Note: Descriptions are shown in the official language in which they were submitted.
1069543
This invention relates generally to a method of
preparing a molten glass composition.
The prior glass melting methods restrict glass composi-
tions to compositions containing only those constituents which
can survive the environment of the glass melting apparatus. By
currently known methods of preparing molten glass, having
particular properties or forming characteristics, it is necessary
to introduce into the melting furnace all of the constituents
that must be present in the final molten glass composition to
produce those properties or characteristics. Many times the
presence of those constituents in the melter is undesirable
because of their volatility, corrosiveness, or environmental
affects. The consequence, recognized for years is that the
compositions of some glasses are impractical to produce
commercially because of the volatility, corrosiveness or environ-
mental affect of their constituents.
Certain hostile glasses, however, have desirable
properties and are commercially produced under such adverse
conditions as to add significantly to their cost. For example,
20 borosilicate glass compositions generally contain volatile `~
constituents such as boric oxide (B203), fluorine (F2), and
sodium borate (Na20 XB203). These constituents not only
volatilize at melter operating temperatures but also shorten
melter life by their chemical attack upon refractory materials.
The present invention relates to an improved method for
preparing molten glass compositions suitable for subsequent
forming into useful glass products. By m~ method of making glass
the constituents of the desired molten glass composition are
selectively classified into two or more melting groups. The
melting groups are separately prepared, preferably as molten
il)69S43
masses. One group, generally the one of greatest mass, is chosen
as a base or host glass into which the other groups may be
sequentially mixed and homogenized to form the desired molten
glass composition.
The classification criteria for example by which the
melting groups are formulated may be based upon fusion temperature
of the constituents, or any other mutual processing characteristic
such as corrosiveness, softening point, volatility, etc. The
classification criteria of one group need not necessarily exclude
constituents of other groups. For example, if the constituents
are classified according to fusion temperature, the temperature r
range of one constituent group may overlap the temperature range
of other constituent groups. Thus, two or more constituent
groups may contain a common constituent. It may also be found
desirable in formulating a particular melting group ~o include
a constituent, otherwise excluded by the group classification
criteria to assist melting of that group or in some other way
alter its properties to obtain the most desirable processing
characteristics for that melting group.
Applying the principles of my invention to the prepara-
tion of a molten fiberizable glass composition comprising silicon
oxide (SiO2), aluminum oxide (A1203), calcium oxide (CaO), boric
oxide (B203), fluorine (F2), and sodium oxide (Na20), two melting
groups may be identified. The highly volatile constituents
B203, F2 and Na20.XB203 are preferably grouped together as a
volatile oxide group. The remaining constituents SiO2, A1203,
Na20 and CaO may be grouped together as a relatively non-volatile
group. The non-volatile group is recognized as soda lime glass,
a composition relatively common to the glass industry and may be
prepared as a molten base glass in a high production glass
-- 2 --
~1
~069543
meltir,g furnace of the continuous type common to the glass making
indust:ry. To this relatively non-volatile molten base glass
composition the volatile constituent group may be added either as
a molt:en composition or as a batch formulation. The volatile
constituent group may be introduced into the molten base composi-
tion at any convenient location downstream of the non-volatile
constituent group's melting area. Preferably the volatile
constituent group is introduced to the molten base glass
immediately downstream of the base glass melter's exit throat
1~ thereby taking advantage of the base glass' exit temperature and
residual heat. However, the volatile constituent group might be
introduced directly into the base glass melter's throat area or
any other favorable or otherwise advantageous location between the
base glass melting area and the glass forming position.
The base composition will generally be identified as
that melting group representing the larger volumetric portion of
the total composition. Thus, for most known commercial glasses
the ratio of base to additive will lie within the range of 1:1 to
20:1.
By my multi-step method of making glass a freedom of
melter design can be realized heretofore unknown in the industry.
Melter design and operation need no longer be dictated by the
molten glass composition produced therefrom. Hostile glass
compositions may be formulated into two or more melting groups
such that the more troublesome constituents such as the highly
volatile, may be removed from the composition and prepared
separate and apart from the less troublesome constituents.
Generally speaking the volatile constituents of most concern in
present day glass making operations are, boric oxide (B2O3),
sodium borates (Na2O.xB2O3) resulting from the presence of Na2O
~' .
1069543
and B2O3, fluorine (F2), and lead oxide (PbO). These constituents
generally represent a minor portion of the total glass composition
and have relatively low fusion temperatures. Therefore, they may
be melted in a specially designed melter smaller in size than the
base glass melter and operated at a lower temperature. Thus,
less volatilization loss will occur and since the volatile melter
is small compared to commercial tank melters, pollution prevention
problems are significantly reduced.
Most volatiles in glass compositions are also solvents
of known refractory materials. Therefore, any amount of volatile
reduction in the glass melter may be expected to extend melter
life. In commercially melting of borosilicate glasses, those
having at least 3% B2O3, I have found that melter life may be
extended approximately 100% by a 50% reduction of B2O3 in the
melter.
