The process of introducing new lubricants to your plant calls for great care, communication, and attention to details.
By Ken Bannister, MEch Eng (UK), CMRP, MLE, Contributing Editor
New lubricants are introduced into plant environments every day. There can be several reasons behind this type of move: a purchase-cost-reduction or purchase-bid program; new equipment for which the manufacturer’s specified lubricant isn’t currently stocked on site; promotion of a specialty lubricant as a way to solve a specific equipment problem; or some form of lubrication-management initiative. Unfortunately, most new lubricants are introduced in an informal, non-controlled manner with little or no communication between the reliability/maintenance, engineering and/or purchasing departments—or much consideration of the impact that the new product can, and will, have on the maintenance and operation of the physical plant.
With no structured lubrication program in place, the mixing of lubricants—greases and oils—can be endemic. This situation is a major cause of lubricant and premature bearing failure due to the cross contamination of base oils and/or additive packages. For example, a product containing acidic additives added to one containing base or alkaline additives can very quickly neutralize a lubricant’s effectiveness and protection ability, often resulting in catastrophic failure. Anyone who has toiled over implementing a lubrication-management program knows that allowing a new lubricant into a plant environment must be formalized and controlled. This process is not necessarily easy.
An essential part of any quality lubrication-management program is an initial consolidation process that reviews and documents all current lubricant products on site, where they are used, and how they are stored, handled, transferred, and delivered to minimize contamination of lubricants and bearings. This essential engineering process, performed by the lubricant manufacturer, looks for opportunities where more modern, often less expensive, products can be standardized for use across the site to replace all redundant, unsafe, and out-of-date oils and greases, and minimize the number required to operate the plant safely and effectively. In many facilities, the number of lubricants stocked and used after consolidation can be less than half the original count. For this standardization to begin, the consolidation process must determine all possible lubricant compatibility issues and propose suitable engineered lubricant change-out/flushing operating procedures.
Once a list of new lubricants is finalized, the plant must take the following steps to formalize the program:
- Prepare a formal approved-lubricant list for purchasing-department personnel and set up a blanket purchase-order for the approved products.
- Inform all affected stakeholders of the impending change(s) to an approved-lubricant list.
- Remove all non-approved lubricant stock from the plant.
- Develop a stock rotation/control procedure for all approved lubricants.
- Obtain up-to-date MSDS sheets for all approved lubricants and remove all non-approved MSDS sheets.
- Purchase dedicated (color-coded) storage and transfer equipment for all approved lubricants.
- Purchase labels for all approved lubricant reservoirs.
- Change all lubrication filters.
- Develop a lubricant change-out flushing procedure and systematically change out all non-approved lubricants in all machine reservoirs; re-label reservoirs.
- Update lubricant-inventory-control software with lube specification, supplier, manufacturer, code numbers, min/max levels, and inventory-turn rate.
- Update affected preventive-maintenance (PM) job tasks in the CMMS (computerized maintenance-management system) to reflect new lubricant changes.
- Update any recommended changes to PM schedules in the CMMS.
- Update equipment manuals to reflect new lubricant changes.
- Update Bill of Materials (BOMs) in the CMMS.
- Update changes to the lubricant disposal procedure.
- Update any changes to reporting requirements in the CMMS.
- Perform staff training for change awareness, product handling and safety issues, and product disposal.
- Inform production.
- Develop a new-lubricant trial/approval procedure for any non-approved oil or grease introduced into the plant.
After a consolidation program has been implemented, only approved lubricants can be brought into the plant for regular use. This policy, however, does not exclude introduction of a new lubricant into the plant on a trial basis. Should a new lubricant trial be required, a formal request must be made to the reliability/maintenance group by completing a “Lubricant Trial Request Form.” That group, in turn, will oversee the lubricant trial.
Typical trial-request-form attributes
A good trial-request form should have enough relevant information to enable the trial to take place and collect enough relevant data from which a yes/no approval decision can be made upon the trial’s completion. The form must elicit answers to all of the W5 questions—Who, What, When, Where, Why, and How—and document the test results. (This translates to seven sections total.)
