IE853240L - Wound rotor arm element and centrifuge rotor fabricated¹therefrom. - Google Patents

Abstract

A centrifuge rotor is fabricated of a stacked plurality of tiers where each tier is formed from a stacked array of wound arms. Each arm is formed from an array of layered turns of anisotropic fibers having parallel side portions connected through curved end turn portions.

Description

This invention relates to a centrifuge rotoc and. in particular. to a centrifuge cotoc fabricated from an array of stacked wound radial rotor ara eleaents. r The trend in the fabrication of rotatable structures has been away fron the use of conventional homogeneous materials, such as aluainua or titaniua. and tovard the use of reinforced fiber coaposite structures. Such structures are advantageous because they provide an increased strength-to-weight ratio with its attendant advantages over the conventionally fabricated hoaogeneous structures.

Typical use of such coaposite structures is found in the area of energy storage devices, such as fly-wheels. Bxeaplary of various alternate eabodiaents of such reinforced fiber coaposite rotable structures are those shown in US-A-4 458 400, US-A-3 672 241, OS-A-3 698 262, US-A-3 737 694, OS-A-3 884 093 and US-A-4 028 962.

The use of reinforced fiber material has also been found in other rotating structures, such as rotor blades and tooling. Exemplary of such uses are those shown in US-A-4 038 885, US-A-4 255 087 and US-A- 3 765 267. US-A-3 262 231 discloses the utilization of strands of high-tensile strength material, such as glass, as internal reinforcement of rotatable articles such as abrasive wheels.

In the area of centrifuge rotors the art discloses attempts to increase the strength-to-weight ratio. For example, US-A-2 447 330 discloses an ultra-centrifuge rotor formed of a metal material which is provided with slots which reduce the weight of the rotor. US-A-3 248 046 discloses a fixed angle centrifuge rotor formed by winding layers of glass material onto a mandrel. US-A-4 468 269 discloses a rotor with a plurality of rings surrounding a bowl-like body portion.

GB-A-2 097 297 discloses a centrifuge rotor rotatable about an axis of rotation, Comprising at least one generally elongated arm having a major axis, the arm being formed from a plurality of turns of a fiber wound in generally parallel side portions connected through curved end turn portions, a sample carrier being positioned within each end turn portion of said arm, the fibers in each side portion being generally parallel to the major axis. The known centrifuge rotor is made of a continuous fibrous composite material composed of continuous high-tensile fibers such as of glass, graphite or boron impregnated with synthetic resin. The continuous fibers 5 extend between diametrically opposed pairs of the sample carriers across the rotor shaft. The height dimension of each rotor arm mid-way along its length is the same as the height dimension of the arm at its ends.

EP-A-0 033 765 discloses a connecting rod having a 10 spool body consisting of fibers. In the spool body, the intermediate portion is less in height than the end-portions. Such spool body is shaped thereafter to become the final connecting rod and surrounded by a sheath of aluminium. In the final connecting rod, the height dimension at the intermediate portion is the same as in the end portions.

When using reinforced fiber materials, in centrifuge rotors it is advantageous to be able to arrange the fibers so that the maximum strength is oriented in a direction 20 parallel to the direction in which maximum centrifugal stress is imposed on the fibers. That is, it is advantageous to be able to provide a three-dimensional spatial relationship of fibers that extend radially outwardly from the central axis of rotation. Most 25 beneficially advantageous is to orient the fibers such -2a- that each fiber passes as close as possible through the rotational axis of the structure.

It is the object of the present invention to provide a centrifuge rotor of the type . as above described, in which the fibers are so arranged that the maximum strength is orientated in a direction parallel to the direction to the direction in which maximum centrifugal stress is imposed on the fibers.

Accordingly, in a first aspect, the present invention provides a centrifuge rotor rotatable about an axis of rotation, comprising at least one generally elongated arm having a major axis, the arm being formed from a plurality of turns of a fiber wound in generally parallel side portions connected through curved end turn portions, a sample carrier being positioned within each end turn portion of said arm, the fibers in each side portion being generally parallel to the major axis, wherein the height dimension of a side portion of the arm at a point substantially midway along its length and close to said axis of rotation is less than the height dimension of the arm at its end.

