A small volumetric extruder using twin conical screws, each with threads of increasing pitch to maintain a constant displacement.

Abstract

The invention relates to an extruder (1) comprising a first conical screw (2) and a second conical screw (3) mounted in a barrel (4) so ​​as to be counter-rotatable and defining volume stages (11) in which the threads (5, 6) interpenetrate with one another to form successive C-shaped closed chambers (7, 8) between the barrel (4) and the screws (2, 3), so as to provide a quantitative operation of the extruder (1), and in at least part of the volume stages the pitches (P5, P6) of the threads of the screws (2, 3) increase according to predetermined compensation laws (LP5_11, LP6_11), which are preferably quadratic, so that the successive closed chambers (7, 8) have individual volumes that remain equal to predetermined constant volumes (V2, V3), respectively, that define the displacement of the screws (2, 3).

Description

[Technical Field]

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

[0002] The invention is particularly applicable to the manufacture of elements for use in the production of tyres for vehicle wheels. [Background technology]

[0003] It is generally known that in extrusion operations, the flow rate of extruded material must be precisely controlled to avoid the production of non-conforming product and therefore waste of said product.

[0004] However, in practice, it can be difficult to ensure accurate control of the flow rate of such extrusion material during transitional stages of the extrusion process, such as start-up, shutdown, and restart stages of the extrusion line, in particular because the temperature of the extrusion tooling, on the one hand, and the speed of the moving mechanical parts of the extruder(s), on the other hand, are not stable during such transitional stages, which leads to fluctuations in the rheological properties and behavior of the extruded material.

[0005] To ensure control of the flow rate of extruded material, known practice has introduced what are known as "volumetric" extruders, in other words extruders equipped with moving mechanical parts such as pistons, gears or interpenetrating twin screws, configured to form one or more chambers therein which, under the influence of the cyclical movement of said moving mechanical parts, first open and increase their volume to accommodate an inflowing material, then close to take in a given amount of said material, and finally contract to mechanically expel said amount of material from the chamber.

[0006] Such an extruder is therefore capable of delivering a constant amount of extruded material, called the "displacement" of the extruder, which is constant with each new repetition of the extruder's cyclical operation, whatever the pressure at the extruder's outlet, i.e., a constant amount of extruded material which, in the above example, corresponds to each return stroke of the piston, or each rotation of the gear, or each rotation of the twin screw.

[0007] Furthermore, equipment using such metered extruders often has a multi-stage structure, with each stage formed by a selected type of extruder capable of performing all of the functions involved in feeding material into the equipment, plasticizing the material, increasing the pressure of the material, and dispensing the material at the outlet of the equipment.

[0008] Thus, for example, a known practice is to combine in series in the same installation a single screw extruder of the Archimedes screw type, which on the one hand is equipped with a screw rotatably mounted in a sheath to ensure the feeding of the material, plasticization by shear and a constant pressure and temperature rise, and on the other hand is equipped with a gear pump, the inlet port of which is connected to the outlet port of the single screw extruder and whose counter-rotating gears cooperate with a casing to ensure the final pressure rise and metering operation of the installation.

[0009] However, such equipment is particularly large and cumbersome.

[0010] This is especially true when these installations are intended for the extrusion of rubber-based materials. Specifically, it is necessary not to expose the rubber-based material to excessively high temperatures, i.e., not to rotate the gear pump wheel at excessively high speeds, so as not to damage the rubber-based material. Therefore, if you want to ensure a sufficient flow rate of the extruded material, you need to select a gear pump with a large displacement, and therefore large dimensions.

[0011] Co-extrusion facilities are also known, such as those described in the applicant's WO 2017 / 109419, in which a first stage formed by a feed screw feeds a second stage with twin interpenetrating screws, thereby ensuring constant feed rate operation. While this configuration has the advantage of allowing a relatively compact extrusion head to be used with an increased number of extrusion paths connected to the same extrusion head, ensuring a relatively high and well-controlled flow rate of each extrusion material, these facilities are nevertheless designed for co-extrusion applications aimed at producing complex profiles combining numerous extrusion materials, and the large number of extrusion paths results in a relatively large overall size.

[0012] Furthermore, known equipment can be relatively expensive to acquire as well as to operate, particularly due to energy consumption and complex maintenance requirements. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2017 / 109419 Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention therefore aims to overcome the above-mentioned drawbacks and to propose a compact extruder of reduced volume and weight while maintaining a satisfactory quantitative operation that allows excellent control of the flow rate of the extruded material. [Means for solving the problem]

[0015] The object of the present invention is to provide an extruder for extruding a material, comprising: - Barrel and a first screw rotatably mounted within the barrel about a first central axis and having a first thread; a second screw rotatably mounted within the barrel about a second central axis and having a second thread; Equipped with The first screw and the second screw are configured to counter-rotate, and the first thread and the second thread interact to convey material from upstream to downstream within the barrel, and the extruder is configured to: - the first screw is conical such that the crest diameter of the first thread decreases in an upstream-downstream direction along the first central axis according to a first predetermined angle of conicity; - the second screw is conical such that the top diameter of the second thread decreases in an upstream-downstream direction along the second central axis according to a second predetermined cone angle; the extruder comprises a stage referred to as a "volumetric stage," in which the first thread of the first screw and the second thread of the second screw are interpenetratingly paired with each other to form, on the one hand, a first series of continuous C-shaped closed chambers along a first central axis between the barrel and the first screw, and, on the other hand, a second series of continuous C-shaped closed chambers along a second central axis between the barrel and the second screw, so that rotation of the first and second screws generates a positive displacement of material entrained in the first series of chambers and material entrained in the second series of chambers; At least a portion of the volumetric stage forms a stage called an "isochoric volumetric stage," and within the isochoric volumetric stage: - the pitch of the first thread increases in the upstream-downstream direction along the first central axis as the top diameter of the first thread decreases, according to a law called the "first law of compensation", which allows a gradual increase in the pitch of the first thread to compensate for the conicity of the first screw, so that the individual volume of each closed chamber of the first series of closed chambers in said isovolume stage is equal to the same predetermined nominal isovolume, called the "first screw displacement", with a maximum tolerance of ±2%, preferably ±1%, or even ±0.5%; - the pitch of the second thread increases in the upstream-downstream direction along the second central axis as the top diameter of the second thread decreases, according to a law called the "second law of compensation", which allows a gradual increase in the pitch of the second thread to compensate for the conicity of the second screw, so that the individual volume of each closed chamber of the second series of closed chambers in said isovolume stages is equal to the same predetermined nominal isovolume, called the "second screw displacement", with a maximum tolerance of ±2%, preferably ±1%, or even ±0.5%; This is achieved by an extruder characterized by:

[0016] The extruder according to the invention advantageously can independently ensure plasticization of the material, pressure build-up and metered operation at precisely controlled flow rates, while occupying a relatively small space.

[0017] The thread arrangement according to the present invention, in which the pitch increases as the screw cone narrows in the isovolumetric stages, advantageously harmonizes the conicity of the screw with the constancy of the volume of each closed chamber as the screw rotates and the chambers progress from upstream to downstream along the central axis of the screw. Thus, the volume of extruded material taken up by the chamber opening at the upstream inlet of an isovolumetric stage is the same captive unit volume conveyed by each closed chamber between the screw and the barrel of the isovolumetric stage, and is the same volume discharged by the chamber opening at the downstream end of the isovolumetric stage. This constant unit volume advantageously corresponds to the volume of extruded material discharged per complete revolution of the screw, in other words, the displacement of the screw.

[0018] At each given moment, the volumes of the various closed chambers defined along the central axis by the same conical screw are constant, or quasi-constant taking into account the above-mentioned tolerances, in other words, said volumes do not substantially decrease or increase whatever position the closed chamber occupies along the axis, so that the material contained in the closed chambers is regularly transported from upstream to downstream of the extruder along the central axis of each screw.

[0019] This ensures a constant volume operation of each conical screw, while preventing problems with local overpressure that may arise if the trapped material in a closed chamber is excessively compressed by trying to reduce the volume of the chamber without giving the trapped material the possibility of leakage, and therefore problems with leakage between successive chambers of the same screw, or problems with local pressure drops and cavitation that may arise if increasing the volume of a closed chamber, i.e. increasing the volume available to the material without increasing the amount of material available in the chamber, tends to cause expansion of the trapped material in the chamber.

