News

The load calculation and safety factor of the crane hook are the core technical parameters to ensure the safety of lifting operations. The following is a systematic analysis from the aspects of theoretical calculation, standard specifications, safety factor selection and practical application:

1. Calculation of hook load

1.  Basic load type

• Static load : The vertical lifting weight (rated load) borne by the hook.

• Dynamic load : Additional force caused by acceleration, impact or swing (usually calculated as 10%~30% of the static load).

• Eccentric load : lateral force caused by asymmetrical distribution of slings (needs to be corrected by angle factor).

2.  Calculation formula

• Vertical load :

  Fv=m⋅gFv​=m⋅g

  (mm is the mass of the hanging object, gg is the acceleration due to gravity)

• Multi-branch sling load (considering the influence of angle):

  Fh=Fvn⋅cos⁡θFh​=n⋅cosθFv​​

  (nn is the number of sling branches, θθ is the angle between the sling and the vertical direction)
  Example : When the angle between the two slings is 60°, the force on a single sling = Fv/(2⋅cos⁡30°)≈0.58FvFv​/(2⋅cos30°)≈0.58Fv​.

• Dynamic load factor :

  Fd=K⋅FvFd​=K⋅Fv​

  (KK is the dynamic load coefficient, usually 1.1~1.3)

3.  Special working condition correction

• Wind load : When working outdoors, it is necessary to calculate the lateral force of wind pressure on the suspended objects.

• Temperature influence : The allowable stress needs to be reduced in high temperature environment (refer to the high temperature strength curve of the material).

2. Determination of safety factor

1.  Definition of safety factor

• International standards (such as ISO, FEM):

  • General purpose hook: n≥4n≥4 (based on yield strength).

  • Frequent use or high-risk situations: n≥5n≥5.

• Chinese Standard (GB/T 10051):

  • Forged hook: n≥4n≥4; plate hook: n≥5n≥5.

2.  Influencing factors

• Material properties : High-strength alloy steel (such as 34CrMo) can reduce the coefficient appropriately, but the toughness must be guaranteed.

• Frequency of use : Frequent operations (such as port cranes) require a 10% to 20% increase in safety factor.

• Consequences of failure : When lifting molten metal or dangerous goods, nn needs to be increased additionally.

3.  Dynamic safety factor

• When considering fatigue life, it is necessary to combine the SN curve and cumulative damage theory (such as Miner's law) for verification.

3. Comparison of Standards and Specifications

4. Practical Application Cases

Case 1: Port container hook selection

• Load : Single box weight 40t, double lifting point operation (angle 45°).

• calculate :

  Fh=40×9.812×cos⁡22.5°≈213 kNh​=2×cos22.5°40×9.81​≈213kN

• Selection : Select a hook with a rated load of 50t (490kN), with a safety factor of n=490/213≈2.3 ( not met ).
  Correction : Select a higher-grade hook (e.g., 80t, with n=784/213≈3.7) or reduce the sling angle.

Case 2: Metallurgical casting hook

• Working conditions : lifting molten steel ladle (high temperature + impact).

• Safety factor : According to the requirements of GB 6067.1, n≥6n≥6, and heat-resistant alloy steel (such as 25Cr2MoV) is used.

5. Frontier Research Directions

1. Fatigue life prediction

   • The crack propagation path under alternating stress was simulated based on finite element analysis (FEA).

2. Intelligent monitoring technology

   • Implanted sensors monitor the strain and temperature of the hook in real time, and combine with AI to predict the remaining lifespan.

3. New Materials Application

   • Nanocrystalline alloys and composite materials improve the strength/weight ratio (for example, titanium alloy hooks reduce weight by 30%).

6. Safety Recommendations

1. Design phase :

   • Nonlinear finite element analysis is used to verify the stress distribution under ultimate load.

2. Use phase :

   • Carry out magnetic particle testing (MT) or ultrasonic testing (UT) regularly and replace the parts immediately if any micro cracks are found.

3. Management measures :

   • Establish a full life cycle archive for the hook to record the load history and inspection results.

Summarize

The load calculation of the hook needs to integrate statics, dynamics and environmental factors, and the selection of the safety factor needs to strictly follow the standards and be combined with the actual working conditions. The development of intelligent and high-strength materials in the future will further improve the safety and economy of the hook. It is recommended that enterprises formulate internal safety specifications that are higher than industry standards based on the characteristics of their own equipment.