Screws and twin-screw assemblies for use in elastomer mixture extruders, and related methods for extruding elastomer mixtures.

Abstract

The screw (21; 22) used in the twin-screw assembly of the elastomer mixture extruder comprises a screw section with a single-start type of thread defining three different sectors (30, 40, 50): an intake sector (30) that captures the mixture supplied from the outside and extrudes it downstream along the longitudinal direction (X-X) and has a through-flow channel cross-section (S) contained between adjacent flanks of the thread, the cross-section (S) being constant over two pitches of the thread or 720° of rotation; a transition sector (40) that has a variable through-flow channel cross-section (S) smaller than the cross-section of the through-flow channel of the intake sector, the cross-section (S) increasing the compressive force acting on the mixture passing through in the longitudinal direction (X-X); and a high-pressure sector (50) that has the smallest cross-section of the through-flow channel, which cross-section is constant over one pitch and causes compression of the mixture to obtain maximum pressure of the mixture.

Description

Technical Field

[0001] The present invention relates to a threaded screw for use in a twin-screw extruder having an intermeshing screw for the extrusion and / or filtration of an elastomer-based mixture, a twin-screw extruder having an intermeshing screw for an elastomer mixture, and a method for extruding an elastomer-based mixture.

Background Art

[0002] It is known that elastomeric materials such as elastomer-based mixtures or compounds are amorphous materials having a glass transition temperature lower than the ambient temperature. In other words, an elastomeric material at a temperature above the ambient temperature is already a highly viscous (viscoelastic) fluid that is already "rubbery" and thus does not need to be melted for further processing.

[0003] These materials are generally known as rubbers and include, for example, natural rubber, polybutadiene, polyisoprene, EPDM, NBR, and SBR.

[0004] In the technical field related to the production of elastomer-based compounds, it is known that there is a need for the latter "filtration". In this operation, the material to be treated is made to flow through a "filter" generally composed of one or more metal mesh structure screens having through-flow openings of an appropriate mesh size with an appropriate machine.

[0005] Typically, this opening has a value in the range between 0.1 mm and 1 mm.

[0006] The purpose of this operation is to retain any possible "objects" (such as impurities, particles of unmixed materials, etc.) within the filter and thus remove them from the compound. This object has dimensions larger than the through-flow openings of the filter mesh.

[0007] A typical example is a compound used to create the visible exterior of an automobile, such as window seals. In this case, a "perfect" surface appearance is a key feature. To achieve this, it is necessary to eliminate all potential causes of surface irregularities from the compound used.

[0008] Another area where filtration is crucial is in the field of compounds used in power supply cables, which must contain absolutely no impurities, especially metallic impurities.

[0009] To filter a compound, it is necessary to "push" or "force" the compound to pass through the filter. This operation is only possible when the compound is in a fluid state, that is, when the compound has a viscous component that is dominant over the elastic component. This state occurs when the compound is not crosslinked (not vulcanized), and therefore the polymer chains are not chemically bonded.

[0010] In its non-crosslinked (so-called "raw") state, elastomer compounds can be considered as a "fluid" that can "flow" or "move freely."

[0011] Even in this state, the fluid in question has a relatively extremely high viscosity. Therefore, during the fluid motion of the compound, an undesirable temperature rise may occur due to high friction within the material.

[0012] Therefore, filtration must be carried out under conditions where the compound is not crosslinked and where no crosslinking occurs during filtration. As a result, filtration is largely dependent on two main factors: temperature and pressure.

[0013] Therefore, temperature increases, such as those caused by friction, must be avoided throughout the entire process. Thus, temperature must be controlled by reducing friction and / or by efficiently dissipating the generated heat.

[0014] The pressure required to supply the compound during processing also depends on the velocity of the "fluid" passing through the filter. All other conditions being equal, in order to obtain increased productivity and thus increased flow rate, it is necessary to increase this velocity precisely, which in turn increases the pressure and therefore the temperature.

[0015] Furthermore, it is known that during all processes involving elastomers subject to velocity gradients, these very "gradients" can cause mechanical stress within the material being processed, and this stress can generally lead to undesirable changes in properties (e.g., a decrease in viscosity due to mechanical fracture of the polymer).

[0016] Therefore, from the perspective of rubber technology, there is a problem in filtering elastomer-based compounds as follows. Under the conditions of high flow rate / productivity. The temperature rise of the compound is limited to a relatively low value, and initial crosslinking is avoided under any circumstances. To avoid deterioration of the mechanical properties of the material, such as unwanted cleavage of polymer chains.

[0017] From an industrial standpoint, filtration processes generally need to ensure the following: The economic sustainability of the processing operations, and therefore, the low cost of those operations (i.e., the cost of machinery, labor, and energy). It must be easy and safe to operate. The plant layout is simple and highly automated. "Environmental" sustainability, meaning limited low-value emissions and waste treatment.

