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Motion of ferromagnetic particles in induction transporters
CanoLun Mem/iurgrcal Quorrdy, Vol. 34, \lo 2. pp. 123-127. 1995 Copyright ,
Pergamon 000&-4433(94)00023-9
MOTION
OF FERROMAGNETIC PARTICLES INDUCTION TRANSPORTERS
H. R. FLORES, P. LEAL, G. VILLAFLOR Institute
and P. VILLAGRAN
de Beneficio de Minerales, INBEMI (UNSa-CONICET), de Investigacibn, UNSa, Buenos Aires 177-4400 (Received
14 September
IN
1993 ; in reoisedform
Facultad de Ingenieria, Salta, Argentina
Consejo
10 Maq‘ 1994)
Abstract-This
paper reports a technique for the transport (linear or rotary) of ferromagnetic particles using an alternating magnetic field produced by a conventional stator of a linear (or rotary) induction motor with iron cores and appropiate copper windings. The use of magnetic fields has obvious advantages over mechanical, hydraulic or pneumatic solid circulation and control systems : there are no moving parts (pumps, blowers, electric motors, etc.) and no fluid flows are required. In order to investigate the influence of the field frequency, size and material of the carried particles, two small-scale models of induction transporters were developed : a linear induction transporter (LIT) and a rotary induction transporter (RIT). Both were tested by applying 10-50 Hz alternating currents. This paper provides the results from the above tests, from the application of LIT as a ferromagnetic separator and comments about the possibility of application of RIT as a magnetohydrostatic separator. RCsumGCet article prtsente une technique de transport (lintaire ou rotationnelle) de particules ferromagnttiques au moyen d’un champ magnktique alternatif. Ce champ est produit par un stator conventionnel d’un moteur B induction linkaire (ou rotationnelle) avec des noyaux de fer et des bobinages de cuivre appropriks. L’utilisation de champs magnetiques prtsente des avantages &dents par rapport B la circulation de solides par des moyens mkaniques, hydrauliques ou pneumatiques et par rapport aux systkmes de
contr6les ; il n’y a pas de parties mobiles (pompes, soufflantes, moteurs electriques, etc.) et aucun passage de Auide n’est requis. Pour pouvoir
Ctudier l’influence
de la frkquence
du champ.
la taille et la nature
des particules
transportCes.
a d&elopp& deux transporteurs a induction de petite raille : un transporteur g induction lintaire (LIT) un transporteur g induction rotationnelle (RIT). On a test& les deux en leur appliquant des courants alternatifs (ac) de 10 B 50 Hz. Cet article fournit les rCsultats des tests mention&s ci-dessus, de l’application d’un LIT en tant que skparateur ferromagnttique et discute des possibilites d’application d’un RIT en tant on et
que skparateur
magnktohydrostatique.
INTRODUCTION Basic
research
on moving
magnetic
field
If the LIT ferromagnetic applications
for
mag-
netic transport of particles has been developing in recent years. Particles may be ferromagnetic or composites of non-magnetic solids (ores [l], yeasts [2], microorganisms [3], catalysts [4, 51, etc.) with ferromagnetic cores. Wallace [6] and Jaraiz [7] tested an elevator tube which operates by moving magnetic fields generated by overlapping the energization times of subsequent coils. The linear induction transporter (LIT) model configuration is the same as a linear induction motor. The windings consist of three saddle-shaped coils (coils IMII, Fig. 1) distributed among 18 slots, and connected to a three-phase power source with controlled frequency. The LIT can be used as a ferromagnetic transporter with particles moving on an acrylic tray or in a glass tube located over the LIT. Only horizontal transport was tested in this step. It is essential that the field provided by the next coil be sufficient to move the particles to the next tooth when the field of the rear coil diminishes, as well as to accelerate the particle when it is free from the influence of the rear coil. 123
is suspended over a belt, separator. The belt is used
it can be used as a to transport the feed
material into the magnetic field region and to transport the non-magnetics out or to feed them to a high-intensity device. The alternating current that passes through the windings generates a moving linear field which attracts ferromagnetic partitles and transports them to a discharge point, as shown in Fig. 2. The rotary induction transporter (RIT) model configuration is the same as the stator of a rotary induction motor. A threephase winding placed on the stator produces a rotating magnetic field of approximately constant magnitude and sinusoidal spatial distribution along the air gap. RIT models can be used for magnetohydrostatic separation (MHS) of particles based on the difference of the combination of their specific gravities and magnetic properties [8]. The effective gravity and the speed of ferromagnetic fluid rotation are both produced magnetically. At the effective specific gravity of separation, a force balance is struck between the net inward buoyant force on a particle (produced by the outward magnetic attraction of the fluid) and a combination of the direct outward centrifugal and magnetic forces.
