Centrifuge Rotor

Abstract

A rotor for a centrifuge apparatus having a substantially cylindrical sidewall forming a bowl-like chamber open on one side thereof, and including a cover secured to the cylindrical sidewall and closing the opening to the chamber. The rotor also includes a resilient sealing lip attached to the sidewall and overhanging the chamber, the lip having an upper surface engaging a lower surface of the cover and having sufficient resiliency to follow movement of the cover under hydrostatic pressures produced in the rotor during centrifugation of liquid products within the chamber.

Description

BACKGROUND OF THE INVENTION

The invention described herein relates generally to rotors for centrifuge apparatus and more particularly to an improved bowl-type rotor of the type employed for zonal centrifugation.

The apparatus is utilized to provide quantitative separations of minute particulate matter, such as tissue cells or cell particles, or the like, in density gradients for the purpose of collecting discrete fractions thereof for subsequent analysis in research and clinical studies. Typically, in a bowl-type rotor, a sample solution is pumped into the central region of a rotor chamber which is filled with an appropriate density gradient solution. During centrifugation, the particles of interest in the sample disperse in a radial direction throughout the density gradient solution and at equilibrium are suspended in concentric layers in the density gradient solution at a location wherein their respective buoyant densities correspond to that of the solution.

During centrifugation of bowl-type rotors tremendous hydrostatic pressures are developed within the rotor at the extremities or outer walls of the bowl. The hydrostatic pressures tend to force the wall of the rotor outwardly and also create an upward thrust on the cover in the region adjacent the joint between the bowl rotor and its cover. The outward pressure on the rotor walls also creates a moment of force around the rotor bowl which, in turn, creates an upward thrust at the central portion of the bowl. The hydrostatic forces are so great that they sometimes cause separation between the cover of the bowl and the wall of the rotor where connected and result in a leakage of the liquid solution from the rotor. In an attempt to overcome this, a resilient seal, such as a resilient O-ring, is sometimes employed between the rotor wall and the cover which will prevent leakage of the solution from the rotor chamber. However, the seal member around the cover or the sidewall of the rotor is placed under extreme stress during the high speed centrifugation and, when the rotor and lid separate, the force of the solution on the seal very often causes the seal member to extrude from its seat thereby releasing the solution from the chamber.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided an improved bowl-type zonal centrifuge rotor including a base having a substantially cylindrical sidewall forming a bowl-shaped chamber over which is mounted a cover member and which is attached to the cylindrical sidewall. A resilient flexible sealing lip protrudes inwardly from the sidewall over the rotor chamber, the lip having a smooth surface adapted to abut against the cover in the region of a resilient sealing member or O-ring seated in an annular slot formed in the cover. The flexible lip maintains a sealing pressure against the cover and its O-ring and, under hydrostatic pressure created during centrifugation, the flexible lip moves with any slight movement of the cover to maintain a constant sealing pressure against the O-ring. A central core positioned within the rotor between the cover and the bottom of the chamber provides a vertical thrust against the bottom wall of the rotor chamber which thrust is opposite from the moment of force created by the centrifugal forces on the sidewall of the rotor. This reduces the upward displacement of the bottom wall of the rotor and reduces the movement of the sidewall in a direction radial to the axis of rotation.

It is an object of the present invention to provide a new and improved bowl-type rotor with an attached cover in which the hydrostatic forces, created by the liquid within the rotor during centrifugation, are reduced in the region of the seal between the cover and the sidewall to which it is attached.

It is another object of this invention to reduce the deflection between the cover and the sidewalls of the bowl by reducing the hydraulic axial loading on the cover.

It is another object of the present invention to provide a bowl-type rotor having a central core designed to oppose the upward thrust normally occurring in the bottom central portion of the bowl-shaped rotor during high speed centrifugation.

