Archive | Lubrication

126

4:05 pm
July 11, 2016
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Use These Steps to Introduce New Lubes

Part of of the process equipment of the mechanism close-up.

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often less expensive, products can be standardized for use across the site to replace all redundant, unsafe, and out-of-date oils and greases, and minimize the number required to operate the plant safely and effectively.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:

  1. Prepare a formal approved-lubricant list for purchasing-department personnel and set up a blanket purchase-order for the approved products.
  2. Inform all affected stakeholders of the impending change(s) to an approved-lubricant list.
  3. Remove all non-approved lubricant stock from the plant.
  4. Develop a stock rotation/control procedure for all approved lubricants.
  5. Obtain up-to-date MSDS sheets for all approved lubricants and remove all non-approved MSDS sheets.
  6. Purchase dedicated (color-coded) storage and transfer equipment for all approved lubricants.
  7. Purchase labels for all approved lubricant reservoirs.
  8. Change all lubrication filters.
  9. Develop a lubricant change-out flushing procedure and systematically change out all non-approved lubricants in all machine reservoirs; re-label reservoirs.   
  10. Update lubricant-inventory-control software with lube specification, supplier, manufacturer, code numbers, min/max levels, and inventory-turn rate.
  11. Update affected preventive-maintenance (PM) job tasks in the CMMS (computerized maintenance-management system) to reflect new lubricant changes.
  12. Update any recommended changes to PM schedules in the CMMS.
  13. Update equipment manuals to reflect new lubricant changes.
  14. Update Bill of Materials (BOMs) in the CMMS.
  15. Update changes to the lubricant disposal procedure.
  16. Update any changes to reporting requirements in the CMMS.
  17. Perform staff training for change awareness, product handling and safety issues, and product disposal.
  18. Inform production.
  19. 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.)

  1. 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.
  2. 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.
  3. When? Contains the expected trial duration, along with commencement and completion dates.
  4. Where? Contains equipment type or specific
    equipment number of the machine on which the lubricant is to be tested.
  5. 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.
  6. 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).
  7. 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 kbannister@engtechindustries.com.

315

9:57 pm
June 13, 2016
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Six Lubrication Myths Debunked

When it comes to machinery health, some lubrication myths are downright dangerous.

When it comes to machinery health, some lubrication myths are downright dangerous.

Despite years of concerted efforts by industry experts and suppliers, some dangerous lubrication myths continue to swirl around many maintenance operations. Motion Industries lubrication specialist Chris Kniestedt takes a down-and-dirty approach to debunk six of them.

Myth 1: All lubricating oils are the same.

From hydraulic fluids to gear lubricants to motor oils, each lubricant, be it synthetic or mineral-based, is uniquely formulated for its application with a specific viscosity; additive package; physical, chemical, and performance properties; and regulatory requirements. Various products may or may not be compatible with each other (see Myth 6).

Myth 2: If a little is good, more is better.

Take grease, for example. Over-greased bearings are a major cause of equipment failure. Blown seals and overheating are just two negative results of using too much grease. A general rule of thumb for normal- or high-speed machinery is that it’s better to err on the side of caution and to always check the OEM’s recommendations.

Overfilling gearboxes will also lead to problems, including failed shaft seals or increased operating temperatures. A gearbox that has too much oil will have to work harder to move through the lubricant, subsequently generating more heat or churning the oil into foam.

Myth 3: Blue, red, or black grease is better than white or clear grease.

Color is not a key factor in selecting grease for an application. There’s no standard for doing so. Instead, pay attention to base-oil viscosity (based on speed, load, and expected operating temperature), thickener type to mitigate incompatibility issues and consistency, and/or how well a product will pump at operating temperatures.

Myth 4: Tacky and stringy greases and oils offer better protection than non-tacky products.

It’s important to understand that lubricants are only 10- to 20-microns thick at the point of contact. Moreover, film thickness is a function of base-oil viscosity at operating temperature and speed (to a lesser degree, load). Thus, always use caution when applying tacky lubricants or greases with higher percentages of thickener at high operating speeds.

Myth 5: Food Grade (NSF H-1) products are never as good as Non-Food Grade (NSF H-2) products.

Advances in base-oil technology and additive chemistry have made Food Grade H1 products stronger than ever, particularly with synthetics. There are many applications where a correct, strong Food Grade H1 product will work as well as a non-Food Grade H2 mineral-oil-based equivalent.

