GB2098515A

GB2098515A - A centrifuge rotor

Info

Publication number: GB2098515A
Application number: GB8208136A
Authority: GB
Original assignee: Heraeus Christ GmbH
Current assignee: Heraeus Sepatech GmbH
Priority date: 1981-04-25
Filing date: 1982-03-19
Publication date: 1982-11-24
Also published as: DE3116520A1; FR2504410A1; JPS57180453A

Abstract

A centrifuge rotor comprises a fibre-reinforced casing, produced from a tubular section 2 as a supporting ring for a central element 1 with which it is coupled in friction-locked manner, for reception of different inserts, such as fixed-angle container inserts or pivoted beaker inserts 11. This represents a hybrid form of construction for accomplishing higher relative centrifugal acceleration values with more economical mass production. <IMAGE>

Description

SPECIFICATION A centrifuge rotor The present invention relates to centrifuge rotors particularly for centrifuges running at high rotation speeds, comprising an inner (core) element of a metallic material of high specific strength and an outer (sheath) element of fibrereinforced synthetic resin. Centrifuge rotors of this nature are known, e.g. in German Patent Specification (Offenlegungsschrift) No. 21 40 331. To this end, glass fibres acting to reinforce the external cylinder of synthetic resin are externally placed on the periphery of the internal rotor element. Both cylindrical rotor elements are intended to have high strength with low specific weight, in particular a high specific tensile strength, to allow of an increase of the speed of revolution of the rotor.

A glass fibre reinforcement of the synthetic resin rotor element is primarily selected on the score of cost. Its drawback however is the inadequate breaking strength, in particular at the high maximum speeds of revolution so-called ultra-high speed centrifuges.

It has already been attempted to utilise other fibres for reinforcement of rotor casings on other grounds, in particular of thermal stability. To this end, the casing had always been wound directly as a peripheral winding, externally on the inner rotor element.

Since these experiments have not yet resulted in a wholly satisfactory conclusion regarding the increase of the maximum speed of revolution range of ultra-high-speed centrifuges, attempts have been made to produce the rotor as a whole (integrally) as a fibre-reinforced synthetic resin composition element. In this connection, it was to be expected that a rotor of this kind could reach higher speeds of revolution despite the lower specific weight, than metal rotors. Unexpectedly, experiments with ultra-high-speed centrifuges consisting solely of a fibrous composition element, did not indicate the required success.

Explosive rotor fracture phenomena intervened within a range of rotation speeds lying below the normal maximum speeds of an ultra-high-speed centrifuge.

The invention consequently follows a wholly different path for resolving the problem of devising a high-strength rotor usable for ultrahigh-speed centrifuges at higher rotation speeds than until now, which may not only be produced more economically but is also more universally applicable in view of its structure: Compared to the one-piece fibrous composition element having a low specific loadbearing capacity, the combination of an inner rotor element of metal with a fibre-reinforced synthetic resin casing appears to be hopelessly inferior.

The invention consists in a centrifuge rotor, particularly for a high speed centrifuge, comprising an inner (core) element of a metallic material of high specific strength and an outer (sheath) element of fibre-reinforced synthetic resin, wherein a central element of a metal alloy of high tensile strength is inset in friction-locked manner in a tubular section consisting of highstrength fibrous composition constructed as a carrying ring. Thus the inner rotor element is no longer utilised as a core for the winding of the fibrous composition, but a separately produced fibrous composition element is joined in frictionlocked manner to a central rotor element which also is produced separately.This hybrid construction is not only more economical because, for example, one winding tool only is required for different rotors, but is also more universally applicable because the different requirements for different rotors required may be complied with more satisfactorily. In particular, the height of the rotor parts but also their composition, in particular of the fibrous composition casing, may be adapted more satisfactorily to the prevailing requirements.

In the known method of external winding on the inner rotor on the contrary, the disadvantage arises that one specific rotor only (two rotors at most in the case of a split core) may be produced in this manner. The invention allows of the application of inserts of different nature, such as of a fixed-angle rotor insert, or of a hinged beaker suspension.

In order that the invention may be more clearly understood reference will now be made to the accompanying drawings which show certain embodiments thereof by way of example, and in which: Figure 1 shows the fundamental element of a centrifuge rotor according to the invention, Figure 2 shows a centrifuge rotor with a fixedangle rotor inserted therein, and a lid, Figure 3 shows a centrifuge rotor with an inset suspension for pivoted beakers.

Figure 4 shows a detail of Figure 1 which to an enlarged scale illustrates the connection between the central element and the casing element of the centrifuge rotor.

Identical parts are given identical reference symbols in all the Figures.

Referring now to the drawings a central element 1 which consists of a metallic substance, in particular of titanium, aluminium or magnesium alloy having these metals as the principal component (... base alloy), is shown in Figure 1.

