Page 45 - Curriculum Visions Dynamic Book

(Right) Light bulbs being produced by the million.
Glass ribbon
Water-cooled rollers
a piece of glass called a flare that holds the filament in the centre of the bulb.
Glass can be sealed easily. The bulb is made with a neck that is attached to a vacuum pump. As the air is drawn out of the bulb, a flame melts the glass of the neck to the flare and so seals the bulb. This is a fast, easy, and cheap way of creating an airtight seal.
Light bulbs can be made of ordinary glass because although the glass heats up quickly, that compresses the glass, making it strong. When the light is turned off, the glass cools slowly, and so the chance of failure (thermal shock) is small.
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