US3854657A - Drum for a centrifuge - Google Patents

Abstract

A centrifuge drum for a discontinuously operating centrifuge, particularly for separating a liquid phase from a fine-fiber solid phase, the drum having an upper and a lower end and being provided with a circumferential wall provided with a plurality of screen zones having perforations communicating with the interior of the drum wall and a plurality of asymmetric reinforcements provided at the exterior of the drum wall in the region of the screen zones and tapering upwardly and inwardly with respect to the drum wall, and merging with the drum wall in downward direction abruptly and via a small rounded portion.

Description

United States Patent [191 Pause et a1.

[ DRUM FOR A CENTRIFUGE [75] Inventors: Kurt Pause, Grevenbroich; Ernst Ullrich Dregger, Neuss; Gottfried Otten, Grevenbroich, all of Germany [73] Assignee: Maschinenfabrik Buckau R. Wolf Aktiengesellschaft, Grevenbroich, Germany [22] Filed: Apr. 23, 1973 [21] Appl. No.: 353,719

[52] U.S. Cl 233/2, 233/27, 233/47 R [51] Int. Cl... B04b 7/16 [58] Field of Search 233/27, 28, 29, 47 R, l R,

[56] References Cited UNlTED STATES PATENTS 888,320 5/1908 Duemer 210/380 1,770,854 7/1930 Johnson l 210/380 2,342,973 2/1944 Schwarz 210/380 3,319,880 5/1967 Pause 233/2 X 3,334,751 8/1967 .laekel et a1 233/2 X 1 Dec. 17, 1974 3,529,767 9/1970 Keith et al. 233/47 R FOREIGN PATENTS OR APPLICATIONS 1,051,235 2/1959 Germany 210/380 22,055 4/1936 Australia 233/1 D 1,936,921 2/1971 Germany 233/2 Primary ExaminerGeorge H. Krizmanich Attorney, Agent, or Firni-Michael S. Striker 5 7 ABSTRACT A centrifuge drum for a discontinuously operating centrifuge, particularly for separating a liquid phase from a fine-fiber solid phase, the drum having an upper and a lower end and being provided with a circumferential wall provided with a plurality of screen zones having perforations communicating with the interior of the drum wall and a plurality of asymmetric reinforcements provided at the exterior of the drum wall in the region of the screen zones and tapering upwardly and inwardly with respect to the drum wall,

and merging with the drum wall in downward direction abruptly and via a small rounded portion.

5 Claims, 4 Drawing Figures PATENTEBBECITIQH 3,854,657

- SHEEI 10; 2

1 DRUM FOR A CENTRIFUGE BACKGROUND OF THE INVENTION The present invention relates to discontinuously operating centrifuge, and in particular to a novel centrifuge drum for such a centrifuge wherein a mixture of liquid and finely divided solid phases is to be centri- The finely divided solid phase which is here meant is a fibrous mass in which the individual fiber has a diameter on the order of hundredth of a millimeter and a length on the order of tenths of a millimeter. If such fibers are poured in dry condition in a heap, the structure of the heap will be very loose so that the volumetric weight of the thus-poured material will be less than one-tenth of the specific weight ofthe same material in solid condition.

A particular typeof such fibrous material is known as Nylflock, consisting of finely chopped nylon filaments. If such Nylflockis to be processed to produce a textile thread which can be woven, it is know to resortto a method in which the fibers are washed, dyed, surface-impregnated to influence electrostatic charging, and finally the formation of thread. It is known to carry out the first three steps of the method in heated vessels provided with stirring arrangements. In the first step,

50 kg of flock are admixed with 1,000 kg of wash solution, in the second step 50 kg of flock are admixed with 1,000 kg of dye solution and in the third step. 50 kg of flock are admixed with 1,000 kg of impregnating solution. Then, the washing, dyeing and impregnating steps SUMMARY OF THE INVENTION benefits.

In keepingwith these objects, and others which will become apparent hereafter, one feature of the invention resides in a novel centrifuge drum, especially for discontinuously centrifuging a mixture of liquid and finely-divided solid plates. The drum is cylindrical and has a circumferential drum wall provided with perforations. In the region of these perforations the drum wall is provided at its outer circumference asymmetrically with reinforcements which taper axially and inwardly towards the upper end of the drum and which merge towards the lower end of the. drum into the wall thereof via a short rounded portion.

