Archive | Lubrication

163

7:54 pm
May 18, 2015
Print Friendly

The Route To Bearing Reliability

Screen Shot 2015-12-18 at 1.54.29 PM

There are no shortcuts, but lubricating correctly makes it easy to follow. The right materials and procedures are key.

Our recent “State of the Lubrication Nation Survey” revealed several roadblocks that prevent many North American industrial sites from moving toward implementation of Good Lubrication Practices (GLP) in their maintenance programs. When such practices aren’t implemented, the reliability of a plant’s equipment and processes can suffer—starting, in many cases, with bearings.

This article addresses several crucial issues involved in the quest to extend bearing life. These issues begin to surface before a bearing even goes into service. For example, when an engineer designs a machine that involves moving parts, he or she is expected to choose the appropriate bearings. Several factors affect this selection, including:

  • Budget
  • Application (radial, axial and planular)
  • Load
  • Speed
  • Space
  • Clearance and fit
  • Length of machine warranty
  • Bearing reliability specification
  • Lubrication entry design and method
  • Expected operating conditions

When a machine goes into service, the reliability baton passes to the end-user maintenance department that must work with the engineer’s final design and an often-vague machine operations and maintenance (O&M) instruction manual that rarely spells out good lubrication instructions. Many maintenance planners will recognize the catch-all instruction “lubricate as necessary,” placing responsibility on the end-user to develop a lubrication strategy suitable for the ambient conditions in which the machine is expected to perform.

Unless the maintenance department literally starves the bearing of lubricant in the first year, most bearings will surpass their warranty period, and the manufacturer probably won’t learn if their design is truly robust and reliable. Ultimately, the design conditions are set, and machine availability and reliability depend on how well the maintenance department understands: 1) bearing design and their lubrication requirements; 2) how machine bearings fail in their working environment; and 3) their ability to design, implement and execute a strategic asset-lubrication program that adequately meets bearing needs.

A noisy bearing  contaminated with paint (Courtesy ENGTECH Industries, Inc.)

A noisy bearing
contaminated with paint (Courtesy ENGTECH Industries, Inc.)

What’s in a bearing?

As highlighted in Part 1 of the article “The Inner Life of Bearings” by reliability expert Neville Sachs, when we think of a bearing, various shapes, sizes and materials come to mind. These components can take on many forms in performing their duty to support sliding or rotating parts.

To recap, sliding contact bearings (commonly known as plain, sleeve or journal bearings) allow full sliding contact between mating surfaces in three specific ways: radially, in which the bearing provides a 360˚support for a rotating shaft or journal; axially, in which the bearing supports any side thrust load from the end of the rotating shaft; and planular, in which a flat bearing surface acts like a slipper to guide moving parts in a straight line.

To help carry the impressed load with minimized friction and wear, a lubricant is introduced into the engineered clearance between the mating surfaces via a specially cut channel to generate hydrodynamic/hydrostatic full fluid film separation of the surfaces to allow them to slide freely over one another. Sliding bearings are most commonly manufactured in yellow metal or composites of brass, bronze and copper, the bearing material designed to be softer than the supported component.

Rolling contact bearings (commonly known as ball bearings, roller bearings and needle bearings) provide a rolling contact that supports both radial and axial thrust—often simultaneously. These bearings are often termed “anti-friction” bearings due to their point contact area, where lightly lubricated rolling elements (balls, rollers and needles) carry the impressed load under an elastohydrodynamic lubricant film.

Rolling-element bearing manufacturers measure the reliability of their bearings using a Load-Life calculation rating, which is known as the L10 rating life. To achieve its reliability design rating, the manufacturer assumes the bearing will be operated within its load-and-speed design limits in a clean operating environment, and that an adequate lubricant film of the correct viscosity is applied on a regular basis (“adequate” meaning a film equal to or greater than the composite roughness of the two mating surfaces). As a result, reliability is the minimum percentage probability of 90% of a group of identical bearings achieving their L10 design life expectancy (operated under identical operating and load conditions). With the advent of cleaner and degassed steels used in rolling-bearing manufacturing, manufacturers are now able to upgrade the L10 rating to L10a designations that promise even higher reliability percentages.

The reality is, many bearings lead a less than ideal life, often subjected to the severest conditions and many forms of abuse within industrial-plant environments. Many maintenance and reliability departments don’t take time to understand the root cause of bearing failures, nor do they implement life-cycle management strategies for these key components.

An over-greased bearing. Maintenance chose not to reset the auto lubricator but to put in place two grease-catchment devices and a PM to empty the grease regularly. (Courtesy ENGTECH Industries, Inc.)

An over-greased bearing. Maintenance chose not to reset the auto lubricator but to put in place two grease-catchment devices and a PM to empty the grease regularly. (Courtesy ENGTECH Industries, Inc.)

The many causes of bearing failure

If asked to project which bearing is most likely to achieve L10 life status in the following scenarios, which would you choose?

Scenario 1: A pillow-block bearing is placed in service in a HEPA-filtered clean-room manufacturing environment. The bearing runs under light load conditions for eight hours per day, is set up using a laser-aligned and balanced drive shaft, and is continually lubricated using an engineered automatic oil lubrication-delivery system.

Scenario 2: The same pillow-block bearing is placed in service in a hot, dirty foundry operating two full shifts per day. The machinery is set up using manual “eye-ball” alignment techniques, and is manually lubricated with a grease gun on a PM schedule with a subjective job task that states “lubricate as required.” 

