As big as it gets

As big as it gets

Canada's huge tar sands mine requires big equipment to do the work and that means big hydraulics.

Energy is big business nowadays, and sometimes it takes a big machine to do big business. When the price of oil began climbing toward $50/barrel in 2005, more attention turned toward a different type of petroleum resource — tar sands (also called oil sands). While it is more expensive to extract and refine oil from tar sands than from traditional underground oil fields, these tar sands deposits represent an astonishing two-thirds of the world's total oil reserves. Canada's Alberta province holds roughly half of the world's supply of tar sands.

Figure 1. Terex's RH400, the world's biggest hydraulic shovel, reigns over Canada's Athabasca Oil Sands area.

Big mine, big equipment
The Syncrude consortium operates one of three mines in the Athabasca Oil Sands area, north of Fort McMurray, Alberta. Syncrude's surface mine is reportedly the largest mine in the world, and this calls for big machinery.

It's appropriate, then, that the consortium chose Terex's RH400 excavator, Figure 1, for use in the operation. The RH400, the world's largest excavator, weighs in at 1078 tons, and has a face shovel capacity of 94 tons. In other words, it can fill up even the largest mining trucks with 3-5 passes!

In the Canadian tar sands — regarded as one of the toughest mining applications known — the RH400 has achieved a new production world record for hydraulic shovels: more than 9900 t/hr during performance testing and more than 6050 t/hr on average.

According to Volker Boernke, product manager for the O&K excavator line in Dortmund, Germany, "Our excavators are often the prime production tool in an open pit mine and the first and therefore, the most important link in the the production chain. Our machines are used 24 hours a day, 365 days a year in really harsh mining conditions — and quite often also severe climactic conditions. Nevertheless, the customers expect uptime well above 90%. Therefore, the main criteria for us to select a supplier are quality, reliability, and after-sales-support in the long run."

Figure 2. RH400's massive size means that it can fill the biggest mining trucks with only a few passes — making operations more efficient.

Big hydraulics
The RH400's two Cummins engines offer a total output of 4400 hp. Each of the two drivetrains includes a pump gearbox to drive a total of 14 hydraulic pumps. Bosch Rexroth main and swing pumps were chosen for their reliability.

Eight variable-displacement, axial-piston main pumps with 61 in.3/rev displacement are used, each capable of delivering 244 gpm (1953 gpm total) at a maximum working pressure of 5221 psi for travelling and 4496 psi for the cylinders.

Six axial-piston pumps with 15.3 in.3/rev displacement and reverse-flow capability serve a closed-loop swing circuit, each delivering 129 gpm (773 gpm total) at a maximum working pressure of 5440 psi.

The entire hydraulic system holds approximately 3400 gal. To meet the Arctic conditions of Canada's winter, several preheating devices for engine oil, coolant, fuel, and hydraulic fluid have been installed, in order to prevent the machine from cooling down when it is parked for maintenance or repair.

An extended valve block configuration ensures that increased engine power is completely transferred to the hydraulic output, i.e. more hydraulic oil flow for faster cylinder movements. This results in average cycle times below 30 sec.

The cylinders are Terex's own design, and use special seals and wiper rings on the pistons and rod guides for maximum service life of seals and guide bushings. Pistons and rods are made of one piece (by forging the piston), so no bolts are inside the cylinder. Also, the wiper ring in the guiding flange can be exchanged without disassembling the cylinder. The cylinders are produced by a German manufacturer that specializes in the production of large cylinders. Two boom cylinders have an outside diameter of 22.5 in., a total extended length of 24.6 ft and weigh 17,850 lb. Two stick and two bucket cylinders have an outside diameter of 17.7 in., a total extended length of 22.5 ft and weigh 10,700 lb each.

The RH400's high-pressure hoses come from a small German supplier that specializes in the production of large hose. The hoses have up to 6 steel layers inside. This, together with a special method to connect the hoses to their SAE end flanges, make them extremely reliable and achieve best possible life expectancy.

Hose for working pressures to 5220 psi is used in diameters up to 1.97 in. and 13-ft lengths, each weighing as much as 66 lb. Test pressure for the hose is approximately 14,500 psi. In areas with lower pressure, Terex uses hose as large as 2.95 in. in diameter and 19.7 ft long, weighing up to 143 lb each.

Smart, versatile controls
A Board Control System (BCS) is the RH400's computer-aided monitoring and data logging system. All vital operating and service data are displayed on a transflective color screen. As soon as any deviations out of tolerance are detected, the operator is alerted by visual and audio alarms.

The system makes troubleshooting much easier and helps prevent lengthy downtimes. All data can be downloaded by a laptop or sent to remote addressees by radio modem or the Internet.

The further developed Pump Managing System (PMS) ensures an optimized adaptation between the hydraulic power demand and power output of the engines. Therefore, overloading of the engines is avoided. PMS fine tunes pump flow for optimized performance, in order to achieve constant engine speed.

The BCS allows adapting joystick characteristics to individual operator requirements. As a result, the machine can be more sensitive and comfortable for the operator. Also, the speed of certain working motions, such as clam closing or boom lowering, can be limited to avoid stress on structural components.