GB2093012A

GB2093012A - Refractory or heat-resistant composite articles

Info

Publication number: GB2093012A
Application number: GB8204316A
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: FR2499974A1; PL235107A1; ES8302615A1; ATA57182A; DE3105595C2; NL8200597A; ES509519A0; ZA821011B; SE8200861L; JPS57149875A; DE3105595A1; NO820443L; DD202136A5; GB2093012B; IT8247790A0; BE892122A

Abstract

A refractory or heat-resistant composite article comprises a shaped portion of any desired refractory material firmly connected to which is an insulating layer made from a fibrous refractory composition alone and/or one of three fibre granulates. The composition and each granulate includes ceramic fibres, clay and/or other finely divided refractory additives and organic and/or phosphate bonding agent.

Description

SPECIFICATION Refractory or heat-resistant composite articles The invention relates to refractory or heat-resistant composite articles and is concerned with that type of such article comprising a shaped portion of any desired refractory or heat-resistant material connected to which is an insulating layer which, depending on its composition, may act as an expansion compensation layer. The invention relates also to a process for the manufacture of such composite articles.

Composite articles are already known which in addition to a shaped portion of any desired refractory material also have an insulating layer. The reason for this is that refrectory shaped articles with good mechanical properties generally have a high thermal conductivity so that it is advantageous in those applications in which large heat losses are to be avoided to provide an insulating layer with a high degree of thermal insulation on such a shaped article.

It is an object of the present invention to provide improved refractory or heat-resistant composite articles of the type referred to above in which the insulating layer comprises substantially ceramic fibres and is very firmly connected to the shaped portion of refractory material and simultaneously has a high resistance to wear and relatively high strength.

According to the present invention there is provided a refractory or heat-resistant composite article comprising a shaped portion of any desired refractory or heat-resistant material firmly connected to which is an insulating layer manufactured from: a) a mixture of 100 parts by weight ceramic fibres, 2 to 1 5 parts by weight clay and/or Awl203 and/or Sio2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide and 1 to 8 parts by weight phosphate bonding agent, calculated as P205, or b1) a first fibre granulate manufactured by mixing 100 parts by weight ceramic fibers, 2 to 1 5 parts by weight clay and/or Awl203 and/or Sio2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, 1 to 8 parts by weight phosphate bonding agent, calculated as P205, with 2 to 100 parts by weight water, compression of the mixture by a volume factor of at least 3, drying and/or heat treating at 250"C to 600"C and/or firing of the product obtained and subsequent comminution thereof, b2) a second fibre granulate manufactured by mixing 100 parts by weight ceramic fibres with 10 to 40 parts by weight water, addition and mixing in of 5 to 20 parts by weight clay and/or Awl 203 and/or Si02 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide and 0 to 10 parts be weight solid organic bonding agent, addition and mixing in of 0.5 to 4 parts by weight organic bonding agent in solution and 1 to 8 parts by weight of a phosphate bonding agent, calculated as P205, drying of the product obtained and subsequent comminution thereof, or a mixture of one or both of fibre granulates b,) and b2) with a third fibre granulate b3) manufactured by mixing 100 parts by weight ceramic fibres with 2 to 1 5 parts by weight clay and/or Al203 and/or Si02 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, 1 to 10 parts by weight organic bonding agent, calculated in solid form, and 5 to 100 parts by weight water, compression of the mixture obtained by a volume factor of at least 3, drying of the product and subsequent comminution thereof, or c) from a mixture of a) and one or more or fibre granulates b1),b2) and b3.

The invention also relates to a process for the manufacture of such compostie articles.

The ceramic fibres used for the manufacture of the compostie articles in accordance with the invention can be all usual fibres of this type, e.g. rock wool or fibres based on aluminium silicate, preferably with a particularly high Al203 content in the region of 45 to 95% by weight.

Naturally mixtures of different ceramic fibres can also be used. The fibres are, however, preferably based on Al203 and Si02 with at least 40% by weight Al203 and are preferably capable of being used at temperatures in excess of 11 0'C. This will in general exclude inorganic fibres based on, for instance, basalt, slag and glass and natural absetos fibres whose use temperature is below 11 00'C, but such fibres may be and preferably are used as a subsidiary component is addition to those whose use temperature is above 11 00'C.

The clay used for the manufacture of the composite articles in accordance with the invention can be a conventional clay or a special bonding clay, advantageously bentonite. This clay is commonly used in an amount of 2 to 1 5 parts by weight in composition a) and granulates b1) and bs) and 5 to 100 parts by weight of the ceramic fibres.

Furthermore up to 10 parts by weight of other refractory additives can be used in the manufacture of the composite articles, examples of which are procelain powder, fire clay or hollow sphere corundum.

The total proportion of clay plus other refractory additives is advantageously 20 parts by weight to 100 parts by weight of the ceramic fibres.

