Anti‑Corrosion Treatment Methods for Rigid PVC Injection Molds

During rigid PVC injection molding, corrosive acidic gas will be released, which causes cavity pitting, rust spots and surface peeling. These defects damage plastic appearance and shorten mold service life. Anti‑corrosion measures shall cover material selection, surface treatment, production operation and shutdown maintenance to mitigate acid‑medium erosion on mold surfaces.

1. Anti‑Corrosion Based on Mold Steel Substrate Selection

Steel substrate lays the foundation of anti‑corrosion performance. Ordinary pre‑hardened steels are not suitable for direct rigid‑PVC molding. Chromium‑containing corrosion‑resistant mold steel forms passive protective films to resist chloride erosion decomposed from PVC. Common grades include S136 and 420 series stainless steel, which obtain balanced hardness and corrosion resistance after quenching and tempering. Avoid NAK80, P20, 718 and other conventional pre‑hardened steels with low chromium content; they are vulnerable to pitting rust under long‑term rigid‑PVC production. If cost constraints force adoption of ordinary steel, complete surface protection treatment must be implemented before production.

2. Cavity Surface Coating Protection Treatment

Surface coating is a widely‑used anti‑corrosion solution for rigid‑PVC molds. Dense isolation layers separate acidic gas from metal substrate. Chromium nitride and hard chrome plating are mature industrial options. Coatings shall evenly cover cavities, inserts, runners and gates without missing spots. Hard chrome plating delivers both anti‑corrosion and wear‑resistance for mass‑production appearance‑critical molds. Chromium‑nitride coatings feature stronger adhesion and resist peeling on complex curved surfaces and thin ribs. Complete high‑grade polishing before coating to eliminate sand holes and pinholes. Once coating breaks, corrosion will spread rapidly underneath, so re‑coating is required timely.

3. Anti‑Corrosion Design for Gating and Venting System

Corrosive gas decomposed from rigid‑PVC accumulates heavily inside runners, gates and vent slots, where corrosion proceeds faster than product cavities. Fabricate runner, gate and vent‑slot inserts with corrosion‑resistant steel plus protective coating. Set proper vent depth to exhaust corrosive gas rapidly and reduce gas residue. Minimize dead corners and blind grooves in mold structure, where volatile corrosive substances tend to accumulate. Optimize cooling layout to achieve uniform mold temperature. Local overheating accelerates PVC decomposition and increases corrosive‑medium output.

4. Anti‑Corrosion Control During Production

Strictly control barrel and mold temperature to prevent excessive heat‑induced PVC cracking and acid‑gas generation. Implement standardized raw‑material drying; moisture accelerates both PVC decomposition and mold electrochemical corrosion. Select neutral mold‑release agents compatible with PVC. Acidic or alkaline release‑agent residues will aggravate surface corrosion. Clean white decomposed precipitates on parting surfaces and vent slots regularly during production intervals, as these residues are corrosive and will damage polished surfaces.

5. Shutdown and Daily Anti‑Corrosion Maintenance

For short‑term shutdown, fully close mold cavities and spray dedicated anti‑rust agent to isolate ambient air. For long‑term storage, thoroughly wipe off precipitates on cavities, runners and vents before anti‑rust spraying. Inspect cavities for tiny rust spots and coating damage after every mold offline. Polish minor rust spots immediately to stop pitting expansion. Stop rigid‑PVC production once local coating peels off; re‑surface coating is mandatory.

ConclusionAnti‑corrosion for rigid‑PVC injection molds cannot rely on anti‑rust spray alone. Coordinate steel‑grade selection, surface coating, structural optimization, production‑process constraints and shutdown maintenance. Adopt corrosion‑resistant stainless‑steel substrate with reliable surface coating, reduce generation and retention of acidic PVC decomposition gas, and execute cleaning and protection during production and shutdown, so as to slow mold corrosion, stabilize plastic‑part appearance and extend mold service life.