FR2479080A1 - PROCESS AND DEVICE FOR MANUFACTURING BENT PIPES - Google Patents

Abstract

The invention relates to processes and devices for producing curved pipes from a curable material containing, if appropriate, reinforcing inserts and/or fillers. In said processes and devices the material is moulded by centrifugal casting in a cylindrical mould which is rotatable about a horizontal axis, deformable in a curved manner and made of elastically deformable material. After completion of the rotation the mould containing the still-uncured pipe is deformed in a curved manner and the curved pipe is cured and removed from the mould. Before the mould is deformed in a curved manner, a flexible film bellows can be introduced into the pipe produced and be inflated with compressed gas to prevent undesired deformation of the pipe during the curved deformation. The mould can have a cavity located between the inner wall and outer wall, into which cavity liquid can be introduced during the centrifugal casting to produce a uniform curvature.

Description

 The present invention relates to a method and a device for manufacturing bent pipes made of a composite material, and more particularly relates to a method and a device for manufacturing such bent pipes, according to which a pipe made of a composite material containing a resin and fillers, such as reinforcing material and aggregates, are molded by centrifugal molding and the resulting pipe is bent when in the uncured state.

 The quality of the pipes made from a composite material of the above-mentioned tire has improved considerably in recent years. Improvements in manufacturing efficiency have also been achieved, so that these pipes can be produced at relatively low costs. As a result, these pipes are now widely used in various types of piping. However, in the manufacture of bent pipes, the difficulty lies in the fact that one cannot apply a high efficiency process such as that which is used at present for the manufacture of straight pipes. bent pipes consists in using a mandrel adapted to the shape of the bent pipe to be manufactured, and in wrapping around the outer periphery of the mandrel a reinforcement material impregnated with resin, or else in filling the space between an inner mold and an outer mold with a mixture of a resin and fillers, such as a reinforcing material or the like. As a result, the production efficiency of bent pipes is very low, which results in a high manufacturing cost.

 The essential object of the invention is therefore to offer a method and a device making it possible to manufacture, with good yield, bent pipes made of a composite material. A fundamental principle employed according to the invention to achieve this object consists in molding by centrifugal molding a straight pipe made up of a composite material, then in transforming the molded pipe into a bent pipe by bending it while it is at not hardened state.

However, if the pipe produced by centrifugal molding is extracted from the mold as it is in the uncured state and subjected to bending, it is not possible to correctly maintain the configuration of the section of the pipe and therefore it is not possible to obtain a suitable bent pipe. in use. The invention provides a solution to this technical problem in order to achieve the essential aim indicated above.

 To achieve this object, the invention provides a method of manufacturing bent pipes which comprises the following operations: a substantially cylindrical molding tool which is designed so that it can be deformed between a profile, is rotated around a straight horizontal mandrel. with a straight axis and a profile with a curved axis, materials are introduced into the molding tool, this tool is bent when a pipe made up of the materials contained inside and molded by centrifugal molding is in the uncured state , and the resulting bent pipe is extracted from the tool, after having allowed this pipe to harden.By molding a straight pipe by centrifugal molding using such a deformable molding tool, then bending the pipe together and tool with the hose retained in the tool, as shown above, it is possible to correctly maintain the configuration of the hose section during the bending operation. One can thus effectively obtain bent pipes with tight tolerances using the centrifugal molding technique.

 The invention provides a device for manufacturing bent pipes comprising a practically cylindrical molding tool which is designed so that it can be deformed between a profile with a straight axis and a profile with a bent axis, means for releasably holding the molding tool in a position in which its axis is rectilinear, means of rotation intended to turn the tool, maintained in rectilinear position, around a horizontal mandrel, and means of bending intended to bend the tool when it is released from the means of rotation.

 These rotation means preferably consist of a cylindrical rotating structure which is designed so as to rotate around the horizontal mandrel and whose inner periphery fulfills the function of the means intended to maintain the axis of the rectilinear molding tool.

However, according to a variant, the rotating structure which is designed so as to enclose or receive the molding tool, may be in the form of a bellows, and there may be means intended to limit the movement of the bellows in the axial direction, these means being able to be used to maintain the axis of the rectilinear molding tool.

 In a preferred embodiment of the invention, a bag constituted by a flexible sheet is introduced into a pipe molded by centrifugal molding and it is inflated with air or compressed gas so as to be applied against the internal wall of the pipe before the molding tool is bent, so that the surface of the inner wall of the pipe can be straightened and the configuration of the section of the pipe can effectively undergo no deformation during the bending operation. It is even more preferable that a layer of absorbent material be placed on the outside surface of the bag to remove air bubbles, or gas, which may appear on the surface of the inside wall of the pipe.

 In another preferred embodiment of the invention, the molding tool is constituted by an elastic material such as rubber and there is between the inner and outer walls of the tool an empty space which can be filled with a liquid during the centrifugal molding operation. Even in the presence of a dimensional deformation or an eccentricity of the tool or of the structure, the configuration is such that it makes it possible to obtain perfect roundness of the interior of the tool during the operation. centrifugal molding, and thus obtain pipes with a uniform wall thickness. Another advantage of this configuration is that it is possible to enlarge the internal diameter of the molding tool during the operation extraction of the hose, by evacuating the liquid contained in the hollow chamber, by the application of a certain pressure inside the tool, thanks to which the hose can be easily removed from the tool.

