GB2093010A

GB2093010A - Moulded articles

Info

Publication number: GB2093010A
Application number: GB8204314A
Authority: GB
Original assignee: Didier Werke AG
Current assignee: Didier Werke AG
Priority date: 1981-02-16
Filing date: 1982-02-15
Publication date: 1982-08-25
Also published as: JPS57145085A; ES8301854A1; CA1190946A; PL235103A1; IT8247791A0; NL8200602A; SE8200862L; FR2499975B1; FR2499975A1; GB2093010B; ZA821008B; BE892123A; DD208970A5; NO820444L; YU31682A; ES509209A0; DE3105596C2; DE3105596A1

Abstract

A moulded article is manufactured by mixing 100 parts by weight of loosened ceramic fibres, or of a mixture comprising at least 20% by weight loosened ceramic fibres and up to 80% by weight of a fired bonded granular material comprising ceramic fibres, bonding agent and refractory materials, together with 0 to 2 parts by weight clay or other finely divided refractory substances, 2 to 8 parts by weight phosphate bonding agent, 0 to 10 parts by weight organic whilst simultaneously moulding it to the desired shape and the moulded article is then dried and/or tempered and/or fired. The article has a density of 0.5 to 1.8 g/cm<3> and a hot bending strength at 1000 DEG C of at least 0.8 N/mm<2>.

Description

SPECIFICATION Moulded articles The invention relates to moulded articles and is concerned with such articles having high mechanical stability at high termperatures and relates also to a process for their manufacture and their use.

Heat insulating ceramic fibre bodies comprising refractory fibres and organic or inorganic bonding agent having either low strength and high compressibility or high values for their strength, density and constancy of shape are known. Thus DE-AS 1 2 74 490 describes a combustion chamber for ovens which is made by forming out a fibre mass mixed with bonding agent and in which the concentration of bonding agent decreases over the cross-section of the wall. Clays, alkaline silicates, aluminium phosphate, colloidal silica with a proportion by weight of 5 to 35%, optimally 10%, are named as suitable bonding agents. The fibre body is however not suitable for subjection to high loads due to the fact that one wall surface is compact and hard whilst the opposing wall surface is soft and flexible.

In the process disclosed in DE-AS 27 32 387 a mineral fibre plate prebonded with an organic plastics bonding agent is supposed to be strengthened by soaking with an aqueous slurry of a bonding clay and subsequent tempering. Furthermore, plates are disclosed in European Patent Application No. 0006362 which contain glass-like inorganic fibres in a matrix of a plastic clay as a reinforcement. The proportion of clay lies in the region of 29 to 80% by weight and the proportion of the glass-like inorganic fibres in the region of 1 5 to 55% by weight of the plate.

It is an object of the invention to provide moulded articles with improved mechanical and thermal properties which, in particular, can serve as a replacement for light refractory plates.

According to the present invention there is provided a moulded article manufactured from the following composition: 100 parts by weight of either loosened ceramic fibres or a mixture comprising at least 20% by weight loosened ceramic fibres and up to 80% by weight of a fired, bonded, granular material comprising ceramic fibres, bonding agent and refractory material, 0 to 2 parts by weight clay and/or Al203 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, 2 to 8 parts by weight phosphate bonding agent, 0 to 10 parts by weight organic bonding agent, and 1 to 10 parts by weight other refractory additives, the article having a density of 0.5 to 1.8 g/cm3 and a hot bending strength at 1000"C of at least 0.8 N/mm2.

The invention also embraces a process of making such an article and in accordance with a further aspect of the present invention there is provided a process for the manufacture of a moulded article including the following steps: a) 100 parts by weight of either loosened ceramic fibres or a mixture comprising at least 20% by weight loosened ceramic fibres and up to 80% by weight of a fired bonded granular material comprising ceramic fibres, bonding agent and refractory material, 0 to 2 parts by weight clay and/or Al203 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, 2 to 8 parts by weight phosphate bonding agent, calculated as P205, 0 to 10 parts by weight organic bonding agent, 0 to 10 parts by weight other refractory additives and water are thoroughly mixed, b) the mixture obtained in step a) is compressed by a minimum volume factor of 3 when only using ceramic fibres decreasing linearly to 1.5 when using a mixture of 80 parts by weight of the bonded granular material and 20 parts by weight ceramic fibres whilst moulding the mixture to the desired shape, and c) the moulded article manufactured in step b) is dried and/or tempered and/or fired.

