Controllers for reducing hot runner problems and downtime
Time proportioning heating
Basic controllers and integrated machine controls for hot runners typically offer only time proportioning heater output control, which means that even at power output values of 1% or less, during bake out, the controller supplies short bursts of full mains voltage, increasing the possibility of arc over in the heater element. More advanced controllers employ phase angle firing during soft start to manage the dispersal of any potential moisture using reduced voltage and ground fault detection. Mold-Masters controllers have ground fault detection and phase angle firing soft start, enabling the company to offer a 10-year warranty of the heater circuits.
Phase angle firing
The raw power used for mains voltage heaters in Europe is typically 220/240V AC (alternating current), 50Hz. In other words, voltage swings from plus and minus at a frequency of 50 times a second. Graphically it can be represented by a continuous sine wave.
The most basic method of percentage control of AC power is by adjusting the ratio of on-time to the off-time to achieve the amount of power required, or time proportioning control. Whereas this system requires simpler low speed multiplexed control electronics, there are major disadvantages with regard to response times and the full mains voltage pulses applied during start up.
An alternative method of output power adjustment – phase angle firing – is achieved by delaying the switch on point to part way through each half cycle of the AC mains power. High performance hot runner controllers with dedicated high speed CPU electronics can make control decisions and alter the switch on time during each half cycle of the mains, with a control resolution suitable for effective control measured in microseconds.
This has two advantages. First of all the output power is absolutely correct every half cycle= 10 milliseconds. Secondly, for output values below 50% the voltage is reduced, which is the main factor related to heater arc over. At 1% output the voltage is measured sub 20 V, where arc over due to dampness is not possible.