GB2165533A - Imitation coal - Google Patents

Abstract

In the method of making an imitation coal element 10, a mass 11 of raw ceramic bulk fibres is impregnated with a liquid stiffening agent 12 before being squeezed and shaped to form a coal-shaped pellet or lump 14, which lump 14 is subsequently hardened by being dried in an oven 15. Thereafter, the hardened lump 14 is partly or wholly coated with a glaze 17 of a colour or colours which resemble any of the colours produced by a heated coal element and thereafter fired in a kiln 23. Any part of the surface of the lump 14 which is unglazed can be coated black and allowed to air dry. <IMAGE>

Description

SPECIFICATION Imitation coal This invention concerns imitation coal, primarily for use in simulated fuel effect gas fires.

It is well known to use imitation coal elements in open domestic fireg rates. A number of the elements are arranged in the firegrate and gas flames are played thereon from below. The gas flames not only heat the imitation coal elements, so that the elements radiate heat, but also flicker above the elements and contribute significantly to achieving the appearance of a traditional open-grate coal fire.

Such elements are generally made of cement and/or concrete. Therefore, they are heavy. Furthermore, they have a substantial heat absorbing capacity and take up a considerable amount of heat before reaching a temperature at which their radiation is perceptible. However, adequate radiation has rarely been achievable and open-grate fireplaces employing such imitation coal elements have generally been regarded as being of decorative utility rather than being effective heating appliances.

In order to overcome the inherent disadvantages in imitation coal elements as aforesaid, the present applicant has proposed (as disclosed in his United States Patent No. 4233348) imitation coal elements, in the form of pellets or lumps which will glow and radiate heat effectively when heated by a gas flame in an open-type firegrate, made of raw ceramic bulk fibres. An appropriate mass of said fibres is moistened with a cold and/or hot binding or stiffening agent such as cold potato starch or hot colloidal silicate and is then squeezed to shape it into its pellet or lump shape and to express any excess moisture; then it is baked to set the cold stiffening agent and fix the shape of the pellet or lump.Thereafter the element is coloured by use of a black metallic oxide/colloidal sodium silicate impregnantwhich is applied twice in successive dipping and baking operations.

However, although the imitation coal element of U.S. Patent No. 4233348 has the advantages over other known such elements of being light in weight, having a low heat absorbency, and being capable of readily being brought to red heat so that it will radiate heat effectively, it shares with said other known imitation coal elements the disadvantage, aesthetically speaking, of not being very appealing to the eye when the firegrate is unlit. Its dull or black colour gives the unheated imitation heating element a 'cold look'.

It is an object of the present invention to produce an imitation coal element which does not have the forementioned particular disadvantage.

In order to achieve this object the present invention provides a method of producing an imitation coal element comprising the steps of coating part of or all of the outer surface of a hardened mass of raw ceramic bulk fibres, shaped into its desired coal element shape, with a glaze of colour or colours which resemble any of the colours produced by a heated coal element, and thereafterfireing or baking the glazed hardened mass to harden and to render permanent the glaze.

The preferred method of the invention provides for the production of an imitation coal element which in its unheated state has the same or a similar appearance to that which it has in its heated state.

Furthermore, the coal element of the invention can withstand the higher operating temperatures of modern fuel effect gas fires (such as Airamatic and Bray-trade names) which utilise airmix burners.

The invention will be described further, by way of example, with reference to the accompanying drawing in which Figures 1 to 8 illustrate the various stages of a preferred method of the invention for producing the imitation coal element illustrated in Figure 9, it being understood that the following is illustrative and not limitative of the scope of the invention.

Referring firstly to Figure 9, the imitation coal element 10 produced by the preferred method the invention is made from a mass 11 (Figure 1) of ceramic bulk fibres. The mass 11 may initially be in the form of loosely felted mats or blankets of appearance, for example of cotton wool, for use as insulating materials, e.g. for lagging, domestic or industrial heat insulating and so on.

Referring now to Figures 1 to 8, as a first step (Figure 1) in making the imitation coal element 10 conforming to the invention, an appropriate amount of the mass 11 (or blanket) is taken and is impregnated with a liquid stiffening agent 12 contained, for example, in a bath 13 for ease of application. The agent 12 may be inorganic or organic such as, for instance, potato starch dispersion, or a commercially-available ceramic rigidiser.

The impregnation having been effected, the fibre mass 11 is squeezed and shaped, e.g. by hand, to form it into a shape conforming to a coal-shaped pellet or lump 14 (Figure 2), the squeezing or shaping serving, at the same time, to express any excess moisture. Thereupon, the pellet or lump 14 is transferred into an oven 15 (Figure 3) wherein it is baked, at a temperature in the range of 200"C to 300"C, preferably about 250"C, to set the stiffening agent 12, for a period of 5 to 10 hours. The pellet or lump 14, as subsequently taken from the oven 15, is set in its shape or configuration conforming to the desired shape of the imitation coal element 10.The ridigity of the pellet or lump 14 is sufficient for its shape not to be significantly affected by usual handling, although of course its shape can be changed by the application of relatively strong forces, e.g. upon strong compression, or filing, or cutting, or sawing.

This is, of course, already known from the applicant's United States Patent No. 4233348.

