WO1992018390A1

WO1992018390A1 - Capping assembly enabling the use of sealed tubes in a swinging bucket centrifuge

Info

Publication number: WO1992018390A1
Application number: PCT/US1992/002132
Authority: WO
Inventors: William Andrew Romanauskas; Edward Thomas Sheeran, Jr.
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1991-04-11
Filing date: 1992-03-25
Publication date: 1992-10-29
Also published as: CA2107801A1; JPH06506652A; EP0578779A1; EP0578779A4

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 (12) to a tube (10). The force transmitting member (38) may be integral with the sleeve (24) 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.

Description

TITLE

CAPPING ASSEMBLY ENABLING THE USE OF SEALED TUBES IN A SWINGING BUCKET CENTRIFUGE

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 especially adapted to permit the use of a centrifuge tube of this type in a swinging bucket rotor.

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.

BSTITUTE SHEET 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 and Company as the

"ULTRACRIMP"TM 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

SUBSTI speed the bucket B assumes a position wherein the axis 10A 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 10A of the tube and would tend to axially compress the tube. The transverse component FB, 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 "ULTRACRIMP"™ 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.

SUMMARY OF THE INVENTION

Disclosed is a capping assembly for a centrifuge tube made of a deformable material. The tube has a neck which

SUBSTITUTE SHEE 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.

auBsriTUTi 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.

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; and

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. 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 10A. 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

SUBSTITUTE SHEET 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.

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

SUBSTITUTE SHE 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 circumferentially 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

SUBSTITUTE SHEET 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 Fp 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

SUBSTITUTE SHEET 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.

-o-O-o-

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

SUBSTITUTE SHEET 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'-1 , 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'-1 , 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'-1 , 38'-2. If the integral form of the member 38' is used, it is first inserted over the neck 16 of the

SUBSTITUTE SHEE 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 TO, 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'-1 , 38'-2, the segments 38'- 1, 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'-1 , 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.

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 a centrifuge tube adapted for rotation about an axis while carried in a swinging bucket of a swinging bucket centrifuge rotor, when rotating the capping assembly being subjected to a body force resolvable into an compressing component acting along the axis of the tube and a bending component acting perpendicular to the axis of the tube; 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 capping assembly comprising: a stopper having a plug portion sized and configured for close fitting receipt on the interior of the neck; 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 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; the improvement which comprises: a force transmitting member formed integrally with and flaring outwardly from the sleeve, the force transmitting member distributing both the bending component of the body force and the compressing component of the body force into the transition portion of the tube.

2. The capping assembly of claim 1 wherein the tube has a body portion having a predetermined dimension measured transversely to its axis, and wherein the force transmitting member has a predetermined dimension measured transversely to the axis that is substantially equal to the transverse dimension of the body portion of the tube.

3. The capping assembly of claim 2 wherein the force transmitting member further comprises an integral band having a generally cylindrical peripheral surface thereon, the peripheral surface being engageable against a swinging bucket to transmit a portion of the bending component of the body force into the bucket.

4. The capping assembly of claim 3 wherein the band extends toward the sleeve.

5. The capping assembly of claim 3 wherein the band extends away from the sleeve.

6. The capping assembly of claim 1 wherein the undersurface corresponds to the configuration of the transition portion of the tube.

7. In a capping assembly for a centrifuge tube adapted for rotation about an axis while carried in a swinging bucket of a swinging bucket centrifuge rotor, when rotating the capping assembly being subjected to a body force resolvable into an compressing component acting along the axis of the tube and a bending component acting perpendicular to the axis of the tube;

SUBSTITUTE SHEE 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 capping assembly comprising: a stopper having a plug portion sized and configured for close fitting receipt on the interior of the neck; 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, 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; the improvement which comprises: a force transmitting member having an engaging surface engageable with the end of the sleeve, an undersurface and a peripheral surface thereon, the force transmitting member distributing both the compressing component of the body force and a portion of the bending component of the body force into the transition portion of the tube through abutment between the undersurface of the member and the transition portion of the tube, the force transmitting member distributing a portion of the bending component of the body force into a swinging bucket through abutment between the peripheral surface of the force transmitting member and the bucket.

8. The capping assembly of claim 7 wherein the undersurface corresponds to the configuration of the transition portion of the tube.

9. The capping assembly of claim 7 wherein the force transmitting member is an integrally formed member.

10. The capping assembly of claim 7 wherein the force transmitting member comprises a first and a second segment which when conjoined define the force transmitting member.

11. The capping assembly of claim 7 wherein the force segments each have a channel therein which, when conjoined, define a cylindrical surface adapted to engage against the sleeve.