MINIATURIZED VOLUMETRIC EXTRUDER USING TWIN CONICAL SCREWS FORMING A FEEDING STAGE FOLLOWED BY A VOLUMETRIC STAGE

Abstract

The invention relates to an extruder (1) comprising a first conical screw (2) and a second conical screw (3), mounted counter-rotatingly in a sleeve (4), which successively define, from upstream to downstream: a feeding stage (30), a transition zone (31) having a thread break (40) to allow for material homogenization, and then a volumetric stage (11) in which the threads (5, 6) are interpenetrated and conjugate with respect to each other so as to form, between the sleeve (4) and the screws (2, 3), a succession of closed, C-shaped chambers (7, 8) in order to give the extruder (1) volumetric operation. Figure 16

Description

Title of the invention: MINIATURIZED VOLUMETRIC EXTRUDER USING TWIN CONICAL SCREWS FORMING A FEEDING STAGE FOLLOWED BY A VOLUMETRIC STAGE

[0001] The present invention relates to the general field of extrusion, and more particularly to the field of extrusion of rubber-based materials.

[0002] The present invention finds particular application in the manufacture of elements intended to be used in the construction of tires for vehicle wheels.

[0003] It is known that extrusion operations generally require precise control of the flow rate of the extruded material, to avoid the generation of non-conforming products, and therefore the disposal of said products.

[0004] However, in practice, it is sometimes difficult to ensure such precise control of the extruded material flow rate during transient phases of the extrusion process, such as the start-up, shutdown, and restart phases of the extrusion line. This difficulty stems in particular from the fact that, during such transient phases, the temperature of the extrusion tools, on the one hand, and the speed of the moving mechanical components of the extruder(s), on the other hand, are not stabilized, which causes variations in the rheological properties and behavior of the extruded material.

[0005] To ensure control of the flow of the extruded material, it is known to set up so-called "volumetric" extruders, that is to say extruders which are equipped with moving mechanical parts, such as pistons, gears or interpenetrating twin screws, which are arranged so as to create, within the extruder, one or more chambers which will, under the effect of the cyclic movement of said moving mechanical parts, first open and increase their volume to receive the incoming material, then close so as to trap a given quantity of said material, and finally contract to mechanically expel said captive quantity of material from the chamber.

[0006] Thus, such extruders are capable of delivering, regardless of the pressure at the outlet of the extruder, a volume of extruded material, called the "displacement" of the extruder, which is constant for each new iteration of the cyclic operation of the extruder, that is to say, in the example above, a volume of extruded material which is identical at each back and forth of the piston, respectively at each turn of the gears, or at each turn of the twin screws.

[0007] Installations using such volumetric extruders often have a multi-stage structure, each stage being formed by a extruder of a chosen type, in order to be able to ensure all the functions which represent the supply of material to the installation, the plasticization of the material, the pressure increase of the material, and then the volumetric dosing of the material at the outlet of the installation.

[0008] Thus, for example, it is known to associate in series, within the same installation, a single-screw extruder, of the Archimedes screw type, on the one hand, which includes a screw mounted in rotation in a sleeve and which ensures the feeding, plasticizing, and a certain rise in pressure and temperature of the material by shearing, with on the other hand a gear pump, whose inlet port is connected to the outlet port of the single-screw extruder, and whose counter-rotating gears ensure, in cooperation with the housing of said gear pump, the final rise in pressure and the volumetric operation of the installation.

[0009] However, such installations are particularly bulky and heavy.

[0010] This is particularly true when these installations are intended for extruding a rubber-based material. Indeed, in order to avoid degrading the rubber-based material, it is necessary to avoid exposing it to excessively high temperatures, which means that the gear pump impellers must not rotate at too high a speed. Therefore, if a sufficient flow rate of extruded material is to be ensured, it is necessary to choose a gear pump with a large displacement, and consequently, large dimensions.

[0011] Co-extrusion installations such as that described in application WO-2017 / 109419 filed by the applicant are also known, in which a first stage consisting of a feed screw supplies a second stage comprising interpenetrating and coupled twin screws that perform the volumetric operation. While such an arrangement advantageously allows for multiplying the number of extrusion paths connected to a single extrusion head while maintaining a relatively compact extrusion head, and guarantees a relatively high and well-controlled flow rate of each of the extruded materials, installations of this type remain dedicated to co-extrusion applications aimed at producing complex profiles combining numerous extruded materials, and, overall, due to the multiplicity of extrusion paths, have a relatively large footprint.

[0012] Moreover, known installations can prove to be relatively costly, not only to acquire but also to operate, due in particular to their energy consumption and their complexity of maintenance.

[0013] The objects assigned to the invention therefore aim to remedy the aforementioned drawbacks and to provide a miniaturized extruder with a compact size and a reduced weight while maintaining satisfactory volumetric operation that allows excellent control of the flow rate of the extruded material.

[0014] The objects assigned to the invention are reached by means of an extruder intended to extrude a material, said extruder comprising: - a barrel, - a first screw which is mounted to rotate in the sheath around a first central axis and which is provided with a first thread, - a second screw which is mounted to rotate in the sheath around a second central axis and which is provided with a second thread, said first screw and second screw being counter-rotating and arranged so that the first thread and the second thread cooperate to convey the material from the upstream to the downstream end of the barrel, said extruder being characterized in that: - the first screw is conical, so that the apex diameter of the first thread decreases along the first central axis, in the upstream-downstream direction, according to a first predetermined angle of taper, - the second screw is conical, so that the apex diameter of the second thread decreases along the second central axis, in the upstream-downstream direction, according to a second predetermined angle of taper, in that said extruder comprises a stage called the "volumetric stage" in which the first thread of the first screw and the second thread of the second screw are interpenetrated and conjugated with respect to each other so as to form, on the one hand, between the barrel and the first screw, along the first central axis, a first series of successive closed C-shaped chambers and, on the other hand, between the barrel and the second screw, along the second central axis, a second series of successive closed C-shaped chambers, so that the rotation of the first and second screws generates a positive displacement of the material captured by the first series of chambers and of the material captured by the second series of chambers, and in that at least part of the volumetric floor forms a floor called an "isochoric volumetric floor", within which: - the pitch of the first thread increases along the first central axis, in the upstream-downstream direction, as the apex diameter of the first thread decreases, according to a law called the "first compensation law" which allows the progressive increase in the pitch of the first thread to compensate for the taper of the first screw so that, in said isochoric volumetric stage, the individual volume of each of the closed chambers of the first series of closed chambers remains equal to the same predetermined constant nominal volume, called the "first screw displacement", with a maximum tolerance of + / - 2%, preferably + / - 1%, or even + / - 0.5%, and - the pitch of the second thread increases along the second central axis, in the upstream-downstream direction, as the apex diameter of the second thread decreases, according to a law called "second law of compensation" which allows the progressive increase of the pitch of the second thread to compensate for the taper of the second screw so that, in said isochoric volumetric stage, the individual volume of each of the closed chambers of the second series of closed chambers remains equal to the same predetermined constant nominal volume, called "second screw displacement", with a maximum tolerance of + / - 2%, preferably + / -1%, or even + / -0.5%.

[0015] Advantageously, the extruder according to the invention makes it possible to ensure by itself the plasticization of the material, the pressure increase, and a volumetric operation at a precisely controlled flow rate, and this while occupying a relatively small space.

[0016] The arrangement of the threads according to the invention, the pitch of which increases in the isochoric volumetric stage as the screw cone narrows, advantageously reconciles the screw taper with the constant volume of each closed chamber as said chamber progresses from upstream to downstream along the central axis of the screw, as the screw rotates. Thus, the volume of extruded material captured by the chamber opening at the upstream inlet of the isochoric volumetric stage is the same captive unit volume transported by each closed chamber of the isochoric volumetric stage located between the screw and the sleeve, and the same volume expelled by the chamber opening at the downstream end of the isochoric volumetric stage.This constant unit volume advantageously corresponds to the volume of extruded material that is expelled at each complete revolution of the screw in question, i.e. to the cylinder capacity of said screw.

[0017] Because, at each instant considered, the volume of the different closed chambers defined along its central axis by the same conical screw is constant, or almost constant taking into account the aforementioned permissible tolerances, that is to say that said volume does not undergo any substantial reduction or increase, whatever the position that the closed chamber considered occupies along the axis, a regular conveying of the material contained in the closed chambers is obtained, along the central axis of each screw, from upstream to downstream of the extruder.

[0018] This ensures volumetric operation of each conical screw while avoiding, in particular, problems of local overpressure and therefore leakage problems between successive chambers of the same screw, which could occur if the captive material of a closed chamber were excessively compressed by attempting to reduce the volume of said chamber without allowing said material to escape, or problems of local pressure drop and cavitation, which could occur if one were to create an expansion of the captive material of a closed chamber by increasing the volume of said chamber, i.e., by increasing the accessible volume of said material, without increasing the quantity of material available in said chamber.

[0019] In this respect, it will be noted that, as will be seen below, it is advantageous to associate with the volumetric stage, upstream of said volumetric stage and within the same first and second screws, a feeding stage which will allow the material to be worked and compressed in order to ensure feeding of the volumetric stage.

[0020] In this respect, the invention also relates as such to an extruder intended for extruding a material, said extruder comprising: - a barrel, - a first screw which is mounted to rotate in the sheath around a first central axis and which is provided with a first thread, - a second screw which is mounted to rotate in the sheath around a second central axis and which is provided with a second thread, said first screw and second screw being counter-rotating and arranged so that the first thread and the second thread cooperate to convey the material from the upstream to the downstream end of the barrel, said extruder being characterized in that: - the first screw is conical, so that the apex diameter of the first thread decreases along the first central axis, in the upstream-downstream direction, according to a first predetermined angle of taper, - the second screw is conical, so that the apex diameter of the second thread decreases along the second central axis, in the upstream-downstream direction, according to a second predetermined angle of taper, in that said extruder comprises a stage called the "volumetric stage" in which the first thread of the first screw and the second thread of the second screw are interpenetrated and conjugated with respect to each other so as to form, on the one hand, between the barrel and the first screw, along the first central axis, a first series of successive closed C-shaped chambers and, on the other hand, between the barrel and the second screw, along the second central axis, a second series of successive closed C-shaped chambers, so that the rotation of the first and second screws generates a positive displacement of the material captured by the first series of chambers and of the material captured by the second series of chambers, in that said extruder also comprises a stage called the "feeding stage" which precedes the volumetric stage and within which the first thread of the first screw is arranged so that, as the apex diameter of said first thread decreases along the first central axis, in the upstream-downstream direction, according to the first taper angle, the pitch of said first thread also decreases, along the first central axis, in the upstream-downstream direction, in accordance with a law called " "First law of compression," so as to promote compression of the material as it approaches the volumetric stage, in that the first screw presents, between the feed stage and the volumetric stage, a transition zone within which the first thread has a thread interruption that creates a break in continuity between the upstream portion of the first thread, which occupies the feed stage, and the downstream portion of the first thread, which occupies the volumetric stage, and in that the axial length of the volumetric stage, considered along the first central axis, represents at least 33%, preferably at least 36%, lower value, of the axial length of the first screw, considered along the first central axis from the upstream end of the feed stage to the downstream end of the volumetric stage, and at most 65%, preferably at most 55%, upper value, of said axial length of the first screw, considered along the first central axis from the upstream end of the feed stage to the downstream end of the volumetric stage, and more preferably is between 36% and 55% of said length of the first screw.

