Note: Descriptions are shown in the official language in which they were submitted.
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~ Background of the Invention
.
- The present invention relates to glass fiber compositions having
lncreased tensile strengths over conventional "E" glass fibers.
Glasses in order to be suited for glass fiber manufacture must
satisfy several criteria.
Since fine glass fibers present a large surface area to volume
ratio, compositions resistant to water and chemical attack are necessary.
High alkali content is undesirable since water adsorbed from the atmosphere
can tissolve the alkall, initiating reaction with the silicate in the glass
and ultimately deseroying the glass. Therefore, the alkali metal content
of glass fiber compositions must be limited.
In the formation of flne glass fibers, it iB desirable to have
a glass compos~tion which may be melted and refined at high rates at
relatively low temperatures. The glass should have a workable viscosity
over a wide range of relatively low temperatures. The glass should have
a low liquldus temperature and a llmlted devltrlflcation rate. It 19
desirable for the color of the glass, as melted, to be such that heat 19
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readily transmitted through the glass.
0f particular importance is the use of glass fibers for rein-
forcing resinous articles known as laminates. Laminates are formed by
impregnating glass fiber cloth, glass fiber chopped strand, or glass
fiber mat with a resinous composition. The function of the glass fibers
is to reinforce the article and provide a strength far superior to the
hardened resin composition alone. In addition, glass fibers have found
great utility in the reinforcement of rubber articles such as tires,
power transmission belts, and the like. The glass fibers are normally
incorporated into these rubber-reinforced articles in cord form to
provide additional strength to these elastomeric type articles. There-
fore, it is apparent that glass fibers having high tensile strength to
impart strength to rubber-reinforced articles are desired.
The most common glass fiber composition used for reinforcement
of articles is the "E" glass composition which typically consists of
54.4 percent SiO2, 13.~4 percent A12O3, 21.7 percent CaO, 0.4 percent NgO,
8.5 percent B2O3, 0.5 percent F2, 0.7 percent Na2O, 0.5 percent TiO2,
and 0.2 percent Fe2O3.
This "E" glass composition demonstrates tensile strengths of
400,000 to 500,000 pounds per square inch for fibers measuring from
12.5 x 10-5 inches to 70 x 10-5 inches in diameter.
Other compositions than "E" glass exhibiting high tensile
strengths in fibrous form are also known. These glass compositions typi-
cally have an extremely high percentage of SiO2, usually greater than
65 percent, and, in addition, have an increased amount of A12O3, typically
greater than 25 percent. These glass compositions produce fibers which
demonstrate tensile strengths on the order of 600,000 pounds per square inch
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for fibers measuring from 35 x 10-5 inches to 64 x 10-5 inches in di-
ameter. Tensile strengths arrived at by these glass compositions are
very advantageous for reinforcing purposes. ~owever, due to the high
amount of SiO2 and A1203 present in these glasses, the liquidus tempera-
tures of these compositions are normally greater than 2600F., which
substantially reduces the life of refractories and metals used in the
melting and forming operations producing these fibers. An example of
a high tensile strength glass is disclosed in U.S. Patent 3,402,055.
This glass consists of 65 percent SiO2, 25 percent A12O3 and 10 percent
MgO and exhibits tensile strengths of about 637,000 pounds per square inch.
This magnesia-silica-alumina glass will hereinafter be referred to as "S"
glass. The liquidus temperature for this glass is between 2630 and 2650F.
Glasses with liquidus temperatures such as these require increased melting
and processing temperatures over "E" glass, thus having adverse effects
- on refractory lining in melting tanks and on bushing life.
- Therefore, it is still a desire in the art to produce glass
fibers useful for reinforcement of articles which have tensile strength
greater than "E" glass from a glass composition which has a relatively
low liquidus temperature, maximum chemical inertness, maximum heat trans-
fer through the glass, and a limited devitrification rate.
Summary of the Invention
- In accordance with the practice of the instant invention, the
aforementioned properties and other properties can be achieved by preparing
a glass fiber composition which contains 53 to 57.3 percent by weight as
- SiO2, 16.3 to 18.5 percent by weight as A1203, 6.6 to 10.5 percent by
weight as MgO, 8.5 to 12.7 percent by weight as CaO, 0.6 to 0.8 percent
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by weight as TiO2, 2.0 to 4.1 percent by weight as B203, 0.8 to 3.3
percent by welght as Na20, 0.0 to 4.1 yercent by welght as BaO and 0.0
to 1.0 percent by welght as L120.
The comblnation of the components at the levels deslgnated
lmpart the necessary properties to the glass fibers formed therefrom.
Other components such as Fe203 may be present due to
impurltles in the starting glass batch materials. However, Fe203 should
be llmited to about 0.3 percent maximum, otherwise the glass melt com-
position may have inadequate heat penetration during processing.
