Sizing your overhead cranes
The size of a crane is determined by some key figures in plant engineering. Usually, in hot dip galvanizing plants, these key elements are the distance between the rails – dictated by the building size – and the maximum weight to be lifted. Once these have been determined, sizes also have to abide strict international rules. However, another important element in the design of a crane is the so called FEM class. The FEM class is an expression of two important separate indexes: a classification of the steel parts to be used and a classification of the lifting mechanisms deployed. The first index (A) expresses the ratio between the number of operational cycles in the life of a machine and its load range (a forecast of the average load in relation to the nominal load). The second index (M) is the expression of the ratio between the total time of use (in hrs) and the load range.
FEM classes go from A1 (light) to A8 (heavy) for mechanical parts, and from M1 to M8. Usually in hot dip galvanizing plants the most common lifting equipment ranges from class A4/M4 in the racking and un-racking areas, to class A6/M7 for the “heavier” areas (galvanizing and pretreatment areas).Overhead bridge crane sizing