Specialists in Plastic Extrusion

Plastic Extrusion Design -

Rigid profiles

These are design points to ensure cost-effective, consistent good quality rigid plastic profiles. Thermoplastic extrusion is a continuous process, in which plastic material passes through a die and into a former (or callibrator),which together control the definition and dimensions of a plastic profile, as the plastic is cooled and turned from liquid to solid. We can advise on the suitability of the thermoplastic material, such as PVC, PETG or Polycarbonate.


		Design with a regular wall thickness
		Always try to achieve a regular wall thickness in your design, otherwise the flow of plastic material will be difficult to regulate and cooling will be faster in some places than others. Irregular walls will lead to difficulties in production, increased costs, and the plastic profile may be impossible to manufacture.

		Avoid details inside hollow profiles
		Unlike aluminium extrusion, thermoplastic extrusion relies upon calibrating (or forming) after the material passes through the die. This is where the definition of the plastic profile is achieved, while being cooled and turned from liquid to solid. Because plastic extrusion is a continuous process there is no way of getting inside hollow sections to hold details in place while the material is still liquid. The result is that anything more than the shortest of legs inside hollow plastic sections will droop while the outside of the plastic profile is being held to shape.

		Avoid hollows within hollows
		For much the same reason as above, one hollow within another cannot be prevented from changing shape and position. Gravity will inevitably force the intended internal design out of shape and position before the thermoplastic solidifies.

		Provide good access for internal detail
		So long as good access can be achieved, legs, grooves, snap-in features and other details can be incorporated internally, but there must be a way in. The outside of the plastic profile cannot be a totally closed plastic section.

		Length tolerance
		Where possible design a little tolerance into your required length. Thermoplastics contract and expand with temperature, and cutting plastic profiles to a very critical length may add unnecessarily to cost. Typically, +/-2mm on a 500mm length is maintainable. Tighter tolerances are naturally achievable, but are generally cut out of line, adding to handling and cost.

		Mating parts
		Where a custom profile is being designed to fit another component, we would like to have a sample of that mating part as soon as possible. This enables the intended connection detail to be considered at the tool design stage, and again when trialling your plastic profile for the first time, to ensure correct fit. Always bear in mind that both components have tolerances that need to be accounted for.

		Clear profiles
		When considering clear rigid PVC for a plastic profile design, please note that this material is not glass clear. Generally speaking the thinner the wall the better the clarity. Also, because clear PVC is tin based (rather than calcium zinc based) its melt temperature is lower, so that swarf on cut ends has a tendency to stick, and may need additional cleaning off. In order to obtain much higher clarity we would recommend PETG or Polycarbonate, depending on your design criteria.

Copyright Condale Plastics Ltd. 2008 - Specialists in thermoplastic extrusion

Independent Business Park, Imberhorne Lane, East Grinstead, West Sussex RH19 1TU - UK

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