2 is a section taken along the line ll-ll in Figure 1, illustrating a stage in the manufacture of the heat exchanger by one embodiment of a method according to the invention; Figure 3 is a similar view to Figure 2 on an enlarged scale, illustrating another stage in the manufacture of the heat exchanger; Figure 4 is a longitudinal sectional view of part of the heat exchanger, illustrating a still further stage in the manufacturing process; Figure 5is a similar view to Figure 2, but illustrating a second embodiment of the invention; Figure 6 is a similar view of Figure 3, again illustrating the second embodiment;; Figure 7 is a section through a tubeplate of a modified heat exchanger; and Figure 8 is a sectional view of part of the modified heat exchanger, illustrating a third embodiment of the invention.

In the ensuing description, the invention will be described with reference to the securement of a tube to a tubeplate in a heat exchanger. However, it is to be appreciated that the invention has a much broader applicability than this, and in particular can be employed to secure any suitable element to any suitable support.

In Figure 1, there is shown part of a heat exchangerwherein a tube 10 (through which a fluid is passed in use) extends through an aperture 11 in a support 12: in the illustrated arrangement, the support takes the form of a tubeplate, although it may equally well be a baffle and the ensuing description is to be read accordingly. Figure 2 shows the tube 10 prior to securementto the tubeplate 12.

The manner in which the joint between these two parts is formed will now be explained.

The tube 10 illustrated in Figure 2 has an external surface 13 which is circular in cross-section. The aperture 11 in the tubeplate 12 is also circular, but is of slightly larger diameter than the tube surface 13.

Formed in a side wall 14 of the aperture 11 are a series of channels 15 which are equi-angularly spaced around the major axis (referenced 16) of the aperture. In the illustrated embodiment, eight such channels are provided, this being the preferred number where the aperture 11 is between, say, 6.0 mm and 10.0 mm in diameter. For smaller apertures the number of channels may be reduced, while a greater number of channels may be provided for larger apertures. Each of the channels 15 extends parallel to the axis 16 and opens at its ends onto the surfaces of the tubeplate 12, respectively.

One of the channels 15 is shown in detail in Figure 3, it being understood that the remaining channels are identical to this. Each channel has a width was measured circumferentially of the aperture 11, the sum of the widths of all the channels preferably being approximately half the total circumference of the aperture, though this may be varied if desired.

Each channel has a base surface 17 which lies on an imaginary surface of circular cross-section centred on the axis 16 and larger in diameter than the aperture side wall, so that the channel is of constant depth across its width. Corners of the channel in cross-section are radiussed as indicated at 18 and 19: these radii are preferably both equal to 1/2d, although one may be larger and the other may be smaller than this.

During manufacture of the heat exchanger, the tube 10 is inserted through the aperture 11 after the latter has been formed in the tubeplate 12 (see Figure 2). If appropriate, the tube 10 is then expanded at least in the vicinity of the aperture 11 to bring its external surface 13 into close engagement with the aperture side wall 14 except where the channels 15 are provided, as indicated in Figure 3.

Gaps thus remain between the expanded tube and the tubeplate 12 in the locations of the channels. As illustrated in Figure 4, a material S is capable of securing and/or sealing the tube 10 relative to the tubeplate 12 is then applied by any convenient means as a fillet F to the juncture between the tube exterior and one side surface 12a of the tubeplate.

(As an alternative, such fillets of the material can alternatively be applied to both side surfaces of the tubeplate). As will be explained later, the dimensions of the aforementioned gaps remaining between the tube and the tubeplate will normally be such as to cause the materials to be drawn from the fillet F into the channels 15 by capillary action. In this way, proper penetration of the materials into the aperture is ensured, resulting in a much stronger joint than has previously been possible at an economic level.

Any suitable material can be employed for this purpose: however, if solder or brazing alloy is used, then it is found that a high degree of penetration is also achieved between the external surface 13 of the tube and those parts of the aperture side wall 14 where the channels 15 are not provided, thereby further improving the robustness of the joint.

The above-described capillary effect is achieved as follows. Suppose that the tube 10 in its unexpanded state has a wall thickness oft, and that each channel 15 has a depth d. After expansion, the tube wall thins slightly where it comes into contact with the aperture side wall 14, so that its thickness is reduced tot'.

However, no such thinning occurs where the channels 15 are provided, and therefore in these locations the tube retains its initial wall thickness t. This means that the effective depth of each channel 15 will be reduced to d'. The expansion operation is controlled so that the dimension d' is within an optimum range for achieving capillary attraction of the aforesaid material, having regard to the nature of the material itself and the material from which the tube and the tubeplate are made.

Where the material chosen has a poor capillary attraction (as in the case for certain adhesives), the depth dofeach channel can be increased to allow the material to flow naturally into the channels.

