Hot runner thermocouples belong to vulnerable precision sensing components; under normal production conditions, high-quality standard products can work stably for 6 to 12 months, while improper installation, daily maintenance and mold operation habits will shorten the service life to less than two months. Formulating standardized regular maintenance and operation protection steps can effectively slow down thermocouple aging speed, reduce procurement replacement frequency and lower mold production comprehensive cost. The maintenance steps cover pre-installation inspection, daily production protection, regular mold disassembly maintenance and storage management during mold shutdown.
Pre-installation standardized inspection and installation is the primary step to avoid early failure. Before installing thermocouples on hot runner nozzles and manifolds, maintenance personnel need to visually check whether the sheath has scratch deformation, whether the outer wire protective sleeve is damaged, and whether the plug terminal has oxidation rust spots. Use a multimeter to conduct open circuit and short circuit detection to confirm that the internal alloy wire is intact. When installing flat-head manifold thermocouples, clean the carbon deposits and oil stains on the manifold temperature measuring plane first, then install the compression spring and sensing head in sequence, ensuring no sundries are sandwiched between the contact surfaces; sundry isolation will cause unstable temperature measurement and accelerate local overheating aging of the sensing head. For inserted probe thermocouples, polish the inner wall of the nozzle temperature measuring hole to remove carbon deposits, insert the probe gently without forced hammering, as impact will cause internal alloy wire breakage inside the thin sheath. The outgoing wire shall reserve sufficient margin beside the mold plate, avoiding tension state during mold opening and closing; fix the wire with high-temperature resistant cable ties to prevent friction scratch with mold sharp edges.
Daily production real-time protection reduces accidental damage. During continuous injection molding production, operators should regularly observe the temperature value change curve on the temperature control box every two hours. If slow drift or irregular jump is found, clean the thermocouple contact surface carbon deposits in advance during machine shutdown maintenance to avoid fault deterioration leading to open circuit shutdown. When cleaning mold plastic carbonization residues, do not use sharp metal tools to scrape the thermocouple sheath surface, which will scratch the alloy protective layer and cause accelerated corrosion. When adding recycled materials containing glass fiber and flame retardant, appropriately shorten the thermocouple regular replacement cycle, as the volatile gas of such materials has strong corrosiveness to the sheath. Avoid long-term overload heating of hot runners; long-term temperature exceeding the rated working temperature of thermocouples will accelerate alloy wire oxidation and permanent temperature drift.
Regular deep maintenance during mold disassembly and mold switching. Every time the mold is offline for replacement or repair, all thermocouples matched with the hot runner shall be removed for comprehensive maintenance. Use soft copper brush matching high-temperature cleaning agent to wipe off carbon deposits and plastic oil stains on the sheath and sensing head surface; severe carbon adhesion can be soaked in neutral cleaning solution for short time before wiping, never use strong acid cleaning agent to corrode the sheath. Check the aging degree of the outgoing wire protective sleeve and shielding braid; replace the whole thermocouple once local embrittlement, crack and wire exposure appear. Test the elastic performance of compression springs for button and flat-head thermocouples; replace fatigue springs with insufficient elasticity to maintain tight contact between sensing head and hot runner metal surface. Apply a thin layer of high-temperature thermal conductive paste on the contact surface before reinstallation to improve heat transfer efficiency and reduce thermal isolation caused by carbon deposition.
Standardized storage management during long-term mold shutdown. When the mold needs to be stored offline for more than one month, disassemble all thermocouples from the hot runner separately instead of storing them together with the mold. Wipe clean surface oil stains and carbon deposits, wrap with anti-rust oil paper and place in dry constant temperature storage box, avoiding damp workshop environment leading to terminal rust and internal alloy wire oxidation. Do not stack heavy objects on the stored thermocouples to prevent sheath compression deformation. When reusing stored thermocouples after several months, conduct multimeter open circuit and temperature measurement accuracy test first to confirm no hidden aging faults before reinstallation.
Following the above complete maintenance steps can extend the average service life of hot runner thermocouples by more than 50%, reduce the frequency of emergency shutdown caused by sensor damage, and stabilize the continuous production efficiency of injection molding workshops.
