GB2189862A - Composite tubular elements and methods of fabrication - Google Patents

Description

GB2189862A 1 SPECIFICATION drive shafts have satisfactory operating char

acteristics, they have been found difficult and Composite tubular elements and methods expensive to produce on a high volume pro of fabrication duction basis.

70 BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION

The present invention relates generally to fiber The present invention relates to a unique reinforced tubular elements such as vehicle fiber reinforced aluminum drive shaft, along drive shafts and, in particular, to a graphite with a unique method for producing such drive reinforced aluminum drive shaft and a method 75 shafts on a production basis.

for producing such a drive shaft. The drive shaft of the present invention in Over the past decade, there has been an cludes a cylindrical metal tube having a longi ongoing endeavor by the industry to reduce tudinal axis which, in the preferred embodi the weight of vehicles in order to improve fuel ment of the invention, is typically constructed economy. In addition to downsizing and rede- 80 of aluminum. An isolation layer of cloth ma signing vehicles to make the most efficient terial surrounds the aluminum tube and is ad use of the available space, a great deal of hered to the outer surface of the tube. A rein attention has been given to constructing vari- forcing fiber layer also surrounds the tube and ous vehicular components of lighter weight is adhered to the outer surface of the isolation materials. For example, in the area of drive 85 layer. In accordance with the present inven shafts, it has been proposed to replace con- tion, the reinforcing fiber layer includes a plu ventional steel drive shafts with lighter weight rality of individual reinforcing graphite fibers aluminum tubes. However, depending on the which are orientated parallel to the longitudinal length of the drive shaft, and the maximum axis of the tube and are uniformly positioned speed at which the drive shaft is to be ro- 90 about the circumference of the tube. In the tated, vibration problems can arise. above discussed prior art, the graphite fibers

While typically the tubular steel or aluminum were specifically located non-parallei with the drive shafts are adequate to transmit the torlongitudinal axis. Finally, the drive shaft in sional forces involved, there is a tendency for cludes a covering layer of fiber material sur a shaft to---whip-or resonate mechanically 95 rounding the tube and adhered to the outer when the shaft reaches a certain vehicle surface of the reinforcing fiber layer.

speed, typically referred to as a critical speed. The present invention includes a unique ap Consequently, in order to overcome the critical proach to producing the fiber reinforced drive speed limitations of single long drive shafts, shafts on a production basis. In the method of typically multiple sections of shafts are em- 100 the present invention, a plurality of cylindrical ployed. In these instances, adjacent individual metal tubes each having a longitudinal axis are drive shaft sections are connected to one coupled to one another in an end-to-end rela another by means of a universal joint as- tionship by a plurality of joining plastic plug sembly which in turn is supported by a bear- members to form a longitudinally extending ing mounting unit affixed to the vehicle frame. 105 series of metal tubes. The series of metal In order to accommodate a longer drive tubes are fed along a longitudinal path through shaft such that the universal joint assemblies an apparatus for applying the individual layers and the bearing mounting units can be elimi- of the composite fiber sleeve to the tube.

nated, it has been proposed to reinforce metal Initially, the isolation layer of cloth material tubes with a fiber reinforced sleeve portion to 110 is applied around the outer surface of the increase the axial stiffness of the shaft with- tube. Next, the plurality of individual reinforc out substantially increasing its weight. For ing fibers are applied about the circumference example, United States Patent Nos. of the tube such that the individual reinforcing 4,131,701; 4,173,670; and 4,214,932 all dis- fibers are parallel to the longitudinal axis of close fiber composite aluminum drive shafts 115 the tubes. Next, the covering layer of fiber wherein aluminum tubes are wrapped with al- material is applied around the outer surface of ternating layers of resin-impregnated woven the reinforcing fiber layer.

