Screw extruder and method for controlling the extrusion pressure in a screw extruder

Abstract

A screw extruder for extruding high-viscosity materials has a screw (9) rotatably positioned within a bore (16) in a housing. The housing has a base portion (11) having an inlet (2) for material supply and an extrusion portion (14) having a compression chamber (7) and an extrusion die opening (6), and one or more conveying and compression portions (12,13) ​​are positioned between the base portion (11) and the extrusion portion (14). At least one of the housing portions (11-14) has one or more fluid conduits (4) and one or more fluid connectors (10) for connection to a fluid supply and circulation system, thereby allowing the temperature of at least one of the housing portions to be controlled individually.

Description

[Technical Field]

[0001] The present invention relates to a screw extruder for extruding high-viscosity materials, such as metals like aluminum or aluminum alloys, or other metal matrix composites or alloys. More specifically, the present invention relates to a screw extruder as shown in the premise of claim 1, and to a method for controlling the extrusion pressure in a screw extruder as shown in the premise of claim 12.

[0002] Background of the Invention Prior art includes U.S. Patent Application Publication No. 2007 / 121421, which describes a multi-screw extruder having a core with an external leading channel for a coolant. At least two housing segments are provided with a cooling circuit having interconnected cooling bore holes for a coolant, distributed circumferentially and parallel to the axial direction, and located on the portion of the housing segment facing the process chamber. The housing segments provided with cooling bores also have heating means on their outer circumference. Each housing segment provided with both cooling bores and heating means preferably has a control device that controls both the heating means and the flow of coolant through the cooling bores so that the optimal processing temperature and material temperature can be adjusted to be as low as possible.

[0003] Prior art also includes U.S. Patent No. 1,0035291, which describes a device for lateral flow filling into an extruder. In this device, material is supplied to at least one conveyor screw located within the extruder housing. The material includes a gaseous associated substance, and a venting housing for receiving an airflow is located on the extruder housing, which acts within the extruder housing and is directed in the opposite direction to the conveying direction of the conveyor screw.

[0004] Prior art also includes German Patent Application Publication No. 10356423, which describes an extruder barrel consisting of connected sections with liners for housing channels for temperature-controlled fluid. Inlets for feed material or additive material are provided on the side between the joints of the sections. The inlet port has a widened section, which houses a bush with an annular groove providing a passage for the temperature-controlled fluid. Several grooves may be used, and preferably the total cross-sectional area is not reduced by more than 10% from the flow area available for the temperature-controlled fluid in the rest of the extruder. Side feeding can be done from a pump or a side extruder, such as a twin-screw extruder.

[0005] Various types of extruders are also described in U.S. Patent No. 3,199,147 and Chinese Utility Model Patent No. 211074655.

[0006] Prior art also includes International Publication No. 2008 / 063076, which describes a screw extruder for continuously extruding high-viscosity materials, particularly metals such as aluminum and its alloys. The extruder includes an Archimedes screw rotatably mounted in a liner of a screw housing having an inlet for supplying the material to be extruded, an extrusion die assembly having a compression or extrusion chamber and a die for forming the shape of the desired extruded product. The screw and liner are designed so that the required compression occurs at the downstream end of the screw toward the extrusion chamber, which corresponds to a maximum rotation of 540 degrees of the screw, or a maximum of 1.5 rotations of the screw's flight length. Solid plugs of metal thus formed at the end of the screw and in the extrusion chamber restrict rigid rotation in order to obtain the required compression and extrusion pressures.

[0007] Figure 1 is a schematic diagram illustrating the general principle of a screw extruder. The screw 51 is located inside a bore 55 within the extruder housing (also called the "barrel") 50. The material to be extruded is fed through an inlet 52 to a feed zone F. The material, which may contain a mixture of substances, is conveyed by the rotating screw along the bore through a heating-mixing zone M, where the mixture is then compressed in a compression zone C and subsequently pushed into an extrusion chamber 53 and extruded through an extrusion die 54.