Despite the automation obtainable in accordance with the present-invention it is desired to be able to the loose flock, the liquid having largely run off through the wall of the bag and thereupon through the perforations in the centrifuge drum. When the bag is filled it is closed and a new bag is inserted into thev drum, which is then also filled. This continues until the entire charge of kg of flock has been accommodated in such bags, and usually four bags are required for this purpose. Thereupon the operator starts up the centrifuge and centrifugally removes the last remaining liquid from the flock contained in the various bags in the drum. When the centrifuging process is completed the bags are manually removed from the centrifuge drum,

taken to the next vessel and emptied into the same, for

admixture with the next solution, for instance the dye solution or the impregnating solution. .The empty bags are kept on hand for the next batch of flock.

This manual operation is evidently time-consuming as well as expe sive in terms of the labor involved. In addition it is unpleasant for the operation because the flock and the solution are at temperatures in excess of C. This makes it necessary for theoperator to wear protective clothing, goggles and gloves, but despite this the operator can be annoyed or even endangered by various vapors.

avoid cleaning the centrifuge following each operation. In other words, the centrifuge is to be. able to process charges of flock having undergone anyof the three aforementioned processing steps, that is washing, dyeing and impregnation, and it should not require separate cleaning between the introduction into it of flock having just undergone various different ones of these steps. Pneumatic and/or hydraulic conveying devices used should be self-cleaning, or leave behind no'residual flock. The vesselswith the stirring devices are to be capable of being maintained free of flock residue by pneumatic flushing. The walls, screens and other parts of the centrifuge should be free of flock when the centrifuge contents have been discharged, and stationary components musr be so configurated that mixture cannot splash onto themand contaminate them.

The residual moisture of the flock which hasbeen centrifuged should be identical in all types of flock, that is all types having undergone the various different processing steps, asrelated to the fiber surface. The filling quantity is to be supplied to the drum via a pump.

The admixture of flock and liquid phase takes place in a ratio of 1:20 and assures that if the fiber of the flock is evenly distributed in the liquid, the resulting mixture will rheologically act in the same manner as water. Investigations have shown that the coefficient of flow of such a mixture'is no different from that of water.

Additional investigations have shown that if the mixture contains a uniform fiber thickness inthe solution, the free movement of the individual fibers is lost if the ratio of fibers to solution is changed from 1:20 to 1:15. This means that the distribution of the mixture in the centrifuge drum must be carried out in a condition into one another is no longer possible. In the centrifuge drum, however, after the residual liquid phase has been removed by centrifuging, and assuming a highest speed of rotation of the centrifuge, a volumetric weight is obtained for the fibers of 0.3 kg/dm. This means that an interfelted ring of fibers is formed in the centrifuge drum, and is compressed in radially outward direction. Because the inter-felting prevents the ring of fibers from accommodating itself to its increasing inner diameter, the ring will tear from its inner periphery towards its outer periphery and wedge-shaped gaps will form which converge in outward direction towards the surrounding wall of the drum and extend in longitudinal or axial direction of the drum. If the distribution was even over the circumference and the height of the drum while the fibers had 'freedom of relative movement,

then the tearing of the ring of flock fibers will be evenly distributed over its circumference during further compacting, and will not disadvantageously influence the operations. However, if even distribution did not exist, then the ring will tear unevenly and form imbalances which necessitate shutting-down of the centrifuge.

Because of this it is necessary that the filling of the fiber-liquid mixture into the centrifuge drum take place while the drum rotates, and in order to obtain a controlled exit of the liquid the drum must rotate at increasing speed.

Calculations and empirical tests have made it possible to determine a total outflow cross section which not only reduces the loss of liquid to a minimum, but which also does not prevent an even distribution of the fibers in the incoming fiber-liquid mixture over the circumference and the height of the centrifuge drum.

It is theoretically possible to fill an entire charge of 2,090 dm into a stationary centrifuge drum, and only thereafter to start up and accelerate the drum. In order under these conditions to obtain a uniform distribution over the circumference and height of the drum, the mixture would have to be accelerated to at least 500 rotations per minute, and this would have to be carried out while the fibers are completely free to move relative to one another in the mixture introduced into the drum. This, however, would require that none of the liquid would leave the drum until the rotational speed of 500 rpm is reached. This in turn would mean that the outflow cross section of the perforations in the drum would have to be extremely small, because the acceleration of the drum with the mixture in it would require approximately oneminute from to 500 rpm. In addition, the drum would have to have a volumetric content of 2,000 dm. During increased rpm the pressure of liquid at the inner side of the outflow openings in the drum increases, but the small total outflow cross section would nevertheless require an excessively long centrifuging time. In addition, so large a quantity of rotating mixture which can flow freely in the drum, constitutes a potential danger because of its gyroscopic instability.

