GB2486671A

GB2486671A - A Heat Exchanger, a Tube for a Heat Exchanger, a Method of making a tube for a Heat Exchanger and a Method of Making a Heat Exchanger

Info

Publication number: GB2486671A
Application number: GB1021667.9A
Authority: GB
Inventors: Mario Ciaffarafa
Original assignee: Denso Marston Ltd
Current assignee: Denso Marston Ltd
Priority date: 2010-12-22
Filing date: 2010-12-22
Publication date: 2012-06-27
Also published as: GB201117938D0; GB2486788A; GB201021667D0; GB201121595D0; GB2486788B

Abstract

A tube 10 for a tube-and-fin brazed heat exchanger is made from a metal strip bent around to form the tube. The tube 10 includes at least one fold 40 or seam 26 which defines a longitudinal channel 24 in the surface of the tube 10, the or each channel 24 being welded so that it is filled at the end portions of the tube 10 by weld material 28, the middle part of the or each channel 24 being unfilled.

Description

A Heat Exchanger, a Tube for a Heat Exchanger, a Method of Making a Tube for a Heat Exchanger and a Method of Making a Heat Exchanger The invention relates to a heat exchanger, a tube for a heat exchanger, a method of making a tube for a heat exchanger and a method of making a heat exchanger, Brazed tube-and-fin type heat exchangers are commonly used as automotive radiators, but may also be used for automotive charge air coolers or exhaust gas recirculation coolers. Such heat exchangers include a plurality of flattened tubes, the ends of the tubes being received in header plates. As heat exchangers have become deeper to increase capacity, the flattened tubes of the heat exchangers have also become deeper, but this reduces their strength. In order to strengthen the tube, it is known to use a tube which is in a B shape, having a central support across the tube dividing the tube into two chambers. A known B tube is shown in Fig. 1. The tube 10 is made of a bent, flat strip of, for example, aluminium, copper or stainless steel material. The outer parts 12 of the flat strip are folded inwards over a central portion 16, and the free edges of the strip are folded at 90° to form supporting legs 14, the ends 18 of which contact the central portion 16. The legs 14 thus form a support across the width of the tube 10, and divide the tube into two chambers 20, 22.

When such folded tubes 10 are inserted into a flat sided slot in a header plate, a small gap 24 will remain at the location of the tube seam 26 due to the radius r between each leg 14 and folded part 12.

This is not such a problem where the gap is small, as during brazing of the heat exchanger to connect the tube and header plate, the brazing filler material on the external surface of the tube will enter the gap in a sufficient amount to seal it. As manufacturers seek to continually increase the durability and pressure resistance of automotive heat exchangers in general, the materials from which they are constructed need to be made ever thicker. Increasing the material gauge of the tube increases the bend radius at the seam and hence enlarges the gap to be filled where it meets the header plate, which in turn increases the likelihood of leaks forming in the heat exchanger.

This problem is more acute in vacuum brazing than in controlled atmosphere brazing (CAB). In CAB the flux applied prior to brazing is able to fill larger gaps than can be filled in fluxless vacuum brazing.

US7,665,512 (Modine) and US6,230,533 (Valeo) seek to address this problem by the manufacturing step of reducing the bend radius r on legs 14. This has the disadvantage of creating a sharp internal bend which acts as a stress raiser during normal operation of the heat exchanger creating a potential failure point. Increased erosion during brazing may further weaken the tube in this area.

FR2780 153 discloses a construction in which small protrusions are added to the header plate slots to fit into the tube seams during assembly of the heat exchanger 4 to thereby block the leak path. However, if the tubes are not precisely aligned during insertion into the header plate, then these pointed projections will score or damage the tubes.

According to one aspect of the invention there is provided a tube for a heat exchanger, the tube being made from a metal strip bent around to form the tube, the tube including at least one fold or seam which defines a longitudinal channel in the surface of the tube, the or each channel being filled at the end portions of the tube, at least part of the middle part of the or each channel being unfilled.

In this way, no gap is created between the tube and header plate at the position of the seam or fold and so there will not be a leak path. By only filling specific portions of the tube, a seal is guaranteed where it is needed without the waste associated with filling the full length of the tube. The invention permits thicker gauges of material to be used to form the tubes without increasing leak rates. This also permits the use of folded tubes in charge air coolers which typically use thicker materials than automotive radiators.

The or each channel may be filled in any suitable way and may be filled with S material by welding. Depending on the welding technique used, the welding material filling the or each channel may be foreign material introduced to the welding site or may be native material which has melted and flowed to fill the or each channel.

The middle part of the or each channel may be welded in spots or sections, but in a preferred embodiment the middle section is entirely unfilled.

