Up: Glassmaking
Sheet of Glass
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During this century three commercial flat drawn
processes have been evolved:--
- Fourcault process.
- Colburn or Libbey Owen Process.
- Pittsburg process.
Time does not permit a description of the first
two processes in any detail. Each has its own peculiarities and difficulties
to overcome; the Fourcault draws its sheet vertically from a slot in a
depressed fireclay float, and our enemy, devitrification, is our constant
companion. The Libbey Owen process draws its sheet vertically from an open
bath, thus avoiding intensive devitrification, but the sheet when formed is
reheated and bent to the horizontal by passing over a bending roller which
tends to spoil the surface of the glass. The third process, the Pittsburg
process, is now extensively used by us, and although it is exceedingly
difficult to operate, we are very satisfied with its results. The process
avoids the inherent defects of the Fourcault and the Libbey-Owen processes.
The sheet is drawn vertically from an open bath of glass in which a bar of
submerged fireclay defines the position of generation of the sheet, and the
width is maintained by a peculiar device known as the "Edge Bowl."
The edge bowl serves two purposes; the edge of the
sheet is restrained by the sides of the slit with which it comes in contact,
and it acts as a screen to shield the edges of the sheet from the radiant
heat from the glass in the tank. The edge, therefore, cools quicker and
becomes rigid sooner.
As soon as the sheet has set it is engaged between
pairs of rollers which drive it vertically through an enclosed tower. When
it emerges at the top it is
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