IL38304A - Method and apparatus for the continuous manufacture of tubular elements - Google Patents

Description

Method and apparatus for the continuous manufacture of t boXar elemaita Je -J c¾ e3 WALTER 38304/2 This invention relates to continuous methods and machines for manufacturing handed leaksetight tubes.

Banded leak-tight tubes comprise an extruded inner saheath of leak-tight plastic material surrounded by a so-called "banding jacket" produced by winding on to the inner sheath of leak-tight plastic material surrounded by a so-called "banding jacket" produced by winding on to the inner sheath several layers of strengthening threads, braids or ribbons, especially glaes fibre. This assembly is impregnated with a binder, usually a resin such as an epoxy resin, or a polyester resin.

In United Kingdom latent Ho. 1,145,762 (Jacques alther) is described and illustrated apparatus for continually producing^ banded ledfc-tight tube including an extruded head for producing the inner sheath and means for winding on layers of reinforcement material in the dry state and be ore the last winding is started the binder is projected into the existing layers and forced between them by the final winding* This prior Patent Specification also suggests the provision of a covering produced by helically winding on the impregnated banded leak-tight tube, an outside covering of overlapping astrips of polyvinyl chloride to increase the abrasion resistance of the tubular element.

The main object of the present invention is to 38304/2 Jacket than heretofore obtained results.

A further main object of the invention is to improve the method of operation by making it more straight forward and making the machine less complex thereby enhancing reliability and reducing maintenance costs.

Another main objec of the invention is to improve the properties of the banded leak-tight tubes b producing the integral nature of the inner and outer tubes through the intermediate reinforcement.

A method of continuously manufacturin a banded leak tight tube as hereinbefore defined with an outer covering of abrasion resistant material according to the present invention, wherein the covering s constituted by an outer sheath extruded on to the jacket while the binder is still mobile, said banded leak tight tube being progressively impregnated with the binder as it is advanced in a downstream direction and then guided through a hollow mandrel on to which the outer sheath is extruded and calibrated as it glides downstream until the outer sheath embraces the impregnated jacket on leaving the hollo mandrel, elongating the outer sheath to cause su icient radial contraction on to the jacket to develop in the outer sheath a uniform radial pressure around the jacket which-'pressure forces the still mobile binder into intimate and uniform relation wit the windings of the jacke and the polymerising the binder imprisoned in the jacket by the outer sheath.

In a method of manufacture according to the present 38304/2 jacket and extruded outer sheath may "be supported in the area subjected to elongation against sagging by a cushion of air, the air cushion under the upstream area off he outer sheath subjected to elongation is constituted by hot air to soften the outer sheath and facilitate elongation and the air cushion under the downstream area of the elongated outer sheath is constituted by cold air whereby incipient cooling of the contracted outer sheath is achieved and the degree of contraction substantially consolidated in the outer sheath.

The penetration of the binder into the jacket achieved by the radial pressure derived from the outer sheath may be completed by applying to the contracted outer sheath radial calibration forces uniformly distributed about the periphery of the jacket.

Preferably, in accordance with the present invention the binder is polymerized at a relatively low temperature by means of ultraviolet radiation.

The materials employed for the fabrication of the inner and outer sheaths ca be of essentially variable nature and either identical or different in the case o the two sheaths, depending on requirements; in particular, these sheaths can be formed of high or low-density polyethylene , of acrylonitrile butadiene styrene , of polyvinyl chloride, of polystyrene, of polypropylene and so forth. The impregnating binder of the reinforcement jacket can be constituted by any thermosetting or thermo 38304/2 τ · A production machine for the continuous manufacture of a banded leak tight tube according to the present invention may comprise means for continually producing the inner sheath of plastic leak tight material* traction means for advancing the inner sheath downstream through the machine, winding means for covering the sheath with reinforcing material, impregnatin means including a tank for accommodating a volume of hardenable binder surrounding the reinforced sheath, an outlet for e impregnated sheath at the downstream end of the tank, a hollow mandrel extending downstream from said outlet an extruder surrounding the hollow mandrel at the upstream end thereof for producing the outer sheath of plastic leak tight material so that the outer sheath is calibrated as it glides downstream in the hot state on the outside of the hollow mandrel while the inner sheath and impregnated jacket is guided downstream by the inside of the hollow mandrel thereby the mandrel wall separates the inner sheath from the extruded material and on leaving the wall the outer sheath progressivel embraces the impregnated jacket, complementary stretching means for elongating the outer sheath in contact with the jacket, operative on the outer sheath on the mandrel and on the outer sheath in contact with the jacket repsectively, means for buoyantly supporting the outer sheath against sagging in the area being stretched, and means f rther downstream 38304/2 The hollow mandrel may be provided within the thickness of the separating wall with a fluid-circuit for circulating a coolant, whereby adhesion of the outer sheath to the hoHow mandrel is avoided and to ensure the thermal isolation of the binder from the heat in the extruded material advancing along the mandrel.

The external surface of the hollow mandre_l may be provided with a covering formed of material having a low coefficient of friction over which the outer sheath slides, A production machine according to the present invention preferably comprises an extruder, for delivering the outer sheath, wHiich is of the right-angle head type in which the axis coincides with the axis of the inner sheath.

The stretching means, employed in a production machine according to the invention preferably com--prises a set of at least two retractable wheels which are capable of clamping the sheath between said wheels and the hollow mandrel, which is directed towards the downstream end, and a traction belt, engaging the outer sheath in contact with the reinforced inner sheath, driven at a speed which is slightly higher than the speed of the retractable wheels.

The means for supporting the outer sheath while causing the radial shrinkage are preferably constituted b two successive cushions formed b blowin hot air 38304/2 means and upstream of the polymerisation means* She buoyancy means for supporting the outer sheath against sagging is preferably constituted by a reservoir which is traversed axially and continuously by the banded leak-tight tube, said reservoir being filled with a liquid at a controlled temperature which applies a hydrostatic pressure on the moving outer sheath, means being provided for ensuring leak-tidiness in the inlet and outlet zones of the tubula element within the reservoir and meane for maintaining the pressure and temperature of the liquid at constat^ values.

A production machine according to the invention preferably includes means for ensuring leak tightness at the downstream extremity of the inner sheath, comprising a sealing plug over the periphery of which said sheath is capable of sliding, wherein said sealing plug comprises a cental body in which are formed grooves having the shape of equidistant sectors forming guides for the supports of transverse rollers which are applied against the ¾all of the sheath tinder the action of restoring springs housed between each support and the base of the corresponding sector, said rollers each having the shape of an elongated oval which is capable of conforming substantiall to the curvature of the wall of the inner sheath.

