US1456737A - Centrifugal separating means - Google Patents

Description

May 2 9, 1.923.

3 Sheets-Sheet l FiledA Aug. '7, 1920 O Mmod: 3 e 15 a y @e ,1111 ,M4/ M 0 3 1 3 wl 2, nknuu Mw/ 0. .2 .,f w /:MAJ 1 am Bl.. 3f Q 1.@ A. ,5 6 5 .a 3 a l.. y Vv.

Patented May ,29, 1923.

' rase/3i RALH E. LAPHAIM, OF OAKLAND, CALIFORNIA.

Application filed August 7, 1920. Serial Nel L101383.

, T 0 all whom. it may concern:

Be it. known that I. RALi'ii E. LAPHAM, a citizen of the United States, residing at Oakland. in the county of Alameda and State ofl California. have invented-certain new-and useful lniproveinentsin Centrifugal Sep arating Means, of which the following is a specicat-ion.

The present invention relates to certain improvements in the construction of separat ing machines of that character which uti'- lize centrifugal force for the separation of heavier values such as gold and platinum from aurifeious and platinileious sands, such sands being found in large quantities on the sea shore and even in inland places, and being commonly known as blacksa'nd.

Among the objects of the invention is to provide for a smooth flow ofthe mercury or other mobile separating medium which is utilized to bring about the separation of the heavier values from the sand. chief desideratums of a'linachine of this character is to obtain an efficient mercurial circuit which is automatic in its How, and which will not permit the mercury to be disseminated or lost.` Mercury, being a metal as well as a liquid, isicapable of beinoffloured or broken into many small glohules if handled violently. ence the mercury as it circulates through the machine must flow smoothly, especiallv since it is subjected to great centrifugal force. and if permitted to jump through space and inipinge violently upon soniesolid Aportion of the machine vwould becoinebrolien up and lioured. In other words, the mercury must be united continuously throughout entire course of travel by a liquid inassof appreciable depth or flow over an amalgamated surface, andthe flow mustbe smooth and unbroken. Aequiring of this result is an art involving delicate manipulation. and one 'of' the ob'iects of this invention has been to provide a construetion `which will insure such allow of the mercury or mobile separating medium 'at all times and under all conditions when the ma# chine is in operation.

A further object of the'invention is to pro vide for conserving the supply vof the mercury or'mobile separating medium and pre` vent the escape thereof withthe tailings. Owing to the high velocity at which the ma chine Yis driven when in operation thelayer of sand which is superposed upon the iner- One of the vlCENTRTUGAL SEPARATING MEANS.

euryis dense and there is a tendency to form a knife edge Vat the point Where the mercury and sand finally separate. It has been found that ,globules of mercuryare sometimes separated'from the main body of the mercury by this knife edge, and the density of the sand wall prevents these particles of mercury from again reaching the main body of inercury, and this loss, which might be considerable attiines, is prevented by the present construction.

lWith these and other objects in View, the

invention consists in certain combinations,`

arrangementsand associations of the parts,

as will more fully appear as the-description proceeds, Athe novel features thereof being pointed out in the appended claims.

For a full understanding of the invention Vreference is to be lia-d to the following description and accompanying drawings, in which Figure l is a .vertical sectional View through '3a centrifugal .separating machine which is constructed -in accordance with the invention, the mercury or mobile separating medium being shown as filling the main supply reservoir and in the position assumed.

when the machine is at rest.

lligure 2 an enlarged sectional view through one half 'of the. rotating bowl and4 .associated parts, showing the mercury lcircuit when the machine is in operation.

Figure 3 is an enlarged fragmentary sec-` tional' view of the upper edge of the rotating bowl. showing the mercury supply conserving device.

V Figures 4 and are enlarged sectional views through portions of the -main mercury reservoir; showing the flanges which are carried by the rotating bowl Yand dip into the mercury to provide for the continuous circuit tliereof, the surface of the mercury being illustrated in the position assumed when the machine is in operation.

