Miniaturized positive displacement extruder using biconical screws each provided with threads and having increased pitch to maintain 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) for counter rotation, the first conical screw (2) and the second conical screw (3) defining a volumetric stage (11) in which threads (5, 6) interpenetrate and conjugate with each other, a continuous closed C-shaped chamber (7, 8) is formed between the cylinder (4) and the screw (2, 3) for volumetric operation of the extruder (1). According to the invention, in at least part of the volume stage, the pitch (P5, P6) of the threads of the screw (2, 3) is increased according to a predetermined compensation law (LP511, LP611), preferably quadratic, such that the continuous closed chambers (7, 8) each have a separate volume that remains equal to a predetermined constant volume (V2, V3) forming the displacement of the screw (2, 3) in question.

Description

Field of the Invention

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

[0002] The present invention is particularly applicable to the manufacture of elements intended to be used in the production of vehicle tires. Background Art

[0003] It is known that extrusion operations generally require precise control of the flow rate of the extruded material in order to avoid producing non-conforming products, which are then discarded.

[0004] However, in practice, it is sometimes difficult to ensure such precise control of the flow rate of the extruded material during the transition phases of the extrusion process (such as the start-up, stop and restart phases of an extrusion production line). This difficulty is due in particular to the fact that during such transition phases, on the one hand, the temperature of the extrusion tool is unstable and, on the other hand, the speed of the moving mechanical parts of the extruder is also unstable, which causes changes in the rheological properties and behavior of the extruded material.

[0005] To ensure control of the flow rate of the extruded material, it is known practice to implement so-called "positive displacement" extruders, that is to say extruders provided with moving mechanical parts such as pistons, gears or intermeshing twin screws, which are arranged in such a way as to create one or more chambers within the extruder, the chambers being first opened and increasing their volume under the action of the cyclic movement of the moving mechanical parts to receive the incoming material, then closed to trap a given quantity of said material, and finally contracted to mechanically force the trapped quantity of material out of the chamber.

[0006] Thus, regardless of the pressure present at the outlet of the extruder, such an extruder is capable of delivering a certain volume of extruded material, said volume being referred to as the "displacement" of the extruder (which is constant for each new repetition of the cyclic operation of the extruder), that is to say the volume of extruded material equivalent to each return stroke of the piston or each revolution of the gear or each revolution of the twin screws in the above examples.

[0007] Equipment using such positive displacement extruders generally also has a multi-stage structure, each stage being formed by a selected type of extruder in order to be able to perform all the functions involved: supplying the equipment with material, plasticizing the material, increasing the pressure of the material, and then volumetrically dispensing the material at the outlet of the equipment.

[0008] Thus, for example, it is known practice to combine in series, within the same device, on the one hand, a single-screw extruder of the Archimedes screw type, which comprises a screw rotatably mounted in a sheath and ensures, by shearing, the supply, the plasticization of the material and a certain increase in terms of pressure and temperature, and on the other hand, a gear pump, the inlet of which is connected to the outlet of the single-screw extruder and the counter-rotating gears of which, in cooperation with the housing of the gear pump, ensure the final pressure increase and the volumetric operation of the device.

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

[0010] This is particularly true when these devices are intended to extrude rubber-based materials. Specifically, in order not to damage the rubber-based materials, it is necessary to avoid exposing such materials to excessive temperatures, which means not rotating the wheels of the gear pump at excessive speeds. Thus, if it is desired to ensure that the flow rate of the extruded material is sufficient, it is necessary to select a gear pump with a large displacement and thus a large size.

[0011] Coextrusion devices are also known, such as those described in patent application WO 2017 / 109419 filed by the applicant, in which a first stage formed by a feed screw feeds a second stage comprising intermeshing and conjugated twin screws, the twin screws ensuring volumetric operation. Although such an arrangement advantageously makes it possible to greatly increase the number of extrusion paths connected to the same extrusion head while still having a relatively compact extrusion head and to ensure a relatively high and well-controlled flow rate of each extruded material, this type of device is designed for coextrusion applications, the aim of which is to produce complex profiles incorporating several extruded materials, and, due to the diversity of the extrusion paths, generally has a large volume.

[0012] In addition, known devices can be relatively expensive both to purchase and to operate (especially due to their energy consumption and complex maintenance requirements). SUMMARY OF THE INVENTION

[0013] Accordingly, an object of the present invention is to overcome the above-mentioned drawbacks and to propose a miniaturized extruder having a reduced volume and weight while maintaining a satisfactory volumetric operation, which makes it possible to well control the flow rate of the extruded material.

[0014] The object of the present invention is achieved by an extruder intended to extrude a material, the extruder comprising:

[0015] - a barrel,

[0016] - a first screw rotatably mounted in the barrel about a first central axis and provided with a first thread,

[0017] - A second screw, which is rotatably mounted in the barrel about a second central axis and is provided with a second thread,

[0018] The first screw and the second screw rotate in opposite directions and are arranged such that the first thread and the second thread interact to convey the material from the upstream to the downstream in the barrel. The extruder is characterized in that:

[0019] - The first screw is conical, such that the top diameter of the first thread decreases along the first central axis in the upstream to downstream direction according to a first predetermined taper angle,

[0020] - The second screw is conical, such that the top diameter of the second thread decreases along the second central axis in the upstream to downstream direction according to a second predetermined taper angle,

[0021] The extruder includes a stage called the "volumetric stage", within which the first thread of the first screw and the second thread of the second screw interpenetrate and are conjugate to each other, such that on the one hand a first series of continuous C-shaped closed chambers are formed between the barrel and the first screw along the first central axis and on the other hand a second series of continuous C-shaped closed chambers are formed between the barrel and the second screw along the second central axis, so that the rotation of the first screw and the second screw produces a positive displacement of the material captured by the first series of chambers and the material captured by the second series of chambers.

[0022] At least a part of the volumetric stage forms a stage called the "isochoric volumetric stage", within which:

[0023] - According to a law called the "first compensation law", as the top diameter of the first thread decreases, the pitch of the first thread increases along the first central axis in the upstream to downstream direction. The first compensation law causes the pitch of the first thread to increase gradually to compensate for the taper of the first screw, so that in the isochoric volumetric stage, the individual volume of each closed chamber 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

[0024] - According to a law called the "second compensation law", as the pitch diameter of the second thread decreases, the pitch of the second thread increases in the upstream to downstream direction along the second central axis. The second compensation law causes the pitch of the second thread to gradually increase to compensate for the taper of the second screw, so that in the isochoric volume stage, the individual volume of each closed chamber of the second series of closed chambers remains equal to the same predetermined constant nominal volume called the "second screw displacement", with a maximum tolerance of + / - 2%, preferably + / - 1%, or even + / - 0.5%.

[0025] Advantageously, the extruder according to the present invention can independently ensure the plasticization of the material, the increase in pressure, and the volumetric operation at a precisely controlled flow rate, while occupying a smaller space.

[0026] The arrangement of the thread according to the present invention, in which the pitch increases as the cone of the screw narrows in the isochoric volume stage, advantageously makes it possible to coordinate the taper of the screw with the constancy of the volume of the chamber while the screw rotates on its own and each closed chamber progresses from upstream to downstream along the central axis of the screw. Therefore, the volume of the extruded material captured by the chamber opened at the upstream inlet of the isochoric volume stage is the same as the captured unit volume transported by each closed chamber between the screw and the barrel of the isochoric volume stage, and is the same as the volume discharged by the chamber opened at the downstream end of the isochoric volume stage. This constant unit volume advantageously corresponds to the volume of the extruded material discharged by the mentioned screw in each complete rotation, in other words, corresponds to the displacement of the screw.

[0027] Since the volume of each closed chamber defined by the same conical screw along its central axis at each given moment is constant, or almost constant considering the above-mentioned allowable tolerances, in other words, the volume neither decreases significantly nor increases significantly, the material contained in the closed chamber is regularly transported from the upstream to the downstream of the extruder along the central axis of each screw regardless of the position occupied by the mentioned closed chamber along the axis.

[0028] This ensures the volumetric operation of each conical screw, and in particular prevents problems of local overpressure, thus preventing problems of leakage between consecutive chambers of the same screw (which may occur if the captured material in the closed chamber is overcompressed by trying to reduce the volume of the chamber without allowing the material to escape) or problems in terms of local pressure drop and cavitation (which may occur if the captured material in the closed chamber tends to expand by increasing the volume of the chamber, i.e., by increasing the volume into which the material can enter, without increasing the amount of material available in the chamber).