[0021] Advantageously, the presence of a transition zone in which the first thread, and respectively the second thread, have a thread interruption, between the feed stage and the volumetric stage, ensures good homogenization of the material, here of the rubber-based mixture, and efficient feeding of the volumetric stage.

[0022] The axial proportions given to the volumetric stage according to the invention also advantageously make it possible to reconcile certain sometimes conflicting requirements, namely: - to provide sufficient axial length to the volumetric stage, to ensure a sealed operation of said volumetric stage, in particular through a sufficient number of consecutive chambers; - avoid, on the contrary, creating a volumetric stage that would be too long axially, because this would have the consequence of increasing, at a given rotation speed, the working power delivered to the material, and would therefore require limiting the rotation speed of the screws, and therefore the flow rate of the extruder, to avoid causing excessive heating of said material, which would be detrimental to the latter; - and maintain, for a given screw length, which we want here to be as short as possible in order to optimize the compactness of the extruder, a sufficient available length to allow for the integration, advantageously within the same screw as the one ensuring the volumetric pumping function, of a fully functional feeding stage and transition zone, to ensure good homogenization of the material and ensuring sufficient feeding pressure at the inlet of the volumetric stage.

[0023] The dimensioning according to the invention advantageously allows for optimal operation of the extruder, in particular because, as the inventors have established, it is thus possible to combine, along each of the first and second twin conical screws, in a very small footprint, and with an arrangement compatible with the implementation of relatively high rotational speeds guaranteeing a high material flow rate, on the one hand, a volumetric pumping function, performed by the volumetric stage, which requires minimizing leakage to prevent undesired backflow of material from downstream to upstream, and on the other hand, in the inlet stage and then the transition zone, inlet, mixing and homogenization functions of said material, before the introduction of said material into the volumetric stage, functions which, unlike the volumetric pumping function,material seepage and passage through narrow but intentionally non-sealed spaces between the threaded tip and the sleeve.

[0024] The taper of the screws has several advantages.

[0025] A first advantage of the conical shape is that the upstream portion of the screw, which corresponds to the large base of the frustoconical envelope in which said screw is inscribed, has a large diameter and therefore offers wide access for the introduction of the material into the extruder, which makes it possible to ensure the feeding function under good conditions.

[0026] A second advantage of the taper is that the projected surface area of ​​the thread, considered in a plane normal to the central axis of the screw, decreases along the axis, so that said projected surface area is minimal at the downstream end of the tapered screw, which corresponds to the small base of the frustoconical shell in which said screw is inscribed. Thus, said projected surface area of ​​the thread is minimal precisely in the area where the material exerts the highest pressure against the screw, necessary to overcome the pressure at the extruder outlet and propel the material through the extrusion die connected to the extruder outlet.By minimizing the area of ​​the projected surface subjected to pressure exerted on the screw by the material being extruded, the resulting axial force exerted by the material against the screw and the bearings that support it and allow its rotation within the barrel is reduced. Consequently, the size of these bearings can be safely reduced, thus improving compactness and weight.

[0027] A third advantage of taper is to reduce the wetted surface of the screw, that is, the surface of the screw that is in contact with the material, compared to what this same wetted surface would be in a straight cylindrical screw that would have a constant diameter and an axial length equal to the length of the conical screw. By reducing the wetted surface area, as well as the lever arm corresponding, at each point of said wetted surface, to the radial distance measured between the central axis of the screw and said point in question, the resisting torque exerted by the material, due to its viscosity, against the rotation of the screw is reduced. An extruder according to the invention therefore requires a relatively low drive torque, which makes it possible to reduce the size, as well as the weight, of the motor(s) and gearbox(s) that drive the first and second screws in rotation.

[0028] For all these reasons, the invention advantageously allows the implementation of a compact, lightweight extruder, relatively little subject to mechanical inertia, thermal inertia, and vibrations.

[0029] Advantageously, due to its lightness and compactness, such an extruder can be mounted on a transport device which allows the said extruder to be moved and positioned dynamically in relation to a receiving support on which the desired object is built, which makes it possible to produce said object by three-dimensional printing by depositing the extruded material on said receiving support in the desired places and in the desired quantities.

[0030] Other objects, features and advantages of the invention will become apparent in more detail from the following description and with the aid of the accompanying drawings, which are provided by way of illustration only and are not intended to be limiting, among which:

[0031] Fig. 1 illustrates, in perspective view, a pair of first and second counter-rotating screws coupled according to a first variant of the invention, in which the volumetric stage is preceded by a feed stage in which each of the first and second screws is single-threaded.

[0032] Fig. 2 is a detail view of the top of one screw of the pair of screws in Fig. 1.

[0033] Figure 3 illustrates, in perspective view, a pair of first screws and of A second contra-rotating screw is paired according to a second embodiment of the invention, in which the volumetric stage is preceded by a feed stage in which each of the first and second screws has multiple threads, in this case, double threads. An interruption in the first and second threads then ensures the transition between the feed stage and the volumetric stage.

[0034] Fig. 4 is a top view of one screw of the pair of screws in Fig. 3.

[0035] Figure 5 illustrates, according to a detailed perspective view, the volumetric floor isochore of a pair of twin counter-rotating conical screws used in an extruder according to the invention, for example the pair of screws of [Fig.1] or that of [Fig.3].

[0036] Fig. 6 is a top view of the pair of screws in Fig. 5.

[0037] Fig. 7 is a front view, from downstream, of the pair of screws in Figures 5 and 6.

[0038] Fig. 8 is a cross-sectional view, in a plane containing the first central axis of the first screw and the second central axis of the second conical screw, of the isochoric volumetric stage of an extruder according to the invention, in which the screws of Figures 5 to 7 cooperate with a sleeve to form two series of closed C-shaped chambers.

[0039] Fig. 9 is a perspective view of the volumes defined, along the first central axis, by the first closed chamber and the last closed chamber of the first series of C-shaped closed chambers of the volumetric stage, and more particularly of the isochoric volumetric stage, of an extruder according to the invention.

[0040] [Fig. 10] illustrates, superimposed on the chambers of [Fig. 9], on the one hand the fictitious external frustoconical envelope inside which the top of the first thread is inscribed, and which therefore corresponds to the overall frustoconical envelope of the first screw, and on the other hand the fictitious internal frustoconical envelope which is inscribed in the bottom of the first thread, and which therefore corresponds to the frustoconical envelope of the core of the first screw, in the isochoric volumetric stage.

[0041] Fig. 11 is a top view of the chambers shown in Figures 9 and 10, and of the external fictitious truncated conical envelope.

[0042] Fig. 12 is a side view, from upstream of the screw, of the chambers illustrated in figures 9 to 11.

[0043] Fig. 13 illustrates, according to a view folded down in a reference plane which is, by convention, normal to the first central axis and tangent to the upstream axial end of the isochoric volumetric stage of the first conical screw, a dimensioning principle of said isochoric stage of the first conical screw.

[0044] The [Fig. 14] is an example of an extrusion installation implementing a mobile laying head which incorporates a twin conical screw extruder according to the invention.

[0045] The [Fig. 15] is an example of thread dimensioning laws of a conical screw used by the invention, here in preferential relation with the first variant illustrated in figures 1 and 2, showing the quadratic increase of the thread pitch in the isochoric volumetric stage, and the reduction of the thread in the feed stage which precedes said isochoric volumetric stage.

[0046] Fig. 16 is an example of thread dimensioning laws for a tapered screw used by the invention, here in preferential connection with the second variant illustrated in Figures 3 and 4, said Fig. 16 showing the increase, here preferably quadratic, of the thread pitch in the isochoric volumetric stage, the reduction, for example linear, of the thread in the feed stage which precedes said isochoric volumetric stage, and the strong local variations of the thread pitch induced by the beak-shaped deviations located on either side of the thread interruption.

[0047] The present invention relates to an extruder 1, intended for extruding a material, and more particularly to a "twin-screw" type extruder 1.

[0048] Said extruder comprises, in a manner known per se, a barrel 4, preferably metallic.

[0049] Said extruder 1 comprises, as can be clearly seen in figures 1 to 8: - a first screw 2 which is mounted in rotation in the sleeve 4 around a first central axis X2 and which is provided with a first thread 5, - a second screw 3 which is mounted in rotation in the sleeve 4 around a second central axis X3 and which is provided with a second thread 6.

[0050] Said first and second screws 2, 3 are counter-rotating and arranged so that the first thread 5 and the second thread 6 cooperate to convey the material from upstream to downstream of the sleeve 4, according to an overall forward movement noted herein as "FWD".

[0051] For convenience of description, "axial" will be designated as a direction parallel to the central axis X2, X3 of the screw 2, 3 considered, and "radial" as a direction perpendicular to the central axis X2, X3 of the screw 2, 3 considered.

[0052] It should be noted that the first central axis X2 and the second central axis X3 are geometrically intersecting.

[0053] By "contrarotating", it is indicated that the first screw 2 and the second screw 3 rotate in opposite directions of rotation.

[0054] In addition, the said first and second screws 2, 3 are synchronous, that is to say, they advantageously rotate at rotational speeds which are equal to each other in absolute value, although of opposite signs.

[0055] The first thread 5 can, in particular depending on the stage of the first screw 2 which is considered along the first central axis X2, comprise a single thread, or, alternatively, several threads having the same pitch and offset angularly.

[0056] The term "first channel" 9 refers to the helical groove, or, in the case of a plurality of threads, each of the helical grooves, which is delimited by and between two solid profiles of the first thread 5 which follow each other axially, that is to say which separates two solid profiles of the first thread 5, one of which is immediately adjacent to the other.

[0057] Similarly, the second thread 6 can, depending on the stage of the second screw 3 which is considered along the second central axis X3, comprise one or more threads, preferably in a number equal to the number of thread(s) of the first thread 5 with which said second thread 6 cooperates.

[0058] The term "second channel" 10 refers to the helical groove, or, in the case of a plurality of threads, each of the helical grooves, which is delimited by and between two solid profiles of the second thread 6 which follow each other axially, that is to say which separates two solid profiles of the second thread 6, one of which is immediately adjacent to the other.

[0059] The direction of the first thread 5 will be opposite to the direction of the second thread 6, that is to say that the first screw 2 may have a left-hand thread 5 while the second screw 3 has a right-hand thread 6, or conversely, the first screw 2 may have a right-hand thread 5 while the second screw 3 has a left-hand thread 6.

[0060] More generally, the second screw 3 is preferably the mirror image of the first screw 2, so that the characteristics of one can be deduced identically, by symmetry, from the characteristics of the other.

[0061] According to the invention, the first screw 2 is conical, so that the apex diameter D_5C of the first thread 5 decreases along the first central axis X2, in the upstream-downstream direction, according to a first predetermined taper angle A5.

[0062] Similarly, the second screw 3 is conical, so that the apex diameter D_6C of the second thread 6 decreases along the second central axis X3, in the upstream-downstream direction, according to a second predetermined conicity angle A6.

[0063] As can be seen in figures 2, 4, 6, 8 and 11, the conicity angle A5, A6 corresponds to the angle of inclination formed, in a plane containing the central axis X2, X3 of the screw 2, 3 considered, by the fictitious frustoconical envelope E2, E3 in which said screw 2, 3 is inscribed, frustoconical envelope E2, E3 which is therefore tangent to the successive vertices 5C, 6C of the thread 5, 6 of the screw 2, 3 considered, with respect to the fictitious right cylinder with circular base, centered on the central axis X2, X3, and in which the screw 2, 3 considered is inscribed.

