Long-term cyclic fluctuation between shutdown ambient room temperature and formal molding working temperature brings repeated thermal expansion and cold shrinkage alternating load to thermocouple supporting Husky and domestic uninterrupted batch production hot runner equipment, gradually accelerating sheath surface oxidation scaling, internal magnesia filler loosening and core alloy wire crystalline grain aging, which counts as the most dominant natural aging factor shortening the rated design service lifespan of various specification thermocouple products. In every single startup-shutdown circulation process, stainless steel sheath expands outward under lasting high molding heat and contracts inward rapidly when equipment stops production and cools down to ambient temperature; repeated cyclic elastic-plastic deformation makes originally compacted high-density magnesia insulation filler produce invisible tiny intergranular gaps step by step, floating workshop moist air, oil mist and corrosive plastic pyrolysis gas continuously penetrate inward along accumulated crevices under long-time daily production accumulation. Ordinary 304 stainless steel sheath continuously operating above 420℃ will generate thick loose iron oxide scaling layer after several months of uninterrupted high-temperature oxidation, oxidized brittle layer peels off intermittently with temperature cycling and gradually reduces effective sheath wall thickness, greatly increasing pitting corrosion penetration risk especially under corrosive workshop production environment filled with acidic plastic volatile matter. Meanwhile thermocouple core alloy endures long-term persistent high-temperature grain coarsening, internal metal crystal arrangement and lattice structure change irreversibly, leading fixed inherent Seebeck coefficient to drift permanently and forming slow cumulative measuring deviation that cannot be eliminated merely by controller built-in parameter compensation and calibration adjustment.
For continuous nonstop production hot runner running over 20 hours every single day all year round without regular long shutdown, standardized optimized configuration upgrades outer sheath material from conventional cheap 304 stainless steel to high-grade 316L molybdenum-containing stainless steel or high-performance Inconel nickel-based alloy with outstanding high-temperature oxidation resistance and thermal fatigue resistance; core wire adopts vacuum secondary smelting high-purity thermo-alloy raw material to slow down high-temperature crystalline aging speed remarkably and stabilize long-term thermoelectric performance. Daily on-site production patrol regularly records actual operating temperature fluctuation range, daily startup-shutdown frequency and runtime duration of each independent hot runner temperature channel, sorts out long-term component aging change rule statistical data to arrange planned centralized replacement during annual equipment overhaul downtime instead of waiting for sudden on-site breakdown and unexpected emergency production shutdown which brings substantial defective product loss and rush-order spare part premium cost. Equipment management department archives full-year aging-induced scrap classification statistical report systematically, feeds back sorted field operation data to enterprise purchasing department to adjust raw material grade and sheath material selection benchmark for high-cycle frequent startup production line projects, reasonably controls long-term annual thermocouple total consumption cost and stabilizes continuous injection molding production quality.