The other components which may be used in the manufacture of the composite articles instead of or as well as the clay are Al203 and/or SiO2 and/or magnesia and/or titanium dioxide and/or chromium oxide, all of which are preferably present in very finely divided form, and/or aluminium hydroxides. These are all components whose use is known in the refractory field. The term "very finely divided" is used here to mean that these components are present in very finely ground or in colloidal state.The very finely divided refractory materials preferably have a grain size of less than 50 ,um, 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 1 part by weight of such a bonding agent.

The phosphate bonding agent used in the manufacture of the composite articles in accordance with the invention may be a conventional phosphate bonding agent, whereby the given quantities in parts by weight refer to P205 in the bonding agent.

An example of such phosphate bonding agent is sodium polyphosphate with a degree of polymerisation of n 2 4 and preferably with a degree of polymerisation of 6 to 10. A further suitable phosphate bonding agent is monoaluminium phosphate that is a commercially available product both in solid ground form and also in aqueous solution with 50% by weight MAP.

Conventional plasticising agents can additionally be used in the manufacture of composite articles in accordance with the invention, such as surface active compounds or, in particular, methyl cellulose.

Organic bonding agents can additionally be used in the manufacture of the compostie articles in accordance with the invention, examples of which are molasses, sulphite lye or waste and, in particular, methyl cellulose.

In an advantageous embodiment of the composite article in accordance with the invention the ceramic fibres are used in the form of loosened fibres. For this purpose commercial grade fibres are put in their delivery state into an impact mixer (for instance a tubulent rapid mixer of the type manufactured by Drais) in which the fibres, which are commonly delivered as fibre bundles, are converted into loosened fibres. Such an impact mixer comprises a mixing unit with rapidly rotating knife heads in which any agglomerates which may be present in the fibres, which are generally partially in strongly compressed form, are loosened without the fibres being thereby unacceptably strongly crushed or comminuted.

The manufacture of the composite articles in accordance with the invention can occur by two different processes.

In the first process a mixture is first made up in a step a) in a mixer from 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, calculated as P205, if required an addition of plasticising agent with 2 to 100 parts by weight water. A conventional Drais mixer or Eirich mixer can be used as the mixer.

The mixture is then pressed in a step b) onto at least one surface of the shaped article of any desired refractory material whilst compressing it by a volume factor of at least 3 and advantageously of 5 to 8.

This pressing on can occur, for instance in the case of a moulded brick, in that the mixture produced in step a) is first put into a mould and then the shaped article is laid on it and subsequently a pressing together is effected. The reverse procedure is also possible, i.e. a shaped article of any desired refractory material can first be laid in a mould, and a mixture as produced in step a) put onto the shaped article and then the pressing is effected by the given compression factor.

The production of an insulating layer on the external surface of a tube is particularly simple.

For this the finished tubular article of any desired refractory material is put into a mould with a larger diameter than the external diameter of the tube and the mixture produced in step a) is filled into the intermediate space between the tube and the mould and either stamped in or pressed in.

In an alternative embodiment a fibre granulate bt), b2) or b3) or a mixture thereof, which are to be described below, is additionally briefly mixed into the mixture after the production of the mixture and then this composition is pressed onto at least one side of a shaped article of any desired refractory or heat resistant material whilst compressing it. When using a mixture as described above without addition of a fibre granulate the compression must occur by a volume factor of at least 3, advantageously between 5 and 8. The maximum compression factor which can be achieved with conventional presses is of the order of 1 2 to 14. If one or more of the fibre granulates referred to above is added to the mixture such a high compression is not possible, however the volume factor of the compression should in any cse be at least about 1.5.

An advantageous range of the compression factor when using a mixture containing one or more fibre granulates is between 2.5 and 4. The reason for this lower compression factor is that the fibre granulates can not be so strongly compressed and this is particularly true for the fibre granulates b1) and b3) which have already been compressed in their manufacture.

Advantaaeouslv the weiaht ratios of mixture a). without the Drooortion of water. to the fibre granulate(s) are from 20:80 to 80:20. Due to the addition of a fibre granulate more mixing water is naturally required so that the total added water quantity must be increased. This can however be determined in each case by simple prior experiments.

In an alternative embodiment of the process described above, one of the fibre granulates b,) or b2), which are described below, is made up, if required with the addition of further bonding agent, particularly of inorganic bonding agent and particularly preferably one of the phosphate bonding agent and particularly preferably of inorganic bonding agent and particularly preferably one of the phosphate bonding agents referred to above with a suitable quantity of water, which can be provided by the solvent water when using dissolved bonding agents, whereby the quantity of water commonly amounts to 2 to 30 parts by weight of water to 100 parts by weight of the fibre granulate. The quantity of water depends on the fibre granulate.The quantity of water depends on the fibre granulate used and this is particularly the case when using fibre granulate b,) which can be used both in the dried and in the tempered of fired state. The determination of the water quantity necessary in each case is, however, possible without difficulty by means of simple prior experiments. Instead of one of fibre granulates b,) or b2) or a mixture thereof, a fibre granulate b,) and/or b2) together with a third fibre granulate b3), which is described below, can be used for the manufacture of which only organic bonding agent is used.