- Who? Contains the name, title, department, and contact details of the trial requestor, as well as details of the lubricant supplier and manufacturer name and primary contact persons. It also provides the person(s), title(s), and department performing the trial.
- What? Contains the trial lubricant specification data that will include its name, oil or grease, base-oil type, viscosity, VI (viscosity index) rating, additives, virgin-oil sample datasheet #/attachment, MSDS sheet, expected compatibility issues with other approved products, seals, and production raw materials.
- When? Contains the expected trial duration, along with commencement and completion dates.
- Where? Contains equipment type or specific
equipment number of the machine on which the lubricant is to be tested.
- Why? Details reasons for the lubricant trial, in what way it will benefit the trial equipment and expected results, such as temperature reduction, energy reduction, life-increase expectation of lubricant and/or bearing surfaces and sustainability, and what bearing-failure reduction the trial is expected to accomplish.
- How? Documents the actual test procedure specifics, including lubricant disposal after the test and the conditions to be tested, i.e., amperage draw, temperature of bearings/lubricant, and lubrication-system pressure (cold and hot running).
- Results? Details findings data and conclusions relevant to the test, including before and after data readings, photos, infrared images, vibration readings, risk/benefit analysis, a return-on-investment statement, and a recommendation for approving or not approving the lubricant for purchase and use in the plant.
Be sure to alert plant personnel whenever a lubricant trial is being performed. Communicate this fact by placing a placard or sign on the equipment that states “Machine Under Test with New [insert name] Lubricant.” (Specifically call out the name of the lubricant). Make operators aware of such tests and notify maintenance personnel of anything unusual regarding noise, vibration, smell, and leakage during the procedure.
Before proceeding with any lubricant trial, always consult with manufacturer(s) of your approved lubricants to establish:
- whether they have already performed a compatibility test of the trial product with your approved lubricants.
- if, as suppliers of your approved lubricant, they have a comparable product available to test, or that you may already stock. You should also contact trial-lubricant manufacturer personnel and ask if they have conducted any compatibility tests with your approved lubricants. If no testing has taken place, you can ask if any party is willing to test compatibility on your behalf.
- In the case of new oils, when no compatibility information is available or forthcoming—and you are unable to establish compatibility—you can perform your own testing, as follows:
- Take samples of both lubricants and blend three mixed samples in ratios of 50:50, 90:10, and 10:90.
- Send the three mixed samples to an oil-analysis laboratory and have them tested for filterability, sediment, and color/clarity. Also ask the lab to perform an RPVOT (rotating pressure-vessel oxidization test) to determine the new lubricant’s resistance to oxidation, and a storage-stability comparison.
- For accurate results, tests should be performed three times and the results normalized.
- Ask the lab to assist you in determining any cross-contamination risk.
- Share the test results with the manufacturer of the new lubricant and ask for a change-out/flush procedure.
Note that an RPVOT can be quite expensive to perform. Thus, in the case of non-critical equipment, and if you won’t need to complete a large number of lubricant changeovers, you could forego the RPVOT and simply ask the manufacturer of a new lubricant to recommend a neutral flushing oil.
In the case of new greases, similar steps are followed. The process starts by blending mixed samples of new and existing greases in 75:25 and 25:75 ratios, and sending them to an oil-analysis lab to test for consistency, dropping point, and shear stability.
If a new-lubricant trial is deemed successful, and none of your existing approved lubricants can perform the required job, the new product can be accepted as an “approved” lubricant. The acceptance process, however, calls for the reliability/maintenance group to once again go through the appropriate steps listed above to formally integrate the new lubricant into your plant. MT
Ken Bannister is managing partner and principal consultant for EngTech Industries Inc., (Innerkip, Ontario, Canada), an asset management-consulting firm now specializing in the implementation of certifiable ISO 55001 lubrication-management programs and asset-management systems. For further details, telephone (519) 469-9173, or email firstname.lastname@example.org.
With a 20-yr. history in the industrial sector, and $2.2 billion in capital raised since inception, IGP has extensive experience building global manufacturing businesses. According to the company, it concentrates on leading niche manufacturers of engineered products used in critical applications, and partners with their management teams to pursue strategic initiatives focused on achieving long-term shareholder value.
