Solutions for Plasticising

Plasticisation is the process step in which plastic granules are melted and homogenised in the plasticising unit. The rotation of the screw generates pressure and shear heat, which, together with the barrel heating, transform the granules into a uniform, processable melt. This thus forms the basis for every subsequent injection process.

If the granules are not sufficiently homogenised during plasticisation, temperature variations or unmelted particles remain in the melt. The consequences are directly visible on the component: weight variations, air entrapments, discolouration or incomplete mould filling. Stable plasticisation is therefore a fundamental prerequisite for consistent component quality.

Plasticisation takes place in the screw, which is divided into feed, compression and metering zones. An interesting fact here is that the majority of the heat required to melt the material is not generated by the barrel heating, but by friction as the screw rotates. The geometry therefore plays a decisive role in determining how homogeneous the melt ultimately becomes.

If the material remains in the barrel for too long, it may undergo thermal decomposition. If it remains for too short a time, plasticisation is incomplete and the melt is non-uniform (leading to increased wear). The appropriate residence time depends on the screw size and cycle time – hence the correct machine design is crucial.

Demanding materials sometimes require reduced shear input without temperature peaks, or precisely the opposite – more shear for greater melting capacity – which pushes standard screws to their limits. Specialised screws with additional mixing elements or different pitch, flight depth, zone configuration or design modifications (twin-screw, barrier screw) ensure a homogeneous melt even at high throughput rates.