The advantage of the use of the fibre granulate b3) in a composite article in accordance with the invention is that this fibre granulate b3) is still present after the manufacture of the composite article at least partially in the form of fibres. Since this fibre granulate contains only organic bonding agent which burns away on using the composite article, i.e. after the first heating to a high temperature, individual grains of this fibre granulate b3) remain in the composite article as discrete regions.The fibres within the fibre grains experience either no or only slight bonding by the inorganic bonding agents which may penetrate right through them, and maintain as a consequence a certain elasticity by vitue of the fact that the ceramic fibres are not firmly bonded to one another so that a layer containing such a fibre granulate b3) is suitable, in particular, as an expansion compensation layer since it has relatively good elastic properties.

This is true to a certain extent also when using fibre granulate b2) in which, by virtue of its particular manufacture, only small quantities of phosphate bonding agent penetrate into the fibre grain so that even after a temperature treatment of a composite article manufactured with such a fibre granulate b2) the interior of the fibre grains remains elastic so that altogether the insulating layer or expansion compensation layer maintains very good elastic properties.

In the other process in accordance with the invention, an insulating layer which comprises a shaped article matching, i.e. complimentary to, the shaped article of any desired refractory material is first produced from one of the mixtures referred to above by pressing or stamping again whilst compressing by the given volume factor. This fibre granulate shaped article is then dried and/or tempered and/or fired and can then be glued or cemented to the shaped article of any desired refractory material. For sticking on or cementing conventional refractory cements or a concentrated solution of a phosphate bonding agent can be used.

In this embodiment of the process in which an insulating layer shaped article is glued to the shaped article of any desired refractory material or cemented thereto, advantageously only a drying of this insulating layer shaped article is carred out in step c) since this insulating layer shaped article still has a certain elasticity or deformability in such a case with the result that it can better adapt to the shape of the article of refractory material to which it is to be connected.

The comments made above regarding the advantages of the use of a mixture containing fibre granulates when producing the insulating layer apply also in this case, i.e. the use of the fibre granulates, and in particular the fibre granulates b2) and b3), results in the insulating layer being capable of acting as an expansion compensation layer and having particularly elastic and stress accommodating properties.

As stated above, the reason for this elasticity is probably that the ceramic fibres in the individual particles of the fibre granulate, in whose production no compression was used or in whose production a larger volume proportion of organic bonding agent and a smaller proportion of phosphate bonding agent was used, retain their elastic properties in the individual grains of the insulating layer when this is subjected to high temperatures so that elastic or stress compensating individual regions or individual grains are present in this layer.

When producing the fibre granulates b,), b2) and b3) loosened fibres, as described above, are also advantageously used as when producing the mixture a).

The remaining starting materials used when producing these fibre granulates correspond to the starting materials described above.

The fibre granulates b,), b2) and b3) are described in more detail in British Patent Applications Nos. (Case 3123), (Case 3155) and (Case 3154) of the present applicants which were filed on the same day as the present application.

The production of these granulates will be described below Fibre granulate b,) The production of this fibre granulate is effected by a method including 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, if necessary with addition of a plasticising agent are thoroughly mixed in a mixer with about 2 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 dried and/or heat treated at a temperature of 250 to 600"C and/or fired, e.g. at a temperature above 600"C, and subsequently comminuted.

The composition given here corresponds to the composition as was described above with reference to the mixture a) which may be present in the insulating layer of the composite article of the present invention. In the production of this fibre granulate the compression in step b) is preferably carried out by a volume factor of 5 to 8. The water quantity added in step a) is dependant on the compression device in which the compression is carried out. When using a briquetting device or a rotary table press a water quantity of 2 to 25 parts by weight is generally sufficient, whilst when using an extruder as the compression device up to 100 parts by weight of water must be added since for this a more strongly plastic mass is necessary.

Fibre granulate b2) The production of this fibre granulate is effected by a method including the following steps: a) 100 parts by weight ceramic fibres are mixed in a mixer with 10 to 40 parts by weight water, 5 to 20 parts by weight clay and/or Awl203 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide and also 0 to 10 parts by weight organic bonding agent are added to the mixture obtained in step a) and mixed in with it, c) 0.5 to 4 parts by weight of an organic bonding agent, calculated as solid material, in solution, and also 1 to 8 parts by weight of a phosphate bonding agent, calculated as P2Os, are added to the mixture obtained in step c) is dried and granulated.

Fibre granulate b3) The production of this fibre granulate is effected by a method including the following steps: a) 100 parts by weight ceramic fibres, 2 to 1 5 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, optionally up to 10 parts by weight other refractory additives and 1 to 10 parts by weight organic bonding agent, calculated in solid form, are thoroughly mixed in a mixer with about 5 to 100 parts by weight of water, and b) the mixture obtained in step a) is compressed by a volume factor of at least 3, dried and then comminuted.