According to the concepts of the present inven~ion a
desired composition of glass can be made by separating the high
temperature and the low temperature constituents of the composi-
tion into at least two portions and separately processing each,
the high temperature constituents being processed to a molten
condition. With the high temperature material in a molten state
the low temperature materials can be combined directly therewith
whereupon the two are quickly if not immediately subjected to a
vigorous working or intermixing of incremental segments by
application of external forces to a degree such that the combina-
tion is in effect homogenized. Before appreciable effluence of the
low temperature constituents can occur if the high temperature
homogenized combination is not then to be used directly, it is
preferably lowered in temperature closer to its new softening
temperature to reduce tendencies for the volatile ingredients to
evolve as effluents.
~ - 4 -
1(~69543
In accordance with this invention, a
method of forming a fiberizable borosilicate glass
includes the step of separating batch ingredients
for the glass into ingredients for forming a host -
glass and a B203-containing additive glass~ The
ingredients for forming the ho t glass are pellet-
ized, and are pre-heated in their pellet form to
a temperature which is just below the fusion tempera- ~
ture of the host glass composition and at which ~ -
the pellets will not agglomerate. The heated
pellets are melted in a generally horizontally-
disposed, continuous-flow main melter, and the
:, ;.
molten host glass is flowed from the main meltér ~
,~
to a location where glass fibers are to be formed.
The additive glass i~ separately melted and com-
bined (below the surface of the molten host glass
and with mechanical mixing) with a larger portion `
of the molten host glass prior to the fiber-forming
location, to form a fiberizable borosilicate glass.
Borosilicate fiber is formed at the fiber forming
location from the fiberizable glass. At least a
major portion of the B203 content of the fiber is
supplied by the additive glass, and thus the melter
exhibits longer life and the volatilization losses
of B203 are substantially less than that which re-
sult when melting the ingredients of the additi~e
and host glasses together in a melter.
- 4a -
~069543
One advantage f ~he invention is that the high
temperature portion of the composition in the absence of the
constituents of the low temperature portion can be efficiently
preheated in a batch state to a much higher temperature prior to
initiation of conversion to a molten mass than when the two
portions are in combination in a common batch as in conventional
glass producing process.
Energy consumption, effluent evolution and the size
of the melter can all be reduced according to the concepts of
the present invention. In addition, the life of the refractory
for containing the major portion of the molten material can be
increased considerably. Still further, since the residence time
of the low temperature materials in high temperature zones is
greatly reduced, consumption of the low temperature materials
required to produce a composition i8 much less than experienced
in producing glass by conventional melting techniques. Such low
temperature materials include fluxes required to lower the melting
temperature and additives for improving the durability of the
final glass. These constituent are usually considerably more
expensive than the base silica material of the composition.
Accordingly to produce a glass of the desired composition, the cost
of raw input material can also be reduced considerably.
A feature of the present invention relates to an
improved method for producing molten glass and products therefor,
particularly although not necessarily glass fibers, and more
particularly a method for eliminating, controlling or simplifying
the control of effluent to the atmosphere from the volatile
bearing constituents in the batch formulation, consisting of at
least 3% boric oxide bearing constituents with or without
fluorine bearing constituents. For example, glass compositions
1069S43
suitable for glass fiber manufacture for the production of glass
wool,, or plastics reinforcements or other end products are
generally borosilicate glasses and their compositions contain
volatile constituents in quantities sufficient to affect their
forming characteristics, such as boron oxide (B2~3), fluorine
(F2), and/or sodium borate (Na2OxB2O3). These constituents not
only volatilize at melter operating temperatures, but also their
presence in the melt shorten melterlife by corrosive or chemical
attack upon refractory materials.
When removing the volatile constituents from boro-
silicate glasses and particularly glasses used for the production
of glass fibers it has been discovered that the remaining glass
forming constituents can be practica~ly melted in a conventional
type furnace, either in that the remaining constituents form what
may be regarded as a eutectic; that is, among the lowest liquidus
melting temperature compositions, or at least the remaining
constituents are sufficiently capable of being melted in a
conventional furnace; but in either case, the forming character-
istics of the remaining constituents when in the molten state are
incapable of effective manipulation and forming into the desired
end product, principally because viscosity and/or liquidus
temperatures are excessive and unsuitable for forming in a
practicable way. In accordance with the present invention, the
volatilizable constituents are separately melted and then added
to the molten mass of the remaining constituents, the intimately
mixed, preferably by stirring mechanically, to homogenize and
provide the proper forming characteristics, and ~hereafter formed
into end products.
It is known in the industry that the efficiency of the
glass making process may be improved by pre-heating of the
-- 6 --
~069~43
formulated batch prior to charging it to the melter. Hcwever,
the efficiency gain is recognized as being limited by the
particular batch formulation sintering temperature. By applica-
tion of my multi-step glass making technique the sintering
temperature of the base glass batch formulation, which represents
the greater bulk of the total, may be significantly raised by
selectively eliminating the relatively low sintering ingredients
such as soda ash. The lower sintering ingredients may be
separately processed as a group, with or without pre-heating, in
a manner most efficient for the particular ingredients therein.
