Sheet of Glass
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ribbon which passes over a roller bed into a roller lehr or annealing
There is something rather grand and a little
terrifying if one can visualise the inexorable march of this ribbon which,
if it was not cut, would in six months time stretch from St. Helens to
GRINDING AND POLISHING.
Having made a rough glass we have now got to grind and polish it. The first
stage is the grinding of the surface by means of a cast-iron runner, fed with
coarse sea-sand until the whole of the rough cast surface has been removed,
and then with graded sands, which become progressive finer, until a frosted
surface of the finest possible texture is obtained. Then comes the very
delicate process of polishing, which consists of rubbing the glass with felt
discs fed with rouge. The rouge, obtained by carefully calcining ferrous
sulphate to a definite colour, acts as an abrasive in the earlier stages, but
to what extent molecular flow contributes to the final polish is a rather
contentious subject which I have not time to discuss to-night.
There are two main methods of grinding and polishing
METHOD. In the round table method the glass is laid and
ground and polished on a circular table 36 ft. in diameter and weighing 60
tons. There is not time to describe the details, but by comparison with
the Continuous Grinder, which will be described in detail, the process has
the following marked disadvantages--
- The round table method.
- The continuous method.
1. The glass has to be cut to cover the whole table,