Electric heater

Abstract

The present invention provides an electric heater (1) comprising at least one outer tubular cartridge (2) having at least one PTC resistor (3) therein, and an aluminum or aluminum alloy block (4) overmolded by die casting around the at least one outer tubular cartridge (2), with a plastic material coating layer (5) applied around the aluminum block (4). The present invention also provides a manufacturing process for the electric heater (1).

Description

[Technical field]

[0001] The present invention relates to an electric heater for any application in which it is necessary to ensure a high level of safety even at the maximum temperatures reached by the system and to ensure optimal heat transfer. [Background technology]

[0002] Electric heaters comprising resistors and / or outer tubular cartridges comprising at least one resistive wire embedded in magnesium oxide are available on the market.

[0003] The first drawback is represented by the fact that temperature regulation is carried out by means of additional components such as a thermostat or a thermocouple.

[0004] A second drawback is represented by the fact that in many cases the heat exchange between these outer tubular cartridges and other components attached to the outside of the cartridge is not optimal due to the presence of air between the component in question and the outer tubular cartridge.

[0005] Therefore, a need is felt for an electric heater that can overcome the background art. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the invention is to produce an electric heater which is simpler from a constructive and functional point of view.

[0007] Another object of the present invention is to produce an electric heater that optimizes the heat exchange between the outer tubular cartridge and the external component with which it is associated.

[0008] A further object of the present invention is to manufacture an electric heater that ensures a maximum system temperature without the possibility of malfunction, even in the event of a possible temperature sensor failure.

[0009] Another object of the present invention is to manufacture an electric heater that can reduce energy consumption by adjusting the power according to the operating temperature. [Means for solving the problem]

[0010] The present invention achieves at least one of these and other objects which will become apparent in light of the present description by providing an electric heater comprising: at least one outer tubular cartridge having at least one PTC resistor therein; a block of aluminum or an alloy thereof overmolded by die casting around said at least one outer tubular cartridge; Equipped with There is a coating layer of plastic material applied around the block of aluminium.

[0011] According to one aspect, the present invention also includes a process for manufacturing the electric heater described above, said process comprising the steps of: Providing at least one outer tubular cartridge having at least one PTC resistor therein; overmolding by die casting a block of aluminum or an alloy thereof around said at least one outer tubular cartridge; - applying a plastic material around said block of aluminium (4) to produce a coating layer; Includes.

[0012] In the solution of the invention, at least one outer tubular cartridge is placed inside the aluminum die casting and generates heat by application of at least one PTC stone.

[0013] Thanks to this cartridge, no further temperature control system is necessary, because thanks to the PTC effect of the stone, the stone will never exceed the preselected temperature threshold.

[0014] In fact, a positive temperature coefficient (PTC) resistor increases in resistance as temperature increases, thereby limiting the maximum current that can flow through a circuit so that a certain maximum temperature is not exceeded. Effect of the Invention

[0015] Among the advantages of the solution of the invention are the following: The die casting process is now at a high level of industrialization, resulting in low costs and high productivity. Armored tubular cartridges with die-cast aluminum exterior improve heat exchange since during the die-casting process the aluminum solidifies under pressure directly around the cartridge, avoiding the formation of air bubbles which reduce the thermal efficiency of the system as air is a thermal insulator. Eliminates the need to electrically insulate the aluminum block. If a PTC resistor is used to heat a liquid, e.g. water, the PTC resistor will not be damaged even after the liquid has evaporated. PTC resistors have a long operating life, under normal circumstances, the service life is up to 10 years.

[0016] Advantageously, the electric heater of the present invention can be used in domestic or industrial evaporators or in coffee machines.

[0017] Further features and advantages of the present invention will become more apparent in light of the detailed description of illustrative, but non-exhaustive, embodiments.

[0018] The dependent claims describe particular embodiments of the invention. [Brief description of the drawings]

[0019] In describing the invention, reference is made to the accompanying drawings, which are provided as non-limiting examples.

[0020] [Figure 1]1 shows a partial cross-sectional perspective view of components of a first embodiment of an electric heater according to the present invention; [Diagram 2] 2 shows a cross section of the view in FIG. [Diagram 3] FIG. 2 shows a cross-sectional view of the first embodiment of an electric heater according to the invention. [Figure 4] FIG. 2 shows a side view of components of a second embodiment of an electric heater according to the present invention. [Diagram 5] FIG. 2 shows a side view of components of a third embodiment of an electric heater according to the present invention. [Figure 6] FIG. 13 shows a side view of components of a fourth embodiment of an electric heater according to the present invention. [Figure 7] 4 shows a cross-sectional view of a variant of the electric heater according to the invention. [Figure 8] 4 shows a cross-sectional view of a further variant of the electric heater according to the invention.