Thus, for a given desired glass composition a melting process and
apparatus may be engineered to achieve the greatest thermal
efficiency.
Thus, by my multi-step method of glass making it is
no longer necessary to melt all of the desired glass compositions'
constituents in a common glass melter as one all inclusive batch
formulation. For a given desired glass composition a melting
process and apparatus may now be engineered to achieve the most
optimum process in view of environmental affects, energy
expenditure, melter life or a cor~ination thereof depending upon
the goal to be achieved.
Figure 1 presents a phase diagram for the SiO2 - Na2O -
CaO system showing isotherms for the Na2O3CaO6SiO2 region.
Figure 2 presents the phase diagram for the SiO2 -
A12O3 - CaO system showing the eutectic point composition and
related isotherms.
Figure 3 presents a flow diagram for use in describing
Example VI.
Figure 4 presents a plot of representative curves
illustrating the viscosity differerlces between molten compositions
of Example II.
-- 7 --
. ~i'
~069S~3
Figure 5 shows a typical glass fiber forming operation
embodying the present invention.
Figure 6 is a pictorial vièw showing the general
configuration of forehearth mixing apparatus suitable for prac-
ticing the invention.
Figure 7 is a schematic plan view of the forehearth
mixing apparatus of Figure 6 showing the elements thereof.
Figure 8 presents a side elevation taken along line 8-8
of Figure 7 showing the molten glass flow pattern.
Figure 9 presents an end elevation taken along line 9-9
of Figure 7 looking upstream in the forehearth.
Figure 10 presents an elevational schematic showing
elements of a two zone glass melter suitable for practicing my
invention.
Figure 11 presents an elevational schematic showing
elements of melting apparatus suitable for practicing my invention.
My invention is particularly useful for preparing
borosilicate glasses as commonly used to manufacture glass fibers.
However, as will be disclosed below, it offers advantages to all
areas of the glass making industry, Although the following
discussion will be especially directed toward the glass fiber
industry it is to be understood that the broad principles of the
invention may be practiced by other glass melting operations.
According to "The Handbook of Glass Manufacture," 1974
edition by Dr. Fay V. Tooley, a glass composition may contain
most any of the periodic table elements. However, few glass
compositions are without substantial quantities of silicon, boron,
or phosphorous. Most often these elements exist in oxide form.
The glass making industry refers to these and other glass forming
3n oxides as "glass formers" and those oxides which have little glass
- 8 -
~(~69S43
forming characteristics as "modifiers" with a group therebetween
identified as "intermediates". Dr. Tooley, at page 3 of the
above cited work, provides the following classification of glass
formers, intermediates and modifiers:
TABLE I
Glass Formers Intermediates Modifiers
B2O3 A123 MgO
Sio2 Sb23 Li20
GeO2 Zr2 BaO
P2O5 TiO2 CaO
V25 PbO SrO
AS23 BeO Na2
ZnO K2O
The glass making potential of the above table of oxides
decreases as you progress from top to bottom of each column
moving left to right. Thus, B2O3 exhibits the greatest-glass
forming characteristic and K2O the least. No sharp line of
distinction exists between As2O3 and A12O3 nor between ZnO and
MgO.
Dr. Tooley, at page 5 of the above cited work, lists
the approximate commercial glass compositions presented in Table
II. It is noted from Table II that the Borosilicate and Lead glass
compositions contain two very good formers, B2O3 and SiO2 along
with A12O3 which although classified as an intermediate in
Table I may act as a former. Thus, these glasses are especially
good candidates for producing by my method of glass making. Each
of these glasses may be formulated into two separate glass
compositions or melting groups. For example, one formulation may
use SiO2 as its glass former and t~e other ~23 Another
possibility may be to take advantage of the glass forming
_ g _
~ ,, .
1069543
characteristics of intermediate A1203 and formulate three separate
giass compositions, the third having A1203 as its forming oxide.
Each of these melting groups may in turn be formulated to obtain
certa.in processing advantages depending upon the particular
constraints confronting the glass maker.
-- 10 --
~069S43
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1~6954~
The container glass compositions given in Table II may
also be prepared in accordance with the principles of my inven-
tion by again taking advantage of the forming characteristics
of Al2O3 as a forming oxide for one composition. However, a
more practical possibility for producing these glasses in accord
with my invention might be to formulate a common base composition
of SiO2, Na2O and CaO and an additive composition containing the
remaining constituents plus an additional portion of SiO2 to act
as a former therein. The exact composition and mixing ratio can
be a compromise of desired melting characteristics of the two
glasses. For example, if our goal is to reduce the melter
operating temperature, we may desire to formulate a base composi-
tion from the SiO2 - Na2O - CaO phase diagram, Figure 1, that
lies within the Na2O3Ca06SiO2 region having a melter temperature
between 800C. and 1050C, to obtain the lowest practical melter
operating temperature. The additive composition and mixing ratio
would accordingly be fixed.
Having a general idea of how my glass making method may
be applied consider the following specific examples and benefits
obtained thereby.
EXAMPLE I
BOROSILICATE INSULATING WOOL GLASS
U. S. Patent Numbers 2,877,124 and 2,882,173 teach glass
compositions suitable for the manufacture of glass wool products.
