Apparatus and method for continuous extrusion of highly viscous materials

Abstract

An apparatus and method for continuously extruding highly viscous materials, particularly materials containing metals such as aluminum, magnesium, titanium, zinc, copper, nickel, and their alloys, comprising an Archimedes screw rotatably mounted within the liner of a screw housing having a feed opening (Fo) for feeding the material to be extruded, an extrusion zone (Ez), and an extrusion die assembly with a die for forming the desired extruded product shape. The apparatus further comprises a material preparation / mixing zone (PMz) for the material, in which the input material is processed in an appropriate manner and may be composed of various parts and material types, a material feed zone (Fz) for the material that communicates with the feed opening (Fo) of the housing, a conveying and compression zone (TCz) for the material within the screw extruder, and a material compression and pressure development zone (CPz) for the material that is connected to the extrusion zone (Ez) and in which the required compression and extrusion pressure and temperature are achieved. The apparatus may be provided with means for controlling and adjusting the temperature and pressure of the material to set ranges before the material is extruded. Prior to operation, samples of the material to be processed may be analyzed and classified in order to adjust the process parameters of the equipment.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for continuously extruding high viscosity materials. [Background technology]

[0002] The material may be a light metal such as aluminum, titanium, magnesium, and alloys or mixtures thereof. Other materials such as Cu, Ni, and Zn may be suitable.

[0003] High viscosity metals and materials with reinforcing particles or fibers may also be viable candidates for this application.

[0004] The apparatus includes an extruder including an Archimedes screw disposed within a screw housing with an inlet for feeding the material to be extruded, a compression and / or extrusion chamber, and an extrusion die assembly with a die for forming the shape of the desired extruded product.

[0005] The extruder is preferably fed with granular metal at a temperature T below Ts, where Ts is the temperature at which the metal will have adhesive friction. The granular metal can be heated within the extruder by contact with the screw and vessel walls, or preferably preheated to the desired temperature before entering the device. As adhesive friction occurs, the metal is further heated by frictional heat and deformation. When the semi-compressed metal reaches the pressure-building zone, it adheres to the "wings" of the already compressed metal and is kneaded and fully compressed. Summary of the Invention [Means for solving the problem]

[0006] According to one aspect of the present invention, the operation of the apparatus can be controlled by a controller, which is a computer equipped with a software program, or similarly a PLC. The apparatus includes sensors for measuring physical parameters such as temperature and / or pressure inside the apparatus and torque and / or speed of the screw. According to one aspect of the present invention, the axial force acting on the screw can also be measured by sensors. Signals from these sensors are collected by a computer and input into the software program. In addition, a system can be provided for controlling the temperature of the material as it propagates through the various zones of the apparatus. Inputs / outputs from these systems are communicated to / from the computer.

[0007] Extrusion of highly viscous light metals such as aluminum, magnesium, or titanium requires fairly high pressures, typically 100-500 MPa, to force the material through the die block and die. The current conventional technology for aluminum extrusion is dominated by ram extrusion, a batch process in which a billet is loaded into a container and forced (pushed) through a die by a moving piston.

[0008] In the prior art, a continuous screw extrusion process based on the Robertson Hansson extruder, US Pat. No. 3,693,394, is used to produce lead and lead alloy profiles, in which the lead is fed into the extruder in liquid form and solidifies during the extrusion process.

[0009] Lead behaves differently than, for example, aluminum, because it has "sliding" friction: the friction between the lead and the container material (steel) is proportional to the pressure.

[0010] However, aluminum and many other metals have adhesive friction at extrusion temperatures, i.e., the metal will weld to the container and screw material.

[0011] As a result of this behavior, screw extrusion of aluminum and other highly adhesive metals with high viscosity has been difficult and impractical due to the large forces required to overcome the frictional forces between, for example, the aluminum and steel.

