To the naked eye, a lubricant sample might look clean, but in fact, contains tiny wearcausing contaminants, including dirt, dust, sand, metal shards and other elements. Subsurface initiated fatigue in the outer ring load zone surface initiated fatigue in the outer ring of a spherical roller bearing. It is sometimes difficult to determine the real cause. An explanation for nearthreshold corrosion fatigue crack. Rolling contact fatigue an overview sciencedirect topics. Shaffer, battelle laboratories contact fatigue is a surfacepittingtype failure commonly found in ball or roller bearings. An explanation for nearthreshold corrosion fatigue crack growth. Corrosion fatigue is characterized by brittle fracture. The sources of the hydrogen can be water, but also electrolysis and corrosion aided by water.
Photomicrograph of the spalled surface of a ball from a small seized bearing showing the remnant contact fatigue cracks arrows at the edge of the spall, as shown in figure 25. Choosing a material with the correct values for hardness, corrosion resistance, strength, fracture toughness and fatigue life ensures that a bearing will function reliably within an applications operational and environmental parameters. Moisture corrosion in wind gearboxes is usually not seen during skf investigations. Hydrogen embrittlement of a roller bearing outer ring. For example, tiny, very flat pits can appear under a relatively low load and simultaneous slippage. Cracks, chips wear rust, corrosion others discoloration heat generation, chemical action fig. Bearings may fail earlier than the expected rolling fatigue life. Adhesive wear adhesive wear electrical erosion wear corrosion fracture and cracking fatigue plastic deformation abrasive wear ref iso 15243 rolling bearings damages and failures terms, characteristics and causes. Fatigue in roller bearings may differ from ball beating contact fatigue. Limits of acceptability1 bearings with subsurface initiated fatigue should always be scrapped. Rolling element bearing surface fatigue is characterized by spalling. If youve been following this series, you can see that insufficient lubrication contributes to most of the above listed types of bearing damage, including smearing. Premature failure initiated by corrosion in some applications, bearings fatigue develops faster than expected.
Corrosion fatigue cracks propagate generally by transgranular mechanism through the grains along crystallographic planes. Material analysis of the fatigue mechanism of rollers in. Bearing rust and corrosion are pits on the surface of rings and. Fatigue strength, especially of lowmeltingpoint materials such as babbitt and leadbased overlays, is greatly reduced at high temperatures. Flaking may be caused early by overload, excessive load due to improper handling, poor shaft or housing accuracy, installation error, ingress of foreign objects, rusting, etc. Cylindrical roller bearings played a seminal role in the development of the continuous rolling mill, now used in the manufacture of billions of tonnes of widestrip steel 6. As with plain bearings, analysing and diagnosing rolling bearing failures is all about recognising the visual signs associated with typical failure modes the first step is therefore to perform a careful inspection of the failed roller bearing race, cage and housing. Wear in rolling element bearings and gears how age and contamination affect them bruce t. The interaction of corrosion fatigue and stresscorrosion.
Propagation of surface initiated rolling contact fatigue. Lubricating helps disperse heat from the bearing, remove wear particles and contaminants from the rolling contact areas, protect against corrosion and increase bearing seal bonds. Premature bearing failures in wind gearboxes and white. Understanding how fatigue contributes to bearing failure fatigue is one of the primary causes of rolling bearing failure. The surface finishes on races and rolling elements makes them susceptible to corrosion if not adequately protected. All six bearings were cracked through the ball thickness in the axial direction. Premature bearing failures in wind gearboxes and white etching. Fatigue life assessment of rolling bearings made from aisi. Corrosion fatigue cracks are generally not brunched a few secondary cracks may form in the regions adjacent to the main fatigue crack. Aisi 52100 is easily forged, heat treated and machined, with through hardening producing the fracture toughness required to avoid, or more specifically reduce, surface and subsurface cracking from rolling contact fatigue rcf. Roller microstructure and crack morphology were investigated through scanning electron microscopy. Corrosion, commonly known as rusting, is a natural chemical or electrochemical reaction between a bearing and its environment. Contact fatigue has been identified in metal alloys both.
