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42.3 Splay Troubleshooting 429
Case Study: Splay on Polypropylene
This was a case where splay started to show up on an unfilled polypropylene
part that never previously had splay. During process troubleshooting it was
determined that the gaylord of material had gotten stored under a leak in
the roof. The material was literally dripping wet when it was loaded into the
machine, which created the splay. This material was dried for a couple
of hours, which eliminated the splay. There are even situations where silo
material can become wet from a leak or an open hatch.
42.3.4.3 Material: Wrong Material
It is always worthwhile to ensure that the correct material has been loaded into the
molding machine. Many defects can be created if the wrong material is added to
the molding machine. Verify that the material labels match the required material
on the bill of materials. Be aware that this can create hazardous conditions due to
severe material degradation.
42.3.4.4 Material: Blowing Agent
When using a blowing agent or microcellular foam process, gas is of course intro-
duced into the plastic in the barrel intentionally. This gas results in a foamed ma-
terial that will often be used in thick cross sections to avoid sink and reduce weight
and cycle time. Because gas is being added to the material splay will be evident
across the whole part. There are things that will improve the surface of the part
such as gas counter pressure but it will be very difficult to completely remove all of
the surface splay when running with a blowing agent or microcellular foam.
If blowing agent is introduced into a material that was not intended to be foamed
the result will be splay. Treat this like any other contamination in the material.