 In another preferred embodiment, an intermediate structure that can be divided into several circumferential parts, or a flexible intermediate structure of the bellows type consisting of a strip material continuously wound in a helix, is interposed between the rotating structure and the tool molding formed by an elastic material. This configuration has the advantage of being able to effectively prevent any deformation which the elastic molding tool could undergo when this tool is extracted from the rotating structure. More specifically, when a flexible intermediate structure is used, it is possible to accomplish the bending operation while the elastic tool is held in the intermediate structure, whereby the configuration of the section of the tool, and therefore of the pipe, can be safely maintained unchanged during the bending operation . When extracting the pipe, one can easily remove the stress exerted on the elastic tool by twisting the intermediate structure in the opposite direction to that of the winding of the strip material, and the pipe can therefore be extracted easily.

 The bending operation can be carried out using any known method, such as that in which pressure is produced by means of a force exerted on the upper side and a force exerted on the lower side, or that in which the tool is supported at both ends and in an intermediate position, after which the support points are changed as necessary.

The invention will be better understood on reading the following description of embodiments and with reference to the accompanying drawings in which
Figure 1 is a longitudinal section, in elevation, of a centrifugal molding device, with the upper half, above the axis of rotation, representing what we see when forming the female end of a pipe and the bottom half representing what you see when a pipe has been molded
FIG. 2 is a representation in elevation and partially in section showing an intermediate structure and a molding tool, both extracted from a rotating structure located on a conveyor
Figure 3 is a cross section corresponding to a side view and in elevation of the device of Figure 2
Figure 4 is a side view, partially in section, of the molding tool which is transferred from the conveyor to bending means
Figure 5 is an elevational view partially in section of the bending means, showing the molding tool received and held in position
Figure 6 is a view similar to that of Figure 5 showing the conditions after the bending operation
Figure 7 is a section along the line Vil-Vil of Figure 5
Figures 8a - Bd are longitudinal sections showing important aspects of various phases of the process of centrifugal molding of a pipe
Figure 9 is an elevational and partially sectional view of an improved bag
Figure 10 is a longitudinal section, in elevation, of another modified form of bag
Figure 11 is a longitudinal elevational view of another form of centriguge molding device
Figure 12 is a longitudinal elevational view of yet another form of centrifugal molding device
Figure 13 is a cross section corresponding to a side view and in elevation of the device of Figure 12
Figure 14 is an enlarged section of the part which is indicated by the arrow A in Figure 12
Figure 15 is a front view showing the intermediate structure and the molding tool in their bent state
Figure 16 is an enlarged section of the part indicated by arrow B in Figure 15
Figure 17 is an enlarged section of the part indicated by the arrow C in Figure 15
Figure 18 is a longitudinal section in elevation of bag introduction means; and
Figure 19 is a representation similar to that of Figure 18 showing the introduction of a bag.

 We will now consider Figures 1 to 7 which show a manufacturing device constituting the first embodiment of the invention. In FIG. 1, a rotating structure 2 able to rotate around a horizontal mandrel 1 comprises a cylindrical body 3 and annular parts 4 mounted at the two ends of the body and resting on rotation drive means 5. The latter comprise a rotating shaft 8 supported by a pair of fixed frames 6 by means of bearings 7, wheels 9 mounted at both ends of the rotating shaft 8, an annular projection 10 formed integrally on one side of each of the wheels 9, and a drive mechanism (not shown) intended to transmit energy to the rotating shaft 8. The outer periphery of the wheel 9 has a surface 11 having the shape of an arc of a circle. contact 12, intended to come into rolling contact with the wheel 9, is defined at the outer periphery of the annular part 4. A circumferential groove 13 in which the annular projection 10 adjusts is formed on one side of the surface of rolling contact 12.

The annular part 4 also comprises a convex annular surface 14 located on the inside of the circumferential groove 13, in the radial direction. Each of the opposite faces of the two opposite annular parts 4 has an annular toothed part 15. Annular parts 16, projecting outwards, are formed at the two ends of the cylindrical body 3, in one piece with the latter. The annular parts 16 are respectively tightly fitted in the annular parts 15 indicated and they are fixed to the annular parts 4 by fastening elements 17, at several locations distributed circumferentially. The reference 18 designates an intermediate structure which is housed in the cylindrical body 4 and which is held in position by the latter. The intermediate structure 18 is divisible into several separate parts (divisible in two) and it is for example made of aluminum. The reference 19 designates an elastic molding tool which is housed in the intermediate structure 18 and which is held in position by the latter. The elastic molding tool 19, constituted by an elastic material such as fluorinated rubber, silicone rubber or rubber of the polyurethane type, has at its two ends collars 20, 21, projecting outward circumferentially . The collar 20 which is on the side of the female end of the molding pipe is in contact with a pressure ring 22 and the collar 21 which is on the side of the mold end of the molding pipe is in contact with a shaped part. shoulder of the intermediate structure 18. An end holding device 23, designed so as to be able to pass through the cylindrical body 3, is mounted at the end of the intermediate structure 18 which is on the side of the male end. There is also an end holding device 24 at the end corresponding to the female end, and this device comprises a collar 24a intended to be fixed to the pressure ring 22 by means of a fixing part 25, and a tubular part 24b formed integrally with the collar 24a and extending a certain distance, in an axial direction, on one side of the intermediate structure, from the inner periphery of the collar 24a. end retaining devices 23, 24 is fixed in position by holding a retaining plate 26 on one side of the retaining device 23 or 24 and on one side of the annular piece 4, then tightening the retaining plate 26 together, the annular part 4 and the annular part 16 by means of clamping elements 27, at several locations distributed circumferentially.