This Invention relates to a reinforced fiber composite centrifuge rotor capable of rotating a sample carried in a sample carrier at very high speeds. The structure in its broadest aspect comprises a generally elongated arm element having an elongated major axis. The arm element is formed from a plurality of turns of a fiber material arranged in generally parallel side portions connected through curved end turn portions. With such a structure the fibers forming each element pass as close as possible to the axis of rotation of the rotor and still provide continuous support for the sample carriers along the direction of maximum stress. The axes of each of the fibers in each of the side portions are substantially parallel to each other, parallel to the major axis of the elongated arm and substantially perpendicular to the rotor's axis of rotation. The height dimension of a side portion of the arm element is preferably less (i.e.. the arm is thinner) at a point substantially mid-way along its length than at its curved end turn. The cross Sectional area taken through a side portion of the arm element is substantially equal to the cross sectional area of the element taken through an end turn portion. A sample carrier is connectable to each arm element within each end. turn thereof. The sample carrier may be tubular segment having a predetermined length which may be provided with a closed end in some instances. A drive connection is made to the arm mid-way between the ends of the arm. Transverse and/or inclined reinforcing wrappings and/or bracing fibers may also be provided. in another aspect the rotor takes the form of one. two or more vertical tiers, each tier being formed of a stacked plurality of arm elements. In an H-place rotor. N arms are arranged to torn an individual tier. where N equals one-half H. The major axis of each arm in a tier is offset fcom the major axis of the adjacent acm in the tier by an angle equal 5 to 180* divided by N. In forming a stacked tier the height dimension Hc of each rotor arm in the vicinity of its center is preferably about 1/N times the height dimension Hg at its end. thus permitting the N arms defining a tier to exhibit a substantially 10 uniform height profile to facilitate stacking. Of course the height dimension H£ of each arm may be greater or less than the preferred height dimension ratio discussed above.

In rotors formed of at least two tiers, when the IS tiers are stacked selected ones of the elongated elements in each tier are vertically registered with respect to each other so that the sample carriers segments connectable at each end thereof may communicate to provide a sample receiving volume 20 adapted to receive a specimen therein. Alternatively the volume may be defined by a continuous carrier that is secured through the vertically registered ends of the elements in each tiec. A drive fitting having II faces on its periphery passes centrally and axially 25 through the stacked tiers. Bach arm element in each tier is connected along a different pair of opposed faces of the fitting.

A rotor in accordance with this invention may be implemented either in a fixed angle or a vertical tube 30 configuration.

The invention will 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 isolated perspective view of an individual elongated wound radial rotor arm element in accordance with the present Invention; Figure 2 is a plan view of the wound rotor arm 5 element shown in Figure 1 while Figure 3 is a plan view of an alternate construction of such an arm element; Figure 4 is a side elevational view of the rotor arm element shown in Figures 2 and 3: Figures 5A and SB are, respectively, sectional views taken along section lines SA-SA and 5B-5B in Figure 2: Figure 6 is a plan view of an eight-place centrifuge rotor fabricated of a plurality of tiers of IS rotor arm elements stacked in accordance with- the present invention: Figure 7 is a side elevational view of the rotor shown in Figure 6 while Figure 7A is an enlarged view of the rotor more clearly illustrating the stepped 20 relationship of the ends of the arms; Figure 8 is a section view taken along section lines 8-8 of Figure 6; Figures 9 and 10 are alternate configurations of a rotor formed of stacked tiers of wound arm elements 2S in accordance with the present invention; Figures 11 and 12 are. respectively, plan and side elevational views (respectively similar to Figures 2 or 3 and Figure 4) illustrating a wound radial acm element in accordance with this invention 30 adapted for the fabrication of a vertical tube centrifuge cotoc; Figures 13 and 14 ace. cespectively, a plan and side elevation view of an accangement foe winding a cotoc acm in accordance with the present Invention: Figures IS, 16 and 17 are. respectively, a plan, side elevation and end view of a mold used in winding a rotor arm in accordance with the present invention; and S Figures 18, 19 and 20 illustrate various procedures used in winding a rotor an in accordance with the present invention.

