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VAC has extensive know-how in the manufacture of magnetic materials. Our detailled knowledge of the material properties in combination with funtional demands of the application leads to innovative solutions made by VAC. As an example, the "Butterfly Magnet" for motors with low cogging torque, patented throughout the world, was developed.

Sintered magnets are subject to an anisotropic sintering contraction. Subsequent final machining is usually unavoidable. Conventional straight arc segments magnets are ground in continuous processes with high productivity.

The twisted parallelogram of skewed arc segment magnets only makes contact at two points during grinding and thus does not have any stable lateral guidance. The skewed arv segment can therefore not be ground in a continuous process. Every surface to be ground needs a clamping device. The costs of these separate grinding processes are several times as high as grinding in a continuous process.

Conventional straight and skewed arc segment; New development Butterfly

Vacuumschmelze has solved this problem with a worldwide patented arc segment shape that is called BUTTERFLY for short because of its shape. Thanks to its stable three-point contact, this arc segment can be ground in a continuous process. Because of the skew in the arc segment, the smallest cogging torques are achieved. This means that the butterfly magnet combines the advantages of the low-cost manufacture of the straight arc segment with the low cogging torque of the conventional skewed arc segment. It is also advantageous that the axial force components that occur because of the double skew of the magnetic field compensate for each other. In conventionally skewed arc segments the bearings are charged axially and when the direction of torque changes, the rotor is shifted within the bearing play.

Comparison of cogging torque

Mehr dazu können Sie in unserer Publication (0.18 MB, PDF)   + nachlesen.

Last update: 02.07.2012


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