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A bulk-handling crane is one that, instead of a simple hook that can handle a range of slung loads, has an integral grab for lifting bulk cargoes such as coal, mineral ore etc.
Where the grab is a two-piece hinged bucket, it is known as a shell grab or shell bucket. Working the grab requires extra cables from the crane jib, so requires a specialised design of crane throughout, not merely an attachment. Some grabs use 2 cables for lift and control, others use 4.
In 1927, Stothert & Pitt of Bath, Somerset produced the first specialised bulk-handling crane.[1] This was to unload coal at Barking power station in London.
The grab has to be selected so that the combined weight of grab and contents does not exceed the grabbing safe working load of the crane. The mass of the contents depends upon the properties of the product being handled; its density, flow characteristics, angle of repose, lump/grain size, purity (e.g. is it wet or dry) and, in some cases, degree of settlement (e.g. a ship's cargo has compacted due to vibration, rolling, pitching and yawing over a long voyage).
Most bulk-handling cranes are dedicated to a single product, but others will handle various materials and need a selection of grabs. Some applications (e.g. manganese ore) may also require the use of teeth fitted to the grab jaws to enable penetration. Other applications (e.g. rape seed) may require to be self-sealing and have offset lower jaws with serrated, angle cut side cutters to restrain easy-flow properties.
When off-loading a ship, the grab may be more efficient if designed with a low-profile extended body which enables reaching under the ship's hatches, negating any need to centre the product with human and machinery access. The grab mechanism may be four rope, double rope, single rope ring discharge, single rope self-dumping, double chain, single chain self-dumping, single chain ring discharge, hydraulic or electro-hydraulic.
- ^ "Bulk Handling Cranes". Clarke Chapman. Archived from the original on May 6, 2008.