The reference 28 designates internal molding means, in the form of a tube, which are fitted in the end holding device 24 which is located on the side of the female end and which are movable in the axial direction of the mandrel 1. These means are designed so as to mold the inside of the female end when they project towards the inside of the molding tool 19 from the end holding device 24. The tubular part 24b of the holding device d end 24 contains a ball 30 which is biased inwardly, in the radial direction, by a spring 29. The outer peripheral surface of the interior molding means, 28, comprises two cavities 31, 32 mutually spaced in the axial direction of the mandrel 1 and these cavities are designed so as to resiliently receive the ball 31. The locations of the cavities 31, 32 are calculated so that the ball 30 is housed in the cavity 31 when the inner end of the device retaining ex end 24 is aligned with the inner end of the interior molding means, 28, and so that the ball 30 is housed in the cavity 32 when the interior molding means, 28, cover the interior periphery of the female end. The reference 33 designates a pivoting control lever which is fixed at an intermediate point to one side of the fixed frame 6, by means of a horizontal axis 34. The upper end of the control lever 33 is curved on one side and the lower face of the curved upper part has a concave shape allowing it to come into contact with the convex surface 14 of the annular part 4, in order to constitute a control surface 35.

 The lower end of the control lever 33 is curved towards the other side. This curved part constitutes a locking element relative to the fixed frame 6. A cylinder 37 intended to pivot the control lever 33 is mounted between the locking element 36 and the fixed frame 6.

The reference 80 designates a bag consisting of a tube-shaped film of a solvent-resistant material, such as silicone rubber with the addition of paraffin, or fluorinated rubber. One end of the bag 80 is closed
W by a clamping element 81 and there is at the other end of the bag a connecting element 83 intended to receive air or compressed gas via a shut-off valve 32. The connector 83 can be connected to another connector element 84 which is placed next to the rotating structure 2, the latter connector element communicating with an air supply source (not shown). There are also means (not shown) suitably arranged to introduce the bag 80 into the molding tool after completion of a cycle of the centrifugal molding operation.

 We will now explain how the centrifugal molding operation is carried out using the centrifugal molding device described above.

 The internal molding means 28 being placed outside the molding tool 19 and held in this position by the ball 30 housed in the cavity 31, as shown in FIG. 1 and more particularly the part in this figure which is located above the axis of rotation, the rotary drive means 5 are actuated to rotate the molding tool 19, with the rotating structure 2, around the mandrel 1. Next, by a hole which passes centrally through the end holding device 23 or 24, charges, such as reinforcing fibers and sand, are introduced into the molding tool 19, at its end molding part female. A liquid resin is introduced similarly at medium hardening speed, comprising a mixture of a resin to which an accelerator and a catalyst have been added. In this way the female end 38a of a pipe 38 is molded, as shown in Figure 8a. The internal molding means are then pushed inside, 28. The position to which the internal molding means, 28, are pushed is maintained by the ball 30 which is housed in the cavity 32. again introduces fillers into the inner peripheral part of the resin forming the female end, 38a, which is not covered by the molding means from the inside, 28, then a quick-setting liquid resin is introduced, comprising a mixture of a resin to which an accelerator and a co-accelerator and a catalyst have been added. We then proceed to centrifugal molding of a shoulder-shaped part 38b of the female end, as shown in FIG. 8b. We then introduce on the inner periphery of the molding tool 19, between the shouldered part 38b of the female end and a point adjacent to the end corresponding to the male end, fillers as well as a relatively slow-hardening liquid resin constituted by a mixture of a resin to which an accelerator has been added and of a catalyst to which a inhibitor, in order to mold a body part 38c by centrifugal molding, as shown in FIG. 8c.

Fillers and a quick-setting liquid resin are then introduced onto the remaining part of the inner periphery of the molding tool 19, in the same manner as in the case of the shouldered part 38b of the female end, and a part is molded. male end 38d, by centrifugal molding, as shown in Figure 8d. By proceeding in this way, it is possible to ensure that the female end 38a hardens at ordinary speed, that the shouldered portion 38b of the female end and the male end 38d harden or solidify as soon as the materials have been introduced, and that the body portion 38c hardens relatively slowly. Thus, when the pipe is extracted after the molding operation, the female end 38a, the shouldered part 38b of the female end and the male end 38d have hardened while the body part 38c has the consistency of a gel. allowing the parts rich in resin, like the ends of the pipe and the angles, to harden quickly, it is possible to avoid the risk of formation of cavities or voids, under the effect of a flow of resin after stopping the rotation. Subsequent bending is accomplished on the body portion 38c of the pipe. If the liquid resin mentioned above is a general-purpose resin, such as for example an unsaturated polyester resin, cobalt naphthenate and cobalt octoate are preferably used as accelerators; dimethylaniline as a co-accelerator; methyl ethyl ketone peroxide as a catalyst; and hydroquinone as an inhibitor.

 When the molding of the pipe is finished, the rotation of the rotating structure 2 is stopped, then, as can be seen in FIG. 1, a bag 80 is introduced into the molded pipe 38, by appropriate means, and the bag by injecting compressed air inside, so that it is applied against the inner periphery of the pipe 38. The shut-off valve 82 is then closed and the connecting elements are separated from one another 83 and 84.

The inside of the pipe is thus straightened by the bag 80. It will also be noted that, in this way, the pipe can be protected against any deformation of the configuration of its section which could occur during the subsequent bending operation, if we didn't do it that way.

