Throwback Thursday: Improving Shear-Induced Imbalance in Hot Runner Systems

Even melt distribution and balanced filling to and across all cavities while avoiding restrictive mixers is possible with hot runner manifold construction that incorporates a melt rotation design.


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There is so much great content to share on Throwback Thursday. Over the last 20 years, we have had numerous contributions from experts in technologies that help streamline the moldmaking process, not to mention those who know a thing or two about mold design, mold repair and maintenance and so on. 

For today’s TBT, I decided to look back to MMT’s August 2005 issue in which an article was presented about melt distribution and balanced filling of multi-cavity molds. It is titled “Improving Shear-Induced Imbalance in Hot Runner Systems,” and I suspect that the discussion and tips included in it are still fairly relevant today. 

The author, who represented hot runner supplier Incoe Corp., first discusses how shear thinning, especially prevalent along the flow channel wall, reduces viscosity of the plastic material.

He then goes on to discuss the relationship between viscosity and imbalance in the filling characteristics of the inner and outer cavities, creating imperfections in the molded parts. There is further discussion on addressing imbalance issues, using melt rotation to achieve symmetry and balanced filling in all cavities, and a real-world application is shared to give readers a more in-depth grasp of the processes suggested for addressing shear-induced imbalance. 

Look, too, for a mention about another article in which Beaumont Technologies shares a five-step test developed by John Beaumont that can be used to discover whether a mold’s cavities are experiencing any imbalances. It’s titled Five-Step Process Accelerates Part-to-Production Leadtimes.