Lattice Boom Crawler Crane

Overview

A lattice boom crawler crane is a heavy mobile crane that lifts large loads while standing on two wide steel tracks instead of wheels and outriggers. The Crawler Undercarriage spreads the crane's weight over a large ground area, so the machine can work and even travel with a load on ground too soft for a wheeled crane. The lifting structure is a Lattice Boom built from a triangulated steel framework rather than a solid box, which gives great length for little weight. These two features let the crane reach high and far for tasks such as erecting tower cranes, setting bridge girders, building wind turbines, and lifting plant modules at refineries.

Above the tracks sits the Upper Carbody and Turntable, a rotating deck that carries the boom foot, the winches, the engine, the counterweight, and the cab. It turns a full circle on a slew bearing so the crane can pick a load on one side and place it on another. Almost every motion is hydraulic: the Diesel-Hydraulic Power Pack turns diesel fuel into pressurized oil, and the Hydraulic System sends that oil to the winch, slew, and travel motors. The Operator Cab and Control System gives the operator the controls and a load moment indicator that keeps the lift inside the rated chart.

Crawler undercarriage

The Crawler Undercarriage has two Track Frame units joined by a central carbody. Each frame runs an endless Track Chain of forged Track Link members carrying bolt-on Track Pad (Grouser Shoe) shoes up to about 1.5 m wide. A Drive Sprocket at the rear pulls the chain while a Front Idler at the front guides it, and a row of Track Roller wheels carries the crane weight onto the chain along the ground. A Track Tensioner keeps the chain taut. Each track is driven by its own Travel Drive, a hydraulic Travel Motor turning a planetary Travel Gearbox, so running the tracks at different speeds steers the crane and running them opposite turns it on the spot.

Upper carbody and slewing

The Revolving Frame is the welded steel deck that holds everything that turns. It sits on a Slew Bearing, a large three-row roller ring with internal gear teeth that carries the overturning moment from the load. Two Slew Drive units, each a Slew Motor and reducer ending in a Slew Pinion, mesh that ring gear to rotate the deck, and a Slew Brake holds the position when the operator stops turning. The boom heel pins to the frame through the Boom Foot Pin connections.

The lattice boom

The Lattice Boom is what makes this crane class distinct. It is assembled from a Boom Foot Section at the bottom, a chosen number of Boom Insert Section sections in the middle, and a Boom Head at the top. Each section is a frame of four tubular Boom Chord members tied together by diagonal Lacing Tube tubes. Sections join end to end through a Boom Connecting Pin at each corner, so the boom is built up on the ground and raised as a unit. Inserts are added or removed to set the length for the job, which is why the same crane can run a short stiff boom for heavy picks or a long boom for high reach. The Boom Head carries a set of Head Sheave wheels that turn the hoist ropes down to the hooks.

Raising the boom and hoisting the load

A lattice boom has no hydraulic cylinder to lift it. Instead the Boom Hoist System system raises it: a Boom Hoist Winch reeves rope through the Gantry (A-Frame), an A-frame on the deck, and down through a Bridle (Equalizer) connected by Boom Pendant Rope ropes to the boom head. Spooling that rope in pulls the boom up; paying it out lets the boom down. The load itself is lifted by the Main Hoist Winch, a winch whose Winch Drum spools the Wire Rope over the boom head and down to the Main Hook Block, a multi-sheave block reeved with several rope parts to multiply the lift. A separate Auxiliary (Whip) Hoist runs a single line to the Whip Hook Block for fast handling of lighter loads. Every winch carries a spring-applied Winch Holding Brake that holds the load if the hydraulics stop.

Power, balance, and control

The Diesel-Hydraulic Power Pack is built around a turbocharged Diesel Engine that drives the Main Hydraulic Pump units. Their oil passes through the Main Control Valve bank, which meters flow to each function, and a Center Swivel Joint carries oil across the slew axis to the rotating deck. At the rear, the Counterweight Stack stack of bolt-on Counterweight Slab slabs balances the load moment, and operators add or remove slabs to match the planned lift. The Operator Cab and Control System holds two Control Joystick controls feeding a Crane Control PLC, and a Load Moment Indicator compares the measured line pull from a Load Cell and the Boom Angle Sensor reading against the load chart, warning the operator and stopping motions before the crane is overloaded.