Further objects and advantages of the invention will become apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a rotor bowl assembly made in accordance with the present invention;

FIG. 2 is a plan view taken generally along the line 2--2 with portions of the rotor bowl assembly broken away to illustrate the location of the central core and the core wings with respect to the chamber in the rotor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing, and, more particularly, to FIG. 1, there is shown a rotor bowl 1 having a substantially cylindrical sidewall 4 enclosing a bowl-shaped chamber 3 over which there is positioned a lid or cover member 2. In order to retain the cover 2 in place, the sidewall 4 of the rotor is provided with threads 5 adjacent the open end thereof and the outer edge portion 4a of the rotor sidewall is adapted to fit snugly within an annular cavity 6 formed in the cover 2. Threads 7 on the cavity wall are adapted to mate with the thread 5 on the rotor sidewall so that the cover may be threaded down tightly onto the sidewall of the motor. The overhanging edge 2a of the cover helps retain the sidewall 4 in place against the centrifugal forces produced during high speed rotation of the apparatus. In the base portion 1a of the rotor, there is provided a well 8 which is adapted to receive a drive spindle (not shown) extending from the driving mechanism of a centrifuge apparatus.

Within the chamber 3, there is provided a rotor core or centerpiece 9 which is a relatively solid member, formed of a suitable metal, and which is tapered slightly in an outward direction from bottom to top. The core is provided with a plurality of slots 12 (see FIG. 2) formed in the outer surface thereof in a direction parallel to the vertical axis of the core 9. A plurality of projecting vanes or wings 11 (three of which are shown in FIG. 2) each have one end positioned in one of the slots 12 and extend radially outward thereby dividing the rotor chamber into equal sector compartments for minimizing turbulence during operation of the apparatus. Because the core or centerpiece 9 is subjected to high axial loading and because the core wings 11 must extend to the cavity wall under the lip 47, it is necessary to construct the core 9 and vanes 11 as separate parts and assemble them in the rotor chamber 3.

In assembling the rotor core 9 within the chamber 3, the vanes 11 are first inserted into the camber 3 and positioned generally into their relative positions therein. The core 9 is then inserted into the chamber so that the ends of the vanes extend into slots 12 formed in the rotor core. In order to facilitate insertion of the core or centerpiece 9 and permit orientation of the vanes 11 within the slots 12, each of the slots 12 is indented in the lower end adjacent the bottom of the core and tapered or beveled to form a ramp 10 so that there is a slight tolerance, permitting the ends of the vanes to fit initially into the slots 12. As the core centerpiece 9 is moved downwardly into the chamber, the ramp 10 forces the vanes 11 outwardly against the inner surface of the sidewall of the motor chamber. The outer ends of the vanes 11 conform to the bowl shape of the chamber and fit snugly against the sidewall beneath the lip 47. The rotor core abuts the bottom 32 of the cavity and legs or abutments 31 support the core thereon.

Inserted centrally within the rotor core is a feed or transfer tube assembly 13 which extends downwardly through an aperture 14 formed in the cover 2 into a cavity 16 formed in the rotor core 9. The lower end of the transfer tube 13 is provided with screw threads 17 which mate with internally formed threads 18 formed within the cavity 16 of the rotor core. The transfer tube 13 includes an outer conduit 19 (or plurality of conduits 19) formed as slots in the outer surface of the shaft 13. Slots 19 communicate with an enlarged opening 16a in the upper portion of the rotor core. This opening 16a in turn communicates with radial passages 22 in the wall of the core each of which communicate with passages 23 extending through each of the vanes or wings 11 and opening into the chamber 3 at the end of each wing. An opening 24, formed in a beveled or cutaway portion 26 of each vane, communicates with the upper portion of the chamber. The core member acts as a manifold to deliver fluids into each of the vanes 11.

