The purpose of a breaker plate in single screw extrusion.

Flow of the plastic in a single screw extruder is circumferential.  Also, each flow channel if divided by a flight.

The breaker plate has several functions:

1. It provides a seal between the barrel and the head.
2. It changes the circumferential flow into linear flow.
3. It creates back pressure in the melt resulting in effective shear melting of the plastic material.
4. It can support a screen pack which filters impurities from the melt and will create further back pressure.
5. Without a breaker plate the flights can show as spider line on the product.
6. Without a breaker plate the circumferential flow may be replicated in the melt resulting in a product with an uneven surface.