The reference 2 denotes the casing of fibrereinforced synthetic resin. Carbon fibres which are impregnated or steeped in synthetic resin like epoxy resins, polyimides, polyesters, primarily serve this purpose. Aramide and Kevlar (R.T.M.) fibres, in this order, are also appropriate, apart from carbon fibrins. A synthetic resin casing produces as a carbon fibre winding element which was joined in friction-locked manner to a central titanium alloy element, proved to be particularly appropriate.The production of the composite element occurred as follows: On a winding core acting as a tool, element 2 is produced separately from element 1, a carbon fibre of a thickness of 5 to 200ym being impregnated or steeped with epoxy resin prior to winding, so that the total fibre thickness may rise up to approximately ten times the carbon fibre thickness. The winding operation occurs at 1 5 to 600 to the axis of rotation of the winding core, preferably in the region of 300. Criss-cross windings were first wound in several layers radially from the inside towards the outside, then preferably alternating with layers of peripheral windings, then again criss-cross windings and radially externally situated several layers of peripheral windings.The wound aggregate is smoothed externally, until it has a palpably (mirror-) smooth outer or casing surface. The modulus of elasticity of the composite amounted to approximately 13x10p N/cm2. The modulus of elasticity (E modulus) characterises the elongation behaviour of a material under load, which is of considerably importance in this case, apart from the strength of the material.

The casing element produced in this manner advantageously has a high load-carrying capacity in the axial direction as well as a uniform receptivity for forces acting in the peripheral direction. The carbon fibre composite element withstood more than five times the "breaking length" of titanium. The term "breaking length" conveys the meaning of the quotient between the tensile strength and the density of a material. This value is extremely important for the implementation of the invention. An intensification of the centrifugal field (in g) at constant sample or operating volume, as well as an increase of the sample and operating volume for an existing centrifugal field, or else the increase of both performance criteria, should be understood thereby.The inertial mass is also reduced with this composite element, meaning that it is possible to shorten the acceleration and breaking periods of the rotor of an ultra-high-speed centrifuge. The E modulus of the carbon fibre composition exceeded that of the titanium alloy utilised for the central element (namely 1 x 1 oe N/cm2 for an alloy containing 6% of aluminium and 4% of vanadium, the residue being titanium). The breaking length of this titanium alloy amounts to approximately 20 kilometres, whereas the breaking length of the fibrous composite element as produced above, amounted to approximately 1 0O kilometres.The internal diameter of the rotor section acting as the bearing ring of the finished centrifuge rotor, was within the range of approximately 200 mms, the external diameter amounted to approximately 240 mms. Wall thicknesses of 20 to 50 mms and more, as well as external diameters of up to 400 or 500 mms, may be produced without difficulty. The fibrous composite casing was joined to the central titanium alloy element, which is equally produced separately, in accordance with example of embodiment 4, by a kind of groove and detent spring or rather catch joint comprising an encircling rim 3, a bead, projections or the like on the basin-shaped or bowl-shaped element 1 and recesses 4 in element 2 appropriately formed for reception and retention.

The connection between the casing element 2 and the central element 1 is established in advantageous manner in that the casing element is seated on a projection, collar, stop or the like 5, for better retention and reception of axial forces.

The raised wall 6 of the basin-like element 2 according to Figure 2 serves the purpose of retention, e.g. with an angle of inclination as illustrated, or with a raised rim 7 in the case of a bowl-shaped central element according to Figure 1 (illustrated therein in dashed lines).

Experiments demonstrated that such a rotor of hybrid structure was substantially better than for example a rotor which had been produced as a one-piece fibrous composite element. This latter reached its maximum at 47,500 mien~' after steady increase of the rotation speed, meaning that fracture occurred at this speed or 252,000xg. A rotor of this kind expanded constantly (the relative centrifugal acceleration RZB is specified as a multiple of terrestrial acceleration, because the radial extension of the rotor comes into this quantity in this case).

In the case of a hybrid rotor of the invention, the maximum deformation had already been reached at 47,500 mien~' or 228,000xg, and more. This demonstrates that the rotor allows of an increase in performance by a factor of two to three times, as compared to a drum or cylinder rotor of solid titanium. Since the rotor materials utilised until now according to the prior art are stressed up to the limit of plastic deformation, it is apparent that the form of construction of the invention in which a tubular section of fibrous composite constructed as a supporting ring which receives the forces acting on the central metal element via a friction-locked joint is the first to allow of accomplishing the inventive aim specified above.A so-called fixed-angle rotor marked as an insert element 8 may in one case be inserted into the fundamental element according to Figure 1. Receivers 9 for sample containers for analytical or productive purposes and having a capacity of a few too many cubic centimetres are present one above another in the same. The angle between their principal axis and the axis of rotation amounts to either 0 or 450, but may also amount to up to 900 inclusive.

