FR2896862A1 - COLLECTOR BOX WITH COVER FOR HIGH PRESSURE FLUID, HEAT EXCHANGER COMPRISING SUCH BOX AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Abstract

The box has a collector plate (26) comprising openings (28) for inserting heat exchange tubes (18). A cover (44) is formed by machining a metal bar and comprises an internal surface (72) and external surface. Distribution channels (70) e.g. groove, are formed in the metal bar by emerging on the internal surface while permitting material of the bar to close a volume of the cover at the level of longitudinal ends of the cover, where the channels communicate with the heat exchange tubes. An independent claim is also included for a method for fabricating a collector box.

Description

Slip box with lid for high pressure fluid, heat exchanger

  heat comprising such a box 5 and method for its manufacture

  The invention relates to the field of heat exchangers and in particular to exchangers intended to be traversed by a fluid under high pressure. In this respect, the invention relates more particularly to air conditioning evaporators that can be traversed by a gaseous refrigerant, as is the case with natural gases such as carbon dioxide or CO2. Such exchangers find particular application in motor vehicles.

  It will be recalled that, in an air conditioning circuit traversed by a refrigerant of this type, this fluid 20 remains essentially in the gaseous state and under a very high pressure which is between 100 and 150 bar. As a result, such heat exchangers, and in particular their manifolds, must be able to withstand such high pressures, the recommended burst pressure being generally three times the value of the nominal operating pressure.

  Collector boxes obtained by brazing which are designed to withstand such high pressures are already known.

  Thus, document FR 2 793 016 discloses a manifold box formed of a multiplicity of stacked flat plates having fluid passage slots. The distribution is ensured by these flat plates and the header comprises a cover also composed of a multiplicity of stacked plates. All these plates are assembled together by brazing.

  JP 2002-1588722 discloses a header box having an extruded reservoir closed by end plate plates. The abutment of the tubes is provided either by an intermediate flat plate disposed between the tubes and the tank, or by a specific profile of the tank section.

  Other such manifolds are also disclosed in JP 2002-43332, WO / 03 102 486 and EP 0 563 471.

  All of these known manifolds are either difficult to braze or require a significant number of manufacturing operations making their manufacturing process complex and expensive to perform.

  The object of the invention is in particular to overcome the aforementioned drawbacks. The invention proposes for this purpose a heat exchanger collector box, comprising a collector plate provided with openings for the insertion of heat exchange tubes, and a cover defining distribution channels communicating with the tubes. .

  According to the invention, the lid is a metal bar having an inner face and an opposite outer face, while the distribution channels are grooves made in the material thickness of the metal bar, opening on the inner face, while allowing the material to remain so as to: close the volume of the lid at its longitudinal ends.

  Thus, the cover is made by machining a thick metal bar, which simplifies its manufacture and allows for an element that can withstand high pressures.

  Communication passages are advantageously provided between the cover and the collector plate. In a first embodiment of the invention, the communication passages are delimited by a distribution plate interposed between the collector plate and the inner face of the cover. In a second embodiment of the invention, the communication passages are grooves of the metal bar opening on the one hand on the distribution channels and on the other hand on the inner face of the lid. This embodiment thus makes it possible to economize the distribution plate of the preceding embodiment, which eliminates a component.

  According to an advantageous characteristic of the invention, the distribution channels and the communication passages are machined. Because the grooves forming the channels are non-emergent, this avoids the use of end plates and thus makes it possible to decrease the number of pieces. According to another characteristic of the invention, the lid is obtained from an extruded metal bar.

  In an advantageous embodiment, the outer face of the extruded metal bar is shaped to have a profile comprising a plurality of domes, or arches, in correspondence of the channels. The distribution channels may have a corresponding inner section over their entire length, or a variable inner section along their entire length.

  The lid may comprise a single series of channels which each extend over the length of the metal bar. This is particularly the case of a return cover, located opposite a cover having arrangements for the entry and exit of the fluid.

  The lid may also include at least two sets of channels each extending over a portion of the length of the metal bar. This is particularly the case of a lid comprising, as mentioned above, arrangements for the entry and exit of the fluid.

  In the invention, the channels advantageously have a bottom with a transverse U-shaped profile, which makes it possible to improve the resistance to the pressure of the fluid. The channels advantageously have, in the vicinity of an end face. of the metal bar, a curved longitudinal profile delimited by a radius.

