Why Do Thermocouples Fail in High-Temperature Hot Runner Systems?

In high-temperature hot runner systems processing engineering plastics such as PEEK, PPS and LCP, thermocouples often face accelerated aging, signal drift, open circuit and short circuit. The main reasons include high-temperature oxidation, material corrosion, thermal stress damage and unsuitable structure. Understanding these causes can help users select appropriate sensors and reduce failures. Top brands such as Synventive, Mold-Masters and Husky design special high-temperature thermocouples to solve these problems. The most common cause of failure is high-temperature oxidation. Ordinary thermocouple materials will oxidize rapidly at temperatures above 300°C, resulting in changes in electrode characteristics and signal drift. K-type sensors are more resistant to oxidation than J-type, but they will still drift under long-term ultra-high temperature. In addition, the high-temperature melt will corrode the sheath and junction, leading to damage and short circuit. Thermal stress is another important factor. The sensor is subjected to repeated thermal expansion and contraction during heating and cooling, which is easy to cause internal wire breakage and sheath cracking, resulting in open circuit. Vibration during mold operation will accelerate fatigue damage. In addition, improper installation depth, poor contact and excessive torque will also lead to sensor damage in advance. High-temperature thermocouple products usually use high-temperature alloys, seamless sheaths, sealed junctions and high-purity magnesium oxide insulation. These structures can resist oxidation and corrosion and extend service life. Brands also provide customized high-temperature sensors for special materials to adapt to extreme process conditions. Common failures in high-temperature systems include open circuit, short circuit, severe signal drift, sheath deformation and poor contact. These problems will lead to temperature out of control, material degradation and product scrapping. Solutions include selecting special high-temperature K-type thermocouples, avoiding long-term over-temperature operation, regular calibration and maintenance, and standardizing installation. In a word, the failure of thermocouples in high-temperature systems is mainly caused by oxidation, corrosion, thermal stress and improper use. Choosing high-performance high-temperature special sensors and correct maintenance can greatly reduce failures and ensure stable production.