GB1558747A - Centrifuge and method of operating same - Google Patents

Description

(54) CENTRIFUGE AND METHOD OF OPERATING SAME (71) We, KRAUSS-MAFFEI AKTIENGESELLSCHAFT, a German Body Corporate, of 2 Krauss-Maffei Strasse, Miinchen, Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a centrifuge comprising a centrifugal drum which comprises a perforated jacket and is widened towards the discharge end and to a method of operating such a centrifuge.

Such tumbling centrifuges comprising frusto-conical centrifugal drums are known, for example from German patent specifications Nos. 1,072,199, 1,198,295 and 1,288,990. The purpose of the centrifugal drum tumbling movement is to ensure that for short periods each place on the centrifugal drum jacket is at intervals located at an angle to the centrifugal force action so that the sliding angle of the material subjected to the centrifugal process is reached or even exceeded, so that the material subjected to the centrifugal process slides towards the open drum edge, constantly giving off moisture, and is finally discharged. Consequently, the inclination of the centrifugal drum wall does not have to be adapted to the sliding angle but may be relatively small, which results in constructional advantages.

Tumbling centrifuges used for the separation of materials which are filtered relatively rapidly have, in principle, had proven success. However, a disadvantage of such centrifuges consists in the fact that, due to the tumbling movement, the transporting conditions are dependent on the sliding characteristics of the materials subjected to the centrifugal process, i.e. on the coefficient of friction ,u (My). The various solid substances separated in tumbling centrifuges have different coefficients of friction. In order to make possible an adaption of the respective operating condition to the product characteristics, it is known from German patent specification No. 1,151,223 to make the tumbling angle T adjustable.However, such a mechanical adjustment necessitates a large constructional expenditure, the more so since there arise in tumbling centrifuges considerable restoring forces which have to be absorbed by the tumbling head bearing and, if the tumbling angle is adjustable, also by the adjusting mechanism.

The present invention may eliminate these disadvantages and provide a tumbling centrifuge in which the transport impulse acting on a solid particle can be set without a large, relatively complicated mechanical device.

According to the prior art, the difference between the rotational speeds of the core shaft (n1) and the hollow shaft (n2) is kept small and constant, the hollow shaft rotating approximately 10% more slowly than the core shaft does (see the illustrations in the mentioned patent specifications). By contrast, the invention is based on the novel realisation that the transporting impulse can be varied without any constructional change of the angle between the intersecting shafts and can thus be adjusted for the respective product.This means that the constructionally fixed tumbling angle T is in its effect not identical with the tumbling angle T' which actually brings about the discharge of the material but that the tumbling angle T', which is effective for the transportation of the material, can be varied by way of a change in the speed difference between the core shaft and the hollow shaft.

Thus, according to the invention there is provided a method of operating a centrifuge having a centrifuge drum which comprises a perforated jacket, is widened towards the discharge end and is so mounted as to rotate in use simultaneously about the axis of the drum and about a second axis intersecting but relatively inclined to the drum axis, the former rotation being effected by a core shaft and the latter by a hollow shaft, said method comprising independently driving the core shaft and the hollow shaft at such rotational speeds that the ratio n2 n1 where n1 is the rotational speed of the core shaft and n2 is the rotational speed of the hollow shaft, lies between -5.0 and -0.1, between +0.1 and +0.85, between +1.05 and +1.9 or between +2.1 and +6.0.

The invention also provides a centrifuge constructed in such a manner enabling the method according to the invention to be carried out.

Those value ranges of the speed ratio n2 n1 in which, due to the interrelations, the transporting impulse is 0 or at least so small that a conveyance of the material no longer takes place (values around 0 and 2) and in which there does not take place a transportation across the entire drum, since a speed difference does not exist, or in which the sliding generating line travels too slowly around the drum (value around 1) are to be excluded.

In the value ranges of the speed ratio n2 n, which are smaller than 0 and larger than 2, the effective tumbling angle t' is given a negative value. This means in practice that the position of the sliding generating line is displaced relative to the range of the values from 0 to 2 by 180C in the circumferential direction of the drum. Within these ranges, the absolute value of the effective tumbling angle T' can take larger values than the constructional tumbling angle T does. It is thus possible, by means of the invention, to bring about with a small constructional tumbling angle T the effect of a larger tumbling angle, which brings considerable advantages of space.

The effective tumbling angle T' is approximately given by n2 r'=l 1 -(- ]T, n, when T is the constructional tumbling angle, i.e. the angle between the axis of the drum and the second axis.

The invention is particularly effective if n2 n1 lies between -3.0 and -0.1 or between +2.1 and +5.0.

The setting of the desired speed difference, and consequently the desired effective tumbling angle T', is thus effected in a simple manner, according to the invention, for example by way of the exchange of one of the belt pulleys in the case of a drive through belt pulleys and/or by the interposition of a reversing gear.

