Rotating Motion: The Role of Ball Bearings

Rotating Motion: The Role of Ball Bearings

by Kevin Sweeney
12 July, 2023
5 min read

Ball bearings are mechanical components designed to reduce friction between moving parts while supporting rotary motion. They consist of an inner ring, an outer ring, and a set of steel or ceramic balls positioned between them. Balls made of steel or ceramic, are precisely spaced by a cage, facilitating free rotation.

Construction of Ball Bearings

Ball bearings consist of an Inner ring or raceway, an outer ring or outer raceway and balls with our without a retainer. 

Fig. 1 Construction of Ball Bearings

1. Inner and outer ring are made of chrome steel 52100 (100Cr6) or 440C or (X65Cr13) stainless steel or Cronidur 30 (X30CrMoN15-1)
2. Ceramic or steel balls
3. Retaining cage sheet steel, polymide, or phenolic
4. Load-carrying lubricants thousands to choose from
5. Shields and seals made of sheet steel, Teflon-coated fiberglass fabrics or reinforced Phenolic

Working Principles of Ball Bearings

Ball bearings operate based on the principles of rolling contact, which differ from the sliding contact encountered in plain bearings. The working principles involve the following concepts:

Rolling Contact: As an external force is applied to the bearing, the balls roll between the inner and outer rings. This rolling action significantly reduces friction compared to sliding contact, enabling smoother rotation.

Raceway Curvature: The inner and outer rings of a ball bearing have carefully engineered curved surfaces known as raceways. These raceways ensure that the balls make contact at specific points, distributing the load evenly and minimizing stress concentrations.

Lubrication: Proper lubrication is needed for efficient operation of ball bearings. Lubricants reduce friction, dissipate heat, and protect against wear and corrosion. Common lubricants include grease and oil, chosen based on the application’s speed, temperature, and load requirements.

The Role of Ball Bearings in Rotary Motion

Ball bearings are used for their ability to minimize friction between moving parts. By introducing rolling contact between the balls and the inner and outer rings, they significantly reduce frictional resistance. Friction reduction leads to enhanced efficiency, decreased energy consumption, and reduced wear.

Load Distribution

In many applications,  loads need to be supported during rotary motion. Ball bearing design distributes the loads evenly across the inner and outer rings. The use of multiple balls in a bearing increases the contact area and allows for the transfer of higher loads without compromising the smoothness of rotation.

Working Principles of Ball Bearings

Ball bearings operate on fundamental principles of physics, including Newton’s laws of motion and Hertzian contact theory. When a load is applied to the bearing, the balls roll between the rings reducing the frictional forces. The rolling action allows the bearing to accommodate both radial and axial loads, ensuring stable and efficient rotation.

Examples and Calculations

Rolling Resistance Calculation:

The rolling resistance of a ball bearing can be calculated using the formula:

R = (0.002/3) × f × W × D


R = Rolling resistance (N)

f = Coefficient of rolling resistance (typically ranging from 0.001 to 0.003)

W = Load on the bearing (N)

D = Bearing diameter (m)

By calculating the rolling resistance, engineers can optimize bearing selection, reducing energy consumption and improving overall performance.

Preload Calculation

Preload refers to the intentional application of a slight internal axial load on a ball bearing to improve its stiffness and reduce operational clearance. The preload force can be determined using equations that consider the bearing geometry, the desired preload level, and the intended application’s load requirements.

The application of ball bearings has revolutionized the field of engineering by facilitating smooth, low-friction rotary motion in a myriad of mechanical systems. Through their ability to reduce friction, evenly distribute loads, and enhance operational efficiency, ball bearings have become indispensable components in a wide range of industries. Understanding the working principles, employing scientific calculations, and optimizing their use enable engineers to harness the full potential of ball bearings, ensuring enhanced performance, reduced energy consumption, and extended machinery lifespan. As technology advances, further innovations in ball bearing design and materials will continue to shape the landscape of rotary motion, propelling engineering achievements to new heights.

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Written by

Kevin Sweeney

Founder and CEO at Pacific International Bearing Sales Inc (PIB)
Education: BS Business and Economics California State University Hayward Ca
CBS (Certified Bearing Specialist)

My role with Pacific International Bearings (PIB) is currently CEO. Since 1976, I have been deeply involved in the bearing industry, working in manufacturing sales at NTN Bearing and subsequently in Bearing Distribution. Before establishing PIB in 1990, I gathered valuable experience in bearing manufacturing and distribution. The last 45 + years in the bearing industry have been both rewarding and challenging, assisting customers across a large number of diverse bearing applications.
Outside of the bearing industry, my interests are family, woodworking, motorcycling, cars, gardening, and golf.
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