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Detection of damage and assessment of running rolling bearings

Rolling bearing damage
Detection of damage and assessment of running rolling bearings

Publ. WL 82 102/2 DA as of 2000

Preface

Rolling bearings are machine elements with a wide range of applications. They also prove to be reliable under tough conditions. Premature failures are very rare. Rolling bearing damage can primarily be recognized by an unusual operating behavior of the bearing. A wide variety of characteristics can be identified when examining damaged bearings. In order to find the cause of the damage, an assessment of the bearing alone is usually not enough; rather, the surrounding parts, the lubrication and sealing as well as the operating and environmental conditions must also be taken into account. A planned approach to the investigation makes it easier to find the causes. This publication is intended primarily as a manual for workshops. It gives an overview of typical rolling bearing damage, its causes and remedial measures. In addition to the explanation of damage patterns, possibilities are also presented at the beginning to identify bearing damage at an early stage. As part of the preventive maintenance that is carried out frequently, there are also bearings that are not classified as defective. For this reason, examples of bearings with normal running characteristics for the respective term are shown.

On the cover picture: What at first glance looks like a landscape of dunes photographed from great height is in reality the undulating deformation and wear profile of an axial cylindrical roller bearing. The differences between mountain and valley are less than 1 m. Mixed friction occurs in the contact surfaces subject to sliding stress at low speeds. The cause of the "rippling" are stick-slip effects.
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content

1 1.1 1.2 1.2.1 1.2.2 1.3 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 3 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.3 3.3.1 3.3.1.1 3.3.1.2 3.3.2 3.3.2.1 3.3.2.2 3.3.2.3 3.3.2.4 3.3.2.5 3.3.2.6 3.3.3 3.3.3.1 3.3.3.2 3.3.3.3 3.3.4 3.3.4.1 3.3.4.2

Page Unusual operating behavior as an indication of damage. . . . . . . . . . . . . . . . . . . 4 Subjective damage detection. . . . . . . . . . . . . . 4 Warehouse monitoring with technical aids. 4 extensive damage. . . . . . . . . . . . . . . . . . . . . 4 Punctual damage. . . . . . . . . . . . . . . . . . . . . . . 6 Urgency of bearing replacement Remaining service life. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Securing defective bearings. . . . . . . . . . . . . . . . Establishing the operating data. . . . . . . . . . . . . . . . Taking and assessing lubricant samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Checking the warehouse environment. . . . . . . . . . . . Assessment of the bearing in the installed state. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dismantling the damaged bearing. . . . . . . . . . . Control of the seats. . . . . . . . . . . . . . . . . . . . . . . . Assessment of the entire warehouse. . . . . . . . . . Shipping to FAG or assessment of the individual warehouse parts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assessment of running and damage features on the dismantled warehouse. . . . . . . . . . . . . . . . . . . . . Preparatory Actions. . . . . . . . . . . . . . . . . Identification of the individual parts. . . . . . . . . . . . . . . Measurements on the entire warehouse. . . . . . . . . . . . . . Disassembly of the bearing into individual parts. . . . . . . . . . . . . Assessment of the storage parts. . . . . . . . . . . . . . . . . The condition of the seats. . . . . . . . . . . . . . . . . Fretting corrosion, fretting corrosion. . . . . . . . . . . . . . . . Scuff marks or sliding wear. . . . . . . . . . . . . . Uneven support of the bearing rings. . Lateral rubbing marks. . . . . . . . . . . . . . . . . . . . The appearance of the rolling contacts. . . . . . . Origin and meaning of running tracks. . . . Normal running tracks. . . . . . . . . . . . . . . . . . . . . . Unusual tracks. . . . . . . . . . . . . . . . . Depressions in raceways and rolling element surfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outbreaks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosion damage. . . . . . . . . . . . . . . . . . . . . . . . Standstill markings. . . . . . . . . . . . . . . . . . . . Rolling body impressions. . . . . . . . . . . . . . . . . . . . . . Craters and corrugations as a result of the passage of electricity. . . . . Rolling body edge run. . . . . . . . . . . . . . . . . . . . Ring breaks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Endurance breaks as a result of fatigue in the career. . . . . . Axial cracks or tears in inner rings. . . . Outer ring breaks in the circumferential direction. . . . . . . . Raising and smearing on the contact surfaces. . . . . . . . . . . . . . . . . . . . . . . . . . Wear due to insufficient lubrication. Scoring on rolling body surfaces. . . . . . . . . . 9 9 9 10 10 10 10 10 10 11 14 14 14 14 14 15 15 16 17 18 19 19 19 21 27 27 34 36 37 38 39 40 40 40 41 42 42 44

