Tiêu chuẩn iso 07146 1 2008

Reference numberISO 7146-1:2008E© ISO 2008 First edition2008-10-15 Plain bearings — Appearance and characterization of damage to metallic hydrodynamic bearings — Copyright International

Damage

Plain bearing damage significantly impairs their tribological performance and is often accompanied by noticeable changes in appearance This damage begins from initial causes and progresses throughout the bearing’s service life, ultimately leading to failure Proper diagnosis and maintenance are crucial to prevent extensive damage and extend the bearing's operational lifespan.

As long as no abnormal conditions occur, service life of the plain bearing relates to the service life of the machine

Typical indicators observed during machine operation are: continuously increasing service temperature, decline of lubricant pressure, noise, vibration, and bad smell.

Damage causes

The cause is the practical event that initiates and leads to damage The majority of damage causes will be found outside the bearing.

Damage appearances

Damage appearance is a defined visible picture of the bearing surface and/or of the bearing back Damage appearances are clearly different from each other

A plain bearing failure can show various damage appearances Usually damage appearances are directly associated with damage characteristics, but not directly with the damage cause (for exceptions, see 6.8 and 6.9)

Damage appearances in materials can include depositions, creep deformation, and deformation caused by temperature cycles, which often lead to thermal cracks Fatigue cracks are common signs of repeated stress, while material relief or loss of bond indicates deterioration Frictional corrosion results from frictional wear, and melting out or seizure may occur due to excessive heat Polishing and scoring are physical damage indicators, alongside traces of mixed lubrication and worn material showing inadequate lubrication Discoloration such as blue or black hues signals thermal oxidation, while corrosion and fluid erosion degrade material integrity Embedded particles, particle-migration tracks, and wire wool formation point to contamination issues, whereas electric arc craters reveal electrical fault damage Cavitation erosion appears as worn-out material due to fluid impacts, highlighting different failure modes in engineering components.

Damage characterization

4.4.1 General A damage characterization is a description of what has happened based on a detected typical combination of damage appearances Defined characteristics provide the basis for establishing the cause of damage

Damage characterizations are clearly different from each other, as specified in 4.4.2 to 4.4.11

4.4.2 Static overload: material is loaded above compressive yield strength corresponding to actual operation temperature

4.4.3 Dynamic overload: material is loaded above fatigue strength corresponding to actual operation temperature Intensive dynamic load also favours damage by weakening the fit

Wear by friction involves changes in microgeometry and material loss resulting from interactions between the journal and bearing Additionally, movement between the backing and housing can promote further wear by friction, impacting the overall durability of mechanical components Proper lubrication and maintenance are essential to minimize frictional wear and extend the lifespan of machinery.

Overheating occurs when the heat balance in the lubricant, bearing, environment, and cooling system—designed during the planning stage—is not maintained, leading to higher-than-expected temperatures Elevated temperatures cause a decrease in lubricant viscosity and load capacity, which further exacerbates heat buildup This creates a vicious cycle where increasing temperature compromises bearing stability, especially if the cooling system fails to prevent further temperature rise, risking operational failure.

4.4.6 Insufficient lubrication (starvation): affecting the tribological system

4.4.7 Contamination of lubricant with foreign particles or reaction products can result in damage to a bearing Foreign particles embedded between bearing backing and housing also favour damage

Cavitation erosion occurs when decreased pressure in liquids causes vapor bubble formation, which then implode as pressure increases, generating intense localized pressures This process leads to the erosion of sliding surfaces, compromising the integrity of the material over time Proper understanding of cavitation is essential for designing durable machinery and preventing damage caused by this phenomenon.

4.4.9 Electroerosion: a potential difference between journal and bearing can lead to an electric arc with locally high current flow which damages journal and bearing surface

4.4.10 Hydrogen diffusion: hydrogen may be incorporated in the steel backing or in an electroplated layer of the bearing If hydrogen diffusion is blocked by a layer, blisters will occur

4.4.11 Bond failure: delamination between lining and backing or between layers A metallographic examination is required to distinguish from other damage characterizations.

