Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 121

At the blank‐side the three different forming processes come to play as explained in Section 3. Molds at the blank‐side are usually made of laminar cast‐iron. The glass gob is loaded into these molds and is formed into the parison. Because of process‐sequence, the parison is formed upside down, the finish facing downward and the bottom of the container upward before the invert leads to the proper upright formed final container. Upon forming of the parison, the mold is always cooled by air to allow fast heat extraction from the glass. As already explained, this is necessary to have a stable parison with a high enough viscosity after the mold has opened. If the parison is too hot and hence has a too low viscosity, it may collapse after opening the mold, causing section failure.

Different mold‐cooling techniques are available. Most dominant are inside‐mold cooling systems, where air is lead through channels in the mold either from below or from above and an older technique called stack‐cooling. Here, fins are attached to the outside of the mold and the mold is streamed by air. This version is less efficient than inside mold cooling so that it usually leads to lower machine speeds.