The grab bucket's volume is determined by the desired bulk cargo capacity and two physical-mechanical parameters of the bulk cargo: bulk density and natural slope angle. Therefore, when a grab bucket designed for one type of bulk cargo is used to grab another, the nominal volume of the grab bucket and the actual volume of the bulk cargo grabbed often differ.
While the bulk density of the bulk cargo is determined, the natural slope angle often varies significantly due to differences in the bulk's density and moisture content.
To adapt the grab bucket to handle different bulk cargoes with similar capacities, the grab bucket volume is often adjusted by varying the jaw plate height. Given the main geometric dimensions of the grab bucket's jaw plates and the natural slope angle of the bulk cargo.
The following figure shows the stacking volume of a double-jaw (clamshell)grab bucket.
