WO1994027879A1

WO1994027879A1 - Capping assembly for use with sealed tubes

Info

Publication number: WO1994027879A1
Application number: PCT/US1994/005710
Authority: WO
Inventors: William Andrew Romanaukas; Edward Thomas Sheeran, Jr.
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1993-05-27
Filing date: 1994-05-25
Publication date: 1994-12-08

Abstract

A tube capping assembly (12) includes a force transmitting member (38) that transmits axial and bending components of the body force of the capping assembly to a tube (10). The force transmitting member may be integral with the sleeve of the capping assembly or may be an annular washer-like member separate from the capping assembly. The separate member may be integrally formed or may be formed from conjoinable segments. The capping assembly may be used in a swinging bucket, a fixed angle or a vertical angle centrifuge rotor.

Description

TITLE

CAPPING ASSEMBLY FOR USE WITH SEALED TUBES

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Serial Number 07/683,927, filed April 11, 1991 (IP-0868), filed in the names of Romanauskas and Sheeran and assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION

Field of the Invention The present invention relates to a tube capping assembly having a plug and an associated crimpable sleeve that, when deformed, forms a seal with the neck of a centrifuge tube, and in particular, to a tube capping assembly having a skirt portion thereon especially adapted to permit the use of a centrifuge tube of this type in a swinging bucket rotor as well as in fixed and vertical angle rotors.

Description of the Prior Art A swinging bucket centrifuge rotor is a rotor of the type in which the sample carrying container (either a centrifuge tube or a bottle) is received within a pivotally movable bucket. At rest the bucket occupies a first, generally vertical, position in which the axis of the container lies generally parallel to an axis of rotation VCL. As the rotor spins the bucket swings from the first position toward a second, generally horizontal, position. In the second position (Figure 3) the axis of the container is almost aligned with a horizontal reference datum HR extending perpendicular to the axis of rotation.

Sample receiving bottles typically include a corresponding capping arrangement. On the other hand, centrifuge tubes of the open-mouth variety are most commonly used in a swinging bucket rotor. Since the mouth of the tube is not subject to hydrostatic pressure during operation of the rotor no capping arrangement is used to retain the sample in the tube.

Recently, however, due primarily to the hazardous nature of many of the materials being processed, the demand to seal the sample receiving tube within the swinging bucket rotor has increased.

Tube capping arrangements for open mouth tubes adapting the same for use in a vertical rotor or a fixed angle rotor are known. Representative of such capping arrangements are those disclosed in United States Patent 3,938,735 (Wright) and in United States Patent 3,635,370 (Romanauskas), United States Patent 4,166,573 (Webster), United States Patent 4,190,196 (Larsen) and United States Patent 4,222,513 (Webster et al.), all of the latter being assigned to the assignee of the present invention. Since such capping assemblies are relatively massive and difficult to use, their applicability to seal open mouth tubes in a swinging bucket would appear to be somewhat limited. The substantial mass of a capping arrangement for an open mouth tube is undesirable since the walls of the tube, the bucket and the rotor body are subject to additional load during centrifugation from the body forces of such a capping assembly. As a result, possible premature failure of any one of the above components may occur or reduced performance may be derived from the rotor system.

Sealed centrifuge tubes having a reduced diameter neck portion have been commonly used in rotors having vertical or fixed angle cavities. Exemplary of such sealed tubes are those disclosed in United States Patent 4,301,963 (Nielsen), heat sealable in the manner disclosed in United States Patent 4,291,964 (Ishimaru), and those manufactured and sold by Nalgene Inc. as the "UltraLok" tube.

Attempts have been made to use such sealed tubes in a swinging bucket rotor. The use of tubes as exemplified by the last-mentioned patents is described in the Beckman Instruments Inc. Rotor and Tubes User Manual, April 1990. To facilitate such use a floating spacer, similar to that described in United States Patent 4,304,356 (Chulay et al.), is required. This arrangement is believed disadvantageous inasmuch as sealing of the tube requires exposure of the sample under test to the potentially harmful effects of heat.