3.3.4.3 3.3.4.4 3.3.5 3.4 3.4.1 3.4.1.1 3.4.1.2 3.4.1.3 3.4.1.4 3.4.2 3.4.3 3.4.3.1 3.4.3.2 3.5 3.5.1 3.5.2 3.5.3 3.5.4 3.5.5 3.5.6 3.5.7 3.6 3.6.1 3.6.2 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7

Side slip marks. . . . . . . . . . . . . . . . . . . . . . . . . . . 45 focus marks. . . . . . . . . . . . . . . . . . . . . . . . . . . 46 medical expenses. . . . . . . . . . . . . . . . . . . . . . . . . 47 Assessment of shipboard contacts. . . . . . . . . . . . . . . 48 Damage to the rim and roller face of roller bearings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Tightening due to foreign bodies. . . . . . . . . . 48 free appearances in on-board contact. . . . . . . . . . . 49 Wear in contact with the ship. . . . . . . . . . . . . . . . . 50 sideways. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Wear of cage guide surfaces. . . . . . . . . . 52 Damage to sealing surfaces. . . . . . . . . . . . 53 Incorporated sealing lip tracks. . . . . . . . . 53 Discoloration of the seal tracks. . . . . . . . . . . . 53 cage damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Wear due to lack of lubricant and contamination. . . . . . . . . . . . . . . . . . . . . . . . . . 54 Wear due to excessive speed. . . . . . . . 54 Wear due to restricted roles. . . . . . . . . . 55 Wear on ball bearing cages due to tilting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Breakage of cage connections. . . . . . . . . . . . . . . 56 Broken cage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Damage due to improper assembly. . . . . . . . 57 Damaged seals. . . . . . . . . . . . . . . . . . . . . . . . 58 Wear of the sealing lips. . . . . . . . . . . . . . . . . . 58 Damage due to improper assembly. . . . . . . . 59 Further investigation options at FAG. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geometric measurement of bearings or bearing parts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lubricant analyzes and lubricant tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control of the material condition. . . . . . . . . . . . . X-ray fine structure analysis. . . . . . . . . . . . . . . . . Scanning electron microscopic examinations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Component tests. . . . . . . . . . . . . . . . . . . . . . . . . . Mathematical check of the load conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 60 63 65 66 67 69 71

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Unusual operating behavior as an indication of damage


Subjective damage detection Warehouse monitoring with technical aids

1 Unusual operating behavior as an indication of damage


Bearing damage usually manifests itself as the operating behavior gradually deteriorates. Spontaneous damage is rare, e.g. B. caused by assembly errors or a lack of lubricant, which lead to immediate machine downtime. Depending on the operating conditions, it can take a few minutes, and possibly even months, from the start of the damage to the actual failure. The type of bearing monitoring depends on the application and the effects of bearing damage on machine operation. 1: Damage detection by the operating personnel
Operating behavior Restless running Possible causes Damage to rings and rolling elements Examples of motor vehicles: increasing fluttering of the wheels increased tilting play Jolting of the steering elements Fans: increasing jolts Gates: increasing sticks and knocks in the stilts Reduced working accuracy Wear due to soiling or insufficient lubrication Change of position (air or preload) Lathe: Gradual occurrence of chatter marks on the workpiece Grinding machines: Wavy grinding pattern Cold rolling mill: Occurrence of mostly periodic surface defects on the rolling stock, such as shading, wave formation, etc.

pollution

too much clearance

1.1 Subjective damage detection


In the majority of applications of rolling bearings, to avoid major damage, it is sufficient for the operating personnel to pay attention to uneven running or unusual noises from the bearing, Table 1.
Unusual running sound: howling or whistling sound, rumbling or uneven sound

operating air too small

1.2 Warehouse monitoring with technical aids


Storage in which damage represents a safety risk or can lead to major production downtimes, on the other hand, require precise, continuous monitoring. Examples of this are aircraft turbines or paper machines. In order to be reliable, the type of monitoring must be based on the type of damage to be expected. 1.2.1 Large-scale damage An essential requirement for trouble-free operation is an adequate supply of clean lubricant. Unfavorable changes can be determined by:
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Excessive operating air Damage to the roller surfaces Contamination of unsuitable lubricant

Electric motors gearboxes (with gearboxes, rolling bearing noise is difficult to detect, as the gear noise generally predominates)

gradual change in the running noise

Change in the operating air due to temperature influences Damage to the runway (e.g. due to soiling or fatigue)

Unusual operating behavior as an indication of damage


Warehouse monitoring with technical aids

2: Temperature profile with intact main spindle bearings of a machine tool. Test conditions: n dm = 750,000 min-1 mm. 3: Temperature profile with a disturbed floating bearing function. Test conditions: n dm = 750,000 min-1 mm.