[0018] Different types of single-screw or multi-screw extruders are known in various technical fields related to the processing of plastic compounds such as PVC and PP.

[0019] Plastic compounds have a glass transition temperature higher than the ambient temperature. Therefore, plastic compounds must be introduced into the extruder in a solid state and heated within the extruder so that they can be "melted" for processing. Consequently, processes and extruders designed for plastic materials are unsuitable for the proper processing of elastomer compounds, where the aforementioned heating must be avoided as much as possible. Thus, the two technical fields are considered to be extremely different from each other.

[0020] Known extruders for heating compounds and processing plastic materials are described, for example, in US20150184655A1, which proposes the use of a profiled constant-pitch screw, and in US2508495, which proposes the use of a screw having a thread pitch and width that changes continuously and progressively between the compound inlet and outlet.

[0021] GB1,359,672 describes a single-screw or twin-screw extruder equipped with a non-meshing screw for processing solid plastic materials such as PET, and a heating means for melting the plastic material. The volume contained between adjacent peaks of the screw threads is varied by "lands" protruding from the bottom of the threads. Due to the presence of these protruding lands, the screw cannot be used in a twin-screw extruder equipped with a meshing screw for processing elastomer workpieces.

[0022] Such screws and extruders are not suitable for the extrusion and filtration of elastomeric compounds because they are equipped with heating means (diathermic oil or electrical resistance) designed to heat the plastic material being processed to the high temperatures required for melting (rather, because they can damage elastomeric materials that should not be melted), and due to the non-intermeshing screws, there is play between the screws, resulting in excessive loss of flow rate and inability to reach sufficient pressure for the extrusion / filtration of elastomers. Further, non-intermeshing screws operate along substantially separate and independent compound flow paths.

[0023] Devices for filtering elastomeric compounds include known intermeshing twin-screw / multi-screw extruders. These generally comprise screws configured to rotate in opposite directions and generate high pressure in the compound at the filter.

[0024] However, these known extruders have the following processing problems. When loaded into the extruder at ambient pressure, a large amount of air may be trapped within the compound and may remain "trapped" within the compound until the filtration stage. As a result, the final product contains air bubbles inside and is difficult / impossible to use in downstream filtration processes. They have a relatively long screw length to reduce backflow against the main movement and obtain the desired pumping effect. However, since the heat generated by the friction between the compound, the surface of the screw, and the cylinder increases with the increase of its surface, this length has the opposite effect for the purpose of controlling the temperature rise of the compound.

[0025] Furthermore, the greater the contact area with the compound, the higher the likelihood that the properties of the compound being processed will change significantly due to the friction between the compound and the surface.

Prior Art Documents

Patent Documents

[0026] [Patent Document 1] US20150184655A1 [Patent Document 2] US2508495 [Patent Document 3] GB1,359,672 [Summary of the Invention] [Problems to be Solved by the Invention]

[0027] Therefore, the technical problem posed is, in particular, to provide a screw having parallel rotating shafts arranged to mesh with each other, having an improved design suitable for use in a twin-screw extruder for elastomer mixtures with axial discharge, thereby overcoming or at least reducing the drawbacks of the prior art.

[0028] The specific problem posed is to create the screw geometry such that air present in the elastomer mixture can be discharged before filtering the elastomer mixture and / or such that the temperature rise and change in physical properties of the mixture being processed can be reduced.

[0029] The technical problem that has been posed is also to provide a twin-screw extruder for elastomer mixtures, which is as follows. That is, It comprises a loading system operating at ambient pressure and / or It does not require lubrication for the material being processed (i.e., there is no loss of the mixture) and / or It is highly productive and / or It guarantees improved heat exchange, i.e., less heat generation and / or It has a screw design that ensures high pressure only within the target zone and along a relatively short section and / or It can discharge the air trapped within the mixture before the mixture reaches the filtration zone and / or It does not cause any change in the physical properties of the mixture.

[0030] In relation to this problem, twin-screw assemblies and / or extruders are also required to be easy and inexpensive to manufacture and assemble, to be small in size, and to be easily installed in any location the user desires. [Means for solving the problem]

[0031] These results are obtained by the present invention with a screw according to the features of claim 1 and a twin-screw assembly according to claim 9.

[0032] The present invention further relates to a method for extruding an elastomer mixture according to claim 20.