[0008] A critical parameter for the successful operation of a screw extruder to extrude high-viscosity materials is the temperature along the screw housing, or more specifically, the temperature along the bore where the extruder screw is located. Efficient screw extrusion of such materials (e.g., aluminum) requires a specific temperature along the screw. A high temperature in the forward region (i.e., near the extrusion chamber 53) increases adhesive friction and reduces the force required for material deformation, while a temperature limit further back (i.e., near the inlet 52) ​​prevents adhesive friction and material compression. Therefore, the ability to control the temperature gradient along the extruder bore is necessary to avoid these problems. The objective of the present invention is to improve cooling capacity and provide a robust and stable extrusion process.

[0009] There is a need for apparatus and methods that can control friction along the barrel, and consequently the extrusion pressure, more precisely than is possible with conventional extruders, and that can further optimize quality and yield.

[0010] Summary of the Invention The present invention is described and characterized in the independent claims, while the dependent claims describe other features of the present invention.

[0011] Therefore, a screw extruder for extruding high-viscosity materials, such as aluminum, aluminum alloys, or other metal matrix composites or alloys, having a screw rotatably arranged in a bore within a housing, - The housing has a base portion having an inlet for supplying material into the extruder, and an extrusion portion having a compression chamber and an extrusion die opening. In a screw extruder, Screw extruders are - It comprises one or more conveying and compressing parts positioned between the base part and the extrusion part, and the housing parts are interconnected by removably connecting their ends. A screw extruder is provided, characterized by the following features.

[0012] In one embodiment, at least one gap is provided between at least two adjacent housing portions, and at least one gap is either an air gap or holds an insulating material, thereby limiting heat transfer between adjacent housing portions. In one embodiment, at least one gap holds an element having a thermal conductivity equal to or higher than the thermal conductivity of the material in the housing portion, thereby improving heat transfer between adjacent housing portions.

[0013] At least one of the housing sections has one or more fluid conduits and one or more fluid connectors for connecting to a fluid supply and circulation system, thereby allowing the temperature of at least one housing section to be controlled individually. In one embodiment, one or more fluid conduits are embedded in at least one housing section.

[0014] In one embodiment, at least one conveying and compressing section has an outer body with an inner liner, the liner being located within an inner bore of the outer body, and at least a portion of the extruder bore is formed within the liner. In one embodiment, the material of the liner has a higher thermal conductivity than the material of the outer body.

[0015] The liner is preferably fixed to the outer body, thereby preventing the liner from rotating inside the outer body. In one embodiment, the inner surface of the outer body and the outer surface of the liner have complementary shapes. In one embodiment, the inner surface of the outer body and the outer surface of the liner have complementary frustoconical shapes with a common cone angle, and the liner has a frustoconical shape with its base on the downstream side of the aforementioned portion.

[0016] In one embodiment, the outer surface of the liner has a helical groove that forms a fluid conduit when the insert is positioned in the outer body, and the outer body has a channel that terminates in the outer fluid connector when the insert is positioned in the outer body, and is aligned with each end of the helical groove.

[0017] Furthermore, a method for controlling the extrusion pressure in a screw extruder for extruding one or more high-viscosity materials, such as aluminum, aluminum alloys, or other metal matrix composites or alloys, wherein the screw extruder has a screw rotatably arranged in a bore within a housing, The method is provided, characterized by including controlling the temperature of the screw and the temperature of the bore wall so that the temperature of the screw is higher than the temperature of the bore wall while the screw is rotating and one or more materials are in the mixing and compression zone of the extruder.

[0018] In one embodiment, the method includes, at the start of the mixing and compression zone, maintaining the temperature of the screw above the temperature of the bore wall while raising at least the temperature of the bore wall to a level above the adhesion friction temperature of the one or more materials being extruded. In one embodiment of the method, the screw extruder has an extruder as specified above according to the invention. In one embodiment, the method includes individually controlling the temperature within each housing portion by circulating a fluid through at least one fluid conduit of each housing portion, the fluid being a coolant, and the temperature of the coolant supplied to the fluid conduit being based on one or more temperatures detected within each housing portion.

[0019] The improved extrusion pressure control enabled by the present invention makes it possible to optimize the extrusion efficiency, i.e., the relationship between the extrusion volume and the energy consumption.