The shaped articles in accordance with the invention can be used for many purposes, in particular as a replacement for known light refractory plates. Their advantage for this is that they have a lower density than these known plates and they have a very close pore size distribution and low pore size. Despite the compression in the manufacture of the moulded articles their thermal conductivity is of the same order as those articles known per se of glass fibres which are not compressed in their manufacture but which are manufactured using a vacuum suction process. By comparison with these plates the moulded articles in accordance with the invention exhibit, however, a substantially higher strength.

By reason of their high mechanical strength the articles in accordance with the invention are suitable particularly as a firing aid, i.e. supports for objects to be fired, particularly objects of porcelain.

The moulded articles in accordance with the invention can contain all conventional ceramic fibres, such as rock wool or fibres based on aluminium silicate, preferably with an Al203 content of about 40 to 95% by weight, though these must be loosened, as will be explained in more detail below. The fibres are, however, preferably based on Al203 and SiO2 with at least 40% by weight Awl203 and are preferably capable of being used at temperatures in excess of 11 00'C.

This will in general exclude inorganic fibres based on, for instance, basalt, slag and glass and natural asbestos fibres whose use temperature is below 11 00'C, but such fibres may be used as a subsidiary component in addition to those whose use temperature is above 11 00'C. The other refractory additives used in the articles in accordc,nce with the invention are those additives conventionally used in shaped fibre articles such as porcelain powder, fire clay, hollow sphere corundum or vermiculite.

The bonding agent or agents which must be present in the articles in accordance with the invention are phosphate containing bonding agents, e.g. boron phosphate, aluminium phosphate or sodium polyphosphate, preferably with a degree of polymerisation n'4 and in particular n = 6 to 10.

The organic bonding agents which may be present in the articles in accordance with the invention may be those bonding agents commonly used in refractory or heat-resistant shaped articles such as starch, sulphite lye or waste, molasses and, in particular, methyl cellulose. The given amount of bonding agent relates to solide organic bonding agent, i.e. without a proportion of water.

Both the phosphate bonding agent and the organic bonding agent can be added both in dissolved form or in solid form. When using methyl cellulose, which is commonly added as a 5% by weight aqueous solution, a part of this methyl cellulose is, however, advantageously used in solid finely divided form, particularly when adding larger quantities of methyl cellulose, since otherwise the quantity of water introduced into the composition by such a bonding agent solution would be too large.

Those additives present instead of or as well as the clay, i.e. Al2O3 and/or SiO2 and/or magnesia and/or titanium dioxide and/or chromium oxide, all of which are preferably used in very finely divided form, and/or aluminium hydroxides, are components whose use is known in the refractory field. If clay should be used, this may be a conventional bonding clay or more preferably a special clay, such as bentonite. The term "very finely divided" is to be understood to mean that these components are present in a very finely divided or a colloidal state.The very finely divided refractory materials preferably have a grain size of less than 50 pm, more preferably less than 10 ,um. Particularly when using such materials in the colloidal state, such as colloidal SiO2 or colloidal aluminium oxide, it is possible to use only small quantities of bonding agent, namely close to the lower threshold value of 2 parts by weight of such a phosphate bonding agent. The bonding agent can comprise either only one phosphate bonding agent or a mixture of both phosphate bonding agent and an organic bonding agent, and the use of approximately the same parts by weight of phosphate bonding agent and methyl cellulose as an organic bonding agent is particularly preferred.

Advantageously the composition of the moulded articles in accordance with the invention contains 0.5 to 1.5 parts by weight of clay and/or the other said components to 100 parts by weight of the ceramic fibres. Particularly advantageous is the use of a mixture of clay, in particular of bentonite, and one or the other components referred to above, particularly of colloidal silica or of colloidal Awl203.

When manufacturing the moulded articles in accordance with the invention a mixture is produced of loosened ceramic fibres or a mixture of loosened ceramic fibres and the fired, bonded, granular material, clay and/or the other refractory components, if present, the phosphate bonding agent, the other refractory additives, if used, and the optionally used organic bonding agent with the addition of water. If the phosphate bonding agent and/or the organic bonding agent are used in the form of a solution, commonly an aqueous solution, the addition of water may not be necessary. In step a) of the process in accordance with the invention there are preferably 5 to 25 parts by weight of water added to 100 parts by weight of the ceramic fibres or ceramic fibre/granular material mixture.Phosphate bonding agents, such as sodium polyphosphate and monoaluminium phosphate, as well as organic bonding agents, such as sulphite waste and methyl cellulose, can be used in solid ground form or they may be added partially in the form of a solution and the remainder in solid form.

