US3409521A - Method of manufacturing centrifuge discs by electrochemical machining - Google Patents

Description

Nov. 5, 1968 SHARP T. D LES METHOD OF MANUFACTURING CENTRIFUGE DISCS BY ELECTROCHEMICAL cumme Filed April 2 1965 INVENTOR.

THOMAS D. SHARPLES W I ATTORNEY United States Patent I 3,409,521 p v METHOD OF MANUFACTURING CENTRIFUGE" DISCS BY ELECTROCHEMICAL MACHINING Thomas D. Sharples, Lansdale, Pa., assignor to 'Pennsalt Chemicals Corporation, Philadelph ia,=1?a;, a corporation of Pennsylvania I Filed Apr. 22, 19 65, Ser. No. 449,965 f 6 Claims. (Cl. 204143) I ABSTRACT THE DISCLOSURE 1 Centrifuge discs are madeby s uli'n'g a discblankof frusto-conical shape to an electrode and placing an electrode of opposite polarity 'in spaced opposing relation theretoimasking off portionsiofthel'disc which areitofbecome protruding spacer portions on the,, disc,' flowing an electrolyte through the space between the disc'blank} and the electrode of oppos'itefpolarity, and passing an electric current between the two electrodes in order to electrochemically machine ing portions.

.This invention relates to centrifuge discs. More specifically. this invention relates to frusto-conical discs .adapted to be stacked and positionedinside a centrifuge bowl to increase the separating efliciency; The inventionparticularly relates to -a centrifuge disc having special sanitar features and to a process for making such adisc.

The prior artisreplete with centrifuge bowlsaofithe solid type adapted to be run continuously. In operation such solid bowl centrifuges continuously receive a feed mixture. Centrifugal force will. move the heavier particles outward toward the periphery of. thebowlwhile the. lighter particles will be displacedinwardly. In-such an operation efiiciency is low because each lighter particle disposedad: jacent the periphery of the bowl as it'moves inward bucks the outward movement of the heavier particles, and viceversa. v p

To improve eflicie ncy a stack of frusto-conical discs, one nested within the other, is provided in the bowl. The outwardly flowing particles form an outwardly flowing layer on the underside ofeach frusto-gonical disc while the inwardly moving lighter particles form an inward layer on the upper side of each disc.. In this mannerthe 3,409,521 trea e oer-.5112

In most 'cases "the frusto-conical' b'ody' portion ofj the disc has been'a stamping -'of sheet metal formed from a flat sheetand drawn to'the frusto-conical fshapefAlter n'ativcly, the discs, especially in the large dimensions,'have been cut from a flat sheet and spun about a' mandrel.

A common wayof forming the spacing element-to the individual disc-member has been to cutout individual strips and secure them in a radial disposition to the top of the disc elements by spot-welding techniques. This, how- 'ever, is a multi-ste'ppr'o'cedure and has a primary objection in that cracks appear between the 'spacing'ele'ment and the individual disc members'These cracks provide away the space between the protrudopenings in' which process' fiuids may 'stagnate andco'ntaminate the subsequent process fluid. Such ctacks are difficult to clean. In sanitary applicatlhns, for"inst ance, milk purifying, the condition is extremely serious.- To over' come this objection soft solder: has been placed along the juncture between' the sides of the spacers and the'discs to'create' fillets to keep out contaminants and'make the discs easier toclean. However, this hasadded yet another step to the already complicated and expensive disc-manufacturing procedure.

Spot-welding techniques for securing the spacing elements to the disc member have also been objectionable in that certain metals of which the parts must occasionally be made are weldable only in certain inert atmospheres.