The speed control, which can be obtained simply and cheaply, particularly with present-day technology, allows a fine effective tumbling angle T adjustability, which is easy to manipulate during the operation; the speed ranges excluded according to the invention being in this case included, for example for the purpose of a transport stoppage.

In addition to the use of a variable speed gear, it is preferred to use a first electric motor for driving the core shaft and a second electric motor, whose speed can preferably be adjusted for driving the hollow shaft.

The invention is shown in an exemplified embodiment, which will be explained in detail hereafter, in the drawing showing a tumbling centrifuge in a longitudinal section.

The bottom 2 of the centrifuge housing is suspended in pendulum fashion with the aid of three columns 1, of which only one is shown in the drawing. A core shaft 3 is provided with a belt pulley 4 which is connected via vee belts to a belt pulley of a motor 5. At the upper end of the core shaft 3, there is provided a joint driver 8 (Carden joint), on whose opposite side the actual drum shaft 9 is arranged. Connected to the latter is a conical collecting tray 14, to which there is secured by means of ribs 20 a conical centrifugal drum 15 which has the taper angle y and whose jacket is designed as a seive. The collecting tray 14 is screwed to the drum shaft 9 by a nut 13, together with a sliding head 10 which is rotatably arranged between a bearing disc 11 and a sleeve piece 12.

The bearing disc 11 and the sleeve piece 12 are firmly connected to a hollow shaft 7 which is rotatably mounted on the core shaft 3 and merges on its underside in a belt pulley 6. The belt pulley 6 is connected via vee belts to a second motor 19 which is speed adjustable in a manner that is not shown in detail. If the speeds or the directions of rotation of the core shaft 3 and the hollow shaft 7 differ, the collecting tray 14 tumbles, together with the centrifugal drum 15, around the hollow shaft 7.

In the drawing, there is furthermore shown a feeding hopper 17, while 16 represents a cone-shaped shell for draining the liquid expelled by the centrifugal force, 18 represents the outer centrifuge housing with the liquid trough and 21 represents the centrifuge housing.

Hereafter, the tumbling process will be described in detail. As already stated above, the core shaft 3 and the centrifugal drum 15 connected thereto revolve at a differential speed An, which follows from the difference between the two initiated speeds n1 for the core shaft 3 and n2 for the hollow shaft 7, namely: An=n1-n2. (1) According to the prior art, it is usual to keep the differential speed An small relative to n1 and n2 since this was adequate for the required transporting conditions and the bearings were designed for these operating conditions. According to the prior art, different coefficients of friction are considered for different products and, in conjunction therewith, the adaptation of the transporting impulse by a change of the tumbling angle and/or the taper angle y of the centrifugal drum 15.These measures are very expensive from the point of view of both cost and expenditure of time.

However, a consideration of the kinematics of the tumbling centrifuge according to the invention shows that the additionally acting centrifugal acceleration from the relative speed An and the Coriolis acceleration resulting therefrom influence the effectiveness of the tumbling angle; i.e.

the effective tumbling angle T' differs from the construction-dependent tumbling angle 7 if the speed difference is changed. The following relationship exists with a good approximation: n2 T =[ 2|-T- (2) n, This formula shows in which speed range the influence of the differential speed An on the effective tumbling angle to is particularly great.In fact, for small differential speeds An, n2 n1 becomes 1; i.e. the effective tumbling angle T' coincides with the constructiondependent tumbling angle T; this is as a rule 5--7". The greater the difference between n2 and n1, the more the effective tumbling angle T differs from the constructional tumbling angle t.

If n2 - =2, n1 Tl becomes =0; i.e. the tumbling effect is cancelled in this case. An apparatus in which the ratio n2 n, is adjustable during operation thus makes possible a transporting stoppage, i.e. a centrifugation interval. If the values of n2 n, are greater than 2 and the directions of rotation of the shafts 3 and 7 are the same or n2 n, is less than zero so that the directions of rotation the shafts 3 and 7 are oppositely directed, a negative effective tumbling angle 2' is given.

By way of a change of the differential speed, in that either the speed n, or n2 is changed, it is possible to adapt the transporting impulse to the respective product conditions in a simple manner.

There is thus no need for the timeconsuming adjustment of the constructiondependent tumbling angle T. The number of centrifugal drums of varying taper angles, of which a stock had to be laid in with the known tumbling centrifuge without an adjusting means for the tumbling angle, can at least be reduced.

WHAT WE CLAIM IS: 1. A centrifuge comprising a centrifuge drum which comprises a perforated jacket, is widened towards the discharge end and is so mounted as to rotate in use simultaneously about the axis of the drum and about a second axis intersecting but relatively inclined to the drum axis, the former rotation being effected by a core shaft and the latter by a hollow shaft, characterized by means for independently driving the core shaft and the hollow shaft at such rotational speeds that the ratio n2 n1,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   14 tumbles, together with the centrifugal drum 15, around the hollow shaft 7.

