Centrifugal separator having a planetary hub

Centrifugal separator comprising a drum (8) driven in rotation by a main electric motor (1), via a machine pulley (5), a first drive shaft (6) and a reducer (7), a screw (17), surrounded by the drum and driven in rotation by a secondary electric motor (9), via a second and third drive shaft (10, 16), coaxial with the first shaft (6), wherein a module is mounted between the secondary electric motor (9) and the reducer (7) comprising a casing (11), a sleeve (13) and a planetary hub (15), the hub passing through the casing and comprising a first planetary gear (25) rigidly attached in rotation to the hub, the sleeve (13) being disposed around a part of the hub (15) and comprising, rigidly attached in rotation, a second planetary gear (26), at least one axle (27) being mounted parallel to the hub (15) and comprising two satellite gears (29,30,31,32), rigidly attached in rotation to the axle, which engage with the first planetary gear (25) and the secondary planetary gear (26) respectively, at least one of the said axles being mounted so as to turn on the casing (11).

CROSS REFERENCE TO RELATED APPLICATIONS 
This application claims priority from French patent application number 96 
03947 filed Mar. 29, 1996. 
The invention concerns a High Precision Centrifugal Separator with a screw 
conveyor. 
A centrifugal separator comprises a screw conveyor contained in a drum, 
more particularly a cylindro-conical drum, with the same main axis as the 
screw. The drum is driven in rotation by a main electric motor at a speed 
different from the screw which is driven in rotation by a secondary 
electric motor and by a reducer. 
If the speed of rotation of the drum is called V.sub.B the speed of 
rotation of the secondary motor is called V.sub.S and the reduction ratio 
of the reducer is called k, the speed of rotation of the screw is given by 
the formula 
##EQU1## 
i.e. a relative speed of rotation of the screw with respect to the drum of 
##EQU2## 
The user of the centrifugal separator will wish to be able to apply an 
increasing torque to the centrifugal separator to compress the solid part 
decanted to the maximum and thus to increase the dryness of this part. 
The speeds required of the drum and the screw are also very high. These 
high speeds have brought about an increase in the slip of asynchronous 
motors, and similarly an increase in the imprecision of the relative speed 
V.sub.R, in particular for low values of V.sub.R, such as 2 to 3 rpm used 
for compacting the solid. 
It will be seen from equation (2) that in order to obtain greater precision 
for the speed V.sub.R, it is necessary to increase k. 
Now, the usual values of k are situated between 25 and 87 in the case of a 
single stage. It would be desirable to have k ratios which are greater 
than these values, in particular of the order of twice as great, while 
having available a less complex drive system, taking up less space and 
being less costly. 
One would have thought that, in order to achieve this increase in k, that 
it would simply be necessary to mount a single reducer with a ratio of 2 
in series with the k reducer. However, this apparently simply solution is 
not suitable, since although it is true that is enables the precision of 
the relative speed to be increased, it causes on the other hand the torque 
to be divided by two and, moreover, the speed to be multiplied by two, 
which is not acceptable, by reason of the permitted speed for secondary 
motors as well as by reason of the fact that the recycled power remains 
constant. 
Other solutions have been proposed in the form of complex assemblies which 
are both bulky and costly. 
A centrifugal separator is already known from GB-2 016 306 comprising a 
drum driven in rotation by a main electric motor, via a machine pulley, a 
first drive shaft and a first epicyclic reducer, a screw, surrounded by 
the drum and driven in rotation by a secondary electric motor via a second 
drive shaft which is coaxial with the first drive shaft, and a second 
reducer. 
In this document GB-2 016 306, the torque between the screw and the drum is 
measured by measuring the strength of the current through the secondary 
motor and the relative speed is adjusted by a frequency variator, by 
causing the second drive shaft to rotate. 
If the secondary motor has a fixed speed, it is necessary to adjust the 
speed of the casing of the second reducer to obtain the desired relative 
speed. If the secondary motor is controlled by a regulating system, it is 
necessary to make use of costly systems such as a direct current motor and 
a corresponding variator or a mechanical motor-driven variator. 
In either case, the system according to the patent GB-2 016 306 requires an 
adjustment to the speed of the casing. In addition, variations in the 
relative speed are limited on account of the minimum ratio of the cyclos 
of 1/11 for the small reducer and of 1/25 for the main reducer, that is a 
minimum of 1/275. 
Finally, in the case of a variation in the speed of the shaft with a motor 
driven frequency variator, it is absolutely necessary for the speed of the 
shaft to be greater than the speed of the casing in order to drive. In the 
contrary case, the variator disconnects. In follows that the shaft turns 
at high speeds (3000 to 6000 rpm) which is detrimental. 