1 Also the metallurgy of such metals has broken down a during the welding.

- Another common way to form spacers has been to raise a protuberance on the upper surface of the disc.This is disclosed in US. Patent 1,474,379. In making stacks of discs formed in this fashion the discs are staggered to avoid inward and outward movement of the respective layers,

are efliected without the hindrance of the, oppositely moving particles. This results in greatly improved efficiency, There have been may varieties of discs disclosed in the prior'art. Almost all of thesediscs incorporate as an integral portion of their structure or as a separate attachment spacer elements, usually radial, which extend upward from the top surface. of the frusto-conical disc. :These spacer elements serve to hold each disc apart from theone above it so that there is a frusto-conical channel in between the two adjacent discs permitting the previously mentioned layer' movement therebetween. Each of the discs of the prior art have also been provided with central openings adapted to receive the centrifuge center tube. The openings have radial slotswhichreceive a key-on the center tube to hold the discs'in rotation' 'with'the centrifuge bowl. The slots and key also assure thaton the coincidence of a proturberance with an indentation on the underside of the'disc above. An objectionto this method of making discs is the turbulence caused by the indentation on the underside of the discs. 1

. Spacing elements havealso been provided by actually puncturing the discs and bending on a metal staple-like applianceto serve as a spacer. Such'an arrangement" is shown in the U8. Patent 1,026,271. Y

In many cases the spacing elements serve as vanes to assure the rotary movement of the fluidwithin the disc stack. For reasons well recited in the prior art, it has occasionally been desirable to make the spacing elements of arcuate shape and secure them to the top of disc stack members. This procedure has involved individual plotting and cutting of the spacing elements and carefully securing them to the top of the individual disc member. Slight irregularities in the shape of 'the individual spacing. elements have raised a balancing problem and even' this expensive and complicated manufacturing procedure has not produced an entirely satisfactory product. Therefore it rnay readily be seen that for years the art has searched for a suitable process for manufacturingcentrifuge discs having integral spacers, a process that would be simple and inexpensive and produce an integral sanitary product.

' 1 The present invention provides the answer for which reassembly the discs will 'be returned to'the -dis'c"stack in the same radial orientation in which they were dis-*- as'sembled. This is: important since balance is"extremely significant in centrifuges of high speed. In addition, 'it' assures alignment of the spacer elementsone on'top of the other so that'the stack is not springy under compression; "*1 Methods for producing the discs which-comprise' the disc stack of the i rior=arthave been many varied.

the art has been seeking. It involves a centrifuge disc electrode and placing an electrode of opposite polarity in spaced opposing relation thereto, masking'off por-' tions of the disc which are to become the protruding rp'ortio'ns, flowing an electrolyte through 'the space be-' tween the disc blank and the electrode of opposite polarity and passing an electric current between the .two electrodes to electro-chemically tween the spacers.

machine away the space .be-'

g per electrode positioned thereabove;

Other features of the invention will be understood from a reading of the following specification and reference to the drawings in which:

FIGURE 1 is a schematic view representing a frustoconical disc blank mounted on an electrode with the up- FIGURE 2 is an enlarged fragmentary sectional view of a portion of the disc blank which will form a protruding portion such as a spacer element and clamped into the electro-chernical machining device;

FIGURE 3 is an enlarged fragmentary sectional view taken on the line 3-3 of FIGURE FIGURE 4 is an enlarged fragmentary sectional view taken on the line 4-4 of FIGURE 5;

FIGURE 5 is a top plan view of a centrifuge disc made in accordance with the process described herein; and

FIGURE 6 is a top plan view of an alternate form of centrifuge disc made in accordance with the process described herein.

Referring more specifically to the drawings, FIGURE 1 shows in schematic fashion a portion of the aapparatus by which the centrifuge discs 'herein are manufactured. The apparatus comprises an upper electrode which may, for instance, be the anode A and a lower electrode which may be the cathode B. These electrodes comprise the socalled tools for making the product described herein. In operation a stamped or spun disc blank 10 is mounted on one of the electrodes, for instance, electrode B. A plastic cup C may be set on top of electrode B and be shaped to exactly receive the slotted opening of the blank. This orients the blank and keeps the edges about the opening from being e'lectro-chemically machined. The electrodes are drawn together until the blank is clamped therebetween. The electrode A is provided with insulating strips D which may protrude downward from the underside of the electrode and correspond to the areas of the finished centrifuge discs which are raised, as to form the spacing elements.

