GB2502665A

GB2502665A - Electric heater element with two layers of sintered ceramic insulation

Info

Publication number: GB2502665A
Application number: GB201303838A
Authority: GB
Inventors: Mario Roberto Ravaglia
Original assignee: ROTFIL Srl
Current assignee: ROTFIL Srl
Priority date: 2012-03-06
Filing date: 2013-03-04
Publication date: 2013-12-04
Anticipated expiration: 2033-03-04
Also published as: FR2987884B3; FR2987884A3; ITMI20120087U1; GB2502665B; GB201303838D0

Abstract

A heat storage dry radiator comprises at least one electric heater 4 having a resistive electric element e.g. coil 5 buried in a first insulting protection body 6 made of sintered ceramic. The first body is in turn buried in a second insulating protection body 7 made of sintered ceramic. The first 6 and second 7 insulating bodies may be formed and then fired together in a single firing step. The insulating bodies 6, 7 may have different colouring to provide visual indication of any damage to the outer layer. One or both of the layers may comprise sintered ceramic steatite and / or cordierite.

Description

DESCRIPTION

The present invention relates to a heat storage dry radiator, to be

used hi the civil or industrial field.

Heat storage dry radiators having a natural stone electric heater have been present on the market for some time.

This electric heater is obtained by interposing a flat flexible electric heating element between two slabs of natural stone.

The stone, which may be natural steatite, lavastone or serpentine, is extracted from quarries and processed to form slabs of the desired size and shape.

The surface of the slab in contact with the electric heating element must be appropriately dressed so as to guarantee excellent heat exchange.

The flat electric heater in turn is provided by interposing a resistive circuit usually produced by means of resistive metal wire straps between two layers of dielectric insulating material, typically micanite.

The assembled item thus produced is sealed using silicone at a high temperature interposed perimetrally between the two slabs.

Therefore the general structure of such an electric heater appears to be rather complex and characterised by high intrinsic assembly costs.

Furthennore, as well as being expensive, natural stone has a certain degree of unclosed porosity that cannot guarantee total protection against the penetration of water and/or humidity.

Consequently, hi order to have a suitable level of protection against electric shocks such an electric heater must be equipped with an earthing system which also implies a further structural and assembly complication and consequently a further increase in cost.

The task set by the present invention is, therefore, that of eliminating the disadvantages complained of in the known art, providing a heat storage dry radiator having a suitable level of protection against electric shocks.

Within the scope of this task, an object of the invention is that of providing a heat storage dry radiator that ensures the necessary level of protection against electric shocks without the need to provide an earthing system.

Another object of the invention is that of providing a heat storage dry radiator having an extremely simple general structure, extremely simple assembly and consequently an extremely limited manufacturing cost.

The task and these and other objects, according to the present invention, are reached by providing a heat storage dry radiator, characterised in that it comprises at least one electric healer having at least one resistive electric circuit buried hi a first insulating protection body made of sintered ceramic in turn buried hi a second insulating protection body made of sintered ceramic.

The first and second protection body are made of a sintered ceramic material having closed porosity and preferably a porosity value not exceeding 0.5.

The sintered ceramic material of the first and/or second protection body preferably comprises sintered ceramic steatite and/or sintered ceramic cordierite.

Preferably the electric heater is produced by a single fifing for siiiteriiig a cold moulded piece and comprising the resistive electric circuit buried in the first protection body to be sintered iii turn buried in the second protection body to be sintered.

Advantageously tile electric heater, being obtained by sintering ceramic material, especially steatite and/or cordierite, does not have any defects such as open porosity, does not emit dust, does not absorb humidity, is waterproof, and is therefore effectively suitable, particularly due to the double barrier ensured by the two protection bodies, to guarantee excellent protection against electric shocks which does not require the provision of a special earthing system.

Further characteristics and advantages will become more apparent from the following detailed description of the heat storage dry radiator according to the invention, illustrated by way of non-limiting example in the accompanying figures, wherein: Figure 1 shows an axonometric view of the radiator and the electric heater disassembled from the radiator; Figure 2 shows an axonometric view of the radiator of Figure 1 with the electric heater assembled; Figure 3 shows an axonometric view of the radiator of Figure 1 partially sectioned; Figure 4 shows a partially sectioned plan view of the electric heater of Figure 1; Figure 5 shows a section of the electric radiator along line 5-5 of Figure 4.

With reference to the figures mentioned, a heat storage dry radiator is shown indicated overall with the reference number 1.

The radiator to which reference is made can be used indifferently in the civil or the industrial field and has a power comprised between 700 and 2000 Watt.

The radiator 1, comprises a metal finned body 2, generally but not necessarily made of aluminium, having an internal housing pocket 3 for an electric heater 4.

The electric heater 4 has a resistive electric circuit 5 buried in a first insulating protection body 6 made of sintered ceramic in turn buried hi a second insulating protection body 7 made of sintered ceramic.

The resistive electric circuit preferably comprises a metal alloy wire with a high melting point wound iii a spiral.

The first protection body 6 and the second protection body 7 are particularly made of a sintered ceramic material having closed porosity and advantageously having a porosity value not exceeding 0.5.

Such sintered ceraniic material constituted by the first protection body 6 and/or the second protection body 7 comprises sintered ceramic steatite.