50 C 40 3 2 1 4 5

50 C 40 3 2 1 4 5

30 temperature 20

30 temperature 20

10 0 1 2 3

10 1 run time h 4 5 2 0 1 2 3 1 run time h 4 5 2

Monitoring of the lubricant supply Oil level sight glass Oil pressure measurement Oil flow measurement Discontinuous wear measurement in the lubricant Magnetic plug Spectral analysis of lubricant samples Examination of oil samples in the laboratory Continuous magnetic signal generator Determination of the particle quantity flowing through with online particle counter Temperature measurement usually with thermocouples

Temperature measurement in particular is very reliable and relatively easy to use to identify damage caused by lubricants. Normal temperature behavior: Reaching a steady-state temperature in stationary operation, Figure 2. Faulty behavior: sudden temperature increase, caused by lack of lubricant or the onset of radial or axial distortion of the bearing, Figure 3. B. when the grease service life has been reached, Figure 4. However, temperature measurements are not suitable to detect local damage, e.g. B. Fatigue to register early.

4: Temperature curve over time with failed grease lubrication. Test conditions: n dm = 200,000 min-1 mm.

80 C

60

temperature
40

2 time

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Unusual operating behavior as an indication of damage


Warehouse monitoring with technical aids

1.2.2 Punctual damage If localized damage occurs in a warehouse, such as B. rolling body impressions, standstill corrosion or breakouts, these can be determined the earliest by vibration measurements. When rolling over the local depressions, shock waves arise that can be recorded by displacement, speed or acceleration sensors. Depending on the operating conditions and the expected accuracy, these signals can be further processed in a more or less complex manner. The most widespread are RMS measurement, shock pulse measurement, signal analysis by means of envelope detection (HKD). Good experience with regard to reliability and practical use has been made with the last-mentioned method in particular. Due to the special type of signal processing, it is even possible to infer the damaged bearing components, Figures 5 and 6. Further information can be found in our publication WL 80 136 Diagnosis of rolling bearings in machines and systems> FAG Rolling Bearing Analyzer <. 6: Inner ring damage on a spherical roller bearing of a paper machine identified using the HKD method

5: Frequency spectrum of the envelope signal between 0 and 200 Hz, below: undamaged bearing; Above: damaged bearing nIR inner ring speed [min1] Frequency of the inner ring signal (rolling frequency) [Hz] fIR
0.086g damaged bearing
nIR for nIR sidebands

Harmonics 2fIR 3fIR nIR nIR nIR nIR sidebands 4fIR

Vibration acceleration

0 0.086g undamaged bearing

20

40

60

80

100

120

140

160

180

200

Frequency [Hz]

7: Temperature profile and shock pulse (shock value) over the time after the lubrication has been switched off. Spindle bearing B7216E.TPA; P / C = 0.1; n = 9000 min-1; Lubricant ISO VG100.

160 C 140 temperature 120

300

100 shock pulse 80

100

60

80 0 4 running time 8 12 16

40 20 min 24

Lubrication switched off

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Unusual operating behavior as an indication of damage


Warehouse monitoring with technical aids Urgency of bearing replacement

The vibration measurement methods are very well suited to determine fatigue damage. This is easiest for bearings with point contact (ball bearings), but with more sophisticated evaluation methods, such as B. the envelope detection, damage to roller bearings are also reliably detected. However, they are less suitable for observing the lubrication status. As described above, a failure of the lubricant supply can be reliably recognized by a temperature measurement. This can be seen particularly well in the comparison in Figure 7. The shock pulse measurement reacts here much less sensitive than the temperature sensor. In particular, temperature and vibration measurements in technically complex systems are a useful complement to each other.

In very many cases, however, it will still be possible to continue operating the machine without any loss of quality of the product, even if the product is damaged. How long in this case depends on the bearing load, the speed, the

Lubrication and the cleanliness of the lubricant. Extensive investigations were carried out on ball bearings to determine the progress of the damage under different loads. The most important findings from this are:

8: Development of fatigue damage in an angular ball bearing inner ring raceway. The interval between the inspections and the beginning of the damage is specified in% of the nominal service life L10.

1.3 Urgency of bearing replacement - remaining service life


Once bearing damage has been detected, the question arises as to whether an immediate change is necessary or whether the bearing can remain in use until the next scheduled downtime of the machine. The answer to this question depends on a number of conditions. If, for example, the reduced working accuracy of a machine tool gives rise to the assumption of bearing damage, then the urgency of the bearing change depends primarily on how long parts of usable quality can still be manufactured. In the case of bearings that are blocked by Heilauf in a very short time due to an undetected interruption of the lubricant supply at high speed, an immediate change is of course necessary.
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Unusual operating behavior as an indication of damage


Urgency of the exchange of bearings

Damage size in% of the circumference of the lane

If the load is moderate, damage only progresses very slowly, so that it is usually possible to wait until the next scheduled standstill before changing the bearings. As the load increases, the damage spreads much faster. At the beginning the damage grows slowly. The speed of propagation increases sharply as the damage increases. These findings are illustrated in Figures 8 (page 7), 9 and 10.

