Book Bits
From the book "Lubricants and Lubrication":

Long-life and reliability are the criteria for the commercial vehicle sector. The HD (Heavy Duty) oils have to match these requirements. The predominant requirements are the dispersion of large concentrations of soot particles as well as the neutralization of sulfuric acid combustion by-products. Performance is also judged by piston cleanliness, wear and bore polishing. Oxidation and soot-related deposits, mainly in the top ring groove lead to poor piston evaluations and an increase in wear. This, in turn, leads to the abrasion of the honing patterns in the cylinders, a problem better known as bore polishing. The result is increased oil consumption and poorer piston lubrications because the oil cannot be trapped by the honing rings. Inadequate soot and sludge dispersion as well as chemical corrosion can lead to premature bearing wear. And finally, advanced turbocharged diesel engines have also been evaluated. Blow-by gases always carry some oil mist into the exhaust and turbochargers are very sensitive to unstable oil components.

Today's Tip

Inclined or vertical shafts can lead to grease escaping from the bearing due to gravity. This will eventually lead to lubricant starvation and eventual premature failure of the bearing. Consider using a grease with good adhesive properties of penetration class 2 to 3. In addition a baffle plate, mounted in the housing below the bearing, will help to retain the grease where it is needed - in the bearing. (Tip submitted by Derek Peasley, FAG Sales Europe. Thanks Derek!)

Q & A

"I am aware that many grease thickener types are incompatible when mixed. However, if I use two greases with compatible thickeners, but different brands, how do I know if the additives and base oils are compatible, or does it matter?"

In critical applications it matters. Remember grease is not a thick oil, it's an oil with a thickener. The base oils, viscosities, and additives used in grease can vary considerably, even between general-purpose greases. As such, there may be a loss of performance (antiwear, antioxidation, antirust, etc.). This is a risk that may not be worth taking. Unlike grease thickener incompatibility, the effects of additive incompatibility may be considerably less obvious and contribute to problems over a longer period of time.

Daily Tips

- Antifoam agents, commonly called defoamants, are an additive
used to reduce foaming in oil and hydraulic fluids. They use
silicone to weaken surface bubbles allowing them to quickly
collapse.

The defoamant is not dissolved, but is a suspended micro-
globule (about 10 microns in size). Their performance declines
if the oil is contaminated (water, grease, soaps, etc.)
causing interfacial tension to drop. Decreased performance can
also be expected if the defoamant coalesces or transfers out
of the oil (filtration/settling).

- There are a lot of advantages to hard piping a lube supply
to various machines throughout a facility. Here are some
considerations to keep in mind:

• Cost of components: pumps, valves, piping, volume meters,
  storage containers
• Number of products required for delivery
• Distance from storage to delivery locations
• Exposure to extreme temperatures (cold weather concern)
• Cost benefit from reduced labor required to handle
  inventory
• Cost benefit from reduced labor for hauling lubricants
  to equipment
• Cost benefit from improved oil cleanliness
  

More Great Tips

Today we are going to look at an excerpt from the book
"Identification of Parts Failures." This book has a ton of
great part failure descriptions and photos and covers a variety
of machine types. The following passage is about identifying
piston failures in gasoline engines. For brevity we will focus
on the two lubrication related failures: scuffing and scoring
and corrosive wear.

Identifying Piston Failures in Gasoline Engines

"Although some failures in pistons operating in gasoline engines are the same as in diesel engines, there are enough differences to justify separate groupings.

"The principal causes of piston failures in gasoline engines are:

• Detonation
• Preignition
• Scuffing and scoring
• Corrosive wear
• Physical damage to pistons

SCUFFING AND SCORING

"Scuffing and scoring (adhesive wear) is caused by too much heat. When two metal parts rub and the heat builds up to the welding point, a small deposit or "hot spot" of metal is pulled out and deposited on the cooler surface.

"Scuffing leaves discolored areas on the surface of rings, pistons and cylinder walls.

"Scuffing starts as tiny surface disturbances. If they are not
removed, scuffing spreads and becomes noticeable and more severe. It is then called scoring. Any engine condition which heats rubbing parts to the welding point, or which prevents the transfer of heat from these surfaces, influences scuffing.

"The following are possible causes of scuffing and scoring:

• Improper warm-up
• Lubricating system not functioning
• Cooling system plugged
• Combustion knock and preignition
• Lugging or overloading
• Misaligned connecting rod

"Occasionally an unusual wear pattern results from a misaligned
connecting rod. Contact with cylinder wall shows on the bottom of the skirt at left, and at the ring lands on the right (arrows).
There is also a diagonal wear pattern extending across the skirt
of the piston. This uneven wear is due to a bent or twisted
connecting rod or shaft. When connecting rods are misaligned,
rings do not have proper contact with cylinder wall, pistons wear
rapidly and unevenly, oil consumption is excessive and the engine is prone to scuff or score. Always check rod alignment.

CORROSIVE WEAR

"Corrosive wear shows up as spotted grayish pitted surface on
pistons or cylinder walls.

"The following are possible causes of corrosive wear:

• Leaking coolant
• Cold engine operation or putting engine under load before it has reached operating temperature
• Wrong lubricating oil or dirty oil
• Acids resulting from combustion or the reaction of moisture and sulfur in the lubricating oil

"Other corrosion may be harder to find. If excessive wear is found, and scuffing and scoring are eliminated as causes, suspect corrosive wear."

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.

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!)

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.