Less-magnetic
particles
and/or
those
of a lower
specific
H. R. FLORES et ul. : FERROMAGNETIC
124
PLAN
PARTICLES
IN INDUCTION EXPERIMENTS
Wmm LIT
TRANSPORTERS AND TEST
RESULTS
model
In order to investigate the effects of the system variables listed below, a LIT laboratory model, based on a 3-mm inside diameter tube, was constructed. The horizontal linear velocity of particles was measured for different values of the following parameters : particles : physical properties are given in Table 1 ; frequency : three-phase alternating current of lo-50 Hz ; distance from LIT to tube : c-80 mm ; current magnitude : 0.1-0.9 amps.
Fig. 1. Schematic diagram of LIT.
gravity move radially inwards; more magnetic and/or higher specific gravity particles move radially outwards. Two products or multi-product separation may be obtained depending on the number and radial locations of splitters. A schematic diagram of the model RIT and its separator is shown in Fig. 3. These models are, at present, at the pilot stage of development.
Feed
e!ics
regulated 1
Magnetics
Ferrom>gnetics
Feed
0 A
Side tiew
be1t/ sectiorti
t Ferromagnetics of ferromagnetic
separator
Fig. 2. Ferromagnetic particle separator LIT suspended over the belt of ring-type magnetic separator.
The magnetic field intensity produced at the axis of the tube, in the direction of particle movement: was between 0 and & 0.050 Teslas. With the aim of determining the magnetic field intensity as a function of time and position, a gaussimeter test probe connected to a personal computer I/O stage was displaced along with the particles. Field measures 1000/s were taken during a test time of 3.61 s. The field waveform (curve H-t) is shown in Fig. 4. It has previously been observed that the distance from the LIT to the tube has a strong effect on the efficiency of transport. For distances above 70 mm the forces developed by the LIT are insufficient to enable reproducible operation. For distances less than 8 mm the particle velocities identified from both measurements and visual observations are not always welldefined and repeatable at the same experimental conditions. In this case the influence of the teeth under the particle is too strong and the particle does not advance but instead vibrates about a unique position. In the range 8-70 mm, it was found that the travel time of particles between two marks made on a graduated glass tube is not a function of either the distance or the current magnitude (as would be expected for a synchronous electrical machine). Above a given particle velocity, it becomes a repeatable and unique function of the applied field frequency. The effects of magnetic field frequency (f’) on the lineal velocity of the particle (v) for the four different types of particle listed in Table 1 are shown in Fig. 5. Here it is noticed that the initial slope of the (cl IV) -,fcurve diminishes when particle size increases. At high frequencies, heavier particles (1 and 4) reach terminal velocity before light particles (2 or 3). Heavy particles move at higher linear velocity than light particles. (This becomes evident in a u -fcurve, not shown here.) The field wave velocity is given by )V (cm/s) = 18 f’ (cps). If the ratio of the particle velocity to the wave velocity (a/w) is plotted versus frequency the slope is approximately constant for every particle. This relative velocity diminishes when frequency increases as shown on the right of Fig. 5. The LIT as u ,fhromagnetic separator. LIT was tested with borate ore samples (30-80 mesh) containing magnetite as impurity [9]. These particles were totally liberated because they were added to the borate deposit by wind action. The LIT produced tailings contain relatively little ferromagnetic material. Tailings were kept on the belt and were then treated in a ring-type magnetic separator. The results and the operating conditions are shown in Table 2.
