Despite many processors’ fears, screens do not actually increase the pressure by a considerable amount (only 50-100psi). It is the trapped contamination that causes an increase in pressure and if a mass of contamination is suddenly trapped there will be a quick pressure spike in the extruder.

You can avoid this from becoming an issue by having a safety system in place such as a rupture disc, shear pins and/or an alarm connected to the pressure gauge and changing your screens will immediately cause the pressure to drop.

In single vented, two stage extruders the second stage output will be reduced as build up on the screens increase backpressure, whilst the first stage output remains unaffected.

At approximately 2,500 psi, backpressure melt from the first stage will start to ooze out of the vent. You can avoid this by changing screens at a lower target pressure or placing gear pumps after the screen pack to delay the occurrence of vent flow. This will mean that the screw does not have to work against the die’s resistance in addition to that of the screen.

It’s also important to keep breaker plates clean. But, if torched-cleaned too aggressively they can become distorted. If this happens sealing surfaces can get damaged and sliding surfaces may not mate as well, which can also lead to leaks.

Leaks are then time-consuming to clean up and can damage heaters. Leaking melts can also affect thermocouple readings and in worse case scenarios, even lead to fires.

Read more about the importance of a clean screen by clicking here.