Impurity-mixed recycled waste plastics containing residual paint residue, waste rubber fragments and irregular unknown chemical additives are extensively applied in low-end daily commodity hot runner molding matched with domestic economical hot runner brands, and unstable complex impurity composition of recycled raw materials releases diversified corrosive volatile gas plus irregular solid carbon deposits under high-temperature melting, greatly shortening matched thermocouple average service lifespan compared with pure virgin resin continuous production environment. Distinct from well-formulated standardized new plastic pellets, recycled plastic carries residual organic solvent, heavy metal compound and miscellaneous halogen impurities left from waste sorting and recycling procedures; once heated above 280℃ inside hot runner manifold flow channels and nozzle inner cavities, these foreign impurities thermally decompose into composite acidic volatile fume that continuously attacks unpolished ordinary stainless steel thermocouple outer sheath, gradually penetrating internal insulation structure and eroding core thermo-alloy wires.
Uncontrollable irregular thermal decomposition of recycled plastics easily triggers local hot runner partial overheating and massive carbon accumulation; hard compact carbonized dirt piles around thermocouple mounting position and completely wraps probe measuring end, forming thick heat insulation barrier and cutting off effective heat conduction between sensing tip and hot runner metal base, resulting in slow progressive measurement drift and invalid closed-loop temperature regulation. Regular carbon layer cleaning forces periodic thermocouple disassembly every 20,000 molding cycles, and frequent repeated plug-in and pull-out operation gradually fatigues built-in bayonet spring elasticity and indirectly shortens overall component service cycle. Besides, recycled plastic often mixes hard inorganic sand and grit impurities; these solid particles abrade nozzle inner runner wall during high-speed melt flowing and splash onto exposed thermocouple outer wiring during periodic mold opening movement, scratching outer insulation coating and accelerating wire breakage failure.
For production lines dedicated to long-term recycled plastic molding, industry technical guidelines suggest upgrading original ordinary sensors to electropolished 316L mineral-insulated thermocouple with full Teflon outer wiring for strengthened anti-corrosion and anti-abrasion capability; economical 304 J-type standard thermocouple is only allowed for short-term intermittent recycled material trial production rather than continuous mass processing. Many small-scale processors still persist in selecting ultra-low-cost generic sensors to save initial procurement investment, leading to monthly regular thermocouple replacement and frequent unplanned production shutdown loss far exceeding extra cost needed for high-spec anti-corrosion customized products.
An effective auxiliary optimization measure installs independent exhaust structure on hot runner manifold plate to discharge most corrosive decomposition gas out of mold inner space in advance and reduce ambient chemical erosion degree of surrounding thermocouple accessories. Driven by global environmental protection policies boosting recycled plastic comprehensive utilization rate, anti-corrosion targeted customized thermocouple for recycled resin molding gradually grows into stable incremental profit market segment for domestic professional temperature sensor manufacturers.
