Glass manufacturing

An improvement is provided in forming a B.sub.2 O.sub.3 containing glass from heated glass batch agglomerates by using an uncalcined, mineral sodium calcium borate which contains chemically bound water to form the agglomerates. These agglomerates can be heated, prior to melting, to a temperature in excess of that needed to substantially remove all of said chemically bound water without the water release causing the agglomerates to disintegrate.

FIELD OF INVENTION 
The present invention relates generally to glass manufacturing and, more 
particularly, it relates to glass manufacturing wherein the glass batch is 
first formed into agglomerates, for example with water, and subsequently 
melted to produce a molten glass. 
BACKGROUND 
It is known in the glass manufacturing art that glass batch materials may 
be formed into agglomerates and that these agglomerates may then be 
discharged to a melting furnace for vitrification of the batch 
ingredients. These agglomerates are, generally, composite, integral, self 
supporting masses of batch materials and may be in the form of extrusions, 
discs, briquettes, or pellets. Exemplary teachings as to this may be found 
in U.S. Pat. No. 3,880,639. For further exemplification, as to a manner in 
which glass batch may be formed into agglomerates, as for example, by 
forming the batch into pellets with water, reference may be had to U.S. 
Pat. No. 3,914,364 which is assigned to the Dravo Corporation. U.S. Pat. 
No. 3,366,473 also discloses forming glass batch into agglomerates. 
In the fibrous glass manufacturing industry, B.sub.2 O.sub.3 containing 
glasses have been manufactured extensively for some period of time. 
Exemplary of such glasses are those set forth in U.S. Pat. Nos. 2,877,124 
and 2,882,173 which compositions are generally employed for thermal 
insulation products. Generally the glasses which have been commercialized 
in the past for such products may be referrred to as soda-lime 
aluminoborosilicate glasses in that they substantially comprise a 
combination of Na.sub.2 O, CaO, Al.sub.2 O.sub.3, B.sub.2 O.sub.3, and 
SiO.sub.2. The source of B.sub.2 O.sub.3 in these glasses has commonly 
been a borax, i.e., borax itself, anhydrous borax or 5 mole borax. If 
desired, boric acid may also be employed, as the B.sub.2 O.sub.3 source, 
as may ulexite or colemanite as taught in U.S. Pat. No. 3,274,006. 
The manufacture of B.sub.2 O.sub.3 containing glasses, for example the 
above fibrous glass products, by the use of agglomerates is highly 
desirable. This is especially true in those instances where the 
agglomerates are heated at a temperature and for a time sufficient to 
remove water, i.e., dry them (as where the batch has been formed into 
pellets with water) and then to further heat these pellets to an elevated 
temperature, which is short of their sintering or melting temperature, 
followed by discharging such preheated pellets into the melting furnace. 
Applicant has found however, that all B.sub.2 O.sub.3 sources are not 
equivalent for such a process. For example, when a borax is employed as 
the source of B.sub.2 O.sub.3, agglomerates formed by consolidating the 
batch into individualized units with water, for example as pellets, may 
slump when heated which substantially precludes the pellets from being 
conveyed to the melting furnace in an acceptable economical manner. That 
is, when a borax is employed to form batch into pellets with water, for 
example pellets on the size of at least about 1/4 inch, and generally in 
the range of about 1/4 to 3/4 inch, with the water employed for 
pelletization being about 5 to about 20 percent by weight, these pellets 
have a latent, unacceptable rheological property. As several layers of 
these pellets are first heated under conditions of time and temperature to 
dry them and then further heated (preheated) to a temperature short of 
their sintering, or fusion, temperature, instead of remaining as 
non-aggregated, discrete flowable pellets which can be conveniently 
conveyed to a melting furnace, they transform, or coalesce into an 
unacceptable, aggregated mass. Boric acid likewise, is not suitable for 
such a process because it has an unacceptably low softening or fusion 
point which severely handicaps the ability to heat such pellets, prior to 
discharging or conveying them into the melting furnace, to an elevated 
temperature. Colemanite and calcined colemanite are also not satisfactory 
for purposes of making the above indicated B.sub.2 O.sub.3 containing 
glass products from preheated pellets. For example, calcined colemanite is 
economically not suited for soda-lime alumino borosilicate glasses because 
these glasses are relatively inexpensive glasses and the employment of 
such a material as the B.sub.2 O.sub.3 source in the agglomerate cannot be 
competively tolerated. 
U.S. Pat. Nos. 4,074,989, 4,074,990, and 4,074,991 are directed to methods 
for preparing B.sub.2 O.sub.3 containing batch in the form of pellets 
respectively employing anhydrous boric acid, colemanite and boric acid. As 
indicated previously, such materials are not suitable for the purposes 
contemplated herein. For example, B.sub.2 O.sub.3 has a melting point on 
the order of 450.degree. to 500.degree. C. which substantially precludes 
pellets made with such a material from being heated to an elevated 
temperature. Boric acid, on the other hand, tends to steam distill when 
the water containing agglomerates are heated and thus cause B.sub.2 
O.sub.3 losses. 
