Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Patent
1997-02-18
1998-08-04
Group, Karl
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
501 38, 501 70, C03C 1306
Patent
active
057893292
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF INVENTION
This invention relates to continuous glass fibers having glass compositions that are boron-free--i.e., essentially free of boron. The glass fibers are useful as reinforcement and textile glass fibers.
BACKGROUND OF INVENTION
The standard glass composition for making continuous glass fiber strands is "E" glass, which dates back to the 1940's. Despite the passing of fifty years, E glass, which is generally described in U.S. Pat. No. 2,334,961, still is the most common glass for making textile and reinforcement glass fibers. The key advantage of E glass is that its liquidus temperature is 200.degree. F. (93.degree. C.) below its forming temperature, the temperature at which the viscosity of the glass is customarily near 1000 poise.
E glass melts and refines at relatively low temperatures. E glass has a workable viscosity over a wide range of relatively low temperatures, a low liquidus temperature range, and a low devitrification rate. Generally, these glass compositions allow operating temperatures for producing glass fibers around 1900.degree. F. to 2400.degree. F. (1038.degree. C. to 1316.degree. C.) where the liquidus temperature is approximately 2100.degree. F. (1149.degree. C.) or lower. Industry typically maintains a fiber-forming temperature around 100.degree. F. (38.degree. C.) greater than the liquidus temperature for continuous fiber production in order to avoid devitrification in the glass delivery system and bushing.
In the mid 1970's, boron- and fluorine-contalning glasses were developed which met these operating conditions. See U.S. Pat. No. 4,026,715. However, boron and fluorine in glass melts are volatile components that contribute significantly to the total emissions evolved from a glass melting operation.
Glass compositions free of boron or fluorine are known, e.g., as disclosed in British Patent Specification No. 520,427. However, known boron- and fluorine-free glass compositions have posed problems.
Such textile glasses as disclosed in British Patent Specification No. 520,427 melt and form at higher temperatures requiring operating conditions which could not be practically met. Devitrification (crystallization) in the bushing or during forming often occurred. For example, British Patent Specification No. 520,247 discloses glass compositions that are substantially alkaline-free containing CaO, MgO, Al.sub.2 O.sub.3, and SiO.sub.2, that may be modified by the addition of B.sub.2 O.sub.3, CaF.sub.2, P.sub.2 O.sub.5, or a small amount of an alkali such as Na.sub.2 O, K.sub.2 O, or lithia. However, only a few of these fiberize, and only the boron-containing glasses fiberize in a continuous fiber process without difficulty. Glass No. 1 on page 2 of the British reference is one of the boron-free glasses which could be fiberized in a continuous fiber process by virtue of its 100.degree. F. (38.degree. C.) difference between its liquidus and forming temperatures, but its forming temperature, at 2350.degree. F. (1288.degree. C.), is too high to be formed according to earlier known processes. The viscosity of Glass No. 2 in the British reference is 1000 poise at a temperature only 87.degree. F. (31.degree. C.) above the liquidus temperature. This probably would result in devitrification during forming in continuous glass fiber production. British Patent No. 520,247 teaches that this glass is preferably for insulating wool glasses, which can be formed with smaller differences between the liquidus and forming temperatures than can continuous fibers. Glass No. 3 is also preferably for insulating wool glasses. The liquidus temperature of Glass No. 3 of the British reference is 52.degree. F. (11.degree. C.) above the forming temperature and would crystallize in the bushing in a continuous fiber operation.
U.S. Pat. No. 4,542,106 to Sproull discloses boron- and fluorine-free glass fiber compositions. In general, they contain 58 to 60 percent SiO.sub.2, 11 to 13 percent Al.sub.2 O.sub.3, 21 to 23 percent CaO, 2 to 4 percent MgO, and 1 to 5 percen
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Eastes Walter L.
Hofmann Douglas A.
Wingert John W.
Eckert Inger H.
Gegenheimer C. Michael
Group Karl
Owens Corning Fiberglas Technology Inc.
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