Founded in 1983 when it brought the first desiccant breather to market, Des-Case now provides an array of fluid-cleanliness products, services, and training that improve equipment reliability and extend lubricant life in industrial plants around the globe. It, in fact, has enjoyed the growth-opportunity benefits of private-equity investments since 2013, when it was acquired by Pfingsten Partners L.L.C.
In 2014, Des-Case announced its own acquisition of the visual-oil-analysis line of ESCO Products Inc., the well-known, family-owned, Houston-based manufacturer of various fluid-monitoring technologies and distributor of Copaltite and Dow Corning products. The acquired portfolio included ESCO’s 3-D BullsEye Viewport, oil sight glasses, indicators and level monitors.
“I am honored and excited to be a part of writing the next chapter in the Des-Case growth story alongside our valued customers, partners and investors,” noted company president and CEO Brian Gleason. “IGP has over two decades of experience investing in the industrial sector with a proven track record of building world-class global businesses. We are looking forward to the partnership.”
Other than the report that Des-Case’s management team has retained a substantial ownership stake in the company, terms of the July 6, 2016 transaction haven’t been disclosed.
For more information on Des-Case, CLICK HERE.
To learn more about Industrial Growth Partners, CLICK HERE.
CorrLube VpCI EP grease is lithium complex grease formulated with premium quality, severely hydro treated base stock. Said to provide excellent resistance to oxidation and with high temperature stability, it is suitable for operating and lay-up conditions. The formula is designed with properties that protect against salt water, brine, H2S, HC1, and other corrosive agents. It also incorporates Vapor phase Corrosion Inhibitors (VpCI) for areas not in direct contact with the grease. The grease remains effective in extreme operating conditions such as high temperature, high pressure, and shock loading, and aids in the suspension of solid additives such as graphite, molybdenum, and disulfide. Thicker film consistency allows it to operate on worn parts.
St. Paul, MN
Learn the latest on the top five causes of failed motor bearings to help stop these problems in their tracks.
According to the bearing experts at SKF (Gothenburg, Sweden, and Lansdale, PA) these five damage mechanisms are the most common causes of motor-bearing failures. Understanding them as you examine a failed bearing can help you prevent their recurrence.
Electric erosion (arcing) can occur when a current passes from one ring to the other through the rolling elements of a bearing. While the extent of the damage depends on the amount of energy and its duration, the result is usually the same: pitting damage to the rolling elements and raceways, rapid degradation of the lubricant, and premature bearing failure. To prevent damage from electric-current passage, an electrically insulated bearing at the non-drive end is usually installed.
Inadequate lubrication and contamination
If the lubricant film between a bearing’s rolling elements and raceways is too thin due to inadequate viscosity or contamination, metal-to-metal contact occurs. Check first whether the appropriate lubricant is being used and that re-greasing intervals and quantity are sufficient for the application. If the lubricant contains contaminants, check the seals to determine whether they should be replaced or upgraded. In some cases, depending on the application, a lubricant with a higher viscosity may be needed to increase the oil-film thickness.
Damage from vibration
Motors transported without the rotor shaft held securely in place can be subjected to vibrations within the bearing clearance that could damage these components. Similarly, if a motor is at a standstill and subjected to external vibrations over a period of time, its bearings can also be damaged. To prevent these problems, secure the bearings during transport in the following manner: Lock the shaft axially using a flat steel bent in a U-shape, while carefully preloading the ball bearing at the non-drive end. Then radially lock the bearing at the drive end with a strap. In case of prolonged periods of standstill, turn the shaft from time to time.
Damage caused by improper installation and set-up
Common mistakes in installation include using a hammer or similar tool to mount a coupling half or belt pulley onto a shaft; misalignment; imbalance; excessive belt tension; and incorrect mounting resulting in overloading. To prevent these problems, use precision instruments such as shaft-alignment tools and vibration analyzers and other appropriate tools and methods when mounting bearings.
