Industry statistical data shows over 72% abnormal hot runner temperature failures during on-site injection production originate from thermocouple damage, improper installation or wrong model matching; five most frequent typical faults include open-circuit fracture, poor loose contact, reversed wiring, high-temperature long-term drift and external electromagnetic signal disorder, each fault corresponds unique controller temperature display anomaly and specific finished plastic defective manifestation. First, thermocouple open-circuit breakage ranks highest failure rate, mainly caused by mold repeated clamping extrusion cutting outer wire, long-term high-temperature aging alloy wire fatigue fracture and corrosive plastic gas eroding armored sheath crack; when open circuit happens, temperature controller displays over-limit ultrahigh value or error alarm code, corresponding hot runner nozzle/manifold keeps overheating without temperature regulation, leading to local plastic carbonization and gate scorch defect of finished products. Regular inspection of wiring channel and fixed wire clamping every 50,000 molding cycles can effectively reduce open-circuit failure probability.
Second, poor loose contact mostly occurs on spring bayonet thermocouple installation end: long-time thermal expansion and cold contraction of hot runner metal plus continuous mold vibration make built-in spring fatigue failure, resulting in probe separating from measured metal surface; controller temperature value randomly fluctuates up and down with large deviation, hot runner heating works intermittently and melt viscosity changes irregularly, generating finished product unfilled short shot and uneven wall thickness defects. Replacing aging spring and re-calibrating preload compression allowance during routine maintenance is effective troubleshooting measure. Third, positive-negative reversed wiring fault comes from irregular field wiring operation: after reversing thermocouple two core leads, controller shows continuously decreasing temperature reading while hot runner keeps uninterrupted heating, plastic overflows gate to form burr flash; re-switch two signal wires at controller terminal block can rapidly solve this problem without component replacement.
Fourth, long-term high-temperature measurement drift usually appears on non-original low-quality replacement thermocouple with inferior thermo-alloy core; inferior alloy oxidizes quickly under continuous high temperature, causing measured temperature gradually deviate from actual value, hot runner real temperature far higher than set parameter and finished parts generate drooling and stringing at gate. Replacing with standard qualified K/J-type thermocouple and calibrating controller temperature compensation coefficient can fix drift issue fundamentally. Fifth, external electromagnetic interference disorder induced by nearby high-power servo motor and frequency converter: alternating current signal invades thermocouple unshielded wire and triggers instantaneous temperature value jumping, hot runner PID heating logic confuses to cause intermittent overheat or underheat; upgrading double-layer braided shielded single-end grounding wire can isolate external interference thoroughly.