  In another aspect, the invention relates to a heat exchanger comprising a bundle of tubes and the moirs a collector box as defined above. This heat exchanger is advantageously produced in the form of an evaporator.

  A particular embodiment proposes that the heat exchanger comprises at least two passes and that the inner sections of the distribution channels make it possible to control and balance the flow rate of the fluid in the passes.

  In still another aspect, the invention provides a method of manufacturing a heat exchanger collector box, as defined above: which comprises the following operations:

  a) forming a header plate having tube receiving apertures; b) providing distribution means comprising communication passages

  c) making a cover from a metal bar having an inner face and an opposite outer face, by machining distribution channels scus the shape of grooves obtained by machining the metal bar in the longitudinal direction thereof in opening on said inner face; and d) assembling the cover on the header plate with interposition of the distribution means so that the communication passages open on the one hand on the distribution channels and on the other hand on the openings of the header plate.

  In a first embodiment, the operation b) comprises the preparation of a distribution plate delimiting the communication passages, while the operation d) comprises the interposition of the distribution plate between the collector plate and the face inside the lid.

  In a second embodiment, the operation b) comprises the realization of the communication passages in the form of grooves made by machining in the transverse direction of the metal bar, opening on the one hand on the distribution channels and on the other hand. on the other hand on the inside of the lid, while the operation b) comprises the direct assembly of the collector plate against the inner face of the lid.

  Advantageously, the operation c) comprises the preparation of an extruded metal bar and the machining of the channels by means of a multistage rotary tool capable of simultaneously machining the channels over at least a portion of the length of the metal bar. .

  In the description which follows, made only by way of example, reference is made to the accompanying drawings, in which: FIG. 1 is an exploded perspective view of a heat exchanger, in the example an evaporator for a cooling circuit; air conditioning, comprising a tube bundle mounted between two manifolds according to the invention; FIG. 2 is a partial cross-sectional view of one of the manifolds of the heat exchanger of FIG. 1; FIG. 3 is an end view of the cover of the manifold of FIG. 2, before machining; - Figure 4 is a view similar to Figure 3, after machining the channels of the cover; - Figure 5 shows schematically the machining of a cover by means of a rotary multi-stage tool; FIG. 6 is a partial view in longitudinal section of the lid showing the end of a channel, made in a non-emergent manner; Figure 7 is a longitudinal sectional view of a cover having two series of channels; - Figure 8 is a longitudinal sectional view of a cover having a single series of channels; Figure 9 is a variant of Figure 7 in which the section of the channels has an evolutionary form; FIG. 10 is a variant of FIG. 8 in which the section of the channels has a progressive form; FIG. 11 is a longitudinal sectional view of a cover of which a channel has another evolutionary form; - Figure 12 is a view similar to Figure 11 in another embodiment;

  Figure 13 schematically illustrates a flow distribution for a four-pass evaporator having two manifolds according to the invention;

  - Figure 14 illustrates the inner face of a cover which comprises both longitudinal grooves and parallel transverse grooves made by machining; FIG. 15 is a partial cross-sectional view of a header box comprising a cover according to FIG. 14; and

  Figure 16 is another partial cross-sectional view of the manifold of Figure 15.

  Referring first to Figure 1 which shows, = n exploded view, a heat exchanger 10 having a bundle 12 mounted between an upper manifold 14 and a lower manifold 16, the heat exchanger being considered in FIG. vertical position.

  The beam 12 is composed, in the example, of two :: angels 30 of tubes 18 (only one of which is visible in FIG. 1) and corrugated inserts 20 common to the two rows of tubes. The manifold 14 is provided with two inlet / outlet manifolds 22 and 24 respectively for the admission and discharge of a fluid flowing through the tubes of the bundle.

  In the example, the heat exchanger 10 is in the form of an evaporator capable of being traversed by a refrigerant fluid operating in the supercritical state, in particular CO2, the pressure of which can reach values of order of 100 to 150 bars. This fluid exchanges heat with a flow of air which sweeps the tube bundle to produce a flow of air conditioning, in part: in a motor vehicle.

  It can be seen that the header box 14 comprises a header plate 26 provided with openings 28 for receiving the tubes of the bundle. The openings 28 are of elongate shape and arranged in two rows corresponding to the two rows of tubes.