[0033] Further details can be obtained from the following description of non-limiting examples of embodiments of the subject matter of the present invention, provided with reference to the accompanying drawings. [Brief explanation of the drawing]

[0034] [Figure 1] This is a side view of the screw according to the present invention. Three different longitudinal portions of the screw are highlighted. [Figure 2] Figure 1 is a side view of the screw. Various characteristic parameters are shown. [Figure 3] This is an exploded view of the twin-screw assembly according to the present invention. [Figure 4] Figure 3 is a perspective view of the twin-screw assembly as it is assembled and with the housing cylinder open. [Figure 5] Figure 3 shows a perspective view of the extruder according to the present invention, assembled with the twin-screw assembly. [Figure 6] This is a schematic cross-sectional view of an extruder according to the present invention, showing the play present between the screws and between the screws and the cylinder. [Figure 7a] This is a schematic diagram of the play that exists between the screws. [Figure 7b] This is a schematic diagram of the play between the screws, and corresponding graphs of the pressures obtained in various sectors. [Figure 8a] A perspective view of a pair of screws in a twin-screw assembly. The C-chamber is highlighted. [Figure 8b] A perspective view of a pair of screws in a twin-screw assembly. The C-chamber is highlighted. [Figure 8c] This is a partial side view of a pair of screws in a twin-screw assembly. The C-chamber is highlighted and the different flow rates involved are shown. [Figure 9] This figure shows an example of the rate of change of the volume of the C chamber according to the axial position of the chamber in the passage from the mixture intake zone to the high-pressure / output zone of the extruder. [Figure 10] This figure shows an example of the actual flow rate progression and the change in the volume of the C-chamber along the screw's rotation axis in a preferred embodiment of the twin-screw assembly of the present invention. The local width (W) of the thread crest is shown along the x-axis. [Figure 11] This is a schematic diagram of the cross-section of the flow-through channel of the screw according to the present invention when the rotation angle of the screw thread is changed. [Figure 12] Figures a through e show examples of screw geometry according to the present invention. [Figure 13] Figures a through e show examples of pairs of meshing, counter-rotating screws in a mirror arrangement, each formed by the respective screws shown in Figure 12. [Figure 14] Figures 14A to 14E show examples of characteristic progression of the through-section of a twin-screw assembly according to Figure 13, depending on the thread winding angle. [Modes for carrying out the invention]

[0035] As illustrated, for the sake of ease of explanation and without any restrictive meaning, we assume a set of three reference axes: a longitudinal direction X-X corresponding to the axial length dimension of the screw and the direction of mixture supply; a transverse direction Y-Y corresponding to the radial width dimension of the screw; and a perpendicular direction Z-Z that, during use in a twin-screw assembly, is parallel to the interaxial plane between the rotation axes of the two screws and perpendicular to the other two directions. The screw according to the present invention has a threaded section. Its threading is of the single-thread type, and the threads are raised relative to the core, defining three different longitudinal sectors, namely 30, 40, and 50, respectively.

[0036] Referring to Figures 2 and 6, some characteristic parameters of the screw according to the present invention are described below. These characteristic parameters will be referenced further in the description. P = screw pitch. It is measured as the axial distance between the centerlines of two thread peaks that are spaced 360° apart (a complete rotation of the threads around the screw axis). In the applications of this invention, the pitch is generally constant along the entire screw and preferably coincides with the outer diameter D. D = outer diameter of the screw. It is generally constant along the entire length of the screw. d = the inner diameter of the screw corresponding to the core diameter. d may vary along the length of the screw, but is preferably constant in the intake and high-pressure sectors. Flow channel: The free volume contained between adjacent flanks in a screw thread (corresponding to the grooves of the screw thread). Top: The upper surface that connects two consecutive flanks. (Channel) Through-flow cross-section: The cross-section of a through-flow channel (or groove) along the axial plane through which the screw passes along its axis of rotation. W = width measured along the axial direction of the top of the screw thread. H = Height of the mixture permeable channel L = length of the threaded portion of the screw.

[0037] Preferably, the thread profile may have a trapezoidal or flattened triangular shape.

[0038] Further definitions are also provided for the purpose of describing the twin-screw assembly according to the present invention. I = the distance between the axes of the screws in the screw assembly (Figure 6). O' = the distance between the top of one screw and the core of the other screw (Figure 6). δ = the distance between the top of one screw and the inner surface of the housing cavity of the containment cylinder (Figure 6). C-chamber: A C-shaped chamber defined by the free volume between the screws inside the housing cylinder, contained within one turn of a screw's thread (in other words, the "pitch"). (Flow) through-channel: The free volume between screws inside a containment cylinder that defines the flow path of a mixture. A through-channel for flow is formed by joining all the C-chambers of two screws.

[0039] Referring to Figures 3 and 4, the upstream portion M corresponding to the intake zone of the mixture to be filtered and the downstream portion V corresponding to the output zone of the filtered mixture are also defined. The twin-screw assembly according to the present invention substantially includes the following: A "cylinder" 10 comprises a body 11 having an upper upstream opening 13 and a downstream axial outlet opening 12 suitable for taking in a mixture. The cylinder may be conveniently divided into two semi-cylindrical parts 11a and 11b to facilitate its assembly.

[0040] The cylinder has a suitable internal cavity with a shape appropriate for housing two screws 21 and 22, respectively. The two screws 21 and 22 are arranged so that their axes of rotation are parallel, mesh, and rotate in opposite directions during use.

