Lube Tips

Book Bits
Inspection of Working Surfaces
From "The Lubrication Field Test and Inspection Guide".

Working surfaces include gears, bearings, cams, valve components, and pistons. These surfaces experience rolling and/ or sliding tribological contracts during operation. During routine PM's and repairs they should be examined for corrosion, abrasion, varnish, burnishing, denting, cavitation, galling, pitting, fretting, tempering, fatigue, etc. Many of these problems are related. For instance, a highly polished surface may be caused by an overly aggressive EP additive or high concentrations of abrasive fines in the oil.

Today's Tip
When checking differential filter clogging indicators, also ensure that the pilot holes in the filter body (the ones that feed the indicator with oil pressure) are clear of debris. This helps ensure you are receiving the correct signal. (Submitted by Tim Monk, regional filtration specialist, Wyko Fluid Power Services. Thanks Tim!)

Q & A
Motor Rebuilder Grease Compatibility
"We recently switched electric motor rebuild shops. Since switching, a number of bearings have failed, typically just a few months after putting the motor back into service. For the most part, these failures have been attributable to inadequate lubrication. On closer inspection, the grease appeared to have thinned-out to almost a liquid consistency. We suspected that the rebuild shop was using a grease inferior to our electric motor grease, but they assure us they are using a premium-quality synthetic grease. What is your opinion?"

Without more details, it's hard to attribute an exact root cause. However with greases, one of the most commonly encountered problems is incompatibility between different types of grease made from different thickeners.

For electric motors, the most commonly used greases are made either from a lithium complex soap thickener or polyurea material. While both polyurea and Li complex-based greases can be used in this application, the two are usually considered to be incompatible with each other and should not be mixed unless proper compatibility testing has been performed.

To avoid these types of problems, it is advisable to request that the rebuild shop use the same grease that you plan to use to re-grease the bearings, or at the very least, indicate the exact type and brand of grease being used, so that you can determine if there are any serious compatibility issues between the two greases.

It is often advisable to provide a tube of grease to the rebuild shop whenever a motor is sent to rebuild to avoid these issues.

Mark Barnes, senior technical consultant, Noria Corporation

Book Bits
Additives for Heavier Loads
From the book "Practical Lubrication for Industrial Facilities":

There are different degrees of severity under which boundary lubrication conditions prevail. Some are only moderate, others extreme. Boundary conditions are met by a variety of special lubricants with properties corresponding to the severity of the particular application. These properties are derived from various additives contained in the oil, some singly, some in combination with other additives. Their effect is to increase the load- carrying ability of the oil.

Where loads are only mildly severe, an additive of the class known as oiliness agents or film-strength additives is applicable. Worm-gear and pneumatic-tool lubricants are often fortified with these types of agents. Where loads are moderately severe, anti-wear agents or mild EP additives are used. These additives are particularly desirable in hydraulic oils and engine oils. For more heavily loaded parts, a more potent class of additives is required; these are called extreme pressure (EP) agents.

Today's Tip
In a refinery, you can use a hot steam turbine case for a quick crackle test to assess the presence of water in oil. This works just as well as a hot plate. (Tip submitted by Randy Hardin, Reliability Tech, Phillips Petroleum Co.)

Q & A
Varying Viscosities
"We are using an onsite viscometer to measure viscosity at 40 °C. At the same time, our lube supplier is testing samples from the same system regularly. However, our viscosity numbers are often up to 10 percent different from the lube suppliers. What are we doing wrong?"

Because the viscosity of an oil is probably its single most important property, it makes sense to measure viscosity frequently, using onsite test equipment. However, like all onsite equipment, it's important to understand how these instruments work and their relative strengths and weaknesses.

When it comes to viscosity, there are two determinable parameters, absolute and kinematic viscosity. Kinematic viscosity measures the resistance of an oil to flow and shear under gravity, such as oil flowing through a funnel. Absolute viscosity, on the other hand, determines an oil's internal resistance to flow and shear. To visualize absolute viscosity, imagine the force needed to stir an oil using a metal rod.