Preparing these compositions by my melting technique is
particularly advantageous as will be seen from the following
discussion. Generally, fiberizable wool glass compositions have
the following composition by weight.
- :L2 -
-- 1069543
CONSTITUENT CO~5POSITION RANGE TYPICAL
IN PERCENT COMPOSITION
.
SiQ2 50-65 61. 5
A123 0--8 4 . 0
CaO 3-14 8. 0
MgO 0-10 3.5
Na2O, K2O, Li2O 10-20 15.5
B2O3 5--157 . 5
TiO2 0--8 ____
Zr2 0-8 ----
BaO 0-8 ----
e23 0-12 ____
MnO 0-12 ----
ZnO 0-2 --~-
The primary volatile from the above molten glass
composition is sodium borate which forms by the reaction of Na~O
and B203 present in the molten glas~ composition. Accounting for
the presence of sodium borate, the compos.ition, may be written as:
CONSTITUENTPERCENT BY WEIGHT
SiO2 61.5
A123 4'
CaO 8.0
MgO 3.5
K20 1.0
Na20 11. 0
*Na2O 3. 5
2 3
*Sodium borate constituents
Within the principles of my invention the constituents
30 may be classified according to their relative volatility into two
melting groups.
- 13 -
1069S~3
Group I (non-volatile constituents)
CONSTITUENTSCOMPOSITION RANGETYPICAL
IN PERCENT COMPOSITION
SiO2 55-80 69.0
A123 0-10 4.5
CaO 3-10 9.0
MgO 0-12 3.9
K2O 0-2 1.1
Na2O 8-16 12.3
Group II (volatile constituents)
CONSTITUENTS COMPOSITION RANGETYPICAL
IN PERCENTCOMPOSITION
Na2O 20-40 30.8
B2O3 60-80 69.2
The group I composition may be identified as a soda
lime silica glass closely resembling plate glass compositions,
which although fiberizable are unsuitable as an insulating wool
because of the absence of B2O3. The presence of B2O3 being
necessary to provide thermal resistance and the necessary fiber
surface chemistry to bond with phenol formaldehyde binders.
However, soda lime silica glasses are less hostile to prepare
than the desired borosilicate wool glass composition given above.
The group II composition however, is highly volatile and
corrosive. Therefore, the group I constituents are prepared as
a molten base glass composition in a continuous glass melting
unit common to the glass making industry. The sodium borate
constituents of group II are then introduced into the molten base
glass composition of group I either as a melt or raw batch
formulation.
Since the group II composition represents approximately
- 14 -
1(~69543
11~ by weight of the total glass composition, it may be melted in
a significantl~ smaller melting unit and at a substantially lower
operating temperature than the host composition. Thus, you may
expect less sodium borate loss by volatilization simplifying the
task of pollutant control. Further, since the soda lime silica
glass of group I is approximately half as corrosive as the boro-
silicate wool glass composition one may expect a 100% increase
in melter refractory life.
EXAMPLE II
BOROSILICATE TEXTILE FIBER GLASS
U. S. Patent Number 2,334,961 teaches a borosilicate
glass composition commonly referred to as E-glass which is easily
formed into textile fibers and principally used as a reinforcement
for plastics, tires, etc. Generally, E-glass has the following
composition by weight:
CONSTITUENTCOMPOSITION RANGETYPICAL
IN PERCENTCOMPOSITION
SiO2 ~ 50-65 55.0
A123 5-20 15.0
CaO 5-25 22.0
MgO 0-10 ----
B~03 0-11 7.0
Na2O 0-10 0.5
TiO2 0-4 ____
F2 0-4 0.5
2 3 0-2 ____
The volatile constituents of concern within this
molten glass composition are B2O3, F2 and Na2O Therefore,
similar to the wool glass example above, two melting groups may
be identified as follows:
~ .
-- 1069S43
Group I (non-volatile constituents)
CONSTITUENT COMPOSITION RANGE TYPICAL
.
IN PERCENT COMPOSITION
A B
SiO2 50-70 64.5 62.0
A123 5-20 16.0 17.0
CaO 5-30 13.0 21.0
Na2O 0-10 0-5 ~~~~
2 3 0-2 ____ ____
Group II (volatile constituents)
CONSTITUENT COMPOSITION RANGE TYPICAL
IN PERCENT COMPOSITION
A B
SiO2 0-20 5.0 8.0
B2O3 40-90 47.0 47.0
F2 0-10 4.5 5.0
Na2O 0-10 ---- 3.5
2 3 0-20 1.0 ----
CaO 0-50 40.0 33.0
RO+R2O30-5 1.5 3.5
e23 0-2 ____ ____
MgO 0-10 ---- ----
TiO2 0-10 ---_ ____
Fe23 0-4 ____ ____
By the above grouping the highly volatile constituents
of group II, representing approximately 8% by weight of the
desired fiberizable molten glass composition, may be separately
prepared in a relatively small melter and added to the molten
base composition realizing similar benefits as in preparation of
the wool glass composition.