Throughout the following detailed description similar reference numerals refer to similar elements 10 in all figures of the drawings. with reference to Figure 1 shown is an isolated perspective view of an individual wound rotor arm element or arm 10 in accordance with the present invention. The arm 10 is a generally elongated is element having a major axis 11. Each end 12A and 12B of the arm 10 is adapted to receive a sample carrier 14A and 14B respectively. The details of the sample carriers 14 and the manner in which they define a sample receiving volume are discussed herein. A drive 20 connection 16 is mounted to the arm 10 at a point midway between the ends 12A and 12B thereof. Although it should be appreciated that the drive connection 16 may be provided at any convenient location on the arm 10 providing that symmetry about the centerline CL is 25 maintained. In Figure 1 the drive connection 16 is shown as a member having opposed flat surfaces 16F which engage the arm 10. The drive connection 16 may take any suitable form, as discussed herein, and is arranged to permit the arm 10 to be mounted on a 30 suitable drive spindle or the like for rotation about the axis of rotation CL extending substantially perpendicular to the major axis 11 of the arm 10.

The arm 10 is formed from a plurality of layered turns of an anisotropic fiber material. The arm 10 is wound in a manner to be discufesed so aa to provide generally parallel aide portions 18R and 18L which are connected through curved end turn portions 20A and 20B. Each sample carrier 14A and 14B is respectively S positioned within its associated end turn portion 20A and 20B. The side portions 18 are spaced by a gap 22 having a predetermined dimension. The gap 22 may remain substantially equal to the diametric dimension of the carrier 14. as shown in Figures 1 and 2. 10 Preferably, however, the fibers of the arm 10 may partially wrap about the carrier 14. as shown in Figure 3. to define a narrower gap 22'.

Each sample carrier 14 is a substantially cylindrical tubular member which may be mounted such 15 that the axis thereof is either parallel to or slightly inclined inwardly with respect to the axis of rotation CL to respectively define a vertical tube rotor (as shown, e.g.. in Figures 11 and 12) or a fixed angle rotor as shown in Figures l. 2. 3 and 4. 20 Each carrier 14 may be formed as an open or a closed ended member. A closed ended tubular member 14' is shown in Figures 8 through 10. The sample carrier may be provided during fabrication of the arm or thereafter. The carrier 14 may directly receive a 25 sample under test or may. be sized to receive a separate container (as a test tube) which carries the sample under test. As is developed herein (Figures 8. 9 and 10) a rotor may be formed from at least two stacks of tiers of arms. Each tier is itself formed 30 from a stack of individual arms. In this instance selected arms in each tier lie in vertical registration. A sample receiving volume may be defined by the registration of segmented carriers or by the insertion of an integral carrier 14 into the 35 registered ends of the arms. 8 As seen with reference to Figures 1 and 3. the arm 10 is wound such that the side portions 18 are thin rectanguloid members which merge into the flaring, substantially horseshoe-shaped curved end S turn portions 20. As suggested in Figure 4 by the dashed lines, the individual fibers in the side portions 18 are arrayed such that their axes are parallel to each other and to the major axis 11 of the arm 10 while the fibers diverge from each other in the 10 end turn portions 20.

The fibers are surrounded and aupported in a suitable resin-based support matrix 24 best seen in Figures 5A and 5B. The arms 10 exhibit a profile in which the height dimension He (Figure 4) of a side 15 portion 18 (measured in the central region between the flared ends) is less than the height dimension Hg of an end portion turn 20. It should be understood, however, that the profile of the arm element 10 need not be limited to that shown in the Figures. For 20 example, the rectanguloid central region of the side portions of the arm may extend for a lesser distance along the length of the side portion and the taper of the end turn portions may concomitantly increase in length and become more gradual.

The arm 10 shown in Figures 1 through 4 are configured for the fabrication of a fixed angle centrifuge. However, for use in a vertical tube centrifuge arms 10.' such as shown in Figures 11 and 12 may be used. The arms 10' are identical in all 30 material respects to that discussed in Figures l through 4. except that the sample carriers 14 are supported in their associated end turn portions 20 so that the axis 15 of the carrier 14 is parallel to the axis of rotation CL. In the fixed angle case shown in 35 Figures 1 through 4. the axes 15 of the carriers 14 9 at* inclined at a predetermined fixed angle to tbe axis CL. It should be noted that the arm 10* may i exhibit either gap configuration 22. 22' as shown in Figures 2 or 3.

