It’s difficult to name any type of primary mine production and comminution equipment that doesn’t require lubrication in some form. Trucks, shovels, crushers, mills, conveyors and even electrical transformers need oil—and generally, lots of it. Add to that the various tanks, barrels and other containers used for oil storage and transfer, and it’s easy to see why a mine or plant’s productivity and cost-of-operation figures can slide smoothly upward—or quickly downward—on the presence or absence of a thin film of oil.
According to oil filtration specialist C.C. Jensen A/S (CJC), contamination causes 80% of all oil system failures. Palle Maschoreck, head of the Danish company’s mining business segment, recently described his company’s approach to contamination control and prevention to E&MJ: “We have taken technology, which is widely known and used in the global wind [turbine] industry and applied it to mining. We employ a different filtration technology—offline filtration—than the standard inline filters, which enables us to clean and keep oil very clean during operation.”
Maschoreck showed two photos, explaining, “[Here’s] a clear indication of this. These are microphotos of used engine oil. The first picture is oil after only nine hours of operation—the oil is clearly dark and already contaminated; this is under normal operating conditions without CJC filtration. The second picture is the same oil after 963 hours of operation using CJC filtration. There is a clear, visible difference. Imagine the impact this has on the equipment.”
Overall, CJC’s approach for avoiding oil system failures rests on the premise that the best way to control oil contamination is to stop the contaminants from entering the system in the first place. This entails ensuring that all machine components are clean when installed and that oil systems are thoroughly flushed before operation. The oil system should be sealed from the environment as thoroughly as possible with seals and gaskets, as well as with high-quality tank breathers that provide fine particle and moisture-retention protection.
The oil should be pre-filtered before coming in contact with any machine component, preferably by continuous filtration in the lube room/storage area or when transferred to machines. Proper oil contamination control also includes maintenance procedures for topping up with oil, replacing parts, taking oil samples, etc.
Solid particles account for the majority of all failures in an oil system. The most harmful are particles of similar size or slightly larger than the dynamic tolerance between the moving parts in the oil system. Dynamic tolerances in an oil system are extremely fine. How fine? Take a look at the figures in the table below.
These microphotographs show engine oil after only nine hours of operation using conventional inline ﬁ ltration (left), and after 963 hours with ofﬂ ine ﬁ ltration technology.
Other modes of contamination that may play a role in system failure include water contamination, oil degradation and acidity contamination—any or all of which can reduce the protection offered by even premium oils against machine damage.
CJC noted that determining whether to replace oil on the basis of time or operating hours is expensive and unnecessary. Basing oil changes on its condition is the best approach—and this is where oil analysis can help. A good oil analysis report will answer key questions:
- Is the oil suitable for further use?
- Has a critical wear situation developed?
- What level of contaminants is evident?
- Is oil degradation speeding up? Could a severe varnish problem occur soon?
The company maintains that the best method for capturing and retaining fine particles as well as water and varnish is by installing an offline filter. An offline filter operates continuously, circulating the oil volume in the system many times per day. CJC said its offline oil filters remove oil degradation products such as sludge and varnish through polar attraction to the filter medium. A combination of adsorption and absorption fills each cellulose filter fiber with oil degradation products until the insert is completely saturated. The filters operate at low pressures and flow rates—conditions conducive to efficient filtration.
In comparison, conventional inline pressure filters—typically glass fiber-based—operate under high pressure and high flow conditions to create as little restriction as possible to oil passage. The filter element is pleated in order to increase the surface area and reduce the pressure drop. Because they are installed after the main system pump, inline filters are subjected to cyclic flows and frequent stops and starts, which degrades filtering efficiency. Glass fiber-based pressure filters are capable of removing solid particles only—and due to the relatively small filter depth and volume, have a restricted dirt-holding capacity.
Two recent examples illustrate the potential improvements that can be gained by offline oil filtration. In one application involving a large fleet of Volvo FMX440 haul trucks at a Kinross gold mine in Ghana, a dusty environment and rough operating conditions required engine lube oil changes every 500 hours (hr)—yet the mine still experienced high wear rates on the trucks’ engines. To address the problem, the mine tested CJC Heavy Duty HD HDU 15/12 oil filters with CJC BG 15/12 filter inserts.
The test showed that with offline filtration, oil change intervals could be extended from 500 hr to beyond 1,500 hr, and that engine wear could be significantly reduced by keeping oil clean during operation with kidney loop filtration. Extending the service intervals enabled the mine to reduce annual service intervals from 480 to 160 intervals per year, given an average 6,000 hr/y of operation per truck. On average, the trucks required a major engine overhaul every 10,000 hours. For a fleet of 40 trucks, this represents 24 overhauls per year, each at a cost of $66,000 per engine and $3,000 in labor. Keeping the oil clean during operation allowed Kinross to extend the engine overhaul interval to 18,000 hr, or just 13 overhauls per year. Total savings from reduced oil consumption, extended change intervals and longer service and overhaul intervals amounts to $681,800 annually.
In another example, the oil in a large Fuller-Traylor gyratory crusher at Minera Escondida in Chile was subject to severe contamination from its dusty environment, leading to breakdown of oil-lubricated components. The 6,000-ton-per-year (t/h) crusher, with oil capacity of 4,000 liters (1,000 gal), experienced frequent unplanned maintenance attention due to component failures and required a full oil change every 60 days. Each oil change involved an eight-hr shutdown.
A CJC Fine Filter HDU 427/108 was installed with 16 B 27/27 filter inserts with dirt-retention capacity of 64 kg (4 kg per insert). With the CJC offline filter removing up to 150 kg of dirt every two months, contamination of the oil system was minimized, leading to increased oil service life and reduced cost for component changeout. After the CJC filter was installed, the unit’s inline filter consumption was almost eliminated and three out of four of oil changes were avoided. Productivity was increased significantly, downtime was reduced by 87%, and the mine has benefitted from savings of up to $479,600 annually.