In a production machine constructed according to the present invention, the polymerisation means for effecting the hardening of the impregnating binder 58304/2 traversed axially by the banded leak-tight tube and comprising three adjacent compartments disposed at angular intervals of 120° about the axis of the enclosure, each compartment being provided in transverse section along a plane at righ angles to the axis with a profile in the form of an ellipse, one ocus of which is occupied b a high-intensity source of ultraviolet light and βMo er focus of which coincides with the corresponding foci of the other compartments and with the axis of the enclosure, the walls of said compartments being constituted by a material which reflects the light emitted by the sources towards the axis of the banded leak-tight tube.

Moreover, a production machine according to the present invention preferably comprises a m&n<¾Bl or ealibtfating the inner sheath and/or a hollow mandrel on which the hot outer sheath slides which comprise a sleeve mounted coaxially on a supporting tube and having a plurality of completely closed continuous raceways extending in planes which pass through the axis of the sleeve, said raceways being intended to aceommodate metallic balls which project slightly beyond the apparent contour of the sleeve along the generator-lines parallel to its axis and oh which the sheath is capable of sliding.

These and other features of a production machine constructed according to tie present inventio will no be described and are ointed out i the a ended claims. 38504/2 I tight tube having an outer extruded covering of abrasion resistance material which has been shrunk on to a banded leak tight tube while the binder is still mobile.

In order that the present invention may be more fully understood reference will now be made, b way of example, to the accompanying drawings which illustrate preferred embbdimats of the invention.

In the drawings:- - Pigs. 1,2 and 3 are diagrammatic views of three successive portions of the machinejLllustrating the different stages of execution of the method of fabrication of a tubular Xelement; - fig. 4 is a sectional view to a larger scale showing the extruder which permits continuous fabrication of the inner sheath and showing the means for carrying out the advance of this latter downstream within the machine; - Figs. 5 and 6 are views to an even larger scale, respectively in longitudinal section and in end elevation, of the sealing plug which is mounted at the extremity of the inner sheath of the tubular element in order that a pressure of compressed air may be established within said sheath; - Pig. 7 is a front vief of the means employed for advancing the inner sheath downstream within the machine.

- Pig.8 is a view in elevation of the extruder which permits continuous fabrication of the outer sheath at the same time as impregnation of the banding jacket of the inner sheath with a thermosetting binder; 38304/2 to exert on the outer sheath a radial force whic is applied to the jacket of the inner sheath - Fig. 11 is a view in partial perspective of the chamber employed for polymerizing the impregnating bidder of the reinforcement material which forms the jacket of the inner sheath.

- Fig. 12 illustrates another alternative form of construction of the means which permit, after impregnation of the jacket of the inner sheath and simultaneous covering by the outer sheath, the forcible application of said sheath against the jacket and its radial shrinkage - Fig. 13 is a view in elevation and, in section shoving an alternative form of construction of the calibrating mandrel which may be associated with the extruders f>r. continuous fabrication of either the inner sheath and/or the outer sheath; - Fig. 14 is a view in transverse section to a larger scale and taken along line X-X of Fig. 13 - Fig. 15 is another sectional view of Fig. 13, taken along line Y-Y of this latter.

The machine which is illustrated diagrammatically as a whole in Figs. 1, 2 and 3 is primarily intended for the -8b. continuous fabrication of a tubular element constituted by a thin and leak-tight inner sheath 1 of synthetic plastic material, by an intermediate jacket 2 which is intended to constitute a high-strength external banding element and finally by an outer sheath 3 of plastic material which can be of the same kind or different from the inner sheath This machine is made up of a series of separate but successive stations which are designated in Figs. 1 to 3 by the references A to L, each of these stations being intended to carry out a precise and well-determined operation on a portion of the tubular element 4· progressively as this latter follows its path of travel within the machine. The machine rests on a horizontal bed S, the three portions illustrated in Figs. 1, 2 and 3 being successive and placed one after the other in the order of these figures. The tubular element which is delivered from the last station of the machine is continuously displaced from the left towards the right. Under these conditions, the station A is the farthest upstream and the station L is the farthest downstream. The machine is supported on rails or the like (not shown) which are fixed on the bed S and is driven from one or a number of motors M, the synchronism of the different operations which are carried out being ensured by means of suitable countershafts and transmission systems or by means of any other suitable expedient.

These operations are briefly as follows : the inner sheath 1 which is shaped and calibrated is fabricated continuously in the first station A, especially by means of an extruder of the conventional right-angle head type, then transferred into the station B in which a movement of tr i! -on in the downstream direction is exerted on said 38304/2 sheath. She sheath 1 which may have sufficient inherent rigidity or may be suitably maintained in a tubular shape by a pressure of compressed air if the nature of the sheath so requires, then passes into the stations C, D and E in which it receives in the dry state the covering 2 formed of threads or ribbons of glass fibre, respectively designated by the references 2c,2d,2e, in figre 1 which are wound or deposited successively on the sheath. There takes place in station F (Figure 2) on the one hand the impregnation of the jacket 2 with a hardenable binder, especially a resin, at the same time the outer sheath 3 is delivered to and calibrated on a hollow mandrel disposed to act as a guide or the inner sheath and jacket as they move downstream immediately after being impregnated. ¾Jhen the outer sheath leaves the hollow mandrel it converges on to and surrounds the impregnated jacket 2, embracing the latter, and distributes the impregnating resin within the windings of the jacket. In the stations § and H, the outer sheath 3 undergoes a limited movement of elongation and is thus applied in intimate contact over the entire surface of the jacket 2; the station X which is loca between the stations Q and H serves to subject said sheath during its elongation to a suitable heat treatment and to apply the outer sheath in a suitable manner against the jacket 2 which covers the inner sheath. In station J (Figure 3)» the outer sheath 3 is calibrated externally in order to achieve a further improvement in the distribution and penetration of the binder 38304/2 is carried oat in station E. Finally, in station L, the final tabular element 4 is drawn continuously to the exterior of the machine.

The coniructional detail of each station mentioned above will now be described with reference also to the other figures of the accompanying drawings by reviewing the different stages of operation of the method according to the invention, from the upstream end towards the downstream end.

Figs. 1 and 4 thus illustrate the essential elements of the first station 1 which permits continuous fabrication of the inner sheath 1, especially in the case in which this latter does not have a sufficient degree of inherent rigidity and is consequently associated with means for giving the sheath a suitable tubular shape and maintaining this shape while it passes through the machine. Said station A is mainly composed of an extruder for plastics, of a type which is known per se , comprising a frame 7 which contains an endless screw and means for heating the plastic material 8 to a temperature which produces a paste consistency. This plastic material can be polyethylene, for example, and is fed into the extruder, especially in the form of granules, through a hopper 9. The frame 7 terminates in a head 10 into which the plastic material is forced through a narrow annular passageway 11 and consequently appears at the outlet of the extruder in the form of a thin tubular envelope which constitutes the sheath 1.