[0012] U.S. Patent No. 9,616,633 (Norsk Hydro ASA) relates to a screw extruder for the continuous extrusion of highly viscous materials, particularly metals such as aluminum and its alloys. The extruder includes an Archimedes screw rotatably mounted within a liner in a screw housing. The housing is provided with an inlet for supplying the material to be extruded, a compression or extrusion chamber, and an extrusion die assembly with a die for forming the desired extruded product shape. The screw and liner are designed such that the required compression occurs at the downstream end of the screw toward the extrusion chamber, corresponding to a maximum of 540° of screw rotation or a maximum of 1.5 revolutions of the screw flight length, and a solid plug of metal is formed at the end of the screw and extrusion chamber, further restricting it from rigidly rotating to achieve the required compression and extrusion pressure.

[0013] The present invention benefits from several principles such as those disclosed in US Patent No. 9,616,633. However, the present invention achieves many improvements over prior art screw extrusion processes.

[0014] The inventors have carried out numerous tests and proposed improvements relating to prior art screw extruders and also to the corresponding process parameters and methods of operating the extruders.

[0015] According to the claims, the present invention describes an efficient extruder and method of operating it, which allows for the production of products from a variety of starting materials in a steady-state process in an efficient manner.

[0016] The device according to the invention is characterized by the features as defined in the attached independent claim 1.

[0017] Preferred embodiments of the device are further defined in the attached dependent claims 2 to 6.

[0018] The method for continuous extrusion of highly viscous materials is characterized by the features as defined in the attached independent claim 7.

[0019] Preferred embodiments of this method are further defined in the attached dependent claims 7-12.

[0020] The invention is further described below, by way of example, with reference to the drawings. [Brief explanation of the drawings]

[0021] [Figure 1] 1 shows a schematic view of an extruder apparatus according to the invention, the extruder being shown in cutaway view. [Figure 2] 2 shows a side view of the extruder apparatus shown in FIG. 1, which is controlled by a computer. [Figure 3] FIG. 1 shows a cutaway view of the screw housing / vessel of an extruder apparatus having multiple cooling / heating zones in the liner portion of the extruder. [Figure 4] In one embodiment, details relating to temperature measurement and control are shown with respect to FIG. [Figure 5] Details of the processing zones in a screw extruder according to the present invention are disclosed. [Figure 6] Details of the extruder compression head are disclosed. [Figure 7] Details of the extruder compression head are disclosed. [Figure 8] Details relating to extruder heat control are disclosed. [Figure 9] Details of the liner construction are disclosed that promote adhesive friction in desired areas and provide a galling-resistant surface in other areas. [Figure 10] The principles and associated control parameters for controlling a screw extruder device are generally disclosed. DETAILED DESCRIPTION OF THE INVENTION

[0022] As shown in FIG. 1, a screw extruder according to the present invention may be included in an apparatus comprising the following main process zones: - Material preparation / mixing zone PMz - Supply Zone Fz - Transport and conditioning zone TCz - Compression and pressure generation zone CPz - Extrusion Zone Ez - Cutting / Packaging Analysis Zone CPAz - Extrusion Products 7

[0023] The materials are prepared and mixed in preparation / mixing zone PMz before being fed into the screw extruder.

[0024] The screw extruder primarily receives its material in a feed zone Fz, which has a feed opening Fo for the extruder, conveys and conditions it in a conveying and conditioning zone TCz, and compresses and subjects the material to pressure in zone CPz.

[0025] The material is extruded in extrusion zone Ez and finally cut and packaged in cutting, packaging and analysis zone CPAz.

[0026] A motor M is provided for generating torque and rotating the screw of the screw extrusion device.

[0027] The screws can be single-flighted or multi-flighted, with fixed or no progressive pitch. Multi-flighted screws improve material flow conditions, while single-flighted screws improve maximum volumetric capacity. Progressive flights allow for larger feed rates, while a constant pitch makes it easier to control the axial temperature gradient.

[0028] Preferably, the screw is made with a polished and hardened working surface and a core with higher elastic properties.

[0029] Furthermore, as previously mentioned, the input material can be of many different types and portions. The material feed can preferably be a metered force feed.

