This invention relates to hollow members, such as structural support holes, made from filaments, such as glass fibre, or bunches of filaments, made by being formed on a tapered mandrel by continuous winding along and about the mandrel, the filaments being embedded in a suitable binder, such as polyester resin.

A known advantage of making structural members such as hollow tapered poles from filament-wound glass fibre reinforced plastic (GRP) is that the filaments can be orientated generally along the length of the structural member to thus impart stiffness and hence provide an optimum strength to weight ratio. It is also well known that optimum strength occurs when the filaments remain uncut or unbroken but, in practice, it is necessary to provide joints where the structural member has to be connected to other elements, such as being fixed to the ground or by attaching fixing joints to the structural member above the ground by which other elements can be attached to it. This is very difficult to achieve without cutting or drilling into the GRP and hence the mechanical advantage of maintaining continuously round filaments under tension is lost at the points where they are cut for such purposes.

The present invention is derived from the realisation that there is a need for filament wound structural members in or on which are formed flanged formations which provide fixing points by which e.g. the structural member, if a hollow pole, may be secured to the ground at one end and to which another element or elements may be affixed whilst maintaining a continuity of all or most of the filaments so that they remain wound and in tension thereafter, to thereby maximise the strength of the structural member.

According to a first aspect of the invention there is provided a method of forming one or more flanges or formations, which may conveniently be inwardly facing, on or in a hollow continuously wound structural member, such as a hollow pole, the method including the steps of providing a tapered mandrel on which to continuously wind a loop of filament or filaments to form a hollow structural member, providing an end-forming plate at at least one end of the mandrel, placing one or more formers on the outside of the mandrel adjacent to but spaced from the or each end plate by a required amount to form one or more flanges when the member has been fully wound and set within a resin, and subsequently removing the continuously wound structural member from the mandrel.

Conveniently, the or each flange or formation is inwardly facing, such as radially inwardly facing, at one or both ends of the structural member, although it will be understood that other flanges or formations of different shape may be formed at intermediate points along the length of the structural member, each being shaped by the presence of a corresponding former thereunder or thereabout.

Preferably, the or each former is removed from the inside of the structural member once the latter has been removed from the mandrel, by the use of a segmented former or formers allowing each such segment to be removed sequentially. Alternatively, the or each former may be elastomeric in nature or otherwise bendable, being strong enough to allow the formation of a flanged or otherwise formed region but pliant enough to be removed from the inside of the structural member upon completion of the fabrication process. Further alternatively, the former may instead be left in position within the structural member, particularly if the former is itself hollow, thereby enabling it to be used in conjunction with the or each flange or formation for the purposes of attaching the structural member to another element, such as the ground, or to another structural element, such as a weight-bearing arm of an electricity pylon.

According to a second aspect of the invention there is provided a structural member made in accordance with the method according to the first aspect of the invention. In particular, the structural member may comprise a tubular post having continuously wound inwardly facing flanges at each end, by which the post may be secured to another element, such as the ground, at one end and to another element at its other end, such as a laterally extending support arm of e.g. a pylon for supporting electricity transmission cables.

According to a third aspect of the invention there is provided apparatus for making a support member in accordance with the second aspect of the invention which includes a tapered mandrel, at least one former adapted to fit against an outside surface of the mandrel adjacent to but spaced from an end- forming plate, and filament winding means for continuously winding filament over the length of the mandrel to the limit imposed by the presence of the or each end-forming plate including in the gap between the or each former and the or each end-forming plate to thereby form at least one flange or other formation in that region. With the arrangements described with respect to the first, second and third aspects of the invention it is therefore possible to provide a continuously wound structural member with one or more inwardly facing flanges or other formations therefor without the need to, separately, attach flanges or other fixing elements to the structural member, which is therefore commensurately stronger than would otherwise be the case. In particular, to fix such a structural member to the ground it is instead simply necessary to either drill holes through the inwardly facing flange or formation at the largest-diameter end and thereafter bolt the structural member to the ground, causing relatively minimal damage to the continuity of the filament windings. However, it will also be understood that e.g. swan-neck metal fixing plates may be used instead to clamp the flanged or formed region to the ground without the need to drill holes or otherwise cut the filaments in this region. In a similar manner, if a flange has been formed at the other end of the structural member it can be used to attach it to some other fixture, such as the weight-bearing arm of a pylon.