H. R. FLORES et al. : FERROMAGNETIC
PARTICLES
IN INDUCTION
125
TRANSPORTERS
Fixed flowguide (optional)
1-1
Middlings
- --=\-I\
Heavier
and magnetics
Feed
Exci
Water
tina coil
15omm
Fig. 3. Configuration and dimension of the model RIT and rotating magnetic fluid separator.
RIT model The RIT model was tested with a ferromagnetic slurry using a ferrosilicon suspension in a cylindrical receptacle. Revolution speeds of this slurry were measured with frequency as a parameter. Ferrosilicon of 15% Si grade, 90% 325 mesh size, 6.8 g/cm’ specific gravity was employed as the dry component of the suspension. The specific gravity of the slurry was 3.2 g/cm’. Figure 6 shows a plot of the ferromagnetic slurry revolution speed (n) as a function of current intensity (0 for three different frequencies. Below a threshold current, the forces developed by
the RIT are insufficient to rotate the suspension. Beyond this current the ability of the suspension to flow increases faster than the applied field intensity: IZ is greater when I increases. This differs noticeably from the LIT behavior. Tracer experiments using layered bands of colored solids have demonstrated that the RIT has a central region in which forces are very small. This potential problem could be avoided by providing an annular separation space outside a fixed inner wall or a flowguide as shown in Fig. 3. Measurements of linear velocity L’ (or revolution speed n) were repeated many times. Only in those cases where the results of a given set of conditions were repeated 10 times was the
Table 1, Physical properties of particles Particle number I Substance (Fe304) Size (mm) Specific weight (g/cm’) Sp.Sl susceptibility (lo4 &/kg) Weight (mg)
--_-
Artificial 0.83 4.33 3.77 1.30
2 Artificial 0.41 3.93 3.20 0.14
3 Artificial 0.32 3.91 3.21 0.07
4 Natural 0.83 4.60 2.72 1.40
126
H. R. FLORES
el al. : FERROMAGNETIC
PARTICLES
IN INDUCTION
TRANSPORTERS 100 vi/(w
vwvi, cm/(sec mg)
H (Gnuss)
WI),
l/mg
12
60 r--
ssc
=Ow
6
750
800
850 time,
Fig. 4. LIT
950
900
e, CPS
1000
t (microsec.)
*v1/w1 -M-vl/wWl
magnetic field waveform
+- v2/w2 -n- v2lwW2
-#-
v3lw3
*
v4fw4
+
v3/ww3
-)(-
v4lwW4
: ratios tG/Wi and vi/( Wi w) as a function of magnetic field frequencies (f) (w = wave velocity). Particles as identified in Table 1.
Fig. 5. LIT
experiment considered successful. The values of c (or n) are the average of the 10 measurements.
CONCLUSIONS The physical viability of two induction transporters for ferromagnetic solids, the linear induction transporter (LIT) and the rotary induction transporter (RIT), have been demonstrated. It was anticipated that the LIT and RIT models, like any electromagnetic machine, would be sensitive to both the coil current and the frequency. This is the case for the RIT model, as demonstrated with ferromagnetic slurries. However, particle velocity in the LIT model is a function of frequency ; it does not depend on the current magnitude. LIT effectiveness for ferromagnetic separations is good. However, it was observed in the laboratory model that its efficiency as a ferromagnetic transporter is limited. Based on the experimental results: a LIT prototype is being designed for practical use. In order to improve the transporter efficiency it is necessary to optimize the coil configuration to produce a strong moving magnetic field in a wide gap. The RIT model was used to rotate ferromagnetic slurries. This achieves adequate conditions for separation of particles
0, rpm
100
80 -
60 -
40 -
20 -
Table 2. The LIT operating as a ferromagnetic separator I
Partial weight W)
Fraction 30-80 mesh feed Magnetic product Non-magnetic product Distance
from
LIT
100.0 I.0 99.0
Specific susceptibility (K 10’ m’/kg) 21.6 2300.0 4.7
Fe content (%I 0.71 37.0 0.33
to belt : D = 2 cm, H = 0.0 15 Teslas. f = 40 cps
0 0.25 0.5 0.75
I
I
I
I
1 1.25 1.5 1.75 2 2.25 2.5 I, amp.