Relationship between damage appearance and damage characterizations

Damage characterization and damage appearance alter with the progress of damage from a primary to a secondary characteristic (see Figure 1)

Different damage characterizations can correspond to the same damage appearance

One damage characterization can correspond to various damage appearances

Multiple damage characteristics can be found in one failure event

The damage characteristics provide the basis for analysing the cause (see Figure 2)

Table 1 illustrates typical relationship patterns between damage to the sliding surface and the bearing back It serves as a key diagnostic guideline, helping identify the root cause of final damage based on observed damage characteristics Analyzing these damage appearances allows for accurate determination of underlying issues, improving maintenance and prevention strategies.

Copyright International Organization for Standardization

Provided by IHS under license with ISO

Figure 1 — Damage appearances alter with the progress from primary to secondary characteristics a Damage cause b Damage characteristics c Damage appearances

Figure 2 — Damage characteristics provide the basis for analysing the cause

Table 1 — Interaction of damage appearances and damage characterizations

Damage appearance Damage characterizations Subclause

Depositions and creep deformation are caused by temperature cycles, leading to thermal cracks, fatigue cracks, and material relief due to bond loss Corrosion mechanisms include fractional corrosion, melting, scoring, polishing, and scoring, alongside traces of mixed lubrication and worn material evidenced by blue or black coloring Corrosion damage can result in fluid erosion, embedded particles, particle migration trails, and wire wool formation Electric arc cracks contribute to cavity erosion, with worn-out material indicating significant wear Static overload is rated as 6.2, while dynamic overloads (a and b) are rated 6.3 and 7.2 respectively Wear by friction (a and b) is rated 6.4 and 7.3, with overheating assessed at 6.5 Insufficient lubrication or starvation is rated 6.6 Contamination from particles and chemicals (a and b) are rated 6.7 and 7.4, respectively, and cavitation erosion is also a significant factor in material degradation.

ISO 7146-2 × Electro-erosion 6.9 × Hydrogen diffusion 6.10 × Bond failure 6.11 a Damage to the sliding surface b Damage to the bearing back

General

Analysis should be undertaken only by experts experienced in bearing metallurgy, bearing technology and bearing damage Damage analyses based on photos alone are mostly unsuccessful

The following steps are a guideline for damage analysis.

Step 1

The service life of equipment significantly influences the nature of damage observed While similar damage appearances can occur in both short and long service life scenarios, the underlying causes often differ Understanding the distinction between these cases is crucial for accurate diagnosis and effective maintenance strategies, ensuring prolonged equipment performance and reliability.

Typical causes of damage after short service life: faults in geometry or assembling, dirt, effect from a previous damage, modified service conditions since last start up

Typical cause of damage after long service life: modified service conditions

Typical cause of damage after very long service life: reduced dynamic material capability due to fatigue.

Step 2

Strictly distinguishing between damage characterization and damage appearance is essential for comprehensive analysis All visible damage appearances should be thoroughly assessed and integrated into one or more damage characterizations, following the guidelines outlined in Table 1 This approach ensures accurate identification and evaluation of damage types, supporting effective maintenance and safety decisions Proper damage characterization enhances the reliability of structural assessments by providing clear, detailed information about the nature and extent of visible damages.

Step 3

Take into consideration the total system: bearing — shaft — lubricant — housing

It is helpful to make a chemical analysis of a sample from the bearing layer and to check its microstructure If necessary, lubricant and filter content should be analysed.

Step 4

All information in connection with the period before the detected damage and the period during the damage should be brought together.

Step 5

Reviewing the initial list of damage characteristics alongside the findings from steps 3 and 4 helps to narrow down the potential causes of damage This process streamlines the identification of the most relevant damage factors, ultimately enabling more accurate determination of the damage cause.