[0029] In this regard, it should be noted that, as shown below, it is advantageous to connect the volumetric stage to the feed stage upstream of the volumetric stage and within the same first and second screws, the feed stage enabling the processing and compression of the material to ensure feeding to the volumetric stage.

[0030] The taper of the screw has several advantages.

[0031] The first advantage of the taper is that the upstream part of the screw corresponding to the large base of the frustoconical envelope (the screw is inscribed in the envelope) has a large diameter, thus providing a wide entrance for introducing the material into the extruder, which provides good conditions for the performance of the feeding function.

[0032] The second advantage of the taper is that the projected area of the thread considered in a plane perpendicular to the central axis of the screw decreases along the axis, such that the projected area is minimum at the downstream end of the tapered screw corresponding to the small base of the frustoconical envelope (the screw is inscribed in the envelope). Thus, the projected area of the thread is exactly minimum in the region where the material exerts the highest pressure on the screw, which is necessary to overcome the pressure existing at the exit of the extruder and drive the material through the extrusion die connected to the exit of the extruder. Minimizing the area of the projected area subjected to the pressure (which is the pressure exerted by the material acted upon by the extruder on the screw) reduces the resultant axial force exerted by the material on the screw and the bearings (which support the screw and enable it to rotate within the barrel). Therefore, the size of these bearings can be safely reduced, making the extruder more compact and lightweight.

[0033] The third advantage of the taper is that it makes the wetted area of the screw (i.e., the area of contact between the screw and the material) smaller compared to the wetted area within a straight cylindrical screw with a constant diameter and an axial length equal to the length of the tapered screw. Reducing the wetted area and the lever arm (which corresponds to the radial distance measured between the central axis of the screw and the given point at each point of the wetted area) reduces the resistance torque exerted by the material on the rotation of the screw due to its viscosity. Therefore, the extruder according to the present invention requires a relatively low driving torque, which makes it possible to reduce the size and weight of the motor and the reduction gear for rotating the first and second screws.

[0034] For all these reasons, the present invention advantageously makes it possible to achieve a compact and lightweight extruder that is relatively less affected by mechanical inertia, thermal inertia, and vibrations.

[0035] Advantageously, such an extruder can be mounted on a conveying device due to its light weight and compactness, and the conveying device can move and position the extruder dynamically relative to a receiving support (on which the desired object is constructed), which enables the production of the object via three-dimensional printing by depositing the extruded material in the desired amount at the desired position on the receiving support. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other objects, features, and advantages of the present invention will become more apparent by reading the following description in detail and with the aid of the drawings, which are provided by way of non-limiting illustration only, in which:

[0037] Figure 1 A pair of first and second counter-rotating twin screws according to a first variant form of the present invention is shown in a perspective view, in which a feeding stage is located before a volumetric stage, and each of the first screw and the second screw is a single-thread screw.

[0038] Figure 2 is Figure 1 a detailed top view of one of the pair of screws.

[0039] Figure 3 A pair of first and second counter-rotating twin screws according to a second variant form of the present invention is shown in a perspective view, in which a feeding stage is located before a volumetric stage, and each of the first screw and the second screw is a double-thread screw.

[0040] Figure 4 is Figure 3 a top view of one of the pair of screws.

[0041] Figure 5 An isochoric volumetric stage of a pair of counter-rotating double-conical screws (such as Figure 1 the pair of screws in Figure 3 or the pair of screws in is shown in a detailed perspective view.

[0042] Figure 6 is Figure 5 a top view of one of the pair of screws.

[0043] Figure 7 is Figure 5 and Figure 6 an end view of one of the pair of screws as seen from downstream.

[0044] Figure 8 is a cross-sectional view of the isochoric volumetric stage of the extruder according to the present invention in a plane containing a first central axis of a first screw and a second central axis of a second conical screw, in which Figures 5 to 7 the screws in interact with the barrel to form two series of C-shaped closed chambers.

[0045] Figure 9 A perspective view of the volume defined by the first and last closed chambers of the first series of C-shaped closed chambers of the volumetric stage (more specifically, the isochoric volumetric stage) of the extruder according to the present invention along the first central axis.

[0046] Figure 10 Shows that in the isochoric volumetric stage, Figure 9 On one side of the chambers superimposed thereon is a virtual outer frustoconical envelope in which the top of the first thread is inscribed, and on the other side is a virtual inner frustoconical envelope inscribed in the root of the first thread. The virtual outer frustoconical envelope thus corresponds to the entire frustoconical envelope of the first screw, and the virtual inner frustoconical envelope thus corresponds to the frustoconical envelope of the core of the first screw.

[0047] Figure 11 Is Figure 9 And Figure 10 A top view of the chamber shown and the virtual outer frustoconical envelope.

[0048] Figure 12 Is Figures 9 to 11 A side view of the chamber shown as viewed from upstream of the screw.

[0049] Figure 13 Shows the sizing principle of the isochoric stage of the first conical screw in a view arranged in a reference plane which, by convention, is perpendicular to the first central axis and tangent to the upstream axial end of the isochoric volumetric stage of the first conical screw.

[0050] Figure 14 An embodiment of an extrusion device implementing a mobile laying head which carries an extruder with a double conical screw according to the present invention.

[0051] Figure 15 An embodiment of the sizing law for the threads of the conical screw used in the present invention (in this case preferably related to Figure 1 And Figure 2 The first variant form shown), depicting the quadratic increase in the pitch of the threads in the isochoric volumetric stage and the reduction of the threads in the feed stage before the isochoric volumetric stage. Detailed Description

[0052] The present invention relates to an extruder 1 for extruding materials, more specifically an extruder 1 of the "twin-screw" type.

[0053] The extruder includes a barrel 4 in a manner known per se, which barrel 4 is preferably made of metal.

[0054] As is clearly visible in Figures 1 to 8 as shown in Figures 1 to 8 , the extruder 1 comprises: - a first screw 2 rotatably mounted in a barrel 4 about a first central axis X2 and provided with a first thread 5,

[0055] - a second screw 3 rotatably mounted in the barrel 4 about a second central axis X3 and provided with a second thread 6,

[0056] The first screw 2 and the second screw 3 rotate in opposite directions and are arranged such that the first thread 5 and the second thread 6 interact to convey the material from upstream to downstream in the barrel 4, the overall forward movement being indicated herein as "FWD".

[0057] For the sake of description, "axial" will denote the direction parallel to the central axes X2, X3 of the mentioned screws 2, 3, and "radial" will denote the direction perpendicular to the central axes X2, X3 of the mentioned screws 2, 3.

[0058] It should be noted that the first central axis X2 and the second central axis X3 intersect geometrically.

[0059] "Rotating in opposite directions" means that the first screw 2 and the second screw 3 rotate in opposite rotational directions.

[0060] Furthermore, the first screw 2 and the second screw 3 are synchronous, i.e., advantageously rotate at speeds with opposite signs but equal absolute values with respect to each other.

[0061] Particularly according to the stage of the first screw 2 considered along the first central axis X2, the first thread 5 may comprise a single thread or, as a variant form, a multi-thread with the same pitch and angular offset.

[0062] The term "first channel" 9 denotes each of the helical grooves or, in the case of a multi-thread, each of the helical grooves delimited between two solid profiles of the first thread 5 that are axially successive with respect to each other, i.e., that separate two solid profiles of the first thread 5 that are directly adjacent to each other.

[0063] Similarly, according to the stage of the second screw 3 considered along the second central axis X3, the second thread 6 may comprise one or more threads, preferably, the number of which is equal to the number of threads of the first thread 5 that interacts with the second thread 6.

[0064] The term "second channel" 10 denotes each of the helical grooves or, in the case of a multi-thread, each of the helical grooves delimited between two solid profiles of the second thread 6 that are axially successive with respect to each other, i.e., that separate two solid profiles of the second thread 6 that are directly adjacent to each other.

[0065] The direction of the first thread 5 is opposite to that of the second thread 6. In other words, the first screw 2 may have a left-handed thread 5 while the second screw 3 has a right-handed thread 6, or conversely, the first screw 2 may have a right-handed thread 5 while the second screw 3 has a left-handed thread 6.

[0066] More generally, the second screw 3 is preferably a mirror image of the first screw 2, such that the characteristics of one screw can be identically inferred from the characteristics of the other screw by symmetry.

[0067] According to the invention, the first screw 2 is conical, such that the top diameter D_5C of the first thread 5 decreases along the first central axis X2 in the upstream to downstream direction according to a first predetermined taper angle A5.