Myth 6: All products are compatible.

Consider greases. In addition to their base oils and additive packages, greases are formulated with various thickeners (lithium, lithium complex, aluminum complex, calcium, polyurea, bentone, and silica gel), which aren’t necessarily compatible with each other. Always exercise caution when changing greases. Laboratory compatibility testing will clear up any doubts. If incompatibility exists between old and new products, purge bearings before changing to the new one. Oils aren’t always compatible either, especially with the new generation of synthetics. Finally, mixing Food Grade H1 lubricants with Non-Food Grade H2 will create contamination issues, which will cause you to lose H1 designation. MT

Chris Kniestedt is lubrication specialist for the San Francisco Division of Birmingham, AL-based Motion Industries. For more information visit www.motionindustries.com.

293

5:03 pm
June 13, 2016
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The Color of Lubrication

Add visual management to your lube-program toolbox through an array of color-coded solutions.

By Ken Bannister, MEch Eng (UK), CMRP, MLE, Contributing Editor

When you hear the word lubrication, what color comes to mind? If you answer brown, or allude to some shade of it, you’re in good company. More than 80% of maintainers to whom I’ve posed this question over the past 30 years have responded the same way.

The reality is that oil and grease products come in a rainbow of colors and shades, including white, gray, black, silver, blue, green, red, purple, and every variation of brown, from golden honey to dark, earth tones. Manufacturers typically color these products for their own purposes. Unfortunately, there’s no formal industry standard or convention regarding their choices, with the exception that most food-grade greases tend to be white.

Most lubricant colors are naturally influenced by the color of the crude base-oil stock and its additive package. For example, when molybdenum disulphide (MoS2) is added in any quantity, it can significantly darken the lubricant to near black in color. Manufacturers, though, add colorants to their respective lubricants to help identify different brands and/or make products more appealing and marketable to the end user.

Despite incongruent colorization, maintenance departments can take advantage of differences in lubricant colors in their plants. For example, if two or more grease brands or different colors are employed in a facility, personnel can be made aware of which color belongs to what bearing by a photo of that grease color posted on the machine or close to the grease nipple. If a trace amount of the previously used grease is evident at the bearing or grease nipple, maintainers would (should be made to) understand that they are not to pump a grease of a different color or shade on top of the original grease.

Oil colors are a different matter. Oil ages in service and its additive package will deplete through contamination, heat, and oxidation. This causes a natural darkening in color. That visual cue has been used for many years in industry and the automotive world to manage oil changes. Sadly, this somewhat risky strategy can fall flat when an oil is changed out with one of a different color and additive composition—especially in the case of darker oils.

Introducing color coding

In 1950, the prestigious UK Scientific Lubrication Journal published an article by M.J. Harrison titled “Color Codes.” In it, Harrison, who at the time was an engineer in the technical department of the UK’s C.C. Wakefield & Co. (now known as Castrol), detailed a symbol/color-control system methodology for identifying the lubricants used in an industrial plant. As he pointed out, employing symbols to denote frequency of application and colors to signify lubricant type would ensure that unskilled workers were able to perform “factory lubrication” in a consistent manner, with scientific precision.

Harrison went on to recommend the use of different 1-in.-high geometric symbols painted on lubricant reservoirs or at lube points to represent lubrication-interval schedules. He proposed a circle to represent the need for daily lubrication, a triangle for weekly lubrication, and a square to represent monthly intervals between lubrication activities. For activities conducted on a quarterly basis (or over longer periods), the square was to again be used, but this time with a number painted inside the square to highlight the number of interval months.

To determine the correct lubricant to apply, each symbol was to be painted one of three primary colors: yellow, red, or blue to correspond with an already-determined lubricant legend. If more than three lubricants were to be used, the same colors were used again, but with the addition of a bold black diagonal stripe across the symbol.

But Harrison didn’t stop with the design and color of symbols and shapes to help identify different lubricant and application intervals in a facility. He also advocated color-coding reservoirs and dedicated transfer equipment to eliminate cross-contamination problems.

Which colors to use

Screen Shot 2016-06-13 at 2.46.48 PM

Color identification is an ideal means of ensuring that the right lubricant ends up in the right place, at the right time. The actual colors themselves are not as important as their consistent use, i.e., assigning a specific color to a single lubricant and all dedicated equipment employed in its use, storage, and transfer within the plant environment, as depicted in Fig. 1.