Corresponding and like parts are referred to in the following description` and indicated in all of the views of the drawings by like referentie characters. This invention is an in'iprovement upon thel centrifugal separating machines shown by-iny Patent No. 1,336,968 of April 13, 1920, and my co-peiiding application Serial No. 327,713, filed October l, 1919. There are numerous structural details whichare iden tical with what is shown by my prior patent,

Vir'.nalled'at its upper end in a suitable bearing bodiment of the invention, .the numeral 1 designates a base, and 2 a *supporting frame or casing which is superposed upon the base.

and rigidly secured thereto. Rotatably mounted within the casing 2 is a bowl 3 which is adapted to be driven at a high rate of speed when the machine is in operation. A vertical shaft 4 to whichlthe bowl is rigidly secured extends upwardly therethrough at the axis of the bowl and'is jour- 5 at the top of the casing 2. The lower end of the shaft extends downwardly below the bowl and is joui-nailed in a bearing 6 on the base 1. Surrounding` the lower bearing 6 is a casing 7 which is formed with a neck upon which a drive pulley 8 is journalled. A helical spring 9 which surroundsthe shaft L1 and has the respective ends thereof connect` ed to the bowl and pulley provides a resilient connection between the two members so that there will be no sudden shocks or jars imparted to the bowl as it is rotated-through the medium of power applied to the drive pulley.

A feed hopper 10for the sand or gangue is located within the upper portion of the bowl at the( center thereof, and a supply chute 11 extends upwardly Jfrom the feed hopper through an opening in the top of the casing 2. rllhe gangue is discharged from the feed hopper upon'a bottom member 12 which is arranged within the bowl and which has long sweeping curves so that the gangue circulates downwardly and outwardly upon the bottom and at the periphery thereof is deflected upwardly so that it will travel upwardly over the annular side wall of the bowl.

The bottom member 12 is spaced Jtrom the bottom of the bowl, and an annular mercury reservoir 13 is provided under thisfbottom member or plate 12. An Vannul ar wall member 14 is fitted within the bowl 3 and rigidly secured in position therein, the lower edge of the wall member being shown as extending downwardly into the mercury reservoir 13, and said wall member being spaced from the bowl as indicated at 15 to provide a return circuitforthe mercury afterV it has been caused to flow upwardly over the inner sur- :face of the wall. The said inner surface of the wall is provided with the usual annular, pockets 16 which are preferably V shaped in cross section` and in which the heavier values which pass through the film of mercury and are thereby separated from the sand collect.

The upward flow of the mercury over the annular wall la from the reservoir 13 is Yat 31.

ineen/a7 preferably controlled by some kind of a valve mechanism. The valve construction provided for this purpose may be similar to Ythat showncinkmy above identified co-pending application, including a rotary valve plate 17 provided with openings 18 which are adapted to be moved into and o ut of registry with corresponding openings in a channel member 19 which is arranged be tween the periphery of the bottom plate 12 and the wall 111. The adjustment of this .W