9: The extent of the damage as a function of the running time since the damage was detected (if approx. 0.1% of the circumference of the lane has been cut off)

12 10 8 6 4 2 0

10

20

30

40

Duration with damage [% L10]

10: Average remaining service life of angular ball bearings after detection of fatigue damage, depending on the load, up to 1/10 of the circumference of the track is damaged. Operating conditions before the first fatigue damage occurs: maximum cleanliness in the EHD lubrication gap.

Average runtime after damage detection [% L10]

30 25

20 15

10

5 0 1 900

2 000

2 100

2 200

2 300

2 400

2 500

2 600

max. Hertzian surface pressure [MPa]

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Securing defective bearings


Establishing the operating data, taking and assessing lubricant samples

2 Securing defective bearings


If a defective bearing is to be removed from a machine, it is essential to clarify what caused the damage and how a renewed failure can be avoided in the future. If you want to get the most reliable information possible, then a systematic approach to securing and inspecting the camp is advisable. Many of the points listed below should also be observed when inspecting bearings that are dismantled as part of preventive maintenance. The following sequence of measures is recommended: Establishing the operating data, evaluating the records of bearing monitoring devices, taking lubricant samples, checking the bearing environment for external influences and other damage, assessing the bearing when it is installed, marking the installation position, removing the bearing, marking the bearing, checking the bearing seats, examining the entire bearing, examining it of the individual parts in the warehouse or shipping to FAG If the damage assessment process is inexpedient, important aspects of finding the cause can be irretrievably lost. Likewise, errors in securing the damaged bearing can blur the damage pattern or at least make it much more difficult to correctly interpret the damage characteristics. Application: Machine (device), installation point, reached runtime, how many machines of the same type and how many failures on these machines Bearing structure: Fixed bearing, floating bearing, floating bearing, adjustable bearing (springy, rigid; with intermediate rings, via Paschi washers) Speed: constant, changing (inner ring and outer ring ) Acceleration, deceleration Load: axial, radial, combined, tilting moment constant, alternating (collective) oscillating (acceleration, oscillation path) Centrifugal forces Point load, circumferential load (which ring rotates?) Surrounding parts: Shaft seat, housing seat (fits) Fastening parts (e.g. Art the shaft nut, expansion screws, etc.) Environmental conditions: External heat, cooling Special media (e.g. nitrogen, vacuum, radiation) Vibrations at standstill Dust, dirt, moisture, corrosive media Electrical or magnetic fields Lubrication: Lubricant, lubricant quantity Lubricant supply Relubrication interval Time of the last Relubrication / last oil change sels sealing: touching, not touching history of the defective bearing: initial installation or replacement bearing changes at the installation site / machine in the past previous failure frequency calculated L10 service life usually achieved service life special features during the previous operating time repairs to other machine parts (construction work, welding work) operational disruptions that were traced back to other machine elements (e.g. B. Damage to seals, loss of oil) Transport route and means of transport of the machine or the warehouse Packaging If available, evaluate the records of the warehouse monitoring devices

2.2 Taking and assessing lubricant samples


A wide range of information about the causes of damage in rolling bearings can be obtained from the lubricant. A prerequisite, however, is a suitable sampling procedure (only for open bearings), see also DIN 51750, ASTM Standard D270-65 or 4057-81. Grease lubrication: Documentation of the distribution and color of grease in the bearing environment. Taking samples at various points in the bearing and the bearing environment with the appropriate identification Take immediately afterwards in order to obtain a representative distribution of foreign substances Do not take samples from the floor or directly behind filters (incorrect particle concentration)
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2.1 Establishing the operating data


When examining a rolling bearing damage, one not only checks the bearing itself, but also clarifies the environmental and operating conditions beforehand (if possible in conjunction with an installation drawing).

Securing defective bearings

Filter residues must also be stored and examined separately from the oil samples (information on the history of the damage) General How often was relubrication or an oil change carried out beforehand; when was this last? Check oil or grease for any fragments from the store or other components.Use clean vessels made of suitable materials (e.g. glass) to store the samples. In the case of oil samples, there should be enough space in the vessels for good resuspension of the sample in the laboratory Analysis of the samples can take place at the customer's, in an independent lubricant laboratory or at FAG. The degree of contamination and the type of contamination (sand, steel, soft particles, water, coolant) and an analysis of the lubricity (e.g. aging, solidification, color, coking, additive content) are usually of interest. If possible, a sample of the fresh fat or food should be given and examined (in the case of unknown lubricants, batch influences)