Fig. 2. This yellow-color-coded, transfer container is from OilSafe, Rockwall, TX (oilsafe.com).

Fig. 2. This yellow-color-coded, transfer container is from OilSafe, Rockwall, TX (oilsafe.com).

Harrison initially promoted the three primary colors of red, blue, and yellow for his system. In modern plant environments, however, we’re comfortable using primary and secondary color palettes, including green, orange, and purple. This is clearly evidenced by the breadth of today’s commercially available, color-coded lubrication-handling systems, including the example transfer products shown in Figs. 2 and 3.

Fig. 3. Shown is an orange-color-coded, clear-body, pistol-grip grease gun from OilSafe, Rockwall, TX (oilsafe.com).

Fig. 3. Shown is an orange-color-coded, clear-body, pistol-grip grease gun from OilSafe, Rockwall, TX (oilsafe.com).

Lubricant storage and transfer systems, though, reflect just one area where colorization pays off for a site. Another important use of color identification involves a condition-based approach to filling oil reservoirs.

Fig. 4. Color-coding is used on this condition-based Hi–Lo lubricant-reservoir-fill application. (courtesy EngTech Industries Inc.)

Fig. 4. Color-coding is used on this condition-based Hi–Lo lubricant-reservoir-fill application. (courtesy EngTech Industries Inc.)

Figure 4 is a good example of this Hi-Lo technique. It involves using red, amber (yellow), and green lines taped on the side of an automated-lubrication-system reservoir. This arrangement is known as a RAG (red/amber/green), or the traffic-light indicator system:

  • The green line indicates the upper fill level.
  • The amber (yellow) line indicates a level at which the operator is to contact the maintenance department with a first request to fill the reservoir.
  • The red line alerts the operator to call in a priority request to fill the reservoir.

Coloring your efforts

Today, you’ll find an array of color-coded tags and transfer equipment in the marketplace. These types of innovative solutions are relatively inexpensive to purchase and implement—and highly effective when used consistently. The question is, “Just how colorful are your lubrication efforts?”  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 kbannister@engtechindustries.com.

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100

7:27 pm
April 11, 2016
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Fund Your Lubrication Program Through Energy Savings

Good lubrication practices can help cut a site’s energy consumption and, in the process, possibly turn lubrication personnel into corporate heroes.

By Ken Bannister, MEch Eng (UK) CMRP, MLE

If you want to assure a reasonable life span for mechanical equipment with rotational and/or sliding elements built into its design, you must lubricate it. The benefits of doing so, however, go well beyond the health of the lubricated equipment.

Virtually all machine designs facilitate some form of lubrication by incorporating one or more means of lubricating bearing surfaces. These solutions range from something as simple and austere as grease nipples at major bearing points to full-blown, centralized, automated re-circulating-oil systems. Regardless of the method/system, it’s incumbent on the end user to understand all of the benefits that can be achieved through effective lubrication practices, and the importance of implementing and adhering to a lubrication regime based not on OEM recommendations, but rather on ambient and machine operating conditions.

Arguably, of all the interactions that can be performed between a person and a machine, lubrication will be one of the least expensive and, collectively, will deliver the greatest impact on machine performance in terms of its life cycle, availability, reliability, production throughput, quality, energy use, and carbon footprint.

Stamping-press case study 

The stamping press featured in this story is one of five 500-ton pure mechanical, straight-side presses at a site. The press stamps out automotive body pieces—requiring significant energy transfer.

This press employs an OEM-designed centralized box-cam-style automated recirculating-lubrication system that delivers a local re-refined (reclaimed) extreme-pressure (EP) 150 Gib and Way oil to rotating main and countershaft bearings and sliding surfaces. The system had not been calibrated since commissioning.

Energy is supplied by an electric variable-speed drive (VSD), and the press is used 12 shifts each week, for a total annual usage of 4,800 hr. Equipment monitors energy consumption over a 48-hr. period calculated an average use of 25.2 kW p/hr.

The press was observed under load with an infrared camera that showed lubrication delivery was unbalanced on the main and counterbalance shaft bearings. A 45 F temperature range between bearings indicated the need for immediate re-calibration of the lubrication system. The lubrication system also had numerous dirty filters. After the lubricant and filters were changed out, the press was restarted and the cam lubricators re-calibrated.