[0064] Equivalently, the conicity angle A5, A6 corresponds to half the angle at the apex of the fictitious frustoconical envelope E2, E3 in which the screw 2, 3 considered is inscribed, and therefore to the angle formed between the central axis X2, X3 and each generating line of the inclined wall of the fictitious frustoconical envelope E2, E3 in which the screw 2, 3 is inscribed.

[0065] In practice, the first conicity angle A5 is equal to the second conicity angle A6.

[0066] More specifically, the first central axis X2 and the second central axis X3 being geometrically secant, the first conic angle A5 and the second conic angle A6 are each equal to half the vertex angle formed by the intersection of the first central axis X2 and the second central axis X3, as can be seen in [Fig.11].

[0067] Naturally, the inner wall of the sleeve 4, which cooperates with one of the screws 2, 3, also has a conical profile, conjugate to the conical profile of said screw 2, 3, that is to say, which follows overall the same fictitious frustoconical envelope, being circumscribed by said frustoconical envelope E2, E3. The inner wall of the sleeve 4 therefore generally narrows as one travels along said sleeve 4 in the upstream-downstream direction FWD, according to the same angle of taper A5, 46 as the screw 2, 3.

[0068] Preferably, the first conicity angle A5 and the second conicity angle A6 are each between 1.8 degrees and 3 degrees, preferably between 2 degrees and 2.5 degrees, even more preferably equal to 2.5 degrees.

[0069] The inventors have indeed found that, for a given screw length, and therefore for a given size, these taper angle values ​​correspond to a good compromise between, on the one hand, the resisting forces exerted on the screw 2, 3, which we seek to minimize, and on the other hand, the ability of the screws to receive and be able to exploit a relatively high motor torque.

[0070] In particular, an optimal compromise will be sought between: - a taper angle A5, A6 which is sufficiently high (i) to obtain a significant reduction in the terminal surface of the screw 2, 3, which corresponds to the small base of the frustoconical envelope E2, E3 in which said screw 2, 3 is inscribed, and consequently to obtain a significant reduction in the axial forces resulting from the pressure exerted by the extruded material against the screw 2, 3 in question, which makes it possible to reduce the size of the bearings and axial thrust bearings that axially support the screw 2, 3, and ii) to create a sufficient center distance between the first screw 2 and the second screw 3, at the level of the upstream zone 2U, 3U of said screws 2, 3, in order to have sufficient space to accommodate a robust and powerful gearbox as well as large diameter shafts capable of driving said screws 2, 3 and imparting a high motor torque to each of them, and - a taper angle A5, A6 that is sufficiently moderate (i) so that the diameter of the screw 2, 3 in the upstream zone 2U, 3U remains sufficiently small to avoid giving the extruded material a large lever arm with respect to the central axis X2, X3 of the screw, and thus limit the resisting torque that said extruded material opposes to the rotation of the screw 2, 3, and ii) so as not to make the screws 2, 3 too thin at their tip, that is to say so that the cores of the first screw 2 and the second screw 3 have, up to and including the downstream end 2D, 3D of said screws 2, 3, a thickness of material sufficient to be able to support and transmit without damage, in particular without irreversible torsional deformation, a high motor torque.

[0071] In view of the conicity angle values ​​A5, A6 mentioned above, the vertex angle formed by the (fictitious) intersection of the first central axis X2 with the second central axis X3, which is equal to the sum of the two vertex angles A5 and A6, and therefore more preferably double the vertex angle A5, will be between 3.6 degrees and 6 degrees, preferably equal to 5 degrees.

[0072] According to the invention, the extruder 1 comprises a stage 11 called the "volumetric stage" in which the first thread 5 of the first screw 2 and the second thread 6 of the second screw 3 are interpenetrated and conjugated with respect to each other so as to form on the one hand, between the sleeve 4 and the first screw 2, along the first central axis X2, a first series of successive closed chambers 7 in the shape of C and on the other hand, between the sleeve 4 and the second screw 3, along the second central axis X3, a second series of successive closed chambers 8 in the shape of C, so that the rotation of the first and second screws 2, 3 generates a positive displacement of the material captured by the first series of chambers 7 and of the material captured by the second series of chambers 8.

[0073] By "interpenetrating", it is indicated that, as can be clearly seen in figures 1, 3, 5, 6, and 8, the first and second threads 5, 6 are arranged so that the top 5C of the first thread 5 comes substantially at the level of the bottom 6R of the second thread 6, and conversely, the top 6C of the second thread 6 comes substantially at the level of the bottom 5R of the first thread 5, so that the thread 5, 6 of each screw 2, 3 penetrates the channel 10, 9 defined by the thread 6, 5 of the other screw 3, 2 over the entire radial height of said channel 10, 9.

[0074] As an indication, a functional radial clearance JRI is provided between the top 5C, 6C of one thread and the bottom 6R, 5R of the other thread which is, admittedly, not zero to ensure a smooth relative movement of one screw 2 with respect to the other screw 3, but which is, above all, preferably less than or equal to 0.3 mm to ensure volumetric operation without leakage.

[0075] By "conjugates", it is indicated that, as can be clearly seen in figures 1, 3, 5, 6, and 8, the first thread 5 and the second thread 6 are arranged so that the full axial width of the first thread 5, that is to say the axial width of the full section of the profile of the first thread 5, fills the axial width of the second channel 10 defined by the second thread 6 and delimited axially between two successive flanks 6F of the second thread 6 and, conversely, the full axial width of the second thread 6 fills the axial width of the first channel 9 defined by the first thread 5 and delimited axially between two successive flanks 5F of the first thread 5. Thus, the flanks 5F of the first thread substantially follow the flanks 6F of the second thread and vice versa.

[0076] As an indication, to ensure leak-free volumetric operation, a functional axial clearance JAI of less than or equal to 0.3 mm may be provided between the flank 5F, 6F of one thread and the portion of the flank 6F, 5F of the other thread closest.

[0077] For the same reasons of operation and sealing in operation, a radial clearance JR2 will be provided between the apex 5C, 6C of the thread of the screw 2, 3 and the radially innermost portion of the wall of the sleeve 4, with which the considered apex 5C, 6C of the thread cooperates, which radial clearance JR2 is non-zero and, preferably, equal to or less than 0.1 mm, in particular in the volumetric stage 11.

[0078] Advantageously, as schematically illustrated in Figures 8, 9, 10, and 11, each of the first and second series of chambers 7, 8 created in the volumetric stage 11 first captures the material in a first chamber 7, 8, forming the upstream access to the volumetric stage 11. The rotation of the screw 2, 3 closes this first chamber over the extruded material, thus maintaining a corresponding volume of said extruded material captive within said closed chamber, which is delimited by the C-shaped space between said screw 2, 3 and the sleeve 4. The material is then conveyed downstream 2D, 3D within said closed chamber 7, 8 by progressively moving said chamber 7, 8 downstream 2D, 3D along the central axis X2, X3, according to an overall forward movement. translation, noted here FWD, thanks to the rotational movement of screw 2, 3.

[0079] By their very nature, the closed chambers 7, 8 of the same series of chambers do not communicate with each other, so that each unit volume of extruded material contained in a chamber 7 is isolated from the unit volume of extruded material contained in each of the other chambers 7, in particular in each of the adjacent chambers. Advantageously, the extruded material cannot therefore flow back upstream 2U, 3U of the screw 2, 3, regardless of the pressure at the downstream end 2D, 3D of the conical screw 2, 3, at the point where the last chamber 7, 8 of the series of chambers 7, 8 opens onto the outlet of the extruder 1.

[0080] Thus, at each complete rotation of the screws 2, 3, the chambers 7, 8 shift downstream 2D, 3D, and therefore advance the extruded material, along the axis X2, X3 of each screw considered, by an axial distance which is equal to the pitch P5, P6 of the thread 5, 6 at the location considered.

[0081] The volume of extruded material which is delivered at the outlet of the extruder 1 at each complete turn of the screws 2, 3, in other words the total "displacement" of the extruder 1, thus corresponds to the sum of the unit volumes contained respectively in the last closed chamber 7 of the first succession of chambers 7, delimited by the first screw 2, and in the last closed chamber 8 of the second succession of chambers 8, delimited by the second screw 3, that is to say to the sum of the displacement of the first screw 2 and the displacement of the second screw 3.

[0082] This volumetric capacity of the extruder 1 allows the flow rate of the extruded material to be precisely adjusted by adjusting the rotation speed of the screws 2, 3.

[0083] Advantageously, it should be noted that the fact that each screw 2, 3 generates, with the sleeve 4, a multiplicity of chambers 7, 8 which follow one another axially, and which are separated from each other by the thread 5, 6 of the screw 2, 3 considered, makes it possible to strengthen the overall sealing of the extruder 1, and to reduce the sensitivity of this sealing to wear of said screws 2, 3, by forming as many successive obstacles against possible backflow of the extruded material in the downstream direction. 2D, 3D upstream 2U, 3U, along sleeve 4, between sleeve 4 and screw 2, 3 considered.

[0084] According to the invention, and as can be clearly seen in Figures 1, 3, 5, 6, 8 and 15, at least a part of the volumetric stage 11, and more preferably the entire volumetric stage 11, forms a stage called the "isochoric volumetric stage" 11A, within which: - the pitch P5 of the first thread 5 increases along the first central axis X2, in the upstream-downstream direction, as the apex diameter of the first thread D_5C decreases, according to a law called the "first compensation law" LP5_11 which allows the progressive increase of the pitch P5 of the first thread 5 to compensate for the taper of the first screw 2 so that, in said isochoric volumetric stage 11 A, the individual volume of each of the closed chambers 7 of the first series of closed chambers remains equal to the same predetermined constant nominal volume V2, called the "first screw displacement" V2, with a maximum tolerance of + / - 2%, preferably + / - 1%, or even + / - 0.5%, and - the pitch P6 of the second thread 6 increases along the second central axis X3, in the upstream-downstream direction, as the apex diameter of the second thread D_6C decreases, according to a law called "second compensation law" LP6_11 which allows the progressive increase of the pitch P6 of the second thread 6 to compensate for the taper of the second screw 3 so that, in said isochoric volumetric stage 11 A, the individual volume of each of the closed chambers 8 of the second series of closed chambers remains equal to the same predetermined constant nominal volume V3, called "second screw displacement" V3, with a maximum tolerance of + / - 2%, preferably + / -1%, or even + / -0.5%.

[0085] In other words, each of the closed chambers 7 delimited by the first screw 2 and the sleeve 4 will have substantially or exactly the same individual volume, substantially or exactly equal to the individual volume of the neighboring chambers 7, and substantially or exactly equal to the volume of the first screw's cylinder V2, that is to say here an individual volume equal to V2 + / - 2%, preferably equal to V2 + / - 1%, or even equal to V2 + / - 0.5%.

[0086] Similarly, each of the closed chambers 8 delimited by the second screw 3 and the sleeve 4 will have substantially or exactly the same individual volume, substantially or exactly equal to the individual volume of the neighboring chambers 8, and substantially or exactly equal to the volume of the second screw's cylinder V3, that is to say here an individual volume equal to V3 + / - 2%, preferably equal to V3 + / - 1%, or even equal to V3 + / - 0.5%.

