Bearing Selection

Factors for Choosing a Bearing

Load

To select the proper bearing the direction of the load need to be considered. If the majority of the load is being applied perpendicular to the shaft then a radial bearing should be selected. These bearing can withstand a lot of force along the radial direction as well as a small amount of force in the axial direction. If the majority of the force is along the axial direction then an axial or thrust bearing should be selected. These bearings can withstand a high load in the axial direction (along the axle) and a small load in the radial direction. Bearings can also be combined to achieve complex loading situations.

Speed

A machine will require a different bearing depending on the operating speed. A high-speed bearing will need to be able to operate safely with slight misalignments to the shaft that could be magnified at higher speeds. Below is a table of bearings that operate well at a high or low speed:

Temperature 

A bearing can create a lot of heat in a system and they also have heat added to them by other neighbouring components in the system. Another decision that needs to make when choosing a bearing is how it handles heat. Lubrication is important to control the temperature of the bearing. Bearings made from ceramic can withstand high heat applications. The inner and outer races are made from either Silicon Nitride (Si3N4), Zirconium Oxide (ZrO2) or Silicon carbide (SiC). Silicon Bearings can run in high load, high speed and extreme temperature conditions, they have an increased life span, a minimal need for lubrication and are highly efficient.

Sealing

A seal on the bearing keeps the lubricant clean and increases the life span of the bearing. The type of seal need depends on the kind of lubricant, the force it will endure and the environment it will be used in.

Contact Seals

• • Create an effective seal by applying pressure to the outer ring. This seal keeps out solids and fluids, but they cause friction within the bearing decreasing the life of the bearing.

Non-Contact Seals 

• • Performs similarly to contact seals accept have far less friction. this type of seal also lets fluid lubricant leak out over time.

Bearing Isolators Seals

• • This type of bearing combines the properties of contact bearings and non-contact bearings. These seals have more protection than contact bearings and non-contact bearings and can be used with oil or grease lubrication. this is a more costly option but provides better protection.

Contacting Isolators

• • Uses rare earth magnets to apply pressure between lapping components create a seal that stops vapour and liquids, but has a surface speed limitation of 3600 rpm with a 100mm shaft.

Labyrinth Isolators

• •  Prevents vapor and ingress while the machine is off and reduces friction and heat while running. The design uses an O-ring to create a seal that keeps the labyrinth channel closed

Shaft Slingers 

• • Create a seal while the machine is running using centrifugal forces and release the seal while off.

Size

To find the necessary size for the hole with tolerance needed to insert a bearing into a hole use: https://amesweb.info/fits-tolerances/tolerance-calculator.aspx

To use this calculator:

• • Input the nominal size of the bearing. For example, if the you are using a 10mm bearing input 10mm to the nominal size section.

• After calculating, the hole needed will be shown in the hole section and the bearing hole size will be shown by the shaft section. Each section will give the maximum and minimum hole and shaft size.
• This calculator can also be used to determine the shaft size needed to fit into the bearing center bore.

Creating your Own Bearing

Use this online calculator to determine the proper number of rolling elements and size needed when creating your own bearing: https://www.mesys.ch/calc/ballbearing.fcgi?lang=en

• Input the outer diameter, inner diameter, nominal diametral clearance and the radial and axial forces applied to your bearing.

References

Content

https://www.dxpe.com/choosing-the-right-bearing-selection-guide-different-styles-sizes/

https://www.ortechceramics.com/product-category/ceramic-bearings/?gclid=Cj0KCQjwit_8BRCoARIsAIx3Rj4QXIMehhE9ZWfI2Kdvzl8Yk43qbQG2b5atZmLwkUgAEtVLJcL6Xt0aAqTGEALw_wcB

https://www.bocabearings.com/general/full-ceramic-and-ceramic-hybrid-bearings#:~:text=Ceramic%20Balls%20are%20suitable%20for,corrosive%20and%20lighter%20than%20steel.

https://www.efficientplantmag.com/2014/02/selecting-the-correct-bearing-seal/#:~:text=The%20types%20of%20seals%20most,contact%20seals%20in%20different%20ways.

Image Links

https://www.dxpe.com/wp-content/uploads/2019/08/industrial-bearing-selection-guide.jpg