valve `may beaccomplished by means of a shaft 2O which is arranged within the tubular upper end of the main shaft 4 and has its upperend in a threaded engagement, as at 21, with a fixed plate 22. A handle 23 is fitted upon the upper end of the shaft 20 and provides a means for rotating the 'same to imparta bodily up and down'longitudinal movement to the shaft. The lower end of the shaft 2O is formed with a reduced por- Vtion which engages the forked end of a lever 24 which is pivoted at an intermediate point 1n its length. The other end of this lever 24 engages a bel-l crank lever 25 which is in turn connected`to a shifting lever 2G, said lever being` arranged under the bottom plate 12 andpivotally connected at 27 to the bottom of the bowl. The outer end of the shifting` lever 2G engages the valve plate 17, and itrwill be obvious that with this construction the said valve plate can be rotated to bring the openings 1S thereof into or out ofregistry with'the openings of the'channel I member 19 and thereby regulate the upward .circulation or How of the mercury-from the inner wall of thc discharge launder 30, Ythe outlet for the said launder being indicated The overflow rim is formed with a fiange 282L whichrextends downwardly into thev bowl and engages the vertical flange of an angle iron ring 32 which is fitted within a seat at the top of the bowl. flow rim 28 and angle iron ring 32 thus The overcooperate with each other to provide anannular mercury receiving pocket A. When thc mercury reaches the top of the-wall 14: is carried into this pocket by an angle iron guide ring 33 which is secured to the upper edge of the bowl7 one flange of the ring eX- tending into the pocket. There is a 'substantially quiescent body'of mercury in the pocket A and the `upwardly flowing film of mercury flows smoothly from .the wall 14 into this body of mercury without any vio? lence or undue agitation. The depth of the mercury which is permitted to collect withinl this annular mercury pocket A before it overflows into the return circuit is determined by the amount the iiange -of the ring 32 projects into the bowl. The pro.- jection of this flange into the bowl is slightly less than the projection of the overflow rim 28 so that `the substantially vertical face of the mercury in the pocket will never reach the edge ofthe overflow rim 28 extend outwardly to the exterior of the bowl and lead to the base of a flange 35 which extends downwardly in a spaced relation to the bowl and termina-tes in an edge which projects into a-trough 36 forming a part of a main mercury reservoir B which is arranged under the periphery of the bowl and is formed in connection with the main casing 2. The trough 36 is s lightlyelevated from the bottom ofthe reservoir so -thatf .mercury can flow under the same, and the inner portion of the reservoir is provided with an annular depression 37 into which` the edge of' a. second flange 38of thel bowl projects. This inner flange 38 is arranged at an inclination and at the base of the l .ange ports 39 are provided inthe bottom of the. bowl lead to the reservoir 13.v

A gage 40 is ii'f. rcommunication with the depression 37 ofthe reservoir through a pipe 41 and shows the level of the mercury within, thegreservoir at this point. A drain opening aff' the bottom of the gage is pro-- vided for withdrawing the mercury from the reservoir when desired, the said drain opening being normally closed by means of' a plug 42. Y I

rlhe annular wall member 14 is preferably formed of'copper or a composition comprising practically copper and 10% tin. Similarly, the circulation flanges 35 and`38 of the bowl are-.preferably formed'of. some material such as copper for which mercury has an aiiinity, and may be electro-silver plated to provide for a mosteicient amal- Igamation of the mercurv with the metal. The mcrcurvthus has what may be termed an amalgamatcd contact with these members and can flow over them in a Very thin film. lt will be understood, however, that theV recovery of the metal values is not due to amalgamation, but is entirely the result of the centrifugal action of the machine, the

metal values which it is desired toirecover bowl the return cirhaving a greater specific gravity than thc mercury and passingthrough the same into the grooves' 16, while the sand or gangue has a less specific gravity than that of mercur'y and circulates upwardly along the surface of the mercury film, being finally discharged into the discharge launder 30. In the operation of the machine the sand or material to be treated is deposited in the feed hopper 10 and permitted to be fed intov the bowl as the latter is rapidly rot-ated. The rotation of the bowl causes the mercury 'which may have collected in the reservoir 13 of the bowl to flow upwardly over the inner face ofthe annular wa1l`14 in a thin film which has an amalgamated contacttherewith. The sand or gangue circulates downwardly andoutwardly over the curved walls of' the bottom member 12 and is deected upwardly at the periphery of the C said member so as to flow upwardly over the mercury film in engagement therewith. The centrifugal force produced by the rapid rotationof the bowl has the effect of magnitying or` increasing the relative weights of s.