-'-f=5l.5
cps +f=40.6
Fig. 6. RIT : ferromagnetic slurry current magnitude
cps -f=31;5
cps
revolution speed (n) as function (I) (f= frequency).
of
H. R. FLORES rt al. : FERROMAGNETIC with similar specific gravities and/or magnetic characteristics. At present it is in the pilot plant stage of development.
REFERENCES 1. P. Parsonage, Znnr.J. Miner.
Process. 24, 269
(1988)
PARTICLES
IN INDUCTION
TRANSPORTERS
127
2. R. Daver and E. Dunlop, Biorechnol. Bioengng 37. 1021 (1991). 3. R. Mitchell, G. Bitton and J. Oberteuffer, Waste Treafment .4dt. 4(2), 267 (1975). 4. J. Lindley. IEEE Trans. Magnetics 18 (1982). 5. 1. Zrunchev and T. Popova, Powder Tech&. 64. 175 (1991). 6. A. Wallace and U. Ranawake, Powder Tech&. 64. 125 (1991) 7. E. Jaraiz and J. Briz, Inqenieria Quimica 203, 103 (1986). 8. M. Waler and A. Deverioe, Miner. Process. 31, 195 (1991). 9. H. R. Flores and P. Villagrin, Ma,gtiet. Electr. Separ. 3. 155 (1992).
Pergamon 000&-4433(94)00023-9
MOTION
OF FERROMAGNETIC PARTICLES INDUCTION TRANSPORTERS
H. R. FLORES, P. LEAL, G. VILLAFLOR Institute
and P. VILLAGRAN
de Beneficio de Minerales, INBEMI (UNSa-CONICET), de Investigacibn, UNSa, Buenos Aires 177-4400 (Received
14 September
IN
1993 ; in reoisedform
Facultad de Ingenieria, Salta, Argentina
Consejo
10 Maq‘ 1994)
Abstract-This
paper reports a technique for the transport (linear or rotary) of ferromagnetic particles using an alternating magnetic field produced by a conventional stator of a linear (or rotary) induction motor with iron cores and appropiate copper windings. The use of magnetic fields has obvious advantages over mechanical, hydraulic or pneumatic solid circulation and control systems : there are no moving parts (pumps, blowers, electric motors, etc.) and no fluid flows are required. In order to investigate the influence of the field frequency, size and material of the carried particles, two small-scale models of induction transporters were developed : a linear induction transporter (LIT) and a rotary induction transporter (RIT). Both were tested by applying 10-50 Hz alternating currents. This paper provides the results from the above tests, from the application of LIT as a ferromagnetic separator and comments about the possibility of application of RIT as a magnetohydrostatic separator. RCsumGCet article prtsente une technique de transport (lintaire ou rotationnelle) de particules ferromagnttiques au moyen d’un champ magnktique alternatif. Ce champ est produit par un stator conventionnel d’un moteur B induction linkaire (ou rotationnelle) avec des noyaux de fer et des bobinages de cuivre appropriks. L’utilisation de champs magnetiques prtsente des avantages &dents par rapport B la circulation de solides par des moyens mkaniques, hydrauliques ou pneumatiques et par rapport aux systkmes de
contr6les ; il n’y a pas de parties mobiles (pompes, soufflantes, moteurs electriques, etc.) et aucun passage de Auide n’est requis. Pour pouvoir
Ctudier l’influence
de la frkquence
du champ.