As in the production of fibre granulate b1) the quantity of water to be added is dependent on the compression device in which the compression of the mixture obtained in step a) occurs, whereby in conventional compression devices such as briquetting presses and rotary table presses 5 to 25 parts by weight of water are necessary, whilst if compressing in an extruder up to 100 parts by weight water may be added to produce a more strongly plastic starting mixture in step a).

For further details of the production of fibre granulates b,, b2) and b3) reference is made to the Patent Applications of the present applicants referred to above. The production of these fibre granulates will now be illustrated in more detail with reference to examples.

In these examples two different sorts of ceramic fibres were used, namely A) ceramic fibres of the Al203-SiO2 system with 47% Al203 and 53% SiO2, whose threshold use temperature is 1 260on, and B) ceramic fibres of the Al203 system with 95% Al203 and 5% SiO2 which permit higher use temperatures up to above 1 500 C.

In these examples the information relates to parts by weight if no indication to the contrary is given.

Production of fibre granulate b,) Example 1 100 parts by weight of ceramic fibres A), 10 parts by weight bonding clay with an Awl203 content of 35% and 1.5 parts by weight dry methyl cellulose in powder from were put into an Eirich mixer and mixed together for 10 minutes. 10 parts by weight of 50% by weight monoaluminium phosphate solution and 2 parts by weight water were then sprayed onto the mass in the mixer whilst continuing to mix and were mixed in for a further 30 minutes.

The mixture was taken out of the mixer and pressed in a plate press into a plate-shaped product with a thickness of 30 mm at a pressing pressure of 30'N/mm2 thereby compressing the mixture by a factor of 5.5.

The plate-shaped product was subsequently dried in an oven for 24 hours at 110"C and samples were then fired at differing temperatures for 24 hours and subsequently comminuted to a maximum grain size of 3mm.

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 Pore volume, Pg, (Vol. %) 47.7 43.7 35.6 Chemical analysis (%) Al203 44.7 SiO2 50.7 P205 2.95 Example 2 The method of Example 1 was repeated but an impact mixer was used to loosen the fibres.

Two samples were pressed at pressing pressures in step b) of 10 and 1 5 N/mm2 respectively, achieving compression factors 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 Example 3 The method of Example I was repeated but the proportion of monoaluminium phosphate solution was increased to 1 5 parts by weight, the proportion of water to 5 parts by weight and the mixing time shortened to 20 minutes. After firing at 1 350'C for 24 hours and comminution the granulate had the following properties: Table III R (g/cm3) 1.29 S (g/cm3) 2.69 Pg (Vol. %) 53.8 Example 4 The method of Example 1 was repeated but additionally 8 parts by weight fire clay powder were added in step a).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 180it and samples were fired at the differing temperatures given in the following Table IV. Subsequently the dried or fired product was comminuted to a maximum grain size of 3mm.

The granulates obtained had the following properties: Table IV Treatment temp. ("C) 180 800 1200 1300 1500 Weight per unit volume R (g/cm3) 1.30 1.26 1.31 1.34 1.48 Spec. weight (g/cm3) 2.60 2.60 2.65 2.68 2.72 Pg. (Vol. %) 50.0 51.5 50.5 50.0 45.6 Example 5 The method of Example 1 was repeated but instead of the bonding clay 10 parts by weight of very finely divided colloidal aluminium hydroxide were used. This aluminium hydroxide was present as a highly viscous solution. 8 parts by weight monoaluminium phosphate solution and 3 parts by weight water were added in the mixing step.

The compression in the pressing step occurred at a pressing pressure of 30 N/mm2 which resulted in a compression by a volume factor of 5.4.

The further treatment occurred as in Example 1, whereby the drying temperature however was 120"C and samples of the plate-shaped material were fired at the different temperatures shown in the following Table V. Subsequently the material was granulated as in Example 1.

The fibre granulates had the following properties; Table V Treatment temp. ("C) 120 800 1200 1300 1500 Weight per unit volume R (g/cm3) 1.34 1.32 1.38 1.39 1.44 Spec. weight (g/cm3) 2.72 2.72 2.77 2.79 2.83 Pg (Vol. %) 50.7 51.5 50.2 50.1 49.1 Example 6 The method of Example 1 was repeated with the exception that instead of the 50% by weight monoaluminium phosphate solution 4.5 parts by weight of solid sodium polyphosphate were added in the mixing step. The water quantity used was 9 parts by weight.

When compressing with a pressing pressure of 30 N/mm2 a compression by a volume factor 5.5 was achieved.

The further treatment occurred as before, whereby the drying was effected at 1 20'C. In the following table the properties of the fibre granulates obtained in accordance with the method of Example 1 from the dry product or the products fired at different firing temperatures are given.

