GB2152026A - Method of producing temperature-resistant rock fibres - Google Patents

Abstract

The invention relates to a method of producing inorganic fibre products for heat insulating purposes, usable up to limit usage temperatures (LUT) of at least 750 DEG C up to approx. a maximum of 900 DEG C or as a substitute for asbestos in specific asbestos-containing products, preferably with a thermal loading. According to the invention, the high temperature resistance of this fibre product is achieved in that to produce the melt and the fibres to be produced therefrom, raw materials are used which contain the mineral "chlorite". Such fibres guarantee an extremely high dispersion of Fe<2+> and Fe<3+> ions in the melt and in the fibreglass.

Description

SPECIFICATION Method of producing temperature-resistant rock fibres.

The invention relates to a method of producing inorganic fibre products for heat insulating purposes, usable up to limit usage temperatures (LUT) of at least 750 up to a maximum of approx. 900"C, depending upon their formulation, the method of incorporation and their complex thermal/chemical/mechanical loading during their journey through the furnace or for substitution of asbestos in certain asbestos-containing products, preferably with a thermal loading.

For energy-intensive heating installations of all kinds, not only conventional heavy fireproof structural and heat insulating materials are used for highly effective modern partial or whole fibre linings. The following fibre products are being used to an increasing extent: - Fire resistant fibres of various types with a LUT of 11 000C which find only limited application by reason by reason of their high price, i.e., on the fireside.

- Mineral or slag or rock fibres which are produced inexpensively as mass fibres and which, by virtue of their inadequate qualities (fluctuating material content, heterogeneous microstructure and unfavourable sinter/crystallisation behaviour of the glass fibre) can only be used up to an LUT of approx. 200 to a maximum of approx. 550do.

By reason of the lack of keenly priced fibre insulating materials for the mid-range temperatures, modern whole fibre linings have been hitherto indicated as a combination of fire resistant fibres and mineral wool with a maximum LUT of approx. 550"C, which made it necessary increasingly to use very expensive fireproof fibre products also for the mid-range temperatures, for example up to shift limit temperatures of approx.

550 C. For economic reasons, the endeavour is therefore to develop favourable fibre products for mid-range temperatures up to approx. 800"C LUT in order to reduce the use of expensive fireproof fibre products or so as to be able to use combinations of fire insulants: fireproof fibres/temperature resistant rock fibres with an LUT of approx. 800 C/mineral wool and to reduce the lining costs with extensive application of the most modern highly-effective whole fibre linings to economically justifiable proportions.

- Rock fibres with an LUT of approx. 800"C At the present time, only a few fibre products are internationally known for the aforesaid mid-range temperatures, and they are in most cases produced from conventional fusible raw materials and conventional method of producing mass fibres for sound and heat insulating purposes.

The causes for the relatively favourable temperature resistance of few of these fibre products arise presumably from the lower FeO and higher CaO+ MgO or A1203 contents and/or a more homogeneous glass fibre with relatively favourable microstructure. The present level of knowledge is insufficient.

An object of the invention is to produce at a favourable cost inorganic fibre products which are temperature resistant up to approx. 800"C LUT when installed behind fireproof structural or heat insulating materials or in direct contact with the hot gases from heating installations of all kinds, i.e., do not show any unjustifiable sintering or softening and no disintegration due to thermal ageing or oxidation of the FeO or due to unsuitable crystallisation of the glass fibre. This means that under continual use, form and existing fibre structure of the heat insulating material must be largely retained so that there is no deterioration of the properties of use, particularly of the heat insulation properties.

The use of loose fibres directly for plugging or spray-on insulation without further preparation is possible.

For use as panels, mats or modules, appropriate preparation using suitable binders and using known methods will be required. Furthermore, it is an object of the invention to replace asbestos in certain asbestos-containing products with preferably a thermal loading up to approx. 800"C but also with combined thermal/chemical/mechanical loading other than in an extremely alkaline matrix, by using the fibres proposed.

