This invention relates to a method of manufacture of annular components, and to components manufactured using the method. In particular, the invention relates to the manufacture of annular fibre reinforced composite material components, for example suitable for use as spacer rings in serially bonded magnet structures.

There are a number of applications in which annular components are manufactured from fibre reinforced composite materials. By way of example, an elongate glass fibre filament may be wound upon a mandrel of a suitable size and shape. The fibre is conveniently passed through a resin bath before winding onto the mandrel. Once wound onto the mandrel, the winding process typically resulting in a number of fibre layers being wound upon one another, the winding angles used during winding being selected to achieve desired physical properties in the finished product, the resin is cured or allowed to cure to form an annular product of the required shape, size and strength characteristics. Whilst the fibre may be passed through a resin bath prior to winding, other manufacturing techniques are known. By way of example, in some arrangements the fibres may be wound onto the mandrel in a dry condition, a suitable resin subsequently being applied to the wound fibres as part of the manufacturing process.

Other manufacturing methods involve laying up layers of a suitable fabric material onto a mould or mandrel and subsequently impregnating the layers with a resin material.

It is an object of the invention to provide a manufacturing technique by which annular components of a fibre reinforced composite material can be manufactured in a relatively simple, convenient and economic manner.

Difficulties can be faced in reliably producing components to a required production specification in a simple, convenient and economic manner. By way of example, satisfying dimensional constraints or density or coefficient of thermal expansion constraints can be difficult. It is an object of the invention to provide a manufacturing technique by which annular components of a fibre reinforced composite material can be manufactured in a relatively simple, convenient and economic manner, and to a high degree of accuracy.

According to the present invention there is provided a method of manufacture of an annular component comprising applying fibres and resin to the inner surface of a hollow mould having a cylindrical inner profile, rotating the mould to achieve a substantially uniform distribution of the resin and fibres within the mould, curing the resin or allowing the resin to cure, removing the cured resin and fibre material product from the mould, and machining at least an inner peripheral surface of the cured resin and fibre material to form the product to a desired specification. The method may include a further step of cutting the product to form one or more annular components.

The mould is preferably rotated whilst the fibres and resin are applied thereto. As a result, uniform distribution of the resin and fibres within the mould is easier to achieve.

The rotation of the mould is further advantageous in that the centripetal forces experienced by the resin and fibres will tend to result in the product being free of voids, or the presence of voids therein being kept to a low level. A substantially consistent fibre volume fraction can be maintained within the product.

The mould is preferably rotated whilst curing of the resin occurs. By continuing to rotate the mould whilst the resin cures, the product can be of enhanced uniformity.

The fibres conveniently take the form of short lengths of fibres, for example the fibres may be of chopped glass fibre form. The fibres may be delivered into the mould by spraying, the fibres being carried by, for example a flow of a suitable liquid or gas. By appropriate control over the speed of rotation of the mould before and during curing, orientation of the fibres within the product may be controlled, at least to a degree. By way of example, where the mould is rotated at a high speed, then the chopped lengths of the fibres will tend to become orientated in a direction substantially parallel to the axis of the mould. When rotated at a lower speed before and during curing, the orientation of the fibres will be more dependent upon their orientations when sprayed or otherwise delivered into the mould, and so may be substantially randomly orientated, depending upon the manner in which the fibres are delivered to the mould.

By manufacturing a product which is subsequently cut into separate annular components, manufacturing efficiency can be enhanced.

The invention further relates to an annular component manufactured using the method set out hereinbefore. Whilst the annular components may be used in a range of applications, one particular application in which they may be used is as spacer rings for use in serially bonded magnets. Where used in such an application, it is desirable for the spacer rings to be of electrically insulating form, and for the coefficients of thermal expansion thereof to be matched to other parts of the serially bonded magnet structure.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic representation illustrating steps in the process for manufacturing an annular component; and

Figure 2 is a representation of an annular component manufactured using the method illustrated in Figure 1. Referring to the accompanying drawings, an annular component 10 is shown that is of fibre reinforced composite material form, made up of chopped glass fibres and a suitable epoxy resin. Whilst these represent suitable materials for use in the manufacture of the component 10, it will be appreciated that the invention is not restricted in this regard and that other materials may be used if desired.

