Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 83

After the fining process, the melt is cooled down and homogenized thermally in a steady way. Small residual bubbles resorb themselves because the solubilities of most volatile species strongly decrease with increasing temperatures (Chapter 5.5). For this reason, care has to be taken to prevent local temperature rises from happening during the homogenization process otherwise the so‐called reboil bubbles would form in the melt and could not be removed in any way. Among dissolved gases, N₂ distinguishes itself by its decreasing solubility with decreasing temperatures. Thus, N₂‐containing bubbles escaping the fining process appear as very tiny bubbles called seeds in the final glass. Their number per unit mass of glass represents an important quality criterion. In container glass, a few tens of seeds per 100 g of glass are accepted. Float glass requires a much higher quality (one visible defect per 20 m² already is considered a high defect density) and hence, much longer dwell times (approx. 1.5–2 days vs. 1 day for container glass) in the melting compartment.