US2720982A

US2720982A - Centrifuge

Info

Publication number: US2720982A
Application number: US258392A
Authority: US
Inventors: Ii Joseph Stuart
Original assignee: Hercules Powder Co
Current assignee: Hercules Powder Co
Priority date: 1951-11-27
Filing date: 1951-11-27
Publication date: 1955-10-18
Anticipated expiration: 1972-10-18

Description

J. STUART II:

Oct. 18, 1955 CENTRIFUGE 5 Sheets-Sheet 1 Filed Nov. 27, 1951 JOSEPH STUARTH W q. PM

AGENT.

J. STUART II Oct. 18, 1955 CENTRIFUGE 5 Sheets-Sheet 2 Filed Nov. 27, 1951 MQE AGENT.

J. STUART IE CENTRIFUGE Oct. 18, 1955 5 Sheets-Sheet 3 Filed Nov. 27 1951 JOSEPH STUART g INVENTOR.

AGENT.

Oct. 18, 1955 STUART 11 2,720,982

CENTRIFUGE Filed Nov. 27, 1951 5 Sheets-Shaw?- 4 45 Q J I 43 FIG- 9 JOSEPH STUAR'T U INVENTOR.

BY PM AGENT.

J. STUART III Oct. 18, 1955 CENTRIFUGE 5 Sheets-Sheet 5 Filed Nov. 27, 1951 JOSEPH STUART l law 516 AGENT.

2,720,982 Patented Oct. 18, 1955 CENTRIFUGE Joseph Stuart H, Wilmington, Del., assignor to Hercules Powder Compan Wilmington, Del., a corporation of Delaware Application November 27, 1951, Serial No. 258,392 2 Claims. (Cl. 210-68) This invention relates to an apparatus and process for separating liquids from solid material. In a specific aspect this invention relates to an apparatus and process for separating spent nitrating acid from nitrocellulose and then washing the separated nitrocellulose.

Centrifuges of various types have been employed heretofore to separate liquids from solid material. In many instances the centrifuges employed have been of the batch type, and in order to decrease the operating costs of the apparatus, efforts have been made to improve upon the batch-type centrifuges and to construct a continuous type of centrifuge. One continuous type has employed a scraping or peeling knife within the separating drum in order to provide for continuous removal of separated material from the drum. Another type of continuous centrifuge has achieved continuous operation by providing means for axially moving the peripheral wall of the separating drum over an annular wall or walls in order to obtain automatic discharge of the separated solid material from the centrifuge. The various centrifuges employed heretofore have had obvious disadvantages, particularly when employed in such opertaions as the nitration of cellulose Where the nitrated cellulose is separated from spent nitrating acid by centrifuging and then washed free of remaining spent nitrating 'acid by a series of water washes.

Conventional practice in the manufacture of nitrocellulose involves treating, for example, cotton with nitrating acid for a desired period of time by a batch procedure. Upon completion of the nitration, the discharge valve of the nitrator is opened and the reaction mixture is rapidly metered into a centrifuge which is brought up to the necessary speed for removal of acid from the nitrated cellulose. Spent acid is run by gravity from the outer jacket of the centrifuge to suitable recovery equipment.

The centrifuge is stopped and the nitrocellulose is manually forked out through the bottom of the centrifuge and drowned in a water immersion basin below. The manual handling of the nitrocellulose and the delay incident to discontinuous operation are objectionable, and the stopping of the centrifuge to fork out the nitrocellulose requires excessive time and causes too much delay for highest quality of product.

It is an object of this invention to provide a novel apparatus and method for separating solids from liquids.

.It is another object of this invention to provide a novel apparatus and method for separating cellulose derivatives from liqiud medium employed in the preparation of said cellulose derivatives.

It is a further object of this invention to provide a novel apparatus and method for separating nitrocellulose from spent nitrating acid obtained during the preparation of said nitrocellulose and for washing said nitrocellulose.