the materials in the well known manner, and a most effect-ive separatmg action is thereby obtained. The gold 'and platinum particles, being heavier than the mercury, l vwill-pass through the film of mercury and .2

collect in the pocketslG, while the gangue whic-hiis lighter than the mercury will circulate upwardly over the inner surface thereof. The mercury circuit induced by the-,rotation of the bowl isillustrated by Fig'2 of the drawings. A t the top of the annular separating wall 14 the flowing film of mercury travels over the guide ring 33 quiescent body of mercury in the pocket A.

vThesand and gangue will continue to eirculate upwardly over the surface ofl the mercury in the pocket A, and when the thicknessof sand which may have accumulated Yupon the mercury is sufficient will `pass -over the overflow rim 25 and enter the discharge launder 30. As the mercury collects in the pocket/A and the vertical wall thereof tends to move inwardly toward the axis of the bowl, the mercury will overflow the flange orv ring 32 and be directed through passage 43 into' the return passage 15 which is provided between the bowl 3 and the separating wall member 14. This is indicated more clearly by Fig. 3.

At the lower end of the return passage 15 the mercury passes outwardly through the ports 34 into an'lalgamated engagement with the annular flange The lower edge ofvthis flange dips slightly into the mercuryin the trough 3G and thel frictional engagement of themercury with the flange will cause the mercury in the trough to rotate as Vthe bowl is rotated. However, the rotation of the body of mercury within the Iel) lil() and;- becomes merged in the substantially llO han

trough 3G will act centrifugally thereon and cause the mercury to overflow the outer wall ot the trough. At the same time the surface of the mercury within the trough will become inclined. as indicatcdby Figures 2 and 5, with the result that the edge ofthe flange will not dip so deeply therein and will not have as great a frictional engagement with the mercury. It is desired that the edge ot the flange shall dip as little as possible into the mercury when the machine is in operation,` although it is necessary for the flange to touch the mercury in order that there may be a smooth and uninterrupted downward flow of the Incr-l cury along the inner face of the flange 35 and into the mercury in the reservoir. N

The mercury which is thus caused to overflow the trough 3G of the reservoirB circulates under the trough and accumulates in the annular depression 3T into which the inner circulation flange 38 projects. The body of mercury in this annular depression Il? will also Arotate to a certain extent with the bowl, owinrr to the Jrrictional engagement between the mercury and the flange. 'lhe surface of the mercury in the annular depression 37 will thus assume an inclination, asv indicated by Figures 2 and 4. lIt will be noted that theinner circulation flange 38 is inclinedjinwardly and downwardly and the portion of the :mercury which overlies the edge` of the flange will have a considerable frictional engagement with the flange and ybeeaused to rotate there-- with. This ir'otationio'tt-he mercury .results i -l .in a centrifugal torce'. which is sufficient to cause the mercury to flow upwardly along the `l'ace ot the Aflange and pass through the ports 39 into the reservoir 13 at the bottom ot' the bowl. As previously stated these flanges are formed ot copper or some metal with which mercury has an aliinity so that the mercury is man amalgamatedengage nient with the flanges` and a` smooth even flow of the mercury over the flanges and in a thin film is thus brought about. The mer-l 'cury is thus caused to circulate continuously around the mercury circuit when the howl is rotated. and there is a smooth even flow of the mercury at all pointsot the circuit so that there is no possibility of the mercury becoming broken up or-flouredby being brought violently into-contact with some surtace.

ln the operation of machines ot this charl acter it has been found that under certain conditions there will be a lossy ot the mercury, since vportions thereof will become separatedtrom Vthe main body ot the mercury and be discharged with the tailings. This is due very largely to the fact that the sand which accumulates on the surface of the mercury in the pocketv A has a comparatively sharp edge at the lower portion portions Vof the mercury from thefilm thereof which is passing laround the guide ring 32 into the pocket A. Any particles of mercury which may be separated at this point would pass upwardly over the sand accumulation, and the density ot this accumulation is such that it is -impossible for theV mercury to penetrate through the same to reach the body ofmercury in the pocket A. I have accordingly found it desirable to make provision for recovering or preventing the loss of suchy particles of mercury. For

