GB2126860A

GB2126860A - Electric heating element

Info

Publication number: GB2126860A
Application number: GB08324082A
Authority: GB
Inventors: Peter Brasier
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-09-08
Filing date: 1983-09-08
Publication date: 1984-03-28
Also published as: GB2126860B; GB8324082D0

Abstract

An electric heating element comprises a helix of resistance wire 1 supported in two vertical slotted plates 2, 3, the turns of the helix being held by the plates. A retaining strip of mica 6 may be provided. <IMAGE>

Description

SPECIFICATION Electric heating element The invention relates to an electric heating element, particularly for convector heaters. In order to heat air efficiently by convection it is important to ensure that the heating surface is distributed and offers little resistance to the flow of air. Also, of course, the resistance-wire must be electrically insulated from its surroundings.

A conventional form of heating element consists of a resistance wire supported concentrically within a metal sleeve by a jacket of electrically insulating particles, such as magnesium oxide powder. To ensure efficient heat transfer, fins are usually attached to the element. Such an arrangement is expensive to manufacture and it is difficult to provide a sufficiently unobstructed through-flow of air.

Another form of heating element consists of a helically wound resistance-wire supported to allow air to flow directly past it. However, such a helix of thin wire is difficult to support over its length in an insulated manner since it is liable to sagging and vibration. It is an advantage to use a long length of resistance-wire with a consequently short pitch of the helix. However, there is then the risk of adjacent turns of the helix touching each other and short-circuiting. The nature of the support arrangement places restrictions on the rigidity of the helix and on the diameter of the resistance-wire and pitch of the helix.

An object of the present invention is to provide an improved support arrangement for a helical resistance-wire heating element.

According to the invention there is provided an electric heating element which comprises a helix of resistance-wire and one or more elongate support members running the length of the helix substantially along respective sides thereof, the or each support member comprising a rigid plate of electrically insulating and heat-resistant material, the plate having a number of parallel slots through which adjacent turns of the helix project, retaining means being provided for holding the helix in the slots.

In one embodiment of the invention the retaining means comprises a retaining member for each plate, the retaining member being of electrically insulating and heat resistant material, and each retaining member being inserted between the projecting parts of the helix and the plate to hold the helix in position.

Although it is envisaged that there may be only one support member or perhaps three, a preferred embodiment of the invention provides two support members. In use these can be arranged parallel to each other and vertical so as to offer minimum impedance to the flow of convection air.

Preferably the or each slotted plate is made of mica. The or each retaining member may also be a mica strip. Alternatively, the retaining member may be a heat-resistant string.

In another form of the invention the retaining means-comprises four metal channel members, each extending along a respective edge of a plate, the edge of the plate being held tightly in the channel member so that the whole assembly can be rigidly mounted in a casing by virtue of the channel members.

The invention will further be described with reference to the accompanying drawings, of which Figure 1 is a perspective view of a heating element in accordance with the invention Figure 2 is an end elevation of the element of Figure 1; Figure 3 is a perspective view of another heating element in accordance with the invention; and Figure 4 is a cross-section taken at 'A-A- A-A' of Figure 3.

Referring to Figures 1 and 2, the heating element comprises a helix 1 of electrical resistance-wire and two support members 2 and 3. Each support member comprises a plate 4 of mica having slots 5 punched therein. Each slot accommodates a respective turn of the helix 1 which projects through the slot.

A mica strip 6 is inserted between the projecting part of the helix and the plate, thereby retaining the helix in position in the plate.

In use, one or both plates is vertically mounted in a heater cabinet.

Referring to Figures 3 and 4 the support arrangement comprises four aluminium channel members 7 which are folded over the edges of the plates so as to hold the plates tightly and they extend beyond the ends of the plates whereby the assembly can be mounted rigidly in a heater cabinet.

Claims

1. An electric heating element which comprises a helix of resistance-wire and one or more elongate support members running the length of the helix substantially along respective sides thereof the or each support member comprising a rigid plate of electrically insulating and heat-resistant material the plate having a number of parallel slots through which adjacent turns of the helix project, retaining means being provided for holding the helix in the slots.

