EP2629585A1

EP2629585A1 - Heating device, in particular for heating the passenger compartment of an automobile, and relative method of assembly of said device

Info

Publication number: EP2629585A1
Application number: EP13425027.3A
Authority: EP
Inventors: Fabrizio Promutico
Original assignee: Bitron SpA
Current assignee: Bitron SpA
Priority date: 2012-02-20
Filing date: 2013-02-15
Publication date: 2013-08-21
Anticipated expiration: 2033-02-15
Also published as: ITRM20120056A1; EP2629585B1

Abstract

The present invention concerns a heating device (1, 1a), connectable to a power supply, comprising: a support frame (2); one or more radiating elements (3), fixed to said support frame (2), each radiating element (3) comprising a containment tube (31) capable to operate as an electrode and connectable with said power supply, a longitudinal housing (32), arranged within said containment tube (31), a longitudinal electrode (33, 33a), connectable with said power supply and arranged within said longitudinal housing (32), so as to be isolated from said containment tube (31), means for generating heat (34), such as one or more PTC (Positive Temperature Coefficient) elements (34), inserted within said containment tube (31) and arranged between, and in contact with, said longitudinal electrode (33, 33a) and said containment tube (31), so that, by applying an electric current between said containment tube (31) and said longitudinal electrode (33), said heat generating means (34) generate heat, and compression means (35, 35a) housed within said longitudinal housing (32), interposed between said longitudinal housing (32) and said longitudinal electrode (33), said compression means (35, 35a) being adapted to ensure the electrical contact between said longitudinal electrode (33, 33a) and said heat generating means (34) and to ensure the electrical and thermal contact between said containment tube (31) and said heat generating means (34); and one or more dissipation fins (4) capable to dissipate the heat generated by said radiating elements (3).

The present invention even concerns a method for assembling a heating device (1, 1 a).

Description

The present invention relates to a heating device, in particular for heating the passenger compartment of an automobile, and relative method of assembly of said device.
More specifically, the invention concerns a heating device, or heater, for the passenger compartment of an automobile, studied and realized in particular to allow a high operation efficiency and an optimized construction.
In the following, the description will be directed to the use in a passenger compartment of an automobile but it is clear that the same should not be considered limited to this specific use.
As it is well known, currently the internal combustion engines, and in particular diesel engines, take some time to heat up, in case of they are not initially required high performance.
Electrical energy absorbed by the heater is converted in its turn into heat used to ensure greater comfort for users of the vehicle. The air flow passing through the heater, cooling the radiating mass typically heated by PTC pill (Positive Temperature Coefficient), reaches the ventilation openings present on the board of the automobile with a temperature 10 - 15° C higher with respect to that of the environment.
The heater is usually operated automatically from the car upon the occurrence of certain events, such as:

external temperature below a threshold preset by the manufacturer (e.g. 15 ° C);
appropriate energy balance: the battery voltage must be sufficient to ensure the regular operation of the essential functions of the car such as, for example, the engine management, lighting and safety devices power supply;
engine coolant temperature is below a threshold preset by the manufacturer (e.g. 60°C).

