FR2504851A1 - Extrusion die mechanisms for producing mesh profiles - by causing adjacent extrudate strips to periodically join tangentially - Google Patents

Abstract

Extrusion die for producing a mesh profile has an array of rotating or oscillating nozzles so positioned and moving that output strands from adjacented nozzles periodically meet and fuse tangentially. Used for producing (polyolefin) mesh with a combination of fused and crossed strand intersections, the fused intersections being of similar thickness to a constituent strand. Opt. ancillary strip materials may be interlaced longitudinally through the mesh pattern, in line with the fused intersections. It can operate at high outputs, requiring relatively little power. Access to individual die heads for adjustment/replacement is easy.

Description

 The invention relates to an extrusion die of a net or mesh made of thermo-plastic material, constituted by the interlacing and the tangency of filiform elementary strands.

 Dies of this type currently existing carry out the extrusion of two superimposed layers of substantially parallel strands by means of two sets of extrusion orifices. Each set of orifices is laterally driven by an alternative translational movement, the movement of one set being in phase opposition with respect to the other. The strands of each tablecloth somehow describe sinusoldes, intersect and are welded at their crossing.

 There are also dies made up of two concentric extrusion dies, respectively provided with extrusion orifices and driven in a rotation movement in opposite directions. In this case, the two dies extrude two layers of strands, respectively cylindrical which intersect.

 For such dies, the welds of the strands of the two layers are made at their intersection.

 One of the aims of the present invention is to propose an extrusion die, for which the welding of the strands is carried out mainly, not at the level of the crossing of the strands, but in zones where they pitch each other.

 Another object of the present invention is to provide a die, which advantageously makes it possible to add one or more rectilinear strands to the grid or extruded net.

 Another object of the present invention is to provide a die which makes it possible to associate with the mesh, during its extrusion, an independent reinforcing strip, linked to the mesh by interlacing in its meshes.

 Other objects and advantages of the present invention will emerge during the description which follows, which is however only given for information, and which is not intended to limit it.

 The extrusion die of a thermo-plastic net or mesh, constituted by the interlacing and the tangency of filiform elementary strands, is characterized by the fact that it comprises a plurality of juxtaposed heads respectively movable in rotation relative to to an axis substantially parallel to the general direction of extrusion, respectively provided at their periphery with extrusion orifices of the elementary strands, equidistant from the axis of rotation, that the distance between two successive heads is substantially equal to or slightly greater than the sum of the distances from any of their respective extrusion orifices to their respective axis of rotation, and that cyclic control means entered the rotating heads so that, during the cycle, the extruded strands of a head tangent the extruded strands of an adjacent head substantially in the plane of their axis of rotation, causing their welding.

 The invention will be better understood if reference is made to the description below, as well as to the accompanying drawings which form an integral part thereof.

 FIG. 1 schematically and without limitation represents a die according to the invention, front view, in partial section through the plane marked at B in FIG. 2.

 FIG. 2 is a top view of the die of FIG. 1, in partial section through the plane marked at A, the extrusion heads having been turned 90 degrees relative to their position in FIG. 1.

 FIG. 3 diagrammatically, without limitation, by way of illustration, a grid obtained from the die shown in FIGS. 1 and 2.

 FIGS. 4 and 6 schematize respectively in front view, and in partial section, two variants of the die shown in FIGS. 1 and 2.

 Figures 5 and 7 are respectively side views of the dies shown in Figures 4 and 6, respectively in section through the planes identified in C and D.

 FIG. 8 shows diagrammatically by way of illustration, without limitation, a grid obtained from the dies shown in FIGS. 4 and 5.

 In FIG. 1, a die 1 has been shown diagrammatically. This die comprises a plurality of extrusion heads. In the figures, four heads 2 to 5 have been shown. This number is not limitative, and any other higher or lower number is suitable.

 Each head, 2 to 5 is movable around an axis of rotation, respectively 6 to 9, and these axes are substantially parallel to each other.

 Preferably, they are coplanar. However, other provisions could be adopted. In particular, they could have left at> (sum of a polygon or a broken line.

 Each head is provided with extrusion orifices. The heads 2 to 5 shown in the figures respectively have two extrusion orifices, 10 and 11 for the head 2, 12 and 13 for the head 3, 14 and 15 for the head 15, and 16 and 17 for the head 5 This number is not limitative, and any other higher or lower number is suitable.

 For an extrusion head, the orifices are equidistant from its axis of rotation. Furthermore, preferably, for all of the heads, the orifices are located in the same plane perpendicular to their axis of rotation.