The extruder referred-to above, which is of the type comprising a so-called right-angle head but the constructional design of which has little bearing on the invention, is associated with a cylindrical mandrel 12. In a first embodiment as illustrated in Fig. 4, the external surface of this mandrel 12 is provided with a covering 13 formed of material having a low coefficient of friction, especially "Teflon" which is deposited by a conventional method. The mandrel 12 is provided along its axis with a bore 14 and supports at that extremity 12a which has a smaller diameter, a steel head ring 15 which is locked against the mandrel by means of a nut 16. pipe 17 which serves to supply through the mandrel 12 to the sheath 1 compressed air at a constant pressure which is appreciably higher than atmospheric pressure and can be chosen between 200 g cm 2 and 2 kg/cm 2, depending in particular on the nature of the sheath . This air pressure is produced by a centrifugal compressor P (shown in Fig. l) which is located externally of the extruder and has a high delivery which can vary considerably without resulting in too substantial modifications in the value of the pressure which must remain constant. The compressed air which is discharged from the tube 17 passes through the extremity 12a of the mandrel by means of a duct 18 and inflates the sheath 1 on the downstream side progressively as this latter advances at the outlet of the extruder head 10 , from which the sheath slides onto the covering 13 of the mandrel 12 and encases this latter, thereby providing said sheet with a constant internal diameter which is substantially equal to the external diameter of said mandrel.

In order to prevent the air pressure from pro-ducing the abrupt separation of the sheath upstream of the ring 15 in the region of said sheath which is in contact with the covering 13 , the mandrel has a dynamic seal device constituted by a simple channel 19 which is formed at the rear end of the ring 15 and the bottom of which is connected by means of calibrated holes 20 to the annular space 21 which is formed between the bore 1 of the mandrel and the tube 17 and put into direct relation with the atmosphere. Over the entire portion of the mandrel 12 which is surrounded by the covering 13 » the sheath 1 is therefore at equal pressure on both faces and slides over said covering r m r wh und r oin th des r d calibration without impairment of its internal surface which remains wholly smooth and impermeable.

The mandrel 12 is provided at its extremity 12a with a fastening-piece 22 to which a cable eyelet 25 is attached by means of a locking-pin or the like, said eyelet being provided at the end of a cable 24 which extends axial-ly within the interior of the tubular sheath 1 over the entire length of this latter up to the point at which the tubular element passes out of the machine, said cable being secured at the extremity remote from the mandrel 12 to a sealing plug 25 (shown in Fig. 3 ) which is so designed that the pressure of compressed air within the sheath is continuously maintained in spite of any leakage, on the one hand through the holes 20 of the channel 19 at the upstream end and on the other hand within the residual clearance which is left free between the plug 25 and the internal wall of the tubular element 4, that is to say of the inner sheath 1 . The sealing plug 25 is illustrated in detail and to a larger scale in Figs. 5 and 6.

Said plug mainly comprises an elongated body 26, the upstream extremity of which has a fastening-piece 27 for the corresponding extremity of the cable 2 and a transverse spider 28 which is rigidly fixed to the body 26 and on which runner-wheels 29 are mounted to rotate freely about bearing shafts 29a , said runner-wheels being applied against the internal surface of the tubular element 4 in order to ensure correct centering of the plug within this latter. The body 26 also comprises a head 30 on which is fixed a covering end-plate 31 secured by means of a screw 32 against a cylindrical portion 33 which forms an extension of the head 30 at the forward end.

Between said cylindrical portion 33 and the cover 31 , there is formed a space 34- in which is mounted a series of small yokes 35 « As shown in plan in Fig. 6 , said yokes have the shape of circular sectors having identical angles at the center. Restoring springs 36 are fitted within the yokes 35 and bear on the one hand against the bases of said yokes and on the other hand against stops 37 which form guide pins for said springs, each stop being fixed at 38 in the portion 33 of the head 30 . By virtue of the action of the springs 36 , the yokes 35 are thus thrust in the radial direction towards the internal surface of the tubular element 4 and apply against this latter rollers 39 which are carried freely by spindles 0 extending along chords of the circular sectors and each having the shape of an elongated olive, thereby enabling said rollers to conform substantially to the contour of the inner sheath 1 while maintaining a sufficient degree of leak-tightness with respect to the pressure of compressed air. It is readily apparent that the rollers 39 are formed of material such that the sheath 1 is capable of sliding over these rollers without any danger of damage to its internal surface which is reinforced externally at this point of the tubular element by the jacket 2 and by the sheath 3 » Pigs. and 7 also illustrate in greater detail the construction of the station B which serves to apply to the sheath 1 as it passes out of the extruder head 10 and is calibrated by the mandrel 12 a suitable tractive force which permits the progressive displacement of said sheath through the other sections of the machine, in conjunction with the drawing action produced by the means of the station wheels 42 and 3 which are rotatably mounted on parallel shafts 44 and 45 at right angles to the axis of the sheath 1 and the spacing of which can be adjusted at will, said wheels 42 and 43 being driven in synchronism and in opposite directions by means of a control motor (not shown in the drawings ) .

As shown more especially in Fig. 7, each of the above-mentioned wheels is provided in the central portion thereof with a hollow portion 46 forming a groove so that, as a result of suitable spacing of their shafts, said wheels are permitted to pinch the sheath 1 laterally but without completely flattening this latter in order that a sufficient passage may be left in the central portion of the sheath both for inflation with compressed air and for the cable 24 at the extremity of which is mounted the sealing plug 25» The wheels 42 and 43 can be formed in particular of rubber or any light material which is chosen so as to ensure that the lateral flattening of the sheath 1 which is produced by said wheels can always be limited and withstood by the sheath by reason of its natural elasticity .

As has already been stated with reference to Fig. 1, the inner sheath 1 which is formed in the station A and transferred into the station B receives during its transfer through the stations C, D and A an intermediate jacket 2 consisting of threads or ribbons of suitable reinforcement material, especially having a base of glass fibers. After impregnation with a binder and hardening of this latter, the jacket is intended to form a strengthening band having the function of endowing the tubular element 4 with mechanical properties which are impossible to obtain comprises a first winding machine of the so-called "Centerless" type or any other kind which may or may not be usually adopted in the technique of winding on a mandrel. There can thus be formed on the sheath 1 which has been made sufficiently rigid by the internal pressure of compressed air a first winding of threads 2a_ which may if necessary have a given orientation with respect to the axis of the tubular element. In the following station D, the winding 2c_ is in turn covered with an assembly of longitudinal threads 2d delivered from a creel (not shown) of a type which is also known. Finally, in the third station E, the longitudinal threads 2d are in turn covered with a second winding 2c_ obtained from a second winding machine which may or may not be identical with the first winding machine of the station C ; the threads of the winding 2d also have a given orientation with respect to the axis of the tubular element but this orientation is preferably opposite to that of the threads of the winding 2c_.