[0087] From a dynamic point of view, the individual volume of each chamber 7, 8 closed at C thus varies by less than 2%, less than 1%, or even less than 0.5% compared to to the individual reference volume which constitutes the screw displacement V2, V3, or even remains equal to said individual reference volume, over all the successive axial positions occupied by the closed chamber 7, 8 considered during its transfer from upstream to downstream of the isochoric volumetric stage 1 IA under the effect of the rotation of the screw 2, 3, and more preferably from the closing of said chamber 7, 8 at the upstream limit 11U of the volumetric stage 11 until the reopening of said chamber at the downstream limit 11D of the volumetric stage 11, here at the exit of the extruder 1.

[0088] Equivalently, if we consider, rather than a dynamic view of the transfer of a chamber along the axis, a static view of the distribution of the chambers 7, 8 of the same series of chambers at a given instant, this amounts to saying that all the closed chambers 7, 8 of the series of closed chambers 7, 8 delimited by the screw 2, 3 considered all have an individual volume substantially or even exactly identical, equal to the unit reference volume, to + / -2%, preferably to + / - 1%, or even to + / - 0.5%.

[0089] It will be noted that the arrangement proposed by the invention allows the extruder 1 to ensure a volumetric flow accuracy of less than or equal to 2%, or even less than or equal to 1%, that is to say, to deliver a constant volume to + / - 2%, or even + / -1% per screw turn, and this preferably, for outlet pressures that can be between 200 bar and 500 bar, and for a volumetric flow rate between 1 dm3 / min and 6 dm3 / min.

[0090] Preferably, the cylinder size of the first screw V2 is equal to the cylinder size of the second screw V3.

[0091] Preferably, the first screw V2 and the second screw V3 displacement are each between 8 cm3 and 50 cm3, for example between 10 cm3 and 30 cm3, in particular between 10 cm3 and 20 cm3.

[0092] As indicated above, the pitch P5 of the first thread 5 increases progressively, in the isochoric volumetric stage 11 A, and more preferentially over the whole of the volumetric stage 11, along the first central axis X2 of the first screw 2, in the direction going from upstream to downstream, as the diameter of said first screw 2 decreases, so that the pitch P5 is strictly larger at the downstream end 11D of the volumetric stage of the first screw 2, at the level of the last chamber 7 forming the output chamber of said first screw 2, than said pitch P5 is at the upstream end 11U of the volumetric stage of the first screw 2, at the level of the first chamber 7 forming the inlet chamber.

[0093] This increase in the pitch P5 of the first thread 5 is preferably monotonic, and more preferably linear, along the central axis X2, between on the one hand the value of said pitch P5 considered at the upstream end of the volumetric stage isochore 1 IA, here the upstream end 11U of the volumetric stage 11, value which is said "input step" P5_in, and on the other hand the higher value of said step P5 considered at the level of the downstream end of the isochore volumetric stage 11A, here the downstream end 11D of the volumetric stage 11, value which is said "output step" P5_out.

[0094] This variation of the pitch P5 of the first thread 5, here a continuous enlargement of said pitch P5 along the central axis X2, over the entire isochoric volumetric stage 1 IA, and more preferably over the entire volumetric stage 11, of the first screw 2, makes it possible to progressively increase the axial width W9 of the channel 9 defined by the first thread 5, as can be clearly seen in figures 1, 2, 3, 8, 9 and 11, so as to compensate for the corresponding variation, here a continuous narrowing, of the diameter of the first screw 2, in this case a narrowing which affects at least the apex diameter of the first thread D_5C, and preferably also the bottom diameter of the first thread D_5R, and this in order to maintain the individual volume of each closed chamber 7 substantially or even exactly constant, while said chamber 7 is progressively transferred downstream by the rotational movement of the first screw 2.

[0095] In other words, the first channel 9 defined by the thread 5 of the first screw has, in the isochoric volumetric stage 11A, and preferably over the entire volumetric stage 11, a pitch P5 and a width W9 which increase progressively along the central axis X2, and more particularly which increase continuously according to an increasing function of the distance traveled along the central axis X2, so that each substantially annular portion of said first channel 9 which is delimited simultaneously by the first screw 2, by the inner wall of the sleeve 4 (or, equivalently, by the frustoconical envelope E2), and by the thread 6 of the second screw 3 which closes the ends of said portion of the first channel 9, so that said portion of the first channel 9 forms one of the chambers 7 closed at C,presents a volume which is invariant when said chamber 7 moves from upstream to downstream under the effect of the joint rotation of the first and second screws 2, 3, and, at each instant considered, which is equal to the volume of the neighboring closed chambers 7 of the same series of closed chambers 7.

[0096] The above considerations relating to the variation of the pitch P5 of the first thread 5, and therefore of the axial width W9 of the first channel 9, apply of course mutatis mutandis to the pitch P6 of the second thread 6 and the axial width W10 of the second channel 10, which, similarly, increase monotonically along the second central axis X3, so that the pitch P6 of the second thread evolves between a minimum value corresponding to an inlet pitch P6_in at the upstream end of the isochoric volumetric stage 11 A, which preferably coincides with the upstream end 11U of the volumetric stage 11, and a maximum value corresponding to an outlet pitch P6_out at the downstream end of the isochoric volumetric stage 11A, which preferably coincides with the downstream end 11D of the volumetric stage 11. Thus, the individual volume of each closed chamber 8 is kept substantially constant.

[0097] In all cases, to ensure a smooth meshing of the first and second screws 2, 3, the pitch P5 of the first thread 5 is equal to the pitch P6 of the second thread, at each abscissa considered along the bisector of the angle at the apex which is formed by the intersection of the first central axis X2 and the second central axis X3.

[0098] Of course, as can be clearly seen in figures 2, 4, 5, 6, 8 and 15, as is the case for the axial widths W9, W10 of the channels 9, 10, i.e. of the hollow portions of the first and second threads 5, 6, the axial width of the solid portion of the profile of the first thread 5 increases with the pitch P5 of said first thread 5, and similarly for the axial width of the solid portion of the profile of the second thread 6 which increases with the pitch P6 of said second thread 6, so that the first and second threads 5, 6 remain conjugate along the screws 2, 3, and thus maintain the sealing of the chambers 7, 8, by each occupying the entire width of the channel 10, 9 delimited by the thread 6, 5 of the other screw.In other words, in the isochoric volumetric stage 1 IA, and more preferably in the whole of the volumetric stage 11, each of the first and second threads 5, 6 simultaneously increases its pitch P5 and thickens its profile, along the central axis X2, X3, as the diameter of its conical screw 2, 3 decreases.

[0099] Preferably, the first compensation law LP5_11 is an increasing quadratic function of the value of axial abscissa considered along the first central axis X2.

[0100] Preferably, respectively, the second compensation law LP6_11 is an increasing quadratic function of the value of axial abscissa considered along the second central axis X3.

[0101] Advantageously, the first compensation law LP5_11 and the second compensation law LP6_11 can be expressed as a second-degree polynomial as a function of the axial abscissa.

[0102] Preferably, the first and second screws 5, 6 being images of each other, the first compensation law LP5_11 and the second compensation law LP6_11 will be identical.

[0103] The advantage of quadratic functions is that one can compensate by an increase in the pitch P5, P6 of the thread 5, 6 a narrowing which is surface, therefore two-dimensional, and which is linked to a joint narrowing of the apex diameter D_5C, D_6C of the thread 5, 6 and of the root diameter D_5R, D_6R of the thread 5, 6.

[0104] Indeed, preferably, in the isochoric volumetric stage 1 IA, and more preferably in the entire volumetric stage 11, the core 12 of the first screw 2 and the top of the thread 5 of this same first screw 2 shrink together, each according to a conicity angle, and more preferably according to the same conicity angle A5 so that they therefore follow overall, in a radial cutting plane containing the central axis X2, parallel slopes.

[0105] In other words, preferably, at least in the volumetric stage 11, the root diameter of the first thread D_5R decreases along the first taper angle A5, so that the height of the first thread H5 is constant along the first central axis X2, in said volumetric stage 11.

[0106] Advantageously, this makes it possible to limit the axial expansion of the pitch P5 of the thread 5, at each helical turn of the thread, necessary to maintain the constant cylinder size of the screw V2, but also to maintain a significant cylinder size of the first screw V2 and good circulation of the material in the channel 9. Conversely, it will be understood that if the height H5 of the first thread were decreasing, in particular decreasing sharply, for example with respect to a cylindrical core 12, then it would be necessary to greatly lengthen the pitch P5 of the thread 5 to maintain the constant cylinder size V2, which would require lengthening the screw 2 and would be potentially detrimental to the sealing of the chambers 7.

[0107] As an indication, it may be possible, for example, to retain, in particular in the volumetric stage 11, a thread pitch P5 which is less than the smallest diameter D_5C_min of the apex of said thread 5 in said volumetric stage 11.

[0108] Similarly, in the isochoric volumetric stage 1 IA, and more preferably in the entire volumetric stage 11, the core 13 of the second screw 3 and the top of the thread 6 of this same second screw 3 shrink together, each according to a taper angle, preferably according to the same taper angle A6 in order to follow globally, in a radial cutting plane containing the central axis X2, parallel slopes.

[0109] Thus, the apex diameter D_5C, D_6C of the thread 5, 6 of each of the first and second screws 2, 3, i.e., the external diameter of the screw 2, 3, as well as the root diameter D_5R, D_6R of said thread 5, 6, i.e., the internal diameter of said screw 2, 3, decrease continuously along the central axis X2, X3 of the screw 2, 3 considered, according to the same predetermined taper angle A5, A6, while the pitch P5, P6 of the thread 5, 6 increases continuously, in order to compensate for the joint decrease in the root diameter of the thread D_5R, D_6R and the apex diameter of the thread D_5C, D_6C, so that the successive closed chambers 7, 8 delimited by the screw 2, 3 considered each have an individual volume that is substantially constant. 7, 8 to the other, along the central axis X2, X3.

[0110] Thus, the thread height H5 of the first conical screw 2, referred to as "first thread height H5", is preferably constant along the central axis X2 of said first conical screw 2, at least in the volumetric stage 11.

[0111] The same will preferably apply to the thread height H6 of the second screw conical 3.

[0112] Typically, the thread height H5 of the first screw 2 designates, as shown in [Fig. 8], the distance between the midpoint of the bottom 5R of the first channel 9, considered axially midway between the two flanks 5F bordering said channel, and, on the one hand, the generatrix line tangent to the vertices 5C of the first thread bordering said first channel 9, i.e., the line corresponding to the intersection of the frustoconical envelope E2 with said radial cutting plane. In other words, the thread height H5 is the length of the line segment perpendicular to the generatrix of the frustoconical envelope E2 and passing through the midpoint of the bottom 5R of the first channel 9.

[0113] Similarly for the height H6 of the thread 6 of the second screw 3, considered perpendicular to the frustoconical envelope E3.

[0114] However, for convenience of calculation in what follows, we may also consider the projection H5', H6' of the thread height H5, H6 in a plane normal to the central axis X2, X3 of the screw 2, 3 considered.

[0115] Preferably, in the volumetric stage 11, whatever the angular position which is adopted respectively by each of the first and second screws 2, 3 around its central axis X2, X3 during the counter-rotating movement of said first and second screws 2, 3, the number of chambers 7 of the first series, which are simultaneously in a closed state, as well as the number of chambers 8 of the second series, which are simultaneously in a closed state, is equal to or greater than four, or even equal to or greater than five, lower limit, and preferably less than or equal to twenty, or even less than or equal to twelve, upper limit, for example between four and ten, or between five and eight.

