Part of every employee’s job is to prevent resin losses through these three major causes: contamination, excess regrind and overweight containers. Resin in any form must be free of contaminants like dirt, metal, or any foreign matter and can not be processed through a blowmoulding machine unless it is perfectly clean.
This includes virgin pellets, flash, or out-of-spec containers. The most frequent cause of contamination occurs because something other than clean plastic is inserted into the granulator.
When this happens, it too gets ground up and blended with the regrind and ultimately gets sent through the extruder. Unfortunately, this problem is usually detected after it has caused others.
Contaminants
Contaminants can get stuck in the extruder and if deemed necessary, production must be stopped while the machine is dismantled and cleaned. If dirty material does manage to get extruded, the parts made with it will have to be discarded.
Machine downtime hurts production efficiency and discarded articles affect resin expense. Contamination can be avoided by careful inspection of anything hand fed into the granulator. Whether it’s flash, out-of-spec containers, or purgings – a check for cleanliness is time well spent.
Automatic flash conveying systems include magnets located to catch ferrous metal parts or tools which may find their way into the system.
Floor sweepings should never be ground up, as even a small amount of dirt could be harmful to the process. Another measure to prevent contamination is to maintain tight fitting guarding under press sections on part conveyers and around inspection stations.
Never Ground Up Floor Sweepings
Contamination also occurs when dissimilar resins are mixed. Combining one resin with another ruins both and makes the batch unusable. Such losses can be prevented by thoroughly cleaning the material system when changing over from one resin to another or from one colour to another. Extreme care should be taken to ensure that the correct resin and colour goes into the right system.
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