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Factors of 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.
Radial | Axial (Thrust) |
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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:
High Speeds | Low Speeds |
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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 made 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 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 vapour 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.