EP2655000A1

EP2655000A1 - Brazing method for a heat exchanger, and corresponding tube and heat exchanger

Info

Publication number: EP2655000A1
Application number: EP11805448.5A
Authority: EP
Inventors: Laurent Moreau; Alain Bauerheim; Philippe Metayer
Original assignee: Valeo Systemes Thermiques SAS
Current assignee: Valeo Systemes Thermiques SAS
Priority date: 2010-12-20
Filing date: 2011-12-13
Publication date: 2013-10-30
Also published as: FR2969018B1; FR2969018A1; CN103702791A; US20140158331A1; JP2014501621A; WO2012084584A1

Abstract

The invention relates to a method for brazing a tube (1) of a heat exchanger, including the following steps: folding a metal strip (11) such as to form at least one tube (1); providing, inside the tube (1), a disturbance insert (7) having a thickness substantially equal to or lower than 150 pm, wherein said metal strip (11) and/or said insert (7) comprises a plating layer on at least one surface to be brazed such that the ratio between the volume of the plating layer and the volume to be brazed is substantially higher than or equal to a predetermined threshold on the basis of the average gap between said insert (7) and said tube (1); and brazing said tube (1) and said insert (7). The invention also relates to a tube (1) obtained by such a method, and to a heat exchanger including an array of such tubes (1).

Description

Brazing process for heat exchanger, tube and corresponding heat exchanger

The invention relates to a brazing process for a heat exchanger, particularly for motor vehicles, a tube and a heat exchanger thus obtained.

The invention relates to the field of heat exchangers, especially for motor vehicles.

Generally, the heat exchangers conventionally comprise a bundle of tubes and two collector plates traversed by the ends of the tubes of the bundle of tubes and capped by covers of fluid distribution boxes. Interlayers may also be provided between the tubes of said bundle to improve heat exchange.

For solder-jointed exchangers, all components are assembled and then brazed in a suitable furnace to form the heat exchanger.

The brazing is carried out with a supply of brazing, most often made in the form of a veneer.

In general, the tubes used in the brazed heat exchangers are made of a low oxidation metal material, such as aluminum or an aluminum alloy.

Brazed heat exchangers are known whose bundle tubes are extruded so as to define a plurality of circulation channels for the flow of the fluid. However, this solution can be relatively expensive.

According to another known solution, interlayers or disturbance fins, for example corrugated, are arranged inside the tubes of the heat exchanger bundle to increase the heat exchange surface and thus improve the performance of the heat exchanger .

The sealing of such tubes having two parts is therefore more difficult to obtain. When soldering, it is advisable to ensure the correct brazing at all contact between the spacers and the tubes.

Indeed, in case of non-soldering between an undulating peak of an interlayer and the inner surface of a tube, the mechanical strength of the tube is degraded and the tube may burst prematurely under pressure.

The object of the invention is to overcome these drawbacks of the prior art by guaranteeing proper brazing of the surfaces inside the heat exchanger tubes at a lower cost.

For this purpose, the subject of the invention is a brazing process for a heat exchanger between at least a first and a second fluid, said exchanger comprising a bundle of tubes for the flow of said first fluid, characterized in that it comprises the steps following:

a metal strip is folded so as to form at least one tube,

a perturbation spacer of thickness substantially less than or equal to 150 μιη is arranged inside said tube, and

said metal strip and / or said interlayer comprises a plating layer on at least one surface to be brazed so that the ratio of the volume of the plating layer to the volume to be brazed is substantially greater than or equal to a predetermined threshold as a function of the mean distance between said spacer and said tube, and

said tube and said insert are deformed.

The method may further comprise one or more of the following features, taken separately or in combination:

said threshold is substantially of the order of 1.5 for an average difference of the order 0.05 mm between a tube and a spacer;

said threshold is substantially of the order of 1.75 for an average difference of the order of 0.05 mm between a tube and a spacer;

said interlayer comprises a plating layer;

the inner surface of said tube comprises a plating layer; said method comprises the following steps:

A plurality of tubes comprising a plating layer on at least one surface to be brazed outside said tubes are prepared;

A plurality of tubes are stacked by interposing flow interferers of said second fluid between said tubes, and

a plating layer is disposed on the outer surface of said tubes;

- A plating layer is disposed on the inner surface and on the outer surface of said tubes. The invention also relates to a heat exchanger tube formed by folding a metal strip, characterized in that it is brazed according to a soldering method as defined above.