Insofar as the filling of the mixture into the drum is concerned, it is necessary that themixture be admitted evenly distributed flock which appears at the near the bottom thereof and will barely rotate, and no splashing of mixture out of the drum will take place. Later, however, the mixture accommodated in the drum will rotate faster and will move up along the wall of the drum, and in addition the thickness of the ring increases in the direction towards the axis of rotation of the drum. Towards the end of the filling operation the drum is almost completely filled and the mixture accommodated in it rotates at a speed which is greaterthan the flow speed of the incoming stream of mixture. Because the incoming quantity of mixture is relatively large per unit of time, its admission inform of a solid stream would cause a local damming pressure on contact with the rotating mixture already in the drum, and would cause strong and uncontrolled splashing. It

is therefore necessary according to the invention that filling of the centrifuge drum be accomplished in such a manner that the mixture is uniformly distributed over the circumference and height of the drum.

The wall of the centrifuge drum is so perforated that the quantity of liquid which passes through the perforations at the intermediate speed of rotation is equal to the incoming quantity of liquid in the stream.

Because the filling operation is carried out while the drum is being accelerated, the volumetric capacity of the drum need be less than half the volume of the total quantity of mixture to be admitted into the drum, namely only 900 dm. This is so because of the following considerations: The mixture is admitted into the drum, which begins to rotate as the admission begins, in an even stream. The pressure of liquid at the inlet to the perforations in the drum wall is initially very low,

and only a little liquid will therefore-pass out of the drum through the-perforations, resulting in the mixture remainging fully flowable so that the fibers in the mixture can move relative to one another. The-smooth inner circumferential surface of the centrifuge drum can accelerate the mixture only as a result of friction, but this friction initially is low and the slip-of mixture and centrifuge wall relative to one another is high. Beacause of this, a quantity of mixture will accumulate in the centrifuge drum. Finally, however, condensed fibrous flock will become deposited on the inner surface of the drum wall and this causes an increase in the friction between this thus-deposited flock and the liquid mixture located in the drum. As a result of this, the ring of liquid rotates faster and this in turn causes an increases in the pressure exerted by the liquid at the inner ends of the perforations in the drum wall. This, in turn, means that an increasing amount of the liquid will pass through the perforations per unit of time. The amount of flock which is deposited and adheres to the inner surface of the drum wall becomes evenly compacted and increases, but the newly incoming mixture of flock and liquid still slips with respect to this ring of compacted fibrous flock and remains fully flowable.'Thus, the ring of flock and mixture in the drum will increase, but the newly incoming mixture will always contact a rotaing liquid mass on which it can become evenly dis tributed. The removal of liquid through the perforations of the drum wall is at the expense of the already of the drum wall. g

The quantity of liquid introduced into the drum during the filling operation increases steadily, and so does the compression of the fibers therein. Finally, 900 drn will be accommodated in the drum, and 1,100 dm will inner side have been centrifugally ejected through the perforations. The flock remaining at the completion of centrifuging will have a volume of only 300 dm In order to assure that the contents after centrifuging can be removed from the drum without leaving any residue behind, the drum must be cylindrical in its configuration and its walls must be without any steps, projections, gaps or undercuts. Because the drum must be a screen drum the original suggestion which offers itself is to place onto the perforated'drum a course screen on the interior, and over this a further interior fine-mesh screen. Usually, such screens are of several pieces and are interconnected in circumferential direction so as to be able to insert it as more or less free standing cylinders into the drum. The pressure of the centrifuged material then presses the screen against the drum wall, and also presses the course and fine screens together. However, it is well known that with such constructions it is impossible to avoid the formation of gaps between the portions of the individual screens, and this would be disadvantageous in the present circumstances.

The drum which is required for use in a centrifuge capable of handling the type of material herein under discussion, must have a certain only limited combined cross sectional area of its perforations, for the reasons set out earlier, in order to obtain a controlled escape of liquid, and this means that the relatively large drum will have relatively few perforations. Moreover, these perforations need not be uniformly distributed over the entire circumferential wall of the drum.

