Study of the Flowability of a Batch for Producing Borosilicate Glasses
Abstract Generated abstract
This study examines how moisture content affects the flowability of a borosilicate glass batch intended for granulation, using the batch composition employed at the Novosibirsk Ekran plant. Flowability was evaluated as the inverse of cohesiveness, measured by shear resistance of freely poured material and material compacted under a pressure of 2.5 kg/cm2 for different holding times, with bulk density also determined. The results indicate that flowability decreases as moisture rises, sharply from 0 to 3 percent, more slowly to about 5 to 6 percent, and to very low values by 10 percent, while holding under load becomes notably influential at moisture contents of 4 percent and above. The authors recommend premoistening the batch to 4 to 4.5 percent to reduce segregation, with the remaining water added directly in the granulator.
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STUDY OF THE FLOWABILITY OF BATCH FOR THE PRODUCTION OF BOROSILICATE GLASSES
V. M. Vityugin, L. G. Lotova
(Presented by the scientific seminar of the Department of General Chemical Technology)
In 1967, at the Department of General Chemical Technology, a technology was developed for granulating batches for the production of borosilicate glasses. During the development it was established that the granulation process depends on the amount of water and the manner in which it is introduced. For designing a plant-scale continuously operating granulation unit, it proved necessary to study the flowability of batches before granulation as a function of their moisture content.
For the study, the batch used at the Novosibirsk “Ekran” plant was taken, with the following composition:
sand — 69 g,
alumina — 3.59 g,
boric acid — 50.44 g,
soda — 9.9 g,
saltpeter — 15.52 g.
Total: 148.45 g of batch per 100 g of finished glass mass.
Under production conditions, the batch is usually prepared from dry components and is not moistened, unlike the technology of preparing it with granulation.
In the study, the moisture content of the batch was varied from 0 to 10 percent at intervals of 1 percent. Flowability was evaluated by the cohesiveness of the batch layer. It was assumed that the degree of flowability \((C)\) of the batch is inversely proportional to the cohesiveness \((G)\):
\[ C = \frac{1}{G}. \]
Cohesiveness was determined by the method generally accepted in soil science, based on the time resistance of a material layer to shear. The shear resistance of the material layer was evaluated both when it was freely poured and when the material was compacted for a time under a pressure of \(2.5\ \text{kg}/\text{cm}^2\), which partially reflects the conditions under which the material is held in a bunker. In parallel, the bulk density of the batch was determined for use in selecting technological equipment and the optimal moisture content of the batch.
The data obtained are presented in Fig. 1.
It was established that the flowability of the batch, when the moisture content changes from 0 to 3%, decreases; from 3 to 5–6% it decreases only slightly; and from 6 to 10% it decreases to a very small value. At the same time, it was observed that the flowability of the material depends on the time \((t)\) for which it is held under load.
Fig. 1. Dependence of the flowability of the batch on moisture content. 1 — with free filling of the batch; 2 — under a load of \(2.5\ \mathrm{kg/cm^2}\), \(\tau = 5\ \mathrm{min}\); 3 — change in the bulk density of the batch.
Table 1
Change in the flowability of the batch as a function of its moisture content and compaction time
| No. | Batch moisture content, % | Bulk density of batch, g/cm³ | \(C\) of batch, \(P = 2.5\ \mathrm{kg/cm^2}\), \(t = 5\ \mathrm{min}\) | \(C\) of batch, \(P = 2.5\ \mathrm{kg/cm^2}\), \(t = 15\ \mathrm{min}\) |
|---|---|---|---|---|
| 1 | 1 | 0,970 | 0,44 | 0,346 |
| 2 | 2 | 0,835 | 0,376 | 0,322 |
| 3 | 3 | 0,840 | 0,293 | 0,231 |
| 4 | 4 | 0,842 | 0,286 | 0,186 |
| 5 | 6 | 0,860 | 0,268 | 0,179 |
| 6 | 8 | 0,870 | 0,240 | 0,183 |
| 7 | 10 | 1,040 | 0,154 | 1,130 |
The importance of this conclusion lies in the fact that it determines the holding time of the material under load in the bunker.
The data presented in Table 1 show that a noticeable influence of holding time occurs at a moisture content of 4% and higher. It is advisable to provide for the following preparation of the batch with respect to moisture before granulation: initially moisten the batch to 4–4.5%, which at the same time will eliminate its segregation, and feed the remaining water required for granulation directly to the granulator.