Use of the "UltraLok" tube in a swinging bucket rotor requires the use of a spacer sold by Nalgene Inc. as the UltraLok Swinging Bucket Spacer. This spacer completely surrounds the small diameter neck portion and an intermediate diameter capping portion at the top of the tube. The spacer is split in two semi-cylindrical parts to enable installation and removal of the spacer from the tube. This system carries the disadvantage of adding undesirable load to the tube due to the mass of the spacer. Moreover, multiple pieces must be handled and stored. The disadvantages of each of the above-referenced sealed centrifuge tubes are believed overcome using the centrifuge tube having a reduced diameter neck portion as sold by E. I. Du Pont de Nemours & Co. as the "ULTRACRIMP"™ tube and the sealing assembly therefor disclosed in United States Patent 4,552,278 (Romanauskas), assigned to the assignee of the present invention.

As noted earlier, during operation of a swinging bucket rotor the bucket pivots from a first, generally vertical, position to a second, generally horizontal, position. As may be seen with reference to Figure 3, when rotating at operational speed the bucket B assumes a position wherein the axis 10 A of the tube 10 lies an predetermined angular distance Θ below the horizontal reference HR. This orientation is due to the weight of the pivoting bucket assembly B, the tube 10 and the sample acting in conjunction with centrifugal force. Rotation of the rotor R generates a horizontal, radially outwardly directed total force F on the tube 10. The total force F, acting through the center of gravity (CG) of the capping assembly, is resolvable into an axial component Fc and a transverse component Fβ. The axial component Fc, having a magnitude equal to F (cos Θ), acts along the axis 10 A of the tube and would tend to axially compress the tube. The transverse component Fβ, having a magnitude equal to F (sin Θ), acts in a direction perpendicular to the axis 10A of the tube and would tend the bend the neck of the tube toward the side of the bucket. If unchecked, either force component would cause damage to the sealed tube. Heretofore, no arrangement exists for accommodating such compressing and bending forces to permit the use of a sealed "ULTRACRIMP¹¹™ tube in a swinging bucket centrifuge rotor. Accordingly it is believed advantageous to provide a capping assembly that would accommodate both the compressing and the bending components imposed by the capping assembly on the tube when it is received in a swinging bucket, thereby maintaining, in a swinging bucket rotor environment, the advantages attendant with the "ULTRACRIMP"™ tube and its associated sealing assembly.

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The capping assembly for sealing the above-referenced "ULTRACRIMP"™ tube includes a stopper received within the neck of the tube. A sleeve is telescopically received around the neck of the tube and over the top of the stopper. To seal the tube the sleeve is subjected to a crimping force directed radially inwardly with respect to the neck of the tube.

It is common practice to use such a sealed tube in a vertical angle rotor, i. e., a rotor of the type wherein the cavities formed in the rotor are oriented such that their axes lie parallel to the axis of rotation. If it is desired to use such a sealed tube in a vertical angle rotor a suitable support member, such as an appropriate tube capping arrangement or an adapter (e. g., similar to that disclosed in PCT publication WO 91/06373) may be used. This support member, whether a tube capping arrangement or an adapter, should include a surface that conforms to the frustoconical transition surface of a sealed tube.

In the vertical angle case during centrifugation a hydrostatic force F is generated by the liquid within the sealed tube. The hydrostatic force acts on the undersurface of the stopper. The direction of this force F is illustrated in Figure 13. If there exists any vertical clearance between the top of the sleeve and the inside of the support member the possibility exists that this hydrostatic force may be sufficient to overcome the crimp seal and cause the tube to leak. In addition, owing to the hydrostatic pressure gradient defined radially across the inside of the tube the hydrostatic force seeks to pivot the stopper with respect to the support member. If there is any radial clearance between the sides of the sleeve and the inside of the support member a moment is created, primarily by the force Fβ, that tends to rotate the sealing assembly. The moment may be sufficient to overcome the crimp seal or to deform the neck of the tube. In either event the tube may leak.

A fixed angle rotor is a rotor wherein the cavities formed thereof are oriented such that their axes define a predetermined angle with respect to the axis of rotation. The situation in a fixed angle case, shown in Figure 14, is generally similar. However, owing to the inclination of the tube in the fixed angle cavity of the rotor there exists a component of force F_c that acts on the stopper along the tube axis. This component F_c of the centrifugal force F counteracts the hydrostatic force F . However, the possibility still exits that if a clearance is defined between the undersurface of the support member the hydrostatic force F may overcome the crimp seal and cause leakage. Similar to the situation in the vertical angle case a moment may be generated by the force component

In view of the foregoing it is believed advantageous to provide a capping assembly that would prevent the possibility that the hydrostatic force or the moment will overcome the crimp seal when a sealed "ULTRACRIMP"™ tube is used in a vertical angle or in a fixed angle rotor.