The feed or transfer tube 13 is also provided with a central tubular conduit 27 which extends completely through the axial length of the transfer tube and communicates with a passage 28 formed in the lower end of the core. Passages 29 formed in the lower end of the rotor core 9 by means of abutments or shoulders 31 communicate with the passage 28 in the core. At least one of the passages 29 leads into each of the segments between the vanes 11 within the chamber. Attached to the upper end of the transfer tube is a cup 34 having an opening 35 therein which communicates with the passages 19 and 27 in the transfer tube. In operation, a liquid delivery means (not shown) is inserted into the opening of the cup 34 for introducing liquid gradient and sample materials through the passages 19 and 27 and thence into the rotor chamber. Cup 34 is firmly attached to the end of the transfer tube 13 and is tightly pulled downwardly against the upper surface 36 of the lid 2 so that an O-ring 37 formed within an annular slot in the lower surface of the cup abuts in sealing fashion against the upper surface 36 of the lid.

In order to provide a seal between the passages 23 formed in the vanes 11 and the passages 22 formed in the rotor centerpiece, a small O-ring or resilient seal ring 41 is provided within an enlarged opening surrounding the pasage 23. O-ring 41 seals around the surface of the pasage 23 and the surface of the core leading into the opening 22. Another resilient seal member 42 is fitted within a slot formed on the surface of the transfer tube 13 and abuts against the inner surface of the cavity 21 in the upper end 16a of the core centerpiece. This seal 42 prevents the flow of liquid beyond the upper end 16a of the cavity 21 and forces liquid from the cavity into the passages 22 and thence into the passages 23 formed in vanes 11. In order to prevent leakage around the upper surface of the core centerpiece 9, there is also provided an annular sealing means in the form of a resilient O-ring 43 positioned within an annular slot 44 in the upper surface of the core. The O-ring 43 abuts against the lower surface 46 of the cover 2 when the cover is tightened down onto the rotor. In addition the cover actually has its lower surface 46 abutting tightly against the upper flat surfaces of the core.

In a typical operation of the above-described rotor, a rotatable liquid delivery means (not shown) is inserted into the cup 34 through which a liquid may be pumped into the rotor. The rotor bowl is first loaded with a liquid gradient which is pumped into the bowl through the conduits 19, 21, 22 and 23. During the loading operation, the rotor bowl is rotated at a low speed (500-3,000 r.p.m.) causing the gradient liquid to form concentric annular "zones" of constant density liquid. The vanes 11 extend radially through the "zones," segmenting them and reducing mixing between adjacent zones of different densities. After the rotor bowl is filled with a liquid of graded density, a sample to be centrifuged is pumped through the conduit or transfer tube passage 27 where it flows through the passage 28 and the passages 29 beneath the rotor core into the center portion of the rotor chamber. The sample is normally followed by an overlay of low density liquid to move the sample clear of the core 9 and to assure complete removal of the sample from beneath the rotor core. The means for inserting the liquid materials into the rotor is then removed and the cap 34 is closed with a suitable sealing cap (not shown) to close the passages 19 and 27. The rotor is then accelerated for the actual centrifuging operation.

When centifugation has been completed, the rotor bowl is decelerated to unloading speed (500-3,000 r.p.m.) and the rotor contents emptied through the liquid delivery means by pumping high density fluid to the outer wall of the rotor cavity through the passages 19, 21 22 and passages 23. The high density fluid forces the gradient and the sample, dispersed in the annular gradient rings, toward the rotor core 9 and the taper on the exteral surface of the rotor core forces each of the gradient rings to flow downwardly through the passages 29 and up the central passage 27 of the transfer tube and thence out through the delivery means attached to the upper end of the transfer tube.

As the rotor is subjected to the high angular velocity by a drive hub at 8, the resulting hydraulic forces within the chamber cause the cover 2 and the bowl 1 to tend to move relative to one another. These members are restrained only by the threads and the overhanging lip 2a of the cover at 2a. This hydraulic force is proportional to the fourth power of the maximum radius at which it can act. In order to effectively reduce the radius at which these forces may act on the cover, the rotor is provided with a lip 47 extending from an upper portion of the sidewall 4, which intrudes radially into the clearance volume adjacent the lid 2 of the rotor. The lip 47 has a lower curved surface 47a and an upper flat surface 47b. At its base or connection with sidewall 4, the lip is relatively thick but it gradually tapers toward the end intruding into the chamber.

