Tubular electric heater

Abstract

A tubular electric heater (1), in particular a sheathed resistor, comprising - a metal casing (2); - a first pin (3), arranged inside the metal casing (2); - a heating wire (5), adapted to generate heat when it is electrically powered, wound about an axis (X); - a thermal fuse (6); wherein the heating wire (5) comprises an end stretch (51), formed by one or more coils having a first diameter (D1) welded to the first pin (3), a central stretch (54), formed by coils having a second diameter (D4), which is greater than the first diameter (D1), and a transition stretch (53) extending between the end stretch (51) and the central stretch (54), wherein the coils of said transition stretch (53) have an increasing diameter, in particular towards the central stretch (54); the tubular electric heater (1) further comprising a metal body (7) in which the first pin (3) and the thermal fuse (6) are at least partially arranged; wherein said metal body (7) fixes, in particular mechanically fixes, the first pin (3) and the thermal fuse (6) to each other and electrically connects the first pin (3) and the thermal fuse (6) to each other wherein the central stretch (54) is configured to generate a specific thermal power of at least 20 W / cm2.

Description

[0001] TUBULAR ELECTRIC HEATER

[0002] Field of the invention

[0003] The present invention relates to the field of tubular electric heaters, in particular to the field of sheathed resistors.

[0004] In particular, the invention relates to a tubular electric heater adapted to generate a high specific thermal power (in particular per area unit), preferably adapted to operate in water.

[0005] Background art

[0006] Tubular electric heaters typically comprise a metal casing or metal sheath inside which a resistive element is arranged, in particular a metal wire, adapted to generate heat by Joule effect.

[0007] Some tubular electric heaters are designed to generate great specific powers and operate in water.

[0008] For safety reasons, tubular electric heaters can be provided with at least one thermal fuse.

[0009] The thermal fuse intervenes, for example in dry operating conditions or in other abnormal working conditions, in which there is an undesired overheating.

[0010] The thermal fuse can be electrically connected to a pin to which the metal wire is welded.

[0011] In particular for this type of tubular electric heaters, which are adapted to generate great specific powers and operate in water, it is not trivial to both optimize the features which allow optimizing normal working conditions and the intervention of the thermal fuse in abnormal working conditions, and also to produce the tubular electric heater in a particularly simple manner.

[0012] In particular, it is not trivial to design a tubular electric heater configured to generate a great specific power and in which the thermal fuse can intervene quickly.

[0013] Summary of the invention

[0014] It is an object of the present invention to produce a tubular electric heater, in particular adapted to generate a great specific thermal power and operate in water, which allows optimizing normal working conditions and the intervention of the thermal fuse in abnormal working conditions, and which can also be produced in a particularly simple manner with fewer structural constraints relative to the pin electrically connected to the thermal fuse and welded to the resistive wire.

[0015] In particular, it is an object of the invention to produce a tubular electric heater adapted to generate a great specific thermal power, which allows an effective and efficient heating in normal working conditions, and which also allows a rapid intervention of the thermal fuse in the event of abnormal working conditions.

[0016] The present invention achieves at least one of such objects, and other objects which will become apparent in the light of the present description, by means of a tubular electric heater, in particular a sheathed resistor, according to claim 1 , comprising

[0017] - a metal casing;

[0018] - a first pin, or internal pin, arranged inside the metal casing;

[0019] - a heating wire, adapted to generate heat when it is electrically powered, wound about an axis;

[0020] - a thermal fuse; wherein the heating wire comprises an end stretch, formed by one or more coils having a first diameter, the one or more coils being welded to the first pin, a central stretch, formed by coils having a second diameter greater than the first diameter, and a transition stretch extending between the end stretch and the central stretch, wherein the coils of said transition stretch have an increasing diameter, in particular towards the central stretch; the tubular electric heater further comprising a metal body in which the first pin and the thermal fuse are at least partially arranged; wherein said metal body fixes, in particular mechanically fixes, the first pin and the thermal fuse to each other and electrically connects the first pin and the thermal fuse to each other; wherein the central stretch is configured to generate a specific thermal power of at least 20 W / cm2, preferably from 20 W / cm2to 60 W / cm2

[0021] The invention also relates to a method, according to claim 14, to produce a tubular electric heater, wherein the first pin and the thermal fuse are inserted into the metal body, in particular wherein the first pin and the thermal fuse are inserted in sequence or simultaneously into the metal body.

