GB1564611A

GB1564611A - Refractory compostions

Info

Publication number: GB1564611A
Application number: GB36804/76A
Authority: GB
Original assignee: HOLTER PATENTVERWERT
Current assignee: HOLTER PATENTVERWERT
Priority date: 1975-09-19
Filing date: 1976-09-06
Publication date: 1980-04-10
Also published as: FR2324593A1; JPS5248577A; CA1079312A; IT1070803B; NO763003L

Description

(54) IMPROVEMENTS IN OR RELATING TO REFRACTORY COMPOSITIONS (71) We, HOLTER GESELLSCHAFT FUR PATENTVERWERTUNGS VERFAHREN mbH, a German Company, of Fritz-Kohl-Strasse 9, 6500 Mainz, German Federal Republic do hereby declare the invention for which I pray that a Patent may be granted to me and the method by which it is to be performed to be particularly described in and by the following statement: This invention is concerned with improvements in or relating to refractory compositions, of the kind comprising an hydraulic cement and an aggregate.

In the manufacture of refractory compositions there is used as aggregate, or there is incorporated in the composition, various materials to obtain or improve the heatresistance, and particularly fire-resistance and/or resistance to temperature changes, of the refractory composition. For the purpose of improving these properties it is customary to use, e.g. asbestos fibre, mineral wool, glass wool, pearlites, vermiculites, fragmented pumice stone, refractory clay, powdered refractory clay, slag-sand, quart sand, sintered corundum, sintered dolomite, alumina, powdered dolomite and gypsum. However, these materials fulfill the above listed requirements only in part, or only imperfectly, or they raise problems in the production or processability of the materials.In addition, some of these materials are expensive or scarce, and others, such as asbestos, present considerable health risks which make their use undesirable.

According to this invention there is provided a refractory composition comprising an aggregate, at least 7% by weight of hydraulic cement, and as a filler material, from 20 to 50% by weight of silicon dioxide, of which at least 82% is amorphous, not more than 18% is crystalline quartz, which has a bulk weight within the range 0.25 to 0.50 gram per millilitre, and of which at least 95% has a grain size below 50 microns.

The term "aggregate" is used herein to include mineral materials commonly mixed with cement in the manufacture of, for example concrete, but does not include the silicon dioxide filler material.

The content of said silicon dioxide most advantageously is between 20% and 30% by weight.

The refractory composition itself may be utilised in the manufacture of a material required to have high fire and/or heat resistance, such as in the manufacture of refractory bricks, or refractory concrete. Alternatively, the refractory composition may be utilised in improving the fire and/or heat resistance of an article, by being sprayed onto the article.

Thus, this invention also provides a method of improving the fire and/or heat resistance of an article, the method comprising the step of applying to the article a coating of a refractory composition in accordance with this invention.

It has been found that not only does a refractory composition in accordance with this invention exhibit significantly improved fire and/or heat resistance, but additionally improves other physical properties when used in the manufacture of various articles.

This allows the refractory composition in accordance with this invention to be used in the manufacture of a variety of articles, improving not only the fire and/or heat resistance of the article, but also improving other qualities, such as the sound absorbancy thereof.

Thus, this invention also provides a refractory composition suitable for imparting fire, flame and heat resistance to material, such as concrete or refractory bricks, chipboard, concrete slabs, fire-retarding panels, sound proofing panels, moulded plastics panels, corrosion resistant panels, refractory materials, heat insulating materials, electrical insulation materials, sound insulation materials, refractory moulding sand, emery paste, in which the refractory composition is incorporated in or applied to the material, the composition comprising an aggregate, at least 7% by weight of hydraulic cement, and, as a filler material, from 20 to 50%buy weight of silicon dioxide of which at least 82% is amorphous, not more than 18% is crystalline quartz, which has a bulk weight within the range 0.25 to 0.50 gram per millilitre, and of which at least 95 % has a grain size below 50 microns.

Conveniently, the filler material is obtained as a by-product produced in the electro-thermic production of ferro-silicon and/or silicon, such as an electro-thermic process operating within a temperature of 1500 to 3000"C. The basic constituent of this substance is a fine, dust-like xray-amorphous sio2 (approximately 82 to 95 Wo) some at least of which may have been produced by direct sublimation from the vapour to the solid phase, with a small amount of crystalline quartz (approximately 5 to 18%).

X-ray examination has shown that with the exception of the comparatively small quartz content this dust or powder may be classified as being x-ray amorphous. In addition, the filler material may contain small amounts of oxides of iron and/or calcium and magnesium, and carbon.

