Explosion-Proof Crane Selection for Steel Bridge Fabrication

Plate Unit Fabrication: Precision Lifting for Large Steel Plates

Plate units are the fundamental building blocks of steel bridge segments, comprising top plates, bottom plates, web plates, and diaphragm plates. Steel plate thickness ranges from 10–50 mm, with individual plate weights of 2–15 t. The plate unit fabrication process includes steel plate pretreatment, CNC cutting, groove preparation, unit assembly, and straightening. A QD-type crane rated at 10–20 t with a span of 22–31.5 m is recommended to cover the entire plate unit production area. Flatness requirements are stringent (≤2 mm/m), so plates must be lifted using a multi-point spreader beam with 4–8 suspension points to prevent plastic deformation during handling. Kelude plate unit cranes come standard with an electromagnetic lifting magnet (adjustable magnetic force) and a multi-point spreader beam, improving plate handling efficiency by approximately 50% compared to conventional wire rope and hook configurations.

CNC cutting machines and groove processing equipment are heavy-duty machine tools requiring foundations 1–2 m deep. The crane rail foundation must be positioned clear of these equipment foundations. Kelude employs an offset rail layout in the plate unit workshop—the crane covers the steel plate storage yard (2/3 of the span) and the processing equipment area (1/3 of the span)—maximizing floor space utilization. A two-speed hoisting mechanism of 8/2 m/min is recommended. The spacing of steel plate storage racks (vertical or horizontal) must be coordinated with the crane's suspension point spacing. Kelude's plate unit crane investment typically ranges from $30,000–$75,000.

Segment Assembly: Twin Trolley Synchronization for Heavy-Duty Turnover

Bridge segments are fabricated by assembling and welding plate units. Segments typically measure 6–20 m in length, 3–6 m in width, and 2–5 m in height, weighing 20–80 t each. The assembly process includes bottom plate setup, web plate installation, top plate closure, internal welding, and end face alignment. A QD-type double-girder crane rated at 20–50 t with twin trolleys is recommended. The twin trolleys can operate in synchronized mode for lifting long segments (two-point lifting) or independently—one trolley handles the main load while the other manages auxiliary tasks. Kelude's segment assembly cranes feature a twin trolley interlocking control system with one-touch switching between independent and synchronized modes via radio remote control. Segment turnover is a critical challenge in assembly—after welding one side, the segment must be rotated 180° to weld the other. This operation uses the crane in conjunction with a turnover jig, requiring constant-speed hoisting at 0.5–2 m/min with speed variation kept within ±3%.

Segment assembly workshops generate heavy welding fumes. Crane electrical cabinets must be sealed and dustproof to IP54. Kelude offers an integrated welding fume extraction system that interlocks with the crane—when welding is in progress, fume collection hoods automatically lower over the crane area to minimize fume dispersion. After assembly, segments undergo dimensional inspection (overall length tolerance ≤ L/5000, cross-section tolerance ≤ ±3 mm). The auxiliary trolley handles lifting of inspection platforms and measuring tools. Investment for segment assembly cranes ranges from $45,000–$120,000. For outdoor storage yards, a gantry crane (50–150 t) is recommended for segment turnover and transport; Kelude provides outdoor wind protection solutions including rail clamps, anchor devices, and anemometer interlocking.

Bridge Erection: Heavy-Duty Gantry Cranes for Outdoor Service

Bridge segment erection takes place at the construction site, typically using large gantry cranes or bridge erecting machines. However, trial assembly must be performed at the fabrication plant—3 to 5 segments are dry-fitted to verify bolt hole alignment accuracy before shipment. The trial assembly area is usually outdoors, requiring a gantry crane (50–150 t) to cover the assembly zone. Kelude outdoor gantry cranes feature a box-type double-girder structure with spans of 30–50 m and lifting heights of 20–30 m. Core safety features include: ① anemometer (automatic alarm at wind force ≥6, automatic lockout at ≥8); ② rail clamps and anchor devices; ③ anti-slip control; ④ lightning protection. The crane bridge travel system uses variable-frequency drive (VFD), with emergency stop braking distance ≤500 mm.

Trial assembly demands high bolt hole alignment accuracy between segments (hole diameter deviation ≤0.5 mm), requiring millimeter-level positioning capability. Kelude gantry cranes employ a dual-feedback positioning system combining laser distance measurement and encoders, achieving crane bridge positioning accuracy of ±5 mm. The rail foundation in the assembly area must be designed for traffic loading—typically a reinforced concrete strip foundation rated at 30–80 t per meter. Power supply is via enclosed conductor rail or cable reel. Kelude's in-plant gantry cranes for bridge erection represent an investment of $75,000–$300,000 (including rail foundation). For facilities with an indoor assembly bay, a QD-type overhead crane can be used as an alternative to a gantry crane.

Coating & Corrosion Protection: Explosion-Proof Cranes with Ventilation Interlock

Coating and corrosion protection is the final critical step in steel bridge fabrication, encompassing sandblasting, rust removal, primer application, intermediate coat, and topcoat. The painting workshop uses flammable solvents (epoxy resins, polyurethane paints), making explosion-proof cranes mandatory. An LD-type explosion-proof crane rated at 5–10 t is recommended, with explosion protection class Ex d IIB T4. Cranes in the painting workshop must interlock with the ventilation system—the crane cannot be energized unless the ventilation is running, eliminating the risk of solvent vapor accumulation igniting from crane sparks. Kelude coating workshop cranes feature a fully explosion-proof electrical system (explosion-proof motor, explosion-proof control box, explosion-proof limit switches, and explosion-proof pushbuttons) plus a ventilation interlocking control box. The crane rail height must be at least 2 m above the tallest workpiece to allow unobstructed segment transport and turnover within the coating line.

Steel Bridge Manufacturing Crane Configuration Comparison

FAQ: Explosion-Proof Cranes for Steel Fabrication