Reusability of Tapered Bearings {7000, 7551} Caterpillar

Off-Highway Truck/Tractor

All

Introduction

Table 1

Revision	Summary of Changes in SEBF8190
08	Revised definition for abrasive wear, updated boilerplate information.
07	Updated introduction, added Canceled Part Numbers section, and updated group effectivity.
06	Corrected Text for Illustrations 53 and 54.
05	Added Models 773E, 793F, and 797F.

© 2018 Caterpillar All Rights Reserved. This guideline is for the use of Cat dealers only. Unauthorized use of this document or the proprietary processes therein without permission may be violation of intellectual property law.

Information contained in this document is considered Caterpillar: Confidential Yellow.

This Reuse and Salvage Guideline contains the necessary information to allow a dealer to establish a parts reusability program. Reuse and salvage information enables Caterpillar dealers and customers to benefit from cost reductions. Every effort has been made to provide the most current information that is known to Caterpillar. Continuing improvement and advancement of product design might have caused changes to your product which are not included in this publication. This Reuse and Salvage Guideline must be used with the latest technical information that is available from Caterpillar.

For technical questions when using this document, work with your Dealer Technical Communicator (TC).

To report suspected errors, inaccuracies, or suggestions regarding the document, submit a form for feedback in the Service Information System (SIS Web) interface.

Canceled Part Numbers and Replaced Part Numbers

This document may include canceled part numbers and replaced part numbers. Use the Numerical Part Record (NPR) on the Service Information System Website (SIS Web) for information about canceled part numbers and replaced part numbers. NPR will provide the current part numbers for replaced parts.

Important Safety Information

Illustration 1	g02139237

Work safely. Most accidents that involve product operation, maintenance, and repair are caused by failure to observe basic safety rules or precautions. An accident can often be avoided by recognizing potentially hazardous situations before an accident occurs. A person must be alert to potential hazards. This person should also have the necessary training, skills, and tools to perform these functions properly. Safety precautions and warnings are provided in this instruction and on the product. If these hazard warnings are not heeded, bodily injury or death could occur to you or to other persons. Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard. Therefore, the warnings in this publication and the warnings that are on the product are not all inclusive. If a tool, a procedure, a work method, or operating technique that is not recommended by Caterpillar is used, ensure that it is safe for you and for other people to use. Ensure that the product will not be damaged or the product will not be made unsafe by the operation, lubrication, maintenance, or the repair procedures that are used.

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Improper operation, lubrication, maintenance or repair of this product can be dangerous and could result in injury or death. Do not operate or perform any lubrication, maintenance or repair on this product, until you have read and understood the operation, lubrication, maintenance and repair information.

Safety precautions and warnings are provided in this manual and on the product. If these hazard warnings are not heeded, bodily injury or death could occur to you or to other persons.

The hazards are identified by the “Safety Alert Symbol” which is followed by a “Signal Word” such as “DANGER”, “WARNING” or “CAUTION”. Refer to Illustration 2 for an example of a “WARNING” Safety Alert Symbol.

Illustration 2	g00008666

This safety alert symbol means:

Pay Attention!

Become Alert!

Your safety is Involved.

The message that appears under the safety alert symbol explains the hazard.

Operations that may cause product damage are identified by "NOTICE" labels on the product and in this publication.

Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard. The safety information in this document and the safety information on the machine are not all inclusive. Determine that the tools, procedures, work methods, and operating techniques are safe. Determine that the operation, lubrication, maintenance, and repair procedures will not damage the machine. Also, determine that the operation, lubrication, maintenance, and repair procedures will not make the machine unsafe.

The information, the specifications, and the illustrations that exist in this guideline are based on information which was available at the time of publication. The specifications, torques, pressures, measurements, adjustments, illustrations, and other items can change at any time. These changes can affect the service that is given to the product. Obtain the complete, most current information before you start any job. Caterpillar dealers can supply the most current information.

Summary

The purpose of this guideline is to help in the identification of the cause of a bearing failure. Usually, the question of reusability will not be an issue. If the bearing has any amount of abnormal damage, the bearing should be replaced. However, if the cause of that damage is not corrected, the replacement bearing will also have a shortened life. Use the information and illustrations that show normal and abnormal wear to help identify the cause of the damage and then correct the problem before installing new bearings.

The beginning of the guideline gives the correct nomenclature for tapered roller bearings. The section follows this section on the design and operational characteristics of bearings. Later in the guideline, a series of photos of normal wear are shown. Finally, the remainder of this guideline illustrates various examples of abnormal damage.

The suggestions on reusing bearings in this guideline should be followed. Before installing a new part, correct any conditions that may have caused the original failure or wear.

References

Table 2

References
Media Number	Publication Type & Title
NENG2500	Special Publication "Dealer Service Tool Catalog"
SEBF8187	Reuse and Salvage Guidelines "Standardized Parts Marking Procedures"
SEHS9031	Special Instruction "Storage Procedure for Caterpillar Products"

Service Advisories, Service Letters, and Technical Service Bulletins

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NOTICE
The most recent Service Advisories, Service Letters, and Technical Service Bulletins that are related to this component should be reviewed before beginning work. Often Service Advisories, Service Letters, and Technical Service Bulletins contain upgrades in repair procedures, parts, and safety information which pertain to the components being repaired.

Tooling and Equipment

Note: The Tooling and Equipment in Table 3 is not an all inclusive list of Tooling required to perform every task within this document. Tooling needs may vary for scope of work to be performed for each specific rebuild.

Table 3

Required Tooling and Equipment
Part Number	Description	Designation
(1)	Personal Protective Equipment (PPE)	Personal Protection
8H-8581	Feeler Gauge 0.038 - 0.635 mm (0.0015 - 0.0250 inch)	Thickness Measurement Checks
9U-7377	Metal Marking Pen	Parts Marking
6V-2010	Polishing Stone	Gear Polishing
8T-7765	Surface Reconditioning Pad (180 Grit)	General Cleaning
162-5791	Towel	General Cleaning
—	Solvent Cleaner	General Cleaning
5P-1720	Seal Pick	Step Inspection
5P-7414	Seal Pick Kit	Step Inspection
1U-9978	Brush	Application
349-4202	Thermometer Infrared -12:1 Ratio	Temperature Checks
8S-2257	Magnifying Glass	Visual Surface Inspection (VT)
9U-6182	Mirror (Telescoping)	Visual Surface Inspection (VT)
269-3123	Leak Detector Light Pen (Blue)	Visual Surface Inspection (VT)
9U-7231	Flashing Lights Conversion Kit	Visual Surface Inspection (VT)
4C-9442	Light	Visual Surface Inspection (VT)
— (1)	Bright Incandescent Light	Visual Surface Inspection (VT)
—	Reflective Surface for Inspection	Visual Surface Inspection (VT)
262-8390	Microscope (40-Power) Pocket	Crack/ Measurement Inspection
288-4209	Paper Towel	Liquid Penetrant Testing (PT)
—	Developer	Liquid Penetrant Testing (PT)
—	Penetrating Oil	Liquid Penetrant Testing (PT)
—	Solvent Cleaner	General Cleaning/ Liquid Penetrant Testing (PT)
263-7184	Crack Detection Kit (Magnetic Particle)	Dry Magnetic Particle Testing (MPT)
—	Paint Pen	Dry Magnetic Particle Testing (MPT)
459-0184	Lamp Group Ultraviolet	Wet Magnetic Particle Testing (MPT)
505-8671	Fluid Ultrasonic Wear Indicator	Ultrasonic Testing (UT)
415-4055	Tool Group(Ultrasonic)	Ultrasonic Testing (UT)
263-7184	Crack Detection Kit (Magnetic Particle)	Dry Magnetic Particle Testing (MPT)
—	Paint Pen	Dry Magnetic Particle Testing (MPT)
459-0184	Lamp Group Ultraviolet	Wet Magnetic Particle Testing (MPT)
505-8671	Fluid Ultrasonic Wear Indicator	Ultrasonic Testing (UT)
415-4055	Tool Group(Ultrasonic)	Ultrasonic Testing (UT)

(1)	Refer to NENG2500Special Publication, "Dealer Service Tool Catalog" for Personal Protective Equipment (PPE) part numbers suitable by geographic location and local safety standards.

Replacement Parts

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Personal injury can result when using cleaner solvents. To help prevent personal injury, follow the instructions and warnings on the cleaner solvent container before using.

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Personal injury can result from air pressure. Personal injury can result without following proper procedure. When using pressure air, wear a protective face shield and protective clothing. Maximum air pressure at the nozzle must be less than 205 kPa (30 psi) for cleaning purposes.