  The collecting plate 26 is generally rectangular in shape and comprises, along its two long sides, crimping members 30. It comprises an extension 32 in which holes 34 and 36 are provided for the respective mounting of the tubes 22 and 24. .

  Above the manifold plate 26 is placed a distribution plate 38 having two rows of slotted communication passages 40, each communicating with a tube 18 and a row of slotted communication passages 42, d = greater width which each communicate with two adjacent tubes belonging to the two rows of the beam. The passages 40 and 42 contribute to the distribution of the fluid and to its circulation in the tubes of the bundle along a defined path, which will be described below with reference to FIG. 13.

  Above the distribution plate 38 there is a cover 44 intended to be held against the collecting plate, trapping the distribution plate 38, under the action of the crimping members 30.

  The lower manifold 16 is made in a similar manner except that it has no extension. It consists of a collector plate 46, a distribution plate 48 and a cover 150. Note that the distribution plate 48 has two rows of passages 52, in the form of slots, each communicating with a beam tube at its lower part.

  Referring now to Figure 2 which shows a cross-sectional view of the manifold L4. FIG. 2 shows the collecting plate 26, the distribution plate 38 and the cover 44. The collecting plate 26 is a stamped plate having a planar inner face 54 for receiving the distribution plate 38 and an outer face 56 for from which extend flanges 58 respectively surrounding the openings 28 for receiving the tubes.

  In the example shown, the outer face 56 is directed downwards and the collars 58 are also directed downwards. These collars are thus arranged in two rows corresponding to the two rows of openings 28. In the example, the collars and the openings have a rectangular general section to allow the reception of flat tubes 18 having a homologous external section.

  The crimping members 30 are, as already indicated, formed along the two long sides of the collecting plate 26. They are in the form of a folded, slot-shaped edge with a number of tabs or teeth 60 (see also Figure 1).

  The distribution plate 38 has a flat inner face 62 adapted to come into contact with the flat inner face 54 of the header plate and an opposite outer plane face 64, able to receive the cover 44.

  In the thickness of the distribution plate, are arranged passages 40 and 42, in the form of slits, supra. In Figure 2 there are two passages 40 which communicate respectively with two adjacent tubes respectively belonging to the two rows of tubes of the beam.

  At the same time, the distribution plate 38 forms an insertion stop for the tubes as seen in FIG. 2. As a result, the respective ends of the tubes can not exceed the plane defined by the. inner face 54 of the collector plate.

  The cover 44 is made from a thick metal bar having two parallel edges 66 (FIG. 2) for supporting the crimping members 30. Thus, when the tabs 60 are folded, they hold the cover in the direction of the collector plate by trapping the distribution plate. The lid 44 has, as seen in the section of Figure 2, a series of bosses 68, six in number following transverse dilation. These bosses 68 delimit respectively channels 70 communicating with the tubes of the beam via the communication passages 40 and 42 (fent-shaped = s) of the distribution plate.

  These bosses are suitably arranged to allow the refrigerant fluid to penetrate inside the manifold 14 via the manifold 22, then circulate in the tubes of the bundle between the manifold 14 and the manifold 16 and leave the exchanger by the outlet pipe 24. The manner in which the circulation of the fluid occurs in the beam will be described in detail below.

  As seen in Figures 1 and 2, the cover 44 has a generally rectangular shape, the bosses 68 each extending in the longitudinal direction.

  The metal bar forming the cover 44 is a thick bar having an inner face 72, made flat, adapted to be applied against the outer plane face 64 of the distribution plate 38 (Figure 2). It is more specifically an extruded bar whose profile, before machining, is shown in FIG. 3. It can be seen that this bar comprises, opposite the inner face 72, a shaped outer face 74, whose profile defines the six bosses 68, dome-shaped or arched, as well as the two bearing edges 66. The profile of the bar is further limited by two lateral faces 76.

  According to the invention, the channels 70 are obtained by machining from the inner face 72 to obtain the profile shown in FIG. 4. It can be seen that the channels 70 are formed by grooves with a U profile and thus a rounded bottom in correspondence domes or arches mentioned above. As a result, the profile obtained after machining (Figure 4) defines a succession of arches having a sufficient thickness to allow good resistance to pressure. Given the fact that the machining is carried out in a metal bar, the thickness of the latter can be controlled so as to obtain each time a wall of sufficient thickness to withstand the pressio: .zs operation of the collector box and therefore the heat exchanger.

