Common Reasons for Bearing Failures: Unveiling the Culprits

Bearing Failure Modes & Their Causes

The American National Standards Institute (ANSI) and the American Bearing Manufacturers Association (ABMA) have introduced a comprehensive framework for classifying bearing failures. This framework is based on the standards for classifying bearing failures developed by the International Organization for Standardization (ISO). The ISO 15243-2017 standard identifies different modes of bearing failure by categorizing them into specific classes. These include fatigue, wear, corrosion, electrical erosion, plastic deformation, fracture, and cracking.

The ISO standard defines the mode of failure as the specific way a bearing fails, apart from its causes. To improve the lifetime and reliability of bearings, we need to understand that failure modes are different from their root causes. These causes include lubrication issues, material surface imperfections, contamination susceptibility, environmental impact (both direct and indirect), electrical factors (overloading), cyclic loading, and thermal factors (extreme temperatures or rapid changes). Identifying the main contributors of bearing failure modes is important for effective prevention, as these causes often interact in a complex way.

The table below pairs common failure modes of roller bearings with their potential causes to facilitate effective troubleshooting. Correlating observed failure modes with their respective causes helps identify and address the root causes of the problems. This table offers a practical guide for fast issue identification and resolution.

Table 1. ISO 15243 Bearing Failure Modes and Their Main Causes

Now, let’s delve into the primary causes, examining their distinct roles and impacts leading to bearing failures. By using these insights you will be able to understand and mitigate these causes and enhance both bearing reliability and operational performance.

• 1. Improper Lubrication
• 2. Cyclic Loading
• 3. Material Defects and Surface Imperfections
• 4. Excessive Loads
• 5. Misalignment & Improper Installation
• 6. Electrical Factors
• 7. Thermal Factors
• 8. Contamination and Foreign Particle Ingress
• 9. Environmental Factors

1. Improper Lubrication

Improper lubrication is one of the major culprits behind bearing failures. Specifically, it plays a significant role in subsurface initiated fatigue and adhesive wear.

Subsurface initiated fatigue is characterized by cracks or spalling beneath the bearing's surface. Inadequate lubrication fails to form a protective film between rolling elements and raceways. This results in direct metal-to-metal contact. Such contact subsequently induces micro-pitting, cracking - culminating ultimately in fatigue failure.

Adhesive wear occurs when inadequate lubrication fails to prevent metal-to-metal contact and allows for adhesive forces to take hold, resulting in surface damage and wear. Material transfer, galling, and increased friction can all be indications of adhesive wear.

⚠ Watch for signs of overheating, increased friction, or unusual noise during bearing operation. These symptoms may indicate improper lubrication. Additionally, monitor the condition and effectiveness of the lubricant over time.

🛠 Prevent improper lubrication by:

• Selecting the correct lubricant type and grade for the application.
• Ensuring proper lubrication intervals and quantities according to manufacturer recommendations.
• Implementing effective seals to protect against lubricant loss and contamination.
• Regularly monitoring lubricant condition and undertaking timely relubrication as needed.

2. Cyclic Loading

Cyclic loading, The fluctuation of loads over time, known as cyclic loading, can be a major contributor to various bearing failure modes. These include subsurface initiated fatigue, surface initiated fatigue, fretting corrosion, and fatigue fracture—each with its own set of challenges.

Subjecting bearings to repetitive stress cycles through cyclic loading can cause subsurface initiated fatigue. This leads to the formation of microcracks beneath the bearing surface.

⚠ Signs to look for include a gradual increase in vibration and noise.

🛠 To prevent, consider load calculations and material selection that can handle cyclic stresses. Ensure proper lubrication and maintain controlled loading conditions.

Cyclic loading can also induce surface initiated fatigue. Surface cracks form due to repeated stress cycles. This can ultimately lead to spalling or pitting.

⚠ Keep an eye out for surface abnormalities, such as localized damage or visible cracks.

🛠 To prevent:

• Apply appropriate load calculations.
• Choose bearings with adequate load capacity.
• Ensure optimal lubrication practices.