The sheath 1 which is thus covered with its jacket 2 then passes into the station F, the constructional detail of which is shown on a larger scale in Fig. 8. This station comprises in particular an extruder 47 having a right-angle head 48 which is similar in general structure to the extruder 7 of the station A. This extruder 7 is designed to effect the continuous supply of the outer sheath 3 of plastic material which is intended to cover the jacket 2 of the inner sheath 1 while at the same time producing the impregnation of the threads or ribbons of said jacket with a suitable binder. To this end, the head 48 of the extruder 47 is provided axially on its rear portion with a member 4 havin an extension in the form of a c lindrical sleeve 50 which surrounds with substantial clearance both the inner sheath 1 and its jacket 2. A duct joined to said sleeve 0 is connected at the extremity of the extruder 47 to a vessel R (shown in Fig, 2 ) containing a reserve supply of binder and especially resin 2 which is delivered by a pump (not shown in the drawings) into the duct 51 and from this latter into the sleeve 0 which forms a tank, thus coming into contact with the jacket 2. By virtue of the continuous progression of the tubular element 4 within the machine, and provided that the output of the pump which delivers the resin as well as the clearance left between the sleeve 0 and the jacket 2 are suitably determined, this resin cannot flow towards the upstream end of the sleeve which has the effect, both directly and permanently, of ensuring dynamic leak-tightness of the apparatus as a result of these arrangements.

The member 49 has a further extension, but in the downstream direction, in the form of a second axial sleeve 53 which serves as a guide both for the sheath 3 and for the sheath 1 together with its jacket 2 while separating these latter up to its extremity. The sleeve 53 is constituted by two coaxial casings 54 and 55 between which is arranged a series of passages 56 forming baffles and supplied with a suitable cooling fluid, especially water, which is admitted between the two casings and 55 through a pipe 57 and discharged therefrom through a pipe 58 . This circulation of coolant essentially makes it possible to prevent adhesion of the sheath 3 to the axial sleeve 53 while cooling the sheath as it passes out of the extruder and also to ensure that the resin 52 which forms a binder and h been de osited on the acket 2 but has not et completely impregnated this latter is isolated from the extruder and protected against overheating. In the alternative form of construction under consideration, the external surface of the sleeve 53 over which the sheath 3 slides is covered with material having a low coefficient of friction such as "Teflon", for example, in the same manner as the external surface of the mandrel 12 of the extruder 7 which delivers the inner sheath 1 (see Fig, 4)» In order to cause the displacement of the outer sheath 3 progressively as the tubular element 4 passes within the interior of the machine, said sheath is clamped within the station G between the external surface of the sleeve 53 which is cooled by the circulation of coolant and two wheels 59 and 60 which are rotatably mounted respectively on two shafts 61 and 62 located at right angles to the axis of the tubular element 4, Said shafts are in turn carried by pivotal levers 63 and 6 which permit their positional adjustment with respect to the sleeve 63= The wheels 59 and 60 are driven by means of pulleys 65 and 66 which are rigidly fixed to the wheels, driving belts 67 and 68 being passed within the grooves of said pulleys.

As is further shown in Fig, 2, the levers 63 and 64 are pivotally mounted on two shafts 65 and 66 parallel to the shafts 61 and 62, and rigidly fixed to two toothed rings 67 and 68 which are disposed respectively in meshing relation in order that the movements of closure or of separation of the wheels 59 and 60 with respect to the sleeve 53 always take place in a wholly symmetrical manner. A ballast-weight 69 and a counter-weight 69a which are rigid-ly fixed respectively to the levers 63 and 64 serve to ad ust the roximit of said wheels while reventin flattening of the sleeve 53 "by compression and while making it possible to clamp the sheath 3 against this latter in order to draw it towards the outlet of the extruder 4-7 .

The outer sheath 3 which is thus formed therefore prevents any loss of resin since it covers the jacket 2 of the sheath 1 both completely and permanently but has an internal diameter which is equal to the external diameter of the sleeve 53 and is therefore greater than that of the jacket 2 „ It is therefore necessary to subject the outer sheath to a limited axial elongation between the stations G and H. To this end, the sheath is drawn into the station H by means of two traction belts 70 and 71 having variable spacing and driven in the appropriate direction at the same speed, which is the speed of transfer of the tubular element within the machine and which is also slightly higher than the speed of the wheels 59 and 60. The sheath 3 which is drawn axially between the wheels and the traction belts has thus a tendency to decrease slightly in diameter and to be tightly applied against the jacket 2 of the inner sheath 1, the surface of said jacket being impregnated with the resin 52 inside the sleeve 50 . Moreover, in order that this distribution of resin should be carried out in a wholly uniform and homogeneous manner throughout the thickness of the jacket 2 , the outer sheath 3 is subjected within the station I which is located between the stations G and H to a series of successive operations which have the effect of improving the application of the sheath and the penetration of the resin which forms a binder.

In the example described, the station I comprises in accordance with one particular form of construction a first blowing nozzle 72 (shown in Fig. 2 ) which is sup lied with hot air through a duct 73. This nozzle delivers beneath the sheath 3 a hot-air cushion which softens the sheath while supporting this latter from underneath, thereby preventing the formation of resin bulges resulting from the weight of this latter. Provision is made immediately after the nozzle 72 for a second nozzle ^ supplied at 75 with a stream of cold air which also forms a cushion for supporting the sheath and permits incipient cooling of this latter, thereby causing it to shrink radially onto the jacket 2 and the resin 52 which has been deposited on this latter and which, from that time onwards, is progressively but completely driven between the fibers of the windings 2c, 2d, 2e of the jacket 2, There is additionally mounted between the two nozzles 72 and 4 a progressive-clamping collar 76 which exerts on the external sheath 3 a uniformly distributed radial force which further improves its application against the jacket 2 while at the same time effecting the guiding of the tubular element progressively as it travels through the machine „ Finally, after passing between the traction belts 70 and 71, said tubular element is subjected the station J to a further external calibration by means of other collars such as the collar 77 which permit a further improvement in the distribution of the resin between the fibers of the threads or ribbons of the banding jacket.

