Magnetic bearing is a kind of support form which supports the load or suspension rotor by the magnetic field force.These bearings have developed rapidly in recent years, especially in high speed, low friction, high (low) temperature and vacuum applications.Compared with other supporting forms, magnetic bearing has its unique advantages and has a bright future.Several typical magnetic bearings
1.Permanent magnet type magnetic bearing
Permanent magnet type magnetic bearings are made of permanent magnets and can be made into various shapes.The bearing capacity and stiffness of the bearing are determined by the type of permanent magnet material, the shape, area, thickness and configuration of the magnetic poles, the bearing clearance, and the size of the soft magnetic steel part.The theoretical calculation of this bearing is very difficult, and the "experimental similarity method" is often used for structural design.By means of experiments, several typical bearing structures are determined and their bearing capacity and stiffness are measured.As long as the bearing of the new design takes the same material, the structural form and size are determined in proportion, its performance can be calculated in proportion, such as the bearing capacity is proportional to the square of the bearing characteristic size.
2.Passive ac driven magnetic bearing
Thrust bearings are usually combined in pairs, with each bearing acting as an electromagnet.The geometric shape of the iron core is generally E - shaped, U - shaped or circular.There are two kinds of tuning modes: series and parallel.
I. characteristics and classification
1.The characteristics of
Small friction, low power consumption, can achieve ultra-high speed operation.
Support high precision, stable work, reliable.
(3) can operate in high temperature, cryogenic and vacuum environment.
Complex structure, demanding conditions, magnetic interference to the environment, but no other pollution.
Magnetic bearings are classified according to their control mode, source of magnetic energy and structure.In addition, according to the type of magnetic field can be divided into permanent magnet type, electromagnet type and permanent magnet - electromagnet hybrid type.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 two types: low-temperature superconducting and high-temperature superconducting.
There are some special limitations between the different types in the above categories, which should be paid special attention to.
(1) permanent magnet bearing can only be passive (passive), and passive bearing can not be stable in three directions, at least one direction should be used in the active type.
Dc driven bearings can only be active type (active type).
Pure electromagnet bearings can only be 5 degrees of freedom control bearings, its volume, mass and power consumption are relatively large.
Repulsion type magnetic bearing, due to the low utilization of magnetic force, the structure is more complex than the suction type, generally rarely used.
Application examples of magnetic bearing
1.The application of machine tool in the machine tool spindle is limited, belongs to the trial nature.
(1) precision machine spindle
France S2M company has manufactured a precision spindle supported by a 5-dof controlled magnetic bearing. The dn value of the radial bearing is 4X106mm · r/min, the journal speed is 200m/s, the dn value of the thrust bearing is 8X106mm · r/min, and the thrust journal speed is 400m/s.
(2) ultra-precision lens lathe
The spindle of the ultra-precision lens lathe supported by the active magnetic bearing of S2M company in France has a speed of 2000r/min, a power of lkW and a machining accuracy of 0.05ttm.
2.Applications in precision instruments
The British national physical laboratory has developed an automatic resolution measuring instrument using maglev guide rail. In the frequency band of lkHz, the supporting stiffness is 175N/gm and the resolution is up to 0.1nm.
3.Applications in pump classes
(1) blood pump
The magnetic bearing blood pump developed by the university of Tokyo and NTN corporation.The spindle is supported by 5-dof active control magnetic bearing. The bearing capacity of the imported radial bearing is 18N, the radial bearing capacity of the export bearing is 22N, and the bearing capacity of the thrust bearing is 9.2n.
(2) circulating pump France SEP company adopts S2M company's active magnetic bearing to develop liquid oxygen and liquid hydrogen circulating pump for rocket engine.
4.Applications in space technology
Japan's NAL&MELCO and NAL&TOSIBA use active magnetic bearings to support the space attitude control inertia wheel.
5.Applications in physics experiments
(1) high precision particle beam converter Germany Uranit company has introduced three kinds of particle beam converter with magnetic bearing supporting the rotor.
(2) neutron selector
The neutron selector manufactured by KFA of Germany adopts a single degree of freedom passive magnetic bearing to support the rotor with a rotating speed of 36000r/min.