Estudiante

2732

I EEE T RANSACTIONS ON M AGNETICS. V OL. 2 5. N O. 3. M AY 1989

New Permanent Magnetic Separator with NdFeB
Meets Theoretical Predictions
M ARLENE MARINESCU, NICOLAE MARINESCU, K.-H. UNKELBACH, HANS-GEORG SCHNABEL,
S TEFAN H OCK, HEINRICH KRAMMIG, ROLF WAGNER, A N D R OLAND ZOLLER

Absfract-A permanent magnet drum separator was designed, assembled, and tested, which useshigh-energy magnets made of N dFeBtype VACODYM@. The new separator called PERMOS@is of the medium field type having more than 0.4-T flux density at the drum surf ace. Calculations and measurements of the field strength and the magnetic forces are in good agreement. Preliminary tests with the separator
gave promising results.

I . DESCRIPTION T HE M AGNETIC
OF
SYSTEM
HE MAGNETIC SYSTEM for producingoptimum
magnetic field used in this separator, called PERM OS, consists of forty magnet bars arranged closely next
to each other. They are mounted on a soft magnetic iron
support which acts as a yoke, at least at the axial ends of
the magnet array. The direction of magnetization, applied
to the center of mass of each such bar corresponds to

T

4 B = --n4/l
(1)
4 Abeing the polar angleof the center of a bar in relation
to an arbitrary but fixed axis of the system; n is an arbitrary positive number. The direction of magnetization also
has to coincide with the preferred direction of the material, the magnetic easy axis in each bar [ I ] . The theory of
such systems was described in detail in earlier papers [2][41.
Fig. 1 shows a photograph of the magnetic system made
forPERMOS, the arrangement of the magnetic bars, and
the direction of magnetization of each bar being marked
on the end surface of the system.
Fig. 2 shows the flux distribution of the system, calculated with the finite element method in two-dimensional
polar coordinates. As can be seen, practically the whole
f lux ranges in the external space of the system, i.e., in the
separation region. Only atthe ends of the system, where
the multipole field is distorted in relation to a complete
multipole, is part of the flux led through the soft magnetic
support.
Manuscript received May 5 , 1988; revised October 17, 1988.
M . Marineacu and N . Marinescu are with the 1ng:Biiro fur Magnettechnik, Frankfurt, FRG.
K.-H. Unkelbach and H.-G. Schnabel are with K H D Humboldt Wedag,
D-5000 K6ln 91,FRG.
S . H ock, H . Krammig, R. Wagner. and R. Zoller are with Vacuumschmelze GmbH, D-6450 Hanau 1. F RG.
l EEE L og Number 8927002.

Fig. 1 . Separator drum in the bogie.

Fig. 2. Magnetic f lux distribution i n the assembled system.

The fact that there are minimum absolute field variations in combination with high f lux densities in regions of
tangential field directions can be explainedby the kind of
mutual magnetization and demagnetization of the bars i n
this new magnet arrangement. The strongest demagnization appears in those bars which are positioned next to the
polar axis of the generated multipole field (see Fig. 2).
Therefore, in designing the system care must be taken to
ensure that these domains correspond to the linear part of
the demagnetization curve of thepermanent magnet material.

0018-9464/89/0500-2732$01.OO

O 1989 I EEE

2 733

M ARINESCU er a l . : N E W P E R M A N E N T M A G N E T SEPARATOR WITH NdFeB

Drum

Permanent
( NaFeBI

MOqnetS

F ig. 3 . G eometry of the separator d rum

11. D ESIGN,
CONSTRUCTION, D P ERMANENT
AN
MAGNET
O
MATERIALF T HE SYSTEM
To meet the two aims: high flux density and optimum
gradient asmuch as possible, a system with n = 6 and 40
bars was constructed. The dimensions of the system are
(Fig. 3 ):

outer radius of the magnet system
inner radius of the magnet system
height of the magnet bars
axial length of the system
angular range of the system

R2 = 293.6 mm
R , = 265.6 mm
h , = 2 8 mm
h =600mm
$,n = 1 50”.

T he magnet bars, which are 600 mm long, consist of 12...