Back in production and monitored over another 48-hr. period, the stamping press showed a dramatic 18% reduction in energy consumption, i.e., with average usage at 20.5 kW p/hr.

Based on 4,800 running hr./yr. and a delivered energy price of 10 cents/kWhr the energy-reduction savings for one press was calculated as follows:

(25.2 x 4,800 x 0.1) – (20.5 x 4,800 x 0.1)  = (12,096 – 9,840)  = approx. $2,256 per press (or $11,280 for all five presses) 

The energy savings of 112,800 kWhr was also calculated against the carbon footprint. Using the Carbon Trust calculation of 1 kWhr = 0.000537 emission tonne equivalency, this automotive manufacturer accrued a carbon credit of approximately 60 tonnes—for just its presses.

Additional accrued benefits from the lubrication program implementation included:

  • reduced purchase costs through lubricant consolidation
  • reduced lubricant and replacement bearing carry costs
  • reduced lubricant stock rotation requirement
  • increased inventory real estate
  • reduced lubricant waste that could meet corporate environment and sustainability program mandates (ISO 14000 mandate).

Making engineered choices in lubricants, lubricant application devices/systems, and lubrication control will ensure that equipment delivers as designed, and, as an added bonus, help a site significantly cut its annual energy costs. The bottom line? A good-lubrication-practices program can front energy-waste-elimination efforts and be solely underwritten by the energy savings. MT

Contributing editor Ken Bannister is a Certified Maintenance and Reliability Professional and certified Machinery Lubrication Engineer (Canada). The author of Lubrication for Industry (Industrial Press, South Norwalk, CT) and the Lubrication Section of the 28th Edition of Machinery’s Handbook (Industrial Press), he can be reached at kbannister@engtechindustries.com.

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1576

7:09 pm
July 8, 2015
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Troubleshoot Hot Hydraulics

0715hydraulic1

High oil temperatures in industrial hydraulic systems can lead to a world of hurt. Don’t let them get you down.

By Jane Alexander, Managing Editor

Remember that hydraulic system running at 145 F last fall? The one you didn’t worry about with cooler weather on the way? In the middle of summer, it could be operating even hotter—if it hasn’t already shut down. That’s because any industrial hydraulic system that runs higher than 140 F is too hot. The resulting problems are costly:

  • Every 15-deg. increase in temperature over 140 F cuts oil life in half.
  • Sludge and varnish build-up makes valve spools stick.
  • Oil bypass increases in pumps and hydraulic motors, causing machines to operate at a slower speed.
  • O-rings harden, leading to system leaks.

In some cases, high oil temperatures lead to wasted electricity by forcing the pump-drive motor to pull more current to operate the system.

Fluid power specialist Al Smiley of GPM Hydraulic Consulting, Monroe, GA, has dealt with countless hydraulic systems in industrial operations throughout the past 20 years. We asked him for ways to troubleshoot hot-running systems.

Understand system capabilities

“First things first,” said Smiley, “it’s important to keep in mind that all hydraulic systems generate a certain amount of heat.” Approximately 25% of the input electrical horsepower will be used to overcome heat losses in a system. Whenever oil is ported back to the reservoir, and no useful work is done, heat will be generated.

The tolerances inside pumps and valves normally permit a small amount of oil to continuously bypass a system’s internal components, causing the fluid temperature to rise. When oil flows through the lines, several resistance points are encountered. For example, flow-control, proportional, and servo valves control the flow by restricting it. When oil flows through those valves, a pressure drop occurs. This means a higher pressure will exist at the inlet port than at the outlet port. Any time oil flows from a higher to a lower pressure, heat is generated and absorbed in the oil.

When a hydraulic system is designed, the reservoir and heat exchangers are sized to remove that heat—some of which is allowed to dissipate through the reservoir walls to the atmosphere. “Heat exchangers, if properly sized,” Smiley noted, “should remove the balance of the heat and allow the system to operate at approximately 120 F.”

Fig. 1. Pressure-compensating piston pumps are the most common type used in industrial hydraulic systems. The tolerances between the pistons and barrel are approximately 0.0004 in.

Fig. 1. Pressure-compensating piston pumps are the most common type used in industrial hydraulic systems. The tolerances between the pistons and barrel are approximately 0.0004 in.

