NZ195782A - Heat storage slab;element embedded between two moulded slabs - Google Patents

Description

195782 NEW ZEALAND PATENTS ACT, 1953 No.: 195782 Date: 8th December 1980' COMPLETE SPECIFICATION IMPROVEMENTS IN OR RELATING TO HEAT STORAGE MEANS T/We, RALTA LIMITED, A New Zealand company of 1043 Tremaine Avenue, Palmerston North, New Zealand hereby declare the invention for which I / we pray that a patent may be granted to me/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - 195782.

Improvements in or relating to methods of forming heat storage means and/or heat storage means and/or appliances incorporating said heat storage means.

The ability to convert electrical energy into heat and to store that heat in some heat storage medium has been used widely. The present invention is particularly concerned with the use of a heat storage means in a food tray or stand allowing the food supported thereon to be kept hot without any source of energy connected thereto when the tray or stand is on the table or in similar use. However, the invention is not restricted to this application and is capable of being applied to any construction requiring the formation of heat storage means.

One of the difficulties in forming heat storage means is the accurate location of the heating element and this particularly important where it is desired to achieve an even heat over the used surface of the heat storage means.

I It is therefore an object of the present invention to provide a method of forming heat storage means and/or heat storage means formed thereby and/or appliances incorporating said heat storage means which will allow for the accurate placement of an element within the heat storage medium or will at least provide a useful choice over the methods previously known for forming such heat storage means.

In one aspect the invention consists in a method of manufacturing a heat storage means comprising the steps of moulding a cementitious mix into a biscuit slab forming element holding means in said biscuit slab engaging an 195782 * « electric heating element with said element holding means placing said biscuit slab with element attached in a further mould and moulding a cemetitious mix to embed said element and complete the heat storage means.

In a further aspect the invention consists in heat storage means formed in accordance with the method according to the preceding paragraph.

In a yet further aspect the invention consists in a heat storage appliance using a heat storage means according to the two preceding paragraphs.

One preferred form of the present invention will' now be I described with reference to the accompanying drawings in which i Figure 1 is a view of the inner biscuit showing the element holding grooves, Figure 2 is a sectional view through a heat storage slab formed according to the present invention, Figure 3 is a plan view of a slab used in a food tray, Figure 4 is a pictorial view of a food tray according to the present invention, and Figure 5 is a view of the tray showing the components in an exploded relationship.

A heat storage slab 1 is designed to fit within and provide the major component of the heated tray 2. As indicated previously the present invention is not restricted to the application of the heat storage slab to this type of appliance and it could have other application. 195782 In order to form the heat storage slab 1 an inner biscuit 2 is moulded under pressure from a suitable cemen-titious mix. This mix is normally formed from a mortar sand and cement and may include additives such as a suitable emolsifying additive. A dry mix is moulded under pressure to form a green biscuit which is then allowed to cure.

The green biscuit can be moulded as a rectangular slab without any grooves 3 formed therein. These grooves can subsequently be cut using a diamond saw. Alternatively the grooves could be moulded in the green biscuit using a suitable platen plate with ribs which will generate the desired i pattern of grooves in the green biscuit.

Once the biscuit has cured, and this normally would require a period of some days, for example 14 days, the biscuit can have engaged therewith an heating element 4, for example a bare nichrome 31 SWG element which is wound about the grooves to provide the element circuit in association with the biscuit 2.

The biscuit with the element engaged is then placed in a larger mould with the smooth surface of the biscuit providing one face of the finished slab. An embedding slab 5 is then moulded under pressure about the element and biscuit to form a completed slab having a cross-sectional shape similar to that illustrated in figure 2.

In order to enhance the bonding it is desirable to coat the surfaces of the biscuit contacting the embedding slab with a suitable cementitious adhesive. For convenience in the heated tray a corner section 6 of the biscuit is stepped 195/82 back and the corresponding corner section 7 in the embedding slab is also stepped back to allow for an electrical connector 8. In the simplest form the element wire through connections 9 and 10 is engaged with pins in the connector 8 with the third pin connected to earth 11 in the usual manner. A cut back section 12 is formed in the embedding slab to provid space for control components as will be described later.

The completed tray 2 is illustrated in figure 4 and has the components thereof shown in more detail in figure 5. The completed heat storage slab 13 provides the major component of -the heated tray and this slab is electrically connected to the input socket 8. A slightly more sophisticated control is provided over the simple connection illustrated in figure 3. A thermal fuse 14 is connected in the circuit and rests in one arm of the L-shaped recess 12. A thermostat 15 is also connected in the circuit and is engaged in the other arm of the recess 12.

The tray itself comprises a metal base 16, a metal top 17, handles 18 and an insulating layer 19. The top 17 is preferably finished with a suitable decorative surface but one capable of withstanding the heat applied the heat storage slab 13. The insulating layer 19 is preferably a layer of fibreglass and restricts the transfer of heat from the slab through to the base 16. The handles 18 are formed from a non-conductive material preferably a suitable plastic and have projections 20 extending from the sides thereof to form four feet upon which the tray will be supported in use, thereby ensuring that heat from the tray is not readily transferred to the supporting table or other surface. 195782 The use of the appliance according to the present invention will be obvious from the aforesaid description. The tray is connected by a suitable electrical connector not shown to a source of electrical energy. This energy heats the slab 13 with the slab retaining a store of heat which will be available when the electrical energy is disconnected. The food tray is heated ready for use and when it is required is disconnected and placed normally on a table and used as a stand or tray on which is supported the food container to be kept hot. 135782

Claims (10)

WHAT WE CLAIM IS:

1. A method of manufacturing a heat storage means comprising the steps of moulding a cementitious mix into a biscuit slab forming element holding means in said biscuit slab engaging an electric heating element with said element holding means placing said biscuit slab with element attached in a further mould and moulding a cementitiuos mix to embed said element and complete the heat storage means.

2. A method as claimed in claim 1 wherein the cementitious mix is moulded under pressure to form the biscuit slab and to complete the heat storage means.

3. A method as claimed in claim 1 or claim 2 wherein the element holding means are grooves cut in a surface of the biscuit slab after the slab has been allowed to cure.

4. A method as claimed in claim 1 or claim 2 wherein the element holding means are grooves moulded in a surface of the biscuit slab.

5. A method as claimed in any one of the preceding claims wherein a cement adhesive is used to enhance bonding between the biscuit slab and the cementitious mix which embeds the heating element.

6. A method as claimed in any one of the preceding claims wherein the slab includes recesses or cutback sections for electrical controls and connectors.

7. A method of manufacturing a heat storage means when performed substantially as herein described with reference to the accompanying drawi ngs. 195782

8. A heat storage means when formed from a method according to any one of the preceding claims.

9. A heat storage appliance incorporating the heat storage means manufactured according to any one of claims 1 to 7.

10. A heat storage tray incorporating the heat storage means as claimed in claim 8 and when constructed, arranged and operable substantially as herein described with reference to the accompanying drawi ngs. DATED THIS n4* DAY OFTJ&cz19 A. J. PARK & SON AGENTS FOR THE APPLICANTS