1. What are the overall selection principles for sealed packaging of galvanized coils? How can protection requirements be quickly matched?
There is no single answer to the selection of sealed packaging for galvanized coils. It requires dynamic matching based on three main variables: transportation method (sea or land), storage period (short-term or long-term), and the surface condition of the steel coil (whether the galvanized layer is intact).
For sea freight or long-term storage (rust prevention period exceeding six months): It is strongly recommended to use VCI vapor phase corrosion inhibitor film as the inner sealing layer, reinforced with steel straps. Its advantage lies in providing an ultra-long rust prevention period of 12 to 24 months and continuously releasing rust-preventing gases, forming a protective film on all metal surfaces in a sealed environment.
For inland short-distance transportation or short-term storage (rust prevention period of 1-3 months): PE stretch film can be used as the main sealing layer, combined with corner protectors and wooden pads. This solution is lower in cost and meets basic protection requirements in dry environments.
For galvanized coils: For galvanized products, it is essential to use neutral rust-preventive paper or vapor phase rust-preventive paper specifically designed for galvanized sheets to effectively prevent adverse reactions in the zinc layer.
2.How to Choose the Right Rust-Preventing Paper for Galvanized Coil? What are the Key Considerations?
Rust-preventing paper is the core material that directly contacts the inner layer of the galvanized coil. Choosing the wrong type will not only fail to prevent rust but may even accelerate corrosion.
The material must be neutral: This is the most crucial principle. The galvanized layer is sensitive to acidic environments, so ordinary rust-preventing paper containing acidic substances must never be used. Neutral kraft paper or VCI vapor phase rust-preventing paper must be selected to avoid chemical reactions with the zinc layer. Furthermore, rust-preventing paper specifically designed for galvanized steel sheets should be used, not those specifically for cold-rolled steel sheets or silicon steel sheets. Strictly speaking, these types cannot be mixed.
3.What key points should be considered when selecting packaging for harsh environments such as sea freight and container shipping?
The high humidity, large temperature differences, and high salt spray environment inside sea freight and containers pose a high risk of oxidation and rust on galvanized coils. Packaging selection must adopt a more rigorous combination strategy.
Preferably, VCI (Vacuum Phase Inhibitor) technology is preferred: In a sealed container, VCI film or rust-preventive paper is the core weapon. It continuously releases rust-preventive gases, which automatically adsorb onto all metal surfaces in the confined space, including hard-to-reach areas such as the coil core and edges, forming a nano-level protective layer for comprehensive protection. This allows for oil-free packaging, avoiding the tedious degreasing and cleaning work afterwards, saving time and keeping costs under control.
Use multi-layered packaging: A single film is often insufficient. A proper export packaging structure typically consists of: an inner layer of VCI film/rust-preventive paper, an outer layer of robust waterproof packaging such as woven fabric or sheet metal, and finally, reinforcement with steel straps. At the same time, a sufficient amount of silica gel desiccant should be placed in the sealed packaging with gaps to actively absorb residual moisture.
4. What are the key points in the execution of sealed packaging? How can physical support and sealing requirements be ensured?
After the packaging selection is determined, the execution is the final step that determines the success or failure of the protection. The ultimate goal of sealed packaging is to create a "microenvironment" that isolates the external environment, which requires the coordination of physical support and sealing technology.
Physical support is fundamental: When using outer packaging panels, choose steel panels with a thickness of 0.4–0.6 mm or plastic panels with a thickness of 1.2–1.4 mm, and lay them on the packaging frame (composed of two wooden blocks with a spacing matching the width of the steel coil). When laying the PVC plastic film layer, ensure that the material is intact, flat, and free of damage and wrinkles; the recommended overlap is between 100 and 300 mm.
Establish a strict inner and outer sealing system: After completing the physical support, begin laying the rust-proof paper layer. The coated side of the rust-preventive paper should be placed upwards, tightly overlapping the core paper roll. The width of the core paper should be approximately 0-60 mm less than the width of the steel roll, and it must be completely sealed with tape. Then, wrap the rust-preventive paper upwards along the circumference of the steel roll, ensuring an overlap of 50 mm with the core paper and at least 100 mm of its own overlap. All seams and end creases must be securely sealed with adhesive tape to ensure a completely airtight seal. The tape applied to all overlapping areas should be sufficiently wide and firmly adhered.
5. What are the specific requirements and standards for export sea freight packaging?
For exported galvanized coils, sealed packaging must not only be rust-proof but also comply with international trade regulations.
**Definition of Packaging Grade:** Based on transportation distance and environmental differences, the commonly used packaging grade for exports is premium packaging (or high-quality packaging). This type of packaging has a reinforced inner sealing layer and is typically suitable for products shipped by sea to high-temperature and high-humidity areas in the south, as well as high-profit products for key users.
**Standard Compliance:** Sealed packaging operations should follow current national rust-proof packaging standards (such as GB/T 4879-2016) to ensure that material indicators (such as moisture permeability) meet technical requirements.
**Detailed Labeling Information:** The final packaging surface should clearly and firmly label the product name, specifications, coating weight, batch number, net weight and gross weight, manufacturer's name, production date, destination, and necessary "waterproof and moisture-proof" and storage and transportation symbols.