See Annex A for an example of use of Table 1

6 Damage to the bearing surface — damage characteristics, typical damage appearances and possible damage causes

General

A discussion of damage to the bearing surface follows For each damage characterization given in 4.4, typical damage appearances, possible damage causes and typical examples are given.

Static overload

Creep deformation involves shallow depressions in the bearing material at regions of maximum load and temperature, initially appearing smooth and progressing into crack-free semicircular bulges aligned with the direction of rotation These deformation features can resemble wave crests, indicating material flow and stress effects under prolonged exposure to operational conditions, which are critical for understanding bearing wear and longevity.

Traces of mixed lubrication (see Figure 4), depositions, thermal cracks

Loading of the bearing was higher than that allowed for in the design and/or the bearing temperature was higher than estimated for an extended period

6.2.3 Typical examples (see Figures 3 and 4)

Figure 3 — Creep deformation, shown by crack-free semicircular bulges in the direction of rotation

(material: steel/tin-based white metal)

Figure 4 — Propeller shaft bearing, showing the effects of too slow a speed in relation to load capacity

Dynamic overload

Fatigue cracks: Cracks which extend from the sliding surface in the loaded zone propagating as a network The cracks change direction above the bonding area

Lining material from the backing is the final result of the development of fatigue cracks (see Figure 5)

See also possible damage appearances such as frictional corrosion on the bearing back (7.1)

Cracks in bearings typically initiate when the applied dynamic load surpasses the material's fatigue limit at the operating temperature This type of damage is not caused by bond faults but results from repetitive stress exceeding the bearing's endurance capacity, leading to material fatigue and crack formation Proper understanding of load conditions and material properties is essential for preventing bearing failure due to fatigue-related cracks.

6.3.3 Typical examples (see Figures 5 to 12)

Figure 5 — Schematic diagram of progress of fatigue cracks a) under inertial load b) under gas load

Figure 6 — Typical fatigue cracks of internal combustion engine bearing

Figure 7 illustrates the direction of shaft rotation and highlights cracks in the electroplated overlay, which is composed of steel, lead bronze, and electroplated material The section from Figure 7a) shows the lower half of the shaft at increased magnification, revealing detailed crack formations in the electroplated overlay that can impact the component's durability and performance Understanding these crack patterns is essential for assessing the structural integrity of electroplated steel and lead bronze components subjected to rotational forces.

Figure 8 — Cracks in the overlay of a multilayer bearing in a narrow area of high loading

(material: steel/lead bronze/electroplated overlay)

NOTE The crack runs at a small distance from the bonding area

Figure 9 — Section of spalled layer (material: steel/tin-based white metal)

Figure 10 — Fatigue cracks and material relief by dynamic overload

Figure 11 — Material relief by dynamic overload because of insufficient fit on the bearing back

14 a) b) section from Figure 12 a): clear illustration of the defect at increased magnification

Figure 12 — Detachment of the overlay leaving occasional residual islands relieved by a dark background (material: steel/lead bronze/electroplated overlay)

Wear by friction

Polishing occurs during brief periods of mixed lubrication during engine start and stop conditions As long as this polishing does not lead to a measurable decrease in wall thickness, these running-in marks are considered normal and not indicative of damage According to ISO 7146 standards, such marks are expected and do not constitute the types of damage defined in the guidelines.

Scoring occurs during extended periods of continuous or recurrent mixed-film lubrication, primarily affecting the most heavily loaded regions of the bearing These scoring marks typically span the entire width of the bearing and develop gradually from unmarked to marked areas The formation of scoring results in a significant reduction in wall thickness, compromising bearing integrity and performance.

Segmented plain bearings often exhibit significant wear when subjected to high rubbing surface temperatures Initially, these bearings show signs of mixed lubrication, which gradually leads to material transfer between segments Over time, worn material from one segment is deposited onto the leading edge of the next segment in the direction of rotation, indicating progressive wear and material redistribution within the bearing assembly.