[0041] The output zone 60 is located at the downstream end of the twin-screw assembly. The aforementioned zone includes the filtration zone 70 (Figure 5). The mixture enters the filtration zone 70, proceeds toward the outlet in the supply direction, and passes through a filter (not shown).

[0042] For the sake of clarity, this description will always refer to a twin-screw assembly in which the screws are mirrored to each other. However, it is also possible to consider different configurations of the twin-screw assembly according to the present invention, in which the two screws mesh and rotate in opposite directions.

[0043] The cylinder and screw assembly defines three distinct sectors in the longitudinal direction of the twin-screw assembly (Figure 3), corresponding to the three longitudinal sectors of the screw threads. Intake, or upstream, sector 30. The mixture is introduced into cylinder 10 under ambient pressure and "captured" by the rotation of screws 21, 22. Intermediate or transitional sector 40. Located downstream of the intake sector 30, the pressing force pushing the mixture downstream gradually increases through the operation of two screws 21, 22. High-voltage sector 50. Located between the transition sector and the output zone 60 below.

[0044] As shown in Figure 7, and as will become clearer below, along the mixture intake sector 30, there is a large amount of play between the screws to create a large "free" volume capable of facilitating the inflow of large amounts of mixture. Along the transition sector 40, the play between the screws gradually decreases. Also, along the high-pressure sector 50, the play between the screws is very small, i.e., smaller than the play in the intake zone 30 and the transition zone 40. This is to minimize backflow and create a small through-channel or free volume that can achieve the high pressure required for filtration.

[0045] The three longitudinal sectors of the screw can be defined in accordance with the change in the flow channel formed in the free volume inside the cylinder with respect to the rotation angle.

[0046] In this context, we also refer to the known concept of a "C-chamber" (Figures 8a-8c) used to identify a channel Cx (Figure 8c) of a pair of meshing screws, having a free volume of shape C, defined between the screws and contained within one turn (in other words, the "pitch") of the threads of one screw.

[0047] More specifically, according to the present invention, the twin-screw assembly according to the present invention is characterized by a single through-channel. The single through-channel comprises at least three different sectors (20, 30, 40) of the screw along the longitudinal direction (X-X) from upstream to downstream. That is, The intake sector (30) has sufficient volume for the C chambers c1–c3 that form the flow path. It is optimized to capture the mixture supplied from the outside and push it downstream along the longitudinal direction (X–X). It remains constant over at least two pitches of the threads of each screw. Transition sector (40). Located downstream of the intake sector, it has a variable volume of C chambers c1–c3. This is smaller than the volume of the C chambers of intake sector 30, decreasing (in the direction of forward motion X–X) in particular to increase the pressing force acting on the mixture as it passes through in the longitudinal direction X–X and to expel trapped air as the mixture is loaded. High-pressure sector 50. Located downstream of the transition sector 40, it has the volume of C chambers c6, c7 which form a through-channel. This volume is constant over at least one pitch and is smaller than the volume of the intake and transition sectors. Thus, sector 50, having the minimum volume C chamber, is optimized to compress the mixture and obtain the maximum pressure of the mixture in the output zone 60.

[0048] According to a preferred embodiment of the present invention, the configuration of the geometry of the three longitudinal sectors of each screw is developed to create a law of variation of the through-channel, and therefore the C-chamber, ensuring an optimized configuration for the specific function intended for each sector. In particular, this geometry is such that it maximizes intake performance at atmospheric pressure while simultaneously accommodating intake sectors requiring large-volume C-chambers, and therefore small top widths W. As a result, flow rate is maximized, and the compression of the mixture is maximized in the high-pressure sector 50 located just upstream of the filtration zone.

[0049] In particular, in a preferred embodiment of the screw used in the twin-screw assembly according to the present invention, the intake sector has the following parameters. W = (0.025 - 0.20)D, constant at least 2, 3, or 4 pitches, preferably (0.05 - 0.10)D. P is constant, preferably = D. O' = (0.0025 - 0.030)D, preferably (0.005 - 0.015)D. δ = (0.0025 - 0.030)D, preferably (0.005 - 0.015)D. H = (0.3 - 0.8)D, preferably (0.54 - 0.6)D. Li (axial length of the intake zone) = (3-4)D.

[0050] The preferred geometric variables for a screw in the intake sector are as follows for a single-thread screw: The relatively low W value and high H value allow for obtaining the maximum volume of the C chamber. When the values ​​of O' and δ are low and the axial transport value (P=D) is low, the performance of both "capturing" the mixture at input to the extruder and the feeding of the mixture can be maximized.

[0051] To generate the required pressure only in the high-pressure sector adjacent to the filter and reduce heat generation and backflow losses, the C-chamber in this zone has a smaller, fixed volume than in other zones of the screw, and the play is mechanically as small as possible.

