Patent Grant
7823417
The present invention is generally directed to a method of manufacturing continuous glass fibers for use in high-strength applications and fibers made thereby.
The most common glass composition for making continuous glass fiber strands is “E-Glass.” The liquidus temperature of E-Glass is approximately 2100° F. (1149° C.) or lower. One advantage of E-Glass is that its liquidus temperature allows operating temperatures for producing glass fibers to be approximately 1900° F. to 2400° F. (1038° C. to 1316° C.). The ASTM classification for E-glass fiber yarns used in printed circuit boards and aerospace applications defines the composition to be 52 to 56 weight % SiO2, 16 to 25 weight % CaO, 12 to 16 weight % Al2O3, 5 to 10 weight % B2O3, 0 to 5 weight % MgO, 0 to 2 weight % Na2O and K2O, 0 to 0.8 weight % TiO2, 0.05 to 0.4 weight % Fe2O3 and 0 to 1.0 weight % Fluorine.
Boron-free fibers are sold under the trademark ADVANTEX (Owens Corning, Toledo, Ohio, USA). Boron-Free fibers, such as are disclosed in U.S. Pat. No. 5,789,329, incorporated herein by reference in its entirety, offer a significant improvement in operating temperatures over boron-containing E-glass. Boron-Free glass fibers fall under the ASTM definition for E-glass fibers for use in general-use applications.
S-Glass is a family of glasses composed primarily of the oxides of magnesium, aluminum, and silicon with a chemical composition that produces glass fibers having a higher mechanical strength than E-Glass fibers. The composition for forming S-Glass includes approximately 65 weight % SiO2, 25 weight % Al2O3, and 10 weight % MgO. S-glass has a composition that was originally designed to be used in high-strength applications such as ballistic armor.
R-Glass is a family of glasses that are composed primarily of the oxides of silicon, aluminum, magnesium, and calcium with a chemical composition that produces glass fibers with a higher mechanical strength than E-Glass fibers. R-Glass has a composition that contains approximately 58-60 weight % SiO2, 23.5-25.5 weight % Al2O3, 14-17 weight % CaO plus MgO, 0% B2O3, 0% F2 and less than 2 weight % miscellaneous components. R-Glass contains more alumina and silica than E-Glass and requires higher melting and processing temperatures during fiber forming. Typically, the melting and processing temperatures for R-Glass are at least 160° C. higher than those for E-Glass. This increase in processing temperature requires the use of a high-cost platinum-lined melter. In addition, the close proximity of the liquidus temperature to the forming temperature in R-Glass requires that the glass be fiberized at a viscosity lower than E-Glass, which is customarily fiberized at or near 1000 poise. Fiberizing R-Glass at the customary 1000 poise viscosity would likely result in glass devitrification, which causes process interruptions and reduced productivity.
Tables IA-IE set forth the compositions for a number of conventional high-strength glass compositions.
R-Glass and S-Glass are produced by melting the constituents of the compositions in a platinum-lined melting container. The costs of forming R-Glass and S-Glass fibers are dramatically higher than E-Glass fibers due to the cost of producing the fibers in such melters. Thus, there is a need in the art for methods of forming glass compositions useful in the formation of high performance glass fibers from a direct-melt process in a refractory-lined furnace and fibers formed by the method.
The invention, in part, is a method of manufacturing a glass composition for the formation of continuous glass fibers that are suitable for use in high-strength applications. The composition useful in the present invention may be inexpensively formed into glass fibers using low-cost, direct melting in refractory-lined furnaces due to the relatively low fiberizing temperature of the glass fibers. Once formed into fibers, the glass composition provides the strength characteristics of higher-priced glass fibers such as S-Glass. The composition of the present invention includes about 60.5 to about 70.5 weight % SiO2, about 10.0 to about 24.5 weight % Al2O3, about 6.0 to about 20.0 weight % RO, where RO equals the sum of MgO, CaO, SrO and BaO, and about 0.0 to about 3.0 weight % alkali metal oxides. In a preferred embodiment, the glass composition is composed of about 61 to about 68 weight % SiO2, about 15 to about 19 weight % Al2O3, about 15 to about 20 weight % RO, where RO equals the sum of MgO, CaO, SrO and BaO, and about 0 to about 3 weight % alkali metal oxides. The composition preferably does not contain more than about 4 weight % of oxides or halogens selected from the group consisting of ZnO, SO3, Fluorine, B2O3, TiO2, ZrO2 and Fe2O3. The desired properties of the high performance composite fibers manufactured by the present invention include a fiberizing temperature of less than about 2650° F. and a liquidus temperature that is preferably below the fiberizing temperature by at least about 80° F., more preferably by at least about 120° F., and most preferably by at least about 150° F.