The fired granular material which may be used in the manufacture of the moulded articles in accordance with the invention is preferably that described in more detail in British Patent Application (Case) of the present appiicant which was filed on the same day as the present application. Its manufacture includes the following steps: a) 100 parts by weight ceramic fibres, 2 to 1 5 parts by weight clay and/or Al2O3 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, optionally up to 10 parts by weight other refractory additives and 1 to 8 parts by weight phosphate bonding agent, optionally with the addition of plasticising agent, are thoroughly mixed in a mixer with about 2 to 25 parts, or in some circumstances up to 100 parts by weight water, b) the mixture obtained in step a) is compressed by a volume factor of at least 3, and c) the product obtained in step b) is optionally dried and then fired at temperatures of 800 to 1 550 C and subsequently comminuted.

The materials used in the manufacture of this granular material, i.e. ceramic fibres, clay or the other components referred to, the refractory additives and the phosphate bonding agent correspond to the materials as described above. However, the ceramic fibres do not have to be in loosened form but it is preferred that they are. Methyl cellulose is preferably used in the composition of the granular material as the plasticising agent. The compression in step b) can be effected in a extruder, a rotary table press or a briquetting device. The mixing of the components in step a) in the manufacture of the granular material can occur in any suitable mixer, for instance in a Drais mixer.Advantageously, separated or loosened ceramic fibres are used as the ceramic fibres in the manufacture of the granular material as are also used in the manufacture of the moulded articles in accordance with the invention. The comminution in step c) of the manufacture of the granular material can occur in any suitable device, preferably to a maximum grain size of 6 mm. This comminution can, however, be set to a predetermined range, for instance a granulate can without difficulty be obtained with a grain size between 2 and 3 mm by comminution in conventional crushing devices and, if necessary, sieving out of the desired grain sizes. The granular material obtained thereby has a density of 0.7 to 1.75 g/cm3 and has a pore volume of the order of 35 - 75%.The quantity of the plasticising agent which may be added in step a) of the manufacture of the granular material depends on the compression device used in step b). For example, when using methyl cellulose and compressing in an extruder a quantity of 4 parts by weight methyl cellulose is preferably added, half preferably being added as a 5% solution in water and the other half as dry methyl cellulose.

When using an extruder, however, up to 100 parts by weight water may be added in order to obtain a more plastic mass. The quantity of water used in the manufacture of the moulded articles in accordance with the invention should be kept as small as possible. Advantageously only up to 1 5 parts, or more preferably 10 parts, by weight water are mixed in with 100 parts by weight of the ceramic fibres or the fibres/granular material mixture thus producing a doughlike mass.

The advantage of using a mixture of ceramic fibres and a fired fibre granulate material resides in that when manufacturing the moulded articles in accordance with the invention a smaller quantity of water is necessary. In this connection the water quantity depends on the relative proportions of ceramic fibres and fired granular material in the mixture, with the necessary water quantity reducing as the proportion of fired granular material in the mixture increases. The use of a mixture of 50% by weight ceramic fibres and 50% by weight of the fired granular material has shown itself to be particularly advantageous.

The dough-like mass obtained in step a) when manufacturing the moulded articles is put into a suitable press in step b) of the process, for instance a plate press or table press or even an isostatic press, and pressed for a suitable period of time, this time depending on the type of press used. In a plate press the pressing time is commonly 5 to 20 seconds.

It is of importance when manufacturing the shaped articles in step b) of the process that the compression is effected by a volume factor of at least 3 when using only ceramic fibres or by a volume factor of at least 1.5 when using a mixture of 80 parts by weight of the fired granular material and 20 parts by weight ceramic fibres. Advantageously this volume factor is 5 to 8 when only using ceramic fibres and 2.5 to 4 when using a mixture of 80 parts by weight of the granular material and 20 parts by weight ceramic fibres. The volume factors when using mixtures of a different composition vary linearly between these given values.

In a preferred embodiment of the invention the mixture obtained in step a) of the process is moulded into plates and these may have a thickness of 1 to 50 mm.

After pressing, the moulded articles are dried in step c) of the process in accordance with the invention, advantageously at between 110 and 180"C, and/or they are tempered, e.g. at temperatures between 250"C and 600"C, and/or fired, e.g. at temperatures between 800"C and 1 650'C. The maximum firing temperature and also the threshold use temperature depends primarily on the ceramic fibres used in the starting mixture and less on the other refractory additives which may be present.