Since the transverse centrifugal forces in the region of the drive connection 16 may have a tendency to separate the parallel side portions 18 of the arm in some instances it may be desired to provide wrappings formed of arrays of transversely wound 10 fiberB 28A and 2BB disposed across the sides 18R and 18L. In addition or as an alternative reinforcing fibers 26A and 26B located in the transition region between the sides 18 and the end turns 20 may be provided. The windings 26 and/or 28 may be used with 15 any embodiment of the arms 10 or 10' shown herein but are illustrated only in Figures 1 through 3 for clarity of illustration.

The arm 10 or 10* may be fabricated in any convenient manner as described in connection with 20 Figures 13 through 20. For example, a mold 30. preferably formed in conjoinable sections 30A and 30B (as seen in Figures 15. 16 and 17). is provided with a peripheral groove 32 formed in the three-dimensional shape of an individual arm 10 or 10'. The sections 25 30A and 30B are releasably conjoined by end posts 31. The depth of the groove defined about the periphery of the conjoined sections 30A and 30B corresponds to the width of the side portions 18 and end portions 20 of the arm 10 or 10'. As seen from Figures 13 and 14 the 30 mold 30 is mounted for rotational movement about an axle 38 journaled in a fixture 40 mounted on a work table 42. Motive energy for rotation of the mold 30 is derived from a motor 44 conveniently mounted to the fixture 40. The motor 44 causes the mold 30 to rotate 35 in the direction of the arrows 46.

A strand of high-tensile strength anisotropic fiber is wrapped in the groove 32 around the mold 30 so as to build-up substantially uniform fiber layers. The fiber layers are arranged atop each other from the 5 base of the groove in a manner akin to the winding of a fishing reel with line with the axis of the individual fibers in the side portions of the arms being substantially parallel to each other with the fibers in the end turn diverging as discussed. 10 Suitable for use as the fiber is 1140 denier aramid fiber such as that manufactured by E. I. du Pont de Nemours and Company. Inc.. and sold under the trademark KEVLAH .

The fiber wrapped onto the mold is coated with 15 any suitable matrix 24 (Figures 5A. SB) such as epoxy. thermoplastic or other curable resin which imparts a tackiness to the exterior of the fiber and permits the fiber to adhere to adjacent turns in adjacent layers.

The fiber is taken from a supply spool 48 20 mounted on a commercial unwind 50 such as that sold by Compensating Tension Controls, Inc. under model 800C 012. The fiber passes over a tensioning arm array 52 and through a vertical guide roll 54 to a horizontal grooved guide roller 56. The roller 56 is 25 mounted for traversing movement in the direction of arrows 58 on a shaft 60 of a traverse 62. The fiber passes partially around the roller 56. The roller 56 may be provided with a nonstick surface to preclude adhesion. The guide roller 56 is traversed 30 horizontally (i.e., in a direction parallel to the axis of the shaft 38) as needed to distribute fiber in the groove 32 on the mold 30.

As seen from Figures 18 and 19. the base of the groove 32 has been coated with a tacky material, such 35 as a layer of double-stick tape 64. The leading end 11 66 of the fiber is pressed against the exterior surface of the tape 64 and the mold rotated in the direction 46. The fiber adheres to the tape 64 forming the base fiber layer. If the arm is to be S provided with a narrowed gap 22' (Figure 3) the initial turns of fiber are guided onto the tape 64 using an implement 68 (Figure 19) which is urged in an inward direction 70 of the mold 30 to cause the initial layers of the fiber to enter the groove 32 and 10 be forced into place against the tape 64 at the bottom. After a number of initial turns forms a predetermined number of layera the implement 68 is no longer needed.

A pressing roller 74 is mounted on a fixture 76 15 for traversing movement in the directions 80 (parallel to the direction 58) (Figure 13). The roller 74 is biased by a spring 82 to press the fiber to preceding layers. The traverse of the roller 74 is synchronized with the rotation of the mold to impart a level 20 distribution to the fiber at all points of the mold (Figure 20). The mold sections are preferably bolted in place (by bolts 33 (Figure 16) extending through posts 31) to apply pressure to the fiber.

