How To Calculate The Load Of Steel Mill Crane?

How To Calculate The Load Of Steel Mill Crane?

 

1. Basic principles of calculation
 

In order to ensure the safe and normal operation of the crane, its metal structure and parts of the mechanism should meet the requirements of strength, stability and rigidity.
 

Strength and stability requirements mean that the internal force generated by structural members under load should not exceed the allowable bearing capacity (referring to the allowable bearing capacity in terms of strength, fatigue strength and stability); stiffness requirements mean that the structure under load The resulting deformation should not exceed the allowable deformation value, and the natural vibration period of the structure should not exceed the allowable vibration period.
 

The parts and metal structures of the crane should be calculated as follows: ① Calculation of fatigue, wear or heat; ② Strength calculation; ③ Strength check.
 

Compatible with these three types of calculations, the calculated load of the crane has the following three combinations:
 

 

(1) Calculation load for life (durability)—Type I load.
 

This load is used to calculate the durability, wear or heating of the component or metal structure. The calculation is carried out according to the equivalent load during normal operation, not only the size of the load is calculated, but also their action time is considered.
 

For mechanical parts and metal structures subjected to variable loads, fatigue calculations should be performed when the number of stress change cycles is large enough; when the number of stress change cycles is small or very few, fatigue calculations are unnecessary.
 

The metal structural components and mechanism parts of the cranes whose working level is A6, A7, and A8 should be checked for fatigue.
 

(2) Strength calculation load--type II load.
 

This type of load is used to calculate the strength of parts or metal structures, the stability of compression and plane bending members, the stiffness of structural parts, the overall stability and wheel pressure of the crane, and the strength is calculated according to the maximum load in the working state.
 

When determining the strength calculation load, the most unfavorable load combination that may occur should be selected.
 

(3) Checking load--type III load.
 

This type of load is used to check the strength and stability of components of certain devices (such as rail clamps) of the crane, luffing mechanism, certain parts and metal structures supporting the rotating device, and the overall stability of the crane. The maximum load in the non-working state and special loads (installation load, transportation load and impact load, etc.) are checked for strength.
 

When dealing with crane accidents in steel mills, necessary checks should be made for accidents caused by damage to metal structures and parts of mechanisms. When checking and calculating, carry out according to the actual load of the actual working condition.
 

 

2. Calculation method
 

At present, the calculation of steel plant cranes adopts the allowable stress method, that is, the yield limit of the material is used in the strength calculation, the stable critical stress is used in the stability calculation, and the fatigue strength limit is divided by a certain safety factor in the fatigue strength calculation. In addition, allowable stresses for strength, stability and fatigue strength are obtained. The calculated stresses of structural members shall not exceed their corresponding allowable values.
 

The calculation steps of the allowable stress method are: determine the calculated stress according to the corresponding calculated load, determine the strength limit according to the mechanical properties of the materials used, and then compare them so that the ratio of the strength limit to the calculated stress is equal to or greater than the safety factor.
 

 

3. Safety factor
 

The basic condition for strength calculation and fatigue calculation is that the calculated stress of the dangerous section of the part shall not be greater than the allowable stress, that is, a multiple smaller than the ultimate stress of the material, and this multiple is the safety factor.
 

The choice of safety factor should not only ensure safety, reliability and durability, but also make full use of materials to achieve advanced technology and reasonable economy.
 

Where damage to any part of a steelworks crane would cause an item to fall, a jib to fall, a rotating part to capsize, the crane to overturn, or cause a severe impact when the crane hits a stop or an adjacent crane, such parts shall have Higher safety factor; when some parts of the crane are damaged and only stop the crane from working, the safety factor can be lower.
 

Lower values may be used for forgings and rolled parts; higher values should be used for castings.
 

(1) Safety factor calculated for metal structures.
 

For metallurgy and metal structural parts of cranes used in foundries, the strength, stiffness and stability should be calculated, and the plasticity of materials is generally not considered. Fatigue shall be checked for components with working levels of A6, A7 and A8.
 

(2) Factor of safety for parts calculation.
 

The strength calculation of parts includes static strength calculation and life calculation.
 

Calculation of static strength includes check calculation of brittle fracture and plastic deformation of parts; calculation of life includes calculation of fatigue strength of parts and calculation of wear resistance of sliding friction parts coverage.
 

The calculation stress of the dangerous point is calculated by the usual method of material mechanics, and the composite stress is synthesized according to the appropriate strength theory.
 

Note: For particularly important metallurgy such as transporting molten metal and dangerous goods, the safety factor of casting cranes should be appropriately increased.