Considering Bearing Types for Selecting Fan
Selecting the right fan is crucial to meeting your thermal goals. Besides choosing the fan based on basic requirements like CFM, static pressure, power and noise, there are also bearing types to consider. This brief article will explain the pros and cons to help you select which bearing type is best suited for your application.
2 Bearing Types: Ball Bearing and Sleeve Bearing
Bearing types can be broken down into two groups, ball bearings and sleeve bearings. Both bearings have an inner and outer race to mount the rotor shaft to the fan frame and have grease in-between to reduce heat, friction, and degradation. However, ball bearings use steel (or ceramic) balls to help distribute the load while sleeve bearings rely only on grease as the primary interface.
How To Select Bearing Types
To determine which type is best suited for your application, the design engineer must decide on the following:
- What is the needed fan service life?
- How will the fan be mounted (orientation wise)?
- What is the acoustic noise requirement, short-term and long-term needs?
- What is the cost (unit wise or system cost)?
Let’s examine each question:
1. Fan Service Life
- How long is the fan expected to operate in the field, what is the lifespan of the system the fan is used in?
- Is the system used in a remote location that is difficult to service year-round?
- What temperature range is the fan exposed to?
- As the temperature gets higher, the L10 life shortens for both types but is more detrimental to the sleeve bearing.
2. Acoustic Noise: Short Term and Long Term
- Sleeve bearings are quieter than ball bearings at low speeds in their early life (2-3 years).
- Ball bearings are quieter at high RPMs and for longer lifespan.
3. Fan Mounting Orientation
- Will the fan be mounted vertically or horizontally?
- The life span of a fan with sleeve bearing is reduced if oriented other than vertically due to uneven loading of the sleeve.
- Fans with ball bearings can be mounted in any orientation without affecting life span due to a preloaded spring.
4. Cost
- Sleeve bearing fans are less expensive per unit than ball bearing fans, but ball bearing fans have a longer service life, so over time ball bearings will provide a greater value per dollar due to a lower system maintenance cost.
Summary of Characteristics
The table below summarizes these characteristics of ball bearing and sleeve bearing*:
*Data compiled from several ball bearing supplies
In summary, as a rule:
- If the system has a short life span (< 3 years) or is exposed to low levels of heat or only mounted vertically then sleeve bearing fans may be used.
- However, if longer life span, endurance to higher temperatures or horizontal orientation is required, ball bearing fans should be used.
Rest assured; all SANYO DENKI fans use only dual ball bearings to ensure a long service life at higher operating temperatures resulting in a lower system cost.
Please feel free to contact your local SANYO DENKI AMERICA sales office or sales representatives with any questions and we will be glad to help you.
Written by Gary Masessa
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