WO2015052737A1

WO2015052737A1 - Method of manufacturing a coaxial electric resistance and coaxial electric resistance

Info

Publication number: WO2015052737A1
Application number: PCT/IT2013/000282
Authority: WO
Inventors: Renzo Re; Pierpaolo Laveni; Daniele FERRI
Original assignee: GAMMA SpA
Current assignee: GAMMA SpA
Priority date: 2013-10-11
Filing date: 2013-10-11
Publication date: 2015-04-16
Anticipated expiration: 2016-04-11
Also published as: AR097979A1

Abstract

A method of manufacturing a coaxial electric resistance (1) comprises preparing a first insulating support (2) comprising a predetermined number of first blades (3) and winding a resistive wire (1 1) around the first insulating support (2) forming a first winding (9). A hollow insulating body (12) is fitted onto the first winding (9) in a position radially outside with respect to the first winding (9). A second insulating support (13) comprising a predetermined number of second blades (14) is arranged in a position radially outside the hollow insulating body (12). The resistive wire (11) is wound around the second insulating support (13) forming a second winding (17).

Description

DESCRIPTION

METHOD OF MANUFACTURING A COAXIAL ELECTRIC RESISTANCE AND COAXIAL ELECTRIC RESISTANCE

Technical field

The present invention has as its subject a method of manufacturing a coaxial electric resistance.

The present invention also has as its subject a coaxial electric resistance.

State of the art

The coaxial electric resistance according to the present invention is usable for heating airflows for example in hairdryers, hand dryers, paint strippers or other similar devices.

As is well-known, the term 'coaxial electric resistance' is used to mean an electric resistance in which the resistive wire (or the resistive wires) form two heating windings, the one arranged inside the other. Preferably the term coaxial indicates that the axes of the two heating windings coincide, even though resistances can be made with axes slightly offset or inclined with respect to each other.

A known example of coaxial electric resistance is described and illustrated in Italian patent IT1289406. In accordance with this example, a plurality of blades mutually intersect at a central axis and at the same time form a support for an inner winding and a support for an outer winding formed from a resistive wire shaped according to at least one predetermined waveform. To mutually insulate the two windings, an insulating sleeve is provided, machined so as to have a plurality of axial slots, each adapted to receive a blade. The insulating sleeve thus prepared is inserted axially between the two windings already wound onto the blades.

The insulating sleeve makes it possible to reduce the distance between the two windings and therefore the overall radial dimension of the resistance, thus avoiding the possibility of an electric arc being formed between the windings themselves. Furthermore, both the presence of the insulating sleeve and the limited distance between the windings means that there are limited flows of cold air.

On the other hand the electrical resistance according to the known art presents some disadvantages that limit productivity at the manufacturing stage and limit its operation in use.

In the first place the need to have a slotted insulating sleeve requires machining of the sleeve itself which lengthens production times, increases the number of machines involved and is additional to the automatic production of the resistance itself.

Again because of the machining of the insulating sleeve, the dimensions of the sleeve itself and therefore of the electrical resistance are constrained by the material of the sleeve in order to avoid excessive weakening.

Even if the above precautions are adopted, this machining inevitably weakens the structure of the insulating sleeve, constrains the number of blades to the number of possible slots and makes even more delicate and complex the stage of insertion between the two windings, in which it is necessary to accurately line up and insert each blade in a respective axial slot in the sleeve.

This insertion stage must be performed manually, interrupting automatic production of the resistance, and under constant ohmic monitoring to check that there is no risk of short circuit between the two windings.

In addition to the above, the insulating sleeve inevitably has a continuous portion, i.e. containing no slots, which in the assembled configuration of the resistance extends externally to the windings in an axial direction, increasing the axial dimensions of the resistance itself.