[0022] Advantageously, the aforesaid features of the electric heater are correlated to one another and have a synergic effect.

[0023] In particular, the central stretch is configured to generate a specific thermal power of at least 20 W / cm2, i.e. a high specific thermal power; and therefore it is very important for the thermal fuse to be able to intervene rapidly. Advantageously, the metal body allows improving the heat exchange between the first pin and the thermal fuse, in particular with respect to a fixing by means of crimping between the pin and the thermal fuse; in particular, the metal body offers a large heat exchange surface.

[0024] Advantageously, the coils of the central stretch can be particularly close to the metal casing; therefore, the central stretch transmits more heat outwards and less heat to the first pin in normal working conditions, whereby the thermal fuse remains cooler. Thus, the thermal fuse can be selected (or set) so as to intervene at a lower temperature, and therefore it can intervene more quickly.

[0025] The aforesaid transition stretch is particularly advantageous because it allows optimizing the normal working conditions and the intervention of the thermal fuse in abnormal conditions, in particular in a tubular electric heater adapted to generate a great specific thermal power and to operate in water.

[0026] In particular, the transition stretch has the function of modulating the electric power. More in detail, the transition stretch has the function of modulating the electric power so that the central stretch heats adequately while the temperature of the zone close to the thermal fuse remains relatively low, during normal working; and so that the thermal fuse can intervene quickly in the event of abnormal working, i.e. in the event of overheating of the central stretch, as in the case of dry working, for example.

[0027] To further improve the rapid intervention of the thermal fuse, it is particularly preferable that the first pin is made of copper or copper alloy; the use of the pin made of copper or copper alloy is made possible by the fixing by means of the metal body, as the mechanical properties of the copper or of a copper alloy would not allow a reliable fixing by means of crimping between the pin and thermal fuse. A tubular electric heater according to the invention, in particular according to claim 1 , is advantageous with respect to a tubular electric heater in which, instead of the metal body fixing and electrically connecting the first pin and the thermal fuse to each other, the thermal fuse and the first pin are crimped to each other. In fact, the crimping requires the first pin to have suitable mechanical properties. In particular, the crimping imposes structural constraints, in particular relative to the first pin, whereby, as a whole, it is less easy to produce the tubular electric heater.

[0028] The mechanical and electrical connection between the first pin and the thermal fuse made by means of the aforesaid metal body, or metal cage or metal sleeve, advantageously offers greater possibilities of choice of the material of the first pin (which can be made, for example of copper or copper alloy). Whereas, crimping obliges selecting materials with suitable properties to undergo the crimping, in particular suitable mechanical properties.

[0029] Further features and advantages of the invention will become more apparent in the light of the detailed description of exemplary but non-exclusive embodiments.

[0030] The dependent claims describe particular embodiments of the invention.

[0031] Brief description of the drawings

[0032] The description of the invention refers to the accompanying drawings, which are provided by way of non-limiting example, in which:

[0033] Figure 1 diagrammatically shows a top plan view of the electric heater according to the invention;

[0034] Figure 2 diagrammatically shows a view, in particular, of internal components of the electric heater in Fig. 1 ;

[0035] Figure 3 diagrammatically shows some components of an electric heater according to the invention;

[0036] Figure 4 shows a side view of a component of an electric heater according to the invention;

[0037] Figure 5 shows a section of the component in Fig. 4.

[0038] The same elements or components have the same reference numerals.

[0039] Description of exemplary embodiments of the invention

[0040] With reference to the Figures, exemplary embodiments of a tubular electric heater 1 , in particular of a sheathed resistor, are described. The tubular electric heater 1 is preferably configured to operate in water, in particular it is preferably configured to be immersed at least partially in water.

