WO2015185610A1

WO2015185610A1 - Sacrificial coating for a motor vehicle heat exchanger

Info

Publication number: WO2015185610A1
Application number: PCT/EP2015/062354
Authority: WO
Inventors: Erwan ETIENNE; Patrick Boisselle; Samuel BRY
Original assignee: Valeo Systemes Thermiques
Priority date: 2014-06-06
Filing date: 2015-06-03
Publication date: 2015-12-10
Also published as: FR3022018A1; FR3022018B1

Abstract

The invention relates to a heat exchanger element (10) for a motor vehicle, adapted such that a heat transfer fluid can pass therethrough. The element comprises a coating (18) intended to be in contact with the heat transfer fluid and said coating (18) comprises at least 95% zinc, preferably 99%.

Description

Sacrificial coating for motor vehicle heat exchanger

The present invention relates to the technical field of heat exchangers for a motor vehicle. More specifically, the invention relates to a sacrificial coating of a member of a heat exchanger for protecting the exchanger against corrosion.

The heat exchangers concerned by the invention are made of an aluminum alloy. They generally comprise a bundle of tubes connected to one or more manifolds and are intended to be traversed by a coolant, which can be corrosive.

It is known that the circulation of a corrosive fluid inside the exchanger considerably affects the integrity of the constituent elements of the exchanger. The exchanger tubes, whose walls are particularly thin, are in fact the object of corrosion phenomena directly related to the circulation of the corrosive heat transfer fluid. The corrosion of the tubes is particularly harmful for the heat exchanger because it can go as far as the piercing of the tubes causing the heat transfer fluid to leak.

In the case where the heat transfer fluid circulates in a cooling circuit of a heat engine, leaks can cause overheating of the engine up to its damage and the immobilization of the vehicle.

In order to protect the aluminum tubes against corrosion, it is possible to make use of a protective strip of the wall of the aluminum tube, in particular by means of a bonding strip which may for example be made from an alloy aluminum-zinc corresponding for example to the grade 7072 according to the standard EN 573-1. In the case of mechanical technology exchangers, it is very difficult and expensive to use welded tubes from co-laminated aluminum strip because the assembly process requires the passage of tools inside the tubes. .

Another way to protect the exchanger against corrosion is proposed in WO03100337. This solution proposes to implement a reserve of material forming a sacrificial anode because of the low electrochemical potential of the elements that compose it.

FEUI LLE OF REM PLACEM ENT (RULE 26) However, a major disadvantage of this solution is that after a certain period of use, the stock of finished material wears out. Indeed, it tends to disintegrate because of the combination of corrosion and erosion generated by friction of the heat transfer fluid. Thus, debris and pieces of the sacrificial reserve detach and are carried by the fluid inside the tubes. These debris and pieces of material may be relatively large in size, which generally leads to clogging or clogging of the tube orifices. The obstruction of the tubes has the effect of degrading the overall heat exchange efficiency of the exchanger. When the heat exchanger is used to cool the engine of a vehicle, it is understood that the clogging of the tubes of the heat exchanger can therefore have a catastrophic effect on the engine. In addition, the presence of this reserve of material is an obstacle to the flow of heat transfer fluid which increases the pressure losses of the circuit and thus the consumption of the vehicle.

The object of the invention is to solve the above drawbacks by providing a reliable solution over time which makes it possible to protect the internal walls of the heat exchanger against corrosion and to prevent clogging of the tubes.

For this purpose, the subject of the invention is an element of a heat exchanger for a motor vehicle adapted to be traversed by a coolant comprising a coating intended to be in contact with the coolant and comprising at least 95% of zinc, preferably 99%. Thus, the internal surfaces of the heat exchanger are protected against corrosion. In fact, the coating serves as a sacrificial anode because the zinc has a lower electronegative potential than that of aluminum, material in which are manufactured the internal walls of the exchanger, including the walls of the tubes.

It is specified that the percentages of zinc are expressed relative to pure zinc.

Furthermore, the fact that an element of the exchanger comprises the coating implies that there is no need to add a reserve of sacrificial material in its own right, that is to say an additional element in the exchanger. Thus, the circulation of the fluid inside the exchanger is not affected by the presence of an additional element as is the case in the prior art, and loss problems. load and debris removal causing an obstruction of the tubes can not occur. In this solution, preference is given to the zinc surface in contact with the coolant rather than the zinc volume of an anode.

The above element may further include one or more of the following features, taken alone or in combination.

It can be expected that the coating has a roughness having an arithmetic mean greater than 6 microns. Thus, the specific surface area of the coating is high enough to promote significant ion exchange between the coating and the walls of the tubes, which improves corrosion protection.

It is also possible that the thickness of the coating is between 30 and 150 micrometers. Thus, the protection against corrosion of the exchanger is ensured for a relatively substantial duration and it is no longer necessary to provide for the replacement of a sacrificial reserve as described in the prior art.

The invention also relates to a water box provided on its inner surface with a coating comprising at least 95% zinc, preferably 99%.

The subject of the invention is also a method for surface treatment of an element of a motor vehicle heat exchanger comprising at least one step of depositing a layer of zinc on the surface of an element, the layer of zinc comprising at least 95% zinc, preferably 99%. Such a method has the advantage of being applicable to any internal element of a heat exchanger, such as for example a polymer water box or a collector plate made of aluminum.