Poor lubrication generates very different damage patterns depending on the load situation. Rolling bearings sometimes fracture earlier than expected. This ballbearing inner ring suffered extreme fatigue spalling that led to a. Rated life of bearing expressed as the period at which equipment or machine element. With this method corrosion pits are assumed to act as defects, which could initiate fatigue cracks. The spall pattern is fine grained contrasted to that of normal fatigue. Eac that covers he, scc and corrosion fatigue in this class of the steel.
Rolling contact fatigue includes triaxial stress state, high hydrostatic stress component, nonproportional loading, and during loading cycles changing planes of maximum shear stress, that leads to subsurface cracks. Practically all roller bearings consist of four basic parts. This will etch the surface and result in the detachment of flakes of rusted material. A result of bearing failures bearings in large industrial gearboxes or drive train applications, such as paper mills, crusher mill gearboxes, lifting gear drives or especially in wind turbine gearboxes are often subjected to a wide variety of operating conditions that, under certain circumstances, may push them beyond. Roller bearing service damage and causes figure 21 lubrication failure raceway here is an example showing an advanced stage of failure in a spherical roller bearing outer ring resulting from inadequate lubrication. Kuhnell, monash university the work disovered that surface cracks can result in pitting only. Where possible, use ball bearings instead of roller bearings. A microhardness test was performed to investigate the strain hardening of the roller. Fatigue results from having dynamic loads that exceed the fatigue strength of the bearing material at operating temperature. Fracture of the outer ring increased the clearance, which lead to the secondary damage to the rollers, cage inner and outer ring sunning surfaces. Generally, the service life of bearings is expressed either as a period of time or as the total number of rotations before the occurrence of failures in the inner ring, outer ring or rolling element because of rolling fatigue, due to repeated stress. Proper lubrication is so critical to bearing operation.
The first step is therefore to perform a careful inspection of the failed roller bearing race, cage and housing. The service life of bearings is expressed either as a period of time or as the total number of rotations before the occurrence of failures in the inner ring, outer ring or in rolling element ball or roller because of rolling fatigue, due to repeated stress. How to diagnose rolling bearing failures neale consulting. Failure analysis performed on some failed rolling bearings used in wind turbines revealed fretting corrosion bands on the inner ring bore having positions that coincide circumferentially with zones of subsurface wecs and surface axial cracks on the raceways. Ball, cylindrical roller and needle roller bearings selfaligning roller bearings, tapered roller bearings and thrust needle roller bearings 20 selfaligning thrust roller bearings 30 3. Since corrosion fatigue cracks initiate at a metals surface, surface treatments like plating. Fundamental considerations of fatigue, stress corrosion. As shown in figure 2, the prime reason roller bearings fail to reach life expectancy is due to lubricant contamination from particles. Under these conditions, surface asperities can oxidise and then be rubbed from the surface. Residual stress austenite pitting corrosion carbide fatigue crack bearing steel. Poor lubrication is another cause of surface fatigue. Compile a summary report of all data for discussion with timken sales or service engineers.
In more serious cases, the corrosion will begin to eat into bearing surfaces. Mar, 20 premature bearing failures in wind gearboxes and white etching cracks wec march, 20 18 minutes wind turbine gearboxes are subjected to a wide variety of operating conditions, some of which may push the bearings beyond their limits. This article summarizes the authors findings on wear in rolling element bearings and gears. Flaking inspection of bearings after operation howto. Pdf rolling contact fatigue is the main failure mechanism of tapered roller bearings. Bearings failed due to electrical arcing, deteriated greese, and heavy axial loading. Much premature wind gearbox bearing damage results in a failure mode that is not caused by the classic rolling contact fatigue rcf. The fatigue process is thought to cause rupture of the protective passive film, upon which corrosion is accelerated. Fatigue and fracture mechanisms in large rolling element. How to identify tapered roller bearing damage know your. Find out what happened to your bearing with our expert guide. The most common material used to manufacture ball and roller bearing rings is alloy steel aisi 52100, a 1. Bearings for corrosive environments spacea products nsk.