[0041] In all the embodiments, the tubular electric heater 1 comprises

[0042] - a metal casing 2, or metal sheath;

[0043] - a first pin 3, or internal pin, arranged inside the metal casing 2;

[0044] - a heating wire 5, adapted to generate heat when it is electrically powered, i.e. adapted to generate heat due to the Joule effect, wound about an axis X;

[0045] - a thermal fuse 6; wherein the heating wire 5 comprises an end stretch 51 , formed by one or more coils having a diameter D1 , or a first diameter D1 for descriptive purposes, the one or more coils being welded to the first pin 3, a central stretch 54 (or heating stretch), formed by coils having a diameter D4, or a second diameter D4 for descriptive purposes, greater than the first diameter D1 , and a stretch 53, also referred to as transition stretch 53, extending between the end stretch 51 and the central stretch 54, wherein the coils of said transition stretch 53 have an increasing diameter, in particular towards the central stretch 54; the tubular electric heater 1 further comprising a metal body 7, or metal sleeve, in which the first pin 3 and the thermal fuse 6 are at least partially arranged; wherein said metal body 7 fixes, in particular mechanically fixes, the first pin 3 and the thermal fuse 6 to each other and electrically connects the first pin 3 and the thermal fuse 6 to each other; wherein the central stretch 54 is configured to generate a specific thermal power of at least 20 W / cm2, preferably from 20 W / cm2to 60 W / cm2

[0046] In particular, the end stretch 51 , the transition stretch 53 and the central stretch 54 are axial stretches. In other words, each of said end stretch 51 , transition stretch 53 and central stretch 54 is formed by a plurality of coils of heating wire 5, wound about a respective stretch of axis X. In particular, the term “coils” is understood to mean coils of the winding formed by the heating wire 5. In particular, the heating wire 5 is helical or substantially helical.

[0047] The aforesaid axis X can be a rectilinear axis, a curved axis or an axis comprising one or more rectilinear stretches and one or more curved stretches.

[0048] In the non-limiting example shown, the axis X comprises two rectilinear stretches joined to each other by a curved stretch, in particular so as to substantially form a “U” shape.

[0049] As said, the coils of said transition stretch 53 have an increasing diameter, i.e. which increases from one coil to the next. The diameter of any coil of the transition stretch 53 is preferably lower than the diameter of the transition stretch coil 53 successive thereto, where successive is understood to mean closer to the central stretch 54.

[0050] Preferably, a surface S3, or envelope, tangent to the coils of the transition stretch 53 is frustoconical or substantially frustoconical.

[0051] Preferably, the first pin 3 and the thermal fuse 6 are separate from each other, in particular separate from each other along said axis X.

[0052] Preferably, the metal body 7 has no abutment zones against which the first pin 3 and the thermal fuse 6 could axially abut; advantageously, in this way the metal body 7 does not hinder any possible axial thermal dilations of the first pin 3 and / or of the thermal fuse 6.

[0053] Preferably, said metal body 7 fixes the first pin 3 and the thermal fuse 6 to each other exerting an elastic force thereon, in particular an elastic recall force; and / or said metal body 7 fixes the first pin 3 and the thermal fuse 6 to each other by interference.

[0054] Said metal body 7 preferably has elastic properties, in particular it is preferably adapted to elastically deform when the first pin 3 and the thermal fuse 6 are inserted into the metal body 7.

[0055] Said metal body 7 is preferably a metal cage, in particular an elastic metal cage.

[0056] The first pin 3 is preferably partially arranged, in particular only partially arranged, in the metal body 7. The first pin 3 is in particular adapted to lead an electric current to the heating wire 5.

[0057] The first pin 3 can be made, for example, of steel or copper or copper alloy, preferably of copper or copper alloy. Advantageously, the use of the body 7 allows utilizing a first pin 3 made of copper or copper alloy, which has a thermal conductivity greater than steel, but a mechanical resistance lower than steel.

[0058] The aforesaid second diameter D4 of each coil of the central stretch 54 is preferably from 3 to 7 mm.

[0059] The aforesaid first diameter D1 is preferably from 1 to 5 mm.

[0060] In particular, the tubular electric heater 1 comprises a second pin 4, or external pin, for the electrical connection to a source of electricity. The second pin 4 is arranged at least partially outside the metal casing 2, e.g. partially inside and partially outside the metal casing 2. The second pin 4 is in contact, in particular directly in contact, with the thermal fuse 6. The second pin 4 is preferably crimped to the thermal fuse 6.