[0020] These and other features of the present invention will become apparent from the following description of embodiments of the invention provided as non-limiting examples, with reference to the accompanying schematic drawings.

Brief Description of the Drawings

[0021] [Figure 1] It is a schematic side view of a screw extruder according to the prior art. [Figure 2] It is a perspective view of an embodiment of an extruder according to the present invention. [Figure 3] It is an axial cross-sectional view of an embodiment of an extruder according to the present invention. [Figure 4] It is an axial cross-sectional view (extrusion screw shown excluding the flights) of another embodiment of an extruder according to the present invention. [Figure 5] FIG. 5a is an axial cross-sectional view of the embodiment of the extruder shown in FIG. 4 with the screw of the extruder removed, and FIG. 5b is an enlarged view of region "A" in FIG. 5a. [Figure 6] FIG. 6a is a view similar to FIG. 5a, and FIG. 6b is an enlarged view of region "B" in FIG. 6a. [Figure 7] This is an X-ray perspective view of an embodiment of the base barrel, showing the internal cooling conduit. [Figure 8] This is an elevation view of an embodiment of the intermediate housing portion as seen in the axial direction of the extruder. [Figure 9] This is an X-ray perspective view of an embodiment of the intermediate housing portion, showing the internal cooling conduit. [Figure 10] This is an X-ray perspective view of an embodiment of the compression housing portion, showing the internal cooling conduit. [Figure 11] This is a perspective view of another embodiment of the intermediate housing portion, including the inner liner. [Figure 12] Figure 11 is an elevation view of the housing portion. [Figure 13] This is an illustrative diagram showing frictional force and shear strength in relation to temperature.

[0022] Detailed description of embodiments of the present invention In the following description, terms such as “horizontal,” “vertical,” “lateral,” “front and back,” “up and down,” “upper side,” “lower side,” “inside,” “outside,” “front,” and “rear” may be used. These terms generally refer to the views and orientations shown in the drawings relating to the ordinary use of the invention. The terms are used for the convenience of the reader only and are not limiting.

[0023] Referring first to Figures 2 and 3, the present invention has a screw extruder 1 for extruding high-viscosity materials, such as metals like aluminum or aluminum alloys. The screw extruder has a screw 9 rotatably arranged in a bore 16 within a housing. The screw 9 may be an Archimedes screw or any other screw device suitable for the purpose of extrusion, and is operated (rotated) by a motor and control device (not shown) commonly known in the art. The extruder is connected to a control-drive unit (not shown) via a flanged connector 5 and connected to a fixed support in a manner known in the art. As described below, reference numeral 4 indicates a fluid conduit and reference numeral 10 indicates a connector to a fluid conduit.

[0024] The housing, also called the "barrel," has multiple housing sections 11-14 that are interconnected by connecting their ends.

[0025] The proximal housing portion (also called the "base portion") 11 is located in front of the power transmission path (not shown) and has an inlet 2 (material supply opening) for receiving material to be compressed and extruded, and a portion of the bore 16 described above.

[0026] The distal housing portion (also called the "extrusion portion") 14 is located in the region of the downstream end of the screw 9 and bore 16 and has a compression chamber 7 and an extrusion die opening 6 configured to shape the extruded product.

[0027] Between the base portion 11 and the extrusion portion 14 are several intermediate housing portions (also referred to as "conveying and compression portions") 12, 13, each intermediate housing portion containing a portion of the bore 16. Although two conveying and compression portions 12, 13 are shown in the drawing, the screw extruder may have more or fewer conveying and compression portions.

[0028] The housing portions are interconnected via bolts or screws 15, etc. These bolts or screws 15, etc., connect the portions to a fixed support and facilitate simple replacement or repair of screws and housing portions, as well as the addition of further intermediate housing portions. The housing portions are formed from materials known in the art and suitable for the intended purpose.

[0029] Referring further to Figures 4 to 6, in one embodiment, a gap 3 is provided between adjacent housing portions. To limit heat transfer between adjacent housing portions, the gap is either an air gap or contains an insulating material (not shown). Alternatively, to increase heat transfer between adjacent housing portions, the gap contains an element (not shown) having a thermal conductivity equal to or higher than that of the material within the housing portion.