As is more particularly apparent from Figs„ 9 and 10, the collars 76 and 77 are each constituted especially by a ring 78 of plastic material ("Teflon", polyethylene) carried by a washer 79 which is in turn mounted in a sup-port 80. There is mounted between a flange 80a of said which forms an inflation chambe of rubber or any suitable elastic material, said tube being connected to a compressed-air supply pipe 82 „ As shown in Fig„ 10 , the ring 78 has a series of longitudinal slots 83 which are uniformly spaced around said ring in order to endow this latter with suitable radial flexibility such that, under the effect of inflation of the tube 81, the ring 78 shrinks radially, thereby clamping the outer sheath 3 and applying this latter even more tightly against the jacket 2 of the inner sheet 1 , This radial clamping effort which is repeated by a plurality of successive collars having progressive actions produces a perfectly uniform final distribution of the resin 5 which passes between the fibers of the different windings between the two sheaths 1 and 3 .

Calibration of the tubular element 4 and impregnation of the jacket being thus completed, the final operation consists in carrying out in the station K the polymerization at a relatively low temperature of the resin which impregnates the jacket 2. Accordingly, as the tubular element follows its path of travel within the machine, it passes through an elongated cylindrical enclosure 8 within which are provided three adjacent compartments 85 , 86 and 87 located at angular intervals of 120° with respect to each other about the axis of the enclosure 8 „ The compartments aforesaid are delimited in the direction of generator-lines parallel to the axis by walls designated respectively by the references 88 , 89 and 0 and assuming the shape of ellipses when seen in transverse cross-section along a plane at right angles to said axis, the three ellipses considered being such as to intersect from one compartment to the next so as At one of the foci of each of the ellipses is mounted a high-power source of ultraviolet light, these sources which are designated respectively "by the references 91 » 92 and 93 being locked in position with respect to the ends of the walls 88 , 89 and 90 by fastening means such as the members 94 , 5 and 96 ; on the other hand, the second foci of the three ellipses coincide along the axis of the tubular element 4 . The walls 88 , 89 or 90 of the compartments of the enclosure 84 are finally formed of material which is capable of reflecting radiations emanating from the sources, the focal mounting of these latter being such as to permit convergence of all these radiations towards the axis of the tubular element. There then takes place under the action of said radiations the rapid cold polymerization of the impregnation resin progressively as the tubular element 4 passes within the enclosure 84, However, in order not to cause damage during this operation to the inner sheath and especially to the outer sheath which is located on the path of the radiations, in particular by reason of the inevitable evolution of heat resulting from the polymerization of the resin and from the visible fringes of the ultraviolet radiation itself, the casing 84 is advantageously fitted with a transparent tube 97 which surrounds the tubular element 4 with a substantial clearance and is located coaxially with this latter, said tube 97 being maintained against the walls 88 , 89 and 90 by means of tie-braces 98 . The central portion of said tube 97 communicates with a duct 99 (shown in Fig. 3 ) , said duct being connected to a high-power fan (not shown) which delivers a high-velocity air-stream into the tube, thereby mm d r m n h he roduced Mor over s id be 97 protects the sources 91 » 92 and 93 from the effects of the air-stream itself. At the outlet of the enclosure 84, the tubular element is finally displaced by the two traction belts 100 and 101 of the station L, a sufficient tractive force being applied to the element to permit this latter to pass continuously out of the installation.

Another alternative arrangement can advantageously be contemplated in regard to the particular arrangement of means which, at the outlet of the head of the extruder which produces the outer sheath (shown in Fig. 8), serve to apply said sheath against the intermediate jacket with a uniform and homogeneous distribution of the binder between the fibers or windings of the reinforcement material which constitutes said jacket as well as means which may be required to effect polymerization of said binder such as those which have just been described in the foregoing.

In Fig 12, there are again shown the tubular element 4 with its inner sheath, its intermediate jacket and its outer sheath. At the outlet of the extruder, this ele-ment is caused to pass through a reservoir 102 constituted by a cylindrical shell 103 which is closed at both ends by end-plates designated respectively by the references 10 and 105 and disposed at right angles to the axis of the tubular element which coincides with the direction of forward motion of said element as this latter is being produced. These end-plates 104 and 105 are provided with central openings 106 and 10? having a diameter which is very slightly greater than that of the tubular element 4 in order to permit the continuous passage of .this latter.

Since the reservoir 102 is intended to contain a li uid under ressure and es eciall water which is brou ht to a controlled temperature, the openings 106 and 107 are associated outside the reservoir and in the vicinity of the end-plates 10 and 105 with two sealing rings 108 and 109 -These rings can advantageously be formed in the same manner as the collars 76 which were described earlier (with reference to Fig. 9 ) in order to cause progressive clamping of the outer sheath against the inner sheath or they can be of a different type. In this case, these sealing rings comprise at least one collar formed by a ring of plastic material which is made flexible by means of slots uniformly spaced over the internal contour of said collar. This ring is traversed axially by the tubular element 4 and is associated with an elastic chamber which applies a distributed radial compressive force to the ring by admission of a suitable pressure of compressed air into said chamber.

In order that inevitable leakage of water from the reservoir through the sealing rings 108 and 109 should nevertheless be recovered progressively as the tubular element advances, the end-plates 104 and 105 are placed in adjacent relation to recovery headers designated respectively by the reference numerals 110 and 111 . These headers each have a flat end-plate into which opens a pipe 112 or 113 for the discharge of recovered water. Similarly, the cylindrical shell 103 of the reservoir 102 comprises a duct 114 which is connected to a heating installation of the same kind as a conventional boiler 115 which serves to heat the water of the reservoir to a suitable and regularly controlled temperature. The outlet of the boiler 115 is connected to a circulating pump 116 which returns the water through a pipe 117 to an upper tank 118 which is placed above the reservoir, the level 119 within said tank being maintained at a constant value for measuring the hydrostatic pressure exerted on the tubular element 4 by the water of the reservoir which is connected to the tank 118 by means of the duct 124. The ends of two other pipes, respectively 120 and 121, also open into said tank 118 and are connected to the recovery ducts 112 and 113 of the headers 110 and 111 , said pipes 120 and 121 being provided with circulating pumps 122 and 123 for continuously returning leakage water through the rings 108 and 109 .