Insufficient bearing load Bearings always need to have a minimum load to function well. If they don’t, damage will appear as smearing on the rolling elements and raceways. To prevent these problems, be sure to apply a sufficiently large external load to the bearings. This is crucial with cylindrical roller bearings, since they are typically used to accommodate heavier loads. (This, however, does not apply to preloaded bearings.)
SKF is s a global supplier of bearings, seals, mechatronics, lubrication systems, and services that include technical support, maintenance and reliability services, and engineering consulting and training. For more information on motor bearings and other technologies and topics, visit skf.com.
To realize maximum life from the gears and reducers in your plant, pay attention to their metallurgies and the operating viscosities of their lubricants.
By Neville Sachs, P.E.
In a typical facility, gears are usually the most common method of transmitting power and changing shaft speeds. Vast numbers of equipment systems, from cooling towers to paper machines, will rapidly grind to a halt if their gears aren’t kept in good condition. Gear hardness and lubricant viscosity are two factors in the health of these components.
Metal hardness concerns
Understanding gear hardness is an important first maintenance step. This is necessary because of the very different metallurgies commonly used in these components and their varying damage tolerances.
Case-hardened gears (also called surface-hardened gears) have an extremely hard outer layer over a tough, yet softer, core. This case is usually somewhere between 0.015 and 0.125-in. thick, and as hard as bearing steel. Because their cases are so hard, these types of gears have great wear resistance and should run for many years with no visible pitting.
On a case-hardened gear, any pitting you can see is cause for concern. If the load is strong enough to break down a gear’s hard case, the lifespan for the underlying metal is guaranteed to be shorter.
Through-hardened gears reflect the same hardness all the way through the tooth. Some are very soft steel; others are about as hard as a Grade 8 bolt. Although through-hardened gears aren’t anywhere near as hard as case-hardened types, and their hardness will vary based on application, they are designed to withstand significant wear. (Note: Sixty years ago, almost all North American gears, whether open designs, such as those found on a kiln, or enclosed designs, such as small reducers, were through hardened. Because of economics and market pressures, however, almost all enclosed reducer gears today are case hardened.)
In short, case-hardened gears should not show any wear, i.e., pitting. Through-hardened gears, however, can take a tremendous amount of wear before you need to begin worrying about failure.
How do you know whether a gear is case or through hardened? Perform a hardness test. No expensive equipment is required (although a good hardness tester is a valuable tool in a maintenance department). The procedure is simple.
If you don’t have a hardness tester, simply rub a file over the corner of a gear tooth:
- If the file skids across the tooth, the gear is case hardened.
- If the file cuts the tooth, the gear is through hardened.
(Note: You can skip this hardness test for enclosed reducers made in the past 20 years. Almost all of them incorporate case-hardened components.)
Prior to shutting gears down, measure the lubricant temperature while the components are running at close-to-the-peak loads—preferably on a hot day. Then, referring to a viscosity chart for that oil, determine if the actual operating viscosity meets the manufacturer’s specifications.
This test is crucial for enclosed reducers purchased in the past 20 years. It was during this time that suppliers began downsizing the casings and increasing the power density of these units. The result is that normal heat generated by the gear and seal action has been transmitted out to the environment through ever-smaller surfaces, leading, in turn, to reducers that tend to run hot. The presence of a thin layer of dust—a common occurrence in plants—acts as insulation, which can make the problem even worse.
Improved maintenance procedures
Hardness and lubricant viscosity are two key factors to consider in your inspections of gears and reducers. Tips for improving the maintenance of these components, which can vary somewhat based on specific type, will be discussed in future Maintenance + Reliability Center sections. MT
Neville Sachs has spent many years working in the field of machinery reliability and lubrication for a wide range of industries. The author of two books on failure analysis and a contributor of sections to others, he has also written more than 40 articles on these topics. A Registered Professional Engineer, Sachs holds STLE’s CLS certification, among others. Contact him at email@example.com.
As machine designs evolve and energy efficiency remains a priority, synthetic lubricants are providing reliability professionals with an improved return on investment.
By Grant Gerke, Contributing Editor
Synthetic lubricants are quietly finding new footing in manufacturing. Maintenance teams and reliability programs are learning more about how polyalphaolefins, glycols, and esters achieve better viscosity at higher temperatures. They can also provide excellent friction coefficients for machines that operate at high temperatures and loads.