la taille et la nature
des particules
transportCes.
a d&elopp& deux transporteurs a induction de petite raille : un transporteur g induction lintaire (LIT) un transporteur g induction rotationnelle (RIT). On a test& les deux en leur appliquant des courants alternatifs (ac) de 10 B 50 Hz. Cet article fournit les rCsultats des tests mention&s ci-dessus, de l’application d’un LIT en tant que skparateur ferromagnttique et discute des possibilites d’application d’un RIT en tant on et
que skparateur
magnktohydrostatique.
INTRODUCTION Basic
research
on moving
magnetic
field
If the LIT ferromagnetic applications
for
mag-
netic transport of particles has been developing in recent years. Particles may be ferromagnetic or composites of non-magnetic solids (ores [l], yeasts [2], microorganisms [3], catalysts [4, 51, etc.) with ferromagnetic cores. Wallace [6] and Jaraiz [7] tested an elevator tube which operates by moving magnetic fields generated by overlapping the energization times of subsequent coils. The linear induction transporter (LIT) model configuration is the same as a linear induction motor. The windings consist of three saddle-shaped coils (coils IMII, Fig. 1) distributed among 18 slots, and connected to a three-phase power source with controlled frequency. The LIT can be used as a ferromagnetic transporter with particles moving on an acrylic tray or in a glass tube located over the LIT. Only horizontal transport was tested in this step. It is essential that the field provided by the next coil be sufficient to move the particles to the next tooth when the field of the rear coil diminishes, as well as to accelerate the particle when it is free from the influence of the rear coil. 123
is suspended over a belt, separator. The belt is used
it can be used as a to transport the feed
material into the magnetic field region and to transport the non-magnetics out or to feed them to a high-intensity device. The alternating current that passes through the windings generates a moving linear field which attracts ferromagnetic partitles and transports them to a discharge point, as shown in Fig. 2. The rotary induction transporter (RIT) model configuration is the same as the stator of a rotary induction motor. A threephase winding placed on the stator produces a rotating magnetic field of approximately constant magnitude and sinusoidal spatial distribution along the air gap. RIT models can be used for magnetohydrostatic separation (MHS) of particles based on the difference of the combination of their specific gravities and magnetic properties [8]. The effective gravity and the speed of ferromagnetic fluid rotation are both produced magnetically. At the effective specific gravity of separation, a force balance is struck between the net inward buoyant force on a particle (produced by the outward magnetic attraction of the fluid) and a combination of the direct outward centrifugal and magnetic forces.
Less-magnetic
particles
and/or
those
of a lower
specific
H. R. FLORES et ul. : FERROMAGNETIC
124
PLAN
PARTICLES
IN INDUCTION EXPERIMENTS
Wmm LIT
TRANSPORTERS AND TEST
RESULTS
model
In order to investigate the effects of the system variables listed below, a LIT laboratory model, based on a 3-mm inside diameter tube, was constructed. The horizontal linear velocity of particles was measured for different values of the following parameters : particles : physical properties are given in Table 1 ; frequency : three-phase alternating current of lo-50 Hz ; distance from LIT to tube : c-80 mm ; current magnitude : 0.1-0.9 amps.
Fig. 1. Schematic diagram of LIT.
gravity move radially inwards; more magnetic and/or higher specific gravity particles move radially outwards. Two products or multi-product separation may be obtained depending on the number and radial locations of splitters. A schematic diagram of the model RIT and its separator is shown in Fig. 3. These models are, at present, at the pilot stage of development.
Feed
e!ics
regulated 1
Magnetics
Ferrom>gnetics
Feed
0 A
Side tiew
be1t/ sectiorti
t Ferromagnetics of ferromagnetic
separator
Fig. 2. Ferromagnetic particle separator LIT suspended over the belt of ring-type magnetic separator.
