Carbon deposition is an inevitable byproduct formed when molten plastic decomposes under prolonged high temperature, and it gradually accumulates on the surface of hot runner thermocouple probes inside manifolds and nozzles. Over time, this layered carbon residue forms a thermal insulation barrier that severely weakens heat conduction between the mold steel and the temperature measuring junction. Even if the thermocouple itself remains intact without wire aging or internal damage, the thick carbon layer delays real-time temperature transmission, resulting in measured values far deviating from the actual runner temperature. As the controller receives lagging and lower temperature feedback, it continuously increases heating output, causing severe overheating inside the hot runner, further accelerating plastic decomposition and forming more carbon accumulation in a vicious cycle.
Excessive carbon deposition also leads to inconsistent temperature response among different cavities in multi-cavity molds. Individual probes covered with thicker carbon layers exhibit slower sensing speed and larger temperature deviation, breaking the original thermal balance and causing unbalanced melt viscosity, uneven product weight, dimensional tolerance deviation and obvious weld lines in batch production. In high-precision industries such as medical devices and 5G electronic components, even minor carbon-induced temperature errors can trigger micro-shrinkage, warpage and assembly mismatch.
Moreover, hardened carbon deposits cling tightly to the probe surface and cannot fall off naturally during mold operation. They also absorb moisture and corrosive gas from the workshop environment, accelerating sheath oxidation and micro-corrosion, and indirectly shortening the service life of thermocouples. Regular mold disassembly and professional cleaning of thermocouple probe carbon buildup are essential maintenance steps to restore temperature sensing sensitivity, maintain hot runner thermal balance and reduce the defective rate caused by thermal conduction obstruction.