 The distance between the axes of rotation of the two adjacent heads is substantially equal, or slightly greater, taking into account the thickness of the extruded strands, to the sum of the distances from any of their extrusion orifices to their axis of rotation . For the different heads, the angular arrangement of the extrusion orifices around the axis of rotation is either substantially identical or reverse and symmetrical. This arrangement depends on the direction of rotation of the different heads, which will appear later. In the case of heads 2 to 5, having two extrusion orifices, these orifices are diametrically opposite.

 As can be seen from FIG. 2, for the head 2, preferably, the heads consist of a main shaft 18, substantially cylindrical of revolution and of axis 6. This shaft is guided, in its rotational movement, by example by a die body 19. Preferably, the shaft 18 is mounted on the body 19 by means of bearings 20 and seals 21.

 The shaft 18 is extended by two branches 23 and 23 at the ends of which are located the extrusion orifices 10 and 11. Naturally, the number of branches depends on the number of extrusion orifices of the head. Furthermore, these branches could be replaced by a disc provided at its periphery with extrusion orifices.

 The extrusion orifices 10 and 11, for the head 2, are the ends of the extrusion channels 24 and 25, which converge towards the axis 6 of the head or they open into the main channel 26 of the shaft 18. Preferably, in the middle part of the shaft, the channel 26 is divided into two sub-channels 27 and 28, oriented in directions diametrically opposite with respect to the axis 6, which runs right through the shaft 18, and at least one of which opens into a cavity 29. As can be seen in FIG. 1, the cavity 29 covers the periphery of the shaft 18, at the level of the sub-channels 27 and 28 over more than 180 degrees, so that at least one of these subchannels opens into the cavity, whatever the # angular position of the head.

 The cavity 29 is supplied with thermo-plastic material in fusion, for example by a main conduit 30, which is divided into secondary conduits 31 and into sub-conduits 32 for the supply of each of the heads by the cavities such as the cavity 29.

 Naturally, any other mode of supplying molten materials, which supplies the various extrusion orifices, is suitable.

 According to the invention, the extrusion heads are respectively driven by a cyclic rotational movement. The angular movement of the different heads is preferably synchronous. The direction of rotation of the two adjacent heads can however be the same, or vice versa.

 The respective angular positions of the heads, and the arrangement of the extrusion orifices of each head, when their number is greater than 2, is determined so that at regular intervals, extruded strands of two adjacent heads come to tangent in the plane of the axes of rotation of these heads, substantially immediately after their extrusion, and therefore weld each other.

 In the case of FIGS. 1 and 2, where the extrusion orifices of each head are diametrically opposite, the relative angular positions of departure of the heads are determined so that all of the extrusion orifices are located in the plane axes of rotation substantially simultaneously, as shown diagrammatically in FIG. 2. Therefore, whatever the direction of rotation of the different heads, the extrusion orifices of each head will have another common simultaneous position shown diagrammatically in FIG. 1.

 The movement of the heads can be a continuous rotary movement. In this case, each head extrudes continuous helices, each helix being locally welded, at regular intervals, to one or two helices, extruded by the adjacent head or heads.

 The movement of the two adjacent heads can have the same direction or be reverse. Advantageously, the synchronization of the movements is ensured by a train of identical gears in engagement two two, and, respectively secured to the shafts of the heads, 33 for the head 2, 34 for the head 3, 35 for the head 4 and 36 for the head 5.

One of these gears is driven in motion by any means appropriate to the person skilled in the art.

 According to another variant, the rotational movement of the heads is alternating. In the case of FIGS. 1 and 2, where each head has two extrusion orifices, this reciprocating movement preferably has as position of equilibrium the position of the heads represented in FIG. 1, and an angular amplitude of 90 degrees, from both else of this equilibrium position. These extreme positions therefore correspond to the positions of the heads shown in FIG. 2.

 As in the case of continuous rotational movement, the direction of rotation of two adjacent heads can be the same or opposite.

The means for controlling the rotation of the heads may be substantially identical, and for example constituted by the gears 33 to 36.

 Preferably, after the extrusion, the net or the mesh thus obtained is laminated so as to flatten the structure which it presents and to give it the configuration of two layers of strands superimposed. Laminating can be combined with stretching.

 By way of illustration, FIG. 3 shows diagrammatically a grid obtained from the die of FIGS. 1 and 2, by a continuous rotation movement of the heads.

