In This Issue:

• Up Front: Automatic Lubricator Tip

• Book Bits: Keep Them Clean!

• Today's Tip: The Chain Reaction of Abrasive Wear

• Q & A: Sorting Out Particle Counts
  

Up Front

Automatic Lubricator Tip

We started our company based on minimum staffing levels, and only skilled lubrication personnel performed the greasing of bearings. The intention was that artisans would do the greasing as part of their daily tasks. This was difficult to control, however, because they always had tasks more urgent than lubrication (which could seemingly be postponed for tomorrow and beyond etc.).

We installed 1500 gas-cartridge automatic grease lubricators which would last for one year on the bearings in our plant. One advantage of these lubricators is that personnel must visually check them only once a month to determine whether the grease level is still high enough.

This was until the first bearings started to fail due to lack of lubrication - with enough grease still in the cartridges. Due to relative high ambient temperatures, vibration and the long time between refills, the grease base and oil separated, leaving only the grease base in the lubricator.

After the oil ran out of the lubricators, the higher viscosity of the remaining base caused the lubricators to move much slower, giving the impression that enough grease remained in the cartridge, sufficiently lubricating the bearings.

We learned that automatic grease lubricators need to be watched closely. Use a small cartridge to prevent long times between cartridge refills. Keep meticious record of lubricator lifetime - too slow or too fast movement will both spell trouble. (Submitted by K.W. Heese, Iscor Steel. Thanks K.W.!)

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Book Bits

Keep Them Clean!

From "Lubrication Fundamentals":

An adequate cleaning facility is an oil house essential. Dispensing equipment (grease guns and the like) must be cleaned regularly for proper functioning. Airborne dirt and dust collect quickly on oil wetted surfaces, so oil containers, faucets and similar equipment should be cleaned regularly to remove these contaminants.

More information about "Lubrication Fundamentals".

Today's Tip

• Abrasive wear can cause a chain reaction in lubricated machinery. The typical chain reaction is:

  • Abrasive particles become work-hardened.

  • Work-hardened particles produce more particles.

  • New particles become work-hardened.

  • Chain reaction continues until the particles are removed by filtration, or the machine fails.

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Q & A

Sorting Out Particle Counts

"We typically sets target fluid cleanliness levels of ISO 16/14/11 for our mobile hydraulic systems. We recently received a report that indicated the oil was at 18/16/13, with a visual examination indicating dirt ingression. However, our spectrometric analysis data indicated that the silicon level was only 1 ppm. How can the contamination be dirt if the lab reports only 1 ppm of silicon?"

To answer the question, we need to consider what the two are actually measuring. ISO particle counting measures the particle size distribution in the oil, while spectrometric analysis measures elemental concentrations in parts-per-million. These are in fact two different measurements, which should not be confused.

There are two basic reasons why the two results may not appear to correlate. Firstly, elemental analysis, as measured by ICP (Inductively Coupled Plasma) or RDE (Rotating Disc Electrode), is limited in its sensitivity to particles 3 to 8 microns in size. This size limitation depends on the particle type and instrumentation used. ISO particle counting, on the other hand, measures fluid contamination levels in three size ranges, >4, >6 and >14 microns. Because of this difference in size ranges, the particles counted during a typical ISO particle count will not show up in elemental analysis.

Secondly, ISO particle counting is in general a more sensitive test to dirt contamination than ICP or RDE. To understand this, consider the following: Take a 1 ug "chunk" of material (such as silicon) and dissolve it in 1 g of oil. What is the concentration?

Because a ppm is ug/g (or mg/Kg), the answer is simple, 1 ppm. But what is the particle count? The count is obviously very low, because we only have one particle. Now let's crush the same particle into a thousand pieces. What is the elemental silicon concentration? Obviously crushing the particle doesn't change the mass of material present so the answer is still 1 ppm, but now what's the particle count? By crushing the chunk into a thousand particles, we introduced many smaller particles, causing the ISO particle count to increase significantly.

In fact, assuming a typical particle size distribution, an ISO count of ISO 18/16/13 corresponds to approximately 1 ppm of a material such as silicon, so it's not surprising that your particle count results are not reflected in the elemental analysis.

Mark Barnes, Senior Technical Consultant, Noria Corporation

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