GB2180909A - Concentric and/or telescopic tube manufacture - Google Patents

Abstract

A method of making a number of close-fitting, concentric and/or telescopic tubes (16,22) of fibre-reinforced plastics material, the tubes being formed by winding in succession on a single mandrel (10). Each tube is wound; cured; and its outer surface machined to give a smooth surface (18) and coated with a film (20) of a mould release agent. The next tube is then wound over the film of release agent, the same procedure being followed again. If a greater clearance between two adjacent tubes is desired, the tubes are made as described above, and after removing the outer tube (22) the outer surface of the inner tube (16) is machined further. The material may comprise epoxy-impregnated carbon tow. The tubes may be employed in solar array looms on space craft, robots in the nuclear energy industry or gas bearings. <IMAGE>

Description

SPECIFICATION Composite tube manufacture This invention relates to a method for making tubes of fibre reinforced plastics material.

A known method for making a tube of a precisely defined inner diameter involves applying fibres and resin to the surfaceofa cylindrical former or mandrel, such thatthe diameterofthe mandrel determinestheinner diameterofthetube. The application ofthefibres and resin may involve filament winding, braiding,wrapping, or hand-laying; and the design ofthe mandrel musttake into account dimensional changes ofthefibre reinforced material which occur as a consequence of the curing process.Where it is desired to make a number of nesting tubes of accurately sized inner and outer dimensions to fit inside each other, for examplefora telescopic tube structure or for an air bearing, then this known technique necessitates the use of an equal number of appropriately sized mandrels, and so can lead to considerable expense.

According to the present invention there is provided a method for making a plurality of nesting tubes of a fibre reinforced plastics material wherein one tube is made and is then used as a former in making the next tube, this being repeated until the desired number of tubes has been made. Preferably the method comprises, applying a firsttubular layer of resin impregnated fibres to a former; then curing the resin; then machining the external surface ofthe cured layer to provide desired external dimensions thereof and a smooth surface; then coating the surface with a film of a release agent of predetermined thickness; then applying a second tubular layer of resin impregnated fibres over the film of release agent; then curing the resin of the second layer; and repeating the operations of machining, coating, applying and curing until the desired number of nesting tubular layers has been formed.

All thetublular layers are thus formed in succession on a common former, sothsatonly one former is required. In the preferred process, each layer is applied by a filament winding process, and the outer portion of each layerwhich isto be machined off is wound at about 90"to the longitudinal axis ofthetubular layer. The inner portion of each layer may be wound atthesame orata different angle. When the desired numberof tubular layers has been formed, they can be separated from each other by virtue of the films of release agent, so providing the required number of nesting tubes. The separation between successive nesting tubes is determined by the thickness ofthefilm of release agent.

If it is desired to provide a greater separation between two adjacenttubes then can be achieved with thefilm of release agent, this may be achieved by making the wall of the innertube thicker than desired but so thatthe bore of the outertube has the desired value, removing the outertube, and again machining the outer surface of the innertube to provide the desired external diameter and hence the desired clearance between the two tubes. Thickening ofthewall ofthe innertube can be accomplished by applying fibre reinforced resin as described above; or by applying overthe desired wall material a layer of redundant material which can subsequently be removed.For example, the redundant material could be the matrix resin without fibres, or an alternative resin that can be applied to give a thick uniform coating, our a layer of a high melting point wax, ora wrapping of waxed cord or string, or a wrapping of a non-stick polymertape. The advantage of the lattertwo alternatives is that the redundant layer can easily be stripped off by unwinding after the tubes have been separated. By this method it is also possible to make nesting tubes where the clearance between two adjacent tubes varies along their length for example because of steps in the outer surface ofthe innertube.

The invention will now be further described by way of example and with reference to the accompanying drawings, which show diagrammatic sectional views of successive stages in the manufacture of two nesting tubes. The method involved the following steps: Step 1 Referring to Figure 1 a, a cylindrical aluminium alloy mandrel 10, ofdiameter85mm and length S20mmwas prepared with a release film 12 using the following procedure: (a) Spray one coat of'Mold-Wiz' FW-157 release agent preparation and allow to dry.

(b) Polish surface with soft cloth.

(c) Spray one coat of 'Mold-Wiz' PAT607/A release agent and allow to dry.

(d) Polish surface with soft cloth.

(e) Spray one coat of'TBA' release agent and allow to dry.