Although on the one hand the known art is advantageous in that the blades themselves provide support both for the inner winding and for the outer winding, thus obtaining a saving in material, on the other hand this aspect is disadvantageous due to the fact that the number of waves in the inner winding is constrained by the number of blades. Furthermore, the fact that the blades rest on the inner winding implies that the height of the wave of the inner winding is defined by the geometry of the blades and makes the positioning of the blades themselves particularly critical.

Finally the modalities of manufacturing the inner winding limit the choice of the diameters and waveforms of the resistive wire.

Object of the invention

In this context, the technical task at the base of the present invention is to provide a method of manufacturing a coaxial electric resistance and a coaxial electric resistance which overcome at least one of the aforementioned disadvantages of the known art.

In particular, it is an object of the present invention to make available a method of manufacturing a coaxial electric resistance wherein the stages of machining and the machines necessary for their execution are limited and as far as possible automated so as to reduce costs and production times.

A further object of the present invention is to propose a method of manufacturing a coaxial electric resistance which eliminates the steps which require excessive attention and manual input or which require the application of constant checks or which constitute a risk of wastage through breakages or incorrect alignments.

Yet another object of the present invention is to propose a coaxial resistance of modest dimensions which is versatile from the viewpoint of the independent configuration of the two windings and of the relative waveforms.

The technical task set and the objects specified are substantially attained by a method of manufacturing a coaxial electric resistance and a coaxial electric resistance, each comprising the technical characteristics as set out in one or more of the accompanying claims. The dependent claims correspond to different embodiments of the invention.

Brief description of the drawings

Further characteristics and advantages of the present invention will more fully emerge from the indicative, and therefore non-limiting, description of a preferred but not exclusive embodiment of a method of manufacturing a coaxial electric resistance and a coaxial electric resistance, as illustrated in the accompanying drawings, in which:

figure 1 is a schematic perspective view of a first stage of the method according to the present invention;

figure 2 is a schematic perspective view of a subsequent stage of the method according to the present invention;

figure 3 is a schematic perspective view of a subsequent stage of the method according to the present invention;

- figure 4 is a schematic perspective view of a subsequent stage of the method according to the present invention;

figure 5 is a schematic side view of figure 4;

figure 6 is a schematic perspective view of a subsequent stage of the method according to the present invention;

- figure 7 is a schematic side view of figure 6;

figure 8 is a schematic perspective view of a subsequent stage of the method according to the present invention;

figure 9 is a schematic side view of figure 8;

figure 10 is a schematic perspective view of a subsequent stage of the method according to the present invention;

figure 11 is a schematic perspective view of a subsequent stage of the method according to the present invention;

figure 12 is a schematic perspective view of a subsequent stage of the method according to the present invention corresponding to a schematic perspective view of a possible embodiment of a coaxial electric resistance according to the present invention;

figure 13 is a schematic front view of figure 12;

figure 14 is a schematic perspective view of a possible embodiment of a coaxial electric resistance according to the present invention;

- figure 15 is a schematic side view of figure 14;

figure 16 is a schematic front view of figure 14. Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, in particular to figures 12 and 13, no. 1 comprehensively indicates a coaxial electric resistance.

A first insulating support 2, more clearly indicated in figure 2, comprises a predetermined number of first blades 3 extending on planes mutually intersecting at a central axis 4. The first blades 3 are preferably made of electrically insulating and heat-resistant material, for example mica or other anti-static material.

With reference to figures 1 and 2, a first blade 3 comprises a slot 5 arranged along the central axis 4 and debouching at the outside of the first blade at an end portion 6 of the first blade itself. No. 7 indicates two teeth having the function of stops as will be described later.

Preferably the first insulating support 2 and in particular each first blade 3 comprises a series of housings 8 distributed along the central axis 4 on opposite sides of each first blade, whose functions will be described in detail in what follows.

According to the embodiment of figures 1 and 2, the first insulating support 2 comprises two first blades intersecting each other at the central axis 4 and arranged at 90° to each other. In this case the end portions 6 of the two first blades 3 are respectively opposed so that the two slots mutually face each other.