An embodiment comprising a centrally screwed-in hinged beaker insert 10 in the form af a suspension system is illustrated in Figure 3, the pivoted beakers 11 being shown at the left in the wholly outwardly pivoted state and at the right in the idle condition.

These beakers hang from rigid hooks 12 which for their part are firmly connected to bar springs 13 which are secured in the central element coaxially to the axis of rotation. A lid 1 5 shuts off the rotor chamber containing the insert 8, e.g. of glass-fibre-reinforced polyamide, in hermetic manner. by means of a screw 1 7 secured centrally at 16.

As apparent from the left-hand half of Figure 3, the preferably curved (convex) base 14 of the beaker 11 bears on the inner surface of the bowl rim 7 of 1 raised beyond the point of contact of the beaker bases in the wholly outwardly pivoted state (construction shown dashed in Figure 1).

The forces acting on the periphery of the central element 1 increase as the rotation speed rises, in particular the centrifugal forces, and are transferred from the element 1 via the frictionlocked joint (Figure 4) to the glass fibre composite element 2 and are safely borne by the same. The lid 1 5 is also usable in this case, and the screw 17 then also holds fast the casing 10 and keeps the rotor chamber shut in vacuum-tight manner.

Modifications of the embodiments shown may be made as desired. In particular, other forms of the inserts and/or lids in the rotor casing 2 and/or the fundamental element 1 according to Figure 1, may also be envisaged. As unitary as possible a size of the external diameter of the inserts or rather of the internal diameter of the casing or of the central element is sought however.

Other friction-locked joints are also applicable, e.g. in mortise and tenon form of construction.

Other metallic materials and other fibrous materials are applicable if they fulfill the conditions specified. The materials in the order specified in the foregoing are preferred for this purpose however. The fibrous compound may also be modified by combining external windings of fibres having a high E modulus with internal windings of fibres having a lower E modulus. In this connection, it is possible to join these elements firmly in one piece or in another manner.

The fibrous compound is produced in one piece by curing of the synthetic resins in particular. Other joining means than windings, such as known per in the technology of fibrous compounds, e.g.

imbedment of aligned fibre sections in a plastics material matrix, are also applicable.

Claims

1. Centrifuge rotor, particularly for a high speed centrifuge, comprising an inner (core) element of a metallic material of high specific strength and an outer (sheath) element of fibre-reinforced synthetic resin, wherein a central element of a metal alloy of high tensile strength is inset in friction-locked manner in a tubular section consisting of high-strength fibrous composition constructed as a carrying ring.

2. A centrifuge rotor as claimed in claim 1, wherein the tubular section consists of a composition comprising carbon fibres, aramide fibres, or fibres impregnated with a synthetic resin such as an epoxide, a polyimide or a polyester.

3. A centrifuge rotor as claimed in claim 1, wherein the central element consists of a titanium-based alloy, an aluminium-based alloy or a magnesium-based alloy.

4. A centrifuge rotor as claimed in any of the preceding claims, wherein the central element is constructed as a fixed-angle rotor, with an angle of 0 to 900 between the axis of rotation and the axis of the sample container or of the samplereception chamber.

5. A centrifuge rotor as claimed in any of the preceding claims, wherein the central element comprises a tilting beaker mounting suspension device.

6. A centrifuge rotor as claimed in claim 1 or 2, wherein the fibrous composition comprises a plurality of mutually intersection windings of the fibres, peripheral windings of the fibres being arranged to enflank the criss-cross windings at least in the outer portion of the tubular section, and the tubular section having a smooth surface at its periphery.

7. A centrifuge rotor as claimed in claim 6, wherein the fibrous composition is so constructed radially ourwards from the inside, that the number of the criss-cross windings or of their layers is preponderant towards the centre of rotation, and the criss-cross windings are complemented in radially outward direction by several alternating peripheral windings, and wherein multilayer peripheral windings are located radially at the extreme outside, said windings being delimited by a smooth surface of a synthetic resin.

8. A centrifuge rotor as claimed in any of the preceding claims, wherein the central element is constructed in tub form or bowl form with the rim drawn upwards at least beyond the point of contact of the beaker bases in the fully outwardly pivoted state.

9. A centrifuge rotor as claimed in any of the preceding claims, wherein, apart from the construction of projections, beads or mortise/tenon arrangement serving the purpose of the friction lock, the central element comprises extensions, stops or a collar incorporated in axial direction.

1 0. A centrifuge rotor as claimed in any of the preceding claims, which comprises a lid closure with a seal, in particular for operation under vacuum.

11. A centrifuge rotor substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

12. A centrifuge rotor substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

1 3. A centrifuge rotor substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.