Step 2 Seven passes or coverings of carbon fibre (10,000 filaments per tow) impregnated with Giba-Geigy MY750 epoxide resin mixed with HY906 hardener and DY062 accelerator in proportions 100 : 90 : 1 by weight, were wound over the release film 12 on the mandrel 10 in the hoop mode, i.e. at 900 to the tube axis 14, so forming a tubularlayerl6.

Step 3 The layer 16 was then cured, on the mandrel 10, for 2 hours at 1 20 C and 7 hours at170'C.

Step 4 Referring to Figure 1b,the outside ofthe cured composite tubular layer 1 6 still mounted on the mandrel 10, was ground to produce a smooth uniform surface 18.

Step 5 The ground surface 18 was degreased and dried and then treated as in Step 1. In Step 1(e), however, several coats of TBA spray were applied to give a film 20 of thickness approximately 0.01 27mm.

Step 6 Afurther seven coverings of carbon fibre and resin were wound over the film 20 and cured as in Step 3,to produce a second tubular layer 22 offibre reinforced plastics material.

Step 7 After cutting off any excess material atthe ends of the tubes, the two tubes 16 and 22 were slid offthe mandrel 10. The innertube 1 6 was slid outofthe outertube 22, andthefilms 12,20 of release agent cleaned off.

The innertube 16 proved to be a smooth sliding fit inside the boreofthe outertube 22 and could be spun or rotated, performing a large number of free rotations after the initial impulse before coming to a rest.

Measurement ofthe outer diameter of the innertube 16 and the inner diameter of the outer tube 22 gave the following results: Innertube O.D. 88.6435 + 0.0025mm Outer tube l.D. 88.760 + 0.013 mm The method has been described above for the manufacture of two nesting tubes 16 and 22 but it will be understood that steps 4to 6 can be repeated to produce any desired number of concentric nesting tubes, before step 7 is performed. It will be appreciated that, where the required spacing of tube walls can be accomplished by means of a film 20 of release agent, only one machining operation per tube is required.If a larger spacing between the walls is required, two machining operations on the outer surface of each innertube are necessary, one as the set oftubes is built up, and the other after each outer tube is removed from the set.

Where spacer rings are to be left on an innertube the second machining operation may not have to produce such a smooth surface as in the first operation.

Telescopic systems consisting of a series of concentric tubes of increasing diameter, such that each tube can be retracted into the bore of the preceding tube, are frequently used where an extendable arm of variable length is required. Examples are booms on spacecraft which can be deployed when the craft is in orbitto support, e.g. solar arrays; and certain types of industrial robots and remote handling equipment in,for example, nucleartechnology. The tubes of such telescopic systems must be dimensioned either such thatthe bore of one is a smooth sliding fit overthe outer surface of the next smaller tu be, orthatthe tubes slide smoothly over spacers separating adjacent surfaces, and it will be appreciated that the present invention provides a method for making tubes of eithertype.

Concentrictubes made by the method ofthe invention are also suitable for use in gas bearings of the hydrodynamictype, which operate by virtue of the viscosity ofthe gas and the relative motion of the bearing surfaces. Such bearings produce very little energy loss, and can be run at very high speeds without overheating.

The Mold-Wiz release agents were supplied by GRP Materials Suppliers Ltd. of Portsmouth, and theTBA release agents were supplied by TBA Industrial Products Ltd., of Rochdale, England. It will be appreciated that alternative release agents may be used.

Claims (4)

1. A method for making a plurality of nesting tubes of a fibre reinforced plastics material wherein one tube is made and is then used a former in making the next tube, this being repeated until the desired number of tubes has been made.

2. A method as claimed in Claim 1 comprising applying a first tubular layer of resin impregnated fibres to a former; then curing the resin; then machining the external surface ofthe cured layer to provide desired external dimensions thereof and a smooth surface; then coating the surface with a film of a release agent of predetermined thickness; then applying a second tubular layer of resin impregnated fibres overthe film of release agent; then curing the resin ofthe second layer; and repeating the operations of machining, coating, applying and curing until the desired number of nesting tubular layers has been formed.

3. A method as claimed in Claim 2 wherein a said tubular layer is made of greater thickness than desired but such that the next successively formed layer has desired internal dimensions, and wherein the method includes further machining the external surface of the said tubular layer to provide the desired thickness, after curing and removal ofthe successively formed layer.

4. A method substantially as hereinbefore described with reference to the accompanying drawings.