“A lot of companies out there don’t understand what lubrication is all about,” said Ken Bannister, principal asset-management consultant at EngTech Industries, Innerkip, Ontario, and Maintenance Technology contributing editor. “Manufacturers don’t treat the lubricant as a component of the machine, such as a pump or a motor. They just treat it as a consumable.”
Most original-equipment manufacturers (OEMs) provide general types of oil guidelines for their customers that fall into these categories: resistance and oxidation (R&O), anti-wear (AW), extreme pressure (EP), compounded, and motor oil. While providing general guidelines, OEMs place the onus on manufacturers to specify the right lubricant.
“Synthetic lubricants are ideal for use in newer machine designs with smaller components that operate at higher temperatures and/or greater rotational speeds,” stated Les Rudnick, consultant at Designed Materials Group, Scottsdale, AZ. “Synthetic fluids perform very well in more extreme conditions, both at high temperatures and under lower ambient conditions. Longer drain intervals and energy efficiency are also benefits of many synthetic formulated oils.”
All base oils for industrial and retail lubricants, including mineral oils from a refinery, are split into five different categories, according to the American Petroleum Institute, Washington. Synthetic oils comprise Groups III through V, with the latter two categories originating from a chemical plant. Mineral-based oils fall into the first three categories. Group IV includes polyalphaolefins (PAO) and Group V is silicones, esters, and glycols.
For worm-gear applications, Hermann Siebert, head of marketing & application engineering at Kluber Lubrication, East Europe, recently conducted synthetic base testing on how lower friction can improve efficiency. Higher-end glycol-based synthetics show “significant friction reduction for worm gears and produce lower energy consumption at constant output power.” Additionally, the testing indicated that, “when polyglycol oils are used in heavily loaded worm gears, temperature reductions by more than 40 C and energy savings of 30% are realistic.”
For Group IV synthetics, such as PAOs, Siebert noted “that these types could be recommended for old gears in food processing and pharmaceutical machinery where compatibility with paints and seals of unknown origin are a particular priority.”
Synthetic-lubricant performance has shown dramatic step-change improvements with viscosity and other performance characteristics, but additives are the other part of the equation. “Synthetic base oil doesn’t deplete, but the additives can decompose and rigorous lab analysis needs to be done by machinery OEMs or third parties,” said Bannister. He added, “If a manufacturer continually runs equipment at 105% or 110% over its design capacity, machines will fail, usually because of a bearing issue due to a lubricant failure.”
Innovation through flexibility
Manteno, IL-based High Performance Lubricants LLC (HPL), is a producer of synthetic oils for industrial and retail customers, with an emphasis on new formula iterations. The company formulates synthetic greases and lubricants from base oils—in API’s Groups III through V—and chemically processed additives. The synthetic additives can include corrosion inhibitors, viscosity index improvers, and anti-wear and extreme-pressure additives.
“We were in lubrication distribution before we ever decided to make our own product,” said David Ward, principal at HPL. “We wanted flexibility to be responsive to a customer’s needs. One big advantage is being able to produce multiple samples of an oil or grease in days, instead of months.”
HPL differs from large lubricant producers by providing smaller (1,000 to 3,000 gal.) blends to customers. The company also offers solutions to partners with limited knowledge and bandwidth for lubrication.
HPL’s business model includes white-labeling synthetic lubricants in the retail and industrial industries, and developing custom formulations for National Hot Rod Association (NHRA) race teams. The company also formulates synthetics for several NHRA teams and teams at other levels of motor-sport racing.
“We recommend that customers judge our performance via oil analysis and field data,” said Ward. For manufacturing, HPL hires third-party oil analysts to perform lubricant tests for customers, providing essential feedback for synthetic formulations.
The three-year old Manteno formulation facility encompasses approximately 45,000 sq. ft. and houses a blending area, warehouse, quality-control lab, and offices. One of the first things you notice upon entering the company’s lubricant plant is its cleanliness.