Further and additional objects and advantages of this invention will be apparent from the detailed disclosure hereinbelow.

The objects and advantages of this invention will be clearly apparent from the detailed description of the apparatus shown on the accompanying drawings and the operations thereof with reference symbols referring to like parts wherever they occur.

. Apparatus Fig. 1' is anelevati'onal view of the apparatuswith the reciprocating piston in its inactivated position.

Fig. 2 is a plan view of the apparatus through section 2-2.

Fig. 3 is an enlarged elevational view of the centrifuge basket and accompanying equipment with the reciprocating piston in its activated position.

Fig. 4 is an enlarged plan view of the reciprocating piston through section 44.

Fig. 5 is an enlarged elevational view of the reciprocating piston in its inactivated position through section Fig. 6 is an enlarged plan view of the bottom or base of the centrifuge basket through section 66.

Fig. 7 is an enlarged elevational view of a section of the bar screen or internal side wall of the centrifuge basket.

Fig. 8 is an enlarged plan view of a section of the bar screen-0n the interior of the centrifuge basket.

Fig. 9 is an enlarged elevational view through section Fig. 10 is an elevational view of the feeding mechanism for the apparatus.

Fig. 11 is a plan view of the feeding mechanism through section'11-11.

Fig. 12 is an enlargedview of the centrifuge basket and accompanying equipment with the reciprocating piston in its inactivated position and depicting an alternative slurry distributor and splash sleeve arrangement.

Referring now to the accompanying drawings, Fig. 1

'is an elevational view of a centrifuge that can be.used

to effect the desired separation of liquids and solids. The centrifuge shown in Fig. 1 contains a foraminous or per forate basket supported and driven by rotor shaft 1. Rotor shaft 1 is attached to and operated by a driving mechanism not shown, and the lower portion of rotor shaft 1, as shown on Fig. 1, is combined with the necessary bearings, packings, snubbers, snubbe'r rings, oil and grease lines, and the like, for the operation of rotor shaft 1. Since this equipment is conventional and since it does not form a part of the invention, a detailed description thereof is not necessary for an understanding of the invention. However, this conventional equipment is maintained free of corrosive fluids such as acid fumes by air line 2. Air under pressure is continually passed through line 2 and in this manner the entrance of corrosive fluids to the critical mechanism surrounding shaft 1 is prevented.

Rotor shaft 1 is attached to cylindrical casing 3 which is capped by stop nut 4. Surrounding casing 3 and contiguous thereto is a second cylindrical casing 5 which is rigidly attached to and moves in conjunction with a rotor piston which is inside the basket of the centrifuge and which will be described in detail infra.

Rotor bottom 6 which forms the bottom of the centrifuge basket is rigidly attached to casing 3 at its inner extremity, and at its outer extremity it is rigidly attached to the upwardly or vertically disposed side wall 7 of the centrifuge basket. The upper portion of side wall. 7 is perforated to permit the passage of separated liquids therethrough while retaining separated solids on the inner surface of the vertical side wall. Disposed above rotor bottom 6 is rotor piston 8 which on its lower or bottom side contains a plurality of indentations which surround and thus mesh with elevated and upwardly extending sections 6A of rotor bottom 6. Attached to the upper surface of rotor piston'8 is rotor piston face 9 which moves irrconjunction with piston 8, but; if desired, piston face 9 and piston 8 can be combined and made integral to form the rotor piston for the apparatus.

The upper portion of the centrifuge side wall 7 is perforated in order to permit the passage of liquid through the side wall. The actual construction ofthe side wall will depend upon such variables as the ultimate use of the centrifuge and the liquids andsolids to be separated. A suitable perforated side wall for the separation of spent nitrating acid from a slurry thereof 'with nitrocellulose has been found to include an outer casing containing a plurality of small openings. Within the outer casing and attached thereto is a screen formed by placing a plurality of vertically disposed metallic bars at regularly spaced distances around the inner surface of the outer casing. This preferred foraminous sidewall will be described in greater detail by reference to Figs. 7, Sand 9.

