Twin Screw Element Wear Effects on Tensile / Flex. Mod. 1

[shayne31]

I was wondering if anyone knows if / what relationship exists between wearing ZME (WP thermal mixing element) elements and the resulting tensile strength of a given product. Is it a gradual effect as seen with a single screw mixer, or is it immediate? We recently had an issue regarding a 50% loss in physicals on a glass-filled PA6; needless to say the FG supplier claims that their strand integrity is above board. Despite the PdM program that is peformed qurterly on the extruder screws, the focus is shifting to the ZME elements. If anyone has any similar experiences or any knowledge regarding this issue, it would be greatly appreciated.

Thanks,
Shayne31

 

[shashak]

Hi Shayne,

The TME (Toothed mixing element) (a.k.a. ZME in German from WP origination) is a distributive mixing element. It is usually recommended for use with low viscosity polymers or compounds, where it performs with higher distributive mixing efficiency than kneading paddle blocks.

If you use TME/ZME with GF-PA6, it will result in poor wetting of the glass with the polymer. There are two ways to resolve the issue:
A) Use silane treated glass for better wettability and interfacial adhesion
B) On the extruder, we (B&P Process Equipment, formerly Baker Perkins) typically use no more than ONE (1) 90 degree offset (Neutral) paddle block (narrow width, typically D/4) at the end of the mixing section, to do the trick. It enables decent fiber wet-out without too much of a wear issue, and gives good results with respect to nominal fiber length, as compared to a ZME.

So depending on your situation you might try A or B or both. I feel that you will be better off trying solution B first, and replace the ZME with a KB90.

Let me know how it goes. Best Luck!

Shashank Kasliwal
Materials Engineer, B&P