Condra has manufactured and delivered a complex crane with traditionally opposing specifications, namely compact dimensions and higher-than-normal lifting height.

The 30/10 t double-girder electric overhead travelling crane for dragline house maintenance was delivered on December 9 after Condra received the order in August.

A 30 t crab-mounted main hoist will service hydraulic cylinders, motors and gearboxes within the house, while an auxiliary 10 t underslung hoist executes additional duties, including external loading and unloading of equipment.

“[The] crane design was made complex by two customer specifications: first, the need for the main hoist to deliver a higher-than- normal lifting height measured as a percentage of the available vertical dimension. Second, the requirement for overall dimensions to be sufficiently compact to enable the working crane to move in and out of the existing crane aperture in the wall of the dragline house,” Condra MD Marc Kleiner explains.

“These two design requirements run contrary to one another, in that a greater lift height is usually achieved by designing a physically bigger hoist working from a larger crane.”

Condra’s machine will clear the aperture frame with just 50 mm to spare.

Condra met the specification through the careful design of the main hoist around a high-tensile rope with reduced diameter, which allows a smaller rope-drum and more compact hoist.

Smaller wheels, suitably hardened, were used on the long and cross-travels of the crane, driven by more powerful motors, and the girder webs were made smaller and combined with the top and bottom flanges of thicker steel plate to maintain deflection criteria.

“In a nutshell, we met the customer specification by designing key crane elements to be smaller but stronger,” explains Kleiner.

The newly delivered crane features digital load cell read-outs, remote control, lights and a buffer to protect the underslung hoist against damage by other machinery working in the confined space of the dragline house.