The viscosity reported by your lube supplier and oil analysis lab is likely the kinematic viscosity, as determined by ASTM D445. There are two main reasons why your onsite measurements may not correlate directly with the lab data.

First, most onsite test equipment actually measures absolute viscosity, but calculates the kinematic viscosity by dividing absolute viscosity by density. Because the onsite viscometers don't actually measure density but rather estimate it from the oil's spec sheets, an error can occur when translating absolute viscosity into kinematic viscosity. The measure of the absolute viscosity is correct, but because the density of the oil is only estimated, the conversion to kinematic viscosity can become overstated. Contamination and oxidation, among other things, can cause a rise in the density of used oil.

Second, if your onsite instrument does not heat the oil to 40 °C, and most do not, you are likely determining the oil's viscosity at the temperature of the onsite lab (typically in the 20°C - 25°C range), and extrapolating, again using a software algorithm to determine the viscosity at 40°C. This extrapolation can also introduce errors into the reported measurement due to changes in viscosity index of the used oil.

Despite these limitations (which are actually not negatives), used properly, onsite viscometers make very valuable additions to any onsite test program. As a general rule, always baseline your new oils using your own onsite viscometer to determine nonconforming used oil viscosities quickly and simply.

Mark Barnes, Senior Technical Consultant, Noria Corporation

Up Front
The Red-Headed Stepchild of Lubrication

It isn't pretty and it doesn't smell very good. You probably don't treasure or care for it like your new chrome-finished alloy wrench set. You might call it the red-headed stepchild of the lubrication industry. Of course, it's the grease gun.

If you're working toward lubrication best practice, don't overlook proper grease gun use and management. After all, the grease gun is one of the most widely used tools in lubrication and it takes care of you a lot more than you take care of it.

There are many important aspects to grease gun management. For example, do you know how many grams of grease per stroke your lever-style grease guns produce? You could find that it varies considerably from gun-to-gun.

How are you storing your grease gun? Do you wipe-off the nozzle prior to use? Are contaminants being introduced when you load new grease into the gun? Are guns labeled or marked with the type of grease they hold?

You'll find a great article on this topic in the upcoming issue of Machinery Lubrication Magazine. If you aren't receiving ML Magazine, be sure to sign up for your free subscription if you live in the U.S., Canada or Europe.

Mike Ramsey
mramsey@noria.com

Book Bits
From "How to Establish a Win-Win Relationship With Your Oil Analysis Lab":

You Get What You Pay For

Large corporate users should avoid the temptation of buying oil analysis services by going out on bid and buying from the lowest bidder. What message is this sending the lab about the value assigned to quality and service? A company should be focused on cost savings springing from the value that a quality oil analysis program creates, such as the reduction of operating costs and maximizing machine reliability.

It is never wise to push a laboratory on price to the realm of unprofitablity. This takes the lab out of the comfort zone as the service provider and puts stress in the business relationship. The concept that "you always get what you pay for" rest in the minds of those locked into such low-margin contracts. And, when it comes to oil analysis, end-users should take the view that no data is preferred to unreliable or untimely data. It is a basic principle that the lab must be in a profitable relationship to be motivated and stay viable as a value-producing business entity.

Today's Tip
Grease may be used for the lubrication of as many as 90 percent of all rolling element bearings. There are a number of cases, particularly in pump and compressor applications, where there is a requirement for low-noise generation in bearings. The noise generated by the grease is generally originating from the concentration of solid particles in the grease. If the total number of particles can be reduced, then bearings will operate quieter.

There are a number of specialty grease manufacturers who can supply these low-noise greases, and as an added bonus, your bearing will also give longer operating life as this is also highly dependent on cleanliness of the lubricant. Procedures for determining the solid contaminants in grease include ASTM D1404 and DIN 51 813. In the DIN procedure, a sample of grease is pressed through a mesh screen and the solids are weighed. Some grease manufacturers have modified the procedure using finer mesh sizes (down to 1.2 microns). Low noise greases generally have a maximum of 300 mg of particles over 1.2 microns with some products as low as 100 mg! (Tip submitted by Derek Peasley, FAG Bearing Europe)