EP0791798A1 - Plastic header box for heat exchanger - Google Patents

Abstract

The chamber has a cover (5) made from a plastic material and especially a thermoplastic with high mechanical strength, such as polypropylene or polyamide reinforced with 10-60 wt.% of glass fibres. The cover is lined with a chemically inert material, especially a thermoplastic able to withstand temperatures of 150-200 degrees C, such as phenylene polysulphide in a layer < 1 mm thick and preferably 0.5 mm thick. The cover and lining can be made by co-injection, with the cover having a minimal thickness of 2 mm and the lining 0.2-0.4 mm.

Description

The invention relates to a plastic manifold suitable for being part of a heat exchanger, in particular for a motor vehicle.

Collector boxes of this type, also called "water boxes", comprise a basic structure obtained by molding a plastic material. This basic structure essentially comprises a wall forming a box and capable of being capped by a collecting plate, also called a "hole plate", into which the ends of the tubes of a bundle are introduced.

Such a manifold must have good mechanical strength to resist impact and to allow assembly of the manifold plate, by means of lugs of the latter, which are folded against a heel of the manifold.

Furthermore, such a manifold must be able to withstand the pressure and the temperature of the heat transfer fluid which flows through the heat exchanger.

When such a heat exchanger is used as a radiator for cooling a heat engine or radiator for heating the passenger compartment of a motor vehicle, the heat transfer fluid, usually glycol water, can reach temperatures of around 120 to 130 ° C. The heat exchanger, and in particular the manifold, must be able to withstand temperatures which can even reach 150-200 ° C.

Another problem associated with manifolds resides in the fact that the latter must also resist degradation, in particular by hydrolysis, under the action of the heat transfer fluid.

Most plastic manifolds currently used on heat exchangers are made of a single material and formed from polyamide. This plastic material has the advantage of having a high impact resistance. By cons, this plastic has the disadvantage of having a low resistance to hydrolysis. To overcome this drawback, it is necessary to oversize the thickness of the manifold to avoid rupture or premature fatigue as a result of the hydrolysis, even partial, of its internal face in contact with the heat transfer fluid.

Furthermore, it is also known to use manifolds made of phenylene polysulphide, because this particular plastic material has the advantage of resisting degradation by hydrolysis, under the action of the heat transfer fluid. Unfortunately, this plastic material has a low impact resistance.

This is the reason why it is generally preferred to use polyamide manifolds, by oversizing the thickness of the base structure, in particular of the wall whose internal face is in contact with the heat transfer liquid.

In addition, another drawback of known manifolds is that the cost of the plastic used is high, in particular for polyphenylene sulfide boxes, the cost of the material of which is substantially three times that of a polyamide box.

It is also known, from publication FR-A-2 461 916, to manufacture heat exchangers from a composite material comprising a support layer of an aluminum-based alloy and a coating layer in another aluminum-based alloy to resist corrosion.

However, this material is suitable for the manufacture of brazed heat exchangers, that is to say a technique different from that of mechanically assembled heat exchangers, the manifolds of which are made of plastic.

The object of the invention is in particular to overcome the aforementioned drawbacks.

To this end, it offers a manifold for a heat exchanger, of the type comprising a basic structure of molded plastic.

According to the invention, this base structure is provided with an internal coating of a chemically inert material capable of forming a chemical barrier between the base structure and a heat transfer fluid passing through the heat exchanger.

Thus, the manifold of the invention combines a basic structure of plastic and an internal coating of a chemically inert material.

The plastic of the basic structure is chosen above all for its mechanical strength qualities, in particular impact resistance.

As for the chemically inert material, it need not in itself have good mechanical strength. It is chosen for its qualities of chemical inertness, in order to constitute a chemical barrier between the basic structure and the heat transfer fluid which flows through the heat exchanger, and thus prevent the degradation of the basic structure by hydrolysis.

In a preferred embodiment of the invention, the basic structure is made of a plastic material, in particular a thermoplastic material, having good mechanical strength.

By way of example, this plastic material can be chosen in particular from polypropylene or polyamide.

In this regard, it is preferred to use polypropylene because its cost price is more economical than that of polyamide and especially that of phenylene polysulfide.

The plastic of the basic structure is advantageously reinforced with a reinforcing material, for example glass fibers.

In a preferred embodiment of the invention, the plastic material of the basic structure is a polypropylene reinforced with glass fibers, the content of glass fibers being between 10% and 60% by weight. The glass fibers used can be long or short fibers.

The internal coating of the manifold of the invention is preferably a plastic material, in particular a thermoplastic material, capable of withstanding temperatures which can range up to 150-200 ° C. This plastic material must be chemically inert with respect to the heat transfer fluid.

The coating can, for example, be made of phenylene polysulphide, taking into account the hydrolysis resistance properties of this particular material.

Furthermore, the advantage of phenylene polysulphide is that it can be easily used, in particular by molding, and that it is compatible with the plastics used in the manufacture of manifolds for heat exchangers.

Because the mechanical strength of the manifold is provided essentially by the basic structure, the internal coating can have a small thickness, which also reduces its cost and constitutes a non-negligible advantage, in particular in the case of phenylene polysulfide, the material cost is high.

Generally, the internal coating will have a thickness of less than 1 mm, preferably less than 0.5 mm.

The manifold of the invention can be obtained by different manufacturing methods.