this purpose an annulus 44 is carried by the overflow rim 28, being rigidly secured thereto lat 45. This annulus 44 has a substantially L shaped cross section and overhangs the overflow rim, being provided at its point of connection thereto with outlets 46 through which the tailings escape. The overhanging portion of the annulus 44 is 'provided with a ring 47 which has a substantially U ,shaped formation, the curved portion ot the ring being arranged to project inwardly toward the surface of the mercury in the pocket A. and into substantial engagement therewith. This ring 47 thus projects into the body of sand or gangue which accumulates upon the 'surface ot the mercury betere passing over the over- How flange. The sand or gangue must pass under this ring 47 in a thin film or layer before it is finally discharged. Any particles of mercury which might be severed by the sharp edge at X and separated from the main body otl the mercury Will also pass under ring 47, and the layer or thickneii ot the sand under the ring is so thin that thc mercury will readilypen'etrate through the same and become-merged in\ the large body of mercury in the pocket A. The sup-y ply oitl mercury will thus be conserved and Y loss thereof reduced to a minimum. Furtherinore, the discharge of the tailings under the upper flange of the annulus 44 and through the passages 46,-caused by centrifugal force, will tend to produce a partial vacuum within the annulus 44, and this pan tial vacuum will assist the overflow of the sand. l

The overflow rim `28 is shown as provided with a baffle" flange 48, and a cooperating baflle flange 4t) is provided `at the tree edge of the mercury guide ring 33. These battle flanges provide a barrier or trap for any sand working in along the line between the upper member and the body of mercury, and also prevent sand from being washed down the ret-urn space l5 when washing down the machine to clean the same. The baille flange 48 is preferably l. shaped, as indirzo cated, to rprovide in a more effective manner for catching the sand.

Themercury in its upward movement over the wall 14, caused by the pressure generatedin the reservoir 13, assumes a. va.- riable curve due to the combined action of gravity and centrifugal force, and will approach and departfrom the perpendicular 1n direct proportion to the force produced, gravity remaining constant. The mercury in its downward movement through the narrow return space l5, which is of increasing diameter. will assume a film of varying thickness decreasing slightly in depth at the lower part of the channel due to the action of the combined forces of gravity and centrifugal force. The rateof How of the mercu-v rial circuit depends upon the amount issuing through the Valve controlled ports at the bottom of the bowl. At a given speed of the bowl,but with various rates of flow,

- the inclination, curvature, and thiclmessof mercury on the separating wall 14: remain constant. At a high rate of flow the inner surface of the iilm of mercury travels upwardly/faster, giving a greater capacity of sand whileA the mercury in the outer chanvnels travelsA downwardly faster, vgivingfa greater capacity for the mercury. The mercurialQcircuitl throughoutthe moving parts of the machine gradually increases radially, that is, the circuit through which the mercury passes increases in diameter in the d1- rection of flow of the liquid, terminating in the largest diameter at the lower edge of the iange'B.

While I haveillust-rated and described one particular embodiment of the invention, it will be understood that many changes can be made `in the details of construction without departing in any manner from the spirit .of the invention or the scope of the' appended claims.

Having thus described the invention, what I claim 'as new and desireto secure by Letters Patent is a 1. A centrifugal separating machine of n the character described including a rotating bowl provided with a wall over which the' separating medium and pulp -flow, a stationary reservoir for the separating medium, and an annular circulation flange carried by the bowland projecting into the separating medium, said flange being formed of a materialfor which the separating medium has an affinity and over which it flows in an amalgamated engagement. A

'2. A centrifugal separating machine in-v cludingla rotating bowl provided with a Wall over w ich the separating medium and pulp liowin one direction and also with a return" passage for the separating medium, a sta` tionary reservoir for the separating medium, and a pair of circulation flanges carried by the bowl and projecting into the separating medium in the stationary reservoir to provide for the feed and return of the separating medium.

