# Patent

## Title
Method of manufacturing S-glass fibers in a direct melt operation and products formed therefrom

## Abstract

A method of forming high strength glass fibers in a refractory-lined glass melter, products made there from and batch compositions suited for use in the method are disclosed. The glass composition for use in the method of the present invention is up to about 64-75 weight percent SiO2, 16-24 weight percent Al2O3, 8-12 weight percent MgO and 0.25-3 weight percent R2O, where R2O equals the sum of Li2O and Na2O, has a fiberizing temperature less than about 2650° F., and a ΔT of at least 80° F. By using oxide-based refractory-lined furnaces the cost of production of glass fibers is substantially reduced in comparison with the cost of fibers produced using a platinum-lined melting furnace. High strength composite articles including the high strength glass fibers are also disclosed.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation application of U.S. Ser. No. 12/403,955, filed Mar. 13, 2009, titled “METHOD OF MANFACTURING S-GLASS FIBERS IN A DIRECT MELT OPERATION AND PRODUCTS FORMED THERE FROM”, which is a Continuation-in-Part of U.S. patent application Ser. No. 12/341,985, now U.S. Pat. No. 8,338,319, entitled “Composition for High Performance Glass Fibers and Fibers Formed Therewith” filed Dec. 22, 2008, the entire content of which is expressly incorporated herein by reference. This application is also a Continuation-in-Part of U.S. patent application Ser. No. 11/267,702, now U.S. Pat. No. 7,823,417, entitled “Method of Manufacturing High Performance Glass Fibers in a Refractory Lined Melter and Fibers Formed Thereby” filed Nov. 4, 2005, the entire content of which is also expressly incorporated herein by reference. This application is also a Continuation-in-Part of U.S. patent application Ser. No. 11/267,739, now U.S. Pat. No. 7,799,713, entitled “Composition for High Performance Glass, High Performance Glass Fibers and Articles Therefrom” filed Nov. 4, 2005, the entire content of which is also expressly incorporated herein by reference.


TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention is generally directed to a method of manufacturing continuous glass fibers for use in high-strength applications and products made there from, such as ballistic armor, pressure vessels, structural aerospace materials, structural marine materials, and structural materials for wind energy such as windmill masts and blades.
BACKGROUND OF THE INVENTION
Fiberglass reinforced composite materials have been available for use in marine and aerospace materials for some time. Other fiber materials such as carbon and aramid fibers are available for use, although at substantially higher cost. The articles of the present invention may use any known manufacturing method, including compression molding, laminating, spray up, hand laying, prefabricated lay-up (prepreg), compression molding, vacuum bag molding, pressure bag molding, press molding, transfer molding, vacuum assisted resin transfer molding, pultrusion molding, filament winding, casting, autoclave molding, centrifugal casting resin transfer and continuous casting. The properties of the composite are controlled by the fibers and the resin, and synergy between the two, that produces material properties unavailable from the individual materials.
A number of resins are useful in the manufacture of composite articles including polyester resin, vinylester resin and epoxy resin. Polyester resin is suitable for a number of situations. Vinylester resin has lower viscosity precure and more flexible postcure than polyester resin and is typically more resistant to degradation. Epoxy resin is typically transparent when cured. Epoxy resin is a polyether resin formed by the polymerization bisphenol A, bisphenol F, bisphenol C, and compounds of similar structure with epichlorohydrin resulting in the formation of the reactive oxirane linkage. Epoxy resins may react with a variety of curing agents, including amines, anhydrides, mercaptans, polyesters to form an infusable solid. The reaction is a condensation reaction typically does not create by-products. Cured epoxy resins have high strength, and low shrinkage during curing. They are used as coatings, adhesives, castings, composites, or foam. Epoxy resins are also desirable for use in high strength applications as a structural matrix material or as a structural glue. Phenolics are thermosetting resins formed by the condensation of phenol, or of a phenol derivative, with an aldehyde, typically a formaldehyde. Phenolics are used chiefly in the manufacture of paints and plastics. Other specific high strength modulus resins include bismaleimide, poly-amide, vinyl ester phenolic, ethylene-acrylate or methacrylate copolymers, high strength medium modulus thermoplastics such as an ionomer (i.e. crosslinked ethylene-methyl acrylate or methyl methacrylate copolymer), polycarbonate, polyurethane, nylon, aramid, modified epoxies.
The most common high strength glass composition for making continuous glass fiber strands is “S-Glass,” 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. A commonly used member of the S-Glass family is known as S2-Glass. S2-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 typically 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 higher temperature than E-Glass.
Tables IA-IE set forth the compositions for a number of conventional high-strength glass compositions.











