These two original mining methods are relatively unchanged in their outline over the centuries. Of course the tools have changed, as has the scale. Open-pit or strip mining involves the removal of dirt (overburden) from the top of the ore deposit and then scraping away the ore. Underground mining requires tunneling to where the ore body is located, and then extracting the ore for further refining. Many ores, such as gold and coal, are mined both ways.

The most basic open-pit mines are sand and gravel pits while more sophisticated operations recover coal, iron or copper ore. In many small mines the only equipment needed are typical surface vehicles such as front-end loaders and vocational vehicles such as dump trucks. In the larger pits there are more specialized and massive pieces of equipment such as ore haulers, draglines and power shovels, as well as oversized front-end loaders.

Copper is one of the many open-pit products mined worldwide. U.S. copper production amounts to over 2 billion pounds annually – about 8 percent of the world total – and one of the leading copper producers is Freeport McMoRan, headquartered in Phoenix, Ariz. Its Sierrita mine south of Tucson is capable of producing up to 200 million pounds of copper a year, plus small volumes of molybdenum, gold and rhenium (a rare, high-value metal).

Giants at Work

The Sierrita mine uses some of the largest equipment available to mine and process its ore, said Sam Copley, a foreman there. Its trucks are from Empire (Caterpillar), and are diesel powered with mechanical drives, rather than electromotive. The mine has a P&H 2800XPB shovel with huge shovel capacity – a good match for its existing truck fleet. Its 44-cubic-yard P&H Optima dipper loads the mines 260-ton haul trucks. Front-end loaders and other equipment are sized on a similar scale to optimize production.

Sierrita also has ore concentration facilities that take relatively large-size ore and break it down to a powder the consistency of flour. Gyratory crushers take relatively large pieces of ore and break them down to a smaller size, which then is ground to a fine powder in ball and autogenous mills. The powder is then treated with flotation chemicals to concentrate the copper minerals. It next goes to smelting facilities where it is treated by thermal and electrolytic processes to make raw copper. Interestingly, the byproducts of the electrolytic step are often gold and silver – sufficient in some cases to pay for the electricity needed for the process.

Currently, Sierrita uses conventional fluids and greases, Copley told LubesnGreases. Since all water runoff is contained within the confines of the mine area, water pollution is not a significant problem, so biodegradable and specialized environmental fluids are not currently required.

For all of this equipment, except the ore haulers, heavy-duty engine oils are required which meet at least API CI-4-PLUS category performance. When the next round of emissions controls reach the off-road marketplace in 2014, new vehicles are expected to require low-ash API CJ-4.

Weighty Matters

Ore haulers are a unique exception. Often electromotive powered, they use railroad-type engines or very large displacement engines which drive electric generators. The generator provides the current needed to operate electric motors which power the driving wheels. In many cases, older versions of these engines call for mono-grade engine oils meeting the now-obsolete API CF or CF-2 category. MTU and Cummins engines are used as well as the classic ElectroMotive Diesel locomotive engines (now owned by Caterpillar). Cat also offers a mechanical-drive ore hauler which uses torque converters and appears to be the only major supplier to do so.

For the hydraulic systems on the draglines and loaders, a number of different lubricant products can be needed, including first-intent hydraulic oils and multipurpose products such as tractor-hydraulic fluids. Hydraulic oils are designed to success-fully lubricate the pumps and servo valves found in these hardworking vehicles.

Transmissions in most of the vehicles are either lubricated by heavy-duty transmission fluids such as API category MT-1 oils, Allison C-4 or Caterpillar TO-4 type products, or by a tractor-hydraulic fluid shared with the vehicles gears and hydraulic systems. Wear protection, oxidation and seal compatibility are among the key properties for these lubes.

There are some gear applications in mining vehicles, most of them rear-axle applications. There also are a large numbers of gear boxes elsewhere in the Sierrita mine that run conveyor belts and ore crushers. These use industrial gear oils meeting American Gear Manufacturers Association standards. Additionally, some units require gear oils that resist being thrown or slung off the gears and cables they are protecting. These are often asphalt based materials.