The incorporation of the silicon dioxide as a filler material in a refractory composition according to this invention not only contributes substantially to an improvement in the heat resistance, particularly fire resistance of the refractory composition, but surprisingly contributes to an improvement in other physical properties, such as mechanical abrasion strength, resistance to temperature changes, thermal insulation, sound insulation, electrical insulation properties, and improvements in the workability of masses, compositions or mixtures, in particular building mixtures.

In particular. a refractory composition according to this invention is well suited for use as or in a fire-inhibiting or fire-resistant material or mass, in particular a mixture or composition capable of being sprayed or tamped down for building purposes.

Fire-inhibiting refractory materials, which according to current custom and knowledge in the art consist of a mixture of cement and asbestos fibres, are, for example, sprayed on steel girders to protect these against the action of fire. Whilst these conventional refractory materials certainly ensure the required fire protection, they are nevertheless very expensive.

Thus, by the use of this invention, a refractory composition having better fire protection may be obtained in a less expensive manner. Such a material has a high thermal insulation value which is, at least partly, due to the low density of the filler material, and over and above this it also has great resistance to mechanical abrasion.

It is possible to improve or to further improve the various properties of the refractory composition by adding other materials, either by utilising such other materials as aggregate, or by including such other materials in the composition in conjunction with aggregate. For example, the thermal insulation value thereof may be improved by the use of glass- or mineral- wool waste. Conveniently such materials are obtained from the by-products or waste materials produced in the manufacture of insulating matting.

It is also possible to improve the adhesion properties and the strength/density ratio, bu utilising, in the preparation of the refractory composition, wetting and/or flocculating agents and/or materials of a similar kind.

Where the filler material is in the form of the dust-like products emitted in the electrothermic manufacture of ferro-silicon, chemical and physical reactions with other components of the refractory composition are considerably enhanced and shrinkage, with resulting crack formation under heat, is minimised, the filler material having the effect of improving the thermal characteristics of the refractory composition with increasing temperature exposure.

It is also possible to include further additives with fire-inhibiting properties to the mixture of mass, such as calcium sulphate, advantageously in the form of waste products occurring in the desulphurization of flue or smoke gases and containing predominantly or exclusively CaSO4.

The refractory composition according to this invention may be used in the preparation of a sprayable or a tampable mass for use in the building industry generally, particularly in pre-stressed concrete buildings, for insulating and protecting steel girders. Such material may also be used in, e.g. steelworks, coke-ovens and foundries.

EXAMPLE I A refractory composition according to this invention was experimentally tested. For this purpose a sectional steel girder (profile HEB 220 , 3.600 mm long with foot plates welded to top and bottom thereof was subjected to a load of 133 t, after a protective layer had been applied to the girder of a fire-proofing refractory composition, comprising mineral wool as aggregate, portland cement and the silicon dioxide filler material, according to the invention, in a layer which was 23 mm thick, and the girder was then exposed, over a length of 3.100 mm, to temperatures rising from 8"C to approximately 980"C in the course of 1.5 hours. The girder showed no reduction in its load bearing capacity.The protective layer shrank in the course of the testing time to an average thickness of 16 Comparative tests were carried out with commercially available conventional asbestos-bearing spray-materials. For achieving fire protection corresponding to class F 90, it was necessary to use 10 kg/m2 of the conventional refractory composition containing asbestos, but only 7kg/m2 were required with the same result of the refractory composition according to this invention.

Specifically, the refractory composition which was used contained by weight approximately 60% mineral wool, 20% cement, and 20 % of the silicon dioxide filler material. The mixture was prepared with 25 kg dry substance for 15 1. of water with 75 ml of Lensodel, (Registered Trade Mark), a tenside based on ethyleneoxide condensates, included in the mixture. The layer thickness required to meet the demands of fire protection class F 90 for a material containing approximately by weight 60% mineral wool, 20% pearlite and 20% hydraulic cement was approximately 60 mm.Using the refractory composition according to this invention and of the above specified composition only approximately 5 mm layer-thickness was needed, but because such thin layerthickness was needed, but because such thin layers cannot be very evenly applied it was found necessary in actual practice to apply a layer thickness of approximately 15 mm. The constituents of the above mentioned refractory composition of the may be varied within very wide limits depending on the mechanical and thermal demands and it is also possible to add further conventional materials to the mixture, such as, e.g. pearlites which have good heat insulation properties.

Another field of application of this invention is the manufacture of building panels. It is common practice to produce (for example) ceiling panels, partition walls and doors from composition material panels, wherein the basic material may be a chip-board or hardboard material, sprayed with the fireproofing materials or mixtures. However, this type of production is rather expensive.

