Signal and Electrical Problems
Direct Thermocouple Wire Burnout: When the thermocouple wire melts due to excessive welding current and heat input, the temperature measurement signal is completely interrupted and the instrument displays the maximum full-scale value.
Inadequate Welding Signal Drift: Inadequate welding energy and current cause the weld ball to partially fuse, creating a virtual connection. This leads to an unstable output thermoelectric potential, which prevents reliable temperature measurement and causes constant oscillations in the instrument display.
Short circuit due to insulation breakdown: A short circuit between the two wires at a non-measuring end results from uncontrolled heat input during welding, which melts the thermocouple's outer insulation layer at high temperatures. The temperature that the monitor shows is significantly lower than the temperature of the hot runner.
Inaccuracies in Temperature Measurement:Thermoelectric Characteristic Drift: The alloy composition is changed by oxidation and carburisation of the weld ball and adjacent wires due to inadequate welding shielding and argon gas flow. This causes the thermoelectric potential of the thermocouple to vary systematically, which results in a temperature measurement error greater than ±10°C. Excessive Parasitic Potential: Under temperature gradients, an overly wide heat-affected zone (HAZ) and an uneven material distribution in the thermocouple wires produce additional parasitic potentials, which cause unmanageable systematic variations in temperature measurement findings.
Failures in Long-Term Reliability
Solder Joint Embrittlement and Fracture: Overheating the thermocouple wires due to excessive welding current results in coarse granules and embrittlement in the HAZ. The solder junctions are quite vulnerable to fatigue fracture under prolonged high-temperature vibration conditions in the hot runner.
Quick High-Temperature Failure: The solder balls still include a lot of porosity and slag inclusions. The contacts quickly oxidise and corrode during prolonged high-temperature duty in the hot runner, directly reducing the thermocouple's lifespan by about 60%.
These malfunctions immediately result in imprecise hot runner temperature regulation, which can lead to unanticipated production line shutdowns and moulding flaws in injection-molded goods.