[0052] In detail, the high-pressure sector preferably has the following parameters: W = (0.3 - 0.4)D, preferably (0.33 - 0.37)D, constant at a pitch of 1 or 2. P is constant, preferably = D. σ = (0.0025 - 0.020)D, preferably (0.005 - 0.015)D. δ = (0.0025 - 0.030)D, preferably (0.005 - 0.015)D. H = (0.3 - 0.8)D, preferably (0.54 - 0.6)D. Lp (axial length of the high-voltage sector) = 1 - 2D. Generally, a constant cross-sectional area for through-flow.

[0053] The geometric variables of the high-pressure zone are as follows: Pumping performance is maximized when the values ​​of δ and σ are low and the value of W is high. In other words, the ratio between the main flow (supply direction) and the counterflow opposing the main movement is maximized. When H is high and P=D, the flow rate is maximized simultaneously.

[0054] Therefore, the screws of the twin-screw assembly according to the present invention can be advantageously configured to simultaneously achieve high pressure in sector 50 near the filter, where the play between the screws and between the screws and the cylinder is relatively small (to reduce backflow against the main motion), and high capture and flow rate of the mixture in the intake zone, due to the high free volume, i.e., the space that can potentially be filled with the mixture.

[0055] Considering the different performance characteristics required for the two sectors mentioned above, namely the upstream / ambient pressure intake sector and the downstream / high-pressure sector, the intake sector with a large volume C-chamber at low pressure and the high-pressure sector with a small volume C-chamber upstream of the filtration zone are advantageously configured with variable C-chamber volumes, in particular to achieve the following: When the mixture enters the extruder, any trapped air in the mixture is removed. Avoid abrupt and unexpected geometric changes that could result in a lack of uniformity in the material during processing, and the occurrence of localized pressure peaks.

[0056] Therefore, preferably, the transition sector 40 has a decreasing volume of the C chamber. In particular, the cross-section of the flow channel of the mixture preferably decreases in the direction of the forward motion of the mixture, substantially continuous and especially generally according to laws of primary and / or secondary and / or higher-order changes.

[0057] Preferably, the change in the flow channel of the mixture in the transition sector is obtained by the geometry that changes the thread crest width W of the screw, while other parameters of the screw can be kept constant in the transition sector.

[0058] According to a particularly suitable geometry for a screw used in a twin-screw assembly according to the present invention, the transition sector has the following parameters: W is continuously variable between the W value of the intake sector and the W value of the high-pressure sector. P is constant, preferably = D. σ = (0.0025 - 0.030)D, preferably (0.005 - 0.015)D. δ = (0.025 - 0.030)D, preferably (0.005 - 0.015)D. H = (0.3 - 0.12)D, preferably (0.54 - 0.6)D. Lt (axial length of the transition sector) = 1 - 3D.

[0059] Therefore, a gradual transition is achieved between intake performance and high-pressure performance. Changes to the through-channel may follow appropriate rules, such as optimizing the required performance.

[0060] In order to limit the undesirable temperature rise, which is typical in the case of long extruders known in the art, such as L / D > 10, it is particularly preferable to limit the axial length of the screw threads so that a ratio L / D ≤ ​​8, i.e., a short ratio, is obtained.

[0061] A screw is provided having a geometry obtained based on the laws of change of the internal channel according to the aforementioned laws, and designed to define the three different processing zones described above.

[0062] Referring again to Figure 8c and the flow channels for the mixture defined by the C chambers of the twin-screw assembly, if there are no flow losses, the theoretical maximum flow rate Qth of a twin-screw extruder having a single thread and two screws meshing in a mirror arrangement and rotating in opposite directions will be equal to the volume Vc of the two C chambers multiplied by the rotational speed N of the aforementioned screws. Theoretical maximum flow: Qth=2·Vc·N. Vc = volume of the C chamber. N = rotational speed (rpm)

[0063] Furthermore, it is known that in practice, the theoretical maximum flow rate is never reached due to flow loss caused by play between the screws and between the screws and the cylinder, as well as backflow opposing the main motion. It is also known that the greater the play, the greater the flow loss, and this also depends on the progression of pressure between the loading zone and the filtration zone.

[0064] Furthermore, referring to Figure 8c, the main flow losses are as follows: Qc = calendar leakage. Qt = tetrahedral leakage. Qf = Flight gap leakage. Qs = Leakage from the side gap.

[0065] Therefore, the resulting effective flow rate Q is obtained from the algebraic sum of the theoretical maximum flow rate (Qth), which is directly derived from the volume of the C chamber, and the total flow loss (Ql), which is due to backflow caused by play and pressure between the screws and between the screws and the cylinder. Total loss of flow / backflow: Ql = Qf + Qs + Qt + Qc Effective flow rate: Q = Qth - Ql

[0066] According to a preferred configuration of the twin-screw assembly, the aforementioned assembly is configured to obtain a substantially constant effective flow rate Q along the longitudinal direction in which the mixture moves forward from the intake sector to the end of the high-pressure sector. Thus, the efficiency is calculated as the ratio Q / Qth and gradually increases toward the output zone.