3. A centrifugalI separating machine of wvliich the mercury has an affinityY and over lwhich it will flow in an 'amalgamated engagement and-.the feed flange being con-- stru'cted'to utilize the motion thereof to induce a passage of the mercury from the reservoir to the bowl.

4.' A centrifugal separating machine including a rotating bowl provided with an interior annular wall over which the separating medium and pulp flow in one direction, the exterior` of the bowl being provided with a return passage alongw ich the separating medium flows in the oipiposite direction, a stationary reservoir for the separating medium, and concentric annular circulatingflanges carried by the b o'wl and projecting -into the separating medium in the stationary., reservoirso as -to provide for `the feed and returnof the separating medium.

5, A centrifugal separating machine ofthe character described including a rotating bowl provided withv an annular wall overl which' the' separating medium and pulp flow, v

a stationary reservoir l:for the separating e-A dium, andv apair of circular flanges carried by the bowl and'projecting into the separating medium in the stationary reservoir to provide for the feed and return of the separating medium, the feed flange having an inclined edge portion which is arranged so that the separating medium will be centrifugally .forcedalong the flange of the bowl as the separating medium upon the edge of the flange is caused to rotate by frictional engagement therewith.

6. A centrifugal Aseparating machine of the character described including a rotating bowl provided with an annular wall over which the separating medium and pulp flow,

a stationary reservoir for the separating me -dium, and means including circulation angescarried by the bowl lfor roducmg a l continuous circuit of the separatmg medium between the bowl and the stationary reservoir and-over the said annular wall* of the bowl, the said stationary reservoir being provided with independent trough portions for the circulation flanges.

7. A centrifugal separating machine of the character described including a rotating bowl provided with. an annular wall over which the separating medium and pulp flow, a stationary reservoir forv the separating'medium, and means including a pair of annular return' flange being at a higher elevation.

than the trough for the feed fiangeso that the sepi-irating medium returned to the reservoir from the bowl `will be first received in the trough at a higher elevation and then overflow said trough and flow by gravity' into the trough at a'lower elevation.

8. A centrifugal separating machine `of the character described including a rotating bowl provided with an annular wall over which the separating medium and pulp How,

a stationary reservoir for the separating medium arranged under the rotating bowl, and means including annular feed and return circulation flanges carried by the 1oowl and projecting into the stationary resefvoir for producing a continuous circulation of the separating medium bach lind forth between the bowl and the reservoir and over the beforeinentioned -wall of the bowl, the stationary reservoir being provided with independent annular trouglr portions for the cir-` culation flanges and thereturn flange p rojecting into the trough at a higher elevation so that the separating medium rcturnedto the reservoir will be .first received within the higher trough and after overflowing the sameflow by gravity into the lower trough provided for the feed fiange, said feed fiange having an inclined edge portionwhic'h is arranged so that as the separatingmednnn rotates by frictional engagement therewith the centrifugalA force produced will drive the separating medium over the flange to the bowl.

9. A centrifugal separating machine of the character described including a rotating bowl provided with an annular wall over which the mercury and pulp flow, a stationary mercury reservoir, and a circulation flange carried bythebowl and projecting into the stationary reservoir, said flange being formed of a metal for which mercury has an affinity and over which the mercury will flow in an amalgamated engagement.

l0. A centrifugal separating machine of the character described including a rotating bowl `provided with an annular wall over which the mercury and pulp flow, a stationary mercury reservoir, and annular feed and circulation fianges carried by the bowl and projecting into the stationary reservoir to convey the mercury back and forth between the reservoir and the bowl, said flanges being formed of metal for which mercury has an affinity land over which it will fiow in an amalgamated contact. the feed fiange being inclined and arranged so that the mercury in the reservoinwhich is engaged thereby and caused to rotateby frictional engagement therewith will be driven along the flange to the bowl by the centrifugal force thereby produced.