[0068] Similarly, the second screw 3 is conical, such that the top diameter D_6C of the second thread 6 decreases along the second central axis X3 in the upstream to downstream direction according to a second predetermined taper angle A6.

[0069] As visible in Figure 2 , Figure 4 , Figure 6 , Figure 8 and Figure 11 , the taper angles A5, A6 correspond to the inclination angles formed by the virtual frustoconical envelopes E2, E3 with respect to the virtual straight cylinder in the plane containing the central axes X2, X3 of the mentioned screws 2, 3, the screws 2, 3 being inscribed in the virtual frustoconical envelopes E2, E3, the frustoconical envelopes E2, E3 thus being tangent to the successive tops 5C, 6C of the threads 5, 6 of the mentioned screws 2, 3, the virtual straight cylinder having circular bases centered on the central axes X2, X3 and the mentioned screws 2, 3 being inscribed therein.

[0070] Equivalently, the taper angles A5, A6 correspond to the half-angles at the vertices of the virtual frustoconical envelopes E2, E3 in which the mentioned screws 2, 3 are inscribed, and thus correspond to the angles formed between the central axes X2, X3 and each generatrix of the inclined walls of the virtual frustoconical envelopes E2, E3 in which the screws 2, 3 are inscribed.

[0071] In fact, the first taper angle A5 is equal to the second taper angle A6.

[0072] More specifically, since the first central axis X2 and the second central axis X3 intersect geometrically, the first taper angle A5 and the second taper angle A6 each equal half of the angle formed at the vertex formed by the intersection of the first central axis X2 and the second central axis X3, as visible in Figure 11 .

[0073] Naturally, the inner wall of the barrel 4 that interacts with one of the screws 2, 3 also has a conical profile that matches the conical profiles of the said screws 2, 3, i.e., it generally extends along the same virtual frustoconical envelope, thus circumscribing the said frustoconical envelopes E2, E3. Therefore, the inner wall of the barrel 4 generally narrows at the same taper angles A5, A6 as the screws 2, 3 in the direction of movement through the barrel 4 in the upstream-to-downstream direction FWD.

[0074] Preferably, 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, and even more preferably equal to 2.5 degrees.

[0075] In fact, the inventors have found that for a given screw length and thus for a given volume, these taper angle values represent a good compromise between, on the one hand, the resistance exerted on the screws 2, 3 (which is desired to be minimized), and on the other hand, the ability of the screws to receive and be able to utilize a relatively high driving torque.

[0076] In particular, an optimal compromise is sought between:

[0077] - Sufficiently high taper angles A5, A6,

[0078] i) Such that the end surfaces of the screws 2, 3 (which correspond to the small bases of the frustoconical envelopes E2, E3 in which the said screws 2, 3 are inscribed) are significantly reduced, and thus the axial forces caused by the pressure exerted by the extruded material on the said screws 2, 3 are significantly reduced, which makes it possible to reduce the size of the bearings and axial stops that axially support the screws 2, 3, and

[0079] ii) Such that a sufficient center distance is created between the first screw 2 and the second screw 3 in the upstream regions 2U, 3U of the said screws 2, 3 to be able to have sufficient space to accommodate therein a robust reduction gear and a large-diameter shaft that can drive the said screws 2, 3 and impart a high driving torque to each screw, and

[0080] - Sufficiently moderate taper angles A5, A6,

[0081] i) Such that the diameters of the screws 2, 3 in the upstream regions 2U, 3U remain small enough to avoid providing a strong lever arm for the extruded material with respect to the central axes X2, X3 of the screws, thus limiting the resistance moment of the said extruded material against the rotation of the screws 2, 3, and

[0082] ii) so as to avoid the screws 2, 3 being too thin at their tips, i.e., such that the cores of the first screw 2 and the second screw 3 have a sufficient material thickness up to the downstream ends 2D, 3D of said screws 2, 3 to be able to support and transmit a high driving torque without being damaged, in particular without undergoing irreversible torsional deformation.

[0083] Given the values of the above-mentioned taper angles A5, A6, the angle at the vertex formed by the (virtual) intersection of the first central axis X2 and the second central axis X3 is between 3.6 degrees and 6 degrees, preferably equal to 5 degrees, said angle being equal to the sum of the two apex angles A5 and A6 and thus more preferably being twice the apex angle A5.

[0084] According to the invention, the extruder 1 comprises a stage 11 called the "volumetric stage", within which the first thread 5 of the first screw 2 and the second thread 6 of the second screw 3 interpenetrate and conjugate with each other such that, on the one hand, a first series of continuous C-shaped closed chambers 7 are formed between the barrel 4 and the first screw 2 along the first central axis X2 and, on the other hand, a second series of continuous C-shaped closed chambers 8 are formed between the barrel 4 and the second screw 3 along the second central axis X3, so that the rotation of the first screw 2 and the second screw 3 generates a positive displacement of the material captured by the first series of chambers 7 and the material captured by the second series of chambers 8.

[0085] As is clearly visible in Figure 1 , Figure 3 , Figure 5 , Figure 6 and Figure 8 , "interpenetrate" means that the first thread 5 and the second thread 6 are arranged such that the top 5C of the first thread 5 substantially reaches the root 6R of the second thread 6 and, conversely, the top 6C of the second thread 6 substantially reaches the root 5R of the first thread 5, so that the threads 5, 6 of each of the screws 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.

[0086] By way of illustration, a functional radial clearance JR1 is provided between the top 5C, 6C of one thread and the root 6R, 5R of the other thread, said functional radial clearance JR1 being non-zero of course to ensure a smooth relative movement of one screw 2 with respect to the other screw 3, but most importantly, said functional radial clearance JR1 is preferably less than or equal to 0.3 mm to ensure a volumetric operation without leakage.

[0087] As in Figure 1 , Figure 3 , Figure 5 , Figure 6 and Figure 8As is clearly visible, "conjugate" means that the first thread 5 and the second thread 6 are arranged such that the full axial width of the first thread 5 (in other words, the axial width of the full cross-section of the profile of the first thread 5) occupies the axial width of the second channel 10 defined by the second thread 6 and axially delimited between two consecutive sides 6F of the second thread 6, and vice versa, the full axial width of the second thread 6 occupies the axial width of the first channel 9 defined by the first thread 5 and axially delimited between two consecutive sides 5F of the first thread 5. Thus, the sides 5F of the first thread substantially match the sides 6F of the second thread, and vice versa.

[0088] By way of illustration, in order to ensure a leak-free volumetric operation, a functional axial clearance JA1 of less than or equal to 0.3 mm can be provided between the closest parts of the sides 5F, 6F of one thread and the sides 6F, 5F of the other thread.

[0089] For the same reasons of operation and operational tightness, a radial clearance JR2 is provided between the tops 5C, 6C of the threads of the screws 2, 3 and the radially innermost part of the wall of the barrel 4 (which interacts with the mentioned tops 5C, 6C of the threads), said radial clearance JR2 being non-zero and preferably equal to or less than 0.1 mm, especially in the volumetric stage 11.

[0090] Advantageously, as Figure 8 、 Figure 9 、 Figure 10 and Figure 11 schematically shown, each series of the first series of chambers 7 and the second series of chambers 8 generated in the volumetric stage 11 enables the material to be first trapped in the first chambers 7, 8, which form the upstream inlets into the volumetric stage 11, and the rotation of the screws 2, 3 closes the first chambers so as to hold the corresponding volume of the extruded material trapped within the closed chambers (delimited by the C-shaped space between the screws 2, 3 and the barrel 4), and then, by means of the rotational movement of the screws 2, 3, the material within the closed chambers 7, 8 is conveyed along the central axes X2, X3 in a way of overall translational forward movement (represented herein as FWD) by gradually transforming the chambers 7, 8 to the downstream 2D, 3D.

[0091] Essentially, the closed chambers 7, 8 of the same series of chambers are not in communication with each other, such that each unit volume of the extruded material contained in chamber 7 is isolated from each unit volume of the extruded material contained in each of the other chambers 7 (especially each of the adjacent chambers). Advantageously, regardless of the pressure at the downstream ends 2D, 3D of the tapered screws 2, 3 (i.e., at the level where the last chambers 7, 8 of the consecutive chambers 7, 8 lead to the outlet of the extruder 1), the extruded material cannot move backward along the screws 2, 3 to the upstream 2U, 3U.