Roller bearings use cylinders instead of balls and have a greater load bearing capacity because of the greater contact between the rolling element and the rings. Fatigue and fracture mechanisms in large rolling element bearings. Pdf material analysis of the fatigue mechanism of rollers in. Water can be particularly damaging to steel bearings where a rolling element touches the race, especially if the bearing is idle for a period.
Bearing steels possess specific characteristics that play a critical role in bearing performance. Investigation on the mechanisms of white etching crack wec formation in rolling contact fatigue and identification of a root cause for bearing premature failure october 2016 doi. Under normal conditions, bearing materials are not attacked by lubricating oils, but there are some adverse circumstances in which corrosion can occur. Material analysis of the fatigue mechanism of rollers in tapered roller. Continued cyclic contact stress may initiate cracks that can then propagate by fracture, leading to the removal of surface material. Bell 429 tr pitch change link bearing failure aerossurance. Other forms of damage show up as flaking or cracks. Pdf investigation on the mechanisms of white etching. Real operating conditions might differ from the specifications. Failure analysis of machine shafts efficient plant. Early failure is mostly attributable to inadequate handling or maintenance. The bottom of these depressions may be bright or dull and oxidized. Quite often the pitting occurs in the inner race at the contact zone of the roller ends.
National renewable energy laboratory national wind technology center. Fatigue and corrosion fatigue pose longterm threats to the reliability and lifecycle costs of advanced highstrength ship structures. In tapered roller bearings, this can show up as scoring on the large end of the roller and guiding rib of rings. The work disovered that surface cracks can result in pitting only. Forensic failure analysis, corrosion investigation, metallurgical testing and engineering located in mooresville, nc. In addition to this, the main reason for bearing failures is an improper handlingandmounting procedure, corrosion, wear and manufacturing defects 2. In order to estimate the fatigue life or the maximal capacity of the roller bearing, it is necessary to use the sn curves of the material. Since corrosionfatigue cracks initiate at a metals surface, surface treatments like plating, cladding, nitriding and shot peening were found.
Esz bearings have corrosion resistant, and are superior to martensitic stainless steel. Tapered roller bearing speed capability guidelines. Corrosion can lead to early fatigue failures through the rust that forms in the bearing, especially if rust occurs in the raceways or on the roller elements, then the bearing becomes unusable. Rollingcontact fatigue rcf is defined as a failure or material removal driven by crack propagation caused by the nearsurface alternating stress field. Corrosion resistance ratings bearings should have a corrosion life about the same as their expected service life.
Pdf investigation on the mechanisms of white etching crack wec. Among prevalent tribological failures, notably in rolling element bearings for wind turbines, an unusual rollingsliding contact fatigue failure mode has been identified as white etching cracks. The principal difference between these two types of environment. Rolling contact fatigue is the main failure mechanism of tapered roller bearings. Examine operating conditions and adopt bearings with larger capacity as necessary. Highcyclelowload operation of the bearing propagated a fatigue crack through the bearing ring. Jun 07, 20 corrosion can lead to early fatigue failures through the rust that forms in the bearing, especially if rust occurs in the raceways or on the roller elements, then the bearing becomes unusable. Corrosion of the lead in copperlead and leadbronze alloys, and of leadbased babbitt, may be caused by acidic oil oxidation products formed in service, by ingress of water or coolant liquid.