The thinner portion of the lip 47 are somewhat resilient and flex under the influence of axial hydraulic force such that as the lid 2 moves upwardly under the hydraulic pressure, the lip 47 moves just enough to follow the cover's motion and maintains contact with a resilient O-ring seal 48 positioned in an annular slot 49 within the lower surface of the cover. The upper surface 47b of the lip 47 is flat and maintains continuous contact with the O-ring 48 as the cover and sidewalls of the motor move relative to each other. At the base of the lip 47, it is much thicker and much less resilient so that any load exerted by the hydraulic forces is prevented from being transmitted to the cover in this region. The hydraulic forces may be transmitted in an upward direction toward the cover only at the inner edge of the resilient lip 47. Since this is at a radius much less than the outer extremity of the rotor wall, the hydraulic pressure exerted against the inner surface of the cover 2 is less than would normally be present if there were no resilient lip or seal abutting the lower surface of the cover.

Under the influence of centrifugal force, the wall of the rotor at 51 tends to move radially outward. Since this wall is attached to the base and restrained by the base, this tendency to move outward results in a moment about the center of the base causing the center to move upwardly relative to the threads of the cylindrical wall at 7. This upward movement of the central portion of the base is restrained by virtue of the force exerted by the cover 2 downwardly against the heavy metallic core member 9 which tends to exert a force axially against the base. By restraining the center of the base from bulging upward by the use of the rigid central core 9, the radial excursion of the sidewall 4 of the rotor is reduced with a corresponding reduction in stresses in the sidewall 4 under high speed centrifugation.

While in accordance with the patent statutes there has been described what at present is considered to be the preferred embodiment of the invention, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, the aim of the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

What is claimed is:

1. A rotor for a centrifuge apparatus comprising

a rotatable bowl having a base and a substantially cylindrical sidewall forming a chamber having an open side substantially coextensive with said cylindrical sidewall;

a cover for closing said open side of said chamber;

means for securing said cover to said sidewall of said rotatable bowl; and

a resilient lip attached to said sidewall and overhanging said chamber, said lip having an upper surface engaging the lower surface of said cover, said lip having sufficient resiliency to permit it to move and follow movement of said cover thereby maintaining sealing contact with said cover during centrifugation of liquid products within said chamber.

2. A rotor for a centrifuge apparatus comprising

a rotatable bowl having a base and a substantially cylindrical sidewall forming a chamber having an open side substantially coextensive with said cylindrical sidewall;

a cover for closing said open side of said chamber, including means engaging said sidewall for supporting said cover over said chamber, said cover having a substantially flat lower surface;

means for delivering liquid gradient and sample products through said cover into said chamber; and

a resilient lip attached to said sidewall and overhanging said chamber, said lip having an upper surface engaging said substantially flat surface of said cover, said lip having sufficient resiliency to permit it to move and follow movement of said cover thereby maintaining sealing contact with said cover during centrifugation of liquid products within said chamber.

3. The rotor defined in claim 2 in which said cover includes an annular groove formed in the lower surface thereof in which is mounted a resilient O-ring and said resilient lip extending from said sidewall is so constructed and arranged as to engage said O-ring and follow movement thereof to maintain sealing contact with said O-ring during centrifugation of liquid products within said chamber.

4. The rotor defined in claim 1 in which said resilient lip is relatively thick at its attachment to said sidewall and gradually reduces in thickness to form a resilient portion which moves in response to hydrostatic pressure in said chamber created during centrifugation thereby forcing said resilient lip to maintain contact with said cover.

5. The rotor defined in claim 4 in which said cover is provided with an annular groove in the lower surface facing said chamber, and an O-ring is disposed in said groove and said resilient lip is so positioned and disposed as to engage said O-ring thereby maintaining sealing contact with said O-ring and said cover during centrifugation of liquid products within said chamber.