[0092] Thus, each time the screws 2, 3 make a complete revolution, the chambers 7, 8 are converted downstream by 2D, 3D, so that the extruded material advances a certain axial distance along the axes X2, X3 of each of the mentioned screws, said axial distance being equal to the pitches P5, P6 of the threads 5, 6 at the mentioned positions.

[0093] Thus, the volume of the extruded material conveyed at the outlet of the extruder 1 each time the screws 2, 3 make a complete revolution (in other words, the total "displacement" of the extruder 1) corresponds to the sum of the unit volumes contained in the last closed chamber 7 of the first continuous chamber 7 (which is delimited by the first screw 2) and the last closed chamber 8 of the second continuous chamber 8 (which is delimited by the second screw 3), that is, corresponds to the sum of the displacements of the first screw 2 and the second screw 3.

[0094] This volumetric displacement of the extruder 1 makes it possible to precisely adjust the flow rate of the extruded material by adjusting the rotational speeds of the screws 2, 3.

[0095] Advantageously, it should be noted that each of the screws 2, 3 together with the barrel 4 creates a plurality of chambers 7, 8 that are axially successive to each other and separated from each other by the threads 5, 6 of the mentioned screws 2, 3, which makes it possible to generally enhance the sealing of the extruder 1 and to reduce the sensitivity of this sealing to the wear of the said screws 2, 3 in the following way: by forming a number of continuous barriers between the barrel 4 and the mentioned screws 2, 3 to prevent the possibility of the extruded material moving backwards along the barrel 4 in the direction from downstream 2D, 3D to upstream 2U, 3U.

[0096] According to the present invention, as is clearly visible in Figure 1 , Figure 3 , Figure 5 , Figure 6 , Figure 8 and Figure 15 , at least a part (more preferably the whole) of the volumetric stage 11 forms a stage called "isochoric volumetric stage" 11A, in which:

[0097] - According to a law called "first compensation law" LP5_11, as the top diameter D_5C of the first thread decreases, the pitch P5 of the first thread 5 increases in the upstream to downstream direction along the first central axis X2, said first compensation law LP5_11 causing the pitch P5 of the first thread 5 to gradually increase so as to compensate for the taper of the first screw 2, so that in the said isochoric volumetric stage 11A, the individual volume of each closed chamber 7 of the first series of closed chambers remains equal to the same predetermined constant nominal volume V2 called "first screw displacement", with a maximum tolerance of + / -2%, preferably + / -1%, or even + / -0.5%, and

[0098] - According to a law called the "second compensation law" LP6_11, as the major diameter D_6C of the second thread decreases, the pitch P6 of the second thread 6 increases in the upstream to downstream direction along the second central axis X3. The second compensation law LP6_11 causes the pitch P6 of the second thread 6 to gradually increase so as to compensate for the taper of the second screw 3, such that in the isochoric volume stage portion 11A, the individual volume of each of the closed chambers of the second series of closed chambers 8 remains equal to the same predetermined constant nominal volume V3 called the "second screw displacement", with a maximum tolerance of + / -2%, preferably + / -1%, or even + / -0.5%.

[0099] In other words, each of the closed chambers 7 defined by the first screw 2 and the barrel 4 has a substantially or even exactly the same individual volume, which is substantially or even exactly equal to the individual volume of the adjacent chamber 7, and is substantially or even exactly equal to the volume of the first screw displacement V2, that is, in this case the individual volume is equal to V2 + / -2%, preferably equal to V2 + / -1%, or even equal to V2 + / -0.5%.

[0100] Similarly, each of the closed chambers 8 defined by the second screw 3 and the barrel 4 has a substantially or even exactly the same individual volume, which is substantially or even exactly equal to the individual volume of the adjacent chamber 8, and is substantially or even exactly equal to the volume of the second screw displacement V3, that is, in this case the individual volume is equal to V3 + / -2%, preferably equal to V3 + / -1%, or even equal to V3 + / -0.5%.

[0101] From a dynamic perspective, therefore, at all of the following consecutive axial positions, the individual volume of each of the C-shaped closed chambers 7, 8 changes by less than 2%, less than 1%, or even less than 0.5% relative to the reference individual volume constituted by the screw displacements V2, V3, or even equals the reference individual volume: the consecutive axial positions occupied by the closed chambers 7, 8 during the rotation of the screws 2, 3 when the mentioned closed chambers 7, 8 are converted from the upstream to the downstream of the isochoric volume stage portion 11A (more preferably, from the closure of the chambers 7, 8 at the upstream limit 11U of the volume stage portion 11 until the chambers are reopened at the downstream limit 11D of the volume stage portion 11 (in this case at the outlet of the extruder 1)).

[0102] Equivalently, considering that at a given moment, the chambers 7 and 8 of the same series of chambers have a static visual distribution, rather than a dynamic visual of the chambers moving along the axis, this is equivalent to saying that all the closed chambers 7 and 8 of the series of closed chambers 7 and 8 defined by the mentioned screws 2 and 3 have substantially or even exactly the same individual volume, which is equal to the reference unit volume, within + / - 2%, preferably within + / - 1%, or even within + / - 0.5%.

[0103] It should be noted that the arrangement proposed by the present invention enables the extruder 1 to ensure an accuracy of the volume flow rate of less than or equal to 2%, even less than or equal to 1%, in other words, to convey a constant volume within + / - 2% or even + / - 1% per revolution of the screw, and for this purpose, preferably, the outlet pressure can be between 200 bar and 500 bar, and the volume flow rate can be between 1 dm 3 / min and 6 dm 3 / min.

[0104] Preferably, the first screw displacement V2 is equal to the second screw displacement V3.

[0105] Preferably, the first screw displacement V2 and the second screw displacement V3 are each between 8 cm 3 and 50 cm 3 , for example, between 10 cm 3 and 30 cm 3 , especially between 10 cm 3 and 20 cm 3 .

[0106] As described above, along the first central axis X2 of the first screw 2, in the direction from upstream to downstream, as the diameter of the first screw 2 decreases, the pitch P5 of the first thread 5 gradually increases in the isovolumetric volume stage portion 11A, and more preferably on the entire volume stage portion 11, such that the pitch P5 at the downstream end 11D of the volume stage portion of the first screw 2 (at 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 portion of the first screw 2 (at the first chamber 7 forming the inlet chamber).

[0107] This increase of the pitch P5 of the first thread 5 along the central axis X2 between the following two values is preferably monotonic, and more preferably linear: on the one hand, the value of the pitch P5 considered at the upstream end of the isovolumetric volume stage portion 11A (in this case, the upstream end 11U of the volume stage portion 11), which is the value of the so-called "inlet pitch" P5_in, and on the other hand, the higher value of the pitch P5 considered at the downstream end of the isovolumetric volume stage portion 11A (in this case, the downstream end 11D of the volume stage portion 11), which is the value of the so-called "outlet pitch" P5_out.

[0108] Over the entire isochoric volume stage section 11A, and more preferably over the entire volume stage section 11 of the first screw 2, this variation of the pitch P5 of the first thread 5 along the central axis X2 (in this case a continuous increase of the pitch P5) enables the axial width W9 of the channel 9 defined by the first thread 5 to be gradually increased (as clearly visible in Figure 1 , Figure 2 , Figure 3 , Figure 8 , Figure 9 and Figure 11 ), in order to compensate for the corresponding variation of the diameter of the first screw 2 (in this case a continuous decrease which, in this case, affects at least the outer diameter D_5C of the first thread and preferably also the root diameter D_5R of the first thread), so as to keep the individual volume of said chamber 7 substantially or even completely constant while each closed chamber 7 is gradually transferred downstream by the rotational movement of the first screw 2.

[0109] In other words, the first channel 9 defined by the thread 5 of the first screw has a pitch P5 and a width W9 which increase gradually along the central axis X2 in the isochoric volume stage section 11A (preferably over the entire volume stage section 11), more specifically a pitch P5 and a width W9 which increase continuously along the central axis X2 as an increasing function of the distance travelled, such that each substantially annular portion of said first channel 9 (which is delimited 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 (closing the end of said portion of the first channel 9) such that said portion of the first channel 9 forms a C-shaped closed chamber 7) has a volume which remains constant at each given moment when said chamber 7 is transformed from upstream to downstream under the action of the combined rotation of the first screw 2 and the second screw 3, said volume being equal to the volume of an adjacent closed chamber 7 of the same series of closed chambers 7.