“We’re climate controlled, so everything is contained in the building and nothing is susceptible to moisture,” said Ward. “Everything that’s in the building is clean, pure, and dry.” When oil and additives are delivered to the building, the raw materials are immediately tested for cleanliness and how closely they match the manufacturer’s sample specifications.
The company invested $600,000 in a state-of-the-art testing laboratory for quality-control procedures and rapid formulations. “We make blends quickly and very accurately,” said Ward. “We also blend by weight here, instead of volume.” For example, HPL can blend with a 1,000-gal. tank and have an accuracy be within 0.1 lb.
“Our blend controllers are made by Mettler Toledo, and we have the ability to transmit the formula from the lab to our blend tanks,” he stated. “The system has the capability of recording every ingredient that goes into a batch and storing it in a database. If a customer calls, we can enter the batch number and, in 30 seconds, we can have a full screen of information about that formulation and product’s quality-control data.”
High-performing synthetics from HPL have helped a government fleet of 14,000 vehicles realize savings from increasing a 3,000-mile oil change average to approximately 15,000 to 20,000 miles. For this fleet, the company created an engine lubricant from a blend of Group III, IV, and V base oils. The fleet customer now uses a third of the amount of oil it used in the previous three years.
“If you formulate for quality with better base oils and additives, then you can actually save money based on performance,” explained Ward.
Slicing the competition
Urschel Laboratories Inc., Chesterton, IN, produces several types of food machinery. The 105-yr.-old company is known for its slicing, dicing, and grinding food machines. “All of our machines have rotating gears, knives, or blades,” said Mike Jacko, vice president of engineering. “These simple-to-use machines are easy to take apart, change cut sizes, reassemble, and keep sanitary.”
Urschel values continuous improvement and research and design for its machines as the food industry rapidly changes. Early in the company’s history, most of its machines used an open-sleeve bearing design, with shafts leading through to spindles that had knives attached to them.
About 20 years ago, Urschel’s designers adopted an internal spindle design based on an enclosure that eliminated sanitary issues. This design isolated internal moving parts from food. In doing so, the design required new thinking on spindle lubricants.
“One of my projects included an all-purpose dicer that could slice and dice anything from 0.28 to 0.70 in.,” said Jacko. “The spindle had articulated knives with little cams and would rotate at 12,000 rpm, and you had to pump grease basically every hour to keep that spindle live.”
Stopping a machine on a food-plant floor every hour to grease a spindle isn’t an option for its customers. So, Urschel’s engineering team began testing different food-grade greases, from higher-end synthetics to non-PAO greases that contained clay. After two months of exhaustive spindle testing that included simulated food-plant conditions, including water-contact applications, the company chose the first synthetic lubricant in its history.
“During testing, the machine’s spindle ran for 30 to 40 hours with the synthetic grease and did it under the worst conditions—water and heat,” stated Jacko. “Going forward, Urschel instructed clients that re-greasing could take place every eight hours with the new synthetic product.”
Urschel has been sourcing Group IV synthetic grease lubricants from HPL and, in the process, now offers food producers private-label lubricants with considerable benchmarked, performance data behind them. “There’s a big confidence level when people talk about Urschel and our lubricants,” said Jacko.
His company’s equipment needs are just one example of the demands that today’s manufacturing machinery places on lubricants. The ability to protect bearings and gears at ever-increasing speeds, often in harsh (heat, corrosion, moisture) conditions, and the desire to extend maintenance cycles have been—and will continue to be—the major hurdles lubricants must clear. In most applications, industries have reached a point where conventional mineral lubricants can no longer measure up. Synthetic lubricants are rapidly filling the void and, in many cases, meeting and exceeding performance requirements. MT
Grant Gerke is a business writer with more than 15 years covering manufacturing and enterprise software, automation platforms, packaging applications, and energy infrastructure.
Racing and Testing
When you see hot rods and motorcycles racing past spectators in a matter of seconds, durability isn’t the first thing that comes to mind. However, the legendary National Hot Rod Association (NHRA) Vance and Hines race team turned to High Performance Lubricants (HPL), Manteno, IL, in a quest to reduce its pro stock Suzuki elapsed times.
