How Molten Plastic Becomes a Shape

Copyright (c) 2010 Nadine Davis

Plastic manufacturers have had a huge influence on the modern world, and delivered a dazzling array of PVC plastic products which are used in every conceivable scenario and circumstance, from toys to motor vehicles, medical equipment, building materials and others too many to contemplate.

Plastics extrusion is highly automated, and operates continuously without much in the way of human intervention. This has driven the cost of production down to the levels we see today, making plastic a very inexpensive material.

The process can best be described as forcing molten plastic under pressure through a die to produce a specific product. The range of products varies from short items cut to length such as piping or tubing, through to continuous plastic sheeting.

Plastic granules or resins are gravity-fed into a hopper connected to a screw drive with a dual purpose - to mix the plastic if more than one type is being used, and to melt the plastic as it makes its way through the screw drive.

The following are just a few of the many different types of plastics extrusion, with a brief explanation of the manufacturing process for each one:

Standard Plastic Extrusion:

The liquid plastic is screened through a filter to remove any particles, then forced through the die and into a cooling bath before being cut into lengths or rolled into sheets, depending on the product requirement.

Sheet/Film Extrusion:

For plastic sheets or film, the product is pulled through a series of cooling rollers which both cool the plastic and determine the sheet thickness and texture. The liquid packaging industry relies on plastic extrusion to meld plastic to paper and also aluminium foil to create such packaging staples as juice cartons and wine casks.

Blown Film Extrusion:

Blown film extrusion is used to make plastic shopping bags. When the product reaches the die, in this case an upright cylinder of varying dimensions, it is pulled upwards to a height ranging from a few metres up to 20 metres, depending on the amount of cooling it requires. Compressed air is forced into the centre of the extruded material, creating a bubble which is flattened by rollers into a double layer of film.

Tubing Extrusion:

The process is the same until the product reaches the die, which has a pin in the centre to create a hollow cross-section which becomes tubing. This pin is connected to a pressure source to stop the tubing from collapsing when it enters the cooling bath.

Plastic manufacturers use a range of materials in extrusion including polyethylene, polypropylene, acrylic, nylon, polystyrene and polycarbonate, among others. The vast flexibility of what can be done with PVC Plastic, along with its good cost efficiency means that this is a material which will keep on advancing as technical advancements occur within the industry.