If you are like most, you will have voted scenario #1 as the likely winner. In reality, both bearings are likely to prematurely fail if maintenance has not understood how failure can occur and planned accordingly to prevent it! The top 10 causes of bearing failures—confirmed through this author’s 40+ years of investigating real-world failures—are as follows:

  • Lack of lubrication training
  • Lack of lubrication-application engineering
  • Poor housekeeping (lack of order and cleanliness)
  • Over-lubrication of bearings
  • Under-lubrication of bearings
  • Use of dirty or contaminated new lubricants
  • Infrequent oil/filter changes
  • Bearing lubricant contaminated with an incompatible lubricant
  • Bearing lubricated with the incorrect lubricant
  • Bearing mounted out of square or misaligned when set up

Note that nine out of 10 items on this list are due directly or indirectly to ineffective lubrication practices.

Taking the path to bearing reliability

The first step to reliability is to stop reacting to failure symptoms. For example, a simple oil leak is not always a failure if the type of shaft seal used is designed to leak. If this is not the case, other causes could include a cross-threaded drain plug, a drain plug refitted with no washer, a plugged breather, a damaged seal or even a porous casting.

By contrast, an oil leak in a hydraulic system can be caused by dirt-contaminated hydraulic oil scoring lapped spools and nicking seals. Both show the same oil-leak symptom, but can have very different root causes. Implementing a root cause analysis of failure (RCAF) program to weed out the real reasons your bearings are failing, and using those findings to implement a strategic lubrication management program will make an excellent first step. Here are other steps to take:

Training

Use your RCAF findings as a kick-start to educate your maintenance staff on the value of good lubrication practices soon to be adopted.

Lubricant choice

Solicit the assistance of a reputable lubricant consultant and/or lubricant manufacturer/supplier to facilitate an engineered lubricant-consolidation program. The purpose will be to determine the most suitable lubricant selection for all your bearings, and picking the correct oil viscosity and additive package designed to work in your ambient conditions that will reduce lubricant degradation and the number of oil changes.

Lubricant contamination

Contaminants are literally “bearing assassins,” the biggest culprits being dirt and water. Contamination avoidance is achievable by implementing a simple housekeeping program designed to keep gearboxes clean of dirt and shielded from water; and dedicated transfer and delivery equipment for each lubricant type, clearly labeled to eliminate dirt contamination and lubricant cross-contamination.

Also, ensure all grease guns and nipples are cleaned before and after use with lint-free rags. And test all bulk fluids to determine their fluid cleanliness and additive package formulation before use to determine if they’ve been delivered in a clean-state specification.

Engineered application

Excessive heat is a common problem found in many manually greased bearings that have received too much grease. Virtually no two grease guns are alike in their grease displacement; a single shot in one can amount to five or more shots in another. Yet a PM task may ask for two shots of grease, which results in over-greasing. Furthermore, a good-hearted maintainer may contribute to the problem by choosing to add an extra “shot or two” in the mistaken belief that more is better!

Bearing cavities are designed to operate with a grease charge of less than 50%.  Filling the cavity until the grease passes by the seal is more than two times the required amount of grease. Excess grease causes internal fluid friction in the bearing. In turn, this creates a significant rise in bearing temperature, resulting in reduced bearing life and a greater increase in energy use. Ensure all grease guns in the plant deliver the same amount of grease displacement.

Navigating your way to bearing reliability is not expensive or difficult. You only need to recognize the value of effective lubrication practice and choose to do it. 

Ken Bannister of EngTech Industries, Inc., is a Lubrication Management Specialist and author of Lubrication for Industry (Industrial Press), and the 28th Edition Machinery’s Handbook Lubrication section (Industrial Press). Contact him at 519-469 9173 or kbannister@engtechindustries.com.

91

7:51 pm
May 18, 2015
Print Friendly

From Our Perspective: Protecting Your Golden Goose

kennewmugBy Ken Bannister, Contributing Editor
kbannister@engtechindustries.com

Who among us is not familiar with Aesop’s Fables? One of my favorites is “The Goose That Laid the Golden Eggs,” a poignant tale of greed and ignorance that has major implications for industrial operations.

The story involves a farmer who was fortunate to own a goose that produced one solid-gold egg every day. In his myopic quest to accumulate even more wealth, the man decided to kill the bird and plunder the treasure source that he believed was in its belly. As he eventually discovered, however, the golden treasure was actually in the eggs themselves, and could only be increased by keeping the goose alive. (The English may have summed up the moral of this story best with the following well-known idiom: “Do not perform a short-sighted action that might destroy the profitability of an asset!”)

Analyze this fable deeper and you will recognize that the farmer ignored the fact that the goose he cared for was the asset that made him profitable: Alas, without the goose, there are no eggs.

With regard to physical assets—like a site’s production machines that are expected to reliably “deliver the goods” per their design specifications, day in and day out—we must care for them on a daily basis. After all, they are really the “golden goose” of a production facility! But are we tending them adequately?

In December 2014, this publication shared the first scorecard for the state of lubrication practices in North American industries. Results were disappointing, with the response indicating a score of 43 out of a possible 100. If accurate, that means, in real terms, that mechanical losses due to ineffective lubrication practices could have cost North America’s plants $1 trillion last year! That’s an unacceptable price tag when virtually every facility is looking internally to cut costs. Plant management, regardless of sector, should be angry about the economic impact of these losses—especially when they are so easily preventable, and with little or no capital outlay.

Lubricants are the life-blood of industrial equipment systems. They should be viewed as a critical component that plays a principal role in the uptime, throughput and rate of quality success of any facility’s operational machinery.

I have toured hundreds of plants over the course of my career and am amazed by the cavalier and reckless attitude toward lubrication that I continue to see. Too many managers remain ill-informed regarding: 1) the benefits of effective lubrication; 2) the staggering cost of ineffective lubrication; and 3) how inexpensive it is to implement an engineered lubrication-management program.

Management can take this to the bank: Placing unmarked grease guns full of unmarked lubricants into the hands of untrained personnel and telling them to manually fire at will into remote bearing points does not constitute an effective lubrication program. Instead of saving money, this type of shortsighted approach will destroy the profitability of a plant’s assets!