The tube may define a plurality of longitudinal channels in the surface of the tube, each channel being filled at end portions of the tube, at least part of the middle part of the channel being unfilled. The tube may define at least one fold and at least one seam defining such longitudinal channels.

Each filled portion may comprise a length of channel of up to about 100 mm, preferably at least 25 mm, preferably up to 60 mm.

According to another aspect of the invention there is provided a heat exchanger, the heat exchanger including header plates and tubes in slots in the header plates, each tube being a tube according to the first aspect of the invention, each end portion of each tube being received in a slot in a header plate.

According to a further aspect of the invention there is provided a heat exchanger, the heat exchanger including tubes received in slots in header plates, each tube being made from a metal strip bent around to form the tube, the tube including at least one fold or seam which defines a longitudinal channel in the surface of the tube, the or each channel being filled at the portions of the tube which are received in a slot in a header plate, at least part of the middle part of the or each channel being unfilled.

According to another aspect of the invention there is provided a method of making a tube for a heat exchanger, the method comprising the steps of: bending a metal strip to form a tube, the tube including at least one fold or seam which defines a longitudinal channel in the surface of the tube, and filling the or each channel at the end portions of the tube, at least part of the middle part of the channel being unfilled.

The step of filling the channel may comprise welding the channel to fill the channel with welding material. Depending on the welding technique used, the welding material filling the or each channel may be foreign material introduced to the welding site or may be native material which has melted and flowed to fill the or each channel. The welding may be performed by any suitable known method, but preferably comprises high frequency welding or laser welding.

The method may include a finishing step in which the filled area is made flat.

In a preferred embodiment, the strip comprises tube stock sufficient to make a plurality of tubes, the or each fold or seam in the tube stock is filled at regular intervals, and the tube stock is cut into tubes by cutting through the tube stock at the filled portions to create a plurality of tubes which have filled end portions. This is an efficient manufacturing process. Preferably, the tube stock is cut substantially centrally of the filled portions.

According to a further aspect of the invention there is provided a method of making a heat exchanger comprising making tubes according to the method of the preceding aspect of the invention, assembling the tubes with header plates so that each end portion of each tube is received in a slot in a header plate, and brazing the assembly.

According to another aspect of the invention there is provided a method of making a heat exchanger comprising assembling a plurality of tubes according to the first aspect of the invention with header plates so that each end portion of each tube is received in a slot in a header plate, and brazing the assembly.

The heat exchanger may be brazed by controlled atmosphere brazing, and in the example of brazing an Al-Si tube and fin heat exchanger, a potassium fluoroaluminate based flux may be used such as Nocolok (trade mark) flux, but preferably the heat exchanger is brazed by vacuum brazing. This allows the use of high strength alloys, such as alloys with magnesium, as there is no flux, so no possibility of reaction with the flux, as there would be with CAB. Vacuum brazing can also allow the use of thin material.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is an end view of a known B profile tube; Fig. 2a is an end view of a tube in a first embodiment of the invention; Fig 2b is a perspective view of the tube of Fig. 2a; Fig 2c is a plan view of the tube of Fig 2a in a header plate; and, Fig 3 is an end view of a tube in a second embodiment of the invention.

Fig. 2a shows a tube 10 which is the same as the known tube of Fig. 1 except that the channel 24 formed at the seam 26 between the legs 14 has been welded so that the channel 24 has been filled with welding material 28. As shown in Fig. 2b, the weld material 28 is only included at the end portions 30, 32 of the tube 10. The middle portion 34 is not welded and so the channel 24 is unfilled in this region. As shown in Fig 2c, when the end of the tube 10 is inserted into a slot 36 in a header plate 38 of a heat exchanger, the end portion 30 lies in the slot 36 and there is no gap between the tube 10 and the header plate 38 at the seam 26, so the construction will be leak tight once brazed. The assembled tubes 10 and header plates 38 are preferably vacuum brazed.

To manufacture the tube 10 of the embodiment, tube stock in the form of a continuous flat strip of metal is passed through a succession of rollers to form the folded tube shape: the B shape. In this embodiment, the strip is aluminium with brazing filler material on one surface, which will be the outer surface of the tube once shaped. After the continuous tube is shaped, but before it is cut into individual tubes, an intermittent weld is made along the seam 26 of the folded joint by high frequency welding. The individual welds are 50 mm long. Thus the material of the tube stock is locally melted to flow and fill the channel 24. The tube stock will then be cut centrally of the welded regions to form tubes 10 as shown in Figs. 2a and 2b. The welded regions may be finished to make them flat, for example by abrasion.

Fig 3 shows a tube in a second embodiment. Only the differences from the first embodiment will be described. The same reference numerals will be used for equivalent features.