The magnetic field intensity produced at the axis of the tube, in the direction of particle movement: was between 0 and & 0.050 Teslas. With the aim of determining the magnetic field intensity as a function of time and position, a gaussimeter test probe connected to a personal computer I/O stage was displaced along with the particles. Field measures 1000/s were taken during a test time of 3.61 s. The field waveform (curve H-t) is shown in Fig. 4. It has previously been observed that the distance from the LIT to the tube has a strong effect on the efficiency of transport. For distances above 70 mm the forces developed by the LIT are insufficient to enable reproducible operation. For distances less than 8 mm the particle velocities identified from both measurements and visual observations are not always welldefined and repeatable at the same experimental conditions. In this case the influence of the teeth under the particle is too strong and the particle does not advance but instead vibrates about a unique position. In the range 8-70 mm, it was found that the travel time of particles between two marks made on a graduated glass tube is not a function of either the distance or the current magnitude (as would be expected for a synchronous electrical machine). Above a given particle velocity, it becomes a repeatable and unique function of the applied field frequency. The effects of magnetic field frequency (f’) on the lineal velocity of the particle (v) for the four different types of particle listed in Table 1 are shown in Fig. 5. Here it is noticed that the initial slope of the (cl IV) -,fcurve diminishes when particle size increases. At high frequencies, heavier particles (1 and 4) reach terminal velocity before light particles (2 or 3). Heavy particles move at higher linear velocity than light particles. (This becomes evident in a u -fcurve, not shown here.) The field wave velocity is given by )V (cm/s) = 18 f’ (cps). If the ratio of the particle velocity to the wave velocity (a/w) is plotted versus frequency the slope is approximately constant for every particle. This relative velocity diminishes when frequency increases as shown on the right of Fig. 5. The LIT as u ,fhromagnetic separator. LIT was tested with borate ore samples (30-80 mesh) containing magnetite as impurity [9]. These particles were totally liberated because they were added to the borate deposit by wind action. The LIT produced tailings contain relatively little ferromagnetic material. Tailings were kept on the belt and were then treated in a ring-type magnetic separator. The results and the operating conditions are shown in Table 2.
H. R. FLORES et al. : FERROMAGNETIC
PARTICLES
IN INDUCTION
125
TRANSPORTERS
Fixed flowguide (optional)
1-1
Middlings
- --=\-I\
Heavier
and magnetics
Feed
Exci
Water
tina coil
15omm
Fig. 3. Configuration and dimension of the model RIT and rotating magnetic fluid separator.
RIT model The RIT model was tested with a ferromagnetic slurry using a ferrosilicon suspension in a cylindrical receptacle. Revolution speeds of this slurry were measured with frequency as a parameter. Ferrosilicon of 15% Si grade, 90% 325 mesh size, 6.8 g/cm’ specific gravity was employed as the dry component of the suspension. The specific gravity of the slurry was 3.2 g/cm’. Figure 6 shows a plot of the ferromagnetic slurry revolution speed (n) as a function of current intensity (0 for three different frequencies. Below a threshold current, the forces developed by
the RIT are insufficient to rotate the suspension. Beyond this current the ability of the suspension to flow increases faster than the applied field intensity: IZ is greater when I increases. This differs noticeably from the LIT behavior. Tracer experiments using layered bands of colored solids have demonstrated that the RIT has a central region in which forces are very small. This potential problem could be avoided by providing an annular separation space outside a fixed inner wall or a flowguide as shown in Fig. 3. Measurements of linear velocity L’ (or revolution speed n) were repeated many times. Only in those cases where the results of a given set of conditions were repeated 10 times was the
Table 1, Physical properties of particles Particle number I Substance (Fe304) Size (mm) Specific weight (g/cm’) Sp.Sl susceptibility (lo4 &/kg) Weight (mg)
--_-
Artificial 0.83 4.33 3.77 1.30
2 Artificial 0.41 3.93 3.20 0.14
3 Artificial 0.32 3.91 3.21 0.07
4 Natural 0.83 4.60 2.72 1.40
126
H. R. FLORES
el al. : FERROMAGNETIC
PARTICLES
IN INDUCTION
TRANSPORTERS 100 vi/(w
vwvi, cm/(sec mg)
H (Gnuss)
WI),
l/mg
12
60 r--
ssc
=Ow
6
750
800
850 time,
Fig. 4. LIT
950
900
e, CPS
1000
t (microsec.)
