Meaning
Quantitative threshold for the concentration of foreign materials allowed within a polymer supply. Standards for contamination limits ensure that the resin remains suitable for its intended processing method and final application.
Part Integrity
Structural integrity of a part is threatened when the levels of dirt, metal, moisture and degraded polymer exceed the specification. In the moulding of precision components, even small amounts of foreign matter cause stress concentrators that lead to premature cracking. These inclusions act as points of weakness that reduce the fatigue life of the plastic.
Visual Quality
Visual quality is the first property to fail when contamination limits are breached. Black specks in a transparent or light coloured resin indicate the presence of charred material from the extruder or external dust. These defects increase the scrap rate and may lead to the rejection of the entire production lot.
Procurement Specification
Buyer requirements define the acceptable level of non-target materials in both virgin and regrind resins. While a datasheet for virgin resin might specify zero contamination, a regrind contract will often allow for a small percentage of secondary polymers. Excessive contamination leads to structural failure in injection moulded parts and frequent downtime for filter cleaning.