Surroundingcylindrical casing and forming an annular space therewith is a third cylindrical casing 10 which is rigidly attached to rotor piston face 9. Attached to both casing 10 and rotor piston face 9 is slurry distributor 11 which is eoncavely shaped and which directs the flow of the incoming slurry feed toward the side wall of the rotor basket when the centrifuge is in operation. Disposed above casing 10 and attached to the upper extremity thereof is a frusto-conical casing 12 surrounding the lower portion of the activating liquid tube tobe described infra; Since both casing 10 and distributor 11 are attached to piston face 9, these members, as well as casing 12, move in conjunction with piston face 9.

[The upper portion of the centrifuge is provided with fume tube 13 for removing undesirable fumes from the centrifuge and with activating liquid tube 14 for introduction of the liquid necessary for the hydraulic operation of piston 8 and movement of suitably attached members. Tube 14 extends downwardly into casing 12 and it is'provided with a second tube 15 of smaller diameter for additional removal of air and fumes displaced from the nitrocellulose. Tube 15 communicates with tube 13 through connecting line 16. Extending downwardly into the centrifuge and with their lower extremities within the cylindrical side wall of the centrifuge are a plurality of-tubes 17, "18, 19 20, 21 and 22 for the introduction ofwash liquids to the centrifuge. The lower extremities ofthese wash tubes are at varying levels'and spaced so that the separated solids in'the form ofa layer or mat on the inner periphery 'of-the side wall of the centrifuge can be subjected to a plurality of washings. The centrifu ge is provided with cover 23 to which are attached a pluralityof splash sleeve hangers'24. Hangers 24 extend downwardly into the centrifuge, and at their lower extremities they are'attached to splash sleeve 25 which forms an annular space with slurry distributor lljfor passage of the feed slurry to the centrifuge. Perforate blowoutpanel 40 is disposed between cover 23'and. curb 26.

Disposed outside the centrifuge basket are a plurality of

curbs

26, 27,28, 29, 30, 31 and 32 for removal of separated solid material, separated liquids and wash liquids. Separated solids are'removed via outlet 33 and the separated liquid and wash liquids are removed by suitable outlets provided between the lower extremities of the curbs. Typical curb outlets for liquid removal are-shown on the drawing as

outlets

34 and 35. Water or other suitable inert liquid is introduced to the base of the centrifuge via inlet 36.

The lower portion of side wall 7 is provided with a plurality of thief valves 37 and a second plurality of openings 38. The importance of and the necessity for these openings in side wall 7 will be more fully explained in the subsequent discussion of the operation of the centrifuge.- Opening 39 in rotor piston 8 permits the lubrication of the adjoining surfaces of side wall 7 and piston 8-and piston face 9 by the actuating liquid.

Fig. 2 is a plan view through section 22. This figure shows the relative locations of

wash pipes

17, 18,19," 20,

21 and 22. Fig. 2 also shows the location of splash sleeve 25 which is cylindrically shaped and flared at its lower extremity. Splash sleeve 25 is connected to cover 23 by three vertically disposed splash sleeve hangers 24 extending downwardly into the centrifuge. Splash sleeve 25 is maintained motionless by its attachment to hangers 24. Sleeve 25 does not revolve when the centrifuge is in operation and it does not move in conjunction w'itli the hydraulic activation and deactivation of rotor piston 82 Fig. 3 is an enlarged elevational view of the centrifuge showing rotor piston 8 in its activated position. Rotor piston 8 is activated by the introduction of activating liquid through activating liquid tube 14 and thence via the annular space between casing 5 and casing 10. The rotation and acceleration of the mass of activating liquid hydraulically elevates rotor piston 8 and attached rotor piston face 9 to the point where cylindrical casing 5 approaches but preferably avoids actually contacting stop nut 4 and to the point where the lower extremity of. rotor piston 8 at least partially uncovers opening 38.