[0110] Of course, the above considerations relating to the variation of the pitch P5 of the first thread 5 and thus to the variation of the axial width W9 of the first channel 9, with the necessary modifications, apply to the pitch P6 of the second thread 6 and the axial width W10 of the second channel 10, said pitch P6 and axial width W10 varying monotonically in a similar manner along the second central axis X3 such that the pitch P6 of the second thread evolves between a minimum value corresponding to the inlet pitch P6_in at the upstream end of the isochoric volume stage section 11A (which preferably coincides with the upstream end 11U of the volume stage section 11) and a maximum value corresponding to the outlet pitch P6_out at the downstream end of the isochoric volume stage section 11A (which preferably coincides with the downstream end 11D of the volume stage section 11). Thus, the individual volume of each closed chamber 8 remains substantially constant.

[0111] In all cases, in order to ensure the smooth engagement of the first screw 2 and the second screw 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 angle bisector at the vertex formed by the intersection of the first central axis X2 and the second central axis X3.

[0112] Naturally, as is clearly visible in Figure 2 , Figure 4 , Figure 5 , Figure 6 , Figure 8 and Figure 15 , as is the case with the axial widths W9, W10 of the channels 9, 10 (i.e., the recessed portions of the first thread 5 and the second thread 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, such that the first thread 5 and the second thread 6 are conjugate along the screws 2, 3, thereby maintaining the sealing of the chambers 7, 8 when each screw occupies the entire width of the channels 10, 9 defined by the threads 6, 5 of the other screw. In other words, in the isochoric volume stage 11A, more preferably in the entire volume stage 11, as the diameters of the tapered screws 2, 3 decrease, the pitch P5 and the profile thickness of each of the first thread 5 and the second thread 6 increase simultaneously along the central axes X2, X3.

[0113] Preferably, the first compensation law LP5_11 is an increasing quadratic function of the mentioned axial abscissa values along the first central axis X2.

[0114] Preferably, correspondingly, the second compensation law LP6_11 is an increasing quadratic function of the mentioned axial abscissa values along the second central axis X3.

[0115] Advantageously, the first compensation law LP5_11 and the second compensation law LP6_11 can be expressed in the form of a quadratic polynomial as a function of the axial abscissa.

[0116] Preferably, since the first screw 5 and the second screw 6 are mirror images of each other, the first compensation law LP5_11 and the second compensation law LP6_11 are the same.

[0117] The advantage of the quadratic function is that the increase in the pitches P5, P6 of the threads 5, 6 can compensate for the decrease in the surface area, which decrease is thus two-dimensional and is related to the decrease in the top diameters D_5C, D_6C of the threads 5, 6 and the decrease in the root diameters D_5R, D_6R of the threads 5, 6.

[0118] In particular, preferably, in the isovolumetric volume stage 11A, more preferably in the entire volume stage 11, the core 12 of the first screw 2 and the top of the flight 5 of the same first screw 2 narrow together, each according to a taper angle, more preferably according to the same taper angle A5, so that they therefore generally follow parallel slopes in a radial cross-sectional plane containing the central axis X2.

[0119] In other words, preferably, at least in the volume step 11, the root diameter D_5R of the first thread decreases according to the first taper angle A5, so that the height H5 of the first thread varies along the first center axis X2 in the volume step 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 center axis X2.

[0120] Advantageously, this makes it possible to limit the axial expansion of the pitch P5 of the thread 5 per one helical revolution of the thread, which is necessary to keep the screw displacement V2 constant, and also necessary to maintain a significant first screw displacement V2 and a good circulation of the material in the channel 9. Otherwise, it will be understood that if the height H5 of the first thread were reduced, in particular drastically, for example relative to the cylindrical core 12, it would be necessary to significantly lengthen the pitch P5 of the thread 5 in order to keep the displacement V2 constant, which would require lengthening the screw 2 and could have adverse effects on the tightness of the chamber 7.

[0121] As an illustration, for example, in particular in the volume stage 11 , the thread pitch P5 may be kept smaller than the minimum top diameter D_5C_min of the thread 5 in the volume stage 11 .

[0122] Similarly, in the isovolumetric volume stage 11A, and more preferably in the entire volume stage 11, the core 13 of the second screw 3 and the top of the flight 6 of this same second screw 3 narrow together, each according to a taper angle, preferably according to the same taper angle A6, so as to generally follow parallel slopes in a radial cross-sectional plane containing the central axis X2.

[0123] Therefore, the top diameter D_5C, D_6C of the thread 5, 6 of each of the first screw 2 and the second screw 3 (i.e., the outer diameter of the screws 2, 3) and the root diameter D_5R, D_6R of the thread 5, 6 (i.e., the inner diameter of the screws 2, 3) continuously decrease along the central axis X2, X3 of the mentioned screws 2, 3 according to the same predetermined taper angle A5, A6, while the pitch P5, P6 of the thread 5, 6 continuously increases to compensate for the common decrease in the root diameter D_5R, D_6R of the thread and the top diameter D_5C, D_6C of the thread, so that the continuous closed chambers 7, 8 defined by the mentioned screws 2, 3 each have a separate volume that is basically constant from one chamber 7, 8 to the next chamber along the central axis X2, X3.

[0124] 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 the first conical screw 2 at least in the volumetric stage section 11.

[0125] This preferably also applies to the thread height H6 of the second conical screw 3.

[0126] Generally, as can be seen in Figure 8 the thread height H5 of the first screw 2 represents the distance separating, on the one hand, the midpoint of the root 5R of the first channel 9 considered at the axial intermediate distance from the two lateral faces 5F adjoining the channel and, on the other hand, the generatrix tangent to the top 5C of the first thread adjoining the first channel 9, in other words the line corresponding to the intersection of the frustoconical envelope E2 and the said radial section plane. In other words, the thread height H5 is the length of the following straight-line segment: the straight-line segment perpendicular to the generatrix of the frustoconical envelope E2 and passing through the midpoint of the root 5R of the first channel 9.

[0127] This also applies to the height H6 of the thread 6 of the second screw 3 considered perpendicular to the frustoconical envelope E3.

[0128] However, for the sake of facilitating the calculations below, it is also possible to consider the projections H5', H6' of the thread heights H5, H6 in a plane perpendicular to the central axes X2, X3 of the screws 2, 3 mentioned.

[0129] Preferably, in the volumetric stage section 11, regardless of the angular positions respectively adopted by each of the first screw 2 and the second screw 3 around their central axes X2, X3 during the reverse rotational movement of the first screw 2 and the second screw 3, the number of chambers 7 of the first series that are simultaneously in the closed state and the number of chambers 8 of the second series that are simultaneously in the closed state are both 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.

[0130] In fact, the inventors have found that it is necessary to provide several axially consecutive chambers 7, 8 along the same screws 2, 3, in this case at least four or even at least five chambers, in order to obtain satisfactory sealing and thus satisfactory volumetric operation, including in the case where there is a high pressure at the outlet of the extruder 1.

[0131] 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 lengths L2, L3 of the screws 2, 3, usually by providing fewer than twenty, fewer than twelve, or even fewer than ten chambers along the same screw, in particular to prevent the risk of overprocessing the material, since overprocessing can cause the material to overheat, which can be detrimental to the material, so that using long screws 2, 3 with a greater number of chambers 7, 8 would require prophylactically reducing the rotational speed of the screws 2, 3, thereby limiting the maximum processing flow rate of the extruder 1.

[0132] Furthermore, limiting the lengths L2, L3 of the screws 2, 3 and the number of chambers reduces the resistance moment of the material resistance, thereby reducing the driving torque required to drive the screws 2, 3, which makes it possible to limit the energy consumption while ensuring good efficiency of the extruder 1, in particular a good mass flow rate.

[0133] It should be noted that the above dimensions are particularly suitable for the extrusion of rubber-based materials, since the short screw length limits the residence time of the extruded material in the extruder 1 (during which the extruded material is subjected to the processing of the screws 2, 3). This advantageously prevents overheating and thus prevents damage to the rubber-based material.

[0134] It should also be noted that the extruder 1 according to the present invention does not require a very large screw length L2, L3 to ensure satisfactory sealing when designed for extruding rubber-based materials. In particular, the axial screw lengths L2, L3 (more specifically the thread axial length) can be between 4 and 10 times the maximum diameter of the screws 2, 3, which is different from known extruders intended for thermoplastic materials, which must have a large length, typically about 40 times the maximum diameter of the screw, due to the significant fluidity of this thermoplastic material.

[0135] Therefore, the extruder 1 according to the present invention can be much shorter and lighter than known extruders, while still having a satisfactory volumetric displacement.