~ 16 -
'
~q~
106~543
EXAMPLE I I I
TEXTILE FIBER GLASS HAVING EUTECTIC BASE
-
The present invention offers further advantages with
respect to the preparation of E-glass compositions as discussed
in Example II above. Consider the CaO - A12O3 - SiO2 system
phase diagram of Figure 2. If the non-volatile group is
reformulated to:
CONSTITUENTPERGENT - BY WEIGHT
SiO2 6 2 . 0
A123 15 . 0
CaO 23.0
the eutectic composition is obtained. Thus, the main melter used
to melt the group I non-volatile composition may be operated at
a minimum operating temperature.
The remnant constituents are added to the group II
volatile composition which now becomes:
CONSTITUENTPERCENT BY WEIGHT
SiO2 13.0
CaO 12.9
A123 12.3
B2O3 54.0
2 3.9
Na2O 3.9
A further advantage realized is that this formulation allows the
use of less expensive raw materials, such as colemanite, as a
partial source of B2O3 reducing the need for more expensive boric
acid.
EXAMPLE IV
SODA LIME GLASSES
3Q A common glass composition useful in the manufacture of
window or bottle glass is as follows:
- 17 -
, '~ : '~, , 1 ' ' ' ,
1069543
CONSTITUENT PERCENT BYTYPICAL TYPICAL
WEIGHT BOTTLEWINDOW
SiO2 65-85 74.0 72.0
Na2O 10-20 13.0 14.3
A123 0-10 1.8 1.3
CaO 0-15 8.8 8.2
MgO 0-5 1.4 3.5
BaO 0-5 0.2 0.2
F2 0-5 0.3
K2O 0-5 0.3 0.2
so3 0-1 0.1 0.3
Fe23 0-1 0.3 0.2
These glass compositions contain a substantial percentage of
Na2O which has a high corrosive action upon the melter refractory.
Thus, it would be advantageous to reduce the amount of Na2O
therein in the interest of melter life and economy.
In accord with the principles of my invention two
possible melting groups may be identified as follows:
Group I (low corrosive melt)
CONSTITUENT PERCENT BYTYPICAL TYPICAL
WEIGHT BOTTLEWINDOW
SiO2 60-90 77.4 75.7
Na2O 0-5 1.1 1.2
A123 0-10 2.9 2.1
CaO 0-30 14.5 13.9
MgO 0-10 2.3 5.9
K2O 0-10 0.5 0.4
BaO - 0-10 0. 3 ----
F2 0-10 0.5 ----
Fe23 0-2 0.3 0.3
so3 0-2 0.1 0.5
- 18 -
.: . , ..... : .. ...
, , , , . " .. .
~6~6~543
GROUP II (high corrosive melt)
CONSTITUENT PERCENT BYTYPICAL TYPICAL
WEIGHT BOTTLE WINDOW
SiO2 60-75 68.6 66.5
Na2O 10-40 31.0 33.2
A123 0-10 0.1 0.1
Fe23 0-2 0.2 0.2
The group I low corrosive melt represents the largest
portion of the two melts and therefore may be prepared as a base
glass in a large continuous melter commonly used in the prepara-
tion of molten glass. The expected campaign life of the base
glass melter will be extended by the substantial reduction of the
composition's corrosiveness.
The group II high corrosive melt may be prepared in
a relatively small melter and introduced to the base glass as
a melt or a frit. Alternatively, the group II composition may be
introduced to the molten base glass as a formulated batch there~y
eliminating the need for an additive melter.
EXAMPLE V
EUTECTIC SODA LIME GLASS
The liquidus temperature of the group I base glass in
Example IV is estimated at 3100F, and 1600F. for the group II
additive glass. By reformulating the group I melt to its best
eutectic composition of: ;
CONSTITUENTPERCENT BY WEIGHT
SiO2 61.6
A123
CaO 29.7
MgO 7.9
Fe23 0.3
-- 19 --
~069543
we may effectively lower its liquidus temperature to approximately
2380CF. for improved thermal efficiency in melting.
Accordingly the group II additive will become:
CONSTITUENTPERCENT BY WEIGHT
SiO2 72.7
A123 1.6
CaO 3-9
MgO 2.7
Na2O 18.3
K2O 0.3
Fe23 0.4
EXAMPLE VI
MULTIPLE PRODUCT GLASS
Figure 3 represents a flow diagram for a glass plant
capable of producing a wool glass product, a textile glass
product, an E glass product and a chemically resistant-"C" glass
product from one common glass composition,- The master glass
composition may comprise the composition:
CONSTITUENTPERCENT BY WEIGHT
SiO2 63.4
A123 16.0
CaO 19.0
TiO2 0.6
Since the master composition is free of volatile and corrosive
constituents a relatively long melter life may be expected and
the problem of volatile loss with the corresponding pollutant r
emission has been eliminated.
