CA1190946A

CA1190946A - Moulded articles

Info

Publication number: CA1190946A
Application number: CA000396281A
Authority: CA
Inventors: Axel Eschner; Hermann Stein
Original assignee: Didier Werke AG
Current assignee: Didier Werke AG
Priority date: 1981-02-16
Filing date: 1982-02-15
Publication date: 1985-07-23
Also published as: DD208970A5; BE892123A; IT8247791A0; ES509209A0; YU31682A; ZA821008B; DE3105596A1; ES8301854A1; GB2093010A; PL235103A1; SE8200862L; FR2499975A1; GB2093010B; DE3105596C2; NO820444L; FR2499975B1; NL8200602A; JPS57145085A

Abstract

ABSTRACT
MOULDED ARTICLES

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 bonding agent and water. The mixture is compressed 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/cm3 and a hot bending strength at 1000°C of at least 0.8 N/mm2.

Description

1. 23843-108 ~OIJLDED A~TICLES
~, The invention relates to moulded articles and is concerned with such artic:les havitlg high mecllanical stability at high temperatures and relates also to a process ~For their manufacture and their use.
Heal; insulating cerami.c fibre bodi.es comprising refractory fibres and organic or inorganic bonding agent having either low strength and high compress-ibility or high values for their strength, density and constancy of shape are known. Thus l)E-AS 12 74 490 describes a combustion chamber for ovens which is made by forming out a fibre mass mixed with bonding agent cm d in which the con-centration 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 :Eibre plate pre-bonded with an organic plastics bonding agent is supposed to be strengthened by soaking wi.th a~ aqueous slurry of a bonding clay and subsequent tempering.
It i.s an object of the invention to pro-vide moulded articles with im-proved mechanical ancl thermal properti.es which, in particular, can serve as areplacement 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 com-pri.sing at least 20% by weight loosened ceramic fibres and up to 80% by weight of a fired, bonded, granular material comprising ceramic fibres, bond-ing agent and refractory materia:l, PA .5124/B ~XR/Sa/Le ,,

2.
-O to 2 parts by weight clay and/or A1203 and/or SiO2 and/or aluminiumhydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, 2 tc~ 8 parts by weight phosphate bonding agent, O tc, 10 parts by weight organic bonding agent, and 1 tc, 10 parts by weight other refractory additives, the article having a densi.ty of 0.5 to 1.8 g/cm3 and a hot bending strength at 1000 C of at ].east 0.8 N/mm .
The invention also embraces a process of making SUC]I an arti.cle and in accordance with a further aspect of the present lnvention there is provided a process for the manufacture o:E a moulded article inclucling 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 5. comprising ceramic fibres, bonding agent and refractory material, 0 to 2 parts by weight clay and/or ~1203 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 10. 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 miY~ture obtained in step a) is co~pressed by 15. 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 20. 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 25. replacement for known light refractory plates. Their advantage for this is that they have a lower ~ensity than these known plates and they have a very close pore size distri~ution and low pore size. Despite the compression in the manufacture of the moulded 30. 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 5. in accordance with the invention exhibit, however, a substantially higher strength.
By reason of their high mechanical strength the artic~les in accordance with the invention are suitable particularly as a firing aid, i.e. supports for 10. objects to be fired, particularly ob~ects of porcelain.
The moulded articles in accordance with the inverltion can contain all conventional ceramic fibres, such as rock wool or fibres based on aluminium silicate, preferably with an A1203 content of about 40 lS. to 95~ by weight, though these must be loosened, as will be explained in more detail below. The fibxes are, however, preferably based on A1203 and SiO2 with at least: 40~ by weight A1203 and are preferably capable of being used at temperatures in excess of 1100C.
20. This will in general exclude inorganic fibres based on, for instance, basalt, slay and glass and natural asbestos ibres whose use temperature is below 1100 C, but such fibres may be used as a subsidiary component in addition to those whose use temperature is 25. above 1100 C. The other refractory additives used in the articles in accordance with the invention are those additives conventionally used in shaped fibre articles such as porcelain powder, fire clay, hollow sphere corundum or vermiculite.
30. The bonding agent or agents which must be present - 5.

