AU601338B2 - Waterbed heater - Google Patents

Description

COMMONWEALTH OF AUSTRALIA Patent Act 1952 CO0M PL ET E SP EC IF IC A TIO N

(ORIGINAL)

Class Int. Class Application Number :PJ0445 Lodged :15 September 1988 Complete Specification Lodged Accepted Published tt Z Ott r Priority: Related Art 15CC C C C CC C CC CC

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(SIC

ICC( C C I C Name of Applicant Address of Applicant Actual Inventor Address for Service -DALREGOv'RC ORTO-T- L MTE LDMiTk -1-8a=LawsonStre-,Red-fer-n-,New- So~ith-Wales.,Commonwea--t-h-of, a-14-a- NS Vj FRANYO NAJDEK F. B. RICE CO., Patent Attorneys, 28A Montague Street, BALMAIN. 2041.

Ctf Complete Specification for the invention entitled: "WATERBED HEATER" The followIng statement is a full description of this invention including the best method of performing it known to Me:- S0 10138 1/98 14/09/89 -2ate Ogg* 00a 00 at a ar 0 t a 0000 O a a 00a 00aa 0 a The present invention relates to a waterbed electric heater, the object of the invention being to provide a waterbed electric heater that will offer a greater degree of safety and reliability than is available in existing heaters.

Waterbed electric heaters normally consist of a sealed plastic (PVC) envelope of a size of up to about 1,000mm x 300mm that encloses an electrical resistor which may take the form of a metal alloy wire or a sheet of carbon. Such heaters are flexible to the extent that they may be rolled up to form a convenient package for transport purposes.

Existing waterbed electric heaters, if installed and used strictly in accordance with the instructions provided 15 with them function quite satisfactorily and safely.

Unfortunately some users disregard the instructions and as a result the heater can fail.

The prime source of failure, and in particular hazardous failure, appears to stem from incorrect 20 installation of the flexible waterbed heaters.

Heaters supplied in roll up form (which is the present normal method of packaging) are often not straightened flat and are installed with creases or even with the ends turned over. This leads to spot over 25 heating, resulting in burn out and possible fire risk.

Heaters are not positioned on a true flat surface i.e.

they are positioned over joints in timber base, allowing movement and distortion of heater into joint area (a timber joint may look true and even on a new bed, but the timber on drying out may open up joints).

Likewise timber knots, positioned under heaters may dry out, shrink and even fall out and allow the heater element to protrude into the knot hole. This can lead to over-heating and fire risk.

Also, heaters positioned too close to the side of a 3 4 A..

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ji d bed may inadvertently have the bed clothes tucked over them restricting the heat dissipation. Again, this can cause scorching and possible fires.

The present invention seeks to overcome these difficulties by a combination of two features one being the inclusion in the heater of a backing member of sufficient stiffness to maintain the heater in a flat condition and prevent it from being folded or rolled up and the other being the provision of a layer of material preferably aluminium foil w:hich acts to distribute heat uniformly over the whole area of the heater.

The present invention comprises a waterbed electric heater consisting of a heater element in a sealed plastic envelope, a backing member extending over the whole area of the heater of sufficient stiffness to maintain the heater in a flat condition and prevent rolling or folding and between the heater element and the backing member a sheet of material of high conductivity, such as aluminium foil, arranged to distribute heat more or less uniformly over the whole area of the heater. Preferably also the heater incorporates a microtherm sensor arranged to restrict the build up of heat in the heater if the waterbed is emptied while the heater is still connected to the mains power.

In order that the nature of the invention may be better understood a preferred form thereof is hereinafter described by way of example with reference to the accompanying drawings in which:- Fig. 1 is a perspective view of an electric heater according to the invention, broken away to show the various elements of construction; and Fig. 2 is a graph showing the results of a test carried out on heaters including a heater according to the invention.

As seen in the drawing the heater consists of a

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4 nickel copper resistance wire element B which is contained in a sealed envelope consisting of fire retardant PVC sheets A and C of 1.0 x 305 x 958mm dimension. Beneath the sheet C is a sheet D of aluminium foil covering the whole area of the heater and beneath this a sheet of masonite board E. Beneath this is a further sheet of fire retardant PVC F which is sealed to the sheets A and C.

Preferred dimensions of the various elements of the heater are shown in the drawing.

The heater also includes two safety devices neither of which are seen one being a microtherm sensor capable of restricting the heat buildup if the waterbed is emptied while the heater is still connected to the main power. It also includes a low ampere fuse located in the heater itself. This cannot be tampered with or a different control system substituted. Neither of these elements are shown in the drawing.

The curves in Fig. 2 show the results of an experiment performed to demonstrate the heat dispersion 20 qualities of the layer of aluminium foil included in a a t t preferred form of the present invention. In the first V"1 C part of the experiment a conventional heater without foil was placed under a water mattress with a 12 centimeter wide strip of woollen underblanket covering an end 25 section. In less than thirty minutes the temperature rise S under the woollen section exceeded 150 0C and was continuing to rise. At this point it was considered pointless to continue the experiment as the temperature had reached a dangerous level. The curve showing this 1-30 rise in temperature is at the left hand side of Fig. 2.

SA similar heater incorporating a layer of aluminium foil when subjected to the same test took five hours to reach a maximum of only 106 0C and then levelled off and did not exceed this for a further three hours. At this temperature, no damage was evident to the heater or woollen cover. The change in temperature over two days of testing are shown on Fig. 2.

A heater according to the invention provides a considerably increased degree of protection against accidental misuse or abuse plus an improvement in performance over conventional heaters.

The preferred form of the invention described above is given by way of example only as constituting one form of construction within the scope of the invention as defined broadly above.

It will be recognised by persons skilled in the art that numerous variations and modifications may be made to the invention as described above without departing from the spirit or scope of the invention as broadly described.

Ir Ir arC rt I o 4

Claims (3)

1. A waterbed electric heater consisting of a heater element in a sealed plastic envelope, a backing member extending over the whole area of the heater of sufficient stiffness to maintain the heater in a flat condition and prevent rolling or folding and between the heater element and the backing member a sheet of material of high conductivity, such as aluminium foil, arranged to distribute heat more or less uniformly over the whole area of the heater.

2. A waterbed electric heater as claimed in Claim 1 incorporating a microtherm sensor arranged to restrict the tbuild-up of heat in the heater if the waterbed is emptied while the heater is still connected to the mains power.

3. A waterbed electric heater substantially as illustrated in and as described with reference to Figure 1 in the accompanying drawings. DATED this 12th day of September 1989 uoo -LR eoK~ .zMUREeORPOQRAT-ON=PTYt Patent Attorneys for the Applicant: 0A TF.B. RICE CO. (ttr i Is :d ii-