U.S. Pat. No. 4,074,990 discloses the use of colemanite as a batch 
ingredient for glass manufacturing. If the colemanite is not calcined, in 
accordance with that patent, the agglomerates (pellets) cannot be heated 
above 410.degree. C.; otherwise the pellets will disintegrate. Obviously 
this is not acceptable because it limits the temperature to which the 
pellets can be heated before being supplied to a melter and this is an 
especially serious handicap when it is desired to salvage sensible heat in 
flue gases by using them to preheat the agglomerates by passing the gases 
directly through a bed of such agglomerates. If it is desired to heat the 
pellets above 410.degree. C., this patent states that the chemically bound 
water must be removed, by calcination, prior to using the material to form 
pellets. Such required pre-processing serves to increase batch cost and, 
consequently, glass cost. 
Thus, in accordance with this invention, Applicant provides for an 
improvement in processes of the above type as relates to glass 
manufacturing wherein a B.sub.2 O.sub.3 --containing glass is produced by 
forming batch ingredients therefor, including an uncalcined, mineral 
sodium calcium borate which contains about 5 or more moles of chemically 
combined water as a source of B.sub.2 O.sub.3, into a plurality of 
individual agglomerates with water. Preferably the agglomerates will be in 
the form of pellets containing about 5-20% by weight free water. These 
agglomerates may then be dried, under conditions of time and temperature 
to remove substantially all unbound water and convert them into dried, 
free-flowing agglomerates; the dried, free-flowing agglomerates may then 
be further heated, or preheated, to temperature higher than that needed to 
remove substantially all chemically bound water, for example a temperature 
in excess of about 500.degree. C. but short of the fusion temperature of 
the composition, to produce a mass of hot, free-flowing non-aggregated, 
dried agglomerates which may be transported in any convenient manner to a 
glass melter for melting. There is absolutely nothing in the above prior 
art which would suggest, certainly not with any predictability of success, 
that such borates can be employed as the source of B.sub.2 O.sub.3 in such 
agglomerates so as to allow one to practice such a process without 
substantial steam distillation losses and without disintegration by 
release of chemical water. 
Acceptable results will be realized when the borate is the major (e.g. 
greater than 50%) source of B.sub.2 O.sub.3 in the batch. Outstanding 
results are obtained when such borate is present as substantially the sole 
source or, for example, an admixture with a borax may be employed with the 
weight ratio of such borate to such borax being at least about 2:1. The 
batch may be formed into agglomerates using conventional techniques. For 
example, when pellets are formed, these pellets may be formed by hand, but 
it is preferred to employ commercial pelletizing equipment such as a 
rotary disk like that commercially available from the Dravo Corporation. 
When pelletizing on a disk with water, it will be found that most 
preferably the particle size of the ulexite will be -200 mesh. Outstanding 
results will be obtained in practicing this method when producing a 
soda-lime alumino borosilicate glass consisting essentially of the 
following in approximate weight percent: SiO.sub.2 59-64; Al.sub.2 O.sub.3 
3.5-5.5; CaO 7.5-9.5; MgO 0.1-3.7; B.sub.2 O.sub.3 4-12; Na.sub. 2 O 
12-16; K.sub.2 O 0.2-2.8; Fe.sub.2 O.sub.3 0.1-0.3; TiO.sub.2 0-0.4; SrO 
0-0.4; BaO 0-2.4; Li.sub.2 O 0-0.2; and SO.sub.3 0-0.5. Preferably the 
batch for such a composition will comprise sand, clay, dolomite or burnt 
dolomite, the uncalcined, mineral sodium calcium borate and soda-ash. When 
producing a Na.sub.2 O and B.sub.2 O.sub.3 containing glass, as will 
subsequently be seen, by using such borate and a sodium carbonate as the 
sources of B.sub.2 O.sub.3 and Na.sub.2 O, these materials uniquely 
interact to form agglomerates having unexpectedly high dry strengths. The 
significance of this is readily apparent. 
Uncalcined, mineral sodium calcium borates contemplated for use herein may 
be specifically exemplified by the formula NaCaB.sub.5 O.sub.9.X H.sub.2 
O, wherein X is between 5 and 8. More specifically such borates are 
represented by natural occurring deposits of ulexite and/or probertite. 