Flow and pressure concerns

The pressure-compensating piston pump (Fig. 1) is the most commonly used type in industrial hydraulic systems. Tolerances between the pistons and barrel are approximately 0.0004 in. A small amount of oil at the pump outlet port will bypass through these tolerances, flow into the pump case, and then be ported back to the reservoir through the case-drain line. “This case-drain flow,” noted Smiley, “does no useful work and is, therefore, converted into heat.”

According to Smiley, the normal flow rate out of the case-drain line is 1% to 3% of the maximum pump volume. For example, a 30-gpm pump should have approximately 0.3 to 0.9 gpm of oil returning to the tank through the case drain. “A severe increase in this flow rate,” he explained, “will cause the oil temperature to rise considerably.”

To check the flow rate, the line can be ported into a container of known size and the flow timed “unless personnel have verified that the pressure in the hose is near zero psi,” Smiley warned, “they should not hold the line during this test.” The line should, instead, be secured to the container, he advised.

A flow meter can also be permanently installed in the case-drain line to monitor flow rates. Check it regularly to determine the amount of bypassing. The pump should be changed when the oil flow reaches 10% of the pump volume.

Fig. 2 (top). During normal operation of this typical variable-displacement, pressure-compensating pump, when system pressure is below the compensator setting (1,200 psi), the internal swash plate is held at maximum angle by the spring. This arrangement allows the pistons to fully stroke in and out, permitting the pump to deliver maximum volume. Flow from the outlet port of the pump is blocked through the compensator spool. Fig. 3 (bottom). Once the pressure builds to 1,200 psi, the compensator spool shifts, directing oil to the internal cylinder. As the cylinder extends the angle of the swash plate, it moves to a near-vertical position. At this point, the pump will only deliver enough oil to maintain the 1,200-psi spring setting. The only heat generated by the pump at this time is from the oil flowing past the pistons and through the case-drain line.

Fig. 2 (top). During normal operation of this typical variable-displacement, pressure-compensating pump, when system pressure is below the compensator setting (1,200 psi), the internal swash plate is held at maximum angle by the spring. This arrangement allows the pistons to fully stroke in and out, permitting the pump to deliver maximum volume. Flow from the outlet port of the pump is blocked through the compensator spool.
Fig. 3 (bottom). Once the pressure builds to 1,200 psi, the compensator spool shifts, directing oil to the internal cylinder. As the cylinder extends the angle of the swash plate, it moves to a near-vertical position. At this point, the pump will only deliver enough oil to maintain the 1,200-psi spring setting. The only heat generated by the pump at this time is from the oil flowing past the pistons and through the case-drain line.

Figure 2 is a diagram of a typical variable-displacement pressure-compensating pump. During normal operation, when the system pressure is below the compensator setting (1,200 psi), the internal swash plate is held at maximum angle by the spring. This allows the pistons to fully stroke in and out and let the pump deliver maximum volume. Flow from the pump’s outlet port is blocked through the compensator spool.

Figure 3 shows the condition of the same pump when pressure reaches 1,200 psi, and the compensator spool shifts, directing oil to the internal cylinder. As the cylinder extends the angle of the swash plate, it moves to a near-vertical position. At that point, the pump will only deliver enough oil to maintain the 1,200-psi spring setting. “The only heat generated by the pump at this time,” Smiley noted, “is from the oil flowing past the pistons and through the case-drain line.”

The following formula, which measures horsepower, is used to determine the amount of heat a pump generates when compensating:

hp = gpm x psi x 0.000583

Assuming the pump is bypassing 0.9 gpm and the compensator is set to 1,200 psi, the amount of heat generation is:

hp = 0.9 x 1,200 x 0.000583

hp = 0.6296

“As long as the system cooler and reservoir can remove at least 0.6296 horsepower of heat,” Smiley stated, “the oil temperature should not increase.” If the bypassing increases to 5 gpm (as shown below), the heat load increases to 3.5 horsepower. If the cooler and reservoir aren’t capable of removing at least 3.5 horsepower, he said, the oil temperature will increase.

hp = 5 x 1,200 x 0.000583

hp = 3.50

Fig. 4. Many pressure-compensating pumps incorporate a relief valve as a safety backup in case the compensator spool sticks in the closed position. The relief valve should be set 250 psi above the pressure-compensator setting. Since the relief-valve setting is above that of the compensator, no oil should flow through the relief-valve spool. Therefore, the valve tank line should be at ambient temperature.