fiberglass cloth and resin-impregnated fiber re- While the individual layers are being applied inforcing sheets. The reinforcing sheets are to the tube, a vinylester liquid resin material is comprised of continuous unindirectional graph- 120 applied to saturate the individual layers, and ite fiber layers, with the graphite fibers ar- the drive shaft having the saturated layers ap ranged at angles between 5' to 20' with plied thereto is then passed through a heated respect to the longitudinal axis of the tube. forming die wherein the liquid resin is cured to Another approach to reinforcing a tubular firmly adhere the individual layers to the series metallic drive shaft is disclosed in United 125 of tubes. As the series of tubes having the States Patent No. 4,272,971, which discloses cured composite sleeve thereon exits the a drive shaft wherein the fiber reinforcing layer apparatus, the tubes are severed at each of is applied to the inside surface of an aluminum the joining plugs to produce a plurality of indi tube. vidual fiber reinforced drive shafts. In some While the above-discussed fiber-reinforced 130 instances, wherein a connecting member such 2 GB2189862A 2 as a yoke portion or a splined shaft is to be driven member (not shown). While the con welded to the end of the drive shafts, it has necting members are shown as yoke portions been found desirable to strip a selected end for connection to an associated universal joint portion of the composite reinforcing layer from assembly (not shown), it will be appreciated the drive shaft to prevent heat damage to the 70 that other types of connecting members such end of the composite sleeve during the weld- as, for example, a splined shaft end can be ing operation. used.

The present invention also concerns alter- The connecting members 16 and 18 are nate methods of manufacturing the drive typically secured to the ends of the metal shafts. 75 tube 14 by a welding operation. To prevent heat damage to the composite sleeve 12 BRIEF DESCRIPTION OF THE DRAWINGS when the connecting members are attached,

The above, as well as other advantages of the ends of the reinforcing sleeve 12 are the present invention, will become readily ap- spaced inwardly from the ends of the metal parent to one skilled in the art from the fol- 80 tube 14 to provide exposed metal end por lowing detailed description of the preferred tions 20 and 22. As will appear more fully embodiments of the invention when consi- below, in the preferred method of manufac dered in light of the accompanying drawings, ture, the reinforcing sleeve 12 is initially in which: formed along the entire length of the metal Fig. 1 is a side elevational view of a fiber 85 tube 14 and is subsequently stripped from the reinforced composite tubular element of the end portions 20 and 22 by severing it circum present invention, shown for use as a drive ferentially with a saw, and peeling it off. in shaft; other methods of manufacture, the reinforcing Fig. 2 is a fragmentary sectional view taken sleeve 12 is formed so that it initially does along line 2-2 in Fig. 1 and showing the indi- 90 not cover end portions 20 and 22.

vidual layers which constitute the preferred Turning now to Fig. 2, there is shown a embodiment of the fiber composite sleeve; cross-section through the tube 14 and the Fig. 3 is a schematic diagram showing one preferred embodiment of the composite rein method of fabricating the fiber composite tu- forcing sleeve 12. Typically, the metal tube 14 bular element of the invention on a continuous 95 is a cylindrical aluminum tube fabricated in a basis wherein the fiber composite sleeve is conventional manner. The length, diameter, formed and cured about a series of individual and wall thickness of the tube, along with the metal tubes temporarily joined together and particular aluminum alloy from which the tube moving in a longitudinal path; is formed, may vary from application to appli- Fig. 4 is a side elevational view of a com- 100 cation, depending on the particular power posite fiber reinforced tubular element pro- transmission requirements of the drive shaft.

duced according to the method schematically In any event, the use of the composite rein illustrated in Fig. 3; forcing sleeve 12 having the specific construc Fig. 5 is a schematic drawing which illus- tion of the present invention has been found trates an alternate method of assembly of the 105 to sufficiently increase the axial stiffness of drive shaft wherein individual previously the aluminum tube such that weight of the formed and cured fiber composite sleeves are tube can be substantially reduced as com slipped over and adhesively secured to an as- pared with a tubular aluminum drive shaft sociated metal tube; and without the reinforcing sleeve.

Fig. 6 is a schematic drawing which illus- 110 The composite reinforcing sleeve 12 basi trates a further alternate method of manufac- cally consists of three sections: an isolation ture wherein a preformed and uncured, resin- layer 32, a fiber reinforcing layer 34, and a saturated fiber reinforcing sleeve is slipped covering layer 36. As will be discussed, in the over a metal tube member and subsequently preferred method of manufacture, the indivi cured thereon. 115 dual layers of the sleeve 12 are bonded to one another and the tube by a vinylester re DESCRIPTION OF THE PREFERRED EMBODI- sin.