Finally, in order to ensure that the tubular element which is filled with air in the internal portion thereof is not subjected to any harmful bending stress under the pressure of the water within the reservoir, provision is made in the top portion of the reservoir for a longitudinal beam 125 which supports a series of yokes 126 fitted with horizontal pins 12? on which are mounted waisted or so-called "hour-glass" rollers 128. These latter conform substantially to the curvature of the tubular element and are intended to maintain this latter substantially in the axis of the openings 106 and 107 which are provided in the end-plates 104 and 105 , During operation, the hydrostatic pressure of the water contained in the tank on the tubular element applies an evenly distributed force over the entire outer sheath, with the result that the windings or fibers of the reinforcement material constituting the banding jacket which is located between the inner sheath and the outer sheath are impregnated with the thermosetting binder in a uniform and homogeneous manner. The formation of pockets of binder at the bottom portion of the outer sheath is thus made prac provided at the extremities of the reservoir achieve a further improvement in the application of the outer sheath against the intermediate jacket. Finally, it is possible by means of this device to carry out an immediate and accurate adjustment of the temperature of the water contained in the reservoir and consequently to adjust the progressive value of radial shrinkage of the outer sheath onto the jacket and onto the inner sheath at the same time as the polymerization of the binder itself. All these factors permit the manufacture of a tubular element having higher mechanical strength and properties which remain constant at any point of this element.

In the example of construction which was described above, both the inner sheath and the outer sheath are produced continuously in the stations A and F (shown in Figs. 1 and 2) from extrusion machines comprising in the first case an axial mandrel 12 (Fig. ) and in the second case a hollow sleeve 53 (Fig. 8) on the external surface of which slide the plastic sheaths before being subjected in the manner already explained to different operations which play a part in producing at the delivery end of the machine a final tubular element having the characteristics already set forth. In this example, the external surface of the mandrel 12 as well as that of the sleeve 53 are covered with a material which provides adequate sliding, in particular of steel or of polytetrafluoroethylene or "Teflon", thereby avoiding any danger of tearing or creasing of the sheaths as these latter are being produced. Figs. 13 to 15 of the accompanying drawings illustrate another alternative form of construction which improves the sliding properties obtained o In these figures, the block 132 of an extruder head 131 which can be either that of the station B or that of the station F supports a calibration mandrel which is generally designated by the reference 135 » Said mandrel is mounted within a housing 136 of the block 132 and extends outside this latter in the axis of the slot 133 through which a sheath 134- is delivered. Subject to the necessary details of manufacture which have already been explained, the sheath can be either the inner sheath 1 or the outer sheath 3 of the element 4. Said mandrel 133 is mainly composed of a metallic supporting tube 137 on which is mounted in front of the block 132 a coaxial sleeve 138 , the sheath 13 being intended to slide over the external surface of said sleeve. The same supporting tube 137 is also provided with a transverse ring 139 which is placed downstream of the sleeve 138 and a guiding member 140 which is placed even further downstream. The sleeve 138 , the ring 139 and the guiding member 140 constitute together the calibrating mandrel and are suitably spaced relative to each other along the length of the tube 137 .

As can be seen more especially from Fig. 14 which is a transverse sectional view of the mandrel at the level of the sleeve 138 , this latter comprises a series of radial grooves such as the groove 138a , in which are mounted ball raceways, thereby improving the sliding of the sheath 134 over the sleeve 138 while enabling said sheath to assume a uniform shape of revolution about the axis of the mandrel.

Preferably, the transverse cross-section of the sleeve 138 has the shape of a regular polygon having a number of vertices corresponding to the number of ball racewa s and the grooves 138a extend in radial lanes which pass through the edges of the right prism which is constituted by the sleeve 138. There are mounted in each of the above-mentioned grooves two side-plates 141a and 141b located in oppositel -facing relation and mounted against each other by means of transverse screws 142. Each side-plate has a channel designated respectively by the references 143 or 144 and both delimiting, once the two side-plates have been mounted together, a continuous raceway 143 in which are mounted metallic balls 146. These latter project slightly from the apparent contour of the sleeve 138 along the edges of this latter and the sheath 134 which passes out of the annular slot 133 of the extruder head, thus slides directly over the balls which facilitate transfer of the sheath and uniform shaping around the sleeve.

In order to maintain the sleeve 138 at a relatively low temperature during operation and to ensure as a result of contact the cooling of the sleeve which slides over the balls 146, said sleeve is provided between the grooves 138a with circulation ducts 147 which extend parallel to the axis of the sleeve and traverse this latter completely, said ducts 147 being intended to open into two end headers designated respectively by the references 148 and 149 and delimited by means of closure plates 150 and 151 which are parallel to the end faces of the sleeve and connected to these latter in leak-tight manner. These end-plates 150 and 1 1 are pierced at their center by an opening which permits leak-tight insertion of the supporting tube 137 on which the sleeve 138 is mounted. The header 148 is connected by means of a tube 152 to an external source of liquid, especially water, this latter being discharged the tubes 152 and 153 are surrounded by an outer protective casing 15 which is attached to the surface of the supporting tube 137 by means of a ring 15 .

The transverse ring 139 which is placed downstream of the sleeve 8 on the supporting tube 137 of the sleeve has two flat and parallel flanges 157 and 158 which extend at right angles to the axis of the supporting tube, there being formed between said flanges an annular recess 159 » the base of which is constituted by a cylindrical portion 160 which joins said flanges 157 and 158 together. Said recess 159 in turn communicates with a cavity 162 by means of orifices 161 which are formed in the portion 160, said cavity being connected to the surrounding atmosphere through a tube 163 which extends parallel to the axis of the mandrel.

By virtue of this arrangement, the ring 139 continuously performs the function of a sealing member between the sheath 13 which slides over the periphery of the flanges 157 and 158 and an inflation fluid which is admitted through the interior of the tube 137 ; in spite of its natural lack of rigidity, the sheath is permitted by said fluid to retain its tubular shape beyond the mandrel 135 . Since the recess 159 is in fact at atmospheric pressure, namely below the pressure which prevails within the sheath 13 downstream of the ring 139 j leak-tightness is continuously maintained on said ring while preventing in particular any excessive leakage of inflation fluid and especially any uncontrolled detachment of the sheath from the sleeve 138, with the local deformations which would consequently take place.

The calibration mandrel in accordance with the invention is finall com leted b means of the guiding member 140 which is located downstream of the ring 139 and of the sleeve 138. This member 140 serves to carry out the displacement of the sheath 134 as this latter passes out of the annular slot 133 of the extruder head 131 . Said member 140 which is illustrated in greater detail in the transverse sectional view of Fig. 15 comprises a body 164 having a right section of slightly oblong shape and having two parallel flat faces designated respectively by the references 165 and 166, these faces being intended to co-operate with two flat rollers 167 and 168 which clamp the sheath between said rollers and the body 164 while permitting the displacement of the sheath in the downstream direction. The external surface of the body 164 advantageously carries a "Teflon" covering which limits the sliding motion of the sheath without any danger of damage to this latter. Finally, there is fixed at the extremity of the supporting tube 137 a member 169 which is fitted with a fastening-piece 170 for the end of a cable 1 1 » the other end of the cable (not shown) being intended to carry a sealing plug which makes it possible in conjunction with the ring 139 to put the sheath under pressure and inflate this latter with air which is admitted into said sheath through the interior of the supporting tube in the manner which has already been explained.