[0030] Referring further to Figure 7, the base section 11 has, preferably, one fluid conduit 4 on each side of the inlet 2. Arrow F indicates the fluid flow through the conduit, and reference numeral 10 indicates a connector for connecting to a cooling fluid supply and circulation system (not shown). The cooling fluid supply and circulation system is connected to a control unit (not shown). Figures 8 and 9 show the fluid conduit 4 and connector 10 in the conveying and compression sections 12 and 13, and Figure 10 shows the fluid conduit 4 and connector 10 in the extrusion section 14.

[0031] Because the fluid conduit 4 is embedded in the housing rather than in a separate outer liner, the fluid conduit is located close to the bore 16 (see, for example, Figures 3 and 8). This proximity between the fluid conduit and the bore facilitates improved cooling capacity and faster response compared to conventional cooling systems.

[0032] During extruder operation, housing portions 12 and 13 are exposed to intense heat generation due to deformation of the extruded material. Heat flow from the housing to the cooling channel is limited by the thermal conductivity of the housing material, and thermal runaway generates thermal stress, which may cause plastic deformation and / or crack formation in the extruder bore 16. This problem is mitigated or even avoided by the present invention, i.e., by incorporating an inner liner having a material with sufficiently high thermal conductivity to dissipate the generated heat. Accordingly, Figures 11 and 12 show an alternative embodiment of the above intermediate housing portions 12 and 13, indicated by reference numeral 20. Housing portion 20 comprises an outer body 21 and an inner liner 17. The inner liner 17 is located in the inner bore of the outer body 21, coaxially with the outer body 21. The extruder bore 16 is formed within the liner 17. The liner material has a higher thermal conductivity than the material of the outer body. As a non-limiting example, the thermal conductivity of the liner 17 is in the range of 40-80 W / (mK), while the thermal conductivity of the outer body 21 is approximately 25 W / (mK). As a non-limiting example, the material of the liner 17 is high thermal conductivity steel or beryllium copper, while the material of the outer body 21 is ordinary tool-grade steel.

[0033] The liner 17 is subjected to torsion by the extruded material due to the torque caused by the rotating screw of the extruder, and is therefore fixed to the outer body 21 to prevent the liner from rotating within the outer body (as described above, the outer body is fixed to a support). In the embodiment shown in Figure 11, the inner surface 18 of the outer body 21 and the outer surface 19 of the liner 17 have complementary shapes, thereby preventing the liner from rotating inside the outer body. In the illustrated embodiment, the surfaces 18,19 are radially corrugated and have six lobes. It should be understood that these surfaces may have other shapes.

[0034] Referring to Figure 12, surfaces 18 and 19 have complementary frustoconical shapes with a common cone angle α. Thus, the liner 17 is a frustoconical shape with its base on the downstream side D of portion 20 (the letter "M" indicates the flow direction of the extruded material). This configuration ensures a press fit between the liner and the outer body and prevents unintended separation when portion 20 is removed from the extruder. In the illustrated embodiment, the outer surface of the liner 17 has a helical groove 22 that forms the fluid conduit 4 when the insert is placed in the outer body 21, as shown in Figure 12. Channels 23a and 23b are formed in the outer body and are aligned with the respective ends of the helical groove 22 when the insert is placed in the outer body, terminating at the respective fluid connectors 10.

[0035] In all of the above embodiments, the cooling fluid circulating within the fluid conduit 4 may be a liquid, such as water. The coolant may be water containing additives to raise its boiling point, or any other suitable coolant. The cooling fluid may also be a gas, such as a mixture of air or other gases. In one embodiment, the coolant is used to control the temperature of the base section 11 and / or the conveying and compression sections 12,13;20, while the gas (such as air) is used to control the temperature of the extrusion section 14.

[0036] Each housing section 11-14;20 has a connector 10 for external supply and circulation of cooling fluid, so that the temperature of each housing section can be controlled individually. During operation of the extruder, controlling the temperature of the coolant controls the temperature of each housing section, and consequently, the friction between the bore wall and the material.