When delivered, ceramic fibres are generally in the form of a loose wool which is partially strongly compressed. To manufacture the moulded articles in accordance with the invention these fibres must be in loosened form to enable a better bonding of the fibres by the bonding agent used and an excellent wetting of the surface of the fibres by liquids in very low concentrations.

By using loosened ceramic fibres it is possible also to manufacture moulded articles without the addition of clay, or the other components referred to, to the starting mixture and to compress this mixture without too marked a springing back of the pressed article occurring after the compression step. The separation or the loosening of the ceramic fibres before their use is therefore absolutely necessary.

For this purpose mixing units with rapidly rotating knife heads, so called impact mixers, can be used whereby the larger agglomerates present in the delivery state of the fibres are loosened without the fibres being thereby unacceptably strongly crushed (e.g. of Drais type).

If none of the fired granular material is used it is possible to carry out step a) of the process in such an impact mixer, i.e. a mixer with rapidly rotating knife heads. This means that the loosening of the fibres and the mixing with the added components are both carried out in step a) of the process In this case, however, only dry solid materials are added in order both to achieve a loosening of the agglomerated fibres and a homogeneous mixing in of the added materials. Subsequently water, and bonding agent if present in the form of a solution, are sprayed into the mixing container and mixed in.

Naturally it is, however, also possible firstly to effect the loosening of the ceramic fibres in an impact mixer and then to add the other materials in another mixer, e.g. a Drais mixer or an Eirich mixer. This mode of operation is particularly appropriate when using vermiculite or hollow sphere corundum as a further refractory additive or when using the fired granular material in the mixture with ceramic fibres since otherwise a crushing of these materials would occur.

The moulded articles in accordance with the invention exhibit the particular advantage that they have very good thermal insulating properties due to the relatively good mechanical stability due to the relatively high content of ceramic fibres and also a relatively good mechanical stability due to the compression during their manufacture by a volume factor of at least 3 or 1.5. The articles also have an excellent resistance to sudden changes of temperature, that is to say thermal shock resistance is preferably in excess of 25 air quenchings measured in accordance with German standard DIN 51068, part 2, on prismatic bodies of e.g.

124 X 64 X 64 mm. The bodies are repeatedly heated to 950"C and then quenched by blowing them with air at room temperature through an 8 mm nozzle. After cooling the bodies are tested with a bending stress of 0.3 N/mm2. The thermal shock resistance is the number of cycles before failure.

Further features and details of the invention will be apparent from the following examples both of making a fired fibre-containing granular material and of making moulded articles in accordance with the invention.

In the following examples two different types of ceramic fibres, both based on Al2O3 and SiO2, were used, namely fibre material A with 47% Al203 and 53% SiO2 with a use temperature of up to 1260on and fibre material B suitable for higher use temperatures with 95% Al203 and 5% Six2.

The mixtures were in part made up in step a) by using only an impact mixer which was provided with a rapidly rotating knife head (3000 RPM). In this impact mixer the ceramic fibre material is well loosened and also a pourable and fluid granular material is formed which is uniformly intermingled with the mixture components. This mixture is then processed in presses into fibre-containing materials with low to high gross density and a particularly homogeneous composition. Alternatively, a less intensive loosening of the fibres and a not so homogeneous preparation of the mixture is achieved with a mixer which has mixing arms rotating at a relatively lower speed, e.g. an Eirich mixer. The 50% monoaluminium phosphate solution is introduced in the mixer in the region of the rapidly rotating knife head as a spray.In this manner a complete wetting of the agglomerate surfaces is achieved with the smallest volumes of liquid, e.g. 10% by weight MPA = 6.6 litres. Water is subsequently sprayed in in the same manner. The water dissolves any dry methyl cellulose which may be present and thus brings about a good green strength of the shaped article.

When using a fired fibre-containing granular material which could be excessively mechanically comminuted, i.e. crushed, in an impact mixer it is, however, convenient first to loosen only the ceramic fibres in an impact mixer, for example by treatment for 2 to 20 minutes in such an impact mixer, and then to put the loosened ceramic fibres into an Eirich mixer in which the mixing of the fired granular material with the other componenets occurs. For this, one advantageously first mixes the granular material and the other components, except the water, and then the loosened fibres are added and finally the water is put into the Eirich mixer and briefly mixed in.

