The boom is the load-bearing arm of an excavator, crane or wheel loader, at whose end the tool or load hangs. It determines reach, digging depth/lift height and working radius of the machine. On excavators, distinction is made between main boom and stick (arm), connected via the boom joint. On cranes, the boom is one-piece (lattice boom, telescopic boom or luffing jib).
Excavator boom designs: mono-boom (standard, fixed boom length), variable-angle boom (hydraulically adjustable boom geometry for reach adjustment), long-reach boom (extended design for large reach in watercourse maintenance or high-reach demolition), two-piece boom with additional joint for compact transport position, triple-articulated boom for special access into confined spaces. Standard boom length: on 22-t excavators 5.7-6.3 m boom + 2.5-3.2 m stick, giving digging depth up to 6.5 m and reach up to 10.5 m.
Crane boom systems: telescopic boom (5-8 hydraulic segments) for mobile cranes — standard on Liebherr LTM series, Grove GMK, Tadano Faun. Lattice boom (segment-extendable 30-190 m) for large mobile cranes and crawler cranes — Liebherr LG and LR series. Luffing jib (fly jib) — 20-40 m lattice extension at the telescopic-boom tip for high-precision lifts. Superlift system — additional ballast carriers increase boom capacity on large cranes.
Construction materials: standard booms are made of high-strength steel (S460 or S690) with internal reinforcement. All larger excavators and cranes have booms in welded construction with double-T or box-section internal frame. Wear-protection blocks (Hardox) at mechanically loaded points (boom back, stick end). Boom joints have roller bearings or hardened sliding bearings — maintenance: greasing every 500 h, bearing inspection every 3,000 h.
Economics: a standard excavator boom is not priced separately because it is integral to the base machine. Conversion between standard and long-reach boom on 30-t excavator: EUR 15,000-35,000 conversion cost, 3-5 days workshop stay. Crane lattice boom segments are priced by length — for Liebherr LR series, a 12-m segment costs EUR 45,000-75,000. Boom maintenance and repair are critical — crack formation leads to boom total failure; DGUV Vorschrift 68 requires annual visual inspection by competent person.