2.4 Assessment of the bearing when installed


Are there any breaks or chipped areas? Are the seals showing signs of damage, especially deformation or deformation? Does the bearing show any deformations on the visible surfaces? Are scratches on foreign parts to be seen? Is the bearing easy or difficult to move when installed? (Influence of fit)

2.7 Assessment of the entire warehouse


The bearings must always be presented uncleaned, i.e. with lubricant residues, for inspection. The following are to be checked: general condition (cleanliness of the bearing and condition of the surfaces, i.e. assembly marks, fretting corrosion, ring breaks, graininess, scuff marks, discoloration) condition of the sealing and cover disks. Photograph or describe the location and extent of any grease leakage. Condition of the cage Manual drain check (indications of contamination, damage or tension) Bearing clearance measurement (displaceability of the rings in relation to each other in radial or axial direction), while loading the bearings evenly and rotating!

2.5 Dismantling the defective bearing


When dismantling a damaged rolling bearing, it is essential to ensure that the damage pattern is not distorted. If this is unavoidable, expansion damage should be marked and noted. The following procedures are to be observed as far as possible: Do not conduct dismantling forces via the rolling elements High dismantling forces may indicate a disturbed floating bearing function Sealed bearings do not open heat-sensitive parts (lubricant, seal, cage) do not destroy or damage the bearing (installation location, installation direction)

2.8 Dispatch to FAG or assessment of the individual warehouse parts


In many cases, the fundamental possible causes of failure of a warehouse can already be identified by the customer himself or by a FAG employee on site. Depending on the severity of the individual damage features, it must then be decided whether further special examinations are necessary. The procedure for examining the individual warehouse parts is described in detail in the following section. If, however, only an examination at FAG is possible from the outset, the following steps should be followed when shipping the parts: If possible, do not dismantle or clean the bearing. Under no circumstances wash with cold cleaner or petrol (indications from the lubrication are lost, susceptibility to corrosion).

2.3 Review of the warehouse environment


Could surrounding parts touch bearing parts at any point? Are other components damaged in the vicinity of the bearing (consequential damage or primary damage)? Cleanliness inside and outside of the seals (have foreign bodies penetrated the storage room?) Loosening forces of the bearing fastening parts (have deformations been imposed on the bearing? Are the fastenings loose?)
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2.6 Checking the seats


Dimensions of shaft and housing (tension, seats that are too loose) Shape tolerances of the seats (oval tension) Roughness of the seats (excessive loss) Fretting corrosion (if the distribution varies from place to place, indication of uneven support, load direction)

Securing defective bearings Assessment of running and damage features on the dismantled warehouse

Avoid contamination after removal. If possible, wrap the bearings individually in clean foil, because paper or rags may drain the grease. Choose sufficiently strong and tight packaging so that no transport damage occurs.

3 Assessment of running and damage features on the dismantled warehouse


Bearing damage should not only be understood as the total failure of a rolling bearing, but also a reduction in the performance of the bearing. In this context, it should also be taken into account that the causes of malfunctions in the warehouse process can be identified more reliably the earlier the suspect warehouse is removed. A bearing can only function properly if the operating and ambient conditions and the components of the bearing (bearing, surrounding parts, lubrication, sealing) are properly coordinated with one another. The cause of a bearing damage must not be looked for in the bearing alone. Damage that can be traced back to material or manufacturing defects in the bearing occurs very rarely. Before examining a bearing damage on the basis of the individual parts, the assessor should obtain an overview of the possible causes of damage based on the facts determined in Section 2. The operating conditions or external characteristics of the bearing often give indications of certain tendencies for the cause of the damage. In table, Figure 12, the most important damage features are assigned to the typical causes of rolling bearing damage. This summary can certainly not go into all possible damage, but only give a rough overview. It should also be noted that a number of types of damage occur exclusively or at least preferentially with certain types of bearings or under special operating conditions. In many cases, several damage features can be observed on a bearing at the same time. In such a case, it is often difficult to determine the primary cause of failure. In this case, only a systematic clarification of various damage hypotheses usually helps. The systematic procedure described below is useful for this purpose.

