WO2000065875A1

WO2000065875A1 - Methods for forming heating elements for glass ceramic cooking hobs, and heating element obtained by the method

Info

Publication number: WO2000065875A1
Application number: PCT/EP2000/003461
Authority: WO
Inventors: Josef Vallet
Original assignee: I.R.C.A. S.P.A. - Industria Resistenze Corazzate E Affini
Priority date: 1999-04-23
Filing date: 2000-04-17
Publication date: 2000-11-02
Also published as: AU5392100A; ITVE990016A1; IT1311785B1; ITVE990016A0

Abstract

A method for forming heating elements for glass ceramic cooking hobs, characterised by: forming a resistive strip to a predetermined pattern from a thin metal sheet, forming from heat-resistant dielectric material a disc comprising projections defining at least one channel, the pattern of which corresponds to that of the strip, freely inserting said strip into said channel, inserting said disc into a metal container, closing the container with a glass plate.

Description

METHOD FOR FORMING HEATING ELEMENTS FOR GLASS CERAMIC COOKING HOBS, AND HEATING ELEMENT OBTAINED BY THE METHOD.

This invention relates to a method for forming heating elements for glass ceramic cooking hobs, and a heating element obtained by the method. Heating elements for glass ceramic cooking hobs are well known.

These heating elements generally consists of a metal container internally housing a heat-resistant dielectric body provided with a mixed-line channel containing a resistive wire or an edgewise-inserted resistive strip with a thickness of between 0.05 and 0.1 mm and a width of between 2 and 4 mm. On its outside the resistive strip generally comprises retention clips for its fixing to the base of the heating element which houses it. This type of arrangement has however the drawback that during heating, as a result of thermal expansion, the variation in the length of the strip causes it to curve and to vary its contact with the channel walls, so that the heat becomes non- uniformly distributed within the heating element.

An object of the invention is to provide a heating element for glass ceramic cooking hobs in which the resistive element is freely housed within the channels.

This and further objects which will be apparent from the ensuing description are attained by a method for forming heating elements for glass ceramic cooking hobs as described in claim 1.

A preferred embodiment of the invention together with some variants are described in detail hereinafter by way of non-limiting example with reference to the accompanying drawings, on which: Figures 1-4 show different geometrical shapes of the resistive plate, Figure 5 show a strip housed in the refractory disc, Figure 6 is a cross-section through the disc on the line VI-VI of 5,

Figures 7-12 show different strip profiles,

Figure 13 shows in detail the strip end to which the mains supply cables are connected, Figures 14-17 show different elements for locking the strip in the channels.

As can be seen from the figures, the method of the invention comprises a first stage in which a resistive strip 2 of any desired geometrical shape is formed from a thin metal sheet by punching or by acid incision. The various geometrical shapes are shown in Figures 1 to 4, Figure 1 showing two resistive elements 2, 2' which can be formed separately, whereas Figures 2, 3 and 4 show a strip 2 formed in one piece.

In order to reinforce the shape of the strip, this is profiled longitudinally or transversely to its length, as clearly shown in Figures 7 to 12. Specifically, the strip 2 can have a cross-section in the shape of a inverted V (see Figure 7), a curve with its concavity facing upwards (see Figure 8), a curve with its concavity facing downwards (see Figure 9), an inverted V with find (see Figure 10), a U (see Figure 10), or a zig-zag (see Figure 12).

In the method of the invention a heat-resistant dielectric body 4 is formed separately. This body is substantially in the shape of a cylindrical disc, which is positioned in a metal container 6 and is provided on its upper surface with a plurality of ribs 8 defining a channel 10 corresponding substantially to the geometrical development of the strip 2. The distance between the parallel ribs 8 is greater than the width of the strip 2. The resistive strip 2 is then positioned freely within said channels such as to enable it to move freely. This freedom of movement ensures that during the heating and consequent expansion of the strip, this does not curve and deform to hence rest against the walls.

To prevent the strip from rising, bars 12 formed from steatite or similar materials extend transversely above the channels and rest with their ends on the perimetral edge 14 of the heating body.

A heat-sensitive element 18 is provided in a position above said strip, and then entire assembly is closed by a glass plate 20. In the embodiment shown in Figure 15 the bars are positioned triangularly above the open parts of the channels.

In Figure 16 retention staples 16 are shown, to be driven into the insulating base spaced apart from each other above the strip to prevent this escaping from the channels.

In Figure 17 the strip is retained by nail-like elements 18 positioned within points of curvature of the strip.

The elements 18 enable the strip to expand but not to rise.

Claims

C L A I M S

1. A method for forming heating elements for glass ceramic cooking hobs, characterised by:

- forming a resistive strip to a predetermined pattern from a thin metal sheet, - forming from heat-resistant dielectric material a disc comprising projections defining at least one channel, the pattern of which corresponds to that of the strip, - freely inserting said strip into said channel,

- inserting said disc into a metal container, - closing the container with a glass plate.

2. A method as claimed in claim 1 , characterised by resting at least one bar on said projections.

3. A method as claimed in claim 2, characterised by using a bar of heat- insulating material.

4. A method as claimed in claim 2, characterised in that the bars are arranged triangularly above the open parts of the channel.

5. A method as claimed in claim 1 , characterised by forming a strip having an inverted V cross-section.

6. A method as claimed in claim 1 , characterised by forming a strip having a cross-section in the form of an inverted V with fins.

7. A method as claimed in claim 1 , characterised by forming a strip having a U cross-section.

8. A method as claimed in claim 1 , characterised by forming a strip of zigzag shape.

9. A method as claimed in claim 1 , characterised in that the strip is retained in the channel by inserting nail-like elements positioned within the points of curvature of the strip.

10. A heating element for cooking hobs characterised by comprising a metal container (6) housing in its interior a disc (4) of heat-resistant dielectric material comprising projections (8) defining at least one channel, and a resistive strip (2) shaped in accordance with the development of the channel.

11. A heating element as claimed in claim 1 , characterised by comprising at least one bar (12) of heat-insulating material resting on the channel projections (8).

12. A heating element as claimed in claim 9, characterised by comprising retention staples (16) straddling the strip.

13. A heating element as claimed in claim 9, characterised by comprising nail-like elements (18) positioned within the points of curvature of the strip.