GB/T 10051.5-2010 Laminated Hook Standard Guide
GB/T 10051.5-2010, "Lifting Hooks — Part 5: Laminated Hooks," is the product standard for laminated hooks. It specifies the classification, technical requirements, test methods, and inspection rules for laminated hooks (also known as plate hooks or lamellar hooks), and is applicable to laminated hooks used in ladle cranes, metallurgical cranes, and other large-tonnage or critical-duty applications.
Structural Design and Material Requirements
A laminated hook is built from multiple Q345B steel plates stacked together, offering a key advantage in fracture safety—if one plate fails, the overall strength of the hook is not compromised, a significant improvement over the sudden fracture mode of forged hooks. Each plate is 6–12 mm thick, with the number of plates determined by the required lifting capacity. A 0.3–0.5 mm gap is maintained between adjacent plates to ensure each plate carries its load independently. The plates are cut to shape using laser or plasma cutting, producing smooth, burr-free edges.
The primary advantage of a laminated hook lies in its fail-safe design: a fracture in one plate does not cause complete hook failure. Operators can spot a cracked plate during routine visual inspection and replace it before it becomes a problem. This progressive failure mode makes laminated hooks the preferred choice for critical, high-capacity applications such as foundries and steel mills. The 0.3–0.5 mm gap between plates ensures independent load sharing and also makes it easier to inspect for cracks in individual plates.
After the Q345B plates are laser- or plasma-cut to profile, the edges are ground smooth to remove burrs and any heat-affected zone. Each plate is stamped with its heat number and batch number for full traceability. During assembly, the plates are stacked in sequence and the bolted connections are tightened to the specified tightening torque. Laminated hooks typically have a rated lifting capacity of 100 t or more, with some designs reaching up to 500 t.
Safety Factor and Discard Criteria
The safety factor (relative to the material's yield strength) is ≥4. Under fatigue loading, the plates of a laminated hook fracture one by one, and the significant deformation that occurs before failure provides ample warning. Discard criteria: the entire hook must be scrapped if any single plate develops a crack; the hook must also be scrapped if the throat opening increases by more than 15% of its original dimension, or if deformation compromises safe operation.
Multiple Q345B plates
Based on yield strength
With visible warning
Large tonnage
Deformation
Flaw detection every 6 months
| Parameter | Forged Hook | Laminated Hook |
|---|---|---|
| Material | 20Steel/DG20Mn | Q345B (≈S355J2)Steel Plate |
| Fracture Mode | One-time Fracture | Piece-by-piece Fracture Pre-indicative |
| Safety factor | ≥4 | ≥4 |
| applicable tonnage | ≤100t | ≥100t |
| Inspection | Magnetic Particle Inspection (MPI) | Ultrasonic Testing (UT) |
The required safety factor of ≥4 specified in the standard is based on the material's yield strength. Q345B steel plate has a yield strength of ≥345 MPa, which corresponds to a working stress of ≤86 MPa at a safety factor of 4. The laminated hook plates primarily endure bending stress, with the maximum tensile stress zone located on the inner side of the hook's curved section. During service, the wear and deformation on the inner side of the hook curve should be inspected periodically.
Testing and Inspection
Each batch of laminated hooks must undergo a static test with 1.5 times the rated load (held for 10 minutes) and non-destructive testing (Magnetic Particle Inspection or Ultrasonic Testing). In-service hooks require non-destructive testing every six months, and any crack detected mandates immediate scrapping. The standard also requires that the heat number and batch number be stamped on each hook steel plate.
| inspection items | technical requirements | Period | Method |
|---|---|---|---|
| Static load test | 1.5Times×10min | type test | Visual+Measuring tool |
| Non-destructive testing | None Crack | Semi-annual | Magnetic particle/Ultrasonic |
| throat opening | ≤Original15% | Monthly | Caliper measurement |
| Hook lamella inspection | None Deformation | Monthly | Visual |
Kelude supplies lifting hooks in all specifications as part of its supporting services.
Lifting Hook FAQ
Q: What is the difference between a laminated hook and a forged hook?
A: A laminated hook is built from multiple Q345B (≈S355J2) steel plates stacked together. If one plate fractures, the remaining plates maintain the hook's overall integrity, and failure is preceded by visible warning signs. A forged hook, by contrast, carries a higher risk of sudden, complete fracture. Laminated hooks are the preferred choice for large-tonnage applications (≥100 t) and critical operating conditions such as metallurgy and foundry work.
Q: What safety factor does a laminated hook provide?
A: The safety factor relative to material yield strength is ≥4. The hook plates are made of Q345B steel plate with a minimum yield strength of 345 MPa. Each plate is individually load-tested to verify its independent load-bearing capacity.
Q: What are the discard criteria for laminated hooks?
A: The entire hook must be scrapped immediately if any single plate develops a crack. A throat opening that has increased by more than 15% of its original dimension also requires scrapping. Any deformation that impairs normal operation is grounds for discard. If plate wear exceeds 20% of the original thickness, the affected plate must be replaced.
Q: What inspection requirements apply to laminated hooks?
A: Each production batch must pass a static load test at 1.5 times the rated load, held for 10 minutes. In-service hooks require non-destructive testing (magnetic particle or ultrasonic) every six months. Each steel plate must be stamped with its heat number and batch number for traceability.
