mould steel corrosion reasons and solutions

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Rusting of plastic molds is a normal phenomenon and  caused by special reasons.It is not always due to quality problems of steel products.


  • Melt Decomposition




mould steel corrosionSome plastic raw materials will release volatile gases after being heated, which are corrosive and corrode the mold steel.

Therefore, when the injection machine stops , wipe the mold clean with soft rag and close the mold.

If the mold downtime is for a long time, anti-rust  spray shall be used in the mold cavity.

Butter shall be used to plug the gate when the mold is closed.


  • Cooling Water




Cooling water is mostly used in the mold for cooling, so there is more moisture around and inside plastic mold.

If the mold is cooled below the dew point, moisture in the air will become water droplets on the surface of the mold, which will easily rust if it is not wiped off in time.

Even after the mold stops working for a short time, condensed water will be seen soon.

Therefore, when the molding is stopped, the cooling water should also be cut off and blow mold dry. 


  • Carbide Residue




Carbide residue is produced after the mold works for a long time, carbide is precipitated and decomposed in the molding material, which often causes the mold to corrode or rust.

If carbide residue is found, it should be removed immediately. The gas or residue produced by plastic materials decomposition is the most common corrosion source to plastic molds.

In order to prevent the mold from rusting, the most widely used method is to chrome-plate the mold cavity, but chrome-plating cannot fully solve the problem, because the decomposed gas also corrode the deep hole.

These are the places that cannot be plated.


  • How to solve?




Short-term: Wipe the surface of the mold cavity lightly with a rag. Fully dry the plastic material and reduce the temperature of the barrel to prevent the resin from decomposing.

Long-term: change to a new material that does not corrode the mold for decomposition. 

due to differences in plastic materials , such as PVC, POM, EVA, PC, foaming materials, etc. Some resin may decompose to release corrosive gas inside the mold, the plastic mold should be chrome plated. 

During the plastic mold short downtime, the mold cavity need to be  sprayed with anti-rust agent, and then the mold is closed. When the mold downtime is long , coat the outside of the mold and the movable parts with butter.

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