Since activating liquid is removed via opening 38 to halt the upward movement of cylindrical casing 5, the position of rotor piston 8, as shown in Fig. 3, is one of complete activation. In this position of complete activation rotor piston 8 has been elevated substantially above the elevated sections 6A of rotor bottom 6, but the indenta-- tions in rotor piston 8 still partially mesh with the ele,

vated portions 6A of rotor bottom 6, i. e., the lower extremity of rotor piston 8 is slightly below the upper extremity of the elevated sections 6A of rotor bottom 6;:-

Fig. 3 also shows the relative position of slurry distributor 11 and splash sleeve 25 when rotor piston 8 and rotor piston face 9 are in a position of complete activation. Additionally, Fig. 3 depicts the relative positions of the lower extremities of the six wash pipes. These wash pipes are positioned so as to wash the separated solid material adjacent to the side wall of the centrifuge'at various levels as the separated solid material is pushed upwardly along the centrifuge side wall in the form of amat or layer thereon by the operation of rotor piston 8 Fig. 5 is an enlarged elevational view through section 55 showing rotor piston 8 and rotor piston face 9 in an inactivated position. Fig. 4 is an enlarged plan view of rotor piston 8 through section 4-4,'and Fig. 6 is an enlarged plan view of rotor bottom 6 with its plurality of elevated sections 6A which mesh with and fit into the plurality of indentations in the base of rotor piston 8. In order to activate rotor piston 8, activating liquid, after introduction via tube 14 and the annular space between casing 5 and casing 10, passes via openings in rotor piston 8. This activating liquid then enters the spaces between the elevated sections 6A of rotor bottom 6 and the indentations in rotor piston 8. The-activating liquid in these spaces exerts the force imparted to it by the centrifugal action of the apparatus,.and, consequently, rotor piston 8 is moved upwardly. Rotor piston 8 is then in an activated position and it assumes a position of deactivation as the activating liquid is removedfrom the piston via openings 38 and thief valves 37.

Fig. 7 is an enlarged elevational viewof the foraminous portion of side wall 7. It will be'understoodthat the construction of side wall 7 will be determined by a con-; sideration of various factors, and the type of construction desired will depend to a large extent upon the centrifugal force to be exerted upon it and upon the liquids and solids in the slurry to be resolved. cellulose from spent nitrating acid it was found desirableto employ anouter perforate casing with a bar screen of vertically extending metallic bars disposed along the inner periphery of the outer casing. Fig. 7 depicts the 7 upper portion of side wall 7 comprised of outer'perfora'te l casing 41, containing a series of perforations or openings 42, and of inner perforate bar screen 43. Bar screen In order to separate nitro- 43 is composed of a plurality of vertically disposed metallic bars 44 spaced at regular intervals around the inner periphery of perforate casing 41. The individual bars 44 are rigidly maintained in place by a plurality of circular metallic rings 45 each disposed in a horizontal plane. Fig. 8 is an enlarged plan view of metallic bars 44 and circular ring 45, and Fig. 9 is an enlarged elevational view through section 99 showing metallic bar 44 and circular ring 45.

Fig. 10 is an elevational view of the feeding unit that was found effective for introducing the slurry feed to the centrifuge. Fig. 10 also shows the preferred relative position of the feeding unit with other members of the centrifuge such as activating liquid tube 14, splash sleeve and slurry distributor 11. The feeding unit consists of a cylindrical inlet tube 51 through which the feed slurry enters feeder box 52. Thence the feed slurry enters the centrifuge via the base of feeder box 52 and the annular space between splash sleeve 25 and slurry distributor 11. Fig. 11 is a plan view of the base of feeder box 52 showing opening 53 through which the feed slurry enters the centrifuge. The cross-sectional area of opening 53 corresponds substantially with the cross-sectional area of feeder tube 51 to provide for even and unhindered flow of feed slurry through the feeding unit and into the centrifuge.

