Neodymium magnets turbo compressor

Increased demand to improve energy efficiency has encouraged the study and development of a new technology in the mechanical architecture of motors destined for turbomachinery.

The revolution consists in the construction of a slotless stator. The rotor is made up of permanent ring magnets featuring multi-pole magnetisation in the right sequence (Array Halbach technology), retained by a carbon fibre jacket with high mechanical strength, because it has to deal with rotation speeds from 10,000 to 20,000 r.p.m..

The rotor and the stator never come into contact with each other. The rotor is suspended thanks to the presence of magnetic bearings that support the shaft. When the shaft turns at very high speed, a film of air naturally forms between the bearing and the shaft. This air guarantees rotor levitation without any friction and without the need for any lubricants. Furthermore, there is no need for any additional fan or cooling system. The load capacity of the bearings increases proportionally with the revolutions of the motor.

A motor with this type of design means the possibility of cutting running costs by up to 40% compared to a conventional motor. And a reduction in noise levels and vibrations thanks to the lack of contact between the rotor and stator. This type of motor does not require any type of lubricant.

We can now analyse the specifications of a fundamental component of the application described above: the magnet.

The magnet used for this application is made of pulverised neodymium, resistant to maximum temperatures up to 220°C. Centrifugal retention is achieved by a carbon fibre jacket. Levitation of the rotor inside the stator is guaranteed by 3 magnetic bearings supporting the shaft. These magnetic bearings are necessary to guarantee the rotational movement of the rotor during the entire speed interval.

Halbach magnetisation is adopted for this kind of magnets.

(Did you know that…?)

“A Halbach Array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while by interference cancelling the magnetic field on the other side. In the diagram, the magnetic field underneath is reinforced and the magnetic field above is cancelled. This rotating pattern (on the front face, on the left, up, right, down) can be continued indefinitely and have the same effect. The effect of this arrangement is similar to many horseshoe magnets placed adjacent to each other, with similar poles touching.”

Thanks to this solution, when the rotor is turning, it never touches the surrounding surfaces: this construction requires absolutely no oil and none of its components are subject to wear, achieving maximum efficiency and reliability. It also includes the possibility of correcting the residual imbalance of the rotor or unexpected heat deformations.

Assembly, balancing and testing are all carried out in Italy.