Method for filtering impurities in industrial oil

Impurity filtration of industrial oil is a key step to maintain equipment performance and extend the life of oil products. The following are methods, equipment and operation points for filtering impurities in industrial oil:

Common impurity types

1. Solid particles: metal wear debris, dust, fiber, etc. (particle size ranges from a few microns to millimeters).

2. Water: free water or emulsified water.

3. Gel/sludge: oil oxidation products.

4. Other oils: mixed pollution of different oils.

iltration methods and equipment

1. Mechanical filtration (for solid particles)

- Equipment:

- Filter element:

- Use paper, metal mesh, or glass fiber filter element, with an accuracy of 1~100μm.

- Suitable for hydraulic oil and lubricating oil (such as regular maintenance of the excavator hydraulic system).

- Bag filter:

- Handle large flow oil, with an accuracy of 5~50μm (such as batch filtration of gearbox oil).

- Self-cleaning filter:

- With a scraper or backwash function, reduce downtime (such as a continuous production line in a steel mill).

- Key points of operation:

- ｒｅｐｌａｃｅ the filter element regularly to avoid excessive pressure difference, causing filter element rupture.

- The filter element accuracy should match the equipment requirements (such as a servo valve requires NAS level 5 cleanliness).

2. Centrifugal separation (solid particles + water)

- Principle: Use centrifugal force to separate impurities and water with a density greater than oil.

- Equipment:

- Disc centrifuge: high-speed rotation (such as ship diesel engine oil purification).

- Tubular centrifuge: handles high-viscosity oil (such as rolling oil recovery).

- Advantages: no consumables are required, suitable for highly polluted oil.

3. Vacuum dehydration (for water)

- Equipment: vacuum oil filter

- Evaporate water through heating (60~70℃) + negative pressure, and filter particles at the same time.

- Applicable scenarios: transformer insulating oil, turbine oil (water content must be ≤50ppm).

4. Adsorption filtration (colloid/trace impurities)

- Materials:

- Activated clay: adsorption of oxidation products (such as the regeneration of old lubricating oil).

- Silica gel/molecular sieve: deep water removal (such as aviation hydraulic oil).

- Electrostatic adsorption: used for ultra-fine filtration (such as precision instrument oil).

5. Coagulation separation (oil-water emulsion)

- Equipment: Coagulation oil filter

- First coalesce tiny water droplets, then separate through a hydrophobic filter element (such as cutting fluid purification).

Basis for selecting the filtration system

| Parameters | Considerations | Examples |

|----------------|-------------------------------------|-----------------------------|

| Oil type | Viscosity, chemical stability | High-viscosity gear oil needs to be heated to reduce viscosity before filtering |

| Impurity characteristics | Particle size, water content, whether emulsified | Emulsified oil needs to be demulsified first (add centrifuge or chemical agent) |

| Flow requirements | Online filtration for continuous production, offline for intermittent | Circulating filtration system for injection molding machine |

| Cleanliness standard | Refer to ISO 4406 or NAS 1638 level | Hydraulic system requires NAS level 7 or below |

Precautions

1. Safety:

- Prevent scalding when filtering hot oil, and use explosion-proof vacuum equipment.

2. Compatibility:

- The filter material must be oil-resistant (e.g. nitrile rubber seals are not suitable for phosphate ester hydraulic oil).

3. Environmental protection:

- Waste filter elements are treated as hazardous waste (when containing heavy metals).

Industry application cases

- Wind power gearbox: online filtration system + moisture sensor, real-time monitoring.

- Injection molding machine: magnetic filter + 10μm filter element combination to capture metal chips and dust.