For information on possible damage appearance on the bearing back, see 7.3

Extreme operating conditions, including slow turning or starting under load, short and intense contact with the counterface, and geometrical defects like misalignment or faulty mounting, contribute significantly to wear caused by friction Proper maintenance and precise alignment are essential to minimize friction-related wear and ensure optimal equipment performance.

Figure 13 — Running-in polishing and burnishing in the main loaded area of a thin-walled bearing

Figure 14 — Abrasive wear of the overlay in the main loaded area on a thin-walled bearing

Figure 15 — Abrasive wear near the ends of the bearing (joint face area) in a thick-walled journal bearing, due to faulty mounting (material: steel/tin-based white metal)

Figure 16 illustrates wear caused by friction during segment assembly at various levels, where worn material from one segment deposits onto the leading edge of the next segment in the direction of rotation This process results in increased wear and damage, with specific secondary effects such as a reduction in oil supply, indicating a loss of lubricant Proper assembly and maintenance are essential to minimize frictional wear and prevent secondary damage like lubricant depletion.

Figure 17 — Wear by misalignment between bearing backing and shaft

Overheating

Overheating in lubrication systems causes the ageing of the lubricant, leading to thermal decomposition and deposit formation This phenomenon primarily occurs in the minimum oil film region and other areas within the oil circulation system, especially when oil additives have been depleted Proper temperature management and regular oil maintenance are essential to prevent deposit buildup and maintain optimal system performance.

Brown or black deposits on bearing surfaces are caused by thin, lacquer-like oxidized layers that form in areas of maximum temperature, rather than chemical attack with the lubricant These discolored layers are relatively soft and can typically be removed with solvent cleaning fluids or by gently scratching with a pointed instrument.

Creep deformation involves shallow depressions in the bearing material at the region of maximum load and temperature Initially smooth, these areas develop into crack-free semicircular bulges that extend in the direction of rotation Sometimes, these bulges resemble wave crests, indicating the progression of material deformation over time (see Figure 18).

Temperature-induced deformations in tin crystals occur because of their anisotropic thermal expansion along different crystal axes Prolonged exposure to excessive start-up cycles can lead to thermal ratcheting between crystals, which may ultimately cause intercrystalline cracking in extreme cases.

Thermal cracks have an irregular unsystematic orientation characteristic These typical appearances can be characterized as creep deformation, traces of mixed lubrication and worn material (see Figure 21)

Failure of heat flow, resulting in overheating

Defects in oil cooling, increased surrounding temperature, hot oil carry-over

Reduced melting point due to alloy impurities will favour thermal cracks

6.5.3 Typical examples (see Figures 18 to 21) direction of shaft rotation →

Figure 18 — Creep deformation due to overheating with formation of black depositions

Figure 19 — Thrust bearing tilting pad with deposits of oil carbon

NOTE The black/brown deposit is easily removed using the thumbnail (see lowest segment)

Figure 20 — Deposit of oil carbon on a thrust bearing ring (material: steel/tin-based white metal)

Figure 21 — Radial segments with thermal cracks and worn material

Insufficient lubrication (starvation)

Blue, black colour on the bearing, shaft, housing

Traces of mixed lubrication, worn material

Melting out, seizure (adhesive wear)

Reduction of lubricant supply due to geometric deviations (e.g missing wedge gap or missing bearing clearance)

Most damage in a late secondary stage will end with loss of lubrication

Figure 22 — Seizure on a multilayer plain bearing with totally detached intermediate layer, accompanied by melting, metal wear and severe scoring (material: steel/lead bronze/electroplated overlay)

Figure 23 — Destruction of bearing metal due to loss of lubricant in a thick-walled bearing

Figure 24 — Bearing metal molten along the surface due to overheating and loss of lubricant, followed by cracking of the (etched) bearing metal (material: steel/tin-based white metal)

