Things You Need to Know About Bearing Loads in Mechanical Systems

Mechanical systems rely on precise engineering, and understanding bearing loads is essential for creating durable designs. Bearings enable smooth, efficient movement in devices ranging from small clocks to large machines.

In this post, we’ll explain the basics of bearing loads that every mechanic and designer should know.

We’ll cover the different types of loads, how they affect bearings, and give simple tips on choosing and caring for them. Get ready to learn how these important parts help machines work smoothly!

What Is a Bearing Load?

A bearing load is the force a bearing carries to help a machine part move smoothly. This force usually starts at the shaft, passes through the bearing’s inner ring, moves through small parts called rolling elements (like balls or rollers), and ends at the outer ring of the bearing.

How Forces Move Through Bearings

When a machine runs, the shaft’s force goes through the inner ring, then the rolling elements, and finally to the outer ring. This force isn’t always spread out evenly, which can cause stress in some parts of the bearing. When the machine spins very fast, centrifugal force adds extra pressure on the outside of the bearing. That’s why you need to think about both speed and load when picking the right bearing.

Why Handling Loads Properly Matters

Using bearings correctly helps machines last longer and work better. If the load is too much or handled wrong, problems can happen:

1. Fatigue & Pitting: Too much force can wear down the bearing surface over time.
2. Deformation: Overloading can permanently bend or damage parts of the bearing.
3. Friction & Heat: When the load isn’t handled right, parts rub more, making the bearing hotter and causing it to wear out sooner.
4. Lower Efficiency: Lower efficiency means the machine uses more energy, costs more to run, and performs less effectively.

Tips to Prevent Bearing Load Problems

• Choose bearings that fit the type and size of the load.
• Install and align bearings properly.
• Regularly check and maintain bearings to spot problems early.

Understanding bearing loads helps you choose the right parts, prevent damage, and keep machines running smoothly for longer. Proper load handling improves machine performance and extends bearing life.

Types of Bearing Loads

1. Radial Loads: Sideways forces perpendicular to the shaft (like pushing on a wheel’s axle). Common in motors, conveyors, and wheels. Suitable bearings include deep groove ball bearings, cylindrical roller bearings (for heavy loads), and needle roller bearings (for space-constrained applications).
2. Axial (Thrust) Loads: Forces pushing or pulling along the shaft’s length. Found in screw conveyors, car hubs, and machine spindles. Appropriate bearings include thrust ball bearings (for single-direction axial loads), angular contact ball bearings (for combined loads), and tapered roller bearings (also for combined loads).
3. Combined Loads: Combined loads push bearings sideways and lengthwise at once. Engineers use angular contact or tapered roller bearings to manage these loads in machines like wind turbines, car suspensions, and spindles.
4. Preload: Preload applies an initial load to bearings to boost stiffness, accuracy, and smoothness, especially in precise uses like machine spindles and robotics.
5. Centrifugal Loads: Outward forces from the spinning bearing components. Increases with speed and bearing size. This affects load distribution and bearing selection for high-speed applications.

Calculating Bearing Loads

1.       Static Load Rating (C₀)

This is the maximum load a non-moving bearing can take without getting damaged.

• Why it matters: It protects the bearing from permanent dents or deformations, especially during heavy assembly pressure or shocks.

2.     Dynamic Load Rating (C)

The amount of constant load a rotating bearing can handle for at least one million revolutions.

• Why it matters: It’s used to predict the bearing’s lifespan when it’s working continuously.

3.     Equivalent Dynamic Load (P)

What it means: This combines radial (side) and axial (end) forces into one value. This makes it easier to calculate performance when a bearing is under mixed loading.

Formula:

P = X × Fr + Y × Fa

Where:

• P = Combined (equivalent) load
  • Fr = Radial load
  • Fa = Axial load
  • X and Y = Constants that depend on the bearing type and how the load is applied

4.    Bearing Life (L₁₀)

What it means: This tells you how long a bearing is expected to last. Specifically, 90% of a group of identical bearings will last at least this long.

Formula:

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

Where:

• L₁₀ = Expected life in revolutions
  • C = Dynamic load rating
  • P = Equivalent load (from the formula above)

Best Practices for Bearing Selection

1.       Assessing Application Requirements

• Identify Load Types: Determine whether the application involves radial loads (perpendicular to the shaft), axial (thrust) loads (parallel to the shaft), or a combination of both. This identification is essential for selecting a bearing that can handle the specific load conditions.
  • Evaluate Load Magnitude and Duration: Understand the magnitude of the loads and whether they are static (constant) or dynamic (varying). This evaluation helps in choosing bearings with appropriate load ratings to prevent premature failure.
  • Consider Operating Speed: Assess the rotational speed of the application. High-speed applications require bearings designed to minimize heat generation and withstand centrifugal forces.
  • Assess Temperature and Environmental Conditions: Evaluate the operating temperature range and environmental factors such as exposure to dust, moisture, or chemicals. These conditions influence the choice of bearing materials and seals to ensure durability and performance.

2.     Selecting the Right Bearing Type

• Match Bearing Design to Load Requirements: Choose a bearing type that aligns with the identified load conditions. For example, deep groove ball bearings are suitable for radial loads, while angular contact bearings can handle combined radial and axial loads.
  • Consider Material, Size, and Configuration: Choose bearing materials and sizes based on load needs, corrosion resistance, weight, space limits, and performance goals.

3.     Accounting for Safety Factors

• Incorporate Appropriate Safety Margins: Design bearings to handle loads above the expected maximum to account for uncertainties and improve reliability, preventing unexpected failures.
  • Avoid Under-Specification and Over-Specification: Under-specifying bearings can lead to premature failures, while over-specifying can result in unnecessary costs and increased weight. Striking the right balance ensures optimal performance and cost-effectiveness.
  • Determine Suitable Safety Factors: Choose the safety factor based on the application’s importance: 1.5 to 2.0 for standard machinery, and 3.0 to 4.0 for critical uses like aerospace or medical devices to ensure higher safety and reliability.

Conclusion

Understanding bearing loads is key to designing reliable machines. Selecting the right bearing involves considering load types (radial, axial, or combined), speed, environment, and preload. Properly calculating load ratings and expected bearing life, while applying safety factors, helps prevent failures and extend machine durability. This knowledge enables engineers to build smoother, more efficient, and longer-lasting systems.