The upper electrode A is provided with a central opening B through which electrolyte flows. As shown in the sectional view FIGURE 2, the electrolyte flows preferably under considerable head into the space between the blank 10 and the upper electrode A. In actual operation the electrolyte may comprise a salt solution, aqueous mineral acid, caustic potash or caustic soda in aqueous solution. Various additives may be used in the electrolyte to effect results well known in the art. It will be seen that the insulator strip D tightly engages the upper surface of the blank and masks off what is to 'become the spacing element 12 from the electro-chemical machining operation.

With the electrolyte flowing in the channels between the upper electrode and the blank, electric current is passed between the two electrodes. The current density may vary in accordance with the material of the blank and the results to be obtained. If the discs are to be made out of steel, for instance, a current density of 1100 amps. per square inch may be used to elfect a penetration rate on the order of 0.1 inch per minute. If the blank is made from aluminum a slightly higher density, such as 1190 amps. may be employed to achieve the same rate. Depending on the size of the disc to be made and the height of the spacers to be formed an appropriate rate and time of exposure may be selected by one skilled in the electro-cheinical machining art. It will be noted from FIGURE 2 that the electro-chemical machining process will remove the metal from the upper surface of the blank which is not covered by the insulator D.

It should be understood that an electrolyte after passing through channels between the upper electrode and disc may be purified to have metal particles and other foreign matter removed. This material may be ferric hydroxide for instance in the processing of steel. The purified electrolyte is returned to the machining apparatus for passage through the opening E and is reused.

In view of the fact that the blank which is to be rnachined is of frusto-conical shape, it will be apparent that the coverage of the electrolyte toward the center of the disc will be much greater than adjacent the outer periphery. In discs of diameter of say 2 /2" this will make no difference. But in making larger discs it may be desirable to supply additional electrolyte through apertures in the upper electrode spaced outward from'the center at locations immediately above portions of the blank.

The sectional view of FIGURE 3 shows the product which results from the above-described process. The disc 10 is provided with the upwardly protruding spacer element 12 which is an integral part of the disc. As' an example the disc will have a thickness between spacers of DOS-.035 inch. The spacer may be .007-.150 inch thick additionally. Actual dimensions will be specified according to the use to which the disc is put. A fillet 14 is formed in the electro-chemical machining operation between the respective sidewalls of the spacer element and disc body. This fillet is especially significant in sanitary operations since it precludes the accumulation in the area of process solids which the centrifuge is separating, It also makes the disc easier to clean. The fillet will most desirably have a radius in the range of .005 to .025 inch, although greater radii are obtainable by appropriate adjustment of the machining technique.

Another benefit of the invention is shown in FIGURE 4 wherein the uppermost portion of the disc terminates in an inward horizontal flange 10a which may be of various thickness depending on whether or not it is masked off by an insulating body during the electro-chemical machining. It will be understood that the height of the flange will control the height of the opening between flanges on adjacent discs so that the annular passage between adjacent discs at their inner periphery may be controlled thereby. Therefore, if it is desired to have a large flow of'fluid through this annular opening, the flange may not be masked during the machining. This will result in a flange having approximately the thickness of the disc between adjacent spacers. If alternatively a limited flow is desired, masking may be used and a thicker flange (shown in phantom) may result. a a

Reference to FIGURE 5 shows that the central portion of the disc is stamped out to provide positioning of the discs in a stack about the centrifuge center tube. This is preferably done prior to electro-chemical machining. A number of slots 20 are alsostarnped in the disc about the central opening to mate with correspondingly positioned keys on the centrifuge center tube to assure proper reorientation of the discs. One slot and key may be shaped differently if desired to assure only one correct radial orientation of the discs.

