GB2113958A

GB2113958A - Electric flexible heating arrangements e.g. electric blankets

Info

Publication number: GB2113958A
Application number: GB08201090A
Authority: GB
Inventors: Roy Edward Buckingham
Original assignee: Dreamland Electrical Appliances PLC
Current assignee: Dreamland Electrical Appliances PLC
Priority date: 1982-01-15
Filing date: 1982-01-15
Publication date: 1983-08-10
Also published as: GB2113958B; BE895597A; NZ202942A; AU1009983A; DE3300776A1; NL8300050A; AU555736B2

Abstract

A heating arrangement comprises a flexible heating device (22) and a control device. A flexible cable (14) incorporated within the heating device (22) extends between the heating device and control device by being disposed within passageways (12) in a flexible sheath (10). The sheath (10) is secured to both the heating device (22) and the control device in such a manner as not substantially to compress the cable (14). The sheath (10) has bonded thereto at least one reinforcing element (20) that is less extensible than the sheath per se. <IMAGE>

Description

SPECIFICATION Heating arrangements This invention relates to heating arrangments comprising flexible heating devices such as electric blankets (overblankets or underblankets) or electrid pads.

Electric blankets and pads generally comprise one or more flexible heating cables or elements together with a control device separate from the blanket or pad proper. The control device may simply comprise an on/off switch, but will nowadays generally be of a more sophisticated nature and comprise, for example, variable heat control means for switching between heating cables having different heat outputs and/or for controlling the heat output of a particular cable or cables to a desired, selectable level, or means for de-energising the blanket or pad in the event of an overheat situation or other fault. The control device must of course be electricaily connected to the cable or cables within the blanket or pad proper.It is known for such connection to be effected by running the ends of the heating cable or element to the control device via passageways in a sheath extending between the control device and the blanket proper. The known sheath was of a generally cylindrical form and was clamped in place at the control device by a plate which deformed the sheath and the cable lengths therein. The sheath was provided with a loose string reinforcement which had to be tied to the control device at one end of the sheath and sewn to the blanket at the other end. The cable employed was of a simple, basic type comprising a single insulated resistance wire.

Although such simple cables comprising single insulated resistance wires are still employed in the art to some extent, their use is increasingly being superseded by more sophisticated cables comprising two or more conductors separated by a material whose impedance is monitored by the control device to determine the temperature of the cable to provide normal temperature and/or overtemperature heating control and/or to provide protection against both localised overheating (e.g.

due to arcing or a ruck) and/or general overheating and/or conductor breakage. The material separating the conductors may be, for example, polyvinyl chloride (PVC) which may or may not be doped with a material that enhances its resistivity, whereby an analogue signal representing the temperature of the cable can be obtained by monitoring the impedance. The material between the conductors may instead or also comprise a material which melts in the event of overheating to allow contact between the conductors, which is indicated by the impedance dropping abruptly to a low value.Such a cable is typically of the form known in the art as a "dual-concentric" cable, comprising an inner conductor (which may be a heating conductor), the separating material and a coaxially arranged outer conductor, which is typically a sensor conductor carrying no or very little current in normal use but which may instead be another heating conductor. These more sophisticated cables require reasonably careful treatment in order to operate satisfactorily. in particular, they must not be unduly stretched or compressed. The above-described known technique for running the simple, basic type of heating cable up to the control device is not satisfactory for this purpose and the practice has therefore grown up of terminating the heating cable or cables within the blanket and connecting its or their ends to the control device by means of a separate cord set.As can well be imagined, the connection of the conductors of the separate cord set, typically of copper stranded wire, to the resistance heating cable wire is troublesome to effect in manufacture and can lead to problems in practice.

According to the present invention there is provided a heating arrangement comprising a flexible heating device incorporating at least one flexible cable, a control device, and a flexible sheath extending between the heating device and the control device and incorporating a plurality of passageways through which the or each cable extends for electrical connection to the control device, wherein the sheath is secured to both the heating device and the control device in such a manner as not substantially to compress the cable or cables, and the sheath has bonded thereto at least one reinforcing element that is less extensible than the sheath per se.

In a heating arrangement embodying the invention, at least one flexible cable of the heating device extends to and is connected to the control device thereby avoiding the above-mentioned problems involved in joining it to a separate cord set extending between the control device and heating device. However, due to the fact that the sheath is secured to both the heating device and the control device in such a manner as not substantially to compress the cable, it is possible to use cables - e.g. the above-discussed more modern type of cable comprising two or more conductors -- which should not be compressed.

Furthermore, the fact that the sheath has bonded thereto a reinforcing element that renders it less extensible than the sheath per se means that the cable or cables running through the sheath are protected against undue tensile stresses without the inconvenience of the provision of a loose form of reinforcing element which requires special fixing to the control device and blanket and which might become detached from one or more of the devices in use.

The reinforcing element or elements may be bonded to the sheath by being moulded therewith during manufacture. The reinforcing element or elements may be bonded within the sheath or may be bonded to the exterior thereof.

