MAN-MADE VITREOUS FIBRES

The invention provides a method of manufacture of man-made vitreous fibres (MMVF) comprising: providing a fiberising apparatus, wherein the fiberising apparatus comprises: a set of at least three rotors each mounted for rotation about a different substantially horizontal axis; wherein each rotor has a driving means; rotating the rotors; wherein the first rotor rotates to give an acceleration field of from 25 to 60 km/s 2 and the second and third rotors each rotate to give an acceleration field of at least 125 km/s 2 , providing a mineral melt, wherein the melt has a composition comprising the following, expressed by wt of oxides: SiO 2 in an amount of from 33 to 45 wt%, Al 2 O 3 in an amount of from 16 to 24 wt%, an amount of K 2 O and/or Na 2 O, an amount of CaO and/or MgO, wherein the ratio of the amount of Al 2 O 3 to the amount of SiO 2 is in the range 0.34-0.73, wherein the ratio of the total amount of K 2 O and Na 2 O, to the total amount of CaO and MgO, is less than 1; pouring the melt on to the periphery of the first rotor; wherein melt poured on to the periphery of the first rotor in the set is thrown on to the periphery of the subsequent rotors in turn and fibres are thrown off the rotors; and collecting the fibres that are formed. Man-made vitreous fibres (MMVF) can thus be formed having a median length of 100 to 300µm, a median diameter of not more than 2.5µm, and wherein the ratio of the median fibre length to median fibre diameter is 25 to 500.