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Book Bits

From "The Practical Handbook of Machinery Lubrication":

This section of the book identifies five reasons for regular and timely oil change intervals. Here is reason number 3:

ADDITIVE DEPLETION. When base oils are formulated and blended with additives, these elements are slowly "used up" in performing their functions. Anti-wear and extreme pressure agents are depleted as they are deposited on metal surfaces. Detergents and dispersants are used up as they continue to counteract various contaminant particles in the oil. Additives which protect against acid attacks, are depleted as they counteract acid formations within the oil.

The additive package will eventually become depleted or ineffective, if the oil is allowed to remain in service for extended periods.

Click here for more information about The Practical Handbook of Machinery Lubrication.

Today's Tip

• Traditionally 130°F (55°C) has been considered the ideal operating temperature for a gear box. However, for today's equipment that would be considered on the low side. Cincinnati Milacron suggests 160°F (70°C) as maximum on its extruder gear boxes. When gearboxes overheat, and ambient conditions are not the cause, there are two possible sources:

  A: Metal-to-metal contact
  B: Fluid friction, or churning of the lubricant

  If equipment inspection or fluid analysis indicate excessive wear, then metal contact is a problem. In this case consider a lubricant of higher viscosity. Fluids with higher extreme pressure resistance (such as measured by the Four Ball test) can also be of value.

  If wear is not a problem, then high fluid viscosity may be the cause. However, before switching to a lower viscosity check with the equipment and lubricant suppliers. Lowering the viscosity may increase metal contact and wear. In this case consider using a synthetic lubricant. Synthetics can often lower the temperature. Even if the temperature remains the same, the synthetic fluid will typically resist oxidation and deterioration better than mineral oil. (Tip submitted by Tom Muckian, Whitmore's Technical Services. Thanks Tom!)

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Q & A

"I was told that a good way to monitor the health of your machines is to routinely inspect used oil filters when they are changed. How is this done?"

For many machines the filter is the final resting place for contaminant and wear particles. As such, there is somewhat of a recorded history that is captured within the filter. To get these particles in a suitable visible form, cut a section of the filter media, say four square inches. Always take this section from the same place on the pleated element.

Next, place the section of used filter media in a small beaker of superclean solvent, such as mineral spirits or kerosene. The beaker is then placed in an ultrasonic bath for four minutes. The membrane should be carefully lifted using laboratory forceps, shaken in the solvent several times and then removed (leaving the particles behind in the solvent). Next follow the procedure described in the articles (links that follow) to prepare a patch for analysis of the particles under a common microscope: Article 1 and Article 2.

In addition to microscopic analysis, the patch with the particles can also be examined by XRF spectroscopy. In examining the particles on the patch consider the hours/months the filter was in service, amount of makeup oil added, timing of last oil change, quality of system filtration, and machine application. One unique advantage of examining wear particles deposited on a used filter is the fact that most of these particles are in their original shape; that is, they haven't been reworked (crushed, etc.) by the machines working surfaces and frictional contacts.

Practice makes perfect. By using this method routinely on critical equipment it is possible to quickly identify abnormal wear conditions that may be occurring.

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