It is known that a cylindrical body will deform, and become outwardly enlarged on rotation about its axis. Despite different wall-thicknesses the degree of deformation will be the same, given the same material, as long as additional forces act upon the cylinder other than those originating in the material of the cylindrical body. If additional forces act upon it, such as material being centrifuged, then a cylindrical body of lesser wall-thickness will deform to a greater extent than a body of greater wall-thickness, given the same additional forces. It is also known that in the case of various wall-thickness but identical additional forces, the deformations which occur in the different wallthicknesses cannot be strictly considered independently of one another, because the zone of heavier wall-thickness will retard the deformation of the zone of lesser wall-thickness. The accommodation of this mutal influence of the portions of different wallthicknesses results in the formation of annular waves in the wall, with the length of one wave being dependent upon a constant andthe root of the product of theradius and the wall-thickness. This means that given the problem involved, the drum wall must be reinforced at appropriate locations. In the case, i.e. with the use of interior screens made of strips which are connected together and form these screens, this means that gaps would form between these strips and that residue of material could accumulate in these gaps. It is, however, precisely a consideration of the present invention that The present invention achieves this by making the centrifuge drum cylindrical, as pointed out before, and

even the last amounts of residue fibers and liquid films be removed from the drum. Even the amount of liquid film which adheres directly to the inner circumferential surface .of the drum wall, is to be removed. This can be obtained only if a pressure differential is formed which in turn can be developed only by a radial difference.

reinforcing it in its outer circumference asymmetrically in the region where the drum wall is perforated. These reinforcements taper upwardly and inwardly, and downwardly (upwardly and downwardly refer to the vertical orientation of the drum) they merge abruptly with a small rounding into the drum wall.

The drum wall is cylindrically recessed over the screen thickness and width. At a distance from one another which corresponds to the width of a screw head, there are provided two'annular channels the bottom walls of which have perforations formed in them. Screen strips inserted into the recess so as to overlie these grooves are of narrow width and are therefore stiff enough so that they can be held by means of countersunk screws without any formation of waves, gaps or the like in these grooves.

The wall of the drum has been given the inventive configuration because of considerations of the forces which are applicable to it duringrotation in filled condition, and in order to assure that even the last remaining film of liquid will flow out of the centrifuge during operation.

The grooves mentioned above, and the tapering of the reinforcing portions upwardly into the relatively thin circumferential wall, provide for a gentle taperingoff of the deformation waves. v

The invention assures that when the centrifugal force of the contents acts upon the screen strip, it will become inclined relative to the circumference of the wall. Directly under the end of the screen strip the smallest deformation will be obtained, and in the sense of the flow gradient of liquid this will be the highest point. The inclination of the strip with reference to the circumference of the wall negates the trough formation resulting from the deformation of the load.

The appropriate selection of the reinforcing means, related to the spacing of the screen strips from one another and the drum radium, creates conditions which assure that even the last residual film of liquid will flow out of the drum during centrifuging.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a somewhat diagrammatic axial section through a novel centrifuge drum according to the present invention;

FIG. 2 is a fragmentary section through a portion of the drum wall, showing the condition the drum wall will assume during centrifugal operation but in the absence of any contents in the drum;

FIG. 3 shows the same portion of the drum wall illustrated in FIG. 2, but this time illustrating how it becomes deformed when there are contents in the drum during centrifugal operation; and

FIG. 4 is a fragmentary sectional detail view, on an enlarged scale, of the detail A in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Discussing now FIGS. 14, it will be seen that in FIG. 1 there is illustrated a novel centrifuge drum according to the present invention. It has a circumferential wall 1 which is vertically oriented for operation of the drum, and is provided with a cover 2 at the upper end and a bottom wall 3 at the lower end. The bottom wall 3 is provided with a bell-shaped hub 4 extending into the interior of the drum and serving to journal the drum for rotation in known manner. In addition, the drum wall, that is the peripheral drum wall, is provided with several zones 5, 6, 7 and 8 in which perforations are provided in the circumferential wall.

The inner surface 9 of the circumferential wall 1 is provided with annular recesses 10 corresponding to the zones S-8, and these grooves 10 have inserted into them cylindrical screen strips 11 (see particularly FIG. 4). The depths of the grooves 10 is such that the exposed surface 12 of the respective strips 11 is flush with the innercircumferential surface 9 of the wall 1.

In the region of the recesses 10 there are always provided two annular channels 13, 14 which extend further inwardly than the basic recess 10, and in whose bottom walls there are provided the perforations 15, 16 through which liquid can escape to the exterior of the drum. The channels 13 and 14 are spaced from one another to such an extent that countersunk screws 17 can be threaded into appropriate bores provided in the wall 1 intermediate them, which screws 17 serve to hold the screen strips 11 in place.