In general, the heater cannot be turned on or off by the driver.
Examples of heating devices according to the prior art are given by patent application DE 102007032896 and by patent EP 1528838 B1 .
Heating devices described above have manufacturing problems for an industrial production, as they have complications in the arrangement of the electrode-PTC pill assembly.
In light of the above, it is, therefore, object of the present invention providing a heating device that allows an effective assembly and a high efficiency of operation.
It is therefore specific object of the present invention a heating device, connectable to a power supply, comprising: a support frame; one or more radiating elements, fixed to said support frame, each radiating element comprising a containment tube capable to operate as an electrode and connectable with said power supply, a longitudinal housing, arranged within said containment tube, a longitudinal electrode, connectable with said power supply and arranged within said longitudinal housing, so as to be isolated from said containment tube, means for generating heat, such as one or more PTC (Positive Temperature Coefficient) elements, inserted within said containment tube and arranged between, and in contact with, said longitudinal electrode and said containment tube, so that, by applying an electric current between said containment tube and said longitudinal electrode, said heat generating means generate heat, and compression means housed within said longitudinal housing, interposed between said longitudinal housing and said longitudinal electrode, said compression means being adapted to ensure the electrical contact between said longitudinal electrode and said heat generating means and to ensure the electrical and thermal contact between said containment tube and said heat generating means; and one or more dissipation fins capable to dissipate the heat generated by said radiating elements.
Always according to the invention, said dissipation fins could be arranged parallel to each other and each one of them are provided with one or more holes, in number corresponding to the number of said radiating elements, said radiating elements being inserted in said holes, and said dissipation fins being fixed to the lateral surface of said radiating elements.
Still according to the invention, said longitudinal housing could be internally provided with lateral reliefs, and said longitudinal electrode could comprise laterally a plurality of grooves, arranged and spaced correspondingly to said protrusions, such that, by exerting a pressure on said compression means by said longitudinal electrode and moving longitudinally said longitudinal electrode with respect to said compression means, said longitudinal electrode arranges below said reliefs, so as to compress and/or preload said compression means.
Advantageously according to the invention, said longitudinal housing could be provided with two lateral guides, and said device could comprise a pair of rods, each respectively insertable in one of said lateral guides of said longitudinal housing, said rods interacting with said compression means, so as to compress and/or preload them.
Further according to the invention, said compression means could comprise one or more springs.
Always according to the invention, each of said springs could comprise side tabs capable to interact with said rods.
Still according to the invention, said compression means could comprise a longitudinal metal plate and said springs are arranged in series and formed by notch on said longitudinal metal plate.
Further according to the invention, said support frame could comprise an upper support, provided with an electric connector for connecting with an electric power supply, a support base, provided with one or more holes for housing and locking said radiating elements, and/or a lateral containment structure of said one or more dissipation fins, said longitudinal electrodes and said containment tubes being electrically connected with said electrical connector.
Advantageously according to the invention, said longitudinal electrodes could be connected with a first polarity of said power supply, preferably a positive polarity, and said containment tubes could be connected with a second polarity of said power supply, opposite to said first polarity, preferably the negative polarity.
It is further object of the present invention a method for assembling a heating device, as described above, comprising the following steps: (A) installing said containment tubes on said frame; (B) stacking said dissipation fins, by inserting each dissipation fins so that the containment tubes are inserted through said holes; (C) fixing said dissipation fins to said containment tubes; and (D) assembling said radiating elements.
Always according to the invention, said step (C) could comprise the step of mechanically expanding said containment tube, so that said dissipation fins adhere and fixe to the containment tube.
Still according to the invention, said step (D) could comprise the substeps of: arranging said compression means in said longitudinal housing; arranging said longitudinal electrode of said compression means; applying on said longitudinal electrode a perpendicular pressure and a longitudinal movement along a preset first direction so as to compress said compression means and arranging the longitudinal electrode below said reliefs of said longitudinal housing, so as to compress and/or preload said compression means; arranging said heat generating means in contact with said longitudinal electrode; inserting said longitudinal housing within said housing tube; and applying on said longitudinal electrode a longitudinal movement along a second direction, opposite to said first direction, so as to release longitudinal electrode from said reliefs of said longitudinal housing, raising said longitudinal electrode, pressing said PTC elements on said containment tube.
Advantageously according to the invention, said step (D) could comprise the substeps of: arranging springs in said longitudinal housing, in respective seats; placing said longitudinal electrode on said springs; arranging said heat generating means on said longitudinal electrode, in respective seats formed on said longitudinal housing; applying on said heat generating means a defined pressure, so as to compress said springs, to release said two lateral guides obtained on said longitudinal housing; inserting said two rods in said lateral guides, so that said rods interact with said lateral tabs of said springs, so as to compress them; inserting said longitudinal housing in said containment tube; and extracting said rods from said lateral guides.
The present invention will be now described, for illustrative but not limitative purposes, according to its preferred embodiments, with particular reference to the figures of the enclosed drawings, wherein:

figure 1 shows a perspective view of the heating device according to the present invention;
figure 2 shows a radiating fin of the heating device according to figure 1;
figure 3 shows an exploded view of the heating device according to figure 1;
figure 4 shows an exploded view of a radiating element of the heating device according to figure 1;
figure 5 shows the electrical connection of the terminals of the heating device according to figure 1;
figure 6 shows a detail of the dissipation fins insertion in a containment tube of the heating device according to the present invention;
figure 7 shows a containment tube of the heating device according to the present invention before the expansion;
figure 8 shows a containment tube of the heating device according to the present invention after dilatation;
figure 9a shows a sectional side view of of a springs, longitudinal electrode and PTC element assembly of the heating device according to the present invention, in which the springs are not compressed;
figure 9b shows a front view of figure 9a;
figure 10a shows a lateral section of a springs, longitudinal electrode and PTC element assembly of the heating device according to the present invention, in which the springs are compressed;
figure 10b shows a front view of figure 10a;
figure 11 shows the inserting step of a pair of rods in a longitudinal housing of the heating device according to the present invention;
figure 12 shows a front view of figure 11;
figure 13 shows the insertion of a pair of rods;
figure 14 shows the insertion of longitudinal slots in the respective containment tube of the heating device according to the present invention;
figure 15 shows a side view of the heating device according to the present invention, in which the rods are extracted from the longitudinal housing;
the figure 16a shows a sectional view of the heating device according to figure 15, in which the rods are not yet extracted;
figure 16b shows a sectional view of the heating device according to figure 15, in which the rods are extracted;
figure 17 shows an exploded view of a second embodiment of the heating device according to the present invention;
figure 18 shows an exploded view of a radiating element of the heating device according to figure 17;
figure 19 shows the insertion of an assembly step of the radiating element according to figure 18;
figure 20a shows a side sectional view of the radiant element of figure 18, in which the springs are not compressed;
figure 20b shows a cross section of the radiant element of figure 20a;
the figure 21a shows a side sectional view of the radiant element of figure 18, in which the springs are compressed;
figure 21b shows a cross section of the radiant element of figure 21a;
figure 22 shows a perspective view of the radiating element according to figure 18 in the springs compression step;
figure 23 shows the insertion of longitudinal slots in the respective containment tube of the heating device according to the present invention;
figure 24 shows a perspective view of the radiating element according to figure 18 in the springs release step;
the figure 25a shows a sectional view of the heating device according to figure 17, in which the springs are still compressed; and
figure 25b shows a sectional view of the heating device according to figure 17, in which the springs are released.

In the various figures, similar parts will be indicated by the same reference numbers.
Referring to figures 1-3, a heating device 1 according to the present invention can be observed.
Said heating device 1 comprises a support frame 2, one or more radiating elements or bars 3 or even radiating bars, installed on said support frame 2, and a plurality of dissipation fins 4 in thermal contact with said radiating bars 3, as it will be better described below.
Said support frame 2 comprises a support base 21, provided with holes 21' (which are visible in the following figure 14) and an upper support 22. Said upper support 22 also includes an electrical connector 23, connectable to a plug of the automobile, in which said heating device 1 is installed.
Said radiating bars 3, which are four in this embodiment, are adapted to generate the heat, which is radiated from the dissipation fins 4. Said radiating bars 3 have each one end 3', possibly removably fixable to said support base 21, and one end 3", possibly removably fixable to said upper support 22. Said radiating bars 3 also comprise (see figure 4) a containment tube 31, hollow inside and made of a material capable of conducting heat and electric current, so that said containment tube 31 can also act as electrical terminal, and a longitudinal housing 32, arranged within said containment tube 31 and provided with two lateral guides 32' and 32", whose function will be better explained below.