Table VI Treatment temp. ("C) 120 800 1200 1300 1500 Weight per unit volume R (g/cm3) 1.22 1.19 1.32 1.38 1.41 Spec. Weight (g/cm3) 2.60 2.61 2.65 2.69 2.73 Pg (Vol. %) 53.1 54.4 50.1 48.6 48.4 Example 7 In this example the compression was effected by extrusion.

Firstly 100 parts by weight of ceramic fibres B) were mixed for 10 to 20 minutes in an Eirich mixer with 1.5 parts by weight dry methtyl cellulose. Then 10 parts by weight of the bonding clay used in Example 1 and 2 parts by weight of very finely divided chromium oxide with a maximum particle size of 63 ym were put into the running mixer and briefly mixed in.

Subsequently 10 parts by weight of 50% by weight of 50% by weight solution of monoaluminium phosphate and 80 parts by weight water were added and thoroughly mixed in. The extrusion occurred in a conventional extrusion device, whereby the nozzle has a cross-section of 250 x 190 mm. The volume factor achieved in the compression was 3.9. The material exiting from the nozzle was cut off in suitable clump lengths. These were firstly dried for 24 hours at 110"C and then samples were fired at the different firing temperatures given in Table VII for 24 hours. Then these treated sample clumps were comminuted to a fibre granulate with a maximum grain size of 6 mm.

The properties obtained in these fibre granulates were as follows: Table Vll Treatment temp. ("C) 110 900 1100 1 300 1 500 Weight per unit volume R (g/cm3) 0.90 0.87 0.92 1.00 1.27 Spec. weight (g/cm3) 2.60 2.61 2.63 2.65 2.73 Pg (Vol. %) 65.4 66.6 65.0 62.2 53.5 Example 8 Firstly 100 parts by weight fibres were loosened for 20 minutes in an impact mixer with 1.5 parts by weight dry methyl cellulose, subsequently 10 parts by weight colloidal SiO2 in solid form were added and mixed with the fibres. Subsequently 8 parts by weight of solid powder-like monoaluminium phosphate and 8 parts by weight of water were added and mixed in for a further 12 minutes.

The crumb-like mixture obtained was compressed in a briquetting device by a volume factor of 4.9 and was subsequently dried for 24 hours at 120"C. A further sample was heat treated for 24 hours at 400"C without previous drying and a further sample was fired for 24 hours at 1000"C , also without previous drying.

The treated samples obtained were comminuted to a maximum grain size of 4 mm and the following properties were measured on the fibre granulates obtained: Table VIII Treatment temp. ("C) 120 400 1000 Weight per unit volume R (g/cm3) 1.15 1.10 1.13 Spec. weight (g/cm3) 2.58 2.57 2.65 Pg (Vol. %) 55.4 57.2 57.3 Production of fibre granulate b2) Example 9 to ii The following compositions were used, the quantities being parts by weight:: Example 9 10 11 Fibres A 100 100 100 H20 30 15 40 Bentonite 10 EM 1 5 AI2O3 5 5 TiO2 - 2 Solid methyl cellulose 4 - 3.5 Solid sulphite waste - 5 Sulphite waste solution, 10% by weight. - 2 Methyl cellulose solution, 5% by weight 0.5 - 3 Solid monoaluminium phosphate 4 - 8 Solid sodium polyphosphate - 2.5 Firstly the ceramic fibres were put into an Eirich mixer and the given quantities of water were sprayed onto them and mixed for 10 minutes. Subsequently the bentonite, Awl203 or TiO2 and the solid methyl cellulose or solid suphite waste were added to this mixture and mixed in for a further 8 minutes.

Thereafter the given solutions of sulphite waste or methyl cellulose, to which the finely divided solid phosphate bonding agents had been added, were sprayed into the mixer and mixed in for a further 10 minutes.

The crumbly mixture obtained was removed from the mixer and dried for 6 hours at 120"C and subsequently comminited in a roller crusher to a maximum grain size of 4 mm.

The properties determined on the products were as follows: Example 9 10 11 Weight per unit volume (g/cm3) 0.22 0.14 0.40 Examples 12 to 14 The method of Examples 9 to 11 was repeated but loosend ceramic fibres B were used. The loosening of the fibres ocurred in an impact mixer (manufacturer Drais). The fibres were treated in this rapidly rotating mixer equipped with knife heads for 5 minutes. These loosened fibres B were transferred into an Eirich mixer, in which the further components corresponding to the compositions of Examples 9 to 11 were added.

Fibre granulates were also produced from the products of Examples 1 2 to 14.