According to a first possible embodiment, for example illustrated in figures 1 and 2, the first insulating support 2 comprises a waiting axial portion 2a and an operative axial portion 2b whose functions will be described in detail in what follows.

It should be noted that, as will be described below, the waiting axial portion 2a can also be absent and the insulating support 2 can comprise solely the operative axial portion 2b (figures 14 and 15).

Figures 1 and 2 illustrate furthermore two stages of a method of manufacturing a coaxial electric resistance the first insulating support 2 is envisaged as being prepared as described above. With reference to figures 12 and 13, the coaxial electric resistance 1 comprises a first winding 9. This first winding, more clearly illustrated in figure 6, is made up of a plurality of first turns 10 of resistive wire 11 wound round the first insulating support 2. Preferably the resistive wire 11 is shaped according to at least one predetermined waveform which can comprise sinusoidal and/or zig-zag and/or square-wave and/or spiral and, more generally, any form of undulations.

Each first turn 10 is housed in one of the housings 8, for example at a peak of one of the waves. Between a first blade and the next a constant or variable number of waves can be provided.

Figure 6 corresponds also to a stage of the method of manufacturing a coaxial electric resistance wherein the resistive wire 11 is envisaged as being prepared and wound round the first insulating support 2, making it advance along the central axis, for example along a first direction of advancement X, and forming a predetermined number of first turns 10, so that the set of first turns 10 forms the first winding 9 of the coaxial electric resistance.

In accordance with a possible embodiment, for example illustrated in figures 12 and 13, the first insulating support 2 has a length I (figure 7), measured along the major central axis 4, greater than a first length L1 of the first winding 9. In particular the first winding 9 is wound radially outside the operative axial portion 2b of the first insulating support 2, having therefore a length at least equal to L1 .

No. 12 indicates a hollow insulating body comprising a lateral wall 12a arranged radially outside the first winding 9. The hollow insulating body 12 is preferably made of electrically insulating and heat-resistant material, for example mica or other anti-static material.

Figures 3-9 illustrate more clearly the characteristics of the hollow insulating body 12 whose lateral wall 12a delimits a cavity 14 open at opposite ends with respect to a longitudinal direction A of the hollow insulating body itself. It should be noted that in figures 3-9, in particular in figure 3, the longitudinal direction A coincides with the central axis 4 since these drawings illustrate some stages of the method according to the present invention wherein the hollow insulating body 12 is envisaged as being arranged as previously described and fitted longitudinally and coaxially over the first winding so that the lateral wall 12a is arranged radially outside the first winding 9.

In particular, figures 3-9 correspond to a first possible embodiment of the method according to the present invention wherein the following is envisaged:

- preparing the first insulating support 2 having a length I measured along the central axis 4 greater than the first length L1 of the first winding (in the specific case illustrated in figures 3-9, the first insulating support 2 comprises the waiting axial portion 2a and the operative axial portion 2b),

- forming the first winding 9 of the coaxial electric resistance by winding the resistive wire 1 1 around the operative axial portion 2b of the first insulating support 2.

In more detail, figures 3-9 correspond to a first possible embodiment of the method according to the present invention wherein the following is envisaged:

- fitting the hollow insulating body 12 over the first insulating support 2 (figure 3);

- putting the hollow insulating body 12 in waiting onto the waiting axial portion 2a of the first insulating support 2 (figure 4 and 5);

- fitting the hollow insulating body externally over the first winding 9 which is radially wound outside the operative axial portion 2b of the first insulating support 2.

In even more detail, figures 3-9 correspond to a possible embodiment of the method according to the present invention wherein the following is envisaged:

- fitting the hollow insulating body 12 onto the first insulating support 2 previously to the formation of the first winding 9 (figure 3); - putting the hollow insulating body 12 in waiting in the waiting axial portion 2a of the first insulating support 2 during the formation of the first winding 9 around the operative axial portion 2b of the first insulating support 2 (figure 6).