After winding the wound structure is generally 25 cured in an autoclave at a temperature and for a time sufficient to release any volatile constituents and/or to cure the matrix so that the resultant wrapped structure becomes a rigid self-supporting member. Thereafter, the mold is disassembled and the composite 30 structure so formed removed. The sample carriers 14 (if any) are then secured into the end turn regions 20 of the arm by any suitable means of attachment. such as epoxy glue or the like. Thereafter, the wrappings 26. 28 are wound about the arm. It should be noted 35 that the arm 10 or 10' may be wound using ribbons. 12 braids or twisted elements or other textile structural Corns. These alternatives lie within the contemplation of the present Invention.

As seen from Figures 5A and SB the individual 5 fibers in each layer of fiber are arranged in complimentary positions in the end portions 20 and the side portions 18 the arm. Owing to the different shapes of the side portion 18 and the end turn portion 20 of the arm, individual fibers may shift their 10 relative position with respect to each other as they travel from the central region of the side portions 18 of the rotor arm 10 (or 10') to the end turn portions. The general relationship of fibers in the end and side turn regions is indicated in Figures 5A IS and 5B. As seen in these Figures, in a side portion 18R (Figure SB) each of the individual layers 90A through 90D of fibers are arranged to define a predetermined dimension measured in the radial direction 92 from the center line CL that Is greater 20 than the corresponding dimension measured in the same direction for the fiber layers in an end turn region (Figure 5A). Conversely, in the end turn region 20 as shown on these Figures the fiber layers 90A through 90D exhibit a dimension in the direction 94 parallel 25 to the center axis CL that is greater in the end turn region than the corresponding dimension in the side region as measured in Figure SB. However, it is noted that the surface area of a cross section taken through a side portion 18 (Figure 5B) is equal to the surface 30 area of a cross-section of the arm taken through an end turn 20 (Figure 5A). Basically there is a reorientation of the fibers during the transition from the end region 20 (Figure 5A) to the side region 18 (Figure SB). The fibers in the innermost layer 90A of 35 the end turn portion (Figure 5A) reorient to form 13 sublayers 9OA indicated in the side portion IBB (Figure SB). A similar orientation occurs with layers 90B. 90C and 90D. It should be understood that any predetermined number of layers of fibers may be used. and that the four layers shown in Figures 5A and 5B are selected only for convenience of illustrating the .concepts involved.

Several desirable winding modifications can be effected. For example, the structures above described 10 can be wound using more than one strand of fiber with the different strands having a relatively higher specific modulus of elasticity being disposed in radially outer layers. By way of simplified example, with reference to Figures 5A and SB. the inner layer 15 9OA (or innermost layers, as the case may be) may be wound using a fiber having a first specific modulus of elasticity. The intermediate layers, e.g.. the layers 90B and 90C. may thereafter be wound atop the inner layer(s) using a fiber having a relatively greater 20 specific modulus of elasticity (i.e. stiffer). The outermost layer 90D (or outermost layers) may be wound with the fiber having a yet greater specific modulus of elasticity (i.e.. stiffer still). Such a constructional arrangement is believed preferable 25 since it more evenly distributes the ability of individual strands and layers of strands to withstand centrifugal stresses. In the above example the innermost layer may be formed of a K-29 KEVLAH aramid fiber, the intermediate layers of the K-«9 KEVLAH 30 aramid fiber while the outer layer may be formed of AS4 carbon filament fibers such as that manufactured by Hercules Incorporated. Wilmington, Delaware.

In the alternate embodiment of the arm shown in Figure 3 the arm 10 is wrapped in a manner which 35 closes or narrows the gap 22' between side portions 14 18. This aode of wrapping ensures that the total length of a fiber In a layer on the Inner side of a reference line or neutral axis 96 is as close to being equal as possible to the length of a fiber in an outer 5 layer spaced corresponding outwardly with respect to the neutral axis 96. Such a winding pattern has a tendency of imparting a more uniform load capability to the fibers.

Other possible fiber arrangements may include 10 variations in the number of fibers in different locations. For example. additional overwrapped systems (similar to the wrappings 28) in which additional fibers may be added to carry secondary loads.

In another example a plurality of additional bracing fibers 97 are oriented substantially parallel to the axis of the fibers in the side portions and are placed in high stress regions of the arm to reduce the stress. Generally the fibers 97 are disposed 20 substantially midway along the radial outer surface of each side portion 18 of the armi. The additional fibers 97 could be of the form of ribbons, braids or twisted elements.