The “wheels of industry” today rely on lubricant films mere microns in thickness. Thus, it is essential that management of our operations becomes better informed about good lubrication practices and the fact that they must be deployed daily to protect our “golden geese.” Good Luck!  

1069

11:12 pm
February 18, 2015
Print Friendly

Lubrication Checkup: ISO 55001 Certification

0814lubecheckupBy Dr. Lube, aka Ken Bannister

Symptom:

“Our company wants the maintenance department certified to the new ISO 55001 Maintenance Standard within two years. Should we update our lubrication practices?” 

Diagnosis:

Any opportunity to review and update your lubrication practices should be embraced. A well-managed lubrication program is an integral part of any asset-management program, and lends itself to ISO standards like 55001-Asset Management, 50001-Energy Management and 14001-Environment Management. ISO 55001, which debuted as a global standard in 2014, is tailored to the maintenance and reliability community. Focusing on the life-cycle management and value of a corporation’s assets, it encompasses all lubricated machinery and physical assets.

Prescription:

Preparing for certification will require an internal audit of your current maintenance strategies, methods, processes and procedures to ensure they align with the standard’s requirements. ISO 55001 demands that the asset-management group’s approach to maintenance directly align with corporate values, goals and objectives. For example, a company may have holistic stated objectives involving energy use/savings and environmental sustainability edicts. It will also have business objectives that could include increased service levels and manufacturing throughput and reduced capital spending and/or operating costs.

To certify, a maintenance department must clearly demonstrate corporate alignment of its asset-management approach (e.g., asset-management system). This includes maintenance policy, strategic asset-management plan, asset-management goals and objectives, and development and implementation of plans and reports to validate the system’s effectiveness. ISO 55001 calls for a value-based approach toward assets to assure their dependability (e.g., availability, reliability, maintainability and maintenance support) and life-cycle-costing/management.

Effective lubrication practices are crucial to the dependability and life of physical assets and their moving parts. The hallmarks of a best-practice lubrication program are those designed to meet the needs of the asset(s), improve the maintainability process, increase production/operations quality and throughput, and help reduce corporate energy use and carbon footprint with minimal capital outlay.

Yes, ISO 55001 is a great opportunity to review your current practices and implement an integrated, lubrication program designed to help you meet your certification requirements. Certification, and the process to achieve it, will also help you better serve your company, clients and assets. Good luck! MT

Ken Bannister of Engtech Industries, Inc., is a Lubrication Management Specialist and author of Lubrication for Industry (Industrial Press), and the Lubrication section of the 28th Edition Machinery’s Handbook (Industrial Press). For in-house ICML lubrication-certification training, contact him at 519-469-9173 or kbannister@engtechindustries.com.

106

7:41 pm
February 18, 2015
Print Friendly

Procuring The Highest-Quality Oil Sample

Screen Shot 2015-12-18 at 1.44.13 PM

Oil samples can reveal a lot about the condition of your equipment. Make sure they’re accurate.

By Ken Bannister, Contributing Editor
kbannister@engtechindustries.com

As in all aspects of life, the end result of any endeavor is only as good as the effort put into the exercise and the quality of elements used to create the result. Such is the case in lubricant and wear-particle analysis. Here, accuracy of results is highly dependent upon the care and method used to collect and then deliver a quality used-oil sample into the hands of a laboratory for analysis.

Screen Shot 2015-12-18 at 1.40.59 PM

Procuring and delivering an analysis-ready, superior-quality used-oil sample requires discipline and consistency, as summed up in the “7 Best-Practice Principles of Oil Sampling” in Table I. Choosing the best procedure, method, hardware and sample location is key. These choices will likely differ based on whether they are taken from a pressurized or non-pressurized system, and whether the machine or gearbox is designed or set up for best-practice sampling techniques. They may also differ due to the consistency of the sampling methods, the training of the person taking the sample and the sampling cleanliness protocol used.   

The best sample choices for a piece of equipment are driven by three main objectives: 1) to maximize sample data density; 2) to minimize sample-data disturbance; and 3) to maximize sampling consistency.

Data density

Each oil sample carries a unique time-stamped composition signature of base oil chemistry, additive-package level and chemistry, and wear-particle type, size and count. These factors are then compared against a virgin oil sample to determine the oil’s chemical condition and the machine’s moving-parts condition at that moment in time. In turn, the more representative the sample is, the more accurate the diagnosis. Every sample, consequently, must contain the maximum amount of data density (representative data) it can—which is best achieved by extracting the sample in the most appropriate place.

For pressurized systems, e.g. hydraulic, and recirculating oil systems, oil is pumped from a reservoir under pressure, through a series of filters in a piping distribution system to the bearing surface areas, from where it is returned to the reservoir to be once again filtered and cooled for recirculation. Maximum data density is always found downstream of the lubricated bearings and upstream of the return filter, where it is laden with contaminants that have just been washed from the bearing surfaces. To assure the most representative sample, take it:

  • When the machine is running at temperature and under regular working condition load.
  • From a live fluid zone, meaning no dead pipe legs (static areas) or line ends.
  • From a sample port connected to an elbow used to create a turbulent zone and ensure a colloidal (well-mixed) sample.

Samples can be extracted in a low-pressure (LP) system using a simple ball valve drain tap screwed into an elbow. For high-pressure (HP) systems, a ball valve can still be employed, but with the addition of a helical coil attachment used to reduce the pressure of the fluid stream once the valve is opened. A more sophisticated way to take HP samples is to use a vacuum pump connected to a push-style sample port (similar to the way a grease nipple works): The probe attached to the pump is inserted into the spring-loaded sample port to allow pressurized oil to flow into the sample bottle that’s screw-attached to the vacuum pump unit.

