In the hot runner injection molding process, the thermocouple undertakes the key task of real-time temperature collection and feedback. Once it fails ages or deviates, it will break the thermal balance of the hot runner system, and then trigger a series of product molding defects, affecting yield and production efficiency. Many injection molding enterprises ignore the maintenance and replacement of thermocouples, resulting in long-term unstable production and increased production cost.
When the thermocouple temperature measurement is delayed or deviated, the temperature controller cannot adjust the heating power in real time. The nozzle tip temperature is too high, which will cause plastic melt salivation and wire drawing, resulting in material waste and product burrs; if the temperature is too low, the melt fluidity decreases, leading to insufficient product filling, shrinkage pits and sink marks. For multi-cavity mold hot runners, the failure of a single thermocouple will cause temperature difference between cavities, resulting in inconsistent product size, weight and appearance of each cavity, unable to meet mass production standards.
Thermocouple open circuit and short circuit will cause hot runner temperature runaway. Local overheating will lead to plastic carbonization and decomposition, producing black spots, yellow lines and impurities on the product surface, which seriously affects the appearance quality of precision parts. Carbonized materials will also block the runner channel, resulting in mold disassembly and cleaning, delaying production progress. At the same time, long-term overheating will accelerate the aging of heating rings and hot runner mechanical parts, increasing mold maintenance and replacement costs.
In addition, the aging insulation layer of thermocouple lead wire will cause signal interference and temperature jump, making the process parameters unable to be fixed. The production personnel cannot stabilize the injection pressure, speed and holding pressure, resulting in frequent adjustment of the process and unstable product quality. It can be seen that thermocouple is a small component with decisive impact, and regular inspection, maintenance and timely replacement are the key measures to ensure the stable operation of hot runner and improve molding yield.