The same also applies to panels or slabs made of concrete, gypsum or the like if these are to be fire-proofed.

However, by the use of this invention, heat resistance and particularly fire resistance of such building panels is substantially improved if the above described refractory composition is used in a basic mixture for building panels, particularly concrete slabs or panels and chipboard panels, or subsequently sprayed onto the article.

Advantageously such a panel may consist of a flame-proof fabric of plastic or wire reinforced with a sealing layer of paper or thin plastics foil and a layering on one or both sides thereof of the above mentioned refractory composition. This provides a considerable simplification in the manufacture of building panels because, e.g. the wire mesh, which is reinforcingly sealed, may be drawn continuously off a roll to be subsequently rolled, sprayed or tamped on one or both sides thereof with the refractory composition. Again the precise ingredients of the refractory may be varied to suit mechanical and thermal demands.

It is also possible to construct a building panel, and especially a fire-proof panel or mat in such a way that it comprises an inner core of compressed mineral and/or glass wool and an adhesive and protective layer of the refractory composition according to this invention, the aggregate comprising granulated or powdered stone.

Advantageously the refractory composition according to this invention may be used to provide protective coatings for refractory bricks.

This invention is also suitable for making refractory compositions in the form of fireproof concrete, which is particularly in demand for high-rise buildings. For achieving economical production without loss of strength in the concrete, the silicon dioxide filler material may be admixed with conventional ingredients of concrete. By an appropriate addition of the silicon dioxide filler material, it is possible to attain fireprotection safety factors of, for example Class F 90, Class F 120 or even Class F 240.

The amount of the silicon dioxide filler material in the concrete is preferably between 20 and 30% by weight. The concrete may also contain further heat-resistant additives including mineral wool. In conventional concretes intended for exposure to very high temperatures, Portland cement is less suitable as hydraulic binding agent, and special binding agents which have so far been commonly employed for the manufacture of the fire-proof concrete have been required.

However, by the use of this invention, it is not necessary to use special binding agents, and hydrualic cement may be retained as binding agent. Experiments have shown that the concrete according to this invention may withstand a temperature of approximately 1200"C for several hours.

The refractory composition in accordance with this invention may further be employed with great advantage in making refractory bricks and high temperature resistant linings for industrial furnaces and for the metallurgical industries. Conventional tamping masses may be mixed with the silicon dioxide filler material in amounts up to approximately 35% by weight, and conventional spray masses up to approximately 50% by weight. These masses show a low degree of potential shrinkage and a low starting point for sinter reaction, but a high degree of fire resistance, strong adhesion to their background, high surface hardness and good elas ticity.For example, a refractory composition comprising by weight 30% refractory clay (grain size 80%between 0 and 0.5 mm), 30% sand (0 to 0.5 mm) 10% alumina flux cement and 30 % of the silicon dioxide filler material, to which 20% by weight of water is added, is extremely suitable for spray application in repair work to the interior lining of coke ovens. In coke ovens, owing to the high temperature gradient of approximately 800"C in the vicinity of the door up to about 1,200 C in the middle of the firing chamber, it has hitherto been necessary to employ several differently constituted repair mixtures which were adapted to these different temperature zones. However, the above specified refractory composition may be successfully used in every region of the coke oven walls.

After the mixture has been sprayed on, it may provide a substantially completely fissure-free coating which adheres firmly to the wall and shows very good mechanical strength and durability.

A special advantage arises from the fact that when the refractory composition according to this invention is used as or in refractory and high temperature resistant materials it is no longer necessary to add alkalies. Previously conventional refractory and high temperature resistant masses have required an addition of alkalies, i.e. sodium silicate, to ensure adequate adhesion of the mass to the refractory bricks. However, this means that one has to accept a lower mollification point and damage to the bricks.

EXAMPLE II A tamping mass for use in the repair of coke oven doors may by the use of this invention comprise by weight 15% alumina cement and 20% of the silicon dioxide filler material. Such a tamping mass has a temperature resistance of 1,100 C.

EXAMPLE III A tamping mass suitable for use in foundries comprises by weight 66% sand (granulation 0-0.4 mm). 5% chamotte A, 7% Portland cement 45 " and 22% of the silicon dioxide filler material. This tamping mass has temperature resistance up to 1,550"C.

In all of the above mentioned cases, where control tests were carried out using extremely finely ground crystalline silicon dioxide. it was found impossible to obtain similarly good results to those achieved when using the refractory composition of this invention comprising predominantly amorphous, dust-like silicon dioxide.

