Up: Glassmaking
Flat Glass: 56 of 66
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thence into the lehr. When the bait reaches the end of the flattening
table, about ten feet from the bending roll, it is cracked off and
removed and the sheet of glass is allowed to continue on its way through
the 200-foot annealing lehr.
The natural question that arises when describing
the formation of the sheet of glass in the Colburn machine is: "Why
doesn't the sheet pull to a point? What is it that sustains it at a
constant width?"
The answer is that the sheet is kept at an
even width by passing the outer edges of the sheet between two sets of
water-cooled, knurled rolls, placed an inch or two above the surface of
the molten glass, just inside the edges of the drawing pot. These knurled
rolls engage the sheet for about two inches on each side and serve to
sustain it at a constant pre-determined width. These edges are thicker
than the intervening sheet of glass. The real pulling of the sheet is
accomplished by engaging the outer edges of the sheet-- after it
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