Why Do Hot Runner Thermocouples Fail?

Thermocouple failure is a common fault in the operation of hot runner systems, which will directly lead to shutdown, product scrapping and increased production costs. As an electric heating expert focusing on hot runners, I will analyze the main causes of thermocouple failure in the hot runner industry and provide targeted preventive solutions. The failure of hot runner thermocouples is mostly caused by high-temperature aging, melt erosion, mechanical damage, installation error and electromagnetic interference, rather than natural damage. First of all, long-term high-temperature operation is the primary cause of thermocouple aging. The hot runner system works in a high-temperature environment for a long time, and the internal alloy wires will oxidize, recrystallize and drift, resulting in inaccurate temperature measurement. If the working temperature exceeds the limit of the thermocouple for a long time, the aging speed will be accelerated, and even open circuit and short circuit will occur. Secondly, melt leakage and erosion are unique to the hot runner industry. Once the plastic melt seeps into the interior of the thermocouple, it will carbonize the insulation layer, damage the conductor structure and lead to complete failure. Mechanical stress and improper installation are also important factors. In the process of installation and replacement, excessive bending, pulling and extrusion will damage the internal conductor of the thermocouple. Vibration generated during the operation of the injection molding machine will also cause the thermocouple junction to loose or the cable to break. In addition, poor contact of the connector, water vapor and oil pollution will cause signal instability and accelerate failure. Electromagnetic interference generated by the hot runner heater will also cause signal drift, which is mistaken for thermocouple damage. To reduce the failure rate, users should standardize installation, avoid over-temperature operation, strengthen sealing protection and regularly check the cable and connector. Selecting thermocouples with high-temperature resistance and anti-seepage design can significantly improve the service life. Understanding the failure mechanism helps enterprises take preventive measures in advance, reduce downtime and improve production stability. For the hot runner system, reducing the thermocouple failure rate is equivalent to improving the overall operation efficiency and economic benefits.