Process Encyclopaedia
Glass forming
Overview
Sheet glass is produced by drawing, rolling, and floating. Drawing is also used to produce fibres, rods and tubes.
Discrete glass products (e.g. bottles) are made by blowing, pressing and casting.
All these processes begin with molten glass (which looks like red-hot thick syrup). A further process, called sagging, is useful for products with shallow curves (e.g. plates) or light embossings.Materials and shapes
- There are over 750 types of glass, but they can all basically be formed in the same ways.
- Drawing and rolling give a rough finish which normally needs grinding and polishing. Float glass has a smooth surface.
- A variant of drawing is used to make rods and tubes.
- Blowing is used to produce hollow thin-walled items; it is similar to blow moulding of thermoplastics. The surface finish is acceptable for most applications.
- Pressing produces parts with greater dimensional accuracy, but cannot be used for items with thin walls or inward curves.
Economics
- Production rates and costs strongly depend on the type of process and the size of component.
- The different processes are generally suited to different shapes, so there tends to be little competition.
- Blowing of light bulbs takes place on expensive fully automated equipment, but over 1000 bulbs per minute can be formed.
- Fibre optics can be drawn at speeds of up to 500m/s.
Typical products
- table tops
- bottles
- vases
- television tubes
- windows
- headlights
- light bulbs
- mirrors
- dishes
- optical fibres