For extrusion or extrusion blow molding systems, the components that are installed between the extruder adapter plate and the die(s)/head(s) are often places where production material hangs up, acquires heat history and degrades. This "downstream plumbing" (including transfer piping, melt pumps, static mixers, etc.) should be considered carefully when developing purging procedures for system maintenance.
Monday, June 28, 2010
Tuesday, June 22, 2010
As we read, almost every day, about the environmental crisis caused by "indestructible" plastic waste entering the environment, it's enlightening to learn about a different point of view. For some folks, the problem is that plastic materials are ephemeral. They are here for a short time and then they crumble and decay. Something must be done!
Are you having cognitive dissonance yet?
An article in the current number of New Scientist titled Drastic Measures Save Plastic Treasures describes how museum conservators are struggling against the deterioration of plastic artifacts that are mere decades old. Cultural artifacts and works of art from the last century are degrading under normal environmental stresses of UV, oxidation and thermal effects.
In a deliciously ironic example, we learn that a medieval manuscript known as Codex Eyckensis, was "conserved" in the 1950's by laminating each page of the 8th century document with clear PVC film. Now, the PVC is deteriorating so badly that it must be removed, with painstaking care, from the paper. The paper lasted 1,200 years. The plastic lasted 50 years.
Why does this matter? To quote from the article:
Does that matter? Yes, indeed, says Lars Christensen of the National Museum of Denmark. Every generation of humans writes its own history through the artefacts it bequeaths to its successors. As we struggle to piece together the fragmentary records left behind by our ancestors, we should be mindful of our own legacy, he says. "If our plastic items were lost it would very much affect how future generations would interpret today's culture."
So work proceeds on finding ways to slow the dissolution of plastics. And we see that plastic materials are really only "indestructible" or long-lived in the time-frames of our own hour upon the stage. In historic (not to mention geologic) time frames, plastics would seem to be insubstantial.
Of course we need to be good stewards of our environment, and of course we need to take responsibility for the end-of-life disposition of our products. But a little perspective couldn't hurt.
Tuesday, June 15, 2010
In extrusion systems, downstream plumbing and auxiliary components often provide places for material to hang up, acquire excess heat history and degrade. Mechanical screen changers, filters, melt pumps, static mixers, flow dividers and connector pipes are all potential problem areas. Don't focus on the die and neglect these other potential problem areas.
Ensure that they are thoroughly cleaned; if using a chemical purging product, consider raising the temperature at these components to maximize purging effectiveness.
Thursday, June 3, 2010
When purging extrusion blow molding systems that are equipped with accumulators or accumulator heads, you have to be certain that the purging material has effective access to these components.
If the less than 100% of the accumulator's capacity is being used, increase the set point(s) by about 10% of capacity. Run the accumulators on automatic while loading the system with purging material, allowing them to cycle at least twice (four times is better). This will ensure that they are entirely filled with purging material, and will increase the likelihood of having a fully successful purge.