US3662947A

US3662947A - Centrifuge drum with discharge openings

Info

Publication number: US3662947A
Application number: US23337A
Authority: US
Inventors: Kurt Pause
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-03-27
Filing date: 1970-03-27
Publication date: 1972-05-16
Anticipated expiration: 1989-05-16

Abstract

A drum for centrifuges processing substances of relatively high viscosity. The drum has a peripheral wall concentric with its axis of rotation and opposite axial end walls. Outlets are provided in the region of the opposite axial end walls. A plurality of outlet openings are provided in the peripheral wall and each of these has the configuration of a geometric ellipse with the longer axis of the ellipse being normal to the axis of rotation of the drum. A method of making such a drum is disclosed also.

Description

United States Patent Pause 1 May 16,1972

[ CENTRIFUGE DRUM WITH DISCHARGE OPENINGS [72] Inventor: Kurt Pause, Zedemstrasse l3, Grevenbroich, Germany [22] Filed: Mar. 27, 1970 [21] Appl. No.: 23,337

[30] Foreign Application Priority Data Feb. 27, 1970 Germany ..P 19 16 280.2

[52] US. Cl. ..233/47 R, 210/380 [51] Int. Cl [58] Field of Search ..233/1 R, 2, l C, 46, 47 R,

[56] References Cited UNITED STATES PATENTS 955,889 4/1910 Marshall ..233/2 2,688,437 9/1954 Monnet ..233/46R FOREIGN PATENTS OR APPLICATIONS 436,496 10/1935 Great Britain ..233/46 190,91 1 4/1906 Germany ..233/2 945,318 7/1956 Germany ..233/2 336,865 10/1930 Great Britain ..233/2 Pn'mary Examiner-Jordan Franklin Assistant Examiner-George H. Krizmanich Attorney-Michael S. Striker Filed under Rule 478 [57] ABSTRACT 5 Claims, 2 Drawing Figures Patented May 16, 1972 3,662,947

I I Q i y g 1 v. v I;

FIG. 2

INVENTORI Kwz'r PAUSE ATTORNEY CENTRIFUGE DRUM WITH DISCHARGE OPENINGS BACKGROUND OF THE INVENTION The present invention relates to a centrifuge, and more particularly to a drum for a centrifuge. Still more particularly the present invention relates to a drum for a centrifuge which processes at least at times materials of relatively high viscosity, and to a method of making such a drum.

During the periodic operation of a centrifuge the drum is subjected to increasing loading, that is from start-up the load acting upon the drum increases from zero to a maximum value. This recurs during each operation of the drum and because the recurrence is very frequent, the life expectancy of the drum must be evaluated with reference to the dynamic behavior of the material from which the drum is made. It is therefore necessary in constructing such a drum to consider all occurring stresses in terms of the strength and resistance characteristics of the material under the influence of such stresses.

Centrifuges are used in the sugar-producing industry for processing so-called filler mass. There are wide differences between the separating behavior of filler masses in that sometimes the separated liquid phase may have a low viscosity whereas at other times it may have a rather high viscosity. If the liquid phase has a lowviscosity it is necessary, in order to assure proper operation of the centrifuge and proper separation, to throttle the escape of the low-viscosity liquid phase for which purpose the centrifuge drum is provided with outlet openings only in its opposite axial end walls, or in the region thereof. This arrangement has the advantage that the outlet openings are arranged in those regions of the drum where the stresses acting upon the drum are at a minimum. Because of this it is possible to substantially reduce the wall thickness of the center part of the drum. In other words, the largest portion of the peripheral wall of drums used for separating from filler liquid phase of low viscosity, is imperforate. This of course necessitates long distances to be'traversed by the liquid phase before it can issue from the outlet openings of the drum. However, where the liquid phase is of low viscosity this is of no importance and thus the wall thickness of the circumferential wall of the drum may be selected in accordance with nominal stresses and the drum can be economically manufactured and lightin weight because stress-concentration factors and notch fatigue strength need not be considered.

However, drums constructed in this manner cannot be used for the processing of masses where the liquid or flowable phase is highly viscous, for instance molasses. Under these circumstances the flow paths to be traversed by the separated flowable phase are too large or long, so that the separation of the flowable phase will be irregular and operating difficulties are experienced. The reason for these operating difficulties has been found to be the following: Using thin-walled centrifuge drums of the type which is conventionally employed with filler masses from, which low-viscosity phase is to be separated, for the separation of high-viscosity phase, causes outward bulging or deformation of the circumferential wall of the drum, and an accumulation of separated syrup-that is relatively high-viscosity phase-at the inner side of such bulge. When the drum is braked down, the thus accumulated syrup will flow to the lowermost axial endof the drum under the influence of centrifugal force and leave the drum through the outlet openings provided in the region of this axial end. However, while this presents no problem if the syrup has relatively low viscosity, a difficulty arises if the syrup is of relatively high viscosity. Specifically, high viscosity does not have sufficient time during the short braking period of the drum to flow towards the lower axial end of the drum and instead becomes backed up and is drawn back into the already dry sugar by capillary action, that is its'ejection under the influence of centrifugal force during rotation of the centrifuge is reversed as soon as the centrifuge is braked.

