posted May 20, 2004 06:40 AM            

I'm trying to made some compound of soft PVC with my ZSK 25, this machine is 40 D long, is a machine too long to do this compound?,what screw configuration can i use to try out? or what are the main points that i have to consider (in the screw design)? what machine speed, i don't know how sensitive could be soft PVC to shear.
On the other hand has anybody heard something about normalized capacity and specific mechanical energy ? and its calculation.

posted May 20, 2004 09:09 AM               

Processing of the PVC depends on the viscosity of the PVC and it's ability to resist degradation at high temperatures. Often PVC is provessed on ZSK style twin screws at low screw RPMs and with a single screw extruder creating the discharge pressure. If the twin screw is used to create the discharge pressure, degradative overheating is likely.

For more temperature stable polymers output is typically:

Max HP * 5 = lbs/hr

Optimally:

Max HP * 7.5 = lbs/hr

PVC likely functions under different rules. I would use this formula as a starting point;

Max HP * 150/Max RPMs * 5 = Lbs/hr

Good luck,

posted May 28, 2004 09:19 AM               

Processing is generally monitored through specific energy. The correct value is not known until some tests are done.

Polymer processing usually falls in the range of 0.1 to 0.3 Kw/Kg. Below that range and you likely have not melted or mixed properly. Above that range and your polymer is likely degraded.

Hopefully you can find a value where you are making good product. Again, PVC is difficult to process on this type of equipment. Recent advances in the technology may help.