Figure 25 — Bearing metal layer exhibiting surface melting with entrained carbonaceous residue, unetched (material: steel/tin-based white metal)

Figure 26 — Melting at the bearing edge and within the groove (material: steel/lead bronze/electroplated overlay)

Figure 27 — Coloured surface due to loss of lubricant, melting out, seizure

Contamination

1 journal 5 embedded particle usually with a highly reflective raised ring (halo) of bearing material around it (see also Figure 29)

2 lubricant 6 craters or scratches left by displaced particles (see also Figures 30 and 32)

3 lining material 7 particle of bearing metal from a damage site elsewhere in the bearing smeared onto the bearing surface (see also Figure 29)

4 backing material 8 particle with entry track

Figure 28 — Schematic diagram of possible embeddings

Particle-migration tracks (see Figures 29, 32, 33 and 34)

Particles embedded in the bearing surface cause raised bearing metal to become displaced, forming a highly reflective halo around each embedded particle (see Figure 30) This halo interacts with the counterface, indicating the presence of mixed lubrication and worn material traces.

Wire wool formation occurs when hard foreign particles become embedded in the bearing surface and cut into the rotating shaft, leading to material removal from the shaft surface This process can cause wire wool to re-embed into the bearing metal, significantly increasing the risk of rapid bearing failure Proper understanding and prevention of foreign particle intrusion are essential to maintain bearing longevity and prevent damage (see Figure 35).

Chevron appearances are particle-migration tracks generated by hard particles The chevrons point in a direction opposite to the direction of rotation of the journal (see Figure 36)

Foreign particles in the oil can also lead to fluid erosion

With regard to possible damage appearances on the bearing back, see also 7.4

Particle contamination of oil often originates from residues such as metal turnings, casting sand, or paint during manufacturing, assembly, or commissioning, especially due to poor maintenance or damaged filters Wear and damage to bearings or other machine components can generate additional particles that pollute the oil Furthermore, damaged seals allow external contaminants, like cement dust in the cement industry, to enter the lubrication system, leading to increased particle contamination and potential equipment failure Effective filter maintenance and sealing integrity are crucial for minimizing oil particle contamination and ensuring optimal machinery performance.

Wire wool formation occurs when shaft steel contains chromium, leading to hard particles embedded in the bearing surface These particles cut into the rotating shaft, removing material and resulting in wire wool buildup Proper maintenance and material analysis are essential to prevent this issue and ensure smooth shaft operation.

Chevron appearances are caused by migration tracks resulting from particles originating on the surface of nitrided journals These particles, which possess magnetic properties, spall from the journal surfaces due to inadequate grinding and the failure to remove the white friable layer, leading to characteristic mark formations Proper surface treatment and thorough grinding are essential to prevent the formation of such tracks and ensure journal integrity.

Fluid erosion is caused by lubricant under high shear rate with included foreign hard particles such as wear debris, dust, and combustion residue

6.7.1.3 Typical examples (see Figures 29 to 36)

Figure 29 — Embedding of particles, characteristic of embedding, see Figure 28, and migration tracks

Figure 30 illustrates a crater left by a displaced particle surrounded by a reflective halo, characteristic of the embedding process observed in steel, lead bronze, or electroplated overlay materials (see Figure 28, label 6) The figure highlights deformation at the lining surface in a cross-sectional view, emphasizing material behavior under stress Additionally, Figure 31 shows a deep circumferential score with displaced bearing metal alongside, indicating wear patterns and material displacement consistent with operational conditions in bearing components These observations are crucial for understanding damage mechanisms in steel and bronze overlays used in engineering applications.

