Melt Flow Figures Quoted without Their Load and Temperature
An unconditioned melt flow value lacks physical meaning without its test load, temperature, and standard protocol specified.
Process Scrap Rate
Meaning
Manufacturing efficiency metric calculating the proportion of input raw polymer resin that yields non-conforming moulded parts, purge waste, runner scrap, or startup losses relative to total processed resin weight. Calculating this metric allows moulders to evaluate process stability, material utilization efficiency, and tool design performance. A lower process scrap rate directly improves manufacturing margins, especially when processing expensive engineering resins where regrind re-use is restricted by specification.
The metric stops applying to post-consumer waste generated after parts leave the manufacturing facility.
Scrap Quantification
Calculating scrap requires weighing discarded purge material, non-conforming parts, and ungrindable runners against total resin consumed during a production run. Scrap percentages vary significantly between cold runner tools, which generate runner scrap, and hot runner tools, which eliminate runner waste entirely. Closed-loop granulators re-introduce clean runner regrind into the material stream, lowering net material loss.
Root Cause
Process instability, incorrect barrel temperatures, contaminated resin, and improper mold venting cause part defects like short shots or sink marks. Startup purge cycles generate initial scrap until thermal equilibrium and steady-state processing parameters are reached. Unoptimized runner designs and long changeover times increase scrap volumes significantly.
Economic Consequences
Uncontrolled scrap rates inflate raw material costs and consume processing capacity without generating saleable output. High scrap volumes increase regrind usage, which can alter polymer viscosity and thermal stability across extended runs. Tracking scrap rates by cause code enables targeted corrective actions that improve overall process yield.