A new counterweight technology is being deployed on a 2300-t (2535-ton) crawler crane that Manitowoc Co. plans to begin shipping in 2010. The new balancing technique reduces the amount of ground that needs to be prepared for the crane’s operation.
The Model 31000 crane employs a variable-position counterweight (VPC) to reduce its operating footprint to 50 x 66 ft (15 x 20 m), compact for a crane with main boom range of up to 344 ft (105 m) and fixed jibs ranging up to 137 ft (42 m).
The VPC lift enhancer is mounted on a rack and pinion mechanism so it can automatically extend when more counterweight moment is needed during the lift. That keeps its footprint low while letting the crane lift heavy loads.
“The counterweigth put the weight in the center, distributing it on all four tracks. That helps reduce the ground bearing pressure. With some cranes of this size you have to pour a concrete base,” said Larry Weyers,
The VPC’s mechanical actuator is controlled by the crane’s EPIC control system, which monitors the boom angle and applied load to determine where to position the counterweight. During operation, the counterweight is mechanically locked to prevent inadvertent movement.
The VPC extends from the rear of the crane and ranges from about 27 ft (8 m) when fully retracted to 95 ft (29 m) when fully extended. The VPC also allows for pick-and-carry of all rated loads, making it much easier to maneuver around the job site.
The Model 31000 is mounted on four separate, trunion-mounted tracks, rather than the traditional two. “This provides an efficient means of crawler assembly and allows the crawler tracks to oscillate during travel to provide uniform load distribution,” said Bill O’Neil, Lead Engineer.
The crane, powered by dual 600-hp (447-kW) Cummins engines, can be assembled in 12 days. Excluding the main boom, most of its components measure less than 12 ft (3.7 m).
“It only takes 85 truckloads to deliver. Competitors take up to 200 truckloads,” Weyers said.