Figure 32 — Cement mill bearing with contamination by cement particles entrained by the oil as a result of damaged seals Particle-migration tracks are visible

Figure 33 — Contamination by foreign particles containing Fe — particle-migration tracks are visible

Figure 34 — Particle-migration tracks concentrated to the pocket area of a thin-walled bearing

30 a) wire wool on a journal pad (material: steel/tin-based white metal) b) wire wool on the shaft

Figure 35 — Attack caused by abrasive and adhesive effects in the initial stage

Figure 36 — Chevron-like defect caused by particles from iron nitride compound layer of nitrided shafts (material: steel/lead bronze/electroplated overlay)

The corrosive nature of lubricants can be present from the start or develop over time due to contamination from water, antifreeze, or combustion residues Even minor leaks in the lubrication system can trigger chemical reactions that lead to corrosion Corrosion of the overlay is intensified when corrosion-resistant components are absent initially or diminish over time through diffusion at high temperatures, accelerating material degradation.

Lubricant contamination can occur due to halogenated hydrocarbons from refrigerants or other chemicals, leading to the dissolution of copper from oil cooler tubes This dissolved copper may be electrolytically deposited on metal surfaces within tribological systems, especially at elevated temperatures Higher temperatures accelerate these reactions, promoting copper diffusion and resulting in corrosion that can impair system performance and longevity.

Corrosion caused by water in oil typically occurs when water exceeds a critical concentration, which varies based on oil type and operating conditions Generally, water levels above 1% by volume can lead to corrosion issues, emphasizing the importance of monitoring water content to prevent equipment damage and maintain optimal performance.

Corrosion-induced dissolution of bearing material results in fluid erosion, compromising the bearing's integrity The removal of the anti-oxidative layer by fluid erosion can cause premature corrosion, which further accelerates fluid erosion, creating a destructive cycle that undermines bearing performance.

6.7.2.3 Typical examples (see Figures 37 to 42)

Figure 37 — Discoloration of the bearing surface in the main loaded zone by tribochemical reaction

Figure 38 illustrates the corrosive detachment of the overlay around the oil hole and highlights a selective corrosive detachment on the right-hand side of the bearing lining, which is composed of steel, lead bronze, and electroplated overlay This image emphasizes the impact of corrosion on bearing materials, potentially compromising their structural integrity and performance Recognizing patterns of corrosive detachment is essential for assessing wear and extending the lifespan of bearing components Proper maintenance and corrosion-resistant coatings can prevent such issues, ensuring reliable operation of machinery.

Figure 39 — Tin oxide corrosion due to water in the oil, unetched

← direction of shaft rotation a) structure weakened by corrosion of lead phase after wear of overlay

(material: steel/lead bronze/electroplated overlay) b) microcut at increased magnification (material: steel/lead bronze/electroplated overlay)

Figure 42 — Deposit of oil carbon on galvanic surface

Cavitation erosion

Cavitation occurs when the static pressure in a liquid drops below its vapor pressure at a specific temperature, leading to the formation of vapor bubbles This process happens as the liquid's molecules vaporize due to the insufficient pressure, causing vapor cavities to develop within the liquid Understanding cavitation is essential in various engineering applications, as it can impact the performance and longevity of hydraulic machinery.

With increase of pressure, these bubbles collapse and typically cause very strong local shockwaves in the liquid which damage the bearing surface resulting in cavitation erosion

Cavitation erosion appearances are characterized by typical worn-out material

Cavitation erosion often results from faulty design, incorrect geometry, unsuitable materials, operational conditions, or contamination with foreign fluid elements, as outlined in ISO 7146-2 On established equipment, water inclusion is a common contributing factor to cavitation damage.

