Folded tube for heat exchanger, and heat exchanger including such tubes

Abstract

The invention relates to a tube for a heat exchanger, consisting of a metal strip having an inner face and an outer face, this strip having two extremities which are folded locally towards the inner face of the tube so as to form two borders (28, 30) placed one beside the other. Passages (38) are formed in at least one of the extremities of the metal strip for introduction of a brazing flux. These passages (38) can be formed in the two extremities of the metal strip, and offset with respect to one another. The passages extend over a distance greater than the height of the borders (28, 30) in such a way as to form an inlet (40) for the brazing flux.

Description

BACKGROUND OF THE INVENTION

[0001] The invention relates to a folded tube suitable for forming part of a heat exchanger such as a radiator for cooling a motor-vehicle engine, for example.

[0002] It relates more particularly to a folded tube for a heat exchanger, consisting of a metal strip having an outer face and an inner face, this strip having two extremities folded locally towards the inner face of the tube so as to form two borders placed one beside the other.

[0003] Tubes of this type are already known. After folding, they are assembled with spacers or fins, placed in a furnace and brazed. The brazing alloy is generally added by way of a plating of brazing alloy arranged on the outer face of the metal strip, while the inner face is coated with an anti-corrosion plating.

[0004] In order to achieve high-quality brazing, it is necessary to add a brazing flux which has the function of protecting the metal against oxidation during the brazing. According to the present-day technique, the brazing flux is deposited by immersion coating. This gives rise to the situation that the two faces of the metal strip, both the inner face and the outer face, are coated with brazing flux. After brazing, residues prejudicial to the internal corrosion resistance of the radiator are left behind.

[0005] The precise object of the present invention is a tube for a heat exchanger and a method of manufacturing this tube, embodiments of which may at least partially remedy these drawbacks.

BRIEF SUMMARY OF THE INVENTION

[0006] This can be achieved by the fact that passages are formed in at least one of the extremities of the metal strip for introduction of a brazing flux. By virtue of these passages, the brazing flux can penetrate between the side-by-side borders, which prevents them oxidizing.

[0007] According to a variant embodiment, passages are formed in the two extremities of the metal strip. In this case, the passages at one extremity are advantageously offset with respect to the passages of the other extremity of the metal strip.

[0008] According to one embodiment, the passages are produced by knurling of the extremities of the metal strip. The metal strip is preferably folded by passing through a series of successive rollers, and the knurling is carried out before passing through the forming rollers.

[0009] The passages can be formed substantially perpendicularly to the extremities of the metal strip or obliquely with respect to these extremities.

[0010] The passages preferably extend over a distance greater than the height of the borders in such a way as to form an inlet for the brazing flux.

[0011] The invention also relates to a heat exchanger, especially for a motor vehicle, comprising a bank of tubes alternating with cooling spacers, in which the tubes are in accordance with the invention.

[0012] Finally, the invention relates to a method of manufacturing a tube for a heat exchanger by folding and brazing of a metal strip, this strip including an inner face and an outer face.

[0013] According to the method of the invention, a brazing flux is suitably deposited solely on the outer face of the tube, preferably by spraying.

[0014] Other characteristics and advantages of the present invention will emerge further upon reading the description which follows of an embodiment example given purely illustratively with reference to the attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In these figures:

[0016] FIG. 1 is an overall view of a heat exchanger for which a tube in accordance with the present invention is intended;

[0017] FIG. 2 is a view in cross section of a tube in accordance with the present invention;

[0018] FIGS. 3 and 4 are partial views on an enlarged scale, respectively in cross section and from above, of the tube represented in FIG. 2; and

[0019] FIG. 5 is a partial view, on an enlarged scale, in perspective, of the tube represented in FIGS. 2 to 4.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The heat exchanger represented in FIG. 1 comprises a tube bank 10 mounted between two manifold chambers 12 and 14. The bank 10 consists of a multiplicity of tubes 16 arranged parallel to each other and alternating with spacers 15. These spacers, also called fins, are of the corrugated type. They are formed from metal foil which is folded so as to constitute corrugations. Hence, a spacer 15 arranged between two adjacent tubes 16 comes into contact with two tubes via end regions of the corrugations.

[0021] The heat exchanger further includes two checks 17, also called crosspieces, which frame the tube bank and are arranged parallel to the tubes 16.

