Man-made vitreous fibres

Abstract

The invention provides a method of manufacture of man-made vitreous fibers (MMVF) comprising: providing a fiberizing apparatus, wherein the fiberizing 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/sand the second and third rotors each rotate to give an acceleration field of at least 125 km/s, providing a mineral melt, wherein the melt has a composition comprising the following, expressed by wt of oxides: SiOin an amount of from 33 to 45 wt %, AlOin an amount of from 16 to 24 wt %, an amount of KO and/or NaO, an amount of CaO and/or MgO, wherein the ratio of the amount of AlOto the amount of SiOis in the range 0.34-0.73, wherein the ratio of the total amount of KO and NaO, 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 fibers are thrown off the rotors; and collecting the fibers that are formed. Man-made vitreous fibers (MMVF) can thus be formed having a median length of 100 to 300 μm, a median diameter of not more than 2.5 μm, and wherein the ratio of the median fiber length to median fiber diameter is 25 to 500.