[0067] A particularly preferred example of this configuration is shown in Figure 9, which illustrates the geometry of the counter-rotating screw and the law of change of the associated C-chambers forming the mixture flow path. The corresponding effective flow rate Q = Qth - Ql through the flow path is constant in the extrusion direction and is shown by a black dashed line in Figure 10.

[0068] Figure 11 shows a schematic diagram of the cross-section S of the flow-through channel when the rotation angle of the screw threads of the screw according to the present invention is changed.

[0069] Further preferred embodiments of the screw and the corresponding twin-screw assembly according to the present invention are shown in Figures 12 and 13, respectively.

[0070] Figure 14 shows the changes in the cross-sectional area of ​​the flow channel for the mixture in the corresponding twin-screw assembly.

[0071] More specifically, the screw in Figure 12a has the following cross-section of the flow channel: in the intake sector 30, it is constant (and maximum) over three 360° rotations (3I) of the screw thread (3 pitches), in the transition zone, it decreases over three rotations of the screw thread, and in the high-pressure zone, it is constant (minimum) over two pitches (2P).

[0072] The cross-sections of the C-chamber and mixture flow channel for the twin-screw assembly shown in Figure 13a follow similar laws of variation, as shown in Figure 14a.

[0073] The screw in Figure 12b has the following cross-section of the flow channel: in the intake sector 30, it is constant (and maximum) over four 360° rotations of the thread; in the transition zone, it decreases over one 360° rotation of the thread; and in the high-pressure zone, it is constant (minimum) over two pitches. The cross-section of the C-chamber and mixture flow channel for the twin-screw assembly in Figure 13b follows a similar law of change, as shown in Figure 14b.

[0074] The screw in Figure 12c has the following cross-section of the flow channel: in the intake sector 30, it is constant (and maximum) over four 360° rotations of the thread; in the transition zone, it decreases over two pitches (2L) of the thread; and in the high-pressure zone, it is constant (minimum) over two pitches. The cross-section of the C-chamber and mixture flow channel for the twin-screw assembly in Figure 13c follows a similar law of change, as shown in Figure 14c.

[0075] The screws and twin-screw assemblies in Figures 12d, 13d, and 14d are similar to those in Figures 12c, 13c, and 13d. However, in this case, the change in cross-section in the transition sector 40 has a decreasing quadratic progression (2L).

[0076] The screw at e in Figure 12 has the following cross-section of the flow channel: in the intake sector 30, it is constant (and maximum) over four 360° rotations of the thread (3 pitches); in the transition zone, it decreases over three rotations of the thread; and in the high-pressure zone 50, it is constant (minimum) over three 360° rotations of the thread.

[0077] The cross-section of the C-chamber and the flow channel for the mixture for the twin-screw assembly shown in Figure 13e follows a similar law of change, as shown in Figure 14e.

[0078] Advantageously, although these are only some of the possible geometries, all preferred examples shown can keep the length of the screw threads within a thread pitch of 10, preferably 8.

[0079] In addition to this, the following is possible: When the screw length and the limited ratio L / D = transition zone length / diameter + pressure zone are equal to 5, high pressure (even exceeding 300 bar) and high flow rates can be achieved. Therefore, filtration is possible even when using extremely fine mesh (<0.1 mm). Even at high rotational speeds and flow rates, the temperature rise in the mixture can be controlled and limited. Because the screw is short, it is possible to use a relatively low drive torque. This prevents the screw from deflecting excessively and prevents the screw from contacting the cylinder. Air that may become trapped when the mixture enters can be discharged through the intake opening.

[0080] In a preferred embodiment of the extruder according to the present invention, the filtration / output section 70 of the extruded mixture is assumed to include a filter holder plate 71. The filter holder plate 71 is coupled to a connecting flange 60 and closed by a molding head 73.

[0081] A "filter" (not shown here), generally consisting of one or more metal meshes, is placed between the connecting flange 61 and the filter holder plate 71. The mixture is forced to flow through this filter by the thrust generated by the rotation of the screw. This filter holds impurities larger than the mesh openings.

[0082] Preferably, one or more pressure and temperature sensors 61 are located on the flange 60. The pressure and temperature sensors 61 allow for continuous monitoring of the pressure and temperature of the mixture being processed for complete control throughout the filtration step.

[0083] Figures 6 and 7 show cross-sectional views of the inside of the cylinder 10, passing through the housings of screws 21 and 22.

[0084] It can be seen that the play δ between the top of each screw and the cylinder 10, and the play δ between the top of one screw and the core of the other screw are very small, and in either case, simultaneous pumping operation can be guaranteed, and there is no contact between the screw and the cylinder.