 In FIG. 1, the reference 85 designates a mold lubricant chamber which is defined by the inner periphery of the tubular part 24b of the end holding device 24 and, in association with the seals 86a, 86b which are adjacent, the lubricant chamber 85 protects the molding means from the inside, 28, to prevent the resin from rendering them unusable. The inner peripheries of the end holding device 23 as molding means for the interior, 28, have a frustoconical shape (87, 88) with a decreasing diameter in the direction of their respective ends facing the molding tool 19, so that any piece of material falling on these regions is discharged to the outside by centrifugal force. In addition, the respective ends of the end holding device 23 and the interior molding means, 28, which face the molding tool 19 have annular projections 89, 90 which penetrate into the tool. molding 19 and these projections have the function of preventing the appearance of burrs in the corner regions.

 Reference will now be made to FIGS. 2 to 4 to explain the means which are used to extract the intermediate structure 18 and the molding tool from the rotating structure 2. The reference 39 designates drawing means intended to pull the intermediate structure 18 outside the rotating structure 12, by gripping the end holding device 24 which is coupled to the intermediate structure 18. The pulling means comprise a cylinder 40 disposed on the extension of the previously mentioned axis of rotation of the mandrel 1, a plate 42 which is fixed to the front end of a piston rod 41 of the cylinder 40, a pair of pivoting arms 44a, 44b mounted on the face of the plate 42 via axes 43a, 43b, locking elements 45a, 45b which consist of the inwardly curved front parts of the pivoting arms 44a, 44b, and a cylinder 41 which is intended to actuate the pair of pivoting arms 44a, 44b to approach and distance them one of the other. The reference 47 designates a conveyor which is placed between the rotating structure 2 and the drawing means 39 in order to receive the intermediate structure 18 that the drawing means 39 pull out of the rotating structure 2. The conveyor 47 comprises a pair of shafts turning 49, 50 supported on a frame 48 and arranged at a certain distance from each other in the direction of the pull, pairs of chain wheels 51, 52 mounted on the rotating shafts 49, 50, at a rate of a pair for each shaft, a pair of roller shafts 53 passing over the chain wheels 51, 52, rails 55 mounted on the frame 48 for guiding the rollers 54 of the roller chains 53 and receiving plates 56, of concave shape, mounted on two opposite sides along the path of movement of the roller chains on the rails 55, these receiving plates being arranged at determined intervals in the longitudinal direction of the chains 53.

Each side of the upper part of each receiving plate 56 has a pivoting locking part 52. A tilting pin 57 is placed at the lower part of the frame 48, on one side of this frame, and it passes through the frame 48 in being arranged parallel to the mandrel 1. The axis 57 is rotatably supported by brackets 59 mounted on the ground 58. A cylinder 60 intended to rotate the frame 48 is placed between the ground 58 and the other side of the part bottom of the frame 48. The reference 61 designates a stop intended to stop the end of the frame 48 which is on the side of the cylinder 60. The reference 63 designates bending means to which the extracted molding tool must be transferred.

 We will now explain the operation of the drawing means. The rotation of the rotating structure 2 being stopped while the pipe 38 has been molded by the centrifugal molding device, the clamping elements 27 are removed and the retaining plates 26 are removed so as to allow the extraction of the intermediate structure 18.

The cylinder 40 is then passed into the extended position while the pivoting arms 44a, 44b are kept apart from each other, and these pivoting arms 44a, 44b are positioned outside the holding device for end 24. The pivoting arms 44a, 44b are approached from one another by retracting the cylinder 46, whereby the locking elements 45a, 45b of the pivoting arms 44a, 44b come into contact with the holding device d end 24. Then, by retracting the cylinder 40, the intermediate structure 18 is pulled out of the rotating structure 2, by means of the end holding device 24, and the molding tool 19 and the pipe 38 are pulled together. The receiving plates 47 located on the conveyor receive the intermediate structure 18 as it is pulled. It will be noted in this regard that the force produced by pulling the intermediate structure 18 can be used to actuate the conveyor 47 in order to move it, or alternatively, the conveyor can be moved by a forced drive. As shown in FIG. 2, the intermediate structure 18 which is pulled out of the rotating structure 2 is thus entirely received by the conveyor 47. Then, the cylinder 46 is passed into the extension position to move the arms 44a, 44b further apart. relative to each other, as shown by the dashed lines in Figure 2.

Then, as shown by the dashed lines in Figure 3, the upper half of the divisible intermediate structure 18 is lifted by means of a hoist or the like (not shown), while the lower half is held by the locking pieces 62.

Then, as shown in solid lines in FIG. 4, the conveyor 47 is pivoted around the tilting shaft 57 which passes through the frame 48, whereby the molding tool 19 and the pipe 38 which it contains are transferred from the lower half of the intermediate structure 18 to the bending means 63, as shown in phantom in FIG. 4.

 We will now describe the bending means 63 with reference to Figures 5 to 7. The bending means 63 are of a carriage type and therefore comprise a base plate 64 whose underside is provided with several wheels. Two frames 66a, 66b are mounted on the base plate 64, at a certain distance from each other in the axial direction of the molding tool 19. A camshaft 68 is supported horizontally by bearings 67a, 67b between the upper end parts of these frames 66a, 66b. The camshaft 68 is coupled by a belt transmission mechanism 70 to a motor 69 which is mounted on the base plate 64. There are also on the two sides of the base plate 64 two side plates which extend towards the top from the base plate 64 and which are arranged parallel to the axis of the molding tool 19. The reference 72a designates a support block of concave shape which supports from below the end holding device 24. Similarly, the reference 72b designates a support block of concave shape which supports from below the end retaining device 23. The support blocks 72a, 72b include contact parts 72a ', 72b' which have for the function of preventing the movement of the end retaining devices 24, 23 in the axial direction. The references 72c, 72d, 72e, 72f designate support blocks of concave shape which support the molding tool 19 from below, at several points. The support blocks 72a - 72f are individually fixed on bases 73a - 73f which are themselves detachably blocked on inverted U structures, 74a - 74f by blocking elements (screws and nuts). inverted U structures 74a - 74f are in contact with the outer surface of the side plates 71a, 71b, so that the inverted U structures 74a - 74f cannot rotate but can move up and down, and move forwards and backwards. Operating blocks 76a - 76f which have respective cam grooves 77a - 77f are individually mounted on the underside of the top plates of the inverted U structures 74a - 74f.

