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Know-how
Oil Cleanliness Codes
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The contamination level in hydraulic and lubricating oils is characterized by the so called oil cleanliness code.
Due to their shape, fit, dirt sensitivity, function and operating method different components tolerate different contamination levels of operating fluids. In order to meet this circumstance, by means of the contamination's particle distribution the contamination level of operating liquids is divided in different classifications, the so-called oil cleanliness codes.
The most frequently used classification for oil cleanliness codes in fluid power is defined by the international standard ISO 4406. Another important standard for oil cleanliness codes is represented by the SAE 4059 which replaces the recently valid NAS 1638.
Oil cleanliness codes as per ISO 4406
(excerpt from ISO 4406, issue 1999)
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| From | To | ISO Code | | 64 | 130 | 7 | | 130 | 250 | 8 | | 250 | 500 | 9 | | 500 | 1.000 | 10 | | 1.000 | 2.000 | 11 | | 2.000 | 4.000 | 12 | | 4.000 | 8.000 | 13 | | 8.000 | 16.000 | 14 | | 16.000 | 32.000 | 15 | | 32.000 | 64.000 | 16 | | 64.000 | 130.000 | 17 | | 130.000 | 250.000 | 18 | | 250.000 | 500.000 | 19 | | 500.000 | 1.000.000 | 20 | | 1.000.000 | 2.000.000 | 21 | | 2.000.000 | 4.000.000 | 22 | | 4.000.000 | 8.000.000 | 23 |
The classification of the cleanliness level
The oil cleanliness codes according to ISO 4406 may measured either by automatic or microscopically particle counting.
Automatic particle counting
The classification of the cleanliness level of an hydraulic oil consists usually out of an 3-digit code indicating the cleanliness code for particles > 4µm , > 6µm und > 14 µm
Example:
The oil sample taken from a hydraulic system was measured with an automatic particle counter.
The result of the particle count is as follows:
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| 92.350 | Particles > 4 µm (c) | 17 | | 17.812 | Particle > 6 µm (c) | 15 | | 1.219 | Particle > 14 µm (c) | 11 |
Result: According to ISO 4406 this hydraulic oil has an oil cleanliness of: ISO 17 / 15 / 11.
If an automatic particle counter is used during the analysis of an oil sample the above mentioned 3-digit-code is used.
Microscopically particle counting:
Due to its condition an oil sample has to be counted in some cases using a light microscope. In that case a 2-digit-code is used only. This code belongs to all particles > 5µm and >15µm.
Example:
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| 92.350 | Particles > 5 µm | 17 | | 17.812 | Particles > 15 µm | 15 |
Oil cleanliness codes as per SAE AS 4059
(Excerpt)
As an alternative to the ISO 4406 the NAS 1638 was used up to now in fluid power.
This standard has now been replaced by the SAE standard AS 4059.
In contrary to the ISO 4406 this standard does not classify only the fine and silt particles but also coarse particles > 70 µm.
Maximum no. of particles for indicated cleanliness code in 100 ml sample.
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| Calibration NAS 1638 | >1µm | >5µm | >15µm | >25µm | >50µm | >100µm | | Calibration NAS SAE AS 4059 | >4µm | >6µm | >14µm | >21µm | >38µm | >70µm | | Range | A | B | C | D | E | F | | Code 0 | 780 | 304 | 54 | 10 | 2 | 0 | | Code 1 | 1.560 | 609 | 109 | 20 | 4 | 1 | | Code 2 | 3.120 | 1.220 | 217 | 39 | 7 | 1 | | Code 3 | 6.520 | 2.430 | 432 | 76 | 13 | 2 | | Code 4 | 12.500 | 4.860 | 864 | 152 | 26 | 4 | | Code 5 | 25.000 | 9.730 | 1.730 | 306 | 53 | 8 | | Code 6 | 50.000 | 19.500 | 3.460 | 612 | 106 | 16 | | Code 7 | 100.000 | 38.900 | 6.920 | 1.220 | 212 | 32 | | Code 8 | 200.000 | 77.900 | 13.900 | 2.450 | 424 | 64 | | Code 9 | 400.000 | 156.000 | 27.700 | 4.900 | 848 | 128 | | Code 10 | 800.000 | 311.000 | 55.400 | 9.800 | 1.700 | 256 | | Code 11 | 1.600.000 | 623.000 | 111.000 | 19.600 | 3.390 | 512 | | Code 12 | 3.200.000 | 1.250.000 | 222.000 | 39.200 | 6.780 | 1.024 |
The complete standards of ISO 4406 resp. SAE 4059 are distributed through the relating organisations (ISO, SAE) |
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