1.Why is rust-proof packaging necessary?
Characteristics of cold-rolled coils: Cold-rolled coils have a high surface smoothness, free of oxide scale and coatings (unlike galvanized and color-coated coils), exposing the fresh metal substrate, making them chemically reactive and highly susceptible to corrosion.
Harshness of the maritime environment:
High humidity and high salt spray: Marine air contains a large amount of salt, which adheres to the steel surface, greatly accelerating electrochemical corrosion.
Large diurnal temperature range: This can cause condensation on the cargo surface, essentially covering the steel with a film of water.
Risk of seawater corrosion: Although not in direct contact with seawater, cargo on deck may be exposed to seawater droplets or other unexpected conditions.
Long transportation time: Sea transport typically takes weeks or even months, providing ample time for corrosion.
2.What are some basic rust-proof packaging methods?
Applying anti-rust oil: A thin, even layer of anti-rust oil is sprayed onto the surface of the cold-rolled coil, forming an oil film to isolate it from air and moisture. This is the most common, low-cost, and effective method.
Inner packaging for rust prevention: VCI (vapor phase corrosion inhibitor) paper or anti-rust film is used to wrap the inner and outer rings of each coil of steel. This material slowly releases anti-rust gases, forming a protective layer on the steel surface.
3.What are the standard rust-proof packaging features?
Steps: Apply rust-preventive oil + wrap with VCI rust-preventive paper + cover with a waterproof plastic film (such as PE film).
Function: The waterproof film effectively prevents condensation from directly contacting the steel and protects against external moisture and seawater droplets. This is the most cost-effective solution.
4.What are some advanced rust-proof packaging methods?
Steps: Apply rust-preventive oil + wrap with VCI rust-preventive paper + waterproof plastic film + externally cover and secure with high-strength waterproof woven fabric or sheet metal/fiberboard protective cover.
Function: Provides physical protection, preventing the film from being torn during loading, unloading, and storage, and provides double waterproof protection.
5.What are some other key points to note?
Packaging Material Compatibility: Ensure that the rust-preventive oil and VCI paper used are compatible with the cold-rolled coil material and will not adversely affect subsequent processing (such as cleaning and electroplating).
Lifting and Securing: Packaging design should consider lifting and securing points to prevent damage during transportation.
Clear Labeling: Clearly label the packaging with "Keep Dry," "Do Not Rain," "This Side Up," etc., and possibly indicate the rust prevention method used, so that the recipient understands.
Contract and Liability: The standards and requirements for rust-preventive packaging must be clearly stipulated in the sales contract and letter of credit. This clarifies responsibilities and avoids difficulties in determining whether a claim due to rust is due to a production or transportation issue.