Machinery Lubrication

Machinery Lubrication May June 2014

Machinery Lubrication magazine published by Noria Corporation

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www.machinerylubrication.com | May - June 2014 | 55 analysis is conducted to track wear metal concentrations for trending and troubleshooting. Among the metals that are tested for include iron, nickel, sodium, lead, silver, phosphorus, copper, tin, zinc, chro- mium, silicon, calcium, aluminum, boron and barium. The National Aerospace Standard (NAS) classification reference is to the NAS 1638 standard, which was used to indicate particle counts. It has been discontinued and replaced with SAE AS4059E. Inherent Problems The problems associated with using clear and bright as accep- tance criteria for lubricants in operating machinery should be fairly obvious. "Clear" refers to the lack of particles, which are generally measured in microns. One micron is 39 millionths of an inch. The human eye can see particles down to the 40-micron range. A human hair is between 30 and 120 microns. The oil film on a journal bearing runs from 5 to 200 microns, but on rolling-element bear- ings, it is usually less than 1 micron. The table on page 56 offers a comparison of clearances for various components. Suffice it to say, it would be nearly impossible to see the particles that are doing the damage. Particles in the size range of the working clearance cause the most damage. Several of the larger pieces of marine equipment use journal bearings, so to a certain degree they are designed to be more forgiving of the smaller, submicron parti- cles. However, in the case of rolling-element bearings, it is a different story. As previously stated, the lubricant film in rolling-element bearings is usually less than 1 micron. According to SKF, the cleaner the lubricant, the longer bearings will last. In fact, the bearing company has gone so far as to state, "Bearings can have an infinite life when particles larger than the lubricant film are removed." SKF has conducted case studies and determined that roughly 70 CLASS Maximum Particles/100mL in Specified Size Ranges (┬Ám) 5-15 15-25 25-50 50-100 >100 00 125 22 4 1 0 0 250 44 8 2 0 1 500 89 16 3 1 2 1,000 178 32 6 1 3 2,000 356 63 11 2 4 4,000 712 126 22 4 5 8,000 1,425 253 45 8 6 16,000 2,850 506 90 16 7 32,000 5,700 1,012 180 32 8 64,000 11,400 2,025 360 64 9 128,000 22,800 4,050 720 128 10 256,000 45,600 8,100 1,440 256 11 512,000 91,200 16,200 2,880 512 12 1,024,000 182,400 32,400 5,760 1,024 The NAS 1638 Contamination Classification System, which has been discontinued and replaced with SAE AS4059E

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