For non-pressurized systems such as a self-contained splash- or bath-lubricated gearbox, a sample can be extracted three ways. The first (and least desirable) method uses a simple ball valve screwed into the reservoir drain port. Although easy to set up, a large flush volume is needed prior to taking the actual sample—and the user still runs a high risk of picking up sludge contamination from the bottom of the reservoir. (To lessen this risk, a pilot sample tube can be inserted to the one-third level mark of the reservoir.)

The second method employs a drop tube attached to a rod to ensure the tube opening is approximately positioned at the one-third reservoir level mark when the tube is lowered into the reservoir through a fill opening. This is done to help ensure no non-representative sludge contamination is allowed in the sample. The tube is then connected to a suction or vampire pump to extract the sample. Again, sample disturbance can be high if the sampling procedure is not performed carefully.

The third and ideal sample method employs a combination pilot-tube/level-gauge device affixed at the correct reservoir sample level. As most reservoirs don’t come with such devices, this approach will require an after-market equipment purchase and installation

Data disturbance

It’s important that your oil-sample data be neither disturbed nor contaminated by the actual sampling and sample-handling processes. For example, if they’re not minimized, reservoir sludge, dirty sample/drop tubes and dirty sample bottles can all distort data readings. Simple, but effective, tactics for managing data disturbance, sometimes referred to as “interference,” include:

  • Cleaning hands, cleaning the sampling port/area, cleaning sampling equipment.
  • Using only virgin sample bottles designed for oil-analysis sampling (glass is preOnly filling sample bottles 60% to 70%, providing headspace that lets the lab agitate and successfully re-suspend the solids for testing purposes.
  • Performing the 10x flush rule for every sample, e.g., flushing the sample valve and tube (when used) with approximately 10x the required sample-volume space of the oil that’s to be sampled into a non-sample container before the real sample is taken.
  • Using a ziplock sandwich bag as a glove to handle clean sample containers, that when filled, can be stored untouched, ready for shipping (thus minimizing the time sample bottles are open to the elements).

Sampling consistency

To ensure high-quality sample results that can be trusted, the sampling protocol must assure consistency. This is achieved by:

Developing an engineered oil-sampling program in which every sampling port and method is documented and regular sampling frequencies are set up in a work order system. (Commencing such a program, bearings are usually start-sampled on a 500-hr. frequency; industrial hydraulic systems on a 700-hr. hour frequency, light-duty gearboxes on a 1000-hr. frequency; and heavy-duty gearboxes on a 300-hr. frequency.)

  • Using an oil-sampling program to develop, as well as train on, standard operating procedures;
  • Always sampling from the same location.
  • Regularly sampling virgin-oil when new lubricant stock arrives on site.
  • Using the same laboratory for sampling, and ask for dedicated lab technician(s) to perform your plant’s sampling.
  • Always filling in the sample-data form accurately, including sampling date and time stamp.   
  • Sending a sample to the lab within 24 hours of its collection (if longer than 24 hours, the sample must be retaken).   

Ken Bannister is a certified Maintenance and Lubrication Management Consultant for ENGTECH Industries, Inc. Contact him at 519-469-9173 or kbannister@engtechindustries.com.

261

7:29 pm
February 18, 2015
Print Friendly

The Inner Life of Bearings, Part 1: How Lubrication Really Works

What some personnel don’t know can hurt your equipment and processes. Expert advice bears repeating.

By Neville Sachs, P.E.

As a facility considers implementation of a sophisticated lubrication program, it’s not uncommon for someone to strongly insist that “oil’s oil,” and that “all our applications can be handled by one multi-purpose grease.” The numbers of mineral-based and synthetic lubricants in vendor catalogs run counter to those arguments. Manufacturers commonly list over 40 greases and lubricating oils, available in at least 10 viscosity ranges. Categories include aviation oils, automotive and light truck engine oils, gear oils, compressor oils, heavy-duty engine oils, gas engine oils, turbine oils and way oils, to name but a few.

Accounts of someone’s brother-in-law or friend who “never changed the oil in his truck,” or “used ATF (automatic transmission fluid) in his car engine,” may be more urban legend than truth—and they don’t reflect lasting solutions: Some oils will temporarily work in an incorrect application, but they won’t provide long, reliable service. Unproven theories and/or ill-informed theorists should carry no weight in a facility’s approach to lubrication, but often do.

Overcoming the harmful impact misinformation and flawed thinking can have in today’s industrial operations calls for continuous emphasis on correct information. This two-part article recaps lubrication fundamentals that have been covered in these pages before. But when it comes to the bearings in your plant’s critical equipment systems—and the ever-changing workforce that may be maintaining them—regular reinforcement of these principles is crucial.

Back to the basics

Friction, lubrication and wear (i.e., “tribology”) constitute a complex body of knowledge that involves, among other things, three basic types of bearings with very different “wear-prevention” mechanisms and critical point-of-contact temperatures.

For lubrication to be effective, a bearing’s mating pieces must be separated. In conventional plain bearings and rolling element designs, this separation depends on the lubricant’s viscosity. The success of a sliding application is governed by the lubricant’s additive package.

Screen Shot 2015-12-18 at 1.31.29 PM

One of the most important aspects of lubrication is relative lubricant film thickness. Figure 1 illustrates this film thickness by depicting two pieces of metal as viewed through a microscope. Note that these pieces are not perfectly flat: R1 and R2 refer to their average roughness measurements. Between the two pieces, h is a measure of the separation resulting from the lubricant. Represented by the symbol λ, relative film thickness is calculated as:

λ =  h/(R12 + R22)1/2

Within reason, the greater the λ value, the lower the wear rate.

Screen Shot 2015-12-18 at 1.31.42 PM

Another important principle of lubrication can be seen in the Stribeck Curve in Fig. 2. Developed in 1902 by the German engineer and scientist Richard Stribeck, it shows how the coefficient of plain-bearing friction varies with surface speed and lubricant viscosity. Referring to the diagram, we can see that when a lubricant is supplied and the surface speed between two properly designed parts increases, the friction first rapidly drops off,  then slowly increases. This curve is also helpful in that it shows the three lubrication zones—which basically equate to the three most common bearing types. Low-speed plain bearings and sliding applications fall into the boundary-friction zone; ball and roller bearings into the mixed-film (elastohydrodynamic) zone; and high-speed plain bearings into the full-film zone.

