US3168474A - Centrifuge apparatus - Google Patents

Description

Feb. 2, 1965 R. c. STALLMAN ETAL 3,168,474

CENT'RIFUGE APPARATUS Filed April 25, 1963 2 Sheets-Sheet 1 INVENTUM EDWARD G, PICKELS RICHARD C. STALLMAN ATTORNEYS Feb. 2, 1965 R. c. STALLMAN ETAL 3,158,474

CENTRIFUGE: APPARATUS Filed April 25, 195s 2 sheets-sheet 2 INVENTORS EDWARD G. PICKELS RICHARD C. STALLMAN ATTORNEYS United States Patent O 3,163,474 CEN'HREFUGE APPARATUS Richard C. Stallman, San Carlos, and Edward G. Picirels, Atherton, Calif., assignors to Beckman instruments, Inc., a corporation of California Filed Apr. 25, 1963, Ser. No. 275,563 1 Claim. (Ci. 233-33) This invention pertains to an improved rotor for high and ultrahigh speed centrifuge apparatus. Such a rotor is particularly useful in, though not limited to, ultrahigh speed continuous ilow centrifugation. For example, the rotor is also useful in improving batch separation and for density gradient centrifugation.

In a high speed centrifuge, rotor vibrations contribute to stirring or mixing of fluids being centrifuged. It will be readily appreciated, therefore, that vibration during centrifugation at rotor speeds on the order of 20,000 to 30,000 r.p.m. or above can impose substantial problems of mixing, not to mention difficult mechanical problems involved in trying lto maintain rotor balance at such speeds.

While it has been possible to build and drive rotors empty at these speeds with only the slightest of vibration, the introduction of fluids tends to generate severe vibrations whether the iiuid is moving in a stream through the rotor during centrifugation (as in continuous flow operation), or not. This condition can be referred to as dynamic instability.

Dynamic instability occurs in several different types of equipment.` However, it is particularly noticeable in the so-called continuous How equipment wherein a iiuid stream is fed into and withdrawn from the rotor during centrifugation. The following description, therefore, has been based on such a system.

In general, it is an object of this invention to provide an improved centrifuge rotor wherein rotor vibration is minimized.

Another object of the invention is toreduce dynamic instability in a centrifuge rotor caused by the presence in the rotor of fluids to be centrifuged.

A more particular object of the invention is to provide a rotor with means for reducing dynamic instability which further serve to reduce fluid slippage at ultrahigh speeds of centrifugng.

Other objects of the invention will be more readily apparent from the following description of a preferred embodiment when taken in conjunction with the accompanying drawings, in which:

FIGURE l is a side elevational view, partly in section, showing a continuous flow centrifuge apparatus;

FIGURE 2 is an enlarged sectional view, in plan, taken generally along the line 2-2 of FIGURE 1;

FIGURE 3 is an enlarged view, partly in section, showing the centrifuge rotor, feed shaft and coupling of the shaft to the rotor; and

FIGURE 4 is a reduced schematic perspective view showing an intermediate length of the rotor core and a portion of Vanes supported thereby.

In the following description, there is provided a centrifuge rotor together with means for supporting and driving same. The rotor comprises, in general, a body member adapted -to be driven at high speed about an axis of rotation. (In the continuous flow equipment described further below, the body member includes a hollow cylindrical bowl.) Means carried in the body member serve to subdivide the body member into a number `member 52.

$168,474 Patented Feb. 2, 1965 lee of compartments extending generally lengthwise thereof. Based on certain observations to be described, the minimum number of compartments is at least substantially equal to the normal operating speed of rotation of the rotor during centrifugation as measured in thousands of revolutions per minute.

Referring to FIGURE l, the centrifuge apparatus illustrated includes an outer housing 11 which encloses the drive means and rotor housing. The top of housing 11 is provided with an opening 12 through which a rotor 13 may be passed for mounting within a rotor chamber 17 on a drive shaft or spindle 14, as will be presently described. A door 16 threadably receives and supports an upper bearing and seal assembly 20. Door 16 is provided with spaced rollers 18 which ride in spaced channels 19 secured to the sides of housing 11 to provide easy access to chamber 17. A latch mechanism (not shown) works in conjunction with controls (not shown) to releasably lock door 16.

The side walls of rotor chamber 17 include a cylindrical steel member 21 which acts as a guard should the rotor explode under the strain created by the relatively high rotational velocity at which it is operated. The lower end of member 21 receives the bottom wall 22, likewise made of relatively strong material. The interior of chamber 17 may be provided with refrigeration means including evaporator coils 23 which serve to control the temperature therein.

