The Hidden Dangers of Lubricant Starvation.doc

7/27/2019 The Hidden Dangers of Lubricant Starvation.doc

http://slidepdf.com/reader/full/the-hidden-dangers-of-lubricant-starvationdoc 1/21

The Hidden Dangers of LubricantStarvation

••

•

• Jim Fitch, Noria Corporation Tags: industrial lubricants

For those who strive for lubrication-enabled reliability (LER), more than 95 percent of the

opportunity comes from paying close attention to the “Big Four.” These are critical attributes

to the optimum reference state (ORS) needed to achieve lubrication excellence. The “Big

Four” individually and collectively influence the state of lubrication, and are largely

controllable by machinery maintainers. They are well-known but frequently not well-

achieved. The “Big Four” are:

1. Correct lubricant selection

2. Stabilized lubricant health

http://www.machinerylubrication.com/Authors/Detail/1


http://www.machinerylubrication.com/Meta/Tags/industrial%20lubricants





3. Contamination control

4. Adequate and sustained lubricant level/supply

The first three of the “Big Four” have benefited from considerable industry attention,

especially in recent years. Conversely, the last one has gone relatively unnoticed yet is noless important. Therefore, it will be the central focus of this article.

Over the past few decades, researchers and tribologists have compiled countless listings

that rank the chief causes of machine failure. We’ve published many of these in Machinery

Lubrication magazine. The lists ascribe the causes of abnormal machine wear to the usual

suspects: contamination, overheating, misalignment, installation error, etc. There’s typically

a lubrication root-cause category that is a catch-all for one or more causes that can’t be

easily specified or named. I’ve seen terms used like “inadequate lubrication” and “wrong

lubrication.”

Understandably, it is difficult for failure investigators and analysts to trace back the exactsequence of events beginning with one or more root causes. Evidence of these causes is

often destroyed in the course of failure or in a cover-up during the cleanup and repair.

Having led several hundred such investigations over the years, I’ve learned that one root

cause in particular is too often overlooked - lubricant starvation.

81%of lubrication professionals have seen the

effects of lubricant starvation in the machines

at their plant, according to a recent survey at

machinerylubrication.com

Although most everyone knows about this in principle and realizes the common sense of

adequate lubricant supply, it is frequently ignored because many typical forms of lubricant

starvation are largely hidden from view. For instance, who notices the quasi-dry friction that

accelerates wear each time you start an automobile engine? This is a form of lubricant

starvation. It’s not a sudden-death failure, but it is a precipitous wear event nonetheless.

Each time controllable wear goes uncontrolled, an opportunity is lost to prolong service life

and increase reliability.

The Nature of Lubricant Starvation

Machines don’t just need some lubricant or any lubricant. Rather, they need a sustained and

adequate supply of the right lubricant. Adequate doesn’t just mean dampness or the nearby

presence of lubricant. What’s defined as adequate varies somewhat from machine to

machine but is critical nonetheless. High-speed equipment running at full hydrodynamic film

has the greatest lubricant appetite and is also the most punished when starved. Machines

running at low speeds and loads are more forgiving when lube supply is restricted. Even

these machines can fail suddenly when severe starvation occurs.



The table below illustrates how lubricants reach frictional surfaces in numerous ways.

There are six primary functions of a lubricating oil. These are friction control, wear control,

temperature control, corrosion control, contamination control and transmittance of force and

motion (hydraulics). Each of these functions is adversely influenced by starvation

conditions. The worst would be friction, wear and temperature control. Even partial

starvation intensifies the formation of frictional heat. It also slows the transport of that heat

out of the zone. This is a compounding, self-propagating condition that results in collapsed

oil films, galling, adhesive wear and abrasion (Figure 1).

Figure 1. Starvation Illustrated

In the case of grease, starvation-induced heating (from friction) of the load zone accelerates

grease dry-out, which escalates starvation further. Heat rapidly drains oil out of the grease

thickener, causing volatilization and base oil oxidation, all of which contributes to hardening

and greater starvation.

Lubricating oil needs reinforcement, which is lost when flow becomes restricted or static.

Flow brings in bulk viscosity for hydrodynamic lift. In fact, lack of adequate lubricant supply

is functionally equivalent to inadequate viscosity from the standpoint of film strength.

4 Keys to Solving Starvation Problems Using

Proactive Maintenance

1. Identify the required lube supply or level to optimize reliability.

2. Establish and deploy a means to sustain the optimized supply or level.

3. Establish a monitoring program to verify the optimized supply or level is consistently

achieved.