According to one embodiment, said metal strip comprises aluminum. The invention also relates to a heat exchanger, in particular for a motor vehicle, comprising a bundle of tubes, characterized in that it is brazed according to a soldering method as defined above.

Other features and advantages of the invention will emerge more clearly on reading the following description, given by way of illustrative and nonlimiting example, and the appended drawings among which:

FIG. 1 partially and schematically represents a heat exchanger,

FIG. 2 is a cross-sectional view of a tube of the exchanger of FIG. 1, and

FIG. 3 schematically illustrates a metal strip serving for forming the tube of FIG. 2.

In these figures, the substantially identical elements bear the same references. The invention relates to a method of brazing tubes 1 suitable for use in brazed heat exchangers.

An example of a heat exchanger is air conditioning condensers for motor vehicles. In this case, the heat exchange is between a first fluid such as a refrigerant, and a second cooling fluid such as glycol water.

As is partially illustrated in FIG. 1, a heat exchanger 3 conventionally comprises a plurality of longitudinal tubes 1 mounted between two distribution boxes in which a first fluid circulates, via collecting plates 5 (represented partially and schematically) deposited transversely relative to the tubes 1 and having orifices (not shown) for receiving the ends of these tubes 1.

Interlayers or disruption fins 7 (Figure 2), for example of substantially undulating shape, are disposed inside the tubes 1 so as to disturb the flow of the first fluid in the tubes 1 by increasing the exchange surface. These spacers 7 are for example brazed to the tubes 1 at the vertices 7a of their corrugations and for example at the ends 7b of the spacers 7.

The disturbance generated by the presence of these spacers 7 in the tubes 1 facilitates the heat exchange between the two fluids.

These spacers 7 are made thin, that is to say substantially less than 150 μιη, to reduce costs. According to a preferred embodiment, the spacers 7 have a thickness of the order of 100 μιη.

These spacers 7 are well known to those skilled in the art and are not described in more detail herein.

The tubes 1 can be separated from each other by disruptors 9 (FIG. 1), for example corrugated, traversed by the second fluid for a heat exchange with the first fluid. These disruptors 9 are in the illustrated example arranged transversely to the longitudinal axis of the tubes 1. Referring now to Figure 2 which shows a sectional view of a tube 1 of such exchanger 3.

The tube 1 is made from a metal strip 11 folded and brazed. This is called "folded tube".

This metal strip 11 (Figure 3) is preferably aluminum or aluminum alloy.

The metal strip 11 is for example of generally rectangular shape and comprises a first face called outer face 13 and a second face said inner face 15 parallel to the outer face 13 and opposite thereto. The terms "internal" and "external" are defined with respect to the inside and outside of the folded tube 1. The metal strip 11 forming the tube is provided with a plating layer on at least one surface to be brazed. In other words, there is provided a metal strip 11 having a plating layer at least disposed at the areas to be brazed.

One embodiment proposes that the surface to be brazed is intended to be located inside said tube once it is assembled.

According to the example illustrated in Figure 2, the tube 1 formed has a substantially "B" cross section. Of course, other sections may be provided.

The cross-section at "B" of the tube 1 illustrated, has two parallel fluid circulation channels juxtaposed 17a and 17b and separated by a partition 19 forming a spacer.

To form such a tube 1, the metal strip 11 is folded so as to form the envelope of the two parallel channels juxtaposed 17a and 17b. More specifically, the metal strip 11 is folded so that its inner face 15 delimits the two channels 17a, 17b.