Fig. 12 is an enlarged elevational view showing rotor piston 8 in its activated position and showing an alternative slurry distributor and splash sleeve. In this drawing slurry distributor 11A is substantially straight on approximately a degree angle, and it does not have the can cave curvature of distributor 11 in Fig. 3. Distributor 11A is rigidly attached to rotor piston face 9 and to casing 10, and distributor 11A moves in conjunction with those members to which it is attached. Splash sleeve 25A, which is disposed on about a 75 degree angle with the horizontal, forms an annular space with distributor 11A, and it is through this annular space that feed slurry is introduced to the separating action of the centrifuge. Sleeve 25A at its upper extremity is attached to and moves in conjunction with casing 10, and, consequently, the position of sleeve 25A relative to distributor 11A remains unchanged during the operation of the centrifuge. The slurry distributor and splash sleeve shown in Fig. 3 are described in detail and claimed in the copending application, Serial No. 258,364, filed November 27, 1951.

It will be understood that the apparatus described above in detail has wide application for the separation of a slurry of liquid and solid material. One application for which the apparatus is particularly suitable is for the separation of nitrocellulose from spent nitrating acids that are obtained during the nitration of cellulosic material. It is a preferred application of this apparatus to effect such a separation of nitrocellulose from spent nitrating acid, and the actual operation of the apparatus will be described in detail employing a feed slurry of nitrocellulose and spent nitrating acids from a cellulose nitration process.

Operation To initiate the separation, the operation of the centrifuge is begun by the driving mechanism (not shown) operating on shaft 1 which in turn effects the revolution of the centrifuge basket and accompanying members. It Will be understood that the centrifuge can be operated at a speed suitable for effecting the necessary separation. With a feed slurry of nitrocellulose and spent nitrating acids and with a centrifuge basket having a diameter of about 23 inches a minimum speed of 700800 R. P. M. can be employed, and the maxmum preferred speed has been found to be about 1700 R. P. M. With the centrifuge at the desired speed and with the rotor piston in the inactivated position as shown in Fig. 1 and Fig. 5, a measured quantity of feed slurry is introduced to the apparatus via feeding tube 51. The feed slurry passes through feeding box 52 containing slot or opening 53 and it then passes through the annular space between splash sleeve 25 and distributor 11. Since the centrifuge is revolving rapidly, the feed slurry is accelerated and transferred toward bar screen 43 along the inner periphery of side wall 7. For effective separation of a slurry of nitrocellulose and spent nitrating acid it is preferred that the maximum space between the metallic bars of bar screen 43 be no greater than 0.01 inch. The operation of the centrifuge is continued and spent nitrating acid is forced out of the nitrocellulose while the latter is retained in a mat on the inner surface of the bar screen. The spent nitrating acid passes through the bar screen and through openings 42 in perforated casing 41 surrounding the bar screen, and after passage along curb 32 it is recovered for further use. After a sufficient period of time has elapsed for removal of spent nitrating acid from the solid nitrocellulose, activating liquid is introduced to the centrifuge via tube 14. This activating liquid may be any liquid, preferably compatible with the spent nitrating acid, that will provide suitable hydraulic operation of piston 8 and the actual liquid that is employed will vary with the separation that is being effected by the centrifuge. In some instances water will be found to be a suitable activating liquid. For the separation of nitrocellulose from spent nitrating acid a portion of the spent nitrating acid itself can be used as the activating liquid. Thus, in the preferred operation being described, a predetermined quantity of spent nitrating acid enters the centrifuge via tube 14 and it passes through the annular space between casing 5 and casing 10. Then it passes through openings in piston 8 and it enters the space between the indentations in piston 8 and the elevated sections 6A of bottom plate 6. The activating liquid builds up sufficient pressure, due to the centrifugal action, to hydraulically elevate piston 8, and consequently the movement of piston 8 and attached piston face 9 effects an upward movement of the mat of nitrocellulose on the bar screen equivalent in distance to the length of stroke of piston 8. The activating liquid causes the movement of piston 8 sufficient to bring the lower extremity of that piston in such a position that openings 38 in side wall 7 are at least partially uncovered, and activating liquid then escapes through openings 38. Thus, the upward movement of rotor piston 8 is controlled by escape of the activating liquid and by the volume of activating liquid employed. Any number of openings in side wall 7 corresponding to opening 38 can be used to effect the desired removal of activating liquid. Actually, in operation twenty-four openings have been employed, but this number can be widely varied, and the number used will depend upon the actual size of the individual openings. During the activation of rotor piston 8, thief valves 37 in side wall 7 are open continuously, and consequently activating liquid is continuously escaping through these valves. The area of these valves is considerably less than the area of openings 38, and the area of valves 37 is adjusted to effect the desired lowering or inactivation of rotor piston 8 in a predetermined time interval. The upper limit of the stroke of piston 8 is determined by the position of openings 38, and the rate of release of activating liquid through valves 37 determines the speed at which rotor piston 8 is returned to its inactivated position. The number of thief valves that is necessary for the efiicient operation of the centrifuge is variable over relatively Wide limits. In operation eight thief valves corresponding to valve 37 have been employed in side wall 7, but it will be seen that this number can be varied while remaining within the scope of the invention.

