Meaning
Mass of resin wasted while flushing out previous material or resin degradation products during extruder start-ups and product changeovers measures transition inefficiency. Purge loss accounts for raw resin consumed until the extrusion line reaches stable processing conditions and acceptable quality standards. The metric stops applying during steady-state production where output meets customer quality specifications.
Transition Scrap
Material switches require running purging compounds or raw resin through the extruder barrel to clear residual polymer and colorants. High molecular weight purge resins strip degraded material from screw flights, but generate heavy purge blocks that must be disposed of or reground. Frequent product shifts multiply cumulative transition losses across a manufacturing schedule.
Resin Waste
Machine operators record purge mass during every changeover to monitor material waste trends and evaluate purging compound performance. Commercial purging compounds reduce flushing time and resin volume compared to purging with standard virgin resin. Reducing purge material volume directly lowers operating costs and decreases machine downtime between production runs.
Changeover Cost
Financial impact of transition waste includes both wasted raw material costs and unrecovered machine hourly operating expenses. Running large barrel extruders exacerbates purge loss due to large internal melt volumes that require extensive flushing. Small prototype machines incur minimal transition loss, making pilot run economics poor predictors of purge scrap costs on commercial scale extrusion lines.
Supplier resin forecasts must incorporate planned changeover purge allowances to maintain accurate stock levels during multi-product campaign runs. Declaring a changeover procedure optimized before measuring purge loss weight across all machine sizes results in inaccurate product cost models.