From the document FR-A-2 610 058 a module is known comprising a casing, a 
sleeve and a planetary gear hub, the hub passing through the casing and 
comprising a first planetary gear rigidly attached in rotation to the hub, 
the sleeve being disposed around part of the hub and comprising, rigidly 
attached in rotation, a second planetary gear, an axle being mounted 
parallel to the hub and comprising two satellite gears which engage with 
the first planetary gear and second planetary gear respectively. In 
addition, a satellite gear carrier is provided on which are mounted the 
axles of the satellite gears so that they can rotate, the satellite gear 
carrier being maintained, rigidly attached in rotation by a reaction arm 
acting on the end of the shaft of the satellite gear carrier, the axles of 
the satellite gears not being rigidly attached to the casing of the 
device. To replace the second reducer of the device described in GB-2 016 
306 by the module described in FR-A-2 610 058, would make the system 
costly and complex. 
In addition, to replace the second reducer of GB-2 016 306 by the module of 
FR-A-2 610 058 would bring about the following disadvantages. Since the 
input shaft is driven by the satellite gears and the secondary motor, the 
latter being fixed, the relative speed would then be nil. In addition, if 
the motor is made to revolve in one direction or the other, the first 
planetary gear will shift the speeds between the satellite gears and the 
input shaft, resulting in a positive or negative relative speed. It 
follows that the relative speed only depends on the speed of the motor 
which is always driving. It follows that the relative speed cannot vary in 
relation to requirements, in particular in relation to the degree of 
dryness of the solid to be centrifuged. In order to vary this relative 
speed, it is necessary to add a motor-driven reducer to the assembly, 
which makes the system even more complex. The installed power is low on 
account of the fact that the reduction ratio is of the order of 1/200, 
i.e. for V.sub.R =5 a motor speed of 1000 rpm, which is low. The system is 
thus costly if it is desired to obtain a high torque. In addition, it is 
difficult to position a bearing on the end of the block due to the 
diameter being too large and due to difficulties in precisely centring the 
rotor on the drum, taking into account the large number of parts packed 
together. 
SUMMARY OF THE INVENTION 
The invention concerns a centrifugal separator with a screw conveyor which 
makes it possible to obtain a better precision over the relative speed 
with a reduction in the installed power of the motor, this device being 
however in the form of a simple assembly which is economical and takes up 
little space. 
According to the invention, a Redex module is provided, mounted between the 
secondary motor and the epicyclic reducer. 
This Redex module (trade name) which can be obtained from the Redex Company 
45210 FERRIERES, FRANCE, is described in detail in the REDEX company's 
catalogue entitled "Differentials and Reducers-Series Module SR 50 to 280 
000 Nm". 
This combination of a cyclo-reducer, a centrifuge and a Redex module thus 
enables the overall reduction ratio to be increased while maintaining the 
applied torque between the screw and the drum and while reducing the 
recycled power. This result is obtained by simply adding a Redex module. 
The final assembly is simple and takes up little space and hence is not 
costly. 
Moreover, the Redex module is easily added to the existing module and may 
be manufactured on a large scale in an economical manner. It is easy to 
override without dismantling in order to obtain relative speeds which are 
doubled when the machine is multi-purpose and can process several 
products. 
This Redex module is constructed according to the principle involving a 
system with a train of epicyclic gears with multiple satellite gears, and 
a description of this is given below. 
According to one advantageous embodiment, the Redex module is mounted 
directly at the output from the secondary drive motor, coaxially to the 
drive shaft of the screw, a shaft which is driven in rotation by the 
secondary drive motor and upstream from the machine pulley which is 
mounted rigidly on the drive shaft of the outer casing of the main 
reducer, rigidly attached in rotation to the cylindro-conical drum, and 
which is driven by the main motor via a first pulley coaxial with the 
shaft coming from the main motor and by a belt transmitting the movement 
of the first coaxial pulley to the machine pulley. 
This embodiment is particularly small and easy to construct. Moreover, it 
allows easy access to the Redex module and enables it to be replaced by a 
Redex module having different parameters according to the requirements 
relating to each application for the centrifuge. 
According to an improvement of the invention, the planetary sleeve of the 
Redex module is mounted rigidly in rotation to the machine pulley which 
transmits the torque of the main motor to the outer casing of the reducer, 
itself mounted rigidly in rotation to the drum, while the hub of the Redex 
module is mounted rigidly in rotation to the drive shaft of the screw and 
the outer casing of the Redex module is mounted rigidly to the output 
shaft of the main motor. 
The speed of rotation of the hub is then exactly proportional to the speed 
of rotation of the casing, in a ratio K. The same relationship is thus 
obtained, as regards the relationship between these two speeds of 
rotation, as in the case where another single reducer is mounted in series 
with the reducer, without however having to suffer the disadvantages 
associated with the use of a single reducer (increase in speed without 
reduction in power). 
If the sleeve is not locked and is driven for example by the drive pulley, 
the relationship between the speeds of rotation will be certainly more 
complex, but the precision over the relative drum-screw speed will however 
be improved in relation to devices of the prior art, whilst also reducing 
the power applied. 
According to an improvement to the invention, it is also possible to 
provide detachable means for fixing the sleeve for example by sliding, 
designed to attach the sleeve rigidly in rotation to the outer casing of 
the Redex module in a releasable manner. 
