Technical know-how

Practical notes on process, part defects and machine maintenance, for operators, supervisors and process engineers.

Build the barrel temperature profile from hopper to nozzle

Zone temperatures should rise gradually from the hopper to the nozzle. An overheated feed zone softens the material before it reaches the screw and makes feeding unstable.

Part defects

Short shot: find the cause before raising the pressure

Raising injection pressure is the usual first reaction, but the cause is often shot size, melt temperature, mold venting or the check ring.

Part defects

Flash: it's not always the mold

Flash can come from insufficient clamp force, non-parallel platens, excessive pressure or a worn parting line.

Part defects

Sink marks and the role of holding pressure and time

Sink marks in thick sections come from shrinkage as the material cools, and are usually fixed by tuning the holding phase.

Materials

Take drying of hygroscopic materials seriously

Materials such as PA, PC, PET and ABS absorb moisture. Molding them wet causes silver streaks, bubbles and a severe loss of part strength.

Maintenance

Hydraulic oil: the cheapest insurance for your machine

Many pump and valve failures start with contaminated or overheated oil. Monitoring temperature, filters and oil analysis prevents heavy costs.