Regular disassembly inspection of thermocouples will occupy mold production time, and many injection molding enterprises lack unified aging judgment standards, often replacing sensors only after complete failure. Mastering non-disassembly aging identification methods can accurately judge the attenuation degree of thermoelectric alloy, spring elasticity and insulation performance during normal production shifts, arrange planned batch replacement in advance, and eliminate unplanned shutdown hidden dangers caused by sudden probe failure.
Method one: continuous temperature drift tracking comparison. Establish daily temperature record sheets for each hot runner temperature zone, recording the controller displayed value and real metal temperature measured by a portable standard thermometer every morning before startup. Calculate the daily temperature error difference; if the error value gradually increases by more than 0.2℃ every month and cannot be eliminated by cleaning contact surfaces and adjusting cold junction offset parameters, the internal thermoelectric alloy wire has obvious metallographic aging, and the thermocouple has entered the late service life stage. New qualified thermocouples maintain stable error within ±1℃ for the first six months of use, and obvious drift acceleration after eight months of continuous production is a typical aging signal.
Method two: temperature response speed test without disassembly. After the hot runner reaches constant temperature, manually reduce the set temperature of a single zone by 20℃ and record the time required for the displayed temperature to drop to the new set value. New intact grounded thermocouples complete temperature feedback within 0.5 seconds; aging probes with alloy fatigue, spring elasticity attenuation and contact gap increase need more than 1.2 seconds to respond to temperature changes. Slow response speed indicates that the measuring contact and internal alloy wire have aging damage, which will cause frequent temperature overshoot and material burning defects in subsequent production.
Method three: signal stability observation under vibration interference. During the injection molding cycle, focus on the temperature value fluctuation range of each zone when the mold opens and closes and the valve needle acts. New anti-fatigue thermocouples have a fluctuation range controlled within ±0.3℃ under mechanical vibration; aging probes with internal micro-cracks and loose connectors will produce irregular fluctuation exceeding ±1℃, and occasional TC OPEN intermittent alarms appear with vibration. This phenomenon proves that the alloy wire has formed hidden fatigue fractures inside the sheath, and complete open-circuit failure will occur soon.
Method four: insulation resistance online auxiliary detection. Most new intelligent hot runner controllers support single-channel insulation resistance real-time detection function. Call the insulation test interface before each daily startup; qualified new thermocouples maintain insulation resistance above 100MΩ. If the reading gradually drops to below 50MΩ without water cooling pipeline leakage and mold dampness, the sheath has micro-pores and internal magnesium oxide insulation powder is aging and absorbing moisture, belonging to serious aging that needs priority replacement.
Method five: cross zone swap comparison verification. For molds with multiple identical specification thermocouples, swap two probes with obvious error difference to different controller channels. If the large temperature deviation follows the thermocouple to the new channel instead of staying on the original control channel, the sensor itself has irreversible aging attenuation, rather than controller parameter or wiring faults. This method can accurately distinguish equipment faults and thermocouple aging without disassembling the mold manifold.
Integrate the above five non-disassembly testing methods into daily equipment inspection specifications, classify thermocouples into normal service period, early aging warning period and late failure risk period according to test results, and formulate targeted maintenance and replacement plans. Non-disassembly aging judgment avoids frequent mold shutdown disassembly losses, realizes predictive maintenance of thermocouple spare parts, and effectively improves the continuous operation rate of hot runner production lines.
