GB2198619A

GB2198619A - Radiant heating element

Info

Publication number: GB2198619A
Application number: GB08726041A
Authority: GB
Inventors: Josef Hecht
Original assignee: AKO Werke GmbH and Co KG
Current assignee: AKO Werke GmbH and Co KG
Priority date: 1986-12-01
Filing date: 1987-11-06
Publication date: 1988-06-15
Anticipated expiration: 2007-11-06
Also published as: AT398674B; GB8726041D0; GB2198619B; DE3640999A1; ATA269987A; DE3640999C2

Abstract

In a radiant heating element for ceramic hot plates, a heating coil 5 is located on an insulating tray 2 by means of holding elements 7. The holding elements 7 should be able to be fitted to the insulating tray 2 before the heating coil 5 is laid so that the heating coil 5 is held on the insulating tray 2 by the holding elements 7 immediately after being laid. For this purpose, the holding element 7 comprises a neck 9 projecting above the upper surface 3,6 of the insulating tray 2. A hook- like projection 10 for the wire 5' of the heating coil is formed on this neck. <IMAGE>

Description

RADIANT HEATING ELEMENT This invention relates to a radiant heating element for ceremic hot plates of the kind in which a heating coil is located on an insulating tray by means of holding elements which are positioned in the insulating tray by foot members.

Such a radiant heating element is described in DD-PS 106 522. In this case the holding element is formed from a U-shaped metal clip which is pressed into the insulating tray by its two ends. The metal clips have to be placed in position after the heating coil has been laid in a spiral on the insulating tray. During the fitting of the clips, the heating coil has to be held in its spiral position. This makes fixing of the heating coil more difficult. In addition, the clips must be placed between the turns of the heating coil so that they only engage over those parts of the turns resting on the insulat- ing tray but not over the upper parts thereof. The placing of the clips is made more difficult as a result.

Another clip technique is known wherein the turns of the heating coil are completely engaged by clips. In this case, however, sufficiently large electrical insulating spacing must be ensured between the clips. This often makes an unwanted enlargement of the spacing of the turns of the heating coil necessary.

It is an object of the invention to provide a radiant heating element of which the construction is such that assembly thereof is simplified.

The invention accordingly provides a heating element of the kind mentioned, wherein each holding element comprises a neck projecting above the surface of the insulating tray and a hook-like projection formed on the end of said neck which engages over the wire of the heating coil.

Since the holding elements are so constructed that they engage and hold the heating coil as it is laidt the holding elements can be pressed into the material of the insulating tray before the heating coil is laid in place. As a result, insulating trays can be equipped with the holding elements in advance independently of the heating coils to be laid later. This represents a simplification in manufacture. In addition, the holding elements can easily be fitted to the insulating tray because the heating coil is not in the way.

When being laid, on the insulating tray, the heating coil is snapped onto the holding elements. The inherent springy resilient nature of the heating coil enables this.

As a result, the heating coil is held on the insulating tray without further fixing being necessary.

The heating coil is not rigidly gripped by the holding elements. As a result, thermal expansion of the heating coil is not hampered. This extends the life of the heating coil.

Since the holding elements have negligible contact with the heating coil, , they do not hamper the free heat radiation of the heating coil. This results in a high efficiency of the heating coil.

The holding elements are also suitable for heating coils of thin resistance wire with a small pitch.

In a preferred embodiment of the invention, the said projection of each holding element has, on the side facing away from the neck, at least one straight or arcuate guiding slope. When the heating coil is pushed into position, the wire of the heating coil can slide on the guiding slope until it snaps under the projection. The laying of the heating coil is thus simplified.

The invention is illustrated by way of example in the accompanying drawings, in which: Figure 1 is a partial sectional elevation of a radiant heating element according to the invention, illustrating one embodiment of holding element, Figures 2 to 8 are side elevations of further examples of embodiments of holding elements, and Figure 9 is a further embodiment of a radiant heating means according to the invention in partial sectional elevation.

Referring to the drawings, on a sheet metal pan plate 1 there is provided an insulating tray 2 which may consist of for example aluminium silicate fibres. A channel 4 to receive a heating coil 5 is preformed on the surface 3 of the insulating tray 2 although this surface 3 may also be plane.

A plurality of holding elements 7 one of which is shown in each of the Figures, are pressed into the insulating tray 2 at the bottom 6 of the channel 4.

The holding element 7 comprises one or more foot members 8 which are firmly embedded in the material of the insulating tray 2. Extending upwardly from the foot members 8 there is a neck 9 which projects above the surface 3 or through the bottom 6 of the insulating tray 2 A hook-like projection 10 is formed on the neck 9. This projection comprises, at its side remote from the neck 9, at least one guide slope 11 which is shown as being straight in the drawings. It may, however, also be made arcuate.

The holding elements 7 shown in Figures 1 to 5 are formed from stamped metal parts. They may also be formed from shaped ceramic parts.

