Machinery Lubrication magazine published by Noria Corporation
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blockage data from the third-party laboratory was reported using the ISO 4406 reporting standard. For all SEM data, this reporting standard was maintained, but it was also decided to report particles larger than 2 microns to provide an additional perspective on the data. In the first sample, the particle count was fairly comparable between the SEM and pore blockage results. In the second and third samples, the sizes and counts of the actual particles varied. This could be attributed to sample representativeness between the two samples that were divided for submission to the lab. While this seems likely, it could indicate some of the differences in the testing methodologies, including sample preparation, and particle sizing techniques. For example, pore blockage tech- nology (ISO 21018-3) does not actually count individual parti- cles but rather estimates the particle size distribution using an algorithm based on a measured flow decay across a membrane or a rise in differen- tial pressure. A total number of particles is calculated using an algorithm derived from exten- sive empirical testing. On the other hand, SEM detects, scans and measures each particle individually, providing size analyses accurate to 0.5 microns. In all three samples, the largest discrepancies between the two technologies came in the smaller sized particles. While the ISO standard requires that only particles larger than 4 microns are reported, the SEM data could demonstrate the limitations of the pore blockage method as the particle sizes get smaller. Coinci- dently, this same range of particle sizes (between 2 and 4 microns) would also represent the particles reported by the ICP results. Chemical Composition results Table 3 presents the chemical composition data for all three www.machinerylubrication.com | January - February 2014 31 4406 ISO BIN SAMPLE 1 SAMPLE 2 SAMPLE 3 SEM POrE BLOCKAGE SEM POrE BLOCKAGE SEM POrE BLOCKAGE >2 µm 9,226 16,180 3,198 >4 µm 4,254 5,513 5,898 10,096 912 4,018 >6 µm 2,228 2,144 2,674 3,926 404 1,562 >14 µm 296 163 112 299 66 119 >50 µm 12 7 4 13 0 5 >100 µm 8 0 0 0 0 0 Note: Data for all samples are normalized to 1 ml Table 2. Comparison of SEM and pore blockage data for three samples