Classification – Cranes, Designed for the JobMany factors must be taken into consideration when investing in a crane. These factors include lifting capacity, crane use and application and the number of annual crane operating hours, in other words, the number of work cycles that a crane undergoes.
Owing to the various operating modes (heavy loads, containers or grab operation), the strain on a crane is not uniform. Loads also vary greatly, sometimes containers or grabs are full, and sometimes they are empty. And in heavy-load operation, cranes work near the limit of their lifting capacity.
The load spectra include these different parameters, as demonstrated in the F.E.M. Design Rules, F.E.M. 1.001, which attempt to define clearly the realistic strains on a crane structure.
The total of four loading spectra (designated by Q1 to Q4) refer to the intensity of crane operation and take into account, for example, whether the crane is required to move predominantly small loads and maximum permissible loads only seldom, or whether it frequently moves maximum loads.
While the type of load is a matter of how intensively the crane is used, the loading capacity relates more to the way the crane is actually built. The crane can be designed according to eight appliance groups as per F.E.M. (with the designations A1 to A8). The higher the appliance group, the greater the wall thicknesses of the steel sheets and tubes used, and the more robust the crane will be as a result.
The estimated number of work cycles and the service life of a crane can be derived from the type of loading and the loading spectrum on the one hand, and the loading capacity (steel construction, mechanical design and condition of the crane) on the other.
The higher the appliance group, also known as “classification”, the longer the service life of the crane when subjected to the same loading spectrum. For example, a crane classified in appliance group A8 is designed for more than four million work cycles, whereas a crane in appliance group A6 used for the same types of load will have reached the end of its service life after only 500,000 cycles.
Gottwald takes all these different factors into account when designing the Generation 5 Harbour
Cranes so as to select the most suitable classification to meet each customer's specific
requirements.
Given the same type of load, an increase in the appliance group by one level, e.g. from A6 to A7, corresponds to a doubling of the expected service life. By analogy, the effect of changing from A7 to A8 will be a further doubling.
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