The properties determined on the products were as follows: Example 12 13 14 Weight per unit volume (g/cm3) 0.25 0.1 7 0.45 Production of fibre granulate b3) Examples 15 to 19 The following compositions were used: Example 15 16 17 18 19 Ceramic fibres A 100 - - - 50 Ceramic fibres B - 100 100 100 50 Bonding clay (with 35% Al2O3) 1 5 6 - 4 Chromium oxide, < 63,um - 4 4 - Colloidal SiO2 - - 6 2 4 Colloidal AI2O3 - - - - 6 Solid methyl cellulose 6 - - 4 1 Solid sulphite waste - 7 2 - Fire clay powder 2 - - - - Water 25 10 15 12 25 The ceramic fibres were mixed with bonding clay and/or the other refractory components for 5 minutes in an Eirich mixer, then the organic bonding agent or mixture of bonding agents was put in and finally the water added. This was mixed for a total of 20 minutes.

This mixture was compressed in a briquetting device (e.g. of the type manufactured by Kloeckner Humboldt-Deutz) by the given volume factors, then dried for 12 hours at 120 C and finally comminuted to a maximum grain size of about 6mm. The following properties were determined on the fibre granulates obtained: Example 15 16 17 18 19 Weight per unit volume R (g/cm3) 1.25 1.09 1.15 1.20 1.23 Compression factor 5.4 7.2 6.8 6.0 6.5 Pore volume, Pg, (Vol. %) 49.5 69.7 68.0 53.8 62.6 Examples 20 to 24 The compositions of Examples 15 to 1 9 were repeated but loosened fibres were used. The loosening of the fibres occurred in an impact mixer (manufacturer Drais) for 5 minutes.

Subsequently the remaining additives were added and mixed in for 2 minutes.

The compression occured in a hydraulic press into bricks of 250 X 1 25 X 30 mm which were dried for 1 2 hours at 120 C and subsequently comminuted to a maximum grain size of 6 mm.

The following properties were determined on the fibre granulates obtained: Example 20 21 22 23 24 R (g/cm3) 1.10 0.95 1.01 1.04 1.09 Compression factor 6.0 7.9 7.2 6.9 7.3 Pg (Vol. %) 56.0 73.5 71.7 59.9 66.6 Example 25 The composition of Example 20 was used with the difference that 80 parts by weight water were mixed in. The compression occurred in an extruder, the cross-section of whose nozzle was 250 X 1 90 mm. The crude clumps exiting from the extruder were cut off at suitable lengths and dried for 24 hours at 120 C. Subsequently the dried clumps obtained were comminuted to a maximum grain size of 3 mm.The following properties were measured on the fibre granulates obtained: R (g/cm3) 0.95 Compression factor 3.2 Pg (Vol. %) 62.7 The manufacture of composite articles in accordance with the invention will now be described in more detail with reference to examples.

Example 26 A fibre mass was produced using the following components: Parts by weight Ceramic fibres A 100 Bonding clay with 35% Awl203 10 Fire clay, < 63 63,um 10 Solid monoaluminium phosphate 6 The components referred to above were put into a positive mixer (Zyklus type) and mixed together for 2 minutes. Subsequently 25 parts by weight water were put in and mixed for a further 1 5 minutes.

A fired tube of alumina was arranged vertically in a moulding box of metal plate with an open top so that a space remained between the outer surface of this tube and the inner surface of the metal plate moulding box. The previously produced fibre mass was filled into this space and stamped in with a pressurized air hammer. Subsequently the upper edge of the tube was broken off flush.

The composite article thus obtained was dried for 24 hours at 120"C and subsequently fired for 5 hours at 1350"C.

During the firing process the fibre mass, i.e. the insulating layer on the tube, crumpled up and became firmly connected to the inner tube of refractory material thus forming a single composite unit.

Such composite units can be used as an insulated gas line, even with gasses which are to be fed at high temperatures of, for instance, 1100 to 1150"C and/or high gas velocity. Under such conditions an insulating material without an inner tube of refractory material could be used. In this case the inner tube is of fired alumina but if it is to be used in an atmosphere which is not oxidising it could be of silicon carbide.

Example 27 A fibre mass was produced using the following components: Parts by weight Ceramic fibres B 100 Clay (about 40% by weight AI2O3) 4 AI2O3 below 0.064 mm 6 Solid monoaluminium phosphate 6 The ceramic fibres B were previously loosened in an impact mixer for 4 minutes. The further processing of the mass occurred as in Example 26.

A tube of silicone carbide with a diameter of 25 cm was used as the inner tube. Subsequent to the stamping in the unfinished article obtained was dried at 300"C for 24 hours. Then it was heated to 1000"C by means of an electric heating element built into the inner tube. Numerous temperature cycles were carried out, i.e. the composite article was allowed to cool to ambient temperature and then heated up again to 1000 C. The composite article has an excellant service life and the firmly connected insulating layer exhibited no cracks or peeling away. This means that the fibre mass forming the insulating layer is elastic enough despite it high strength to absorb the different thermal expansions of silicon carbide of the inner tube on the one hand and the fibre mass forming the insulating layer on the other hand.