According to the invention, the high temperature resistance of this fibre product is achieved in that fusible raw materials containing a high proportion e.g., at least 35% by weight of the mineral 'chlorite' are used for producing the molten batch and the fibres to be manufactured therefrom. According to the batch atmosphere, iron rich rock glasses containing FeO/FeO+Fe2O3 within the proportion limits of about 80% to 20% result.

The product may be made by oxidation fusing of a particulate or dust material containing at least 35% by weight of chlorite and at least 25% of other minerals which may be selected from one or more of the following viz: hornblende, quartz, plagioclase, calcite, pyroxene, fly dust (e.g., cement fly dust), and furnace slag and may include 2 to 10% swellable minerals.

The material may include 5 to 30% furnace slag and/or fly dust e.g., 20%.

The material may blended, formed into pellets and fired under oxidising conditions at a temperature of 1250-1550"C e.g., 1 430"C. The material preferably has a proportion of iron oxide of 5 to 20% preferably 10 to 15% and the ratio of FeOto FeO+Fe2O3 may be 20-80% FeOto80-20% FeO+Fe2O3 preferably 20 to 50% FeO to 80to 50% FeO+Fe2O3. The material may contain 30-45%SiO2, 10-20%A12O3, 10to 20% Fe2O, 5-15% CaO, 3 to 12% MgO, and up to 20% other refractive materials.

The structure of the chlorite materials involve three-layer packages (talc or pyrophyllite layers) including octahedral layers (brucite or hydrargillite). To a great extent, the chlorites form series of isomorphous mixtures and in the brucite layer part of the Hg is replaced above all by Fe2+ (and Al) while in the pyrophyllite layers a part of the Al is replaced by Fe and Mg isomorphous. The suggested chlorite-containing raw materials consequently guarantee an extremely high dispersion of the Fe2+ and Foe3+ ions in the batch and in conjunction with a suitable oxidising fusion regime also an optimum ratio of Fe2+/Fe3+.The statistical distribution and co-ordination of the abovementioned ions in the chlorite-containing raw materials, in the molten batch and in the fibreglass, which is so extremely favourable for nucleation extend presumably through mixed crystals (spinels) as an intermediate stage, upon re-heating of the fibres produced, to a regular and extremely finevolume crystallisation which starts early, even prior to commencement of sintering. This results in a blocking of and delay in fibre sintering and, inter alia, through the stiffening effect of the crystal reinforcement, the desired increase in temperature resistance of the fibre products.The result is formation of ultra-fine crystals with diameters in the millimetre range which is particularly important since larger crystal diameters in the micromillimetre range would destroy the fibres of a few micromillimetre range.

It has been found that the above-mentioned regular and extremely fine volume crystallisation in the nm range occurs only if the fibreglass has a high concentration of nuclei (speed of nucleation), which could only be achieved with the more highly chlorine-containing raw materials.

It has furthermore been found that an FeO/FeO+Fe203 ratio of 20 to 50% in the fibreglass leads to optimum crystallisation in the sense referred to above i.e., to a particularly high concentration of nuclei or nucleation rate and to particularly small crystals. This always results in a strinkingly gentle loading on the fibreglass during re-heating or during oxidation of the FeO into Fe2O3. The optimum crystallisation explained always occurred with a neutral to oxidising melt. It was also found that under these fusion conditions thermal ageing never occurred, the said thermal ageing, as mentioned above, possibly contributing to a crumbling of the fibre products at temperatures as low as within the range of approx. 200 to 5000C.

By reason of the considerable differences in hardness in the minerals occurring in diabase rocks, the crushing process produces in the fine grain (crushed sand) and quite particularly in the ultra-fine grain or dust which occurs in dust removal plants handling crushed diabase products, to a considerable enrichment of the low hardness minerals, particularly chlorite with a hardness of approx. 2.5 and on the other hand to a rigorous reduction in the minerals of greater hardness such as quartz, feldspar and the like. Crushing sand and in particular dusts have a mineral structure which is not only fundametally different in quality and quantity compared with diabase rocks, but in comparison with these they are also characterised by far less fluctuation in mineral contents - particularly chlorite.On the other hand, with diabase rocks - substantially of the size of crushed rock - from the most widely diverse deposits, considerable fluctuations in mineral content must be anticipated.