Such sintered ceramic material constitutillg the first protection body 6 and/or the second protection body 7 can alternatively or in combination with the sintered steatite ceramic also comprise simmtered ceramic cordierite.

Steatite is a dielectric ceramic mainly comprising crystals of magnesium silicate (MgSiO3) wrapped around a vitreous phase, whereas cordierite, also an insulating ceramic material, is comprised hi weight of 51% silica (Si02), 35% alumina (A1203), and the remaining part magnesium oxide (MgO).

The process for obtaining the electric heater 4 is preferably but not necessarily as follows.

Both steatite and cordierite are obtained starting from mixtures prepared in solution and comprising powders of mainly natural inorganic materials such as talc, clay, feldspar, and alumina.

The mixtures are appropriately dried through a solvent evaporation process so as to obtain an atoniised powder with constant unifonnity.

Therefore, the production process envisages a cold moulding step so as to obtain a semi-processed piece of a consolidated shape.

In particular hi special moulds a first layer of powder is spread into the material that will constitute a first part of the second protective body 7, increasing the thickness of the first layer along the whole perimeter to create a frame adapted to circumscribe the area of deposition of a second layer of powder into the material that will constitute the first protective body 6. After the deposition of the first layer, a pre-compression thereof is performed. Onto this first pre-compressed layer the first layer of the protective body 6 is deposited, and the heating spiral is rested on this layer. The second layer of the protective body 6 is laid above the heating spiral. After the deposition of the second layer of the protective body 6 for a thickness such as to be arranged flush with the frame of the first layer of the protective body?, another layer of powder is deposited onto the second layer of the protective body 6 and onto the frame of the first layer of the protective body 7 which will constitute the second part of the second protective body 7.

Then dry mechanical pressing is performed so as to obtain the consolidated shape of the piece.

Then a heat treatment of firing and drying at a high temperature is performed adapted to obtain the sintering and achieve the desired structural characteristics in terms of closed porosity, porosity value, etc. The type of ceramic material used allows the firing temperature to be limited to less than 1300 °C for the sintering. This obviously implies reduced energy consumption and consequently reduced production costs.

The electric heater 4 can also be obtained through a different process starting not from a powder preparation but a liquid binder in the form of barbottina.

The first protection body 6 has a slab configuration with a thickness of no less than 3 mm whereas the second protection body 7 has a slab configuration of thickness no less than 1 mm.

The first protection body 6 and the second protection body 7 are produced with a different mixture of materials, i.e. the same materials may be present but in different proportions or different materials may be present Preferably the different mixture of materials is adapted to give the first protection body 6 arid the second protection body 7 a different colouring that also visually highlights the double protection iii the event of the second protection body 7 cracking which would expose the first protection body 6.

It has been noted in practice that the heat storage dry radiator according to the invention is particularly advantageous due to the fact that it incorporates a constructively simple electric heater which guarantees suitable protection against electric shocks without needing to provide an earthing system, thanks to the use of special ceramic materials that due to sintering lead to closed porosity which prevents the triggering of cracks and the absorption of humidity.

In a possible embodiment the radiator 1 exclusively consists of the electric heater 4 while the metal body 2 is optional.

Claims

CLAIMSHeat storage dry radiator (1), cliaracterised in that it comprises at least one electric heater (4) having at least one resistive electric circuit (5) buried in a first insulating protection body (6) made of shitered ceramic hi turn buried in a second insulating protection body (7) made of sintered ceramic.
2. Heat storage dry radiator (1) according to claim 1, characterised hi that said first and second protection body (6, 7) are made of a sintered ceramic material having closed porosity.
3. Heat storage dry radiator (1) according to one or niore of the preceding claims, characterised hi that said first and second protection body (6, 7) are made of a sintered ceramic material having a porosity value not exceeding 0.5.
4. Heat storage dry radiator (1) according to one or more of the preceding claims, characterised in that tile sintered ceramic material of said first and/or second protection body (6, 7) comprises sintered ceraniic steatite.
5. Heat storage dry radiator (1) according to one or more of the preceding claims, characterised in that the sintered ceramic material of said first and/or second protection body (6, 7) comprises siiitered ceramic cordierite.
6. Heat storage dry radiator (1) according to one or more of the preceding claims, characterised in that said first protection body (6) has a slab configuration of no less than 3 mm thickness and said second protection body (7) has a slab configuration of no less than 1 mm thickness.
7. Heat storage dry radiator (1) according to one or more of the preceding claims, characterised in that said first protection body (6) and said second protection body (7) are produced with a different mixture of materials.
8. Heat storage dry radiator (1) according to one or niore of the preceding claims, characterised in that said first protection body (6) and said second protection body (7) have a different colouring.
9. Heat storage dry radiator (1) according to one or more of the preceding claims, characterised in that said electric heater (4) is produced by a single sinter firing of a cold moulded piece comprising said at least one resistive electric circuit buried in said at least one protection body (6) to be sintered in turn buried hi said second protection body (7) to be shitered.
10. Heat storage dry radiator (1) according to one or more of the preceding claims, cliaracterised in that said at least one resistive electric circuit (4) comprises a metal alloy wire with a high melting point wound in a spiral.
11. Heat storage dry radiator (1) according to one or more of the preceding claims, characterised hi that it comprises a metal body (2) internally having a housing pocket (3) for said electric heater (4).