Several cam plates 78a - 78f penetrating these cam grooves 77a - 77f are mounted on the camshaft 68. These cam plates 78a - 78f are designed so as to raise and lower the operating blocks while making them swing.

 The bending means 63, constructed as described above, receive the molding tool 19 at a time when all the support blocks 72a - 72f are held in a horizontal position by the penetration of the cam plates 78a - 78f in the operating blocks 76a - 76f. The molding tool 19 is received in such a way that it is supported by the concave surface of the support blocks 72c - 72f, while the end retaining devices 24, 23 are supported by the concave surface of the support blocks 72a, 72b, when the contact pieces 72a ′, 72b ′ of the support blocks 72a, 72b are in contact with the termination devices 24, 23.

When this state is reached, the motor 69 is actuated to rotate the cam plates 78a - 78f via the camshaft 68. When the particular configuration of the cam plates 78a - 78f acts on the cam grooves 77a - 77f, the support blocks 72a - 72f are moved by the operating blocks 76a - 76f, the inverted U structures 74a - 74f and the bases 73a - 73f, whereby the pipe 38 is bent at the same time as the molding tool 19, as shown in FIG. 6.

After the bending operation, the molding tool 19 can be transferred to the next station, intended for example for hardening, and after hardening the pipe is removed from the tool 19.

As regards the bag 80 which, in FIG. 1, consists only of a tube-shaped film, it is preferable that, as shown in FIG. 9, a tubular absorbent layer 91, consisting of fibers resistant to corrosion, such as cotton or polyester, or a porous and flexible corrosion-resistant material, is placed on the outer periphery of the bag 80 and that in addition that a porous film 92, consisting of a material which resists solvents, such as polyethylene, polyester or
Nylon, surrounds the outer periphery of the absorbent layer 91. The reason is that there are often air bubbles inside a pipe 38 in the uncured state, molded by centrifugal molding. a pipe made of a composite material containing reinforcing fibers is subject to the appearance of numerous bubbles due to the rise of these fibers when the rotation of the rotating structure 2 is stopped, this fact necessitating the extraction of these bubbles, i.e. degassing. If a bag 80 consisting solely of a tube-shaped film is inflated in one operation, a layer of air can form between the inner periphery of the pipe and the tube formed by the film, which can cause air to enter in the wall of the pipe. However, if on the contrary an absorbent layer 91 is placed, as shown in FIG. 9, when the bag 80 is inflated and it presses against the internal wall of the pipe 38, the air which is directed towards the inner wall by the compression effect of the bag 80 can pass through the holes of the porous film 92 to penetrate into the absorbent layer 91, whereby there can be no air bubbles inside the pipe 38 and any air bubbles which may be produced can be crushed so as to disappear.

 The structure of the bag is not limited to those which are represented in FIGS. 1 and 9. One can for example use the one which is represented in FIG. 10.

FIG. 10 shows a compressed air supply pipe 93 which can be introduced into the molding tool 19 after passing through the axis of rotation 1 of the rotating structure 2, one end of the supply pipe 93 being stopped by a stop 94 while the other end communicates with a source of compressed air supply (not shown). A bag 95 is fitted around the outer periphery of the supply pipe 93 and the two ends of the bag 95 are hermetically fixed to the supply pipe 93 in which are drilled several holes 96 which communicate the internal passage of the pipe 93 and bag 95 and which are suitably spaced from each other. An absorbent layer 97 and a porous film 98, both similar to those of FIG. 9, are placed around the outer periphery of the bag 95. When this type of bag is used, its insertion into the molding tool 19 can be accomplished by means of the supply pipe 93. If the bend angle of the pipe 38 is large, it is necessary that the supply pipe 93 is of a type capable of properly supporting the bag 95 and having good flexibility .

 FIG. 11 shows another form of the centrifugal molding device, in which there is a rotating structure 102 supported by several rollers 103 so as to rotate about a horizontal axis of rotation 101, the driving force for the rotation of the structure 104 being provided by the rollers 103. The reference 104 designates an intermediate structure divisible in a circular manner in several parts, which is housed inside the rotating structure 102. The reference 105 designates an elastic molding tool which is constituted by an elastic material such as fluorinated rubber, silicone rubber, polyurethane type rubber, or the like, and which is housed in the intermediate structure 104, the molding tool 105 comprising collars 106 at its periphery, 107, at both ends. The references 108, 109 designate pressure rings which come into contact with the rotating structure 102, at its two ends, while being in contact with the collars 106, 107. The references 110, 111 designate end holding devices which are fixed to the two ends of the rotating structure 102 by means of annular fixing pieces 112. The end holding devices comprise flanges 11Oa, Villa intended to be coupled respectively to the pressure rings 108, 109, and tubular parts llOb, it, each of them being designed so as to allow the introduction of one of its end parts into the molding tool 105. The reference 113 designates auxiliary molding means for carrying out the molding from the inside of the female end, which are mounted at the end of the end holding device 111 which faces one end of the molding tool 105. The position of the auxiliary molding means 113 can vary between an advanced position in which they act in the region for molding the female end, 105a, in the molding tool 105, and a retracted position in the end retaining device 111.