in the articles in accordance with the invention are phosE)hate containing bonding agents, e.g. boron phosphate, aluminium phosphate or sodium polyphosphate, preferably with a degree of po]ymerisation n > ~ and in particular 5. n = 6 to 10.
The organic bonding agents which may be present in the a~rticles in accordance with the invention may be those bonding agentC commonly used in refractory or heat-resistant shaped articles such as starch, 10. sulphite lye or wast:e, molasses and, in particular, methyl cellulose. The given amount of bonding agent relates to solid organic bonding agent, i.e. without a proportion of water.
Both the phosphate bonding agent and the organic 15. 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, 20. particularly when adding larger ~uantities 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 25. the clay, i.e. A1203 and/or SiO2 and/or magnesia and/ox 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, 30. th:Ls 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 5. materials preferably have a grain size of less than 50 Llm, more preferably less than 10 Llm. 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 1~. 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 15. 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 20. 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 mi:~ture of clay, in particular of bentonite, and one or the other components referred to above, particularly 25. of colloidal silica or of colloidal A1203.
When manufacturing the moulded articles in accordance with the invention a mixture is produced of loosened cerarnic fibres or a mixture of loosened ceramic fi~res and the fired, bonded, granular material, clay and/or 30- the other refractory components, if present, the phosphate -. ` 7.
bonding agent, the other refractory additives, if used~ and the optionally used organic bonding agent with the addition of water. If the phosphate bondi.ng agent and/or the organic bondillg agent are used ill the form of a solution, com-monly 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 par~s 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 bondi.ng agents, such as sulphite waste and methyl cellulose, can be used in solid ground form or they may be added partially in thc form of a solution and the remainder in solid form.
The fired granular material which may be used in the manufacture o~
the moulded articles in accordance with the invention is preferably that des-cribed below.. Its manufacture includes the following steps:
a) 10() parts by weight ceramic fibres, 2 to 15 parts by weight clay and/
or A1203 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/
or titanium dioxide and/or chromium oxide, optionally up to 10 parts by we:ight other refractory additives and 1 to 8 parts by weight phos-phate bonding agent, optiona.lly with the addition of plasticising agent~
are thoroughly mixed in a mixer with about 2 to .,~'~

8.

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 1550C
and subsequently comminuted.
The materials used in the manufacture of this granular material, i.e. ceramic fibres, clay or the 10. 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. ~ethyl cellulose is preferably 15. 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 20. can occur in any suitable mixer, for instance in a Drals mixer. ~dvantageously,separated or loosened ceramic fibres are used as the ceramic fibres in the manufacture of the granular material as are also usecl in the manufacture of the moulded articles 25. 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 max~mum grain size of 6 mm. This comminution can~
however, be set to a predetermined range, for instance 30. a granulate can without difficulty be obtained with a grain size between 2 and 3 mm by comminution in conventional crushing aevices and, if necessary, sieving out of the desired grain sizes. The granular material obtained thereby has a density of 0.7 to 5. 1.75 g/cm 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 10. 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 lO0 parts by weight water 15. may be added in order to obtain a more plastic mass.
The quantity oE 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 15 parts, or more preferably lO parts, by weight water 20. are mixed in with lO0 parts by weight of the ceramic Eibres or the fibres/granular material mixture thus producing a dough-like mass.
The advantage of using a mixture of ceramic fibres and a fired fibre granulate material resides in that 25. 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 oE ceramic fibres and :Eired granular material in the mixture, with the 30. necessary water quantity reducing as the proportion of fired granular material in the mixture increases.

10 .