[0022] The pieces which constitute the exchanger are held assembled on a table (not represented) and pressure is exerted on the checks 17 in the direction of the arrows F so as to hold the tubes 16, spacers 15 and checks 17 respectively with a view to the brazing operation.

[0023] The tube 16 represented in FIG. 2 is produced from a metal strip, for example of aluminum, folded in several successive operations by virtue of rollers according to a known technique. This is a flat tube which features a substantially rectangular, very much flattened, section comprising two large faces 18 and 20 linked by two semi circular faces 21.

[0024] The large face 18 consists of two parts 24 and 26 which are joined together. The metal strip is folded at right angles to the extremities of the parts 24 and 26 so as to form side-by-side borders 28 and 30 which bear on the large face 20, on the inside of the tube. These borders 28 and 30 have the function, on the one hand, of delimiting separate circulation channels 32 and 34 for a fluid, and, on the other hand, of constituting a distance piece between the two large faces 18 and 20 so as to guarantee that they are parallel and flat.

[0025] In order to allow brazing of the tube, the metal strip is covered externally with a brazing plating (not represented), the inner face being covered with an anti-corrosion plating (not represented). As can be seen, the borders 28 and 30 are placed one beside the other in such a way that the gap which may remain between them is too restricted to allow a brazing flux to be brought in between these borders.

[0026] For this reason, in accordance with the invention, as can can be seen more particularly in FIGS. 3 to 5, passages 38 have been formed in the borders 28 and 30. Although, in the embodiment described, passages 38 had been provided in each of the two borders 28 and 30, it is also possible, according to a variant embodiment, to provide such passages only in one of the two borders.

[0027] In the embodiment example described, the passages 38 are substantially perpendicular to the large faces 18 and 20. This characteristic is not essential, and it would also be possible, in accordance with the invention, to provide passages arranged obliquely with respect to these walls. Likewise, in the embodiment described, the passages are straight-line, but they could also exhibit another shape, for example curved or sinusoidally shaped. As can be seen in FIG. 4, the passages are preferably arranged alternately, one passage 38 of the border 30 being arranged between two passages of the border 28, and vice versa.

[0028] Further preferably, as can be seen in FIG. 3, the length of the passage 38 formed at the extremity of the metal strips is substantially greater than the height of the borders 28 and 30 in such a way as to constitute an inlet 40 which facilitates the introduction of the brazing flux.

[0029] This brazing flux is arranged only on the outer face of the metal strip, preferably by spraying, but it could also be added by another technique, for example by immersion coating.

Claims

1. Tube for a heat exchanger, consisting of a metal strip having an inner face and an outer face, this strip having two extremities which are folded locally towards the inner face of the tube so as to form two borders (28, 30) placed one beside the other, characterized in that passages (38) are formed in at least one of the extremities of the metal strip for introduction of a brazing flux.

2. Tube according to claim 1, characterized in that passages (38) are formed in the two extremities of the metal strip.

3. Tube according to claim 2, characterized in that the passages (38) of one extremity are offset with respect to the passages (38) of the other extremity of the metal strip.

4. Tube according to claim 1, characterized in that the passages (38) are produced by knurling of the extremities of the metal strip.

5. Tube according to claim 4, characterized in that the metal strip is folded by passing through a series of successive rollers, and in that the knurling is carried out before passing through the forming rollers.

6. Tube according to claim 1, characterized in that the passage (38) are produced substantially perpendicularly to the extremities of the metal strip.

7. Tube according to claim 1, characterized in that the passages (38) are produced obliquely with respect to the extremities of the metal strip.

8. Tube according to claim 1, characterized in that the passages extend over a distance greater than the height of the borders (28) and (30) in such a way as to form an inlet (40) for the brazing flux.

9. Tube according to claim 1, characterized in that the outer face of the metal strip is covered with a plating of brazing alloy.

10. Heat exchanger, especially for a motor vehicle, comprising a bank of tubes (16) alternating with cooling spacers (15), characterized in that the tubes are in accordance with claim 1.

11. Method of manufacturing a tube for a heat exchanger, as defined in claim 1, by folding and brazing of a metal strip, this strip including an inner face and an outer face, characterized in that a brazing flux is deposited solely on the outer face of the tube.

12. Manufacturing method according to claim 11, characterized in that the brazing flux is deposited on the outer face of the metal strip by spraying.