[0021] Identical or functionally equivalent elements will have the same reference numbers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The electric heater 1 of the present invention will be described with reference to the drawings, in all its embodiments, At least one outer tubular cartridge 2 with at least one PTC (Positive Temperature Coefficient) resistor 3 therein; a block 4 or element of aluminium or an alloy thereof overmolded by die casting around at least one outer tubular cartridge 2;

[0023] The aluminum block 4 therefore adjoins, preferably completely adjoins, the exterior of the outer tubular cartridge or cartridges 2 .

[0024] Advantageously, the aluminum block 4 completely surrounds a single armored tubular cartridge (FIG. 3) or two or more armored tubular cartridges 2 (FIGS. 7 and 8). Only a power supply cable 9 can protrude from the aluminum block 4, which powers at least one armored tubular cartridge 2. In case of several armored tubular cartridges 2, a pair of power supply cables 9 is provided for each armored tubular cartridge.

[0025] Advantageously, in order to protect the aluminium block 4, a coating layer 5 of plastic material, for example also of polyethylene or polyamide or Teflon, is applied, for example overmolded, around the aluminium block 4. Said coating layer 5 thus adjoins, preferably completely adjoins, the exterior of the aluminium block 4.

[0026] The plastic coating layer 5 may have a thickness of about 0.1 to 5 mm.

[0027] Preferably, inside each outer tubular cartridge 2 there are provided a number of PTC resistors 3, preferably made of ceramic material, connected to one another in sequence along the entire outer tubular cartridge 2. Such PTC resistors are, for example, in the form of stones having the shape of a substantially flat rectangular parallelepiped, connected in series one after the other at their end faces, which end faces have an area that is much smaller than the area of ​​the other faces of the stone.

[0028] The PTC resistor is inserted between two heat sinks or electrodes 8 made of aluminium or its alloy. Each aluminium heat sink or electrode 8 is connected to a respective power supply cable 9 protruding from one end of a respective outer tubular cartridge 2.

[0029] The assembly defined by the aluminium heat sink or electrode 8 and the PTC resistor 3 is surrounded by a layer 10 of insulating material, preferably a layer of powdered magnesium oxide or polyimide, bounded externally by a metal sheath 11, preferably a steel sheath. The block of aluminium 4 is thus overmolded by die casting around the metal sheath 11.

[0030] In the first embodiment shown in Figures 1 to 3, the outer tubular cartridge 2 exclusively defines a straight longitudinal axis X.

[0031] For example, three PTC resistors 3 are provided in series inside the outer tubular cartridge 2. However, the number of PTC resistors 3 may be less than or greater than three.

[0032] In the variant shown in FIG. 3, the shape of the outer tubular cartridge 2 is cylindrical, the metal sheath 11 has a circular cross section, the two heat sinks 8 have a semi-cylindrical shape and are arranged opposite each other, while the cross section of the aluminum block 4 surrounding the cartridge 2 is rectangular.

[0033] The outer tubular cartridge 2 and the aluminum die-cast block 4 can be provided with any other shape. It is not excluded that both the outer tubular cartridge 2 and the aluminum die-cast block 4 are provided to have the same cross-sectional shape.

[0034] A variant of this first embodiment provides exclusively that the outer tubular cartridge 2 defines a curved longitudinal axis rather than a straight longitudinal axis.

[0035] In this first embodiment, inside the die-cast block of aluminum there can be a single outer tubular cartridge 2 or there can be two or more outer tubular cartridges, identical or different from each other.

[0036] Another variant of the electric heater of the invention provides that at least one outer tubular cartridge 2 is provided with two or more stretches or portions, in which case at least one first stretch 6 defines a straight longitudinal axis and at least one second stretch 7 defines a curved axis.

[0037] In a second embodiment, shown in figure 4, the outer tubular cartridge 2 comprises or consists of two straight stretches 6, 6' joined together by at least one curved stretch 7, preferably only by one curved stretch 7. Preferably, the two stretches 6, 6' are perpendicular to each other.

[0038] In a third embodiment shown in FIG. 5, the outer tubular cartridge 2 comprises two straight stretches 6, 6' connected by at least one curved stretch 7, preferably only by one curved stretch 7. A further straight stretch 6" is provided contiguous to the straight stretch 6'.

[0039] Preferably, the stretches 6, 6' are perpendicular to one another, possibly also the stretches 6', 6'' are perpendicular to one another and therefore the stretches 6 and 6'' are parallel to one another.

[0040] A variant of this third embodiment, not shown, can include the presence of a further curved stretch between the straight stretch 6' and the straight stretch 6", said further curved stretch having an opposite radius of curvature to the curved stretch 7.

[0041] Another variant of this third embodiment, not shown, could instead include the presence of two curved stretches, with opposite radii of curvature, between the straight stretch 6 and the straight stretch 6". In this latter case, the straight stretch 6' is not provided.

[0042] In a fourth embodiment shown in FIG. 6, the outer tubular cartridge 2 comprises at least two straight stretches 6, 6', each stretch 6, 6' defining a respective straight longitudinal axis, the straight longitudinal axes being Fold Define the line.