SUMMARY OF THE INVENTION

Disclosed is a capping assembly for a sealing a centrifuge tube made of a deformable material. The tube has a neck which defines a fluid port. The neck communicates with a transition portion having a predetermined exterior configuration. The capping assembly comprises a stopper having a plug sized and configured for close fitting receipt on the interior of the neck of the tube and a sleeve sized and configured for close fitting receipt over the exterior of the neck in concentric telescopic relationship with respect to the plug. The sleeve is responsive to a crimping force to deform and to compress the material of the neck intermediate the plug and the sleeve to form an annular seal between the neck and the plug. The seal resists fluid leakage out of the fluid port from the interior of the tube.

When the sealed tube is rotated in a swinging bucket rotor the capping assembly generates a body force that is resolvable into a compressing component acting generally along the axis of the tube and a bending component acting generally perpendicular to the axis of the tube. In accordance with a first embodiment of the present invention the capping assembly includes a force transmitting member that is integrally formed with and flares from the sleeve. The force transmitting member has an undersurface thereon that corresponds to the configuration of the transition portion of the tube. The force transmitting member distributes both the bending and the compressing components of the body force into the transition portion of the tube where they are opposed by hydrostatic pressure of the sample within the tube. This embodiment of the invention may be modified by the provision of a generally cylindrical band having a peripheral bearing surface thereon. The band may extend toward or away from the sleeve. In these modifications to the first embodiment of the invention the peripheral bearing surface on the band engages the bucket to transmit thereto a portion of the bending force imposed on the tube.

In accordance with a second embodiment of the present invention the force transmitting member takes the form of an annular collar having a central opening therethrough. The collar has an undersurface corresponding in shape to that of the transition region of the tube and a second, generally cylindrical, peripheral bearing surface thereon. A engagement surface is disposed about the opening in the collar that engages the end of the sleeve. The collar may be either formed as an integral member or formed of at least two conjoinable segments. In the former instance the collar must be inserted over the neck of the tube prior to the crimping of the sleeve to the neck of the tube. The present invention may also be used in either a vertical angle or in a fixed angle rotor. In this event the tube is supported in the cavity by a support member having a surface thereon that corresponds in shape to the configuration of the transition portion of the tube. The sleeve overlies at least some portion of the top surface of the plug. When rotating the capping assembly is subjected to a hydrostatic force acting on the undersurface of the stopper. The capping assembly may also be subjected to a moment. In accordance with this aspect of the invention the force transmitting member is disposed between the transition portion of the tube and the surface of the support member. Hydrostatic force generated within the tube during centrifugation is transmitted through the transition portion of the tube to wedge the force transmitting member between the transition portion of the tube and the surface of the support member corresponding in shape thereto. The wedged engagement of the force transmitting member and the surface of the support member imposes through the sleeve a holding force on the stopper that acts to counteract any effect of the hydrostatic force acting on the undersurface of the stopper or the effect of any moment. The force transmitting member may take the form of a relatively thin skirt portion. The force transmitting member may further comprise an integral band having an end thereon, in which event it is the end of the band that is wedged between the transition portion of the tube and the surface of the support member corresponding in shape thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention may be more fully understood from the following detailed description thereof taken in connection with the accompanying drawings which form a part of this application and in which: Figure 1 is an exploded view of a centrifuge tube and a separate capping assembly in accordance with a first embodiment of the present invention; Figure 2 is an elevation view partially in section illustrating the tube capping assembly of Figure 1 in its assembled and sealed relationship with respect to the centrifuge tube, prior to centrifugation of the tube;

Figure 3 is a side elevational view, in section, of a tube sealed with a capping assembly of Figure 1 with the tube being received in a bucket of a swinging bucket rotor, the view being taken during operation of the centrifuge;

Figures 4 and 5 are views similar to Figures 2 and 3, respectively, illustrating a first modification of the embodiment of the invention shown in Figure 1;

Figures 6 and 7 are views similar to Figures 2 and 3, respectively, illustrating a second modification of the embodiment of the invention shown in Figure 1;

