A big transformation

Rusch refurbished and then converted the Cat 5130B mining excavator into a specialty high-reach demolition machine that fit AF Offshore Decom’s demanding application.

While still resembling the mining excavator at the base, Rusch built it into what it called a RS7500 in triple 34-25 configuration. The 34 refers to height in metres that the machine can reach, while 25 refers to weight in metric tonnes of the work tool that the machine can handle at that maximum reach.

Construction of the new boom relied on Rusch’s extensive expertise in crane repair and service. Cranes feature high-tensile steel in their boom construction, allowing for the boom to be lighter, bigger, and stronger. The high-tensile-steel boom that Rusch built for the excavator is four times stronger than rebar, measuring 960 newtons per sq mm. The steel can only be sourced from two suppliers in Europe: SSAB in Sweden and Thies in Germany. It is heat-treated with metallurgy incorporating chrome, nickel, copper, and vanadium for strength. The modular triple 34-25 boom consists of three pieces: a 17-m-long boom, 4-m-long mid stick, and 12-m-long stick.

The machine’s base was also modified to increase stability. In addition to moving the OEM counterweight farther back to balance the machine, the track frames were lengthened and the undercarriage was widened to make a 10-m-long by 10-m-wide footprint, giving the machine a square base to work from.

The three main boom cylinders were built in-house by Rusch for longer stroke and to accommodate torsional forces, while the OEM Cat 5130B boom and stick cylinders were moved up to the mid stick and stick.

A mining excavator requires hydraulic pump priority for slewing (swinging) circuits, so Rusch redirected the hydraulic pumps to prioritize work tool, boom, and stick functions for demolition.

Rusch modified the cab to tilt 40 degrees to give the operator better visibility up to their work area. The cab was also outfitted with bulletproof glass and metal cage guarding to protect the operator from debris.

In addition to the expanded undercarriage footprint and repositioned counterweight, Rusch added a safety system that prevents tipover if the boom is vertically extended too far. Sensors measuring angles and position of each of the three boom sections, in addition to pressure sensors in the hydraulic cylinders, all feed data into a programmable logic controller (PLC), which can warn and then cut boom movement if it exceeds a pre-determined safe working limit. The completed machine was named Big Wolf and shipped to AF Offshore Decom in 2009.