TABLE I-A







RUSSIAN






CONTINUOUS



Chinese
ROVING 
NITTOBO
NITTOBO



High
MAGNESIUM
“T”
“T”



Strength
ALUMINO-
Glass Fabric
Glass Fabric


Constituent
glass
SILICATE
“B”
(Yarn) “C”



















SiO2
55.08
55.81
64.58
64.64


CaO
0.33
0.38
0.44
0.40


Al2O3
25.22
23.78
24.44
24.57


B2O3
1.85

0.03
0.03


MgO
15.96
15.08
9.95
9.92


Na2O
0.12
0.063
0.08
0.09


Fluorine
0.03

0.034
0.037


TiO2
0.023
2.33
0.019
0.018


Fe2O3
1.1
0.388
0.187
0.180


K2O
0.039
0.56
0.007
0.010


ZrO2
0.007
0.15


Cr2O3

0.011
0.003
0.003


Li2O

1.63


CeO2





















TABLE I-B








Nitto
Vetrotex






Boseki
Saint
Polotsk





TE
Gobain
STEKLOVO-



Nitto
Nitto
Glass
SR Glass
LOKNO



Boseki
Boseki
RST-
Stratifils
High



A&P
NT6030
220PA-
SR CG
Strength


Constituent
Yarn
Yarn
535CS
250 P109
Glass




















SiO2
65.51
64.60
64.20
63.90
58.64


CaO
0.44
0.58
0.63
0.26
0.61


Al2O3
24.06
24.60
25.10
24.40
25.41


B2O3




0.04


MgO
9.73
9.90
9.90
10.00
14.18


Na2O
0.04
0.06
0.020
0.039
0.05


Fluorine
0.07



0.02


TiO2
0.016
0.000
0.000
0.210
0.624


Fe2O3
0.067
0.079
0.083
0.520
0.253


K2O
0.020
0.020
0.020
0.540
0.35


ZrO2
0.079


Cr2O3
0.0010


0.001
0.023


Li2O


CeO2





















TABLE I-C






Chinese
Chinese






High
High
Zentron

Advanced 



Strength
Strength
S-2
SOLAIS
Glass



Yarn
Glass
Glass
Glass
Yarns


Constituent
(8 micron)
Roving
Roving
Sample
R Glass




















SiO2
55.22
55.49
64.74
64.81
58.46


CaO
0.73
0.29
0.14
0.55
9.39


Al2O3
24.42
24.88
24.70
24.51
24.55


B2O3
3.46
3.52

0.02
0.04


MgO
12.46
12.28
10.24
9.35
5.91


Na2O
0.104
0.06
0.17
0.16
0.079


Fluorine
0.07


0.02
0.054


TiO2
0.32
0.36
0.015
0.04
0.196


Fe2O3
0.980
0.930
0.045
0.238
0.400


K2O
0.240
0.150
0.005
0.03
0.67


ZrO2


Cr2O3
0.0050


0.007
0.005


Li2O
0.59
0.63


CeO2
1.23
1.25





















TABLE I-D










IVG



Advanced

IVG
IVG
Vertex



Glass

Vertex
Vertex
Outside



Yarns
Culimeta
B96
Glass
#1 Glass


Constituent
S Glass
Roving
675 Yarn
Roving
Roving




















SiO2
64.61
59.37
58.34
58.58
58.12


CaO
0.17
0.27
0.31
0.30
0.31


Al2O3
24.84
25.49
23.81
24.26
24.09


B2O3
0.04
0.05


MgO
10.11
13.47
14.99
15.02
15.36


Na2O
0.118
0.024
0.05
0.02
0.03


Fluorine
0.03

0.04
0.04
0.04


TiO2
0.011
0.530
1.380
0.67
0.91


Fe2O3
0.042
0.374
0.333
0.336
0.303


K2O

0.48
0.42
0.28
0.29


ZrO2

0.152
0.129
0.165
0.157


Cr2O3
0.0050
0.0120
0.0100
0.0120
0.0120


Li2O


CeO2




















TABLE I-E








IVG Vertex
RH CG250




Outside #2
P109 Glass



Constituent
Glass Roving
Fiber Strand




















SiO2
58.69
58.54



CaO
0.29
9.35



Al2O3
24.3
25.39



B2O3



MgO
15.06
6.15



Na2O
0.03
0.10



Fluorine
0.04
0.16



TiO2
0.64
0.008



Fe2O3
0.331
0.069



K2O
0.36
0.14



ZrO2
0.187
0.006



Cr2O3
0.0130



Li2O



CeO2










Both 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 products formed there from.
SUMMARY OF THE INVENTION