[0020] In this regard, it will be noted that, as will be seen below, it is advantageous to associate a feed stage with the volume stage upstream of the volume stage and within the same first and second screws, which allows processing and compression of the material so as to ensure the supply of the volume stage.

[0021] The conicity of the screw has several advantages.

[0022] The first advantage of conicity is that the upstream part of the screw has a large diameter, which corresponds to the large base of the frustoconical envelope in which the screw is inscribed, thus providing a wide passage for introducing material into the extruder and providing good conditions for performing the feeding function.

[0023] A second advantage of conicity is that the projected area of ​​the thread, considered in a plane perpendicular to the central axis of the screw, decreases along the axis and is therefore smallest at the downstream end of the conical screw, corresponding to the small base of the frustoconical envelope inscribed by the screw. Therefore, the projected area of ​​the thread is smallest precisely in the zone where the material exerts the highest pressure on the screw, necessary to overcome the pressure at the extruder outlet and propel the material through the extrusion die connected to the extruder outlet. Minimizing the projected area subjected to the pressure exerted on the screw by the extruded material reduces the resulting axial force that the material exerts on the screw and the bearings that support the screw and enable it to rotate within the barrel. This allows the size of these bearings to be safely reduced, thereby making the extruder more compact and lightweight.

[0024] A third advantage of the conical design is that the wetted area of ​​the screw, i.e., the area of ​​the screw that comes into contact with the material, is reduced compared to the same wetted area in a straight cylindrical screw having a constant diameter and an axial length equal to the length of the conical screw. The wetted area, along with the lever arm corresponding to the radial distance measured between the central axis of the screw and the given point at each point on the wetted area, reduces, thereby reducing the resistance torque that the material exerts on the screw due to its viscosity. Therefore, the extruder according to the present invention requires a relatively low driving torque, thereby reducing the size and weight of the motor(s) and reduction gear(s) that rotate the first and second screws.

[0025] For all these reasons, the present invention advantageously allows for the implementation of a compact, lightweight extruder that is relatively immune to mechanical inertia, thermal inertia and vibration.

[0026] Such extruders are lightweight and compact and can be attached to a transport device that allows for dynamic movement and positioning of the extruder relative to a receiving support on which a desired object is constructed, so that the object can be advantageously produced by three-dimensional printing by depositing extruded material in a desired amount at a desired location on the receiving support.

[0027] Further objects, features and advantages of the present invention will become more fully apparent from the following description taken in conjunction with the accompanying drawings, given for non-limiting illustrative purposes only, in which: [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a perspective view of a pair of first and second counter-rotating twin screws according to a first variant of the invention, in which the feed stage precedes the volume stage and each of the first and second screws is single-threaded. [Figure 2] FIG. 2 is a detailed top view of one screw of the screw pair of FIG. 1. [Figure 3] FIG. 1 is a perspective view of a pair of first and second counter-rotating twin screws according to a second variant of the invention, in which the feed stage precedes the volume stage and each of the first and second screws is double-threaded. [Figure 4] FIG. 4 is a top view of one screw of the screw pair of FIG. 3. [Figure 5] 4 is a perspective detail view of an equal-volume stage of a counter-rotating twin conical screw pair, such as the screw pair of FIG. 1 or the screw pair of FIG. 3, used in an extruder according to the present invention. [Figure 6] FIG. 6 is a top view of the screw pair of FIG. 5. [Figure 7] FIG. 7 is an end view of the screw pair of FIGS. 5 and 6, viewed from downstream. [Figure 8] 8 is a cross-sectional view taken along a plane including a first central axis of a first screw and a second central axis of a second conical screw of an equal-volume stage of an extruder according to the present invention, in which the screws of FIGS. 5 to 7 interact with a barrel to form two series of C-shaped closed chambers. [Figure 9] 1 is a perspective view of a volume stage of an extruder according to the present invention, specifically a volume defined along a first central axis by the first and last closed chambers of a first series of C-shaped closed chambers of an isovolumetric stage. FIG. [Figure 10] This figure shows an imaginary outer frusto-conical envelope surface, on the one hand inscribed with the crest of the first thread and thus corresponding to the overall frusto-conical envelope surface of the first screw, and on the other hand inscribed with the root of the first thread and thus corresponding to the frusto-conical envelope surface of the core of the first screw in equal volume stages, superimposed on the chamber of Figure 9. [Figure 11] FIG. 11 is a top view of the chamber and imaginary outer frustoconical envelope shown in FIGS. 9 and 10. [Figure 12] FIG. 12 is a side view of the chamber shown in FIGS. 9 to 11, seen from upstream of the screw. [Figure 13]FIG. 1 shows the principle of dimensioning the equal-volume stage of the first conical screw, conventionally arranged on a reference plane perpendicular to the first central axis and tangent to the upstream axial end of the equal-volume stage of the first conical screw. [Figure 14] FIG. 1 shows an example of an extrusion installation implementing a mobile laying head holding an extruder with twin conical screws according to the present invention. [Figure 15] FIG. 3 shows an example of dimensioning laws for the threads of a conical screw used according to the invention, showing a quadratic increase in thread pitch in the isovolumetric stage and a decrease in thread pitch in the feed stage preceding said isovolumetric stage, with preferential reference to the first variant shown in FIGS. 1 and 2 . DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention relates to an extruder 1 for extruding materials, in particular to an extruder 1 of the "twin-screw" type.

[0030] The extruder comprises a barrel 4, in a manner known per se, preferably made of metal.

[0031] As can be clearly seen from FIGS. 1 to 8, the extruder 1 includes: a first screw 2 having a first thread 5, mounted rotatably within the barrel 4 about a first central axis X2; a second screw 3 having a second thread 6, mounted rotatably within the barrel 4 about a second central axis X3; Equipped with.

[0032] The first and second screws 2, 3 are arranged to counter-rotate, with the first thread 5 and second thread 6 interacting to transport material from upstream to downstream within the barrel 4, the overall forward motion being designated here as "FWD."

[0033] For convenience of explanation, the "axial direction" refers to a direction parallel to the central axes X2 and X3 of the screws 2 and 3, and the "radial direction" refers to a direction perpendicular to the central axes X2 and X3 of the screws 2 and 3.

[0034] The first central axis X2 and the second central axis X3 geometrically intersect with each other.

[0035] "Counter-rotating" means that the first screw 2 and the second screw 3 rotate in opposite rotational directions.

[0036] Furthermore, said first and second screws 2, 3 are synchronous, i.e. they advantageously rotate at rotational speeds of opposite sign but equal in absolute value.

[0037] The first thread 5 may have a single screw thread according to the stage of the first screw 2 considered along the first central axis X2, or in a variant may have multiple screw threads with the same pitch but angularly offset.

[0038] The term "first channel" 9 means the helical groove defined between two solid profiles of the first thread 5 that are axially adjacent to one another, i.e., the helical groove that separates two solid profiles of the first thread 5 that are one immediately adjacent to the other, or each helical groove in the case of multiple screw threads.

[0039] Similarly, the second thread 6 may have one or more screw threads, preferably equal in number to the number of screw threads of the first thread 5 with which the second thread 6 interacts, depending on the stage of the second screw considered along the second central axis X3.

[0040] The term "second channel" 10 means the helical groove defined between two solid profiles of the second thread 6 that are axially adjacent to one another, i.e., the helical groove separating two solid profiles of the second thread 6 that are one immediately adjacent to the other, or each helical groove in the case of multiple screw threads.

[0041] The direction of the first thread 5 is opposite to the direction of the second thread 6; in other words, the first screw 2 can have a left-handed thread 5 while the second screw 3 has a right-handed thread 6, or conversely, the first screw 2 can have a right-handed thread 5 while the second screw 3 has a left-handed thread 6.

[0042] More generally, the second screw 3 is preferably a mirror image of the first screw 2, so that symmetry allows the properties of one to be equally inferred from the properties of the other.

[0043] According to the invention, the first screw 2 is conical such that the top diameter D_5C of the first thread 5 decreases in the upstream-downstream direction along the first central axis X2 according to a first predetermined angle of conicity A5.

