CA1117148A - Glass manufacturing - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
B2O3-containing, glass forming pellets are set forth which include ulexite as a source of B2O3. These pellets are superior to pellets wherein the source of B2O3 is a borax for purposes of economic glass manufacturing.

Description

The present invention relates yenerally to g]ass manufacturing an~, more particularly, it relates to glass manufacturing wherein the ~lass batch is ~irst formed into agglomerates, for example with water, and subsequently melted to produce a molten glass.
It is ~nown in the glass manufacturing art that glass batch materials may be formed into agglomerates and that these agglomerates may be discharged to a melting furnace ~or vitrification of the batch ingredients. These agglomerates are, generally, composite, integral, self supporting masses of batch materials and may be agglomerated in the form of extrusions, discs, briquettes, or pellets. ~xemplary teachings as to this may be found in U. S. Patent No. 3,880,639, which issued to Bodner et al on April 29, 1975. 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 made to U. S. Patent No. 3,914,364 which issued to Engelleitner et al on October 21, 1975, which is assigned to the Dravo Corporat~ion. U. S. Patent No. 2,366,473 which issued 20 to Baid on January 2, 1945 also discloses forming glass batch into agglomerates.
In the fibrous glass manufacturing industry, B2O3 containing glasses have been manufactured extensively for some period of time. Exemplary of such glasses are those set forth in U. S. Patent Nos. 2,877,124 which issued to Welsch on March 10, 1959 and 2,8a2,173 which issued to Welsch on April 147 1959 which compositions are generally employed for thermal insulation products. Generally the glasses which have been commercialized in the past for such products may be referred to as soda-lime aluminoborosilicate glasses in that they substantially comprise a combination oE Na2O, CaO, A12O3, B2O3, and SiO2. The source of s2o3 in these glasses has commonly been a borax, i.e. borax itself, anhydrous borax or 5 mole borax. If clesired, boric acid may also be employed as the B2O3 source as may ulexite or colemanite as taught in U. S. Patent No. 3,274,006 which issued to MclCinnis on September 20, 1966.
The manufacture of B2O3 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 discharying such preheated pellets into the melting furnace. Applicant has found however, that all B2O3 sources are not equivalent for such a process. For example, when a borax is employed as the source ` of B2O3, agglomerates formed by consolidating the batch into individualized units with water, for example as pellets, 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 of the size of at least ~; ~ about ~ inch, and generally in the range of about ~ 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

- 2 -4~3 as non-acJgre~atecl, discrete ~lowable pelle-ts which can be conveniently conveyed to a melting furnace, they transform, or coalesce into an unacceptable, ac~gregated mass. Boric acid likewise, is not suitable for such a process because it has an unaccep-tably low softening or fusion point which severely handicaps the ability to heat such pellets prior to discharging or conveyiny them into the melting f urnace, to an elevated temperature. Colemanite and calcined colemanite are also not satisfactory for purposes of making the above indicated B2O3 10 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 B2O3 source in the agglomerate cannot be competitively tolerated.
U. S. Patent Nos. 4,074,989, 4,074,990, and 4,074,991 each of which patents issued to Brozozowski et al on February 21, 1978 are directed to methods for preparing B2O3 containing batch in the form of pellets respectively employing anhydrous boric 20 acid, colemanite and boric acid. As indicated previously, such materials are not suitable for the purposes contemplated herein.
For example, B2O3 has a melting point of the order of 450 to 500C
which substantially precludes pellets made wi-th such a material from being heated to an elevated temperature.
According to one aspect of the present invention in a method for producing B2O3 containing glass r the improvement comprises forming batch ingredients, including a sodium calcium borate as a major source of B2O3, into a plurality of individual agglomerates with water, drying said agglomerates under 30 conditions of time and temperature to remove substantially all ~1 17~L4~

