posted September 13, 2003 10:37 AM               

RPM increase.
Change of material or put wrong material in hopper, or material supplier QC problem.
Bridging in the hopper.
Burned out barrel heater.
Stuck on/open barrel cooling.
Temperature controller with poor thermocouple contact.
Exceeding some wear amount in the barrel/screw clearance.
Loss of throat or screw temperature control.
Some processes start up well and then equilibrate to a surging condition. This is either wear or a temperature control problem.

Tom Cunningham

Extrusion Technical Services
Consulting and Software.

posted September 13, 2003 03:01 PM               

Welcome to the single screw extrusion forum- Tom has most of the bases covered, but just to elaborate on an "increase in RPM". Check the drive out, if its belt driven, are they slipping. Are all the pulleys (or gears) in the drive train secure on their shafts.

If your extruder has a melt pump fitted, do the same checks on its drive.

There have been a number of posts that have covered surging problems at this site, take a look at those and you'll start to see some common causes of this symptom. Do a search at SPE's site and check out some of the papers that have been presented at the last few ANTEC's http://www.4plasticsresearch.org/

What materials and additives are you processing, these can have quite a bearing on surging problems.

Steve H

posted September 13, 2003 05:54 PM               

When RPMs are increased in an extruder the point where melting finished is moved further down the screw. Excessive unmelt can block channels as RPMs increase and cause surging.