Li~uidus temperatures of below 2210F are encountered with
the aforementloned range of glass composltlon. Thls liquidus temperature
is surprisingly low in comparison with the tensile strength achleved
by the range of components necessary ln the practice of the instant in-
vention. Thus,the life of the refractories, used in the melting and re-
fining process, which contact the glass is greatly increased while an
increase ~n tensile strength of the glass fibers produced over conventional
"E" glass is realized.
Glasses of the aforementioned range of compositions have
softening points below 1,650F and glass fibres made therefrom have tensile
strengths greater than 570,000 pounds per square inch.
The invention will be more clearly illustrated by the
examples below. However, these examples which describe specific embodiments
should not be construed to limit the invention in any way.
EXAMPLE I
The following raw batch materials were weighed out in the
amounts indicated to formulate the preferred composition A.
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- Table 1
Raw Batch Materials Weight in Grams
Silica 169.0
Clay 198.2
Dolomite 160.0
Magnesium Oxide 6.9
Boric Acid 34.5
Soda Ash 6.4
-
Barlum Carbonate 25.0
The raw batch materials were placed in a Twin Shell Blender
and thoroughly mixed by rotating the blender for 30 minutes. After
- mixing, the batch was transferred to a 4-inch diameter silica crucible
and inserted in a refractory furnace. The batch was heated to a temper-
ature of about 2700F. for a period of 6 hours. After this heating, the
molten glass was removed from the furnace and poured onto a steel plate
to produce a glass patty approximately 1/2 inch thick by about 4 inches
by 4 inches square. The glass patty was placed in a furnace, preheated
to about 1100F. The power to the furnace was turned off and the furnace
was allowed to cool slowly to room temperature over a period of about
- 18 hours to anneal the glass. The annealed glass patty was then removed
from the annealing furnace and broken into small chunks.
- The chunks of glass were then placed in a single orifice -
80 percent platinum, 20 percent rhodium bushing, and remelted and refined
by heatlng the bushing to about 2800F. and holding at this temperature
for 1 hour. The bushing temperature was then lowered to the fiberizing
temperature, 2450F., and a single filament was drawn from the bushing
approximately 40 x 10-5 inches in diameter at a rate of about 1600 feet
per minute.
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The single orifice bushlng used in fabricating the fiber was 3 inches
~long by 1-5/8 inches square. The bushing single orifice was .047 inch in
inside diameter, .080 inch long, and had an exit outside diameter of under
.060 inches.
Immediately after the glass fiber made from the above composition
was drawn, several l-inch samples were obtained. The samples were then
tension loaded in a monofilament tensile testing machine to determine their
tensile breaking load. The tensile strength in pounds per square inch was
then`calculated by dividing the breaking load in pounds by the cross-
sectional area of the fiber in square inches.
- Two batches of glass with a composition as above were made. The
softening points of these compositions were 1620F and 1628F and had
liquidus temperatures of about 2175F. The tensile strength of monofilament
fibers on testing displayed strengths of between 590,000 to 650,000 pounds
per square inch.
The average composition of the glass fibres was 56.6 percent by
weight as Si02, 18.5 percent by weight as A1203, 0.3 percent by weight as
Fe203, 9.3 percent by weight as MgO, 10.7 percent by weight as CaO, 0.6
percent by weight as Ti02, 2.0 percent by weight as B203, 1.0 percent by
weight as Na20 and 1.0 percent by weight as Li2O.
EXAMPLE II
The following raw batch materials were weighed out in the amounts
indicated to formulate the preferred composition B:
- TABLE II
Raw Batch Materials Weight in Grams
Silica 181.5
Clay 203.3
Dolomlte 137.6
Magnesium Oxide 2.0
Boric Acid 28.1
Soda Ash 27.2
Barium Carbonate 20.3
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This batch was melted, refined, annealed, and fibers were drawn
therefrom in accordance with the procedl~re of Example I. This glass batch
had a softening point of 1605~F to 1619F and a liquidus temperature of
between 2060F and 2108F. Testing of monofilament fibers formed as above
described had tensile strengths between 585,000 pounds per square inch
and 630,000 pounds per square inch.
The composition of the glass fibres was 57.3 percent by weight as
SiO2, 16.5 percent by weight as A1203, 0.2 percent by weight as Fe203, 6.6
percent by welght as MgO, 8.8 percent by weight as CaO, 0.7 percent by
weight as TiO2, 3.3 percent by weight as B203 and 3.3 percent by weight
as BaO.
EXANPLE III
The following raw batch materials were weighed out in the amounts
indicated to formulate the composition C:
TABLE 3
Raw Batch MaterialsWeight in Grams
Silica 169.3
Clay 189.2
Dolomite - 192.8
Magnesium Oxide 7.7
Boric Acid 26.2
Soda Ash 8~5
Barium Carbonate 6.3
The above batch materials were melted, refined, annealed, and fibers
were drawn therefrom in accordance with the method of Example I. The glass
- formed from this batch had a softening point of 1623F to 1625F and the
liquidus temperature of between 2200F and 2208F. Tensile strengths of
the glass fibers drawn from these compositions were between 585,000 pounds
per square inch and 650,000 pounds per square inch.