Cyclic loading can cause fretting corrosion. Fretting corrosion is characterized by the wear and corrosion at component contact points.

⚠ Signs include small, fretted particles around the contact areas.

🛠 Prevention measures include proper bearing fit, adequate clearance, and lubrication selection that resists fretting.

Cyclic loading can cause fatigue fractures, where accumulated cyclic stresses result in sudden bearing failure.

⚠ Look out for increased noise and vibration as early warning signs.

🛠 To prevent fatigue fractures, choose bearings with high fatigue resistance, avoid excessive loads, and regularly monitor bearing performance.

3. Material Defects and Surface Imperfections

Material defects and surface imperfections primarily influence surface initiated fatigue in bearings. In an operating bearing, material imperfections become stress concentration points. Increased stress in these points makes them potentially vulnerable to cracks and fatigue failures.

⚠ Signs of surface initiated fatigue include visible surface cracks, pitting, or spalling. Abnormal noise, increased vibration, and decreased performance may also indicate impending bearing failure.

🛠 To prevent surface-initiated fatigue, choose high-quality bearings with minimal material defects and imperfections. Make accurate load calculations to avoid overloading. Maintain sufficient lubrication to reduce friction and wear on susceptible areas. Regular inspection and maintenance can help detect early signs of fatigue and prevent further damage.

4. Excessive Loads

Every bearing has a specified capacity that sets the upper threshold for the loads it can handle. Loads that go beyond the specified capacity may lead to a number of bearing problems. The primary issue is overload plastic deformation - when the key parts of the bearing become permanently deformed. Other issues that are caused by bearing overloading are subsurface initiated fatigue and surface initiated fatigue. To recap, here are the three related failure modes to be aware of:

• Overload plastic deformation that causes permanent changes to bearing components and eventual failure.
• Overloading can lead to increased stress on bearing surfaces, contributing to subsurface initiated fatigue, which results in cracks and spalling beneath the surface.
• Excessive loads can lead to surface initiated fatigue by increasing stress on bearing surfaces, causing cracks, pitting, and eventual spalling.

⚠ Signs of excessive loads include visible distortion or warping of bearing components, increased operating temperature, and unusual noise during operation.

🛠 To prevent excessive loads, choose bearings with specifications that match the applied load. Use load calculations. Keep the parts adequately lubricated to reduce friction and inspect bearings regularly to identify early signs of deformation.

5. Misalignment & Improper Installation

Misalignment and improper installation introduce small relative motions or micro-movements between bearing components. These motions can lead to fretting corrosion, which causes wear and surface damage.

Misalignment and improper installation can also cause false brinelling. False brinelling is a mode of failure characterized by shallow depressions on bearing raceways. It occurs when there are excessive load concentrations due to misalignment.

Misalignment and improper installation can result in excessive axial or radial forces on bearings. These forces can cause forced fracture, leading to bearing failure under extreme loads.

⚠ Signs of misalignment and improper installation include visible wear or surface damage, unusual noise, increased vibration, and reduced performance.

🛠 To prevent these issues, it is important to ensure correct alignment and proper installation of bearings. This can be done by using alignment tools and techniques to minimize misalignment. Employing an appropriate fit with clearance can also prevent false brinelling. Proper axial and radial clearances should be maintained to prevent forced fracture. Regular inspections are crucial for detecting and rectifying misalignment and installation issues promptly.

6. Electrical Factors

Electrical faults and improper grounding can cause excessive current to flow through bearings. This can result in localized overheating and sparking, leading to excessive current erosion.

Insulation breakdown and electrical discharge can cause bearing erosion because of current leakage. Current leakage through bearings creates localized heating and sparking, which contributes to erosion.

⚠ Signs of present or impeding bearing erosion from electrical factors include visible damage and localized overheating. Other indicators may include unusual noise and potential electrical issues in the surrounding system.

🛠 To prevent excessive current erosion and current leakage erosion, it is important to address potential electrical problems. This can be done by maintaining proper insulation and grounding. Also, ensure the integrity of bearing components. Regularly monitor electrical systems to detect issues early and protect bearings.