In the tube 10 of the second embodiment, the central portion 16 includes an inwards fold 40 over the full width of the tube 10. The legs 14 instead of being next to and brazing to one another, lie one to either side of the fold 40 and braze to the sides of the fold 40. This means that the support across the tube 10 is very strong as it consists of four thicknesses of the metal sheet. As seen in Fig 3, however, this means there are three gaps 42, 44, 46 which could form a leak path, namely gaps 42, 44 between the fold 40 and each leg 14 on one side of the tube 10, and a gap 46 at the central portion 16 where it is folded inwards. The gaps 42, 44, 46 are filled with weld material by laser welding. The welded end portions 30, 32 in this embodiment are 30mm long.

Two designs of B tube have been described in the embodiments but it will be apparent to the person skilled in the art that the invention is applicable to a wide variety of such tubes incorporating seams and/or folds.

Although vacuum brazing has been described, the invention is equally applicable to controlled atmosphere brazing with flux.

Although high frequency welding and laser welding have been described, other welding techniques could be used including friction stir welding, TIG welding and MIG welding.

Claims

Ctaims 1. A tube for a heat exchanger, the tube being made from a metal strip bent around to form the tube, the tube including at least one fold or seam which defines a longitudinal channel in the surface of the tube, the or each channel being filled at the end portions of the tube, at least part of the middle part of the or each channel being unfilled.
2. A tube as claimed in claim 1, wherein the or each channel is filled with material by welding.
3. A tube as claimed in claim 1 or claim 2, where in the middle part of the or each channel is entirely unfilled.
4. A tube as claimed in any preceding claim, wherein the tube defines a plurality of longitudinal channels in the surface of the tube, each channel being filled at end portions of the tube, at least part of the middle part of the channel being unfilled.
5. A tube as claimed in claim 4, wherein the tube defines at least one fold and at least one seam defining the said longitudinal channels.
6. A tube as claimed in any preceding claim, wherein each filled portion comprises a length of channel of up to about 100 mm.
7. A tube as claimed in any preceding claim, wherein each filled portion comprises a length of channel of at least 25 mm.
8. A tube as claimed in any preceding claim, wherein each filled portion comprises a length of channel of up to 60 mm.
9. A tube for a heat exchanger, the tube being substantially as described herein with reference to Figures 2a, 2b and 2c or Fig 3 of the accompanying drawings.
10. A heat exchanger, the heat exchanger including header plates and tubes in slots in the header plates, each tube being a tube according to any preceding claim, each end portion of each tube being received in a slot in a header plate.
11. A heat exchanger, the heat exchanger including tubes received in slots in header plates, each tube being made from a metal strip bent around to form the tube, the tube including at least one fold or seam which defines a longitudinal channel in the surface of the tube, the or each channel being filled at the portions of the tube which are received in a slot in a header plate, at least part of the middle part of the or each channel being unfilled.
12. A heat exchanger substantially as described herein with reference to Figures 2a, 2b and 2c or Fig 3 of the accompanying drawings.
13. A method of making a tube for a heat exchanger, the method comprising the steps of: bending a metal strip to form a tube, the tube including at least one fold or seam which defines a longitudinal channel in the surface of the tube, and filling the or each channel at the end portions of the tube, at least part of the middle part of the channel being unfilled.
14 A method as claimed in claim 13, wherein the step of filling the channel comprises welding the channel to fill the channel with welding material.
15. A method as claimed in claim 14, wherein the welding is performed by high frequency welding or laser welding.
16. A method as claimed in any of claims 13 to 15, wherein the method includes a finishing step in which each filled area is made flat.
17. A method as claimed in any of claims 13 to 16, wherein the strip comprises tube stock sufficient to make a plurality of tubes, the or each fold or seam in the tube stock is filled at regular intervals, and the tube stock is cut into tubes by cutting through the tube stock at the filled portions to create a plurality of tubes which have filled end portions.
18. A method as claimed in claim 17, wherein the tube stock is cut substantially centrally of the filled portions.
19. A method of making a heat exchanger comprising making tubes according to the method of any of claims 13 to 18, assembling the tubes with header plates so that each end portion of each tube is received in a slot in a header plate, and brazing the assembly.
20. A method of making a heat exchanger comprising assembling a plurality of tubes as claimed in any of claims 1 to 9 with header plates so that each end portion of each tube is received in a slot in a header plate, and brazing the assembly.
21. A method as claimed in 19 or claim 20, wherein the heat exchanger is brazed by vacuum brazing.
22. A method of making a tube for a heat exchanger substantially as described herein with reference to Figures 2a, 2b and 2c or Fig 3 of the accompanying drawings.
23. A method of making a heat exchanger substantially as described herein with reference to Figures 2a, 2b and 2c or Fig 3 of the accompanying drawings.