With reference to the coaxial electric resistance 1 of figures 12 and 13, no. 13 indicates a second insulating support. The second support 13, more clearly illustrated in figures 10 and 11, comprises a predetermined number of second blades 14. The second blades 14 extend on planes mutually intersecting at the central axis 4. Unlike the first blades 3, the second blades 14 do not intersect each other at the central axis 4 since the second blades 14 are arranged in a position radially outside the hollow insulating body 12.

The second blades 14 are preferably made of electrically insulating and heat- resistant material, for example mica or other anti-static material.

Preferably each second blade 14 comprises two axial stops 15 configured for receiving the hollow insulating body 12. The two axial stops contain the hollow insulating body 12 along the central axis 4 and keep it in position with respect to the first winding 9.

Preferably every second blade 14 comprises a housing 16 configured for receiving the teeth 7 which have the function of stops for the first blades 3 in cases where a first blade lies in the same plane as a second blade. In particular the second blades 14 are externally adjacent to the hollow insulating body 12, embracing the first blades 3 in a radial and axial direction with respect to the central axis. For example, each second blade 14 has a "C" shaped conformation, with an axial portion 14a arranged parallel to the central axis 4 and two radial portions 14b arranged end to end with respect to the axial portion and on opposite sides of the central axis 4.

Preferably the second insulating support 13 and in particular each second blade 14 comprises a series of housings 13a distributed along the central axis 4 on opposite sides of each second blade, whose functions will be described in detail in what follows.

In the assembled configuration of the coaxial electric resistance, at least one of the second blades 14 can be externally adjacent to the hollow insulating body 12 parallel to one of the first blades 3.

According to a possible embodiment for example illustrated in figures 12 and 13, the second insulating support 13 comprises at least two second blades 14 extending on planes mutually intersecting at the central axis 4. In particular the second blades 14 are uniformly distributed around the hollow insulating body 12. Preferably, the number of the second blades 14 can vary from two to twenty, but embodiments with an even greater number of second blades are not excluded.

Figures 10 and 11 which show most clearly the second insulating support

13 correspond to a possible embodiment of the method according to the present invention wherein the second insulating support 13 is envisaged as being prepared as previously described.

In particular it is envisaged that a predetermined number of second blades

14 should be radially arranged with respect to the central axis 4 externally adjacent to the hollow insulating body 12, and kept in position. At the stage of bringing them adjacent to the hollow insulating body 12, the hollow insulating body 12 is arranged between the two axial stops 15 of the second blades 14.

Preferably the second blades 14 are brought externally adjacent to the hollow insulating body, embracing the first blades 3 in a radial and axial direction with respect to the central axis 4.

Preferably at least one of the second blades 14 is brought externally adjacent to the hollow insulating body 12 parallel to one of the first blades 3.

With reference to figures 12 and 13, no. 17 indicates a second winding made up of a plurality of second turns 18 of the resistive wire 11 wound round the second insulating support 13. Each first turn 18 is housed in one of the housings 13a, for example at a peak of one of the waves. Between one second blade and the next there can be provided a constant or variable number of waves.

The resistive wire 1 1 (or different resistive wires) form two heating bodies, one wedged inside the other, consisting respectively of the first and second windings.

Figure 12 corresponds also to a stage of the method according to the present invention wherein the resistive wire 1 1 is envisaged as being wound around the second insulating support 13 making it advance along the central axis 4, according to a second direction of advancement Y, which may be the same as X or different, and forming a predetermined number of second turns 18.

The directions of advancement X and Y can be the same in the event that the windings, inner and outer, are not made with a single wire but with two separate wires, therefore with a break in continuity.

In this case the second winding will also be made in different directions. The set of second turns 18 forms the second winding 17 of the coaxial electric resistance, having a second length L2 measured along the central axis 4.

It should be noted that the hollow insulating body 12 is fitted longitudinally and coaxially onto the first winding 2 subsequently to the formation of the first winding 9 and prior to the formation of the second winding 17.