[0085] Therefore, it is clear how the screw, twin-screw assembly, and extruder comprising this twin-screw assembly according to the present invention provide a solution to the problems of the prior art, and as a result, the following is achieved: There is no further auxiliary equipment available for loading the elastomer mixture to be filtered under ambient pressure. By generating high pressure within a narrow, limited zone, the temperature rise is restricted. This is advantageous because it can be kept below the vulcanization temperature of the elastomer mixture (generally below 100-120°C). Each of the three zones is dedicated to a specific task, and the three zones, configured in relation to each other, optimize overall performance. Due to the specific geometry of the transition zone, there are no localized temperature peaks. When the mixture is introduced into the intake zone, it effectively removes any trapped air from the mixture.

[0086] Although several embodiments and preferred examples of the present invention have been described in relation to this invention, it is understood that the scope of protection of this patent is determined solely by the following claims.

Claims

1. Screws (21; 22) adapted for use in a twin-screw assembly having meshing screws of an elastomer mixture extruder, comprising a threaded portion having a single-thread type that defines at least three different sectors (30, 40, 50) of the screw along the longitudinal direction (X-X) of an axial extension from upstream to downstream, wherein the at least three different sectors are An intake sector (30) is configured to capture a mixture and push it downstream along the longitudinal direction (X-X), and has a cross section (S) of a through channel contained between adjacent flanks of the thread, wherein the cross section (S) is constant over at least two pitches or 720 degrees of rotation of the thread, A transition sector (40) located downstream of the intake sector, having a variable cross-section (S) of the through-channel smaller than the cross-section of the through-channel of the intake sector, wherein the cross-section (S) is designed to increase the pressing force acting on the mixture as it passes in the longitudinal direction (X-X), A high-pressure sector (50) located downstream of the transition sector, having the minimum cross-section of the through-channel, the cross-section being constant over at least one pitch, and designed to cause compression of the mixture to obtain the maximum pressure of the mixture, The threads of the screw portion are single-start threads, and the screw geometry in the high-pressure sector (50) has a top width W = (0.3 to 0.4)D, where D is the outer diameter of the screw and is constant over 1 or 2 pitches, the screw (21; 22).

2. A screw according to claim 1, wherein the intake sector has a cross-sectional and / or thread crest width (W) of a through-channel that is constant over at least two pitches, preferably over at least three pitches, and particularly over two, three, or four pitches.

3. A screw according to claim 1, wherein in the intake sector, the geometry of the screw is The width of the top W = (0.025 - 0.20)D, preferably (0.05 - 0.10)D, where D is the outer diameter of the screw and is constant over at least 2, 3, or 4 pitches, and / or The thread pitch P is constant, preferably equal to the outer diameter D, and / or The height H of the through-channel is H = (0.3 - 0.8)D, preferably (0.54 - 0.6)D, and / or, A screw characterized in that the axial length of the intake zone Li = (3-4)P and / or (3-4)D.

4. The screw according to claim 1, wherein in the high-pressure sector (50), the geometry of the screw is The width of the top W = (0.33 - 0.37)D is constant over one or two pitches. Here, D is characterized in that the screw is the outer diameter of the screw.

5. A screw according to claim 1, characterized in that it has a constant pitch throughout the entire threaded portion.

6. A screw according to claim 1, characterized in that the length of the threaded portion is 10D or less, where D is the outer diameter of the screw, and / or 10P or less, where P is the pitch of the threads.

7. A screw according to claim 1, wherein in the transition sector, the change in the through-channel for the passage of the mixture is obtained by a geometry that changes the width (W) of the thread crest of the screw.

8. A screw according to claim 7, wherein in the transition sector, the width W of the top is continuously variable between a minimum value of W corresponding to the width of the top of the intake sector and a maximum value of W corresponding to the value of W in the high-pressure sector, and the geometry of the screw in the transition sector is preferably The pitch P is constant, preferably equal to the outer diameter D, and / or The height H of the through-channel is preferably constant and / or between (0.3–0.12)D, preferably between (0.54–0.6)D, and / or The axial length of the transition sector is Lt = 1 - 3D. Here, D is the outer diameter of the screw.

9. A twin-screw assembly (10, 20) for an elastomer mixture extruder, comprising two screws (21, 22) having single-threaded threads, the two screws meshing and arranged to rotate in opposite directions on parallel longitudinal axes of rotation (X-X) inside the cylinder (10), thereby forming a through-channel for the passage of a mixture flow consisting of a combination of multiple C-chambers (Cx), each C-chamber defined by the free volume inside the cylinder (10) and encompassing one rotation of the threads of one screw, The twin-screw assembly is provided with an upstream opening (13) for taking the mixture into the through-channel. The through-channel for the passage of the flow comprises at least three different sectors (30, 40, 50) in the longitudinal direction (X-X) of the axial extension of the screw from upstream to downstream, and in the forward motion of the mixture, wherein the at least three different sectors are An intake sector (30) is configured to capture a mixture supplied from the outside and push it downstream along the longitudinal direction (X-X), and has the volume of a C-chamber that forms the flow channel for the passage of the flow, the volume of which is constant over at least two pitches of the threads of each screw, A transition sector (40) located downstream of the intake sector, having a volume of a C-chamber that forms a flow path, wherein the volume is variable, decreases, and is smaller than the volume of the C-chamber of the intake sector, and a transition sector (40), A high-pressure sector (50) located downstream of the transition sector, having a volume of C-chambers forming a flow path, the volume being constant over at least one pitch, and smaller than the volume of the C-chambers of the intake sector and the transition sector, and adapted to cause compression of the mixture to obtain the maximum pressure of the mixture, A twin-screw assembly (10, 20) wherein the other screw of the two screws has the screw configuration described in any one of claims 1 to 8.