Screen Shot 2015-12-18 at 1.31.53 PM

The plot in Fig. 3 uses somewhat different terminology than the Stribeck Curve for the three lubrication zones. It also shows the effect of relative film thickness on wear rates. Hydrodynamic lubrication typically is seen in plain bearings, i.e., in automobile engines and large turbines and generators. Elastohydrodynamic refers to the lubrication mechanisms seen in higher-speed rolling element bearings. Sliding (boundary-friction) lubrication occurs in applications like piston rings, wire ropes and slow-speed rolling element bearings.

How different bearing types operate

Screen Shot 2015-12-18 at 1.32.07 PM

Lubrication occurs in the three categories of bearings by way of very different mechanisms. The diagram of a hydrodynamically lubricated plain bearing in Fig. 4 shows a journal that rotates inside the bearing. (The bearing can be made from any one of many materials, which will be discussed in Part 2 of this article.) Preferably, oil is fed into the gap at the unloaded area of the bearing, whereupon it is swept around the journal. In the process, the oil viscosity develops a wedge that separates the two pieces. The typical film thickness is in the order of 0.01 to 0.05mm (0.0004” to 0.002”). While this type of bearing can withstand tremendous pressures, as the load on it increases, internal shearing of the oil film increases the lubricant temperature, the viscosity drops and leakage increases.

Photo 1: As shown by the uneven wear pattern on this pair of gas-engine main bearing inserts, misalignment and excessive clearance will reduce the life of plain (i.e., hydrodynamically lubricated) bearings.

Photo 1: As shown by the uneven wear pattern on this pair of gas-engine main bearing inserts, misalignment and excessive clearance will reduce the life of plain (i.e., hydrodynamically lubricated) bearings.

Designing a hydrodynamically lubricated bearing primarily involves understanding operating temperatures and viscosities and the need to create a system that delivers more oil than can readily leak out from the edges of the bearing. Misalignment and excessive clearance will greatly reduce the bearing’s life. (As shown in Photo 1, the uneven wear pattern on a pair of gas-engine main bearing inserts contributed to their rapid degradation.)

Screen Shot 2015-12-18 at 1.34.50 PM

As can be seen in Fig. 5, rolling element bearings, ball and roller bearings, have vastly different lubrication mechanisms.

In the operation of a ball or roller bearing, as the element rolls along and traps that easy-flowing oil, viscosity changes significantly (increasing by a factor of 10,000 or more and becoming stiff enough to actually separate the rolling element from the ring). As this occurs, the mating areas of the element and ring flatten elastically to distribute the load across the film and support continued operation. While the lubricant film separation isn’t great (less than a micron [≈0.00004”]) and the pressure is tremendous (typically more than 2GPa [150,000 psi]), the overall effect is substantial: Contact forces are distributed over a much greater area, fatigue stresses are reduced and bearing life is increased.

Photo 2: The inner ring of this spherical roller bearing exhibits the fine-grained spalling that results from inadequate lubrication.

Photo 2: The inner ring of this spherical roller bearing exhibits the fine-grained spalling that results from inadequate lubrication.

Two important factors in this process are lubricant temperature—i.e., the lower the viscosity the thinner the film—and lubricant cleanliness: Because the lubricant film is so thin and the pressures so high, solid particles and water have huge effects on component lives. (Photo 2 shows the inner ring of a spherical roller bearing and the fine-grained spalling that results from inadequate lubrication.)

Photo 3: The dark bands alongside this bearing’s ball paths are oxidized oil deposits.

Photo 3: The dark bands alongside this bearing’s ball paths are oxidized oil deposits.

With the third lubrication mechanism, i.e., in sliding bearings, additives are more critical than oil viscosity. Some additives, such as oxidation inhibitors, are designed to improve oil life. Others, such as anti-wear and high-pressure (EP) additives, are designed to improve oil performance. (The dark bands alongside the ball paths shown in Photo 3 are oxidized oil deposits.)

Screen Shot 2015-12-18 at 1.32.13 PM

Although selection of the correct additive package is important for the lubrication mechanisms shown in Figures 4 and 5, with sliding applications (Fig. 6), the correct additive combination is the key to low wear rates and long component life.

The diagram of contacting metal pieces shown in Fig. 6 could represent piston rings or, alternately, rolling element bearings operating at a speed too low to generate a viscosity conversion. To reduce wear rates in these components, two general types of additives are used: anti-wear (AW) and, as they are known in North America, extreme pressure (EP). (Note: In the rest of the world, extreme pressure additives are characterized as “high pressure.”)

Anti-wear additives are almost always polar molecules—meaning they are compounds that have a positive charge on one end and a negative charge on the other. Because of their polar nature, they are attracted to the metals. An example of this is oleic acid, a fatty acid where one end of the molecule is attracted to the metal and the other end is repelled. With relatively low pressures and low contact temperatures below 100 C, these additives provide a cushion between the two sliding pieces. But at higher-point contact temperatures (and higher pressures), they lose strength and EP additives are needed.

There are two general types of EP additives: liquids and solids. Liquid additives in EP oils are generally compounds of sulfur and phosphorus, and sometimes chlorine, that, when heated, form hard semi-metallic coatings that provide the actual wear resistance. Solid additives found in greases commonly include molybdenum disulfide, graphite and other materials designed to slide between opposing metal parts to provide wear resistance. The proportion of solids varies with individual manufacturers. When using EP lubricants, keep these points in mind:

  • When water is present, some additives will form extremely corrosive chemicals.
  • Solid EP additives tend to disrupt the viscosity transformation that’s critical to higher-speed ball and roller bearing lubrication. (However, if those ball and/or roller bearings are in a gearbox, using EP additives to help preserve the gears is usually much more important than the life of bearings that can be easily monitored and replaced.)