[0044] Similarly, the second screw 3 is conical such that the top diameter D_6C of the second thread 6 decreases in the upstream-downstream direction along the second central axis X3 according to a second predetermined cone angle A6.

[0045] As can be seen in Figures 2, 4, 6, 8 and 11, the conical angles A5, A6 correspond to the inclination angles formed by imaginary truncated conical envelope surfaces E2, E3 that are tangent to the continuous crests 5C, 6C of the threads 5, 6 of the screws 2, 3, in a plane including the central axes X2, X3 of the screws 2, 3, relative to an imaginary right cylinder having a circular base and centered on the central axes X2, X3, and in which the screws 2, 3 are inscribed.

[0046] Equivalently, the conicity angles A5, A6 correspond to the half-angles at the vertices of the imaginary envelopes E2, E3 inscribed by the screws 2, 3, and therefore to the angles formed between the central axes X2, X3 and the respective generatrix lines of the inclined walls of the imaginary frustoconical envelopes E2, E3 inscribed by the screws 2, 3.

[0047] In fact, the first cone angle A5 is equal to the second cone angle A6.

[0048] Specifically, as can be seen in FIG. 11, the first central axis X2 and the second central axis X3 geometrically intersect, so that the first conical angle A5 and the second conical angle A6 are each equal to half the angle at the apex formed by the intersection of the first central axis X2 and the second central axis X3.

[0049] Consequently, the inner wall of barrel 4, which interacts with one of screws 2, 3, also has a conical profile that matches the conical profile of said screws 2, 3, i.e., that generally follows the same imaginary frustoconical envelope surface circumscribing said frustoconical envelope surfaces E2, E3. Thus, the inner wall of barrel 4 generally narrows in the upstream-downstream direction FWD within barrel 4, with the same conical angles A5, A6 as screws 2, 3.

[0050] Preferably, the first conical angle A5 and the second conical angle A6 are each between 1.8 degrees and 3 degrees, preferably between 2 degrees and 2.5 degrees, and more preferably equal to 2.5 degrees.

[0051] In fact, the inventors have found that for a given screw length and therefore a given volume, these values ​​of the cone angle correspond to a good compromise between, on the one hand, the resistance forces on the screws 2, 3 which it is desirable to minimize, and, on the other hand, the capacity of the screws to receive and utilize a relatively high driving torque.

[0052] in particular, i) the terminal surfaces of the screws 2, 3 corresponding to the small bases of the frustoconical envelopes E2, E3 inscribed by the screws 2, 3 are significantly reduced, resulting in a significant reduction in the axial forces resulting from the pressure of the extrusion material on the screws 2, 3, thereby reducing the size of the bearings and axial stops that axially support the screws 2, 3; ii) a sufficient centre distance can be formed between the first screw 2 and the second screw 3 to provide sufficient space in the upstream zones 2U, 3U of the screws 2, 3 to accommodate a solid and powerful reduction gear and a large diameter shaft capable of driving the screws 2, 3 and providing a high driving torque to each of them; The cone angles A5 and A6 are large enough to i) the diameter of the screws 2, 3 in the upstream zones 2U, 3U remains small enough to avoid presenting the extruded material with a strong lever arm relative to the central axes X2, X3 of the screws and thus limit the resistance torque that said extruded material exerts on the rotation of the screws 2, 3; ii) the screws 2, 3 are not too thin at their tips, i.e. the cores of the first screw 2 and the second screw 3 have a sufficient material thickness up to and including the downstream ends 2D, 3D of said screws 2, 3 to be able to support and transmit high driving torques without damage, in particular without irreversible deformation in torsion; The cone angle A5 and A6 are just right, Seek the best compromise between

[0053] In light of the above-mentioned conicity angle values ​​A5 and A6, the angle at the apex formed by the (imaginary) intersection of the first central axis X2 and the second central axis X3, which is equal to the sum of the two apex angles A5 and A6, and therefore more preferably equal to twice the apex angle A5, is 3.6 degrees to 6 degrees, and preferably equal to 5 degrees.

[0054] According to the invention, the extruder 1 comprises a stage 11 called the "volume stage", in which the first thread 5 of the first screw 2 and the second thread 6 of the second screw 3 are interpenetratingly paired with each other so as to form, on the one hand, a first series of continuous C-shaped closed chambers 7 along a first central axis X2 between the barrel 4 and the first screw 2, and, on the other hand, a second series of continuous C-shaped closed chambers 8 along a second central axis X3 between the barrel 4 and the second screw 3, so that rotation of the first and second screws 2, 3 generates a positive displacement of the material taken up in the first series of chambers 7 and of the material taken up in the second series of chambers 8.

[0055] "Interpenetrating" means, as can be clearly seen in Figures 1, 3, 5, 6 and 8, that the first and second threads 5, 6 are arranged so that the crest 5C of the first thread 5 substantially reaches the root 6R of the second thread 6, and conversely, the crest 6C of the second thread 6 substantially reaches the root 5R of the first thread 5, so that the threads 5, 6 of each screw 2, 3 penetrate into the channels 10, 9 defined by the threads 6, 5 of the other screw 3, 2 over the entire radial height of said channels 10, 9.

[0056] For reference, a functional radial clearance JR1 is provided between the crests 5C, 6C of one thread and the roots 6R, 5R of the other thread, which is of course not zero to ensure smooth relative movement of the one screw 2 with respect to the other screw 3, but most importantly is preferably 0.3 mm or less to ensure leak-free, quantitative operation.

[0057] By "paired", as can be clearly seen in Figures 1, 3, 5, 6 and 8, we mean that the first thread 5 and the second thread 6 are arranged in such a way that the entire axial width of the first thread 5, in other words the axial width of the entire cross-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 axially delimited between two consecutive flanks 6F of the second thread 6, and conversely, the entire axial width of the second thread 6 fills the axial width of the first channel 9 defined by the first thread 5 and axially delimited between two consecutive flanks 5F of the first thread 5. Thus, the flanks 5F of the first thread substantially coincide with the flanks 6F of the second thread, and vice versa.

[0058] For reference, to ensure leak-free metered operation, a functional axial clearance JA1 of 0.3 mm or less may be provided between the nearest portions of the flanks 5F, 6F of one thread and the flanks 6F, 5F of the other thread.

[0059] For the same operational reasons and reasons of airtightness during operation, a radial clearance JR2 is provided between the thread crests 5C, 6C of the screws 2, 3 and the radially innermost part of the wall of the barrel 4 with which the thread crests 5C, 6C interact, particularly in the volume stage 11, which is non-zero and preferably less than or equal to 0.1 mm.

[0060] As shown schematically in Figures 8, 9, 10 and 11, each of the first and second series of chambers 7, 8 formed in the volume stage 11 advantageously allows material to be taken into a first chamber 7, 8 forming an upstream access to the volume stage 11, which first confines the extruded material by rotation of the screws 2, 3 to retain a corresponding amount of the extruded material captured inside the closed chamber separated by a C-shaped space between the screws 2, 3 and the barrel 4, and then the rotational movement of the screws 2, 3 gradually moves the chambers 7, 8 downstream 2D, 3D along the central axes X2, X3 with an overall translational forward movement, denoted here as FWD, thereby allowing the material in the closed chambers 7, 8 to be transported downstream 2D, 3D.

[0061] Originally, 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 volumes of extruded material contained in each of the other chambers 7, in particular each of the adjacent chambers. Advantageously, therefore, whatever the pressure at the downstream ends 2D, 3D of the conical screws 2, 3, at the point where the last chamber 7, 8 of the series of chambers 7, 8 opens into the outlet of the extruder 1, the extruded material will not return upstream 2U, 3U along the screws 2, 3.

[0062] Thus, each complete revolution of the screws 2, 3 displaces the chambers 7, 8 downstream 2D, 3D, thus advancing the extruded material along the axis X2, X3 of the respective screw an axial distance equal to the pitch P5, P6 of the threads 5, 6 at that position.

[0063] The amount of extrusion material delivered to the outlet of extruder 1 per complete revolution of screws 2, 3, in other words the total "displacement" of extruder 1, corresponds to the sum of the unit volumes accommodated in the last closed chamber 7 of the first series of chambers 7 defined by first screw 2 and the last closed chamber 8 of the second series of chambers 8 defined by second screw 3, i.e. the sum of the displacements of first screw 2 and second screw 3.

