ENTEK NEWS

Processing Tips (Pumping Efficiency)

Although an excellent mixing device, the pumping efficiency of a co-rotating TSE (twin screw extruder) is poor, approximately 15% efficient.  This is manifested as undesirable temperature rise of the molten compound occurring mostly at the screw tips (discharge end of the extruder).  A restriction here, for example, small diameter die holes and/or a tight mesh screen pack increases the exit melt pressure and results in a temperature rise of the molten compound.  This temperature rise can limit extrusion output rates therefore taking steps to minimize this temperature rise can be crucial to the process.  A test was set up at the ENTEK Pilot Plant to minimize temperature rise by making some simple processing changes without incurring capital expenditure.  This test was performed with a 50% talc filled 12 melt polypropylene masterbatch on a 43mm co-rotating TSE.  Here are the learnings:

  • 40 pitch convey screw elements (CoC-2-40) performed the best.
  • 60 pitch convey (CoC-2-60), single flight convey 60 pitch (CoC-1-60) and undercut feed 60 pitch elements (CoF-2-60) all performed the same.
  • Running the extruder exit barrels (last 2) at significantly lower barrel temperature set points, significantly reduced the compound melt temperature.

The test was carried out by installing 3 different restrictions at the outlet of the extruder to simulate a low, medium and high back pressure of around 500, 900 and 1,300 Psi for this compound.  The temperature probe shown below was used to measure temperature rise.

The last 240mm (5.5 L/D) of convey elements on the extruder screw configuration were altered with different styles and pitches.  Below is a graph showing the resulting temperature rise with respect to the different pitch convey elements.

Operating the last 2 barrels set at a temperatures roughly 200°F colder than the upstream adjacent barrels was explored further to extrapolate the benefit shown in the graph above for higher rates.  Operating at 750 lbs/hr, 600rpm screw speed using 40 pitch convey elements at the discharge end of the screw and a back pressure of 1,260Psi, the melt temperature was 470°F.  The last 2 barrel temperatures were lowered and the pressure increased to 1,385Psi and the melt temperature dropped to 456°F.  This indicated a benefit but a diminished benefit compared to the lower extrusion rates as shown in the graph above.

This test concluded that a 1 D pitch convey screw element is the most efficient pitch for pumping, in this case 40 pitch for a 43mm diameter extruder.  It was also noted that significantly lowering the temperatures of your last barrel or two reduces melt temperature.

ENTEK Lead Acid

Lead Acid

The best batteries in the world are made with ENTEK separators, from SLI, start-stop, deep cycle, motive power and stationary batteries.
Learn More

ENTEK Lead Acid

Lithium

We utilize a unique, wet process manufacturing approach to produce ultrahigh molecular weight polyethylene (UHMWPE) base separators.
Learn More

Translate »