The winding of the resistive wire 1 1 around the second insulating support 13 locks the second blades 14 with respect to the hollow insulating body 12.

It should be noted that the hollow insulating body 12 has a length L (figure 7) measured along its longitudinal direction A (or along the central axis 4 in the assembled configuration of the coaxial electric resistance) such as to mutually insulate the first winding 9 and the second winding 17, so that the lateral wall 12a of the hollow insulating body 12 forms a continuous wall separating the first and second windings. In particular the length L of the hollow insulating body 12 is preferably greater than or equal to the lesser of the first length L1 and the second length L2 respectively of the first and second windings. This length L can even be slightly less than the lesser of the two lengths L1 and L2, but only if this does not prejudice its function as insulation. In the example illustrated in figures 12 and 13, the second winding 13 is envisaged as being formed with a second length L2 (figure 12) greater than the first length L1 of the first winding 9.

In the event that the same resistive wire 11 is used to form both the first winding and the second winding, i.e. proceeding without interrupting the continuity of the resistive wire between the first and the second windings, the following is advantageously envisaged:

- winding the resistive wire around the first insulating support 2 making it advance according to a first direction of advancement X (figure 7) to form the first winding of the coaxial electric resistance;

- fitting the hollow insulating body 12 longitudinally and coaxially onto the first winding 9 according to the first direction of advancement X;

- winding the resistive wire 11 around the second insulating support 13 making it advance according to a second direction of advancement Y (figure 12) opposed to the first direction of advancement X, to form the second winding of the coaxial electric resistance.

Figures 14-16 illustrate a possible embodiment of a coaxial electric resistance wherein the components analogous to those described in the embodiment of figures 12 and 13 are indicated with the same reference number. To manufacture the coaxial electric resistance of figures 14-16, the second winding 17 is envisaged as being formed with a second length L2 substantially equal to the first length L1 of the first winding 9.

In this case the method of manufacturing the coaxial electric resistance comprises the stages previously described with the peculiarity that the hollow insulating body 12 is fitted longitudinally and coaxially onto the first winding 9 while it is fitted onto the first insulating support 2 since, as mentioned above, in this case the insulating support 2 lacks the waiting axial portion 2a. In other words in this case the stage at which the hollow insulating body 12 is fitted longitudinally and coaxially onto the first insulating support 2 is subsequent to the stage of forming the first winding 9.

In the event that the same resistive wire 11 is used to form both the first winding and the second winding, the first direction of advancement X and the second direction of advancement Y are indicated in figure 15.

The method and the coaxial resistance according to the invention make it possible to significantly limit the axial and radial dimensions of the resistance itself, to reduce the number of blades and to deconstrain the number of waves of the first winding with respect to the number of blades in the second insulating support.

Furthermore, since the second blades do not rest on the first winding, the height of the wave of the first winding is independent of the geometry of the second blades and the positioning of the second blades is facilitated. In addition to the above, the relationship between the first and the second blades can be arbitrary.

Furthermore, the method is semi-automated and can be performed on a single machine even with reference to the stage of fitting the hollow insulating body.

The presence of a hollow insulating body having a continuous lateral wall, i.e. without axial slots, makes it possible to choose the preferred dimensions of the insulating body itself, to eliminate waste due to breakages and to limit the overall axial dimension of the electrical resistance.

