Anti Friction Bearing

Definition

An anti-friction bearing is likely a type of bearing that uses rolling elements, such as balls or rollers, to minimize friction between moving parts, making it suitable for applications needing low friction, especially at low speeds.

Function and Use

These bearings reduce friction through rolling motion, commonly used in centrifugal pumps, power pumps, and various machinery, enhancing efficiency by minimizing energy loss through heat.

Types

• Ball Bearings: Use metal balls between races, often for radial and thrust loads.
• Roller Bearings: Use rollers for handling radial, thrust, or combined loads, like in crankshafts.
• Needle Bearings: Subtype of roller bearings with thin rods, used where space is limited.
• Double Row Angular Contact Ball Bearings: Designed for thrust in either direction, supporting radial loads in single-stage pumps.

Background and Definition

An anti-friction bearing, also known as a rolling contact bearing, is a type of bearing that uses rolling elements, such as balls or rollers, to reduce friction between moving parts. Unlike friction bearings, which rely on sliding surfaces with lubrication, anti-friction bearings minimize friction through rolling motion, making them suitable for applications requiring low friction, especially at low speeds. This is evident from the definition provided on Wikipedia: Bearing (mechanical), which highlights their role in reducing sliding friction compared to plain bearings.

Function and Operational Mechanics

The primary function of anti-friction bearings is to support relative motion between parts while minimizing friction and wear. They achieve this by using rolling elements contained within inner and outer races, with a separator maintaining alignment. This rolling motion reduces energy loss through heat, making them ideal for higher loads and speeds. They are commonly used in centrifugal pumps for carrying radial and thrust loads, and as crankshaft bearings in power pumps.

Types and Variations

Anti-friction bearings come in various forms, depending on the application and load requirements. The types include:

1. Ball Bearings: These use metal balls between the bearing races, minimizing contact points and commonly used in centrifugal pumps for both radial and thrust loads. They are designed for specific load-carrying requirements.
2. Roller Bearings: These use rollers instead of balls and can handle pure radial loads, pure thrust loads, or combinations of both. They are often applied as crankshaft bearings in power ends of some power pump designs.
3. Needle Bearings: A subtype of roller bearings, these have thin cylindrical rods and are used where space is limited.
4. Double Row Angular Contact Ball Bearings: These are designed to absorb thrust force in either direction while also supporting radial loads, commonly used in single-stage pumps.

Additional types like tapered roller bearings, self-aligning ball bearings, wire race bearings, and caged roller bearings, each with historical significance and specific applications, such as self-aligning ball bearings patented in 1907 by Sven Wingquist.

Historical and Modern Usage

Historically, anti-friction bearings have evolved with innovations like the self-aligning ball bearing and wire race bearing, as noted in the Wikipedia history section. Modern applications include their use in automotive, machinery, and aerospace industries, where they handle high loads and speeds with minimal friction.

Advantages and Disadvantages

Anti-friction bearings offer several advantages, as detailed in the Emerson Bearing page:

1. Low Friction: They produce less friction, needing less lubrication, ideal for higher loads and speeds.
2. Efficiency: Reduce energy loss through heat, enhancing machine efficiency.
3. Versatility: Handle various load types, making them suitable for diverse applications.

However, there are notable disadvantages:

1. Finite Life: They have a finite life, typically designed for 25,000 hours, as per ScienceDirect, inversely proportional to the cube of actual forces (e.g., forces ½ predicted value increase life 4 times, double forces decrease life 4 times).
2. Complexity: The extra mechanical complexity can drive up costs.
3. Sensitivity to Contaminants: High sensitivity to contaminants due to thinner oil film and high contact pressures, requiring serious sealing and oil cleanliness.

Comparative Analysis with Friction Bearings

Compared to friction bearings, anti-friction bearings offer lower friction and less need for lubrication, but they have a finite life and higher initial complexity. Friction bearings, rely on a fixed surface with lubricating oil, typically softer materials, and are used in applications like bushing and sleeve bearings, which may not handle high speeds as effectively.

Summary Table: Anti-Friction Bearing Characteristics