Super digger unearthed

Engineered around a proven design that emphasises reliability and durability, Hitachi’s flagship excavator has been designed to provide extended operating life and significantly reduce operating and maintenance costs, even under full operating conditions.

Engineered around a proven design that emphasises reliability and durability, Hitachi’s flagship excavator has been designed to provide extended operating life and significantly reduce operating and maintenance costs, even under full operating conditions.

The first words that come to mind about Hitachi’s 800-ton EX8000 hydraulic excavator are big and orange; although trying to hide some 800+ tonnes of fabricated steel could be a challenge, so why not paint it orange! Even parked-up it’s an imposing and impressive piece of engineering.

The new ultra-class digger boasts a series of engineering and technological advances that, according to Hitachi engineers, give the new machine an operating speed and agility equivalent to the company’s smaller class-leading mining excavators.

Built tough

Constructed around a proven rigid box design to resist bending and twisting, the EX8000 utilises the advanced swing system pioneered on the company’s very successful 300-tonne EX3600-5 excavator.

Controlled by six high-torque, axial-piston motors with oil-bathed two-stage planetary gears, the massive swing device is an induction-hardened, heavy duty, triple-row, cylindrical roller bearing. Each gear and pinion is immersed in lubricant and finished with dirt seals.

Power — and there is plenty of it – comes from twin Cummins QSK60 Tier II, US emission-compliant diesels, each developing 1450kW at 1800 rpm. Maximum torque is 20,100 Nm (2 x 10,050 Nm).

The Hitachi-developed ETS (Electronic Total control System) gets the power to where it’s needed. Sixteen variable-displacement, axial piston main hydraulic pumps (for front attachment, travel and swing), regulated by an electric engine-speed sensing control system, along with two gear pumps, six control valves and two sets of flow-assisting valves enable both independent and combined operations of all functions.

All on-board hydraulic circuits have high-quality high-pressure hydraulic filters, down stream of the pumps for easy maintenance access, for protection against oil contamination. Additionally, three oil coolers optimise oil cooling efficiency.

The ETS can also achieve maximum job efficiency by reducing fuel consumption and noise levels, while maximising productivity through the optimisation and control of engine-pump functions.

The construction and dimensions of the machine’s hydraulic cylinders reflect the imposing physical presence of the EX8000. Specifically engineered high-strength piston rods and cylinder tubes are used throughout. Cylinder cushion mechanisms are provided for boom, arm, bucket and dump cylinders and a flow-retarding stroke-end control system is fitted to the arm and bucket cylinders. The bucket cylinder is also provided with protector.

Given the weight of the machine and its potential operating environments, Hitachi has given a lot of attention to track reliability. The track frame has been cast as a solid unit for more strength — a feature exclusive to the company’s large excavators. As well, newly-designed lower rollers, track links and drive tumblers will boost rough ground operational durability.

To maintain correct track tension, nitrogen gas accumulators have been fitted to absorb abnormal track tension — and reduce potential damage. In practice, if accumulator pressure exceeds a preset level, travel is stopped. A warning signal is also sent to the display monitor in the operator’s cab.

The EX8000 sits on two 10.5 metre long undercarriage sections, fitted with the shovel-type tracks incorporating heat-treated, cast steel, triple grouser shoes. Undercarriage width, outside edge to outside edge, is 8.65 metres. L x W = more than 90 square metres of real estate under the machine, providing excellent operational stability.

Each track section is driven by high-torque, axial piston motors, driving through 2-stage planetary gear box plus spur gears reduction device to allow counter rotation of tracks. The spring-set/hydraulic-released disc type parking brake on each track can be manually releasable.

A set of electro-hydraulically retractable folding stairs, mounted on the front of the superstructure, provides safe, easy access. Walkways and stairways are wide (and well-lit for night time operation) and provide excellent access to all engine, hydraulic and electrical components.

Cab improvements

The top of the operator’s cab is almost 10 metres above ground level, which means an operator’s sight line is around 8.5 to 9 metres above ground level — and a perfect view of the loading sequence.

The cab exhibits the traditional Hitachi attention to detail. Well proportioned and laid out, it sits on fluid-filled elastic mounts to absorb vibration. At 1.8 metres wide, more than 3 metres long and 2.1 metres high, the design includes excellent all-round visibility and offers ample utility space behind the operator’s seat for creature comforts such as a table, microwave oven and refrigerator.

Sit in the seat and all controls are in natural reach. Short-stroke electrically-operated joystick controllers fall comfortably to hand. These wrist-activated controls operate with light touch and sensitivity to deliver light, smooth manoeuvring over extended operations and, along with the overall ergonomic layout of the cab, combine to significantly reduce operator fatigue.

Just off to the left, a 266mm colour multi-display LCD shows machine data and operating status. Linked to almost 50 sensors fitted throughout the digger, the display provides instant fault diagnosis, displaying warnings and countermeasures if failure occurs. The system not only finds the fault but tells you how to fix it!

The EX8000 comes standard with a 40m3 bottom dump bucket and is an ideal match for four-pass loading the new generation 300-ton dump trucks.

Peter Ross

Hitachi Mining

rossp@hcma.com.au

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