As rotor piston 8 begins its descent from its activated position to the inactivated position, a second measured quantity of feed slurry is introduced to the centrifuge as previously described, and as spent nitrating acid is being removed from this second portion of feed slurry the first portion of nitrocellulose introduced to the centrifuge is washed with a sufiicient quantity of spent nitrating acid diluted to about a concentration-and introduced 7 second feed portion,

greater number of washing steps 7 above will be found useful, while in other instances no via line. 17 to displace spent nitrating. acid, which gener- Y ally has, a concentration in excess of 60%, remaining in the mat of nitrocellulose. The latter is recovered after passage used as an activating liquid or it can be subjected to suitable steps'for the recovery of the acids. Upon completion of a predetermined time interval during which the first portion of nitrocellulose is washed with 60% acid and s'pent nitrating acid is centrifugally wrung out of the another predetermined amount of activating liquid is introduced to the centrifuge as previously described to effect the upward movement of rotor piston 8 and the mat of nitrocellulose being formed upon the inner walls ofthe ,bar screen,

. Upon continued operation of the centrifuge as previously described, a continuous mat of nitrocellulose is formed upon the inner surface of'the bar screen. As the nitrocellulose progresses upward along the bar screen, it is washed at various levels with varying concentrations of spent nitrating acid. As already pointed out, the first washing was effected with a 60% acid. The second washing can be effected with a 40% acid; the third washing with a 20% acid, and the final washing with water. These acid concentrations are given merely by way of example, and it will be understood that other concentrations can be 'used without departing from the scope of the invention. The acidwhich is displaced from the nitrocellulose during each of the washings is recovered after passage along the respective curbings, and the recovered acids can then be recycled and used to carry out additional washing of the nitrocellulose mat inside the centrifuge. The final washing of the nitrocellulose is effected with water and subsequently the washed nitrocellulose is sloughed over the top of the bar screen and side wall 7 with an additional amount of water. This nitrocellulose and water pass along curbing 27 to the base of the centrifuge. Additional amounts of water are introduced to the centrifuge via inlet 36 to wash the nitrocellulose along the sloped base of the centrifuge and to remove the nitrocellulose via outlet 33. The nitrocellulose thus removed can then be separated from accompanying water by. any suitable process, and it is then ready for any subsequent steps in the nitrocellulose manufacturing process.

The washing of the solid mat on the inner surface of the bar screen,'as described above, is particularly useful in the separation of nitrocellulose from spent nitrating add In effecting other separations of, solid material from accompanying liquids, such washing steps may or may not be necessary. In some instances a fewer or than those described washing steps will be required. It will be understood that the number of washing steps that are employed can'be' varied without departing from the scope of the invention and that it is within the scope and spirit of the invention to operate the centrifuge without any washing steps. Numerous other variations and modifications within the scope of the invention will be apparent to those skilled inthe art from the detailed disclosure above.