11: Causes of failure for rolling bearings (source: antriebstechnik 18 (1979) No. 3, 71-74). Only about 0.35% of all rolling bearings fail before the expected running time.
20% unsuitable lubricant 15% lack of lubricant <1% material and manufacturing defects 10% unsuitable bearing selection (design, size, load capacity) 20% solid contamination 5% consequential damage 5% assembly error 5% liquid contamination

20% Aged Lubricant

11

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Assessment of running and damage features on the dismantled warehouse

12: Notes on rolling bearing damage and its causes


Feature Damaged areas of the bearing Typical causes of rolling bearing damage Installation of seat, rolling surfaces, rim, cage and roller face seal Incorrect assembly process or tools Uncleanliness Too tight fit, too high preload Too loose fit, too little preload Poor support for the rings Misalignment or shaft bending

a) Abnormalities in the operating behavior Uneven running Unusual noise Disturbed temperature behavior b) Appearance of dismantled bearing parts 1 Foreign body impressions 2 Fatigue damage 3 Standstill markings 4 Melting craters and corrugations 5 Slippage damage 6 Rolling body impressions Scratch marks 7 Scuff marks 8 Wear damage 9 Corrosion damage 11 Frictional damage 12 Friction damage

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12

characteristic

Typical causes of rolling bearing damage Overstressing or underloading operational stress Vibrations High speeds Ambient influences Dust, dirt Aggressive media, water External heat Passage of electricity Lubrication Unsuitable lubricant Insufficient lubricant Overlubrication

a) Abnormalities in the operating behavior Uneven running Unusual noise Disturbed temperature behavior b) Appearance of dismantled bearing parts 1 Foreign body impressions 2 Fatigue damage 3 Standstill markings 4 Melting craters and corrugations 5 Slippage damage 6 Rolling body impressions Scratch marks 7 Scuff marks 8 Wear damage 9 Corrosion damage 11 Frictional damage 12 Friction damage

13

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Assessment of running and damage features on the dismantled warehouse


Preparatory Actions

3.1 Preparatory Actions


3.1.1 Identification of the individual parts If there are several bearings with similar internals, number all of the bearing parts and record their arrangement during the installation. Mark the lateral allocation of the bearing parts to each other and in relation to their installation position. Mark the radial installation direction of the rings in relation to the external force.

3.1.4 Assessment of the bearing parts First, you get a first overview of the essential running and installation features visually without tools. With the predominant number of bearings, a microscopic assessment of the bearing parts is also useful or necessary. The following procedure when considering the bearing parts is advisable in most cases: Assessment of the seating surfaces (axial contact surfaces, inner ring bore, outer ring surface) Raceways Borders Sealing seat surfaces or sealing contact surfaces Rolling bodies (in the case of rollers, outer and end surfaces) Automotive seals can sometimes also help to clarify the cause of damage further investigations, such as B. lubricant analyzes, measurements, electron microscopic examinations, etc., may be required. For such cases, competent contact persons are available to you in the FAG laboratories in the area of ​​product research and development (see Section 4). It is often necessary to decide whether a bearing that has been used can continue to be used or has to be replaced. If significant damage is discovered, there is no doubt about how to proceed. In many cases, however, no such damage can be found. Nevertheless, the assessment of the bearings often gives indications of the operating condition. If you recognize unusual features and their causes, you can often avoid major damage. The following sections contain descriptions of the characteristics, notes on their meaning and causes and, where appropriate, measures to avoid them.

3.1.2 Measurements on the complete bearing Noise test Checking radial or axial play Checking radial or axial runouts Frictional torque test

3.1.3 Disassembling the bearing into individual parts If necessary, determine the amount of grease if grease leakage was detected in sealed bearings. If the bearings are sealed, remove the cover washers or sealing washers carefully and without major deformation. Assess the fat distribution in the warehouse. Take fat sample; If the appearance of the lubricant is uneven, several samples. If non-destructive dismantling is not possible, the parts should be destroyed that are assumed to have no influence on the damage caused (e.g. in the case of tapered roller bearings, twist off the retaining flange on the small inner ring diameter). If the dismantling procedure inevitably causes damage, this should be marked and noted.
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Assessment of running and damage features on the dismantled warehouse


Condition of the seats

3.2 The condition of the seats


Various conclusions can be drawn from the condition of the seat surfaces as to the quality of the support of the bearing rings on the shaft or in the housing. Movements of the rings in relation to the seating area cause noises that can often be annoying. But they also lead to fretting corrosion and wear. This leads to lubricant contamination through corrosion or Abrasion particles. In addition, the support of the rings is getting worse and the fretting corrosion can lead to disassembly difficulties. Here are some examples of this.

Use mast-stabilized rings at high operating temperatures (prevents loosening of the fit by opening the rings due to structural damage

stanchions in the steel) Improve the roundness of the seats Check the surface quality of the seats and improve if necessary

13: Fretting corrosion in the bore of a cylindrical roller bearing inner ring with a loose fit

3.2.1 Fretting corrosion - fretting corrosion Characteristics: Brown-black stains on the seats, e.g. Sometimes also brown abrasion near the bearings or in the lubricant. Wear on the surfaces (bore, jacket diameter), with rotating parts (mostly shaft) possible fatigue breakage, with stationary parts (mostly housing) the floating bearing function can be disturbed, Figure 13. From such fretting corrosion, the position and size of the load zone, Figure 14, or that the rings are rotating at the same time. Causes: Micromovements between the mated parts when the fits are too loose in relation to the forces acting, but the rings do not rotate too Form interference of the surfaces Shaft deflection, housing deformation Floating bearing function on the ring with circumferential load Remedy: Provide floating bearing function on the ring with point load Use bearing seats that are as solid as possible Shaft (housing) make coating bearing seats more rigid

14: Fretting corrosion makes the size of the load zone visible on the stationary outer ring.

