GB2061079A

GB2061079A - Electrical heating apparatus

Info

Publication number: GB2061079A
Application number: GB8033298A
Authority: GB
Original assignee: CONSULTANT LAMINATIONS Ltd
Current assignee: CONSULTANT LAMINATIONS Ltd
Priority date: 1979-10-19
Filing date: 1980-10-15
Publication date: 1981-05-07

Abstract

Heating apparatus (25) for heating roadways, sports grounds or the like comprises a heating element in the form of electrically conducting wires (24) enclosed between two cover sheets (15, 22) of a water-permeable, non- degradable material. The material may be fibrous, comprising composite fibres of polypropylene and polyethylene, and the cover sheets (15, 22) may be adhesively bonded to each other or flame- bonded to opposed faces of a matrix shoot (10). Such matrix sheet (10) is of a water-permeable and deformable material such as polyurethane foam. The wires (24) are preferably parallel resistance heating cable. <IMAGE>

Description

SPECIFICATION Heating apparatus This invention relates to heating apparatus and in particular to heating apparatus for the underground heating of roadways, paths, sports grounds and the like.

It is known to provide such apparatus in which an electrical heating element is sandwiched between two layers of polythene sheeting. Such a construction has the disadvantage that the polythene sheeting must be perforated after assembly of the sandwich so as to allow the passage of water therethrough and prevent the collection of water on the surface of the ground above the heating apparatus.

This perforating involves a further process step, thus adding to the cost of the apparatus. Also the polythene sheeting deteriorates in use so that after a period of time, say five years, the apparatus must be replaced. This involves the costly operation of digging up the deteriorated heating apparatus, laying new heating apparatus and relaying the road or playing surface above the new heating apparatus.

It is an object of the present invention to provide heating apparatus which is not subject to the aforementioned disadvantages.

The invention provides heating apparatus comprising a heating element disposed between, so as to be supported by, two cover sheets, each of a water-permeable non-degradable material, said sheets having bonding connections therebetween adjacent said heating element whereby said heating element is enclosed.

Said heating element may be disposed in contact with and supported by a sheet of a deformable water-permeable matrix and said cover may be bonded one to each of the opposed faces of said matrix sheet.

Preferably the matrix sheet comprises a sheet of foam material which is a thickness greater than that of the heating element, and the foam material may be polyurethane or polyethylene, although the former material is preferred for reasons to be explained hereinafter. The thickness of the foam may lie in the range 1 mm to 25mm.

Alternatively said cover sheets may be bonded to each other adjacent said heating element, and said bonding may be by means of an adhesive.

The cover sheets are preferably of a fibrous material and may be of mineral fibres, for example asbestos. Preferably, however, the fibrous material comprises synthetic fibres, for example polypropy lene or polyethylene. A particularly suitable material comprises composite fibres of polypropylene and polyethylene, which may be present in the ratio of 2:1. The sheets may be of knitted, woven or non-woven material, and conveniently may be of a moulded fabric.

The cover sheets, if bonded to a matrix sheet, are preferably bonded to such matrix sheet by flame bonding.

The invention will now be described further, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of one apparatus which may be used in the production of one embodiment of heating apparatus according to the present invention; Figure 2 is a cross-section through heating appar anus so produced; and Figure 3 is a cross-section of an alternative embodiment.

Referring to Figure 1, a supply of polyurethane foam material 10 is provided and the foam is fed to a backing roller 11 around the periphery of which it is passed. Whilst supported by the backing roller 11 the foam 10 is subjected to flaming by means of a flame gun 12 whereby the surface of the foam 10 remote from the backing roller 11 is raised substantially to its 'melting' temperature and becomes tacky. A pressure roller 13 forms a nip 14 with the backing roller 11, and through this nip 14 the now tacky surfaced foam 10 is passed, together with a first cover sheet 15 which is fed from a supply 16 thereof.

As the foam 10 and cover sheet 15 pass through the nip 14 they are pressed in contact with each other and a bond is formed therebetween, the bond being partly mechanical and partly chemical. The mecha nicai bond is created due to the tacky foam adhering to the cover sheet by entering the interstices of the cover sheet material and/or encompassing the ends of the loose fibres thereof. The former occurs whether the cover sheet is of a knitted, woven or non-woven textile material and the latter occurs if the material is formed of fibrous, as opposed to monofil, yarn. The chemical bond is created due to mixing of isocyanates formed by decomposition of the foam material.In a preferred embodiment of the invention the cover sheet comprises a moulded fabric which is formed of composite fibres, the components of the fibres being polypropylene and polyethylene present in the ratio of about 2:1. The foam material, as stated above, is preferably polyurethane although polyester or polyethylene foam may be used. However, on account of the fact that the feed rate past the flame gun 12 possible when using the latter foam materials may be as low as one-third of that possible when using the former material, polyurethane foam is the preferred material.

