Overheating Defects: A short circuit or signal loss in the thermocouple causes the temperature controller to overheat and exceed the preset temperature. When molten plastic is exposed to a hot environment, it suffers thermal decomposition and carbonisation, leaving black spots, yellowing, and scorching scars on the product's surface. In severe circumstances, bubbles and silver streaks may appear inside the product, rendering it useless.
Overheating also generates excessive melt flowability, resulting in severe flash and overflow during injection moulding. Product dimensional accuracy is completely out of control, and extra glue accumulates on the mould parting surface, increasing post-processing and polishing expenses.
Low Temperature Defects: An open circuit or grounding of the thermocouple causes the recorded temperature to be significantly lower than the actual temperature. The temperature controller turns off heating, and the actual temperature of the hot runner is substantially lower than the process requirements. Melt flowability drops dramatically, resulting in inadequate material, short shots, incomplete filling, and mould cavity filling.
At low temperatures, melt fusion performance suffers dramatically, resulting in visible weld lines, insufficient strength, and a high susceptibility to cracking at stress sites, fully failing to meet the mechanical performance requirements of structural components.
Low Temperature Defects: Temperature fluctuation defects: Poor thermocouple contact causes erratic and severe temperature variations, resulting in considerable variances in moulding temperature across different batches of goods within the same mould cavity. This results in significant colour and dimensional variances, severely upsetting batch uniformity and failing to meet the tolerance requirements of precision injection moulding.
Severe temperature changes create melt shear thermal instability, which results in an uneven internal stress distribution in the product. This causes severe warping and deformation following moulding, exceeding essential dimensional tolerances such as flatness and coaxiality, and failing to meet assembly requirements.
These quality flaws are common results of thermocouple failure in Husky hot runner systems. The faulty thermocouples can be promptly identified by examining the product's defect characteristics.