The partition 19 is for example made by folding substantially 90 ° two opposite edges 11a and 11b of the metal strip 11, for example the longitudinal edges of the strip 11. Then, these edges 11a, 11b folded back against one against the other to jointly form the partition 19. The outer face 13 at the edge 11a is therefore opposite the outer face 13 at the opposite edge 11b.

Thus, once the band 11 folded, the outer face 13 of the band 11 forms the outer surface 21 of the tube 1 thus formed, and the inner face 15 of the band 11 forms the inner surface 23 of the tube 1 thus formed.

In addition, the outer surface 21 of the folded tube 1 has two large outer faces 21a, 21b opposite and which are connected by two small side faces 21c and 21d, for example substantially curved.

The tubes 1 obtained can then be assembled with the spacers 7 and corrugated disruptors 9, to form a beam that can be brazed.

Indeed, the various metal components to be joined, such a heat exchanger 3, are first assembled, then their connection is ensured by passing through a brazing furnace.

It is therefore possible to carry out, in a single operation, an exchange bundle comprising a large number of tubes 1, disruption fins 7 inside the tubes 1, and possibly disturbers 9 deposited each time. between two successive tubes 1.

Specifically, during editing:

- The tubes 1 are formed by folding a metal strip 11;

the spacers 7 are arranged inside the tubes 1;

the tubes 1 are engaged in associated orifices of the collector plates 5, on which are mounted the end distribution boxes of the heat exchanger;

disrupters 9 can be mounted between the stacked tubes 1; and

- The whole is assembled permanently by soldering.

The brazing is carried out conventionally with the use of a solder and in order to improve the brazing process it is also possible to use a brazing flux, for example applied in the form of a paste under controlled conditions, which dissolves the solder. oxide layer formed naturally on the surface of the parts to be assembled and wetting the parts to be soldered to thereby allow the solder to spread on the contact surfaces.

Brazing is most often formed of a layer of veneer. For plating, the filler metal has a lower melting temperature than the metal forming the core of the tube 1, for example aluminum. Here, the plating layer is placed directly on the metal strip 11 used for the manufacture of the tube.

As regards the brazing of the surfaces outside the tubes 1, namely between the outer surfaces 21 of the tubes 1 and interfering disruptors 9, it is possible to apply a plating layer disposed on the metal strip 11 so that said layer is disposed on the outer surfaces 21 of the tubes 1 and / or on the interferers 9.

However, the configuration that there is no cladding layer on the outer surfaces 21 of the tubes 1 therefore requires disruptors 9 plated, resulting in additional cost. Accordingly, the plating layer is preferentially disposed on the outer surface 21 of each tube 21.

As regards the brazing of the surfaces inside the tube 1, namely the brazing of the vertices 7a of the spacers 7 and for example the ends 7b of the spacers 7 on the inner surface 23 of the tube 1, the veneer layer may be disposed only on the brazing surfaces of the spacers 7 or alternatively both on the spacers 7 and on the inner surface 23 of each tube 1.

In the configuration that there is no plating layer on the inner surfaces 23 of the tubes 1, the tabs 7 plated have a greater thickness, which increases the cost. Accordingly, the plating layer is preferably also disposed on the inner surface 23 of each tube 1.

Thus, during the brazing process advantageously plate both the inner surface 23 and the outer surface 21 of the tube 1. Moreover, the thickness of the plating layer is standardized. Indeed, the limit of the thickness of the plating layer on the spacers 7 is of the order of 10 to 15% of the material thickness of the interlayer. Similarly, the thickness of the plating layer on the inner surface 23 of the tube 1 is defined by a standard and the limit is of the order of 12.5 to 15% of the material thickness of the tube 1.

In order to guarantee correct brazing inside a tube 1, it is necessary to have a sufficient veneer volume next to the volume to be brazed inside the tube 1, this ratio is called BCR for English "Brazing Confident Ration" (cf relation (1)): β ^ ρ _^ _ Veneer volume

Soldering volume

(D

If the ratio is insufficient and therefore less than a predetermined threshold, the amount of plating will be insufficient compared to the area to be brazed to ensure brazing of all the folds of the spacer 7 on the inner surface 23 of the tube 1.