4. Rapidly remedy non-compliant lube supply or level problems.

Oil flow also refreshes critical additives to the working surfaces. This reserve additive supply

includes anti-wear additives, friction modifiers, corrosion inhibitors and others. Lubricant

starvation produces elevated heat, which rapidly depletes additives.

Next, we know that wear particles are also self-propagating. Particles make more wear

particles by three-body abrasion, surface fatigue and so on. Impaired oil flow inhibits the

purging of these particles from the frictional zones. The result is an accelerated wear

condition.



Finally, moving oil serves as a heat exchanger by displacing localized heat generated in load

zones outward to the walls of the machine, oil reservoir or cooler. The amount of heat

transfer is a function of the flow rate. Starvation impairs flow and heat transfer. This puts

increasing thermal stress on the oil and the machine.

Common Signs of Starvation

When you’re encountering chronic machine reliability problems, think through the “Big Four”

and don’t forget about No. 4. It may not be the type of oil, the age of the oil or even the

contamination in the oil, but rather the quantity of oil. How can you know? The chart on

page 8 reveals some common signs of lubricant starvation.

Lubricant Starvation Examples by MachineType

Lubricant starvation can happen in a number of ways. Most are controllable, but a few are

not. The following abbreviated list identifies how lubricant starvation occurs in common

machines.

Starved Engines

• Dry Starts - Oil drains out down to the oil pan when the engine is turned off. On

restart, frictional zones (turbo bearings, shaft bearings, valve deck, etc.) are

momentarily starved of lubrication (Figure 2).



Figure 2. Dry Engine Starts

• Cold Starts - Cold wintertime conditions slow the movement of oil in the engine

during start-up. This can induce air in the flow line due to cold-temperature suction-

line conditions.

• Low Oil Pressure - This can result from numerous causes, including worn bearings,pump wear, sludge and extreme cold. Oil pressure is the motive force that sends oil

to the zones requiring lubrication.

• Dribbling Injectors - Fuel injector problems can wash oil off cylinder walls and

impair lubrication between the piston/rings and the cylinder wall.

Common Signs of Lubricant Starvation

•

Clogged Spray Nozzles and Orifices - Nozzles and orifices direct oil sprays tocylinder walls, valves and other moving components. Sludge and contaminants are

able to restrict oil flow.

Starved Journal and Tilting-Pad Thrust Bearings

• Oil Groove Problems - Grooves and ports channel oil to the bearing load zones.

Grooves become clogged with debris or sludge, restricting oil flow.



• Restricted Oil Supply - Pumping and oil-lifting devices can become mechanically

faulty. This also may be due to low oil levels, high viscosity, aeration/foam and cold

temperatures.

• Sludge Dam on Bearing Leading Edge - Sludge can build up on the bearing’s

leading edge and restrict the oil supply.

Wet-Sump Bearing and Gearbox Starvation

• Oil Level - Many wet-sump applications require critical control of the oil level (Figure

3).

Figure 3. Common Splash Gear Drive

• High Viscosity - Many oil-feed mechanisms (oil rings, slingers, splash feeders, etc.)

are hampered by viscosity that is too high (wrong oil, cold oil, etc.). Gears can

channel through thick, cold oil, interfering with splash and other feed devices.

• Aeration and Foam - Air contamination dampens oil movement and impairs the

performance of oil-feed devices (Figure 4).



Figure 4. How Aeration Retards Oil Supply

• Non-horizontal Shafts - This can cause drag on oil rings and may interfere with

slinger/flinger feed mechanisms.

• Bottom Sediment and Water (BS&W) - Sump BS&W displaces the oil level. On

vertical shafts, the bottom bearing can become completely submerged in BS&W.

• Defective Constant-Level Oilers - This may be due to plugged connecting pipe

nipples, mounting errors (tilted, cocked, mounted on wrong side, etc.), wrong levelsetting, empty reservoir, etc. (Figure 5).

Figure 5. Mounting Errors of Constant-Level Oilers



• Defective Level Gauge Markings - Level gauges should be accurately calibrated to

the correct oil level.

• Level Gauge Mounting and Viewing Issues - These may be hard to see,

goosenecks, fouled gauge glass, gauge vent problems, etc. (Figure 6).

Figure 6. What is wrong with this picture?

