Hot Extruded Sections for Overhead Crane Booms
Every kilogram in a crane boom is carried by the crane itself before it carries anything else, so the section used has a direct influence on the payload the machine can lift. For this application Montanstahl developed hot extruded special profiles in carbon steel S355J2 where the wall thickness varies along the cross-section, with material added where stresses concentrate and removed where it is not needed, and with the mounting flanges for rope suspensions and trolley systems formed directly into the geometry rather than welded on afterwards.
Where Standard Profiles Reach Their Limit
Crane design places specific demands on both material and geometry, and standard profiles frequently run out of capability when the span grows, the loads increase or the operating conditions become unusual. In overhead crane applications a structural section has to combine load bearing capacity with reduced weight and dimensional stability under dynamic stress, three properties that a catalogue beam balances only by compromise, because its shape was optimised for a general case rather than for this one. To improve efficiency, safety and durability, special profiles are therefore developed specifically around the needs of the crane industry, integrating several functions into a single optimised geometry instead of building them up from separate pieces. Sections of this kind are central to machinery and material handling equipment, where the structure and the mechanism have to be designed together.
Four Demands Pulling in Opposite Directions
Reliable structural performance under demanding conditions meant satisfying four requirements simultaneously. The boom has to withstand high loads, both the point loads applied by the trolley wherever it stops and the dynamic forces generated when the load is lifted, accelerated and braked. Weight has to be optimised, since a lighter structure is easier to assemble and leaves more of the rated capacity available for the payload rather than for the crane itself. Torsional stiffness has to be sufficient for the crane to remain stable at maximum outreach, where an eccentric load twists the boom along its axis. Finally the profile has to be economical to manufacture, because a section that performs perfectly but costs too much never reaches production. Strength, stiffness and lightness conflict directly, and the only way to satisfy all of them is to move material to where it works hardest.
Application Context
Geometry optimisation and material selection together resolved the conflict. Wall thicknesses were varied along the profile, with reinforcement where the section is most highly stressed and material removed elsewhere, which improves the strength to weight ratio without changing the overall envelope the crane was designed around. The mounting flanges for the rope suspensions and the trolley system were integrated directly into the geometry, so features that would otherwise be welded on become part of the extruded shape, removing joints that are both a cost and a fatigue concern. High strength S355 steel provided the tensile and compressive capacity for lighter structures spanning further and lifting more. Hot extrusion suits this kind of section because a single pass produces undercuts and varying wall thicknesses economically, even in limited quantities. Profiles are developed as special profiles from the manufacturer’s drawing, with details in the technical Q&A.