By way of example, in order to determine the volume to be soldered, the total length to be brazed is defined and multiplied by the average distance between the inner surface 23 of the tube 1 and the surface to be brazed of the insert. average deviation is for example of the order of

0.05 mm.

The Applicant has found that for such a difference of the order of 0.05 mm, with a BCR ratio greater than or equal to 1.5, and in particular greater than or equal to 1.75, a correct brazing is obtained.

Indeed, for a BCR of the order of 1.4 with an average deviation of the order of 0.05 mm between a tube 1 and a spacer 7, the Applicant has found that all the folds of the insert 7 are not properly brazed at the inner surface 23 of the tube 1. As soon as a fold is not brazed to the inner surface 23 of a tube 1, the mechanical strength of the tube 1 is degraded.

The BCR ratio greater than or equal to a threshold of 1.75 for an average deviation of 0.05 between a tube 1 and a spacer 7, makes it possible to guarantee correct brazing of the folds of the insert 7 on the inner surface 23 of the tube 1, for spacers 7 of relatively low thickness, for example less than 150 μιη or even of the order of 100 μιη, as previously mentioned.

Thus, the soldering method provides that a plating layer is disposed on the insert 7 at the vertices 7a and possibly the ends 7b, and / or on the inner surface 23 of the tube 1, making sure that the ratio BCR of the volume of the plating layer on the volume to be soldered is greater than the predetermined threshold as a function of the average deviation between the tube 1 and the vertices 7a.

Furthermore, it can be noted that after soldering the volume of plating used for brazing can be determined from the residual amount of plating inside the tubes 1 and the amount of plating present at the joints between the plating. insert 7 and the inner surface 23 of a tube 1.

Thus, with such a method, a low-cost heat exchanger 3 is obtained which has so-called folded tubes 1 and whose perturbation fins 7 are relatively thin, while ensuring contact between all the folds of the disturbance fins 7 on the internal surfaces. 23 of the tubes 1.

Claims

Brazing process for heat exchanger (3) between at least a first and second fluid, said exchanger comprising a bundle of tubes (1) for the flow of said first fluid, characterized in that said method comprises the following steps:

a metal strip is folded so as to form at least one tube,

a perturbation spacer of thickness substantially less than or equal to 150 μιη is arranged inside said tube, and said metal strip and / or said interlayer comprises a plating layer on at least one surface to be soldered so that the ratio the volume of the plating layer on the volume to be soldered is substantially greater than or equal to a predetermined threshold as a function of the average distance between said spacer and said tube, and said tube and said interlayer are bristled.

2. Method according to claim 1, characterized in that said threshold is substantially of the order of 1.5 for an average difference of about 0.05 mm between a tube (1) and a spacer (7).

3. Method according to one of claims 1, characterized in that said threshold is substantially of the order of 1.75 for an average difference of the order of 0.05 mm between a tube (1) and a spacer (7).

4. Method according to any one of the preceding claims, characterized in that a plating layer is disposed on said insert (7).

5. Method according to any one of the preceding claims, characterized in that a plating layer is disposed on the inner surface (23) of said tube (1).

6. Method according to any one of the preceding claims, characterized in that it comprises the following steps:

a plurality of tubes comprising a plating layer is prepared on at least one surface to be brazed outside said tubes (1);

- Stacking a plurality of tubes (1) by interposing interfering (9) flow of said second fluid between said tubes (1).

7. The method of claim 6, characterized in that a plating layer is disposed on the outer surface (21) of said tubes (1).

8. Method according to any one of the preceding claims, characterized in that a plating layer is disposed on the inner surface (23) and on the outer surface (21) of said tubes (1).

9. Heat exchanger tube formed by folding a metal strip, characterized in that it is brazed according to a soldering method according to any one of the preceding claims.

10. Tube according to claim 9, characterized in that said metal strip comprises aluminum.

11. Heat exchanger, particularly for a motor vehicle, comprising a bundle of tubes (1) characterized in that it is soldered by a soldering method according to any one of the preceding claims.