The now bonded composite material 17 is fed to a second backing roller 18 around the periphery of which the material 17 is passed with the cover sheet 15 in contact therewith. The previously unheated surface of the foam material 10 is thereby presented to a second flame gun 19 to be heated thereby before the material 17 is passed through a second nip 20 formed by the backing roller 18 and a second pressure roller 21. A second cover sheet 22 is fed from a supply 23 thereof into the nip 20 so as to be pressed into contact with, and bonded to the material 17. Also passed into the nip 20 is a heating element 24 in the form of an electrical wire or mat.

The element 24 is fed to the nip between the material 17 and the cover sheet 22 so as to be trapped therebetween, the resilience of the foam 10 allowing the element 24 to be embedded therein and allowing sufficient surface of the foam 10 to be bonded to the cover sheet 22. The element 24 contacts the foam 10 at a point sufficiently spaced from the flame gun 19 as to prevent melting or other serious deterioration of the insulating cover of the electrical wire.

The composite material 25, comprising the foam material 10 having a heating element embedded in one surface thereof and a cover sheet bonded to each surface thereof, is then fed away from the nip 20 to take up means (not shown).

The construction of the heating apparatus as described above is shown in Figure 2, which is a cross-section through the composite material 25.

The wires of the heating element 24 may be at, for example, 7.5cm to 30cm centres and may be wired in series or in parallel. The element 24 may be connected to a 240 volt mains supply or may be connected to a 24 volt output of a transformer, the latter having its input connected to a 240 volts mains supply.

Referring now to Figure 3, there is shown wires 30 of a heating element, which wires are disposed between cover sheets 31 of the type described above in relation to Figure 2 embodiment. Lines of adhesive as at 32 are placed on one of the cover sheets 31 prior to the feeding of the two cover sheets 31 and the wires 30 to a pair of nip rolls so as to form a sandwich as shown in Figure 3.

Suitably the embodiment as shown in Figure 3 may be made in one metre wide lengths having three wires 30 extending therethrough as shown.

The wires may be parallel resistance heating cable such as "ECONOTRACE" (Registered Trade Mark) heating cable having a rating at 240 volts of 36 watts per metre. This arrangement would provide 108 watts per square metre which has been found sufficient under normal operating conditions to keep ground frost-free in the region of the surface thereof under or on which the heating apparatus is laid.

The cover sheets 15,22, 31 as described herein are of a material having good heat conductivity properties such that there is good heat transfer iateraliy of the wires 24, 30 so as to provide sufficiently constant heating over all of the surface of the ground.

By means of the invention a heating apparatus which is simple and inexpensive to produce and which is suitable for use in the underground heafing of roads, paths, sports grounds and the like is provided, the heating apparatus allowing for the passage of water therethrough and providing pro tection for the heating element against displacement or fracture in the event of heavy loads passing over the surface to be heated.

Claims

1. Heating apparatus comprising a heating ele ment disposed between, so as to be supported by, two cover sheets, each of a water-permeable, non degradable material, said cover sheets having bond ing connections therebetween adjacent said heating element whereby said heating element is enclosed.

2. Apparatus according to claim 1, wherein said heating element is disposed in contact with and supported by a sheet of a deformable water permeable matrix and said cover sheets are bonded one to each of the opposed faces of said matrix sheet.

3. Apparatus according to claim 2, wherein said matrix sheet comprises foam material.

4; Apparatus according to claim 3, wherein said matrix sheet has a thickness greater than that of said heating element.

5. Apparatus according to claim 4, wherein said matrix sheet has a thickness in the range of 1 to 25mm.

6. - Apparatus according to any one of claims 3 to 5,wherein said matrix sheet is of polyurethane.

7. Apparatus according to claim 1, wherein said cover sheets are bonded to each other adjacent said heating element.

8. Apparatus according to claim 7, wherein said bonding is by means of an adhesive.

9. Apparatus according to claim 7 or8, wherein said cover sheets are of fibrous material.

10. Apparatus according to claim 9, wherein said fibres are mineral fibres.

11. Apparatus according to claim 9, wherein said fibres are synthetic fibres.

12. Apparatus according to claim 11, wherein said fibrous material comprises composite fibres of polypropylene and polyethylene.

13. Apparatus according to claim 11 or 12, -wherein said cover sheets are bonded to opposed faces of a matrix sheet by means of flame bonding.

14. Heating apparatus substantially as hereinbefore described with reference to and as illustrated in Figure 2 or Figure 3 of the accompanying drawings.

15. Heating apparatus when manufactured by a method as hereinbefore described with reference to and as illustrated in Figure 1 of the accompanying drawings.