The treatment of oil on mining and metallurgy sites differs most from an ordinary machining shop in the composition of the contamination sources. The oil here is rarely worn out by the machine itself; the particles come mainly from airborne dust. The temperature difference is no longer seasonal but diurnal and process-related. And the load stays high all year, so the oil remains at high temperature far longer than on an ordinary site. These three together make a completely different treatment logic.
Dust is the most unusual contamination source
On an ordinary industrial site the particles come mainly from the wear of gears, bearings and seals: regular in shape and of medium hardness. The dust on a mining site is mostly quartz and metal oxides, hard and angular. Such particles have two characteristics. First, their abrasive wear action is strong and they score the surface of the filter media and the inner walls of the pipework. Second, they tend to pack into the sealing chambers, the guides and the oil pipe joints, causing sluggish movement and local heating.
The difference in the treatment approach is that a mining site normally needs a stronger pre-filtration capability rather than a very fine accuracy at the end. A portable oil filter trolley with a filtration accuracy of 10~25 μm suits the first barrier at the equipment inlet, keeping large particles out of the precision pipework; the fine filtration stage can then go down to a finer class. When the front end is handled properly, the element life behind it and the running condition of the pump are noticeably different.
The temperature difference is another variable that is easily overlooked
The day-night temperature difference at a mine can exceed twenty degrees, and in the furnace-front area of a metallurgy shop there is a marked difference over a short distance. When this temperature swing acts on the equipment, the first thing it affects is the sealing: metal parts expand and contract, the seals are compressed and relaxed repeatedly through the temperature cycles, and a seal with a long design life may start to weep after two or three seasonal cycles.
Viscosity comes next. The difference in oil temperature between day and night on the same equipment can be enough to produce a marked change in the pump load. When a site feels that the equipment performs well one moment and badly the next, look at whether temperature is the cause before dismantling the pump for inspection. If that step goes in the wrong direction, the dismantling will show nothing, a maintenance window is wasted, and the real evidence of the fault is easily buried.
Heavy load puts the oil into harsher working conditions
Crushing, rolling and lifting equipment run at high loads all year, the drive shafts carry large torques, and the oil works at high temperature and high pressure, so it oxidises much faster than in equipment that runs intermittently. What shows on the outside is a darker oil colour, faster acid formation, and the formation of varnish and sludge. Sludge is the hardest thing for the filtration stage to deal with: it smears over the surface of the media, the differential pressure rises quickly, and repeated cleaning does not return it to its initial state.
So on a heavy-load site, shortening the element replacement interval is often more economical than extending it. A higher filtration accuracy is not necessarily better value; what really determines the consumable cost is the contamination load entering the equipment. The usual site practice is to manage the coarse and the fine stages separately: the coarse stage holds back the large particles, the fine stage holds the accuracy indicators, and the two stages have different replacement intervals.
Water-based and oil-based media do not follow the same rules
Water-based metalworking fluids and emulsions differ greatly from mineral oil in the logic of their treatment. The first point is the form in which the water is present: in an emulsion the water is dispersed as fine droplets rather than as free water, it is very hard to separate by vacuum degassing and has to be separated by settling or by a dedicated demulsifying step. The second point is microbiological growth: a water-based medium that stands unused for a long time, or is kept warm, or has lost concentration, will grow microorganisms, and the acids and biofilms that result affect both the metal parts of the equipment and the stability of the medium itself.
Water-based media have two further limitations. They cannot tolerate high temperature, because heat breaks down the emulsion and accelerates deterioration. And on filtration accuracy the particle size distribution of the medium has to be considered: the dispersed phase in an emulsion is far smaller than ordinary particle contamination, so a slightly coarser medium is already effective, and chasing a fine accuracy tends instead to bring the differential pressure up and cause blockage. Putting mining cutting fluid and mineral oil through the same treatment line is common on site and expensive.
| Comparison item | Oil-based medium | Water-based medium |
|---|---|---|
| Main contamination characteristics | Wear particles, oxidation products, water | Emulsion droplets, microorganisms, suspended solids |
| Suitability for degassing | Vacuum degassing is the main method | Routine vacuum degassing has limited effect |
| Temperature limits | Can be heated within the temperature control range | The upper limit has to be controlled so the emulsion is not broken |
| Filtration focus | Hold the cleanliness and the water content | Control the differential pressure and prevent blockage by biofilm |
| Equipment protection | Standard industrial protection | Added requirements for leak containment and ease of flushing |
What has to be done in addition on site
In a dusty environment the equipment itself needs protection. The oil inlet and the breather are the paths by which dust enters, so the position of the machine has to avoid the direct blast points and it has to be covered when it is out of use. Filtration work should also be scheduled in the periods when the dust is lighter; otherwise a freshly fitted element is driven up in differential pressure by the dust accumulated on its surface within a few hours, and the coarse stage in front of it is left without any purpose.
- Add a coarse filtration stage at the oil inlet end of the equipment to keep large particles out of the precision stage.
- Use separate equipment and pipework for oil-based and water-based media, so that cross-contamination is avoided.
- Keep separate sampling and test records for each type of medium rather than comparing them within one set of data.
- Plan the work in the metallurgy shop by temperature zone, and keep the equipment out of the high-temperature zone in front of the furnace.
The selection logic on a mining or metallurgy site is to start by accepting the contamination environment, and only then decide which configuration to use.