[0064] This volume displacement of the extruder 1 makes it possible to precisely adjust the flow rate of the extruded material by adjusting the rotation speed of the screws 2, 3.

[0065] Advantageously, the fact that each screw 2, 3, together with the barrel 4, generates a plurality of chambers 7, 8 axially connected to one another and separated from one another by the threads 5, 6 of the screws 2, 3, enhances the overall tightness of the extruder 1 and makes it possible to reduce the sensitivity of this tightness to wear of the screws 2, 3 by creating a great number of continuous obstacles to the possibility of the extruded material retreating between the barrel 4 and the screws 2, 3 in the direction from downstream 2D, 3D along the barrel 4 to upstream 2U, 3U.

[0066] According to the present invention, and as can be clearly seen in Figures 1, 3, 5, 6, 8 and 15, at least a portion of the volume stage 11, more preferably the entire volume stage 11, forms a stage called an "isovolumetric stage" 11A, and within this isovolumetric stage: - the pitch P5 of the first thread 5 increases in the upstream-downstream direction along the first central axis X2 as the top diameter D_5C of the first thread decreases, according to a law called "first compensation law" LP5_11, which allows a gradual increase of the pitch P5 of the first thread 5 to compensate for the conicity of the first screw 2, so that the individual volume of each closed chamber 7 of the first series of closed chambers in said isovolume stage 11A is equal to the same predetermined nominal isovolume V2, called "first screw displacement" V2, with a maximum tolerance of ±2%, preferably ±1%, or even ±0.5%, - the pitch P6 of the second thread 6 increases in the upstream-downstream direction along the second central axis X3 as the top diameter D_6C of the second thread decreases, according to a law called the "second compensation law" LP6_11, which gradually increases the pitch P6 of the second thread 6 to compensate for the conicity of the second screw 3, so that the individual volume of each closed chamber 8 of the second series of closed chambers in said isovolume stage 11A is equal to the same predetermined nominal isovolume V3, called the "second screw displacement" V3, with a maximum tolerance of ±2%, preferably ±1%, or even ±0.5%.

[0067] In other words, each of the closed chambers 7 defined by the first screw 2 and barrel 4 will have an individual volume that is substantially or exactly equal to the individual volume of the adjacent chamber 7 and that is substantially or exactly equal to the volume of the first screw displacement V2, i.e., in this case equal to V2±2%, preferably equal to V2±1%, or even equal to V2±0.5%.

[0068] Similarly, each of the closed chambers 8 defined by the second screw 3 and barrel 4 will have an individual volume that is substantially or exactly equal to the individual volume of the adjacent chamber 6 and that is substantially or exactly equal to the volume of the second screw displacement V3, i.e., in this case equal to V3±2%, preferably equal to V3±1%, or even equal to V3±0.5%.

[0069] Therefore, from a dynamic point of view, the individual volume of each C-shaped closed chamber 7, 8, during its movement from upstream to downstream of the isovolume stage 11A under the influence of the rotation of the screws 2, 3, more preferably from the closure of said chambers 7, 8 at the upstream boundary 11U of the volume stage 11 to the reopening of the chamber at the downstream boundary 11D of the volume stage 11, which in this case is the outlet of the extruder 1, varies by less than 2%, by less than 1%, or even by less than 0.5% of the reference individual volume constituted by the screw displacements V2, V3, or is equal to said reference individual volume, over all successive axial positions occupied by said closed chambers 7, 8.

[0070] Equivalently, considering a static vision of the distribution of chambers 7, 8 in the same series of chambers at a given moment, rather than a dynamic vision of the movement of the chambers along the axis, it can be said that all closed chambers 7, 8 in the series of closed chambers 7, 8 defined by the screws 2, 3 in question have substantially or exactly the same individual volumes equal to within ±2%, preferably within ±1% or even ±0.5% of the nominal unit volume.

[0071] It should be noted that the arrangement proposed by the present invention is preferably at an outlet pressure which may be between 200 bar and 500 bar and at 1 dm 3 / min~6dm 3 This enables the extruder 1 to guarantee a volumetric flow rate accuracy of less than 2%, or even less than 1%, in other words to deliver a constant volume per screw revolution within ±2%, or even ±1% for a volumetric flow rate of 1 / min.

[0072] The first screw displacement amount V2 is preferably equal to the second screw displacement amount V3.

[0073] The first screw displacement V2 and the second screw displacement V3 are each 8 cm 3 ~50cm 3 For example, 10cm 3 ~30cm 3 and especially 10cm 3 ~20cm 3 It is preferable that:

[0074] As mentioned above, the pitch P5 of the first thread 5 gradually increases in the upstream-to-downstream direction along the first central axis X2 of the first screw 2 as the diameter of the first screw 2 decreases in the equal volume stages 11A, and more preferentially throughout the entire volume stage 11, so that the pitch P5 at the downstream end 11D of the volume stage of the first screw 2 in the last chamber 7 forming the outlet chamber of the first screw 2 is strictly greater than the pitch P5 at the upstream end 11U of the volume stage of the first screw 2 in the first chamber 7 forming the inlet chamber.

[0075] The increase in pitch P5 of this first thread 5 is preferably monotonic, and more preferably linear, along the central axis X2 between, on the one hand, a value of said pitch P5 called the "inlet pitch" P5_in considered at the upstream end of the equal volume stage 11A, which in this case is the upstream end 11U of the volume stage 11, and, on the other hand, a larger value of pitch P5 called the "outlet pitch" P5_out considered at the downstream end of the equal volume stage 11A, which in this case is the downstream end 11D of the volume stage 11.

[0076] As can be clearly seen in Figures 1, 2, 3, 8, 9 and 11, this variation in the pitch P5 of the first thread 5, which in this case is a continuous increase of said pitch P5 along the central axis of the first screw 2 throughout the entire isovolume stage 11A, and more preferably throughout the entire volume stage 11, makes it possible to gradually increase the axial width W9 of the channel 9 defined by the first thread 5 and to compensate for the corresponding variation, which in this case is a continuous decrease in the diameter of the first screw 2, a decrease that affects at least the crest diameter D_5C of the first thread and preferably also the root diameter D_5R of the first thread, in order to gradually move said chambers 7 downstream by the rotational movement of the first screw 2 while keeping the individual volume of each closed chamber 7 substantially or exactly constant.

[0077] In other words, the first channel 9 defined by the thread 5 of the first screw has a pitch P5 and a width W9 that, in the equal volume stage 11A, preferably gradually increase along the central axis X2 throughout the entire volume stage 11, specifically that increase continuously according to an increasing function of the distance traveled along the central axis X2, so that each substantially annular portion of the first channel 9 defined simultaneously by the first screw 2, the inner wall of the barrel 4 (or equivalently the frustoconical envelope E2), and the thread 6 of the second screw 3, which closes the end of that portion of the first channel 9, thus forming one of the C-shaped closed chambers 7, has a volume that does not change as the chamber 7 moves from upstream to downstream under the influence of the joint rotation of the first and second screws 2, 3, and this volume is equal to the volume of the adjacent closed chamber 7 of the same series of closed chambers 7 at each given moment.

[0078] Naturally, the above considerations regarding the variation of the pitch P5 of the first threads 5 and thus of the axial width W9 of the first channels 9 also apply mutatis mutandis to the pitch P6 of the second threads 6 and the axial width W10 of the second channels 10, which also increase monotonically along the second central axis X3, so that the pitch P6 of the second threads transitions between a minimum value corresponding to the inlet pitch P6_in at the upstream end of the equal volume stage 11A, which preferably coincides with the upstream end 11U of the volume stage 11, and a maximum value corresponding to the outlet pitch P6_out at the downstream end of the equal volume stage 11A, which preferably coincides with the downstream end 11D of the volume stage 11. The individual volume of each closed chamber 8 is therefore kept substantially constant.

[0079] In either case, to ensure smooth engagement of the first and second screws 2, 3, the pitch P5 of the first screw 5 is equal to the pitch P6 of the second screw in each abscissa considered to be along the bisector of the apex angle formed by the intersection of the first central axis X2 and the second central axis X3.