2. An electric heating element as claimed in claim 1 wherein the retaining means comprises a retaining member for each plate, the retaining members being of electrically insulating and heat resistant material, and each retaining member being inserted between the projecting parts of the helix and the plate to hold the helix in position.

3. An electric heating element as claimed in claim 1 wherein the retaining means comprises four metal channel members, each extending along a respective edge of a plate, the edge of the plate being held tightly in the channel member so that the whole assembly can be rigidly mounted in a casing by virtue of the channel members.

4. An electric heating element as claimed in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electric heating element The invention relates to an electric heating element, particularly for convector heaters. In order to heat air efficiently by convection it is important to ensure that the heating surface is distributed and offers little resistance to the flow of air. Also, of course, the resistance-wire must be electrically insulated from its surroundings. A conventional form of heating element consists of a resistance wire supported concentrically within a metal sleeve by a jacket of electrically insulating particles, such as magnesium oxide powder. To ensure efficient heat transfer, fins are usually attached to the element. Such an arrangement is expensive to manufacture and it is difficult to provide a sufficiently unobstructed through-flow of air. Another form of heating element consists of a helically wound resistance-wire supported to allow air to flow directly past it. However, such a helix of thin wire is difficult to support over its length in an insulated manner since it is liable to sagging and vibration. It is an advantage to use a long length of resistance-wire with a consequently short pitch of the helix. However, there is then the risk of adjacent turns of the helix touching each other and short-circuiting. The nature of the support arrangement places restrictions on the rigidity of the helix and on the diameter of the resistance-wire and pitch of the helix. An object of the present invention is to provide an improved support arrangement for a helical resistance-wire heating element. According to the invention there is provided an electric heating element which comprises a helix of resistance-wire and one or more elongate support members running the length of the helix substantially along respective sides thereof, the or each support member comprising a rigid plate of electrically insulating and heat-resistant material, the plate having a number of parallel slots through which adjacent turns of the helix project, retaining means being provided for holding the helix in the slots. In one embodiment of the invention the retaining means comprises a retaining member for each plate, the retaining member being of electrically insulating and heat resistant material, and each retaining member being inserted between the projecting parts of the helix and the plate to hold the helix in position. Although it is envisaged that there may be only one support member or perhaps three, a preferred embodiment of the invention provides two support members. In use these can be arranged parallel to each other and vertical so as to offer minimum impedance to the flow of convection air. Preferably the or each slotted plate is made of mica. The or each retaining member may also be a mica strip. Alternatively, the retaining member may be a heat-resistant string. In another form of the invention the retaining means-comprises four metal channel members, each extending along a respective edge of a plate, the edge of the plate being held tightly in the channel member so that the whole assembly can be rigidly mounted in a casing by virtue of the channel members. The invention will further be described with reference to the accompanying drawings, of which Figure 1 is a perspective view of a heating element in accordance with the invention Figure 2 is an end elevation of the element of Figure 1; Figure 3 is a perspective view of another heating element in accordance with the invention; and Figure 4 is a cross-section taken at 'A-A- A-A' of Figure 3. Referring to Figures 1 and 2, the heating element comprises a helix 1 of electrical resistance-wire and two support members 2 and 3. Each support member comprises a plate 4 of mica having slots 5 punched therein. Each slot accommodates a respective turn of the helix 1 which projects through the slot. A mica strip 6 is inserted between the projecting part of the helix and the plate, thereby retaining the helix in position in the plate. In use, one or both plates is vertically mounted in a heater cabinet. Referring to Figures 3 and 4 the support arrangement comprises four aluminium channel members 7 which are folded over the edges of the plates so as to hold the plates tightly and they extend beyond the ends of the plates whereby the assembly can be mounted rigidly in a heater cabinet. Claims

4. An electric heating element as claimed in any of the preceding claims wherein the or each slotted plate is made of mica.

5. An electric heating element substantially as hereinbefore described with reference to Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.