[0061] In particular, the heating wire 5 is a metal wire.

[0062] In particular, the heating wire 5 is incorporated into an insulating material, which is preferably magnesium oxide.

[0063] The heating wire 5 optionally also comprises a stretch 52 extending between the end stretch 51 and the transition stretch 53, formed by coils having said first diameter D1 . In particular, the coils of the stretch 52 are spaced apart from the first pin 3, in particular they are not welded to the first pin 3. Said stretch 52 is also an axial stretch, formed by a plurality of coils of heating wire 5 wound about a stratch of the axis X. Alternatively, for example, the transition stretch 53 can be consecutive to the end stretch 51.

[0064] Said transition stretch 53 preferably has a length L3 along the axis X from 1 to 30 mm; and / or said central stretch 54 has a length L4 (not shown in the Figures) along the axis X from 50 to 500 mm; and / or said first stretch 52, if provided, has a length L2 along the axis X from 0.3 to 30 mm. The length of the end stretch 51 along the axis X is indicated with reference L1 . The length L1 along the axis X of the end stretch 51 is preferably from 1 to 5 mm. The selection of a length L3 in the aforesaid range, preferably in combination with the aforesaid values D1 and D4, is particularly preferable, as it allows optimizing the distance between the central stretch 54 and the thermal fuse 6 (in particular, so that they are close enough to each other), so as to allow having a zone having a high specific power load (i.e. the heating stretch or central stretch 54), which remains particularly cool during normal working (because the heating wire, close to the sheath exchanges well with the liquid to be heated), and so as to quickly heat the thermal fuse 6 in abnormal conditions.

[0065] The first pin 3 preferably comprises a first part 31 arranged in the metal body 7 and a second part 32 about which the coils of the end stretch 51 extend. Preferably, all or some of the coils of the transition stretch 53 extend about said second part 32 of the pin 3. Preferably, all or some of the coils of the central stretch 54 extend about said second part 32 of the pin 3.

[0066] Advantageously, the first pin 3 can act as a thermal bridge to conduce heat from the central stretch 54 towards the thermal fuse 6, in particular in dry working conditions.

[0067] Preferably, in particular to this end, said second part 32 of the pin 3 comprises a conical portion 322 or a frustoconical portion, which in particular is tapered towards the central stretch 54 of the heating wire 5.

[0068] Preferably, some or all the coils of the transition stretch 53 extend about said conical or frustoconical part 322; some of the coils of the central stretch 54 preferably extend about said conical or frustoconical part 322.

[0069] Said first part 31 of the pin 3 is preferably cylindrical or substantially cylindrical.

[0070] Said second part 32 of the pin preferably comprises a cylindrical or substantially cylindrical portion 321 to which the coils of the end stretch 51 are welded.

[0071] In particular, said first portion 321 of the second part 32 of the pin 3 extends between said first part 31 of the pin 3 and said conical or frustoconical portion 322 of the second part 32 of the pin 3.

[0072] The diameter of the portion 321 of the second part 32 of the pin 3 is preferably smaller than the diameter of said first part 31 of the pin 3.

[0073] In particular, the tubular electric heater 1 comprises two end stretches 11 , 12. In particular, the aforesaid first pin 3, thermal fuse 6, metal body 7, end stretch 51 and transition stretch 53 are part of an end stretch 11 of the tubular electric heater 1.

[0074] The other end stretch 12 can optionally also be provided with a respective thermal fuse and be equal, or substantially equal to the end stretch 11. Alternatively, the other end stretch 12 of the tubular electric heater 1 may not be provided with a thermal fuse. In this case, as shown in Fig. 2, a pin 4a is provided, arranged, for example, partly inside and partly outside the metal casing 2. The pin 4a has an end to which the heating wire 5 is welded and another end for the electrical connection to a source of electricity.

[0075] Optionally, the pin 4a also comprises a conical or frustoconical portion, in particular similar to the frustoconical portion 322, and / or optionally the heating wire 5 comprises another end stretch 51 a, welded to the pin 4a, analogous to the end stretch 51 , and another transition stretch 53a, analogous to the transition stretch 53.