Said radiating bars 3 comprise inside a longitudinal electrode 33, having a terminal 33', which protrudes from said containment tube 31, at the end 3" of said radiating bars 3. Said longitudinal electrode 33 is arranged so as not to get into contact with said containment tube 31, and it is connected with said connector 23.
Furthermore, said bars 3 comprise a plurality of PTC (Positive Temperature Coefficient) radiating elements 34, which are pills made of ceramic, arranged in series with respect to one another, and a plurality of compression means or springs 35. In the embodiment shown, two springs 35 for each PTC element 34 are provided for illustrative and not limitative purpose. Said springs 35 are made of electrically conductive material and are placed in appropriate seats of said longitudinal housing 32 (not shown in the present invention) and arranged below said longitudinal electrode 33. Each spring 35 is provided with a pair of lateral tabs respectively 35' and 35", whose function will be better described below.
Said PTC elements 34 are also arranged in a respective seat obtained on said longitudinal housing 32.
Each of said radiating bars 3 also includes a pair of rods 36' and 36", respectively insertable in said two lateral guides 32' and 32", adapted to interact with said lateral tabs 35' and 35".
Said dissipation fins 4 are made of metal, i.e. of conductive material, and are arranged parallel to each other. Each of said dissipation fins 4 has one or more holes 41, corresponding to the number of bars 3 of said radiating heating device 1.
The operation of the heating device 1 described above is as follows.
When the automobile in which the heating device 1 is installed is powered, electric power is supplied to the heating device 1 by means of the electrical connector 23.
In the embodiment described, with reference to figure 5, it is seen that the radiating tubes 31, which, as mentioned, also operate as electrical terminals, are connected with the negative polarity power supply of the automobile, while terminals 33' of each longitudinal electrode 33 of the radiating bars 3, which, as said, is isolated from the containment tube 31 due to the longitudinal housing 32, in which it is placed, are connected with the power supply positive polarity.
In this way, by means of the assembly described above, the electric current passes through said longitudinal electrodes 33 of said radiating bars 3, through the springs 35, which, as mentioned above, are made of electrically conductive material and preferably shape memory, such as steel, copper or the like, and through said PTC elements 34. Each one of said PTC elements 34 operate as electrical resistance to the passage of the electrical current, so as to generate heat which is transmitted to said radiating tubes 31, and from the latter to said dissipation fins 4, which dissipate it. The electrical circuit is closed with said PTC elements 34 in contact with the radiating tubes 31, which as mentioned, are connected with the power supply negative polarity of said automobile.
Heat produced by said PTC elements 34 is dissipated, as mentioned above, by dissipation fins 4 and is conveyed inside the passenger compartment of the automobile, possibly by means of one fan, so that the airflow passes through said dissipation fins 4, heating up.
Referring now to figures 6-16, different steps of the assembling method of the heating device 1 according to the present invention are shown.
A first assembly step (see figures 3 and 6) consists of inserting the radiating tubes 31 in the base support 21, through said holes 21'.
Subsequently, radiating fins 4 are sheared so as to be stacked and guided by radiating tubes 31. Each single fin 4 is inserted so that the radiating tubes 31 pass through the holes 41.
In a following step (see figures 7 and 8) the containment tube 31 is mechanically expanded (see arrows in figure 7), by means of an ogive or similar means, so as to adhere the dissipation fins 4 to containment tube 31. In this way, interference between the containment tube 31 and the dissipation fins 4 is obtained, which ensures the mechanical connection.
Then, the components are inserted in the longitudinal housing 32. In particular, referring to figures 9a, 9b, 10a, 10b, 11, 12 and 13:

springs 35 are placed in said longitudinal slot 32, in said appropriate locations;
longitudinal electrode 33 is placed on the top of the springs 35, in this case without any pressure; and
PTC elements 34 are placed on said longitudinal electrode 33, in said suitable seats, obtained on the longitudinal housing 32.

Subsequently, a predetermined pressure (see arrow A of figure 9a) is, then, applied on PTC elements 34 and longitudinal housing 32, springs 35, longitudinal terminal 32, and PTC elements 34 assembly is compressed, thus compressing springs 35, up to completely release the two lateral guides 32' and 32", obtained on the longitudinal housing 32, as shown in figures 9b and 10b.
Keeping the assembly compressed, two rods 36' and 36" are inserted respectively into the lateral guides 32' and 32". Said rods 36' and 36" interact, respectively, with the lateral tabs 35' and 35" of each spring 35, so as to prevent said springs 35 to return to their free position, i.e. not compressed, until the longitudinal housings 32, in which the springs 35, longitudinal terminal 32 and PTC elements 34 assembly is contained, is not inserted inside the containment tube 31, as shown in figure 14.
In figures 15, 16a and 16b, rods 36', 36" are pulled in the direction of arrow B. Spring 35 tends to return to its open position, i.e. not compressed, pressing longitudinal terminal 33 and then PTC elements 34 on housing tube 31. The achieved effect with this solution is to ensure a correct pressure between longitudinal terminal 33, PTC element 34 and housing tube 31.
Figures 17-25 show the structure, the operation and the assembly steps of a second embodiment of the heating device 1a according to the present invention.
In particular, even in this case, heating device 1a comprises a support frame 2, provided with the upper support 22 and a lateral containment structure 24, a plurality of dissipation fins 4, and one or more radiating elements 3, in thermal contact with said dissipation fins 4.
Said radiating bars 3 comprise a containment tube 31 hollow inside and made of a material capable of conducting heat and electric current, so that said housing tube 31 can also act as electrical terminal, a longitudinal housing 32, open at the top and provided with lateral reliefs 32a, possibly arranged opposite, which function will be better defined in the following.
Said radiating bars 3 comprise inside a longitudinal electrode 33a, having a terminal 33a', which emerges from said longitudinal housing 32. Said longitudinal electrode 33a comprises laterally a plurality of grooves 33a", corresponding to said reliefs 32a, which function will be better defined in the following.
Between said longitudinal housing 32 and said longitudinal electrode 33a, compression means 35a are interposed, housed within said longitudinal housing 32 and provided with a plurality of springs. In particular, said springs are arranged in series and obtained by carving on a longitudinal metal plate. Finally, above said longitudinal electrode 33a, a plurality of PTC elements 34 is arranged.
The assembly of the radiant element 3a, before its insertion through the dissipation fins 4, is as follows.
Initially, said compression means 35a are located in said housing 32. Then said longitudinal electrode 33a is placed in said housing 32, overlapped to said compression means 35a, by passing the lateral reliefs 32a through said grooves 33a". Said PTC elements 34 are then placed above said longitudinal electrode 33a. To allow (see figures 20a-22) the insertion of housing 32, compression means 35a and longitudinal electrode 33a assembly whitin the housing tube 31, possibly reinserted between the dissipation fins 4, on longitudinal electrode 33a, a stress is exerted on said longitudinal electrode 33a, so as to compress said compression means 35a (arrow C) and translate the longitudinal electrode 33a itself in the direction of arrow D. In this way, there is the effect of moving said lateral reliefs 32a of said longitudinal housing 32 under said longitudinal electrode 33a, keeping in compression the springs of said compression means 35a. Thus, the assembly formed by the housing 32, the compression means 35a and the longitudinal electrode 33a can be easily inserted within a respective containment tube 31 (see figure 23). In other words, it creates an engagement between the longitudinal electrode 33a and the longitudinal housing 32.
Then to allow heat transmission from said PTC elements to said containment tube 31, once that said assembly is inserted into said containment tube 31, the inverse compression operation of the compression means 35a referred above, is carried out. In particular, said longitudinal electrode 33a (see figures 24-25b) is pulled according to arrow E (which has a direction opposite to the arrow D), so translating and allowing each groove 33a" to arrange in correspondence of a respective lateral relief 32a, disengaging longitudinal electrode 33a, allowing it to move vertically. Thus, compression means 35a are disengaged, i.e. no longer kept in compression by said longitudinal electrode 33a, and raise said longitudinal electrode 33a, by pressing (see figures 24-25b) longitudinal terminal 33a, and therefore PTC elements 34, on the housing tube 31, ensuring an optimum pressure between longitudinal terminal 33, PTC element 34 and housing tube 31.
The present invention has been described for illustrative but not limitative purposes, according to its preferred embodiments, but it is to be understood that modifications and/or changes can be introduced by those skilled in the art without departing from the relevant scope as defined in the enclosed claims.

Claims

Heating device (1, 1a), connectable to a power supply, comprising:
a support frame (2);

one or more radiating elements (3), fixed to said support frame (2), each radiating element (3) comprising

a containment tube (31) capable to operate as an electrode and connectable with said power supply,

a longitudinal housing (32), arranged within said containment tube (31),

a longitudinal electrode (33, 33a), connectable with said power supply and arranged within said longitudinal housing (32), so as to be isolated from said containment tube (31),

means for generating heat (34), such as one or more PTC (Positive Temperature Coefficient) elements (34), inserted within said containment tube (31) and arranged between, and in contact with, said longitudinal electrode (33, 33a) and said containment tube (31), so that, by applying an electric current between said containment tube (31) and said longitudinal electrode (33), said heat generating means (34) generate heat, and

compression means (35, 35a) housed within said longitudinal housing (32), interposed between said longitudinal housing (32) and said longitudinal electrode (33), said compression means (35, 35a) being adapted to ensure the electrical contact between said longitudinal electrode (33, 33a) and said heat generating means (34) and to ensure the electrical and thermal contact between said containment tube (31) and said heat generating means (34); and