What I claim and desire to protect by Letters Patent is:

1, In a centrifuge for separating solid substances from liquids, a vertically disposed drumrotatably mounted on a vertical drive shaft, said drum having an imperforate solid-base, an iinperforate cylindrical axial hub attached to said drive shaft and extending upward interiorly of said drum, and a perforate side wall on the inside surface of which solid substances accumulate in the form of a layer during centrifugal action, said base having a plurality of elevated sections disposed interiorly of said drum; a solid piston axially and slidably mounted on said hub within the drum and rotatable with said drum, said piston having an imperforate cylindrical sleeve attached to its upper face concentrically disposed around said axial hub and spaced apartvtherefrorn to form an annular space, aplurality of openings communicating along curb 31, and it can be subsequently with the annular space between said sleeve and said axial hub, and a plurality of indentations in itslower horizontal surface that mesh with said elevated sections of said drum base, said piston being movable axially upward when activated to displace solid substances 'upwardly in the form of a layer on said side wall along the inner periphery of said side wall; and an inlet disposed above and communicating with the annular space between said sleeve and said axial hub for introducing piston-activating liquid between said imperforate drum base and said'piston, said piston being activated axially upward solely by centrifugal force created by rotation of the centrifuge acting upon said activating liquid between said imperforate drum base and said piston; said drum side wall having a first plurality of openings of predetermined cross-sectional area disposed in a horizontal plane immediately below the lower extremity of the piston at the upper limit of its upward stroke for rapid escape of piston-activating liquid and having a second plurality of openings of a predetermined crosssectional area disposed in a horizontal plane with the lower extremity of said piston at the lower'limit of its stroke for slow escape of piston-activating liquid to con trol the rate of movement of said piston from the upper to the lower limit of its stroke;

2. In a centrifuge for separating solid substances from liquids, a verticaly disposed drum rotatably mounted on a vertical drive shaft, said drum having an imperforate solid base, an imperforate cylindrical axial hub attached to said drive shaft and extending upward interiorly of' said drum, and a perforate side wall on the inside surface of which solid substances accumulate in the form. of a layer during centrifugal action, said base having a pluralityof elevated sections disposed interiorly of said drum; a solid piston axially and slidably mounted on said hub within the drum and rotatable with said drum, said piston having an imperforate cylindrical sleeve attached to its upper face concentrically disposed around said axial hub and spaced apart therefrom to form an annular space, a plurality of openings communicating with the annular space between said sleeve and said axial hub, and a plurality of indentations in its lower horizontal surface that mesh with said elevated sections of said drum base, said piston being movable axially upward when activated to displace solid substances upwardly in the form of a layer on said side wall along the inner periphery of said side wall; an inlet disposed above and communicating with the annular space between said sleeve and said axial hub for introducing piston-activating liquid between said imperforate drum base and said piston, said piston being activated axially upward solely by centrifugal'force created by rotation of the centrifuge acting upon said activating liquid between said imperforate drum base and said piston; said drum side wall having a first plurality of openings of'predetermined cross-sectional area disposed in a horizontal plane immediately below the lower extremity of the piston at the upper limit of its upward stroke for rapid escape of piston-activating liquid and? having a second plurality of openings of a predetermined cross-sectional area disposed in a horizontal plane with the lower extremity of said piston at the lower limit of its stroke for slow-escape of piston-activating liquid to control the rate of movement of said piston from'the References Cited in the file of this patent UNITED STATES PATENTS 1,382,142 Sturgeon June 21, 1921 1,928,341 T61 Meer Sept. 26, 1933 (Other references on following page) Altpeter Jan. 23, 1934 Walkup Dec. 6, 1949 Carnagua et a1 Oct. 9, 1951 Bryant Nov. 18, 1952 Sollinger June 16, 1953 Cox et a1 July 21, 1953 10 FOREIGN PATENTS Great Britain 1922 Great Britain Aug. 22, 1918 Great Britain Nov. 9, 1922 France June 18, 1907 Germany Mar. 28, 1897