Figure 8 is an exploded view of a centrifuge tube and a separate capping assembly in accordance with a second embodiment of the present invention;

Figure 9 is an exploded view illustrating a modification of the capping assembly shown in Figure 8;

Figure 10 is a side elevational view, in section, of a tube sealed with a capping assembly of Figure 8 or Figure 9 received in a bucket of a swinging bucket rotor during operation of the centrifuge;

Figure 11 is an exploded view illustrating another modification of the capping assembly shown in Figure 8;

Figure 12 is a side elevational view, in section, of a tube sealed with a capping assembly of Figure 11 received in a bucket of a swinging bucket rotor during operation of the centrifuge;

Figure 13 is a side elevational view, in section, of a tube sealed with a capping assembly of of the embodiment of Figure 1 received in a cavity of a vertical angle rotor during operation of the centrifuge; Figure 14 is a side elevational view, in section, of a tube sealed with a capping assembly of of the embodiment of Figure 1 received in a cavity of a fixed angle rotor during operation of the centrifuge; and

Figures 15 and 16 are side elevational views, in section, of a tube sealed with a capping assembly of the embodiment of Figure 4 as the same would be received in a cavity of a fixed angle rotor or the cavity of a vertical angle, respectively, during operation of the centrifuge.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the following detailed description similar reference numerals refer to similar elements in all figures of the drawings.

Shown in Figure 1 is an ultracentrifuge tube generally indicated by the reference character 10 with which a separate capping assembly generally indicated by the reference character 12 in accordance with the present invention may be utilized to seal the tube 10 and provide the necessary support to permit the use of the tube 10 in a swinging bucket rotor. The tube 10 includes a body portion 14 having a bottom (not shown), a neck portion 16, and a transition region 18 extending between the neck 16 and the body 14. The body 14 has a predetermined dimension 14D measured transversely to the axis 10A of the tube 10. The dimension 14D is greater than the reduced transverse dimension 16D of the neck 16. The main body portion 14 defines a fluid capacity of any predetermined volume dependent upon the volumetric size of the samples which are to be carried therewithin for centrifugation. The neck 16 has an opening 16A therein that defines a fluid port through which a liquid sample under test may be introduced into the tube 10. The transition region 18 has a frustoconical exterior configuration that defines a predetermined angle α with respect to the axis 10 A. It should be understood that the exterior configuration of the transition region 18 may take any other convenient shape. For example, it may be domed. The tube 10 is preferably an extrusion blow molded member formed of a polyallomer plastic material. Of course, the tube 10 can be formed of other deformable materials, such as a co-polyester material such as a polyethylene terephthalate (PET). It should also be understood that the tube 10 can be formed by other molding techniques, such as injection blow molding.

The separate capping assembly 12 is similar to that disclosed and claimed in United States Patent 4,552,278 (Romanauskas) assigned to the assignee of the present invention. This patent is hereby incorporated by reference herein. The separate capping assembly 12 comprises a stopper 22 and a complementary sleeve 24. In the preferred case, the stopper 22 includes an elongated cylindrical plug portion 28 that has a taper 30 at one end thereof and a flange 32 disposed at the opposite end thereof. The cylindrical plug portion 28 is surrounded by an elastomeric skin 34. The external configuration of the plug portion 28, with the elastomeric skin 34 thereon, is configured and sized for close fitting receipt within the opening 16A of the neck 16 of the tube 10. Preferably the diameter of the flange 32 is coextensive with the exterior dimension 16D of the neck 16. The flange 32 serves to limit the extent of entry of the plug portion 28 of the stopper 22 into the neck 16 of the tube 10.

The plug portion 28 of the stopper 22 is formed of a stiff, relatively lightweight material. The material must be of sufficient stiffness to insure that the flange 32, which rests on the edge of the neck 16 of the tube 10, is able to resist any force tending to urge the stopper 22 towards the bottom of the tube 10 during centrifuge operation. A relatively lightweight material reduces the loading that the tube 10 must withstand from the capping assembly during centrifugation. In the preferred case the plug portion 28 is injection molded of polypropylene having a durometer of about 75 on the Shore D scale.

The elastomeric skin 34 is, in the preferred case, insert injection molded onto the plug portion 28. Functionally, the skin 34 provides a resilient sealing layer between the plug portion 28 of the stopper 22 and the neck 16 of the tube 10. A suitable material for the elastomeric skin 34 is a low durometer (about 85 on the Shore A scale) polyethylene. A skin thickness on the order of about .010 inches is suitable.