Examples 28 to 33 The composition used in Example 26 was produced and the fibre granulates listed in the following Table IX were added to 100 parts by weight of this composition in the given quantities together with further quantities of water and mixed in a mixer of 2 minutes. In Examples 29, 31 and 33, however 7.5 parts by weight monoaluminium phosphate were added in distinction from the composition in Example 26. Composite articles with excellant properties could be produced with these compositions in accordance with the method of Example 26.

Table IX Example 28 29 30 31 32 33 fibre granulate type b1) b,) b2) b2) b3) b3) fibre granulate from example 1 5 11 1 2 18 1 9 quantity (parts by weight) 50 200 40 300 20 400 Example 34 The composition used in Example 27 was produced and pressed in a plate press whilst compressing it by a volume factor of 5.2 into plates with a thickness of 3 mm. The plates were dried for 5 hours at 120"C. Pieces with brick dimensions (405 X 1 35 mm) were cut out of these plates and cemented onto a side of fire clay bricks with a refractory cement. The composite articles produced thus had an expansion compensation layer.

Examples 35 to 39 The quantities given in the following Table X (in parts by weight) of fibre granulate(s) of the given types, which had been manufactured in the examples also given in Table X, were put into an Eirich mixer. To 100 parts by weight of the fibre granulate/or mixture of fibre granulates 5 parts by weight of a 50% by weight monoaluminium phosphate solution and 10 parts by weight water were added in each case and were then mixed for a further 3 minutes. The compositions obtained were also stamped in around an inner tube of refractory material, whereby composite articles with excellant properties were obtained.

Table X Example 35 36 37 38 39 Fibre granulate, type b,) 100 - 50 25 25 from Example 4 3 6 7 Fibre granulate, type b2) - 100 50 50 25 from Example 12 12 13 14 Fibre granulate, type b3) - - - 25 50 from Example 17 18 When forming the mixtures of fibre granulates a 3 mm maximum grain size and a proportion of less than 1 mm of about 30% by weight was maintained.

Claims

1. A refractory or heat-resistant composite article comprising a shaped portion of any desired refractory of heat-resistant material firmly connected to which is an insulating layer manufactured from: a) a mixture of 100 parts by weight ceramic fibres, 2 to 1 5 parts by weight clay and/or Awl203 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, and 1 to 8 parts by weight phosphate bonding agent, calculated as P2O5, or b) from one of the following fibre granulates or a mixture of such fibre granulates b,) a first fibre granulate manufactured by mixing 100 parts by weight ceramic fibres, 2 to 1 5 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, 1 to 8 parts by weight phosphate bonding agent, calculated as P2Os, with 2 to 100 parts by weight water, compression of this mixture by a volume factor of at least 3, drying and/or heat treating at 250"C to 600"C and/or firing of the product obtained and subsequent comminution thereof, b2) a second fibre granulate manufacture by mixing 100 parts by weight ceramic fibres with 10 to 40 parts by weight water, addition and mixing in of 5 to 20 parts by weight clay and/or Awl203 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide and 0 to 10 parts by weight solid organic bonding agent, addition and mixing in of 0.5 to 4 parts by weight organic bonding agent in solution and 1 to 8 parts by weight of a phosphate bonding agent, calculated as P205, drying of the product obtained and subsequent comminution thereof, or a mixture of one or both of fibre granulate b,) and b2) with a third fibre granulate b3) manufactured by mixing 100 parts by weight ceramic fibres with 2 to 1 5 parts by weight clay and/or Awl203 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, 1 to 10 parts by weight organic bonding agent, calculated in solid form, and 5 to 100 parts by weight water, compression of the mixture obtained by a volume factor of at least 3, drying of the product and subsequent comminution thereof, or c) from a mixture of a) and one or more of fibre granulates b,, b2) and b3).

2. An article as claimed in Claim 1 in which one or more of composition a), granulate b,) and granulate b3) include up to 10 parts by weight of a further refractory additive.

3. An article as claimed in Claim 2 in which the further refractory additive is one or more of porcelain powder, fire clay or hollow sphere corundum.

4. An article as claimed in any one of the preceding claims in which composition a) and/or granulate b,) additionally contains a plasticising agent.

5. An article as claimed in any one of the preceding claims in which the insulating layer comprises one or more of the fibre granulates bonded together with a bonding agent.

6. An article as claimed in any one of the preceding claims in which the clay is bentonite.

7. An article as claimed in any one of the preceding claims in which the insulating layer contains sodium polyphosphate as phosphate bonding agent.

8. An article as claimed in any one of the preceding claims in which the insulating layer contains monoaluminium phosphate as phosphate bonding agent.

9. An article as claimed in any one of the preceding claims in which the insulating layer contains methyl cellulose as a plasticising agent and/or an organic bonding agent.

10. An article as claimed in any one of the preceding claims in which the insulating layer contains molasses or sulphite waste as an organic bonding agent.

11. An article as claimed in any one of the preceding claims in which the ceramic fibres are in loosened form.

1 2. An article as claimed in any one of the preceding claims in the form of a tube with the insulating layer constituting its outer surface.

