January 2022

Larry Alpert, Medical Extrusion Technology Manager with Graham Engineering, saw a frequently occurring problem with micro bore extrusion. Consistent solids conveyance needed to control a process in a small extruder can be very difficult, primarily due to the size constraints of screw channel depth/root diameters required to withstand the torque requirements of the process versus the pellet geometries used by various manufacturers.

These factors can make it very difficult to control a process that requires tight tolerances of ±0.0005” or less in an open-loop extruder. Process validation activities also require stringent CpK/PpK requirements to ensure minimal variability in the medical device or pharma industries.

Some resins are historically notorious for being very difficult to control in small extruders (≤1”). It is not uncommon to lose solids conveyance entirely with some of them, and many processors will use an off-the-shelf 2 or 3 groove feed section design to counteract this. There are problems associated with this practice. Unless the machine is for dedicated use, the grooved section may not be appropriate for other materials/products/processes. A feed throat can be difficult, time-consuming, and expensive to change with most extruders.

See the below link for the full white paper.


For any questions, please contact Larry Alpert at lalpert@grahamengineering.com.

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