MENTS The isolation layer 32 includes individual Referring now to Fig. 1, there is shown a layers 32a, 32b, and 32c. The first isolation drive shaft 10 which utilizes a composite tu- 120 layer 32a is composed of a plurality of longi bular element embodying the features of the tudinally extending threads of string material present invention. The drive shaft 10 includes equally spaced about the circumference of the an outer composite fiber reinforcing sleeve 12 tube. This layer is not essential to the func which surrounds and is attached to the exte- tioning of the invention but, as will be dis rior of a cylindrical metal tube 14. As illus- 125 cussed, is provided as a visual indicator to trated, first and second connecting members avoid contact of a saw blade (not shown) 16 and 18, which are shown as yoke por- with the metal tube 14 when striping the end tions, are connected to opposite ends of the portions of the reinforcing sleeve 12 as previ metal tube 14 for coupling the drive shaft be- ously described. In the preferred embodiment tween a drive member (not shown) and a 130 of the drive shaft, the layer 32a consists of 3 GB2189862A 3 eight longitudinally extending polyester strings be dependent on the amount of graphite equally spaced about the circumference of the which has been applied to the tube, along tube. with the number of individual glass fibers in The second isolation layer 32b is composed cluded in each strand. In the preferred em of individual strips of a thin screen-like cloth 70 bodiment, each strand is composed of 1,800 material which extend longitudinally and have fibers of fiberglass, and is wrapped about the overlapping lateral edge portions to completely tube to produce twenty wraps per longitudinal surround the tube. This layer functions to iso- inch.

late the fiber reinforcing layer 34, which is The second covering layer 36b is another typically graphite, from the aluminum tube 14, 75 circumferential wrapping, similar to that of the since it has been found that direct contact first covering layer 36a, but with polyester between graphite and aluminum results in un- string, of a type similar to that used in the desirable electrolytic corrosion. The exact first and third isolation layers 32a and 32c. It width of the individual strips will be depen- should be noted that the layers 36a and 36b, dent on the number of strips utilized, along 80 although illustrated as overlying layers, do not with the outside diameter of the tube. While visually form separate layers, since the strands the number of strips of cloth material which of one wrapping will typically fall in between are utilized to surround the tube can vary from the strand of the other, so that layers 40 and application to application, in the preferred em- 42 appear visually as a single layer.

bodiment, four individual strips of cloth ma- 85 The third covering layer 36c, which is the terial are utilized. outermost layer of the sleeve 12, is applied The third isolation layer 32c is similar to the similar to and is identical in material character first layer 32a, and is comprised of a plurality istics to that of the isolation layer 32b, and of longitudinally disposed threads of polyester provides an outer cloth covering which prostring uniformally spaced about the circumfer- 90 duces a smooth outer surface on the drive ence of the tube. In the preferred embodi- shaft.

ment, eight threads are used. Again, this is Turning now to Fig. 3, there is shown sche not an essential layer, but is provided to form matically an apparatus 40 for forming compo and hold the strips of cloth material in place site tubular elements of the type illustrated in on the metal tube 14. It will be appreciated 95 Fig. 2 and a continuous basis. As shown in that, while the isolation string layers 32a and Fig. 3, a plurality of metal tubes, Shown as 32c are shown in Fig. 2 as spacing the isola- 14a, 14b, 14c, 14d, are interconnected in an tion cloth layer 32b from both the tube 14 end-to-end relationship by a plurality of plug and the fiber reinforcing layer 34, there is ac- members 42. The plug members 42, which tually contact between the layer 32b and the 100 typically are constructed of a plastic material, tube 14 and between the layer 32b and the are shown as double-ended, with a centrally reinforcing layer 34 in the regions between located protruding annular flange portion 44 the spaced apart longitudinally extending having an outer diameter greater than the out threads. side diameter of the tubes. As will be dis The fiber reinforcing layer 34 is typically 105 cussed, the protruding flange portion 44, after comprised of graphite and includes a plurality each layer of the composite sleeve has been of individual and independent reinforcing fiber applied and cured on the tubes, provides an strands or---tows-which, in accordance with annular raised portion in the sleeve which the present invention, are preferably located functions as a visual reference to define the parallel to the longitudinal axis of the tube, 110 specific location at which the tubes must been and uniformly positioned about the isolation sawed apart.

