There are many different types of bearings available today with very little information on the differences between them. Maybe you’ve asked yourself “which bearing will be best for your application?” Or “how do I choose a bearing?” This bearing selection guide will help you answer those questions.
First off, you need to know that most bearings with a rolling element fall into two broad groups:
Within these groups, there are sub-categories of bearings that have unique features or optimized designs to enhance performance.
In this bearing selection guide, we’ll cover the four things you need to know about your application in order to choose the right type of bearing.
Bearing loads are generally defined as the reaction force a component places on a bearing when in use.
When choosing the right bearing for your application, first you should find the bearing’s load capacity. The load capacity is the amount of load a bearing can handle and is one of the most important factors when choosing a bearing.
Bearing loads can either be axial (thrust), radial or a combination.
An axial (or thrust) bearing load is when force is parallel to the axis of the shaft.
A radial bearing load is when force is perpendicular to the shaft. Then a combination bearing load is when parallel and perpendicular forces produce an angular force relative to the shaft.
To learn more about axial and radial ball bearings, contact our team of engineers!
Ball bearings are designed with spherical balls and can distribute loads over a medium-sized surface area. They tend to work better for small-to-medium-sized loads, spreading loads via a single point of contact.
Below is a quick reference for the type of bearing load and the best ball bearing for the job:
Roller bearings are designed with cylindrical rollers that can distribute loads over a larger surface area than ball bearings. They tend to work better for heavy load applications.
Below is a quick reference for the type of bearing load and the best roller bearing for the job:
Bearing runout is the amount a shaft orbits from its geometric center as it rotates. Some applications, like cutting tool spindles, will only allow a small deviation to occur on its rotating components.
If you are engineering an application like this, then choose a high precision bearing because it will produce smaller system runouts due to the tight tolerances the bearing was manufactured to.
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Bearing rigidity is the resistance to the force that causes the shaft to deviate from its axis and plays a key role in minimizing shaft runout. Bearing rigidity comes from the interaction of the rolling element with the raceway. The more the rolling element is pressed into the raceway, causing elastic deformation, the higher the rigidity.
Bearing rigidity is usually categorized by:
The higher the bearing rigidity, the more force needed to move the shaft when in use.
Let’s look at how this works with precision angular contact bearings. These bearings typically come with a manufactured offset between the inner and outer raceway. When the angular contact bearings are installed, the offset is removed which causes the balls to press into the raceway without any outside application force. This is called preloading and the process increases bearing rigidity even before the bearing sees any application forces.
Knowing your bearing lubrication needs is important for choosing the right bearings and needs to be considered early in an application design. Improper lubrication is one of the most common causes for bearing failure.
Lubrication creates a film of oil between the rolling element and the bearing raceway that helps prevent friction and overheating.
The most common type of lubrication is grease, which consists of an oil with a thickening agent. The thickening agent keeps the oil in place, so it won’t leave the bearing. As the ball (ball bearing) or roller (roller bearing) rolls over the grease, the thickening agent separates leaving just the film of oil between the rolling element and the bearing raceway. After the rolling element passes by, the oil and thickening agent join back together.
For high-speed applications, knowing the speed at which the oil and thickener can separate and rejoin is important. This is called the application or bearing n*dm value.
Before you select a grease, you need to find your applications ndm value. To do this multiply your applications RPMs by the diameter of the center of the balls in the bearing (dm). Compare your ndm value to the grease’s max speed value, located on the datasheet.
If your n*dm value is higher than the grease max speed value on the datasheet, then the grease won’t be able to provide sufficient lubrication and premature failure will occur.
Another lubrication option for high-speed applications are oil mist systems which mix oil with compressed air and then inject it into the bearing raceway at metered intervals. This option is more costly than grease lubrication because it requires an external mixing and metering system and filtered compressed air. However, oil mist systems allow bearings to operate at higher speeds while generating a lower amount of heat than greased bearings.
For lower speed applications an oil bath is common. An oil bath is when a portion of the bearing is submerged in oil. For bearings that will operate in extreme environments, a dry lubricant can be used instead of a petroleum-based lubricant, but the lifespan of the bearing is typically shortened due to the nature of the lubricant’s film breaking down over time.
There are a couple of other factors that need to be considered when selecting a lubricant for your application, see our in-depth article “How to Choose the Correct Ball Bearing Lubricant".
Cylindrical Roller Bearings are designed to handle radial load at high performance and speed. Because of their particular design, These Bearings are one of the most suitable options for carrying multiple radial loads yet there are some other factors too that define the ultimate outcome or performance of this apparatus. In order to get the maximum results from these, you must optimize their cost, weight, performance, load capacity and durability. As these bearings are used for long term, you have to select the suitable variation according to your need carefully.
DESIGN
These cylindrical roller bearings have two rings called inner and outer ring that are separated by a set of cylinders that not only support both rings, but also reduce the overall frictional force. These cylinders are supported by a rib or cage attached with either inner or outer ring depending on the variation you are using. On the other hand, the number of cylinders or rollers used in a Cylindrical Roller Bearing may vary and effect of increasing this number is increment in overall performance because of the obvious reasons.
MATERIAL AND STRUCTURE
These Bearings are made with several different kind of material based on their applications and use, although alloy steel is a widely used material in these because of it offers maximum durability to rollers, rings and even the roller cage. In order or achieve more performance with high acceleration and speed as well as more carrying capacity while sacrificing durability, these Bearings are made with pressed steel too. In some cases, polyamide cages are used.
APPLICATIONS
As you have anticipated the effectiveness and efficiency of these Bearings, you probably have guessed that Cylindrical Roller Bearings are essential part of any machinery that comes with rotating parts. These are widely used in papermaking industry, electric motors, railways, motorcycles, pumps, wind turbines and gearboxes. Although these Bearings are used in above mentioned industries but their use is not limited there because of their high performance and durability even under stressful conditions.
VARIATIONS AND MODELS
Mainly there are three variations of these Bearings; single row Cylindrical Roller Bearings, double row Cylindrical Roller Bearings and multi row Cylindrical Roller Bearings. The names of these models are self explanatory.
Single Row Bearings
These come with a single set of inner and outer ring as well as a single set of cage and rollers. There are several subtypes of single row Bearings and the difference between them is placement of cage and rollers.
Double row Bearings
These are similar to single row Bearings except they come with two set of inner and outer rings as well as two sets of rollers and cage. This model is used in precision machines because of their augmented strength, increased accuracy and enhanced carrying capacity.
Multi row Bearings
These offer high carrying capacity with lower performance.
ROLLER BEARING SELECTION CRITERIA
Although roller bearings are standardized components, the selection criteria for the correct bearing can only be established to a limited extent, usually based on the application requirements. Still, buyers must consider one of the main dimensions of the bearing, typically the bore diameter, based on the overall design and construction.
Today, computerization of the design process enables manufacturers to create bearings with optimal dimensions. That technology also aids consumers in picking suitable components for use in various pieces of machinery.
When searching for the suitable bearing for use in specific applications, project managers and designers should focus on the following factors:
● Load type and volume
● Mounting requirements – installation space and style of lubrication
● The bearing's functional lifespan
● The bearing's operating parameters (speed and thermal conditions)
● Accuracy requirements
● Maintenance and servicing
● Ambient conditions (vibrations, dirt, etc.)
● Requirements for assembly and disassembly
Do you want to know more about Roller Bearings? Feel free to contact us.