By intermixing the master composition and the following
additive compositions,
- 20 -
~l~
lO~9S~3
CONSTITUENT ADDITIVE PERCENT BY WEIG~T
#1 ~2 #3 #4
SiO2 60.2 47.3 ---- 65.6
2 3 _~ 4.9 --~~
B2O3 8.0 ____48.6 7.2
Na2O 19.3 3.12.8 10.7
CaO 4.2 26.67.7 12.3
MgO 4.0 8.528.2 3.2
2 ~~~~ ~~-- 4.2 ----
Fe23 0.3 ---- 2.8 0.3
2 5.60.7 ____
ZnO ---- 8.8 ---- ----
K2O ----____ ____ 0.7
BaO 3.1 ---- ---- ----
3 0.5 ---- ---- 0.1
the following product glass compositions may be obtained:
CONSTITUENT WOOL TEXTILE E C
GLASS GLASSGLASS GLASS
SiO2 61.1 58.3 54.6 65.2
A123 3.6 10.9 14.5 4.0
B2O3 6.2 ---- 6.9 5.4
Na2O 15.0 1.0 0.4 8.0
CaO 7.7 21.9 18.0 14.1
MgO 3.1 2.7 4.0 2.4
2 ~~~~ ~~~~ 0.6 ----
e23 0.2 ---- 0.4 0.2
TiO2 0.1 2.2 0.6 0.1
ZnO ---- 2.8 ---- ----
K2O 0-3 ---- ____ 0 5
BaO 2.4 ---- ---- ----
SO3 0.4 ---_ ____ 0.1
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1069S43
Because of the mix ratio of additive to master it may
be physically preferably to introduce and homogenize the master
glass composition into additive l and 4. Additive #2 however,
again presents the problem of B2O3 volatilization. It is
suggested to those skiiled in the art that by applying the
principles of my invention to additive #l it may in turn be
prepared by the multi-step method. Thus, the wool glass product
composition would be formed by the combining of three separately
prepared compositions.
Almost any glass composition may be formulated into a
base and one or more additive mixtures that when blended together
and homogenized will produce a predetermined or desired product
glass composition. The particular formulation of the base and
additives will largely be a function of processing goals,
physical properties of each composition, and raw materials
available. Many trade-offs may be necessary to obtain desired
proce~sing goals whatever they may be.
Many problems heretoforç confronting the glass making
industry may be solved or reduced in scope by applying my multi-
step glass making method.
Consider the teachings of U. S. Patent 2,900,264 issued
to Wilbur F. Brown August 18, 1959. Brown teaches a method of
changing the glass composition, within a continuously operating
tank type furnace, from "regular" to glare resistant glass or
vice versa without costly shut down and clean out of the tank.
Changing from "regular" to glare resistant glass according to
Brown requires making up a 0.355~ deficiency of Fe2O3 within the
tank. Brown's teaching requires a 72 hour period to accomplish
the change over and produces a large amount of waste glass product.
By the teachings of my invention herein a base glass composition
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~0695~3
may be formulated from ~hich "regular", glare resistant or highly
glare resistant glass may be produced by working into the base
an appropriate additive composition. Thus, the long change over
period, or tank down time, is no longer necessary and the
amount of waste product is substantially reduced.
Consider further the teachings of U. S. Patent 2,934,444
issued to Rowland D. Smith April 26, 1960. Smith teaches a
method by which the loss of B2O3 by volatilization from a glass
melting tank might be reduced. Smith's teachings, however,
requires first synthesizing borax and boric acid to produce a
sodium polyborate which may then be used as a batch ingredient.
Such pre-processing of raw materials increases the cost of glass
making and reduces the overall thermal efficiency. The problem
may be more efficiently and economically solved by applying the
principles of my invention as taught in my Example I.
Still furthe~, consider U. S. Patent 2,411,031 issued ;?
to Alden J. Deyrup November 12, 1946. Deyrup accounts for
variations in optical glass compositions by the volatilization
of constituents. The principles of my invention may be applied, -
as taught above, to solve the problem o~ volatile losses.
Also, consider the energy savings taught in U. S. Patent
3,607,190 issued to Harvey L. Penberthy by pre-heating of batch
prior to introduction to the melter. Penberthy is cautious not to
pre-heat the batch granules to their fusion or sintering tempera-
ture as they then become tacky and difficult to transport. The
temperature to which batch may be pre-heated is limited by the
lowest sintering temperature of the combined batch ingredients.
Applying the principles of my invention the low sintering
temperature ingredients may be removed from the base batch
formulation thereby elevating the temperature to which the batch
may be pre-heated.
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1069543
Thus, greater thermal efficiency may be achieved.
Further, since the removed volatiles are usually the more
corrosive constituents to the refractory and the volatile
emissions attack the tank crown, their removal provides additional
cost savings by extending melter life.
In practicing my multi-step method of glass making it
will most frequently be necessary to blend and homogenize molten
compositions having significantly different properties, such as
viscosity, density, softening point, working point, liquidus,
surface tension, coefficient of expansion, modulus of elasticity
and electrical resistivity into a workable glass composition
having properties unlike any of the intermixed compositions.
Therefore, the manner by which the molten compositions are inter-
mixed and worked together to form the final desired glass
composition becomes important.