Starved Dry-Sump Circulating Systems

• Restricted Oil Returns - Plugged or partially plugged oil returns will redirect oil

flow away from the bearing or gearbox being lubricated. Sometimes called drip-and-

burn lubrication, the condition is usually caused by sludge buildup or air-lock

conditions in the gravity drain lines returning to the tank.

• Worn Oil Pump - When oil pumps wear, they lose volumetric efficiency (flow decay

results).

• Restricted Pump Suction Line - Strainers and pickup tubes can become plugged

or restricted. This can aerate the fluid, cause cavitation and lead to loss of prime.

• Clogged/Restricted Oil Ways and Nozzles - Oil-feed restrictions due to sludge,

varnish and jammed particles can starve bearings and gears (Figure 7).



Figure 7. Plugged Oil Flow

• Entrained Air and Foam - Oil pumps and flow meters perform poorly (or not at all)

when sumps become contaminated with air (Figure 4).

• Lack of Flow Measurement - Components sensitive to oil supply require constant

oil flow measurement.

• Defective or Miscalibrated Flow Meters - Flow meters, depending on the type

and application, can present a range of problems regarding calibration.

• Low Oil Pressure - Oil follows the path of least resistance. Line breaks and openreturns starve oil from higher resistance flow paths and the machine components

they serve.

Starved Spray-Lubed Chains and Open Gears

• Defective Auto-lube Settings - This relates to correctly setting the lube volume

and frequency.

• Defective Spray Targets/Pattern - The oil spray needs to fully wet the target

location. Spray nozzles can lose aim and become clogged (Figure 8).



Figure 8. Correct Lubricant Spray Patterns

on Open-Gear Tooth Flanks

• Gummed Chain Joints - Many chains become heavily gummed, which prevents oil

from penetrating the pin/bushing interface.

Starvation from Grease Single- and Multi-Point AutoLubrication

• Wrong Regrease Settings - Regreasing settings should enable adequate grease

replenishment at each lube point.

• Cake-Lock - This occurs when grease is being pumped. Under certain conditions,

the grease thickener movement is restricted. Oil flows, but the thickener is log-

jammed in a line or component passage (Figure 9).



Figure 9. Cake-Lock

Grease Starvation

• Defective Injector Flow - This is due to wrong injector settings or restricted

injector displacement.

• Restricted Line Flow - Exceedingly long lines, narrow lines, numerous bends,

ambient heat or cold, etc., can lead to partial or complete blockage of grease flow.

• Single-point Lubricator Issues - These include malfunctioning lubricators from

various causes.

Starvation from Manual Lubrication Issues

• Grease Gun Lubrication - This may include an inaccurate volume calibration, a

faulty grease gun mechanism, the wrong relube frequency, an incorrect relube

volume or an improper relube procedure.

• Manual Oil Lubrication - This would include the wrong relube frequency, volume or

procedure.

• Lube Preventive Maintenance (PM) - Missed PMs may be due to scheduling,

management or maintenance culture issues.

The Crux of the Problem

Lubricant starvation is an almost silent destroyer. While there are telltale signs, they

generally aren’t recognized or understood. Of course, there are varying degrees of

starvation. Complete starvation is sudden and blatant. However, more moderate partial

starvation is what tends to go unnoticed until failure. Then, other suspect causes (the

bearing, lubricant, operator, etc.) may be falsely blamed.



Precision lubrication supply is a fundamental attribute of the optimum reference state and is

included in any engineering specification for lubrication excellence. It’s one of the “Big Four”

and thus is overdue for significant attention.

.

Basic Wear Modes in LubricatedSystems

••

•

• Robert Scott Tags: industrial lubricants

This article provides a basic definition and understanding of the major wear modes or

mechanisms based around the ISO 15243.2004 rolling bearing failure mode classification.

Several other modes of wear that occur in gears, journal bearings, hydraulic pumps and

pistons - but don't occur in rolling bearings - will be discussed.

The ISO system discusses wear in six major categories with 15 subcategories.







Not contained in the ISO classification is Erosion from particles and Cavitation.

Wear mechanisms can also be thought of as occurring in two separate categories: contact

and noncontact modes. Contact wear requires the components to have direct metal-to-

metal contact for wear to occur. Noncontact modes do not require the surfaces to come into

direct contact for them to wear; in other words, a full fluid lubricant film may exist.