[0080] 2, 4, 5, 6, 8 and 15, as is the case with the axial widths W9, W10 of the channels 9, 10, i.e. the widths 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 the first thread 5, and similarly the axial width of the solid portion of the profile of the second thread 6 increases with the pitch P6 of the second thread 6, so that the first and second threads 5, 6 are paired along the screws 2, 3, each occupying the entire width of the channel 10, 9 defined by the threads 6, 5 of the other screw while maintaining the airtightness of the chambers 7, 8. In other words, each of the first and second threads 5, 6 simultaneously increases in pitch P5 along the central axis X2, X3 as the diameter of its conical screw 2, 3 decreases in the equal volume stage 11A, and more preferably throughout the volume stage 11.

[0081] The first compensation law LP5_11 is preferably an increasing quadratic function of the axial abscissa value along the first central axis X2.

[0082] The second compensation law LP6_11 is preferably an increasing quadratic function of the abscissa value in the axial direction along the second central axis X3.

[0083] Advantageously, the first compensation law LP5_11 and the second compensation law LP6_11 can be expressed in the form of a second order polynomial as a function of the axial abscissa.

[0084] Since the first and second screws 5, 6 are images of each other, the first compensation law LP5_11 and the second compensation law LP6_11 are preferably identical.

[0085] The advantage of the quadratic function is that an increase in the pitch P5, P6 of the threads 5, 6 compensates for the decrease in surface area, and therefore in the second dimension, associated with a decrease in both the crest diameter D_5C, D_6C of the threads 5, 6 and the root diameter D_5R, D_6R of the threads 5, 6.

[0086] Specifically, preferably in the equal volume stage 11A, and more preferably throughout the entire volume stage 11, the core 12 of the first screw 2 and the crests of the threads 5 of this same first screw 2 each narrow according to a conical angle, more preferably according to the same conical angle A5, so that they generally follow parallel slopes in a radial cross section including the central axis X2.

[0087] In other words, at least in the volume stage 11, the root diameter D_5R of the first thread decreases according to the first conicity angle A5, and therefore, in the volume stage, the height H5 of the first thread preferably varies along the first central axis X2 by less than 20%, preferably less than 10%, and more preferably less than 5%. For example, the height H5 of the first thread is constant along the first central axis X2.

[0088] This advantageously makes it possible to limit the axial expansion of the pitch P5 of the thread 5 with each helical revolution of the thread, which is necessary not only to keep the screw displacement V2 constant, but also to maintain a significant first screw displacement V2 and a good circulation of material in the channel 9. It will be appreciated that otherwise, if the height H5 of the first thread were to decrease, for example, relative to the cylindrical core 12, especially if it were to decrease too rapidly, it would be necessary to significantly increase the pitch P5 of the thread 5 in order to keep the displacement V2 constant, which would require lengthening the screw 2 and which would potentially compromise the tightness of the chamber 7.

[0089] For reference, for example, in particular in the volume stage 11, it is possible to maintain a thread pitch P5 smaller than the minimum top diameter D_5C_min of the thread 5 in the volume stage 11.

[0090] Similarly, in the equal volume stage 11A, and more preferably throughout the entire volume stage 11, the core 13 of the second screw 3 and the crests of the threads 6 of this same second screw 3 each narrow according to a conical angle, more preferably according to the same conical angle A6, and therefore generally follow parallel slopes in a radial cross section including the central axis X2.

[0091] Thus, the crest diameters D_5C, D_6C of the threads 5, 6 of each of the first and second screws 2, 3, i.e., the outer diameters of the screws 2, 3, and the root diameters D_5R, D_6R of the threads 5, 6, i.e., the inner diameters of the screws 2, 3, decrease along the central axes of the screws according to the same conicity angles A5, A6, whereas the pitches P5, P6 of the threads 5, 6 increase continuously to compensate for the joint decrease of the thread root diameters D_5R, D_6R and the thread crest diameters D_5C, D_6C, so that the successive closed chambers 7, 8 defined by the screws 2, 3 have individual volumes that are substantially constant from one closed chamber 7, 8 to the next along the central axes X2, X3, respectively.

[0092] Therefore, at least in the volume stage 11, the thread height H5 of the first conical screw 2, referred to as the "first thread height H5", is preferably constant along the central axis X2 of the first conical screw 2.

[0093] The same is preferably true for the thread height H6 of the second conical screw 3.

[0094] 8, the thread height H5 of the first screw 2 generally represents the distance separating the midpoint of the root 5R of the first channel 9, considered as the axial midpoint from the two flanks 5F that bound said first channel 9, from the generatrix tangent to the crest 5C of the first thread that bounds said first channel 9, on the one hand, and, in other words, from the line corresponding to the intersection of the frustoconical envelope E2 with the radial cross section, on the other hand. In other words, the thread height H5 is the length of a straight line segment that passes through the midpoint of the root 5R of the first channel 9, perpendicular to the generatrix of the frustoconical envelope E2.

[0095] The same applies to the height H6 of the thread 6 of the second screw 3, which is considered to be perpendicular to the frustoconical envelope surface E3.

[0096] However, in the following, for ease of calculation, it is also possible to consider projections H5', H6' of the thread heights H5, H6 on a plane perpendicular to the central axes X2, X3 of the screws 2, 3.

[0097] In the volume stage 11, regardless of the angular position that each of the first and second screws 2, 3 takes around its central axis X2, X3 during their counter-rotational movement, the number of the first series of chambers 7 that are simultaneously closed and the number of the second series of chambers 8 that are simultaneously closed have a lower limit of 4 or more or 5 or more, and preferably an upper limit of 20 or less or 12 or less, for example, 4 to 10, or 5 to 8.

[0098] In fact, the inventors have discovered that in order to obtain a satisfactory leak-tightness and therefore a satisfactory metering operation, even when high pressures are present at the outlet of the extruder 1, it is necessary to provide several chambers 7, 8 in axial succession along the same screw 2, 3, in this case at least four or at least five chambers.

[0099] Conversely, the inventors have also found that it is preferable to limit the number of chambers 7, 8 along the same screw 2, 3, and more generally the length L2, L3 of said screw 2, 3, typically by providing less than 20, less than 12 or less than 10 chambers along the same screw, in order to avoid the risk of over-processing the material, since over-processing may result in excessive heating of the material, which may have a detrimental effect on the material, and therefore when using longer screws 2, 3 with more chambers 7, 8 it is necessary to preventively reduce the rotation speed of the screws 2, 3, thus limiting the maximum processing throughput of the extruder 1.

[0100] Furthermore, limiting the lengths L2, L3 of the screws 2, 3 together with the number of chambers reduces the resistance torque experienced by the material and therefore the drive torque required to drive the screws 2, 3, making it possible to reduce energy consumption while ensuring good efficiency of the extruder 1, in particular a good mass flow rate.

[0101] It should be noted that the above dimensions are particularly suitable for the extrusion of rubber-based materials, since a short screw length reduces the residence time of the extruded material in extruder 1 where it is subjected to the action of screws 2 and 3. This advantageously prevents overheating and therefore damage to the rubber-based material.

[0102] Furthermore, when the extruder 1 according to the invention is designed for the extrusion of rubber-based materials, unlike known extruders for thermoplastic materials, which, due to the high fluidity of the material, must have a significant length, typically of the order of about 40 times the maximum screw diameter, it is not necessary to have a significant screw length L2, L3 to ensure satisfactory gas-tightness, and it is possible to suffice with an axial screw length L2, L3, in particular the axial length of the threaded portion, which corresponds in particular to 4 to 10 times the maximum diameter of the screws 2, 3.

[0103] The extruder 1 according to the invention can therefore be much shorter and lighter than known extruders and still have a satisfactory volume displacement.

[0104] Advantageously, the length L3 of the second screw 3, which in this case corresponds to the total thread portion length of the second screw 3, is equal to the length L2 of the first screw 2, which in this case corresponds to the total thread portion length of the first screw 2.