A further problem resides-if the phase is highly viscousin the fact that the long flow path to be traversed causes irregular ejection of the phase even while the drum rotates. It is thus necessary that there be short flow paths provided in centrifuge drums in which the flowable mass to be separated by centrifuging has relatively high viscosity. In fact, the critical value for the flow paths is between approximately 200 and 250 mm.

It is for this reason that materials from which highly viscous flowable phases are to be separated are processed in centrifuge drums which are perforated over the entire axial length of their circumferential wall. However, under these circumstances the wall must be particularly thick because of the perforation over the entire axial length. The reason for this is that the selection of field conditions in a field with drilled circular holes is limited by the notch-strength influences. lt is possible to reduce to some extent the notch tension with reference to an individual opening by careful selection of the bore diameter as related to the spacing between the bores within one row of bores in circumferential direction and with reference to the axial distance between the rows of bores. However, the notch influence on the maximum tension at the edge of the bore, which is triple the nominal tension in case of the individual bore, can at most be reduced to 2.5 times the nominal tension. It is not sufficient, and in fact it is impossible by increasing the wall thickness of the drum in such a manner as to proportionately decrease the tension, because owing to the operating circumstances involved in a centrifuge drum the mass of the circumferential wall is self-loading. The inherent or self-loading, expressed in tangential tension, remains constant with reference to the wall thickness of the drum. The considerations in constructing a centrifuge drum must always be such that the material used for the drum will have a permissible load limit which is far above the load to which the drum will be subjected by the presence of its own mass under centrifugal conditions. Only then is it possible for the drum to withstand additional load resulting from the presence of the material to be processed.

0n the other hand, the ability to withstand such an additional load decreases with increasing wall thickness, related to such wall thickness. Once a certain thickness of the wall is reached, a further thickness increase will no longer provide any improvement because the inertial moment of the filled drum becomes so large that the economic feasibility of the entire centrifuging process becomes questionable.

As suggested before, to assure that highly viscous flowable phase separated from the contents of the centrifuge drum will properly be ejected from the drum, it is necessary that bores be provided over the entire surface area of the circumferential wall of the drum. The presence of such bores, however, produces in the circumferential wall notch stresses which are significantly higher than the nominal stress so that heretofore it was necessary to increase the wall thickness of the drum, thus losing the advantages which are obtained from a small wall thickness.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to overcome the aforementioned disadvantages.

More particularly it is an object of the present invention to provide a centrifuge drum which is capable of centrifugally separating high-viscosity flowable phases without difiiculty and without having to forego the advantages of the type of centrifuge drum utilizing a circumferential wall of small thickness.

It is a concomitant object of the present invention to provide also a centrifugal drum wherein the particular flow-path requirements of a highly viscous flowable phase are taken into account.

A concomitant object of the invention is to provide the aforementioned advantages in a centrifugal drum of at least 750 mm axial length.

Still another object of the invention is to provide a method of making such a drum.

In pursuance of the above objects, and others which will become apparent hereafter, one feature of the invention resides in the provision, in a centrifuge and particularly in a periodically rotating centrifuge for substances which are at least at times of high viscosity, of a combination which, briefly stated, comprises a drum mounted for rotation about an axis of rotation and having a peripheral wall which is concentric with this axis of rotation, and further having opposite axial end walls. Outlet means is provided in the region of the opposite axial end walls, and a plurality of outlet openings are provided in the peripheral wall and each have the configuration of a geometric ellipse with the longer axis of the ellipse extending normal to the axis of rotation.

With a drum constructed in this manner the flow paths can be selected in accordance with maximum advantage for highly viscous flowable phase, and the openings constructed in accordance with the present invention may be neglected in the considerations of the drum construction insofar as stresses acting upon the circumferential wall of the drum are concerned.

According to the invention the configuration of each ellipse is to be such that its notch effect is smaller than 2 percent so that the tension increasing influence is within the usual distribution of material strength, filler variations, variations in the number of rotations and the like. In other words, the presence of such elliptical openings must not reduce the strength of the circumferential wall with respect to tensions acting upon it. It has been found in this context that a semiaxis ratio in excess of l 5, and preferably on the order of l is particularly advantageous. A centrifuge constructed in accordance with the present invention and utilizing elliptical outlet openings whose configuration is based on this ratio, can have a wall thickness corresponding to the wall thickness conventionally used for centrifuge drums whose circumferential wall is not perforated.

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 DRAWING FIG. 1 is a somewhat diagrammatic axial section through a centrifuge drum constructed in accordance with the present invention;

FIG. 2 is a diagrammatic illustration of an elliptical outlet opening utilized in the centrifuge drum of FIG. 1 in accordance with the present invention, and with the stresses acting upon such opening being illustrated in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Discussing now the drawing in detail it will be seen that in FIG. 1, I have illustrated a centrifuge drum 1 which is conventional in all particulars except for the provision of the apertures in its circumferential wall. The circumferential wall is identified with reference numeral la and the opposite axial end walls are identified with reference numeral lb. The drum is mounted by means of a hub 3 on a shaft 2 for rotation with the latter about an axis defined by the elongation of the shaft. Reference numeral 4 identifies outlet means provided in the region of the opposite axial end walls 112.