In the embodiments shown in Figures 1, 3, 4 and 5, projections 10 with guide slopes 11 are provided at both sides of the neck 9. In the embodiment of Figure 2, the hook-like projection 10 with the guiding slope 11 is formed on only one side of the neck 9.

In the embodiments shown in Figures 1 and 4, the foot members 8 comprise straddling bevels 12. As a result the foot members 8 are spread apart on being pressed into the material of the insulating tray 2 (see Figure 1) Accordingly, the holding element 7 is held firmly in the insulating tray 2 and positively interlocked therewith.

In the embodiment of Figure 5, barbs are provided at the lower ends of the foot members 8. These improve anchorage of the holding element 7 in the material of the insulating tray 2 in comparison with a simple frictiontight fit.

In the embodiments shown in Figures 2 and 3, only one foot member 8 is provided and this is pointed at its end. The foot member 8 is held in the insulating tray 2 with a friction-tight fit.

The embodiments shown in Figures 6, 7 and 8 show holding elements 7 which are produced from round wire or square- wire in the form of bent wire members. The holding element 7 of Figure 7 comprises the hook-like projection 10 and the guide slope 11 at one side of the neck 9. In the embodiments shown in Figures 6 and 8 on the other hand, the hook-like projection 10 and the guide slope 11 are provided at both sides of the neck 9. With the formation of the foot members 8 shown in Figures 6 and 7, the said spreading apart results when the holding element is pressed into the insulating tray 2.

The holding elements 7 shown in Figures 1 to 8 are pressed into the insulating tray 2 from the upper surface 3. In Figure 9, a holding element 7 is shown which is pressed through the insulating tray 2 from the lower surface so that here again its neck 9 with the hooklike projection 10 and the guide slope 11 extends above the surface 3. Formed on the foot member 8 is a transverse member 1 which comprises points 15 which engage the material of the insulating tray 2 and serve to prevent twisting, thus ensuring that the hook-like projection 10 engages over a wire region 5' of the heating coil 5.

The holding element 7 shown in Figure 9 may be produced in the form of a stamped metal part, a turned part or a shaped part.

In the embodiment shown in Figure 9, an insulating disc 16 is provided between the sheet-metal pan plate 1 and the insulating tray 2. This is necessary, if the holding element 7 consists of metal, in order to prevent the holding element 7 touching the heating coil 5 from forming a short-circuit to the sheet-metal pan plate 1.

If the holding element is a shaped ceramic part, the insulating disc 16 may be omitted.

If the holding element 7 is an axially symmetrical turned part, the transverse member 14 is in the form of a disc. The points 15 can be omitted because then the wire region 5' can engage under the projection 10 in any angular position of the holding element 7. The holding element thus shaped may also be formed from a ceramic shaped part with wedge-shaped points.

The holding elements 7 are fitted to the insulating tray 2, for example by being shot into the tray, before the heating coil 5 is laid. Then the heating coil 5 is superimposed and pressed onto the holding elements 7.

During this operation, a wire region 5' close to the surface 3 can slide along the guide slopes 11. Because of the springy resilient nature of the heating coil 5, the wire region 5' is given a certain initial tension and as soon as it leaves the guide slope 11 it snaps under the projection 10. Finally, the heating coil 5 is located at a plurality of wire regions 5' between the projections 10, the necks 9 and the surface 3 or the bottom 6.

Claims

1. A radiant heating element for ceramic hot plates, which has a heating coil located on an insulating tray by means of holding elements positioned in the insulating tray by foot members, wherein each holding element comprises a neck which projects above the surface of the insulating tray and a hook-like projection formed on the end of said neck which engages over the wire of the heating coil.

2. A radiant heating element as claimed in Claim 1, wherein the said projection of each holding element has, on the side facing away from the neck, at least one straight or arcuate sloping guide surface.

3. A radiant heating element as claimed in Claims 1 or 2, wherein the said projection is provided at both sides of the neck.

4. A radiant heating element as claimed in any one of the preceding Claims, wherein the holding elements are provided at the bottom of a channel for the heating coil.

5. A radiant heating element as claimed in any one of the preceding Claims, wherein the holding element comprises two foot members.

6. A radiant heating element as claimed in Claim 5, wherein the holding element is pressed into the insulating tray from the upper surface and a bevel is formed on each foot member to cause spreading thereof.

7. A radiant heating element as claimed in Claim 5, wherein the holding element is pressed into the insulating tray from the upper surface and a barb is formed on each foot member.

8. A radiant heating element as claimed in any one of Claims 1 to 4, wherein the holding element comprises a transverse member at the lower end and is pushed through the insulating tray from underneath.

9. A radiant heating element substantially as described herein with reference to Fig. 1 of the accompanying drawings, Fig.l as modified by any one of Figs. 2-8, or Fig. 9 of the accompanying drawings.