NAS-1638 Auto Parts Cleanliness Inspection
NAS-1638-1984
is a cleanliness grade standard issued by the American Astronautical
Society, which divides cleanliness into 14 grades according to 5
particle size ranges.
The
particle concentration of each size segment has a fixed range, that is,
the ratio of the number of particles in two adjacent grades is 2, so
this ratio can be used to extrapolate the oil cleanliness of more than
12 grades. In actual operation, according to the distribution of the
measured particle number in 5 size segments, 5 corresponding cleanliness
grades are obtained, and the cleanliness of the oil is determined with
the highest grade. The NAS1638 standard was developed based on the
statistical characteristics of solid particle distribution in
lubricating oils for aircraft hydraulic systems in the 1960s. With the
development of science and technology, the distribution of solid
particles in the hydraulic system lubricating oil has undergone great
changes, especially the large particles larger than 15μm have been
greatly reduced, resulting in the unnecessary setting of the large
particle size segment, which is the international standardization The
purpose and significance of organizing the revision of ISO4406 and
gradually replacing NAS1638. At the same time, the American
Astronautical Society also realized that there are some shortcomings in
the use of the NAS1638 standard, so it has also been improved and has
been revised to AS4509. This standard especially strengthens the control
of small particles, and increases the 000 grade, that is, the particle
size larger than 2 μm is increased. In addition, the particle size is
not divided according to the interval but is classified according to the
upper limit of the size, and the particle count is changed from
interval count to cumulative. count.
