Electric heater

Abstract

 An electric heater comprises a metal support dish (1) having a base (1A) and an upstanding peripheral rim (1B) having a free upper edge, a layer (2) of insulation material in the dish with at least one heating element (3) disposed relative thereto. A ring-shaped insulation member (6) is arranged within the dish adjacent to the peripheral rim and is supported at least in part on the layer of insulation material. Securing means is provided for the ring-shaped insulation member, the securing means comprising at least one narrow strip (5, 5A, 5B) of dish material at the free upper edge of the rim (1B). The or each narrow strip is formed by a slit section (4) of the dish (1) extending substantially parallel to the free upper edge, the or each narrow strip (5, 5A, 5B) being deformed over substantially the entire width thereof to overlyingly engage a portion (8, 9, 10) of the ring-shaped insulation member (6).

Description

[0001] This invention relates to electric heaters particularly, but not exclusively, for use in cooking appliances behind a sheet of a material such as glass-ceramic which may be a cooking surface.

[0002] Electric heaters are well known for use behind glass-ceramic cooking surfaces. Such heaters can comprise a metal support dish formed with a base and an upstanding peripheral rim and having therein a base layer of insulation material, such as microporous thermal and electrical insulation material. At least one electrical heating element is provided, supported on or adjacent to the surface of the base layer. A ring-shaped insulation member is known to be arranged within the dish adjacent to the peripheral rim and supported at least in part on the layer of insulation material. Such ring-shaped insulation member may have a top surface arranged to contact the rear surface of a glass-ceramic cooking plate.

[0003] It is known for such a ring-shaped insulation member to comprise a material such as bound vermiculite, although other materials are also well known to be used.

[0004] The ring-shaped insulation member may be secured in the dish by frictional engagement with the rim, or with a stepped and/or tapered shim of insulation material of the base layer provided between the ring-shaped member and the rim. In practice, however, such frictional engagement can be inadequate, particularly since some softening or shrinkage of the ring-shaped member may occur at elevated temperatures when the heater is subsequently operated. As a result, undesirable detachment of the ring-shaped member from the dish may occur.

[0005] US-A-5 223 697 describes an electric radiant heater in which a snap connection is provided between the peripheral rim of the support dish and the ring-shaped insulation member. A downwardly sloping and inwardly projecting resilient tab is pressed back after the ring-shaped insulation member has been inserted to engage in a vertical slot formed in the peripheral surface of the ring-shaped member. A disadvantage of this arrangement is that, because the free edge of the snap connection is located in the lower region of the peripheral rim, it is not suited to use with a stepped and/or tapered shim of insulation material as described above and this reduces the range of use of the arrangement. A further disadvantage is that the snap connection can be unreliable.

[0006] It is an object of the present invention to overcome or minimise these problems.

[0007] According to the present invention there is provided an electric heater comprising a metal support dish having a base and an upstanding peripheral rim having a free upper edge, a layer of insulation material in the dish with at least one heating element disposed relative thereto, a ring-shaped insulation member arranged within the dish adjacent to the peripheral rim and supported at least in part on the layer of insulation material, and securing means being provided for the ring-shaped insulation member, wherein the securing means comprises at least one narrow strip of dish material at the free upper edge of the rim, and wherein the or each narrow strip is formed by a slit section of the dish extending substantially parallel to the free upper edge, the or each narrow strip being deformed over substantially the entire width thereof to overlyingly engage a portion of the ring-shaped insulation member.

[0008] The portion of the ring-shaped insulation member overlyingly engaged by the or each deformed narrow strip may comprise a protrusion on the member or may comprise a slot, rebate, groove or ledge on or in a section of the member.

[0009] The or each narrow strip may be deformed over substantially the entire width thereof into a loop shape within the dish, which loop shape overlyingly engages a portion of the ring-shaped insulation member. The loop shape may be continuous or discontinuous, that is, broken.

[0010] Alternatively, the or each narrow strip may be cut to form a tine which is shaped to overlyingly engage a portion of the ring-shaped insulation member.