Although, with symmetric loading, the individual 2S arm element 10 or 10' may itself act as a sample carrying device, in accordance with a more preferred embodiment of this invention shown in Figures 6 through 8 a plurality of individual arm elements 10 or 10' are stacked atop each other to form a tier 100 3Q having a sample carrying capacity numbered in even number multiples in excess of two. A typical one of the tiers 100 is shown in Figure 7A. Thus, a M place centrifuge rotor, where N is an even number greater than two. may be formed from a tier of M arms 10 or 35 10' angularly arranged with respect to each other IS about the central axis CL, vhece H equals one-half M. Thus, foe example, a four-place centrifuge tier (M equals four) may be constructed from two radial arms 10 or 10'. The angular spacing between adjacent axes 5 of the arms 10 in the tier is defined by an angle A equal to 180* divided by N. i.e.. ninety degrees. As . a further example, a six place rotor (M equals six) is defined using three arms (R equals three) with the axis of the arms offset from each other by an angle A 10 of sixty degrees. An eight-place rotor may be defined using a tier containing four stacked arms at an angle A of forty-five degrees as shown in Figures 6 through 10.

When used to form a rotor from single or 15 multiple stacked tiers of arms the height dimensions He and Hg of each individual arm 10 or 10* are related such that the height dimension Hg of an end turn portion 20 of an arm 10 or 10' is substantially equal to N times the height dimension Hc- Although this 20 relationship is preferred the relationship between the heights Hc and Hg may be related by any predetermined multiple or fraction of the number H. The preferred structural relationship will permit receipt of that number II of arms necessary to form a complete rotor 25 tier 100 to be stacked and received in the overlying central regions where the midpoints of each arm in the tier 100 are in proximity so that the adjacent arms may oriented in the above-described angular relationship. It should be noted that in practice it 30 may be necessary to provide a spacer formed with a layer of bonding material on the top and bottom surfaces intermediate each arm in the tier. Such a spacer would thus mandate that the height He be slightly . less than 1/N of the height Hg to 35 accommodate the spacer. 16 In the central region where the N arms in a tier cross the vertical registration of the arms forms an M-sided space. Into this space a drive connection 16' (Figure 6) having at least H corresponding surfaces 5 may be introduced. The radial inner surface of both side portions of each arm in the tier is connected directly or through an intermediate element to one of a different opposed pair of surfaces on the drive connection 16'. in a further aspect of the invention, a rotor may be formed from a stacked plurality of tiers 100 of arms 10 or 10'. This structure may be best understood by reference to Figures 6 through 8 which respectively show a plan, side elevational and a sectional view of 15 an eight place centrifuge rotor fabricated from five stacked tiers 100A through 100E of stacked individual arms 10 or 10'. Each tier 100A through 100E contains four arms 10 or 10'. As seen in these Figures, such a rotor is arranged such that each arm 10 or 10' in each 20 tier 100 is in vertical registration with respect to the corresponding angularly oriented arm in the next vertically adjacent tier. The sample carriers 14 provided at the ends of the same angularly oriented arm in each tier 100 are registered to define an 25 elongated, enclosed sample receiving cavity. The carriers 14 disposed in the tiers 100A through 100D are open ended tubular members while the tubular member 14' in the tier 100E is a closed ended tubular member. Alternatively an integral elongated sample 30 carrier may be introduced into the registered ends of the arms and secured in place.

Due to the vertical stacking arrangement the ends of the arms forming a tier 100 are vertically stepped. This stepped effect is believed best shown 35 in Figure 7A where it is seen that the lower surface 17 of the each an 10 ot 10' in a typical tiet 100 is vertically offset by a distance 116. In Figure 7A, to ■ore clearly illustrate this effect, only the aras 10-1. 10-2. 10-3 and 10-4 foraing the tier 100 are 5 illustrated.

The saaple container aay be oriented vertically, i.e.. its axis parallel to the centerline CL. or inclined at a fixed angle toward the centerline CL. In the instance of a stacked fixed angle rotor as 10 shown in Figures 6 through 8. the aras foraing each tier are elongated as one proceeds froa the upper tier 100A toward the lower tier 100E. Accordingly, the aolds used to fabricate the aras for each individual tier aust be aodified accordingly. Alternatively, the IS aras aay be the saae length but the segaents of the carrier or the elongated carrier aay be vertical along the surface reserved in the end turns and provided with an angled inner cavity.

