Temperature overshoot is a common unstable phenomenon in hot runner temperature regulation, which means the actual temperature instantly rises far higher than the set target temperature in the process of heating up to constant temperature, then slowly falls back to the standard range. Excessive temperature overshoot will cause instantaneous local high temperature inside the flow channel, trigger plastic material decomposition and carbonization, and seriously affect product appearance and internal quality. This problem is closely related to thermocouple response speed, heater power matching and PID parameter setting, and can be completely solved through systematic adjustment.
First, check whether the temperature feedback of hot runner thermocouples is delayed seriously. Slow-response aging thermocouples cannot capture temperature rise changes in real time. When the actual temperature has reached the standard value, the controller still receives low temperature signals and continues to output high power for heating, resulting in serious temperature overshoot. The fundamental solution is to replace failed slow-response sensors with high-sensitivity fast-response thermocouples to ensure real-time and accurate signal transmission, and eliminate regulation lag from the source.
Secondly, optimize the matching power of heating components. If the power of coil heaters and manifold heating rings is too large, the heat release speed is far faster than the heat dissipation and temperature collection speed, which is easy to form obvious overshoot in a short time. Appropriately match heating accessories with reasonable power according to the size of hot runner nozzles and manifolds, avoid excessive surplus heating power, and make the heat rise speed match the temperature measurement and regulation speed of thermocouples.
Adjust the internal PID intelligent regulation parameters of the temperature controller is the most commonly used effective method. Reduce the proportional value properly to weaken the rapid heating output intensity in the early stage of temperature rise, increase the differential value to enhance the pre-judgment ability of temperature trend, and reasonably set the heat preservation buffer interval. After parameter optimization, the system can automatically reduce heating power in advance when approaching the set temperature, effectively suppress instantaneous temperature surge, and make the whole temperature rise process gentle and stable.
Reasonable external heat preservation and heat dissipation structure layout can also assist in improving overshoot phenomenon. Strengthen the heat insulation protection of hot runner heating area to reduce rapid heat loss, and keep the internal temperature rising uniformly and slowly. For hot runners used in high-temperature working environment, appropriately increase natural heat dissipation space to avoid excessive heat accumulation. After all adjustments are completed, conduct multiple rounds of heating test runs, fine-tune parameters according to actual overshoot amplitude, and finally make the hot runner constant temperature fluctuation range controlled within the minimum standard range, completely eliminate quality hidden dangers caused by temperature overshoot.