Similar to the capping assembly disclosed in the incorporated United States Patent 4,552,278 (Romanauskas) the sleeve 24 of the capping assembly 12 includes a tubular portion 35. The tubular portion 35 of the sleeve 24, in the preferred case, is open at one end, as at 36. The opposite end 37 may be closed, as is preferred, or may be left open, if desired. The tubular portion 35 of the skirt 24 has an axial length approximately equal to the axial length of the neck 16 of the tube 10. The interior of the tubular portion 35 of the sleeve 24 is sized and configured for close fitting receipt over the exterior of the neck 16 of the tube 10.

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SWINGING BUCKET CASE As noted earlier, in a swinging bucket rotor the axis 10A of the tube 10 does not coincide with a horizontal reference datum HR extending transversely to the axis of rotation VCL of the rotor. Accordingly, the mass of the capping assembly imposes both a compressing force acting along the axis 10A and a bending component acting transversely thereto. In accordance with the present invention the capping assembly further includes a force transmitting member generally indicated by the reference character 38 adapted to transmit both the compressing component and the bending component into the tube 10.

In accordance with a first embodiment of the present invention the force transmitting member 38 is formed integrally at the open end 36 of the tubular portion 35 of the sleeve 24. The undersurface 40 of the force transmitting member 38 matches the frustoconical configuration of the transition portion 18 of the tube 10. Thus, the undersurface 40 forms an angle α with respect to the axis 10A of the tube 10. The largest diameter dimension 38D of the force transmitting member 38 is substantially equal to the diameter 14D of the body 14 of the tube 10. The sleeve 24 with the integral force transmitting member 38 thereon is formed, preferably by progressive die stamping, from aluminum or any crimpably deformable material having sufficient strength to minimize deformation during centrifugation.

In use, the tube 10 is filled and the bi-material stopper 22 inserted into the neck 16 of the tube 10 until the entry thereof is limited by the abutment of the flange 32 against the upper end of the tube neck 16. The sleeve 24 having the integral force transmitting member 38 is telescopically inserted over the neck 16 so that the tubular portion 35 of the sleeve 34 concentrically overlaps a portion of the length of the plug portion 28 of the stopper 22. A radially inwardly directed crimping force is circumf erentially applied about the exterior of the tubular portion 35 of the sleeve 24 using a tool described in above-incorporated United States Patent 4,552,278 (Romanauskas).

Figure 2 is a partially cut-away view of a tube 10 with an assembled and crimped capping assembly in accordance with the first embodiment of the present invention. The tubular portion 35 of the sleeve 24 responds to the radially directed crimping force by crimping to compress the material in the neck 16 of the tube 10 between the outer elastomeric skin 34 of the plug 28 and the tubular portion 35 of the sleeve 24. The radially inwardly directed crimping force is imposed at at least one but preferably at a plurality of spaced axial locations along the neck 16. As a result of the imposition of the radially directed crimping force at least one or a plurality of circumferentially extending sealed interfaces 42A, 42B are defined between the neck 16 and the stopper 22 at each location at which the crimping force is applied due to the compression of the material of the neck 16 between the stopper 22 and the tubular portion 35 of the skirt 24. The seals 42A and 42B developed in the manner described are each able to prevent the leakage of liquid from within the tube 10 during centrifugation.

As is seen in Figure 2, when in the above-described assembled relationship a gap 43 is defined between the undersurface 40 of the force transmitting member 38 of the sleeve 24 and the frustoconical transition region 18 of the tube 10. The gap 43 is due to the crimping action forming the seals 42A, 42B.