7. Thermal Factors

Rapid heating or cooling, along with local overheating, can cause thermal cracking in bearings.

Thermal cracking in bearings occurs due to sudden temperature changes, local overheating, or extreme thermal cycling. This mode of failure is characterized by cracks forming due to thermal stresses.

⚠ Signs of thermal cracking include visible cracks, especially in areas prone to temperature fluctuations. An increased operating temperature, potential noise or performance problems may also signal thermal cracking.

🛠 To prevent thermal cracking, ensure stable operating conditions and control temperature environments. Properly size bearings for the application's thermal demands, regularly lubricate, and use insulation or shielding to minimize rapid temperature fluctuations. Regular inspections help detect early signs of thermal stress and cracking.

8. Contamination and Foreign Particle Ingress

Contamination and foreign particle ingress can result in abrasive wear, another common mode of bearing damage.

Dust, dirt, and other particles can infiltrate bearing assemblies and create abrasive environments. These particles then grind against the surfaces of the bearings and cause abrasive wear.

⚠ Signs of abrasive wear include visible surface damage. A gritty sound during operation, increased vibration and reduced bearing performance may also signify abrasive wear from foreign particles.

🛠 Use effective sealing techniques to prevent contamination and abrasive wear. Regularly inspect and maintain seals. Use proper filtration systems to reduce the risk of contamination. Keep operating environments clean to reduce the risk of contamination. Regularly monitor bearing condition to catch early signs of wear.

9. Environmental Factors

The ways in which environmental factors impact bearing failure modes vary. Exposure to humid or wet environments during operation or storage can lead to moisture corrosion. Storing bearings in excessively high temperatures creates a different thread - it may degrade prefilled lubricants. The third group of factors - the introduction of environmental contaminants - can result in indentations from particles (also see previous section.)

When bearings are exposed to humid or wet environments they become prone to moisture corrosion. When the surface gets corroded, it reduces bearing life and performance. This relates to both storage and operating conditions.

In geographic areas with hot climates, long-term storage in excessively high temperatures can degrade lubricants. When the lubricant breaks down it increases friction and negatively affects bearing performance.

When the environment is contaminated with substantial concentration of dust or foreign particles, it may lead to indentations on bearing surfaces. When dust and particles get into bearings and make dents on the surfaces it inevitably wears out bearings faster.

⚠ Signs of the moisture corrosion failure mode include visible surface corrosion. Lubricant degradation takes place when there is increased friction. Indentations from particles are evident through visible surface damage and increased noise during operation.

🛠 Prevent moisture corrosion by storing bearings in dry environments, and consider protective coatings or seals for extended storage periods. Protect bearings from excessively high temperatures during storage in hot climates to prevent lubricant degradation. Maintain clean operating environments and use effective filtration systems in the facilities to reduce the risk of contamination and subsequent indentations. As with other factors, regular inspections and monitoring are key. They can help detect early signs of damage caused by the environment.

Key Takeaways and Implementation

Optimizing machinery performance and minimizing costly downtime is impossible without understanding the causes of bearing failures and taking proactive steps to prevent them. One of the prerequisites to this approach is to recognize that different modes of failure are not interchangeable, and each comes with its unique set of causes.

Further, you need to gain clarity about the causes that lead to different bearing failure modes. Whether it's lubrication, misalignment, electrical factors, thermal stresses, contamination, or environmental influences, identifying the root causes is the first step towards effective failure prevention strategy.

Once you determine the most significant causes that pertain to your unique situation you will be able to execute a targeted cost-efficient approach to bearing failure troubleshooting and extending their lifespan.

The approach introduced in this guide emphasizes the importance of selection of the right bearing, adherence to proper installation and maintenance practices, continuous monitoring of environmental conditions, and maintaining electrical integrity. Consistent implementation of these preventive measures is key to enhanced operational efficiency, reduced maintenance costs, and improvement in safety practices.

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