[0105] According to a preferred feature, which may constitute an invention in itself, the extruder 1 comprises a stage called a "feed stage" 30 preceding the volume stage 11, in which: - the first threads 5 are arranged such that as the top diameter D_5C of the first threads 5 decreases in the upstream-downstream direction along the first central axis X2 according to a first conicity angle A5, the pitch P5 of the first threads 5 also decreases in the upstream-downstream direction along the first central axis X2 according to a law referred to as a "first compression law" LP5_30, so as to promote compression of the material as it approaches the volume stage 11; - The second threads 6 are arranged such that as the top diameter D_6C of the second threads 6 decreases in the upstream-downstream direction along the second central axis X3 according to a second conicity angle A6, the pitch P6 of the second threads 6 also decreases in the upstream-downstream direction along the second central axis X3 according to a law referred to as the "second compression law" LP6_30, so as to promote compression of the material as it approaches the volume stage 11.

[0106] Said feed stage 30 makes it possible to receive, process and pre-compress the material to ensure the supply of the volume stage, thus optimizing the effective displacement V2, V3 of each screw 2, 3 by ensuring, on the one hand, good filling of the first chambers 7, 8 of each screw 2, and, on the other hand, making it possible to limit the pressure gradient between upstream and downstream of the volume stage 11, thereby avoiding leakage and advantageously preventing the material from retreating in the opposite direction to the desired forward movement FWD.

[0107] Furthermore, the first screw 2 and the second screw 3 interact non-volumetrically within the feed stage 30, which advantageously facilitates the insertion and swallowing of material in the extruder 1, in particular when said material arrives at the extruder in the form of a continuous strip, by making it possible, in particular, to use widened thread pitches P5, P6 of the threads 5, 6 and therefore very wide channels 9, 10.

[0108] It is preferred that the minimum pitch P5, P6 of each screw 2, 3 considered in the feed stage 30 is strictly greater than the maximum pitch P5, P6 of this same screw 2, 3 considered in the volume stage 11, specifically in the equal volume stage 11A.

[0109] For reference, and in order to always maintain a wide flow path to facilitate the acceptance of material, it is preferred that the initial pitches P5, P6 in the feed stage 30 be at least 0.5 times the diameters D_5C, D_6C of the crests of the threads 5, 6 considered at the upstream end of said feed stage 30.

[0110] Of course, it would be possible to provide an inlet with a hopper in some cases in the barrel 4 opposite the feed stage 30 to allow material to enter the barrel 4.

[0111] According to a possible variant embodiment shown in Figures 1, 2 and 15, the first screw 2 and the second screw 3 can be single-threaded in the feed stage 30, more preferably in both the feed stage 30 and the volume stage 11.

[0112] It is therefore advantageously possible to have a single screw thread passing through the volume stage 11 in succession after the feed stage 30 of each screw 2, 3, but with adapted pitches P5, P6.

[0113] However, according to another variant embodiment shown in Figures 3 and 4, in the feed stage 30, both the first screw 2 and the second screw 3 are multi-threaded, preferably double-threaded, and therefore the first thread 5 and the second thread 6 each preferably comprise at least two screw threads angularly offset from one another around the central axis X2, X3 of the screws 2, 3, covering the same common axial extent.

[0114] These multiple screw threads in the feed stage 30 make it easier to grip the material and receive it by the screws 2, 3, especially when the material is fed in strip form.

[0115] This arrangement also improves the processing of the material and its pressure build-up to facilitate feeding into the volume stage 11 located immediately downstream of the feed stage 30 .

[0116] Conversely, the first screw 2 and the second screw 3 are preferably each of single thread type in the volume stage 11 .

[0117] In this case, the screws 2, 3 may have a transition zone 31 between the feed stage 30 and the volume stage 11 that allows a transition from a multi-thread type upstream to a single-thread type downstream and, if appropriate, from one core shape 12, 13 to another core shape 12, 13, for example to adapt the root diameters D_5R, D_6R of the screw threads and / or the conicity angle of the cores 12, 13.

[0118] Specifically, the core 12 of the first screw 2 preferably has a right cylindrical shape at the feed stage 30, or a truncated conical shape whose cone angle is strictly smaller than the first cone angle A5.

[0119] Alternatively, the core 13 of the second screw 3 preferably has a right cylindrical shape at the feed stage 30 or a truncated conical shape with a cone angle strictly smaller than the second cone angle A6.

[0120] In this arrangement, relatively large screw thread root diameters D_5R, D_6R can be maintained in the feed stage 30, which allows a high driving torque to be transmitted to the screws 2, 3 to maintain a "diameter reserve" from which the frustoconical reduction of the cores 12, 13 can continue in the equal volume stage 11A without risking excessive structural weakening of the screws 2, 3.

[0121] Furthermore, the small or zero conicity angle of the cores 12, 13 in the feed stage 30 facilitates a reduction in the volume of the channels 9, 10 under the influence of a reduction in the pitch P5, P6 of the threads 5, 6, thus promoting the compression of the material and therefore its feeding into the volume stage 11.

[0122] As can be seen in Figures 3 and 4, in the transition zone 31, the multiple screw threads of the feed stage 30 can terminate in the form of outlets 32 that open the channels 9, 10 and allow material to enter the chambers 7, 8 of the volume stage 11.

[0123] In practice, the equal volume stages 11A of each of the first and second conical screws 2, 3 can be dimensioned according to the method described below and with reference to FIGS.

[0124] For the sake of simplicity and brevity, only the dimensioning of the first conical screw 2 will be described, taking into account that the dimensioning of the second conical screw 3 is done in a similar manner.

[0125] In absolute terms, it would be possible to provide closed chambers 7, 8 in the volume stage 11, in particular in the axially upstream part of the volume stage 11 preceding the isovolume stage 11A, in which the pitches P5, P6 do not increase, in order to initially obtain an enhanced compression effect between the first and second chambers 7, 8 of the series of chambers in the volume stage 11, in particular after the first chamber has been filled by the feed stage 30. However, for ease of explanation, it would be preferable to consider below a preferred variant embodiment in which the compensation laws LP5_11, LP6_11 apply to the entire volume stage 11, in other words in which the isovolume stage 11A extends throughout the entire axial extent of the volume stage 11, so that the upstream and downstream axial boundaries of the isovolume stage 11A coincide with the upstream and downstream boundaries 11U, 11D of the volume stage 11.

[0126] The "Large outside diameter" D_5C_max, D_6C_max indicate the top diameter of the threads 5, 6 of the screws 2, 3 considered at the upstream end 11U of the equal volume stage 11A, and thus form the circular large base diameter of the frustoconical envelope E2 of the equal volume stage 11A.

[0127] Similarly, the "small outside diameters" D_5C_min, D_6C_min, which are strictly smaller than the large outside diameters D_5C_max, D_6C_max, indicate the top diameters of the threads 5, 6 of the screws 2, 3 considered at the downstream end 11D of the equal volume stage 11A, and thus form the circular small base diameter of the frustoconical envelope E2 of the equal volume stage 11A.

[0128] Advantageously, the major outer diameter D_5C_max of the first screw 2 is equal to the major outer diameter D_6C_max of the second screw 3 and the minor outer diameter D_5C_min of the first screw 2 is equal to the minor outer diameter D_6C_min of the second screw 3 .

[0129] To determine the compensation law LP5_11, first determine the thread crest radius to be used to obtain the desired displacement V2 at several different abscissas along the volume stage 11A, more preferably at least at the upstream end 11U and downstream end 11D of the volume stage 11A, and preferably at one or more further abscissas between these ends, and then interpolate the points thus determined using a second-degree polynomial law constituting the compensation law LP5_11, making it possible to determine the thread crest radius at any abscissa of the volume stage 11A.

[0130] For this purpose, the displacement V2 of the first screw 2, in other words the volume of extruded material discharged per revolution of the first screw 2 around its central axis X2, is first determined. In practice, this displacement V2 corresponds to the constant individual volumes V2 of the various C-shaped chambers 7 of the first series of closed chambers 7. Said closed chambers 7 correspond to various portions of the first channel 9 that are successive along the first central axis X2, each of which is closed on the one hand by the second thread 6 of the other screw 3, which is located between the screw 2 and the inner wall of the barrel 4, and on the other hand 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.