Figure 3 illustrates a tube 10 with an assembled capping assembly 12 of Figure 1 disposed in a bucket B having a cover C operating in a swinging bucket rotor R. The cover C is sealed to the bucket B by an O- ring or other appropriate seal S. The cover C is pivotally mounted to the rotor body R at the pivot location P. For simplicity and clarity of illustration the details of the pivot mechanism have been omitted from Figure 3. The bucket B and the cover C shown are most commonly used to process samples in open mouthed test-tube like containers. Accordingly, no support means are inherent to the bucket B or cover C to accommodate a tube 10 having a reduced diameter neck 16 and a capping arrangement 12. For use with any of the various embodiments or modifications of the invention discussed herein the diameter D of the bucket B should be within a few thousandths of an inch of the dimension 14D of the tube 10. Also, for proper functioning of the invention the tube 10 should be almost entirely filled with sample liquid. During operation of the rotor R the bucket B pivots about the pivot point P from a first, generally vertical, position to a second, generally horizontal, position. As discussed the bucket B assumes a position a predetermined angular distance Θ just below the horizontal reference datum HR. The force transmitting member 38 of the sleeve 24 distributes both the compressive component Fc and the bending component Fβ of the total force F imposed by the capping assembly 12 into the tube 10. The liquid sample within the tube 10 generates a reaction force that counters the compressive component Fc and the bending component Fβ of the total force F imposed thereon. As a result, the neck 16 of the tube 10 is relatively unstressed and the integrity of the tube 10 is preserved during centrifugation.

Figures 4 and 5 illustrate a modification of the first embodiment of the present invention. In Figures 4 and 5 the force transmitting member 38 has a band 44 with a cylindrical bearing surface 46 defined thereon. The band 44 projects toward the end 37 of the sleeve 24. The diameter 44D of the band 44 is substantially equal to the dimension 14D of the body 14 of the tube 10. The band 44 provides additional bearing area against the bucket B to withstand a higher bending component Fβ of the force F of the capping assembly 12. This embodiment of the sleeve 24 with the integral force transmitting member 38 thereon is also preferably formed by progressive die stamping from aluminum or any crimpably deformable material having sufficient strength to minimize deformation during centrifugation. Figures 6 and 7 illustrate another modification of the embodiment of the invention shown in Figures 1 to 3. In this modification the band 44 projects away from the end 37 of the sleeve 24. The body portion 14 of the tube 10 has an annular step 14S formed therein to accept the end 44E of the band 44.

In this arrangement the band 44 also provides additional bearing area against the bucket B to withstand a higher bending component Fβ of the force F of the capping assembly 12. This embodiment of the sleeve 24 is also preferably formed by progressive die stamping from aluminum or any crimpably deformable material having sufficient strength to minimize deformation during centrifugation.

Figures 8 through 11 illustrate various modifications of a second, alternate, embodiment of the present invention. In each of these modifications of the alternate embodiment the force transmitting member 38' is a generally annular washer-like member separate from the sleeve 24 of the capping assembly 12. The member 38' has a central axial passage 47 extending therethrough. The force transmitting member 38' has an undersurface 40' that corresponds in shape to the configuration of the transition region 18 of the tube 10. A peripheral bearing surface 44' is defined on the exterior of the member 38'. The peripheral bearing surface 44' extends generally parallel to the axis 38'A of the member. The member 38' also includes an abutment surface 48 defined adjacent to the opening 47 that engages the end 36 of the sleeve 24 of the capping assembly 12.

In the modification shown in Figure 8 the member 38' is integrally formed, as by machining from a suitable metal (e. g., aluminum) or by machining or molding from a suitable plastic material (e. g., polypropylene, polyphenylene oxide, polyvinyl chloride, polycarbonate or polyethylene). The transition between the undersurface 40' and the peripheral bearing surface 44' is preferably rounded, as shown. The member 38' may be defined by cooperating conjoinable segments 38'-l, 38'-2, as illustrated in Figure 9. As suggested in Figures 8 and 9 the integral member 38' or each of the conjoinable segments 38'-l, 38'-2, may be cored to eliminate excess material in the region 50 between the abutment surface 48 and the peripheral bearing surface 44'. The cored region 50 is indicated in Figures 8 and 9 by dot-dash lines.

