Mold Rust Cause Analysis and Rust Prevention Maintenance Specification

Mold rust comes from multiple factors including ambient condition, material property, processing residue and operation habit. Corrosion will damage the texture of cavity surface, raise the rate of flash and product drag mark, and shorten the service life of molds. Normalized rust prevention maintenance rules help slow down corrosion and stabilize molding performance.

1. Analysis of Common Rust Causes for Molds

Contact with water vapor is the most common cause of rust. High humidity in workshop, cooling water leakage and condensed water left inside molds after shutdown make water attach to steel surface and form oxidation layer together with oxygen in air. Condensation happens easily in plum rain season or when temperature varies greatly between day and night. Guide posts, ejector pins and parting surfaces have higher corrosion risk. Precipitate and residual stains from plastic also accelerate corrosion. Some plastics release acidic volatile substances at high molding temperature. These corrosive media accumulate in vents and insert gaps and erode mold surface gradually. Uncleaned residual melt and carbon deposit after production lock moisture in narrow gaps and form a continuous micro-corrosion environment. 

Contaminants brought in during machining and production trigger electrochemical corrosion. Carbon steel dust and iron scraps fall on the mold surface and form galvanic corrosion. Sweat from hands, chlorine elements in cutting fluid or cleaning agent will lead to pitting rust spots. The rust resistance depends on mold steel grade and surface treatment. Ordinary pre-hardened steel and carbon steel have weak anti-corrosion performance. Polishing defects, texture gaps and dents are the priority positions for rust generation. Once nitriding or coating layers are partially damaged, the substrate steel will be exposed and corrosion spreads quickly. Poor storage management is another important factor. Molds stored in open state without dust cover accumulate floating dust. Rust spreads from the bottom and fitting surfaces when molds are stacked in damp areas with poor ventilation.

2. Daily Rust Prevention Maintenance Specification

During production, the state of cooling water joints and sealing rings is checked regularly. Replace damaged seals immediately once leakage is found. Keep molds slightly open during production breaks to reduce condensation inside cavity. Vents and runner areas are purged periodically to clear carbon deposit and volatile residue. Low-corrosion release agents are selected and strong acid chemicals are prohibited from spraying directly on molding surfaces. For short-term shutdown preservation, wipe cavity, parting surface, ejection system and guide posts with lint-free cloth and approved cleaning agent to remove plastic residue, oil and dust. Spray dedicated mold rust inhibitor evenly on molding surfaces and moving parts after full drying. Cover the mold with fiber-free dust cover after closing. For long-term storage, dehumidification is carried out in storage area. Keep ventilation space between molds instead of sticking to walls or ground. Complete deep cleaning before storage, blow debris out of gaps, and apply long-acting anti-rust oil or wax on textured surfaces, inserts and ejector pins. Record sealing time and set regular inspection cycle. Re-clean and reapply protective coating if film damage or moisture sign is found.

3. Handling Requirements for Early Rust Spots

For slight rust traces, remove rust gently with dedicated rust paste and superfine oil stone along polishing direction. Control grinding force to avoid damaging original texture and dimension. Wipe off rust remover thoroughly, dry completely and reapply protective coating. For large rust areas that penetrate into substrate, arrange professional repair, repolish or re-etch texture after grinding, and increase inspection frequency after repair.

4. Supporting Management Requirements

Set up mold maintenance log to record production time, cleaning operation, rust prevention work and rust inspection result. Operators distinguish anti-rust materials for online production, short-term halt and long-term storage. Monitor workshop humidity and enhance ventilation and dehumidification in high humidity period.