As indicated above, fillets may be applied to one or both side surfaces of the tubeplate 12. Where such application takes place on both surfaces, the material will of course advance down each channel 15 from both ends of the latter. However, there is a possibility that air may become trapped in the channel 15 between the two volumes of advancing material, thereby preventing these volumes for coalescing so that the material is not present for the full length of the channel. In order to prevent this from happening, therefore, it is preferred that a fillet of material is applied to only one surface of the tubeplate.

Because the corners 19 of the channels 15 are radiussed, a smooth transition is provided between the base 17 of each channel and the aperture side wall 14; consequently, a smooth transition is also obtained between the dimensions tand t, of the expanded tube 10. Therefore, stress concentrations in these areas are minimised.

A second embodiment of the invention is shown in Figures 5 and 6, wherein the channels 15 are of generally triangular cross-section rather than being of constant depth across their widths. More particularly, each aperture 11 in each tubeplate 12 is defined by a circle of radius R, and the channels are defined respectively by the corners of a regular polygon which is concentric with the aperture. In the illustrated example six channels are provided, being defined by the corners of a regular hexagon. The apex-to-centre dimension D1 and the like side-tocentre dimension D2 of the polygon are chosen such that: D2 S R < D1 In the case where R = D2, it will be manifest that the sum of the widths of all the channels 15 will be substantially equal to the total circumferential length of the tube exterior 13.This can advantageously be employed to obtain even better distribution and penetration of the sealant.

By suitably selecting the dimensions of the polygon and/or adjusting the number of its sides, the maximum depth d2 (see Figure 6) of each triangular channel 15 is preferably arranged to correspond to the dimension din the previous embodiment. Alternatively, the cross-sectional area of each channel can be arranged substantially to match that of each channel in Figures 2 and 3.

For the purpose of reducing stress concentrations, corners 20, 21 and 22 of each channel are preferably radiussed. In practice, however, it is found that such radiussing is normally required only at the corners 22 which correspond to the apices of the aforementioned polygon.

Although in the last embodiment the channels have been described as being generally triangular in cross-section, it is to be appreciated that they may be of other configurations giving a non-constant depth across their widths, e.g. semi-circular.

In both of the above-described embodiments, each circular aperture 11 is produced by punching or drilling, and the channels 15 are subsequently formed by broaching. These two operations may be performed using separate tools for each, with the broaching tool having a part which initially engages in and is accurately held by the previously formed circular aperture. Alternatively, the two operations may be performed by a single tool. More particularly, where the aperture is produced by punching, the broaches for forming the channels can form part of the punching tool, being located behind the punch proper. On the other hand, where the aperture is produced by drilling, the broaches can be provided on the drill, with the latter being rotationally arrested after drilling the aperture and then being advanced to broach the channels.

Athird embodiment of the invention is shown in Figures 7 and 8. In this embodiment (which is applicable to relatively thin tubeplates), each aperture 11 is formed by a piercing and plunging operation: i.e., an undersize hole is first pierced in the tubeplate 12, this hole subsequently being enlarged to the required size by a plunging operation. Such plunging produces a tubular spigot 23 which surrounds the aperture 11 and which projects from the tubeplate proper, as can be seen to advantage in Figure 7. By suitably shaping the plunging tool, channels 24 (corresponding to the channels 15 in the previous embodiments) can be formed extending for the full axial length of the internal surface of the spigot 23.Whereas in the previous embodiments it is necessary after the aperture 11 has been formed to remove material from the tubeplate 12 in order to produce the channels 15, the channels 23 in Figures 7 and 8 do not require the removal of further material for their formation.

In the above description, the apertures 11 in the tubeplates 12 and the tubes 10 have been described as being of circular cross-section. It will however be appreciated that the invention is equally applicable to apertures and tubes of other shapes. Also, the channels 15 and 23 have been described as extending axially of the apertures 11. In an alternative arrangement, the channels can be given a helical configuration, particularly where the thickness of the tubeplate 12 approaches or exceeds the diameter of the tube 10, in order that an increased amount of material can be incorporated into the joint. A similar effect can be achieved by making the channels of other curved or cranked shape, and if desired these channels may intersect or cross one another.

As has been explained above, the provision of the channels 15 or 23 ensures that gaps are left between the tube exterior and the tubeplate after expansion so that proper penetration of the securing/sealing material into the joint can be obtained, thereby increasing the strength of the joint. The provision of the channels also gives rise to the advantages that the tube expansion operation does not require such critical control as has previously been necessary, the dimensional tolerances on the external diameter and wall thickness of the tubes can be relaxed, and the effects of over-expanding the tube can be better tolerated since any excess tube material will be accommodated within the channels.

It is to be noted that, although the tube 10 has been described as being expanded to achieve initial mechanicalsecurementtothetubeplate 12, such initial securement can be achieved by other means (such as suitable fixing devices), in which case it is possible to dispense with expansion of the tube.