[0037] In one embodiment shown in Figures 3 and 4, the screw 9 has an internal axial fluid conduit (8) connected to a fluid supply and circulation system (not shown), thereby allowing a cooling fluid to circulate within the screw.

[0038] Although not shown in the diagram, it will be understood that the housing portion includes a temperature sensor and means for transmitting the sensor data to the control unit.

[0039] Although not shown in the illustration, the bore 16 of the housing portion may have a coating to reduce friction against the material.

[0040] The fundamental difference between polymer extrusion and metal extrusion is that, in the case of polymers, the frictional force is the product of the applied pressure multiplied by the coefficient of friction and then multiplied by the area; in other words, the frictional force of a polymer is proportional to the pressure. In the case of metals exhibiting adhesive friction, such as aluminum, the force is simply given as the shear strength multiplied by the area. Therefore, the pressure rise in any rotary extruder is fundamentally different for polymers and metals.

[0041] Figure 13 shows how the frictional force F and shear strength τ of a metal change with the temperature of the metal during mixing and compression. Generally, the shear strength τ decreases with increasing temperature, and the frictional force F decreases with increasing temperature t S The temperature remains constant until adhesive friction occurs. S is the material-dependent critical temperature for adhesive friction. In the illustrated example, the material is aluminum, and the adhesive friction F S At a temperature of 300°C t S This is achieved.

[0042] The element (such as metal) extruded along the bore of the extruder by the rotating member is subjected to a positive pressure gradient downstream. This is a fundamental prerequisite for compression and subsequent extrusion. This is the case for conventional screw extruders having a rotating screw inside a substantially smooth bore (barrel), and for the extruder according to the present invention described above. While the affected area, i.e., the geometric and dimensional relationship between the screw and the bore, is important, the absolute requirement for a positive pressure gradient downstream is the relationship between the element and the rotating member (τ R The shear strength between the element and the stationary member (τ Sgreater than the shear strength between it and R > τ S which can be demonstrated. For example, although it depends on the alloy, the ratio of τ R / τ S is preferably considered to be between 1.5 and 3.0.

[0043] Therefore, (in contrast to non-rotary ram extrusion) in order to control the pressure increase for "rotary extrusion" of metal, it is necessary to control the shear strength of the metal on different surfaces in the extruder. The term "rotary extrusion" is used to indicate that this principle applies to conventional screw extruders and any extruder using a rotating member to advance the extruded element. Utilizing the fact that the shear strength of the metal is temperature-dependent, temperature can be used as a control mechanism for pressure generation. Therefore, the temperature of the rotating screw is kept in equilibrium with the temperature of the stationary bore wall to obtain the adhesion friction between the material and the punch and reduce the friction between the material and the bore wall.

[0044] Therefore, the method of the present invention includes controlling the temperature (t R ) of the screw and the temperature (t B ) of the bore wall such that the temperature of the screw is higher than the temperature of the bore wall, that is, t R > t B while the screw is rotating. The method also includes raising at least the temperature (t B ) of the bore wall to a level above the adhesion friction temperature (t S ) of one or more materials extruded at the upstream end of the bore 16, while maintaining the temperature of the screw higher than the temperature of the bore wall, that is, maintaining t R > t B .

[0045] The present invention should be understood to be applicable to the extrusion of high-viscosity materials, such as metals like aluminum and aluminum alloys, or metal matrix composites. The extrusion process may be continuous or carried out by introducing batches of material or material mixtures into the extruder.

[0046] In the embodiments described above, various configurations and details are presented in combination. The fact that multiple configurations are described with respect to a particular example should not be interpreted as meaning that these configurations must necessarily be included in all embodiments of the present invention. Conversely, configurations described with reference to different embodiments should not be interpreted as mutually exclusive. Embodiments incorporating any subset of the configurations described herein, which are not explicitly interdependent, are pre-conceived and intended by the inventors, as will be readily apparent to those skilled in the art. However, an explicit description of all such embodiments would not necessarily contribute to understanding the principles of the present invention, and therefore, some configurations have been omitted for simplicity or brevity. The present invention is defined by the appended claims.