Consider Figure 4 presenting representative curves
depicting molten viscosity-temperature relationships for the
group I, group II and final homogenized product glass compositions
of Example II. Curves representing fused silica glass and 96%
5ilica glass are plotted to provide a qualitative relationship
between curves.
The viscosity of the group I host composition at 2683F.
is log 2.50 and that of the group II additive at 2000F. is log
0.50. The final homogenized product glass composition has a
viscosity of log 2.50 at 2339 F. Thus, intermixing the group II
additive into the group I host may be compared to mixing
ethylene glycol into corn syrup at room temperature.
Figures S through 9 present apparatus which has proven
successful in producing textile fibers in accord with the
principles of my invention. I have found it desirable
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1069543
to me~_hanically blend the molten compositions immediately after
they are brought together. This technique has been found
necessary to prevent composition stratification which if
permitted to occur, makes intermixing nearly impossible.
Figure 5 illustrates typical apparatus for produ~ing
glass fibers embodying the present invention. A continuous
glass melter 10 is charged with the base glass batch formulation
by traversing hopper 11. Molten base glass is withdrawn from
melter 10 and flowed through forehearth 12. Positioned downstream
of melter 10 within forehearth 12 is a molten glass mixing zone
indicated by spiral stirrers 15 and 16. A more detailed descrip-
tion of the mixing zone and function of the stirrers is presented
below. The molten additive composition is prepared in separate
melting apparatus 20 and introduced to the mixing zone through
a suitable conduit 21. By a combined mixing and pumping action
of stirrers lS and 16 the molten additive composition is worked
into and homogenized with the molten base glass composition
forming the final molten glass composition. ~he final molten glass
composition is then conveyed through distribution forehearth 17
to glass fiber forming positions 22 and 23.
Figure 6 presents a pictorial view of the forehearth
mixing zone with stirrers 15 and 16 removed so that the
configuration and orientation of stirxer mixing blocks 13 and 14
may be viewed more clearly. The general flow of molten glass is ;~
from the upper left of Figure 6 to the lower right as indicated
by arrow 30. Mixing blocks 13 and 14 are identical structures;
the only difference being their general orientation within the
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.
.. . .
1069543
forehearth channel. Therefore, to avoid redundant discussion,
the st:ructure of block 13 will be described with the understanding
that block 14 is the same except for orientation and function as
described.
Block 13 extends across the forehearth channel with its
upstream face 31 acting as a barrier or dam to the flow of molten
base glass. Cylindrical stirrer well 33 extends downward from
the top surfac~ 32 of block 13 communicating with slot 34 which
in combination with the forehearth channel floor forms a
rectangular passage extending longitudinally with the forehearth
channel exiting at the block downstream face 35.
Mixing block 14, similar in configuration to block 13,
is positioned downstream of block 13 with its slot 34a facing
upstream and opposite slot 34 of block 13. Extending between
mixing blocks 13 and 14 are ~ey blocks 36L and 36R having an
angular face 37L and 37R slanting from the forehearth side walls
to the forehearth floor thereby forming in combination with the
forehearth floor a flow channel communicating between slot 34 of
block 13 and slot 34a of block 14.
Figures 7 and 8 present a plan and side cross-sectional
elevation view respectively, of mixing blocks 13 and 14 with
screw-type stirrers 43 and 44 positioned therein. Stirrers 43
and 44 comprise a spiral blade wrapped about a central shaft
rotatably powered, as indicated by the arrows in Figure 7, by
any preferred means such as~a geared electric motor (not shown).
Upstream mixing block 13 acts as a dam to the flowing molten base
glass composition causing the base glass to flow over the top of
the block and into the region of influence of stirrer 43.
Immediately upstream of stirrer 43 the molten additive composition
is introduced to the flowing base glass composition, through
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~ ' ~
1069543
conduit 21, as it flows over the upstream portion of mixing
block 13. The molten additive is preferably introduced below the
surfac:e of the flowing base glass composition as shown.
Stirrer 43 mixes the molten base glass and molten
additive while pumping the mixture downward through mixing
block 13 causing the mixture to exit in a downstream direction
from slot 34. Key blocks 36L and 36R channel a major portion
of the exiting mixture to slot 34a of block 14 which acts as
an intake port for block 14. As indicated by arrow 45 in Figure
8 a portion of the molten mixture exiting from slot 34 flows
upward and is drawn back into mixing block 13 and thereby
recycled through stirrer 43. The portion of molten mixture
channeled to slot 34a is then further mixed while being pumped
upward through block 14, by action of stirrer 44. Exiting at
and flowing over the top surface of block 14 is the final molten
glass composition. A portion of the molten glass exiting the
top of block 14 flows upstream, a major portion of which arrow
46 is returned to the intake port 24a of block 14 and recycled;
the lesser portion continues upstream, as indicated by arrow 48,
and is recycled through mixing block 13. The remaining molten
composition indicated by arrow 47 flows downstream to distribution
forehearth 17. The reverse flow patterns, arrows 45, 46 and 48
cause the natural occurrence of a fluidic ~ront or dam to be
established atop mixing block 13 as indicated by line 50.
