Using Virtual Pressure Measurement to Avoid Flaws in Medical Extrusions

Degradation is a significant obstacle that harms the quality of extrusions and adversely affects the mechanical properties of the polymer and the final product.

To meet the increasingly stringent quality requirements for small medical extrusions, US Extruders has developed virtual pressure measurement. Virtual pressure measurement eliminates transducer and rupture disc ports in the barrel and reduces stagnation points where material can degrade.?

The transducer’s diaphragm is flat, but the inner surface of the barrel is curved, so a pocket is created.?On small extruders this pocket can be quite large, and become a point of material stagnation, degradation, and contamination.??

Degraded material that ends up in medical tubing causes a weak point in the final device. This is especially important for applications that demand superior quality beyond dimensional requirements where maintaining mechanical properties is paramount. Examples include balloon tubing, heat shrink tubing and polymer stent tubing.

Virtual Pressure utilizes the axial force of the screw against the thrust bearing as an indirect means of measurement.?The extruder is equipped with a force sensor behind the thrust bearing, and this value is input to an algorithm along with drive torque to calculate virtual pressure, which is scaled to conventional units.?The pressure transducer and rupture disc, and their barrel ports, are eliminated. The design also allows for the last barrel heater to cover the area formerly occupied by the transducer and rupture disc, which creates a cold spot.

Virtual Pressure has been proven to be accurate, reliable, and very beneficial especially in small extruder applications for Medical, Pharma, and Fluoropolymer where the transducer port pocket is relatively large, and degradation and contamination are critical.??

Credits: Bill Kramer, President of US Extruders