 Schematically, the strands 37 to 44 are respectively obtained from the extrusion orifices 10 to 17. The welds of the strands of two adjacent heads, corresponding to the position of the heads shown diagrammatically in FIG. 2, have been identified at 45. Furthermore, at 46, the two extruded strands of the same head intersect. This intersection corresponding to the position of the heads shown diagrammatically in FIG. 1. It should be noted that the superposition is obtained by rolling, and that, at this level, the two strands are welded at least superficially. An alternating movement of the heads would only have repercussions at the level of the intertwining 46, part of which would be reversed.

 As shown in Figure 3, preferably, the mesh has at each of its ends a long strand, 47 and 48. These strands are extruded by the extrusion orifices 49 and 50 of axis parallel to the axis of heads. they are located at each end of the row of extrusion heads. The distance from the axis of the orifices 49 and 50 to the axis of rotation of the head which is adjacent to them is substantially equal to the distance from any of the extrusion orifices of this head to its axis of rotation. Thus, the strands extruded by the extreme ends come to weld at regular intervals to the elongated strands extruded by the orifices 49 and 50.

 Figures 4 to 7 are variants of the yarn which has just been described, which make it possible to carry out the reworking! in Figure 8. This grid is substantially identical to that of Figure 3, apart from the fact that a reinforcing tape 51 is intertwined between the meshes. The position of this ribbon which has been shown is not limiting, and for example the ribbon could be in the position shown diagrammatically at 52.

 Figures 4 and 5 relate to a die for obtaining the grid of Figure 8, with a continuous rotational movement of the heads. The die then includes a feed mouth located between two adjacent heads. This mouth has been shown at 53 for the ribbon 51, and shown diagrammatically at 54 for the ribbon 52.

 The mouth has an elongated shape, and its largest dimension is located perpendicular to the plane defined by the axes of rotation of the two adjacent heads. This larger dimension is of the order of the distance separating the two extrusion orifices from each of the adjacent heads. Its width is slightly greater than the width of the ribbon 51.

 Through this mouth is made the continuous scrolling of the ribbon 51. The scrolling speed is in correspondence with the extrusion speed of the mesh.

 At the level of the mouth 53, parallel to its scrolling movement, the ribbon 51 is animated with an alternating movement oriented parallel to the largest dimension of the mouth 53. This movement has been shown diagrammatically by the double arrow 54. The two extreme positions of this movement correspond to the position of the ribbon 51 at each of the ends of the mouth 53. The central position of the ribbon during this movement is substantially located in the plane of the axes of rotation of the two adjacent heads.

 The reciprocating movement of the ribbon is cyclic, and its period is substantially equal to the period of the rotation movement of the heads.

 The central position of the ribbon in the mouth 53 corresponds to the position of the heads shown diagrammatically in FIG. 4. The two extreme positions 56 and 57 correspond to the position of the heads shown diagrammatically in FIG. 2. Thus, during the extrusion of the mesh or of the net, due to the synchronization of the movement of the ribbon with that of the heads, the ribbon 51 is intertwined in the meshes, and the extruded strands of the two adjacent heads, that is to say heads 3 and 4 in in the case of the ribbon 51 are welded alternately above and below the ribbon as can be seen in FIG. 8. Preferably, the two heads between which the mouth is located are driven in a directional rotation movement reverse. In addition, in the same way, several mouths could be adapted to the sector.

 FIGS. 6 and 7 illustrate another variant, in which the heads are driven in an alternating rotational movement, of approximately 90 degrees of amplitude, around an equilibrium position shown diagrammatically in FIG. 6.

 The interlacing of the ribbon 51 in the meshes of the mesh is similar to that shown in FIG. 8, apart from the differences in the structure of the mesh itself mentioned above. The ribbon 51 travels through a mouth 58, located substantially in the plane of the axes of rotation of the two heads adjacent to the mouth.

 As in the previous case, the speed of movement of the ribbon is determined as a function of the speed of extrusion of the mesh.

The direction of rotation of the alternating rotation movement of the two heads 3 and 4 adjacent to the mouth 58 is preferably the opposite.

 Thus, the two extreme positions of the reciprocating movement of the adjacent heads will come respectively and alternately make their strands tangent sometimes above and sometimes below the ribbon. The welding will therefore take place sometimes below, sometimes above it.

 However, it should be noted that preferably the welding takes place in the plane defined by the axes of rotation of the two heads.

To do this, the scrolling and guiding means of the ribbon allow it to be pushed back slightly by the heads, so that the welding of their strands is effectively carried out in the plane defined by their axis of rotation.