Preparation of dusts (approx. 70% = 0.063 mm) additionally promotes the creation of an extremely homogeneous fibreglass and optimum crystallisation during re-heating, which may well explain the always maximum test results from fibres produced preferably from dusts.

From the foregoing, it can be deduced that the higher chlorite contents of the diabase dusts proposed according to the invention and also the nuclear fineness and consistency of the diabase dusts which are preferably used will, in conjunction with a prescribed fusion process for the production of optimum FeO/FeO+ Fe2O3 proportions and an extremely fine volume crystallisation in the nm range provide the most important basis and prerequisites for the industrially exploitable principle of action in the production of temperature resistant rock fibres.

Example Diabase dust (granulation: 90% smaller than 0.063 mm) with a chemical composition of SiO2 38.2% Al2O3 14.2% Fe2O3ges 14.5% TiO2 3.7% CaO 8.5% MgO 7.5% K2O+Na2O 2.9% MnO 0.2% S as SO3 0.4% GV 8.4% and with a mineral content of chlorite approx. 40 - 45% hornblende approx. 5% quartz 5% plagioclase approx. 10-15% calcite 5% swellable minerals 5% pyroxene 10% and foamed blast-furnace slag with a composition of approx. 38% SiO2, 9.3% Al2O3, 0.5% FeO3ges, 37.3% CaO, 8.6% MgO and 1.8% Na2O+K2O in a ratio of 80/20% is blended and made into pellets. The pellets, with a diameter of 15 to 35 mm, were oxidisingly melted in a cupola furnace at temperatures of approx. 1430 C. The fibre products (mean fibre diameter approx. to 5 um) produced from the melt by a blowing process had the following chemical composition: SiO2 40.9% Al203 14.7% FeO 5.3% Fe2O3 8.3% CaO 18.2% MgO 6.8% K2C+Na2O 3.3% MnO 0.2% TiO2 3.0% SasSO3 0.1% Laboratory and industrial long-term testing proved that the fibre products (loose fibres and panels) produced according to the invention were resistant to temperatures up to approx. 800 to 850 C.

Claims (14)

1. A method of producing refractory fibres for application temperatures of at least 750"C up to approximately a maximum of 900"C characterised in that they are produced by fusing a chlorite-containing raw material having a high proportion of chlorite e.g., at least 35% the proportions of iron oxide being between 5 and 20% percentages by weight.

2. A method as claimed in Claim 1, wherein the chlorite content is 40-45% by weight.

3. A method as claimed in Claim 1 or 2, wherein the iron oxide content is 10 to 15% by weight.

4. A method as claimed in Claim 1,2 or 3, wherein the raw material includes at least 25% of materials selected from the following viz: hornblende, quartz, plagioclase, calcite, pyroxene, fly dust and furnace slag.

5. A method as claimed in Claim 4, wherein the raw material includes 5 to 30% furnace slag and/or fly dust.

6. A method as claimed in any of the preceding claims wherein the raw materials include 2-10% of swellable minerals.

7. A method as claimed in any of the preceding claims wherein the fibres contain a ratio of FeO to FeO+F203 of 1 :4to 4:1.

8. A method as claimed in any of Claims 1-6 wherein the fibres contain a ratio of FeO to FeO+Fe2O3of 1:4to 1:1.

9. A method as claimed in any of Claims 1 to 6, wherein the raw materials contain 30-45% of SiO2, 10-20% Al2O3, 10 to 20% Fe2O3, 5-15% CaO, 3 to 12% MgO and up to 20% other refractory materials.

10. A method as claimed in any of the preceding Claims wherein the raw materials are fused in an electric arc furnace.

11. A method as claimed in any of the preceding Claims 1 to 9, wherein the raw materials are fused in a cupola or shaft cupola furnace.

12. A method of producing refractory fibres according to any of the preceding Claims, wherein the raw material is pelletised or briquetted prior to fusion.

13. A method of producing refractory fibres substantially as described.

14. A method of producing refractory fibres substantially in accordance with the example.