Figure 10 illustrates the relationship of the member 38' and the capping assembly 12 when in use. In Figure 10 the member 38' may be integrally formed or formed from the conjoined segments 38'-l, 38'-2. If the integral form of the member 38' is used, it is first inserted over the neck 16 of the tube 10 prior to crimping of the capping assembly 12] With the sleeve 24 in place, the sleeve 24 is crimped, as described earlier. The end 36 of the sleeve 24 engages the member 38' along the abutment surface 48, the engagement being indicated at reference character 49, effectively transmitting the body forces of the capping assembly 12 during centrifugation to the force transmitting member 38'. The undersurface 40' of the force transmitting member 38' bears against the transition region 18 of the tube 10, transmitting thereinto both the compressing component Fc and the bending component Fβ of the total body force F of the capping assembly 12. Analogous to the situation discussed earlier, the hydrostatic reaction forces generated within the liquid within the tube 10 counteract the compressing component Fc and the bending component Fβ of the total body force F of the capping assembly, thereby preventing damage to the integrity of the tube. In addition, some of the bending component Fβ is accommodated by the interaction of the peripheral bearing surface 44' against the bucket B. If the member 38' is formed using the conjoined segments 38'-l, 38'-2, the segments 38'-l, 38'-2 are inserted beneath the end 36 of the sleeve 24 after the same has been crimped to the neck 16 of the tube 10.

Figure 11 illustrates a modification to the member 38' when the same is formed of conjoinable segments In Figure 11 each of the segments 38'-l, 38'-2 is axially elongated by the provision of an annular portion 52. Each portion 52 has a central groove 54 defined therein, the groove being disposed immediately adjacent to the abutment surface 48. The exterior surface of each of the portions 52 define an axial extension of the peripheral bearing surface 44'. As indicated by the reference character 50 the segments may be cored or uncored. When assembled, as seen in Figure 12, the grooves 54 cooperate to define an interior cylindrical surface that surrounds the exterior of the sleeve 24. The interior cylindrical surface engages the sleeve 24 to transmit a portion of the bending component Fβ to the wall of the bucket B.

Those skilled in the art may appreciate that a capping assembly suitable for use with a tube having a reduced diameter neck in a swinging bucket rotor has been provided. It may also be appreciated that the subject capping assembly provides the necessary seal and support for use in a swinging bucket rotor with minimal additional load exerted on the tube, bucket and rotor body. This capability is attained without adding to the number of components that the user must purchase and handle over what is required to seal identical tubes for use in a fixed angle or vertical rotor.

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FIXED ANGLE OR VERTICAL ANGLE CASES The capping assembly of the present invention also has utility in the fixed angle and in the vertical rotor environments. With reference to Figures 13 and 14 respectively shown are side elevational views in section of a tube 10 sealed with a capping assembly 12 in accordance with the present invention as shown in Figure 1. The tube 10 is received in a cavity C of a vertical angle rotor (Figure 13) and as received in a cavity C of a fixed angle rotor (Figure 14), the views in these Figures being taken during operation of the centrifuge. When supported within the cavities C, C, the tube 10 is received within a suitable support member 60. The support member 60 has a surface 62 therein that corresponds in shape to the configuration of the transition portion 18 of the tube 10. The support member may take the form of an appropriate tube capping arrangement received on threads or the like formed in the rotor (as disclosed in several of the reference patents mentioned earlier in this application) or a separate adapter, e. g., similar to that disclosed in PCT publication WO 91/06373. In the vertical angle case (Figure 13) the centrifugal force effects on the liquid in the tube 10 generates a hydrostatic force F_h therewithin. The hydrostatic force F_h is vertically directed as shown in Figure 13. The magnitude of the hydrostatic force Fh is zero just inside the radially inboard surface of the tube, and reaches a maximum just inside the radially outboard surface. The hydrostatic force F_h acts against the undersurface 28U of the plug portion 28 of the stopper 22 and also acts against the inside surface of the transition portion 18 of the tube 10. The capping assembly 12 includes the force transmitting member

38 in accordance with the first embodiment of the present invention as shown in Figures 1 and 2. As may be seen from Figures 13 through 16 the force transmitting member 38 is again in the form of a relatively thin- walled skirt portion that is formed integrally with and flares outwardly from the open end 36 of the tubular portion 35 of the sleeve 24. In the preferred case the sleeve 35 has a closed end 37 that overlies the top surface 28T of the flange 32 of the plug 28. It should be understood that the end 37 of the sleeve 35 need not be fully closed but may have an opening therein so long as at least some portion of the top surface 28T of the plug 28 is overlaid by the end 37 of the sleeve 35. The force transmitting member 38 is disposed between the exterior of the transition portion 18 of the tube 10 and the surface 62 of the support member 60.