[0076] The invention also relates to a method for producing a tubular electric heater 1 , wherein there is provided a step wherein the first pin 3 and the thermal fuse 6 are inserted into the metal body 7, in particular wherein the first pin 3 and the thermal fuse 6 are inserted in sequence or simultaneously into the metal body 7.

Claims

CLAIMS1. A tubular electric heater (1 ), in particular a sheathed resistor, comprising- a metal casing (2);- a first pin (3), or inner pin, arranged inside the metal casing (2);- a heating wire (5), adapted to generate heat when it is electrically powered, wound about an axis (X);- a thermal fuse (6); wherein the heating wire (5) comprises an end stretch (51 ), formed by one or more coils having a first diameter (D1 ) welded to the first pin (3), a central stretch (54), formed by coils having a second diameter (D4), which is greater than the first diameter (D1 ), and a transition stretch (53) extending between the end stretch (51 ) and the central stretch (54), wherein the coils of said transition stretch (53) have an increasing diameter, in particular towards the central stretch (54); the tubular electric heater (1 ) further comprising a metal body (7) in which the first pin (3) and the thermal fuse (6) are at least partially arranged; wherein said metal body (7) fixes, in particular mechanically fixes, the first pin (3) and the thermal fuse (6) to each other and electrically connects the first pin (3) and the thermal fuse (6) to each other; wherein the central stretch (54) is configured to generate a specific thermal power of at least 20 W / cm22. A tubular electric heater (1 ) according to claim 1 , wherein a surface (S3), or envelope, tangent to the coils of the transition stretch (53) is frustoconical or substantially frustoconical.

3. A tubular electric heater (1 ) according to claim 1 or 2, wherein the first pin (3) and the thermal fuse (6) are separate from each other, in particular separate from each other along said axis (X).

4. A tubular electric heater (1 ) according to any one of the preceding claims, wherein said metal body (7) fixes the first pin (3) and the thermal fuse (6) to each other by exerting an elastic force thereon, and / or by interference.

5. A tubular electric heater (1 ) according to any one of the preceding claims, wherein said metal body (7) is a metal cage, in particular an elastic metal cage.

6. A tubular electric heater (1 ) according to any one of the preceding claims, wherein the first pin (3) is made of steel, or copper or copper alloy.

7. A tubular electric heater (1 ) according to any one of the preceding claims, wherein the first pin (3) is made of copper or copper alloy.

8. A tubular electric heater (1 ) according to any one of the preceding claims, wherein said second diameter (D4) of each coil of the central stretch (54) is from 3 to 7 mm and / or wherein said first diameter (D1 ) is from 1 to 5 mm.

9. A tubular electric heater (1 ) according to any one of the preceding claims, comprising a second pin (4), or outer pin, for the electrical connection to a source of electricity; wherein the second pin (4) is arranged, at least partially, outside the metal casing (2), and is in contact with the thermal fuse (6).

10. A tubular electric heater (1 ) according to any one of the preceding claims, wherein the metal body (7) has no abutment zones against which the first pin (3) and the thermal fuse (6) could axially abut; in particular, so that the metal body (7) does not hinder any possible axial thermal dilations of the first pin (3) and / or of the thermal fuse (6).

11. A tubular electric heater (1 ) according to any one of the preceding claims, wherein said first pin (3) comprises a conical or frustoconical part (322) about which some of the coils of the heating wire (5) extend.

12. A tubular electric heater (1 ) according to claim 11 , wherein some or all the coils of the transition stretch (53) extend about said conical or frustoconical part (322); optionally wherein some of the coils of the central stretch (54) extend about said conical or frustoconical part (322).

13. A tubular electric heater (1 ) according to any one of the preceding claims, wherein said transition stretch (53) has a length (L3) along the axis (X) from 1 to 30 mm.

14. A method of producing a tubular electric heater (1 ) according to any one of the preceding claims, wherein there is provided a step in which the first pin (3) and the thermal fuse (6) are inserted into the metal body (7), in particular wherein the firstpin (3) and the thermal fuse (6) are inserted in sequence or simultaneously into the metal body (7).

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