[0030] Furthermore, the input materials may be pre-treated or prepared in several ways in one or more preparation and mixing steps PMz with respect to separation, sizing (calibration), composition, washing, heating, etc. It is understood that the steps involved may take place in the vicinity of the equipment or may be performed elsewhere depending on the design and layout of the factory.

[0031] Before being introduced into the equipment, the input material can be analyzed and classified according to predetermined criteria, which allows for appropriate adjustment of the process parameters of the equipment. For example, the adhesion-slip criteria of the input material can be investigated before operating the equipment.

[0032] There are several general sources of information that may be applicable in this regard, for example: "Key Engineering Materials,Vol.491;Conditions for Sticking Friction between Aluminum Alloy AA6060 and Tool Steel in Hot Forming;F.Wideroee,Torgeir Welo" URL:https: / / doi.org / 10.4028 / www.scientific.net / KEM.491.121”

[0033] This paper describes a method for determining the adhesive friction conditions of Al6060 material, and the abstract states: "The friction conditions between aluminum AA6060 alloy and tool steel in hot bulk forming were investigated. The compression-rolling method for friction measurements presented in this paper represents an innovative method for defining the thermomechanical conditions required for adhesive friction at the interface of two metals. An aluminum disk containing an inserted contrast material was rotated at one end under various pressures at temperatures ranging from 250°C to 500°C. This, combined with visual inspection of the surface and sectioning of the deformed disk, formed a method for studying how various factors influence the stick-slip criterion in metal forming. The normal contact pressure required for adhesion to occur was found to be strongly dependent on the instantaneous temperature. Comparing the normal contact pressure q with the characteristic shear strength k of the aluminum alloy, it was found that adhesive friction occurred at temperatures above 300°C when q / k > 0.6, while a ratio of 0.7 was required at lower temperatures."

[0034] These principles may be useful in classifying other materials and composites relevant to the present invention.

[0035] As shown in FIG. 2, the apparatus may generally be controlled by a computer C that monitors the process on a monitor or screen Sc via information collected by sensors for torque, temperature, axial force, among other process-related parameters, measured in the rotating screw.

[0036] The process for operating the screw extruder is further described with reference to FIGS.

[0037] The extruder is preferably fed with granular metal through a feed opening Fo at a temperature T below Ts, where Ts is the temperature at which the metal will experience adhesion friction within the device. To ensure the metal maintains this temperature, active cooling is employed in the zone extending from the feed opening Fo. This ensures that the metal moves freely through TCz toward the active zone CPz (Figure 5). The active zone is covered by a liner. When the material is within this liner, it is in CPz and its temperature rises, causing adhesion friction. This temperature rise is primarily due to frictional and deformation heat generated near the tip of the screw where the material is fully consolidated.

[0038] In zone Ez, a "billet" is continuously fed in front of the screw as material flows from the screw channel (Figure 5). At CPz and Ez, the temperature is maintained above Ts, preferably for a length corresponding to about 1 / 2 a turn of the screw (Figure 6), so that a large pressure drives extrusion in front of this "billet." When this length of the screw tip is covered with a large amount of metallic material, heat generation (due to friction and deformation) can be controlled by the screw rotation speed and / or torque and cooling in the same area.

[0039] Therefore, to ensure stable extrusion conditions, a temperature significantly above Ts, such as approximately 0.9Tm (Tm = melt temperature), can be maintained. At the same time, active cooling keeps the temperature outside the processing area significantly below Ts. Maintaining this gradient is important. Furthermore, by manipulating this gradient (via the parameters mentioned above), the degree of mixing / deformation can be adjusted (Figure 7). A steeper gradient can be considered when using approximately 1 / 2 turn of the screw to cover the range from 0.9Tm to less than Ts. This drives production capacity and limits the degree of solids mixing to that region.

[0040] Figures 6 and 7 show two cases, the former with a higher capacity / throughput and the latter with a higher degree of mixing.

[0041] Secondly, as the screw speed increases, so does the heat generation, and therefore active cooling is required to maintain the gradient (or low temperature at a section from the desired axial position).