Fig. 4. Many pressure-compensating pumps incorporate a relief valve as a safety backup in case the compensator spool sticks in the closed position. The relief valve should be set 250 psi above the pressure-compensator setting. Since the relief-valve setting is above that of the compensator, no oil should flow through the relief-valve spool. Therefore, the valve tank line should be at ambient temperature.

Settings matter

Many pressure-compensating pumps incorporate a relief valve as a safety backup in case the compensator spool sticks in the closed position (Fig. 4). According to Smiley, the relief valve should be set 250 psi above the pressure-compensator setting. If the relief valve setting is above that of the compensator, no oil should flow through the relief-valve spool. Therefore, the tank lines of these valves should be at ambient temperature.

If, however, the compensator were to stick in the position shown in Fig. 2, the pump will deliver maximum volume at all times and oil not used by the system will return to the tank through the relief valve. “If this occurs, Smiley said, “significant heat will be generated.”

Smiley lamented that plant personnel often randomly adjust the pressures in these systems in an attempt to make the equipment run better. “If the local knob turner turns the compensator pressure above the setting of the relief valve,” he explained, “the excess oil will return to the tank through the relief valve, causing the oil temperature to rise 30 or 40 degrees. If the compensator fails to shift or is set above the relief-valve setting, a tremendous amount [of heat] will be generated.”

Assuming the maximum pump volume is 30 gpm and the relief valve is set to 1,450 psi, the amount of heat generation can be determined using the following formula.

hp = 30 x 1,450 x 0.000583

hp = 25 hp

If a 30-hp electric motor is used to drive this system, 25 hp will be converted to heat when in the idle mode. Since 746 W = 1 hp, then 18,650 W (746 x 25) or 18.65 kW of electrical energy will be wasted.

Other factors

Smiley cited several other heat-generators in hydraulic systems and the importance of maintaining these components. These include accumulator dump valves and air-bleed valves that fail to open, thus allowing oil to bypass to the reservoir at high pressure. He also pointed to heat generated by oil bypassing cylinder piston seals.

To ensure that excess heat is removed from hydraulic systems, Smiley said it’s also crucial to properly maintain heat exchangers and coolers.

If an air-type heat exchanger is used, clean the cooler fins—using a degreaser, if necessary—on a regularly scheduled basis. The temperature switch that controls the cooler fan should be set at 115 F.

If a water-cooled system is used, a modulating valve should be installed in the water line to regulate the flow through the cooler tubes to 25% of the oil flow.

Smiley noted that reservoirs should be cleaned at least annually, lest sludge and other contaminants coat their bottoms and sides. This would allow the reservoir to act as an incubator instead of dissipating heat to the atmosphere.

Last word

Smiley offered a final helpful hint for hot-hydraulics troubleshooters: “The next time a heat issue surfaces in one of your hydraulic systems, look for oil flowing from a higher to a lower pressure in the system. That is where you’ll find your problem.” MT

Al Smiley is president of GPM Hydraulic Consulting Inc. (gpmhydraulic.com), based in Monroe, GA.

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8:00 pm
May 18, 2015
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The Inner Life of Bearings, Part 2: Lubricant Selection And Application Frequencies

BY Neville Sachs, P.E.

This overview of bearing geometries and operating conditions will help simplify the sometimes difficult process of choosing the right lubricant. Part 1 of this series explored the three types of common industrial bearings. This concluding installment offers quick tips from the real world on how to select the correct lubricants for these bearings and their recommended frequency of application. The approaches vary.

Fig. 1. A general guide to recommended viscosities for ball, roller and roller thrust bearings

Fig. 1. A general guide to recommended viscosities for ball, roller and roller thrust bearings

1. Oil-lubricated ball and roller bearings

Lubricating ball and roller bearing isn’t difficult. Assuming the lubricant is clean and contains no water, its most critical aspect is viscosity. The three heavy horizontal lines in Fig. 1 show a general guide to the minimum recommended viscosities for ball, roller and roller thrust bearings. The figure shows that for a tapered roller bearing running at 140 F (40 C), an ISO 46 is the minimum recommended. (Note: This chart is not applicable for slow-speed applications—those below approximately 50 rpm—and is drawn for oil with a viscosity index of 95.)