“When we started with Vance and Hines, we improved upon their previous oil for their diamond-like coatings for their cam followers but didn’t improve it to the level they wanted to see,” said HPL’s David Ward. “That’s racing; multiple iterations until you get it right. We had to develop four formulations to reach what the team was looking for.”
Small changes to fully synthetic oils for the various engine components can result in small increases in horsepower, which can be the difference between winning and losing. Ward noted that some specialized, traditional racing oils have inherent limitations when it comes to higher heat, such as 120 to 130 F. Racing power and vacuum can fall dramatically if vehicles exceed that temperature range.
“Based on our success with the race engines, Vance and Hines is about to release a synthetic engine oil for street vehicles that will be available in retail stores,” added Ward.
Racing is a valuable development tool for HPL: “It’s a catalyst for the company, said Ward, “we see results very quickly in racing and it allows us to implement lessons learned in racing to our industrial product line as a whole.”
For more information about lubricants, visit the following URLs:
Temperature is critical to the performance and life expectancy of lubricants and the components they protect.
By Ken Bannister, MEch Eng (UK), CMRP, MLE, Contributing Editor
In the lubrication world, temperature presents an interesting paradox and irony.
The paradox is that lubricants require heat to flow efficiently over and around surfaces, most commonly bearings. However, if the temperature gets too hot (exceeds 210 F), lubricants tend to undergo chemical changes that can drastically reduce life expectancy. Conversely, if the temperature becomes too cold, a lubricant will thicken and lose its ability to lubricate bearing surfaces. The irony is that lubricating oil is designed not merely to separate and lubricate a bearing surface, it’s also designed to absorb and carry away frictional heat from the bearing surface.
While the old adage “oil is oil and grease is grease” may have been true in agrarian societies of yesteryear, things have changed. To guarantee asset availability and reliability in today’s complex, high-speed industrial environments, lubricants must be tailored and managed to their machine-host’s specific needs and operating conditions.
The fundamental reason for lubrication is to provide a film that reduces friction between two, often metal, surfaces. If the film is insufficient, the surfaces collide and transfer energy, resulting in rapid heat buildup and metal expansion, which further retards motion until both surfaces eventually weld to one another. To avoid this worst-case scenario, the ideal intent is to guarantee the correct lubricant is available in sufficient quantity to consistently separate the moving surfaces. This ensures that temperatures stay below the magic 210 F operating temperature.
Choosing the correct lubricant for a bearing means selecting one that best matches the ambient and operating temperatures and conditions under which the component will function. This also means choosing a lubricant with the correct viscosity and additive package.
Viscosity—arguably a lubricant’s most important attribute—is a measure of its resistance to flow. A highly viscous oil is thick and resists flow. A low-viscosity oil is thin and flows easily. Again, temperature can have a dramatic impact on lubricant viscosity. A high-temperature condition, depending on the load in the bearing area, could easily collapse the film thickness of a low-viscosity product and create a metal-to-metal contact or “boundary layer” condition detrimental to the bearing and the lubricant.
Avoiding this situation means choosing a lubricant viscosity designed for the maximum operating temperature expected in the bearing area. This is achieved by paying particular attention to a lubricant’s viscosity index (VI). The VI measures the rate of viscosity change due to temperature. Better-quality lubricants have a more-desirable, narrow rate of viscosity change over a standard temperature range and allow good flow at low temperatures while maintaining their thickness at higher temperatures. Generally speaking, the higher the VI, the more stable and desirable the lubricant.
In cold-temperature conditions, hydrocarbon-based oil can thicken to the point at which it will no longer pour, largely due to its wax content. More expensive hydro-treated and synthetic-based oils will largely resolve this problem, or the user can heat the oil reservoir to a temperature that will allow it to flow again.
Heat-related lubricant failure
In the late 19th century, the Swedish Nobel Laureate Svante Arrhenius discovered a direct relationship between temperature change and the chemical-reaction rate in fluids that he put into an equation known as the Arrhenius rule. As summed up in the following statement, this rule is used in the lubrication field to express the temperature-change-dependent failure rate of oils: “For every 18-deg. F (10-deg. C) increase in oil temperature, the lubricant’s life is reduced by half.” Conversely, reducing oil temperature by the same rate doubles the lubricant’s life (see Fig. 1).