Such deposits will compositionally vary depending upon the source. For 
example, domestic source ulexite on a wet basis generally includes about 
25 to 29 percent B.sub.2 O.sub.3, about 21 to 26 percent CaO, about 5 to 
13 percent SiO.sub.2, about 4 to 5 percent Na.sub.2 O, and on the order of 
slightly less than 1 to slightly in excess of 2 percent by weight Al.sub.2 
O.sub.3. Such ulexites include small amounts of other metal oxides and 
also volatiles such as water and carbon dioxide. Ulexite obtained from 
Turkey contains probertite and typically will contain about 38 to 39 
percent B.sub.2 O.sub.3, 15 to 18 percent CaO, 2 to 3 percent SiO.sub.2, 4 
to 7 percent Na.sub.2 O, and trace amount of other oxides including 
Al.sub.2 O.sub.3. That material likewise will include volatiles such as 
for example, water. Ulexite and probertite can be easily detected in these 
sources by x-ray analysis.

While the foregoing adequately sets forth the invention to enable those 
skilled in the art to make and use it, nonetheless, further 
exemplification follows. 
EXAMPLE I 
A B.sub.2 O.sub.3 containing batch was formulated employing 1121 parts by 
weight of Central sand, 325 parts by weight of nepheline syenite, 149 
parts by weight burnt dolomite, 171 parts by weight Spore limestone, 372 
parts by weight of 5 mole borax, 350 parts by weight soda-ash, and 15 
parts by weight salt-cake. Portions of that batch were pelletized with 
water to produce generally spheroidal pellets having a water content in 
the range of about 5 to about 20 percent. The diameters of the pellets 
were about 1/4 inch to about 3/8 inch. These pellets were then positioned 
in several layers upon each other in a crucible having a height of about 
one inch with a crucible then being positioned in an electric furnace held 
at a temperature of about 1200.degree. F. It was observed, that the 
pellets did not remain as a dried, non-agglomerated mass of discrete, 
flowable pellets but they coalesced, or slumped, into an aggregated mass. 
It will be immediately apparent that such pellets cannot be be 
conveniently transported or conveyed to a melting furnace for fusion. 
Substantially similar results were obtained when anhydrous borax was used 
instead of 5 mole borax as the source of B.sub.2 O.sub.3 in a pelletized 
batch for a soda lime alumino borosilicate glass. 
In a separate experiment 5 mole borax was employed as the source of B.sub.2 
O.sub.3 for producing a common alkaline earth, alumino borosilicate 
textile fiber glass i.e., E glass which contains less than about 1 percent 
Na.sub.2 O. Pelletization of the batch ingredients for that composition 
with water followed by drying and further heating showed that the pellets 
fractured as a result of an expansion or blooming characteristic of the 
sodium borate. 
EXAMPLE II 
In an experiment similar to I above, another B.sub.2 O.sub.3 containing 
batch was formulated from about 1098 parts by weight of Central sand, 
about 315 parts by weight naph. syenite, about 154 parts by weight of 
burnt dolomite, about 170 parts by weight of 5 mole borax, about 348 parts 
by weight of domestic ulexite, about 400 parts by weight of soda-ash and 
about 15 parts by weight of salt-cake. Pellets made in a similar fashion 
were positioned in several layers in the crucible and likewise heated. In 
contrast to the result in Example I, where the pellets slumped into an 
aggregated mass, these pellets remain as discrete free-flowing 
agglomerates. That is, although these pellets contact each other, they 
remain in such condition in a non-aggregated discrete form. Hence, it will 
readily be apparent that such pellets when preheated short of their 
sintering temperature can be transported by conventional materials 
handling equipment to a melting furnace for melting in a manner quite 
simple and economical compared to those of Example I. Thus, such pellets 
after they become dry by heating can be further heated to an elevated 
temperature, for example, in excess of 500.degree. C. but short of the 
fusion temperature, and transported to a melting furnace without 
encountering the slumping problem encountered when using a borax. 
The same outstanding results were obtained when employing pellets made from 
a batch of about 45.5 percent by weight Central sand, 7.8 percent by 
weight Ewing clay, 3 percent by weight burnt dolomite, about 0.3 percent 
weight Spore limestone, about 23.6 percent by weight domestic ulexite, and 
about 19.9 percent by weight soda-ash. 
Substantially similar results are obtained when pellets are formed as 
described herein with ulexite as a source of B.sub.2 O.sub.3 and the 
pellets are positioned on a belt conveyor, for example, to a height of on 
the order of 1 to 11/2 inches, and then these pellets are heated with dry 
air, for example, indirectly heated air, to a temperature and for a time 
sufficient to dry the pellets and then further heated to an elevated 
temperature short of the fusion point of those pellets. No slumping or 
pellet disintegration is encountered and such hot pellets for example, 
pellets at a temperature in excess of 500.degree. C. can be transported to 
the melting furnace and melted therein. 
EXAMPLE III 
The following shows the unexpected benefit of using probertite or ulexite 
as the B.sub.2 O.sub.3 source and soda-ash as the Na.sub.2 O source in 
forming pellets of a Na.sub.2 O and B.sub.2 O.sub.3 containing silicage 
glass. Water containing glass batch pellets were manufactured using 
various combinations of sand, soda-ash, ulexite and clay for the batch 
compositions. Table 1 shows the compositions along with the water content 
of the pellets. The green strengths of the pellets were measured, the 
pellets then dryed and the dry pellet strength then determined. Drying was 
done in a laboratory air convection oven at a temperature of about 
230.degree.-240.degree. F. for about 3 hours. Reference to Table 1 will 
clearly indicate the unexpected, unique, synergistic interaction of 
ulexite and soda-ash in producing pellets, or agglomerates, with high dry 
strengths. Similar results will be realized with probertite. 
TABLE I 
__________________________________________________________________________ 
Composition Pellet H.sub.2 O 
Pellet Pellet 
(grams) Content Green Strength 
Dry Strength 
Sand 
Soda Ash 
Ulexite 
Clay 
(% - Dry Basis) 
(lbs.) (lbs.) 
__________________________________________________________________________ 
710 
312 357 122 
17.8 .+-. 1.4 
5.5 .+-. 1.8 
41 .+-. 11 
931 
409 -- 160 
16.7 .+-. 0.3 
10.9 .+-. 1.8 
2.2 .+-. 0.6 
896 
-- 450 154 
12.7 .+-. 5.0 
1.5 .+-. 0.3 
11.8 .+-. 1.8 
773 
339 388 -- 16.3 .+-. 0.4 
7.8 .+-. 0.7 
40 .+-. 9.0 
773 
339 388 -- 14.2 .+-. 0.5 
6.2 .+-. 1.2 
57 .+-. 13 
__________________________________________________________________________ 
Accordingly in order to obtain agglomerates with synergistically improved 
dry strengths, the before mentioned soda lime aluminoborosilicate glasses 
containing about 12-16% Na.sub.2 O and about 4-12% B.sub.2 O.sub.3 will 
desirably employ soda-ash as substantially the sole source of Na.sub.2 O 
and ulexite or probertite, or a mixture thereof, as substantially the sole 
source of B.sub.2 O.sub.3. 
Preferably the present invention will be practiced by forming the batch 
ingredients into water containing agglomerates, drying the agglomerates 
and preheating them to a temperature short of their fusion, or sintering, 
temperature and discharging the preheated pellets to a melter. Preferably 
the pellets are preheated to a temperature in excess of about 500.degree. 
C. Desirably the pellets will be manufactured on a rotary disc pelletizer. 
While pelletizing is art and the pelletizer will need to be adjusted for 
optimum results on any specific glass batch, it is desirable to control 
the pelletizer using the water control scheme generally set forth in 
copending application U.S. Ser. No. 965,632 filed on behalf of Mr. Seng. 
That is a pivotally supported paddle type sensor is employed to control 
the feed of water to the pelletizer. Preferably the paddle will be located 
in the finished pellet stream, as set forth in copending application now 
abandoned Ser. No. 974,470 filed on behalf of Mr. Henry, at about an 8 
to 9 o'clock position. The water supply will include one duct supplying a 
constant flow of water to a main supply line and a second duct containing 
a solenoid valve also in fluid communication with the main supply. The 
paddle sensor is used to operate the solenoid valve in an on-off fashion, 
as set forth in the above Seng application so as to produce substantially 
uniform size pellets. Batch will be supplied to the pelletizer along a 
chord of the disc between about the 5:30 and 6:30 positions with the water 
supply being furnished by sprays located generally on a chord between the 
4 and 8 o'clock positions and to right of a diameter running through the 6 
and 12 o'clock positions of the circular disc of the pelletizer. Desirably 
the pelletizer will also be equipped with a rotary scraper device. This 
device includes two pairs of generally normally related arms with each arm 
having a radius of about one-half the radius of the pelletizer disc and 
has its axis of rotation about midway along the radius of the disc drawn 
to about the 3 o'clock position. One pair of arms, which may be viewed as 
a diameter of the circle through which the device rotates, includes 
scrapers at its diametric end portions adapted to scrape the sidewall of 
the rotating disc pelletizer. The other pair of arms include diametrically 
opposed scrapers operating closely adjacent to the bottom of the disc of 
the pelletizer. Most desirably the pellets will be dried and preheated in 
accordance with the teachings of U.S. Ser. Nos. 031,368 and 031,369, both 
now abandoned filed on behalf of Messrs. Hohnman, Seng, Henry and 
Propster, both of which are hereby incorporated by reference, and then 
melted in either a fossil fueled fired melter or an electrically powered 
melter. Most suitable operation will be effected by using the above 
uncalcined, mineral sodium calcium borates containing at least 5 moles of 
chemical water as substantially the sole source of boric acid or in 
combination with a borax, e.g. 5 mole borax, with the amount of the latter 
being less than about about 2-3% by weight of the batch.