layer 32. Each tow consists of a predeter- The apparatus 40 includes a plurality of indi mined number of longitudinally disposed, indi- vidual application stations which, as discussed vidual graphite fibers. The exact number of in more detail below, are utilized to apply the tows of graphite which are utilized will depend 115 various materials required to form the compo on the number of individual fibers located in site fiber sleeve on the aluminum tube. The each tow and the overall amount of reinforcapparatus also includes a pair of pulling rollers ing which is desired. In one preferred embodi- 46 and 48 for pulling the longitudinally ex ment, 115 longitudinally disposed tows of tending series of tubes through the apparatus graphite fibers are utilized, with each tow be- 120 along a longitudinally extending path at a pre ing composed of 36,000 individual fibers of determined speed.

graphite. As shown in Fig. 3, at first station 50, the The covering or protective layer 36 includes first isolation layer 32a of longitudinally ex individual layers 36a, 36b, and 36c, and func- tending, circumferentially spaced apart string is tions as a means for retaining the longitudinal 125 applied. String from a plurality of rolls 52 graphite strands of the layer 34 adjacent the passes through a guide means 54 and an ap metal tube 14. The first covering layer 36a is plication means 56, which may be pulleys or comprised of a circumferential wrapping of the like, into place on the tube 14. Although fiberglass strands. The number of circumferen- four rolls are shown, eight rolls are used in tial wrappings per given length of the tube will 130 the preferred embodiment of the invention.

4 GB2189862A 4 Also, while shown as tapered rolls or spools, As illustrated, the head 104 contains the the spools used are preferably of the center- fiberglass material of the first covering layer feed type, so that the last turn is on the 36a on the roll 106 and the polyester string outside, and additional rolls can be connected material of the second covering layer 36b on without interrupting the process. 70 the roll 108. As previously described, the Then, at a second station 58, the second layers 36a and 36b are circumferential wrapp isolation layer 32b of strips of cloth material ings which, in the preferred embodiment, are is applied. As shown, the layer 32b is applied applied at a rate of approximately twenty per in four segments. At the second station 58, inch. At a tenth station 110, the resin mix the material of the second layer 32b is applied 75 from the tank 82 is again applied, through a from rolls 60 and 62. While not shown in the line 112 and a dispensing end 114.

drawings, the rolls 62 are preferably located Then, at an eleventh station 116, the final along a line which is perpendicular to the line layer, the third covering layer 36c, is applied.

along which the rolls 60 are located. The indi- A set of rolls 118 contain cloth material iden- vidual strips are urged into conformance with 80 tical to that contained by the rolls 60, which the shape of tube 14 by a conical preformer material is urged into conformance with the 64. tube 14 by a conical performer 120. A set of Next, at a third station 66, the third isola- rolls 122 contain cloth material identical to tion layer 32c of string is applied to form the that contained on the rolls 62, which material cloth layer 32b around the tube 14. As with 85 is urged into conformance with the tube 14 the first station 50, the string from a plurality by a conical entrance 124 of a heated forming of rolls 68 passes through a guide means 70 die 126. As was the case with the rolls 60 and an application means 72 into position and 62, the rolls 118 and 122 are preferably around the tube 14. located along lines perpendicular to one At a fourth station 74, approximately half of 90 another. The forming die 126 not only forms the fiber reinforcing layer 34 is applied. A set the surface of the continuous drive shaft as of rolls 76, although shown as six in number sembly, but also provides appropriate heat in for simplicity, actually number approximately put to effect a rapid cure of the resin mixture half of the total number of graphite tows to as the series of drive shafts are pulled through be applied. The tows supplied from the rolls 95 the apparatus 40.

76 pass through individual apertures in a The continuous chain of composite tubular forming ring 78 into conformance with the elements 10 is then cut apart at protruding shape of the tube 14. Then, at a fifth station flange portions 48, and stripped in a manner 80, a resin mixture is supplied from a tank 82 as described above to form exposed metal through a line 84 to a dispensing end 86, 100 end portions 20 and 22, to which appropriate from which it coats the first half of the fiber connecting members can be attached by con reinforcing layer 34 and the underlying isola- ventional welding. The composite tubular ele tion layer 32. ment produced by the method of Fig. 3 is The resin mix contained in the tank 82 is shown in Fig. 4 prior to the attachment of the preferably a vinylester resin mix of the type 105 connecting members.