No claim is made herein to compositions which include a substantial quantity of sodium silicate.

SUBJECT TO THE ABOVE DIS

Claims

CLAIMER WHAT WE CLAIM IS:

1. A refractory composition comprising an aggregate, at least 7% by weight of hydraulic cement, and, as a filler material, from 20 to 50% by weight silicon dioxide of which at least 82% is amorphous, not more than 18% is crystalline quartz, which has a bulk weight within the range 0.25 to 0.50 gram per millilitre and of which at least 45% has a grain size below 50 microns.

2. A refractory composition according to Claim 1 comprising a wetting or flocculating agent.

3. A refractory composition according to one of Claims 1 and 2 comprising calcium sulphate.

4. A refractory composition according to any one of the preceding claims comprising glass wool.

5. A refractory composition according to any one of the preceding claims comprising mineral wool.

6. A refractory composition according to any one of the preceding claims comprising fired and crushed clay.

7. A refractory composition according to any one of the preceding claims comprising pearlites.

8. A refractory composition according to one of the preceding claims comprising refractory clay.

9. A refractory composition according to any one of the preceding claims comprising between 20% and 30% by weight of said silicon dioxide.

10. A refractory composition according to any one of the preceding claims comprising between 10% and 20% by weight of hydraulic cement.

11. A refractory composition according to any one of the preceding claims comprising between 15 %and 66%by weight of sand.

12. A refractory composition according to Claim 1, comprising approximately 15% by weight of sand, approximately 50% by weight of Chamotte B, approximately 15% by weight of hydraulic cement, and approximately 20%by weight of said silicon dioxide.

13. A refractory compostion according to Claim 1 comprising approximately 66%by weight of sand, approximately 5% by weight of Chamotte A, approximately 7 % by weight of hydraulic cement, and approximately 22% by weight of said silicon dioxide.

14. A refractory composition according to Claim 1, wherein the composition is capable of being sprayed.

15. A refractory composition according to Claim 1, wherein the composition is capable of being tamped.

16. A refractory composition according to any one of the preceding claims wherein not more then 95% by weight of said silicon dioxide is amorphous, and at least 5% by weight is crystalline quartz.

17. A method of improving the fire and/or heat resistance of an article, the method comprising the step of applying to the article a coating of a refractory composition according to Claim 1.

18. A method according to Claim 17 wherein the article is a refractory brick.

19. A method according to Claim 17 wherein the article is a wall of an industrial furnace.

20. A method according to Claim 17 wherein the article is a wall of a metallurgical vessel.

21. A method according to Claim 17 wherein the article is a steel girder.

22. A method according to any one of Claims 17 to 21 wherein the refractory composition is sprayed onto the article.

23. A method according to Claim 17 wherein the composition comprises between land 20%by weight of hydraulic cement.

24. A method according to one of Claims 17 to 23 wherein the composition comprises between 20% and 30% by weight of said silicon dioxide.

25. A method according to any one of Claims 17, 22, 23 and 24 in which water is added to the refractory composition in an amount of approximately 15 litres of water to 25 kilograms of the refractory composition, approximately 75 millilitres of a tenside being incorporated in the mixture.

26. A refractory composition suitable for imparting fire, flame and heat resistance to material, such as concrete or refractory bricks, chip board, concrete slabs, fireretarding panels, sound proofing panels, refractory materials, heat insulating materials, electrical insulation materials, sound insulation materials, refractory moulding sand, emery paste, in which the refractory composition is incorporated in or applied to the material, the composition comprising an aggregate, at least 7% by weight of hydraulic cement, and, as a filler material, from 20 to 50% by weight silicon dioxide, of which at least 82% is amorphous. not more than 18% is crystalline quartz, which has a bulk weight within the range 0.25 to 0.50 gram per millilitre, and of which at least 95% has a grain size below 50 microns.

27. A refractory composition according to Claim 26 comprising between 20% and 30% by weight of said silicon dioxide.

28. A refractory composition according to one of Claims 26 and 27 comprising between 10% and 20% by weight of hydraulic cement.

29. A refractory composition according to any of Claims 26 to 28 comprising between 15% and 66% by weight of sand.

30. A refractory composition according to any one of Claims 26 to 29 wherein not more than 95%by weight of said silicon diox ide is amorphous. and at least 5 C/o by weight is crystalline quartz.

31. A refractory composition according to Claim 1, substantially as hereinbefore described.

32. A method according to Claim 17, when carried out substantially as hereinbefore described.