[0136] The length L3 of the second screw 3 (in this case corresponding to the total thread length of the second screw 3) is advantageously equal to the length L2 of the first screw 2 (in this case corresponding to the total thread length of the first screw 2).

[0137] According to a preferred feature that can independently form the present invention, the extruder 1 includes a stage called the "feeding stage" 30, which is located before the volumetric stage 11. Within the feeding stage 30:

[0138] - The first thread 5 is arranged such that as the top diameter D_5C of the first thread 5 decreases along the first central axis X2 in the upstream to downstream direction according to the first taper angle A5, the pitch P5 of the first thread 5 also decreases along the first central axis X2 in the upstream to downstream direction according to a law called the "first compression law" LP5_30, in such a way as to promote the compression of the material as it approaches the volumetric stage section 11, and

[0139] - The second thread 6 is arranged such that as the top diameter D_6C of the second thread 6 decreases along the second central axis X3 in the upstream to 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 to downstream direction according to a law called the "second compression law" LP6_30, in such a way as to promote the compression of the material as it approaches the volumetric stage section 11.

[0140] Advantageously, the feed stage section 30 makes it possible to receive the material, process it and pre-compress it to ensure feeding to the volumetric stage section, thus on the one hand ensuring good filling of the first chambers 7, 8 of each screw 2, so that the effective displacement V2, V3 of each of the screws 2, 3 can be optimized, and on the other hand limiting the pressure gradient between the upstream and downstream of the volumetric stage section 11, thus preventing leakage and preventing the material from moving backwards in a direction opposite to the desired forward movement FWD.

[0141] It should be noted that, advantageously, the first screw 2 and the second screw 3 interact in a non-volumetric manner within the feed stage section 30, which in particular makes it possible to use the extended pitches P5, P6 of the threads 5, 6 and thus very wide channels 9, 10, thereby facilitating the addition and swallowing of the material in the extruder 1, especially when the material arrives at the extruder in the form of a continuous strip.

[0142] Preferably, the minimum pitch P5, P6 of each of the screws 2, 3 considered in the feed stage section 30 is strictly greater than the longest pitch P5, P6 of the same screw 2, 3 considered in the volumetric stage section 11 (more specifically in the isochoric volumetric stage section 11A).

[0143] By way of illustration, always for the purpose of maintaining wide channels that facilitate the swallowing of the material, the initial pitches P5, P6 in the feed stage section 30 are preferably equal to or greater than 0.5 times the diameters D_5C, D_6C of the tops of the threads 5, 6 considered at the upstream end of the feed stage section 30.

[0144] Of course, an air inlet opposite to the feed stage section 30 can be provided in the barrel 4, and the air inlet may be provided with a hopper to allow the material to enter the barrel 4.

[0145] According to a possible variant embodiment ( Figure 1 、Figure 2 and Figure 15 As shown in Figure 15 , the first screw 2 and the second screw 3 can be single-threaded in the feed stage 30, and more preferably single-threaded in both the feed stage 3 and the volume stage 11.

[0146] Thus, advantageously, a single thread that extends continuously but has its pitch P5, P6 adjusted can pass through the respective feed stages 30 of the screws 2, 3 and then through the volume stage 11.

[0147] However, preferably, according to Figure 3 and Figure 4 In another variant embodiment shown in Figure 4 , in the feed stage 30, both the first screw 2 and the second screw 3 are multi-threaded, preferably double-threaded, such that the first thread 5 and the second thread 6 each include at least two threads that cover the same common axial range and are angularly offset from each other about the central axes X2, X3 of the mentioned screws 2, 3.

[0148] These multi-threads in the feed stage 30 make it possible in particular to facilitate the grasping of the material (especially when the material is supplied in the form of a strip) and the swallowing of the material by the screws 2, 3.

[0149] This arrangement also improves the processing of the material and the increase of its pressure, thus facilitating the feeding to the volume stage 11 that is directly downstream of the feed stage 30.

[0150] Conversely, it is preferred that the first screw 2 and the second screw 3 are each single-threaded in the volume stage 11.

[0151] Thus, the screws 2, 3 can have a transition zone 31 between the feed stage 30 and the volume stage 11, such that it is possible to change from the upstream of the multi-thread to the downstream of the single-thread, and in appropriate cases from one core geometry 12, 13 to another core geometry 12, 13, for example to adjust the root diameter D_5R, D_6R of the thread and / or the taper angle of the cores 12, 13.

[0152] Specifically, it should be noted that preferably the core 12 of the first screw 2 has a straight cylindrical shape or a truncated conical shape in the feed stage 30, and the taper angle of the truncated conical shape is strictly less than the first taper angle A5.

[0153] Correspondingly, the core 13 of the second screw 3 preferably has a straight cylindrical shape or a truncated conical shape in the feed stage 30, and the taper angle of the truncated conical shape is strictly less than the second taper angle A6.

[0154] This arrangement advantageously enables a relatively large root diameter D_5R, D_6R to be maintained in the feed stage 30, which enables a high driving torque to be transmitted to the screws 2, 3 and maintains a certain "diameter reserve", and then the frustoconical reduction of the cores 12, 13 can be continued in the isochoric volume stage 11A based on the diameter reserve, without the risk of structurally overweakening the screws 2, 3.

[0155] Furthermore, the low or even zero taper angle of the cores 12, 13 in the feed stage 30 helps to reduce the volume of the channels 9, 10 under the action of the reduction of the pitches P5, P6 of the threads 5, 6, thereby promoting the compression of the material and thus promoting the feeding to the volume stage 11.

[0156] In the transition zone 31, as visible in Figure 3 and Figure 4 the multi-threads of the feed stage 30 can end in the form of a nozzle 32 that leads to the channels 9, 10 so that the material can enter the chambers 7, 8 of the volume stage 11.

[0157] In fact, the respective isochoric volume stages 11A of the first conical screw 2 and the second conical screw 3 can be dimensioned according to the following method and with reference to Figure 11 、 Figure 12 and Figure 13 to determine the dimensions.

[0158] For the sake of brevity only, the dimensioning of the first conical screw 2 will be described only, taking into account that the dimensioning of the second conical screw 3 will be carried out in a similar manner.

[0159] In absolute terms, closed chambers 7, 8 can be provided within the volume stage 11, in particular in the upstream axial part of the volume stage 11 located before the isochoric volume stage 11A, in which the pitches P5, P6 are set not to increase, so that in particular an enhanced compression effect is first obtained between the first chamber and the second chamber of the mentioned series of chambers 7, 8 within the volume stage 11 after filling the first chamber through the feed stage 30. However, for the sake of description, the preferred variant embodiment will be given priority below, in which the compensation laws LP5_11, LP6_11 relate to the entire volume stage 11, in other words the isochoric volume stage 11A extends over the entire axial extent of the volume stage 11 such that the upstream axial limit and the downstream axial limit of the isochoric volume stage 11A coincide with the upstream limit 11U and the downstream limit 11D of the volume stage 11.

[0160] The "large outer diameter" D_5C_max, D_6C_max represents the pitch diameter of the threads 5, 6 of the screws 2, 3 considered at the upstream end 11U of the constant volume stage section 11A, which thus forms the diameter of the large circular base of the frustoconical envelope E2 of the constant volume stage section 11A.

[0161] Similarly, the "small outer diameter" D_5C_min, D_6C_min, which is strictly smaller than the large outer diameter D_5C_max, D_6C_max, represents the pitch diameter of the threads 5, 6 of the screws 2, 3 considered at the downstream end 11D of the constant volume stage section 11A, which thus forms the diameter of the small circular base of the frustoconical envelope E2 of the constant volume stage section 11A.

[0162] Advantageously, the large outer diameter D_5C_max of the first screw 2 is equal to the large outer diameter D_6C_max of the second screw 3, and the small outer diameter D_5C_min of the first screw 2 is equal to the small outer diameter D_6C_min of the second screw 3.

[0163] To determine the compensation law LP5_11, first, at several different abscissas along the constant volume stage section 11A, more preferably at least at the upstream end 11U and the downstream end 11D of the volume stage section 11A and preferably at one or more additional abscissas between these ends, the radius of the top of the thread for obtaining the required displacement V2 is determined, and then the points thus defined are interpolated by a quadratic polynomial law, which constitutes the compensation law LP5 - 11, so that the radius of the top of the thread 5 can be defined at any abscissa of the constant volume stage section 11A.