Subsurface Fatigue

Subsurface fatigue is a form of wear that occurs after many cycles of high-stress flexing of the metal. This causes cracks in the subsurface of the metal, which then propagate to the

surface, resulting in a piece of surface metal being removed.

It begins with inclusions or faults in the bearing metal below the surface. Subsurface

microcracks form due to long-term repeated load cycles and stress (500,000 psi), causing

elastic deformation (flexing) of the metal. This is typical in all rolling bearing elements and

races and gear teeth, all of which operate in the elastohydrodynamic (EHD) lubrication

regime. The contact stress is concentrated at a point below the metal surface.

These microcracks normally propagate to the surface, which eventually results in a piece of

the surface material being removed or delaminated. They appear as surface damage orwear (large pits) referred to as spalling. Other terms for subsurface fatigue include flaking,

peeling and mechanical pitting. A full oil film exists and no metal-to-metal contact or surface

damage is needed. Subsurface fatigue is not a common issue if better quality metals are

used in bearing manufacture. Most bearings will fail by another mechanism first.

Subsurface fatigue failure is the result of a bearing living out its normal life span based on

the load, speed and lubricant film thickness that it is exposed to. The L10 fatigue life of a



bearing is the average time (in hours or cycles) to fail 10 percent of a set of identical

bearings under certain conditions. An estimate of the L10 life can be calculated, providing a

rating life of a bearing.

Surface-initiated Fatigue

This begins with reduced lubrication regime and a loss of the normal lubricant film. The oil

film is reduced to boundary or a mixed regime. Some metal-to-metal contact and sliding

motion occurs. Surface damage occurs. The high points of the metal surface asperities are

removed, which initially appear as a matted or frosted surface. This is not smearing, as inadhesion (discussed below). This type of surface damage is usually visible with a

magnification of three to five times.

The surface damage is coupled with the cyclic loading of the rollers rolling over the race.

This creates asperity microcracks and microspalling. The cracks start at the surface and

migrate down into the metal. An edge of metal is created at the surface which flexes at the

edge of the surface crack. This creates a cold worked edge which is lighter in color. The

cracks propagate and may intersect within the metal, and a piece of surface material is then

removed. Flaking, mechanical pitting and micropitting are other names used to describe

spalling.

Surface fatigue can also occur as a result of plastic deformation (described below).

Contaminant particles in the oil enter the high-load rolling contact area between rollers and

the race, or between gear teeth, and cause some form of surface damage - a dent.

Improper handling of bearings can cause similar surface damage.



These round-bottomed dents often have a raised berm around their edges. The raised berm

of metal acts as a point of increased load or stress, or creates a reduced lubrication regime

(mixed or boundary), and leads to a lower surface fatigue life. Improved filtration reduces

plastic deformation, and therefore indirectly reduces the occurrence of surface fatigue.

Notice that the term "contact fatigue" is not used by ISO. This is a vague term sometimesused to describe both forms of fatigue. It does not specify whether metal flexing damage

started in the subsurface or from some initial surface damage. It encompasses any change

in the metal structure caused by repeated stresses concentrated at a microscopic scale in

the contact zone between the rolling elements and raceways, and between gear teeth.

Abrasive Wear

Abrasive wear is estimated to be the most common form of wear in lubricated machinery.

Particle contamination and roughened surfaces cause cutting and damage to a mating

surface that is in relative motion to the first.

Three-body abrasion occurs when a relatively hard contaminant (particle of dirt or wear

debris) of roughly the same size as the dynamic clearances (oil film thickness) becomes

imbedded in one metal surface and is squeezed between the two surfaces, which are inrelative motion. When the particle size is greater than the fluid film thickness, scratching,

ploughing or gouging can occur. This creates parallel furrows in the direction of motion, like

rough sanding. Mild abrasion by fine particles may cause polishing with a satiny, matte or

lapped-in appearance. This can be prevented with improved filtration, flushing and sealing

out small particles.



Two-body abrasion occurs when metal asperities (surface roughness, peaks) on one

surface cut directly into a second metal surface. A contaminant particle is not directly

involved. The contact occurs in the boundary lubrication regime due to inadequate

lubrication or excessive surface roughness which could have been caused by some other

form of wear. Higher oil viscosity, increased metal hardness and even demagnetizing

bearings after induction heating during installation may help to reduce two-body abrasion.

Adhesive Wear

Adhesive wear is the transfer of material from one contacting surface to another. It occurs

when high loads, temperatures or pressures cause the asperities on two contacting metal

surfaces, in relative motion, to spot-weld together then immediately tear apart, shearingthe metal in small, discrete areas.

