US2315980A - Centrifuge basket - Google Patents

Description

April 6, 1943. D c. A. oLco'T'r v2,315,980

CENTRIFUGE BASKET Filed March 12, 1941 lNVEA/TOR C. A. 0L C077 7 A T7'ORNEV Patented Apr. d, 1943 INK aerate TENT OFFIC CENTRHUGE BASKET Charles A. Olcott, West Milford, N. J. Application March 12, 1941, Serial No. 382,851

2 Claims.

This invention relates to centrifugal machines and more particularly to the design and construction of an improved basket for such machines, and it is concerned primarily although not exclusively with a basket structure especially adapted for the centrifugal treatment or purging of sugar-bearing materials such as sugar magma massecuite.

A principal object of the present invention is to provide a centrifugal basket having, for a given moment of inertia, a greater strength to resist the disruptive centrifugal forces incident to its operation than has been possible heretofore.

In another aspect of the invention one of its objects is to permit higher rotational velocities in the operation of a centrifugal machine without increasing the danger of the basket flying to pieces and without requiring increased driving power or time to accelerate it to top speed.

Another object of the invention is to facilitate the expulsion of centrifuged materials, such as molasses, through the peripheral apertures or foraminate wall of a centrifugal separator. -A more particular object is to substitute for the tapered apertures or aperture expanders known heretofore.

In accordance with a feature of the invention the foraminate wall of a centrifugal'basket is channeled or grooved in a manner such as to reduce its inertia without correspondingly reducing its strength or such as to increase its strength without a corresponding increase in its inertia.

In accordance with another feature of the invention the tendency of circumferentially grooved portions of the basket to expand, under the influence of centrifugal force, to a greater extent than more rigid portions of the basket is inhibited from causing dangerous stresses or shear.

In another aspect the invention provides for virtual enlargement of the basket apertures without substantially impairing the strength of the basket.

The nature of the present invention and its various objects, features and advantages will appear from a consideration of the embodiment illustrated in the accompanying drawing and hereinafter to be described in detail.

In modern sugar refinery practice the centrifugal machines employed for purging crystalline sugar of mother liquor or the like are in substantially continual operation. They are loaded with a charge of sugar magma, or massecuite, or per- I provide an improved R. P. M., and they represent haps eight cubic feet volume, accelerated rapidly by increased centrifugal forces. These forces are of considerable magnitude in the typical modern centrifugal basket of forty-inch diameter operated at the usual top speed of about two thousand a limiting factor in design and operation inasmuch with further increase the tensile strength of the basket steel may be exceeded and the basket ruptured.

It should be appreciated too that it is possible to make a centrifugal basket of'great strength by using an excessive amount of material, but while the basket would have strength it would have also a correspondingly great moment of inertiaand require so much additional power to accelerate it to top speed in a given time as to offset in large measure the benefits expected from high rotational velocities. The excess material, moreover, itself contributes to the forces tending to disrupt the basket, hence it does not add to the strength of the basket in direct proportion .to its mass.

The present invention is featured in part by a novel and highlyfavorable distribution of the basketsteel calculated to provide greater strength or safety factor with reduced centrifugal stresses.

teferring more particularly now to the :drawing, the invention is there illustrated as embodied in a centrifugal machine of one specific type employed in sugar processing. In general outline the machine comprises the basket I mounted at the top of a vertical drive shaft or spindle 2 and contained within a casing 3. r The casing is so shaped and arranged in well known manner that mother liquor, wash water or the like ex- :pelled through the foraminate wall of the basket them, it will integral annular flange and a corresponding lower head 6 of the same construction. This integral structure is preferably to be forged from a single pierced billet of steel and machined to final dimentions. To the lower head 6 is welded a steel h b I that is fitted to spindle 2 and firmly bolted in position thereon. The welded joint 8 lies in a region where the stresses incident to high speed operation are comparatively small.

The cylindrical wall 4 of basket I has numerous holes If] for the escape of centrifuged molasses or the like. These are arranged in a multiplicity of circumferential rings or rows with the holes in alternate rings preferably staggered in the manner shown in the drawing so that the entire wall is covered with perforations. As aspecific instance of practice which may be borne in mind for better understanding of the principles of the invention, the inside diameter of the basket may be forty inches, its height twenty-four inches, the H holes one-quarter inch in diameter spaced, apart one inch on centers in each ring, with the rings one inch apart.

