DUESSELDORF, Germany—Cleaning liquid silicone rubber molded parts can be difficult, but it is required for some applications. At the recent Silicone Elastomers World Summit in Duesseldorf, two speakers gave presentations on new cleaning methods.
Leopold Puhringer, product engineering manager at Starlim Sterner Spritzguss GmbH, talked about a "unique market-ready" SCD Starlim Carbon Dioxide cleaning process. Starlim is a Marcher, Austria-based silicone rubber molder with global operations that makes 14 billion parts per year.
The company uses SCD-Cleaning during production of silicone components that need to meet very specific requirements regarding the residual content of volatile components. It works by using the very low surface energy of liquid CO2 so that it acts like a solvent that extracts volatile and leachable nonpolar, low molecular weight polar, nonchemically cross-linked siloxane and silicone oils from molded silicone rubber parts.
The CO2 is used under 50 bar pressure at a temperature between 0° C (32° F) and 15° C (59° F) when it is a subcritical liquid between solid, liquid and gaseous phases.
Puhringer said SCD is a low-cost process in a dedicated "washing machine" that reduces volatile and leachable low molecular substances on LSR moldings down to an undetectable level of below 20 parts per million within 30 minutes. This would otherwise need four hours by post-curing at 200°C, and even then not get from 1,500-3,000 ppm down to below 200-400 ppm.