As an alternative to hand shaping the mass 11 of ceramic bulk fibres, matters could be arranged such that said mass 11 is utilised for vacuum forming the pellet or lump shape. In this latter way the element can be either hollow or solid, organic or inorganic.

The vacuum formed element is baked at a temperature of 200or to 3000C in an oven for a period of from Sto 10 hours.

At this stage pellet or lump 14 is inorganic and white. It is readyforcarrying out the glazing step of the invention (Figure 4). Before glazing the pellet or lump 14 is dipped in colloidal silicate and thereafter placed in a kiln at 900or for a short period of time.

This will give the pellet or lump 14 the stability and hardness required for glaze to be applied.

Outer surface 16 of the now hardened pellet or lump 14 is coated either as a whole or in part (for a reason which will be disclosed hereinafter) with a commercially available glaze 17 available from, for example, Ferro Limited. The glaze 17 is, for example, a reddish-orange colour to match the colours given off by a heated imitation coal element and for ease of application to the pellet or lump 14 is contained in a bath 18.

If the mass 11 of ceramic bulk fibres contain organic binders, the organic elements of the binders must be 'burnt out' before glazing the pellet or lump 14 otherwise they will ruin the glaze 17 during the next step of the method of the invention. The said burning out is achieved by heating the pellet or lump 14 in kiln 19 (Figure 5) at 900'C for twenty minutes. In order to maintain the strength and ensure the hardness of the pellet or lump 14 after being burnt out it is dipped in a bath 20 (Figure 6) containing a solution 21 containing 30% colloidal silicate such as, for example, SYTON 30, (Trade Mark) from the Monsanto Chemical Company. This makes the surface of the dry hardened pellet or lump 14 nonporous to prevent the glaze soaking into the hardened pellet or lump 14 and of course the pellet or lump 14 is inorganic.

After applying the glaze the next step (Figure 8) is to fire the glazed hardened pellet or lump 14 in a kiln 23 at 1050 Cforten minutes and allow itto cool down in the kiln 23.

This produces an imitation coal element 10 (Figure 9) which has basically the same colour unheated as it does heated. It is therefore aesthetically more pleasing than hitherto known elements when placed in a fire grate.

As previously stated, the entire outer surface 16 of the pellet or lump 14 can be glazed (for the case where the element 10 is placed in such a position in the firegrate that nearly all of its surface can be seen and where it relys almost entirely on heat reflection for its effect) or as with the element 10 shown in Figure 9 just part 16a of the outer surface 16 (for the case where when placed in a firegrate only the part 16a of the surface 16 can be seen), the other part 16b left unglazed.

In the latter case, there is a cost saving because the glazing of the element 10 is expensive. Secondly there is a maximising of the unglazed fibre surface 1 6b of the element, which surface 1 6b relys for its effect on heat radiation ratherthan heat reflection as in the case of the totally glazed element.

The unglazed surface part 16b of the element 10 can be coloured, for example, black in accordance with the procedure described in U.S. Patent No.

423338 and allowed to air dry or it can be baked in an oven at 250"C until dry.

Claims (1)

1. A method of producing an imitation coal element comprising the steps of coating part of or all of the outer surface of a hardened mass of raw ceramic bulk fibres, shaped into its desired coal element shape, with a glaze of a colour or colours which resemble any of the colours produced by a heated coal element, and thereafterfireing or baking the glazed hardened mass to harden and to render permanent the glaze.

2. A method as claimed in claim 1 wherein the mass of raw ceramic bulk fibres is hardened by being impregnated with a liquid stiffening agent.

3. A method as claimed in claim 2 wherein the liquid stiffening agent is inorganic or organic such as, for instance, potato starch dispersion or a commercially-available ceramic rigidiser.

4. A method as claimed in claim 2 or 3 wherein after being impregnated with stiffening agent the mass is squeezed and shaped to express excess moisture and to form a coal-shaped pellet or lump.

5. A method as claimed in claim 4 wherein the pellet or lump is transferred to an oven and baked at a temperature in the range of 200"C to 3000C, preferably about 250 C, to set the stiffening agent, for a period of 5 to 10 hours.

7. A method as claimed in any preceding claim wherein, if the ceramic bulk fibres contain organic binders, the organic elements of the binders are burnt out of the hardened mass before glazing said mass.

8. A method as claimed in claim 7 wherein the burning out is achieved by heating the pellet or lump form mass in a kiln at 900"C for twenty minutes and thereafter dipping the pellet or lump in a solution containing 30% colloidal silicate such as, for example, SYTON 30 in order to maintain its strength and thereafter allowing the pellet or lump to air dry.

9. A method as claimed in any preceding claim wherein the firing or baking of the glazed hardened pellet or lump is achieved by placing the latter in a kiln at 1 050 C for ten minuted and allowed to cool down in the kiln.

10. A method as claimed in claims 1 to 3 and 5 to 9 wherein the mass of raw ceramic bulk fibres is utilised for vacuum forming the pellet or lump and may be organic or inorganic.

11. A method of producing an imitation coal element substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 4 and 8, or in Figures 1 to 8, of the accompanying drawing.

12. An imitation coal element produced by the method of claims 1 to 9 and as illustrated in Figure 9 of the accompanying drawings and as described hereinbefore.