available under the trade name Derakane. A It will be appreciated that other methods suitable resin mixture is available from Dow can be utilized to produce a fiber-reinforced Chemical of Joliet, Illinois under part number aluminum drive shaft embodying the principal 411-35. In addition, any conventional resin features of the present invention. For example, mixture may be used, although it should be 110 Fig. 5 schematically illustrates a method selected from among those that remain flexi- wherein a stiff, performed, precut and previ ble after curing. Although not shown in the ously cured reinforcing sleeve 130 of a pre drawings, a catalyst or hardener can be mixed determined length is provided, with an internal with the resin mixture shortly before applica- diameter slightly larger than the external dia- tion of the mixture to the partially formed 115 meter of the metal tube 14. As illustrated in sleeve. Fig. 5, the reinforcing sleeve 130 is slipped At a sixth station 88, the remainder of the into position over a metal tube 132, to which desired number of graphite tows are applied a layer of glue 134 has been applied.

from a set of rolls 90 through a forming ring Various types of glues or bonding agents 92 into conformance with the tube 14 and, at 120 may be used for the glue 134. One such a seventh station 94, are again coated with structural adhesive which can be used is com the resin mixture from the tank 82, through a mercially known as Metalbond 1133, and is line 96 and a dispensing end 98. an elastomer modified epoxy material sold by An eighth station 100 and a ninth station the Narmco division of Celanese Corp, New 102 include a spinner head 104 having rolls 125 York, New York. Such adhesives may be ap 106 and 108 for circumferentially wrapping plied by brushing or spraying.

covering layers 36a and 36b respectively. Of Fig. 6 illustrates schematically a further alter course, more than one such spinner head 104 nate method of making a composite tubular may be provided, and more than a single roll element according to the invention, in which a can be used to apply the layers 36a and 36b.130 fiber-reinforced sleeve 140 saturated with un- GB2189862A 5 cured resin, but made to appropriate length, is attached claims.

slipped over a metal tube 142 and is subse

Claims (1)

1. quently cured to bond the sleeve 140 to the CLAIMS metal tube 142. If

   desired, an appropriate 1. A fiber reinforced tubular element com structural adhesive may be used to assist in 70 prising:

   bonding the sleeve to the tube. In Fig. 6, the a cylindrical metal tube having a longitudinal fiber-reinforced sleeve 140 is formed on a axis; mandrel 148, and is saturated with resin from an isolation layer surrounding said tube and a tank 150 through a line 152 and a dispensadhered to the outer surface of said tube; ing end 154, or by any other convenient 75 a reinforcing fiber layer surrounding said means, such as brushing or spraying. As illus- tube and adhered to the outer surface of said trated, the reinforcing sleeve 140 includes isolation layer, said reinforcing fiber layer in three layers, an inner layer of isolation material ciuding a plurality of individual and indepen applied by rolls 156, an intermediate layer of dent reinforcing fibers uniformly positioned longitudinally extending reinforcing fiber ap- 80 about the circumference of said tube; and plied by rolls 158, and an outer layer of a covering layer surrounding said tube and covering material applied by rolls 160. adhered to the outer surface of said reinforc As shown in Fig. 7, there is a supply of ing fiber layer.

   metal tubes 142, onto each of which a rein- 2. The tubular element according to claim 1 forcing sleeve member 140 is placed by slidwherein said reinforcing layers are parallel to ing it off mandrel 148 and onto the tube 142, said longitudinal axis.

   wherein it is urged into position by applying 3. A fiber reinforced tubular element com circumferentially forces 162 in any convenient prising:

   manner, such as by drawing a forming die a cylindrical metal tube having a longitudinal over it. Then, the reinforcing member 140 is 90 axis; cured in place on the metal tube 142, either an isolation layer of cloth material surround by the hssage of time without application of ing said tube and adhered to the outer surface heat, or by the application of heat in any con- of said tube; venient maryner. a reinforcing fiber layer surrounding said The precise embodiment of the reinforcing 95 tube and adhered to the outer surface of said sleeve used in the methods illustrated in Figs. isolation layer, said reinforcing fiber layer in and 6 may differ from the construction cluding a plurality of individual reinforcing shown in Fig. 2 and produced by the method fibers parallel to said longitudinal axis and uni of Fig. 3. For example, the first and third iso- formly positioned about the circumference of lation layers 32a and 32c of Fig. 2, which 100 said tube; and provide a visual indicia for stripping the ends a covering layer of fiber material surrounding of the sleeve in the method of Fig. 3, would said tube and adhered to the outer surface of not be required in the methods of Figs. 5 and said reinforcing fiber layer.

