Underground LHD Loader

Overview

An underground LHD, short for load-haul-dump, is the mucking loader of hard-rock and many soft-rock mines. It digs broken ore from the draw point or muck pile, carries it a short distance, and dumps it into a truck, an ore pass or a stockpile, then returns for the next bucket. The whole machine is built around one constraint that a surface loader never faces: it has to work in a confined heading where height, width and air quality are all limited. That is why it is long, low and articulated rather than tall and rigid, and why its engine and brakes are treated very differently from those on a surface machine.

LHDs come in diesel, and increasingly battery-electric, forms across a wide size range, from compact units for narrow-vein mines to large loaders that fill a haul truck in three or four passes. Whatever the size, the job is the same: maximise the tonnes moved per shift in a tunnel only a little larger than the machine itself, while keeping the operator safe in an environment with no easy escape.

Articulated chassis

The Articulated Chassis is what lets a long loader corner in tight drifts. Instead of steering the wheels, the machine bends in the middle: a Front Frame and a Rear Frame are joined at a central Articulation Joint, and a pair of Steering Cylinder units swing the two halves about that pivot. Because both axles follow the same arc, the machine tracks cleanly around a corner without the rear wheels cutting in. An Oscillation Bearing lets the rear axle rock so all four wheels stay loaded on an uneven floor, keeping traction where it is needed.

Boom and bucket

Loading is done by the Boom & Bucket Linkage. A welded Lift Boom raises and lowers, and a Z-bar Bellcrank driven by the Tilt Cylinder curls the Muck Bucket with high breakout force so it can be rammed into a packed muck pile and filled in one pass. The bucket lip carries replaceable Bucket Tooth castings, and every joint runs on a hardened Pivot Pin because the digging loads and the grit are punishing. Bucket size is matched to the drift and to the haul truck so a whole number of passes fills the truck.

Powertrain and axles

Most LHDs are driven by the Powertrain, a turbocharged Diesel Engine feeding a Torque Converter and Powershift Transmission that send power through driveshafts to both axles. The engine is a low-emission design because the exhaust goes straight into the air the crew breathes. Each Drive Axle carries a Differential, a Planetary Hub reduction at each wheel for high tractive effort at low speed, and oil-immersed Wet Disc Brake discs that shrug off the heat of repeated stops on a ramp. The tires are solid or foam-filled so a rock cannot strand the machine with a flat.

Hydraulics and cabin

The Hydraulic System supplies the lift, tilt, steering and brake circuits from engine-driven pumps through a sectional Main Control Valve, with nitrogen Brake Accumulator storage holding brake pressure in reserve. The operator works from the Operator Cabin, a ROPS and FOPS protected station, often with the seat turned for visibility while tramming, controlling the boom and bucket through electrohydraulic Joystick units and watching machine status on the Operator Display.

Emissions, electrics and safety

Because the machine runs in confined air, the Exhaust Treatment is heavy duty: a Diesel Particulate Filter traps soot, a Oxidation Catalyst and SCR Module cut carbon monoxide, hydrocarbons and NOx to the limits set for underground ventilation. The Electrical System centres on a Vehicle Control Unit that runs the powertrain and feeds telemetry for fleet management, and increasingly the Tramming Camera feeds that let an LHD be driven tele-remotely or run autonomously from surface during blasting re-entry. Protecting all of it, the Fire Suppression System system watches the engine and brake hot spots and discharges agent through fixed nozzles, a system that is mandatory because a fire in a single-access heading leaves nowhere to run.

Variants and use

LHDs span a wide range to suit different mining methods. Narrow-vein and small-orebody mines run compact loaders barely wider than the ore drift, with buckets of a cubic metre or two, while large open-stope operations run loaders that fill a haul truck in three or four passes. The biggest split is in the power source. Diesel LHDs remain the workhorse because they carry their own energy and roam freely, but battery-electric loaders are taking over in deep and hot mines because they put no diesel exhaust or heat into the air, which cuts the ventilation that is one of the largest costs of going deep. An electric LHD swaps the Diesel Engine and its Exhaust Treatment for a battery and a traction motor while keeping the same chassis, linkage and hydraulics. In the cycle, the loader mucks at a draw point or muck pile, trams a short distance, and dumps into a truck, an ore pass or a stockpile, often working in pairs with a haul truck that takes the longer run out. Increasingly the machine is driven tele-remotely or runs autonomously so it can keep mucking during blast re-entry when no person is allowed underground, which is where the Tramming Camera feeds and the telemetry in the Vehicle Control Unit earn their place. The bucket, the wear parts and the tires are the consumables that set the running cost, all chosen for the abrasiveness of the particular ore.