The auxiliary molding means are made of the same elastic material as the molding tool 105. They are normally positioned so as to be retracted by their own elasticity in the end holding device 111. The active surface 113a of these means auxiliary elastic molding 113 has an annular projection 114 which is integrally formed with this surface. The reference 115 designates a tubular operating element which is fitted in the tubular part IIIb of the end holding device 111 and which is movable in the axial direction of the horizontal mandrel 1. This element is designed so as to push the molding means auxiliaries 113 so as to bring them facing the molding region of the female end, 105a, when they extend inside the molding tool 105, from the end holding device 111, on the end side female. The reference 116 designates pushing means 116 which are placed opposite a first end of the operating element 115. The pushing means 116 comprise a cylinder 117 and a floating roller 118 which is mounted on a piston rod of the cylinder 117 and which can be pressed on the first end of the operating element 115. The interior of the body of the molding tool 105 is formed so as to constitute a hollow chamber 119 which is charged with a liquid 120 such as a fluorinated oil or an oil to which an appropriate quantity of powdered material has been added to give it a density greater than that of the resin. The hollow chamber 119 is formed so that there can be no leakage of liquid. Because the hollow chamber 119 is annular in shape, the inner tubular part of the elastic molding tool is coupled to other tubular parts by means of a suitable coupling element 121, or else the hollow chamber 119 is formed by an open pore material so as to prevent deformation of the inner tubular part under the effect of gravity. A liquid reservoir 122 is formed in the tubular part îîOb of the end holding device 110 and this reservoir communicates with the aforementioned hollow chamber -119 by means of several passages 123. The reference 124 designates a liquid introduction orifice.

 The phases involved in the pipe molding operation using this form of centrifugal molding device and in the subsequent cintrago operation are practically identical to those described for the first embodiment. It will be noted that the fact that the annular projection 114 of the auxiliary molding means 113 intended for molding the interior of the female part is pushed by the operating element 115 inside the female end 125a of the pipe 125 which is formed. , results in the formation inside the female end 125a of a peripheral groove intended for the housing of a circular seal. When centrifugal molding is carried out, a satisfactory roundness can be obtained by the action of the liquid introduced. in the hollow chamber 119 from the reservoir 122, through the passage 123, even in the presence of deformations of the interior of the molding tool 105, under the effect of errors or eccentricity which may have appeared. be in the rotating structure 102, the intermediate structure 104 and / or the molding tool 105, during their manufacture. It will also be noted that the hose can easily be extracted after it has been bent, by making the liquid 120 which is contained in the chamber 119 return to the reservoir 122, through the passage 123. To bring the liquid back to the reservoir 122, one method among others consists in subjecting the interior of the molding tool 105 to a pressure produced by compressed air.

 Figures 12 to 17 show yet another embodiment. Considering FIG. 12, we can see a circumferential divisible structure 202, which is supported by several rollers 203 so as to rotate about a horizontal axis of rotation, the driving force for the rotation being provided by the rollers 203. The reference 204 designates an intermediate structure which can be mounted inside the rotating structure 202. As shown in FIGS. 12 to 14, its body is formed by a helically wound strip 205, and the lateral edges adjacent turns of the strip 205 are joined by means of suitable parts 206 which can slide in the direction of the axis of rotation 201, within certain limits. A part 207 in the form of an inner hook bent outward is formed on a lateral edge of the strip 205, and a part 208 in the form of an inwardly curved external hook is formed on the other lateral edge. These hook-shaped parts 207, 208 adapt to one another and, when they are so adapted, they can slide, within certain limits. The reference 201 designates a molding tool constituted by an elastic material which is intended to be housed inside the intermediate structure 204. A hollow chamber formed in its body is loaded with a liquid 211.

The molding tool 210 which is shown does not have a female end forming part, but it can be provided with a female end forming part, in the same manner as in the other embodiments. Collars 212a, 212b are formed at the two ends of the outer periphery of the molding tool 210. The references 213a, 213b designate pressure rings intended to be fitted in the two ends of the rotating structure 202. These rings are in contact with the collars 212a, 212b. The references 214a, 214b designate end holding devices which are intended to be mounted at both ends of the rotating structure 202. The end holding devices 214a, 214b include tubular parts 215a, 215b, one of the ends of each of these parts which can be introduced into the molding tool 210, and collars 216a, 216b which can come into contact with one end or the other of the rotating structure 202 and which are intended to be coupled to the rings pressure 213a, 213b by connecting elements 217a, 217b. The references 218a, 218b designate the interior of frustoconical parts of the end holding devices; the references 219a, 219b designate annular projections; and reference 220 designates a coupling piece which is located in the hollow chamber.

 The pipe molding operation which uses this form of centrifugal molding device is practically identical to that which corresponds to the case of the first embodiment, with the exception that the female end molding phase does not exist. Upon completion of the pipe molding, the rotating structure 202 is opened and the intermediate structure 204, the molding tool 210 and the molded pipe 221 are removed. The end retainers 214a, 214b are also removed from all in one piece with these items. Then we bend the assembly as shown in Figure 15. It will be noted in this respect that, as we can see in Figure 16, there is a slip between certain limits 222 on the side of the outside diameter, so that l the object which is bent lengthens on this side insofar as a certain clearance appears. It can be seen that the side corresponding to the inside diameter is kept within certain limits 209. It follows that the bending of the pipe is carried out by elongation on the side of the outside diameter and without contraction of the side corresponding to the inside diameter. Once the hose in the tool 210 has been bent and hardened, the end retainers 214a, 214b are removed. The intermediate structure 204 is twisted in the opposite direction to the direction of the propeller, in order to increase its diameter, and the molding tool is pulled. The bent pipe is then extracted from the tool 210. It may be added in this respect that when the tool is pulled, the liquid 211 is discharged, and that the diameter of the molding tool is adjusted. by adjusting the quantity of liquid 211 which is introduced.

