Coil Protector Mold Rusting, Complete Anti-rust Methods for Plastic Molds
Coil Protector Mold Rusting, Complete Anti-rust Methods for Plastic Molds Coil protector products are mostly molded by rubber or soft PVC. The mold cavity features tiny structures with dense grooves and narrow gaps, which are highly susceptible to rust. Once rust spots form on the mold, the defects will be copied onto the product surface and lead to appearance rejects. Continuous corrosion will scratch the parting surface and damage molded parts, and severe rust can make the whole mold scrapped. Mold rust prevention cannot rely simply on oil smearing. A full-set anti-corrosion system should cover mold manufacturing, trial molding, production shutdown and long-term storage, combining steel selection, surface treatment, daily operation and sealing specifications.
1. Mold Substrate Selection as Anti-rust Foundation
The anti-rust performance of mold steel itself is the first line of defense. The cavity structure of coil protector mold is fine with many grooves and narrow slits. Stainless mold steel with built-in anti-corrosion performance is preferred. For mass production coil protector molds with high requirements on product appearance, S136, 2083 and other corrosion-resistant mold steel are selected. These steels have high chromium content and form protective film on the surface after passivation to resist water vapor and corrosive medium precipitated from raw material decomposition. Low-cost coil protector molds for small batch production adopt ordinary pre-hardened steel. The steel itself has weak anti-rust performance, so it must rely on surface treatment and strict daily maintenance, and shorten the bare storage time. The inserts, small cores and other tiny parts adopt unified material as far as possible. The matching of different metals is easy to produce galvanic corrosion and accelerate local rust in humid environment.
2. Mold Surface Strengthening Anti-rust Treatment
Build protective film on the surface layer through surface treatment to isolate the erosion of water vapor and acidic gas, adapting to the fine groove structure of coil protector. Ion nitriding can improve surface hardness and corrosion resistance at the same time, but there are micropores in the nitrided layer, which need supporting passivation treatment to seal micropores. Hard chrome plating is suitable for parting surface and groove position of coil protector. The coating is dense, waterproof, wear-resistant and anti-corrosion. Control the coating thickness to avoid size deviation of small holes. PVD coating CrN and AlCrN thin film will not change the original size of cavity, suitable for high-precision thin-wall coil protector molds. Simple passivation can be used for ordinary steel to fill microscopic pores of steel surface and reduce the probability of oxidative corrosion.
3. Anti-rust Control During Machining and Assembly
Residual cutting fluid and cleaning water in narrow gaps during mold CNC machining, polishing and assembly are the high-incidence stage of early rust. Water-based anti-rust cutting fluid is selected in the whole machining process to avoid rust spots induced by residual ordinary water-based cutting fluid. After polishing, use anhydrous alcohol to thoroughly clean cavity and narrow slits to completely remove polishing paste residue. After assembly, blow dry all water stains in gaps with air gun, focusing on residual moisture inside the annular grooves of coil protector mold, and confirm complete drying. During assembly inspection, do not directly touch the cavity surface by hand. Sweat salt on hands will produce rust spots in a short time. Wear cotton gloves during operation.
4. Online Anti-rust During Mass Production
When coil protector raw materials are molded at high temperature, acidic small molecules will precipitate and attach to mold surface to destroy oxide film and accelerate corrosion. Control mold temperature during production and avoid standing at low temperature for a long time. Water vapor is easier to condense on the cavity surface under low temperature. Every shutdown for more than half an hour, clean the cavity surface, wipe off corrosive precipitates of raw materials with special mold cleaner. Dehumidify the production environment and control workshop humidity. Increase inspection frequency in rainy and humid seasons, focusing on annular grooves and exhaust grooves of coil protector where material residue and dirt are easy to accumulate. When slight rust spots are found, do not polish directly with coarse sandpaper. Use polishing paste to remove rust marks finely, then reapply anti-rust protection.
5. Anti-rust Operation for Short-term Shutdown
For short-term storage of shutdown for 1 to 7 days, first clean all cavity and insert gaps of material residue, and dry thoroughly. Spray thin-layer mold anti-rust agent evenly on cavity, parting surface and exhaust grooves. Avoid thick oil accumulation to prevent oil pollution transferring to coil protector products in the next mold opening. Keep slight mold locking force after mold closing to reduce the large-area exposure of cavity in air. The storage position should be away from condensed water and ground moisture, and the bottom of mold should be padded with isolation blocks instead of directly contacting the ground.
6. Complete Sealing Scheme for Long-term Storage
For long-term storage more than half a month after shutdown, more rigorous sealing steps are required. Fully disassemble and clean all inserts and small cores, wash material dirt and dry completely. Spray long-term anti-rust oil on cavity, focus on covering small holes and annular grooves, and dry the anti-rust agent naturally. Apply lubricating anti-rust grease on all moving pairs, then wrap the mold with anti-rust film, and put desiccant together into the mold packaging box. Control temperature and humidity in warehouse environment, open box regularly for sampling inspection to check moisture return and rust spots.
7. Repair Treatment of Rusted Mold
For slight floating rust on mold, use superfine polishing oil stone and diamond polishing paste to remove rust spots step by step. After polishing, clean and dry, re-passivate or spray anti-rust agent. If corrosion is deep and pits have been copied on coil protector products, evaluate the polishing allowance, carry out surface strengthening treatment after polishing. For large-area deep pit corrosion with damaged substrate, carry out welding repair before polishing, and re-surface coating if necessary. After corrosion repair, investigate the root cause of corrosion, whether it is water vapor, raw material corrosion or material problem, to avoid recurrence. The grooves and dead corners of coil protector mold are many, and many hidden corrosion risks are hidden in gaps which are not easy to observe with naked eyes. Implement anti-rust measures in the whole process and carry out regular inspection, which can reduce product defects caused by rust spots, lower mold maintenance cost and extend the service life of the whole mold.