watcr clnd convert ~;aid agc~lomerates into dried, free-flowing agglomerates and heatiny said dried agglomerates so as to produce hot, free-flowing dried, ayglomerates.
According to a further aspect of the present invention a s2O3 con-taining glass batch in the form of non-fractured, flowable agglomerates which have been dried and heated to a temperature less than the sintering temperature contain sodium calcium borate as a major ~ource of said B2O3.
Accordingly with this invention, the applicant provides for an improvement in processes of the above type as related to glass manufacturing wherein a B203-containing glass is produced by forming batch ingredients therefor, including ulexite as a source of B2O3, into a plurality of individual agglomerates with water.
Preferably, the agglomerates will be in the form of pellets containlng about S-20% by weight free water. These agglomerates may then be dried, under conditions of time and temperature, to remove substantially all water and convert them into dried, free-flowing agglomerates; the dried, free-flowing agglomerates may then be further heated, or preheated to an elevated temperature, for example a temperature in excess of about 500C but short of the fusion temperature of the composition, to produce a mass of free-flowing nonaggregated, dried agglomerates which may be transported in any convenient manner to a glass melter for melting. There is nothing in the above prior art which would suggest with any real predictability of success, that ulexite can be employed as the source of B2O3 in such agglomerates so as to allow one to practice such a process.
Acceptable results will be realized when the ulexite 4~3 is the major (e.~. greater than 50%) source of B2O3 in the batch. Outstanding results are obtained when such ulexite is present as substantially sole source of B2O3 or for example, an admixture of ulexite and a borax may be employed preEerably with the weight ratio of ulexite to such borax being at least about 2:1. The batch may be formed into agglomerates using conven-tional techni~ues. 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 sîze 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:
SiO2 59-64; A12O3 3.5-5.5; CaO 7.5-9.5; MgO 0.1-3.7: B2O3 4-12;
Na2O 12-16; K2O 0.2-2.8; Fe2O3 0.1-0.3; TiO2 0-0.4; SrO 0-0.4;
saO 0-2.4; Li2O 0-0.2; and SO3 0-0.5. Preferably the batch for such a composition will comprise sand, clay, dolomite or burnt dolomite, ulexite and soda-ash.
Ulexite, as used herein, is not intended to be limited to a precise crystalline composition bu-t comprehends within its scope that material which is available commercially for glass manufacturing purposes. Such material which is a sodium calcium ; borate will vary depending upon its source. For example, domestic ulexite on a wet basis generally includes about 25 to 29 percent B2O3, about 21 to 26 percent CaO, about 5 to 13 percent SiO2, abaut 4 to 5 percent Na2O, and of the order of slightly less than 1 to slightly in excess of 2 percent by weight A12O3. Such ulexites include small amounts of other metal oxides and also volatiles such as water and carbon dioxide. Ulexite obtained from Turkey typically will contain about 38 to 39 percent B2O3, 15 to 18 percent CaO, 2 to 3 percent SiO2, 4 to 7 percent Na2O, and trace amounts of other oxides including A12O3.
That material likewise will include volatiles such as for example, water.
While the foregoing adequately se-ts forth the invention to enable those skilled in the art -to make and use it, nonethe-less, further exemplification follows.

A B2O3 containing batch was formulated employing 1121 parts by weight of Central sand, 325 parts by weight of naph.
syenite, 149 parts by weigh-t burnt dolomite, 171 parts by weight Spore limestone, 372 parts by weight of 5 mole bora~, 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 cont~nt in the range of about 5 to about 20 percent. The diameters of the pellets were about ~ 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 the crucible then being positioned in an electric furnace held at a temperature of about 1200F. 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 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 B2O3 in a pelletized batch for a soda lime alumino borosilicate glass.

'7~

rn a separate experiment 5 mole borax was employed as the source o~ B2O3 for producing a common alkaline earth, alumino borosllicate textile fiber glass, i.e., E ylass which contains less than about I percent Na2O. Pelle-tization 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 B2O3 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 nonaggregated 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 500C 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 weigh-t Central sand, 7.8 percent by weight Ewing clay, 3 percent by weight burnt dolomite, about 0.3 percent weight Spore lime-stone, 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 o~ B203 and the pellets are positioned on a belt conveyor, for example, to a height of the order of 1 to 1~ 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 is encountered and such hot pellets for example, pellets in the temperature range in excess of 500C can be transported to the melting furnace and melted therein.

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Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for producing B2O3 containing glass, the improvement comprising: forming batch ingredients, including a sodium calcium borate as a major source of B2O3, into a plurality of individual agglomerates with water, drying said agglomerates under conditions of time and temperature to remove substantially all water and convert said agglomerates into dried, free-flowing agglomerates and heating said dried agglomerates so as to produce hot, free-flowing dried, agglomerates.

2. The method of claim 1 wherein said sodium calcium borate is substantially the sole source of B2O3.

3. The method of claim 1 wherein said sodium calcium borate is minus 200 mesh in particle size.

4. The method of claim 1 and further including discharging said dried, hot agglomerates to a melting furnace.

5. The method of claim 1 or 2 or 3 wherein said agglomerates are pellets and wherein said pellets are heated to a temperature in excess of about 500°C.

6. The method of claim 1, 2 or 3 wherein said glass is a soda-lime aluminosilicate glass consisting essentially of the following in approximate weight percent SiO2 59 - 64 CaO 7.5 - 9.5 MgO 0.1 - 3.7 Na2O 12 - 16 K2O 0.2 - 2.8 Fe2O3 0.1 - 0.3 TiO2 0 - 0.4 SrO 0 - 0.4 BaO 0 - 2.4 Li2O 0 - 0.2 SO3 0 - 0.5,

7. The method of claim 1, 2 or 3 wherein said batch ingredients further including sand, clay, dolomite or burnt dolomite, limestone, soda ash.

8. The method of claim 1, 2 or 3 wherein the B2O3 source is sodium calcium borate and a borax with the weight ratio of the former to the latter being at least about 2:1.

9. A B2O3 containing glass batch in the form of non-fractured, flowable aggIomerates which have been dried and heated to a temperature less than the sintering temperature, said agglomerates containing sodium calcium borate as a major source of said B2O3.

10. The batch of claim 9 wherein said glass batch also contains Na2O.

11. The batch of claim 9 or 10 wherein said pellets are at a temperature in excess of about 500°C.