Safety Checks

Safety

1. It is critical to follow all maintenance practices and handling practices for bearings. Failure to follow all installation instructions and failure to maintain proper lubrication can result in equipment failure. Equipment failure creates a risk of serious bodily harm.

2. Never spin a bearing with compressed air. The rollers may be violently expelled from the bearing with great velocity. Bearings that are violently expelled create a risk of serious bodily harm.

3. Do not wash bearings or clean bearings in an enclosed area. Fumes from solvents can be toxic and explosive. Ensure that cleaning is performed in a suitably ventilated area. The cleaning area should never be near open flame, welding, or smoking. Use all applicable Personal Protective Equipment (PPE) as per Safety Data Sheet (SDS) and local regulations.

4. Do not use a hammer and/or hardened steel bar for bearing removal. Fragments from the hammer, bar, or bearing could break off with sufficient velocity. The fragments create a risk of serious bodily harm, especially to the eyes.

5. Wear safety glasses to protect your eyes for installing bearings and removing bearings.

6. Always use insulated gloves that are fireproof to hold the heated cone for heating bearing cones for installation.

Damage of Parts

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When replacement parts are required for this product Caterpillar recommends using Caterpillar replacement parts or parts with equivalent specifications including, but not limited to, physical dimensions, type, strength and material. Failure to heed this warning can lead to premature failures, product damage, personal injury or death.

Proper maintenance and proper handling is critical to obtain the longest possible life from a bearing. Tapered roller bearings must be properly maintained. The performance of tapered roller bearings depends on handling that is careful. The performance depends on regularly scheduled maintenance and lubrication.

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NOTICE
Failure to properly assemble parts or failure to follow established procedures can lead to damage to the parts and assembly. To avoid damage to parts, always identify and mark the parts so that they can be installed into the same location. Never force parts during assembly. Keep parts clean and lubricated.

1. The handling of the bearings should be held to a minimum. Fingerprints on the bearing surface can cause rust. Never drop or handle these precision components roughly. Any sign of a bent cage makes the bearing unusable.

2. Do not mix parts. The cup and the cone should be changed if the cup or the cone needs to be replaced. Do not use old parts with new parts because the raceway of the old parts has a distinct pattern. Mixing the old part with a new mating part will set up edge stresses along the races.

3. Never use a torch to heat a bearing. Heat from a torch is hot. Distributing the heat from a torch evenly is difficult. In a matter of seconds, the metallurgy of the bearing could be altered and the metallurgy could begin to soften. This could cause the bearing to fail. Failure of the bearing could damage other components in the process.

4. Use insulated, fireproof gloves to hold a heated cone against the shoulder until the cone seats. Hot cones can pull away from a cold shoulder unless the cone is held in position.

5. Use a 0.05 mm (0.002 inch) feeler gauge to install cups and cones. Use the feeler gauge to ensure that the seating against the shoulder of the shaft or housing is proper.

6. Cones that have been heated for installation should be lubricated after the cones are properly seated on the shaft and the temperature stabilizes to the ambient air temperature.

7. The shaft and the housing bore should be machined to the proper specifications. The shaft and the housing bore should not be damage. Inspect the shaft and the housing bore.

8. Properly store new bearings and used bearings. For new bearings, do not open the box early. Bearing packaging is designed to protect bearings against dirt and moisture during shipping and storage. All bearings should be stored in a clean area that is dry until the bearings are ready for installation. Avoid temperature changes in the storage area because dramatic temperature changes can cause condensation. Condensation will damage the bearing.

9. Replace worn seals or damaged seals that can allow contaminants to enter the housing of the bearing. Replace worn seals or damaged seals that allow lubrication to escape. Replacing all seals at the time of a rebuild is a good practice.

10. In bearings that are lubricated by grease, too much grease in the bearing, and too much grease in the housing will cause excess mixing of the grease. Excess mixing of the grease will result in high temperatures. These high temperatures can cause the bearing or other mating parts to fail.

11. Use a micrometer to measure the shaft and the housing. The shaft and the housing should be measured whenever a bearing is replaced. Verify that the cone seats and the housing bores are the correct size. All measurements should meet the required specifications.

12. Never raise the temperature of standard bearings to more than 149 °C (300 °F). Never raise the temperature of precise bearings to more than 66 °C (151 °F). The recommended installation procedure in the Service Manual should be followed for installing bearings.

13. Never use liquid nitrogen to lower the temperature of bearings. Using liquid nitrogen to lower the temperature of bearings is an uncontrolled method and not recommended. The process could damage the bearings. Caterpillar recommends using dry ice or a freezer for bearings.

14. Never lower the temperature of a standard bearing below −55 °C (−67 °F).

Glossary of Terms

Abrasive Wear - Abrasives such as dirt or sand in lube systems can also cause bearing failures. If contamination is extensive, bearings can lock up, cause rollers to slide generating adhesive wear, and/or cause races to move in housings or on shafts. If abrasives cause bearings to progress to adhesive wear or spalling, the root cause will be difficult to determine by looking at only the failed bearing. Careful observation of other parts in the same lubrication system however, will generally give evidence of system contamination. Look for the matte or satin finish on other bearings and gears lubricated by the same oil. If there is evidence of abrasive wear, then determine the exact source of the abrasive material. Using magnification to identify what type particle caused the wear is a good practice.

Black Acid Etching - Black acid etching is a type of corrosion that affects the raceway and the surfaces of the rollers of the bearing. Black acid etching is caused through a reaction of temperature and certain oils. Black acid etching can progress from a visual imperfection into damage on the surface that can make the bearing unusable.

Brinelling - Marks from brinelling are dents on the surfaces of the raceways. The marks are caused by the rollers during a period of excessive load. Incorrect assembly can cause brinelling by violently driving the cone and the cup into position. Brinelling can be caused by high shock loads that are experienced during operation or transportation of the machine. Brinelling usually progresses into spalling.

Bruising - The damage can be caused by large particles and contaminants in the lubricant. The metal from a gear or the metal from the failure of a bearing are large particles that can cause bruising. The particles can cause plastic yielding and denting in raceways and on rollers. Hard particles will produce sharp angular dents while softer particles will produce smoother, shallower dents. If the bruising is sharp and angular, the bruising normally leads to spalling.

Corrosion - Corrosion is damage on the surface that is caused by moisture on the bearing surfaces or by moisture in the lubrication system. One type of corrosion is rust, which can develop after the bearing is cleaned. Without a thin film of oil, the bearing can rust rapidly. If moisture is in the lubrication system, corrosion will take place while the machine is shut down. The condition is known as static corrosion or black acid etching.

Creeping - Creeping occurs when the outer race of the bearing turns excessively inside the housing. If a bearing shows signs of creeping, repair the housing or the shaft to the correct dimension.

Discoloration - Some bearings may have the appearance of overheating, but the bearings only have discoloration. The type of oil that is used in the lubrication process can cause discoloration. Discoloration can usually be removed by using a surface reconditioning pad and a cleaning solvent.

Electrical Pitting - Electrical pitting can be caused by relatively high amounts of electrical current passing through the bearing while the bearing is not rotating. Relatively low currents that pass through the bearing over a long period can also cause electric pitting.

End Play - When the bearing is at normal operating temperature, the cone and rollers have a minimal clearance. End Play places more of the load on fewer rollers.

False Brinelling - False brinelling is different from true brinelling. Heavy shock loads do not cause false brinelling. False brinelling is actually fretting or fretting corrosion. The fretting is caused by vibrations of the bearing while the bearing is not turning under load. False brinelling can occur when machinery is shipped long distances by the way of rail. When false brinelling occurs, the elements for rolling vibrate and the elements wear into the surfaces of the raceway.

Fretting Corrosion - Fretting corrosion occurs on the surface of the bearing that contacts the shaft or housing. This type of corrosion indicates that the cup or the cone has moved relative to the shaft or the housing. The damage is caused because the harder surface of the bearing will pick up the softer material from the bore or the shaft.

Handling Damage and Installation Damage - Handling damage consists of any damage that is a result of not handling the bearings properly. Damage from installation is often physical damage to the bearing. The damage is caused by improper installation.

Misalignment - The two halves of the bearing are not aligned with each other. The damage is frequently caused when the shaft and the housing are not correctly aligned. Misalignment allows greater loads to be concentrated on one particular area of the bearing. Damage from misalignment progresses to abnormal wear. The damage may eventually lead to spalling.

Overheating - The bearing temperature exceeds the normal operating temperature from the lack of lubrication or too much of a thrust load. The result of an overheated bearing is a dry, burned appearance. Generally, overheated bearings should not be used again. Also refer to Discoloration.