The use of a mixture of 50% by weight ceramic fibres and 50% by weight of the fired granular makerial has shown itself to be particularly advantageous.
The dough-like mass obtained in step a) when 5. 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 10. 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 15. 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 20. granular material and 20 parts by weight ceramic fibres.
The volume factors when using mixtures of a different composition varv linearly between these given values.
In a preferred embodiment of the invention the mixture obtained in step a) of the process is moulded 25. into plates and these may have a thickness of 1 to 50 mm.
After pressing, the moulded articles are dried in step c1 of the process in accordance with the invention, advantageousl~ at between 110 and 180C, and/or they are tempered, e.g. at temperatures between 30. 250C and 600C, and/or fired, e.g. at temperatures ~V9~i , 11 .

between 800C and 1650C. 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 5. ref:ractory 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 lO. 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 15. 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 20. separation or the loosening of the ceramic fibres before thei.r use is therefore absolutely necessary.
~or this purpose mixing units with rapidly rotating knife heads, so called impact mixers, can be usecl whereby the larger agglomerates present in the 25. deli,very state of the fibres are loosened without the fibres being thereby unacceptably strongly crushed (eOg.
of Drais type).

If none of the fired granular material is used it is possible to carry out step a) of the process in 30. such an impact mixer, i.e. a mixer with rapidly rotating knife heads. This means that the loosening of r~aC~

12, 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 5. 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 ~irstly 10. to effect the loosening o~ 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 15. refractory additive or when using the fired granular material in the mixture with cera~.ic fibres since other-wise a crushing of these materials would occur.
The moulded articles in accordance with the invention e~hibit the particular advantage that they have very 20. good thermal insulating properties due to the relatively good mechanical stability due to the relativel,y hi~h 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.
25. rhe articles also have an excellent resistance to sudden changes of temperature, that is to say thermal shock resistanceO This thermal shock resistanc~ is preferably in excess of 25 air quenchings measured in accordance with German standard DIN 51068, part 2, on 30. prismatic bodies of e.g. 124 x 64 x ~4 mm. The bodies are repeatedly heated to 950 C and then quenched by blowing them with air at room temperature through an ~ 7r~lJer/l~L

- - 13.

8 mm nozzle. After cooling the bodies are tested ~ith 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 5. be apparent from the following examples both of ma]cing 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 A1203 and SiO2, were used, 10. namely fibre material A with 47% A1203 and 53% SiO2 with a use temperature of up to 1260C and fibre material B suitable for higher use temperatures with 95% A1203 and 5% SiO2.
The mixtures were in part made up in step a) by using 15. 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 20. 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.
~he 50% monoaluminium phosphate solution is in~roduced in the mixer in the region of the rapidly rotating knife head as a spray. In this manner a complete 30. wetting of the agglomerate surfaces is achieved with the 14.

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 10. 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 components occurs. For this, one advantageously 15. 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 qranular material:
20. a) 100 parts by weight of ceramic fibres A), 10 parts by weight bonding clay with an A1203 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 25. 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.
30. The mi~ture was taken out of the mixer and pxessed ~9v~

15.

at a pressing pressure of 30 N/mrn in a plate press into plate-shaped articles with a thickness of 30 mrn, whilst obtaining a compression factor of 5.5.
5. The plate-shaped articles were subsequently dried at 110 C for 24 hours in an oven and then fired at different temperatures for 24 hours and subsequently co~ninuted to a maximum grain size of 3 ~n.
The granulates had the following properties:
10. Table I
Firing temperature ( C) 800 1350 1510 Weight per unit volume, R, (g/cm ) 1.34 1.52 1.77 Specific w~ight, S, (g/cm3) 2.60 2.70 2.75 15. Pg (Vol.%) ~7.7 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 15 N/mrn2 respectively and the compression was by a factor of 4 and 5.
20. After firing at 1350 C for 24 hours and comminution~
granulates with the following properties were obtained:
Table II
Pressing pressure (N/mm2) 10 15 25. 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 lncreased 3a . to 15 parts by weight and the proportion of water ~lg~

16.

to 5 parts by weight with the mixing time shortened to 20 minutes. After firillg at 1350C for 24 hours and comminution to the desired granulate this had the following properties:
5. Table III
R (g/cm ) 1.29 S (g/cm3) 2.69 Pg (Vol.~) 53.8 d) Method a) was repeated but additionally 8 parts by 10. 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.
15. The pressing pressure in the compression step b) was 30 N/mm2 which resulted in a compression by a volurne factor of 5.2.
The plate shaped product obtained was dried at 180C and samples were fired at the different 20. temperatures given in the following Table IV.
Subsequently the fired product was comminuted to a maximurn grain size of 3mm.
The granulates obtained had the following properties:
Table IV
25. Treatment temp. ( C) 800 1200 1300 1500 Weight per unit volume R (g/cm ) 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 17.