By virtue of this rigid attachment in rotation, it is thus possible to 
override the Redex module entirely and thus to have available a centrifuge 
with a single reducer, which may be useful in cases where is desired to 
have available a high relative speed between the drum and the screw. 
Table 1 below shows the various ranges of variation for V.sub.R and the 
power necessary for various values of the ratio k.sub.2 of the Redex 
module, compared with the case where a Redex module is not used. 
TABLE 1 
______________________________________ 
k1 k2 k total V.sub.R 
Power 
cyclo Redex k.sub.1 .times. k.sub.2 
rpm kW 
______________________________________ 
71 . . . 71 0 to 28 
17.8 
71 2 144 0 to 16 
7.8 
71 2.72 193 0 to 12 
5.2 
71 3.33 272 0 to 8 
3 
______________________________________

DETAILED DESCRIPTION 
In FIG. 1, the centrifuge comprises a first drive motor 1 from which a 
first drive shaft 2 emerges which transmits the drive torque of the motor 
to a machine pulley 3, to which it is rigidly attached in rotation. 
This machine pulley 3 transmits the movement to a second main machine 
pulley 5 by means of a transmission belt 4. The main machine pulley 5 is 
keyed to a first primary drive shaft 6. This primary shaft 6 is rigidly 
attached in rotation to the outer ring gear of a cyclo-reducer 7 on which 
is mounted the cylindro-conical drum 8 of the separator, rigidly attached 
in rotation. 
The centrifugal separator comprises a second secondary motor 9 from which a 
second drive shaft 10 emerges which is mounted rigidly attached in 
rotation to the outer casing 11 of the Redex module 12. 
The sleeve 13 of the Redex module is mounted rigidly in rotation to the 
main machine pulley 5 by appropriate means of attachment 14 (screw). 
Finally, the hub 15 of the Redex module is mounted rigidly attached in 
rotation to a third drive shaft 16 which is mounted rigidly attached in 
rotation to the screw 17 of the separator. 
The speed of rotation of the main motor may be between 1000 and 2000 rpm 
and the speed of rotation of the secondary motor may be between 2000 and 
4000 rpm, the torques applied being between 100 and 1000 Nm and between 20 
and 200 Nm respectively. 
FIG. 2 is a perspective view of a Redex module 12. 
This Redex module 12 consists of an outer casing 11, made in the form of a 
water-tight monobloc cast iron cylinder and two cast iron side covers 19, 
20, which close off the casing laterally. 
The outer casing 11 is traversed by a cylindrical hub 15 which extends 
coaxially to the axis of the cylinder 18 and which comprises a first 
section extending outwards from the casing 11, on the outside of the cover 
20, a second section extending to the inside of the casing 11, on the side 
of the cover 20, over approximately half the axial length of the cylinder 
18, a third section extending to the inside of the casing 11, on the side 
of the cover 19, over the remainder of the axial length of the cylinder 18 
and a fourth section extending outwards from the casing 11, on the outside 
of the cover 19. The hub 15 is attached to the casing 11 by means of a 
fixing ring 33 so as to be able to turn about its axis. 
A first planetary gear 25 is disposed about a part of the second section, 
rigidly attached in rotation to the hub 15. 
A sleeve 13 is disposed around the third and fourth sections of the hub 15 
and comprises a second planetary gear 26 disposed around a part of the 
third section, rigidly attached in rotation to the sleeve 13. The sleeve 
13 is attached to the casing 11 by a fixing ring 34, so as to be able to 
turn about its axis. 
Two axles 27, 28, parallel to the axis of the cylinder 18, are mounted, so 
as to turn, on the outer casing 11 of the Redex module. The satellite 
gears 29, 30, 31, 32 are mounted coaxially on these axles, covering and 
rigidly attached in rotation with these axles 27, 28. 
The satellite gears 29 and 31 have the form of a toothed wheel and each of 
these engages with the toothed wheel of the second planetary gear 26 while 
the satellite gears 30 and 32 also have the form of a toothed wheel and 
each engages with the toothed wheel of the first planetary gear 25. 
The first drive motor 1 turns a drive shaft 2 which results in rotation of 
the first main pulley 3 and second main pulley 5. Rotation of the second 
main pulley 5 causes rotation of the primary drive shaft 6 which is 
affixed to the outer casing of the cyclo-reducer 7. Rotation of the 
exterior casing of the cyclo-reducer 7 causes rotation of the conical drum 
8. Rotation of the second main machine pulley 5 also causes rotation of 
the sleeve 13 and planetary gear 26 of the module 12. Thus, applying power 
to the first drive motor 1 results in rotation of the conical drum 8, 
sleeve 13 and planetary gear 26. 
The second drive motor 9 is affixed to the outer casing 11 and cylindrical 
hub 15 of the module 12. Rotation of the cylindrical hub 15 results in 
rotation of the drive shaft 16 and screw 17, which passes through the 
reducer 7. Thus, applying power to the second motor 9 causes rotation of 
the outer casing 11, cylindrical hub 15, drive shaft 16 and screw 17. 
By varying the speeds of the first motor 1 and second motor 9, a user can 
alter the rotational speeds of the drum 8 and screw 17.