Claims

1. A screw extruder for extruding high-viscosity materials, such as aluminum, aluminum alloys, or other metal matrix composites or alloys, comprising a screw (9) rotatably arranged within a bore (16) in a housing, - The housing has a base portion (11) having an inlet (2) for supplying material into the extruder, and an extrusion portion (14) having a compression chamber (7) and an extrusion die opening (6). In a screw extruder, The screw extruder is, - The system comprises one or more conveying and compressing sections (12, 13; 20) positioned between the base section (11) and the extrusion section (14), and the housing sections (11-14; 20) are interconnected by removably connecting their ends. A screw extruder characterized by the following features.

2. The screw extruder according to claim 1, wherein at least one gap (3) is provided between at least two adjacent housing portions, and at least one of the gaps is an air gap or holds an insulating material, thereby limiting heat transfer between adjacent housing portions.

3. The screw extruder according to claim 2, wherein at least one gap (3) holds an element having a thermal conductivity equal to or higher than the thermal conductivity of the material in the housing portion, thereby improving heat transfer between adjacent housing portions.

4. The screw extruder according to any one of claims 1 to 3, wherein at least one of the housing portions (11-14; 20) has one or more fluid conduits (4) and one or more fluid connectors (10) for connection to a fluid supply and circulation system, thereby allowing the temperature of at least one of the housing portions to be controlled individually.

5. The screw extruder according to claim 4, wherein one or more of the fluid conduits (4) are embedded in at least one of the housing portions.

6. The screw extruder according to any one of claims 1 to 5, wherein at least one conveying and compressing section (20) has an outer body (21) having an inner liner (17), the liner (17) being located in an inner bore of the outer body (21), and at least a portion of the bore (16) of the extruder is formed within the liner (17).

7. The screw extruder according to claim 6, wherein the material of the liner has a higher thermal conductivity than the material of the outer body.

8. The screw extruder according to claim 6 or 7, wherein the liner (17) is fixed to the outer body (21), thereby preventing the liner from rotating inside the outer body.

9. The screw extruder according to claim 8, wherein the inner surface of the outer body (21) and the outer surface of the liner (17) have complementary shapes.

10. The screw extruder according to any one of claims 6 to 9, wherein the inner surface of the outer body (21) and the outer surface of the liner (17) have complementary frustoconical shapes having a common cone angle (α), and the liner (17) has a frustoconical shape with a base on the downstream side (D) of the portion (20).

11. The screw extruder according to any one of claims 6 to 10, wherein the outer surface of the liner (17) has a helical groove (22) that forms a fluid conduit (4) when the insert is positioned in the outer body (21), and the outer body has channels (23a, b) formed therein that terminate at the outer fluid connector (10) when the insert is positioned in the outer body, and are aligned with the respective ends of the helical groove (22).

12. A method for controlling the extrusion pressure in a screw extruder for extruding one or more high-viscosity materials, such as aluminum, aluminum alloys, or other metal matrix composites or alloys, wherein the screw extruder has a screw (9) rotatably arranged in a bore (16) within a housing, The method involves controlling the temperature of the screw (t) while the screw is rotating and one or more of the materials are in the mixing and compression zone within the extruder. Ｒ ) and the temperature of the bore wall (t Ｂ ) and control so that the temperature of the screw exceeds the temperature of the bore wall (t Ｒ >t Ｂ A method characterized by including the action of doing so.

13. The method includes, at the start of the mixing and compression zone, maintaining the temperature of the screw above the temperature (t Ｂ ) of the bore wall such that (t Ｒ > t Ｂ ), and raising at least the temperature (t Ｂ ) of the bore wall to a level above the adhesion friction temperature (t Ｓ ) of the one or more materials being extruded. The method according to claim 12.

14. The method according to claim 12 or 13, wherein the screw extruder has the extruder described in any one of claims 1 to 11.

15. The method according to claim 14, further comprising individually controlling the temperature within each housing portion (11-14; 20) by circulating a fluid through at least one fluid conduit (4) in each of the housing portions, wherein the fluid is a coolant, and the temperature of the coolant supplied to the fluid conduit is based on one or more temperatures detected within each of the housing portions.

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