Thermocouple replacement is routine maintenance, but it carries significant safety risks-burns, electrical shock, and damage to expensive tooling. Following standardized safety procedures protects personnel and equipment.
Mandatory Power-Off and Full Cooling. The first core rule is mandatory power-off and full cooling before operation. Before disassembling any thermocouple, the operator must completely cut off the total power supply. Wait until the overall temperature of manifolds and nozzles drops below 60℃ before starting disassembly work. Attempting replacement on a hot system risks severe burns and can damage the thermocouple bore due to thermal expansion mismatches.
Lock-Out/Tag-Out Application. Apply lock-out/tag-out procedures to the hot runner controller. Verify with a multimeter that no voltage is present at the heater terminals. Even if the controller display shows zero power, a faulty triac can still supply voltage-always test before touching.
Standardized Wiring Disassembly and Assembly. Follow standardized wiring disassembly and assembly sequences. When removing the nozzle, hold the heating sleeve body instead of pulling the wire section to avoid separating the hot junction from the heater core. Disconnect the thermocouple, disassemble the broken thermocouple from the cutout starting at the base of the pressure tube and pull it out of the bore in the nozzle.
Cleaning and Preparation. Coat the tip of the new thermocouple with heat transferring paste and insert it into the bore in the nozzle as far as it will go. Clean the bore with a brush and compressed air before installation. If the bore is damaged, consult the mold maker before proceeding.
Post-Installation Inspection. After full assembly, conduct multimeter continuity test to rule out open circuits. Measure the thermocouple circuit resistance with a multimeter to confirm it is within the range of 2–10Ω. Power on the temperature controller for low-temperature preheating (80℃ holding 30 minutes) before raising to production temperature. This avoids rapid thermal shock damaging newly installed thermocouples.
Documentation. Record installation date for each probe to arrange periodic replacement plans. Store spare thermocouples in dry constant-temperature cabinets to prevent sheath rust and wire oxidation before use.
Tool Requirements. Use a torque wrench for all threaded connections-never tighten based on experience. Use a multimeter for continuity testing. Use a megohmmeter for insulation resistance testing. Have heat-resistant gloves and safety glasses available.
Spare Parts Management. Mark each zone plug with corresponding heating zone numbers to avoid cross-wiring during replacement. Distinguish positive/negative polarity wires strictly per color coding. Pre-wire spare thermocouples with connectors for quick replacement.