15

FAG

Assessment of running and damage features on the dismantled warehouse


Condition of the seats

3.2.2 Scuff marks or sliding wear Features: Cold welds on the faces (inner ring bore, outer ring surface) and axial contact surfaces or, if the surface roughness is good, also mirror-like contact surfaces, Figure 15, 16.Wear of the pa and face surfaces, Figure 17, possible reduction of the preload or Game enlargement. Causes: Rotational movements between ring and shaft / housing with loose fits under rotating load; Even with static loads under imbalances. Axial fixing of the rings inadequate. Floating bearing pushes sluggishly. Remedy: Use the firmest possible bearing seats. Increase axial contact surfaces. Secure axial fixing. Keep surfaces dry. Improve floating bearing function

16: Scuff marks in the inner ring bore as a result of the inner ring rotating on the shaft

15: Scuff marks on the jacket surface as a result of the outer ring rotating in the housing

17: Circumferential grooves and cold welds on the inner ring side surface as a result of the inner ring rotating on the shaft

FAG

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Assessment of running and damage features on the dismantled warehouse


Condition of the seats

3.2.3 Uneven support of the bearing rings Features: Seat marks not in the area of ​​the expected load zone. Machining structure of the patches worn in areas and still completely intact in other areas, Figure 18, 19. As a result, fatigue damage and fractures due to uneven load distribution and bending of the rings. If the axial support of the tapered roller bearing inner rings is too small, there will also be flange fractures, Figure 20, or if the contact surfaces are too small, there will also be plastic settlement phenomena.

Causes: Unsuitable construction Inaccurate processing

Remedy: Modify the construction of the surrounding parts and ensure that the housing is stiff evenly; possibly also use other bearings. Check the manufacture of the conversion parts

19: Outer ring surface, only supported on half the width

18: Outer ring surface, fretting corrosion at hard points (e.g. ribs) in the housing

20: Edge fracture in a tapered roller bearing inner ring due to insufficient axial support of the end face

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FAG

Assessment of running and damage features on the dismantled warehouse


Condition of the seats

3.2.4 Lateral rubbing marks Features: Circumferential scratch marks or wear on the face of the bearing rings or seals, Figure 21, 22. Causes: Inadequate fixing of the bearings in the housing or on the shaft Too much axial play Remedy: Fix parts properly Ensure lubricant cleanliness Check axial play and narrow it if necessary

21: Circumferential grooves and cold welds on the side surface due to the touching of a surrounding part

22: Damage to the seal due to side rubbing

FAG

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Assessment of running and damage features on the dismantled warehouse


Appearance of the rolling contacts

3.3 The appearance of the rolling contacts


3.3.1 Formation and significance of running marks Irrespective of the occurrence of damage, changes in the contact surfaces between rings and rolling elements can be seen on every bearing that has been run, which are referred to as running marks.Tracks are created by roughening or smoothing the originally manufactured surface structure. They are often also characterized by impressions of rolled-over, often microscopic foreign bodies or by discoloration. From the tracks, conclusions can be drawn about the quality of the lubrication, the cleanliness of the lubricant and the direction of the load as well as the load distribution in the bearing.

3.3.1.1 Normal running marks The rolling elements leave marks on the running tracks under the rotational movement and load, which usually have a light appearance if the lubricating film separates well. The individual appearance of the tracks, however, is heavily dependent on the lighting of the surface. However, the processing structure should still be largely recognizable when viewed with a magnifying glass and microscope (comparison with areas that have not been run on the edge of the track!). Individual impressions of small foreign bodies are also to be regarded as inevitable. With particularly good lubrication, they are the only indications of the position of the load zones in the bearing, Figure 23. In many cases, the raceways or rolling elements are discolored at temperatures above approx. 80 C. They arise from chemical reactions of the steel with the lubricant or its additives and have no negative influence

on the service life of the bearings. On the contrary: these surface layers often indicate that the additives are effective against wear and tear. Usually brown or blue tones emerge. However, the respective color does not allow any clear conclusions to be drawn about the operating temperature that led to its formation. Distinctly different color tones are sometimes observed in the individual rolling elements of a bearing, although the operating conditions are very similar. Under no circumstances should this discolouration be confused with the annealing colors that can be observed in rare cases on failed bearings, which can occur at much higher temperatures, see Section 3.3.5. Running tracks in the form of equatorial bands are also sometimes visible on spheres. They occur in angular ball bearings when the balls always maintain the same axis of rotation. A fundamental reduction in service life cannot be derived from them, Figure 24.

