Mining can be divided into two basic types: surface and subsurface. Each have their challenges with equipment reliability and maintainability.
The surface techniques include:
- Open-pit – digging big holes, often used for minerals like copper or coal
- Quarrying – working on the surface where minerals are extracted
- Strip – removing a long strip of overlying soil and rock (the overburden)
- Placer – removing minerals from sand, gravel, or on the surface includes sluicing and dredging work
The sub-surface techniques include:
- Drift – near-horizontal mining, following the bed of coal or vein of ore
- Slope – tunneling straight down or horizontally towards desired material.
- Shaft – vertical or near-vertical tunnel from the top down
- Hard Rock – digging into solid rock to find the minerals which are normally in ore form
- Borehole – extraction of minerals in the liquid or gaseous state using suction pumps
- Room and Pillar – material is extracted across a horizontal plane, creating horizontal arrays of rooms and pillars.
- Longwall – excavating from tabular deposits, as well as soft mineral deposits with large blocks extracted in a single continuous operation
The various classes of equipment include machines for digging, transferring, processing, and maintaining the mine site. The heavy equipment used is for digging material include front loaders, excavators, dragline as well as tunneling, boring, drilling machines, dredging units. Heavy equipment used for transferring material include dump trucks, large haul trucks, cranes, as well as conveyors and lifts. Processing equipment includes crushers, screening units, washing units, reclaimers, sluicing units, and conveyors. Machines used to maintain a mine site are motor graders, rollers, planers, vibratory plate attachments. Water trucks for dust suppression are also used, especially in drier climates. There are also air compressors and power generators used on site that are integral in the mining operation.
A considerable challenge with mines sites is location.
Often mine sites are in remote areas where replacement equipment, parts, or lubricants many are not readily available. Keeping an emergency inventory as well as operating inventory is common practice and will add to the overall operating costs. Equipment reliability is important due to the large cost of downtime. When an asset fails, it is no longer productive. It is been estimated that many mines have a loss of up to $100,000 per hour for every equipment failure incident. This value may increase if the material is precious metal. Companies are active in establishing regular maintenance of the equipment, maintaining a comprehensive record of maintenance, and establishing a predictive maintenance approach to offset the opportunity of failure. Oil analysis is part of the predictive approach. The mining machinery maintenance costs can make up top 50% of the operating budget of a mining company. This is due to the nature of the work as well as the environment which includes exceptionally heavy loads, long work shifts, high contamination (water, dust, sand, crushed rock, process chemicals). Other factors that cause downtime include equipment idle wait time for asset loading/unloading and environmental disruptions due to weather or ground stability.
All the equipment mentioned rely on lubricants for proper operation as well as fuel and in many instances, coolant. Fluid condition monitoring will provide information on the health state of the assets as well as identifying the potential of impending failure due to contamination, excessive wear, or exhausted performance. Fluid analysis can provide critical early warning of issues before they contribute to significant downtime costs and production disruption. The viscosity, metal concentration, PQI (particle quantifier index for ferrous wear debris identification), and water contamination should be tested in all oil samples. The following are additional tests that should be considered for the various components found in mining equipment:
Fuel Dilution: provides information on injector, fuel pump and ring health as well as combustion efficiency. Increased fuel dilution will reduce oil viscosity and additive concentrations and may lead to wear. Catastrophic engine failure may also result from fuel dilution.
Coolant/Antifreeze Contamination: if found in oil may indicate a breach which will lead to increased oil viscosity, overheating, eventual piston or bearing seizure.
Soot Levels: increasing levels indicate improper and inefficient combustion which will increase oil viscosity leading to overheating as well as absorbing anti-wear additives from the oil leading to increase wear. Also act as a nucleation site for deposit formation.
Oxidation and Nitration: increasing levels indicate the degradation of the base oil and build-up of chemical contamination that forms sludge, varnish, and lacquer. These deposits will adversely affect the oil additive performance.
Transmissions, Hydraulics, Compressors, Power Generation Systems
Particle Size Distribution: particle increase will indicate an increase in contamination levels as well as wear debris.
Oxidation: the free radical formation and acid generation that lead to the cross-linking of the base oil that forms sludge, varnish, and lacquer. These deposits will adversely affect the oil additive performance as well as increasing the opportunity for equipment failure.
Acid Number and/or Initial pH: acid formation increase indicates the initial stages of base oil breakdown. If left unchecked, the acids that form due to thermal and chemical stress will polymerize the base oils leading to a deposit buildup as well as act as a catalyst for increased acid generation as well as reacting with the additive chemistry reducing performance. A low ipH can result in significant levels of corrosion in equipment.
Other fluids such as coolants, fuel and DEF also need to perform correctly. Incorrect or prolonged storage of these fluids can result in fluid degradation and contamination causing extensive equipment problems and even failures. Analysis of physical and chemical properties of these fluids can assist in pin pointing issues before damage occurs to equipment.
ALS Tribology helps the mining industry by provide a comprehensive testing program for the assets. Various lubricants as well as fuel, coolants, and DEF are tested using the most up to date instrumentation and diagnosed by industry experts to provide the highest level of condition monitoring service.