It should be here noted that one of the advantages of the process described in that the surfaces which have been machined away by the electro-chemical method are smooth and polished and require no further finishing prior to their use in the machine. In an actual product the finish is at least substantially equivalent to a number 7 highluster finish as applied to sheet work. This is obviously an expense saving feature since it makes unnecessary such hand finishing.

If flow distribution openings are desired in the'disc, they may be also electro-chemically machined.

FIGURE 6 is a modified form of disc 10' made by the process described herein. The primed form of reference numerals are used. In the modified form the spacers 12' are arcuate in shape. In the prior art it was necessary to carefully plot and cut out each such spacing element and secure them with painstaking care tothe top of the disc member. In accordance with the present invention the machining away of portions between the spacers is accomplished electro-chemically and the arcuate spacers are achieved by the provision of correspondingly arcuate insulating elements D which mask the upper'surface of the blank. Through this simple one-step procedure successive discs are identical and have exactly the same balance characteristics.

It should be understood that the present invention has other applications, that virtually any kind of centrifuge disc provided with a spacer may be manufactured in accordance with the present description. The process may be used to provide bafiles for centrifugal extractors and vanes for centrifuges of the so-called vane-stack type. A wide variety of metals may be used: aside from steel, aluminum, titanium and nickel and alloys thereof are entirely workable in accordance with the invention;

Further, especially on large diameter discs the upper electrode instead of having spacers D may have slots masked with plastic to avoid electro-chemical machining of the blank in these areas. An electrode of this type may at the beginning of the machining operation be spaced from the blank and advance slowly down toward the blank as the machining progresses.

Therefore it is to be understood that the above particular description is by way of illustration and not limitation, and that changes, omissions, additions, substitutions, and/or other modifications may be made without departing from the spirit of the invention, Accordingly, it is intended that the patent shall cover, by suitable expression in the claims, the various features of patentable novelty that reside in the invention.

I claim:

1. A method for making a centrifuge disc comprising a frusto-conical metal body having a central opening and a polished surface on said body portion, integral protruding spacer elements having walls rising substantially perpendicularly from the said polished surface of the body portion, integral fillets disposed between the walls and the said polished surface, the said polished surface, the spacer elements and the fillets being formed in an electrochemical machining operation, said method comprising: providing a frusto-conical blank having a convex conical surface, providing an electrode having a concave conical surface adapted to mate with said convex conical surface, said electrode having a plurality of insulating strips spaced about said concave surface, moving said electrode into proximity with said blank so that said insulating strips are contiguous with said convex surface whereby to define a plurality of gaps between said convex and concave surfaces; fiowing electrolyte through said gaps, applying a source of electrical energy to make said blank predominantly anodic whereby said blank is electrolytically etched and containing said application of said electrical energy until said blank is etched to a depth of at least 0.007 inch.

2. A method as described in claim 1 wherein the fillets have a radius in the range of .005-.025 inch.

3. A method as described in claim 1 wherein said polished surface has a finish at least substantially equivalent to a number 7 high-luster finish as applied to sheet work.

4. A method as described in claim 1 wherein the body portion presents an inward flange about the central opening, the flange having a thickness substantially the same as the body portion between adjacent spacers.

5. A method as described in claim 1 wherein the insulating strips and the resulting spacer elements are arcuate.

6. A method as described in claim 1 wherein the blank is comprised of a metal selected from the group consisting of steel, nickel, titanium and aluminum.

References Cited UNITED STATES PATENTS 961,349 6/1910 Hartman 233-29 X 1,376,365 4/1921 Wertheimer 204-143 2,012,589 8/ 1935 Miller 233-29 X 2,599,619 6/1952 Eckers 233-47 X 3,056,734 10/1962 Scott 204-143 3,239,441 3/1966 Marosi 204-143 3,288,699 11/1966 Trager et a1. 204-143 FOREIGN PATENTS 840,544 7/1960 Great Britain.

RQBERT K. MIHALEK, Primary Examiner,

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