Coming up

Part 2 of this article will focus on oil and grease selection for an application; why speeds and temperatures are important; and why operating environments are critical in determining lubrication frequency.

Neville Sachs has extensive experience in machinery reliability and lubrication. The author of two books on failure analysis and a contributor of sections to other books, he has also written more than 40 articles. A Professional Engineer, Sachs holds STLE’s CLS certification, among others. Contact him at sachscracks@att.net.

74

7:24 pm
February 18, 2015
Print Friendly

From Our Perspective: Revisiting the Power of Twofers and Threefers

kennewmugBy Ken Bannister, Contributing Editor
kbannister@engtechindustries.com

Prior to the Christmas break I was fortunate to visit England with my eldest son and spend quality time with my elderly parents who were celebrating their 60th wedding anniversary. Because geography has rarely favored such multi-generational get-togethers and, taking advantage of the situation as parents often do when grandchildren are around, they relished “spilling the beans” about my youthful traits and transgressions—much to the delight of my adult son! During one of their reminiscences, I experienced a “eureka moment,” recognizing a very specific trait instilled in me as a child that I still employ today. 

As a post-war-England baby boomer, I lived over half my childhood in a frugal world of government rationing with little money to spare for luxuries. With two competing siblings, I was taught that if I wanted something special, I had to present a rational reason for granting my request—essentially make a business case built on need first, want second—for the request to even be considered. In the early days, such prized requests included listening to a rock n’ roll radio program (and, later, television programs), staying up late, using the phone, borrowing the family car, etc.

I learned early on that success was more likely when I reasoned with a holistic view, which my parents called as my “twofer and threefer” approach. I always asked for something I thought was obtainable, and tried to make it easier for them to say yes by spelling out a minimum of two or three benefits for granting my request. For example, I recall my reasons for wanting to watch
Top of the Pops (Britain’s answer to The Ed Sullivan Show) as 1) it allowed me to watch and listen to musicians and study guitarists’ finger positions that would help me learn the guitar; 2) my siblings could watch it with me, and my parents could spend a half hour together in peace; and 3) music would help me become a better person. My approach usually worked. I loved that show!

Thus, it was interesting to see that when the ISO 55001 Asset Management Standard was released last year, it also looks for an asset-management program to deliver its own twofers and threefers. It tasks the organization with demonstrating proof of how its asset-management strategies, plans and objectives directly and holistically align with corporate objectives and culture. It also recommends the same program be designed to meet the identified needs of all program stakeholders.

When an industry employs mechanical equipment, one of the least expensive and most productive means of improving asset function and management is through the design and implementation of a best-practice asset lubrication-management program. This produces obvious internal benefits—increased asset availability, reduced downtime, reduced bearing failure, etc.—that result in a measurable twofer: one for maintenance (by reducing maintenance costs), and one for production (by increasing production throughput). There are other benefits, too,  which can include:

  • Reduced purchase costs through lubricant consolidation
  • Reduced lubricant and replacement-bearing inventory costs
  • Reduced lubricant stock-rotation requirement
  • Increased inventory real estate
  • Reduced lubricant waste
  • Reduced bearing friction
  • Reduced carbon footprint and emissions
  • Improved ability to meet ISO 55001 and other standards requirements

If you are looking to validate the implementation of an asset lubrication program, consider all your stakeholders and position your request based on how the intended program will benefit each. Make it easy for the corporation to say yes. I guarantee you will find more than the usual twofer or threefer in your reasoning, and will be more successful in future requests. Good luck!    

52

9:52 pm
December 14, 2014
Print Friendly

From Our Perspective: The Study

kennewmugBy Ken Bannister, Contributing Editor

In 1964, Professor H. Peter Jost published the results of the world’s first major study on the effects of “Lubrication, Friction and Wear.” His research had been commissioned by the British government, which was keenly interested in these effects on the nation’s Gross Domestic Product (GDP).

Jost’s study proved to be sensational. Industry was astounded by its documentation of the costs associated with poor or ineffective lubrication practices. He found that reversing the trend and making lubrication practices more effective could conservatively save British industry 20% in maintenance and repair costs; 20% in lubricant costs; 7.5% in energy costs; and significant downtime. For his part, Jost received a knighthood and, more important, assured his legacy by naming the study and practice associated with lubrication, friction and wear: He called it “Tribology.”

Six years later, in the hallowed halls of Massachusetts Institute of Technology (MIT), Dr. Ernest Rabinowicz built on Jost’s work and completed his formative study on the “Design, Friction, and Wear of Interacting Bearing Surfaces.” This led to his publication of the seminal tribology text Friction and Wear of Materials, and assurance of his legacy as a lubrication pioneer with the “Rabinowicz Law” that stated, “Every year, 6% of the GDP is lost through mechanical wear.” In his studies, Rabinowicz concluded that 70% of bearing-surface loss of usefulness (bearing failure) is attributed to mechanical wear (50%) and corrosion (20%). Both of these wear mechanisms, we now know, are entirely preventable with Good Lubrication Practices (GLP).

Fast forward 50 years: Great strides have been made in the science of Tribology, particularly in the fields of lubricants and bearing-surface technology—progress that has been driven primarily by the automotive industry and U.S. space program. Additionally, the past 10 years have witnessed significant growth in lubrication awareness through training and certification of lubrication-related personnel by the International Council of Machinery Lubrication (ICML), the Society of Tribologists and Lubrication Engineers (STLE), and the International Organization for Standardization (ISO). Lubrication-delivery systems have also greatly improved, especially in the area of electronic control and programming, and are now affordable to the point that their return on investment (ROI) can be measured in weeks and months in most cases.