[0131] Next, referring to the frustoconical envelope surface E2 of the equal-volume stage 11A of the first screw 2, on the one hand, an inlet radius R2_in, which corresponds to the radius of the crest 5C of the first thread 5 at the upstream end 11U of the equal-volume stage 11A and is therefore equal to half the major outer diameter D_5C_max, which corresponds to the major base diameter of the frustoconical envelope E2; and on the other hand, the outlet radius R2_out of the isovolume stage 11A, which corresponds to the radius of the crest 5C of the first thread 5 at the downstream end 11D of the isovolume stage 11A and is therefore equal to half the small outer diameter D_5C_min, which corresponds to the small base diameter of the frustoconical envelope E2; Calculate.

[0132] To this end, the length L11A of the equal-area step 11A, measured along the first central axis X2, in other words along a straight line that maintains the height of the frustoconical envelope E2 (and therefore corresponds to the bisector of the apex angle of the frustoconical envelope E2 in a cross section that includes the first central axis X2), which is selected by the designer in the same way as the displacement V2; - total length L_tot, which corresponds to the height measured between the large base of the first frustoconical envelope E2 and the apex S2 of the cone of the first frustoconical envelope E2, a cone angle A5 of the first screw 2, also chosen by the designer, preferably within the range of values ​​mentioned above; Consider:

[0133] By simple trigonometry in a radial cross section containing the first central axis X2, and as shown in FIG. R2_in=L_tot * tan(A5) R2_out=(L_tot-L2) * tan(A5)

[0134] Knowing the selected height H5 of the first thread 5 and therefore its projection H5' in a plane perpendicular to the central axis X2, a value R1_in called "inlet apparent half-centre distance" can be derived therefrom, which value corresponds to the radial distance measured of the large base of the first frustoconical envelope E2 in a plane perpendicular to the first central axis X2 between, on the one hand, the central axis X2 and, on the other hand, the intersection point M1 where the plane of the large base of the first frustoconical envelope E2 intersects with a straight line X1 extending equidistantly from the first central axis X2 and the second central axis X3 in a plane containing both the first central axis X2 and the second central axis X3, which corresponds to the central axis of the extruder 1. R1_in=R2_in-(H5' / 2)

[0135] Similarly, in the plane of the small base of the first frustoconical envelope E2, a value R1_out of the outlet apparent half-centre distance is derived. R1_out=R2_out-(H5' / 2)

[0136] Next, as shown in FIG. 13, in the plane of the large base of the first frustoconical envelope E2, a circular segment called the “inlet truncation circular segment” 20_in is identified, which corresponds to the region between, on the one hand, an arc chord C20 passing through the intersection M1 and perpendicular to the radius from the first central axis X2, and, on the other hand, an arc bounded by this arc chord C20 and whose radius corresponds to the inlet radius R2_in.

[0137] The area A20_in of this entrance cut circular segment 20_in is as follows: A20_in=1 / 2 * (R2_in) 2* (alpha_in-sin(alpha_in)) where alpha_in represents the angle covered by the arc that bounds the entrance cut circular segment 20_in, and so: alpha_in=2 * Arccos(R1_in / R2_in)

[0138] Similarly, the area of ​​the outlet cut circular segment 20_out is considered to be: A20_out=1 / 2 * (R2_out) 2* (alpha_out-sin(alpha_out)) where alpha_out represents the angle covered by the arc that bounds the exit cut circular segment 20_out, and so: alpha_out=2 * Arccos(R1_out / R2_out)

[0139] 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 area of ​​the ring between the valley bottom 5R of the first thread 5 and the crest 5C of the first thread on the one hand and the cutting area occupied by the thread 6 of the second screw 3 penetrating into the channel 9 of the first screw 2 on the other hand.

[0140] Said substantially oval cutting area is equal to twice the area A20_in of the inlet cutting circular segment 20_in mentioned above, in view of the symmetrical arrangement of the first screw 2 and the second screw 3.

[0141] Therefore, at the upstream end 11U of the equal volume stage 11A, the crest 5C of the first thread is located at a radius corresponding to the inlet radius R2_in, and the valley bottom 5R of the first thread is located at a radius of height H5' recessed from the crest 5C of the thread, so that: A7_in=π * [(R2_in) 2 -(R2_in-H5') 2 ]-(2 * A20_in)

[0142] Similarly, the plane of the smaller base of the frustoconical shape E2 can define the area A7_out of the outlet chamber 7 at the downstream end 2D of the first screw. A7_out=π * [(R2_out) 2 -(R2_out-H5') 2 ]-(2 * A20_out)

[0143] The inlet pitch P5_in, considered on the axial abscissa of the upstream end 2U of the first screw, is defined as the ratio between the desired displacement V2 and the area A7_in of the inlet chamber mentioned above. P5_in=V2 / A7_in

[0144] Similarly, the outlet pitch P5_out at the downstream end 2D of the first screw 2 is defined as the ratio between this same displacement V2, which is preferably constant, and the area A7_out of the outlet chamber (which is effectively smaller than the area A7_in of the inlet chamber). P5_out=V2 / A7_out

[0145] Once these two extreme pitch values ​​P5_in and P5_out have been determined, the compensation law LP5_11 can be determined by repeating the calculation for one or more intermediate abscissas and applying a regression law, preferably a quadratic polynomial law, to the obtained point cloud.

[0146] As can be seen in FIG. 14, the invention naturally also relates to an installation 100 equipped with an extruder 1 according to any of the above-mentioned characteristics for feeding a material, preferably a rubber-based mixture.

[0147] The installation 100 comprises a base 101. This base advantageously forms a fixed frame of reference and can correspond to the floor of the building housing the installation, or optionally to a frame fixed to the building.

[0148] The installation 100 also comprises a receiving support 102 such as a platform, drum or toroidal core for receiving the material extruded by the extruder 1 .

[0149] The receiving support 102 is held by the base 101 and can be movably mounted relative to the base 101. For example, in the case of a drum or core forming a shape of revolution around a main axis Y102, the drum or core can be rotatably mounted relative to the base 101 around said main axis Y102, preferably using motorized rotation.

[0150] The installation 100 further comprises a robotic transport device 103, such as a Cartesian robot as shown in FIG. 14, or an anthropomorphic robot arm, configured to hold the extruder 1 and move said extruder 1 relative to the receiving support 102 while the extruder 1 is delivering the extruded material so that the extruded material can be placed at different positions on the receiving support 102 according to a predetermined desired arrangement.

[0151] The light weight and compactness of the extruder 1 according to the present invention allows for its use in a mobile laying head 104 mounted on a robotic transport device 103 .

[0152] A robotic transport device 103 holding the extruder 1 is interposed between the base 101 and the extruder 1 so as to be able to move said extruder relative to the base 101 and the receiving support 102 according to an independently controllable movement that is advantageously different from any constant movement that drives the receiving support 102 relative to the base 101 while the extruder is supplying extrusion material.

[0153] Therefore, it is preferred that the robotic transport device 103 is capable of moving the extruder 1 translationally along at least one axis, preferably at least two axes, and even three orthogonal axes, to position the extruder 1 within the reference system of the base 101.

[0154] For example, the robotic transport device 103 may be equipped for this purpose with at least one, preferably two, motorized translation plates 106, 107, for example two horizontal motorized translation plates 106, 107 that are orthogonal to each other.

[0155] Additionally, the robotic transport device 103 is preferably capable of rotationally moving the extruder 1 about at least one, two, or three axes to orient the extruder in a pitch, roll, and / or yaw motion relative to the receiving support 102.

[0156] The laying head 104 comprises a die connected to the outlet of the extruder 1 for giving the extruded material a suitable shape, such as the shape of a flattened ribbon.

[0157] The laying head 104 may also include an applicator member 105, such as a press roller 105, arranged to receive and press the extruded material leaving the extruder 1 through the die onto a support.

[0158] The laying head 104, and in particular the extruder 1, is preferably fed with a continuous strip of material from a storage unit or a production unit.

[0159] Finally, the installation relates to an extrusion method implementing an extruder 1 or installation 100 according to the invention.

[0160] In particular, the invention relates to the use of an extruder 1 according to the invention or an installation 100 according to the invention for extruding rubber-based mixtures, for example for producing parts of vehicle wheel tyres, in particular parts of pneumatic tyres.

[0161] Thus, the extruder 1, and more generally the installation 100, can be configured to place strips of raw rubber on a drum or on a toroidal core.

