MACHINERY LUBRICATION- INDIA NOVEMBER-DECEMBER 2019 | Page 30

BACK PAGE BASICS
NUMBER OF PARTICLES PER mL
SAE AS4059 Rev. E (Cleanliness Classes for Cumulative Counts – Particles per 100 mL)
(1) >1 μm >5 μm >15 μm >25 μm >50 μm >100 μm
More than Up to and
Including Range
Number (2) >4 μm >6 μm >14 μm >21 μm >38 μm >70 μm
5,000,000 10,000,000 30 Size Code
Classes A B C D E F
2,500,000 5,000,000 29 000 195 76 14 3 1 0
1,300,000 2,500,000 28 00 390 152 27 5 1 0
640,000 1,300,000 27 0 780 304 54 10 2 0
320,000 640,000 26 1 1560 609 109 20 4 1
160,000 320,000 25 2 3120 1217 217 39 7 1
80,000 160,000 24 3 6250 2432 432 76 13 2
40,000 80,000 23 4 12500 4864 864 152 26 4
20,000 40,000 22 5 25000 9731 1731 306 53 8
10,000 20,000 21 6 50000 19462 3462 612 106 16
5,000 10,000 20 7 100000 38924 6924 1224 212 32
2,500 5,000 19 8 200000 77849 13849 2449 424 64
1,300 2,500 18 9 400000 155698 27698 4898 848 128
640 1,300 17 10 800000 311396 55396 9796 1696 256
320 640 16 11 1600000 622792 110792 19592 3392 512
160 320 15 12 3200000 1245584 221584 39184 6784 1024
80 160 14 40 80 13 20 40 12 10 20 11 5 10 10 2.5 5 9 1.3 2.5 8 0.64 1.3 7 0.32 0.64 6 0.16 0.32 5 0.08 0.16 4 0.04 0.08 3 0.02 0.04 2 0.01 0.02 1
An ISO 4406 Chart
not the same. Depending on the type of
APC used by the laboratory, there were
inconsistencies when measuring the same
size particles. What was a 5-micron particle
in an optical APC (calibrated to ISO 4402)
28 | November - December 2019 |
(1) Size range, optical microscope, based on longest dimension as measured per
ARP598 or APC calibrated per ISO 4402:1991
(2) Size range, APC calibrated per ISO 11171 or electron microscope, based on
projected area equivalent diameter
(3) Classes and contamination limits identical to NAS 1638
was a 6-micron particle using an SEM.
This led to the need for a new calibration
medium and standard, thus the creation of
ISO 11171 for calibration and ISO 4406:99
for reporting. ISO was presented with a
major decision to make: Should there be
two standards based on the type of APC
and method of calibration, or should the
current standard be adjusted so it would be
compatible with both calibration methods
and APC types? It was decided that two
standards would create confusion, so
the alterative of developing a compatible
standard was accepted.
With subsequent accuracy improvements
in microscope technologies, ISO realized
that the reporting of particles smaller than
5 microns was becoming more reliable.
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Thus, a third micron size was added as an
option to the cleanliness code.
What It All Means
ISO concluded that the concentration of
smaller particles was of greater concern
than the larger ones. The organization
determined that 4-, 6- and 14-micron
particles provided the best representation
of the particles closest to a lubricant’s film
thickness. These particle sizes cause the
most damage to moving surfaces and thus
should be closely monitored.
The method used to calibrate the automatic
particle counter should also be considered.
This rarely will be presented in any oil
analysis report, so you will need to contact
your lab or equipment manufacturer to