  FIG. 5 shows how the machining of the channels can be achieved by means of a single rotating tool 78 made in the form of a multi-stage cutter rotatable about an axis XX and comprising a series of crowns 80 with a profile rounded, here six in number, to simultaneously realize the six channels 70 in the cover 44. The machining is performed by moving the tool in the longitudinal direction of the bar, the axis of rotation of the tool being oriented transversely.

  Referring now to Figure 6 which shows a channel 70 having an end 82 terminating at a distance A of an end face 84 of the cover 44. This end 82 has, in the vicinity of the end face 34, a profile. longitudinal curved delimited by a radius R. The latter advantageously corresponds to the radius of the rings 80 of the machining tool 78. As a result, the end of each of the channels 70 is made non-emergent which avoids the recourse to end plates to close the channels. The other end of the channels 70 is made analogously. In other words, the grooves that form the channels are made in the material thickness of the metal bar, opening on the inner face 72, while allowing the material to remain so as to close the volume of the lid at its ends. longitudinal (end faces 84).

  Referring now to Figure 7 which shows, in longitudinal section, a cover 44 according to the invention in one embodiment. It can be seen that this cover has two series of channels 70A and 70B, the channels 70A having a longer length than the channels 70B and extending on the extension side 32 (FIG. 1). In the example, the channels 70A and 70B have a constant inner section along their entire length.

  Figure 8 shows, in longitudinal section, the cover 50 of the opposed manifold, which extends a shorter length than the cover 44 and which has a single series of channels 70C to form a return. The channels 70C extend over the entire length and here again have a constant inner section. As will be seen below, the cover 44 of FIG. 7 and the cover 50 of FIG. 8 make it possible to define an evaporator with four circulation passes.

  Figure 9 illustrates a variant of the cover 44 of Figure 7 in which the channels 70B have a constant inner section, while the channels 70A have a variable inner section, the bottom of the channels having a slope having an angle A1.

  FIG. 10 illustrates a variant of the cover 5C of FIG. 8 and it can be seen that the channels 70C also have a variable internal section whose bottom has a double slope defined by two opposite angles A2.

  Figure 11 shows another type of variable indoor section profile for a 70C channel. Each of the channels 70C has a main portion 85 produced by a first machining and a deeper central portion 86 made by a second machining. This profile requires a first machining by a tool similar to that described above and a second machining to form, over a portion of the length of the channel, the central portion 86 deeper.

  FIG. 12 illustrates another variant in which the channels 70 have a variable inner section made by a single machining, and therefore by a single tool. The bottom of each channel has an inclined portion 87 defined by a slope of angle A3 and a portion 89 of constant depth. It is understood that the machining tool must be moved in a controlled manner relative to the metal bar to control the machining depth.

  The use of channels of variable internal section, so of varying depth, allows each time to control the flow of fluid in the tubes that open into the channels in question.

  FIG. 13 shows, schematically, the distribution of a fluid for a four-pass exchanger, an evaporator, in which the covers 44 and 50 are shown schematically. The fluid enters the collecting box associated with the cover 44 as shown by the

  16 arrow F1. It opens into 70.1 channels of decreasing depth.

  The fluid then travels a portion of the tubes 18 of a first row corresponding to a first pass P ~. The channels 70.2 extend over the length of the cover 50 and have a profile similar to that of FIG. 10. The fluid then leaves the channels 70. 2 by another part of the tubes of the first row to form a second pass P2 and thus gain channels 70.3 of the cover 44 which, in the example, have a constant inner section. The fluid flows from these channels 70 to other channels 70.4 as shown by the arrow F2. These channels 70.4 also have a constant inner section.

  The fluid then leaves the upper header by traversing a portion of the second row of tubes to form a third pass P3 and gain channels 70.5 also extending over the entire length of cover 50. These channels 70.5 have a channel-like profile. 70.2. The fluid then leaves the lower manifold to form a fourth pass P4 through a portion of the tubes of the second row. The fluid thus gains 70.6 channels having a variable inner section similar to that of the channels 70.1. The fluid then leaves the heat exchanger as shown by the arrow F3.

  Thus, it is possible to work on the distribution of the fluid in the channels by making channels with variable inner section. It is possible to control and balance the flow rate of the fluid in the various passes P 1 to F 4, and this by varying the speed of the fluid by virtue of the different internal sections of the channels.

