Why do bearings keep breaking down? Do you really know why? What are the common bearing damage analysis and treatment methods? In the work, we often encounter problems such as peeling, burns, and crack defects in bearings. How to solve them? SKK engineers share this article with you today, which is very useful for mechanical repair and maintenance.

High-quality bearings, when used correctly, can have a long service life. If damage occurs prematurely, it's often due to incorrect selection, improper usage, or inadequate lubrication.

Therefore, during bearing installation, it's important to record machine type, installation location, operating conditions, and surrounding components. By studying and summarizing the types of bearing damage and the conditions under which problems occur, similar situations can be avoided in the future.

Bearing damage can be categorized according to the following images. The main characteristics shown in the images can help determine the form of bearing damage.

1. Peeling

Symptom: Running surface peeling with noticeable convex-concave shape after peeling.

Causes:

- Excessive load or improper use

- Poor installation

- Poor accuracy of shaft or bearing housing

- Excessive clearance

- Foreign matter intrusion

- Rust

- Hardness reduction due to abnormally high temperatures

Remedies:

- Reevaluate usage conditions

- Choose bearings again

- Reconsider clearance

- Check shaft and bearing housing machining accuracy

- Study bearing surrounding design

- Inspect installation methods

- Check lubricant and lubrication methods

2. Burn

Symptom: Bearing heats up and changes color, eventually leading to burning and inability to rotate.

Causes:

- Insufficient clearance (including inadequate clearance in deformed parts)

- Inadequate lubrication or improper lubricant

- Excessive load (excessive preloading)

- Roller deflection

Remedies:

- Set appropriate clearance (increase clearance)

- Check lubricant type and ensure proper lubricant amount

- Review operating conditions

- Prevent misalignment

- Examine bearing surroundings design (including bearing heat)

- Improve bearing assembly method

3. Cracks and Defects

Symptom: Partial notches and cracks are visible.

Causes:

- Excessive impact load

- Excessive interference fit

- Significant peeling

- Friction cracks

- Poor installation accuracy (excessive corner radius)

- Improper usage (using a copper hammer, inserting large foreign objects)

Remedies:

- Check usage conditions

- Set appropriate interference fit and check material

- Improve installation and usage methods

- Prevent friction cracks (inspect lubricant)

- Check bearing surroundings design

4. Cage Damage

Symptom: Loose or fractured rivets, broken cage.

Causes:

- Excessive torque load

- High-speed rotation or frequent speed changes

- Poor lubrication

- Foreign object entrapment

- High vibration

- Poor installation (installation at an inclined angle)

- Abnormal temperature rise (resin cage)

Remedies:

- Check usage conditions

- Inspect lubrication conditions

- Reevaluate cage selection

- Pay attention to bearing usage

- Study shaft and bearing housing rigidity

5. Abrasion and Scratching

Symptom: Rough surface with minor indentations; scratching between the inner ring groove and roller end face is called "scratching".

Causes:

- Poor lubrication

- Foreign matter intrusion

- Roller deflection caused by bearing misalignment

- Edge surface oil loss caused by axial load

- Excessive surface roughness

- High sliding of rolling elements

Remedies:

- Reevaluate lubricant and lubrication methods

- Check operating conditions

- Set appropriate preload

- Enhance sealing performance

- Use bearings normally

6. Corrosion

Symptom: Local or overall surface rust, resembling rust on the pitch of rolling elements.

Causes:

- Poor storage conditions

- Improper packaging

- Inadequate rust preventive treatment

- Ingress of moisture, acidic solutions, etc.

- Direct handling of bearings with hands

Remedies:

- Prevent rust during storage

- Enhance sealing performance

- Regularly inspect lubricating oil

- Pay attention to bearing usage

7. Abrasion

Symptom: Abrasive wear particles appear on fitting surfaces, showing reddish rust color.

