SHORT SHOTS

Dirty or improper set-up of nozzle • Inspect and clean the nozzle. • Increase the nozzle size. Under-packing of parison cavity • Increase pack/hold pressure and/or time. • Perform a gate seal analysis. Run parts with gate seal and with gate unseal, and then select the best option. Parison mold temperature too low. • Increase the parison mold temperature. Melt viscosity too high. • Increase backpressure on the melt. • Increase the melt temperature. • Increase the screw speed. • Increase injection rate. • Use a resin with lower viscosity. Bad or improper seal of non-return valve • Repair or replace the non-return valve. Hopper is empty or feed throat is clogged • Clean/fill hopper and feed throat. • Verify quality of regrind (i.e., amount of fines or fluff present). Poor resin feeding. • Clean the hopper and check for feed throat blockage. Inconsistent resin viscosity or temperatures • Verify virgin/regrind ratio and proper mixing. • Check for loose or bad thermocouples. • Increase the backpressure to ensure resin is properly worked. • Adjust screw rpm. • Check the velocity and hydraulic injection pressure for consistency. Poor gate seal • Perform a gate seal analysis to verify gate seal. • Increase screw recovery time. Improper flow between cavities • Ensure balance flow from each nozzle. This can be confirmed by viewing a series of short shots. • Verify the mold and manifold temperature controllers are operating correctly. Bad or improper seal of non-return valve • Repair or replace the non-return valve.