Greases are in use everywhere. They are an integral part of the lubrication schedule for the tracked vehicles in the pits. Bulldozers and draglines alike have many grease applications which call for a very sticky, tacky grease to prevent it from being slung out of the area where it is needed. Greases also are used in wheel bearings and need to provide a sure seal to keep dirt out of the bearings themselves.

Deep, Deep Down

Underground mines have many of the same requirements as the open pit operations. However there are some differences. One of them is that often the underground operation uses electrically powered equipment to prevent accumulations of toxic exhaust gases. This is very common in underground coal operations. Another difference involves the use of fire-resistant fluids for hydraulics. These can be water based, glycol or occasionally phosphate esters, and they supply the hydraulic systems as well as other lubricated systems.

One of the major techniques used underground to mine coal is longwall mining. In this system, mechanized cutters chew into the horizontal face of the underground coal vein, dropping the ore onto conveyors directly below that carry it away. Overhead, hydraulic roof supports hold up the ceiling safely above the equipment. As the entire system – cutters, conveyors, roof supports – progresses deeper into the mine, the mines ceiling is allowed to collapse in its wake.

Longwall systems stretch about 800 feet across, and the hydraulic supports that protect and advance their movement are 5 to 10 feet tall. Fire-resistant hydraulic fluid is critical to provide the lift required to operate the hydraulic ceiling supports. The U.S. Mine Safety & Health Administration has a tightly written specification for fire-resistant hydraulic fluids, and maintains a list of fluids approved for use underground.

One of the major suppliers of longwall fluids is Houghton International, headquartered in Valley Forge, Pa. Carsten Moeller, director of Houghtons hydraulic mining division in Wuppertal, Germany, explained that longwall fluids must deliver extreme fire resistance (theirs are about 95 percent water), wear protection, other hydraulic fluid performance criteria, and increasingly, biodegradability.

Moeller noted that North America lags Europe in biodegradability characteristics but is much ahead of the rest of the world, where production needs may outweigh environmental issues. He also pointed out that water-glycol based fire-resistant fluids are used in many machine hydraulic systems, where their more lubricant like properties are important.

Both above- and underground mines have applications calling for pneumatic drill lubricants, or rock drill oils. These oils lubricate the air-driven hammer which strikes the end of the bit, creating the holes needed for blasting and general material removal. These oils have been known to ignite inside the drill due to the high compression required to power them, so it is important that they dont compression-ignite as a diesel fuel does. For this reason, cetane number can be an important criterion for these oils.

More Ore

As is the case in most lubricant markets, energy efficiency and emissions are primary drivers for mine equipment. While regulations for fuel economy have focused primarily on on-road vehicles, mine operators are always looking for improvements on this important parameter. 2014 is the target date for the implementation of federal emissions and fuel economy regulations for the heavy-duty market, and the same engine oils that meet these needs in the on-road market will find their way into the off-road and mining applications.

Emissions regulations for the off-road market (EPA interim Tier IV) were already in place, so emissions compliant lubricants will be required in 2014 for any new equipment that reaches the mining marketplace. The use of API CJ-4 engine oils will likely increase, but the use of monogrades will go on for some time in older equipment.

Water pollution is a constant problem with the mining industry so the use of less toxic and biodegradable lubricants is an area for growth in the mines, as Houghtons Moeller pointed out. Biodegradable hydraulic fluids, tractor hydraulic fluids, greases and general purpose lubricants will be among the first affected.

Mining was probably one of the first of the so-called heavy industries to develop. It has been a part of human development for more than 6,000 years. Empires have risen to power on the basis of innovations in mining and processing ore, and now mining is an integral part of the worlds economic life. Whether its copper, iron, coal or any other material, there really is gold in them thar hills!