Contact between hot glass and wet porous material : Part 2. Trials on a continuously operating container forming machine

Abstract

The narrow neck press and blow process for the production of lightweight bottles uses a slender plunger. It is suspected that the plunger decreases the bursting strength and above all the impact resistance of the bottles by damaging the inner glass surface of the parison. It was the aim of the project to develop a "steam plunger" using a wet porous material, which would protect the glass surface by a developing steam layer between glass and plunger. Trials with different steam plunger constructions show that the production of bottles is possible with this system at normal production speeds. The bursting strength of the bottles produced was a little higher than that of the normal production; the impact resistance remains the same. Steam plungers, permeated by water from the inside, have a tendency to thermal instability The control of the water penetration is essential. The vulnerable point is the tip of the plunger. The control of the contact temperature of the plunger tip after the loading of the gob is very important. For the trials stainless steel was used for the plungers. The results show that, especially for the tip region, a material with a high heat penetration coefficient is advantageous. Bronze would be better than stainless steel. Parallel with the trials, a mathematical model was developed in order to understand better the behaviour of the steam plunger system. The results were in good agreement with the trials.