 Naturally, the mouth 58 could be placed between two other heads or several mouths such that the mouth 58 could be placed between adjacent heads.

 Those skilled in the art will determine the most suitable means of scrolling and guiding for the ribbons 51 in the case of FIGS. 4 to 7.

 Thus, the present invention provides a sector for the production of a mesh of thermoplastic material, constituted by the interlacing and the tangency of strands. This mesh is for example made of polypropylene or polyethylene. Furthermore, the strip 51 is of a known type, for example for its qualities of tensile strength, and of fibrillation when it breaks. This strip could also be metallic.

 The advantages of this sector are numerous. It in fact allows a high extrusion speed, requires a low cost or more generally a low energy for driving the heads. Furthermore, these heads are independent of each other, can be dismantled and maintained, possibly interchanged independently of one another.

 Naturally, the present description is given for information only, and other implementations of the invention could be adopted without departing from the scope thereof.

 In particular, the distance from the extrusion orifices to their axis of rotation could be different from one head to another, so as to obtain a heterogeneous structure of the mesh transversely.

 Furthermore, two or more sets of heads, such as those which have been described, could be combined with other extrusion dies. For example, two assemblies could be placed on either side of a die of a ribbon, the strands of the two heads adjacent to this die coming to tangent the ribbon cyclically and to weld to it. We would thus obtain a grid consisting of a central core and two openwork parts on either side thereof. Other combinations are also possible.

Claims (10)

 1. extrusion die or mesh of thermo-plastic material constituted by the interlacing and the tangency of filiform elementary strands, characterized in that it comprises a plurality of juxtaposed heads (2 to 5), respectively movable in rotation relative to an axis substantially parallel to the general direction of extrusion, respectively provided with extrusion orifices (10 to 17) of the elementary strands, equidistant from the axis of rotation, that the distance between two successive heads is substantially equal to or slightly greater than the sum of the distances from any of their respective extrusion orifices to their respective axis of rotation, and that cyclic control means cause the heads to rotate so that during the cycle, the extruded strands of a head tangent the extruded strands of an adjacent head substantially in the plane of their axis of rotation, causing their mutual welding.  2. Die according to claim 1, characterized in that the heads (2 to 5) are substantially identical.  3. Die according to any one of claims 1 or 2, characterized in that the axes of rotation (6 to 9) of the heads are coplanar.  4. Die according to any one of the preceding claims, characterized in that the rotation movement of the heads (2 to 5) is continuous, and that the direction of rotation of the two adjacent heads is the same or opposite.  5. Die according to any one of claims 1 to 3, characterized in that the rotation movement of the heads (2 to 5) is alternating, each extreme position corresponding for two heads juxtaposed to the alignment between the axes of rotation (6 to 9) of the heads of an extrusion orifice of each of them in the plane defined by the axes of rotation (6 to 9).  6. Die according to claim 3, characterized in that two fixed extrusion orifices are arranged on either side of the rotation heads (2 to 5), substantially in the plane defined by their respective axis of rotation, towards outside, at a distance from the axes of rotation (6 to 9) of the heads which are adjacent to them, substantially equal to or slightly greater than the respective distance of any of the extrusion orifices of these heads from their axis of rotation respective, the strands extruded by these heads coming to tangentially cyclically the strands extruded by the fixed extruder orifices, causing their mutual welding.  7. Die according to any one of the preceding claims, characterized in that the intersecting strands (37 to 44) and tangent are flattened by two rolling rollers.  8. Die according to claim 2, characterized in that it comprises at least one set of two adjacent heads a mouth oriented substantially perpendicular to the plane defined by the axes of rotation of the two heads, continuous supply of a ribbon of reinforcement, continuously scrolling, and that means animate the ribbon at the opening of the mouth with an alternating movement directed parallel to its orientation, synchronized with the movement of rotation of the heads, the extreme positions of the corresponding ribbon substantially has the tangency between the axes of rotation of two strands respectively extruded from each of the adjacent heads, which achieves the elongated interlacing of the ribbon in the meshes formed by the interlacing and the tangency of the strands.  9. A die according to claim 5, characterized in that it comprises, at least between a set of two adjacent heads a supply mouth of a reinforcing tape running continuously, and that the extreme positions of the rotational movement alternating heads realize the tangency and the welding of the strands respectively and alternately above and below the ribbon.  10. Die according to any one of the preceding claims, characterized in that the heads respectively have a shaft extended by at least two branches, the extrusion conduits, the ends of which consist of the extrusion orifices, traversing each of the branches and emerging in a conduit located in the central part of the tree.