Bearings are one of the most critical machine elements in rotating systems. A correctly selected bearing ensures efficient and reliable operation of the machinery while significantly reducing maintenance costs. Therefore, bearing life calculation plays a critical role in engineering design and maintenance planning.

What is Bearing Life?

Bearing life refers to the period of time or number of revolutions that a bearing can operate under specific operating conditions before failure occurs due to fatigue.

According to international standards, the most commonly used concept is L10 life. L10 life signifies the rating life that 90% of a group of identical bearings operating under identical conditions are expected to reach or exceed. In other words, it is accepted that only 10% of the bearings may fail due to fatigue before this period.

Basic Formula (According to ISO 281):

L₁₀ = (C / P)³ × 1,000,000 revolutions

• L₁₀: Basic rating life at 90% reliability (in revolutions)
• C: Dynamic load rating (N)
• P: Equivalent dynamic load applied (N)

If the life is to be calculated in hours:

L_10h = L₁₀ / (60 × n)

• L_10h: Bearing life in hours
• n: Operating speed of the bearing (RPM)

! The P value is calculated assuming that the load is constant and radial. In case of variable loads, it must be adjusted with specific factors.

Bearings are fundamental machine elements that ensure the reliable operation of industrial machinery, automotive systems, and many types of mechanical equipment. However, even the highest quality bearing can fail prematurely due to incorrect mounting, improper lubrication, or unsuitable operating conditions. Therefore, correct mounting and regular maintenance are of great importance for bearing performance and service life.

Correct Mounting Steps:

1. Cleanliness of the Environment:
   The environment where the bearing mounting will take place must be free from dust and dirt.
2. Inspection of Parts:
   It must be checked whether the dimensions of the shaft, housing, and bearing are compatible. The end surfaces must be clean and smooth.
3. Appropriate Mounting Method:
   • Press-fitting: Used for small bearings. The bearing should never be struck directly with a hammer.
   • Thermal Expansion (Induction): For large bearings, the inner ring is heated up to 80–100 °C before mounting.
4. Tightening and Securing:
   After mounting, it must be checked that the bearing is properly seated on the shaft and in the housing. If necessary, it should be secured with a retaining ring, nut, or clamp.
5. Lubrication:
   • The bearing must be properly lubricated with bearing grease or an oil bath.
   • Before the initial operation, it must be ensured that the bearing is fully lubricated.

Points to Consider During Operation:

• Bearing life is severely shortened due to factors such as overload, misalignment, and shaft deflection.
• Grease needs to be replenished at regular intervals.
• Bearings must be inspected more frequently if they operate in vibrating or very high-temperature environments.
• Sealing elements (oil seals, gaskets) must be checked regularly.

Bearing internal clearance refers to the total amount of free movement between the inner ring and the outer ring before the bearing is mounted. This clearance can be measured in either the radial or axial direction.

• Radial internal clearance is the amount of movement of the inner ring relative to the outer ring in the radial direction.
• Axial internal clearance refers to the amount of movement of the inner ring in the axial direction.

After the mounting process is completed, this clearance may decrease due to tight interference fits, operating temperatures, and the effect of loads. Therefore, selecting the correct internal clearance class is of great importance for the operating performance of the bearing.

Why is Bearing Internal Clearance Important?

Internal clearance directly affects the operating characteristics of the bearing. An unsuitable internal clearance can cause the following problems:

• Excessive friction and temperature rise
• High vibration and noise
• Decline in lubrication performance
• Premature fatigue and surface damage
• Increase in energy consumption
• Shortened bearing life

On the other hand, a correctly selected internal clearance ensures a more balanced distribution of the load, contributing to a longer service life and more efficient operation of the bearing.

Bearing Internal Clearance Classes

Bearing internal clearance is divided into specific standard classes. The most commonly used classes are as follows:

Bearing lubrication is a maintenance practice that prevents direct contact between metal surfaces by forming a protective oil film between the rolling elements and the rings. This oil layer reduces friction, minimizes wear, and contributes to the more efficient, quiet, and long-lasting operation of the bearing.

Correct lubrication not only reduces friction but also helps keep the heat generated during operation under control, provides protection against corrosion, and makes it difficult for dust and other contaminants to reach the inside of the bearing.

Basic Functions of Bearing Lubrication

Proper lubrication performs many important functions that directly affect the operating performance of the bearing:

• Reduces friction and wear.
• Dissipates heat to balance the operating temperature.
• Forms a protective film between metal surfaces.
• Helps prevent rust and corrosion.
• Provides protection against foreign substances such as dust, moisture, and dirt.
• Reduces noise and vibration.
• Extends the service life of the bearing.

Different lubrication methods can be applied depending on the operating conditions of the bearing.

Grease Lubrication

Grease is the most commonly used bearing lubrication method in the industry. It is easy to apply and can operate for a long time without requiring maintenance. Its main advantages are as follows:

• Simple application
• Low maintenance requirement
• Sealing capability
• Protection against contamination ingress
• Economical use

Grease lubrication is frequently preferred in electric motor applications, fans, conveyors, pumps, and general industrial machinery.