Preload - When the bearing is at normal operating temperature, the cone and rollers are slightly pressed into the cup. Preloading increases the capacity of the bearing by spreading the applied load over more rollers and over a larger portion of the fixed raceway.

Scoring - Scoring is a small cut or a small groove that extends around the part. Scoring can take place in the roller, cone raceway, or cup raceway. Scoring is most often caused by foreign particles in the oil.

Spalling - Cracks that are under the surface progress, and the cracks reach the surface. This causes pieces of metal to break off the cone or the cup. Spalling can result after pitting, scoring, or other impact damage has occurred on the hardened bearing surface.

Nomenclature

Illustration 3	g06298312
Components of a rear wheel group. (1) Cup (6) Cage (7) Roller (8) Cone (15) Retainer (16) Shim Pack

Illustration 4	g01404751
Tapered Roller Bearing (1) Cup (6) Cage (7) Roller (8) Cone

Illustration 5	g01404754
Basic parts of a tapered roller bearing. (1) Cup (2) Cup raceway (3) Outer diameter of the surface of the cup (4) Front face of the cup (5) Back face of cup (6) Cage (7) Roller (8) Cone (9) Cone raceway (10) Inside diameter of the surface of the cone (11) front face of cone (12) Rib on the front face of the cone (13) Back face of cone (14) Rib on the back face of the cone

Tapered roller bearings consist of four basic components. The basic components are the cone, the cup, tapered rollers, and a cage. Under normal operating conditions, the inner race, the outer race, and the rollers carry the load. The cage spaces the rollers, and the cage retains the rollers. The inner race, the rollers, and the cage are referred to as the inner assembly of the race.

Operational Characteristics and Design Characteristics

This section provides background information on the following:

• Bearing usage

• Loads on bearings

• Manufacturing of bearings

The information in this section may help to determine the cause of bearing failures.

Tapered roller bearings are especially suited for carrying both radial loads and thrust loads. The rollers and the raceways form an angle with the axis of the shaft. Tapered roller bearings are also useful for maintaining precise axial positioning of shafts and housings.

Machine Application

The application is an important consideration for deciding if the wheel bearings can be used again. Assume that the machine has undergone high hours and heavy usage if the machine application is not known. The application should be a factor in deciding to reuse a bearing. A wheel bearing with slight damage may be used again if the machine is undergoing light work and low hours. The same bearing may fail if the machine is undergoing heavy work and high hours.

Note: Caterpillar bearings are designed to last as long as the intended life of the component. Bearings should be replaced at every Planned Component Rebuild (PCR).

Note: If there is any hesitation in reusing the bearing, the bearing should be replaced. A used bearing that fails can damage the other components.

Extending Bearing Life

The useful life of a bearing depends on the proper lubrication of the bearing. When external operating conditions include dirt, moisture, and extreme temperatures, wheel bearings must be properly lubricated. Lubricant aids in carrying away heat from a bearing. Lubricant protects bearing surfaces from corrosion. Also, lubricant reduces friction.

Failure to lubricate bearings correctly will eventually result in bearing damage. Always ensure proper lubrication of bearings.

Proper maintenance procedures are essential for achieving maximum bearing life and performance. Regardless of the type of bearing, the application, or the operating conditions, the regular maintenance of the machine should be followed.

Bearing Characteristics

Anti-friction bearings have the following primary functions:

• Anti-friction bearings support shafts and housings.

• Also, the bearings maintain the alignment of shafts and the alignment of housings.

• Anti-friction bearings allow shafts to turn with minimum friction.

• The bearings carry radial loads and thrust loads.

Loads

Illustration 6	g01404856
Bearing loads on a tapered roller bearing. (17) Radial load (18) Thrust load

The angled raceways allow the tapered roller bearing to carry combinations of radial loads and thrust loads.

Illustration 6 shows the direction of a radial load (1). Radial loads are generally a result of the weight of parts that are supported by the bearings. Also, radial loads are a result of the loads on the shaft that are required to transmit power. The loads on the shaft that are required to transmit power may be belts, chains, and gear drives.

Illustration 6 shows the direction of the thrust load (2). Thrust loads result from the following:

• Engagement forces of clutches

• Forces from wheels over corners

• Unbalanced hydraulic forces that are in line with the shafts

• Weight of parts on a vertical shaft

• Forces from helical gears

Illustration 7	g06298314
Tapered roller bearings are commonly used in pairs. The image shows a pair of tapered roller bearings in the rear wheel groups.

Tapered wheel bearings carry thrust loads in one direction only. Therefore, tapered wheel bearings are found in pairs. The bearings usually face each other. In Illustration 7, the bearings are facing each other. The load on the bearing is adjusted in the direction of the other bearing on the same shaft, which carries thrust loads in the opposite direction.

Bearing Cages

Most anti-friction bearings incorporate a cage to keep the rollers evenly spaced. The cage results in even load distribution to the rollers. The cage keeps rollers from rubbing against each other during normal operation. The cage is typically stamped from steel that is low in carbon and mild because the cage is not normally carrying a load, and the cage serves only to space the rollers around the races.

Illustration 8	g01405068

Also, cages keep cylindrical rollers in line with the shaft. If rollers did not have a cage, the rollers would not roll properly. Rollers that do not roll properly could cause adhesive wear and premature failure. There are many types of cages such as the following:

• Riveted

• Stamped

• Brass

• Electron beam welded

Rollers

Positive alignment of the rollers is one of the major features of tapered roller bearings. The tapered configuration of the roller also generates a force from seating that pushes the roller against the large rib of the inner race.

Stress

Illustration 9	g01405087
The area of stress on a tapered roller bearing is shown.

High areas of stress on roller bearings are concentrated on the inner raceways and the outer raceways. High stress is also on the rollers in the areas of the forces of radial rolling contact. Stresses in tapered roller bearings with high thrust loads will be applied around both raceways, or stresses with preload will be applied around both raceways.

There will also be bending, sliding, and compressive forces due to the contact between the rib of the cone and the large ends of the rollers. This contact is called seating force. Seating force keeps the rollers aligned with the shaft. See Illustration 9.

The Manufacturing of Bearings

Anti-friction bearings are manufactured from steels that bear the highest-quality alloys. Some bearings are vacuum melted. Most bearings are vacuum degreaser for maximum cleanliness. Race blanks that are either cut from tube stock for the small bearings, or the large bearings are made from high-quality steel forgings and then machined to approximate specifications. After machining, the races of cylindrical roller bearings and the races of tapered roller bearings are case hardened to a minimum of RC 58. Then the bearings areground to the final specifications.

Illustration 10	g01405094
The cross section of a cone that shows case hardened depth.

The bearings are then tempered at temperatures of approximately 200 °C (392.0 °F). Case hardened surfaces have good resistance to wear and fatigue. Case hardened surfaces maintain a softer RC 25 to RC 48 core that is more tough. A softer core that is more tough has an increased capability of carrying loads on impact. Illustration 10 shows a cross section of a tapered roller bearing cone. The surface has been etched to highlight the case hardened depth.

Illustration 11	g01405116
Example of a typical roller before heat treating and grinding.

Rollers are forged from the same steel that is used to make bearing cups and bearing cones. Illustration 11 shows an example of a cylindrical roller after cold heading. Heat treating and grinding has not been done to the roller.

Illustration 12	g01405122
The vertical and horizontal cross section of a typical roller.

Illustration 12 shows a cross section of a roller that has been etched. The illustration shows the case hardened depth after heat treatment, and the illustration shows the final machining. The maximum hardness for a roller should be RC 50.

Cleanliness

One of the most common sources of damage in anti-friction bearings is debris that contaminates the lubrication system. Debris can be a major cause of abrasive wear, which can lead to reduced bearing life. Cleanliness during assembly of a component should include the following parts of the assembly:

• Bearings

• Housings

• Shafts

• Tools

• Solvents

• Flushing oils

Bearings should be placed on a clean surface prior to installation. Clean rags and clean gloves should be used to handle bearings without contamination. The following steps will help extend the life of the bearing.

1. Use a cleaning solution such as kerosene or mineral spirits to avoid corrosion. Do not use steam or hot water directly on the bearings.

2. Prior to inspection, make sure that the bearings are free from dirt and excessive oil.

3. If the bearings are stored after inspection, use 4C-6793 Oil or 4C-6794 Oil to cover the bearings. The bearings should be wrapped in a Volatile Corrosion Inhibitor (VCI). VCI paper is recommended. Seal the bearings in a plastic bag. Wrapped bearings should be stored in a clean, dry place. Refer to Special Instruction, SEHS9031, "Storage Procedure For Caterpillar Products" for more information.