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. One composition useful in the present invention includes 64-75 weight % SiO2, 16-24 weight % Al2O3, 8-12 weight % MgO and 0.25 to 3.0 weight % R2O where R2O is the sum of Li2O and Na2O. In certain embodiments, the glass composition is composed of 64-70 weight % SiO2, 17-22 weight % Al2O3, 9-12 weight % MgO and 1.75-3.0 weight % R2O where R2O is the sum of Li2O and Na2O. In another embodiment, a glass composition useful in the present invention is composed of 64-70 weight % SiO2, 17-22 weight % Al2O3, 9-12 weight % MgO and 1.75-3.0 weight % Li2O. In certain embodiments, the composition does not contain more than about 5.0 weight % of compounds such as CaO, P2O5, ZnO, ZrO2, SrO, BaO, SO3, F2, B2O3, TiO2 and Fe2O3.
The composition preferably does not contain more than about 4 weight % of compounds or halogens such as 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 2650° F. and a liquidus temperature that is preferably below the fiberizing temperature by at least 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, melting 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, and products made from such fibers.
The present invention also provides a structural part having improved structural properties with decreased costs and improved manufacturability. The direct melt formation of the continuous glass fibers uses low-cost melting in refractory-lined furnaces. The relatively low fiberizing temperature of the glass fibers used in the high-strength applications of the present invention allows improved fiber processing at decreased cost. The articles of the present invention are typically formed by compression molding, laminating, spray up, hand laying, prefabricated lay-up (prepreg), compression molding, vacuum bag molding, pressure bag molding, press molding, transfer molding, vacuum assisted resin transfer molding, pultrusion molding, filament winding, casting, autoclave molding, centrifugal casting resin transfer or continuous casting. The fibers used in the present invention are substantially less expensive to make and also have good strength and density properties. The density of the fibers used in the present invention range between 2.434-2,486 g/cc and have a measured modulus of 12.71-12.96 MPsi and a measured strength of 688-737 KPsi.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional longitudinal view of a glass melting furnace useful with the method of the present invention;
FIG. 2 is a cross-sectional plan view of the glass melting furnace of FIG. 1 taken along line 2-2;
FIG. 3 is a cross-sectional view of the glass melting furnace of FIG. 1 taken along line 3-3 illustrating two burners adjacent the upstream end wall of the furnace;
FIG. 4 is an alternate cross-sectional plan view of the glass melting furnace of FIG. 1 taken along line 3-3 illustrating one burner adjacent the upstream end wall of the furnace; and
FIG. 5 is a side view, partially in cross section, of a bushing assembly/support structure arrangement for producing continuous glass filaments useful in the method of the present invention.



DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION
Fiberizing properties of the glass composition used to form the glass fibers 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 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 method and 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 glass compositions employed in the present invention are advantageously suitable for melting in traditional, commercially available refractory-lined glass melters. Starting batch components typically include SiO2 (ground silica sand), and Al2O3 (calcined alumina), Li2CO3 (lithium carbonate), H3BO3 (boric acid), NaCaB5O9.8H2O (ulexite), 2CaO-3B2O3-5h2O (colmanite) as well as chain modifiers from source materials such as MgCO3 (magnesite), CaCO3 (limestone), SrCO3 (strontianite), BaCO3 (witherite), ZrSiO4 (zircon), and Na2CO3 (natrite).
FIGS. 1-4 depict a glass melting furnace 10 useful in the method of forming the glass fibers described herein and set forth in the examples and claims below. It may also be desirable to use oxygen-fired heating within the melting furnace, as disclosed in U.S. patent application Ser. No. 10/116,432 entitled “OXYGEN-FIRED FRONT END FOR GLASS FORMING OPERATION”, inventors David J Baker et al., and published as U.S. Published Application No. 2003/0188554, herein incorporated in its entirety by reference. The glass melting furnace 10 provides molten glass to a glass forehearth 12. The molten glass is preferably composed of about 64-75 weight % SiO2, 16-24 weight % Al2O3, 8-12 weight % MgO and 0.25 to 3.0 weight % R2O where R2O is the sum of Li2O and Na2O. In certain embodiments, the composition does not contain more than about 5.0 weight % of oxides or compounds such as CaO, P2O5, ZnO, ZrO2, SrO, BaO, SO3, F2, B2O3, TiO2 and Fe2O3.
In addition, a fiber formed in accordance with the method and composition of the present invention will have a fiberizing temperature of less than 2650° F., and in certain embodiments less than about 2625° F., in other embodiments less than about 2600° F. and in certain embodiments less than about 2575° F. and a liquidus temperature that is below the fiberizing temperature in certain embodiments by at least 80° F., and in other embodiments by at least about 120° F., and in yet other embodiments by at least about 150° F. Further, the glass fibers of the present invention, in certain embodiments, will have a pristine fiber strength in excess of 680 KPSI, and in certain other embodiments a strength in excess of about 700 KPSI, and in yet other embodiments a strength in excess of about 730 KPSI. Further, the glass fibers will advantageously have a modulus greater than 12.0 MPSI, and in certain embodiments greater than about 12.18 MPSI, and in some embodiments greater than about 12.6 MPSI.
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 14, 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 FIG. 1, the glass melting furnace 10 includes three burners 34. A single burner 34 is positioned upstream of two adjacently positioned downstream burners 34. However, it will be appreciated that any number of burners 34 may be positioned at any suitable location in the roof 22 of the furnace 10 over the batch to melt the glass batch composition 30. For example, two burners 34 may be positioned in a side-by-side relationship (FIG. 3) or a single burner may be used (FIG. 4).
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 FIG. 1) or incorporate the refining zone into the main tank of the melter.
As shown in FIG. 5, a bushing assembly 100 includes a bushing 110 and a bushing frame 210. The bushing 110 includes a bushing main body 120 with sidewalls 122 and a tip plate 124 extending between the sidewalls 122. The main body 120 is positioned below a bushing block 300 that, in turn, is positioned beneath a forehearth 310. In practicing the method of the present invention, a stream of molten glass is received by the main body 120 from the forehearth 310. The forehearth 310 receives the molten glass from a melter 10 (shown in FIG. 1). A delivery channel 40 is positioned between the melter 10 and the forehearth 310 to deliver the molten glass batch composition 30 from the melter 10 to the forehearth 310. The forehearth 310 and bushing block 300 may be conventional in construction and may be formed from refractory materials.
The tip plate 124 contains a plurality of nozzles 124a (also referred to 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 use chopped strand fibers, dry use chopped strand fibers, continuous filament mats, chopped strand mats, wet formed mats or air laid mats.
High strength articles of the present invention use the formed fibers described above as glass fiber reinforcement within a polymer matrix material. Typical matrix materials include epoxies, phenolic resins, vinylesters, and polyesters. The articles may be formed by any suitable manufacturing technique including compression molding, laminating, spray up, hand laying, prefabricated lay-up (prepreg), compression molding, vacuum bag molding, pressure bag molding, press molding, transfer molding, vacuum assisted resin transfer molding, pultrusion molding, filament winding, casting, autoclave molding, centrifugal casting resin transfer and continuous casting.
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.
EXAMPLES
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 there from. 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), and Modulus (MPsi) 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.













TABLE II-A





Glass
Ex. 1
Ex. 2
Ex. 3
Ex. 4
Ex. 5
Ex. 6





















SiO2
67.2
69
67
70
70
65


Al2O3
20
22
22
17
17
21


MgO
9.8
9
11
11
10
11


Li2O
3
0
0
2
3
3


Measured
2531
2761
2648
2557
2558
2461


Viscosity (° F.)








1st Measured
2313
2619
2597
2332
2302
2296


Liquidus (° F.)








2nd Measured
2302
2620
2614
2346
2308
2318


Liquidus (° F.)








ΔT (° F.)
218
142
51
225
256
165


Measured
2.459
2.452
2.481
2.450
2.441
2.482


Density (g/cc)






















TABLE II-B





Glass
Ex. 7
Ex. 8
Ex. 9
Ex. 10
Ex. 11
Ex. 12





















SiO2
70
69
70
65
66
65


Al2O3
18
17
21
22
22
22


MgO
9
11
9
11
9
10


Li2O
3
3
0
2
3
3


Measured
2544
2496
2752
2525
2523
2486


Viscosity (° F.)








1st Measured
2311
2234
2597
2468
2391
2361


Liquidus (° F.)








2nd Measured
2324
2343
2603
2462
2394
2382


Liquidus (° F.)








ΔT (° F.)
233
262
155
57
132
125


Measured
2.434
2.455
2.443
2.486
2.460
2.474


Density (g/cc)






















TABLE II-C





Glass
Ex. 13
Ex. 14
Ex. 15
Ex. 16
Ex. 17
Ex. 18





















SiO2
70
67.32
67.57
68.27
68.02
67.76


Al2O3
19
20.49
20.49
20.10
20.10
20.10


MgO
11
10.00
10.00
9.69
9.69
9.69


Li2O
0
2.00
1.75
1.75
2.00
2.25


Measured
2679
2563
2584
2598
2578
2547


Viscosity (° F.)