[0116] The inventors have indeed found that it was necessary to provide an axial succession of several chambers 7, 8 along the same screw 2, 3, here at least four, or even at least five chambers, to obtain a satisfactory seal, and therefore a satisfactory volumetric operation, including in the presence of high pressures at the outlet of the extruder 1.

[0117] Conversely, the inventors also found that it was preferable to limit the number of chambers 7, 8 along a single screw 2, 3, and more generally the length L2, L3 of said screw 2, 3, typically by providing fewer than twenty, fewer than twelve, or even fewer than ten chambers along a single screw, in order in particular to avoid the risk of subjecting the material to excessive work, since excessive work would lead to excessive heating of the material, potentially detrimental to said material, so that the use of long screws 2, 3 multiplying the chambers 7, 8 would require to preventively reduce the rotation speed of screws 2, 3, thus causing a limitation of the maximum useful flow rate of extruder 1.

[0118] Furthermore, by limiting the length L2, L3 of the screws 2, 3, as well as the number of chambers, the resisting torque opposed by the material is reduced, and therefore the motor torque required to drive the screws 2, 3, which makes it possible to limit energy consumption while ensuring good efficiency, and in particular a good mass flow rate, of the extruder 1.

[0119] It should be noted that the aforementioned dimensioning is particularly suitable for the extrusion of a rubber-based material, since the short screw length limits the residence time of the extruded material in the extruder 1, a period during which the said extruded material is exposed to the work of the screws 2, 3. Overheating and therefore alteration of the rubber-based material are thus advantageously avoided.

[0120] It will also be noted that an extruder 1 according to the invention, when dedicated to the extrusion of a rubber-based material, does not require a large screw length L2, L3 to ensure satisfactory sealing, and in particular can be satisfied with an axial screw length L2, L3, more particularly a threaded axial length, which represents between 4 times and 10 times the maximum diameter of said screws 2, 3, unlike known extruders intended for thermoplastic materials and which, due to the high fluidity of such thermoplastic materials, must have a large length, typically on the order of 40 times the maximum diameter of the screw.

[0121] The extruder 1 according to the invention can thus be much shorter and lighter than known extruders, while retaining a satisfactory volumetric capacity.

[0122] The length L3 of the second screw 3, which here corresponds to the total threaded length of said second screw 3, is advantageously equal to the length L2 of the first screw 2, which here corresponds to the total threaded length of said first screw 2.

[0123] According to a preferred feature which may constitute an invention in its own right, the extruder 1 comprises a so-called "feeding stage" 30 which precedes the volumetric stage 11 and within which: - the first thread 5 is arranged so that, as the apex diameter D_5C of said first thread 5 decreases along the first central axis X2, in the upstream-downstream direction, according to the first taper angle A5, the pitch P5 of said first thread 5 also decreases, along the first central axis X2, in the upstream-downstream direction, in accordance with a law called the "first compression law" LP5_30, so as to promote compression of the material as it approaches the volumetric stage 11, and - the second thread 6 is arranged so that, as the apex diameter D_6C of the second thread 6 decreases along the second central axis X3, in the upstream-downstream direction, according to the second taper angle A6, the pitch P6 of the second thread 6 also decreases, along the second central axis X3, in the upstream-downstream direction, in accordance with a so-called "second law of compression" LP6_30, so as to promote compression of the material as it approaches the volumetric stage 11.

[0124] Advantageously, said feed stage 30 allows the material to be received, worked and pre-compressed in order to ensure the feeding of the volumetric stage, and thus on the one hand ensure good filling of the first chamber 7, 8 of each screw 2, which allows the effective displacement V2, V3 of each screw 2, 3 to be optimized, and on the other hand limit the pressure gradient between the upstream and downstream of the volumetric stage 11, which avoids leaks and material rising in the opposite direction to the desired FWD advance movement.

[0125] It will be noted that, advantageously, the first screw 2 and the second screw 3 cooperate in a non-volumetric way within the feeding stage 30, which allows in particular the use of a P5, P6 pitch of thread 5, 6 extended, and therefore of very wide channels 9, 10, which facilitates the insertion and feeding of the material into the extruder 1, in particular when said material arrives at the extruder in the form of a continuous strip.

[0126] Preferably, the smallest pitch P5, P6 of each screw 2, 3 considered in the feed stage 30, will be strictly greater than the longest pitch P5, P6 of this same screw 2, 3 considered in the volumetric stage 11, and more particularly in the isochoric volumetric stage 11 A.

[0127] As an indication, and always with the aim of maintaining wide channels favorable to the ingestion of the material, the initial pitch P5, P6 in the feed stage 30 will preferably be equal to or greater than 0.5 times the diameter D_5C, D_6C of the top of the thread 5, 6 considered at the upstream end of said feed stage 30.

[0128] Of course, an inlet port 41, possibly equipped with a hopper, can be provided in the sleeve 4, opposite the feed stage 30, to allow the material to enter the sleeve 4.

[0129] Preferably, said inlet orifice 41 shall open in the side wall of the sleeve 4, transversely to the first and second central axes X2, X3. Preferably, as shown schematically in dashed lines on [Fig.3], said inlet orifice 41 shall be located opposite the area where the meshing junction occurs between the first thread 5 and the second thread 6, such that, in projection into the reference plane defined by the first central axis X2 and the second central axis X3, the bisector of the vertex angle formed by the intersection of the first central axis X2 and the second central axis X3 is visible through the opening of the inlet orifice 41, and more preferably coincides with the sagittal plane of the inlet orifice 41.

[0130] Such an arrangement promotes the introduction of the incoming material, preferably in the form of a strip, between the first screw 2 and the second screw 3, and thus the pinching and driving of said material by the first and second threads 5, 6.

[0131] According to a possible alternative embodiment, illustrated in figures 1, 2 and 15, the first screw 2 and the second screw 3 can be single-threaded in the feed stage 30, and more preferably both in the feed stage 30 and in the volumetric stage 11.

[0132] Advantageously, we can thus have unique threads which extend continuously, but by adapting their pitch P5, P6, through the feed stage 30 and then the volumetric stage 11 of each screw 2, 3.

[0133] However, preferably, according to another embodiment, illustrated in Figures 3 and 4, in the feed stage 30, the first screw 2, and more preferably both the first screw 2 and the second screw 3, has multiple threads, preferably double thread, so that the first thread 5, respectively the second thread 6, comprises at least two threads which cover the same common axial extent and which are angularly phased with respect to each other around the central axis X2, X3 of the screw 2, 3 considered.

[0134] This multiplication of threads in the feed stage 30 makes it easier in particular to catch the material, especially when it is brought in the form of a strip, and to feed it in through the screws 2, 3.

[0135] This arrangement further improves the working of the material and its pressure rise to promote the feeding of the volumetric stage 11 located directly downstream of the feed stage 30.

[0136] On the other hand, preferably, the first screw 2 and the second screw 3 are each, in the volumetric stage 11, single-threaded.

[0137] The screws 2, 3 may then have a transition zone 31 between the feed stage 30 and the volumetric stage 11, allowing among other things to go from a multi-thread upstream to a single-thread downstream, and where appropriate to go from one core geometry 12, 13 to another core geometry 12, 13, for example to adapt the root diameter of the thread D_5R, D_6R and / or the taper angle of the core 12, 13.

[0138] Indeed, it will be noted that, preferably, the core 12 of the first screw 2 has, in the feed stage 30, a straight cylindrical shape, or a frustoconical shape whose taper angle is strictly less than the first taper angle A5.

[0139] Respectively, the core 13 of the second screw 3 preferably has, in the feed stage 30, a straight cylindrical shape, or a frustoconical shape whose taper angle is strictly less than the second taper angle A6.

[0140] Such an arrangement advantageously allows a relatively large root diameter D_5R, D_6R to be maintained in the feed stage 30, which allows a high motor torque to be transmitted to the screws 2, 3, and to keep a "reserve of diameter" from which the frustoconical reduction of the core 12, 13 can then be carried out in the isochoric volumetric stage 11A, without risk of structurally weakening the screws 2, 3 too much.

[0141] In addition, a low or even zero taper angle of the core 12, 13 in the feed stage 30 facilitates the reduction of the volume of the channels 9, 10 under the effect of the reduction of the pitch P5, P6 of the thread 5, 6, which therefore promotes the compression of the material and thus the feeding of the volumetric stage 11.

[0142] In the transition zone 31, as can be seen in Figures 3 and 4, the multiple threads of the feed stage 30 may terminate in the form of nozzles 32, which open the channels 9, 10 to allow the material to enter the chambers 7, 8 of the volumetric stage 11.

[0143] In practice, the respective isochoric volumetric stages 1 IA of the first and second conical screws 2, 3 can be dimensioned according to the method below, and with reference to figures 11, 12 and 13.

[0144] For the sake of brevity, we will describe the dimensioning of the first conical screw 2, knowing that the dimensioning of the second conical screw 3 will be carried out in a similar manner.

[0145] In absolute terms, one could foresee within the volumetric stage 11, in particular in an upstream axial portion of the volumetric stage 11 which would precede the isochoric volumetric stage 11 A, closed chambers 7, 8 in which one would not foresee an increase in the pitch P5, P6, in particular to obtain initially a reinforced compression effect, within the volumetric stage 11, between the first chamber and the second chamber of the series of chambers 7, 8 considered, after the filling of the first chamber by the supply stage 30.However, for convenience of description, we will preferably consider in what follows a preferred embodiment in which the entire volumetric stage 11 is concerned by the compensation law LP5_11, LP6_11, that is to say that the isochoric volumetric stage 11A extends to the entire volumetric stage 11, over the entire axial extent of the latter, so that the upstream and downstream axial limits of the isochoric volumetric stage 11A coincide with the upstream 11U and downstream 11D limits of the volumetric stage 11. .

[0146] The "large outside diameter" D_5C_max, D_6C_max will be designated as the apex diameter of the thread 5, 6 of the screw 2, 3, considered at the upstream end 11U of the isochoric volumetric stage 1 IA, which thus forms the diameter of the large circular base of the frustoconical envelope E2 of said isochoric volumetric stage 11A.

[0147] Similarly, the "small outside diameter" D_5C_min, D_6C_min, which is strictly less than the large outside diameter D_5C_max, D_6C_max, will be designated as the diameter of the top of the thread 5, 6 of the screw 2, 3, considered at the downstream end 11D of the isochoric volumetric stage 11A, which thus forms the diameter of the small circular base of the frustoconical envelope E2 of said isochoric volumetric stage 11 A.

[0148] Advantageously, the large outside diameter D_5C_max of the first screw 2 will be equal to the large outside diameter D_6C_max of the second screw 3, and the small outside diameter D_5C_min of the first screw 2 will be equal to the small outside diameter D_6C_min of the second screw 3.

[0149] To determine the compensation law LP5_11, we will first determine, at several different abscissas along the isochoric volumetric stage 11A, and more preferably at least at the upstream end 11U and at the downstream end 11D of the volumetric stage 1 IA, and preferably at one or more additional abscissas included between these ends, the radius of the top of the thread to be used to obtain the desired cylinder size V2, then we will interpolate the points thus defined by means of a second degree polynomial law, which will constitute the compensation law LP5_11 allowing us to define the top radius of the thread 5 at any abscissa of the isochoric volumetric stage 11A.