Whatever form of construction is adopted, there is thus provided a machine of simple design which permits continuous production of tubular elements at a cost price which is appreciably lower than design solutions of the prior art.- These tubular elements are of the type described in which an inner sheath associated with an outer sheath ensure leak-ti htness of the elements both with res ect to the fluid which is circulated within these latter and with respect to the surrounding external medium. At the same time, an intermediate reinforcement endows these elements with high mechanical strength and enables them to withstand high loads or pressures which are applied either internally or externally. As has already been stated, the materials constituting the plastic sheaths, the reinforcement threads or ribbons and the impregnation binder can be of variable nature according to the particular applications of the tubular elements to be fabricated.

Furthermore, since the structure of the machine makes use of a series of successive stations which are in fact separated from each other and each perform one or a number of well-determined specific operations, it is possible to contemplate a number of alternative forms by interposing intermediate stations between the main stations which have been described in the foregoin 0 There can be carried out in these intermediate stations other complementary operations such as winding or deposition, between the windings of the reinforcement material, of an additional layer consisting of another material such as plastic foam, polystyrene whether expanded or not, polyurethane foam, or alternatively a deposit consisting of a granular material or the like which may or may not be impregnated with a resin.

As has already been brought out by the foregoing, it is readily apparent that the invention is therefore not limited in any sense to the mode of application of the method or to the example of construction of the machine as described in the foregoing and illustrated in the accompanying drawings but extends on the contrary to all alternative 38304/2 forms* The concomitant production, in accordance with the method of the invention, of the impregnation of the reinforcement material which constitutes the jacket for the inner sheath and o the production of the outer sheath has the essential advantage ofproducing a wholly homogeneous and uniform distribution and penetration of the binder between the fibres of the ghreads or ribbons of the reinforcement jacket. Subsequent hardening of this binder accordingly takes place through the entire thickness of the reinforcement material *ile forming together with this latter an external banding element which has a per-fedtly distributed mechanical resistance thereby limiting considerably, in conjunction with the inner and outer sheaths, any danger of local fracture of the tubular element under the action of various stresses.

Moreover, the method according to the invention prevent any break in continuity in the positioning of the outer sheath on the impregnated reinforcement material, thereby removing any possibility of loss of the binder which cannot fall since it is continuously supported and confined within the outer sheath.

A production machine constructed according to the present invention may include winding machines for winding on the reinforcement materialto produce the jacket on the inner sheath, and extruders for the inner sheath and outer sheath may he of a different type without thereby departing from the scope of the invention as de 38304/2 by other devices which are known per se, especially by a radiofrequency furnace. So also the reservoir for circulation of water at variable temperatures couM be iBplaced by devices known in themselves and used for similar purposes. Further, instead of employing an extruder at the head of the machine(Figure 1) the inner sheath could be formed by means of two strips pressed together and then bonded longitudinally along their two edges.

Claims (29)

1. CLAIMS X. A method of continuously manufacturing a handed leak tight tube, as hereinbefore defined, with an outer coverin of abrasion resistant material, wherein the covering is constituted by an outer sheath extruded on to the Jacket while the binder is .Still mobile, said banded leak tight tube being progressively impregnated with the binder as it is advanced in a downstream direction and then guided . on through a hollow mandrel /to which the outer sheath is extruded and calibrated aa> it glides downstream until the outer sheath embraces the impregnated Jacket on leaving the hollow mandrel, elongating the outer sheath to cause sufficient radial contraction on to the Jacket to develop in the outer s heath a unifrm radial pressure around the Jacket which pressure forces the still mobile binder into intimate and uniform relation with the windings of the Jacke and then polymerising the binder imprisoned in the Jacket by the outer sheath,

2. A method of manufacture according to claim 1, wherein the assembly of the inner sheath, impregnated jacket and extruded outer sheath is supported in th area subjected to elongation against sagging by a cushion of air, the air cushio under theupstream area of the outer sheath subjected to elongation being constituted by hot ai to soften the outer sheath and facilitate elongation and the air cushion under the downstream area of the elongated outer sheath is constituted b. cold air whereby incipien cooling of the contracted outer sheath is achieved and the

3. method of manufacture in accordance with claim 2 wherein the penetration o the binder into the jacket achieved by the radial pressure derived from the outer sheath is completed by applying to the contracted outer sheath radial calibration forces uniformly distributed about the periphery of the jacket.

4. A method of manufacture in accordance with any of claims 1~¾ wherein the binder is polymerized at a relatively low temperature by means of ultraviolet radiation.

5. A production machine for the continuous manufacture of a banded leak tight tube according to the method of claim 1, comprising means for continually producing the inner sheath of plastic leak tight material, traction means for advancing the inne sheath downstream through the machine, winding means for covering the sheath with reinforcing material, impregnating means including a tank for accommodating volume of hardenable binder surroundin the reinforced sheath, an outlet for the impregnated sheath a the downstream end of the .tank, a hollow mandrel extending downstream fro said outlet, an extruder surrounding the hollo mandrel at the upstream end thereof for producing the outer sheath of plastic leak tight material so that the outer sheath is calibrated as it glides downstream in the ho state on the outside of the hollow mandrel while the inner sheath and Impregnated jacket is guided downstream by the inside of the hollow mandre thereb the mandrel wall separates the inne sheath from the extruded material and on leaving the wall the outer sheath progres* in contact stretching means for elongating the outer sheath/with the jacket, operative on the outer sheath on the mandrel and on the outer sheath in contact with the jacket respectively, means for buoyantly supporting the outer sheath against sagging in the area bein stretched, and means further downstream for polymerising the binder held in intimate realtion with windings of the jacket by the outer sheath.

6. A production machine in accordance with claim 5» wherein the hollo mandrel Is provided within the thickness of the separating wall with a fluid-circuit for circulating a coolant, whereby adhesion of the outer sheath to the hollow mandrel is avoided and to ensure the thermal isolation of the binder from the heat in the extruded material advancing along the mandrdL

7. A production machine in accordance with claim 5, wherein the separating wall of the mandrel is provided with a covering formed of material havin a low coefficient of friction over which the outer sheath slides.

8. A production machine in accordance with claim 5, wherei the extruder, which delivers the outer sheath, is of the right-angle head type in which theaxis coincides with the axis of the inner sheath.

9. A production machine in accordance with claim 5, wherein the means for causing elongatio of the outer sheat comprise a set of at least two retractable wheels which are capable of clamping the sheath between said wheels and the hollow mandrel, which is directed towards the downstream end, arri. 38304/2 slightly higher than, the speed of the retractable wheels.