The composition of the glass fibres was 54.7 percent by weight as
SiO2, 15.8 percent by weight as A1203, 0.2 percent by weight as Fe203, 10.5
percent by weight as MgO, 12.7 percent by weight as CaO,0.7 percent by weight
as TiO2, 3.2 percent by weight as B203, 1.1 percent by weight as Na20 and
1.1 percent by welght as BaO.
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EXAMPLE IV
The following raw batch materials were weighed out in the amounts
indicated to formulate the preferred composltlon D:
TABLE 4
.r Raw Batch Materials Weight in Grams
Sillca 147.8
Clay 184.4
Dolomite 169.1
Boric Acid 16.7
Magnesium Oxide 8.3
10 Soda Ash 8.1
Spodumene 65.5
The above ingredients were mlxed, melted, annealed, and flbers
were drawn therefrom according to the procedure in Example I. Glass made
from this batch had a liquidus temperature of 2170F to 2190F and a soft-
ening point of 1560F to 1580F. Tensile strength of fibers drawn from
thls glass composition were between 595,000 pounds per square lnch to
635.000 pounds per square lnch.
The composition of the glass flbers was 54.8 percent by weight as
SiO2, 16.3 percent by weight as A1203, 0.2 percent by weight as Fe203, 8.7
percent by weight as MgO, 10.3 percent by welght as CaO, 0.7 percent by
weight as TiO2, 4.1 percent by weight as B203, 0.8 percent by.weight as
Na20 and 4.1 percent by weight as BaO.
EXAMPLE V
The following raw batch materials were weighed out in the amounts
indicated to formulate the preferred composition E:
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.
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TABLE 5
Raw Batch Material Weight in Grams
Silica 147.6
Clay 223.9
Dolomite 130.6
Boric Acid 30.1
Magnesium Oxide 18.9
Soda Ash 11.3
Barium Carbonate 24.2
The above materials were mixed, melted, annealed, refined, and
fibers were drawn therefrom in accordance with the procedure of Example I.
This glass had a softening point of 1633f and a liquidus temperature of
2200F. Fibers drawn from this glass had a tensile strength of between
585,000 pounds per square inch and 620,000 pounds per square inch.
The composition of the glass fibres was 53.0 percent by weight
as SiO2, 18.5 percent by weight as A1203, 0.2 percent by weight as Fe203,
lO.O percent by weight as MgO, 8.5 percent by weight as CaO, 0.8 percent
by weight as TiO2, 3.6 percent by weight as B203, 1.4 percent by weight
as Na20 and 4.0 percent by weight as BaO.
The liquidus temperature determinations for the above specific
compositions were made by the conventional 24 hour liquidus technique in
which ground glass is placed in a shell or platinum boat, the shell or
boat is then placed in a gradient furnace with one end about 1300F and
the other about 2500F, heated and maintained in equilibrium with the
furnace for 24 hours and then removed for microscopic determination of
the crystal-glass interface of the sample. Correspondence of the crystal-
glass interface with the known lateral position to temperature relation
for the furnace establishes the liquids.
Softening point determination is by the conventional ASTM-C
338-57 method. The glass fiber is prepared and placed in a uniform
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1 temperature furnace. Temperature is lncreased and temperature rise and
2 fiber elongation are recorded. ~hen the elongatlon rate meets the pre-
4 set standard of the test, the temperature is noted as the softenlng
point.
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The foregoing Table represents the properties of the herein-
before set forth Examples and compares the glasses therewith.
Table 6
Composition Softening Point F. Liquidus F. Tensile Strength PSI x 103
A 1620-1628 2175 590-650
B - 1605-1619 2060-2108 585-630
- C 1623-1625 2200-2208 585-650
D 1560-1580 2170-2190 595-635
E - 1633 2200 585-620
"E" Glass 1540-1560 2170-2~90 400-500
"S" Glass 2630-2650 637
The improved tensile strengths of the glass fiber compositions
herein disclosed permit the production of improved glass reinforced plastic
articles and improved glass reinforced rubber articles such as tires and
power transmission belts.
It is anticipated that these fiber glass compositions will find
particular acceptance in the production of various types of aircraft equip-
ment where high strength to weight ratios are important. Glasses with
- these improved properties are readily melted and formed in the conventional
commercial glass fiber strand-producing facilities. Combination of the
various ingredients permits melting and forming at comparable temperatures
with "E" glass while providing improved tensile strengths.
While the present invention has been described in terms of spe-
cific examples, the scope of the invention should not be limited except as
is ~et forth in the appended claims.
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