[0011] A plurality of spaced apart narrow strips of dish material may be provided, formed by a plurality of slit sections of the dish, the narrow strips being deformed over substantially the entire width thereof to overlyingly engage associated portions of the ring-shaped insulation member. The associated portions of the ring-shaped insulation member may comprise a plurality of outwardly directed protrusions provided on and spaced apart around the member, the protrusions having top surfaces overlyingly engaged by the deformed narrow strips. In this embodiment the protrusions may be integral with the member. The protrusions may be of higher density than the remainder of the member.

[0012] The ring-shaped insulation member may comprise bound vermiculite.

[0013] The layer of insulation material may comprise microporous thermal and electrical insulation material.

[0014] A shim of the insulation material of the layer may be provided between at least a portion of the ring-shaped insulation member and the upstanding peripheral rim of the dish. The shim may be of stepped or tapered form, reducing in width towards the top of the peripheral rim of the dish. The ring-shaped insulation member may be of suitably complementary stepped or tapered form for contact with the shim of insulation material.

[0015] The invention is now described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of part of an electric heater according to the present invention;

Figure 2 is an exploded perspective view of an electric heater according to the present invention;

Figure 3 is a perspective view of part of an alternative arrangement for the heater of Figure 2; and

Figure 4 is a perspective view of part of a further alternative arrangement for the heater of Figure 2.

[0016] An electric heater according to the present invention comprises a metal support dish 1 having a base 1A and an upstanding peripheral rim 1B having a free upper edge. A layer 2 of microporous insulation material is provided in the dish 1 with at least one heating element 3, such as of corrugated ribbon or coiled wire form, disposed thereon or adjacent thereto.

[0017] The dish is slit generally in the circumferential direction of the rim at regions 4 between the edge of the rim and the base 1A to provide narrow strips 5 of dish material spaced apart around the rim at the edge thereof. Thus the slits 4 and the narrow strips 5 extend substantially parallel to the free edge of the peripheral rim 1B.

[0018] A ring-shaped insulation member 6, comprising bound vermiculite, is arranged to be located within the dish 1 adjacent to the peripheral rim lB and supported at least in part on the layer 2 of insulation material.

[0019] To reduce the temperature of the peripheral rim lB of the dish, a shim 7 of insulation material of the layer 2, of lower thermal conductivity than the ring-shaped insulation member 6, is optionally provided between the ring-shaped member 6 and the peripheral rim 1B of the dish. This shim 7 may be of stepped or tapered form, reducing in width towards the top of the peripheral rim 1B of the dish. The ring-shaped insulation member 6 is of suitably complementary stepped or tapered form for contact with the shim 7 of insulation material.

[0020] A plurality of outwardly-directed protrusions 8 are provided integral with the ring-shaped member 6 and spaced apart around the peripheral surface of the member. Such protrusions have top surfaces 9 intermediate the top and bottom of the peripheral surface of the member and are preferably formed of a higher density than the ring-shaped member 6 itself. This is achieved by compacting the vermiculite material of the protrusions 8 to a greater extent than the material of the remainder of the ring-shaped member 6 during formation of the ring-shaped member 6.

[0021] The ring-shaped member 6 is located in the heater with the protrusions 8 on the member 6 aligned with the narrow strips 5 of dish material.

[0022] The narrow strips 5 are deformed over substantially the entire width thereof (that is in a direction substantially perpendicular to the free edge) into loop shapes within the dish, which loop shapes overlie and engage the top surfaces 9 of the protrusions 8 and secure the ring-shaped member 6 in position in the heater. Partial deformation of the narrow strips may be effected prior to locating the ring-shaped member in the heater.

[0023] The loop shapes of the narrow strips 5 can be continuous, as shown in Figure 2. They could however be discontinuous (i.e. broken), as shown by reference numeral 5A in Figure 3, by breaking or cutting the narrow strips prior to or during deformation thereof.