A suitable vacuum seal is formed between bottom wall 22 and spindle 14 as it extends upwardly into chamber 17. Preferably, spindle 14 is made of flexible material and extends downwardly with its lower end journaled in an oil-filled bearing assembly 26. Bearing assembly 26 is supported by spaced brackets 27 extending downwardly from a resiliently mounted base 28. Base 28 may be supported from a fixed member 36 by springs 37. A driven pulley 3l is carried by spindle 14 and is driven by a belt 32 from a drive pulley 33 and motor 34. Means (not shown) may be disposed in housing 11 for evacuating air from chamber 17.

Rotor means 13 are provided, as best shown in FIG- URE 3, comprising a cylindrical bowl 41 threaded at its ends 42, 43. End 43 threadably receives a closure member or bottom 44. Bottom 44 includes a well 46 adapted to receive the upper end of spindle 14. Spaced pins 47, 4S are adapted to engage accommodating holes formed in the upper end of spindle 14 to provide a positive drive connection between spindle 14 and bottom 44 whereby bowl 41 can be driven.

Means are provided for holding a core member with respect to bowl 41 whereby the core and bowl rotate together. The upper end of bottom 44 is provided with a boss 45 adapted to receive 'a rotor core 49. Core 49 is provided with holes adapted to receive the upper ends of pins 47, 48 whereby it is pisitively driven by spindle 1 4 to rotate with bowl 41.

The upper end of bowl 41 threadably receives a cover An 0-ring 53 is interposed between a shoulder 54 formed on bowl 41 and the lower edgeof cover member 52. Member 52 is provided with a plurality of radially extending, downwardly sloping conduits 56 adapted to communicate with a plurality of slots 5S formed on the upper, generally flanged end of core member 49. Fluid tlows along slots 5S through conduits 56 to the outer portion of cover member 52 as indicated by arrows 59.

vas slippagei The upper end of core 49 includes an outwardly extending'iiange or hub 61 received within a well 62 formed in cover member 52. An O-ring provides a fluid seal between hub 61 and member 52.

Fluid passage means for axially withdrawing fluid along core member 49 includes a plurality of axially spaced and radially extending openings 71 leading inwardly from a core encircling manifold groove 99. Openings 71 serve to conduct fluid from spaces formed between coremember 49 and bowl 41. The fluid passage means further includes -an upwardly directed axial channel 72 leading to a fluid removal and feed assembly, to be presently described.

Cover `member 52 threadably receives a guide member 76. Guide member 76 maintains and guides a exible feed and removal shaft assembly 77. Shaft assembly 77 comprises lan outer tube 7S having a concentric inner tube 79. Assembly 77 is supported within guide member 76 by a bushing 80. Spaced O-rings 81, 82 provide Ia seal. The lower end of assembly '77 is received by a hea'd 83. A fluid llow ypassage 84, formed in head 83, serves torpass uid between channel 72 and space S5 delined between outer tube 78 and head 83. Outer tube 78 includes radially `directed ports 8d which allow duid to flow upwardly as indicated by arrows 87. As thus indicated, the iiow is into an annular space formed to extend axially between the inside of tube 7S and the outside of tube 79. Fluid is fed into head 83 through tube `79. The lower end of tube 79 is disposed in uid communication with passage 89 formed in head 83. Passage 'Q89 serves, `in turn, to communicate with slots 5S adjacent thereto tol direct uid into passages 56. An O-ring seal is formed between head 83 and the bottom end of shaft assembly 77. -ring 91 provides a seal between core t9 and head 83, while another 0-ring 92 serves to provide sealing between head 83 and guide member 76.

Thus, uid feed can be provided via inner tube 79 to flow outwardly through openings 89, slots 58 and passages 56 to enter space formed between core 49 and bowl 41. Fluid entering bowl 41 is then displaced inwardly to be withdrawn via openings 71, channel 72, passage 84 andthen through the annular space defined between tubes 78, 79.

As noted above, vibrations are generated in an otherwise relatively vibrationless rotor when uid to be centrifuged-is introduced. It has been observed that the presence of the lluid material sets up shock waves which cannot be satisfactorily removed by damping. However, lwe have observed that if the rotor is subdivided into a number of narrow, pie-shaped segmental compartments,

the .shock waves are satisfactorily broken up. The

.minimum number of compartments for preferred results has been observed to be substantially equal to the rotational speed of the rotor during centrifugation taken in Obviously, due to thickness of partitions between compartments, the volumetric capacity of the rotor becomes less and less as more and `more compartments are formed.

Thus,V for a rotor operating Iat 60,000 rpm., it may not be practicable to employ more than fifty compartments. Accordingly, short of a limit dictated by overcrowding the interior of bowl 41, the relationship S=C seems to substantially define the minimum number of compartments to provide a workable lower limit free of adverse shock wave vibration, where S is rotor speed in thousands of revolutions lper minute and C is the number of segmental compartments.