1st Measured
2596
2456
2486
2446
2431
2399


Liquidus (° F.)








2nd Measured
2582
2447
2469
2469
2437
2406


Liquidus (° F.)








ΔT (° F.)
83
111.5
106.5
140.5
144
144.5


Measured
2.453

2.461

2.452



Density (g/cc)









The composition of the present invention may also include chain modifiers such as Na2O, CaO and B2O3. Such compositions are shown in Table II-D (below).













TABLE 11-D





Glass
Ex. 19
Ex. 21
Ex. 22
Ex. 22
Ex. 23
Ex. 24





















SiO2
75
66
65
65
66
74


Al2O3
15
20
20
24
19
15


MgO
8
9
8
8
9
8


Li2O
1
1
2
0
0
0


Na2O
1
2
1
1
2
3


CaO

2
4





B2O3



2
4



Measured
2765
2607
2469
2669

2809


Viscosity








(° F.)








1st Measured
2422
2729

2614
2630
2680


Liquidus (° F.)








ΔT (° F.)
343
−122

55

129









The fibers of the present invention have superior modulus and strength characteristics. The fibers of Example 1 have a Measured Modulus of 12.71 MPsi and a Measured Strength of 688 KPsi. The fibers of Example 3 have a Measured Modulus of 12.96 MPsi and a Measured Strength of 737 KPsi. The fibers of Example 17 have a Measured Modulus of 12.75 MPsi and a Measured Strength of 734 KPsi.
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, lithia, alumina, and magnesia components in commercial practice of the invention or they may be processing aids that are essentially removed during manufacture.
As is 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.

## Claims

1. A process for producing glass fibers from raw glass batch in a refractory-lined glass melter, the process comprising the steps of:
charging raw glass batch to the melting zone of a refractory-lined glass melter, the glass batch comprising:
64-75 weight percent SiO2;
16-24 weight percent Al2O3;
8-11 weight percent MgO;
1.75-3 weight percent Li2O; and
no more than 2.0 weight percent CaO,

heating the glass batch to form a fiberizable molten glass having a fiberizing temperature of less than about 2600° F.; and
fiberizing said molten glass to produce glass fibers having a strength of greater than about 700 KPsi.

2. The process of claim 1, wherein the glass batch comprises:
about 68-69 weight percent SiO2;
about 20-22 weight percent Al2O3;
about 9-10 weight percent MgO; and
no more than 2.0 weight percent CaO.

3. The process of claim 1, wherein the glass batch comprises:
about 68 weight percent SiO2; 
about 20 weight percent Al2O3;
about 10 weight percent MgO; and
no more than 2.0 weight percent CaO.

4. The process of claim 1, wherein the glass batch comprises:
less than 5 weight percent total of compounds selected from the group consisting of P2O3, ZnO, ZrO2, SrO, BaO, SO3, F2, B2O3, TiO2 and Fe2O3.

5. The process of claim 1, wherein said molten glass produced from said batch has a liquidus temperature, wherein the difference (ΔT) between the fiberizing temperature and the liquidus temperature is at least 80° F.

6. The process of claim 5, wherein said molten glass produced from said batch has a ΔT of at least 120° F.

7. The process of claim 1, wherein the glass melter is lined with an oxide-based refractory material.

8. The process of claim 1, wherein the glass melter is lined with a refractory material selected from the group consisting of alumina, silica, chromic oxide, alumina-silica, zircon, zirconia-alumina-silica and combinations thereof.

9. The process of claim 5, wherein said molten glass produced from the batch has a ΔT of at least 140° F.

10. The process of claim 1, wherein said glass batch comprises 2.0-3.0 weight percent Li2O.

11. The process of claim 1, wherein said glass fibers have a density of 2.434 g/cc to 2.486 g/cc.

12. The process of claim 1, wherein said glass fibers have a measured modulus greater than 12.6 MPsi.

13. The process of claim 1, wherein said glass fibers have strength in excess of about 730 KPsi.

14. A process for producing glass from raw glass-forming material in a refractory lined glass melter, the glass melter having a roof, a bottom and side walls, defining an elongated channel having a melting zone and a downstream refining zone, the process comprising the steps of:
charging raw glass batch to the melting zone of the refractory-lined glass melter, the glass batch comprising:
64-75 weight percent SiO2;
16-24 weight percent Al2O3;
8-11 weight percent MgO; and
1.75-3 weight percent Li2O; and
no more than 2.0 weight percent CaO;

providing at least one burner within the roof of the glass melter; and
melting the glass batch to form a fiberizable molten glass, wherein said glass fibers produced have a fiberizing temperature of less than about 2600° F. and a strength of greater than about 700 KPsi.