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

Figure 1 is a perspective view of a rotatable mandrel on which a flanged support post has been formed in accordance with the invention;

Figure 2 is a sectional side elevation along the axis X-X of Figure 1 ;

Figure 3 shows a view of the support post of Figure 1 in an upright position above the ground forming part of a pylon;

Figure 4 is a section across the line Ύ-Υ' of Figure 2, and Figure 5 shows a sectional view of a second embodiment of the invention supported on a mandrel.

Referring firstly to Figure 1 , an elongate tapered mandrel 1 is shown supporting at its widest end an annular end-forming plate 2 and adjacent its narrowest, free, end a disk shaped end-forming plate 3. Between the annular plate 2 and disk plate 3 is shown a wound structural member in the form of a tapered hollow post 4 shown more clearly with reference to Figure 2.

In Figure 2 it will be seen that the post 4 has an inwardly facing flange 5 adjacent the annular plate 2, and another inwardly facing flange 6 adjacent the disk plate 3. The formation of flange 5 is made possible by the provision of a segmented, tapered, annular former 7 placed over and around the mandrel 1 adjacent to but apart from the annular plate 2 so that as the mandrel 1 rotates to form the post 4, filaments from filament winding means (not shown) are able to enter the gap therebetween to form the flange 5. Similarly, the disk 3 is positioned adjacent to, but slightly spaced apart from, the free end of the mandrel 1 , thereby allowing the formation of the flange 6 during the winding operation.

As will be apparent, the formation of the inwardly facing flange 6 does not inhibit removal of the post 4 from the mandrel 1 once the disk plate 3 has been removed, in view of the taper of the mandrel 1 . However, the formation of an inwardly facing flange 5 at the other end of the post 4 would ordinarily be problematic in that it would prevent the post from sliding off the mandrel 1 . This problem is addressed by the use of the segmented annular former 7 which both permits the formation of a raised portion on the mandrel 1 adjacent to the annular plate 2 to thereafter allow formation of the inwardly facing flange 5, and upon completion of the post 4 including the step of allowing the resin to set the post 4, it can simply be removed from the mandrel, hydraulically or manually, whereafter the former 7 can be removed a segment of time. This arrangement is particularly advantageous because it allows for winding about the central axis of the mandrel 1 at a relatively steep angle, such as 10 degrees from the axis, so that relatively deep flanges 5, 6 can be formed with the filaments making up the post 4 being substantially continuously in tension, thereby maximising the strength of the structural member being formed. In turn, the flanges 5, 6 are large enough to provide the necessary strength for fixing to other elements, such as to the ground in the case of flange 5, and in the case of flange 6, to the support arm 8 of an electricity transmission pylon 9, as shown in Figure 3. As a consequence, the mechanical properties of the filament used to make up the post 4 can be fully exploited without the need for separate joints to be attached for fixing the post 4 to e.g. a concrete support base in the ground in any suitable manner.

In Figure 4 there is shown a cross section along the axis Ύ-Υ' of Figure 2 in which it will be seen that the segmented annular former 7 includes two parallel-sided former segments 7a and four quadrant former segments 7b, the segments 7a and 7b collectively defining a trumpet-shaped annulus when mounted on the mandrel 1 . As will be apparent, when the post 4 has been removed from the mandrel 1 removal of each parallel-sided segment 7a is facilitated by sliding them radially inwardly, whereafter the quadrant segments 7b can be removed, leaving the post 4 with a flange end in that region. An alternative approach is shown in Figure 5 in which a pre-moulded GRP annular former 7c is used to form the flange in conjunction with the end plate 2, in this case with the intention of leaving the former 7c in position after the post 4 has been wound and set and thereafter removed from the mandrel 1 .

The invention therefore provides an elegantly simple solution to the problem of securing such structural members, particularly very long members such as pylons or masts, to anchor points without weakening the structural element as a result of some of the filaments being cut in these regions.

Although the invention has been shown with reference to the manufacture of a structural element in the form of a post, having a pair of inwardly facing flanges at each end, it will be apparent that the concept of utilising removable formers on the outside of the mandrel may also be used to form outwardly facing hollow flanges or formations of varying shapes at positions along the length of the mandrel. Similarly, it will be appreciated that although segmented formers have been described the invention also extends to continuous formers which are strong enough to resist undue compression as the structural member is being wound on the mandrel but thereafter resilient enough to allow the former to be released from the inside of the structural member after it has been moved from the mandrel, or to leave the former in situ if preferred.