4. Gloves shall always be used for handling bearings to prevent possible corrosion.

Procedure for Marking

The code is a Caterpillar standard. The code is used to record the history of a bearing. The procedure for marking should include a code. The code will determine if a bearing was reused at the time of an overhaul. Normally, bearings have a specific life and the bearings should not be reused.

Note: Caterpillar bearings are designed to last as long as the intended life of the component. Bearings should be replaced at every Planned Component Rebuild (PCR).

Illustration 13	g01405130
The image shows a bearing with a code. The code (R) was used to show that the bearing was not replaced at the time of overhaul. (R) Code

The mark should be placed on the side of the bearing. When possible, the mark should not be covered by a mating part. The mark shall not be covered by a mating part. Use the metal marking pen that is listed in "Tooling and Equipment" to mark the code onto the bearing.

Illustration 13 shows the proper marking of a bearing.

Refer to Reuse And Salvage Guidelines, SEBF8187, "Standardized Parts Marking Procedures" for more information.

Inspection

Inspection of the bearing is critical. After cleaning, the bearing should be inspected to determine if the bearing could be used again. Bearings can be reused after passing inspection if the bearing came out of a component that did not reach the Planned Component Rebuild (PCR), and the bearing will be reused to finish the original Planned Component Rebuild (PCR). Do not reuse the bearing if the component will be used for another full expected life. Use an incandescent light to illuminate the cup and the cone raceway. A magnifying glass can be used to inspect questionable areas of the raceways.

The cup and the cone should be inspected for cracks, corrosion, damage from foreign objects, spalling, pitting, fretting, uneven wear, misalignment, overheating, brinelling, abrasive wear, and handling damage. The "Inspection" section of this guideline explains the characteristics of both normal and damaged bearings. Careful consideration must be given to the damage that is acceptable for a bearing to be potentially used again. If reusing the bearing is questionable, the bearing should be replaced.

Illustration 14	g01405132
The image shows the inspection of the cup raceway.

Illustration 15	g01405133
The image shows the inspection of the cone raceway.

Illustration 14 and Illustration 15 show the techniques for inspection of the cup and cone. An inspection should be completed to determine the reason for failure. Both the raceway and the outside diameter of the cup should be inspected. The inner raceway, inside diameter, rollers, and the cage of the cone should also be inspected on the cone. Table 4 through Table 7 should help determine the cause of different types of damage.

Table 4

Type of Damage	Probable Cause - Mode of Contact Fatigue
Fatigue from Contact	Incorrect Handling	Incorrect Assembly	Excessive Preload	Excessive End Play	Improper Storage	Misalignment	Deflection	Loose Fit
Stress Concentration		—		—		—	—
Point Surface Contact
Peeling			—					—
Transverse Cracking
Subcase Fatigue
Other Damage
Brinelling				—
False Brinelling				—
Burn Up		—	—
Burn and Fluting Damage
Cage Damage and Breakage	—	—		—
Creeping								—
Etching and Corrosion					—
Gouges or Nicks	—	—						—
Leaky Seals	—	—
Pitting and Grooving
Spalling
Abnormal Surface Wear	—	—	—	—		—
Abrasive Wear
Corrosive Wear
Wear on the ends of rollers				—		—
Wear on the Spindles or Hubs				—		—		—

Table 5

Type of Damage	Probable Cause - Operating Conditions
Fatigue from Contact	Impact or Shock Loads	High Static Overload	Heavy Load	Vibrations and Oscillations
Stress Concentration
Point Surface Contact
Peeling
Transverse Cracking	—	—
Subcase Fatigue			—
Other Damage
Brinelling	—	—
False Brinelling				—
Burn Up
Burn and Fluting Damage
Cage Damage and Breakage	—			—
Creeping
Etching and Corrosion
Gouges or Nicks
Leaky Seals
Pitting and Grooving
Spalling			—
Abnormal Surface Wear
Abrasive Wear
Corrosive Wear
Wear on the Ends of Rollers
Wear on the Spindles or Hubs

Table 6

Type of Damage	Probable Cause - Environment
Fatigue from Contact	Water or Moisture in Lubricant	Metallic Foreign Particles	Other Foreign Particles	Faulty Seals	Improper Cleaning of Housing	Chemical Contamination	Electric Current
Stress Concentration
Point Surface Contact		—	—
Peeling
Transverse Cracking
Subcase Fatigue
Other Damage
Brinelling
False Brinelling
Burn Up
Burn and Fluting Damage							—
Cage Damage and Breakage
Creeping
Etching and Corrosion	—			—		—
Gouges or Nicks		—
Leaky Seals
Pitting and Grooving	—				—
Spalling		—
Abnormal Surface Wear		—
Abrasive Wear		—	—	—	—
Corrosive Wear	—					—
Wear on the Ends of Rollers
Wear on the Spindles or Hubs

Table 7

Type of Damage	Probable Cause - Lubrication
Fatigue from Contact	Quality of Lubricant	Inadequate Lubrication
Stress Concentration	—	—
Point Surface Contact	—	—
Peeling	—	—
Transverse Cracking
Subcase Fatigue
Other Damage
Brinelling
False Brinelling	—	—
Burn Up	—	—
Burn and Fluting Damage
Cage Damage and Breakage	—	—
Creeping
Etching and Corrosion	—	—
Gouges or Nicks
Leaky Seals
Pitting and Grooving
Spalling	—	—
Abnormal Surface Wear	—
Abrasive Wear	—
Corrosive Wear	—
Wear on the Ends of Rollers		—
Wear on the Spindles or Hubs	—	—

Report for Bearing Inspection

The responsibility of parts during inspection and rebuild is becoming more critical because of the increased hours between rebuilds. Tracking the part number, hours and frequency of each rebuild can be helpful in extending the expected life of the part. The cost per hour of machine operation is lowered if the expected life is extended. Refer to the "Crack Detection Methods" section.

Show/hide table

NOTICE
Caterpillar bearings are designed to last as long as the intended life of the component. Bearings should be replaced at every Planned Component Rebuild (PCR).

Illustration 16	g06298317
Bearing Inspection Report

End Play and Preload Adjustment

Failure to set bearing end play to proper specifications will result in the improper adjustment of a bearing. Failure to set preload to proper specifications will result in the improper adjustment of a bearing. This will cause a bearing to fail prematurely. Always follow the procedures in the service manual and the specifications in the service manual for bearing installation.

Incorrect bearing adjustment can cause down time in many ways. Incorrect bearing adjustment can increase expenses for repairs in many ways. The most obvious result is shortened bearing life, but improper bearing adjustment also affects the operation and service life of the spindle, seals, and other mating parts.

Tapered roller bearings are adjusted with shims and a retainer. Some applications are designed to have a minimal clearance between the rollers and the raceway. The minimal clearance is called end play. Other applications operate with a predetermined load. A predetermined load is called preload. The correct type of adjustment (end play or preload) must always be performed during assembly. Always check the Service Manual for the proper specifications for installation.

Illustration 17	g01405205
The adjustment of tapered roller bearings. (19) End Play (20) Preload

Preloading a bearing means that the cone and rollers are slightly pressed into the cup at normal operating temperature. Preloading increases the load capacity of the bearing by spreading the applied load over more rollers and over a larger portion of the fixed raceway. Illustration 17 shows the loading on the rollers of a tapered roller bearing. The bearing is adjusted with end play or preload.

Results of Incorrect Adjustment

Incorrect bearing adjustment can be identified as the root of the problem during the investigation of damaged parts and damaged components. The appearance of a damaged bearing may show that improper bearing adjustment was the root cause of damage of the following components:

• Bearing

• Hub

• Axle

• Seal

Correct adjustment of tapered roller bearings is essential to long bearing life. Incorrect adjustment of bearings during installation can cause the bearings to fail prematurely. This failure can be caused by too much adjustment or this failure can be caused by too little adjustment.

If the preload is too tight, rollers and raceways can be damaged due to a thrust overload. This causes premature fatigue of the surfaces of the bearing. Thrust overload can cause spalling, and future failure.

In applications with horizontal shafts, incorrect adjustment could result in the following issues:

• Heavy wear and spalling on the bearing cone

• Unbalanced wear and spalling on the roller and raceways

• Deformed openings on the roller cage

Visual Inspection of Normal Wear

The damage must be identified as normal or abnormal to determine if a bearing is suitable for further use. This section shows cups, cones, cages, and rollers with normal wear. The visual examples of normal wear show the bearings that could be used again. Only use bearings that did not reach the expected hours for a rebuild. Do not reuse a component if the component will be used for another full life.

