Temperature control failure is the most frequent problem in the operation of hot runner systems, and most of the faults are closely related to the failure, aging and improper installation of supporting thermocouples. Common hot runner temperature control problems include inaccurate temperature measurement, temperature runaway, local heating imbalance, temperature display deviation and frequent alarm of temperature controller, which will directly lead to product salivation, wire drawing, shrinkage, material decomposition and other defective products.
Inaccurate temperature measurement is mainly caused by thermocouple aging, probe oxidation and loose contact. After long-term high-temperature operation, the thermocouple probe is oxidized and corroded by melt gas, resulting in temperature sensing delay and large measurement error. Improper installation gap between thermocouple and heating sleeve will also cause temperature can not be transmitted accurately, making the actual temperature of the hot runner inconsistent with the display temperature.
Temperature runaway is a serious hidden danger of hot runner operation, mostly due to thermocouple circuit open circuit and short circuit. When the thermocouple line is broken or leaked, the temperature controller cannot receive sensing signals, resulting in continuous heating of the heating ring, local overheating of the manifold and nozzle, decomposition and carbonization of plastic melt, and even burning the hot runner components. Heating imbalance often occurs in multi-zone manifold hot runners. The difference of thermocouple sensing accuracy in each zone leads to inconsistent heating temperature of each runner branch, resulting in different filling speed and molding quality of each cavity product.
Temperature display deviation and controller alarm are usually caused by wrong thermocouple model mismatching, wrong positive and negative connection of lead wire and damage of lead wire insulation layer. Many users mistakenly match J-type and K-type thermocouples, resulting in permanent temperature measurement deviation. In addition, the high-temperature lead wire of thermocouple is damaged by mold extrusion and high-temperature aging, which causes signal interference and frequent jump of temperature display. Solving these problems needs to start with regular inspection of thermocouples, standardized installation, regular replacement of aging parts and matching of original model accessories.
