EP1067822B1 - Heating element manufacturing process for heating or cooking apparatus,such heating element and apparatus incorporating it - Google Patents

Abstract

The element is fabricated by moulding (M1, M2) a core (1) from an envelope of a fusible material and allowing to flow in the mould a material of a ferrous alloy which has a fusion temperature close to that of the envelope material. The envelope has a thickness and a thermal inertia sufficient to permit a superficial fusion of the envelope without causing it to deteriorate.

Description

The present invention relates to the manufacture of heating elements intended for radiant, convection or accumulation as well as to cooking appliances such as for example grills.

EP0456173 discloses a method of manufacturing a heating element for heating apparatus, of the type comprising a heating means associated with a heat sink, in which a heating means is placed in a mold consistent with the shapes and dimensions of the heating element, and the molten aluminum is cast in said mold.

The object of the invention is to produce elements of the type comprising, on the one hand, a means generating heat, such as an electrical resistance enclosed in a metallic sheath or other suitable material or fluid coolant circulating in a suitable sheath and, secondly, a dissipator associated closely with said heating means and more precisely with propose a technique of manufacturing such elements making more effective thermal transfers between heat source and dissipator.

For this purpose, the subject of the invention is a method of manufacturing a heating element for heating or cooking appliance, of the type comprising a heating means associated with a heat sink, characterized in that it consists in placing in a mold a heating means acting as a core, said means and the inner wall of the mold being in accordance with shapes and dimensions of the heating element to be produced, said heating means having at least one envelope of fusible material and to flow into the mold a molten material consisting of a particular ferrous alloy to melting temperature substantially equivalent to that of said envelope of calorific means, this envelope having a thickness and an inertia sufficient to allow a superficial melting of the envelope without damaging it.

This gives a heating element formed of a heating means such that for example an electrical resistance enclosed in an envelope metal or a tube of glass product under halogen, embedded in the mass of a ferrous alloy material such as gray cast iron for example, the fusion surface of the envelope of the resistance to contact of said alloy during the molding, ensuring an intimate connection between the materials providing a optimal efficiency of heat transfer.

Any screen such as interstices or air gap between the resistance and its dissipator formed by the alloy drowning resistance, is removed and the quality the connection leads to a longer life of the heating element and that the suppression of differential expansions, sources of noise and constraints, between resistance and thermal diffuser.

The calorific means can be constituted, in addition to the armored resistances or glass-product envelope, by a coolant flowing in a envelope of suitable material, or by the combination in the same heating element from two different sources, for example a resistor shielded electric and heat transfer fluid such as water.

• La figure 1 est une vue en perspective d'un élément chauffant conforme à l'invention ;
• La figure 1a représente la seule résistance électrique de l'élément chauffant de la figure 1 ;
• La figure 2 est une vue en coupe suivant la ligne II-II de l'élément chauffant de la figure 1 ;
• La figure 3 est une vue en coupe suivant la ligne III-III de l'élément chauffant de la figure 1 ;
• La figure 4 est une vue schématique d'un appareil de chauffage rayonnant équipé d'un élément chauffant selon l'invention ;
• La figure 5 est une vue schématique d'un appareil de chauffage convectif équipé d'un élément chauffant selon l'invention ;
• La figure 6 est une vue schématique d'un appareil de chauffage convectif à accumulation équipé d'éléments chauffants selon l'invention ;
• La figure 7 est une vue schématique d'un appareil de chauffage convectif à accumulation équipé d'un élément chauffant selon l'invention, et
• La figure 8 est une vue schématique d'un grill électrique équipé d'un élément chauffant selon l'invention.

Other features and advantages will emerge from the following description of embodiments of the invention, a description given by way of example only and with reference to the appended drawings in which:

• Figure 1 is a perspective view of a heating element according to the invention;
• Figure 1a shows the only electrical resistance of the heating element of Figure 1;
• Figure 2 is a sectional view along the line II-II of the heating element of Figure 1;
• Figure 3 is a sectional view along the line III-III of the heating element of Figure 1;
• Figure 4 is a schematic view of a radiant heater equipped with a heating element according to the invention;
• Figure 5 is a schematic view of a convective heater equipped with a heating element according to the invention;
• Figure 6 is a schematic view of a convective storage heater equipped with heating elements according to the invention;
• FIG. 7 is a schematic view of a convective storage heater equipped with a heating element according to the invention, and
• Figure 8 is a schematic view of an electric grill equipped with a heating element according to the invention.