Ball, radial roller and roller thrust bearings have different geometries, which necessitate different lubricant viscosities:

  • As a ball bearing rolls, it only has point contact and, thus, tolerates variations around its path.
  • A plain roller or tapered roller bearing has a line of contact, which requires a greater film thickness to prevent damage.
  • In an operating thrust bearing, the roller describes an arc with a tremendous difference in surface speed between the innermost and outermost contact points, which means it requires an even thicker film to prevent skidding damage.

The typical lubricating oil for rolling-element bearings will be clean, free of water, and contain the correct additives for the bearing’s ambient working conditions. For example, in water-contaminated applications, it is good for the oil to incorporate additives that reduce the chance of corrosion, but extreme-pressure (EP) additives are only helpful in very-low-speed applications.

2. Grease-lubricated ball and roller bearings

A typical grease is roughly 80% oil, 5% additives and 15% thickener. The role of the thickener is to act as a reservoir for the oil, allowing it to slowly separate as the temperature rises and flow into the bearing; the viscosities shown in Fig. 1 are still critical. But because heat tends to deteriorate a thickener over time and change the rate of oil separation, some operating conditions will require more oil than others.

Figures 2 and 3 reflect empirical charts developed for and used successfully in setting up lubrication programs in several large manufacturing plants and paper mills. (Note: These charts were not the result of laboratory research, but substantial trial and error.)

Fig. 2. A simple guide to re-greasing intervals for bearings

Fig. 2. A simple guide to re-greasing intervals for bearings

The information in Fig. 2 can help determine basic re-greasing intervals for ball and roller bearings. The five curves on the chart are for five different bearing bores (shaft diameters). The approach is to use the shaft speed and diameter to define the basic interval.

Referring to Fig. 2, we can see that the suggested re-greasing interval for a 3-in. diameter shaft rotating at 1750 rpm would be 8000 hours. That value, though, has to be modified by the factors that correct for the actual conditions surrounding the bearing, as shown in Fig. 3.

Fig. 3. Modifying factors for recommended re-greasing intervals of ball and roller bearings based on operating conditions. Click to enlarge.

Fig. 3. Modifying factors for recommended re-greasing intervals of ball and roller bearings based on operating conditions. Click to enlarge.

If that 3-in. (75 mm) shaft in Fig. 2 were horizontal, had two spherical roller bearings on it and was running at about 160 F (71 C) in a dry but slightly dusty environment with very low vibration, the corrected re-greasing period would be found by multiplying the original 8000 hours by each of the correction factors as follows:

Actual period = 8000 hours x Ft x Fc x Fm x Fv x Fp x Fb
= 8000 hours x 0.5 x 1.0 x 1.0 x 1.0 x 1.0 x 0.1 = 400 hours

Accordingly, if the referenced plant were running two eight-hour shifts per day, five days per week, the example bearings would need to be greased every five weeks, and would likely be rounded off to once per month. (Note: This approach does not apply to very-slow-speed bearings.)

3. Oil-lubricated plain bearings

The procedure needed to select the correct lubricant for higher-speed plain bearing applications (over 100 rpm) is beyond the scope of this article. As mentioned in Part 1, and in Ken Bannister’s article this month on the path to bearing reliability, if the oil supply to the bearing exceeds the leakage, the bearing will develop its film. Complicating the situation is the fact that the leakage rate will depend on the clearance, ambient temperature, oil ISO grade and the load, and the correct lube specification requires a long and detailed calculation.

Remember that bearings with babbitt contact faces are far more tolerant of contamination than those with bronze or aluminum contact faces. (Note: Bronze and aluminum lack the embedability of babbitt, and any contamination with solid particles approaching the film thickness can lead to upset conditions.)

4. Grease-lubricated plain bearings

The key to successful lubrication of grease-lubricated plain bearings is the additive package in the grease. Decades ago, it was common to find lead in bronze bearings because the lead would liquefy and provide a lubricant film under high pressures. Today’s environmental concerns have virtually eliminated lead as a lubricant component. Science replaced it with various chemicals, including molybdenum disulfide, sulfurized isobutylene compounds and potassium-boron compounds. These formulations have led to outstanding results. Still, there can be a huge difference in performance from one formulation to the next.

When it comes to setting up a re-lubrication schedule for grease-lubricated plain bearings, it is imperative to consult with—and heed the advice of—an experienced lubrication professional and/or your lubricant supplier. The same is true for other important decisions in your lubrication program.

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.

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7:54 pm
May 18, 2015
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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.

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