Disadvantages of Magnetic Bearings

Disadvantages of Magnetic Bearings

Although significant improvement has been achieved, there are still several disadvantages in comparison with other, conventional bearings. The most important limitations follow.

•  Electromagnetic bearings are relatively much more expensive than other non contact bearings, such as the hydro static bearing. In most cases, this fact makes the electromagnetic bearing an uneconomical alternative.

•  Electromagnetic bearings have less damping of journal vibrations in comparison to hydro static oil bearings.

•  In machine tools and other manufacturing environments, the magnetic force attracts steel or iron chips.

• Magnetic bearings must be quite large in comparison to conventional non contact bearings in order to generate equivalent load capacity. 
• An acceptable-size magnetic bearing has a limited static and dynamic load capacity. 
• The magnetic force that supports static loads is limited by the saturation properties of the electromagnet core material.
•  The maximum magnetic field is reduced with temperature. In addition, the dynamic load capacity of the bearing is limited by the available electrical power  supply from the amplifier.

•  Finally, electromagnetic bearings involve complex design problems to ensure that the heavy spindle, with its high inertia, does not fall and damage the magnetic bearing when power is shut off or momentarily discontinued. Therefore, a non interrupted power supply is required to operate the magnetic bearing, even at no load or at shutdown conditions of the system.
• In order to secure safe operation in case of accidental power failure or support of the rotor during shutdown of the machine, an auxiliary bearing is required. Rolling-element bearings with large clearance are commonly used. During the use of such auxiliary bearings, severe impact can result in premature rolling element failure.