Magnetic bearing

How magnetic bearings work

• Magnetic bearings are working due to targeted generation of magnetic fields in order to support rotating shafts in a contactless and stable manner. Electromagnets generate a magnetic field that centres the shaft and enables floating states.
• Optionally, sensors continuously measure the position of the shaft and a control system immediately adjusts the magnetic field to correct position deviations.
• This avoids mechanical friction and wear, which enables a long service life and efficiency even at high speeds and in extreme environments. In addition, vibrations can be effectively controlled, which increases the overall performance of the systems.

Designs and types of magnetic bearings

• There are two main types of magnetic bearings: active and passive bearings. Active magnetic bearings use electromagnets that are controlled by a control system to precisely stabilise the shaft.
• Passive magnetic bearings, on the other hand, work without active control and are usually based on permanent magnets, which support simple, stable applications but are less flexible.
• There are also hybrid systems that combine passive and active components to optimise stability and energy efficiency and meet different application requirements.

Performance parameters of magnetic bearings

• Resistance: The electrical resistance of the coil is decisive for the current consumption and can be influenced by the thickness of the wire and the number of windings.

• Inductance (L): Measured in Henry (H), the inductance indicates how well the coil generates a magnetic field.
• Maximum temperature: Solenoid coils are designed for specific operating temperatures, which depend on the materials used. Overheating can lead to a loss of magnetic properties or damage to the insulation.

Structure of the magnetic bearing

• Load capacity: The load capacity indicates how much weight the magnetic bearing can hold in a stable suspended state. It is a critical factor when selecting the bearing, as it determines the maximum load that the bearing can handle without destabilising the shaft or losing the levitation state.
• Stiffness: The stiffness describes how resistant the magnetic bearing is to changes in the position of the shaft. Higher stiffness leads to more precise stabilisation, as it corrects mechanical deviations or external influences, such as vibrations, more effectively and maintains an exact position of the shaft.
• Damping: Damping is the ability of the magnetic bearing to reduce oscillations and vibrations caused by rotational movements or external disturbances. Good damping properties improve running smoothness and extend the service life of the entire machine structure by minimising stresses.
• Control speed: The control speed determines how quickly the magnetic bearing system reacts to position deviations and adjusts the magnetic forces. A high control speed is crucial for dynamic applications in which quick corrections are necessary to keep the shaft stable at all times.
• Maximum speed: The maximum speed describes the highest rotational speed that the magnetic bearing can stably support. It is an essential parameter for high-speed applications, as the bearing remains stable when this limit is reached without sacrificing precision or reliability.

Magnetic bearing applications

• Turbomachinery: In compressors, turbines and pumps, magnetic bearings enable high speeds and minimise friction and wear. They are ideal for use in sensitive environments, such as the oil and gas industry, where high reliability is required.
• Medical technology: Magnetic bearings are used in MRI machines and blood centrifuges due to their contactless bearings. They enable vibration-free, precise and hygienic applications without particle abrasion, which is particularly important for sterile environments.
• Power generation: In generators and wind turbines, magnetic bearings offer a durable, low-maintenance solution. The contact-free bearing reduces downtime and extends the service life, which is a great advantage in energy production.
• Vacuum and clean room technology: In semiconductor and coating systems, magnetic bearings prevent contamination from lubricants or abrasion. Their non-contact operation is ideal for applications where a clean environment is essential.

Environmental requirements Magnetic bearings

• Magnetic bearings must fulfil high environmental requirements such as IP protection and temperature resistance. High IP protection (e.g. IP67) protects against dust and water, which is essential in harsh industrial environments. In addition, they are often designed for operating temperatures of up to 150 °C or higher in order to remain stable even in extreme heat. This robustness increases the reliability and longevity of the bearings in demanding applications.