[0164] For this purpose, first, the displacement V2 of the first screw 2 needs to be determined, in other words, the volume of the extruded material discharged by the screw 2 each time the screw 2 makes a complete rotation around its central axis X2. This displacement V2 actually corresponds to the individual and constant volume V2 of each C-shaped chamber 7 of the first series of closed chambers 7. The closed chambers 7 correspond to the respective successive parts of the first channel 9 along the first central axis X2, which are each located on the one hand between the screw 2 and the inner wall of the barrel 4 and on the other hand are closed by the second thread 6 of another screw 3, and the second thread 6 penetrates into the first thread 5 to locally close the first channel 9.

[0165] Then, it is calculated with reference to the frustoconical envelope E2 of the constant volume stage section 11A of the first screw 2:

[0166] - On the one hand, there is the inlet radius R2_in, which corresponds to the radius of the top 5C of the first thread 5 at the upstream end 11U of the isochoric volume stage 11A and is thus equal to half of the large outer diameter D_5C_max corresponding to the diameter of the large base of the frustoconical envelope E2, and

[0167] - On the other hand, there is the outlet radius R2_out of the isochoric volume stage 11A, which corresponds to the radius of the top 5C of the first thread 5 at the downstream end 11D of the isochoric volume stage 11A and is thus equal to half of the small outer diameter D_5C_min corresponding to the diameter of the small base of the frustoconical envelope E2.

[0168] For this purpose, the following are taken into account:

[0169] - The length L11A of the isochoric volume stage 11A, which, like the displacement V2, is selected by the designer, and the length L2 is measured along the first central axis X2, in other words, along the following straight line: the straight line having the height of the frustoconical envelope E2 (and thus corresponding to the angle bisector at the vertex of the frustoconical envelope E in the cross-sectional plane containing the first central axis X2).

[0170] - The total length L_tot, which corresponds to the height measured between the large base of the first frustoconical envelope E2 and the vertex S2 of the cone of the first frustoconical envelope E2, - The taper angle A5 of the first screw 2, which is also selected by the designer, preferably within the range of the above values.

[0171] By means of simple trigonometric functions in the radial cross-sectional plane containing the first central axis X2, as Figure 7 shown, it is obtained that:

[0172] R2_in = L_tot * tan(A5)

[0173] R2_out = (L_tot – L2) * tan(A5)

[0174] Given the selected height H5 of the first thread 5 and thus the projection H5' of said height in the plane perpendicular to the central axis X2, the value R1_in called "inlet apparent semi-central distance" is derived, which in the plane of the large base of the first frustoconical envelope E2 (this plane is perpendicular to the first central axis X2) corresponds to the radial distance measured between: on the one hand, the central axis X2; on the other hand, the intersection point M1 of the plane of the large base of the first frustoconical envelope E2 and the straight line X1, and the straight line X1 corresponds to the central axis of the extruder 1 and extends equidistantly from the first central axis X2 and the second central axis X3 in the plane containing the first central axis X2 and the second central axis X3:

[0175] R1_in = R2_in – (H5’ / 2)

[0176] Similarly, in the plane of the small base of the first frustoconical envelope E2, the value of the outlet apparent semi-central distance R1_out is derived as follows:

[0177] R1_out = R2_out – (H5’ / 2)

[0178] Then, in the plane of the large base of the first frustoconical envelope E2, as shown, an arc segment called the "inlet truncated arc segment" 20_in is identified, which corresponds to the domain between, on the one hand, an arc chord C20 passing through the intersection point M1 and perpendicular to the radius centered on the first central axis X2, and on the other hand, an arc whose radius bounded by this arc chord C20 corresponds to the inlet radius R2_in. Figure 13

[0179] The area A20_in of this inlet truncated arc segment 20_in is:

[0180] A20_in = 1 / 2 * (R2_in) 2 * (alpha_in – sin(alpha_in))

[0181] where alpha_in represents the angle covered by the arc bounding the inlet truncated arc segment 20_in and is thus:

[0182] alpha_in = 2 * Arccos(R1_in / R2_in)

[0183] Similarly, the area of the outlet truncated arc segment 20_out is considered:

[0184] A20_out = 1 / 2 * (R2_out) 2 * (alpha_out – sin(alpha_out))

[0185] where alpha_out represents the angle covered by the arc bounding the arc segment 20_out and is thus:

[0186] alpha_out = 2 * Arccos(R1_out / R2_out)

[0187] In the plane of the large base of the frustoconical shape E2, the area A7_in of the inlet chamber 7 is considered as the difference between, on the one hand, the area of the ring between the root 5R and the top 5C of the first thread 5, and on the other hand, the truncated area occupied by the thread 6 of the second screw 3 penetrating into the channel 9 of the first screw 2.​

[0188] Due to the symmetrical arrangement of the first screw 2 and the second screw 3, the truncated area of the generally elliptical shape is equal to twice the area A20_in of the above-mentioned inlet truncated circular arc section 20_in.

[0189] Therefore, since at the upstream end 11U of the constant volume stage section 11A, the top 5C of the first thread is located at a radius corresponding to the inlet radius R2_in, and the root 5R of the first thread is located at a radius at a height H5’ retracted from the thread top 5C, the following formula is obtained:

[0190] A7_in = π * [(R2_in) 2 – (R2_in – H5’) 2 – (2 * A20_in)

[0191] Similarly, in the plane of the small base of the frustum-shaped E2, the area A7_out of the outlet chamber 7 at the downstream end 2D of the first screw can be defined as:

[0192] A7_out = π * [(R2_out) 2 – (R2_out – H5’) 2 – (2 * A20_out)

[0193] Then, the inlet pitch P5_in considered at the axial abscissa of the upstream end 2U of the first screw is defined as the ratio of the required displacement V2 to the area A7_in of the inlet chamber defined as above:

[0194] P5_in = V2 / A7_in.

[0195] Similarly, the outlet pitch P5_out at the downstream end 2D of the first screw 2 is defined as the ratio of the same displacement V2 (desired to be constant) to the area A7_out of the outlet chamber (which is actually smaller than the area A7_in of the inlet chamber):

[0196] P5_out = V2 / A7_out.

[0197] After these two pitch extremes P5_in, P5_out are determined, the operation can be repeated at one or more intermediate abscissas, and a regression law, preferably a quadratic polynomial law, can be applied to the obtained point cloud, which defines the compensation law LP5_11.

[0198] The present invention of course also relates to a device 100, as can be seen in Figure 14 , the device 100 includes an extruder 1 according to any of the above features to convey a material, preferably a rubber-based mixture.

[0199] The device 100 includes a base 101. Advantageously, the base forms a fixed reference system and may correspond to the floor of the building housing the device or to a frame optionally fixed to the building.

[0200] The device 100 further includes a receiving support 102 intended to receive the material extruded by the extruder 1, such as a platform, a drum or an annular core.

[0201] The receiving support 102 is carried by the base 101 and may be mounted so as to be movable relative to the base 101. For example, in the case where the drum or the core is shaped to rotate about a main axis Y102, the drum or the core may be mounted so as to be rotatable relative to the base 101 about the main axis Y102, preferably electrically.

[0202] The device 100 further includes a robotic conveying device 103, such as a Cartesian robot (as Figure 14 shown), or an anthropomorphic robotic arm, which carries the extruder 1 and is arranged in such a way that the extruder 1 can be moved relative to the receiving support 102 when the extruder 1 conveys the extruded material, so as to be able to lay the extruded material at different positions of the receiving support 102 according to a predetermined desired layout.

[0203] Since the extruder 1 according to the present invention is lightweight and compact, this makes it possible to use the extruder 1 within a mobile laying head 104 mounted on the robotic conveying device 103.

[0204] The robotic conveying device 103 carrying the extruder 1 is interposed between the base 101 and the extruder 1 such that the extruder can be moved relative to the base 101 and relative to the receiving support 102 when the extruder conveys the extruded material, the movement advantageously being different from any inherent movement of the receiving support 102 relative to the base 101 and being controllable independently.

[0205] Thus, the robotic conveying device 103 is preferably capable of moving the extruder 1 translationally along at least one axis, preferably at least two axes or even three orthogonal axes, so as to position the extruder 1 in the reference system of the base 101.

[0206] For this purpose, the robotic conveying device 103 may for example include at least one, preferably two, electric translation plates 106, 107, such as two horizontal electric translation plates 106, 107 intersecting perpendicularly to each other.

[0207] Furthermore, the robotic conveying device 103 can preferably rotate the extruder 1 around at least one axis, two axes, or even three axes so that the extruder is oriented relative to the receiving support 102 in a pitch, roll, and / or yaw manner.

