Mastering rapid on-site troubleshooting steps of thermocouple abnormality can effectively shorten hot runner production downtime and reduce batch scrap loss of plastic finished products; on-site troubleshooting follows four-step fixed flow: fault phenomenon confirmation → wiring inspection → component parameter testing → replacement verification, targeting five common thermocouple failure types with corresponding rapid diagnosis solutions respectively. First step: confirm specific controller abnormal display phenomenon and corresponding finished plastic defect to lock preliminary fault range; if controller shows over-limit high temperature alarm and finished gate appears scorch carbonization, suspect thermocouple open-circuit breakage; if temperature value randomly jumps up and down accompanied with finished short shot and unfilled defect, focus on poor loose contact or shielding wire interference; if reading keeps continuously declining while hot runner continuously overheat, judge positive-negative reversed wiring fault.
Second step: inspect thermocouple outer wiring from controller terminal to hot runner installation end: check whether cable is squeezed, cut, high-temperature scorched or corroded by plastic volatile gas; unplug terminal wiring and re-plug after cleaning oxide dirt on terminal metal contact; for suspected reversed wiring fault, directly swap two core leads at controller terminal block and observe temperature display recovery condition to finish quick verification within 2 minutes without dismantling mold components.
Third step: use multimeter to test thermocouple core circuit continuity and insulation resistance: set multimeter to buzzer continuity gear to detect open-circuit fracture of internal alloy wire; switch to megohm resistance gear to measure insulation value between core wire and outer sheath, insulation resistance below 1MΩ indicates sheath damage and internal short-circuit needing sensor replacement; for measured drift thermocouple, compare actual measured temperature with standard calibrator data to confirm drift error range, slight drift adjusts controller compensation coefficient while over-tolerance drift directly replaces spare thermocouple.
Fourth step: replace suspected faulty thermocouple with qualified same specification spare part for verification test: install spare standard thermocouple into original hot runner mounting hole, power on and observe controller temperature display stability, run 10–30pcs trial injection molding; if temperature returns normal and finished part defects disappear, confirm original thermocouple permanent damage and complete formal replacement. After troubleshooting finishes, record fault cause and maintenance content into equipment maintenance log to accumulate data for later periodic maintenance optimization, reducing recurring same thermocouple failure probability of hot runner system.