As is shown, stirring can also be caused during periods of acceleration and deceleration due to what is referred to I Generally, this can be thought of as the inability of one portion of the fluid to maintain rotational speed with another portion radially displaced therefrom. Compartmentalizing the rotor, therefore, serves to limit mixing from this source as well. However, we have observed that with ever increasing rotor speeds, the inner wall of the bowl or body member, during operation, temporarily takes on a greater diameter. Thus, to avoid slippage `during speed changes during the period that the bowl is enlarged, the partitions forming compartments are free to move radially so as to ride against the wall at all times.

Accordingly, means defining a number of segmental compartments extending generally lengthwise of the rotor are formed by employing a plurality of planar vanes 96. The planes of vanes 96 intersect along the axis of rotation of the rotor. Varies 96 are supported for limited movement radially of the axis of rotation to allow them to move outwardly during centrifugation so as to ride against the inner wall of bowl 41. Thus, vanes 96 follow the radial expansion and contraction of bowl 41 to preclude slippage at the region adjacent the walls.

Accordingly, core 49 is provided with longitudinal slots 94 dimensioned with respect to the thickness of the vanes, so as to loosely receive vanes 96. For example, sufhcient clearance is provided wherein the vanes are of aluminum having a sheet thickness of .032 inch and wherein the slots 94 have a dimension of .034 inch. Vanes 96 extend radially outwardly with their outer edge contacting the inner wall of bowl 41. The axial extent of vanes 96 disposes them loosely in contact, top and bottom, with cover member 52 and bottom 4d, respectively.

As shown in FIGURE 2, thirty-six vanes 96 are preferably provided in bowl d1 wherein the latter has a four inch inside diameter. The normal operating speed of rotation during centrifugation of bowl 41, as illustrated in FIGURE 2, ranges in the neighborhood of 30,000 r.p.rm.

Vanes 96 are readily removable and can, therefore, be removed in multiples of either three or four at a timefor lesser rotor speeds, where increased volumetric capacity within the rotor is desired. Thus, the number of compartments can be readily varied to accommodate centrifugation at different speeds with minimum dynamic instability.

Any suitable means can be employed to feed fluid into shaft assembly 77 and withdraw same via channel '72. Therefore, further description of such known apparatus need not be described. Fluid feed and withdrawal means is, therefore, represented generally by reference numeral 20.

We claim:

In combination, centrifuge apparatus comprising a rotor, said rotor including a hollow cylindrical bowl member adapted to be driven at a suiiiciently high speed about an axis of rotation to cause radial expansion of the side wall thereof, means carried in said bowl member serving to subdivide said bowl member into a plurality of compartments extending generally lengthwise thereof, the last said means including a core member extending coaxially within said bowl member, means holding said core member with respect to said bowl member and serving to cause both said members to be rotated together, a plurality of planar vanes within said bowl member, the planes of said vanes intersecting to define said axis of rotation, and means supporting the vanes for limited movement radially of said axis and serving to allow said vanes to ride outwardly with the inner wall of the cylindrical bowl member and follow radial outward movement of said wall during centrifugation, means for introducing fluid into the compartments of the rotor and means for removing fluid from said compartments, and means serving to support and drive said bowl member normally for centrifugation at high speed on the order of at least 20,000 rpm., the number of compartments being at least substantially equal to the normal operating speed of rotation of said bowl member during centrifugation taken in thousands of revolutions per minute.

(References on following page) 5 6 References Cited in the le of this patent 2,563,550 Quist Aug. 7, 1951 UNITED STATES PATENTS 2,610,788 EdWaIdS S6131. 16, 1952 2,710,718 Denman June 14, 1955 446,210 W'StOP Feb- 10, 1891 3,007,629 Boyland Nov. 7, 1961 4871943 Belmlmg Dec- 131 1892 5 3,073,517 Pickels et a1 Jan. 15, 1963 496,120 Haft APf- 25, 189 3,103,489 Pickels sept. 10, 1963 508,744 Ohlsson Nov. 14, 189s 3,108,955 Boyland Oct. 29, 1963 521,104 DHVIS June 5, 1894 3 109 839 Keith NOV 5 1963 721,186 Hedderich et a1. Feb. 24, 1903 732,886 odeu et a1 July 7, 1903 10 FOREIGN PATENTS 821,554 Truesdell May 22, 1906 852,392 Great Britain Oct. 26, 1960 1,061,656 Black -..1---- May 13J 1913 862,799 Great Britain Mar. 15, 1961 1,508,405 Mazza Sept. 16, 1924

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