23: Normal running track, surface structure still visible, only a few small impressions from foreign bodies

24: Sphere with an equatorial band

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FAG

Assessment of running and damage features on the dismantled warehouse


Appearance of the rolling contacts

25: Radial load on a radial bearing, e.g. B. a deep groove ball bearing. With a point load and a sufficiently rigid housing, the track on the stationary ring is shorter than half the circumference of the track, provided there is no radial preload. In the case of a circumferential load, the track extends over the entire circumference of the track. a: Point load for the outer ring, circumferential load for the inner ring b: Point load for the inner ring, circumferential load for the outer ring

nJ P

nJ P

P nA rotating inner ring constant load direction rotating outer ring rotating load direction

P nA rotating inner ring rotating load direction rotating outer ring constant load direction

25a

25b

The arrangement of the tracks results from the direction of the external load and the circumferential conditions (point load or circumferential load, axial load, combined load), Figures 25 to 27. A target / actual comparison also provides important information on unexpected load conditions, e.g. B. on a disturbed floating bearing function. In the case of a purely radial load, the formation of the running tracks in the circumferential direction on the stationary ring depends essentially on the level of the load, the size of the bearing play and the rigidity of the surrounding parts. The higher the load, the smaller the bearing play and the softer the housing, the longer the load zone and thus also the track.
FAG 20

26: Axial load on a radial bearing, e.g. B. a deep groove ball bearing. The tracks on the inner and outer rings extend eccentrically over the entire circumference of the track. 27: Combined radial-axial load on a deep groove ball bearing. In the case of the inner ring (circumferential load), a constantly wide running track runs over the entire circumference of the raceway. With the outer ring (point load), the track in the radially loaded zone is wider than on the rest of the circumference.

26

27

Assessment of running and damage features on the dismantled warehouse


Appearance of the rolling contacts

3.3.1.2 Unusual tracks Which tracks are normal and which are unusual depends to a large extent on the type of installation. For example B. Bearings have normal tracks that indicate a predominantly radial load; However, for a bearing that should run under axial preload, this would be an indication of incorrect mounting of the bearings. This makes it clear that the operating conditions of the bearings should be known in order to assess the running tracks. However, some basic features can always be assessed using the tracks. Traces in the event of insufficient lubrication Features: The visual appearance of the traces or the fine surface shape, i.e. roughness, allow important conclusions to be drawn about the quality of the lubrication. If the lubricant film does not separate under moderate load, matt, roughened tracks are created.

The influence on the surface is more intense, the thinner the lubricating film; This is referred to as poor surface separation, Figure 28. If the contact surfaces are subjected to high specific loads, there are light, pressure-polished, often mirror-like running tracks that are very clearly demarcated from the unused raceway, Figure 29. Causes: Insufficient amount of lubricant available in the bearing The lubricant has Insufficient viscosity at operating temperature and speed (see FAG rolling bearings catalog, extended service life calculation) Remedy: Improve lubricant supply Adjust lubricant viscosity to operating conditions Use lubricant with tried and tested additives Use bearing parts with surface coating

28: Lane with surface wear

29: Pressure-polished track

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FAG

Assessment of running and damage features on the dismantled warehouse


Appearance of the rolling contacts

Tracks in the event of contamination in the bearing or in the lubricant First and foremost, a distinction must be made between solid and liquid contamination. Characteristics of solid impurities: If solids are rolled over in the raceways, they leave impressions. When examining the tracks under a microscope, one can differentiate between particles made of soft materials, hardened steel and hard minerals, Fig. 30, 31, 32. Large, hard foreign bodies are particularly critical for the service life. This is discussed in more detail in the description of fatigue damage, see also fatigue due to foreign bodies rolling in section 3.3.2.1. A large number of small, hard foreign bodies lead to roughening as shown in Fig. 28 and accelerate abrasive wear.

Characteristics of liquid contaminants: Among the liquid lubricant contaminants, water is particularly common. It can be absorbed by the lubricant in certain small quantities. However, it worsens its lubricating effect and often leads to running tracks similar to those in Figure 29. With larger amounts of moisture in the bearing, dull running marks appear and, as a result of corrosion or, under high load, pressure-polished running marks with fatigue damage, see also fatigue due to poor lubrication in Section 3.3.2.1.

Causes: Inadequate sealing. Unclean assembly conditions. B. Molding sand Temperature differences (formation of condensation) Unclean l Remedy: Improve the construction of the seal Clean assembly and well-washed components, paint if necessary Flush the entire oil system before commissioning (before the first rotation of the bearing!)

30: Impressions from soft foreign bodies