It can be provided that the depositing step is performed from a method selected from the following list; arc-wire method, plasma spraying method, high speed thermal spraying method.

The zinc deposition step may be carried out from at least one zinc wire or at from powdered zinc. Thus, the method allows the use of the zinc element in states that are easily manipulated.

The invention further relates to a heat exchanger comprising heat exchange tubes, grouped into a bundle of tubes, and an element provided with a coating as mentioned above.

Advantageously, the tubes may comprise an inner wall, the inner wall of the tubes being made of an aluminum alloy. Thus, an ion exchange can take place between the coating and the aluminum tubes of the exchanger.

It can be expected that the surface area of the apparent surface of the coating of the element of the exchanger is at least equal to 30% of the sum of the areas of the apparent surfaces of the inner walls of the tubes. Thus, the coating forms a sacrificial anode with a surface large enough to protect the entire inner surface of the tubes.

The invention will be better understood on reading the appended figures, which are provided by way of examples and are in no way limiting, in which:

- Figure 1 is an elevational view of an element of a header box according to the invention, which is a constituent part of a heat exchanger;

FIG. 2 is a sectional view of a portion of the element of FIG. 1;

FIG. 3 is a diagram showing the successive steps of the surface treatment method of the element of FIG. 1.

Referring to Figure 1, there is shown an element 10 which is here a cover of a manifold of a motor vehicle heat exchanger. It is specified that a header box is also called a water box in the prior art. The heat exchanger (not shown) comprises heat exchange tubes whose inner walls are made from an aluminum alloy.

Such a manifold is, for example, part of a cooling radiator of a motor vehicle engine. The radiator is part of a cooling circuit traversed by a heat transfer fluid. The lid 10 of the manifold is provided with a plurality of internal surfaces 12 forming together a substantially parallelepipedal hollow volume into which a manifold 14 is connected to the cooling circuit. The lid is provided with peripheral flanges 16 to be assembled brazed with edges of a header plate (not shown). The lid is optionally provided with a seal.

In order to prevent corrosion or plugging of the tubes, it is expected that the cover 10 has on its inner surfaces 12 a coating 18 comprising a chemical element whose electro-negative potential is much lower than that of aluminum. In the example, the lid is aluminum while the coating 18 comprises at least 99% zinc. The lid of the water box could however be made from a polymeric material.

The peripheral flanges 16 are free of coating 18 to allow tight assembly of the header plate.

Referring to Figure 2, the coating 18 has a surface 20 whose topography is granular and intended to be in contact with the heat transfer fluid. In this example, the coating 18 has a roughness whose arithmetic mean is greater than 6 micrometers. The thickness e of this coating 18 is between 30 and 150 micrometers.

Referring to Figure 3, there will now be described a method of surface treatment of an element of a water box, the element having a zinc coating. This process comprises at least one melting step in which two wires comprising at least 99% zinc are used, said wires being subjected to an electric arc. The zinc son are thus melted and atomized to be then projected, during a deposition step 32, on the element to be coated by a jet of compressed air. Other projection techniques well known to those skilled in the art, such as the plasma process, or the high speed thermal spraying method, could of course be used using a zinc powder.

It is understood that the element of the heat exchanger which comprises the zinc coating may be located at any point inside the heat exchanger, provided that the coating zinc is provided to be in contact with the fluid and that the area of the surface of the coating of the element is at least equal to 30% of the sum of the areas of the surfaces of the inner walls of the tubes.

The invention is not limited to the embodiments presented and other embodiments will become apparent to those skilled in the art. In particular, it is possible to provide for example that the coating is made from a thin sheet of zinc. Also, it is conceivable that the coating is comprised by a header plate or by another pre-existing part of the exchanger, provided that this part is intended to be in contact with the coolant and that it has a sufficient surface with respect to the aluminum surface of the tube bundle to be protected.

Claims

1. Element (10) of a heat exchanger for a motor vehicle adapted to be traversed by a coolant characterized in that it comprises a coating (18) intended to be in contact with the coolant and in that the coating (18) ) comprises at least 95% zinc, preferably 99%.

2. Element (10) according to the preceding claim wherein the coating (18) has a roughness having an arithmetic mean greater than 6 microns.

3. Element according to any one of the preceding claims wherein the thickness (e) of the coating is between 30 and 150 micrometers.

4. Water box provided on its inner surface with a coating comprising at least

95% zinc, preferably 99%.

5. A method of surface treatment of an element of a heat exchanger for a motor vehicle characterized in that it comprises at least one step (32) for depositing a layer of zinc on the surface of the element, the zinc layer comprising at least 95% zinc, preferably 99%.

6. Surface treatment method according to the preceding claim wherein the deposition step is performed from a method selected from the following list; arc-wire method, flame-wire method, plasma spraying method, high speed thermal spraying method.

Surface treatment method according to claim 5 or

6 wherein the step of depositing the zinc layer is made from at least one zinc wire or from zinc powder.

8. Heat exchanger comprising heat exchange tubes and an element

(10) according to any one of claims 1 to 3.

9. Heat exchanger according to the preceding claim wherein the tubes have an inner wall, the inner wall of the tubes being made of an aluminum alloy.

10. Heat exchanger according to the preceding claim wherein the area of the surface of the coating of the element is at least equal to 30% of the sum of the areas of the surfaces of the inner walls of the tubes.