Controllers for reducing hot runner problems and downtime
Small diameter thermocouples typically used in hot runner systems are easily damaged or pinched during mould disassembly. More advanced controllers have functions to diagnose thermocouple problems and overcome faults using various strategies. Common faults are cross or reversed wiring, open circuit, or potentially the worst case, pinching at a point away from the heated zone, in which case a runaway situation can cause serious damage. State-of-the-art controllers incorporate a safety feature which detects the lack of correlation between power output and temperature rise and cuts the power with a relay before any damage is done. Slave mode can be employed if a thermocouple becomes an open circuit, or unreliable in duplicating the power output of any adjacent zone. There are also various auto slave features available that allow for seamless operation in the event of a thermocouple fault without resulting in downtime.
Moreover, additional wiring diagnostics software can detect various heater and thermocouple faults as well as keep a record of heater performance that can be used for comparison on tests at a later date.
A basic control system that allows probes, due to their low mass, to reach set point well ahead of the manifolds, can clamp down the expanding assembly, which can cause long term wear, increasing the possibility of leakage in the future. Depending on the hot runner design, various modes available can either bring all zones to the set point together, manifolds first, then probes – or a sequential process that heats pre-defined groups of zones, one group at a time. Detecting a hidden hot runner leak in the early stages can save substantial downtime and repair costs. Controllers such as the Mold-Masters M2 feature plastic leak detection. When leaks occur, plastic is released into the air gap insulation between the hot runner assembly and the cold cavity plate of the mould.