The present invention includes a process for producing refined glass from a raw glass batch in a refractory lined glass melter. The process includes charging a raw glass batch to a melting zone of a glass melter, melts the raw glass batch within the melting zone and forming fibers from the melt. The present invention also includes fibers formed by such a method
Fiberizing properties of the glass composition used to form the glass fibers utilized in the method of the present invention include the fiberizing temperature, the liquidus, and delta-T. The fiberizing temperature is defined as the temperature that corresponds to a viscosity of about 1000 Poise. As discussed in more detail below, a lowered fiberizing temperature reduces the production cost of the fibers, allows for a longer bushing life, increases throughput, permits the glass to be melted in a refractory-lined melter, and reduces energy usage. For example, at a lower fiberizing temperature, a bushing operates at a cooler temperature and does not “sag” as quickly. Sag is a phenomenon that occurs in bushings that are held at an elevated temperature for extended periods of time. By lowering the fiberizing temperature, the sag rate of the bushing may be reduced and the bushing life can be increased. In addition, a lower fiberizing temperature allows for a higher throughput since more glass can be melted in a given period at a given energy input. As a result, production cost is reduced. In addition, a lower fiberizing temperature will also permit glass formed with the inventive composition to be melted in a refractory-lined melter since both its melting and fiberizing temperatures are below the upper use temperatures of many commercially available refractories.
The liquidus is defined as the highest temperature at which equilibrium exists between liquid glass and its primary crystalline phase. At all temperatures above the liquidus, the glass is free from crystals in its primary phase. At temperatures below the liquidus, crystals may form.
Another fiberizing property is delta-T (ΔT), which is defined as the difference between the fiberizing temperature and the liquidus. A larger ΔT offers a greater degree of flexibility during the formation of the glass fibers and helps to inhibit devitrification of the glass (that is, the formation of crystals within the melt) during melting and fiberizing. Increasing the ΔT also reduces the production cost of the glass fibers by allowing for a greater bushing life and by providing a wider process window for forming fibers.
The glasses of the present invention are suitable for melting in traditional commercially available refractory-lined glass melters which are widely used in the manufacture of glass reinforcement fibers. Starting batch components typically include SiO2 (ground silica sand), and Al2O3 (calcined alumina), as well as chain modifiers from source materials such as MgCO3 (magnesite), CaCO3 (limestone), SrCO3 (strontianite), BaCO3 (witherite), ZrSiO4 (zircon), and Na2CO3 (natrite).
The method of the present invention is preferably performed using the glass melting furnace 10, which includes an elongated channel having an upstream end wall 14a, a downstream end wall 16, side walls 18, a floor 20, and a roof 22. Each of the components of the glass melting furnace 10 are made from appropriate refractory materials such as alumina, chromic oxide, silica, alumina-silica, zircon, zirconia-alumina-silica, or similar oxide-based refractory materials. The roof 22 is shown generally as having an arcuate shape transverse to the longitudinal axis of the composition the channel; however, the roof may have any suitable design. The roof 22 is typically positioned between about 3-10 feet above the surface of the glass batch composition 30. The glass batch material 30 is a mixture of raw materials used in the manufacture of glass in the accordance with the present invention. The glass melting furnace 10 may optionally include one more bubblers 24 and/or electrical boost electrodes (not shown). The bubblers 24 and/or electrical boost electrodes increase the temperature of the bulk glass and increase the molten glass circulation under the batch cover.
In addition, the glass melting furnace 10 may include two successive zones, an upstream melting zone 26 and a downstream refining zone 28. In the melting zone 26, the glass batch composition 30 may be charged into the furnace using a charging device 32 of a type well-known in the art.