[0043] In the variant shown in FIG. 6, three straight stretches 6, 6', 6" are provided. Preferably, but not necessarily, the straight stretches 6, 6' are perpendicular to one another and the intermediate straight stretch 6' is inclined at an acute angle to one of the two stretches 6, 6', preferably between 30° and 60°, for example 45°.

[0044] 4, 5 and 6 the aluminium block 4 surrounding the outer tubular cartridge 2 is not shown.

[0045] In the second, third and fourth embodiments, one exterior tubular cartridge 2 may be provided inside the aluminum die-cast block, or two or more exterior tubular cartridges, which may be the same or different from each other, may be provided.

[0046] In the embodiment of the electric heater according to the invention in which at least two stretches are provided which are different from each other and have a longitudinal axis, each stretch 6, 6', 6'', 7 comprises at least one PTC resistor 3 therein.

[0047] In particular, each stretch 6, 6', 6" comprises a number of PTC resistors 3, preferably of ceramic material, connected to one another in turn along the entire stretch and inserted between two heat sinks or electrodes 8 of aluminium or an alloy thereof, each aluminium heat sink or electrode 8 being connected to a respective power supply cable 9 protruding from one end of the outer tubular cartridge 2.

[0048] In the curvilinear stretch 7, it is possible instead to provide a single PTC resistor 3 with a substantially flat shape and a curved axis, or to provide a plurality of PTC resistors with a substantially flat shape and a straight axis, but with a much shorter longitudinal extension relative to the single PTC resistor with a curvilinear axis. In the latter case, the PTC resistors are arranged such that their straight axes merge into one another along the curvilinear stretch 7.

[0049] Also, in the curved stretch 7, the single PTC resistor or multiple PTC resistors are inserted between two heat sinks or electrodes 8 of aluminium or its alloy, each of which is connected to a respective power supply cable 9 protruding from one end of the outer tubular cartridge 2.

[0050] In the following, the manufacturing process of the electric heater 1 according to the invention will be described.

[0051] In all its embodiments, the process comprises the following steps: providing at least one outer tubular cartridge 2 with at least one PTC resistor 3 therein; overmolding, by die casting, a block 4 of aluminium or an alloy thereof around said at least one outer tubular cartridge 2.

[0052] Advantageously, provision is made for applying a plastic material around said block of aluminium 4 to produce a coating layer 5, for example by overmolding.

Claims

1. at least one outer tubular cartridge (2) with at least one PTC resistor (3) therein; a block (4) of aluminum or an alloy thereof overmolded by die casting around said at least one outer tubular cartridge (2); An electric heater comprising: An electric heater (1) provided with a coating layer (5) of plastic material applied around said block (4) of aluminium.

2. 2. An electric heater (1) according to claim 1, wherein said at least one outer tubular cartridge (2) defines only a straight longitudinal axis X or only a curved longitudinal axis.

3. 2. The electric heater (1) according to claim 1, wherein the at least one outer tubular cartridge (2) comprises two or more stretches, at least one first stretch (6) defining a straight longitudinal axis and at least one second stretch (7) defining a curved axis.

4. 4. An electric heater (1) according to claim 3, wherein said at least two first stretches (6, 6', 6") are provided, preferably only two first stretches (6, 6') being joined together by at least one second stretch (7), preferably by a second stretch (7).

5. 2. The electric heater (1) according to claim 1, wherein the at least one outer tubular cartridge (2) comprises at least two stretches (6, 6'), each stretch (6, 6') defining a respective straight longitudinal axis, the longitudinal axes defining a broken line.

6. 6. An electric heater (1) according to claim 5, wherein three stretches (6, 6', 6") are provided.

7. An electric heater (1) according to any one of claims 1 to 6, wherein a plurality of PTC resistors (3), preferably made of ceramic material, are provided and connected to one another in sequence along the entire outer tubular cartridge (2).

8. 8. The electric heater (1) according to any one of claims 1 to 7, wherein the at least one PTC resistor (3) is inserted between two heat sinks or electrodes (8) of aluminium or its alloy, each aluminium heat sink or electrode (8) being connected to a respective power supply cable (9) protruding from one end of the at least one outer tubular cartridge (2).

9. 9. An electric heater (1) according to claim 8, wherein the assembly defined by the heat sink or electrode (8) of aluminium and the at least one PTC resistor (3) is surrounded by a layer (10) of insulating material, preferably a layer of powdered magnesium oxide or polyimide, bounded externally by a metal sheath (11), preferably a steel sheath.

10. 10. An electric heater (1) according to claim 9, wherein the block (4) of aluminium or its alloy is overmolded around the metal sheath (2) by die casting.

11. A manufacturing process for an electric heater (1) according to any one of claims 1 to 10, comprising: - providing at least one outer tubular cartridge (2) with at least one PTC resistor (3) therein; - overmolding by die-casting a block (4) of aluminum or its alloy around said at least one outer tubular cartridge (2); - applying a plastic material around said block of aluminum (4) to produce a coating layer (5); manufacturing process, including

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