[0024] Instead of the narrow strips 5 being deformed into loop shapes, they could, as shown in Figure 4, be cut to form tines 5B which are shaped to overlie and engage the top surfaces 9 of the protrusions 8 and secure the ring-shaped member 6 in position in the heater.

[0025] Instead of protrusions 8 being provided on the ring-shaped member 6, slots, rebates, grooves or ledges 10 could be provided in the member 6, facing the upstanding peripheral rim 1B of the dish, the deformed narrow strips 5, 5A, 5B, either as loop shapes or tines, engaging with such slots, rebates, grooves or ledges 10 to secure the ring-shaped member 6 in position in the heater.

Claims

1. An electric heater comprising a metal support dish (1) having a base (1A) and an upstanding peripheral rim (1B) having a free upper edge, a layer (2) of insulation material in the dish with at least one heating element (3) disposed relative thereto, a ring-shaped insulation member (6) arranged within the dish adjacent to the peripheral rim and supported at least in part on the layer of insulation material, and securing means being provided for the ring-shaped insulation member characterised in that the securing means comprises at least one narrow strip (5, 5A, 5B) of dish material at the free upper edge of the rim (1B), and in that the or each narrow strip is formed by a slit section (4) of the dish (1) extending substantially parallel to the free upper edge, the or each narrow strip (5, 5A, 5B) being deformed over substantially the entire width thereof to overlyingly engage a portion (8, 9, 10) of the ring-shaped insulation member (6).

2. A heater according to claim 1, characterised in that the portion (8, 9, 10) of the ring-shaped insulation member (6) overlyingly engaged by the or each deformed narrow strip (5) comprises a protrusion (8) on the member (6).

3. A heater according to claim 1, characterised in that the portion (8, 9, 10) of the ring-shaped insulation member (6) overlyingly engaged by the or each deformed narrow strip (5) comprises a slot, rebate, groove or ledge (10) on or in a section of the member (6).

4. A heater according to claim 1, 2 or 3, characterised in that the or each narrow strip (5) is deformed over substantially the entire width thereof into a loop shape within the dish (1), which loop shape overlyingly engages a portion (8, 9, 10) of the ring-shaped insulation member (6).

5. A heater according to claim 4, characterised in that the loop shape is continuous.

6. A heater according to claim 4, characterised in that the loop shape is discontinuous.

7. A heater according to claim 1, 2 or 3, characterised in that the or each narrow strip (5) is cut to form a tine which is shaped to overlyingly engage a portion (8, 9, 10) of the ring-shaped insulation member (6).

8. A heater according to any preceding claim, characterised in that a plurality of spaced apart narrow strips (5) of dish material are provided, formed by a plurality of slit sections (4) of the dish, the narrow strips being deformed over substantially the entire width thereof to overlyingly engage associated portions of the ring-shaped insulation member (6).

9. A heater according to claim 8, characterised in that the associated portions of the ring-shaped insulation member (6) comprise a plurality of outwardly directed protrusions (8) provided on and spaced apart around the member, the protrusions having top surfaces (9) overlyingly engaged by the deformed narrow strips (5).

10. A heater according to claim 9, characterised in that the protrusions (8) are integral with the member (6).

11. A heater according to claim 10, characterised in that the protrusions (8) are of higher density than the remainder of the member (6).

12. A heater according to any preceding claim, characterised in that the ring-shaped insulation member (6) comprises bound vermiculite.

13. A heater according to any preceding claim, characterised in that the layer (2) of insulation material comprises microporous thermal and electrical insulation material.

14. A heater according to any preceding claim, characterised in that a shim (7) of the insulation material of the layer (2) is provided between at least a portion of the ring-shaped insulation member (6) and the upstanding peripheral rim (1B) of the dish (1).

15. A heater according to claim 14, characterised in that the shim (7) is of stepped or tapered form, reducing in width towards the top of the peripheral rim (1B) of the dish.

16. A heater according to claim 15, characterised in that the ring-shaped insulation member (6) is of suitably complementary stepped or tapered form for contact with the shim (7) of insulation material.

Drawing