In addition, the exterior of the drum wall 1 is provided in the region of the zones 5-8 with reinforcements 18 which are asymmetrically configurated (see FIGS. 1 and 2). The portion 19 of each reinforcement 18 extends approximately from the middle of the zones 5-8 and terminates slightly below the lower edge 22 of the screens 11. Approximately one-third of the reinforcements 18 is located above the screens 11. Upwardly of the protion 19 there is provided a merging portion 20 which tapers from the reinforced portion 19 into the wall 1. At the lower end the reinforcement portion 19 merges abruptly via a small rounding 21 into the wall 1.

As pointed out before, the wall portion shown in FIG. 2 illustrates how the appearance of the drum wall will be when the centrifuged drum is rotated but contains no material to be centrifuged. FIG. 3, on the other hand, shows the same drum wall, illustrating how it will become deformed when material to be centrifuged is present in the interior of the drum. Of course, although the deformation tendency is properly shown in FIG. 3,

' it will be appreciated that the actual extent of deformation has been exaggerated in order to more clearly illustrate the point involved.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a novel centrifuge drum, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A centrifuge drum for a discontinuously operating centrifuge, particularly for separating a liquid phase from a fine fiber solid phase, said drum having an upper and a lower end and being provided with a circumferential wall having an outer side and a smooth cylindrical inner side and provided with a plurality of screen zones having perforations communicating with the interior of said drum; and a plurality of asymmetric reinforcements provided at said outer side of said drum wall in the region of said screen zones and each comprising a first section tapering upwardly and inwardly with respect to said drum wall and provided with at least one channel communicating with the interior of said circumferential wall, a second section extending downwardly and parallel with respect to said drum wall from substantially midway of the respective screen zone downwardly below the lower edge of the respective screen zone, merging with said drum wall abruptly via a small rounded portion, and providedwith at least one channel communicating with the interior of said drum wall.

2. A centrifuge drum as defined in claim 1, wherein said circumferential wall is provided with a plurality of inner circumferential grooves each located in one of said screen zones, wherein screen strips are accommodated in the respective grooves, and wherein underneath said screen strips each of said grooves is provided with at least one channel communicating with the exterior of said circumferential drum wall via a plurality of perforations. I

3. A centrifuge drum as defined in claim 2, wherein said screen strips are circumferentially complete rings, and wherein countersunk screws are provided which mount said rings in said recesses so as to be flush with an inner circumferential surface of said circumferential drum wall.

4. A centrifuge drum as defined in claim 1, wherein substantially one-third of said portion is located downwardly below the lower edge of the respective associated screen zone. I I

5. A centrifuge drum as defined in claim 4, said reinforcing portions being configurated to provide a gentle tapering off of deformation waves arising during centrifuging.

Claims (5)

1. A centrifuge drum for a discontinuously operating centrifuge, particularly for separating a liquid phase from a fine fiber solid phase, said drum having an upper and a lower end and being provided with a circumferential wall having an outer side and a smooth cylindrical inner side and provided with a plurality of screen zones having perforations communicating with the interior of said drum; and a plurality of asymmetric reinforcements provided at said outer side of said drum wall in the region of said screen zones and each comprising a first section tapering upwardly and inwardly with respect to said drum wall and provided with at least one channel communicating with the interior of said circumferential wall, a second section extending downwardly and parallel with respect to said drum wall from substantially midway of the respective screen zone downwardly below the lower edge of the respective screen zone, merging with said drum wall abruptly via a small rounded portion, and provided with at least one channel communicating with the interior of said drum wall.

2. A centrifuge drum as defined in claim 1, wherein said circumferential wall is provided with a plurality of inner circumferential grooves each located in one of said screen zones, wherein screen strips are accommodated in the respective grooves, and wherein underneath said screen strips each of said grooves is provided with at least one channel communicating with the exterior of said circumferential drum wall via a plurality of perforations.

3. A centrifuge drum as defined in claim 2, wherein said screen strips are circumferentially complete rings, and wherein countersunk screws are provided which mount said rings in said recesses so as to be flush with an inner circumferential surface of said circumferential drum wall.

4. A centrifuge drum as defined in claim 1, wherein substantially one-third of said portion is located downwardly below the lower edge of the respective associated screen zone.

5. A centrifuge drum as defined in claim 4, said reinforcing portions being configurated to provide a gentle tapering off of deformation waves arising during centrifuging.

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