   6, since the reinforcing sleeves are formed to 4. The tubular element according to claim 3 length before application to the metal tube. In 105 wherein said isolation layer includes a plurality addition, in some instances, the second isola- of longitudinally extending strips of cloth ma tion layer 32b may also not be necessary, terial positioned about the circumference of since the glue used to retain a previously said tube, adjacent ones of said strips having formed cured or uncured reinforcing sleeve to overlapping lateral edges such that the outer a metal tube may by itself provide a suitable 110 surface of the tube is completely surrounded isolation layer between the graphite and the by said strips.

   aluminum. Also, the outer most covering layer 5. The tubular element according to claim 3 36c of Fig. 2, which is provided to form a wherein said isolation layer includes a first iso smooth exterior surface is not an absolutely lation layer consisting of a plurality of longitu necessity, nor is the use of two different ma- 115 dinally extending and circumferentially spaced terials, shown as covering layers 36a and 36b apart string members adhered to the outer to retain the primary reinforcing fiber layer 34 surface of said tube, a second isolation layer in place. of cloth material adhered to and surrounding In accordance with the provisions of the pa- said first isolation layer, and a third isolation tent statutes, the composite tubular element 120 layer of longitudinally extending and circumfer of the present invention, along with the entially spaced apart string members adhered methods of producing the tubular element, to the outer surface of said second isolation have been illustrated and described in its pre- layer.

   ferred embodiments. However, it will be ap- 6. The tubular element according to claim 3 preciated that numerous modifications and varwherein said covering layer includes a fiber iations of the disclosed invention will be ap- glass string material circumferentially wrapped parent to one skilled in the art, including re- about the circumference of said tube.

   arrangement in the ordering of layers and the 7. The tubular element according to claim 3 addition or omission of layers, and may be wherein said covering layer includes a first made without departing from the scope of the 130 covering layer of fiber glass material circumfer- 6 GB2189862A 6 entially wrapped about and adhered to said nal path.

   reinforcing fiber layer, a second covering layer 14. The method according to claim 12 in of string members circumferentially wrapped cluding, subsequent to step (f), the step of about and adhered to said first covering layer, stripping a selected portion of the fiber rein- and a third covering layer of cloth material 70 forced sleeve from at least one end of the adhered to and surrounding said second tubular element to provide an exposed metal covering material. surface.

   8. The tubular element according to claim 3 15. A method of making fiber reinforced tu- wherein said metal tube is constructed of alu- bular elements comprising the steps of:

   minum. 75 (a) providing a plurality of cylindrical metal 9. The tubular element according to claim 3 tubes each having a longitudinal axis; wherein said reinforcing fiber layer includes (b) joining the plurality of metal tubes to graphite fibers. form a longitudinally extending series of metal 10. A method of making a fiber reinforced tubes; tubular element comprising the steps of: 80 (c) feeding the series of joined metal tubes (a) providing a cylindrical metal tube having along a longitudinal path; and a longitudinal axis; (d) applying a reinforcing fiber layer around (b) applying an isolation layer around the the outer surface of the joined metal tubes as outer surface of the metal tube; the tubes travel in a longitudinal path; and (c) applying a reinforcing fiber layer around 85 (e) severing the series of tubes to produce a the outer surface of the isolation layer by po- plurality of individual fiber reinforced tubular sitioning a plurality of individual and indepen- elements.

   dent reinforcing fibers uniformly disposed 16. A method of making fiber reinforced tu about the circumference of the tube; bular elements comprising the steps of:

   (d) applying a covering layer around the 90 (a) providing a plurality of cylindrical metal outer surface of the reinforcing fiber layer; tubes each having a longitudinal axis; (e) applying a liquid resin material to the (b) joining the plurality of metal tubes with a isolation layer, the reinforcing fiber layer, and plurality of joining plug members to form a the covering layer; and longitudinally extending series of metal tubes; (f) curing the liquid resin material to firmly 95 (c) feeding the series of joined metal tubes adhere the isolation layer, the reinforcing fiber along a longitudinal path; layer, and the covering layer to the tube to (d) applying a reinforcing fiber layer around form a fiber reinforced sleeve. the outer surface of the joined metal tubes as 11. The method according to claim 10 the tubes travel in a longitudinal path; wherein step (c) includes the step of position- 100 (e) applying a liquid resin material to the ing the individual reinforcing fibers parallel to reinforcing fiber layer; the longitudinal axis of the tube. (f) curing the liquid resin material to firmly 12. A method of making a fiber reinforced adhere the reinforcing fiber layer to the series tubular element comprising the steps of: of tubes to form a fiber reinforced sleeve; and (a) providing a cylindrical metal tube having 105 (g) severing the series of tubes at each of a longitudinal axis; the joining plugs to produce a plurality of indi- (b) applying an isolation layer of cloth ma- vidual fiber reinforced tubular elements.

   terial around the outer surface of the metal 17. The method according to claim 16 tube; wherein step (d) includes the step of initially (c) applying a reinforcing fiber layer around 110applying an isolation layer of cloth material the outer surface of the isolation layer by po- around the outer surface of the tubes and sitioning a plurality of individual reinforcing wherein the reinforcing layer is applied to the fibers parallel to the longitudinal axis of the outer surface of the isolation layer.

   tube and uniformly disposed about the circum- 18. The method according to claim 16 ference of the tube; 115 wherein step (d) includes the step of subse- (d) applying a covering layer of fiber material quently applying a covering layer of fiber ma around the outer surface of the reinforcing terial around the outer surface of the reinforc- fiber layer; ing fiber layer.

   (e) applying a liquid resin material to the 19. The method according to claim 16 isolation layer, the reinforcing fiber layer, and 120 wherein step (d) includes the step of uniformly the covering layer; and positioning a plurality of individual reinforcing (f) curing the liquid resin material to firmly fibers about the circumference of the tube adhere the isolation layer, the reinforcing fiber such that the individual reinforcing fibers are layer, and the covering layer to the tube to parallel to the longitudinal axis of the tubes.

   form a fiber reinforced sleeve. 125 20. The method according to claim 16 in 13. The method according to claim 12 in- cluding, subsequent to step (g), the step of cluding, subsequent to step (a), the step of stripping a selected portion of the fiber rein feeding the metal tube along a longitudinal forced sleeve from at least one end of the path, and wherein steps (b) through (e) are tubular element to provide an exposed metal performed while the tube travels in a longitudi- 130 end surface.

   7 GB2189862A 7 2 1. A method of making a fiber reinforced tubular element, comprising the steps of:

   (a) providing a cylindrical metal tube; (b) providing a fiber reinforced preformed 5 sleeve; (c) positioning the fiber reinforced sleeve over the metal tube; and (d) securing the sleeve to the tube.

   22. A method of making a fiber reinforced tubular element, comprising the steps of:

   (a) providing a cylindrical metal tube; (b) providing a fiber reinforced preformed sleeve impregnated with a cured resin; (c) applying an adhesive to a portion of the outer surface of the metal tube; and (d) positioning the fiber reinforced sleeve over the metal tube adjacent the adhesive to secure the sleeve to the tube.

   23. The method according to claim 22 wherein the fiber reinforced sleeve provided in step (b) includes a plurality of individual reinforcing fibers parallel to the longitudinal axis of the sleeve.

   24. A method of making a fiber reinforced tubular element, comprising the steps of:

   (a) providing a cylindrical metal tube; (b) providing a fiber reinforced preformed sleeve impregnated with an uncured and curable resin material; (c) placing the uncured fiber reinforced sleeve over the metal tube; and (d) curing the curable resin to firmly adhere the sleeve to the tube.

   25. The method according to claim 24 wherein the fiber reinforced sleeve provided in step (b) includes a plurality of individual reinforcing fibers parallel to the longitudinal axis of the sleeve.

   26. A tubular element substantially as de- scribed herein with reference to, and as shown in, the accompanying drawings.

   27. A method of making a tubular element substantially as described herein.

   Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8991685. 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.