[0150] To this end, the displacement V2 of the first screw 2 is first determined, that is, the volume of extruded material that said screw 2 must expel each time said screw 2 completes a full rotation around its central axis X2. This displacement V2 corresponds in practice to the invariant individual volume V2 of the different chambers 7 in C of the first series of closed chambers 7. Said closed chambers 7 correspond to the different portions of the first channel 9 that follow one another along the first central axis X2 and which are each, on the one hand, contained between said screw 2 and the inner wall of the sleeve 4, and on the other hand, closed by the second thread 6 of the other screw 3, which penetrates the first thread 5 so as to locally close the first channel 9.

[0151] Reference is then made to the frustoconical envelope E2 of the isochoric volumetric stage 11A of the first screw 2 to calculate: - on the one hand the inlet radius R2_in, which corresponds to the radius of the apex 5C of the first thread 5 at the upstream end 11U of the isochoric volumetric stage 1 IA, and which is therefore equal to half of the large external diameter D_5C_max, which corresponds to the diameter of the large base of the truncated conical envelope E2, - and on the other hand, the outlet radius R2_out of the isochoric volumetric stage 1 IA, which corresponds to the radius of the apex 5C of the first thread 5 at the downstream end 11D of the isochoric volumetric stage 1 IA, and which is therefore equal to half the small diameter external D_5C_min, which corresponds to the diameter of the small base of the truncated conical envelope E2.

[0152] For this, we consider: - the length L1 IA of the isochoric volumetric stage 1 IA, which, like the displacement V2, is chosen by the designer, said length L2 being measured along the first central axis X2, that is to say along the line which carries the height of the frustoconical envelope E2 (and which therefore corresponds, in a cutting plane containing the first central axis X2, to the bisector of the angle at the apex of the frustoconical envelope E2), - the total length L_tot which corresponds to the height measured between the major base of the first frustoconical envelope E2 and the apex S2 of the cone of said first frustoconical envelope E2, - the taper angle A5 of the first screw 2, also chosen by the designer, preferably within the ranges of values ​​indicated above.

[0153] By simple trigonometry in a radial cutting plane containing the first central axis X2, and as illustrated in [Fig.7], we have: R2_in = L_tot * tan (A5) R2_out = (L_tot - L2) * tan (A5)

[0154] Knowing the chosen height H5 of the first thread 5, and therefore the projection H5' of said height in a plane normal to the central axis X2, we deduce a value Rl_in called "half apparent inlet center distance", which, in the plane of the large base of the first frustoconical envelope E2, which plane is normal to the first central axis X2, corresponds to the radial distance measured between on the one hand the central axis X2 and on the other hand the intersection Ml of the plane of the large base of the first frustoconical envelope E2 with a line XI which corresponds to the median axis of the extruder 1 and which runs equidistant from the first central axis X2 and the second central axis X3, in the plane which contains both the first central axis X2 and the second central axis X3: Rl_in = R2_in - (H5' / 2)

[0155] Similarly, in the plane of the small base of the first frustoconical envelope E2, the value Rl_out is deduced from the apparent half-center distance of the outlet: Rl_out = R2_out - (H5' / 2)

[0156] In the plane of the large base of the first truncated conical envelope E2, we then identify, as illustrated in [Fig. 13], the circular segment called "circular truncation segment at the entrance" 20_in, which corresponds to the domain between on the one hand the arc chord C20 which passes through the point of intersection M1 and which is perpendicular to the radius from the first central axis X2 and on the other hand the arc of the circle which is delimited by this arc chord C20 and whose radius corresponds to the entrance radius R2_in.

[0157] The area A20_in of this circular truncation segment at input 20_in is: A20_in = * (R2_in)2 * (alpha_in - sin(alpha_in)) where alpha_in represents the angle covered by the arc of the circle that delimits the circular truncation segment in input 20_in, and is therefore equal to: alpha_in = 2 * Arccos (Rl_in / R2_in)

[0158] Similarly, we consider the area of ​​the circular truncation segment at output 20_out: A20_out = Yi * (R2_out)2 * (alpha_out - sin(alpha_out)) where alpha_out represents the angle covered by the arc of the circle that delimits the circular segment 20_out, and is therefore equal to: alpha_out = 2 * Arccos (Rl_out / R2_out)

[0159] In the plane of the large base of the truncated cone shape E2, the area A7_in of the inlet chamber 7 is considered to be the difference between the ring between the bottom 5R of the first thread 5 and the top 5C of the first thread on the one hand, and the truncation area which is occupied by the thread 6 of the second screw 3 which enters the channel 9 of the first screw 2.

[0160] Said truncation area, of substantially oval shape, is equal, in view of the symmetrical arrangement of the first screw 2 and second screw 3, to twice Faire A20_in of the aforementioned circular truncation input segment 20_in.

[0161] Thus, insofar as, at the upstream end 11U of the isochoric volumetric stage 11A, the apex 5C of the first thread is located at a radius corresponding to the inlet radius R2_in, and the bottom 5R of the first thread at a radius located at a height H5' recessed from the apex 5C of the thread, we obtain: A7_in = ji * [(R2_in)2 - (R2_in - H5')2] - (2 * A20_in)

[0162] Similarly, in the plane of the small base of the frustoconical shape E2, we can define Faire A7_out of the outlet chamber 7, at the downstream end 2D of the first screw: A7_out = ji * [(R2_out)2 - (R2_out - H5')2] - (2 * A20_out)

[0163] The entry pitch P5_in, considered at the axial abscissa of the upstream end 2U of the first screw, is then defined as the ratio between the desired displacement V2 and Faire A7_in of the inlet chamber as defined above: P5_in = V2 / A7_in

[0164] Similarly, the output pitch P5_out at the downstream end 2D of the first screw 2 is defined as the ratio of the same constant displacement V2 to the output chamber A7_out (which is, in fact, smaller than the inlet chamber A7_in): P5 out = V2 / A7 out

[0165] Once these two extreme step values ​​P5_in, P5_out are fixed, the operation can be repeated in one or more intermediate abscissas, and a regression law, preferably a second-degree polynomial law, can be applied to the resulting point cloud, which will define the compensation law LP5_11.

[0166] The invention also relates, of course, to an installation 100 which, as can be seen in [Fig. 14], comprises an extruder 1 according to any one of the characteristics described above, for cutting a material, preferably a rubber-based mixture.

[0167] The installation 100 includes a frame 101. This frame advantageously forms a fixed reference frame, and can correspond to the floor of the building housing the installation, or to a chassis possibly fixed to the building.

[0168] The installation 100 also includes a receiving support 102, such as a tray, a drum or a toroidal core, which is intended to receive the material extruded by the extruder 1.

[0169] Said receiving support 102 is carried by the frame 101, and can be mounted movable relative to the frame 101. For example, in the case of a drum or a core forming a shape of revolution around a main axis Y102, said drum or said core can be mounted in rotation, preferably in motorized rotation, relative to the frame 101, around said main axis Y102.

[0170] The installation 100 further includes a robotic transport device 103, such as a Cartesian robot, as illustrated in [Fig.14], or an anthropomorphic robotic arm, which carries the extruder 1 and which is arranged so as to be able, while the extruder 1 is cutting the extruded material, to move said extruder 1 relative to the receiving support 102, in order to be able to place the extruded material in different locations of the receiving support 102, according to a desired predetermined arrangement.

[0171] The lightness and compactness of the extruder 1 according to the invention make it possible to use said extruder 1 within a mobile laying head 104, mounted on the robotic transport device 103.

[0172] The robotic transport device 103 which carries the extruder 1 is interposed between the frame 101 and the extruder 1 so as to be able, while the extruder cuts the extruded material, to move said extruder relative to the frame 101 and relative to the receiving support 102, according to a movement which is advantageously distinct, and controllable separately, from the possible own movement which animates the receiving support 102 relative to the frame 101.

[0173] Thus, the robotic transport device 103 will preferably be able to move the extruder 1 in translation along at least one axis, preferably at least two axes, or even three orthogonal axes in order to position the extruder 1 in the frame reference 101.

[0174] The robotic transport device 103 may, for example, include for this purpose at least one, preferably two, motorized translation plates 106, 107, for example two horizontal motorized translation plates 106, 107, which cross perpendicularly.

[0175] Furthermore, the robotic transport device 103 will preferably be able to move the extruder 1 in rotation along at least one axis, two axes, or even three axes to orient the extruder relative to the receiving support 102 in pitch, roll and / or yaw.

[0176] The laying head 104 shall include a die, connected at the output of the extruder 1, in order to give the extruded material an appropriate shape, for example the shape of a flattened ribbon.

[0177] The laying head 104 may also include an applicator element 105, such as a pressure roller 105, arranged to press against the receiving support the extruded material which exits the extruder 1 through the die.

[0178] The laying head 104, and more particularly the extruder 1, will preferably be fed by a continuous belt of material from a storage unit or a production unit.

[0179] The installation finally relates to an extrusion process using an extruder 1, or an installation 100, according to the invention.

[0180] In particular, the invention relates to the use of an extruder 1 according to the invention, or of an installation 100 according to the invention, for extruding a rubber-based mixture, for example to manufacture a part of a vehicle wheel tire, in particular a part of a pneumatic tire.

[0181] Thus, the extruder 1, and more generally the installation 100, can be arranged to place a strip of raw rubber on a drum or on a toroidal core.

[0182] Preferably, on this occasion, the extruder 1 will provide a mass flow rate greater than or equal to 1 kg / min, for example between 1 kg / min and 6 kg / min, for a rotational speed of each of the first and second screws 2, 3 which is less than or equal to 300 rpm, for example between 10 rpm and 300 rpm

[0183] These performances will preferably be achievable while the pressure at the outlet of the extruder, at the outlet of the last chamber 7, 8 and just at the entrance of the die, is between 150 bar and 500 bar, for a material temperature between 80°C and 150°C.

[0184] As indicated above, the invention may also relate as such to the presence and arrangement of a power supply stage 30, and in particular to the combination of such a stage with a volumetric stage 11, as well as in the proportions allocated to each of these stages to ensure proper operation of extruder 1 while maintaining the compactness of said extruder 1. Of course, the following considerations may apply by taking into account all or part of the different characteristics that have been detailed above.

[0185] Thus, the invention relates in particular as such to an extruder 1 intended for extruding a material, said extruder 1 comprising, as indicated above: - a barrel 4, - a first screw 2 which is mounted for rotation in the sleeve 4 around a first central axis X2 and which is provided with a first thread 5, - a second screw 3 which is mounted in rotation in the sleeve 4 around a second central axis X3 and which is provided with a second thread 6, said first screw 2 and second screw 3 being counter-rotating and arranged so that the first thread 5 and the second thread 6 cooperate to convey the material from upstream to downstream of the sleeve 4.

[0186] As mentioned above, preferably: - the first screw 2 is conical, so that the apex diameter D_5C of the first thread 5 decreases along the first central axis X2, in the upstream-downstream direction, according to a first predetermined taper angle A5, - the second screw 3 is conical, so that the apex diameter (D_6C) of the second thread 6 decreases along the second central axis X3, in the upstream-downstream direction, according to a second predetermined taper angle A6, and the extruder 1 includes a so-called "volumetric stage" 11 in which the first thread 5 of the first screw 2 and the second thread 6 of the second screw 3 are interpenetrated and conjugated with respect to each other so as to form on the one hand, between the sleeve 4 and the first screw 2, along the first central axis X2, a first series of successive closed C-shaped chambers 7 and on the other hand, between the sleeve 4 and the second screw 3, along the second central axis X3, a second series of successive closed C-shaped chambers 8, so that the rotation of the first and second screws 2, 3 generates a positive displacement of the material captured by the first series of chambers 7 and of the material captured by the second series of chambers 8.