Two predominant failure mechanisms occur as oil heats up. The most common is categorized as oxidation failure and the lesser categorized as thermal failure.
Oxidation failure occurs when oxygen reacts with the lubricant base oil. Anti-foaming and anti-oxidant additives, if present in the oil, are designed to slow the process. Once they are depleted, however, the rate of oxidation will accelerate, especially in the presence of water and reactive bearing materials such as copper and iron.
In an oxidized state, hydrocarbon molecules in the oil will transform into a greasy sludge containing harmful, corrosive acids. These will cause the oil to degrade and lose its lubricating properties, effects that are manifested by an increase in lubricant viscosity, specific gravity, acidity (TAN), rapid additive depletion, darkening of the oil, a “rotten egg” odor, and varnishing of the bearing surfaces.
Thermal failure can occur when localized/external heat is transferred to the lubricant or through the adiabatic compression (a thermodynamic process that occurs when entrained air compresses and heats up according to Boyle’s law) of entrained air bubbles in pumps, bearings, and pressurized hydraulic and lubricating systems. The resulting heat causes the lubricant to decompose and its corresponding hydrogen loss to create carbon-rich particles in the form of sludge and carbon deposits. This leads to a decrease in lubricant viscosity indicated by dark fluid with greasy suspensions that smell of burned food, and evidence of coking and varnishing on the bearing surfaces.
Once a lubricant has failed, the molecular-change state is usually irreversible. At the very least, this situation calls for a lubricant change.
Oil-analysis programs monitor lubricant conditions and alert users to possible failures before they occur. The propensity of a lubricant to fail can be checked by subjecting a sample of it to a rotary pressure vessel oxidation test (RPVOT). By simulating failure through a speeded-up oxidation process, this test can provide a good indication of a lubricant’s suitability. It also can predict remaining life in virgin and used oil samples.
Prevent temperature-related failures
Whether your lubricant choice is grease or oil, once the correct product is chosen and employed it will require assistance from the maintainer to ensure that it has a fighting chance to perform and deliver a reasonable life expectancy. This can be achieved by implementing some of the following best practices:
- Keep lubricant transfer-delivery systems immaculately clean. This prevents the ingress of solid contamination that can create sludge, raise lubricant viscosity, and accelerate the oxidation process.
- Ensure the oil/grease delivery method/system is tuned to provide the correct amount of lubrication in a timely manner. Over-lubrication will create fluid-friction heat, compounded by the bearing ball/rollers working overtime to mechanically push through the excess lubricant. Both conditions cause the lubricant to heat up rapidly. Under-lubrication can allow the bearing to go into boundary lubrication, creating surface interaction frictional heat that can “cook” the lubricant.
- Maintain the oil reservoir level between the minimum (“MIN”) and maximum (“MAX”) fluid level to prevent cavitation in the oil pump or oil churn in the reservoir. Either can result in air bubbles accelerating the oxidation process.
- Keep oil reservoirs clean and free of debris. Dirt, dust, and debris can create the effect of a thermal blanket and raise the temperature of the oil inside the reservoir.
- Ensure the integrity of shaft seals. Poor shaft seals lead to excessive lubricant leakage that can quickly result in an under-lubrication state.
- Implement a lubricant test-and-control process to ensure that incompatible lubricants are not mixed together in the same bearing space, something that can lead to a variety of detrimental conditions, including overheating.
- Where hydrocarbon-base lubricants are employed in cold-weather climates, use timed block heaters or blanket-wrap element heaters for reservoir and drum/pail heating. If a lubricant is to protect a bearing surface it must readily flow across the bearing. MT
Lubrication expert Ken Bannister is principal consultant with EngTech Industries, Innerkip, Ontario. The author of Lubrication for Industry and the Lubrication Section of the 28th Edition of Machinery’s Handbook (both Industrial Press, South Norwalk, CT), contact him at firstname.lastname@example.org.
To learn more, see: