Nas and Iso

GreenOil Standard
Date: 15-12-2005
Saved as: Technical Paper 004
Technical Paper 004 Particle Contamination ISO4406 and NAS1638

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Working with ISO4406 and NAS 1638

Particle contamination in oil is specified from particle count. factors influence lifetime and demands to fluid quality. Many Two basic standards the ISO and NAS systems are com- High reliability systems enhance demands to quality, and monly used as contamination reference. The two cleanliness pressure systems and heavy bearing load increase dehigh standards can not be directly compared or converted, as the mands. basic principles within the two systems differ to much. This The last three columns of the tables indicate the range of the is explained in the next pages. GreenOil filter system. Although the filters may be put into service in many application, parameters as fluid volume andHowever, the following tables gives some rough guidelines of common practice for setting targets of cleanliness levels in viscosity should be taken into consideration before expectadifferent systems. As seen both ISO 4406 and NAS 1638 are tions to contamination limits are set. represented. These guidelines are minimum fluid cleanliness levels required for an acceptable lifetime of equipment and components. GreenOil
Hydraulic Equipment and ComponentsMinimum Pressure RangeClass Requirement Filter Inserts T ISO 4406 NAS 1638 Silt sensitive, aerospace, robots, High pressure 250-400 bar Servo systems, injection moulding, High pressure 250-400 bar Proportional and flow valves, High pressure 250-400 bar Piston pumps and motors, Normal pressure 150-250 bar Typical new hydraulic oil 14/12/9 16/14/11 17/15/12 18/16/13 18/16/13 Gear pump and motors, Medium pressure 50-150 bar Cylinders and Flow Control Low pressure 0-50 bar 19/17/14 20/18/15 4 5 6 7 7 8 9 ISO 10/6 NAS 3 H M
Lubrication Oil Equipment and Components Ball bearings, turbine oils, Small and medium gearboxes Roller bearings Transmission gearboxes Journal bearings Industrial gearboxes Mobile equipment and gearboxes Paper mill Diesel engine lubrication
14/12/9 16/14/11 17/15/12 18/16/13 19/17/14
4 5 6 7 8 9 9 10 NAS 7 NAS 5 ISO 14/11
Heavy duty gearboxes Typical new lubrication oil Typical in-line filtration
ISO 16/12
20/18/15 20/18/15 21/19/15
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Technical Paper 004
Introduction
NAS 1638
Particle Classes Size Range per 100 ml 5 to 15 125 250 500 1,000 2,000 4,000 8,000 16,000 32,000 64,000 128,000 256,000 512,000 15 to 25 22 44 89 178 356 712 1,425 2,850 5,700 11,400 22,800 45,600 25 to 50 4 8 16 32 63 126 253 506 1,012 2,025 4,050 8,100 50 to 100 1 2 3 6 11 22 45 90 180 360 720 1,440 > 100 0 0 1 1 2 4 8 16 32 64 128 256 512 1024
Contamination in oil is specified from particle count. TwoClasses basic methods are used: Laser based particle count analysis equipment gives directly information on particle sizes (micron= u) and figures within00 specified size ranges.
0
The other method utilize filtering an oil sample through an 1 very fine mesh filter paper. The particles on the surface of the filter paper is then monitored in a microscope and com- 2 pared to standard contamination pictures to indicate the 3 de4 gree of contamination.
5 6 7
Contamination classes
Instead of specifying particle counts contamination is sepa8 rated into classes defined in two major systems ISO (International Standard Organisation) and NAS (National Air-9 space Standard). Each class defines a range of counts within 10 an exponential scale.
11 12 Unfortunately, the two systems are not identical and can not be converted in simple mathematics. However, some simple guidelines can be given. First of all lets look at the two systems.
91,200 16,200 2,880
1,024,000 182,400 32,400 5,760
NAS1638
The NAS system divides particles in 5 ranges. Furthermore, the NAS system specify different counts within each particle range to score a specific class.
NAS analysis example Particle range 5-15 u 15-25 u 25-50 u 50-100 u Counts 8450 11982 312 46 2 Class 6 5 6 6 3 6
In practice oil samples will show up to gain almost same NAS class rating within the different particle ranges. The system is designed to match the most common found con>100 u tamination which has really many small particles and fever Resulting class big particles. The sidebar example shows a typical oil analysis with counts divided in the 5 classes. As seen the classes ranges from 3 to 6, however, the resulting NAS class is defined as the particle count with the highest (worse) score, and only this class is specified. The sidebar example will be classified as NAS1638 class 6.
Technical Paper 004
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ISO 4406
ISO 4406
Number of particles per 100 ml More Than 8,000,000 4,000,000 2,000,000 1,000,000 500,000 250,000 130,000 64,000 32,000 16,000 8,000 4,000 2,000 1,000 500 250 130 64 32 16 8 4 2 1 0.5 Up to and Including 1,600,000 8,000,000 4,000,000 2,000,000 1,000,000 500,000 250,000 130,000 64,000 32,000 16,000 8,000 4,000 2,000 1,000 500 250 130 64 32 16 8 4 2 1
The ISO system is not as practical orientated as the NAS Class Number system. First of all it consists of 2 or 3 figures. Each figure define a class within a size range. A typical ISO 4406 oil test will be indicated as: 24
23 22 21 Particles > 2 u 20 19 Particles > 5 u 18 17 Particles >15 u 16 15 14 As seen particles less than 2 u are omitted. The original 13 ISO4406 operated with only two digits omitting counts below 12 5 u. This standard is still widely accepted, though it does not 11 relieve the same information as the newer 3 digit ISO version. 10 9 15/12 8 7 Particles > 5 u 6 5 Particles > 15 u 4 3 2 The cleanliness levels represent the particle counts as shown 1 in the table. 0 00
17/15/12
(Not to get stuck in mathematics: the class represents powers of the numeral 2. A cleanliness level 15 indicates counts between 214 (16,383) and 215 (32,768) for a sample of 100 ml fluid). The sidebar example will be classified ISO4406 17/15/12
NAS and ISO

To conclude: NAS and ISO can not be compared directly. As seen both NAS and ISO operates exponentially. In both systems, the particle counts must be halved to reduce the class or cleanliness level one digit.
0.25
0.5
ISO analysis example: 17/15/12 Counts 96,050 23,263 3,150 256 16 3 Class 17 15
In practice the great advantage of the NAS system is that contamination is identified by only one class number. For identi- Particle range <2 u fying contamination sources this could be a limitation which does not apply as much for the ISO system which is more 5-15 u open yet complicated. 15-25 u The NAS and ISO 2-digit systems does not take particles less than 5 u into consideration. The ISO 3-digit system monitors down to 2 u particles. The ISO system has the same class definition throughout the particle ranges. The NAS system has different definition of class within each particle range.
25-50 u 50-100 u >100 u
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GreenOil Standard

Technical Paper 004 Particle Contamination ISO4406 and NAS1638

Working with ISO4406 and NAS 1638

14/12/9 16/14/11 17/15/12 18/16/13 19/17/14

4 5 6 7 8 9 9 10 NAS 7 NAS 5 ISO 14/11

20/18/15 20/18/15 21/19/15

Technical Paper 004

91,200 16,200 2,880

1,024,000 182,400 32,400 5,760

Technical Paper 004

NAS and ISO

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