1 3. An article as claimed in any one of the preceding claims in which hollow spaces are present in the insulating layer.

14. A refractory or heat-resistant composite article substantially as specifically herein described with reference to any one of the accompanying examples 26 to 39.

1 5. A process for manufacturing a compostie article as claimed in any one of claims 1 to 1 3 including the following steps: a) 100 parts by weight ceramic fibres, 2 to 1 5 parts by weight clay and/or Awl203 and/or SiO2 and/or aluminium hydroxide and/or magnesia and/or titanium dioxide and/or chromium oxide, up to 10 parts by weight other refractory additives and 1 to 8 parts by weight phosphate bonding agent, calculated as P205 are thoroughly mixed with 2 to 25 parts by weight water, b) the mixture obtained in step a) is pressed onto at least one side of a shaped article of any desired refractory or heat-resistant material whilst compressing the mixture by a volume factor or at least 3, and the unfinished composite article obtained in step b) is dried and/or tempered at temperatures of 250 to 600"C and/or fired at temperatures of 600 to 1 600'C.

1 6. A process for manufacturing a composite article as claimed in any one of Claims 1 to 1 3 including the following steps: a) 100 parts by weight ceramic fibres, 2 to 1 5 parts by weight clay and/or AI2O3 and/or S,02 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, up to 10 parts by weight other refractory additives and 1 to 8 parts by weight phosphate bonding agent, calculated at P205 are thoroughly mixed with 2 to 25 parts by weight water, b) adding one or more of fibre granulates b1), b2) and b3) and mixing it in, c) the mixture obtained in step a) is pressed onto at least one side of a shaped article of any desired refractory or heat-resistant material whilst compressing the mixture by a volume factor of at least 1.5, and d) the unfinished composite article obtained in step b) is dried and/or tempered at temperatures of 250 to 600"C and/or fired at temperatures of 600 to 1 600 C.

1 7. A process for manufacturing a composite article as claimed in any one of Claims 1 to 13 including the steps of mixing fibre granulate b,) or b2) or a mixture thereof or a mixture of fibre granulate b3) with fibre granulate b,) or b2 or a mixture thereof with water into a pressable composition, pressing this composition onto at least one side of a shaped article of any desired refractory or heat resistant material and drying the composite article and/or tempering it at temperatures of 250 to 600"C and/or firing it at temperatures of 600 to 1 600 C.

1 8. A process as claimed in Claim 1 7 including the step of adding a phosphate bonding agent or an organic bonding agent to the mixture prior to pressing it.

1 9. A process for manufacturing a compostie article as claimed in any one of Claims 1 to 1 3 including the following steps: a) 100 parts by weight ceramic fibres, 2 to 1 5 parts by weight clay and/or Awl203 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, up to 10 parts by weight other refractory additives and 1 to 8 parts by weight phosphate bonding agent are mixed with 2 to 25 parts by weight water, b) the mixture obtained in step a) is compression moulded to an insultating layer whose shape is complimentary to that of a shaped article of any desired refractory or heat-resistant material whilst compressing by a volume factor of at least 3, c) the unfinished insulating layer obtained in step b) is dried and/or tempered at temperatures of 250 to 600"C and/or fired at temperatures of 600 to 1600"C, and d) the insulating layer obtained in step c) is connected to the shaped article by glueing on or cementing.

20. A process for manufacturing a composite article as claimed in any one of Claims 1 to 1 3 including the following steps: a) 100 parts by weight ceramic fibres, 2 to 1 5 parts by weight clay and/or AI2O3 and/or SiO2 and/or aluminium hydroxides and/or magnesia and/or titanium dioxide and/or chromium oxide, up to 10 parts by weight other refractory additives and 1 to 8 parts by weight phosphate bonding agent are mixed with 2 to 25 parts by weight water and fibre granulate b,) or b2) or a mixture thereof or a mixture of fibres granulate b,) and/or b2) with fibre granulate b3).

b) the mixuture obtained in step a) is compression moulded to an insulating layer whose shape is complimentary to that of a shaped article of any desired refractory or heat-resistant material whilst compressing by a volume factor of at least 1.5, c) the unfinished insulating layer obtained in step b) is dried and/or tempered at temperatures of 250 to 600"C and/or fired at temperatures of 600 to 1600"C, and d) the insulating layer obtained in step c) is connected to the shaped article by glueing on or cementing.

21. A process for manufacturing a composite article as claimed in one of Claims 1 6 to 20 in which up to 400 parts by weight of one of fibre granulates b,), b2) or b3) or a mixture thereof are added to 100 parts by weight of composition a).

22. A process for the manufacture of a composite article as claimed in any one of Claims 1 5 to 21 in which the ceramic fibres used in composition a) and/or the or each fibre granulate are in loosened form.

23. A process for the manufacture of a composite article substantially as specifically herein described with reference to any one of the accompanying examples 26 to 39.