In Figures 1 to 3, there is shown a heating element realized according to the method of the invention.

This element consists of a shielded electrical resistance 1 embedded in a plate 2 of ferrous alloy, provided with grooves 3 on both faces.

The plate 2 has a generally rectangular shape, is provided on one side, in its four corners, studs 4 for fixing the heating element on the frame of the receiver.

The electrical resistance 1, which is for example an armored resistance conventional circuit comprising an electrical conductor embedded in the compressed magnesia enclosed in a sheath or metal shell, is arranged in a sinuous path in the thickness of the plate 2.

Resistor 1 is shown alone and in solid lines in FIG. in dashed, embedded in the plate 2 in Figure 1, the only ends 1a, 1b emerging from the plate in a wide notch 5 formed in one of the longitudinal edges of said plate 2.

Said ends 1a, 1b are opposite and reveal the stripped ends of the electrical resistance 6 for their connection to the power supply circuit of the device.

Resistor 1 is bent and extends in a plane that coincides (Figure 2) with the plane of symmetry of the plate 2.

At the level of the resistance 1, the plate 2 has a tubular bulge 7 corresponding to the pattern of the resistance.

The method of manufacturing the heating element 1-2 of FIG. according to the invention, to conform the resistance 1 as illustrated in FIG. 1a and providing the zone of ends 1a, 1b with a core protector 8 covering said ends.

This core 8 is for example made of sand, ceramic, polystyrene or any other suitable material. It is intended to protect ends 1a, 1b and to delimit the notch 5 of the plate 2.

The assembly 1.8 is then put in place in a two-part mold M1, M2 (Figure 2) whose inner wall is shaped according to the shape and dimensions of the plate 2. Said assembly 1.8 can be fixed in position correct by any appropriate means, such as gluing for example. All 1.8 thus forms a core inside the mold M1, M2, which is going to be completely embedded in a particular ferrous liquid alloy conveyed from preferably at the bottom of the mold by a conduit 9 (source casting), the liquid gradually filling the entire mold rising inside this Last, vents are of course provided in appropriate places.

The ferrous alloy used, for example a gray cast iron, is chosen or determined so as to have a melting point close to that of the sheath or shell of the resistor 1. The latter also presents minimum thickness and thermal inertia, so that the contact between the pouring liquid and said sheath or envelope results in only one melting surface of the "skin" of the sheath, without causing deterioration of this last.

This gives an intimate connection between the materials of the sheath or shell of Resistor 1 and casting plate 2.

After cooling, demolding and removal of the protective core 8, obtains the heating element of Figure 1.

Said intimate bond between the materials gives optimum efficiency heat transfers between the resistor 1 and the plate 2 serving as heat sink or diffuser. This results in an increase the longevity of the heating element, as well as the removal of dilatations differentials, sources of noise and stress, between the resistor 1 and the heatsink 2.

The conduct of the casting must be conducted in such a way as not to create overheating areas of the sheath of the resistor 1 inside the mold.

Other casting techniques than spring casting can be used to the extent that the requirement of no overheating is respected recalled above.

The heating element (1, 2) of Figure 1 can equip various types of electric heating appliances. Figures 4 and 5 illustrate an apparatus for radiant heating and a convective heater respectively, each incorporating a heating element (1, 2).

Figure 6 schematically shows a heater convective type convector comprising three heating elements according to the invention, 10, 11 and 12 respectively, formed of a plate disposed on the slice and each wrapping an armored electrical resistor 1. The three plates 10, 11, 12 are placed in a baffle to constrain the flow of air to lick the maximum surface of the plates which, moreover, present, on their facing faces, vertical ribs 13 of channeling the air.

Fig. 7 shows a convective heater having a cylindrical heating element consisting of an electrical resistance 1 helix embedded in a tubular dissipator 14 provided internally with vertical splines 14 and externally covered with an insulating sleeve 16. The whole forms a natural convection heating chimney (or forced).

FIG. 8 represents a grill plate consisting of an element heating element comprising a shielded electrical resistance 1 embedded in a plate 17, for example cast iron, provided with grooves 18 on its face higher.

The heating elements (10, 11, 12, 1.14, 1.17) of FIGS. performed according to the method of the invention. The shapes and dimensions of the resistor 1 and the plate or the like (2, 10 to 12, 14, 17) forming heatsink are variable depending on the type of equipment to equip.

It should be noted that the emitting surface of the dissipator (fluted surface or ribbed) can undergo treatment to confer properties improved or particular thermal.