Claims

1. A method of manufacturing a coaxial electric resistance (1), comprising:

- preparing a first insulating support (2) comprising a predetermined number of first blades (3) extending on planes mutually intersecting at a central axis (4);

- preparing a resistive wire (11) preferably shaped according to at least one predetermined waveform or spiral;

- winding said resistive wire (11) around said first insulating support (2) making it advance along said central axis (4) and forming a predetermined number of first turns (10), the set of said first turns (10) forming a first winding (9) of the coaxial electric resistance (1);

- preparing a hollow insulating body (12) comprising a lateral wall (13) delimiting a cavity (14) open at opposite ends with respect to a longitudinal direction (A) of said hollow insulating body (12);

- fitting said hollow insulating body (12) longitudinally and coaxially over said first winding (9) so that said lateral wall (13) is arranged radially outside said first winding (9);

- preparing a second insulating support (13) comprising a predetermined number of second blades (14) extending on planes mutually intersecting each other at said central axis (4), said second blades (14) being arranged in a position radially outside said hollow insulating body (12);

- winding said resistive wire (11) around said second insulating support (13) making it advance along said central axis (4) and forming a predetermined number of second turns (18), the set of said second turns (18) forming a second winding (17) of the coaxial electric resistance (1); wherein said hollow insulating body (12) has a length (L) measured along said longitudinal direction (A) such as to mutually insulate said first winding (9) and said second winding (17).

2. A method of manufacturing a coaxial electric resistance according to claim 1 , wherein said hollow insulating body (12) is fitted longitudinally and coaxially onto said first winding (9) subsequently to the formation of said first winding (9) and prior to the formation of said second winding (17).

3. A method of manufacturing a coaxial electric resistance according to one or more of the preceding claims, comprising:

- winding said resistive wire (11) around said first insulating support (2) making it advance according to a first direction of advancement (X) to form said first winding (9) of the coaxial electric resistance (1);

- fitting said hollow insulating body (12) longitudinally and coaxially onto said first winding (9) according to said first direction of advancement (X);

- winding said resistive wire (11) around said second insulating support (13) without interrupting its continuity between said first and second windings, making it advance according to a second direction of advancement (Y) opposite to the first direction of advancement (X) to form said second winding (17) of the coaxial electric resistance (1);

4. A method of manufacturing a coaxial electric resistance according to one or more of the preceding claims, comprising:

- winding said resistive wire (11) around said first insulating support (2) to form said first winding (9) which has a first length (L1) measured along said central axis (4);

- preparing and fitting said hollow insulating body (12) which has a determinate length (L) measured along said longitudinal direction (A);

- winding said resistive wire (11) around said first insulating support (13) to form said second winding (17) which has a second length (L2) measured along said central axis (4);

wherein said length (L) of the hollow insulating body (12) is greater or less than or equal to the lesser of the first length (L1) and the second length (L2) respectively of the first and second windings.

5. A method of manufacturing a coaxial electric resistance according to claim 4, comprising forming said second winding (17) with said second length (L2), greater than said first length (L1 ) of said first winding (9).

6. A method of manufacturing a coaxial electric resistance according to claim 5, comprising:

- preparing said first insulating support (2) with a length (I) measured along said central axis (4) greater than said first length (L1 ) of said first winding (9), said first insulating support (2) comprising a waiting axial portion (2a) and an operative axial portion (2b),

- forming said first winding (9) of the coaxial electric resistance (1) winding said resistive wire (1 1) around said operative axial portion (2b).

7. A method of manufacturing a coaxial electric resistance according to claim 4, comprising forming said second winding (17) having said second length (L2) equal to said first length (L1 ) of said first winding (9).

8. A method of manufacturing a coaxial electric resistance according to one or more of the preceding claims, comprising:

- fitting said hollow insulating body (12) over said first insulating support (2);

- putting said hollow insulating body (12) in waiting onto a waiting axial portion (2a) of said first insulating support (2b);

- fitting said hollow insulating body (12) externally onto said first winding (9) which is radially wound outside an operative axial portion (2b) of said first insulating support (2).

9. A method of manufacturing a coaxial electric resistance according to claim 8, comprising:

- fitting said hollow insulating body (12) over said first insulating support (2) prior to the formation of said first winding (9);

- putting said hollow insulating body (12) in waiting in said waiting axial portion (2a) of said first insulating support (2) during the formation of said first winding (9) around said operative axial portion (2b) of said first insulating support (2).