Manufacture of the fired fibre granular material: a) 100 parts by weight of ceramic fibres A), 10 parts by weight bonding clay with an Awl203 content of 35% by weight and 1.5 parts by weight dry methyl cellulose in powder form were put into an Eirich mixer and mixed together for 10 minutes. Then 10 parts by weight of 50% by weight monoaluminium phosphate solution and 2 parts by weight water were sprayed onto the mass in the mixer whilst continuing to mix and mixed in for a further 30 minutes.

The mixture was taken out of the mixer and pressed at a pressing pressure of 30 N/mm2 in a plate press into plate-shaped articles with a thickness of 30 mm, whilst obtaining a compression factor of 5.5.

The plate-shaped articles were subsequently dried at 11 0'C for 24 hours in an oven and then fired at different temperatures for 24 hours and subsequently comminuted to a maximum grain size of 3 mm.

The granulates had the following properties: Table I Firing temperature ("C) 800 1350 1510 Weight per unit volume, R, (g/cm3) 1.34 1.52 1.77 Specific weight, S, (g/cm3) 2.60 2.70 2.75 Pg (Vol. %) 47.7 43.7 35.6 b) Method a) was repeated but an impact mixer was used to loosen the fibres. The pressing pressure in step b) was 10 and 1 5 N/mm2 respectively and the compression was by a factor of 4 and 5.

After firing at 1350"C for 24 hours and comminution, granulates with the following properties were obtained: Table II Pressing pressure (N/mm2) 10 1 5 R (g/cm3) 0.7 1.02 Spec. weight (g/cm3) 2.7 2.7 Pg (Vol. %) 74 63 c) Method a) was repeated but the proportion of monoaluminium phosphate solution was increased to 1 5 parts by weight and the proportion of water to 5-parts by weight with the mixing time shortened to 20 minutes. After firing at 1350 C for 24 hours and comminution to the desired granulate this had the following properties: Table 111 R (g/cm3) 1.29 S(g/cm3) 2.69 Pg (Vol. %) 53.8 d) Method a) was repeated but additionally 8 parts by weight fire clay powder were added in the first step.Furthermore only 8.3 parts by weight of 50% by weight monoaluminium phosphate solution but 4 parts by weight water were added in the mixing step.

The pressing pressure in the compression step b) was 30 N/mm2 which resulted in a compression by a volume factor of 5.2.

The plate-shaped product obtained was dried at 180 C and samples were fired at the different temperatures given in the following Table IV. Subsequently the fired product was comminuted to a maximum grain size of 3mm.

The granulates obtained had the following properties: Table IV Treatment temp. ("C) 800 1200 1300 1500 Weight per unit volume R (g/cm3) 1.26 1.31 1.34 1.48 Spec. weight (g/cm3) 2.60 2.65 2.68 2.72 Pg (Vol. %) 51.5 50.5 50.0 45.6 Manufacture of the moulded articles Example 1 The following composition was used: Parts by weight Fibres B 100 Monoaluminium phosphate solution, (50% by weight) 13 Water 5 Dry methyl cellulose 1.5 100 parts by weight fibres B were loosened for 7 minutes in an impact mixer together with the 1.5 parts by weight solid methyl cellulose. Subsequently the monoaluminium phosphate solution and the water were sprayed into the mixer and mixed in for a further 2 minutes.

Blocks with dimensions 405 x 1 35 X 75 mm were then moulded in a mould in a hydraulic press at a pressing pressure of 10 N/mm2. These blocks were dried at 1 20'C for 24 hours and subsequently fired for 24 hours in two batches at 1350"C and 1500it respectively.

The properties of these blocks were as follows: Table V Firing temperature ("C) 1 350 1 500 R (g/cm3) 0.82 0.87 Compression factor 5.1 5.1 Spec. weight (g/cm3) 3.63 3.68 Pg (Vol. %) 77.4 76.4 Hot bending strength 1000"C (N/mm2) 1.9 2.2 Thermal conductivity (W/m"K at 700"C) 0.30 0.31 Example 2 The following composition was used:: Parts by weight Fibre granulate as made in example b) with R = 1.02 (manufactured at a pressing pressure of 1 5 N/mm2) 70 Ceramic fibres B 30 Al203, dust 1 Chromium oxide, < 63,um 0.5 Monoaluminium phosphate solution, (50% by weight) 1 5 Water 2 30 parts by weight of ceramic fibres B were first loosened for 5 minutes in an impact mixer.

Then the 70 parts by weight fibre granulate b), the Awl203, the chromium oxide and the monoaluminium phosphate solution were put into an Eirich mixer and mixed for 5 minutes.

