How to Effectively Prevent Rust on Molds in Injection Molding Production

Molds are core equipment determining the molding quality and production efficiency of injection products. Mold steel is highly prone to rust due to long-term contact with water vapor, residual plastic, corrosive raw materials and humid workshop air. Mild rust impairs product surface finish, causing poor demolding and dimensional deviations, while severe rust damages cavities, clogs cooling channels, shortens mold service life drastically and increases maintenance costs and downtime. Mold rust prevention is not a single post remedy, but a systematic work throughout daily production, short-term shutdown and long-term storage. Formulating standardized operating norms based on production scenarios and strictly controlling the environment and details can eliminate rust risks from the source and ensure stable mold operation.

1. Daily Production: Basic Rust Prevention to Forestall Problems

Though molds work at high temperatures and seem rust-resistant during continuous daily production, residual water in cooling channels, raw material decomposition products and mold release agent residues create corrosive conditions. The core of rust prevention at this stage is "frequent cleaning, humidity control and hidden danger elimination" to build a solid first line of daily protection.

After each shift, turn off the cooling water supply immediately and purge the channels repeatedly with 0.5-0.7MPa high-pressure air to completely drain residual water, avoiding inner wall rust and scale buildup from prolonged soaking. For highly corrosive raw materials such as PVC, POM and halogen-containing flame retardants, clean the channels weekly with special descaling agents to reduce impurity and corrosive substance adhesion.

Thoroughly clean mold surfaces and structural gaps with a special mold cleaner after each shift to remove residual plastic, oil and mold release agent, preventing local rust from moisture absorption by impurities. Maintain workshop relative humidity at 40%-60% with dehumidifiers for rainy weather to avoid condensation from temperature differences. Regularly apply high-temperature grease to moving parts like guide pillars, bushings and ejector pins to ensure smooth operation and form a dense oil film for dual lubrication and rust prevention.

2. Short-Term Shutdown: Rapid Protection Against Sudden Rust

Short-term shutdown refers to downtime within 7 days such as weekends, mold change, material waiting and temporary order suspension. Molds need no disassembly in such scenarios but are easily neglected, making it a high-risk stage for sudden rust, which requires a standardized and simple rapid rust prevention process with thorough protection.

First, conduct a full cleaning: open the mold and remove residual material and oil from dead corners such as cavities, parting surfaces, threaded holes and slider grooves, wiping repeatedly with lint-free cloth and cleaner to ensure no impurities remain. Then blow the entire mold dry with high-pressure air, focusing on blind holes and gaps prone to water accumulation—drying is the core prerequisite for rust prevention, and never spray rust inhibitor directly without drying, as this will seal moisture on the mold surface and accelerate rusting.

After drying, uniformly spray a thin layer of special short-term rust inhibitor on all metal surfaces including cavities, cores and inserts at a distance of about 20cm, moving the spray gun quickly for a thin and even coating to avoid excessive local oil film affecting product cleanliness in subsequent production. Control the dosage on the sealed parting surface to prevent extrusion overflow. After spraying, close the mold slowly with a small gap to avoid rust inhibitor failure from over-extrusion, then wrap the mold simply with PE protective film and place it on a dry, ventilated special shelf away from the ground and walls to isolate moisture and ensure no rust during short-term storage.

3. Long-Term Storage: In-Depth Protection for Long-Lasting Rust Resistance

For molds out of service for more than 7 days, or requiring warehouse storage and cross-cycle standby, simple short-term rust prevention is insufficient. In-depth disassembly and comprehensive protection with multi-layer measures are necessary to achieve long-term stable rust prevention and avoid large-area rust during prolonged storage.

The first step is complete disassembly and cleaning: remove all moving parts such as ejector pins, sliders, inserts and guide pillars, and clean residual material, carbon deposits and oxide layers by category. Gently treat mild surface rust with neutral rust remover, and never scratch the mold surface with hard tools. After cleaning, dry all parts thoroughly with hot air and high-pressure air to lay a foundation for long-term rust prevention.

Spray long-acting hard film rust inhibitor on core molding parts evenly and let it stand for about 10 minutes to form a firm protective layer after full film formation. Apply an additional thick layer of special rust preventive grease to precision fitting parts like ejector pins and bushings to enhance protection in gaps. Inject rust-proof oil into cooling channels and seal all interfaces to block air and moisture. After closing the mold as a whole, wrap it hermetically with VCI vapor phase rust-proof film and PE film in double layers, place desiccants inside the mold in proportion to absorb residual moisture. For precision molds, conduct vacuum packaging and store them in a moisture-proof mold cabinet with humidity below 45%, away from acid, alkali, corrosive gases and water sources for long-term stable rust prevention.

4. Emergency Rust Treatment: Timely Remedy to Avoid Worsening Damage

Even with good daily protection, mild rust may still occur due to sudden environmental changes or operational omissions. Once rust is found, treat it immediately to prevent mild surface rust from developing into deep rust pits and causing irreversible damage.

For mild surface rust without pitting, gently wipe with non-woven fabric dipped in neutral rust remover paste, clean with alcohol after rust removal, dry with hot air and promptly polish and reapply rust inhibitor to restore the mold surface quickly. For moderate rust with fine pitting, soak briefly in special rust remover, brush lightly with a soft brush to remove rust, rinse with clean water and dry thoroughly, then fine polish with fine sandpaper and polishing paste, and apply double-layer rust prevention after repair to avoid recurrence. If deep rust pits affect mold precision, arrange professional grinding, welding and repair in a timely manner, and conduct a full rust prevention treatment again after repair. For rusted cooling channels, clean cyclically with special channel rust remover, inject rust-proof oil after flushing and drying to restore internal protection capacity.

5. Long-Term Management: Institutional Implementation to Ensure Rust Prevention Effect

The long-term implementation of mold rust prevention relies on standardized management systems to avoid protection failure caused by reliance on manual experience and random operations.

Establish a complete mold rust prevention ledger in the production workshop, clearly recording the rust prevention time, method, downtime and re-inspection cycle of each mold, with responsibilities assigned to specific operators to ensure traceability and controllability of each mold. Formulate rigid operating norms: specify that simple rust prevention must be done for downtime over 4 hours, and corresponding processes must be strictly implemented for short-term shutdown and long-term storage, prohibiting the omission of cleaning and drying steps to eliminate irregular operations institutionally.

Regularly train operators to popularize rust prevention knowledge, standardize operating techniques, clarify the selection criteria and usage skills of rust inhibitors in different scenarios, and improve the whole staff's rust prevention awareness and practical ability. Conduct regular inspections of the mold storage environment and rust prevention status: re-inspect short-term stored molds weekly and fully check long-term stored molds monthly, and reprocess immediately if problems such as damaged rust-proof film, cracked oil film and moisture regain are found. The closed-loop management of "cleaning - protection - inspection - remedy" comprehensively ensures mold integrity, prolongs service life, stabilizes injection production quality, reduces equipment maintenance costs and provides strong support for continuous and stable production.