Yet, despite our innovation and knowledge in these areas, in my capacity as an asset-management and lubrication specialist, I still see too many needless lubrication-related failures and ineffective lubrication practices in every type of industry. But why? Industry needs more than anecdotal information.

With that in mind, I recently worked with the editorial team at Maintenance Technology magazine to develop and conduct a comprehensive (37-question) online reader survey entitled “State of the Nation’s Lubrication Practices.” The Lubrication Nation’s response to it has been significant.

We asked the who, what, when, where, why and how pertaining to your lubrication practices and received a healthy number of fully completed responses from a variety of industry sectors, including manufacturing, automotive, natural resources, pharmaceutical, food and facility management. The results are telling.

In the next few pages, we share some of what our survey told us about North America’s lube practices and provide an initial explanation of what those responses indicate. Look for upcoming articles in Lubrication Technology and on LubricationTechnology.com that respond to and expand on the needs revealed by the study.

For now, please turn to page 4 to read this first article. Over time, I challenge survey respondents and those who were unable to participate in this study to use its findings as a lens through which to view your respective organizations’ states of lubrication; resolve to make positive changes in your practices; and always celebrate your lubrication-program successes. Good luck!    

62

9:49 pm
December 14, 2014
Print Friendly

Optimize Machine Health with Precision Lubrication

lt1214f2-1

By Jane Alexander, Managing Editor

Whether you call it world-class, best-practice or use the currently popular term—precision—the procedure is the same when it comes to lubrication: using the right lubricant for your equipment, in the right amount and at the right frequency. And it requires that lubricant condition be managed.

Jarrod Potteiger of Des-Case explains that the precision approach also excludes two common lubrication practices: the default use of high-quality lubricants and routine over-lubrication. Many steps are required to get a significant benefit from high-performance lubricants in most machines, and performing lubrication tasks at intervals shorter than those required is a waste of time and resources at best, and can lead to component failure at worst. Precision lubrication requires that lubrication PMs be rationalized and optimized to ensure that lubricant conditions and amounts will provide the most effective lubrication. Potteiger offers the following advice on developing and maintaining successful precision-lubrication programs.

Lubricant specs

Program success starts with having the right lubricant—oil and/or grease—in every component. This is probably the simplest precision-lubrication aspect to achieve, yet is rarely done right. Lubricants are often specified incorrectly due to initial misinterpretation of OEM specs or, over time, due to a misdiagnosed problem or misplaced perception of benefit. Whatever the reason, Potteiger says, it’s usually prudent to go through each lube point in a facility and verify or correct the lube specs if it has not been done recently. When specifying lubricants, however, he adds that it is important to not just create a proper spec, but to define the methods by which decisions are made. Doing so eliminates future questions about the accuracy of the selection.

With regard to accuracy, Potteiger notes that while it’s not uncommon for machines to have the wrong oil in them, grease is a different story. As he describes the situation, “Most maintenance professionals don’t really understand grease.” Rather, they tend to characterize different greases by the type of thickener they use or by vague terms such as “hi-temp.”

Grease, though, is actually just thickened lubricating oil. The purpose of the thickener is to hold the lubricating oil in place (like a sponge)—not to provide lubrication. For the most part, grease specification should use the same processes as oil, but with additional considerations.

According to Potteiger, the misunderstanding of grease runs so deep that many OEMs don’t provide adequate descriptions for grease specification. In a precision-lubrication program, each lubricated component should have a generic lube spec that identifies viscosity grade, base oil type and the proper additive system. Grease-lubricated components should have the same, and should include thickener type and NLGI grade.

Application amount and frequency

With the proper lubricant installed in every application, the rest of a precision-lubrication program is designed to ensure the proper condition of those lubricants. Lubricant condition has two components: 1) that the lubricant be suitably free of contaminants; and 2) that the lubricant be in acceptable condition from a chemical and performance standpoint. For oil, this means maintaining the proper oil level and replacing it at the right frequency. For grease, it means installing the correct amount initially, then replenishing with the correct amount at the right frequency going forward.

Oil-fill levels and replacement frequencies are typically pretty straightforward, Potteiger says. “OEM instructions usually cover this adequately.” Correct oil levels, however, can vary for similar components, based on factors such as their orientation or operating speed. OEM oil-level instructions should be reviewed carefully to determine that there is either a single, correct level or that the correct option has been chosen if there is more than one.

Oil-replacement frequencies can also vary. Typical recommendations are conservative because, to be on the safe side, the OEM must recommend for harsh operating conditions. Actual, useful oil service life, however, can vary dramatically. Factors such as high operating temperatures, wear debris, moisture and sludge can shorten oil life. In a given application, the severity of these items, or lack thereof, can alter useful service life by an order of magnitude. Nonetheless, most oil-change frequencies for similar equipment can fit into neat periods, such as three, six or 12 months, and should only be scrutinized when severe conditions exist. Use of oil analysis allows for oil to be replaced based on actual conditions, which, in turn, removes guesswork.

As with grease selection, grease application amounts and frequencies are often wrong. For grease-lubricated bearings, Potteiger says, the most common mistake is “too much grease too often.” This is especially true for electric motors. “The real problem,” he explains, “is that most people don’t realize they have a problem.” When the problem is recognized, correcting it is a simple, though time-consuming process that can depend on tapping several resources for information, including bearing manufacturers, electric-motor manufacturers and lubrication textbooks, among others.

To determine the proper initial fill amounts and replenishment rates for grease-lubricated bearings, one needs to know the bearing sizes, speeds and types. Secondary considerations such as temperature, vibration, contamination and bearing orientation are also important to know for fine-tuning default values. Whichever combination of factors is chosen, it is essential to use a consistent source for both amount and frequency determination.