Furthermore, in all of the above embodiments, the channels have been described as being provided in the side wall of the aperture 11. In cases where the tube 10 has a sufficiently large wall thickness, it is possible alternatively to provide the channels in the external surface of the tube, for example by local embossment or impressment.

Claims (23)

1. A method of securing and/or sealing an element relative to a support, comprising the steps of: (a) forming in the support an aperture whose shape generally conforms to the external crosssectional shape of said element; (b) inserting said element th rough the aperture; (c) providing between the external surface of said element and a side wall of the aperture at least one channel of which opens onto a side surface of the support; (d) providing on said side surface of the support a flowable material capable of securing and/or sealing the element relative to the support; and (e) causing said material to flow into said at least one channel at least partly by capillary action.

2. A method as claimed in claim 1, wherein said element is hollow and, prior to step (e), is expanded at least in the vicinity of the aperture to bring its external surface into close contact with the aperture side wall except where said at least one channel is provided.

3. A method as claimed in claim 1 or 2, wherein in step (d) the material is applied as a fillet to the juncture between the external surface of said element and said side surface of the support.

4. A method as claimed in claim 1,2 or 3 wherein said at least one channel is formed in the side wall of the aperture.

5. A method as claimed in claim 1,2 or 3, wherein said at least one channel is formed in the external surface of said element.

6. A method as claimed in any preceding claim, wherein the or each channel extends axially of the aperture.

7. A method as claimed in any one of claims 1 to 5, wherein the or each channel is helical, spiral, sinuous or otherwise curved or cranked.

8. A method as claimed in any preceding claim, wherein a plurality of channels are provided in spaced relation around the aperture.

9. A method as claimed in claim 9, wherein the channels are equi-angularly spaced about the major axis of the aperture.

10. A method as claimed in any preceding claim, wherein the or each channel is of substantially constant depth across its width.

11. A method as claimed in any one of claims 1 to 9, wherein the or each channel is of non-constant depth across its width.

12. A method as claimed in claim 11, wherein the or each channel is of generally triangular or partcircular cross-section.

13. A method as claimed in any preceding claim, wherein the corners of the or each channel in its cross-section transverse to the major axis of the aperture are radiussed.

14. A method as claimed in any preceding claim, wherein the aperture and the external cross-section of the element are both generally circular in shape.

15. A method as claimed in claim 1, wherein the aperture is defined by a circle of radius Rand the channels are formed in the side wall of the aperture and are defined by the corners of a regular polygon whose apex-to-centre dimension is D1 and whose side-to-centre dimension is D2, wherein: D2 S R < dl

16. A method as claimed in any preceding claim, wherein the aperture is produced by a drilling or punching operation, and said at least one channel is subsequently formed by broaching in a side wall of the aperture.

17. A method as claimed in claim 16, wherein the aperture is produced by punching, and the broach for forming said at least one channel is provided on the punching tool behind the punch proper, whereby both of the punching and broaching operations are performed in a single pass of the tool.

18. A method as claimed in claim 16, wherein the aperture is produced by drilling, the broach is provided on the drill, and rotation of the drill is arrested after the aperture has been produced and the drill is then advanced through the aperture to broach said at least one channel.

19. A method asvclaimed in any one of claims 1 to 15, wherein the support has an integral hollow spigot which surrounds the aperture, and said at least one channel extends along the internal surface of the spigot.

20. A method as claimed in claim 19, wherein said aperture is produced by first forming an undersize opening in the support by a piercing operation, and by subsequently enlarging the opening and producing said spigot and said at least one channel in a single plunge-forming operation.

21. A method of producing heat transfer apparatus, including the steps of: (a) providing at least one tube and at least one tubeplate through which the or each tube is to be passed; (b) forming in the or each tubeplate an aperture for the or each tube, which aperture has a shape generally conforming to the external cross-section of said tube; (c) inserting the or each tube through the respective aperture in the or each tubeplate; (d) providing at least one channel between the external surface of the or each tube and a side wall of the aperture in the or each tubeplate through which the tube passes, said at least one channel opening onto a side surface of the or each said tubeplate; (e) providing on said side surface of the or each said tubeplate a flowable material capable of securing and/or sealing the or each tube relative to said tubeplate; and (f) causing said material to flow into said at least one channel at least partly by capillary action.

22. A method of securing and/or sealing the element relative to a support, substantially as hereinbefore described with reference to Figures 2, 3 and 4 or Figures 5 and 6 or Figures 7 and 8 of the accompanying drawings.

23. A method of producing heat transfer apparatus, substantially as hereinbefore described with reference to Figures 2, 3 and 4 or Figures 5 and 6 or Figures7 and 8 of the accompanying drawings.