Laminated Type Lifting Hook Redundancy Safety Design & Inspection
GB/T 10051.4-2010, "Lifting Hooks — Part 4: Laminated Hooks," is the dedicated standard for laminated hooks used on cranes. A laminated hook is built from multiple steel plates joined by riveting or bolted connections. If one plate fails, the remaining plates continue to carry the load, making this design particularly well-suited for high-temperature radiant environments such as steel mills and foundries.
GB/T 10051.4-2010 is Part 4 of the lifting hook standard series, specifically governing the redundant safety design and inspection methods for laminated hooks. These hooks are formed by stacking multiple steel plates, providing multi-layer safety redundancy. This article provides a detailed breakdown of the standard's core technical requirements.
Standard Positioning and Key Features of Laminated Hooks
GB/T 10051.4-2010 is the fourth part of the GB/T 10051 series, defining the technical requirements for laminated hooks. Unlike forged hooks (covered in Part 3), laminated hooks are assembled from multiple steel plates (typically 5 to 15) joined by rivets or bolts. The primary advantages of laminated hooks include:
- High safety redundancy — A fracture in a single plate does not compromise the overall load-bearing capacity, as the remaining plates continue to support the load.
- Ease of inspection — Plate fractures can be detected by monitoring changes in the gaps between individual laminations.
- High-temperature and radiant-heat resistance — The gaps between plates promote heat dissipation, making these hooks suitable for steelmaking and foundry applications.
The main drawback is higher dead weight — laminated hooks typically weigh 30% to 50% more than forged hooks of the same rated lifting capacity — and they are not recommended for applications requiring frequent high-speed hoisting due to higher inertia.
Structural Types and Material Requirements
The standard specifies the basic structure of laminated hooks:
- Hook body — Formed by stacking multiple steel plates with trapezoidal or T-shaped cross-sections, each plate 4 to 16 mm thick depending on the rated lifting capacity. The laminations create a smooth hook profile along the inner and outer surfaces of the curved section. Plates are secured with rivets (diameter ≥ 16 mm) or high-strength bolts (Grade 8.8 and above), with a bolt spacing not exceeding six times the plate thickness.
- Hook neck — The laminated plates converge into a single- or double-plate configuration at the neck, secured to the hook beam via a hook nut.
- Hook latch — A spring-loaded latch or tongue-type anti-drop device must be fitted at the hook tip.
- Material — Laminated plates are made of Q355B or Q420B steel (offering good cold-bending and welding performance). Plate surfaces must be free of cracks, lamination defects, and significant corrosion. The rolling direction of the steel plates must align with the load direction (along the hook length); plates must not be used with the rolling direction perpendicular to the load path.
Wider range than forged hooks
Each 4–16 mm thick
or Grade 8.8 high-strength bolts
affect remaining plates' load capacity
High-temperature radiant heat
forged hooks of equal capacity
Manufacturing Process and Requirements
The standard sets out the following manufacturing requirements for laminated hooks:
- Plate cutting — Steel plates are cut to the hook profile with smooth, burr-free edges. Cut edges must be chamfered (chamfer ≥ 1 mm).
- Bending and forming — Plates are progressively formed on a bending machine. The bending radius must not be less than eight times the plate thickness for cold bending, or five times for hot bending. Hot bending is performed at 900–1050°C, with the final bending temperature not below 700°C.
- Verification of formed plates — Each plate is checked against a template after forming; the gap between the template and the plate must not exceed 1 mm.
- Assembly — Plates are aligned and drilled together to ensure hole alignment across all laminations. Rivets or bolts are inserted and tightened evenly. For riveted joints, rivets are heated to 800–1000°C before riveting, and the finished rivet heads must be complete and free of cracks.
Testing and Inspection
The standard requires the following testing and inspection for laminated hooks:
- Raw material inspection — Chemical composition and mechanical properties (tensile, bending, impact) are verified for each batch of steel plates.
- Static load test — Every finished hook undergoes a static load test at 2× the rated lifting capacity for general-purpose hooks, or 2.5× for hazardous goods lifting, with the load held for at least 5 minutes. The hook opening is measured before and after the test; residual deformation of the opening must not exceed 0.5% of the original opening size. (This is more lenient than the 0.25% limit for forged hooks, reflecting the greater elastic adjustment capacity of the laminated structure.)
- Lamination gap inspection — After the static load test, gaps between individual laminations are checked; the maximum allowable gap is 0.5 mm.
- Non-destructive testing — Each steel plate is individually subjected to magnetic particle inspection (MPI) before assembly to detect surface cracks and lamination defects. After assembly, MPI spot checks are performed on rivet heads, bolt heads, and the hook neck, with a sampling rate of at least 20%.
- Hardness test — Brinell hardness (HB) is measured at one point on the inner surface and one point on the outer surface of the hook body. Hardness must be within 140–220 HB for Q355B steel, or 170–270 HB for Q420B steel.
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| Comparison Item | Forged Hook(GB/T 10051.3) | Laminated Hook(GB/T 10051.4) |
|---|---|---|
| Material | DG20/DG34CrMoSolid Steel Forging | Q355B (≈S355JR)/Q420BSteel Plate Lamination |
| manufacturing Method | die forging+Heat treatment | Cutting Bending Drilling Riveting |
| Safety Mechanism | Integral Strength | Single Lamella Failure Remainingspare / standby(redundancy) |
| Dead Weight | Lighter | Heavy30%~50% |
| Operating Temperature | ≤300°C | ≤500°C(Good Heat Dissipation) |
| Opening Residual deformation | ≤0.25% | ≤0.5% |
| inspection methods | MT/UTFlaw detection | visual inspection Lamella Gap+MT |
Inspection & Scrapping
A: Laminated hooks require a unique inspection routine during service, as the laminated structure allows internal conditions to be assessed by monitoring changes in the gaps between plates. Daily inspection involves a visual check for foreign objects lodged between the plates and verifying that the anti-drop device is intact. Weekly inspection includes checking rivets and bolts for looseness (tap lightly with a hand hammer and listen for a hollow sound indicating a loose bolt) and measuring and recording the hook opening size. Monthly inspection focuses on the gaps between the laminated steel plates: under normal conditions, the plates should fit tightly together (gap ≤ 0.5 mm). If a plate fractures, a noticeable gap increase will appear between the fractured plate and its adjacent plate (a 0.5 mm feeler gauge can be inserted). If a plate fracture is detected, the hook must be taken out of service immediately. Replace all fractured plates, re-rivet or re-tighten the bolts, and then perform a static load test before returning the hook to service. If the cumulative number of replaced plates exceeds one-third of the total plate count, the entire hook must be scrapped. Kelude Heavy Industry offers both forged hooks and laminated hooks, recommending the most suitable type based on the user's operating conditions.
Laminated Lifting Hook Redundancy Design Comparison
The comparison table below outlines the core parameter configurations for the redundant safety design of laminated lifting hooks, serving as a reference for selection and inspection personnel.
| Hook Grade | Lamella Thickness(mm) | Number of Lamellae | Safety factor | inspection method |
|---|---|---|---|---|
| Light Duty | 6~10 | ≥5 | ≥5 | Magnetic Particle/Ultrasonic Flaw detection |
| Medium Duty | 10~16 | ≥6 | ≥6 | Magnetic Particle/Ultrasonic Flaw detection |
| Heavy Duty | 16~25 | ≥8 | ≥7 | 100%UT+MT |
| Super Heavy Duty | ≥25 | ≥10 | ≥8 | 100%UT+MT+Load |
