Extrusion systems that have additional tooling in place between the extruder and die can be complex. This includes any piping or required flow paths used to transfer material between the extruder outlet and the die. These types of systems are commonly found in blown film, co-ex, and cross-head extrusion.
Realize that once the plasticated material leaves the screw and barrel, it will experience a pressure drop. Which can cause build-up or layering in these areas of additional tooling. Over time these deposits become highly subject to degradation. Which will ultimately lead to carbon contamination in the extrudate, and the problems that can ensue.
Using a mechanical type purging compound on a regular basis will act as a preventative, by minimizing the chances for carbon formation. Especially when routine purging takes place as part of a well-defined purging program. Most importantly when shutting down and sealing. A recommended practice during any prolonged period of system downtime, such as a weekend or holiday shutdown.
However mechanical purges do have limitations for carbon removal when used in these complex extrusion systems. This is because they rely on the machine's power and the shearing action that takes place within the screw and barrel, to do the cleaning and removal work. Once outside of the screw and barrel, the inherent pressure drop reduces the mechanical purge’s effectiveness. As they tend to follow the path of least resistance and may not reach into the entire flow path, such as any walls or edges. While still useful, a mechanical type purge is more so effective as a preventative measure.
This is where a chemical type purging compound or concentrates will excel. By providing a total package of cleaning, prevention, and carbon removal. Chemical-type purging compounds rely on heat and containment to effectively break down and remove deposits that are the cause of carbon contamination. They will also expand during the recommended soak time. Allowing them to reach into areas outside of the normal flow channel or pathway, getting into those out-of-the-way areas mentioned.
Offering up a one-two punch, if there are known trouble spots of build-up and resulting carbon contamination, applying more heat in the localized area will help with accelerating the reaction. Which amplifies the cleaning and carbon removal process on a localized level. As an added benefit chemical purging compounds can also be used as a preventative measure for the shutdown and sealing procedure.
Overall, using a chemical type purging compound provides a cleaning and preventative measure. They are the most effective purging compound solution to remove the presence of carbon contamination within complex extrusion systems.
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