10. A twin-screw assembly according to claim 9, characterized in that the screws are in a mirror image arrangement.

11. A twin-screw assembly according to claim 9, wherein the high-pressure sector has a C-chamber volume that is constant over at least two pitches of each screw.

12. A twin-screw assembly according to claim 9, wherein the take-up sector has a volume of a C-chamber that is constant over at least three pitches, preferably at least four pitches, of each screw.

13. A twin-screw assembly according to claim 9, wherein the transition sector has a C-chamber volume that decreases in the sense of the forward motion of the mixture, and / or a cross section of a substantially continuous through-channel for the passage of a mixture flow that decreases in the sense of the forward motion of the mixture, in particular at least partially generally according to laws of primary and / or secondary and / or higher-order changes.

14. A twin-screw assembly according to claim 9, wherein the screw and the cylinder are arranged and configured to obtain an effective flow rate (Q) through a mixture flow path, which is constant along the longitudinal direction in which the mixture moves forward from the intake sector to the end of the high-pressure sector.

15. A twin-screw assembly according to claim 9, In the aforementioned intake sector, O' = (0.0025 - 0.030)D, preferably (0.005 - 0.015)D, δ = (0.0025 - 0.030)D, preferably (0.005 - 0.015)D. and / or, In the aforementioned high-voltage sector, O' = (0.0025 - 0.020)D, preferably (0.005 - 0.015)D, δ = (0.0025 - 0.030)D, preferably (0.005 - 0.015)D. and / or, In the aforementioned transition sector, O' = (0.0025 - 0.030)D, preferably (0.005 - 0.015)D, δ = (0.025 - 0.030)D, preferably (0.005 - 0.015)D. A twin-screw assembly where O' is the distance between the top of one screw and the core of the other screw, and δ is the distance between the top of one screw and the inner surface of the housing cavity of the housing cylinder.

16. A twin-screw assembly according to claim 9, wherein the upstream opening is configured to supply a mixture to a through-channel in a direction (Z-Z) substantially perpendicular to the longitudinal direction (X-X).

17. An elastomer mixture extruder, characterized by comprising a twin-screw assembly extending in the longitudinal direction (X-X) and a downstream extruder head (70) as described in claim 9.

18. An elastomer mixture extruder according to claim 17, characterized in that it comprises a filtration zone (70) downstream of a high-pressure zone (50) through which a mesh filter is provided to pass the mixture.

19. A method for extruding an elastomer mixture, A step of supplying an elastomer mixture to a twin-screw assembly of a mixture extruder, the twin-screw assembly comprising two screws (21, 22) having threads, the screws (21, 22) being meshed and arranged to rotate in opposite directions on parallel longitudinal axes of rotation (X-X) inside the cylinder (10), thereby forming an upstream-to-downstream through-channel for the passage of a mixture flow consisting of a combination of multiple C-chambers (Cx), each C-chamber being defined by the free volume between each screw inside the cylinder and encompassing one turn of the threads of one screw, The steps include supplying the elastomer mixture through a mixture intake opening (13) into the through-channel for the passage of the mixture flow in the twin-screw assembly, A step of capturing the elastomer mixture and pushing the elastomer mixture downstream through the through-channel for the mixture flow in the intake sector (30) of the twin-screw assembly, wherein the intake sector has a volume of a C-chamber that forms a constant flow path over at least two pitches of the threads of each screw, A step of advancing the elastomer mixture through a transition sector (40) of the through-channel for the passage of a mixture flow, wherein the transition sector (40) is located downstream of the intake sector in the longitudinal direction (X-X) of the axial extension of the screw and has a volume of a C-chamber that advances the movement of the mixture and forms a flow path, the volume of which is variable, decreasing and smaller than the volume of the C-chamber of the intake sector, A step of advancing and compressing the elastomer mixture in a high-pressure sector (50), wherein the high-pressure sector (50) is located downstream of the transition sector and has a volume of a C-chamber that forms a flow path, the volume of which is constant over at least one pitch and is smaller than the volume of the C-chambers of the intake sector and the transition sector, thereby causing compression of the mixture to obtain the maximum pressure of the mixture; A method comprising the step of passing the elastomer mixture through an extrusion head (60) located downstream of the high-pressure sector (50) at maximum pressure.

20. A method according to claim 19, comprising filtering (70) the mixture to be treated, passing it through a mesh filter downstream of the high-pressure sector (50).

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