Upstream of fluidic front 50 is pure base glass. Thus, the
presence of fluidic front 50 directs the flow of unmixed lten
base glass through mixing block 13 preventing fluidic short
circuiting. Alternatively, a structural dam may be constructed
atop block 13 thereby assuring the flow of unmixed base glass
through block 13.
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1069543
Figure 10 presents a cross-sectional elevation of a
two zone furnace also suitable for practicing my invention. The
main melting chamber 60 may employ electric joule effect heating
or fossil fuel firing, whichever is preferred, to melt the base
constituents. The molten base constituents flow through submerged
throat 61 upward through riser 62 and into the pull or suction of
downward pumping stirrer 63. The additive composition formulated
to transform the molten constituents prepared in zone 60 into the
final desired working or product glass composition is preferably
introduced upstream of stirrer 63 through suitable conduit means
64. It may be desired to forcefully blend the molten base
composition as it proceeds upward through riser 62 by placing an
upward pumping stirrer therein. Thus, the residence time for the
molten base composition within zone 60 may be reduced.
Downward pumping stirrer 63 initially blends the base
and additive compositions discharging the blended mixture into
refining zone 65. Depending upon the volatility of the blended
constituents residing in zone 65 it may be preferred to provide
a hood and associated ducting to convey any volatile emissions to
a scrubbing device, not shown.
From refining zone 65 the blended constituent mixture
enters upward pumping stirrer 71 through entry port 70 therein
being finally homogenized and flowing into supply forehearth
72 as a workable molten glass having the desired product forming
characteristics.
Many alternatives to the apparatus of Figure 10 are
possible to improve functional operation. For example, heating
electrodes may be placed in riser 62 to maintain the base
constituent's exit temperature from melting chamber 60 or
elevate its temperature to assist blending of the additive into
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~ , . .... .
1069543
the base composition. Mechanical or thermal mixing apparatus may
be added to refining zone 65 to increase the rate of homogenization
and recluce residence time therein.
Depending upon the composition being worked and their
relative properties, such as viscosity or density it may be
advantageous for example to introduce fluxing constituents in
melter throat area 61 to lower the base compositlon viscosity in
advance of further additive introduction. Thus, the base
composition may be conditioned to receive additional additive
constituents from conduit 64.
Figure 11 presents apparatus for practicing my invention
which is particularly advantageous where three melting groups,
one of which may be in batch form are blended for homogenizing
into a desired product formable glass composition. A molten base
composition 80 is prepared in a melter, not shown, and flowed
into forehearth 81. Positioned within forehearth 81 is mixing
block 82 extending in a dam like manner across the forehearth
similar to block 13 of Figure 8. Extending from the top surface
83 of block 82 is cylindrical passage 84 communicating with exit -
20 85, similar to block 13 of Figure 9. Positioned within passage
84 is stirrer means 86 suitable for blending, homogenizing and
forcefully pumping molten constituents downward through passage
84 and exiting through exit 85 into the downstream portion of the
forehearth. A first additive formulation is prepared as a molten
composition 90 in melter 91 and flowed to exit orifice 92. A
second additive formulation prepared as a molten composition 95
is a separate melter, not shown, is flowed through nozzle 96
which extends through molten composition 90 and into exit
orifice 92 discharging a stream 97 of molten composition 95
within the center of, and encompassed by, stream 98 of molten
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1069543
composition 90 thus forming a composite stream 100. Composite
strealm 100 comprising both the first and second additive flows
into the molten base composition stream upstream of stirrer 86
and is drawn into stirrer 86 along with the molten base composi-
tion. Stirrer 86 blends and homogenizes the three molten
compositions into the final desired product composition.
Apparatus of Figure 11 may be particularly advantageous where
molten composition 95 is highly volatile as it may be completely
surrounded by molten stream 98 preventing volatile losses from
stream 97.
Molten composition 95 may be prepared in a melter of
the type disclosed in U. S. Patent 3,429,972 suitable for
preparing molten compositions of mineral constituents having
relatively high fusion temperatures such as SiO2. Molten
composition 95 may be replaced by an unmelted batch formulation
as taught in U. S. Patent No. 2,371,213.
The apparatus of Figure 11 may be conveniently modified
for processing a product glass composition from two melting
groups. Melters 91 and 96 may be used to prepare the base and
additive compositions respectively. Composite stream 100 may then
be fed directly into any suitable mixing apparatus known in the
art. For example, the apparatus disclosed in U. S. Patent Nos.
3,942,968; 3,811,861; 3,725,025; 3,486,874; 3,174,729; 3,057,175;
2,730,338; 2,716,023; 2,688,469; 2,577,920; 2,570,079; 2,569,459
and 2,520,577 might be used.
By practicing my improved method of preparing molten
glass compositions a new freedom of glass formulating is
available. Not only may speclfic base glasses be formulated to
improve the overall economics of the glass making process but
highly volatile constituents, such as water, may now be formulated
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1069543
into the molten glass composition.
In conclusion, it is pointed out that while the
illustrative examples constitute practical embodiments of the
invention, it is not intended to limit the invention to the exact
details shown since modifications may be made without departing
from the spirit and scope of the invention disclosed.