We will be pleased if this guide book assists the user in preventing early bearing failure or in troubleshooting the causes of bearing failure. Bearing investigation roller bearings are extremely vital components in any railway application. In practice, the reliability of rolling bearings is very high. Gearbox typical failure modes, detection and mitigation methods. Removal of overlays by abrasive wear or scoring by dirt exposes the underlying lead in copperlead or leadbronze bearings to attack, while in severe cases the overlays may be corroded. Once in contact with the free metal within the fissure, the water breaks down and liberates atomic hydrogen. Corrosion fatigue in aqueous media is an electrochemical behavior. Action secure the bearing during transport by radial preloading.
Manufacturing induced hydrogen embrittlement of 52100 bearing. Advantages corrosion resistance, increased dynamic load carrying capacity ehd customer benefits very good fatigue life, robust bearing solution. Corrosion bearing failures failure atlas onyx insight. Stress corrosion cracking stress corrosion cracking scc is the growth of cracks under the combined influences of sustained tensile stress and a seawater environment. It is typically considered that if a bearing is properly mounted, aligned, lubricated, maintained and not overloaded, then the material fails due to rcf 1. Bearing failures and their causes bearings are among the most important components in the vast majority of machines and exacting. As with plain bearings, analysing and diagnosing rolling bearing failures is all about recognising the visual signs associated with typical failure modes. Sep 18, 2017 fracture mechanicsbased testing was used to quantify the stress corrosion cracking and corrosion fatigue behavior of a precipitationhardened martensitic stainless steel custom 465h950 in full. May 10, 2017 an examination of the failed pcl revealed fatigue fractures due to pitting corrosion between the spherical bearing and the bearing housing. Fretting corrosion refers to an oxidised flat spot that develops when two mating parts under load experience repeated micromotion between the contacting surfaces. The flaking progressively increases in extent figs 1 to 4 and eventually makes the bearing unserviceable. Understanding how fatigue contributes to bearing failure. In some cases, contact stress peaks at the roller ends and pitting originates in these locations. Investigation on the mechanisms of white etching crack.
Four of the top reasons roller bearings fail results from poor lubrication or lack thereof. One must differentiate bearing durability determined by loan fatigue during operating speeds and bearing service life, which determines the bearing uptime, before a bearing is for various reasons decommissioned. In this study a simplified method to predict corrosion fatigue properties for the cralloyed bearing steel 100crmnmo8 is proposed. P r e p a r a t i o n a n d a p p r o a c h t o b e a r i n g d a m a g e. Roller surface fatigue is often caused by unsuitable oil with too high water content. Major causes of roller bearing failure and prevention tools. It is the mechanical degradation of a material under the joint action of corrosion and cyclic loading. Paper open access related content fault tree analysis of most. Failure anaysis of ball bearings metallurgical technologies.
The fatigue fractures propagated during operation until the pcl bearing housing fractured, separating the pcl from the blade pitch horn end spherical bearing, resulting in a loss of pitch control to the. Corrosion occurs primarily when either lubricants fail or the seals have failed and the bearings have been exposed to water or corrosive liquids. Nov 05, 2019 it causes a fracture surface similar to ordinary fatigue except that in some cases corrosion products are present in the outer sections of the cracks. Any static overload or severe impact can cause brinelling.
Corrosionfatigue is the result of the combined action of an alternating or cycling stresses and a corrosive environment. Hydrogen sulphide in the oil attacks the copper in coppercontaining alloys, including tinbased whitemetal. Sliding forces can cause failure to originate at the subsurface that propagate parallel to the surface and it may significantly reduce bearing. Corrosion fatigue is fatigue in a corrosive environment. The estimated life of shaft was 2, 00,000 hours however, it was operational for only 1, 63,411 hours. It leads to the eventual decay of bearings through surface material being converted to oxides.