Then the loosened fibres were added and mixed in for a further 20 minutes and subsequently then 2 parts by weight water were put in and mixed for a further 4 minutes. The mixture was removed from the mixer and then moulded at a pressure of 20 N/mm2 in a hydraulic press into blocks with dimensions of 405 X 1 35 X 75 mm. They were subsequently dried for 24 hours at 120"C and then fired for 24 hours at 1350"C. The properties measured on the fired blocks are listed in the following Table VI.

Table VI Firing temperature ("C) 1 350 R (g/cm3) 1.30 Compression factor 2.5 Spec. weight (g/cm3) 3.6 Pg (Vol. %) 64.2 Hot bending strength, 1000"C (N/mm2) 2.4 Thermal conductivity (W/m "K at 700 C) 0.35 Examples 3 to 5 Fibre granulates made by methods a), c) and d), as described above, were used together with ceramic fibres A. The components of the different compositions are given in the following Table VII.

Table VII Example 3 4 5 Fibre granulate type a) c) d) Fibre granulate quantity, parts by weight 20 35 60 Ceramic fibres, parts by weight 80 65 40 Solid methyl cellulose, parts by weight 1.5 1.5 1.5 Monoaluminium phosphate solution (50% by weight) parts by weight 7 9 10 Water, parts by weight 5 3 2 In these Examples the method of Example 2 was used and the processing occurred in accordance with the method of Example 2, i.e. the ceramic fibres were first loosened in an impact mixer. The other components, except the water, were separately mixed for 5 minutes in an Eirich mixer and then the loosened fibres were added.

Subsequently the water was added an mixed in for a further 4 minutes.

These mixtures, as the mixture of Example 2, could be moulded at a pressing pressure of 20 N/mm2 into perfect moulded articles.

Claims

1. A moulded article manufactured from the following composition: 100 parts by weight of either loosened ceramic fibres or a mixture comprising at least 20% by weight loosened ceramic fibres and up to 80% by weight of a fired, bonded, granular material comprising ceramic fibres, bonding agent and refractory material, 0 to 2 parts by weight clay and/or Al203 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, 2 to 8 parts by weight phosphate bonding agent, 0 to 10 parts by weight organic bonding agent, and 0 to 10 parts by weight other refractory additives, the article having a density of 0.5 to 1.8 g/cm3 and a hot bending strength at 1000"C of at least 0.8 N/mm2.

2. An article as claimed in Claim 1 in which the clay is bentonite.

3. An article as claimed in Claim 1 or Claim 2 which contains porcelain powder, fire clay or hollow sphere corundum as a further refractory additive.

4. An article as claimed in any one of Claims 1 to 3 in which the phosphate bonding agent is sodium polyphosphate or monoaluminium phosphate.

5. An article as claimed in Claim 1 in which the organic bonding agent is methyl cellulose.

6. A moulded article substantially as specifically herein described with reference to any one of the accompanying examples 1 to 5.

7. A process for the manufacture of a moulded article including the following steps: a) 100 parts by weight of either loosened ceramic fibres or a mixture comprising at least 20% by weight loosened ceramic fibres and up to 80% by weight of a fired bonded granular material comprising ceramic fibres, bonding agent and refractory material, 0 to 2 parts by weight clay and/or Al203 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, 2 to 8 parts by weight phosphate bonding agent calculated as P205, 0 to 10 parts by weight organic bonding agent, 0 to 10 parts by weight other refractory additives and water are throughly mixed, b) the mixture obtained in step a) is compressed by a minimum volume factor of 3 when only using ceramic fibres decreasing linearly to 1.5 when using a mixture of 80 parts by weight of the bonded granular material and 20 parts by weight ceramic fibres whilst moulding the mixture to the desired shape, and c) the moulded article manufactured in step b) is dried and/or tempered and/or fired.

8. A process as claimed in Claim 7 in which the compression in step b) is carried out by a factor of 5 to 8 when only using ceramic fibres decreasing linearly to a factor of 2.5 to 4 when using a mixture of 80 parts by weight of the bonded granular material and 20 parts by weight ceramic fibres.

9. A process as claimed in Claim 7 or 8 in which the mixture is moulded into plates whilst compressing it in step b).

10. The use of moulded articles as claimed in Claims 1 to 6 as supports for objects to be fired in a furnace.

11. A process for the manufacture of a shaped article substantially as specifically herein described with reference to any one of the accompanying Examples 1 to 5.