Injection Mold Steel Daily Rust Prevention Methods

Injection mold steels are mostly alloy structural steels such as H13 and S136. Their precision molding surfaces and moving components are highly susceptible to rust caused by moisture, oil contamination and high ambient humidity. Rust damages mold accuracy, shortens service life, and causes defects such as burrs, scratches and oil marks on molded parts, directly increasing production costs. Therefore, daily rust prevention for mold steels must follow the principle of “prevention first, classified management, full closed-loop control”. Corresponding measures must be adopted according to production intervals and downtime, combined with standardized cleaning, protection and storage methods to fundamentally reduce and eliminate rust.

Online Rust Prevention During Production

During production, molds experience repeated heating and cooling, which easily forms condensation on cavity surfaces. Combined with release agents, plastic residues and dust, the rusting process accelerates significantly. Online rust prevention focuses on timely cleaning, thin protective coating and humidity control without disrupting production.

During shift intervals every 2–3 hours, key areas including cavities, cores, runners, ejector pins and slides must be cleaned using 0.4–0.6 MPa compressed air and clean lint-free cloths. Special attention should be paid to removing residual plastic, release agents and dust in narrow gaps such as parting lines, vent grooves and ejector holes. Steel tools are strictly prohibited to avoid scratching precision surfaces. Mirror-finish molds require special lint-free cloths to prevent direct fingerprint contact, as moisture and salt in fingerprints easily cause pitting corrosion.

Immediately after cleaning, apply a thin and uniform layer of neutral mold-specific rust inhibitor. The coating thickness on molding surfaces and moving parts should be controlled at 0.01–0.02 mm. High-temperature lubricating anti-rust grease can be applied lightly on guide pillars, guide bushes and ejector pins to maintain both lubrication and rust resistance. Ordinary engine oil or waste lubricants must not be used as substitutes, as they cause carbon buildup, contaminate products and are difficult to remove.

Workshop humidity must be stabilized at 40%–60%. Dehumidifiers must be operated during rainy seasons and high-humidity periods. Desiccants can be placed near molds to reduce condensation. The mold area should be kept away from acid or alkaline gases, corrosive chemicals and excessive dust to minimize corrosion risks.

Short-Term Storage Rust Prevention

Short-term storage refers to downtime of 3–30 days. Molds do not require full disassembly but need thorough cleaning and sealing to prevent hidden rust in gaps.

Deep cleaning includes removing easily disassembled components such as ejector pins and slides, soaking them in weak alkaline mold cleaner for 5–10 minutes to remove oil and carbon deposits, then wiping with anhydrous ethanol and drying in an oven at 60–80°C for 15–20 minutes. Complete removal of moisture is critical to avoid rusting. Cavities and runners can be cleaned with quick-drying online cleaner at 0.3–0.5 MPa to avoid damaging polished surfaces.

After drying, long-term rust inhibitor is applied to molding surfaces, and anti-rust lubricating grease is used on moving parts. Rust-proof paper can be added on parting lines and vulnerable edges. Cooling channels must be completely drained, sealed with plugs after injecting water-soluble anti-rust fluid.

Molds should be kept in a semi-closed state to avoid compression damage. Exposed nozzles, connectors and screws must be covered. Molds should be placed on dedicated racks and inspected weekly for condensation or depleted anti-rust layers.

Long-Term Storage Rust Prevention

Long-term storage applies to downtime exceeding 30 days or warehouse preservation. Molds require complete disassembly and multi-layer protection for stable long-term rust prevention, which can last more than 6 months under proper management.

All moving components including ejector pins, slides, inserts and guide pillars must be fully disassembled and cleaned to remove oil, carbon and oxidation. Light surface rust can be removed with neutral rust remover without damaging base material. All parts must be fully dried, especially in holes and gaps. Mirror surfaces require additional protective coating.

Multi-layer sealing includes spraying long-term hard film rust inhibitor, then double wrapping with VCI anti-rust film and PE film. Desiccants of 50–100g per cubic meter are placed inside. Large molds may use vacuum packaging. Precision molds are recommended to store in dry cabinets with humidity below 40%.

Storage environment must be dry, ventilated and free of corrosive gases. Molds should be placed 10–15 cm above ground and 5–10 cm away from walls. Monthly inspections and re-sealing every 3–6 months are required. Complete maintenance records ensure full traceability.

Key Prohibitions and Emergency Treatment

Water-containing cleaners must not be used before storage. Strong acid or alkaline cleaners are prohibited to avoid base corrosion. Coated or nitrided molds must avoid strong rust removers. Even stainless steels such as S136 require anti-rust treatment in high humidity. Before restarting production, all rust inhibitors must be thoroughly cleaned to prevent oil marks on products.

Light surface rust can be removed with fine polishing paste. Sandpaper grinding is prohibited to maintain surface finish. Moderate rust can be treated with neutral rust remover followed by rapid drying and re-protection. Severe rust requiring base material damage must be repaired by grinding and re-surface treatment such as nitriding or chrome plating.

Standardized rust prevention effectively reduces corrosion, extends mold life, stabilizes product quality and reduces overall production costs.