Low alkali, non-crystalline, vitreous silica fillers
View Patent ↗A substantially white powder for use as a filler and/or extender derived from by-products of manufacturing vitreous low alkali, low iron glass fibers, and a method for producing the powder. The filler has very low alkalinity and by virtue of its being essentially free of crystalline silica is non-hazardous to health and therefore safe for consumer-based and industrial-based uses.
1. A filler or pozzolan product produced by a process comprising:
(a) shredding long entangled strands of low alkali and low iron content vitreous glass fibers, said fibers having by weight an alkali content of less than 2%, and an iron content of less than 0.8% and having little or no color, the fibers being shredded into short fibers of less than 5 mm;
(b) adjusting the moisture content of the short fibers;
(c) grinding the short moisture adjusted fibers in an attrition mill; and
(d) fine powder classifying the ground material through a high performance dual-cyclone, dry air classification system to produce a uniform white product having a reflectance value of at least 80 as measured by a Technibrite TB-1C colorimeter according to the ISO 2467, 2471 method, said classification being conducted with precise control over the maximum particle size and particle size distribution so that said product is characterized by a blocky, equi-dimensional particle shape wherein the average aspect ratio of the particles is less than 2:1, and with no residual high aspect ratio fibers, and a P.S.D. such that at least 95% by weight of the particles are of less than 45 microns E.S.D.
2. A filler or pozzolan product in accordance with claim 1 , wherein said shredded and moisture adjusted short fibers are ground in a vertical attrition mill using an energy input of at least 100 kW/hrs/ton of said fibers.
3. A filler or pozzolan product in accordance with claim 1 , wherein the moisture content of said shredded short fibers is adjusted to less than 10% by weight.
4. A filler or pozzolan product in accordance with claim 3 , wherein the moisture content of said shredded short fibers is adjusted to less than 2% by weight.
5. A filler or pozzolan product in accordance with claim 3 , wherein the moisture content of said shredded short fibers is adjusted to 0.5 to 1.0% by weight.
6. A filler or pozzolan product in accordance with claim 1 , wherein said milling and classification is controlled so that the final product contains substantially no particles which are greater than 5 μm in length and less than 3 μm in diameter with an aspect ratio of greater than or equal to 5:1, whereby said product is substantially free of respirable particles.