On Granule Formation in High-Boron Glass Batch
Abstract Generated abstract
This paper examines granule formation in a high-boron batch for 3S-5K electrovacuum glass, a process of interest because granulation can improve production conditions and reduce losses of volatile boron compounds. The authors determine specific surface area, maximum molecular moisture capacity, capillary moisture capacity, plasticity, and an agglomerability index for the batch and its components, arguing that agglomerability better characterizes granulatability than plasticity alone. The results indicate that boric acid has the highest granulating ability among the components, while the complete batch is moderately granulatable, with an experimentally determined optimum moisture content of about 12 percent, close to its maximum molecular moisture capacity, for obtaining the greatest yield of 3 to 10 mm granules.
Full Text
ON THE QUESTION OF GRANULATION IN HIGH-BORON GLASS BATCH
V. M. Vyutugin, N. I. Lozbina, A. V. Petrov,
L. N. Serdyuk, G. D. Spetstsi
(Presented by the scientific seminar of the Department of General Chemical Technology)
The few published data on the granulation of glass batches concern mainly batches for the production of the most widely used glasses \[1, 2, 3\].
Granulation of boron-containing batches is of particular interest, since it sharply improves production standards and considerably reduces losses of volatile boron compounds in the glass-production process.
As is known, the ability of materials to form granules is determined by their physicochemical properties and by the granulation conditions.
The present work was carried out with the aim of determining the principal parameters that determine the granulatability of the properties of the batch for 3S-5K electrovacuum glass, of the following composition:
boric acid — 37%,
sand — 40%,
soda (calcined) — 11%,
alumina — 0.9%,
sodium nitrate — 10%,
common salt — 1.1%.
The results of determinations for the individual components and for the batch as a whole are given in Table 1.
Table 1
| Material | Specific surface, cm²/g | $W_{\mathrm{mmv}}$, % | $W_{\mathrm{kv}}$, % | K |
|---|---|---|---|---|
| Boric acid | 606 | 28.8 | 60.4 | 0.91 |
| Alumina | 2620 | 19.5 | 60 | 0.48 |
| Sodium nitrate | 420 | 0.68 | 18.4 | 0.068 |
| Soda | 3320 | 48.9 | — | — |
| Common salt | 478 | 0.45 | 27.7 | 0.017 |
| Sand | 234 | 0.09 | 25.6 | 0.0035 |
| Batch | 649 | 12.7 | 49.2 | 0.35 |
The specific surface, maximum molecular and capillary moisture capacities were determined by the generally accepted method.
As is seen from the table, the maximum molecular moisture capacity ($W_{\mathrm{mmv}}$) increases with increasing specific surface, except
in this respect is boric acid. As is usually observed, the values of capillary moisture capacities \((W_{\mathrm{kv}})\) greatly exceed the values of \(W_{\mathrm{mmv}}\).
\(W_{\mathrm{mmv}}\) characterizes the magnitude of the adhesion forces between particles of the material and water and, consequently, is a measure of the hydrophilicity of the material. \(W_{\mathrm{kv}}\) characterizes the structural features of the material. Both of these characteristics are connected with the magnitude of the specific surface and, consequently, with the plasticity of the material.
Some researchers [3] use precisely plasticity as the principal indicator for determining a material’s tendency toward granulation.
All the materials used by us are nonplastic. However, owing to the presence among them of an alkaline component, the plasticity index for the batch, determined by the Vasil’ev method, is 4.3. Thus, the batch should be assigned to the 3rd class of plasticity. Under certain conditions it granulates well.
It seems to us more appropriate to use the agglomerability index to characterize the granulatability of glass batches. This concept, introduced by staff members of the Department of General Chemical Technology of TPI [4], denotes the ability of a material in the aggregated state to resist crushing. Agglomerability is calculated by the formula
\[ K=\frac{W_{\mathrm{mmv}}}{W_{\mathrm{kv}}-W_{\mathrm{mmv}}}. \]
Since agglomerability is determined as a function of \(W_{\mathrm{mmv}}\) and \(W_{\mathrm{kv}}\), it represents a greater number of material properties than does plasticity.
From the values of “\(K\)” given in Table 1 it is clear that boric acid granulates best, whereas the batch has a lower capacity; therefore it can be assigned to moderately granulatable materials.
The optimum moisture content of the batch, obtained experimentally, is 12%, which corresponds to \(W_{\mathrm{mmv}}=12.7\%\). It is at this moisture content that the maximum yield of granules of the 3–10 mm fraction is obtained and granulation proceeds most completely. The strength of the granules immediately after granulation increases as the moisture content decreases, but the amount of fines also increases. The strengthening of the granules required for subsequent processing is achieved by drying.
The strength of the granules depends on a whole series of other factors acting in the process of preparing and granulating the batch.
REFERENCES
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- M. A. Matveev, B. K. Demidovich. Steklo i keramika, No. 10, 1967.
- V. M. Vityugin, A. S. Botma. Izvestiya vuzov. Chernaya metallurgiya, No. 4, 1968.