May 2013

Albright Technologies Monthly Insider


Differences in Molding Silicone vs. Plastic



Written By: Matt Bont



The primary difference between silicone and plastic properties drives the differences in mold design. The largest difference is the temperature profile between silicone and plastic. The mold design and construction will also be dependent on the product geometry, size, materials, equipment, quantities, cycle times, undercuts, flash limitations and parting line and gate restrictions. 




Silicone processing is a curing reaction between two parts. These parts are mixed and driven through a cool barrel and screw. The mixture is injected into a hot mold where the heat accelerates the curing reaction until the product is solid. Silicone has a significantly lower viscosity than plastic melt and flashes into spaces less than 0.0002" requiring precise parting lines and tight shut offs. The low rigidity and low viscosity also prevent the use of knockout pins which can damage parts and cause flash and pin binding. The inherent flexibility and high elongation does provide a means for removal of parts with significant undercuts.  




Thermoplastic pellets are melted and conveyed through a hot screw and barrel and injected into a cool cavity where the melt hardens into the final product shape. The products are typically much more rigid than silicone and can be pushed out of the mold by knockout pins within the mold at the end of each cycle. This rigidity also causes binding of some vertical walls and most undercut features.


Silicones and thermoplastics continue to expand and include many materials with diverse properties that offer more possibilities to designers. Good communication between designers and manufactures can ease start up and improve product quality and function.


For more information or questions, please contact us at or 978-466-5870. Visit to learn more about our products and services. 


Free Silicone Molding Design Manual Available 

New manual cover
Albright Technologies recently released an entirely new version of their popular Silicone Molding Design Manual, a valuable resource used by design engineers in medical and other industry applications. The Silicone Molding Design Manual is searchable, offers users the most extensive compilation of silicone data in the industry and is now available to download for free


The revised manual features white papers from Nusil Silicone Technology, Applied Silicone, Bluestar Silicones, Wacker Silicones and Dow Corning on topics including: short and long term implantable components, silicone gaskets, o-rings and diaphragms, as well as high temperature silicones and vibration dampening silicones. 
For technical information contact Bob Waitt, 978-466-5870 or


Issue: 18

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