MINERAL FIBRES

Abstract: The invention relates to high-temperature resistant mineral fibres having the following composition: SiO2: 34-42 % by weight; Al2O3: 31-38 by weight; TiO2: 0-1 by weight; FeO: 2.5-7.5 by weight; CaO: 17-21 by weight; MgO: 0.5-4.3 by weight; Na2O: 0.3-1.5 by weight; K2O: 0.1-2.3 by weight.

Description: Mineral fibres The present invention relates to mineral fibres which are resistant at high temperatures, and in particular high-temperature resistant mineral fibres for use in thermal insulation, e.g. in energy inten¬ sive furnaces. Fireproof ceramic fibres are known which consist substantially of a major amount of Si0 2 and A1 2 0, and optionally a minor amount of a 0 further component and which has a maximum temperature of use (MTU) of about 1500 β C or more, cf. US patent specifications Nos. 4,240,833, 2,674,539 and 2,710,261, DE laid open patent applications Nos. 1,075,295 and 1,596,842 and NO laid open patent application No. 145,467. Such fibres are manufactured from a melt composed of a 5 mixture of Si0« and AIJ- , and since this mixture does not melt until at a temperature of 1600-1900 C C, the formation of the melt requires an electric furnace whereby the costs associated with the manufacture of said fibres become relatively high. 0 Mineral fibres is another kind of fibres and they consist of a mixture of the following oxides: Si0 2 , A O,, FeO or Fe 2 0-, CaO, MgO and R O wherein R is Na and K. Examples of such mineral fibres are rock wool fibres which typically have an MTU of up to 750 β C and ~ -^-^Ju£h__ ay~ be_manufactured at relatively low costs in coke heated 5 shaft furnaces. There is a need to provide low-cost mineral fibres having a somewhat higher MTU than ordinary rock wool fibres, viz. having an MTU of up to 850°C. 0 DK patent application No. 5453/87 discloses inorganic fibres having an MTU of up to 815°C and having the following composition: Si0 2 : 55-64 % by weight 5 A1 2 0 3 : 0-10 CaO: 29-44 MgO: 0.1-30 - Also SE patent application No. 8406571-3 describes inorganic fibres having a higher MTU than that of ordinary rock wool fibres, viz. an MTU of up to 800°C. These known fibres are manufactured from a chlorite-containing raw material which contains chlorite in an amount of more than 35%, preferably 40-45%, and has an iron oxide content of between 5 and 20%, preferably between 10 and 15%. The known fibres which may for instance have the following composition: Si0 2 : 40.9% A1 2 0 3 : 14.7% FeO: 5.3% Fe 2 0 3 : 8.3% CaO: 10.2% MgO: 6.8% K 2 0+Na 2 0: 3.3% MnO: 0.2% Ti0 £ : 3.0% suffer from the drawback that the colour of the fibres is very dark due to the relatively high iron oxide content. It is the object of the present invention to provide mineral fibres having an MTU which is substantially higher than the MTU of conventional rock wool fibres and which can be manufactured in conventional which are not This object is obtained with the mineral fibres of the invention, said fibres being characterized in having the following composition: This composition is characterized in having a high content of Si0 ? and A1 2 0 3 which provides an increased temperature resistance. The FeO content ensures that a sufficient amount of seed crystal forming agents is present, which is essential to the behaviour of the fibres at temperatures above the crystallization temperature. FeO and CaO reduces the viscosity to a suitable level. The MgO content is kept at a low level as the CaO "content is high; thereby a melting temperature minimum which occurs when the MgO and CaO contents are within the same range is avoided. The improved high-temperature properties obtained with the mineral fibres according to the invention will appear from the drawing which shows the setting of mats made from mineral fibres of the invention (curve A), of conventional rock wool fibres (curve B) and of glass fibres (curve C) as a function of the temperature. As will appear from the drawing the fibre product according to the invention is not only proof against a temperature which is about 100'C higher than that of a corresponding product of rock wool fibres, but the setting is also substantially less (about 30% relative to about 45%) at temperatures above the maximum temperature of use. It is noted that the relevant fibre product according to the invention has the following composition: The following is a particularly preferred composition for the mineral fibres according to the invention: CaO: 18-20 MgO: 1.8-2.7 - Na 2 0: 0.4-0.6 - K 2 0: 1.5-2.1 - The mineral fibres of the invention can be manufactured in a coke heated cupola furnace using a charge of e.g. 25 % by weight of lime and 75 % by weight of briquettes. The briquettes are preferably manufactured of kaoline as matrix (60 % by weight) added with bauxite (20 % by weight) to raise the aluminium content, and iron silicate (20 % by weight) to raise the iron content. The kaoline briquettes melt at relatively low temperatures. First the iron silicate melts, then the kaoline, and finally ' this melt dissolves the bauxite. The final melt is formed by further dissolu¬ tion of the lime in the charge whereby a suitable viscosity for the removal from the cupola furnace and the subsequent spinning process is obtained. When the briquettes are melted in a coke heated cupola furnace, 13.7 % by weight of coke is preferably used (relative to the weight of briquettes and lime) and air is supplied through the tuyeres of the furnace at a rate of 80-96 m 3 /min. to obtain a melting temperature of 1565-1605 β C. The melt which is removed through the melt outlet of the furnace may be supplied to a conventional rock wool fibre spinning apparatus and converted to a fibre web therein. The invention will now be described in further detail with reference to the following example. Example A series of fibre samples were manufactured in the process described above. Thereby fibre samples having the following composition were obtained. Sample No. MnO, The fibre samples manufactured were subjected to a heat stability test (AGI Q132, cf. DIN 52271 A81) at a heating rate of 5 c K/mϊn and at a load of 1.0 kN/m 2 . Hereby the following maximum temperatures of use (MTU) were determined: Sample No. MTU 1 >850°C (at a specific weight of 206 kg/m 3 ) 2 818 β C (at a specific weight of 91 kg/m 3 ) 3 815°C (at a specific weight of 120 kg/m 3 ) 4 821°C (at a specific weight of 111 kg/m 3 )

Claims: C 1 a i m s 1. High-temperature resistant mineral fibres, c h a r a c t e r ¬ i z e d in having the following composition: 2. High-temperature resistant mineral fibres according to claim . 1, c h a r a c t e r i z e d in having the following composition:

Inventors: MOGENSEN GURLI, MOGENSEN, GURLI
Applicants: ROCKWOOL INT, ROCKWOOL INTERNATIONAL A/S
Application year: 1991
Main classification: C03C13
IPC codes: C03C13, C04B35