Claims

1. IN A CENTRIFUGE FOR SEPARATING SOLID SUBSTANCES FROM LIQUIDS, A VERTICALLY DISPOSED DRUM ROTATABLY MOUNTED ON A VERTICAL DRIVE SHAFT, SAID DRUM HAVING AN IMPERFORATE SOLID BASE, AN IMPERFORATE CYLINDRICAL AXIAL HUB ATTACHED TO SAID DRIVE SHAFT AND EXTENDING UPWARD INTERIORLY OF SAID DRUM, AND A PERFORATE SIDE WALL ON THE INTERIORLY OF OF WHICH SOLID SUBSTANCES ACCUMULATE IN THE FORM OF A LAYER DURING CENTRIFUGAL ACTION, SAID BASE HAVING A PLURALITY OF ELEVATED SECTIONS DISPOSED INTERIORLY OF SAID DRUM; A SOLID PISTON AXIALLY AND SLIDABLY MOUNTED ON SAID HUB WITHIN THE DRUM AND ROTATABLE WITH SAID DRUM, SAID PISTON HAVING AN IMPERFORATE CYLINDRICAL SLEEVE ATTACHED TO ITS UPPER FACE CONCENTRICALLY DISPOSED AROUND SAID AXIAL HUB AND SPACED APART THEREFROM TO FORM AN ANNULAR SPACE, A PLURALITY OF OPENINGS COMMUNICATING WITH THE ANNULAR SPACE BETWEEN SAID SLEEVE AND SAID AXIAL HUB, AND A PLURALITY OF INDENTATIONS IN ITS LOWER HORIZONTAL SURFACE THAT MESH WITH SAID ELEVATED SECTIONS OF SAID DRUM BASE, SAID PISTON BEING MOVABLE AXIALLY UPWARD WHEN ACTIVATED TO DISPLACE SOLID SUBSTANCES UPWARDLY IN THE FORM OF A LAYER ON SAID SIDE WALL ALONG THE INNER PERIPHERY OF SAID SIDE WALL; AND AN INLET DISPOSED ABOVE AND COMMUNICATING WITH THE ANNULAR SPACE BETWEEN SAID SLEEVE AND SAID AXIAL HUB FOR INTRODUCING PISTON-ACTIVATING LIQUID BETWEEN SAID IMPERFORATE DRUM BASE AND SAID PISTON, SAID PISTON BEING ACTIVATED AXIALLY UPWARD SOLELY BY CENTRIFUGAL FORCE CREATED BY ROTATION OF THE CENTRIFUGE ACTING UPON SAID ACTIVATING LIQUID BETWEEN SAID IMPERFORATE DRUM BASE AND SAID PISTON; SAID DRUM SIDE WALL HAVING A FIRST PLURALITY OF OPENINGS OF PREDETERMINED CROSS-SECTIONAL AREA DISPOSED IN A HORIZONTAL PLANE IMMEDIATELY BELOW THE LOWER EXTREMITY OF THE PISTON AT THE UPPER LIMIT OF ITS UPWARD STROKE FOR RAPID ESCAPE OF PISTON-ACTIVATING LIQUID AND HAVING A SECOND PLURALITY OF OPENINGS OF A PREDETERMINED CROSSSECTIONAL AREA DISPOSED IN A HORIZONTAL PLANE WITH THE LOWER EXTREMITY OF SAID PISTON AT THE LOWER LIMIT OF ITS STROKE FOR SLOW ESCAPE OF PISTON-ACTIVATING LIQUID TO CONTROL THE RATE OF MOVEMENT OF SAID PISTON FROM THE UPPER TO THE LOWER LIMIT OF ITS STROKE.