The component is manufactured by delivering chopped fibres 12 and a resin material 14 to the inside of a hollow cylindrical mould 16. The fibres 12 and resin material 14 are conveniently delivered by being sprayed into the mould 16 via spray heads 12a, 14a that are able to move in the axial direction of the mould 16. The mould 16 is supported upon bearings or the like to allow the mould 16 to be rotated. A motor 18 is connected to the mould 16 to drive the mould for rotation at high speed. In use, the motor 18 is operated to drive the mould 16 for rotation before the delivery of the resin material 14 and fibres 12 thereto commences, the rotation continuing during the delivery of the resin material 14 and fibres 12 thereto, and continuing during a period of time in which curing of the resin material 14 takes place to form a hollow cylindrical tubular product 20 of substantially uniform wall thickness. By ensuring that the mould 16 is rotated whilst the fibres 12 and resin material 14 are delivered thereto, and by arranging the spray heads 12a, 14a to undergo reciprocating movement whilst spraying or delivery is being undertaken, the fibres 12 and resin material 14 are delivered substantially uniformly to the inner surface of the mould 16. Depending upon the nature of the resin material 14, the curing step may require heating of the mould 16 and its contents. However, this need not always be the case and materials which cure under ambient conditions and/or under the application of certain lighting conditions and the like could be used if desired.

By rotating the mould 16 whilst the fibres 12 and resin materials 14 are applied thereto using reciprocating spray heads 12a, 14a, it will be appreciated that the fibres 12 and resin materials 14 may be substantially uniformly distributed within the mould. Furthermore, the rotation may serve to consolidate the fibres 12 and resin material 14 prior to curing, to reduce the presence of voids within the product 20 and to enhance the uniformity of the product 20. The fibre volume fraction of the product may be accurately controlled. It will be appreciated that by controlling consolidation, degassing and fibre volume fraction in this manner, the coefficient of thermal expansion of the product may be controlled, at least to some degree, and so may be matched to the characteristics of other components with which the annular component 10 is to be used. By continuing to rotate the mould 16 during curing, sagging, running or other deformation of the product that may otherwise occur if the rotation were to be interrupted before or during curing can be avoided, again assisting in ensuring that the product 20 is of a good level of uniformity.

Where the fibres 12 are delivered by being sprayed onto the inner surface of the mould 16, it will be appreciated that the fibre orientation will be or may be substantially random, depending upon the nature of the spraying operation used in the delivery of the fibres 12. Accordingly, the product may be of quasi-isotropic form. Depending upon the speed of rotation of the mould 16, some reorientation of the fibres 12 may occur prior to curing. By way of example, if the mould is rotated at high speed then there is a tendency for at least some of the fibres to become orientated in a direction substantially parallel to the axis of the mould 16. Accordingly, be appropriate control over the rotary speed of the mould 16, the operator may be able to modify certain strength characteristics of the product.

The use of a rotating mould in the manufacture of the product is advantageous in that the products produced using the mould are of consistent, uniform form and have reproducible physical properties.

Once the product has cured, it is removed from the mould 16. Machining of the inner peripheral surface of the product 20, at machining station 22, to a desired size is then undertaken. The rotation of the mould, and forces arising therefrom, tends to result in the inner periphery of the product 20 being substantially free from fibres 12, or containing a reduced volume fraction thereof. Consequently, the machining not only results in the product 20 having a desired inner diameter, but also modifies the net density and coefficient of thermal expansion of the product 20, and so allows the product to be accurately produced to a desired specification. The machining operation is relatively easy to undertake without damaging the product 20 as the machining operation is primarily removing cured resin from the product 20. The product may then be cut or slit to form a number of annular components 10. The cutting of the product into the annular components 10 may be undertaken using a suitable CNC machine or the like.

Although the annular components 10 manufactured using the method set out hereinbefore may be used in a wide range of applications, one application in which they may be employed is as spacer rings for use in serially bonded magnets or the like. The components 10 are particularly suited to such use as the materials thereof are electrically insulating and so the components 10 are of electrically insulating form, and the components 10 can be formed in such a manner that the coefficients of thermal expansion thereof are substantially matched to those of the coils of the magnets using the technique outlined hereinbefore. The manufacturing method allows the bulk manufacture of the components 10 in a relatively simple and convenient manner, the method allowing the components 10 to be formed to a high degree of accuracy using the method outlined hereinbefore, and so ensuring that the components are of consistent form.

Whilst specific embodiments of the invention are described hereinbefore, it will be appreciated that a wide range of modifications and alterations may be made to the arrangements described hereinbefore without departing from the scope of the invention as defined by the appended claims.