 We will finally explain an example of bag introduction means, referring to Figures 18 and 19. In the representation, the rotating structure and the molding tool 301 are simplified and the molding tool is shown in the form of a rotary type tool 301 which can be circumferentially divided. The rotary type molding tool 301 can rotate around a horizontal operating axis 304 by means of several rollers 303; and a bag placement pipe, 305, movable above the horizontal axis of rotation 304, is disposed along the rotating molding tool 301. The bag placement pipe, 305, supported by several rollers 306, can introduce a bag into the rotating tool, and extract it from the latter, under the effect of the rotation in the normal or reverse direction of a drive roller 307. bag place 305 contains a bag 80 in the contracted state.

 One end of the bag positioning pipe 305 which faces the rotating structure 301 has a flared part 308 at the end of which a rubber seal 309 is fixed. An annular air-receiving chamber 310 is formed in the flared part 308 and an ajutago 311 communicating with the air reception chamber 31 # opens in the bag positioning pipe 305 and is in communication with the other end of the pipe. The nozzle 311 may be of the porous type or of the slot type. The air receiving chamber 310 opens at the other end of the bag placement pipe 305, via an air supply passago 312 which is formed in the pipe.

This opening communicates with an air supply source via an air supply pipe 314 which comprises a tap 313.

 As shown in solid lines in FIG. 18, when a pipe 302 is formed on the inner periphery of the rotary molding tool 301, the tool 301 is stopped and the drive roller 307 is actuated.

As shown in phantom, we introduce the bag positioning pipe 305 and we position it in the rotary molding tool 301, then we connect a connecting element 83 to another connecting element 84. We open then the valves 82, 313 to supply air and, simultaneously, the drive roller 307 is driven in the opposite direction to allow the bag positioning pipe to retract gradually. Then, the bag positioning pipe 305 releases a bag 80 so that the latter remains in the pipe 302, and the bag thus released in the pipe 302 is inflated by the air which comes from the side corresponding to the tap 82, so as to be applied against the interior wall of the pipe 302, as shown in FIG. 19. The distance of this application against the interior wall progressively extends from one end to the other of the pipe as the bag placement pipe 305 is pulled, and there is therefore no possibility of a layer of air being formed between the bag 80 and the pipe 302. In addition, since the starting position of the he compression action changes gradually, there is a compression and tightening effect, which accelerates the degassing of the interior of the pipe. During this operation, it is possible that the air introduced into the bag 80 swells the part of the bag which remains in the positioning pipe 305, the resistance produced by this pipe then preventing progressive release of the bag 80 or deteriorating the bag. However, in accordance with the configuration described above, air is introduced between the interior of the positioning pipe 305 and the bag 80, through the nozzle 311.

 The supply air pressure is higher than the pressure present in the bag 80. An air mattress therefore forms between the inside of the positioning pipe 305 and the bag 80, thanks to which the bag 80 is released gradually, without resistance created by pressure. Some of the air from nozzle 311 may have a tendency to discharge, but this is avoided because the rubber seal 309 bears against the bag 80. When the bag 80 is completely extracted from the delivery pipe 305 and is applied against the entire inner wall of the pipe 302, the valves are formed and the connecting elements 83, 84 are simultaneously disconnected.

 It goes without saying that numerous modifications can be made to the device and to the method described and shown, without going beyond the ambit of the invention.

Claims (22)

