Dirty screens will cause pressure to suddenly rise, which is why it is important to replace your screens on a regular basis.

Once you’ve removed your dirty screen, it can be a useful source to find out what it is that’s contaminating your extrude in the first place. After you’ve trapped the contaminants or gels, you will want to find the route of where it’s coming from - but this is not always an easy feat.

It’s often difficult to determine where or what the contamination is. Plastics Technology once reported a case where the processor kept finding black residue on his screen and upon further investigation realised that it was the body parts of flies. After initially blaming the resin supplier, it was later found out that the flies were local to the extruder plant’s location.

You may not always need to delve as deep as this into finding the cause of the contamination; there’s a quicker way to determine whether the contamination is coming from your factory or from your resin supplier. If you have a lot of gels at a start-up phase that then rapidly decrease, it’s likely that they are home-grown, but if they are present straight away and remain constant for several hours, they’ve probably come in with the resin.

Click here to read more about maintenance of your screens and breakers.