The most important performance parameters characterizing the basic working capabilities of lifting machinery are lifting capacity and duty class. Lifting capacity refers to the maximum weight of a load that can be lifted under specified working conditions, i.e., the rated lifting capacity. For cranes equipped with electromagnetic chucks (see lifting chucks) or grabs, the lifting capacity should also include the weight of the electromagnetic chuck or grab. For boom-type cranes, the lifting capacity also includes the weight of the hook assembly. Duty class is a performance parameter reflecting the overall working condition of the lifting machinery and is an important basis for designing and selecting lifting machinery. It is determined by the total number of work cycles and load conditions that the lifting machinery needs to complete within the required service life. The International Organization for Standardization (ISO) classifies lifting machinery into 8 duty classes. China only classifies cranes into 8 classes; light and small lifting equipment, elevators, and overhead monorail systems are not yet classified. For lifting machinery with highly regular and repetitive operating procedures, such as cranes loading and unloading cargo on docks, stacker cranes used in high-bay warehouses, and hopper elevators for feeding blast furnaces, the work cycle is also an important parameter. The work cycle refers to the time required to complete one work cycle. It depends on the working speed of the mechanism and is related to the transport distance. The aforementioned cranes sometimes use productivity as an important parameter, usually expressed as the lifting capacity completed per hour.
Main Parameters
Lifting Capacity G
Lifting capacity G (formerly often represented by the letter Q) refers to the mass of the lifted object, measured in kilograms (kg) or tons (t). It is generally divided into rated lifting capacity, maximum lifting capacity, total lifting capacity, and effective lifting capacity.
1. Rated lifting capacity Gn (excluding the mass of the lifting wire rope, hook, and pulley block) refers to the total mass of the heavy object or material that the crane can lift, along with the mass of separable lifting tools or attachments (such as grab buckets, electromagnetic chucks, balance beams, etc.). For cranes with variable radius, the rated lifting capacity varies with the radius.
2. Maximum lifting capacity Gmax refers to the maximum rated lifting capacity that the crane is allowed to lift under normal working conditions. For cranes with variable radius, the maximum rated lifting capacity that the crane is allowed to lift under safe working conditions at the minimum radius is also called the nominal rated lifting capacity.
3. Gross lifting capacity (Gt) refers to the total mass of the load or material that the crane can lift, including detachable lifting attachments and attachments or accessories permanently fixed to the crane (including hooks, pulley blocks, lifting wire ropes, and other lifting items below the boom or trolley).
4. Effective lifting capacity (Gp) refers to the net mass of the load or material that the crane can lift. For cranes equipped with detachable grab buckets, the mass of material allowed to be grabbed by the grab bucket is the effective lifting capacity; the sum of the grab bucket's mass and the material's mass is the rated lifting capacity.
