Method for the forming of plastics

DETAILED DESCRIPTION The invention relates to a method for the forming of thermoplastic and/or elastomeric resins with the use of a plastics processing machine provided with a screw.
In, for instance, a screw extruder the mass to be extruded is passed from a feed hopper via a conveying, melting and homogenization zone to the outlet opening.
The shape of the outlet opening determines the profile into which the mass is formed.
The melting of the mass takes place mainly in the melting zone.
In the melting zone the mass is raised to a temperature above its melting point owing to the supply of heat through the wall and owing to the generation of heat in the mass in consequence of the work performed by the screw on the mass.
In the melting zone the geometry of the screw is often such as to promote the generation of heat in the mass.
After having left the melting zone, the mass is in a virtually completely molten condition, but internally it still shows great temperature differences.
There are also great differences in the degree of distribution and possible reduction in size of additives through the polymer matrix.
These differences in temperature, mixture and dispersion must be eliminated in the homogenization zone by means of a mixing and/or kneading effect of the screw on the mass, because the result of an inhomogeneous melt is that products of inferior quality are obtained.
The temperature curve of the mass in the extruder is such that, from the feed hopper onwards, there will be a rise, with a peak temperature in the melting zone or just after the melting zone if a dispersion section has been provided for, upon which there will usually be a fall towards the outlet opening through which the mass, still with a high temperature, leaves the extruder.
The temperature at the beginning of the outlet opening is referred to as the final melt temperature.
After the mass has left the machine, its temperature must be lowered by cooling to the ambient temperature or to a temperature suitable for a following process operation