The surface may be left rough and jagged or relatively smooth due to smearing/deformation

of the metal. Metal is transferred from one surface to the other. Adhesion occurs in

equipment operating in the mixed and boundary lubrication regimes due to insufficient lube

supply, inadequate viscosity, incorrect internal clearances, incorrect installation or

misalignment. This can occur in rings and cylinders, bearings and gears.

Normal break-in is a form of mild adhesive wear, as is frosting. Scuffing usually refers to

moderate adhesive wear, while galling, smearing and seizing result from severe adhesion.

Adhesion can be prevented by lower loads, avoiding shock loading and ensuring that thecorrect oil viscosity grade is being used. If necessary, extreme pressure (EP) and antiwear

(AW) additives are used to reduce the damage.



CorrosionMoisture corrosion involves material removal or loss by oxidative chemical reaction of the

metal surface in the presence of moisture (water). It is the dissolution of a metal in an

electrically conductive liquid by low amperage and may involve hydrogen embrittlement. It

is accelerated, like all chemical reactions, by increased temperatures. No metal-to-metal

contact is needed. It will occur with a full oil fluid film.

Corrosion is often caused by the contamination or degradation of lubricants in service. Most

lubricants contain corrosion inhibitors that protect against this type of attack. When the

lubricant additives become depleted due to extended service or excessive contamination by

moisture, combustion or other gases or process fluids, the corrosion inhibitors are no longer

capable of protecting against the acidic (or caustic) corrosive fluid and corrosion-induced

pitting can occur. The pits will appear on the metal surface that was exposed to the

corrosive environment.

This may be the entire metal surface or just the lower portion of the metal that may have

been submerged in water not drained from the oil sump or at the roller/race contact points.

Generally, an even and uniform pattern of pits will result from this form of attack. Mild

forms of moisture corrosion result in surface staining or etching. More severe forms are

referred to as corrosive pitting, electro-corrosion, corrosive spalling or rust.

Frictional corrosion is a general form of wear caused by loaded micromovements orvibration between contacting parts without any water contaminant being present, although

humidity may be necessary. It may also be referred to as fretting wear. It includes both

fretting corrosion and false brinelling, which in the past were often considered to be the

same mechanism.

Fretting corrosion is the mechanical fretting wear damage of surface asperities

accompanied and escalated by corrosion, mostly oxidation in air with some humidity



present. It occurs due to many oscillating micromovements at contacting interfaces between

loaded and mating parts in which the lubricant has not been replenished (an unlubricated

contact). Adhesion is occurring and it is generally considered more severe than false

brinelling.

It usually appears as a reddish-brown oxide color (rust without water being present) onsteel and black on aluminum. Metal wear debris flakes are created or shed off.

Fretting corrosion occurs on many mechanical devices such as gear teeth and splines, not

just rolling element bearings, and can occur on surfaces other than the rolling contact. In

bearings, it is also associated with bearing fit on the shaft and in the housing. It occurs

where there is not any large relative motion between the mating parts such as between the

shaft and the inner race and between the housing and the outer race. Fretting corrosion can

occur on materials that do not oxidize.

False brinelling occurs due to micromovements under cyclic vibrations in either static or

rotating boundary lubrication contacts. Mild adhesion of the metal asperities is occurring.

Shallow depressions or dents are created in which the original machining marks are worn off

and no longer visible due to the wearing damage of the metal. False brinelling occurs on the

rolling elements and raceway, similar to small-scale plastic deformation or brinelling (see

below) and hence the name "false brinelling".

False brinelling is usually associated with static nonrotating equipment and, thus, the wear

appears at the roller contacts with the exact same spacing as the rollers. The depressions in

the metal can appear shiny with black wear debris around the edges. If the equipment is

rotating, the wear appears as a gray, wavy washboard pattern on the raceway. Reduced

bearing life or failure ultimately occurs, sometimes in a catastrophic fashion, through

surface fatigue initiating in these damaged surface layers.

An example of false brinelling occurs in standby electric motors and pumps (and others)

which sit idle for periods of time, but are subjected to vibration from the plant floor up

through the load-bearing rolling elements of the bearings. Antiwear additives may be

beneficial in reducing the wear damage.