one or more dissipation fins (4) capable to dissipate the heat generated by said radiating elements (3).
Heating device (1, 1a) according to claim 1, characterized in that said dissipation fins (4) are arranged parallel to each other and each one of them are provided with one or more holes (41), in number corresponding to the number of said radiating elements (3), said radiating elements (3) being inserted in said holes (41), and said dissipation fins (4) being fixed to the lateral surface of said radiating elements (3).
Heating device (1) according to anyone of the preceding claims, characterized
in that said longitudinal housing (32) is internally provided with lateral reliefs (32a), and
in that said longitudinal electrode (33a) comprises laterally a plurality of grooves (33a"), arranged and spaced correspondingly to said protrusions (32a),
such that, by exerting a pressure on said compression means (35, 35a) by said longitudinal electrode (33a) and moving longitudinally said longitudinal electrode (33a) with respect to said compression means (35, 35a), said longitudinal electrode (33a) arranges below said reliefs (32a), so as to compress and/or preload said compression means (35, 35a).
Heating device (1) according to anyone of claims 1 or 2, characterized
in that said longitudinal housing (32) is provided with two lateral guides (32', 32"), and
in that it comprises a pair of rods (36', 36"), each respectively insertable in one of said lateral guides (32', 32") of said longitudinal housing (32), said rods (36', 36") interacting with said compression means (35), so as to compress and/or preload them.
Heating device (1, 1a) according to anyone of the preceding claims, characterized in that said compression means comprise one or more springs (35).
Heating device (1) according to claim 5, when dependent on claim 4, characterized in that each of said springs (35) comprise side tabs (35', 35") capable to interact with said rods (36', 36").
Heating device (1, 1a) according to anyone of the preceding claims, characterized in that said compression means (35a) comprise a longitudinal metal plate and said springs are arranged in series and formed by notch on said longitudinal metal plate.
Heating device (1, 1a) according to anyone of the preceding claims, characterized in that said support frame (2) comprises an upper support (22), provided with an electric connector (23) for connecting with an electric power supply, a support base (21), provided with one or more holes (21') for housing and locking said radiating elements (3), and/or a lateral containment structure (24) of said one or more dissipation fins (4), said longitudinal electrodes (33) and said containment tubes (31) being electrically connected with said electrical connector (23).
Heating device (1) according to anyone of the preceding claims, characterized in that
said longitudinal electrodes (33, 33a) are connected with a first polarity of said power supply, preferably a positive polarity, and
said containment tubes (31) are connected with a second polarity of said power supply, opposite to said first polarity, preferably the negative polarity.
Method for assembling a heating device (1, 1a), according to anyone of claims 1-9, comprising the following steps:
(A) installing said containment tubes (31) on said frame (2);

(B) stacking said dissipation fins (4), by inserting each dissipation fins (4) so that the containment tubes (31) are inserted through said holes (41);

(C) fixing said dissipation fins (4) to said containment tubes (31);
and

(D) assembling said radiating elements (3, 3a).
Method according to claim 10, characterized in that said step (C) comprises the step of mechanically expanding said containment tube (31), so that said dissipation fins (4) adhere and fixe to the containment tube (31).
Method according to anyone of claims 10 or 11, characterized in that said step (D) comprises the substeps of:
- arranging said compression means (35, 35a) in said longitudinal housing (32);

- arranging said longitudinal electrode (33a) of said compression means (35, 35a);

- applying on said longitudinal electrode (33a) a perpendicular pressure and a longitudinal movement along a preset first direction so as to compress said compression means (35, 35a) and arranging the longitudinal electrode (33a) below said reliefs (32a) of said longitudinal housing (32), so as to compress and/or preload said compression means (35, 35a);

- arranging said heat generating means (34) in contact with said longitudinal electrode (33, 33a);

- inserting said longitudinal housing (32) within said housing tube (31); and

- applying on said longitudinal electrode (33, 33a) a longitudinal movement along a second direction, opposite to said first direction, so as to release longitudinal electrode (33, 33a) from said reliefs (32a) of said longitudinal housing (32), raising said longitudinal electrode (33a), pressing said PTC elements (34) on said containment tube (31).
Method according to anyone of claims 10 - 12, characterized in that said step (D) comprises the substeps of:
- arranging springs (35) in said longitudinal housing (32), in respective seats;

- placing said longitudinal electrode (33) on said springs (35);

- arranging said heat generating means (34) on said longitudinal electrode (33), in respective seats formed on said longitudinal housing (32);

- applying on said heat generating means (34) a defined pressure, so as to compress said springs (35), to release said two lateral guides (32', 32") obtained on said longitudinal housing (32);

- inserting said two rods (36', 36") in said lateral guides (32', 32"), so that said rods (36', 36") interact with said lateral tabs (35', 35") of said springs (35), so as to compress them;

- inserting said longitudinal housing (32) in said containment tube (31); and

- extracting said rods (36', 36") from said lateral guides (32', 32").