Figure 43 — Typical cavitation erosion on a thick-walled bearing (material: steel/tin-based white metal)

Figure 44 — Typical cavitation erosion on a thin-walled bearing

Electro-erosion

The surfaces of journal and bearing show small craters

Magnetic fields and electrostatic charges can give rise to a potential difference between journal and bearing resulting in current flow

Insufficient earthing (grounding) or improper insulation in operation or during maintenance, e.g welding work on the machine, can be a contributory factor

Figure 45 — Surface of a plain bearing attacked by electro-erosion

Figure 46 — Formation of electric arc craters

Figure 47 — Electric arc craters at increased magnification (material: tin-based white metal)

Hydrogen diffusion

For thick-walled bearings: loss of bond between white metal and steel White metal forms typical blisters (see Figure 48)

For electroplated layers: formation of pores with typical blisters on the layer surface (see Figure 49)

The hydrogen diffusion develops usually over a long time and is accelerated by temperature These appearances occur either on operation or on spare part bearings after long storage time

Missing additional heat treatment for hydrogen reduction on the steel backing or the electroplated layer This additional heat treatment is recommended for steel backing thickness above approx 60 mm

Figure 48 — Layer with loss of bond and formation of typical blisters, arising from hydrogen inclusion in the steel (material: steel/tin-based white metal)

Figure 49 — Hydrogen inclusion arising from electroplating — small pores and larger blisters, partially perforated during running (material: steel/lead bronze/electroplated overlay at increased magnification)

Bond failure

Loss of bond: completely detached material in larger areas with clearly defined borders

Faulty procedure during manufacturing process, e.g missing heat treatment, insufficient cleaning, tinning, process temperatures

Figure 50 — Loss of white metal showing a break with clearly defined borders

7 Damage to the bearing back

General

Damage may appear on the bearing back or joint faces, indicating potential issues Often, there is a interrelationship between damage to the bearing back and internal bearing damage, highlighting the importance of comprehensive inspection Recognizing these signs can help in diagnosing bearing failures early and improving maintenance strategies.

Damage to the bearing back is discussed for the following damage characterizations: "dynamic overload",

"wear by friction" and "contamination with particles".

Dynamic overload on the bearing back

An increase in the acting dynamic load can result from local factors like inadequate fit or excessive deformation of the housing This often leads to the appearance of damage such as frictional corrosion on the bearing back or joint face Proper assessment of these conditions is essential to prevent bearing failure and maintain optimal performance.

If the bearing is not sufficiently supported (oil grooves on the bearing back), a local dynamic overload can also occur (see Figure 51)

7.2.3 Typical examples (see Figure 51) a) bearing back with appearance of oil groove and hole in the housing (material: steel)

NOTE The black cracks were produced during operation and contain dirty oil The pale cracks at the sides were produced by bending the bearing open b) bearing surface

Figure 51 — Recessed areas (bearing back and corresponding bearing surface) —

Insufficient support locally of the bearing in relation to the load

Wear by friction on the bearing back

Cumulative small movements of the bearing relative to the housing in the circumferential direction can occur due to excessive elastic deformation, non-uniform support, or stress relaxation in the interference fit Factors such as bolt stretching, inadequate tightening, fractures, or stretching can also contribute to bearing displacement In some cases, these movements may become significant, potentially impacting bearing performance and machine reliability Proper installation and maintenance are essential to prevent excessive bearing movements caused by these factors.

NOTE The locating nicks have been flattened towards the bearing surface

Figure 52 — Circumferential scoring on the bearing back resulting from slippage

Figure 53 illustrates a steel backing fracture originating at the top in an axial direction within an area showing significant movement The crack progresses circumferentially around the component and ultimately deviates toward the flange, indicating a complex failure pattern affected by operational stresses and material fatigue.

Figure 54 — Pitting and transfer of material at the joint faces

Contamination with particles on the bearing back

Depositions, embedded particles, scoring, worn metal

Figure 55 — Schematic diagram of a foreign particle trapped behind a bearing and the resulting raised area

The image illustrates common bearing damage features, including indentation on the bearing back left caused by particles trapped between the bearing and housing, typically made of steel, lead bronze, or electroplated overlay Additionally, it highlights the presence of a corresponding worn metal raised area on the bearing bore, which also involves materials such as steel, lead bronze, or electroplated overlay Understanding these defect patterns is essential for diagnosing bearing failures and ensuring proper maintenance.