This is how this surface can be treated mechanically or chemically or coated with a black, matte or reflective paint for him to confer a state improving thermal exchanges by radiation or convection or favoring one mode of exchange over the other.

Similarly, before pouring the coating material of the sheath or envelope of the resistance 1, it is possible to implement a poteyage of said sheath or envelope, using a liquid or powder containing Refractory or insulating products, in order to avoid attack by the alloy cast, reduce the thermal shock experienced by the resistance, adjust the melting temperature or modify the thermal properties of the heatsink.

In a general way, we will make sure, by the choice or determination of the material of the sheath or envelope of the resistance or analogy and / or casting alloy material, to have fusion of said neighboring materials, this adaptation or adequacy of melting temperatures of the two materials in the presence can also be affected by any technique, such as poteyage among others.

Resistor 1 may be of a type other than armored resistors and for example be constituted by a filament under halogen enclosed in a glass, quartz or similar tube, the temperature of which fusion is close to that of the alloy that is being considered for use.

The metallic sheath of the resistor 1 may comprise possibly diffusing fins.

It should be noted that in the various examples of realization indicated above a same plate or the like (2, 10 to 12, 14, 16) may include several resistors 1 in parallel.

Alternatively, it is also possible to envisage as heating means, place and place of the electrical resistance 1, a coolant, such as water or other fluid circulating in a metal casing embedded in a particularly ferrous alloy material according to the present invention.

A heating element according to the invention may also consist of two different heat sources and of a different nature, for example a combination of an armored electrical resistance and a coolant, the envelopes of the two sources being either juxtaposed or integral with one of the other, the two envelopes possibly being part of the same monobloc assembly. These two envelopes are of course treated as a single envelope and embedded in a cast material.

Finally, the invention is obviously not limited to the embodiments represented and described above, but on the contrary covers all variants, in particular as regards the shapes and dimensions of the calorific means, the dissipator constituted by the material poured around said heating means. The surface of the dissipator can be coated with any material (enamel, teflon, paint) specific to the intended application, and / or have forms that promote heat exchange, such as pimples, fins, etc.

Claims (12)

1. A method of manufacturing a heating element for a heating or cooking appliance, of the type comprising calorific means associated with a thermal dissipater, characterised in that it comprises placing in a mould (M1, M2) calorific means (1) serving as a core, said means, and the internal wall of the mould, being conformed to the shapes and dimensions of the heating element to be produced, said calorific means (1) comprising at least one envelope made from fusible material and pouring into the mould a molten material formed of an alloy, in particular ferrous, with a melting point substantially equivalent to that of said envelope of the calorific means, this envelope having a thickness and thermal inertia sufficient to allow superficial fusion of the envelope without damaging it.
2. A method according to claim 1, characterised in that the envelope of the calorific means, prior to the pouring, is subjected to a lubrication.
3. A heating element obtained in accordance with the method of claim 1 or 2, characterised in that it comprises calorific means (1) embedded in a mass of an alloy, in particular ferrous, said calorific means (1) comprising at least one envelope whose external skin is merged with the surrounding material, said mass forming a thermal dissipater (2).
4. A heating element according to claim 3, characterised in that said calorific means (1) is chosen from the group comprising shielded electrical elements, halogen elements in a tube made from a glass product and heat-transfer fluids circulating in at least superficially fusible envelopes.
5. A heating element according to claim 4, characterised in that the calorific means (1) comprises several elements juxtaposed or housed in a common envelope.
6. A heating element according to claim 4, characterised in that the calorific means (1) comprises an electrical element and a heat-transfer fluid juxtaposed or housed in a common element.
7. A heating element according to one of claims 3 to 6, characterised in that said calorific means (1) is embedded in grey cast iron.
8. A heating element according to one of claims 3 to 7, characterised in that said dissipater forms a plate (2), planar or not.
9. A heating element according to claim 8, characterised in that said plate (2, 10 to 12, 17), comprises, on at least one face, flutes, ribs or the like (3, 12, 15, 18).
10. A heating element according to claim 8 or 9, characterised in that said dissipater provides a cylindrical shape (14) and is fluted internally.
11. A heating element according to one of claims 3 to 10, characterised in that the surface of the dissipater is treated mechanically or chemically or coated with a material, so as to improve heat exchanges or to confer particular heat-exchange properties.
12. A heating or cooking appliance comprising at least one heating element according to any one of claims 3 to 11.

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