In accordance with the invention, external circumferential grooves are cut in the basket wall, each groove' overlying and passing through one of the rings of holes, as illustrated. The grooves I I are preferably of rectangular cross-section but rounded at bottom or at the bottom corners, and the width of each groove is the same as, and in any case not substantially in excess of, th diameter of the holes. In the example set forth above the groove width may therefore be one-quarter inch.

Brief analysis will suffice to show one important advantage resulting from the grooves. Thus, it is evident that the circumferential or annular portions of the basket Wall that lie wholly outside, or between, the rings of holes are circumferentially continuous, and that they are therefore well adapted to resist the tension produced in them by centrifugal action. The annular portions in which the holes lie, on the other hand, have mass and therefore give rise to centrifugal forces but they are not circumferentially continuous, being interrupted or broken by the holes it, and therefore they not only contribute very little if any to holding the basket together but also, in a sense, burden the contiguous, continuous portions with added stresses. Considering now the effect of removing material from the last mentioned annular portions, that is, by grooving be seen that these portions are reduced in mass and therefore develop less centrifugal force to burden adjoining portions, while at the same time there is little or no corresponding loss of strength inasmuch as the strength contribution of the broken rings is negligible anyway.

With respect to the depth of the grooves, it is obvious that enough material must be left to define the holes Ill and to resist the outward urging of whatever within the basket bears directly on the grooved ring and to'provide whatever additional strength may be required to withstand the various stresses, other than centrifugal, to which the basket may be subjected. For the specific example hereinbefore presented the grooves are three-eighths of an inch in a three-quarter inch wall.

It is well known in the'sugar processing arts not pass as readily through a wall aperture of uniform diameter as it will through one that tapers or, flares. In one type of construction that economy involved in grooving has been used for many years the holes in the basket wall are simply conical. Aperture of this form are illustrated in the drawing, where they are provided at 12 in the upper and lower pairs of ungrooved rings.

Dissectingany one of the apertures I: it will be seen that a part extends above and another part below the limits of the smaller diameter of the hole. These parts, extending into the otherwise circumferentially continuous inter-ring portions of the basket wall, therefore reduce the cross-sectional area that is effective, by virtue of circumferential continuity, in providing strength to resist centrifugal force. Effective tapering of the apertures is accordingly achieved in this prior art manner at the expense of reduced strength.

I have found that the function of flaring in facilitating the passage of centrifuged materials through the wall apertures is effectively performed by the circumferential grooves in the structure herein described and illustrated. The expansion of the aperture as secured in this manner'is obviously confined to expansion in the circumferential direction, assuming the groove width to be equal to the hole diameter, but the rate of expansion in this direction is so large as to offset the lack of expansion longitudinally of the basket. Quite aside from the greater ease and the basket wall, as compared with flaring each hole, is the fact that effective expansion of the apertures is secured without impairing the strength of the basket and, in fact, with a net increase in the safety or strength of the basket as explained hereinbefore. Insofar as this specific feature of the invention is concerned it will be appreciated that the advantage of expediting passage of centrifuged materials through the apertures is not dependent on the grooves being circumferentially continuous or otherwise extending much beyond the immediate vicinity of each aperture.

To secure advantages not hereinbefore considered but now to be explained, the present invention provides additionally for limitation of the circumferential grooves to certain rings, and more particularly for a combination involving tapered apertures in some rings and grooves in other rings.

All parts of the basket wall are expanded more or less during high speed operation by the centrifugal forces present. The basket heads 5 and 6 are least affected by th centrifugal action and expand comparatively little. Portions of the basket wall adjacent the heads are, by virtue of their integral connection to the heads, restrained from expanding as much as other portions of the wall nearer the mid-ring of the basket. The restraining effect, being communicated from one portion of the basket to another by forces in shear, is not as great where circumferential grooves intervene, and the grooved portions are moreover not as well adapted to withstand the shear forces present as are the ungrooved'portions. Inasmuch as these forces are greatest in the vicinity of the basket heads it is desirable to confine the grooves to portions of the basket Well removed from the heads. Thus the top and bottom pairs of apertured rings may be left ungrooved as shown in the drawing. If the aperture-expanding function of the grooves is desired for these outside rings it can be obtained, with less likelihood of shear occurring, by flaring the holes in these rings, as illustrated, or in any other equivalent manner.

Although the present invention has been dein a plurality of circumferential rings, and an upper and a lower basket head integral with said cylindrical wall, said wall having a plurality of external circumferentially complete grooves each overlying a. respective one of said rings of holes, at least one of the rings of holes nearest the respective basket heads being ungrooved.

2. A machine in accordance with claim 1 in which the holes in the said ungrooved rings are 10 flared outwardly.

CHARLES A. OLCOTT.

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