8 Special position of damage appearances

Damage to the lining typically occurs near the journal area, with the most affected zone located closest to the journal In an ideal bearing assembly, this damage hotspot is directly influenced by the direction of loading, highlighting the importance of proper load management for extending bearing lifespan [see Figure 57 a)] Proper understanding of load direction and lining damage correlation is essential for effective bearing maintenance and improving equipment reliability.

In practice, other areas may also show wear or fatigue damage This indicates deviation either of the geometry or of the effective loading direction [see Figure 57 b), (1)]

The unexpected shape or position of the damage appearance

Incorrect initial geometry of the bearing assembly, distortion by the load, by incorrect assembly or location of backings, etc., or as a result of unpredictable loading

Normal wear across full width (see Figure 16) b) edge

Tapered shaft, bearing or housing, or bent shaft with rotating load

Angular misalignment between bearing and shaft (including misaligned housing, bent connecting rod, etc.) c) central

Hour-glass bearing or housing, barrel-shaped shaft, possibly associated with transient overheating or oil starvation d) both edges

All around edges (with rotating load)

Barrel-shaped bearing or housing, hour-glass shape of shaft, bent shaft or excessive shaft fillet radii e) near joint face (both)

Both adjacent bearings; unexplained by normal loads

Distorted bearing or bearing housing (possibly due to load)

One bearing near each joint face

Misplaced bearing cap g) small area near joint face

Locating device not fitting in locating slot h) high spot

Local area not due to load

Particle, fretting debris or carbonized oil between bearing back and housing (see Figure 54) i) unexpected area

Unknown additional load, elastic/plastic distortion

Figure 57 — Special appearances of wear or fatigue

Example of use of Table 1

The numbers refer to the labels in Table A.1

Material relief, identified as damage appearance 1 on the bearing, is classified into specific types such as dynamic overload (cell 2a), hydrogen diffusion (cell 2b), and bond failure (cell 2c) When this damage is observed in isolation, these categories help in diagnosing the underlying issue Further investigations often enable engineers to narrow down the number of possible damage mechanisms, leading to more accurate fault characterization in bearings.

If the steel backing of the damaged bearing is already several years old, hydrogen diffusion can be excluded

The likelihood of pinpointing a single damage characterization increases when multiple damage appearances are observed For example, visible signs such as material relief, fatigue cracks, and frictional corrosion on the bearing back collectively indicate dynamic overload Detecting all three damage manifestations significantly suggests that the damage is caused by dynamic overload, warranting further investigation into this cause.

What happened in the machine to produce dynamic overload?

Were there broken parts and/or was mass eccentricity generated?

Did changed operating conditions result in any (higher) impact loads?

Continuation of operation with a damaged bearing increasingly affects hydrodynamic lubrication Mixed friction increases more and more, 8, and secondary damage characterizations wear, 9, and overheating, 10, occur

On the latest stage, the liner metal melts out, 11, and corresponds to the damage characterization insufficient lubrication, 12 Damage progress ends in most cases with the secondary damage characterization insufficient lubrication In such an extreme late stage of damage progress, when no damage appearances beside completely molten metal are visible, an identification of the primary damage characterization is nearly impossible Fortunately, in most cases, several damage appearances are visible and lead to the relevant damage characterization To find the real cause, expert knowledge is necessary and cannot be replaced by this International Standard This International Standard only can give a uniform working basis in order to avoid misunderstanding and misinterpretation

Table A.1 — Example of interaction of damage appearance and damage characterization

Tiêu đề	Appearance and characterization of damage to metallic hydrodynamic bearings
Trường học	ISO
Chuyên ngành	Plain bearings
Thể loại	International standard
Năm xuất bản	2008
Thành phố	Geneva

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Số trang	58
Dung lượng	19,2 MB