The cracks started radial and turned to run parallel to the surface, typical of contact fatigue. Rcf fatigue occurs due to the result of cyclic stresses developed at bearing contact surface during operation. Whats the difference between brinelling, spalling, and. This study investigated the fatigue mechanism of rollers in a tapered roller bearing that failed in a runtofailure test. Fractures are initiated either by pitting or persistent slip bands. Corrosion fatigue may be reduced by alloy additions, inhibition and cathodic protection, all of which reduce pitting. Failure analysis of arcing and contact fatigue of ball bearings. There are lowcycle failures but most industrial fatigue failures weve seen involve more than 1,000,000 load cycles. Surface fatigue spalling in recirculating ball bearings typically begins with a crack that is vshaped a. When smooth rolling surfaces are damaged, through cracks. The subject of this paper is the propagation of surface initiated rolling contact fatigue rcf cracks, which leads to the mode of contact failure known as pitting, characterised by a loss of material from the loadbearing surface in form of cratershaped cavities or pits. Recognizing causes and types of bearing damage can help you prevent further bearing damage resulting in improved bearing life and performance. One cause of whiteetching cracks can be material weakening due to corrosion. Major causes of roller bearing failure and prevention.
Mild corrosion will result in light surface stains without any appreciable depth. Wear in rolling element bearings and gears how age and. Material weakening due to corrosion in hardened bearing steels. A large number of factors need to be considered to select the appropriate bearing for an application. Failure investigations of cracked spherical bearings in aircraft. Possible action check bearings seats for conformity. Cause the bearing has been exposed to vibration while stationary.
Bearing failures and their causes bearings are among the most important components in the vast majority of machines and exacting demands are. Severe brinell marks can cause premature fatigue failure. Corrosion fatigue is similar to stress corrosion cracking in many aspects combine action of stress and corrosion, mechanisms of crack formation, brittle fracture, prevention measures. The bearings are suitable for corrosive environment operating under atmospheric conditions. Spalling damage is progressive and can indicate that a bearing has reached the end of its fatigue life. Wear and surface fatigue in rolling bearings skf evolution. Corrosion fatigue is the result of the combined action of an alternating or cycling stresses and a corrosive environment.
Jul 16, 2012 for a fatigue failure to occur, the forces must have been applied many times. Premature failures are characterized by multiple crack initiation points and cracks that are decorated with the whiteetching areas. Hydrogen embrittlement of a roller bearing outer ring the following article has been extracted from a recent publication by dr paul roffey in the journal of failure analysis and prevention. The bearings are having corrosion resistance equal to precipitation hardening type stainless steel and the hardness is improved more than 30%. The usual result is increased vibration followed by wear, with subsequent increase in radial clearance or loss of preload. Nearly all engineering structures experience some form of alternating stress, and are exposed to harmful environments during their service life. Fatigue corrosion can occur on many different types of metal products, ranging from heavy equipment to the metal panels used in construction and shipbuilding. In other words, a corrosion fatigue crack propagation process, cfc, is triggered. Dr steve lacey of schaeffler describes the various types of fatigue and what measures can be taken to correct any problems that occur. Nearly the entire circumference of the large ball exhibited light etching untempered martensite, indicative of severe overheating, as shown in figure 30.
This type of failure can also be found in gears, cams, valves, rails, and gear couplings. Moisture and water contamination leads to etching or corrosion in bearings. There is evidence that water is attracted to microscopic fatigue cracks in balls and rollers by capillary forces. Dmitri kopeliovich corrosion fatigue cf is the metal cracking caused by combined action of a cycling loading and a corrosive environment. Just as other mechanical components, roller bearings can also undergo premature failure or housing defects for various reasons. Failure analysis performed on some failed rolling bearings used in wind turbines. In some applications, rolling bearings can suffer a substantial loss of material. Manufacturing induced hydrogen embrittlement of 52100. These can occur on both loaded rollers and raceways, as well as roller end faces. Surface fatigue wear in rolling bearings occurs due to the presence of dynamic load conditions. Roller bearings are important components in the vast majority of machines, and are used in simple appliances, such as a wheel chair, to complex machines, such asautomaticprecisiongrindingequipment,whereaccuracy has to be in the range of a micron.