GLASS BOTTLES MAKING

The technique of glass making too is based on similar lines. People learned to make the first glass containers about two thousand years ago. Molten glass was collected on the ends of hollow iron pipes and then expanded by blowing through the pipes. Slowly, people learnt to blow molten glass into moulds. Glass bottle making machines were introduced in the thirties.

The first plastics blow molding machine was designed in the early forties; the first plastic bottles were manufactured using polythene.

In the early seventies, environmentalists began arguing on the grounds that glass and plastic bottles added to pollution. This led to the setting up of numerous recycling centers where people could return bottles for reuse in other bottles. Most of the recycled plastic is used to manufacture lower quality plastic than those used to make bottles.

There are four main ingredients used to manufacture glass:

1. Silica sand,
2. Soda ash,
3. Limestone
4. Recycled glass (cullet).

Small quantities of other materials give glass its colour.

The Process
· All the materials are first weighed then mixed, and then poured into large
furnaces. The temperature in the furnace ranges from about 1100 – 1590
degrees Celsius. This melts all the ingredients into Molten (liquid) glass.
Computers monitor the whole process.

· From the furnace, the Molten glass goes to a bottle-making machine. A
measure of molten glass (this is called a GOB) is delivered to the machine to
make a bottle or jar.

· The bottles then pass through electronic inspection machines, which
automatically detect faults Rejected damaged bottles, are returned to the raw
materials area and recycled for making new glass.

· The bottles are then packed onto pallets. Each pallet can contain as many as
5000 bottles. The pallet is then covered in a large plastic envelope that has
been shrunk until tight. This makes sure the pallet is stable, ready for
transportation to the manufactures for filling.

Bottle Making (Molding Process)

Annealing is done by reheating the glass and gradually cooling it. Such a process removes the stresses and strains in the glass after shaping. This is an important step and if not done may cause the glass to shatter as a result of the build up of tension caused by uneven cooling. After the bottles have cooled to room temperature, they are inspected and finally packaged.

Plastic bottles may be made from polyethylene, polypropylene or polyvinyl chloride. Large cold drink bottles are made of polyethylene terephalate (PET). These bottles are designed in such a way that the gases used to carbonate the soft drinks are unable to escape.

There are three different methods used for processing plastic bottles – extrusion blow molding (in which the parison is tube shaped), injection blow molding (in which the parison is prepared by injecting molten plastic through a small hole) and injection stretch blow molding (in which the plastic is blown into the mould while it is simultaneously being stretched by a metal rod).