Screw cleaning is an essential operation before material/color changes, production transfer, and shutdown maintenance in injection molding. Residues (old material, carbon, color powder, glass fiber) in the screw, barrel, check ring, or nozzle cause defects like black spots, streaks, and color variation, accelerating screw wear. Standard, efficient screw cleaning stabilizes product quality, protects equipment, and reduces downtime.
Preparation Before CleaningClarify the cleaning purpose (material change, color change, or maintenance) to select the appropriate cleaning material (PP, PE, or special cleaning material). Prepare tools: material bucket, copper shovel, lint-free cloth, and gloves. Remove the mold or protect it from contamination. Set the barrel temperature to the cleaning material’s molding temperature—cool down first for high-temperature to low-temperature resin transfer, heat up first for low-temperature to high-temperature transfer. Insulate for 10–15 minutes to fully melt residual material.
Empty the Hopper and Feeding SystemEmpty the remaining raw materials in the hopper, turn off the feeder, and remove/clean the feeding pipe. Thoroughly blow the hopper, hopper base, and magnet frame with an air gun (especially after processing dark, glass fiber, or degradable materials). Add cleaning material to the hopper in small batches to ensure uniform cleaning. This step prevents residual old material from mixing with cleaning material and affecting cleaning efficiency.
Preplasticizing, Emptying, and Sectional CleaningSwitch the injection molding machine to manual mode, preplasticize to fill the screw with cleaning material, then inject to discharge old/dirty material into the waste bucket. Repeat melting-injection 3–5 times for initial flushing. Appropriately increase back pressure to enhance mixing and cleaning efficiency (avoid excessive back pressure to prevent overheating). For large color differences or carbonization, use intermittent cleaning (melt → insulate for 2–3 minutes → inject) to dissolve carbon deposits.
Nozzle Disassembly and CleaningWhen discharged cleaning material is uniform and impurity-free, retract the injection seat, loosen the nozzle, and clean internal residues with a copper shovel (no steel blades to avoid damage). Blow clean with an air gun, reinstall, and inject 2–3 times to confirm smooth flow. Pay extra attention to long, thin nozzles and hot runner nozzles—easy residue hiding spots that often cause subsequent product defects.
Material Change Verification and Transition ProductionWhen discharged cleaning material is uniform, transparent, and impurity-free, add new material to replace residual cleaning material. Compare discharged material with standard samples; start mass production after consistency is confirmed. Light-colored, white, or transparent products require 1–2 extra cleaning cycles to eliminate residual color risk. Restore back pressure, speed, and temperature to normal production parameters.
Post-Cleaning Finishing and On-Site OrganizationClean the waste bucket, spilled material, and tools; restore the hopper and feeding pipe. Set drying parameters for new materials and record cleaning time, material, and effect for traceability. Long shutdowns require full cleaning with cleaning material before cooling and shutting down to prevent carbonization and subsequent startup difficulties.
ConclusionStandard screw cleaning shortens color change time, reduces defects, and protects equipment. Following the process of preparation, emptying, sectional cleaning, nozzle cleaning, and verification ensures efficient, thorough cleaning. Strict implementation of these steps lays the foundation for stable injection molding production, reduces maintenance costs, and improves overall production efficiency.