[0187] The extruder 1 further preferably includes a so-called "feeding stage" 30 which precedes the volumetric stage 11 and in which the first thread 5 of the first screw 2 is arranged such that, as the apex diameter D_5C of said first thread 5 decreases along the first central axis X2, in the upstream-downstream direction, according to the first taper angle A5, the pitch P5 of said first thread 5 also decreases, along the first central axis X2, in the upstream-downstream direction, in accordance with a so-called "first compression law". "LP5_30, so as to promote compression of the material as it approaches volumetric stage 11.

[0188] Of course, it is preferably the same for the second screw 3, whose second thread 6 is arranged so that, as the apex diameter D_6C of the second thread 6 decreases along the second central axis X3, in the upstream-downstream direction, according to the second angle of taper A6, the pitch P6 of the second thread 6 also decreases, along the second central axis X3, in the upstream-downstream direction, in accordance with a so-called "second compression law" LP6_30, so as to promote compression of the material as it approaches the volumetric stage 11.

[0189] It should be noted that, in general, the characteristics, dimensioning rules, proportions, etc. indicated with reference to the first screw 2 may preferably be applied identically to the second screw 3.

[0190] As can be clearly seen in Figures 3, 4 and 16, the first screw 2 has, between the feed stage 30 and the volumetric stage 11, a transition zone 31 in which the first thread 5 has a thread interruption 40 which creates a break in continuity between the upstream portion of the first thread 5, which occupies the feed stage 30, and the downstream portion of the first thread 5, which occupies the volumetric stage 11.

[0191] Of course, preferably, the second screw 3 also has, between the feed stage 30 and the volumetric stage 11, a transition zone 31 within which the second thread 6 has a thread interruption 40 which creates a break in continuity between the upstream portion of the second thread 6, which occupies the feed stage 30, and the downstream portion of the first thread 5, which occupies the volumetric stage 11.

[0192] According to the invention, the axial length L11 of the volumetric stage 11, considered along the first central axis X2, represents at least 33%, preferably at least 36%, lower value, of the axial length L2 of the first screw 2, considered along the first central axis X2 from the upstream end 30U of the feed stage 30 to the downstream end 11D of the volumetric stage 11, and at most 65%, preferably at most 55%, upper value, of said axial length L2 of the first screw 2, considered along the first central axis X2 from the upstream end 30U of the feed stage 30 to the downstream end 11D of the volumetric stage 11, and more preferably is between 36% and 55% of said length L2 of the first screw 2.

[0193] It should be noted that the upstream end 30U of the power supply stage 30 corresponds here preferably, by convention, to the axial position of the upstream end of the upstream portion of the first thread 5 which extends within said power supply stage 30. Similarly, the downstream end 11D of the volumetric stage corresponds preferably, by convention, at the axial position of the downstream end of the downstream portion of the first thread 5 which extends within the volumetric stage 11.

[0194] Of course, the same is preferably true for the second screw 3, in which the axial length L11 of the volumetric stage 11 preferably represents at least 33%, preferably at least 36%, lower value, of the axial length L3 of the second screw 3, considered along the second central axis X3 from the upstream end 30U of the feed stage 30 to the downstream end 11D of the volumetric stage 11, and more preferably is between 36% and 55% of said length L3 of the second screw 3.

[0195] As indicated above, such a dimensioning makes it possible to reconcile, within the same length of screw L2, L3 relatively short, and therefore within a compact extruder 1, a high-performance volumetric stage 11, efficiently fed by the feeding stage 30, which delivers to said volumetric stage, under an adequate feeding pressure, a material well homogenized by the transition zone 31.

[0196] Preferably, as shown in Figures 3, 4 and 16: - the thread(s) constituting the upstream portion of the first thread 5, which occupy the feed stage 30, terminate, in the transition zone 31, by one or respectively of the nozzles 32, 32U, forming one or more upstream nozzles 32U, which open, at the level of the thread interruption 40, the channel(s) 9 delimited by the thread(s) constituting the upstream portion of the first thread 5; and / or: - the thread(s) constituting the downstream portion of the first thread 5, which occupy the volumetric stage 11, begin, in the transition zone 31, with one or respectively beaks 32, 32D, forming one or more downstream beaks 32D, which form, at the level of the thread interruption 40, one or respectively funnel inlets 42 according to which the flanks 5F of the thread(s) constituting the downstream portion of the first thread 5 converge to guide and compress the material towards the first series of chambers 7 formed, in the volumetric stage 11, between the sleeve 4 and the first screw 2.

[0197] The same is preferably true, mutatis mutandis, for the second screw 3.

[0198] Advantageously, the funnel-shaped inlets 42 formed by the downstream spouts 32D at the upstream mouth of the channel 9 of the volumetric stage 11 create a kind of convergent collector, the width of which narrows along the length of the downstream spout 32D, which promotes the admission, penetration and compression of the material in said channel 9, destined for the chambers 7.

[0199] Preferably, the 32, 32U, 32D of the first thread 5 are oriented at a helix angle which is strictly greater, in absolute value, than the helix angle of the thread of which the 32, 32U, 32D considered forms an end.

[0200] Thus, the nozzles 32, 32U, 32D have the effect of locally accentuating the helix angle, and therefore locally increasing the length of the pitch P5 of the first thread 5, and thus of folding back towards the first central axis X2 of the screw 2 considered the flank 5F of the thread against which the material flows; each nozzle 32, 32U, 32D thus locally orients said flank 5F in a direction which is closer to a parallel to the central axis X2 of the screw 2 considered than is the direction of this same flank 5F in the rest of the stage (feeding 30, or respectively volumetric 11) considered.

[0201] Thus, the upstream jaws 32U define maxima of the helix angle, and therefore of the pitch P5, of the upstream portion of the first thread 5, while the downstream jaws 32D define maxima of the helix angle, and therefore of the pitch P5, of the downstream portion of the second thread 5.

[0202] Thus, the deviation formed by the nozzles 32, 32U, 32D makes it possible to bring the helix angle of the thread considered, and therefore the pitch P5 of the thread 5, along the nozzle 32, to a value which is strictly greater, in absolute value, than the helix angle value or values, respectively than the pitch P5 value or values, which this same thread presents in the whole of the stage considered (feeding stage 30 or, respectively, volumetric stage).

[0203] Preferably, the deviation formed by the jaws 32, 32U, 32D allows the helix angle of the considered thread, along the jaw 32, to be brought to a value between 50 degrees and 65 degrees, for example equal to 57 degrees.

[0204] By convention, the upstream and downstream limits of the transition zone 31 can be considered to correspond to the axial position of appearance of the upstream beak 32U, respectively to the axial position of disappearance of the downstream beak 32D.

[0205] Equivalently, as can be clearly seen in [Fig. 16], the upstream and downstream limits of the transition zone 31 will correspond, along the main axis X2, X3 of the screw 2, 3 considered, to the abscissas respectively: - the reversal point of the compression law LP5_30, LP6_30, from which the pitch P5, P6 of the thread 5, 6 of the screw in question increases, in this case increases sharply along an abrupt slope, here up to the interruption 40 of the thread, after having experienced a monotonic decrease according to the compression law LP5_30, LP6_30, - and the reversal point of the compensation law LP5_11, LP6_11, from which, after an abrupt decrease, following the crossing of the interruption of the thread 40 and the downstream beak 32D, the pitch P5, P6 of the thread 5, 6 begins to increase again according to the said compensation law LP5_11, LP6_11, here preferably quadratic.

[0206] Moreover, preferably, the axial length L30 of the power supply stage 30, considered along the first central axis X2, represents at least 10%, at least 15%, at least 20%, or preferably at least 25%, for example between 25% and 30%, of the axial length L2 of the first screw 2, considered along the first central axis X2 from the upstream end 30U of the power supply stage 30 to the downstream end 11D of the volumetric stage 11.

[0207] This allows in particular an efficient intake and compression of the material by the feed stage 30, which then makes this material available to the volumetric stage 11.

[0208] More particularly, the axial extent of the axial length of the portion of the feed stage 30 to which the cylindrical core 12 is assigned, and therefore the axial length of said cylindrical core 12, will represent between 20% and 30%, for example 26%, of the axial length L2 of the first screw 2. This allows in particular good material intake by the feed stage 30.

[0209] The same will preferably apply to the second screw 3.

[0210] The length L2 of the first screw 2, and therefore preferably the length L3 of the second screw 3, preferably equal to the length L2 of the first screw 2, may preferably be between 50 mm and 400 mm, preferably between 200 mm and 350 mm, more preferably between 250 mm and 300 mm, for example equal to 265 mm.

[0211] This will allow us to obtain an extruder 1 that is particularly light, compact, and easy to handle, although it has high volumetric dosing accuracy and a high flow rate.

[0212] Furthermore, in the feed stage 30, and more particularly opposite the inlet port 41, typically on the axial range covered by the cylindrical core 12 of the screw 2 in the feed stage 30, the height H5 of the thread 5 will be adapted so as to promote the introduction of the material, and its capture and then its regular transport by the threads 5, 6 of the counter-rotating screws 2, 3.

[0213] For this purpose, when the material is supplied to the extruder 1 in the form of a continuous strip of given nominal thickness, then a thread height H5 of between 0.5 times and 2 times the nominal thickness of the strip will preferably be chosen, for example a height H5 equal to one times the thickness of the strip.

[0214] Thus, according to a preferred arrangement possibility, at the upstream end 30U of the power supply stage 30, and therefore here more particularly at the upstream end of the first thread 5, the first thread 5 has a height H5: - which is such that the ratio between, in the numerator, the said height H5, and, in the denominator, the radius R2_30U of the large base of the frustoconical envelope E2 of the first screw 2 considered at the upstream end 30U of the feed stage 30 is between 0.30 and 0.50, preferably between 0.40 and 0.45: 0.30 < H5 / R2_30U < 0.50, preferably 0.40 < H5 / R2_30U < 0.45 and / or: - which is between 10 mm and 15 mm, for example equal to 13 mm.

[0215] This is particularly applicable for a basic envelope diameter E2 (equal to 2 x R2_30U), i.e. a maximum diameter of the thread 5 at the upstream end of the feed stage 30, which is between 55 mm and 65 mm, in particular equal to 61 mm (i.e. a radius R2_30U of 30.5 mm).

[0216] Tests have shown that such a dimensioning advantageously allows the extruder 1 to be fed by strips, here rubber strips, whose thickness is between 8 mm and 17 mm.

[0217] As an indication, the height H5 of the thread may gradually decrease along the feed stage 30, for example to go from 13 mm at the upstream end 30U of said feed stage 30, to 10 mm at the arrival at the upstream nozzle 32U.

[0218] Thus, according to one possible arrangement, in the feed stage (30), the ratio between, in the numerator, the height H5 of the thread, and, in the denominator, the diameter D_5C of said thread 5, considered at the same abscissa as the height H5, decreases progressively from upstream to downstream, and remains between 0.25 and 0.15, more preferably between 0.22 and 0.18: 0.15 < H5 / D_5C < 0.25, preferably 0.18 < H5 / D_5C < 0.22.

