Formulating standardized thermocouple maintenance SOP (Standard Operating Procedure) and implementing regular inspection and maintenance can reduce the reject rate caused by temperature control faults of hot runner molds by more than 65%, covering pre-production inspection, daily shift inspection, weekly calibration maintenance and monthly deep disassembly inspection four standardized operation links, which are suitable for injection molding workshops of automotive, medical, electronics and packaging industries.
The pre-production inspection SOP is executed by mold operators before each machine startup. First, visually inspect all thermocouple wire routing to check whether the MI sheath is extruded, cracked or worn, whether the patch contact piece falls off, and whether the terminal wire has loose virtual connection; second, use a multimeter to perform continuity testing on each sensor to eliminate hidden open circuit faults; third, check the tightness of the spring preloading structure to ensure that the sensing tip is completely attached to the hot runner metal surface without gaps leading to temperature delay; finally, confirm that the thermocouple type parameter on the controller menu is consistent with the actual installed sensor alloy type to avoid measurement deviation caused by mismatched parameters. All abnormal thermocouples found in pre-production inspection are replaced before formal injection molding, and hidden faults are not brought into mass production.
Daily shift handover inspection SOP requires the operator to record the temperature fluctuation curve of each heating zone in the production log every two hours. If the temperature fluctuation exceeds ±2℃ continuously, mark the corresponding thermocouple number and inform maintenance personnel to check after the shift. At the end of each shift, clean the plastic decomposition carbon deposits around the thermocouple mounting position on the manifold and nozzle, because carbon accumulation will form heat insulation layers, reduce heat conduction efficiency and cause temperature measurement distortion. It is forbidden to use sharp metal tools to scrape carbon deposits to avoid scratching the thermocouple sheath and damaging internal insulation.
Weekly calibration maintenance SOP is undertaken by professional mold maintenance technicians. Use a handheld high-precision contact pyrometer to compare the actual surface temperature of the hot runner with the reading displayed by the thermocouple controller. If the deviation exceeds ±2℃, calibrate the controller compensation parameters or directly replace the aging drifted thermocouple. Tighten all thermocouple terminal screws on the controller cabinet to eliminate virtual connection faults caused by workshop vibration. Check the integrity of the thermocouple shielding braided mesh and the grounding state of shielding wires, and repair broken shielding sleeves in time to prevent signal jumping interference. Record all calibration deviation data and replacement sensor models in the mold maintenance file to track the aging cycle of each batch of thermocouples.
Monthly deep disassembly maintenance SOP is arranged during the monthly mold shutdown maintenance window. Remove the manifold and nozzle from the mold base, take out all inserted MI thermocouples, inspect the sheath for micro cracks and internal mineral powder carbonization, and replace sensors with obvious aging signs in advance. Clean the mold wiring grooves, replace aging high-temperature insulation gaskets, re-arrange all thermocouple wires with reserved slack length to avoid tensile extrusion during thermal expansion and contraction. For production lines operating 24 hours a day, the monthly maintenance cycle can be adjusted to every 20 days to adapt to high-load working conditions.
Enterprises that fully implement thermocouple maintenance SOP can extend the average service life of sensors by more than 40%, and eliminate mass defective products caused by sudden thermocouple faults. Many small and medium-sized molding factories lack standardized maintenance processes, only replacing thermocouples after obvious alarm failures, resulting in continuous production of defective parts before faults break out, bringing huge material and labor waste losses. Complete written maintenance SOP, matching inspection records and regular technician training form a closed-loop thermocouple management system, which is a low-cost and high-efficiency quality control measure for hot runner injection molding production lines.