  The components of the manifold (manifold plate 26, distribution plate 38 and cover 44) are each made from a metal plate, preferably aluminum alloy, with a shoulder: it is sufficient to withstand the important pressures of the refrigerant. The fact of making several bosses 68 on the cover makes it possible to form small volume channels 70 limiting the effect of the pressure of the fluid on the components of the collector plate.

  These components are intended to be assembled by brazing once a provisional assembly obtained by crimping. It is therefore necessary to provide a braze plating.

  The method of manufacturing the header box 14 essentially comprises the following operations:

  a) producing a collector plate 26 or 46;

  b) achieve distribution means, here a distribution plate 38 or 48;

  c) making a cover 44 or 50 from a metal bar as defined above; and

  d) assembling the cover on the header plate with insertion of the distribution means so that the communication passages 40 or 42 open on the one hand to the distribution channels 38 or 48 and on the other hand to the openings 28 of the In the above embodiment, operation b) comprises the preparation of a distribution plate 38 or 48 which delimits the communication passages 40 and 42, while the operation d) comprises the interposition of the distribution plate between the header plate 26 or 46 and the inner face 72 of the cover.

  Then, the cover 14 is crimped onto the header plate 26 by means of crimping members: 0, enclosing the distribution plate.

  Referring now to Figure 14 which relates to another embodiment in which the cover 88 is similar to the cover 44 described above and corlporte two series of channels 70A and 70B in the form of parallel longitudinal grooves made in the longitudinal direction of the metal bar. The cover further includes communication passages 90 and 92 which are functionally similar to the previously described communication passages 40 and 42. However, these communication passes 90 and 92 are here parallel transverse grooves made by machining in the transverse direction of the metal bar, opening on the one hand on the distribution channels 70A and 70B and on the other hand on the face 94 inside the lid (Figures 15 and 16). The communication passages 90 and 92 are spaced apart by a pitch P corresponding to that of the tubes.

  As a result, it is no longer necessary to insert a distribution plate between the cover and the header plate, thereby eliminating a component. The assembly operation d) thus comprises the direct assembly of the header plate 28 or 46 against the inner face 94 of the cover 88. The cover is then crimped directly onto the header plate.

  In the embodiment of FIGS. 14 to 6, the machining of the grooves of the cover is carried out in two steps: 1) machining of the longitudinal grooves (channels 70A and 70B), 2) machining of the transverse grooves (passages 90 and 92) .

  The cover 88 thus groups the functions of passage and distribution of the fluid. This makes it possible to reduce the number of parts of the heat exchanger, to facilitate the assembly process and to reduce the risks of failure. In addition the inner face 94 of the cover 88 can be machined by forming recesses or steps 96 (Figures 15 and 16) forming stops for the introduction of the tubes 18. Once the manifold thus assembled, the whole of the heat exchanger can be assembled. The components of the bundle 12 (tubes and spacers) are arranged against each other and the ends of the tubes are placed, on one side, in the openings of the manifold 14 and, on the opposite side, in the openings of the box 16. Whatever the embodiment of the header,

  the whole of the heat exchanger can then be brazed, in a single operation, by passing through a suitable brazing furnace. During soldering, solder plating provides a connection between the various components.

  It is possible, in a variant, to braze the collector boxes separately before assembling them to the bundle and brazing the entire heat exchanger.

  The manifold 16 is made in a similar manner to the manifold 14, except that it does not have an extension for mounting fluid inlet and outlet manifolds.

  The manifold of the invention is capable of many variants. It finds a main application to heat exchangers traversed by a high-pressure refrigerant, in particular to air-conditioning evaporators traversed by a supercritical fluid such as CO2, such as those intended for motor vehicles.

Claims (24)