[0208] The laying head 104 includes a die connected to the outlet of the extruder 1 to give the extruded material an appropriate shape, such as the shape of a flat strip.

[0209] The laying head 104 can also include an applicator member 105, such as a pressure roller 105, which is arranged to press the extruded material leaving the extruder 1 through the die against the receiving support.

[0210] Preferably, a continuous strip of material from a storage unit or a production unit is supplied to the laying head 104 (more specifically, the extruder 1).

[0211] Finally, the device relates to an extrusion method for implementing the extruder 1 or the device 100 according to the present invention.

[0212] In particular, the present invention relates to the use of the extruder 1 according to the present invention or the device 100 according to the present invention for extruding a rubber-based mixture, such as for manufacturing a part of a vehicle tire, especially a part of a pneumatic tire.

[0213] Therefore, the extruder 1 (more generally, the device 100) can be arranged to lay a strip of raw rubber on a drum-shaped body or an annular core.

[0214] Preferably, in this case, when the rotational speed of each of the first screw 2 and the second screw 3 is less than or equal to 300 rpm, for example, between 10 rpm and 300 rpm, the extruder 1 can provide a mass flow rate greater than or equal to 1 kg / min, for example, between 1 kg / min and 6 kg / min.

[0215] Preferably, these performance levels can be achieved when the pressure at the outlet of the extruder, the outlets of the last chambers 7, 8, and exactly at the inlet of the die is between 150 bar and 500 bar and the material temperature is between 80 °C and 150 °C.

[0216] Of course, the present invention is in no way limited to the above-described variant embodiments, and those skilled in the art can, in particular, separate or freely combine any of the foregoing features, or replace them with equivalent features.

Claims

1. An extruder (1) intended to extrude a material, said extruder (1) comprising: - A barrel (4), - A first screw (2) rotatably mounted in said barrel (4) about a first central axis (X2) and provided with a first thread (5), - A second screw (3) rotatably mounted in said barrel (4) about a second central axis (X3) and provided with a second thread (6), The first screw (2) and the second screw (3) rotate in opposite directions and are arranged such that the first thread (5) and the second thread (6) interact to convey the material from upstream to downstream in said barrel (4), the extruder (1) being characterized in that: - The first screw (2) is conical such that the top diameter (D_5C) of the first thread (5) decreases along the first central axis (X2) in the upstream to downstream direction according to a first predetermined taper angle (A5), - The second screw (3) is conical such that the top diameter (D_6C) of the second thread (6) decreases along the second central axis (X3) in the upstream to downstream direction according to a second predetermined taper angle (A6), The extruder (1) comprises a stage called the "volumetric stage" (11), within which the first thread (5) of the first screw (2) and the second thread (6) of the second screw (3) interpenetrate and conjugate with each other such that on the one hand a first series of continuous C-shaped closed chambers (7) are formed between the barrel (4) and the first screw (2) along the first central axis (X2) and on the other hand a second series of continuous C-shaped closed chambers (8) are formed between the barrel (4) and the second screw (3) along the second central axis (X3), such that the rotation of the first screw (2) and the second screw (3) produces a positive displacement of the material captured by the first series of chambers (7) and the material captured by the second series of chambers (8), and At least a part of the volumetric stage forms a stage called the "isochoric volumetric stage" (11A), within which: - According to a law called the "first compensation law" (LP5_11), as the top diameter (D_5C) of the first thread decreases, the pitch (P5) of the first thread (5) increases along the first central axis (X2) in the upstream to downstream direction, the first compensation law causing the pitch (P5) of the first thread (5) to increase gradually so as to compensate for the taper of the first screw (2), such that in the isochoric volumetric stage (11A), the individual volume of each closed chamber (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 - According to a law called the "second compensation law" (LP6_11), as the major diameter (D_6C) of the second thread decreases, the pitch (P6) of the second thread (6) increases in the upstream to downstream direction along the second central axis (X3). The second compensation law causes the pitch (P6) of the second thread (6) to gradually increase so as to compensate for the taper of the second screw (3), such that in the isochoric volume stage portion (11A), the individual volume of each closed chamber (8) of the second series of closed chambers is maintained equal to the same predetermined constant nominal volume (V3) called the "second screw displacement" (V3), with a maximum tolerance of + / -2%, preferably + / -1%, or even + / -0.5%.

2. The extruder according to claim 1, wherein The first compensation law (LP5_11) is an increasing quadratic function of the axial abscissa value involved along the first central axis (X2), and correspondingly, the second compensation law (LP6_11) is an increasing quadratic function of the axial abscissa value involved along the second central axis (X3).

3. The extruder according to claim 1 or 2, 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, and even more preferably equal to 2.5 degrees.

4. The extruder according to any one of the preceding claims, characterized in that, In the volume stage portion (11), regardless of what angular positions each of the first screw (2) and the second screw (3) adopt around their central axes (X2, X3) during the reverse rotational movement of the first screw (2) and the second screw (3), the number of chambers (7) of the first series that are simultaneously in the closed state and the number of chambers (8) of the second series that are simultaneously in the closed state are both equal to or greater than four or even equal to or greater than five, which is the lower limit, and preferably less than or equal to twenty or even less than or equal to twelve, which is the upper limit. For example, it is between four and ten, or between five and eight.

5. The extruder according to any one of the preceding claims, characterized in that, The first screw displacement (V2) and the second screw displacement (V3) are each between 8 cm 3 and 50 cm 3 for example between 10 cm 3 and 30 cm 3 especially between 10 cm 3 and 20 cm 3 between.

6. The extruder according to any one of the preceding claims, characterized in that, At least in the volume stage portion (11), the root diameter (D_5R) of the first thread decreases according to the first taper angle (A5), such that the change in the height (H5) of the first thread along the first central axis (X2) in the volume stage portion is less than 20%.

7. The extruder according to any one of the preceding claims, characterized in that, The extruder includes a stage portion called the "feeding stage portion" (30), which is located before the volume stage portion (11). Inside the feeding stage portion: - The first thread (5) is arranged such that as the major diameter (D_5C) of the first thread (5) decreases according to the first taper angle (A5) in the upstream to downstream direction along the first central axis (X2), the pitch (P5) of the first thread (5) also decreases in the upstream to downstream direction along the first central axis (X2) according to a law called the "first compression law" (LP5_30), in such a way as to promote the compression of the material when the material approaches the volume stage portion (11), and - The second thread (6) is arranged such that as the top diameter (D_6C) of the second thread (6) decreases along the second central axis (X3) in the upstream to 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 to downstream direction according to a law called the "second compression law" (LP6_30), in such a way as to promote the compression of the material when the material approaches the volume stage portion (11).

8. The extruder according to claim 7, wherein, The core (12) of the first screw (2) has a straight cylindrical shape or a truncated conical shape in the feed stage portion, and the taper angle of the truncated conical shape is strictly less than the first taper angle (A5); correspondingly, the core of the second screw (3) has a straight cylindrical shape or a truncated conical shape in the feed stage portion (30), and the taper angle of the truncated conical shape is strictly less than the second taper angle (A6).

9. The extruder according to claim 7 or 8, characterized in that, In the feed stage portion (30), both the first screw (2) and the second screw (3) are multi-threaded, preferably double-threaded, such that the first thread (5) and the second thread (6) each include at least two threads, the at least two threads cover the same common axial range, and are angularly offset from each other around the central axes (X2, X3) of the mentioned screws (2, 3).

10. The extruder according to any one of the preceding claims, characterized in that, The first screw (2) and the second screw (3) are each single-threaded in the volume stage portion (11).

11. An apparatus (100) comprising an extruder (1) according to any one of claims 1 to 10 for conveying a material, preferably a rubber-based mixture, the apparatus further comprising a receiving support (102) and a robotic conveying device (103), the receiving support (102) being, for example, a platform, a drum-shaped body or an annular core, the receiving support (102) being intended to receive the material extruded by the extruder (1), the robotic conveying device (103) being, for example, a Cartesian robot or an anthropomorphic robotic arm, the robotic conveying device (103) carrying the extruder (1) and arranged to be able to move the extruder (1) relative to the receiving support (102) when the extruder (1) conveys the material, so as to be able to lay the extruded material at different positions on the receiving support (102) according to a predetermined desired arrangement.

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

13. The use according to claim 12, wherein, When the rotational speed of each of the first screw (2) and the second screw (3) is less than or equal to 300 rpm, for example between 10 rpm and 300 rpm, 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.

Images