Meaning
Technical procurement documentation establishes physical, chemical, rheological and thermal property limits for a raw polymer material batch. A formal resin specification defines target melt flow index ranges, density boundaries, additive loading limits and acceptable regrind percentages for incoming materials. Material suppliers guarantee batch parameters within specified datasheet ranges, whereas moulding operations must adjust barrel temperatures to handle lot-to-lot viscosity shifts.
The specification stops governing once resin enters the moulding machine hopper and undergoes thermal melt processing.
Melt Flow Index Tolerances
Rheological uniformity determines how predictably molten plastic fills thin mold cavities during injection cycles. Broad flow limits within a resin specification lead to short shots or flash when viscosity drifts between shipments. Incoming quality testing checks flow rates before releasing material to production lines.
Regrind Allowance Limits
Reprocessed sprues and runners alter molecular weight distribution when blended back into virgin stock. Strict thresholds inside a resin specification cap regrind additions to prevent loss of impact strength and color shifting. Molders log re-grind blend ratios for quality compliance.
Moisture Threshold Limits
Hygroscopic resins like polyamide and polycarbonate hydrolyze rapidly at elevated processing temperatures. Acceptable moisture content listed in a resin specification requires desiccant drying prior to molding. Processing wet resin degrades molecular chains and creates surface splay.
