How Anchor Chains are Manufactured？
The Birth of the Anchor Chain: From Steel to the Ocean's "Lifeline"
The anchor chain is a ship's "invisible lifeline"—connected to the hull at one end and tied to the anchor at the other. Like a "strongman" when anchored, it bears the entire ship's pull, and ensures the anchor can be safely retracted and deployed during sailing. So, how is the anchor chain made? Let's discuss the process today.
1. Anchor Chain Material Selection
The anchor chain's operating environment is extremely harsh: seawater corrodes it like "acid," waves hammer it like "hammers," and the weight of the anchor bears it like "mountains." Therefore, the material of the anchor chain is crucial.
1. Core Material: High-Strength Alloy Steel
The "skeleton" of the anchor chain is alloy steel, which is simply "steel plus various additives." Carbon (C) makes the steel harder; too much makes it brittle. The carbon content is typically controlled between 0.2% and 0.3%, making it both hard and tough. Next is chromium (Cr) + nickel (Ni): chromium forms a protective film that prevents seawater corrosion, while nickel makes the steel more resistant to high temperatures and acid and alkali stresses.
Molybdenum (Mo) also prevents the anchor chain from breaking suddenly under extreme tension.
Grade Classification: International standards (such as ISO 1704) classify anchor chains into grades such as U2, U3, R3, R4, and R5, with higher numbers indicating greater durability.
U2 and U3 correspond to the raw materials M490 and M690 respectively. R3 grade: tensile strength ≥860 MPa. R5 grade: used for very large oil tankers, with a tensile strength ≥1000 MPa, capable of withstanding even more extreme tension.
2. Multiple Surface Corrosion Protection
Even if the steel itself is corrosion-resistant, it will rust if immersed in seawater for a long time. Therefore, anchor chains require multiple surface corrosion protections.
Hot-dip galvanizing: The anchor chain is immersed directly in molten zinc to form a thicker protective layer. Paint + Epoxy Resin: A layer of anti-rust paint is applied over the galvanized layer, followed by epoxy resin coating to completely isolate the steel from seawater.
II. Manufacturing Process:
The anchor chain manufacturing process involves 10 steps to transform steel into anchor chain. SMEOCEAN utilizes the mainstream "flash welding" method, resulting in a stronger and longer-lasting anchor chain.
1. Feeding - 2. Cutting:
Following up on customer needs, we require information such as the classification society, specifications, and grade when procuring raw materials. We then follow up on the ring production process, cutting the raw materials, and cutting the steel rods into fixed lengths.
3. Heating - 4. Ring Bending:
The cut material is automatically fed into the heating equipment, and the red rods are then bent into the desired ring shape using the anchor chain machine. The joints are then flash welded.
5. Deburring - 6. Threading:
Newly welded anchor chains often have a lot of welding slag and irregular weld fluid on them. This is the process of deburring, which requires squeezing to clean the welds before the chain cools. If the anchor chain has stops, additional stops and compression are required. For U3 and above, the stops must be wrapped.
7. Heat Treatment - 8. Surface Treatment
Freshly welded anchor chains are brittle and require heat treatment to make them tough. Quenching: The anchor chain is heated to 850-900°C and then quickly immersed in a heat treatment solution to cool. This step hardens the steel surface.
Tempering: The chain is heated again to 500-650°C and held for a period of time to eliminate internal stresses and toughen the steel.
The heat treatment process involves alternating hot and cold cycles, which will produce a lot of iron slag on the surface of the anchor chain. To maintain a good appearance, shot blasting is required to remove impurities.
9. Tensile Testing & Classification Society Certification
Every anchor chain undergoes a "hard test" before leaving the factory to ensure it can withstand real sea conditions:
Single Link Test: A randomly selected link is subjected to tension using a hydraulic press until it breaks. Acceptance Criteria: Breaking force ≥ 1.5 times the standard value (for example, the standard tensile force for an R3 link is 450 tons; during testing, it must withstand 675 tons without breaking, equivalent to lifting 450 cars).
Full Chain Test: The entire anchor chain (usually 10-20 links) is secured to a test bench and subjected to the forces of a ship at anchor for 10 minutes, simulating the tensile forces of anchoring. The test must be carried out without deformation.
If classification society certification is required, this process can be completed simultaneously, with each test performed in strict accordance with the classification society's requirements.
10. Painting or Hot-Dip Galvanizing
After completing the above nine steps, the anchor chain is complete. The final step is to apply black paint or hot-dip galvanizing to the surface, depending on the customer's requirements. After drying, the anchor chain is ready for shipment.
III. Application Scenario: The "Division of Labor" of Anchor Chains
Different ships have different requirements for anchor chains:
Ocean-going cargo ships: Use R4-grade anchor chain, with a diameter of 60-76mm (thicker than an adult's wrist), a single section of 25-30 meters, and a total length of over 1,000 meters (enough to circle a football field three times).
Offshore platforms: Use R5-grade ultra-high-strength anchor chain, with a diameter exceeding 100mm (larger than a washbasin). Combined with giant anchors, it can withstand typhoons and currents (as stable as a "sea-stabilizing needle").
Fishing vessels: Use hot-dip galvanized U2 or U3 anchor chain, with a diameter of 20-30mm (about the thickness of a chopstick). This is low-cost and meets the needs of offshore operations.
Salmon fisheries: Norway uses black-painted U2 studless anchor chain, 32mm-42mm, while Chile requires U2 studded anchor chain, 32mm-42mm.
Conclusion
As technology advances, anchor chains are also being upgraded: future anchor chain innovations promise to be lighter, stronger, and more environmentally friendly. SMEOCEAN, with a strong focus on technological innovation, is constantly exploring new technologies to make anchor chains more reliable and environmentally friendly, safeguarding global shipping safety.