*v1/w1 -M-vl/wWl
magnetic field waveform
+- v2/w2 -n- v2lwW2
-#-
v3lw3
*
v4fw4
+
v3/ww3
-)(-
v4lwW4
: ratios tG/Wi and vi/( Wi w) as a function of magnetic field frequencies (f) (w = wave velocity). Particles as identified in Table 1.
Fig. 5. LIT
experiment considered successful. The values of c (or n) are the average of the 10 measurements.
CONCLUSIONS The physical viability of two induction transporters for ferromagnetic solids, the linear induction transporter (LIT) and the rotary induction transporter (RIT), have been demonstrated. It was anticipated that the LIT and RIT models, like any electromagnetic machine, would be sensitive to both the coil current and the frequency. This is the case for the RIT model, as demonstrated with ferromagnetic slurries. However, particle velocity in the LIT model is a function of frequency ; it does not depend on the current magnitude. LIT effectiveness for ferromagnetic separations is good. However, it was observed in the laboratory model that its efficiency as a ferromagnetic transporter is limited. Based on the experimental results: a LIT prototype is being designed for practical use. In order to improve the transporter efficiency it is necessary to optimize the coil configuration to produce a strong moving magnetic field in a wide gap. The RIT model was used to rotate ferromagnetic slurries. This achieves adequate conditions for separation of particles
0, rpm
100
80 -
60 -
40 -
20 -
Table 2. The LIT operating as a ferromagnetic separator I
Partial weight W)
Fraction 30-80 mesh feed Magnetic product Non-magnetic product Distance
from
LIT
100.0 I.0 99.0
Specific susceptibility (K 10’ m’/kg) 21.6 2300.0 4.7
Fe content (%I 0.71 37.0 0.33
to belt : D = 2 cm, H = 0.0 15 Teslas. f = 40 cps
0 0.25 0.5 0.75
I
I
I
I
1 1.25 1.5 1.75 2 2.25 2.5 I, amp.
-'-f=5l.5
cps +f=40.6
Fig. 6. RIT : ferromagnetic slurry current magnitude
cps -f=31;5
cps
revolution speed (n) as function (I) (f= frequency).
of
H. R. FLORES rt al. : FERROMAGNETIC with similar specific gravities and/or magnetic characteristics. At present it is in the pilot plant stage of development.
REFERENCES 1. P. Parsonage, Znnr.J. Miner.
Process. 24, 269
(1988)
PARTICLES
IN INDUCTION
TRANSPORTERS
127
2. R. Daver and E. Dunlop, Biorechnol. Bioengng 37. 1021 (1991). 3. R. Mitchell, G. Bitton and J. Oberteuffer, Waste Treafment .4dt. 4(2), 267 (1975). 4. J. Lindley. IEEE Trans. Magnetics 18 (1982). 5. 1. Zrunchev and T. Popova, Powder Tech&. 64. 175 (1991). 6. A. Wallace and U. Ranawake, Powder Tech&. 64. 125 (1991) 7. E. Jaraiz and J. Briz, Inqenieria Quimica 203, 103 (1986). 8. M. Waler and A. Deverioe, Miner. Process. 31, 195 (1991). 9. H. R. Flores and P. Villagrin, Ma,gtiet. Electr. Separ. 3. 155 (1992).