[0162] In this case, it is preferable that the extruder 1 provides a mass flow rate of 1 kg / min or more, for example, 1 kg / min to 6 kg / min, for each rotation speed of the first screw 2 and the second screw 3, which is 300 rpm or less, for example, 10 rpm to 300 rpm.

[0163] These performance levels are preferably achievable when the pressure at the extruder outlet, the outlet of the last chambers 7, 8 and the die inlet is between 150 bar and 500 bar and the material temperature is between 80°C and 150°C.

[0164] Naturally, the present invention is in no way limited to the variant embodiments described above, and a person skilled in the art can separate any of the features described above, combine them at will, or replace them with equivalents. [Explanation of symbols]

[0165] 2 First screw 2D Downstream zone of the first screw 2U Upstream zone of the first screw 3 Second screw 3D Second screw downstream zone 3U Upstream zone of second screw 5 First Thread 6 Second Thread 7. First series of chambers 8. Second series of chambers 11 Volume stage 11A fixed stacking stage 30 supply stage L2 First screw length L3 Second screw length L11A Length of constant stacking stage LP5_11 First Law of Compensation LP5_30 First compression law LP6_11 Second Law of Compensation LP6_30 Second Compression Law P5 Primary thread pitch P6 Secondary thread pitch X2 First central axis X3 Second central axis

Claims

1. An extruder (1) for extruding a material, comprising: - barrels (4), a first screw (2) having a first thread (5) mounted rotatably within said barrel (4) around a first central axis (X2); a second screw (3) having a second thread (6) rotatably mounted within said barrel (4) around a second central axis (X3); Equipped with The first screw (2) and the second screw (3) are configured to rotate in opposite directions, and the first thread (5) and the second thread (6) interact to convey the material from upstream to downstream in the barrel (4), and the extruder (1) is - said first screw (2) is conical in shape such that the top diameter (D_5C) of said first thread (5) decreases in the upstream-downstream direction along said first central axis (X2) according to a first predetermined conical angle (A5); - said second screw (3) is conical such that the top diameter (D_6C) of said second thread (6) decreases in the upstream-downstream direction along said second central axis (X3) according to a second predetermined conical angle (A6); the extruder (1) comprises a stage called "volume stage" (11), in which the first thread (5) of the first screw (2) and the second thread (6) of the second screw (3) are interpenetratingly paired with each other to form, on the one hand, a first series of continuous C-shaped closed chambers (7) along the first central axis (x2) between the barrel (4) and the first screw (2), and, on the other hand, a second series of continuous C-shaped closed chambers (8) along the second central axis (X3) between the barrel (4) and the second screw (3), so that the rotation of the first and second screws (2, 3) generates a positive displacement of the material taken up in the first series of chambers (7) and the material taken up in the second series of chambers (8); At least a portion of the volumetric stages form a stage called an "isovolumetric stage" (11A), and within the isovolumetric stage (11A): the pitch (P5) of said first thread (5) increases in the upstream-downstream direction along said first central axis (X2) as the top diameter (D_5C) of said first thread (5) decreases, according to a law called "first compensation law" (LP5_11) which allows a gradual increase in the pitch (P5) of said first thread (5) to compensate for the conicity of said first screw (2) so that the individual volume of each closed chamber (7) of said first series of closed chambers in said isovolume stage (11A) is equal to the same predetermined nominal isovolume (V2), called "first screw displacement" (V2), with a maximum tolerance of ±2%, preferably ±1%, or even ±0.5%; the pitch (P6) of said second thread (6) increases in the upstream-downstream direction along said second central axis (X3) as the top diameter (D_6c) of said second thread (6) decreases, according to a law called "Second Compensation Law" (LP6_11) which allows a gradual increase in the pitch (P6) of said second thread (6) to compensate for the conicity of said second screw (3) so that the individual volume of each closed chamber (8) of said second series of closed chambers in said isovolume stage (11A) is equal to the same predetermined nominal isovolume (V3), called "Second Screw Displacement" (V3), with a maximum tolerance of ±2%, preferably ±1%, or even ±0.5%; An extruder characterized by:

2. the first compensation law (LP5_11) is an increasing quadratic function of the axial abscissa value along the first central axis (X2), or the second compensation law (LP6_11) is an increasing quadratic function of the axial abscissa value along the second central axis (X3); 2. The extruder of claim 1.

3. The first conical angle (A5) and the second conical angle (A6) are each between 1.8 degrees and 3 degrees, preferably between 2 degrees and 2.5 degrees, and more preferably equal to 2.5 degrees; 3. The extruder according to claim 1 or 2.

4. In the volume stage (11), the number of the first series of chambers (7) that are simultaneously closed and the number of the second series of chambers (8) that are simultaneously closed, regardless of the angular position of each of the first and second screws (2, 3) around its central axis (X2, X3) during the counter-rotational movements of the first and second screws (2, 3), respectively, is at least 4 or at least 5, and preferably at most 20 or at most 12, for example 4 to 10, or 5 to 8.

4. An extruder according to claim 1, wherein the extruder is a casing.

5. The first screw displacement amount (V2) and the second screw displacement amount (V3) are each 8 cm 3 ~50cm 3 For example, 10 cm 3 ~30cm 3 and especially 10 cm 3 ~20cm 3 That is, 5. An extruder according to claim 1.

6. At least in the volume stage (11), the root diameter (D_5R) of the first thread decreases according to the first conicity angle (A5), so that in the volume stage, the height (H5) of the first thread varies by less than 20% along the first central axis (X2); 6. An extruder according to any one of claims 1 to 5.

7. The extruder comprises a stage called "feed stage" (30) preceding the volume stage (11), in which: the first threads (5) are arranged such that as the top diameter (D_5C) of the first threads (5) decreases in the upstream-downstream direction along the first central axis (X2) according to the first conical angle (A5), the pitch (P5) of the first threads (5) also decreases in the upstream-downstream direction along the first central axis (X2) according to a law called the "first compression law" (LP5_30) so as to promote compression of the material as it approaches the volume stage (11); the second threads (6) are arranged such that as the top diameter (D_6C) of the second threads (6) decreases in the upstream-downstream direction along the second central axis (X3) according to the second conical angle (A6), the pitch (P6) of the second threads (6) also decreases in the upstream-downstream direction along the second central axis (X3) according to a law called the "second compression law" (LP6_30) so as to promote compression of the material as it approaches the volume stage (11); 7. An extruder according to any one of claims 1 to 6.

8. the core (12) of the first screw (2) has a right cylindrical shape or a truncated conical shape with a conical angle strictly smaller than the first conical angle (A5) at the feed stage, or the core (13) of the second screw (3) has a right cylindrical shape or a truncated conical shape with a conical angle strictly smaller than the second conical angle (A6) at the feed stage (30); 8. The extruder of claim 7.

9. in the feed stage (30), the first screw (2) and the second screw (3) are both multi-threaded, preferably double-threaded, so that the first thread (5) and the second thread (6) each comprise at least two screw threads angularly offset from one another around the central axis (X2, X3) of the screws (2, 3) covering the same common axial extent, 9. An extruder according to claim 7 or 8.

10. The first screw (2) and the second screw (3) are each single-threaded in the volume stage (11); 10. An extruder according to any one of claims 1 to 9.

11. An installation (100) for feeding a material, preferably a rubber-based mixture, comprising an extruder (1) according to any one of claims 1 to 10, further comprising a receiving support (102), such as a platform, drum or toroidal core, for receiving the material extruded by the extruder (1), and a robotic transport device (103), such as a Cartesian robot or an anthropomorphic robot arm, configured to hold the extruder (1) and to be able to move the extruder (1) relative to the receiving support (102) while the extruder (1) is feeding the material, so that the extruded material can be placed at different positions on the receiving support (102) according to a predetermined desired arrangement. The facility is characterized by:

12. Use of an extruder (1) according to any one of claims 1 to 10 or an installation (100) according to claim 11 for extruding rubber-based mixtures.

13. the extruder (1) provides a mass flow rate of 1 kg / min or more, for example 1 kg / min to 6 kg / min, for a rotation speed of each of the first and second screws (2, 3) of 300 rpm or less, for example 10 rpm to 300 rpm, 13. The use according to claim 12.

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