Electrical Erosion

This type of wear occurs when electric current passes between two metal surfaces (for

example, bearing roller and race) through the oil or grease film. It is subdivided based on

the severity of the damage. Electrical erosion should not be confused with erosion caused by

particles (discussed below).

Excessive voltage (electrical pitting) is caused by a high electrical current or amperage

passing through only a few asperities on the metal. Voltage builds up and then arcs, causing

localized heating/melting and vaporization of the metal surface. This causes deep, largecraters or pits in the metal surfaces, which may correspond to the spacing between the

rolling elements of the bearing. It is possibly due to welding in the area and inadequate

grounding or insulation. It may also be referred to as electrical pitting, arcing or sparking.

Current leakage (electrical fluting) is a less severe form of damage caused by a lower

continuous electrical current. The damage may be shallow craters that are closely positioned

and appear dark gray in color. If the electrical discharge occurs while the bearing is in

motion, with a full fluid film, a washboard effect or grooves appear on the entire bearing

raceway and is called fluting or corduroying.

Plastic DeformationThis is the denting, indentations or depressions in the race or rollers caused by impact or

overloading. The surface metal flows, causing irreversible deformation (not wear). The

machining marks are still visible in the bottom of the dent. The dents often have a raised lip

which increases stresses and leads to surface-initiated fatigue (surface cracks) and eventual

pit formation or adhesive wear. Plastic deformation consists of three subcategories.



Overload or true brinelling is characterized by static or shock loading, or impact from

operational abuse, causing a permanent dent in the metal without cutting or welding of the

metal. An example occurs in roller bearings when impact causes the rollers to create a

series of dents in the bearing race surface at intervals that match the roller spacing exactly.

Some people consider denting from the impact of hammering on a bearing as overload;

others may consider it as an indentation from handling.

Indentation from debris is a form of plastic deformation but it is caused by a particle

trapped within the dynamic clearances between two machine elements and being over-

rolled. The force causes a round-bottom dent to form in the race or rolling element. Cracks

may propagate down into the metal.

Indentation from handling is similar to that from debris, but results from a bearing being

dropped or hammered, causing localized overloading. It can also be due to nicks from hard

or sharp objects.

It is common to encounter erosion from particles in the oil and cavitation, although this is

not included in the ISO standard for rolling bearings.

Erosion

Erosion could be considered a form of abrasive wear. It occurs principally in high-velocity,

fluid streams where solid particle debris, entrained in the fluid (oil), impinges on a surface

and erodes it away. Hydraulic systems are an example where this type of wear may occur.

Flow rates have a significant influence on these wear rates, which are proportional to at

least the square of the fluid velocity. Erosion typically occurs in pumps, valves and nozzles.

Metal-to-metal contact does not occur. The mechanism of erosion is used to an advantage

in water-jet cutting.

Cavitation

This is a special form of erosion in which vapor bubbles in the fluid form in low-pressure

regions and are then collapsed (imploded) in the higher-pressure regions of the oil system.

The implosion can be powerful enough to create holes or pits, even in hardened metal if the

implosion occurs at the metal surface. This type of wear is most common in hydraulic

pumps, especially those which have restricted suction inlets or are operating at high

elevations.

Restricting the oil from entering the pump suction reduces the pressure on the oil and, thus,

tends to create more vapor bubbles. Cavitation can also occur in journal bearings where thefluid pressure increases in the load zone of the bearing. No metal-to-metal contact is

needed to create cavitation.

Just to be clear, pitting is a general term used in failure analysis to describe almost any

small, rough-bottomed, circular potholes in the metal surface. Pits can be caused by

mechanical pitting (fatigue or cavitation), chemical pitting (corrosion) or by electrical pitting

(stray arcing), all of which are described above.



Failure analysis is used to assign a wear mechanism to a specific failure. If the wear

mechanism can be determined, then some corrective action can be applied to prevent the

failure from recurring. Often, it can be useful to use the process of elimination to determine

which wear mechanisms could not have produced the observed wear pattern, thus reducing

the number of possible mechanisms. Unfortunately, combinations of wear mechanisms exist

in most situations, thus complicating the selection of the optimum wear-resistant system.

Acknowledgment

Several portions of this article may contain residual wording from an article that was

originally written by Rees Llewellyn of the National Research Council of Canada for the

Alberta section of the Society of Tribologists and Lubrication Engineers (STLE).

http://republica-dominicana.muchoviaje.com

The Hidden Dangers of Lubricant Starvation.doc

Documents