nas 1683and iso4406[1]清洁度标准

GreenOil Standard

Date: 15-12-2005

Saved as: Technical Paper 004

Technical Paper 004

Particle Contamination ISO4406 and NAS1638

Page 1 af 3

Working with ISO4406 and NAS 1638

Particle contamination in oil is specified from particle count.

Two basic standards the ISO and NAS systems are com-monly used as contamination reference. The two cleanliness

standards can not be directly compared or converted, as the

basic principles within the two systems differ to much. This

is explained in the next pages.

Many factors influence lifetime and demands to fluid quality.

High reliability systems enhance demands to quality, and

high pressure systems and heavy bearing load increase de-mands.

The last three columns of the tables indicate the range of the

GreenOil filter system. Although the filters may be put into

However, the following tables gives some rough guidelines

service in many application, parameters as fluid volume and

of common practice for setting targets of cleanliness levels in

viscosity should be taken into consideration before expecta-different 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.

Hydraulic Equipment and Components Minimum

Pressure Range Class Requirement

GreenOil

Filter Inserts

H T M

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

ISO 4406 NAS 1638

14/12/9

16/14/11

17/15/12

18/16/13

18/16/13

19/17/14

20/18/15

4

5

6

7

7

8

9

ISO

10/6

NAS

3

Gear pump and motors,

Medium pressure 50-150 bar

Cylinders and Flow Control

Low pressure 0-50 bar

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

20/18/15

20/18/15

21/19/15

4

5

6

7

8

9

9

10

ISO

14/11

NAS

5

Heavy duty gearboxes

Typical new lubrication oil

Typical in-line filtration

ISO

16/12

NAS

7

Page 2

Technical Paper 004

Introduction

Contamination in oil is specified from particle count. Two

basic methods are used:

Laser based particle count analysis equipment gives directly

information on particle sizes (micron= u) and figures within

specified size ranges.

The other method utilize filtering an oil sample through an

very fine mesh filter paper. The particles on the surface of

the filter paper is then monitored in a microscope and com-pared to standard contamination pictures to indicate the de-gree of contamination.

NAS 1638

Classes Particle Classes Size Range per 100 ml

00

0

1

2

3

4

5

6

7

8

9

10

11

12

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

25 to

50

4

8

16

32

63

126

253

506

1,012

50 to

> 100

100

1

2

3

6

11

22

45

90

180

360

720

0

0

1

1

2

4

8

16

32

64

128

256

512

1024

Contamination classes

Instead of specifying particle counts contamination is sepa-rated into classes defined in two major systems ISO

(International Standard Organisation) and NAS (National Air-space Standard). Each class defines a range of counts within

an exponential scale.

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 let’s look at the two sys-tems.

11,400 2,025

22,800 4,050

45,600 8,100 1,440

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.

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-tamination which has really many small particles and fever

big particles. The sidebar example shows a typical oil analy-sis with counts divided in the 5 classes. As seen the classes

ranges from 3 to 6, however, the resulting NAS class is de-fined 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”.

NAS analysis example

Particle range

5-15 u

15-25 u

25-50 u

50-100 u

>100 u

Resulting class

Counts

8450

11982

312

46

2

Class

6

5

6

6

3

6

Technical Paper 004

Page 3

ISO 4406

The ISO system is not as practical orientated as the NAS sys-tem. First of all it consists of 2 or 3 figures. Each figure de-fine a class within a size range. A typical ISO 4406 oil test

will be indicated as:

17/15/12

Particles > 2 u

Particles > 5 u

Particles >15 u

As seen particles less than 2 u are omitted. The original

ISO4406 operated with only two digits omitting counts below

5 u. This standard is still widely accepted, though it does not

relieve the same information as the newer 3 digit ISO version.

15/12

Particles > 5 u

Particles > 15 u

The cleanliness levels represent the particle counts as shown

in the table.

(Not to get stuck in mathematics: the class represents powers

of the numeral 2. A cleanliness level 15 indicates counts be-tween 214 (16,383) and 215 (32,768) for a sample of 100 ml

fluid).

The sidebar example will be classified “ISO4406 17/15/12”

ISO 4406

Class Number 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

0.25

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

0.5

24

23

22

21

20

19

18

17

16

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

00

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.

In practice the great advantage of the NAS system is that con-tamination is identified by only one class number. For identi-fying contamination sources this could be a limitation which

does not apply as much for the ISO system which is more

open yet complicated.

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.

ISO analysis example: 17/15/12

Particle range

<2 u

5-15 u

15-25 u

25-50 u

50-100 u

>100 u

Counts

96,050

23,263

3,150

256

16

3

Class

17

15

12