In one suitable melter configuration, the glass batch material 30 forms a batch layer of solid particles on the surface of the molten glass in the melting zone 26 of the glass melting furnace 10. The floating solid batch particles of the glass batch composition 30 are at least partially melted by at least one burner 34 having a controlled flame shape and length mounted within the roof 22 of the glass melting furnace 10.
In one preferred embodiment, as shown in
Other conventional melters may be used without departing from the present invention. Conventional melters include Air-Gas melters, Oxygen-Gas melters, electrically fired melters, or any fossil fuel fired melter. It is possible to add electric boost or bubblers to any of the melting processes. It is also possible to include a separate refining zone (as shown in
As shown in
The tip plate 124 contains a plurality of nozzles 124a (also referred to herein as orifices) through which a plurality of streams of molten glass may be discharged. The streams of molten material may be mechanically drawn from the tip plate 124 to form continuous filaments 125 via a conventional winder device 400. The filaments 125 may be gathered into a single continuous strand 125a after having received a protective coating of a sizing composition from a sizing applicator 410. The continuous filaments 125a may be wound onto a rotating collet 402 of the winder device 400 to form a package 125b. The continuous filaments 125 may also be processed into other desired composite glass materials including, without limitation, wet used chopped strand fibers, dry use chopped strand fibers, continuous filament mats, chopped strand mats, wet formed mats or air laid mats.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples illustrated below which are provided for purposes of illustration only and are not intended to be all inclusive or limiting unless otherwise specified.
The glasses in the examples listed in Tables IIA-IIC were melted in platinum crucibles or in a continuous platinum-lined melter for determining the mechanical and physical properties of the glass and fibers produced therefrom. The units of measurement for the physical properties are: Viscosity (° F.), Liquidus temperature (° F.) and ΔT (° F.). In some examples the glasses were fiberized and Strength (KPsi), Density (g/cc), Modulus (MPsi), Softening Point (° F.) and coefficient of thermal expansion (CTE) (in/in/(° F.)) were measured.
The fiberizing temperature was measured using a rotating spindle viscometer. The fiberizing viscosity is defined as 1000 Poise. The liquidus was measured by placing a platinum container filled with glass in a thermal gradient furnace for 16 hours. The greatest temperature at which crystals were present was considered the liquidus temperature. The modulus was measured using the sonic technique on a single fiber of glass. The tensile strength was measured on a pristine single fiber. The CTE was measured with a dilatometer over the range of temperature from 25 to 600 degrees C. The softening point temperature was measured using the ASTM C338 fiber-elongation method.
As is understood in the art, the above exemplary inventive compositions do not always total 100% of the listed components due to statistical conventions (such as, rounding and averaging) and the fact that some compositions may include impurities that are not listed. Of course, the actual amounts of all components, including any impurities, in a composition always total 100%. Furthermore, it should be understood that where small quantities of components are specified in the compositions, for example, quantities on the order of about 0.05 weight percent or less, those components may be present in the form of trace impurities present in the raw materials, rather than intentionally added.
Additionally, components may be added to the batch composition, for example, to facilitate processing, that are later eliminated, thereby forming a glass composition that is essentially free of such components. Thus, for instance, minute quantities of components such as fluorine and sulfate may be present as trace impurities in the raw materials providing the silica, calcia, alumina, and magnesia components in commercial practice of the invention or they may be processing aids that are essentially removed during manufacture.
As apparent from the above examples, glass fiber compositions of the invention have advantageous properties, such as low fiberizing temperatures and wide differences between the liquidus temperatures and the fiberizing temperatures (high ΔT values). Other advantages and obvious modifications of the invention will be apparent to the artisan from the above description and further through practice of the invention). The high-performance glass of the present invention melts and refines at relatively low temperatures, has a workable viscosity over a wide range of relatively low temperatures, and a low liquidus temperature range.
The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. Other advantages and obvious modifications of the invention will be apparent to the artisan from the above description and further through practice of the invention. The invention is not otherwise limited, except for the recitation of the claims set forth below.
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