Sulfur-containing stabilizer modified plastic widely used for pipe and rubber-plastic composite part injection on special domestic and modified Husky hot runner decomposes sulfur-based acidic corrosive gas under high molding temperature; sulfur vapor triggers unique intergranular corrosion of stainless steel sheath and progressive internal insulation deterioration of matched thermocouple, ordinary 304 sheath cannot resist sulfur corrosion and quickly forms brittle intercrystalline crack after short service period. Sulfur-containing corrosive gas adheres on sheath outer surface and forms sulfide electrolyte film under alternating hot-cold ambient condition, penetrating stainless steel crystal boundary to develop intergranular corrosion crack which gradually expands inward and finally perforates sheath wall; after corrosion perforation, sulfur gas invades internal magnesia filler and reacts with inorganic oxide to generate soluble sulfate substance, leading filler deliquescence and insulation resistance rapid attenuation, bringing continuous measuring drift and leakage short-circuit fault. Bare copper terminal exposed in sulfur mist environment generates black copper sulfide corrosion layer blocking contact surface and increasing circuit contact resistance steadily.
Medium sulfur corrosion working condition upgrades sheath from 304 to 316L stainless steel plus full sealed epoxy terminal; severe high-sulfur continuous production line selects Inconel alloy sheath customized thermocouple with excellent sulfur corrosion resistance. Install local exhaust hood near hot runner nozzle to timely extract floating sulfur corrosive vapor and reduce gas sedimentation probability on sensor surface. Biweekly maintenance cleans sheath surface sulfide coke residue with special neutral sulfur-removal cleaning solvent to slow corrosion development speed. Purchasing contract adds sulfur resistance aging test clause for corresponding production line bulk thermocouple order to control inferior cheap sheath products entering high-sulfur workshop.