claims   1. Heat exchanger collector box, comprising a header plate (26; 46) provided with openings (28; for insertion of heat exchange tubes (18), and a cover (44; 50; 88); ) delimiting distribution channels (70) communicating with the tubes, characterized in that the cover (44; 50; 88) is a metal bar having an inner face (72; 94) and an opposite outer face (74); and in that the distribution channels (70) are grooves made in the material thickness of the metal bar, opening on the inner face (72; 94), allowing the roof to remain material so as to close the volume lid at its longitudinal ends.   The header box according to claim 1, characterized in that communication passages (40, 42; 9C, 92) are provided between the cover (44; 50; 88) and the header plate (26; 46).   Container according to Claim 2, characterized in that the communication passages (40, 42) are delimited by a distribution plate (38; 48) interposed between the header plate (26; 46) and the inner face (72). ) of the cover (44; 50).   4. collector box according to claim 2, characterized in that the communication passages (90, 92) are grooves of the metal bar opening on the one hand on 21 distribution channels (70) and on the other hand on the face interior (94) of the cover (88).   5. A header according to one of claims 1 to 4, characterized in that the distribution channels (70) and the communication passages (40, 42; 90, 92) are machined.   Container according to one of the claims: at 5, 10 characterized in that the cover (44; 50; 8E) is obtained from an extruded metal bar.   7. Slip-box according to claim 6, characterized in that the outer face (74) of the extruded metal bar is shaped so as to have a profile comprising a plurality of domes (68) corresponding to the distribution channels ( 70).   8. header box according to one of claims 1 to 7, characterized in that the distribution channels (70 have a constant inner section over their entire length.   9. header box according to one of claims 1 to 7, characterized in that the distribution channels (7C) have a variable inner section over their entire length.   10. The header according to claim 9, characterized in that the distribution channels comprise channels (70A) of variable inner section 30 whose bottom has a slope having an angle (Al).   11. Collector box according to the claim. 9, characterized in that the distribution channelsinclude channels (70C) of variable inner section whose bottom has a double slope defined by two opposite angles (A2).   12. Collector box according to claim 9, characterized in that the distribution channels comprise channels (70C) of variable inner section having a main portion (85) made by a first machining and a deeper central portion (86). performed by a second machining.   Container according to claim 9, characterized in that the distribution channels comprise channels (70C) of variable internal cross-section made by a single machining, whose bottom has an inclined part (87) defined by a slope having an angle (A3) and a portion (89) of constant depth.   14. A header according to one of claims 31 to 13, characterized in that the cover (50) comprises a single series of distribution channels (70) which each extend over the length of the metal bar.   15. A header according to one of claims 31 to 13, characterized in that the cover (44) comprises at least two sets of distribution channels (70, each extending over a portion of the length of the metal bar .   Container according to one of claims 1 to 15, characterized in that the distribution channels (70) have a bottom with a transverse U-shaped profile.   17. Collector box according to claim 16, characterized in that the channels (70) have in the vicinity of an end face (84) of the metal bar a curved longitudinal profile delimited by a radius (R).   18. Heat exchanger comprising a bundle of tubes (18) and at least one manifold (14, 16) according to one of claims 1 to 17. 10   19. Heat exchanger according to claim 18, characterized in that said exchanger comprises at least two passes and in that said inner sections of the distribution channels (70) make it possible to control and balance the fluid flow in said passes ( P1, P2, P3 and P4).   20. Heat exchanger according to claim 19, characterized in that it is in the form of an evaporator.   21. A method of manufacturing a manifold for a heat exchanger according to one of claims 1 to 17, characterized in that it comprises the following operations: a) producing a header plate (26; 46) having openings (28) receiving tubes; b) providing distribution means comprising: communication passages (40, 42; 90, 92); c) providing a cover (44; 50; 88) from a metal bar having an inner face (72; 94) and an opposite outer face (74) by machining distribution channels (70) in the form of grooves obtained by machining the metal bar in the longitudinal direction thereof by opening on said inner face; and d) assembling the cover (44; 50; 88) on the collecting lacquer (26; 46) with insertion of the dispensing means so that the communication passages (40,42; 90,92) open on the one hand on the distribution channels (70) and secondly on the openings: (28) of the header plate (26; 46).   22. Process according to claim 21, characterized in that step b) comprises preparing a distribution plate (38; 48) delimiting the communication passages (40, 42) and that the operation d) comprises interposing the distribution plate (38; 48) between the header plate (26; 46) and the inner face (72) of the cover.   23. The method of claim 21, characterized in that the operation b) comprises the realization of the communication gate (90, 92) in the form of grooves made by machining in the transverse direction of the metal bar, opening out of a part on the distribution channels (70) and on the inside (94) of the lid and that the operation d) comprises the direct assembly of the collecting plate (28; 46) against the inner face ( 94) of the cover (88).   24. Method according to one of claims 21 23, characterized in that the operation c) comprises the preparation of an extruded metal bar and the machining26 of the channels (70) by means of a multistage rotary tool ( 78) capable of simultaneously machining the channels over at least a portion of the length of the metal bar.