[0219] This makes it possible in particular to improve the compression capacity of the extruder feed stage 30, which is thus able to raise the pressure of the material over a relatively short axial distance.

[0220] Using the example given above, we find:

[0221] At the upstream end of the feed zone 30, if H5 = 13 mm and D_5C = 2 x R2_30U = 61 mm, then H5 / D_5C = 13 / 61 = 0.21.

[0222] At the downstream end of the feed zone 30, if H5 = 10 mm and D_5C = 2 x R2_30U = 55 mm, then H5 / D_5C = 10 / 55 = 0.18

[0223] Of course, as explained above, at least part of the volumetric stage 11, which volumetric stage is located downstream of the feed stage and more particularly connected downstream of the feed stage 30 via the transition zone 31, preferably forms a stage called an "isochoric volumetric stage" 11 A, which may have any of the characteristics previously set out, in particular concerning the first screw 2, the second screw 3, or the combination of said first and second screws.

[0224] By way of sizing examples, the following configurations may be considered for screws 2, 3 having a length L2, L3 of 265 mm: 1st EXAMPLE Volumetric floor length (LU) = 145 mm, which is 55% (= 145 mm / 265 mm) of the screw length Feed stage length L30 = 80 mm, i.e. 30% of the screw length, of which 70 mm has a straight cylindrical core, i.e. 26% Length L31 of the transition zone 31 = 40 mm, i.e. 15% of the screw length. 2nd EXAMPLE LU = 95 mm, or 36% of the screw length L30 = 80 mm, or 30%, with a cylindrical core of 70 mm L31 = 90 mm, or 34%

[0225] Of course, the invention is by no means limited to the variant embodiments described above, the person skilled in the art being able in particular to isolate or freely combine one or the other of the aforementioned characteristics, or to substitute equivalents for them.

Claims

1. Demands Extruder (1) intended for extruding a material, said extruder (1) comprising: - a barrel (4), - a first screw (2) which is mounted for rotation in the sleeve (4) around a first central axis (X2) and which is provided with a first thread (5), - a second screw (3) which is mounted for rotation in the barrel (4) around a second central axis (X3) and which is provided with a second thread (6), said first screw (2) and second screw (3) being counter-rotating and arranged so that the first thread (5) and the second thread (6) cooperate to convey the material from the upstream to the downstream end of the barrel (4), said extruder (1) being characterized in that: - the first screw (2) is conical, so that the apex diameter (D_5C) of the first thread (5) decreases along the first central axis (X2), in the upstream-downstream direction, according to a predetermined first taper angle (A5), - the second screw (3) is conical, so that the apex diameter (D_6C) of the second thread (6) decreases along the second central axis (X3), in the upstream-downstream direction, according to a second predetermined taper angle (A6), in that said extruder (1) comprises a stage called "volumetric stage" (11) in which the first thread (5) of the first screw (2) and the second thread (6) of the second screw (3) are interpenetrated and conjugated with respect to each other so as to form on the one hand, between the barrel (4) and the first screw (2), along the first central axis (X2), a first series of successive closed C-shaped chambers (7) and on the other hand, between the barrel (4) and the second screw (3), along the second central axis (X3), a second series of successive closed C-shaped chambers (8), so that the rotation of the first and second screws (2, 3) generates a positive displacement of the material captured by the first series of chambers (7) and of the material captured by the second series of chambers (8), in that said extruder (1) also comprises a stage called the "feeding stage" (30) which precedes the volumetric stage (11) and within which the first thread (5) of the first screw (2) is arranged such that, as the apex diameter (D_5C) of said first thread (5) decreases along the first central axis (X2), in the upstream-downstream direction, according to the first taper angle (A5), the pitch (P5) of said first thread (5) also decreases, along the first central axis (X2), in the upstream-downstream direction, in accordance with a law called the "first compression law" (LP5_30), so as to promote compression of the material as it approaches the volumetric stage (11), in that the first screw (2) has, between the feeding stage (30) and the volumetric stage (11), a transition zone (31) within which the first thread (5) has a thread interruption (40) which creates a break in continuity between the upstream portion of the first thread (5),which occupies the feed stage (30), and the downstream portion of the first thread (5), which occupies the volumetric stage (H), and in that the axial length (L11) of the volumetric stage (11), considered along the first central axis (X2), represents at least 33%, preferably at least 36%, lower value, of the axial length (L2) of the first screw (2), considered along the first central axis (X2) from the upstream end (30U) of the feed stage (30) to the downstream end (11D) of the volumetric stage (11), and at most 65%, preferably at most 55%, upper value, of said axial length (L2) of the first screw (2), considered along the first central axis (X2) from the upstream end (30U) of the feed stage (30) to the downstream end (11D) of the stage volumetric (11), and more preferably is between 36% and 55% of said length (L2) of the first screw (2)...,

2. Extruder according to claim 1 characterized in that: - the thread(s) constituting the upstream portion of the first thread (5), which occupy the feeding stage (30), terminate, in the transition zone (31), by one or respectively nozzles (32, 32U), thus forming one or more upstream nozzles (32U), which open, at the level of the thread interruption (40), the channel(s) (9) delimited by the thread(s) constituting the upstream portion of the first thread (5) and / or in that: - the thread(s) constituting the downstream portion of the first thread (5), which occupy the volumetric stage (11), begin, in the transition zone (31), with one or respectively of the beaks (32, 32D), forming one or more downstream beaks (32D), which form, at the level of the thread interruption (40), one or respectively of the funnel inlets (42) according to which the flanks (5F) of the thread(s) constituting the downstream portion of the first thread (5) converge to guide and compress the material towards the first series of chambers (7) formed, in the volumetric stage (11), between the sleeve (4) and the first screw (2).

3. Extruder according to claim 2 characterized in that the nozzle(s) (32, 32U, 32D) of the first thread (5) are oriented at a helix angle which is strictly greater, in absolute value, than the helix angle of the thread of which the nozzle (32, 32U, 32D) considered forms an end, preferably so as to bring said helix angle of said thread, along the nozzle (32), to a value between 50 degrees and 65 degrees, for example equal to 57 degrees.

4. Extruder according to any one of the preceding claims characterized in that the length (L2) of the first screw (2) is between 50 mm and 400 mm, preferably between 200 mm and 350 mm, more preferably between 250 mm and 300 mm, for example equal to 265 mm.

5. Extruder according to any one of the preceding claims characterized in that, at the upstream end (30U) of the feed stage (30), the first thread (5) has a height (H5): - which is such that the ratio between, in the numerator, said height (H5), and, in the denominator, the radius (R2_30U) of the large base of the frustoconical envelope (E2) of the first screw (2) considered at the upstream end (30U) of the feed stage is between 0.30 and 0.50, preferably between 0.40 and 0.45; and / or: - which is between 10 mm and 15 mm, for example equal to 13 mm.

6. Extruder according to any one of the preceding claims characterized in that, in the feeding stage (30), the ratio between, in the numerator, the height (H5) of the thread, and, in the denominator, the diameter (D_5C) of said thread (5), considered at the same abscissa as the height (H5), gradually decreases from upstream to downstream, and remains between 0.25 and 0.15, more preferentially between 0.22 and 0.

18.

7. Extruder according to any one of the preceding claims characterized in that the axial length (L30) of the feed stage (30), considered along the first central axis (X2), represents at least 10% or preferably at least 25%, for example between 25% and 30%, of the axial length (L2) of the first screw (2), considered along the first central axis (X2) from the upstream end (30U) of the feed stage (30) to the downstream end (11D) of the volumetric stage (11).

8. Extruder according to any one of the preceding claims characterized in that the first taper angle (A5) and the second taper angle (A6) are each between 1.8 degrees and 3 degrees, preferably between 2 degrees and 2.5 degrees, even more preferably equal to 2.5 degrees.

9. Extruder according to any one of the preceding claims characterized in that, in the volumetric stage (11), regardless of the angular position adopted respectively by each of the first and second screws (2, 3) around its central axis (X2, X3) during the counter-rotating movement of said first and second screws (2, 3), the number of chambers (7) of the first series, which are simultaneously in a closed state, as well as the number of chambers (8) of the second series, which are simultaneously in a closed state, is equal to or greater than four, or even equal to or greater than five, lower limit, and preferably less than or equal to twenty, or even less than or equal to twelve, upper limit, for example between four and ten, or between five and eight.

10. An extruder according to any one of the preceding claims, characterized in that at least a portion of the volumetric stage (11) forms a stage called an "isochoric volumetric stage" (11A), within which: - the pitch (P5) of the first thread (5) increases along the first central axis (X2), in the upstream-downstream direction, as the crest diameter of the first thread (D_5C) decreases, according to a law called a "first compensation law" (LP5_11), which is preferably a quadratic increasing function of the axial abscissa value considered along the first central axis (X2), which first compensation law (LP5_11) allows the progressive increase of the pitch (P5) of the first thread (5) to compensate for the taper of the first screw (2) so that, in said isochoric volumetric stage (11 A), the individual volume of each of the closed chambers (7) of the first series of closed chambers remains equal to the same predetermined constant nominal volume (V2), called "first screw displacement" (V2), with a maximum tolerance of + / - 2%, preferably + / -1%, or even + / -0.5%.

11. Extruder according to claim 10 characterized in that the first screw (V2) and the second screw (V3) displacement are each between 8 cm3 and 50 cm3, for example between 10 cm3 and 30 cm3, in particular between 10 cm3 and 20 cm3.

12. Extruder according to any one of the preceding claims characterized in that, at least in the volumetric stage (11), the root diameter of the first thread (D_5R) decreases along the first taper angle (A5), so that the height of the first thread (H5) is constant along the first central axis (X2) in said volumetric stage.

13. Extruder according to any one of the preceding claims characterized in that the core (12) of the first screw (2) has, in the feed stage (30), a straight cylindrical shape, or a frustoconical shape whose taper angle is strictly less than the first taper angle (A5)

14. Extruder according to any one of the preceding claims characterized in that, in the feeding stage (30), the first screw (2) has multiple threads, preferably double thread, so that the first thread (5) comprises at least two threads which cover the same common axial extent and which are angularly phase-shifted relative to each other around the central axis (X2) of the screw (2) considered.

15. Extruder according to any one of the preceding claims characterized in that the first screw (2) and the second screw (3) are each, in the volumetric stage (11), single-threaded.

16. An installation (100) comprising an extruder (1) according to any one of claims 1 to 15 for cutting a material, preferably a rubber-based mixture, the installation also comprising a receiving support (102), such as a tray, a drum, or a toroidal core, which is intended to receive the material extruded by the extruder (1), and a robotic transport device (103), such as a Cartesian robot or an anthropomorphic robotic arm, which carries the extruder (1) and which is arranged so as to be able, while the extruder (1) is cutting the material, to move said extruder (1) relative to the receiving support (102), in order to be able to place the extruded material in different locations of the receiving support (102), according to a desired predetermined arrangement.

17. Use of an extruder (1) according to any one of claims 1 to 15, or of an installation (100) according to claim 16, for extruding a rubber-based mixture.

18. Use according to claim 17 characterized in that the extruder (1) provides a mass flow rate greater than or equal to 1 kg / min, for example between 1 kg / min and 6 kg / min, for a rotation speed of each of the first and second screws (2, 3) which is less than or equal to 300 rpm, for example between 10 rpm and 300 rpm.

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