Keep in mind that if the mold has been running well in this machine and the screw has not been changed the cause is probably not related to the screw. There can be cases where degraded material builds up on the screw and leads to conditions where fight depths of the screw are different due to the buildup on the root of the screw. Also, in extreme cases a screw can have so much buildup of carbonized, degraded material that the screw looks like it has a barrier fight from the buildup. If this is causing problems it is critical to establish proper shutdown and purging procedures.