   In the drawing, there is furthermore shown a feeding hopper 17, while 16 represents a cone-shaped shell for draining the liquid expelled by the centrifugal force, 18 represents the outer centrifuge housing with the liquid trough and 21 represents the centrifuge housing.

   Hereafter, the tumbling process will be described in detail. As already stated above, the core shaft 3 and the centrifugal drum 15 connected thereto revolve at a differential speed An, which follows from the difference between the two initiated speeds n1 for the core shaft 3 and n2 for the hollow shaft 7, namely: An=n1-n2. (1) According to the prior art, it is usual to keep the differential speed An small relative to n1 and n2 since this was adequate for the required transporting conditions and the bearings were designed for these operating conditions. According to the prior art, different coefficients of friction are considered for different products and, in conjunction therewith, the adaptation of the transporting impulse by a change of the tumbling angle and/or the taper angle y of the centrifugal drum 15.These measures are very expensive from the point of view of both cost and expenditure of time.

   However, a consideration of the kinematics of the tumbling centrifuge according to the invention shows that the additionally acting centrifugal acceleration from the relative speed An and the Coriolis acceleration resulting therefrom influence the effectiveness of the tumbling angle; i.e.

   the effective tumbling angle T' differs from the construction-dependent tumbling angle 7 if the speed difference is changed. The following relationship exists with a good approximation: n2 T =[ 2|-T- (2) n, This formula shows in which speed range the influence of the differential speed An on the effective tumbling angle to is particularly great.In fact, for small differential speeds An, n2 n1 becomes 1; i.e. the effective tumbling angle T' coincides with the constructiondependent tumbling angle T; this is as a rule 5--7". The greater the difference between n2 and n1, the more the effective tumbling angle T differs from the constructional tumbling angle t.

   If n2 - =2, n1 Tl becomes =0; i.e. the tumbling effect is cancelled in this case. An apparatus in which the ratio n2 n, is adjustable during operation thus makes possible a transporting stoppage, i.e. a centrifugation interval. If the values of n2 n, are greater than 2 and the directions of rotation of the shafts 3 and 7 are the same or n2 n, is less than zero so that the directions of rotation the shafts 3 and 7 are oppositely directed, a negative effective tumbling angle 2' is given.

   By way of a change of the differential speed, in that either the speed n, or n2 is changed, it is possible to adapt the transporting impulse to the respective product conditions in a simple manner.

   There is thus no need for the timeconsuming adjustment of the constructiondependent tumbling angle T. The number of centrifugal drums of varying taper angles, of which a stock had to be laid in with the known tumbling centrifuge without an adjusting means for the tumbling angle, can at least be reduced.

   WHAT WE CLAIM IS: 1. A centrifuge comprising a centrifuge drum which comprises a perforated jacket, is widened towards the discharge end and is so mounted as to rotate in use simultaneously about the axis of the drum and about a second axis intersecting but relatively inclined to the drum axis, the former rotation being effected by a core shaft and the latter by a hollow shaft, characterized by means for independently driving the core shaft and the hollow shaft at such rotational speeds that the ratio n2 n1,

   where n, is the rotational speed of the core shaft and n2 is the rotational speed of the hollow shaft, lies between -5.0 and -0.1, between +0.1 and +0.85, between +1.05 and +1.9 or between +2.1 and +6.0.
2. 2. A centrifuge as claimed in Claim 1, characterized by means for adjusting the ratio n2 n, during operation of the centrifuge.
3. 3. A centrifuge as claimed in Claim 1 or 2, characterized in that the means for independently driving the core shaft and the hollow shaft comprises a first electric motor for driving the core shaft and a second electric motor for driving the hollow shaft.
4. 4. A centrifuge as claimed in Claims 2 and 3, characterized by means for adjusting the speed of the second electric motor.
5. 5. A method of operating a centrifuge having a centrifuge drum which comprises a perforated jacket, is widened towards the discharge end and is so mounted as to rotate in use simultaneously about the axis of the drum and about a second axis intersecting but relatively inclined to the drum axis, the former rotation being effected by a core shaft and the latter by a hollow shaft, said method comprising independently driving the core shaft and the hollow shaft at such rotational speeds that the ratio n2 n1, where n, is the rotational speed of the core shaft and n2 is the rotational speed of the hollow shaft, lies between -5.0 and -0.1, between +0.1 and +0.85, between + 1.05 and +1.9 or between +2.1 and +6.0.
6. 6. A method as claimed in Claim 5, characterized in that the ratio n2 n, lies between -3.0 and -0.1.
7. 7. A method as claimed in Claim 5, characterized in that the ratio n2 n, lies between +2.1 and +5.0.
8. 8. A method as claimed in Claim 5, 6 or 7, characterized in that the value of the effective tumbling angle Tt given by n2 T =[l(I]T n, is greater than the constructional tumbling angle T, the latter being the angle between said axes.
9. 9. A centrifuge as claimed in Claim 1, substantially as hereinbefore described.
10. 10. A method of operating a centrifuge, substantially as hereinbefore described.