Page 54 - Curriculum Visions Dynamic Book

4. Shaped glass
Many glass objects are complicated shapes that could not be produced by blowing. Headlights come from a gob of molten glass pressed in a mould. Windshields are flat pieces of glass that are heated to soften them
a little and then pressed into a mould (press bending) or sagged into a mould under their own weight (sag bending). Both are a means of bending a piece of glass without damaging its surface; the glass is not made to flow as a molten gob would be.
(Below) Headlights are made by pressing the glass into shape in a mould. This is especially useful when thick glass pieces are needed. Pressing produces a better surface finish than blowing.
Empty mould
(Right) Fibreglass is used as home insulation.
Loaded mould
Glass pressed
5. Fibreglass
(Above) Shaped windshield glass.
Finished piece
See Vol. 1: Plastics and Vol. 7: Fi- bres to find out more about glass fibre.
(Below) Glass fibres can be embedded in a plastic (resin) to produce a strong, lightweight material. Fibreglass is easy to mould into shapes such as this canoe.
Fibreglass is a glass fibre wool. It is used for building insulation. Glass fibres are produced
in the same way as plastic fibres, by forcing the molten glass through a die with holes in it called a spinneret. The glass comes out in long strands and is whirled around by the spinning die. A blast of cold air cools the fibres, and they break
into short lengths. An adhesive is sprayed onto the fibres so they can be formed into long mats.
Glass fibre can also be made into cloth using a spinneret. But in this case the fibres are not broken into pieces but pulled out and wound onto a drum. They can then be woven.
Glass fibre is long-lasting as well as fireproof.
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