Causes:

- Insufficient interference fit

- Small rolling angle of the bearing

- Inadequate lubrication (or no lubrication)

- Unstable load

- Vibration during transportation

Remedies:

- Check interference fit and lubricant application status

- When transporting, package inner and outer rings separately; if not possible, apply preload

- Reevaluate lubricant selection

- Choose bearings again

8. Wear

Symptom: Surface wear, causing dimensional changes, often accompanied by abrasion and marks.

Causes:

- Foreign particles mixed with lubricant

- Poor lubrication

- Roller deflection

Remedies:

- Check lubricant and lubrication methods

- Enhance sealing performance

- Prevent misalignment

9. Electrical Erosion

Symptom: Roller surface has pitted craters resembling fire-spout openings, which may develop into wave-like patterns.

Cause: Electric current passing through rolling surfaces.

Remedies: Install bypass valves for electric currents; use insulation measures to prevent current from passing through the bearing internals.

10. Indentation and Impact

Symptom: Surface dents and scratches caused by solid foreign objects or impacts during installation.

Causes:

- Intrusion of solid foreign objects

- Entrapment of peeling fragments

- Impact or detachment caused by poor installation

- Installation in an inclined state

Remedies:

- Improve installation and usage methods

- Prevent foreign object intrusion

- If caused by metal fragments, inspect other areas

11. Creep

Symptom: Inner or outer diameter surfaces slide, resulting in mirror-like or discolored areas, sometimes leading to seizing.

Causes:

- Insufficient interference fit at mating surfaces

- Insufficient tightening of sleeves

- Abnormal temperature rise

- Excessive load

Remedies:

- Reevaluate interference fit

- Study usage conditions

- Check shaft and bearing housing accuracy

In everyday use, bearings require careful attention to their use. Here are seven key points to consider:

1. For riveted components in harvesters such as the cutter assembly, the rivets are generally cold-pressed and should not be heated during riveting. Rivets should be reformed using a forming punch to enhance the firmness between the blade and the knife bar.

2. Vulnerable components, especially pins, shafts, thrust washers, bushings, and shims, should not be replaced or repaired with excessive grease during maintenance. Prolonged use of worn-out components can shorten the lifespan of other machinery.

3. For shaft repairs without a balancing machine, when repairing various types of shafts that require balancing, a thrust bearing can be installed at one end of the shaft, clamped on a lathe chuck, and the other end can be supported with a center point. If the lathe is too short, an SKF bearing can be used to support the other end and corrections can be made until balance is achieved. During counterweighting, screws should be used for tightening rather than welding whenever possible.

4. When repairing keyways on pulleys and shafts, ensure that the dimensions remain unchanged. Never enlarge the size of the key, as it can affect the shaft's strength. Keyways on shafts can be repaired by welding fillers in the opposite direction of the old key after removing the old key. On pulleys, a bushing (transition fit) can be used, and after installation, a set screw can be threaded into the gap of the bushing to secure the key.

5. It's advisable to create oil grooves in the bushing holes whenever possible during the machining of bushing parts. Some parts of harvesters are difficult to lubricate. In such cases, use grease and heavy-duty oil, except for nylon bushings. For parts with nylon bushings, it's best not to use cast iron, copper, or aluminum as replacements, as nylon bushings can withstand certain impacts without deforming.

6. Belt pulleys and keys on shafts should be repaired without changing the dimensions. Keys should never be enlarged. Instead, this could affect the shaft's strength. Keyways on shafts can be repaired by welding filler material in the opposite direction of the old key and then milling a new keyway. For pulleys, a bushing (transition fit) can be used. After installation, a set screw can be threaded into the gap of the bushing to secure the key.

7. During hydraulic repairs of harvesters, remove the distributor and pressure relief valve, etc. Use an air pump to pressurize the various pipe fittings to remove trapped air. When refilling hydraulic oil, ensure filtration and proper venting. The main focus of hydraulic repairs is on sealing components. It's recommended to replace sealing components with new ones whenever possible after removal.