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.