Rollers

Illustration 18	g01405235
The ends of the rollers have normal wear. The bearing could be used again if the bearing came out of a component that did not reach the expected hours for a rebuild. The bearing can be reused to finish the expected hours before a rebuild. Do not reuse the component if the component will be used for another full life. USE THIS PART AGAIN

The wear surfaces on the large end of the rollers and on the rib face of cones are subject to wear because of thrust loads. A thrust load pushes the face of the end of the roller into the rib. Abnormal wear would consist of heavy scoring, scuffing, metal displacement, or heat discoloration. Illustration 18 shows normal wear on the ends of the rollers.

Bearings with high loads or the considerable deflection of the shaft are designed with a crown on the length of the roller. This helps to prevent flattening, overloading, and spalling of the ends of the rollers. The wear pattern is concentrated in the middle of rollers that are designed for high loads. Middle wear occurs more if the applied load has been relatively light.

Note: Caterpillar recommends avoiding the use of extreme pressure oil (EP) in the final drive assembly. See the Service Manual for the proper type and weight of oil.

Illustration 19	g01405236
The discoloration on the radius of the ends of the rollers is caused by extreme pressure oil (EP) in the final drive assembly. USE THIS PART AGAIN

Illustration 20	g01405239
Typical machining marks are shown on the radius of the roller that could appear to be scoring damage. The bearing can be used again if thorough cleaning of the ends reveals that the radius was not scored, as shown above. If scoring caused the damage on the roller, then there should be scoring marks in the corresponding area of the cup. USE THIS PART AGAIN

Illustration 21	g01405240
Pitting on the radius of the roller ends. Rollers may have an appearance of pitting from the use of extreme pressure oil. If the apparent pitting is removed from the rollers, the bearing can be used again. USE THIS PART AGAIN

Illustration 22	g01405241
The abrasive scoring on the roller is from foreign material that may have entered the system through damaged seals or during scheduled maintenance. If a seal pick will not catch on the scored area the bearing can be used again. USE THIS PART AGAIN

Illustration 23	g01405242
The fine marks are caused by debris. If a seal pick will not catch on the damaged area, the bearing can be used again. USE THIS PART AGAIN

Illustration 24	g01405244
The arrows show a wear pattern on the slightly crowned area on the roller. A normal wear pattern will occur in this area and no wear should be seen on the outside edges of the roller. If wear occurs on the outside edges, the bearing has too much preload or the bearing is misaligned. USE THIS PART AGAIN

Bearing Cup

Illustration 25	g01405288
The image shows a crowned roller bearing cup. The raceway on the bearing has a normal wear pattern, which was lightly loaded. The wear patterns on the raceway of this type of bearing will be concentrated toward the middle of the raceway. USE THIS PART AGAIN

Illustration 26	g01405290
Normal bearing wear is on the raceway of the cup. The circumferential scratches on the surface of the raceway are grinding marks. The marks are made more visible with side lighting and magnification. USE THIS PART AGAIN

Illustration 27	g01405292
Normal wear is located across the raceway. Despite the preload or applied load, if the operation of the bearing is normal, the wear should be relatively uniform across the entire surface of the raceway and roller. If the dark appearance is caused by the extreme pressure oil, then the bearing can be used again. The dark appearance may not be caused by overheating. USE THIS PART AGAIN

Illustration 28	g01405293
Normally, grinding marks on the outside diameter of the surface should be visible. The outside surface of the cup should be free of fretting corrosion or creeping. Creeping is caused when the cup turns inside the bore. Refer to "Fretting Corrosion" and refer to "Creeping" for examples of fretting corrosion and creeping. USE THIS PART AGAIN

Illustration 29	g01405294
The wear on the outside surface of the cup is creeping. Check the bore diameter of the housing to make sure that the bore diameter meets the specified tolerance. DO NOT USE THIS PART AGAIN

Illustration 30	g01405295
Light stains on the outside diameter of the cup are acceptable. The stains can be caused by contact with the housing. These stains can also appear on the inside diameter of the cone. Minimal wear should exist on the surfaces. Wear indicates that the race has moved relative to the shaft or relative to the housing. If the bearing appears to have been spinning and the bearing has a blue or black appearance, the bearing should be replaced. USE THIS PART AGAIN

Visual Inspection of Abnormal Wear

Recognizing and Preventing Tapered Roller Bearing Damage

Often, damage is easily identified by the appearance of the bearing. Determining the exact cause of damage can be impossible. The identification of bearings with heat discoloration and scoring on the ribs and on the ends of the rollers is not difficult. The cause may be traced to any one of various issues. The problem may be caused by using the wrong type of lubricant, or the problem may be the result of an excessively tight bearing setting. The problem might be a result of a combination of issues such as setting and lubrication.

Simple examination of bearings may not reveal the cause of the damage. The examination can reveal if the bearing can be reused. The examination must be done thoroughly. Also, the mounting, installation, and operating conditions must be determined to determine the cause of the damage. The cause of the damage must be found and the cause of the damage must be corrected. The replacement bearing might be damaged in the same manner.

The most common causes of bearing failure due to operating conditions are the following:

• Handling and Installation

• Spalling

• Fractures

• Plastic Yielding

• Abrasive Wear

• Corrosion

• Fretting Corrosion

• Creeping

• Electrical Pitting

• Fluting

Use the following key points for analyzing bearings:

• Operating conditions can cause high loads and/or temperatures on raceways and rolling surfaces, which will disturb the oil film. The insufficient oil film may cause abnormal wear, spalling, and/or plastic yielding that can result in failure.

• When one source of damage occurs, the source may generate more damage to the same surface. There is a possibility that two or more types of damage can be present. The secondary damage may be caused by the initial damage.

Handling and Installation Damage

Incorrect practices for installation and incorrect practices for removal may result in damage which can lead to bearing failure.

Using incorrect tooling for removing or installing bearings can also result in damaged bearings. Uneven, violent contact on the components of bearings can cause damage.

Note: Dents in the cup or the cone can interfere with the traveling of rollers. The dents can cause high localized stress, and the dents can initiate spalling. Dents also raise abnormal stress that could result in a crack from fatigue. In either case, this damage can cause the bearing to fail. The damage could possibly result in damage to other components.

Illustration 31	g01405550
The roller shows signs of denting due to rough handling during inspection or installation. DO NOT USE THIS PART AGAIN

Illustration 32	g01405553
The bearing cage was damaged when the bearing was dropped prior to installation. This type of damage can crack the cage and this type of damage can cause the rollers to bind. The rollers may become distorted and the rollers may stop turning. The rollers could also begin skidding. Skidding will damage both the cup and the cone. The rollers could generate heat that will lead to a serious failure. DO NOT USE THIS PART AGAIN

Illustration 33	g01405522
The bearing was installed with the improper tooling. The tooling that was used on this bearing was probably a punch and a hammer. Installing a bearing in this manner may have caused this bearing to crack. DO NOT USE THIS PART AGAIN

Illustration 34	g01405525
The bearing cup was incorrectly installed with a chisel or a punch. The magnification shows the mark from a tool. This type of damage can lead to chipping or cracking of the cone. DO NOT USE THIS PART AGAIN

Illustration 35	g01405526
The bearing cup was incorrectly installed with a hammer or another driving tool. The magnification shows the mark that was left by the round face of the tool. The damage from installation has progressed into spalling. DO NOT USE THIS PART AGAIN

Illustration 36	g01405528
Bearing (21) was adjusted with too much end play and bearing (22) with too much preload. If the cup wears in the thick area on Bearing (21), then the wear is due to too much end play. If the cup wears in the thin area on Bearing (22), then the wear is due to too much preload. The results were abnormal wear and spalling only in one area of the cup. DO NOT USE THIS PART AGAIN (21) Bearing with too much end play (22) Bearing with too much preload

Illustration 37	g01405530
Rollers show signs of spalling on the small end. The damage was probably caused by misalignment or excessive end play. Inspect the opposing bearing on the other end of the shaft for similar damage. DO NOT USE THIS PART AGAIN

Illustration 38	g01405531
The example of damage was caused by inadequate lubrication or too much end play. The metal lip that is protruding on the cage is normally caused by too much end play. The wear that appears similar to an hourglass is normally caused by too much end play. A second possible cause of the wear could be too much preload. The raceway that is mating on the cup showed even wear and spalling. The wear extended all the way across the face. The wear covered the entire circumference. DO NOT USE THIS PART AGAIN

Illustration 39	g01405554
Wear between the roller and the pocket of the cage was probably caused by improper lubrication or excessive end play. DO NOT USE THIS PART AGAIN

Illustration 40	g01405555
High loads of stress caused deep spalling that is rapid on the raceway of the cone. The spalling covers the complete surface of the raceway. DO NOT USE THIS PART AGAIN

Tapered Bore and Shaft

Illustration 41	g01405643
Wear and heat discoloration on the outside diameter of the cup was caused by a tapered housing bore. This bearing was installed into a bore with improper tolerances. The bearing was too tight. The damage was caused by increased temperature due to the reduced clearances between the element that is rolling and the raceway. DO NOT USE THIS PART AGAIN

Tapered shafts or housing bores can cause an overload condition in bearings when the full surface area of the cup or cone is not in complete contact with the mating surface. Damage on the surface of the cup is normally greater near the tight areas between the cup and theinside thebore. Signs of damage to the tapered bore or the tapered shaft are more frequently found on the outer surface of the bearing cup.

