Characteristics and application of magnetic bearings

Magnetic bearing is a form of supporting load by magnetic field force or suspending rotor. This kind of bearing has developed rapidly in recent years, especially in the application of high speed, low friction, high (low) temperature and vacuum environment. Compared with other support forms, magnetic bearings possess their unique advantages and have great development prospects.

Several typical magnetic bearings

1. Permanent magnet type of magnetic bearing

Permanent magnet type of magnetic bearings is made of permanent magnets and can be made into various shapes. The bearing capacity and rigidity of the bearing depend on the type of permanent magnet material, the shape, area, thickness and configuration of the magnetic pole, the bearing gap, and the size of the soft magnetic steel part. The theoretical calculation of this kind of bearing is very difficult, and the "experimental similarity method" is often used for structural design. That is, several typical bearing structures are determined by experimental methods, and their load-bearing capacity and stiffness values are measured. As long as the newly designed bearing uses the same material, the structure and size are determined in proportion, its performance can be calculated in proportion, and such as the bearing capacity is proportional to the square of the bearing's characteristic size.

2. Passive AC excitation magnetic bearing

Magnetic bearings are usually combined in pairs, and each bearing is an electromagnet. The iron core geometry is generally E-shaped, U-shaped or circular. Tuning methods are divided into series and parallel.

 1). Properties and Classification

 (1). Properties

① The friction is small, the power consumption is low, and ultra-high-speed operation can be realized.

②High supporting accuracy, stable and reliable work.

It can operate in high temperature, deep cold and vacuum environment.

The structure is complex, the application environmental conditions are demanding, there is magnetic interference surrounding, but no other pollution.

 2). Classification

Magnetic bearings are classified according to their control mode, source of magnetic energy, and structure form. In addition, it can be divided into permanent magnet type, electromagnet type and permanent magnet- electromagnet hybrid type according to the type of magnetic field. It can also be divided into suction type and repulsion type according to the type of bearing suspension force. Superconducting magnetic bearings are also divided into low temperature superconducting and high temperature superconducting.

There are some special restrictions between the different types in the above categories, which should be paid special attention.

① Permanent magnet type of magnetic bearing. This kind of bearing can only be a passive type (passive type), and a passive type bearing cannot be stable in all three directions. At least one direction should be an active type.

②DC-excited bearings can only be active (active).

③The pure electromagnet type bearing can only be a 5-degree of freedom control bearing, and its volume, mass and power consumption are relatively large.

④Repulsion-type of magnetic bearings. Due to their low utilization of magnetic force and more complex structure compared with suction-type of magnetic bearings, generally rarely use repulsion-type magnetic bearings.

 Application examples of magnetic bearings

1) Application in machine tools

The application in the machine tool spindle is limited and is a trial nature.

(1) Spindle in precision machine tool

S2M Company in France manufactures a spindle that adopts 5 degrees of freedom controlled magnetic bearings to support the spindle of precision machine tools. The dn value of the radial bearing is 4X106mm·r/min, the spindle’s linear speed is 200m/s, and the dn value of the magnetic bearing is 8X106mm·r /Min, the linear velocity of the spindle journal is 400m/s.

(2) Super precision lens lathe

 S2M Company in France manufactures the main shaft of the ultra-precision lens lathe supported by active magnetic bearings, the speed is 2000r/min, the power is lKW, and the machining accuracy is 0.05ttm.

2). Application in precision instruments

 The British National Physics Laboratory has developed an automatic resolution measuring instrument by using maglev rails. In the 1kHz frequency band, the supporting stiffness is 175N/gm and the resolution is 0.1nm.

3). Application in pumps

(1) Blood pump

The University of Tokyo in Japan and NTN Corporation have developed a magnetic bearing for blood pumps. The main shaft is supported by a 5-DOF active-control magnetic bearing. The radial bearing capacity of the bearing at pump inlet is 18N, the radial bearing capacity of the bearing at pump outlet is 22N, and the bearing capacity of the magnetic bearing is 9.2N.

(2) Circulating pump

SEP Company in France uses active magnetic bearings for liquid oxygen and liquid hydrogen circulating pumps on rocket engines developed by SZM Company.

4). Applications in space technology

Japan’s NAL&MELCO and NAL&TOSIBA companies use active magnetic bearings to support the space attitude control inertia wheel.

5). Application in Physics Experiment

(1) Uranit, Germany, has introduced a high-precision particle beam converter that uses three types of magnetic bearings to support the rotor.

(2) Application of Neutron Selector

The neutron selector made by German KFA Company adopts single-degree-of-freedom passive magnetic bearing to support the rotor, and the speed is 36000r/min.