 1. A method of manufacturing bent pipes made of a composite material, characterized in that the following operations are carried out: a practically cylindrical molding tool is turned around a straight and horizontal mandrel (1); 2l0) designed so that it can be deformed between a profile with a straight axis and a profile with a curved axis; materials are introduced into the molding tool, this tool is bent when a pipe consisting of the materials contained in the tool and molded by centrifugal molding is in an uncured state; and the resulting bent pipe is removed from the tool, after allowing it to harden.  2. Method for manufacturing bent pipes according to claim 1, characterized in that a bag (80; 95) made of a flexible material is introduced into the pipe molded by centrifugal molding and this bag is inflated so as to apply it against the inner wall of the pipe which is then subjected to bending.  3. A method of manufacturing bent pipes according to claim 2, characterized in that eliminates air bubbles, or other gases, which may appear on the surface of the inner wall, by means of a layer of absorbent material (91) placed on the outer surface of the bag.  4. A method of manufacturing bent pipes according to any one of claims 1 or 2, characterized in that the rectilinear molding tool (19; 105; 210) is maintained in a rotating structure (2; 102; 202) designed to rotate, and it is extracted from this structure after stopping the rotation of the structure, after which the tool is subjected to bending.  5. A method of manufacturing bent pipes according to claim 4, characterized in that one uses for the molding tool an elastic cylindrical molding tool (105) which is constituted by an elastic material and which has a hollow space (119 ) between inner and outer walls, and the hollow space is filled with a liquid (120) during the centrifugal molding operation.  6. A method of manufacturing bent pipes according to claim 4, characterized in that one uses for the molding tool an elastic molding tool (105) consisting of an elastic material, this tool is maintained in position in an intermediate structure (104) circumferentially divided during the centrifugal molding operation, and at the end of the molding operation, the intermediate structure and the elastic molding tool enclosed in the latter are removed together, then the molding tool is extracted of the intermediate structure and it is subjected to bending.  7. A method of manufacturing bent pipes according to claim 4, characterized in that one uses for the molding tool an elastic molding tool (201) consisting of an elastic material, this tool is kept in position in an intermediate structure flexible (204) which is constituted by a strip wound in a helix (205) continuously, this strip being produced so that the edges of adjacent turns can slide relative to each other in the axial direction, we introduce the flexible intermediate structure in the rotating structure (202) during the centrifugal molding operation, and at the end of the molding operation, the flexible intermediate structure and the elastic molding tool enclosed in the latter are removed together, then subjects the flexible intermediate structure to bending.  8. Device for manufacturing curved pipes made of a composite material, characterized in that it comprises a cylindrical molding tool (19; 205; 210) which is designed so as to be deformed between a profile with a rectilinear axis and a profile with curved axis; means for releasably holding the molding tool in a position with a straight axis; rotation means intended to rotate the tool, kept rectilinear, around a horizontal mandrel, and bending means (63) intended to bend this tool when it is released from the rotation means.  9. Device for manufacturing bent pipes according to claim 8, characterized in that the rotation means comprise a rotating structure (2; 102; 202) designed so as to be rotated, and the inner periphery of this rotating structure constitutes the means for holding the axis of the rectilinear molding tool (19; 105; 210).  10. Device for manufacturing bent pipes according to claim 9, characterized in blistering the m.ou- lava tool (105) is constituted by an elastic material and it comprises a hollow space (119) between its inner and outer walls, this hollow space being filled with a liquid (120).  11. Device for manufacturing bent pipes according to claim 10, characterized in that a liquid reservoir (122) is supported at one end of the rotating structure (102), this reservoir communicating with the hollow space (119).  12. Device for manufacturing bent pipes according to any one of claims 9 or 10, characterized in that the molding tool (105) is constituted by an elastic material, and in that there is an intermediate structure (104) which can be divided into several parts circumferentially and which is designed so as to fit around the outer periphery of the elastic molding tool, in order to enclose and hold this tool in position, the structure intermediate being enclosed within the rotating structure (102).  13. Device for manufacturing bent pipes according to any one of claims 9 or 10, characterized in that the molding tool (210) consists of an elastic material and in that there is a flexible intermediate structure (204 ) which is designed to fit around the outer periphery of the elastic molding tool in order to enclose and maintain in position this tool, and this flexible intermediate structure consists of a helically wound strip (205 ) continuously, this strip being designed so that the adjacent edges of its turns can slide relative to each other in the axial direction, and the flexible intermediate structure being enclosed in the rotating structure (202).  14. Device for manufacturing bent pipes according to claim 9, characterized in that the rotating structure supports a pair of end holding devices (23,24) which bear against the two ends of the molding tool, each of these holding devices bearing against one end or the other.  15. Device for manufacturing bent pipes according to claim 14, characterized in that each end holding device has an annular projection at its inner periphery and this projection is designed so as to extend inside the molding tool.  16. Device for manufacturing bent pipes according to claim 14, characterized in that at least one end of the molding tool has a collar (20) at its outer periphery, this collar is intended to be clamped between the device end retainer (24) and a pressure ring (22); the end retainer includes interior molding means (28) for molding the interior of an end portion of a pipe to be molded, and the molding means from the inside can slide in the axial direction of the pipe.  17. Device for manufacturing bent pipes according to claim 16, characterized in that there exist, on the side of one end of the rotating structure, drawing means (39) intended to pull the molding tool, these means drawing comprising means (45a, 45b) intended to come into contact with the end holding device (24) and being movable in the axial direction of the rotating structure (2).  18. Device for manufacturing bent pipes according to claim 8, characterized in that there is a bag  (80) consisting of a flexible sheet, into which air or another compressed gas can be injected and which is intended to be introduced into the molding tool.  19. Device for manufacturing bent pipes according to claim 18, characterized in that a tubular absorbent layer (91) is forged around the outer periphery of the bag (80), and an additional layer constituted by a porous film (92) is also placed on the absorbent layer.  20. Device for manufacturing bent pipes according to claim 8, characterized in that the bending means (63) comprise several support blocks (72a, ... 72f) intended to support the molding tool (19) at several locations several operating blocks (76a ,. 76f), each of them being fixed to an individual support block and comprising a cam groove (77a, ... 77f); a camshaft (68) on which several cam discs (78a, ... 78f) arranged in relation to the individual operating blocks and designed so as to penetrate into the individual cam grooves; and rotation means (69, 70) for rotating the camshaft so that under the effect of the rotation of the cam disks, the operating blocks move up and down while carrying out a pivoting movement .  21. Device for manufacturing bent pipes according to claim 9, characterized in that it comprises, on one side, in the axial direction of the rotating structure, means (93) intended to introduce into the molding tool (19) held in the rotating structure a bag (95) which is constituted by a flexible sheet and into which one can inject air or another gas under pressure.  22. Device for manufacturing bent pipes according to claim 21, characterized in that the introduction means (93) comprise a bag positioning pipe one end of which can be moved in The molding tool (19), over the entire length of the latter and which contains the bag (95) in a form contracted peripherally; means for injecting compressed air are placed around the inner periphery of the positioning pipe, at one end of the latter, and means  (96) intended to introduce compressed air into the bag are placed at the other end of the rotating structure, these means being able to be connected to one end of the bag which is introduced into the molding tool.