10. A method of manufacturing a coaxial electric resistance according to one or more of the preceding claims, wherein preparing a second insulating support (13) comprises bringing externally adjacent to said hollow insulating body (12) a predetermined number of second blades (14) arranged radially with respect to said central axis (4) and keeping them in position, and wherein the subsequent winding of said resistive wire (11) around said second insulating support (13) locks said second blades (14) with respect to said hollow insulating body (12).

11. A method of manufacturing a coaxial electric resistance according to claim 10, wherein said second blades (14) are brought externally adjacent to said hollow insulating body (12), arranging said hollow insulating body (12) between two axial stops (15) on said second blades (14).

12. A method of manufacturing a coaxial electric resistance according to claim 10 or 11 , wherein said second blades (14) are brought externally adjacent to said hollow insulating body (12), embracing said first blades (3) in a radial and axial direction with respect to said central axis (4).

13. A method of manufacturing a coaxial electric resistance according to one or more of claims 10-12, wherein at least one of said second blades

(14) is brought externally adjacent to said hollow insulating body (12), parallel to one of said first blades (3).

14. A method of manufacturing a coaxial electric resistance according to one or more of the preceding claims, comprising preparing said first insulating support (2) comprising two first blades (3) intersecting each other at said central axis (4) and arranged at 90° to each other.

15. A method of manufacturing a coaxial electric resistance according to one or more of the preceding claims, comprising preparing said second insulating support (13) comprising at least six second blades (14) extending on planes mutually intersecting at said central axis (4), said second blades (14) being uniformly distributed around said hollow insulating body (12).

16. A coaxial electric resistance, comprising:

- a first insulating support (2) comprising a predetermined number of first blades (3) extending on planes mutually intersecting at a central axis (4);

- a first winding (9) made up of a plurality of first turns (10) of resistive wire (11), preferably shaped according to at least one predetermined waveform or spirally, wound around said first insulating support (2);

- a hollow insulating body (12) comprising a lateral wall (13) arranged radially outside said first winding (2);

- a second insulating support (13) comprising a predetermined number of second blades (14) extending on planes mutually intersecting at said central axis (4), said second blades (14) being arranged in a position radially outside said hollow insulating body (12);

- a second winding (17) made up of a plurality of second turns ( 8) of said resistive wire (11) wound around said second insulating support (13);

wherein said hollow insulating body (12) has a length measured along said longitudinal direction (A) such as to mutually insulate said first winding (9) and said second winding (17)

and wherein said lateral wall (13) of said hollow insulating body (12) forms a continuous wall separating said first and second windings.

17. A coaxial electric resistance according to claim 16, wherein said first insulating support (2) has a length (I) measured along said central axis (4) greater than a first length (L1) of said first winding (9), said first insulating support (2) comprising a waiting axial portion (2a) and an operative axial portion (2b), and wherein said first winding (9) is wound radially outside said operative axial portion (2b) of said first insulating support (2).

18. A coaxial electric resistance according to claim 16 or 17, wherein each of said second blades (14) comprises two axial stops (15) configured for receiving said hollow insulating body (12).

19. A coaxial electric resistance according to one or more of claims 16-18, wherein said second blades (14) are brought externally adjacent to said hollow insulating body (12), embracing said first blades (3) in a radial and axial direction with respect to said central axis (4).

20. A coaxial electric resistance according to one or more of claims 16-19, wherein at least one of said second blades (14) is brought externally adjacent to said hollow insulating body (12), parallel to one of said first blades (3).

21. A coaxial electric resistance according to one or more of claims 16-20, wherein said first insulating support (2) comprises two first blades (3) intersecting each other at said central axis (4) and arranged at 90° to each other.

22. A coaxial electric resistance according to one or more of claims 16-21 , wherein said second insulating support (13) comprises at least six second blades (14) extending on planes mutually intersecting at said central axis (4), said second blades (14) being uniformly distributed around said hollow insulating body (12).