One embodiment of the present invention is an improved sheet glass forming apparatus.
In another embodiment, a precise thermal control system redistributes the flow
of molten glass at the weirs to counteract the degradation of the sheet forming
apparatus which inevitably occurs during manufacturing. In yet another embodiment,
the invention introduces a counteracting force to the stresses on the trough in
a manner such that the thermal creep which inevitably occurs has a minimum impact
on the glass flow characteristics of the forming trough. Another embodiment creates
a variable external cross-section which provides hydraulic stresses that are in
opposition to the surface tension and body force stresses and thus, reduces the
influence of surface tension and body forces. In an alternative embodiment, the
glass is preferentially cooled across its width to create forming stresses during
solidification, which ensures that the glass sheet drawn is inherently flat. In
an additional embodiment, the internal pressure is adjusted in each of the major
components of the forming apparatus such that the pressure difference across any
leakage path to the forming zone is essentially zero. Therefore, air leakage in
the apparatus is minimized even though the cracks and openings exist during initial
operation and develop during manufacturing.