If either the bore or the shaft is tapered, correct the problem before installing a new bearing.

Misalignment

Misalignment can cause unusual wear, fatigue from the stress of contact, and spalling. Shafts that are misaligned and housings that are misaligned will normally cause wear or spalling. Wear and spalling can occur within the same raceway. Correct any problems from misalignment before installing a new bearing.

Illustration 42	g01405660
The wear pattern was caused by misalignment. DO NOT USE THIS PART AGAIN

Illustration 43	g01405663
The constant heavy loading of stress has produced spalling. The problem is probably caused by bearing misalignment. DO NOT USE THIS PART AGAIN

Overheating

Lack of lubrication can cause a bearing to become overheated. The resulting high temperature on bearing surfaces, rollers, and surrounding components can cause the metal to become softened. This is known as annealing. Components that have been inadequately lubricated will become discolored. The component will generally appear dry with burned oil.

Discolored bearings should be cleaned with a soft bristle brush or a surface reconditioning pad. Also use clean solvent. If the discoloration is removed, the discoloration is probably due to the buildup of lacquer. If the discoloration remains, the bearing should not be used again.

Illustration 44	g01405682
The raceway of the cup that is shown has a discolored surface. The discoloration was probably caused by a lack of lubrication or excessive rpm. The bearing can be used again if the discoloration is removed with a surface reconditioning pad and solvent. The removal of the discoloration is shown by the arrow. USE THIS PART AGAIN

Illustration 45	g01405685
The raceway of the cup has damage that is caused by overheating. The damage could not be removed with a surface reconditioning pad and solvent. DO NOT USE THIS PART AGAIN

Illustration 46	g01405688
Rollers show signs of overheating due to lack of lubrication. The rollers also show problems with misalignment because the burned area is only at the bottom of the roller. If the rollers are damaged, replace the entire bearing and correct any problems with lubrication or problems with misalignment. DO NOT USE THIS PART AGAIN

Illustration 47	g01405689
Damage from debris can be seen on the raceway. The damage has progressed into the early stages of spalling. DO NOT USE THIS PART AGAIN

Illustration 48	g01405690
An inclusion found in the steel of the bearing was probably caused by foreign material in the lubricating oil. The damaged area has progressed into spalling. DO NOT USE THIS PART AGAIN

Illustration 49	g01405691
The above Illustration shows over heating damage. The discoloration could not be removed with a surface reconditioning pad and solvent. The bearing also shows signs of micro-spalling due to the lack of lubrication and high operating temperatures. DO NOT USE THIS PART AGAIN

Illustration 50	g01405694
Damage on the rollers has progressed into micro-spalling due to the lack of lubrication. DO NOT USE THIS PART AGAIN

Brinelling

Marks from brinelling are dents on the surfaces of the raceway. The dents are caused by excessive loads that are transferred to the raceway by the rollers. Incorrect assembly can cause this condition, by violently driving the cone and the cup into position, or through extremely high shock loads during the operation of the machine. This type of damage occurs when the roller pushes the case hardened surface of the cup into the softer material in the core.

Brinelling can cause inadequate lubrication that is between the race and the roller. Brinelling can cause too much surface contact. Brinelling can cause an overload condition between raceways and rollers. Overloading can progress into spalling. The spalling will start at the marks from brinelling.

Illustration 51	g01405729
Damage from brinelling is shown on the raceway of the cup. DO NOT USE THIS PART AGAIN

Illustration 52	g01405731
The magnified view of the initial stage of brinelling is shown. DO NOT USE THIS PART AGAIN

Illustration 53	g01405732
The dent from brinelling was caused by a severe shock load. This damage occurred after the bearing had been running for many hours. DO NOT USE THIS PART AGAIN

Bruising

Large particles in the lubricant can cause plastic yielding. The contaminants could consist of metal from a gear or bearing failure. Large particles in the lubricant could cause denting on the surface of the raceways and rollers. Denting on the surface is known as bruising. Hard particles will produce sharp angular dents while softer particles will produce smoother, shallower dents. If bruising from hard particles is allowed to run for long enough time, the bruising will lead to spalling.

Illustration 54	g01405753
The illustration shows the raceway of a cup with light bruising. This type of damage will eventually progress into spalling. Base judgment on the application of the bearing and the speed (rpm) of the bearing. Base judgment on the number of hours that are remaining before the bearing will be replaced. USE THIS PART AGAIN

Illustration 55	g01405754
The raceway of cup with moderate bruising and a seal pick will not catch on bruises. This type of damage will eventually progress into spalling. Base judgment on the application of the bearing and the speed (rpm) of the bearing. Base judgment on the number of hours that are remaining before the bearing will be replaced. USE THIS PART AGAIN

Illustration 56	g01405757
The bruising is on the entire raceway. The bruising could be felt with a seal pick. DO NOT USE THIS PART AGAIN

Illustration 57	g01405759
The raceway of the cup has heavy bruising. DO NOT USE THIS PART AGAIN

Illustration 58	g01405762
The magnified image shows the raceway of a cup with heavy bruising. DO NOT USE THIS PART AGAIN

Illustration 59	g01405764
The image shows an extreme case of bruising. DO NOT USE THIS PART AGAIN

Illustration 60	g01405767
The image shows bruising which has progressed into spalling. DO NOT USE THIS PART AGAIN

Illustration 61	g01405770
The large particle that will cause bruising is embedded into the cage. The particle damage the cage and the roller. DO NOT USE THIS PART AGAIN

Abrasive Wear

Abrasive wear can occur on both the raceway and the surfaces of the rollers. This type of wear occurs when there is insufficient oil or grease that is needed to control heat. If the rollers stop turning and the rollers start sliding, heat is produced. Material that is abrasive such as dirt or sand in the lubrication system can become trapped and crushed by the rollers. This wear may eventually lead to bearing failure because of a loss of preload adjustment. Abrasive wear may also develop into small pits that can progress into spalling and cracking from fatigue. If abrasive wear is determined as the cause of the damage, correct any problem that may have allowed foreign material into the lube system.

Illustration 62	g01405835
The image shows abrasive wear. The bearing can be used again if there is no pitting. USE THIS PART AGAIN

Illustration 63	g01405841
The image shows abrasive wear. The bearing can be used again if no pits are found under magnification. USE THIS PART AGAIN

Illustration 64	g01405844
Shown by the arrows, fine abrasive particles have worn the surface of the ends of the rollers and the rib of the cone. DO NOT USE THIS PART AGAIN

Corrosion

Once bearings are removed from a machine and cleaned, the bearings can rust rapidly. All the bearing surfaces and rollers should be lightly oiled after inspection. A light film of oil will prevent atmospheric corrosion.

If moisture enters the lubrication system, corrosion can occur after a bearing has been installed in the machine. The corrosion may take place while the machine is shut down. While the machine is shut down, static corrosion or black acid etching can occur.

To remove the stains from corrosion, the surface of the raceway can be cleaned with a surface reconditioning pad. After cleaning, use magnification to determine if pitting is present. If pitting is present, do not use the bearing again.