Preferably, the reinforcing element or elements are such as to impart a tensile strength or breaking strain to the sheath of at least 200N.

The reinforcing element or elements may comprise one or more cords or strings or braids.

They may be formed of a variety of materials, including cotton, rayon or bunched copper strands.

The sheath is desirably impervious to liquids and heat-resistant. Polyvinyl chloride (PVC) is a material well suited to these requirements. The sheath may have a variety of forms. It may in particular comprise one or more regions -- e.g.

flat regions or "lands" disposed for example at its centre or at its edges - on which a securement (e.g. clamping) pressure may be exerted to secure it to the heating device and/or to the control device without substantial deformation of a portion or portions of the sheath containing the passageways. The sheath may be secured in place by means of the said regions, for instance by sewing, welding, glueing or mechanical clamping.

Alternatively, the passageways may be scalloped or punched through at a position near at least one of the ends of the sheath so that the cables can run out therefrom and the remaining end section of the sheath, not containing the cable, can be used for securing the sheath to the heating device or control device by the application of pressure.

The cable or cables may be of a variety of forms. For instance, the cable may be the abovedescribed simple type of cable essentially comprising only a simple heating conductor, the two ends thereof being run up through two passageways of the sheath for connection to a voltage supply via the control device. Preferably, however, in view of the fact that arrangements embodying the invention are particularly well suited to use with the more modern type of cable described above, i.e. that comprising two or more conductors separated by means whose impedance is monitored by the control device, the cable is of such a form. With such a cable, any protection afforded against overheating or breakage or the like will be provided between the control device and heating device as well as within the heating device.This is an important advantage because problems often arise where the wiring leaves the heating device.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic perspective view of a sheath of a heating arrangement embodying the present invention, the sheath being shown partly broken away to reveal details of its construction; Figure 2 is a sectional view of the sheath taken along the line Il-Il in Figure 1; Figure 3 shows part of a clamp that can be used to hold the sheath in place; Figure 4 is a view of an end portion of the sheath showing how it may be secured to an electric blanket or pad; and Figures 5, 6 and 7 are scrap views of alternative forms of sheath.

Figures 1 , 2 and 4 depict a sheath 1 0 that is preferably extruded from a high temperature, insulating grade PVC material and which incorporates two passageways 12 extending along its entire length. The passageways 1 2 are preferably of circular cross-section and approximately 4 mm in diameter so as to allow the free passage therethrough of a normal size dualconcentric heater/sensor cable or element 1 4 (Figure 4) as conventionally used in the construction of electric blankets and pads.

Portions 1 6 of the sheath 1 0 that include the passageways 12 are separated from one another by a flat region 18 which forms a "land" between the portions 1 6. A strengthening or reinforcing cord or string 20 comprising a high quality cabled cotton string having a breaking strain of approximately 1 5 Kg is integrally moulded into the land 1 8 as the sheath 10 is extruded and extends along the entire length of the sheath.

One end of the sheath 10 is secured to a flexible heating device in the form of an electric blanket or pad 22 (Figure 4). The other end of the sheath 10 is secured to a control device for the electric blanket which control device may, for example, comprise a plastics casing provided with a cord for connection to an electrical power supply. The cable (or cables) 14 may in known manner be tortuously disposed within the blanket or pad 22. There may in fact, for example, be a single cable 14, the two ends of which extend from the blanket to the control device via the respective passageways 12, the two ends of each of the sensor conductors of the cable being connected to circuitry within the control device whereby the impedance between the inner and outer conductors of the cable may be monitored.

The sheath 10 is secured to both the blanket 22 and the control device in such a manner as not substantially to compress the cable. For instance, the sheath 10 may be secured to the control device or blanket 22 by means of a clamp shown in Figure 3, the clamp comprising a central portion 30 that presses tightly against the land 1 8 and two bights 32 that engage the portions 16 of the sheath 10 fairly loosely, the net effect being that the sheath is tightly secured without the cable 14 being subjected to any substantial compressive force.

Figure 4 shows two techniques by which the sheath 10 can be secured to the blanket 22. Either one or both of the two techniques can be used for securing the sheath to the blanket. Similar techniques could be used for securing the sheath to the control device. According to 'one technique, the sheath 10 is longitudinally secured to the blanket 22 over an elongate area 40 (shown cross-hatched) by means of RF thermal welding, adhesive, sewing or some other technique. The longutidinal fixing technique has the advantage that it provides resistance to twisting of the sheath 1 0, which could cause the parts of the cable 14 adjacent the sheath 10 in the blanket to cross over one another within the blanket. As will be seen, the area 40 is disposed along the land 1 8 whereby pressure applied to form the join does not compress the cable 14. When welding is employed, the sheath 10 can be directly RF welded to a PVC reinforcing sheet portion of the blanket 22.

According to a second technique also shown in Figure 4, instead of the cable 1 4 emerging from the end of the sheath 10 it is taken out of a scalloped or punched-out portion 42 of the sheath 10 spaced some distance from its end and the remaining end portion 44, which does not contain the cable 1 4, is welded or in some other way secured to the blanket 22 - e.g. to the PVC reinforcing sheet thereof - in such a manner that the reinforcing string 20 is also secured thereto.