Manufacture of the moulded articles _xample l The following compositon was used:
Parts by weight 5. Fibres B 100 Monoaluminium phosphate solution, (50% by weight) 13 Water 5 Dry methyl cellulose 1.5 10. 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 15. 2 minutes.
Blocks with dimensions 405 x 135 x 75 mm were then moulded in a mould in a hydraulic press at a pressina pressure of 10 N/mm . These blocks were dried at 120 C for 24 hours and subsequently fired for 24 hours 20. in two batches at 1350 C and 1500C respectively.
The properties of these blocks were as follows:
Table V
Firing temperature ( C) 1350 1500 R (g/cm ) 0.82 0.87 25. 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/mm ) 1.9 2.2 30. Thermal conductivity (W/m K at 700C) 0 30 0.31 18.

Example 2 The following composition was used:
Parts by weight Fibre granulate as made in example b) 5- with R = 1.02 (manufactured at a pressing pressure of 15 N/mm ) 70 Cer.amic fibres B 30 A12 3, dust Chromium oxide, < 63 ~m 0.5 10. Monoaluminium phosphate solution, (50% by weight) 15 Water 2 30 parts by weight of ceramic fibres B were first loosened for 5 minutes in an impact mixer. Then the 15. 70 parts by weight fibre granulate b), the A1203, 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 20. then 2 parts by weight water were put in and mixed for a further 4 minutes. The mixture was remo~ed from the mixer and then moulded at a pressure of 20 N/mm in a hydraulic press into blocks with dimensions of 405 x 135 x 75 mm. They were subsequently dried 25. for 24 hours at 120C and then fired for 24 hours at 1350 C. The properties measured on the fired blocks are listed in the following Table VI.

- 19.

Table VI
Firing temperature ( C) 1350 R (g/cm ) 1.30 Compression factor 2.5 5. Spec. weight (g/cm3) 3.6 Pg (Vol.%) 64.2 Hot bending strength, 1000 C (N/mm ) 2.4 ~hermal conductivity 10. ~W/m K at 700C) 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 5. are given in the following Table VII.
Table VII
Example 3 4 5 Fibre granulate type a) c) d) Fibre granulate quantity, 20. 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 25. Monoaluminium phosphate solution (50% by weight) parts by weight 7 9 10 Water, parts by weight 5 3 In these Examples the method of Example 2 was used and the processing occurred in accordance with the method 30. of Example 2, i.e. the ceramic fibres were first loosened - 20.

in an impact mixex. The other components, except the water, were separately mixed for 5 minutes in an Eirich mixer and then the loosened fibres were added.
Subse~uently the water was added an mixed in for a 5- further 4 minutes.
These mixtures~ as the mixture of Example 2, could be moulded at a pressing pressure of 20 N/mm into perfect moulded articles.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

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 at least one compound selected from Al2O3, Sio2,aluminium hydroxides, magnesia, titanium dioxide and 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 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 phos-phate 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 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 at least one compound selected from Al2O3, SiO2, aluminium hydroxides, magnesia, titanium dioxide and chromium oxide, 2 to 8 parts by weight phosphate bonding agent cal-culated as P2O5, 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 of the desired shape, and c) the moulded article manufactured in step b) is then subjected to a step selected from the group of drying, tempering and firing.

7. A process as claimed in Claim 6 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.

8. A process as claimed in Claim 6 or 7 in which the mixture is moulded into plates whilst compressing it in step b).

9. A method of using moulded article as claimed in Claim 1 which com-prising positioning said moulded article as a support for an object to be fired in a furnace, and then firing said object.