Illustration 65	g01405863
The illustration shows the raceway of a cup with static corrosion and with black acid etching. The damage was caused when moisture combined with acids that are produced in used oil. The moisture and acids collected around the elements for rolling and produced dark, evenly spaced stains. Pitting is also present on this raceway. Deep pits can eventually cause cracks from fatigue and spalling. DO NOT USE THIS PART AGAIN

Illustration 66	g01405864
Static corrosion has etched the surface of the metal. Pitting is also present on the roller. This cone is the mating part of the cup in Illustration 65. DO NOT USE THIS PART AGAIN

Illustration 67	g01405866
The image shows corrosive etching. This damage occurred over an extended period while the machine was not being used or the machine was being stored. Corrosive etching can lead to spalling. DO NOT USE THIS PART AGAIN

Illustration 68	g01405869
The above illustration shows static corrosion. This bearing can be reused if pitting is not present and the problem from moisture has been corrected. USE THIS PART AGAIN

Illustration 69	g01405871
The above illustration shows static corrosion with damage from foreign objects (arrow). This bearing can be reused, if pitting has not started and the damage from foreign objects is minimal. USE THIS PART AGAIN

Illustration 70	g01405874
The illustration shows corrosion with moderate damage from foreign objects and acceptable damage from foreign objects. This bearing can be reused, if pitting has not started and the damage from foreign objects is minimal. USE THIS PART AGAIN

Illustration 71	g01405876
The image shows damage from corrosion with pitting. DO NOT USE THIS PART AGAIN

Black Acid Etching

Illustration 72	g01405903
The above illustration shows black acid etching on the rollers. The bearing can be used again if there is no pitting. USE THIS PART AGAIN

Illustration 73	g01405905
The above illustration shows black acid etching that is minor on the raceway of the cup. If the surface finish is not damaged and the surface finish only has visual stains, the bearing can be used again. USE THIS PART AGAIN

Illustration 74	g01405906
Black acid etching that is severe with pitting in the surface of the raceway is shown. DO NOT USE THIS PART AGAIN

Fretting Corrosion

Fretting corrosion or creeping occurs on the surface of the bearing that contacts the housing or the shaft. This type of corrosion indicates the cup or the cone has moved relative to the shaft or the housing. Normally, a bearing is harder than the mating surface of the housing or shaft, and the bearing will pick up the softer material from the bore or the shaft. This softer material can usually be removed and the bearing can be used again.

Illustration 75	g01406112
Fretting corrosion on the OD of the bearing race. DO NOT USE THIS PART AGAIN

Illustration 76	g01406113
Fretting corrosion on the OD of the bearing race. DO NOT USE THIS PART AGAIN

Illustration 77	g01406114
Fretting corrosion on the outside diameter of the bearing race. DO NOT USE THIS PART AGAIN

Creeping

Creeping occurs when the outer race of a bearing turns onthe inside thehousing. If a bearing shows signs of creeping, repair the housing or replace the housing or the shaft to provide the correct fit or the correct tolerance.

Illustration 78	g01406122
The image shows creeping on the race of a bearing. DO NOT USE THIS PART AGAIN

Illustration 79	g01406124
The image shows creeping on the outside diameter of the race of the bearing. When this type of damage occurs, always measure the mating part to make sure that the component is not worn beyond the specified dimension. DO NOT USE THIS PART AGAIN

False Brinelling

False brinelling and true brinelling are different. Heavy shock loads do not cause false brinelling. False brinelling is actually fretting or fretting corrosion that is caused by vibration of the bearing, under load, while the bearing is not turning. False brinelling can occur when the machine is shipped over long distances via a railroad. When false brinelling occurs, the rollers vibrate. The rollers that vibrate wear into the surfaces of the raceway.

Illustration 80	g01406127
The image shows false brinelling. The surface of the bearing has been worn away due to the vibrations of the roller that are moving perpendicular to the raceway. Notice that the wear marks in the bottom of the groove are perpendicular to the cup. In true brinelling, the marks from grinding that are circumferential would be visible in the bottom of the groove. DO NOT USE THIS PART AGAIN

Electrical Pitting

Electrical pitting can be caused by relatively high amounts of electrical current passing through the bearing when the bearing is not rotating. A common cause for this damage is improper welding on the machine. Relatively low currents that pass through the bearing over a prolonged period can also cause electrical pitting if the bearing is rotating. This type of damage can lead to spalling and bearing failure.

Illustration 81	g01406148
The image shows electrical pitting with large localized pits. The Pits (24) are on the raceway. The Pits (23) that are matching are on the roller. The damage was probably caused by incorrectly welding on the machine. These pits will lead to spalling and bearing failure. DO NOT USE THIS PART AGAIN (23) Pits on the roller (24) Pits on the raceway

Illustration 82	g01406152
The image shows a roller with electrical pitting that is caused by the improper grounding of the machine during arc welding. DO NOT USE THIS PART AGAIN

Illustration 83	g01406154
Electric current has passed through this bearing during operation. The current has given the bearing the appearance of small burns. The damage was possibly due to faulty grounding of the electrical system. DO NOT USE THIS PART AGAIN

Illustration 84	g01406155
Electrical pitting has created a rough surface. This damage will be present all the way around the bearing if the application used a preload adjustment. If an end play adjustment was used or the preload adjustment was lost, the damage will only appear on a small portion of the cone. DO NOT USE THIS PART AGAIN

Crack Detection Methods

Show/hide table

NOTICE
Regardless of which crack detection method is used, it is important that the instructions furnished with the detection equipment are followed closely when checking any component. Failure to do so may cause inaccurate results or may cause injury to the operator and/or surroundings.

There are five major crack detection methods or Non-Destructive Testing (NDT) listed in this section: Visual Surface Inspection (VT), Liquid Penetrant Testing (PT), Dry / Wet Magnetic Particle Testing (MPT), and Ultrasonic Testing (UT).

Crack detection methods or NDT is methods for testing components for cracks without damaging the component. VT, PT, Dry/ Wet MPT, and UT are methods recommended. There may be more than one acceptable crack detection method for the testing of a given part, although PT is the most versatile. For example, the PT method can be used when testing smooth machined components such as shafts, gear teeth, and splines, but using the Wet MPT is more accurate. Refer to Table 8 for advantages and disadvantages and Table 9 for standards and requirements for these NDT methods.

Table 8

Crack Detection Methods Advantages vs. Disadvantages
Detection Method	Advantages	Disadvantages
Visual Surface Inspection (VT)	- Least Expensive - Detects most damaging defects. - Immediate Results - Minimum part preparation	- Limited to surface-only defects. - Requires inspectors to have broad knowledge of welding and fabrication in addition to Non-Destructive Testing (NDT).
Liquid Penetrant Testing (PT)	- Inexpensive - Minimal Training - Portable - Works on nonmagnetic material.	- Least Sensitive - Detects surface cracks only. - Rough or porous surfaces interfere with test
Dry Magnetic Particle (MPT)	- Portable - Fast/Immediate Results - Detects surface and subsurface discontinuities	- Works on magnetic material only. - Less sensitive than Wet Magnetic Particle Testing (MPT).
Wet Magnetic Particle (MPT)	- More sensitive than Liquid Penetrant Testing (PT). - Detects subsurface as much as 0.13 mm (0.005 inch).	- Requires power for light. - Works on magnetic material only. - Liquid composition and agitation must be monitored.
Ultrasonic Testing (UT)	- Most Sensitive - Detects deep material defects. - Immediate Results - Wide range of materials and thickness can be inspected	- Most Expensive - Requires operator training and certification. - Surface must be accessible to probe

Table 9

Applicable Crack Detection Standards
Detection Method	Standard	Acceptance Criteria	Minimum Required Personnel Qualifications
Visual Surface Inspection (VT)	EN-ISO 5817 AWS D1.1	EN-ISO 5817 - Level B AWS D1.1 - Table 6.1	EN-ISO 9712 ANSI-ASNT SNT-TC-1A
Liquid Penetrant Testing (PT)	EN-ISO 3452 ASTM E165	EN-ISO 23277 AWS - D1.1	EN-ISO 9712 ANSI-ASNT SNT-TC-1A
Magnetic Particle Testing (MPT)	EN-ISO 17638 ASTM E709	EN-ISO 23278 - Level 1 AWS D1.1 - Table 6.1	EN-ISO 9712 ANSI-ASNT SNT-TC-1A
Ultrasonic Testing (UT)	EN-ISO 17640 - Level B AWS D1.1	EN-ISO 11666 Technique 2 - Level 2 AWS D1.1 - Class A - Table 6.3	EN-ISO 9712 ANSI-ASNT SNT-TC-1A

Visual Surface Inspection (VT)

Illustration 85	g06124166
Example of Visual Surface Inspection (VT) Tooling (A) Flashlight (or adequate light source) (B) Magnifying Glass (C) Tape Measure (or other measuring device) (D) Inspection Mirror

Refer to Tooling and Equipment Table 3 for part numbers.

Components and welds that are to be tested using PT, MPT, or UT shall first be subject to a Visual Surface Inspection (VT). VT is often the most cost-effective inspection method and requires little equipment as seen in Illustration 85. Personnel performing VT shall either be trained to a company standard or have sufficient experience and knowledge regarding the components being inspected. Personnel performing VT shall take routine eye exams.

Liquid Penetrant Testing (PT)

Show/hide table

Personal injury can result from improper handling of chemicals. Make sure you use all the necessary protective equipment required to do the job. Make sure that you read and understand all directions and hazards described on the labels and material safety data sheet of any chemical that is used. Observe all safety precautions recommended by the chemical manufacturer for handling, storage, and disposal of chemicals.

