Improper mold venting can, and frequently does, cause a multitude of processing problems, but now a patented, scientific method and device to help check for proper venting conditions is on the way.
Process & Design Technologies LLC, a consulting firm dedicated to providing solutions for plastics processing issues, has been issued a patent for "Apparatus and Method for checking mold vent condition." P&DT principal Terry L. Schwenk has been working to promote scientific venting for a number of years.
"Scientific venting principles are based on volume displacement over time versus the typical method which involves the vents being calculated as a function of flashing of the material," Schwenk says. "Air and/or gas in the cavity need to be displaced by the molten plastic. If you have poor venting, it will require more pressure and time to displace the air and/or gas in the cavity, with heat being generated as a byproduct."
Schwenk goes on to explain that when molten resin is injected very rapidly into a mold with a marginal vent, a lot of heat is created. Even though there are no burn marks on the part, the material could be much hotter than required. Burn marks are the result of the gases igniting, but Schwenk points out that the material can still be too hot without burn marks. ...