As seen froa Figures 9 and 10. a rotor aay be 20 foraed froa any predeternined number of tiers. Each of these Figures disclose a rotor having two tiers 100A and 100B. However, the aras 10 or 10* foraing each tier 100A and 100B aay be stacked in any predeterained Banner as long as their ends cooperably 25 support the saaple container. Figure 9 discloses a syaaetrical stack in which the corresponding ara 10 or 10* in each tier 100A or 100B occupy the saae relative position. In the stack shown in Figure 10, the corresponding aras 10 or 10' in each tier 100A and 30 100B occupy different relative positions in the stack foraing each tier.

By whatever stacking arrangeaent utilized and by whatever nuaber of tiers desired the resultant stacked coabination of aras is secured together on the drive 35 connection 16' in any convenient aanner. For example. 18 • threaded fastener 120 (Figure 7) may be used. Alternatively, the aras uy be connected to each other by adhesive bonding, by a Belted thermoplastic matrix, or by friction provided by pressure from the fastener. in view of the foregoing there has been disclosed an individual wound radial arm element and a centrifuge rotor fabricated froa a tier of stacked aras or from a plurality of tiers of stacked arms In Which the anisotropic fibers in each ara are oriented 10 in a direction arranged to absorb to their aaxiaua the IfviH carried by that aim. The centrifuge rotors described herein are priaarily used in ultracentrifuge instruaents wherein the rotational speed is in excess of 50.000 revolutions per ainute. although it should be IS understood that their use is not liaited exclusively ttoreto.

Claims (13)

1. A centrifuge rotor rotatable about an axis of rotation, comprising at least one generally elongated arm having a major axis, the arm being formed from a plurality 5 of turns of a fiber wound in generally parallel side portions connected through curved end turn portions, a sample carrier being positioned within each end turn portion of said arm, the fibers in each side portion being generally parallel to the major axis, wherein the height 10 dimension of a side portion of the arm at a point substantially midway along its length and close to said axis of rotation is less than the height dimension of the arm at its end.

2. The rotor of Claim 1, wherein a cross-sectional area 15 taken through a side portion is substantially equal to a cross-sectional area taken through an end turn portion.

3. The rotor of Claim 1 or 2, wherein the specific modulus of elasticity of a fiber lying at a predetermined radial.distance from the axis of rotation is greater than 20 the modulus of a fiber lying radially inwardly of the predetermined radial distance.

4. The rotor of one of Claims 1 to 3, wherein the length - 20 - of a fiber disposed a predetermined distance radially inwardly of a reference axis extending through a side portion is substantially equal to the length of a fiber disposed the same predetermined distance radially 5 outwardly of the reference axis.

5. The rotor of one of Claims 1 to 4 further comprising a wrapping of fibers extending transversely across the side portions of the arms.

6. The rotor of one of Claims 1 to 5 further comprising 10 a plurality of bracing fibers disposed radially outwardly of each side portion generally midway therealong.

7. The rotor of one of Claims 1 to 6, wherein the fiber is coated with a matrix material which is curable to impart rigidity to the arm. 15

8. The rotor of one of Claims 1 to 7, said rotor being an M-place rotor comprising a tiered stack of N of said arms, where N equals one-half H.

9. The rotor of one of Claims 1 to 8, said rotor being an M-place rotor comprising: 20 a first and second tiered stack of N of said arms each, wherein N equals one-half M; each arm in the upper of the tiers being arranged in vertical registry with an arm in the lower of the tiers.

10. The rotor of Claim 9, wherein the axis of each of the 25 n arms of each tier is angularly offset from the axis of - 21 - an adjacent arm by an angle equal to 180° divided by N.

11. The rotor of one of.Claims 8 to 10, wherein the axis of each of the N arms of each tier is angularly offset from the axis of an adjacent arm by an angle equal to 5 180° divided by N.

12. The rotor of one of Claims 8 to 11, wherein the height dimension of each arm in each stacked tier taken substantially at the central portion thereof is equal to 1/N times the height dimension of the arm at its end turn 10 portion.

13. A rotor substantially in accordance with any of the embodiments herein described with reference to, and as shown in, the accompanying drawings. MACLACHLAN & DONALDSON Applicants' Agents 47 Merrion Square DUBLIN 2