10. A production machine in accordance with claim 5» whejE&n the means &■ supporting the outer sheath while causing the radial shrinkage thereof are constituted by two successive cushions formed by blowing hot air then cold air against the underside of the sheath, said cushions bein disposed downstream of the impregnating means and upstream of the polymerisation means.

11.' A production machine in accordance with claim 5, wherein the buoyancy means for supporting the outer sheath against sagging is constituted by a reservoir which is traversed axially and continuously by the banded leak-tight tube, said reservoir being filled with a liquid at a controlled temperature which applies a hydrostatic pressure on the moving outer sheath, means being providedd for ensuring leak-tightness in the inlet and outlet zones of the banded leak-tight tube within the reservoir and means £βτ maintaining the pressure and temperature of the liquid at constant values.

12. A production machine in accordance with claim 11, wherein the banded leak-tight tube is maintained in the axis of the reservoir by means of waisted bearing rollers having horizontal spindles carried by yokes ixed on a longitudinal beam which is mounted et the top ^portion of the rearvolr.

13. A production machine in accordance with claim 11 or 12, wherein the supply of the reservoir with filling liquid is carried out by means of an open tank mounted above the reservoir and communicating therewith, the level of liquid within the tank being maintained at a constant value which by means of a circulating pump which returns the liquid in a closed circuit from said reservoir to said tank after passing through a boiler which continuously controls the temperature of said liquid.

14. A production machine in accordance with any of claims 11-13» wherein the means for ensuring leak-tightness within the inlet and outlet zones of the tubular element within the reservoir are constituted by expansible rings which clamp the banded leak-tight tube and are traversed axially by said leak-tight tube.

15. A production machine in accordance with claim 14» wherein the expansible rings are mounted on each side of the reservoir within leakage collection headers each connedted to the tank located above the reservoir by means of a pipe line comprising a pump.

16. A production machine in accordance with claim 10, comprising supplemental means for clamping the outer sheath against the inner sheath constituted by a collar located in the area of stretching and formed by a ring of plastic material made flexible by means of slots uniformly spaced around the internal contour of said collar, said ring which is traversed axially by the banded leak-tight tube being associated with an elastic annular chamber which applies a distributed radial compressive force on -fee ring under the action of a pressure of compressed air which is admitted into said chamber.

17. A production machine in accordance with claim 16, wherein the supplemental means for completing the uniform of the said clamping means.

18. A production machine in accordance with claim 5, wherein the inner sheath is placed under pressure of a compressed gas, preferably air, and the leak-tightness at the downstream extemity of the inflated sheath is ensured by means of a sealing plug over the periphery of which said sheath is capable of sliding, wherein said sealing plug comprises a central body in which are formed grooves having the shape of equidistant sectors formin guide for the supports of transverse rollers which are applied against the wall of the sheath under the actio of restoring springs housed between each support and the base of the corresponding sector, said rollers each having the shape of an elongated oval which is capable of conforming substantially to the curvature of the wall of the inner sheath.

19. A production machine in accordance with claim 5» wherein the polymerization means for effecting the hardening of the impregnating ¾inder are constituted by an elongated enclosure traversed axially by the banded leak-tight tube and comprising three adjacent compartments disposed at angular intervals of 120° about the axis of the enclosure, each compartment being provided in transverse section along a plane at right angles to the axis with a profile i the form of an ellipse, one focus of which is occupied by a high-intensity source of ultraviolet light and the other focus of which coincides with the corresponding foci of the other compartments and with the axis of the enclosure, the walls of said compartments being constituted by a material which reflects the light emitted b the sources towards the ax the nde -

20. A production machine in accordance with claim 1 t wherein the enclosure is provided axially with at transparent tube surrounding with a substantial clearance the banded leak-tight tube which passes through the enclosure, said tube bein adapted to communicate through a lateral opening of the enclosure qwith a power fan for delivering in contact with the banded leak-tight tube an air-stream which removes the heat generated by the reaction of polymerization of the impregnating binde and by the visible fringes of the ultraviolet radiation emanating f om the sources which are in turn protected from the air-stream by said tube.

21. A production machine in accordance with claim 5» wherein the mandrel for calibrating the inner sheath and/or-the coasial hollow mandrel over which the outer sheath slides comprise a sleeve mounted coaxially on a supportin tube and having a plurality of completely closed continuous raceways extending in planes which pass through the axis of the sleeve, said raceways being intended to accommodate metallic balls .... which project slightly beyond the apparent contour of the sleeve along the generator-lines parallel to its axis and on which the sheath is capable of sliding.

22. production machine in accordance with claim 21, wherein each ball raceway is delimited by two juxtaposed side-plates each provided with a continuous groove for accommodating the balls, said side-plates being placed within longitudinal channels formed in thts thickness of the sleeve.

23. A production machine in accordance with claims 21 and 38304/2 the section taken along a plane at right angles to its axis is a regular polygon, the ball raceways being disposed i planes which pass through the edges of said prism.

24. A production machine in accordance with claim 21, wherein the ball raceways are separated by independent ducts formed within the bod of the sleeve and extending parallel to its axis, said ducts being pro ded for the coolin fluid circuit which opens at the extremities of the sleeve into two distribution headers delimited by plates at right angles to the axis which are pierced for the leak-tight insertion of the axial supporting tube.

25. · A production machine in accordance with claim 21, wherein the sleeve comprises, mounted on the supporting tube and maintained in spaced relation downstream of the sleeve with respect to the direction of sliding motion of the sheath, a transverse rin which ensures leak-tightness of the sheath at the upstream end with respect to ani inflating fluid which is admitted along the axis, said rin being such as to have two parallel edges at right angles to the axis and delimiting between them an annular channel connected through a calibrated orifice to a tube whicii connects the sleeve t o the outer atmosphere,

26. A production machine in accordance with claim 25, wherei the supporting tube is also provided downstream of the transverse ring with a guiding member having two parallel flat external faces cooperating externally with two rollers for displacing the plastic sheath which is 38304/2

27. · A method in accordance with claim 1 or the continuous manufacture of a banded leak-tight tube constituted by an inner sheath, a strenthening jacket and an extruded outer sheath which is advanced to embrace the jacket and is stretched over the inne sheath as both are advanced downstream to engender radial pressure to force the still mobile binder into the windings of the jacket in preparation for polymerising the binder substantially as herein described.

28. , A banded leak-tight tub© produced according to the method of claim 2?»

29. A production machine for the continuous manufacture of a banded leak-tight tube by the method in accordance with claim 1, including stations constructed arranged and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. For the Applicants DR. REIKHOLD COM A D PRITIES