Contamination control

While it’s a given that use of the correct lubricants—and ensuring that they are in suitable chemical condition—is a pre-requisite for success, Potteiger notes that big (i.e., positive) changes in the service-life of components can be achieved through the aggressive management of contamination. In most cases, he notes, the amount of particle contamination in oil is the single biggest factor that determines how long a lubricated component will last. “Many maintenance professionals,” he says, “don’t realize they have a problem with lubrication-related failures because they don’t properly characterize the failure or root cause. Most equipment failures are, in fact, lubrication-related.”

lt1214f1-2

The normal way in which most machines fail is to “wear out,” but wear rates can be controlled, and the primary purpose of lubrication is to do just that. Studies show that approximately half of lost machine life is due to mechanical wear—and, as shown in Fig. 1, approximately 80% of mechanical wear is caused by particle contamination in the oil. It therefore stands to reason that when particle contamination is reduced, wears rates go down and component service life goes up.

Effectively controlling contamination requires, among other things, a good strategy. Potteiger says that while implementing a contamination-control policy may take time and effort, developing the strategy is rather simple:

Step 1: Identify goals in the form of target-lubricant cleanliness and moisture limits for different types of machinery.

Step 2: Identify all potential measures to improve cleanliness.

Step 3: Verify the effectiveness of implemented measures with oil analysis.

The two basic approaches to controlling lubricant contamination are exclusion and remediation. Of these, contamination exclusion is typically the least costly and should always be the first—and sometimes only—measure taken. Improvements to contamination removal capabilities should be considered when exclusion measures prove inadequate.

Contamination exclusion

Preventing contamination in lubricated equipment starts with new oil. For several reasons, new oil from drums or bulk deliveries usually contains anywhere from 2 to 20 times the amount of particles that is acceptable for most lubricated equipment. This is not an indictment of lubricant suppliers, but a fact that must be addressed before cleanliness targets in machinery can be met.

In general, Potteiger says, it’s good practice to maintain the cleanliness of new oil at least two ISO codes cleaner than the targets for in-service oil. This will allow modest amounts of contamination to be introduced during transfer and application while still meeting the targets. Unfortunately, typical handling methods will add a lot more than a modest amount of contamination. Thus, for the average plant, lubricant-handling methods and equipment will need to be revised and upgraded to ensure oil cleanliness.

For small sumps that are filled from oil-cans, transfer containers should be made of plastic, sealed, marked for product type and maintained in a clean state. The use of funnels should be avoided when possible and separate handling equipment should be maintained for different lubricants. The simplest and most effective way to ensure that new oil additions are clean is to simply filter it as it is applied using portable filtration equipment. To do this, the reservoirs must be fitted with the proper fittings to effectively attach the transfer equipment.

Another effective and essential technique for preventing contamination is to stop airborne contaminants from entering machine reservoirs during service. Most reservoirs exchange air with the ambient environment regularly, and if that air is not filtered it can be a major source of contamination for both particles and moisture. “The good news,” Potteiger says, “is that this is one of the easiest problems to address through good headspace management.”

Headspace management is the process of managing the condition of the air that enters a sump when oil level is lowered or air pressure drops when the temperature goes down. Replacing typical OEM breathers with high-quality desiccant breathers will strip particles and moisture from the air as it enters the sump to a point where contamination is negligible. Other methods include purging reservoirs with clean, dry air or nitrogen to maintain positive pressure in the headspace, or using expansion chambers that effectively capture and re-circulate the air in the headspace.

For many common applications, such as small gearboxes and process pumps, contamination exclusion is the only practical approach. This makes good application practices and headspace management all the more crucial.

Contamination removal

Sometimes contamination exclusion is not enough. High ingression rates and/or sensitivity to contamination in some machines like hydraulics and those with circulating lube systems require improvements in contamination-removal capabilities as well. “When this is necessary,” Potteiger says, “the first step is to review existing filtration to see if the filters can be upgraded in terms of pore size, capture-efficiency or other factor.” If this is not the case, or if filter upgrades don’t achieve the desired results, offline filtration may be the best option.

Offline filtration systems, commonly referred to as kidney loops, offer several advantages over active filters in the oil-circulation system. Offline filtration is cost-effective because the kidney loop functions independently and is not bound by the flow rate and pressure requirements of the active circulating system. These systems also allow the use of alternative filter media and types such as depth media, electro-static, water-stripping and others that can remove more than just hard particles.

For critical applications where moisture contamination cannot be prevented, water-removal options include vacuum dehydrators, centrifuges, coalescing filters and water-absorbing filters. Vacuum dehydrators in particular are extremely effective at removing water from lube systems to the point that its presence is insignificant. Additionally, most vac systems include high-efficiency mechanical filters to remove particles, which makes them an excellent choice for contamination removal in any application where the cost can be justified.

Condition monitoring

Although most plants use oil analysis in some fashion, Potteiger believes few reap its full benefit. He views effective oil analysis as “the perfect condition-monitoring technology for proactive maintenance” because it can positively identify and quantify the top three root causes of machine failure: particle contamination, moisture contamination and use of the wrong (or degraded) lubricant.

Oil analysis is not difficult, Potteiger says. “Even a novice can easily learn to use viscosity and elemental analysis to verify oil for use in a machine.” Tests such as acid number, FTIR and QSA can be used to determine if the oil is suitable for use or has degraded, while particle counts and moisture concentrations require no deciphering at all. “Good oil analysis,” he continues, “depends on good oil-sampling practices, data analysis and data management, and with the proper education all of these things can be easily achieved.”

Summary

Potteiger sums up precision lubrication as a fundamental component of any good reliability program. Although it can take time to transform an average program into a great one, he reminds end-users that the fundamentals are simple: “Use the right lubricant, in the right amount, at the right frequency, maintain the lubricant’s condition with aggressive contamination control and verify condition with effective oil analysis.”

Jarrod Potteiger, Sr., is Technical Consultant/Manager–Training Services for Des-Case Corp. (descase.com).

Navigation