How To Deal With Corrosion Inside The Rotational Mold
1. Analysis of corrosion causes
Material factors: mold steel (such as P20, H13) or aluminum alloy oxidized at high temperature, or corroded by acidic/alkaline mold release agents.
Process factors: cooling water residue, accumulation of mold release agent decomposition products (such as chlorine and sulfur elements).
Environmental factors: humid storage or production environment leads to electrochemical corrosion (such as aluminum alloy molds).
2. Emergency treatment measures
(1) Mild corrosion (surface rust or oxidation)
Mechanical grinding: Use fine sandpaper (400# or above) or soft polishing wheel to remove rust to avoid damaging the mold surface accuracy.
Chemical cleaning: Use neutral rust remover (such as citric acid solution) to soak and rinse. Strong acids and alkalis are strictly prohibited.
Passivation treatment: Stainless steel molds can be passivated with nitric acid to form a protective film.
(2) Severe corrosion (deep pits or holes)
Laser cladding/surfacing: Local corrosion areas can be repaired by laser and the surface can be reprocessed.
Insert replacement: Severely corroded areas can be disassembled and replaced with pre-processed inserts.
3. Long-term protection plan
(1) Surface coating protection
Hard chrome plating: Improves hardness and corrosion resistance, suitable for steel molds (but may cause microcracks to penetrate corrosive media).
Nickel-based coating (such as chemical nickel-plated PTFE composite layer): Has both corrosion resistance and mold release properties.
Ceramic coating (such as Al₂O₃, CrN): Resistant to high-temperature corrosion, but relatively expensive.
(2) Material upgrade
Stainless steel molds: Use 316L or 17-4PH stainless steel, which has significantly better corrosion resistance than ordinary mold steel.
Aluminum alloy anodizing: Hard anodize the aluminum mold (thickness 20-30μm) to enhance surface hardness and corrosion resistance.
(3) Process optimization
Control cooling water quality: Use deionized water or add corrosion inhibitors to avoid chloride ion corrosion.
Selection of release agent: Avoid release agents containing sulfur and chlorine, and use neutral silicone or water-based formula instead.
Dry storage: After production, clean the mold thoroughly, spray anti-rust oil (such as WD-40), and store it in a dry environment.
4. Maintenance and monitoring
Regular inspection: Check the mold cavity after every 50-100 productions, especially the corners and cooling water channel interfaces.
Corrosion monitoring: Use an ultrasonic thickness gauge to detect changes in mold wall thickness and detect potential corrosion in advance.
5. Economic considerations
For low-cost products, you can weigh the repair cost and the remaining life of the mold to decide whether to replace the new mold.
For high-value-added products, it is recommended to invest in anti-corrosion coatings or upgrade materials to reduce downtime losses.
Summary
The treatment of rotational mold corrosion requires a combination of a "repair + protection" strategy: mild corrosion can be restored by cleaning and coating, severe corrosion requires local repair or replacement of parts; long-term protection depends on material upgrades (such as stainless steel), surface treatment (plating/anodizing) and process optimization (release agent, cooling water management). Regular maintenance is the key to extending the life of your mold.