Archive | Lubrication

14

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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1358

7:09 pm
July 8, 2015
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Troubleshoot Hot Hydraulics

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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.

112

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.

122

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.

84

7:51 pm
May 18, 2015
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From Our Perspective: Protecting Your Golden Goose

kennewmugBy Ken Bannister, Contributing Editor
kbannister@engtechindustries.com

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

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

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

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

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

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

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

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

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

1058

11:12 pm
February 18, 2015
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Lubrication Checkup: ISO 55001 Certification

0814lubecheckupBy Dr. Lube, aka Ken Bannister

Symptom:

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

Diagnosis:

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

Prescription:

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

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

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

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

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

104

7:41 pm
February 18, 2015
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Procuring The Highest-Quality Oil Sample

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

By Ken Bannister, Contributing Editor
kbannister@engtechindustries.com

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

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

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

Data density

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

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

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

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

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

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

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

Data disturbance

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

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

Sampling consistency

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

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

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

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

135

7:29 pm
February 18, 2015
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The Inner Life of Bearings, Part 1: How Lubrication Really Works

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

By Neville Sachs, P.E.

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

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

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

Back to the basics

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

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

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

λ =  h/(R12 + R22)1/2

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

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

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

How different bearing types operate

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Coming up

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

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

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