The present invention refers to a method for finning a heat exchanger and to the exchanger obtained with the application of the method. To increase the heat exchange surfaces, it is normally common to apply fins to the surfaces. When the material used is aluminum, there is usually no difficulty in making specially shaped extrusions. It involves making a specially shaped extrusion die, which is used to extrude aluminum. Given the characteristics of the material, the costs are limited and acceptable even for limited productions .

In some cases, where the heat exchange needs are not particularly stringent, the heat exchange surfaces are made of carbon steel, considerably cheaper than aluminum. In these cases, the solution of making extrusions appears impractical for steel, especially for small series, due to the high costs of the equipment needed to work the steels. In these cases, the steel fins are welded onto a plate, also made of steel. However, this procedure is excessively expensive, but has practically no alternatives for small and very small series.

Object of the present invention is providing a method for applying fins to a metal plate, particularly suitable for small and medium series productions, since it does not require any specific equipment.

The present invention solves the problem posed by proposing a method and a device, respectively according to their independent claims, for obtaining a heat exchanger of the type which provides a plurality of fins applied to a surface.

The method is of the type that involves applying a plurality of metal fins to a surface that is also metal, the application being carried out by welding, and comprises the following steps: - bringing the plurality of fins (13, 31, 34,

35) in contact with the plate (11, 33), means being provided for maintaining the contact during the subsequent step;

- infiltrating, between the fins (13, 31, 34, 35) and the plate (11, 33), means suitable for favoring the passage of heat between the fins (13, 31, 34, 35) and the plate (11, 33).

According to a preferred embodiment, the fins constitute a grid, so that it is simple and economical to couple the plurality of fins with the plate. In this way, in fact, it is easy to keep the grating in contact with the metal surface, for example by means of some welding points, and to effect the infiltration of metal material, for example by immersion into a bath of molten metal.

The contact made in this phase is not normally a perfect contact, due to the inevitable flatness defects of the plate and alignment of the fins. This fact, however, is not a problem; on the contrary, it favors the infiltration of metal material between plate and fins.

As an alternative to immersion into a molten metal bath, a galvanic bath can be used to carry out an electrolytic deposition of a suitable metal. A further variant can be constituted by a painting with products containing metal powders.

However, the fins can be applied individually, by brazing, by providing suitable means for keeping the fins in position. The latter procedure may be convenient in case of very small series. The device obtained with the method described is a heat exchanger provided with metal fins applied to a plate which is also metal; according to the invention, the fins are connected to the plate by infiltrating, between the fins (13, 31,

34, 35) and the plate (11, 33), means adapted to favor the passage of heat between the fins (13, 31, 34, 35) and the plate (11, 33).

Preferred embodiments and non-trivial variants of the present invention are the subject matter of the dependent claims.

It is understood that all attached claims form an integral part of the present description.

It will be immediately obvious that innumerable variations and modifications (for example relating to shape, dimensions, arrangements and parts with equivalent functionality) can be made to what is described, without departing from the scope of the invention as appears from the attached claims.

The invention will now be described, for illustrative and non-limiting purposes only, according to a preferred embodiment and with reference to the attached figures, in which:

Figure 1 shows a finned plate using the welding method;

- Figures 2 and 3 show finned plates using the method according to the invention;

- Figure 4 shows a possible improvement of the exchanger obtained with the method according to the invention.

With reference to Fig. 1, (1) designates a finned plate obtained according to the known art.

The finned plate (1) comprises a plate (2) and a plurality of fins (3) made by bending the metal strips in an L shape, so that the bases (3a) of the metal strips can be welded to the plate (2) by electric roller welding.

In this way, even though there is a metallic continuity between the base (2) and the fins (3), the heat passage section is not particularly extensive.

This procedure for the realization of the finning, in addition to the extreme manufacturing complexity, has also two serious limitations. First of all, in order to make the bases (3a), it is not possible to use too high thicknesses, thereby reducing the ability to transmit heat. Furthermore, the very width of the bases (3a) forces the fins to be arranged at a considerable distance, so it is not in fact possible to create a dense finning, should it be necessary to disperse heat.

Fig. 2 shows a finned plate (10) obtained with the method according to the invention. The finned plate (10), according to the invention, comprises a plate (11) on which a grid (12) is welded which, in turn, consists of a plurality of first fins (13).

The grating (12) is a grating of a known type, obtained, for example, by electrically welding a plurality of the first fins (13) with cylindrical bars (14).

The finned plate (10) is finally obtained by placing the grating (12) in contact with the plate (11) and immersing it all into a bath of molten zinc, using suitable means to keep the grating (12) in contact with the plate (11). The effect is to obtain, simultaneously with the surface coating, the continuous welding of the first fins (13) to the plate (11), ensuring the metallic continuity between the plate (11) and the fins (13).

As highlighted in the enlarged detail of Fig. 2, the molten zinc is arranged around the base of the fins (13) by enlarging it and consequently increasing the heat passage area. The finned plate (10) can be obtained by placing the first single fins (13) on the plate (11), using suitable means to keep the fins (13) in position during immersion into the molten zinc bath and subsequent cooling.

According to a preferred embodiment, further second fins (31) can be applied on the lower part of the plate (11) to facilitate the heat exchange with the underlying environment. The fins (31) can be part of a device (30) for the accumulation of heat, as will be specified below.

Fig. 3 shows a finned plate (20) obtained with the method according to the invention, using a grating (12a), again obtained by electrically welding a plurality of fins (13) with cylindrical bars (14), but with the addition of longitudinal fins (15) which give greater strength to the whole, making it suitable to perform a structural function as well. Fig. 4 shows a finned plate (10) of the type coupled with the device (30) for the accumulation of heat.

According to a preferred embodiment, the device (30) for the accumulation of heat comprises: the plurality of second fins (31) welded below the plate (11); a container, filled with a phase change material (not shown), formed by four walls (32) and a bottom (33), inside which a plurality of third fins (34), called third fins (34), are offset with respect to the second fins (31).

The fins (31) and (34) will be advantageously welded to the respective plates (11) and (33) with the method according to the invention, preferably using suitable gratings.

With the geometry shown in Fig. 4, the second and third fins (31) and (34) will protrude inside the thermal mass, constituted by the phase change substance, to improve the heat exchange between the phase change substance and the fins (31) and (34).

A similar result, albeit with a decrease in effectiveness, but with a significant saving on production costs, can be obtained with the use of water instead of the phase change substance and without creating the fins (31) and (34).

According to a preferred embodiment, under the plate (33), which constitutes the bottom of the container of the phase change substance, fourth fins (35) can be welded, to improve the heat exchange with the underlying environment. The method according to the invention has been described so far with reference to carbon steel welded by immersion into molten zinc; however, the same method can be used with other types of steel, or with copper welded by immersion into a suitable molten alloy, for example alloys based on tin and/or silver. Obviously in this case the costs will be considerably higher and therefore the materials will be preferably used in cases in which the heat exchange needs are particularly stringent.

According to another preferred embodiment, as an alternative to immersion into a bath of molten metal, a galvanic bath can be used to carry out an electrolytic deposition of a suitable metal. By suitably adjusting the duration of the treatment, the deposited metal layer can be grown until sufficient metal contact between the fins and the base plate is ensured.

According to a further preferred embodiment, the coating of the exchanger can be carried out by painting with products containing metal powders, either by spray painting or by means of cataphoresis treatments.