In operation, hydrostatic force generated within the tube 10 during centrifugation is transmitted through the transition portion 18 of the tube 10. The force transmitting member 38 is thus wedged into intimate engagement between the exterior of the transition portion 18 of the tube 10 and the surface 62 of the support member 60. The wedged engagement is indicated in Figure 13 by the reference characters 64, 64'. Owing to the nature of the hydrostatic force Fh gradient the wedging action is greater on the radially outboard side of the tube 10 (indicated by the character 64) than on the radially inboard side of the tube 10 (indicated by the character 64').

Since the force transmitting member 38 is integrally formed with the sleeve 24 the wedged engagement 64, 64' of the force transmitting member 38 and the surface 62 of the support member 60 imposes a holding force 68 on the stopper 22. The holding force 68 is imposed on the stopper 22 through the end 37 of the sleeve 35 that overlies the top surface 28T of the plug 28. The holding force 68 counteracts any effect of the hydrostatic force Fh acting on the undersurface 28U of the plug 28 of the stopper 22. The holding force 68 produced by the wedged engagement 64, 64' of the force transmitting member 38 also counteracts the effect of any moment produced by the force Fβ.

The force transmitting member 38 may also be used in the fixed angle case, as is illustrated in Figure 14. In this instance the same wedging action 64, 64' as discussed above is generated. The holding force 68 is imposed on the stopper 22 through the closed end 37 of the sleeve 24. It is noted that in the fixed angle case the inclination of the cavity C with respect to the axis of rotation VCL (at the angle Φ) generates the force F_c that assists the holding force 68.

Figures 15 and 16 illustrate a force transmitting member 38 modified as shown in Figures 4 and 5 as the same is received in a cavity C, C, respectively of either a vertical angle rotor (Figure 15) or a fixed angle rotor (Figure 16). If the tube 10 does not have a sufficient length to abut against the support surface 62 of the support member a band 44 may be used to bridge the distance between the transition portion 18 of the tube 10 and the support surface 62. In either the fixed angle or the vertical angle cases the wedging engagement 64, 64' is again generated, but in the instances shown in Figures 15 and 16 the engagement is defined between the upper end 44E of the band 44 and the surface 62. The band 44 also provides additional bearing area against walls of the cavity C, C to withstand a higher bending component Fβ of the body force F of the capping assembly 12.

Those skilled in the art having the benefit of the teachings of the present invention as hereinabove set forth may effect numerous modifications thereto. These modifications are, however, to be construed as lying within the scope of the present invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. In a capping assembly for sealing a centrifuge tube adapted for rotation about an axis while carried in a cavity in a fixed angle or vertical angle centrifuge rotor, the tube being formed of a deformable material, the tube having a neck portion which defines a fluid port, the neck having a predetermined interior and an exterior, the neck portion communicating with a transition portion with a predetermined exterior configuration, the tube being supported in the cavity by a support member having a surface thereon that corresponds in shape to the configuration of the transition portion of the tube, the capping assembly comprising: a stopper having a plug portion sized and configured for close fitting receipt on the interior of the neck, the plug portion of the stopper having an undersurface and a top-surface thereon; and a sleeve sized and configured for close fitting receipt over the exterior of the neck in concentric telescopic relationship with respect to the plug, the sleeve having an end thereon that overlies at least some portion of the top surface of the plug, the sleeve being responsive to a crimping force to deform and compress the material of the neck intermediate the plug and the sleeve to form an annular seal between the neck and the plug which resists fluid leakage out of the fluid port from the interior of the tube; when rotating the capping assembly being subjected to a hydrostatic force acting on the undersurface of the stopper, the improvement which comprises: a force transmitting member formed integrally with and flaring outwardly from the sleeve, the force transmitting member being disposed between the transition portion of the tube and the surface of the support member, hydrostatic force generated within the tube during centrifugation being transmitted through the transition portion of the tube to wedge the force transmitting member between the transition portion of the tube and the surface of the support member corresponding in shape thereto, the wedged engagement of the force transmitting member and the surface of the support member imposing through the sleeve a holding force on the stopper that acts to counteract any effect of the hydrostatic force acting on the undersurface of the stopper.

2. The capping assembly of claim 1 wherein the force transmitting member takes the form of a relatively thin skirt portion.

3. The capping assembly of claim 2 wherein the force transmitting member further comprises an integral band having an end thereon, the end of the band being wedged between the transition portion of the tube and the surface of the support member corresponding in shape thereto.