The glass-to metal interface during container forming processes.

It is known that a newly formed glass container will only possess a very small
fraction of its theoretical strength. This suggests that damage occurs on the surface
of the glass melt during the forming process due to glass to mould contact and hot
glass handling. It might be expected that any damage inflicted on the surface of a
glass article during manufacture would heal at the elevated manufacturing
temperatures used, however this does not appear to be true. Therefore, the actual
mechanism by which glass strength is reduced during forming needs to be fully
understood and the work presented in this thesis addresses this problem.
Experiments, therefore, have been carried out here which simulate the formation
of glass articles using an experimental pressing rig by systematically altering
processing parameters such as the mould material, surface fmish of the mould,
pressing temperature and atmosphere. Processing parameters that are used
industrially for the formation of glass containers were generally reproduced
wherever possible in order to investigate the glass-to-mould interaction.
The interaction of both a cast iron mould material and carbon-carbon composite
materials with a soda-lime-silica glass were examined using the techniques of
scanning electron microscopy, x-ray photoelectron spectroscopy and atomic force
microscopy in order to determine the type and extent of surface damage formed. The surfaces of the pressed glass samples made were found to contain defects of
embedded particles and indented dimples. The embedded particles found were
usually due to bulk material transfer from the plunger material used. The texture
found on the surface of the pressed glass samples was found to be directly affected
by the surface fmish of the plunger. Pressing glass samples using a cast iron
plunger at an initial plunger temperature below 450°C resulted in a randomly
rippled 'chilled' surface. As the initial temperature of the plunger was increased,
the surface texture of the pressed glass became a closer replica of the plunger
surface. The use of vacuum assistance to form the glass samples also resulted in
the surface of the pressed glass becoming a closer replica of the original plunger
surface, even at lower pressing temperatures.
The surfaces of the cast iron and carbon-carbon composite plungers appeared to
have been affected by the initial plunger temperatures used. As the initial pressing
temperature was increased, the amount of oxidation for both material types
increased. In the case of the carbon-carbon composite materials investigated, both
the matrix and fibres were found to have broken down at the pressing
temperatures used.
X-ray photoelectron spectroscopy, of the pressed glass surfaces and the plunger
materials indicated that sodium ions had migrated from the glass melt to the
plunger surface during forming.