Today's KNOWLEDGE Share
So, you do your spiral mold test and conclude that Polymer B has a lower viscosity.....
Maybe not !
When spiral flow is conducted "the old way", i.e. under essentially controlled pressure, the flow stops necessarily at freeze-off. So the ranking of spiral flow length may reflect the thermal conductivity of your material much more than its viscosity. A lower viscosity grade with 50% GF may freeze faster than a higher viscosity grade with only 20%GF.
If you want your spiral flow test to correctly reflect the viscosity ranking, you must mold the spirals under strict constant filling rate and switchover to ZERO packing.
In my experience, few people do this correctly...
source:Vito leo
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