I. The Two Natural Enemies: Salt Fog and Vibration
Before packing, understand the enemy:
Salt Spray Corrosion: Marine atmospheres contain high concentrationsof chloride ions (NaCl) that easily penetrate ordinary plastic bags, causing red rust or white oxidation spots on metal surfaces.
Mechanical Damage: The tossingof containers, impacts during loading/unloading, and stacking pressure can cause permanent dents, scratches, or chipping on precision CNC surfaces or bearing seats.
Conclusion: Ordinary cardboard boxes and bubble wrap are insufficient. You need a dual defenseof “Vapor Phase Rust Prevention” + “Rigid Physical Support.”
II. Defense Line 1: Anti-Corrosion Treatment (Chemical Barrier)
This is the core defense against “Rust.”
1. For Metal Parts (Steel, Iron, Copper Alloys)
First Choice: VCI Packaging (Volatile Corrosion Inhibitor)
Principle: VCI paper or VCI bags release corrosion-inhibiting gases that form a monomolecular protective layer on metal surfaces.
Procedure:
Clean the part surface (freeof cutting oil or sweat stains).
Wrap each part individually with VCI paper, or place it inside a VCI poly bag.
Critical Step: Heat-seal the VCI bagto prevent gas leakage.
Advantage: No cleaning needed after unpacking; no oil contaminationon precision mating surfaces.
Second Choice: Rust Preventive Oil/Grease (For non-precision surfaces)
For large structural parts or non-mating surfaces, spray neutral rust preventive oil. Note: This requires cleaning upon arrival, adding a process step.
2. For Aluminum & Aluminum Alloy Parts
Oxide Film Protection: Ensure parts have undergone Anodizing (Type II/III) or Chromate Conversion Coating.
Moisture Barrier: Use standard Anti-Static Bags combined with desiccant packs. While aluminum doesn’t “rust,” it suffersfrom pitting corrosion.
3. Taboos
No bare-hand contact: Sweat contains salts—always wear Nitrile gloves.
No acidic materials: Avoid untreated wood (acidic) or newspaper (ink) inside packaging.
III. Defense Line 2: Cushioning & Support (Physical Barrier)
This is the defense against “Impact.”
1. Inner Packaging: Individual Isolation & Cushioning
Reject “Bulk Packing”: Never throw multiple parts into one bag or box.
Individual Positioning:
EPE Foam (Cross-linked Polyethylene): CNC milled or die-cut into the exact shape of the part. This is the industrial standard.
Air Bubble Wrap: Wrap 2-3 layers, focusing on edges and machined faces. Note: Bubble wrap is prone to punctures and should not be the sole support.
Corrugated Cardboard: Use as spacers between parts and the carton wall.
2. Outer Packaging: Rigid Cases & Reinforcement
First Choice: Plywood Cases (ISPM 15)
Superior to corrugated boxes. Wood offers high strength against forklift punctures and stack crushing.
Mandatory: Export wood must be fumigated and bear the ISPM 15 stamp; otherwise, customs will hold the cargo.
Second Choice: 5-Ply or 7-Ply Corrugated Boxes
Only for small, lightweight parts. The interior must include Edge Protectors (Corner Boards) and Top/Bottom Liners.
Strictly Prohibit: Using woven sacks, cloth bags, or other soft packaging.
IV. Defense Line 3: “Secondary Lockdown” Inside the Container
Once loaded, the real test begins.
1. Container Inspection
Dry Container: Confirm door gaskets are intact and the floor is freeof standing water or odors.
2. Cargo Securement (Lashing & Dunnage)
Fill Voids: There must be zero sway space between cargo and container walls. Use Inflatable Dunnage Bags or Foam Blocksto lock it tight.
Bottom Bracing: Lay Dunnage Wood (Sleeper Bars) between the container floor and the plywood case. This creates a ventilation gap to prevent bottom soaking.
Lashing: Use Ratchet Straps connectedto the container side rings, tensioned diagonally.
3. Desiccant (Moisture Absorber)
Container Desiccant Strips: Hang along the top inner walls to absorb “container sweat” (condensation).
Inner Pack Desiccant: Place sufficient Calcium Chloride Desiccant Packs (10x more effective than Silica Gel) inside
the wooden case or carton.
| Part Type | Core Risk | Recommended Packing Solution |
| CNC Precision Parts | Dents on mating surfaces, Rust | VCI Bag + EPE CNC-foamed Tray + Plywood Case |
| Sheet Metal Parts | Surface scratches, Deformation | PE Protective Film on surface + Corner protectors + Corrugated Box |
| Casting Parts | Brittle corner breakage, Rust | Bubble wrap on edges + Rust oil coating + Simple wooden crate/pallet |
| Parts with Bearings/Gears | Grease loss, Tooth face damage | Individual wrapping of teeth + Internal foam filling + Rigid case |
VI. Pre-Shipment Checklist
Before sealing the container door, verify:
[1] Cleanliness: Part surface freeof cutting fluid residue and fingerprints.
[2] Protection: Rust oil applied or VCI bag sealed.
[3] Isolation: Parts separated by EPE/bubble wrap, no direct contact.
[4] Void Fill: No rocking inside the box/case; all gaps filled.
[5] Case Closing: Box sealed with tape/nails, fumigation mark visible.
[6] Securement: Inflatable bags pressurized, straps tensioned.
VII. Conclusion
Sea freight packing is not “The thicker, the better,” but a scientific protection system.
If you are shipping high-value, high-precision parts and worry your current packaging cannot withstand ocean transport, contact us immediately.
Our engineering team provides a “Turnkey Packing Solution” including VCI treatment, EPE custom trays, and ISPM 15 plywood cases to ensure perfect delivery.