Don’t assume that when you are getting consistent feed with your volumetric feed system as this needs to be tested.
A customer was having significant issues with a PVC twin screw profile extrusion line where the line would break often during production without any obvious cause as well as provide profiles which would vary in dimensions over time. During investigation it was found that the die pressure fluctuated up and down approximately 10% in 2-3 minute intervals.
After checking some basic items we tested the material feed system and found that a 25% increase in feed (16RPM to 20RPM) resulted in a doubling of material feed (140lbs/hr to 280lbs/hr). After further testing we located a speed which provided the correct amount of material in a consistent manner to get the machine back up and running. After this correction, the inconsistency of the profile decreased.
You often have to check your equipment to ensure it is functioning properly. Just because a material feeder is turning at a steady rate does not mean the material is being conveyed properly in a consistent manner.