ll. A centrifugal separating machinenof the character described including a rotating bowl provided at the bottom thercofwith a reservoir and also with an annular wall over which the separating medium flows upwardly from the reservoir, a return passage Abeing provided 'for' the separating medium after it has circulated over the annular wall,j 'a main stationary reservoir for the separating medium under the bowl, and means utilizing the centrifugal force produced by the rotation of the bowl to convey the separating medium from the fixed reservoir to the reservoir of the-bowl and from the return passage of the bowl tothe stationary reservoir.

l2. A centrifugal separating machine of the character described including a rotating bowl provided at the bottom thereof with a reservoir and also provided with an annular wall over which the separating medium fiows from the reservoir, a return passage being provided for receiving the separating mediumafter, i'thas circulated over the annular wall, a main stationary reservoirl for thev separating medium under the bowl, and annular `feed and return circulation fianges carried by the bowl and projecting into the stationary reservoir, the return fiange h'avey ing the base thereof adjacent the return passage of the bowl and the feed flange supplying the separating medium from the stationary reservoir to the reservoir of the bowl Vand being inclined so that the separating medium frictionally engaged by the( edge of the flange and caused to rotate therewith will be forced over the fiange by the centrifugal .force thereby produced.

roo

13. A centrifugal separating machine ofl i the character described ,including a rotating bowl provided with an annular wall over which the separating medium and pulp flow,V a return passage being provided for the separating medium while the 'gangue overfiows the bowl, and means for catching anyparticles of the separating. medium which may have become separated from-the body thereof and deflecting them back into the main body of the separating medium.

'14. A centrifugal separating machine of the character described including a rotating' bowl provided'with an annular wallover which the separating medium and pulp How, a return passage being provided for the separating medium while the gangue over-l flows the bowl, and means including a baffle ring between which and thebowl the gangue flows, said bafiie ring rojecting into the gangue at a point in a vance of the overflow thereof for directing any portions of the Aseparating medium which may have become separated from the body thereof through the gangue so' that they can reach the before-mentioned return passage.l

15. Acentrifugal separating machine of the character described including'a rotating bowl provided with an annular wall over which the separating medium and pulp How', a return passage being provided for the separating medium while the gangu'e overflows the bowl, an annular body of the'separating medium being maintained adjacent the edge of theannular Wall and over the surface of which the gangue passes prior to being discharged, and an annular ring member between which and said 4body Vof separating medium the gangue flows, said annular ring member being arranged to pro-4 ject into the gangue which is upon this body of the separating medium so that the gangue must pass between the ring and the body of separating medium which may have become mixed with the gang'ue will be defiected into engagement with the annular body of separating medium and preventedvfrom loss.

16. A centrifugal separating machine of thecharacter described including a rotating bowl provided withY an annular wall over which the separating medium and pulp flow,

if an overow rim upon the bowl, a return passage being provided for thev separating mediumy While the gangue4 is discharged over the said overflow rim, an annular body of the separating medium Abeing il. maintained adjacent the overiow rin and carried by the bowl, an annulus carried by the bowl, and 'aring carriedllb'ythe annulus and arranged to project'ifitb the gangne passing over .the annular body of separating medium so that thev gangue will pass between the said ring and body of separating medium in a thin film and any particles of the separating medium which may have become mixed with the gangue will be deflect` edback'tothe body of separating medium and-thereby recovered.`

17.l A centrifugal separating machine'of lthe character'described including a' rotating bowl provided with an .annular 'w'all over which the separatingmedium and pulp flow, an overficw rim for the'bowl, a return passage being provided for the separating medium while' the gangue is discharged over the overflowrim', a guide ring for the separating medium -at the edge ofthe-annular Wall, and 'cooperating baille. flanges carried by the overflow rim and guide ring and providing a tortuous path for the separating medium vas it flows tothe return passage.

18. A centrifugal separating machine of the character described including a rotating bowl provided with an annular wall over l separating medium as it iows tothe returnv passage. v i In testimony whereof I aix my si nature. RALPH LAP AM.

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