Thus far, the drum shown in FIG. 1 is conventional.

However, because the drum of FIG. 1 is to-be capable of operating under circumstances where highly viscous flowable phase is to be separated from the drum contents by centrifuging, and to obtain under these circumstances the advantages which have been outlined and described as desirable above, the drum in FIG. I is further provided with a plurality of outlet openings 5 in its circumferential wall la. These outlet openings are arranged as considered necessary in one or several rows, and in accordance with the desired maximumadvantage flow path which have been found necessary for optimum operation of such drum in separation of high-viscosity flowable phases.

In accordance with the present invention the outlet openings 5 each have the configuration of a geometric ellipse whose longitudinal or major axis extends normal to the axis of rotation of the drum 1, which axis of rotationis coincident with the elongation of the shaft 2. It is necessary, however, that the configuration of the outlet openings 5 be exactly that of a geometric ellipse, as is clearly shown in FIG. 2. In this Figure, I have also illustrated the stresses which act upon the circumferential wall la during rotation of the centrifuge drum 1, in the region of the respective outlet openings 5. The arrow 0' ax in FIG. 2 identifies the axial stress and the arrow at identifies the tangential stress, indicating that the axial stress is so small as to be negligible, so that the centrifuge drum 1 need be constructed only with the expected tangential stresses in mind. The term axial stress of course refers to the axis of the drum 1.

The present invention is based on the realization that two characteristic phenomena take place at outlet openings provided in the circumferential wall of a centrifuge drum. Because of the geometric form chosen for the boundary of the respective outlet opening the surrounding stress is increased to the maximum notch stress. The stress direction acted at the edge of the aperture includes angles with the stress direction of the surrounding stresses and for this reason stress conditions occur at the edge of the aperture which have several axes and which hinder the formations associated with the respective stresses. It follows from this that higher stresses act at the edge of the aperture than would normally occur in the material, and these two influences become evermore' advantageous in an aperture of truly elliptical configuration with stretching of the ellipsis in the tensile direction under maintenance of its exact geometrical elliptical configuration, and reach an optimum at a semi-axis ratio of l 10.-

It must be emphasized that the configuration of the apertures must be in correspondence with an exact geometrical ellipse, and that a merely oval aperture will not provide the results according to the present invention. The reason for this is that an oval aperture will not permit definitions because an oval aperture is terminated at its opposite ends in semi-circular or substantially semi-circular configuration. Because of this the stress-increasing influences which occur in thepresence of an oval aperture are almost equal to those of a circular aperture. They are somewhat more advantageous because the semi-circular curvature merges into the elonga tion of the oval aperture, that the absolute length of the oval is without importance because the notch stresses do not decrease with increasing length of the oval aperture.

It is advantageous, but not necessary, that if the apertures according to the present invention are arranged in rows, the distance between adjacent rows is at most 250 mm, and that the distance between adjacent apertures of any row is also at most 250 mm.

In accordance with the present invention it is advantageous, also, to provide the novel drum by first making the drum with an imperforate wall, and by forming the elliptical apertures by electrochemical material removal. This method of producing the elliptical apertures has the advantage that the material of the circumferential drum wall, particularly at the edge of the aperture, does not undergo any metallurgical changes and remains free of internal tension or stresses. In addition, the configuration of the electrode used for effecting the material removal and formation of the apertures 5, remains unchanged so that the elliptical configuration of the aperture 5 is always reproduceable and the ellipsis will always be geometrically ex act.

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 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.

I claim:

1. In a centrifuge, particularly a periodically rotating centrifuge for substances which are at least at times of high viscosity, in combination, a drum mounted for rotation about an axis of rotation and having a peripheral wall which is concentric with said axis of rotation provided with a smooth inner surface throughout, and opposite axial end walls; outlet means provided in the region of said opposite axial end walls; and a plurality of circumferentially distributed outlet openings provided in said peripheral wall and each having the configuration of a geometric ellipse with the longer axis of the ellipse extending circumferentially of said peripheral wall in a plane which is normal to said axis of rotation, the ratio of the major to minor axes of each ellipse being in the range of substantially 5:1 and 10:1.

2. In a centrifuge as defined in claim 1, wherein said openings are arranged in at least one row.

3. In a centrifuge as defined in claim 1, wherein said openings are arranged in at least two rows which are spaced from one another by a distance of at most 250 mm.

4. In a centrifuge as defined in claim 2, wherein the distance between adjacent ones of said openings is at most 250 mm.

5. In a centrifuge as defined in claim 1, wherein the said ratio is 5: l.

Claims

5. In a centrifuge as defined in claim 1, wherein the said ratio is 5:1.