Materials and Equipment Required

Refer to Tooling and Equipment Table 3 for part numbers.

• Cleaner: Removes dirt before dye application and dissolves the penetrant making possible to wipe the surface clean.

• Penetration Oil: This solution is highly visible, and will seep into openings at the surface of a part with capillary action.

• Developer: Provides a blotting action, bringing the penetrant out of the discontinuities and providing a contrasting background to increase the visibility of the penetrating oil indications.

• Wire Brush: Removes dirt and paint.

• Cloth or Wipes: Use with cleaner and for other miscellaneous uses.

Procedure

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Illustration 86	g06084048
Typical example of pre-cleaning the testing area.

1. Preclean the area to be tested. Spray on cleaner/ remover to loosen any scale, dirt, or any oil. Wipe the area to be tested with a solvent dampened cloth to remove remaining dirt and allow the area to dry. Remove paint where there are visible cracks using paint remover or a wire brush.
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   Illustration 87	g06084053
   Typical example of applying penetrating oil to areas to be tested.

2. Apply penetrating oil by spraying to the entire area to be tested. Allow 10 to 15 minutes for penetrating oil to soak. After the penetrating oil has been allowed to soak, remove the excess penetrating oil with clean, dry wipe.
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   Illustration 88	g06084060
   Typical example of removing penetrating oil with a cloth.

3. The last traces of penetrating oil should be removed with the cleaner solvent dampened cloth or wipe. Allow the area to dry thoroughly.
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   Illustration 89	g06084070
   Typical example of applying the developer.

4. Before using developer, ensure that the developer is mixed thoroughly by shaking the container. Hold the container approximately 203 - 305 mm (8 - 12 inch) away from part. Apply an even, thin layer of developer over the area being tested. A few thin layers are a better application method than one thick layer.
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   Illustration 90	g03773759
   Typical example of cracks found during Liquid Penetrant Testing (PT).

5. Allow the developer to dry completely for 10 to 15 minutes before inspecting for cracks. Defects will show as red lines in white developer background, refer to Illustration 90. Clean the area of application of the developer with solvent cleaner.

Dry Magnetic Particle Testing (MPT)

Materials and Equipment Required

Refer to Tooling and Equipment Table 3 for part numbers.

Illustration 91	g06085930
(A) Indications shown by Dry Magnetic Particle Testing (MPT). (B) Electromagnetic Yoke (C) Dry Powder Bulb

1. Dry magnetic powder shall be of high permeability and low retentively and of suitable sizes and shapes to produce magnetic particle indications. The powder shall be of a color that will provide adequate contrast with the background of the surface being inspected.

2. Dry magnetic particles shall be stored in suitable containers to resist contamination such as moisture, grease, oil, non-magnetic particles such as sand, and excessive heat. Contaminants will manifest in the form of particle color change and particle agglomeration. The degree of contamination will determine further use of the powder.

3. Dry magnetic powder shall be tested in accordance with ASTM E709 Section 18 (Evaluation of System Performance/Sensitivity) when not performing.

4. Equipment should include a "U" shaped electromagnetic yoke made from highly permeable magnetic material, which has a coil wound around the yoke. This coil carries a magnetizing current to impose a localized longitudinal magnetic field into the part. The magnetizing force of the yoke is related to the electromagnetic strength and can be tested by determining the lifting power of a steel plate. The yoke shall have a lifting force of at least 4.5 kg (10 lbs).

5. Check dry powder blower routinely to ensure that the spray is a light, uniform, dust-like coating of the dry magnetic particles. Blower should also have sufficient force to remove excess particles without disturbing those particles that are evidence of indications.

6. All equipment shall be inspected at a minimum of once a year or when accuracy is questionable.

Procedure

1. Ensure surface to be inspected is dry and free from oil, grease, sand, loose rust, mil scale, paint, and other contaminants.

2. Apply the magnetic field using the yoke against the faces and inside diameter of each bore.

3. Simultaneously apply the dry powder using the dry powder blower.

4. Remove excess powder by lightly blowing away the dry particles.

5. Continue around the entire circumference of each bore. Position the yoke twice in each area at 1.57 rad (90°) to ensure that multiple directions of the magnetic field are created.

6. Observe particles and note if any clusters of particles appear revealing an indication.

7. Record the size and shape of any discontinuities or indications found.

Wet Magnetic Particle Testing (MPT)

Materials and Equipment

Refer to Tooling and Equipment Table 3 for part numbers.

Illustration 92	g06085937
(A) Indications shown by Wet Magnetic Particle Testing (MPT). (B) Electromagnetic Yoke (D) Ultraviolet Lamp

Illustration 93	g06003178
Pear Shaped Centrifuge Tube

1. Wet magnetic particles are fluorescent and are suspended in a vehicle in a given concentration that will allow application to the test surface by spraying.

2. Concentration:

   1. The concentration of the suspended magnetic particles shall be as specified by the manufacturer and be checked by settling volume measurements.

   2. Concentrations are determined by measuring the settling volume by using an ASTM pear shaped centrifuge tube with a 1 mL (0.034 oz) stem with 0.05 mL (0.0017 oz) divisions, refer to Illustration 93. Before sampling, the suspension shall be thoroughly mixed to assure suspension of all particles, which could have settled. A 100 mL (3.40 oz) sample of the suspension shall be taken and allowed to settle for 30 minutes. The settling volume should be between 0.1 mL (0.0034 oz) and 0.25 mL (0.0085 oz) in a 100 mL (3.40 oz) sample.

   3. Wet magnetic particles may be suspended in a low viscosity oil or conditioned water.

   4. The oil shall have the following characteristics:

      • Low viscosity not to exceed 5 mm²/_s (5 cSt) at any temperature at which the vehicle is to be used.

      • Low inherent fluorescence and be non-reactive.

   5. The conditioning agents used in the conditioned water shall have the following characteristics:

      • Impart good wetting characteristics and good dispersion.

      • Minimize foaming and be non-corrosive.

      • Low viscosity shall not exceed a maximum viscosity of 5 mm²/_s (5 cSt) at 38° C (100° F).

      • Non-fluorescent, non-reactive, and odorless.

      • Alkalinity shall not exceed a pH of 10.5.

3. Equipment should include a "U" shaped electromagnetic yoke made from highly permeable magnetic material, which has a coil wound around the yoke. This coil carries a magnetizing current to impose a localized longitudinal magnetic field into the part. The magnetizing force of the yoke is related to the electromagnetic strength and can be tested by determining the lifting power of a steel plate. The yoke shall have a lifting force of at least 4.5 kg (10 lbs).

Procedure

1. Ensure surface to be inspected is dry and free from oil, grease, sand, loose rust, mil scale, paint, and any other contaminants.

2. Apply the magnetic field using the yoke against the surface in the area to be inspected.
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   Illustration 94	g03536210

3. For case hardened and ground surfaces:

   • Due to the sensitivity required to locate the grinding cracks, inspection of case hardened and ground surfaces require that the yoke is applied so that the magnetic field is 1.57 rad (90°) to the expected direction of the indications. Also, due to the increased sensitivity resulting when the yoke is energized, the yoke is not moved until the evaluation is completed in the first direction. An AC yoke shall be used. See Illustration 94 for an example of yoke placement.

4. Visually inspect for indications of discontinuities using the proper illumination.

5. Record the size and shape of any discontinuities found.

Ultrasonic Testing (UT)

Note: Crack depth cannot be accurately determined by UT, only full depth cracking can be consistently determined. For cracks that are not full depth, an indication of a partial depth cracks can be detected by an experienced technician. Refer to Table 9 for crack detection standards.

Refer to Tooling and Equipment Table 3 for part numbers.

1. Ultrasonic Testing (UT) is a method of Non-Destructive Testing (NDT) using short ultrasonic pulse waves (with frequencies from 0.1-15 MHz up to 50 MHz) to detect the thickness of the object. Ultrasonic testing consists of an ultrasound transducer connected to a diagnostic machine and passed over the object being inspected.

2. There are two methods of receiving the ultrasound waveform from the transducer: reflection and attenuation.

   1. Reflection - Ultrasonic pulses exit the transducer and travel throughout the thickness of the material. When the sound waves propagate into an object being tested, the waves return to the transducer when a discontinuity is discovered along the sonic path. These waves continue and reflect from the back surface of the material to project the thickness of the material.

   2. Attenuation - A transmitter sends ultrasound through one surface, and a separate receiver detects the amount that has reached it on another surface after traveling through the medium. Any discontinuities or other conditions within the medium will reduce the amount of sound transmitted, revealing the presence of the imperfections.