In a first method, the basic structure is injection molded on the internal coating present in the form of a thin film.

We can thus apply this film on a mold base and then inject the plastic intended to constitute the basic structure.

For example, the basic structure can have a minimum thickness of 2 mm and the internal coating a minimum thickness of 0.2 mm.

In a second process, the basic structure and the internal coating are molded by bi-injection. This means that the respective materials of the base structure and the internal coating are injection molded almost simultaneously.

In such a case, the basic structure advantageously has a minimum thickness of 2 mm and the internal coating a minimum thickness of 0.4 mm.

In the second method, the minimum thickness of the internal coating is in principle greater than the minimum thickness of the first method, in which this internal coating is produced in the form of a pre-existing film.

In the description which follows, given by way of example, reference is made to the appended drawing, in which the single figure represents a partial elevation view, with parts broken away, of a heat exchanger equipped with a manifold according to invention.

The heat exchanger shown in the drawing comprises a plastic collecting box 1 mechanically assembled to a metal collecting plate 2. This collecting plate, also called "plate with holes", receives the ends of a plurality of tubes 3 forming a bundle and crossing a multiplicity of fins 4.

The manifold 1 comprises a basic structure 5, that is to say essentially a wall, of molded plastic material provided with an internal coating 6 intended to come into contact with a heat transfer fluid passing through the heat exchanger. In other words, the internal coating 6 forms an interface or barrier between the base structure 5 and the heat transfer fluid.

In the example shown, the heat exchanger is intended to be used as a radiator for cooling an internal combustion engine of a motor vehicle or also as a radiator for heating the passenger compartment of a motor vehicle. The heat transfer fluid is generally water, added with antifreeze, for example glycol water, the temperature of which can reach values as high as 120-130 ° C. and even exceptionally limit values which can reach 150-200 ° C. .

The plastic material of structure 5 is, in the example, a thermoplastic material chosen from polypropylene and polyamide.

Advantageously, a polypropylene reinforced with glass fibers is used, the content of which is between 10% and 60% by weight. For a radiator of a passenger vehicle, the minimum thickness of the structure 5 is usually of the order of 2 mm.

The internal coating 6 is a plastic material and, more precisely, a thermoplastic material. In the example, it is phenylene polysulfide.

This material is chemically inert and forms a chemical barrier which protects the structure from degradation, in particular by hydrolysis, on the part of the heat transfer fluid.

The internal coating 6 has, in the example, a thickness of less than 0.5 mm.

The coating 6 can be used in the form of a thin film, typically of the order of 0.2 mm, applied in a mold base. Next, the plastic intended to form the structure 5 is injected. The two materials make it possible to obtain a manifold which combines the mechanical strength properties of the plastic of the basic structure 5 and the hydrolysis resistance of the plastic material of the internal coating 6.

In another method, the base structure 5 and the inner lining 6 are molded together by a bi-injection method. The basic structure must, in such cases, have a minimum thickness of 2 mm, as in the previous case.

On the other hand, the internal coating 6 must have a minimum thickness slightly greater than that of the film. As an example, one can use a thickness of 0.4 mm for the internal coating 6 and a thickness of 2.1 mm for the base structure 5, which gives a total thickness of the order of 2.5 mm.

Of course, the invention is not limited to the embodiments described above by way of example.

It is possible to envisage other variants, in particular as regards the choice of the plastic material of the basic structure and the choice of the material of the internal coating.

Claims (12)

Collector box for heat exchanger, of the type comprising a base structure (5) of plastic material, characterized in that the base structure (5) is provided with an internal coating (6) of a chemically inert material capable of forming a chemical barrier between the basic structure (5) and a heat transfer fluid passing through the heat exchanger. Collector box according to claim 1, characterized in that the base structure (5) is made of a plastic material, in particular a thermoplastic material, having good mechanical strength. Collector box according to either of Claims 1 and 2, characterized in that the plastic material of the basic structure (5) is chosen from polypropylene and polyamide. Collector box according to one of claims 1 to 3, characterized in that the plastic of the base structure (5) is reinforced with a reinforcing material, in particular glass fibers. Collector box according to one of claims 1 to 4, characterized in that the plastic material of the basic structure is a polypropylene reinforced with glass fibers, the glass fiber content being between 10% and 60% by weight. Collector box according to one of Claims 1 to 5, characterized in that the internal coating (6) is made of a plastic material, in particular a thermoplastic material, capable of withstanding temperatures of up to 150-200 ° C . Collector box according to one of claims 1 to 6, characterized in that the plastic material of the coating internal material is chemically inert with respect to the heat transfer fluid, such as phenylene polysulfide. Collector box according to one of claims 1 to 7, characterized in that the internal coating (6) has a thickness of less than 1 mm, preferably less than 0.5 mm. Collector box according to one of claims 1 to 8, characterized in that the base structure (5) is injection molded on the internal coating (6) present in the form of a thin film. Collector box according to claim 9, characterized in that the basic structure (5) has a minimum thickness of 2 mm and the internal coating (6) a minimum thickness of 0.2 mm. Collector box according to one of claims 1 to 8, characterized in that the base structure (5) and the internal coating (6) are molded by bi-injection. Collector box according to claim 11, characterized in that the basic structure (5) has a minimum thickness of 2 mm and the internal coating a minimum thickness of 0.4 mm

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