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Service, Parts & Maintenance

Principles of Friction and Bearing Design

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Have you ever effortlessly glided on an ice skating rink? Or slid across a wood floor in your socks? If you haven’t, you definitely need to. If you have, you’ve experienced the exhilarating weightlessness that comes from low friction. While an essential force in our material world, friction can cause problems, especially in machinery.

Air compressors remedy this by using bearings to mitigate friction during the compression process, but not all bearings are created equal. Today we’ll look at the advantages and drawbacks of three types of bearings commonly used in compressors. Before we get started, let’s take a moment to look at the physics of friction.

What is friction?

According to the Merriam-Webster dictionary, friction is “the force that resists relative motion between two bodies in contact.” There are two types of friction: static friction and kinetic friction. Static friction is the force required to initiate movement between two stationary objects. Kinetic friction is the resisting force between two moving objects.

Static friction is greater than kinetic friction. Think about trying to push a heavy box across the floor. You have to apply more force to initiate motion than you do to keep the box moving.

When determining friction between two objects, a couple factors must be considered. The coefficient of friction determines how well the objects grip to each other (each object has its own coefficient), and the normal force presses the objects together. Torque and traction come into play when one of the moving objects is a rotating tire.

High amounts of friction can generate heat and wear objects out. Try rubbing your hands together and you’ll immediately feel warmer. The same principle holds true for parts in a compressor. As they continuously rub against each other and create heat, they wear out faster than they would with less friction. Luckily, elements like bearings offer less friction to air compressors, allowing them to run faster without wearing out.

Types of bearings

There are three main types of bearings used in compressors, each with their own benefits and drawbacks.

Roller bearing 

Roller bearings are typically the least expensive type of bearing. They have radial loads, meaning the load acts at a right angle to the bearing’s axis of rotation. Roller bearings tend to have long lifespan, and are one of the earliest known bearing designs.

Tapered roller bearing

Tapered roller bearings are a type of roller bearings with a conical shape. These are often more expensive than roller bearings, but they can handle both radial and axial loads. An axial load exerts force parallel to the axis of rotation. Because tapered roller bearings can withstand both load forces moderately well, they tend to wear out faster than roller bearings. 

Ball bearings

Ball bearings are the most expensive type of bearing. They can handle both radial and axial loads, and they are highly reliable. There are many types of ball bearings, including angular contact, axial and deep-grove.

Next time you’re out skating or just sliding around the house in your socks, consider the physics behind the fun. While low friction can be enjoyable, it also allows your machine to run more efficiently throughout its lifetime.

What kind of bearing does your compressor use? Let us know your preference in the comments below.

 

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