As will be appreciated, with the arrangement described above.the cable 14 is subjected to substantially no compression by securement of the sheath 10 to the control device and to the blanket 22. Since the reinforcing member 20 is moulded into the sheath 10, the part of the cable 1 4 running through the sheath 10 is protected to a large extent against extension of the sheath 10 in a simple and reliable manner. Furthermore, the present arrangement enables one to avoid the inconvenience and possible unreliability resulting from the use of a separate cord set extending between the control device and the blanket 22 and secured to the ends of the conductors of the cable 14 at a termination area of the blanket.

Furthermore, as a bonus, the fact that the cable 14 runs all the way up to the control device means that the protection against overheating and the Alike that it provides is provided also along the length of the cord formed by the sheath 1 0 and the parts of the cable 1 4 therein.

The invention can of course be performed in other ways than those described above by way of example. For instance, the sheath 10 could be a rubber moulding or a moulding of some other similar flexible insulating material, instead of a PVC extrusion, and the strengthening cord 20 could be of any suitable flexible material having a tensile strength that is suitably great. For instance, rayon or bunched copper strands could be used. Also, more than one flexible cord or string 20 could be used. The profile of the sleeve 10 could adopt various different forms. It may for example be circular or oval and have two opposed fins or flat regions 18', equivalent to the land 18, along its edges, the sheath 10 being secured in place by techniques similar to those described above.

Figures 5 to 7 show three alternative forms of construction of the sleeve 1 0. Instead of or as well as the reinforcing string or strings 20 moulded within the body of the sheath 1 0, one can employ a reinforcing element bonded to the exterior of the sheath 10, for instance a cotton or metal braid 50 moulded into the exterior surface of the sheath 1 0 as shown by way of example in Figure 7, or a reinforcing scrim or string lattice or the like moulded in or on the exterior surface of the sheath, in a similar manner to that used for reinforcing garden hoses.

In the arrangements specifically described above there are two of the passageways 1 2. As mentioned above, these two passageways 1 2 can accommodate one or more cables 14, a typical arrangement being one in which there is a single dual/concentric cable 1 4, the two ends of which each extend through a respective one of the passageways. If there are more than one cable, it is possible for each passageway - or at least one of them - to accommodate two cables, in which case at least that passageway may be of some configuration other than circular, e.g. oval.

Additionally or alternatively, plural cables may be accommodated in more than two passageways 1 2. For example, if there are two cables (e.g. two separate heater/sensor cables or associated but separately arranged heater and sensor cables), the four ends thereof could run through four separate passageways.

Claims

1. A heating arrangement comprising a flexible heating device incorporating at least one flexible cable, a control device, and a flexible sheath extending between the heating device and the control device and incorporating a plurality of passageways through which the or each cable extends for electrical connection to the control device, wherein the sheath is secured to both the heating device and the control device in such a manner as not substantially to compress the cable or cables, and the sheath has bonded thereto at least one reinforcing element that is less extensible than the sheath per se.

2. A heating arrangement according to claim 1, wherein the or each cable comprises at least two relatively coaxially arranged conductors.

3. A heating arrangement according to claim 2, wherein the control device incorporates means for monitoring the impedance between said conductors.

4. A heating arrangement according to claim 1, claim 2 or claim 3, wherein the sheath has one or more regions on which a securement pressure is or has been exerted to secure the sheath to the heating device and/or to the control device without substantial deformation of a portion or portions of the sheath containing the passageways.

5. A heating arrangement according to claim 4, wherein a said region is disposed generally centrally of the sheath and has on each side thereof a said portion containing at least one passageway.

6. A heating arrangement according to claim 4, comprising a said region at each of a pair of opposed edges thereof.

7. A heating arrangement according to any one of the preceding claims, wherein the passageways are scalloped or punched through at a position near at least one end of the sheath, the cable or cables is or are run out therefrom, and the remaining end section of the sheath, not containing the cable or cables, has been used to secure the sheath to the heating device or control device by the application of pressure.

8. A heating arrangement according to any one of the preceding claims, wherein the or each reinforcing element is bonded to the sheath by being moulded therewith during manufacture.

9. A heating arrangement according to any one of the preceding claims, wherein the or at least one said reinforcing element is bonded within the sheath.

1 0. A heating arrangement according to claim 9, wherein the or each said reinforcing element bonded within the sheath comprises a cord or string or the like.

11. A heating arrangement according to any one of the preceding claims, wherein the or at least one said reinforcing element is bonded to the exterior of the sheath.

1 2. A heating arrangement according to claim 1 wherein said reinforcing element bonded to the exterior of the sheath comprises a braid, scrim, lattice or the like.

1 3. A heating arrangement substantially as herein described with reference to Figures 1 to 4, Figure 5, Figure 6 or Figure 7 of the accompanying drawings.