[0042] In this example, temperature control is included in both the screw and the vessel, see FIG. screw: Supply opening;Fo Internal cooling;1 container: Internal cooling;2, External cooling;3, External heating;4.

[0043] Alternatively, a similar response to active cooling can be achieved by increasing the feed rate. This affects the heat balance. As the feed rate increases within the maximum volume of the screw, the same length becomes "active" (heat-generating) volume. As more cold material enters the rear of the screw and exits through the die as hotter material, more energy (heat) leaves the system.

[0044] Q_(heat of deformation) = Q_(active cooling) + Q_(removed with material) - A stable process is obtained by balancing the active cooling and the energy removed with the material against the heat due to deformation of the material being processed. Furthermore, active cooling is employed to maintain the correct temperature gradient, which cannot be ignored. Excessive cooling at CPz and Ez is not beneficial because, as mentioned on the previous page, the temperature there must be well above Ts.

[0045] For some materials, the correct parameters are known, but optimum process windows have been developed for various tool geometries and process materials. For example, tool geometries (reduction rates) affect the pressure that needs to be generated in the screw, different materials (and combinations) have different Ts and flow stresses, etc.

[0046] A system is used to monitor and control various parameters to maintain the correct parameters for a given tool geometry and material. A typical extruder setup consists of the following main elements: See Figure 4. Fo - supply opening 11. Container 12. Screw 13. Drivetrain 14. Weighing unit 15. Runout Table 16. Saw 17. Control Unit

[0047] The control unit adjusts the feed rate by adjusting the rotational speed of the external feed screw to match the feed rate to the weight readings in the feed hopper - see example above.

[0048] The drive train monitors torque and set rpm. According to one aspect of the invention, torque is used as an indirect measure of the relationship between the feed rate and the runout rate measured in a runout table. At steady state, the runout rate increases as torque (and heat generation) increases, followed by CPz or TC. z The extension of CPz should be consistent with the supply rate unless a temperature rise occurs in the TC zone. z This may be increased at the expense of prolongation.

[0049] Once steady state is reached, the process will observe only small fluctuations within a short time frame, for example in the temperature measured along the vessel. To ensure a stable steady state process, the control unit uses measurements of one or more parameters such as feed rate, runout rate, torque, temperature, etc. to maintain a precise axial temperature gradient (and therefore the length of the "active zone"; primarily CPz).

[0050] In the worst case scenario, an erroneous response in the control can be triggered, creating a snowball effect where heat generation leads to further compression of the material in the screw channel. This generates more heat to the point where it again exceeds the active cooling. However, in one embodiment of the present invention, by monitoring the torque (and runout speed), this can be avoided by slightly slowing down the feed rate. The computer can also be programmed to handle this situation.

[0051] Furthermore, in accordance with one aspect of the present invention, monitoring torque at steady state provides additional process information: at the point where the temperature is too high and material melting is likely to occur, the torque drops significantly.

[0052] A similar situation is likely to occur with torque if adhesion during operation is partially or completely lost due to too low a temperature. Torque is constantly monitored by a sensor, and a signal is sent to a controller. The controller compares this information with the temperature measured by one or more sensors in the compression zone; if the temperature is higher or lower than a setpoint, a signal is generated and the controller adjusts the cooling or heating rate to bring the process back within range.

[0053] In short, an extruder control system, in accordance with aspects of the present invention, may generally be based on input parameters from different sources. Drivetrain: - Screw torque and / or speed - Axial load of the screw container: - Temperature distribution Weighing unit: - Material feed rate Runout Table: - Extrusion speed

[0054] According to aspects of the present invention and based on the input parameters, the extrusion process can be controlled by the following parameters: Drivetrain: - screw speed and / or torque Screw / vessel: - Heating / cooling rate Runout Table - cooling rate saw - Cutting length

[0055] In accordance with this aspect of the invention, active cooling in the transport zone should be maintained at a high level, while active cooling in the processing area should be adjusted to a minimum to maintain the desired temperatures described above.

[0056] Material pre-treatment, feeding and mixing The extruder directly mixes multiple materials and passes them from the feed opening Fo to the conveying and conditioning zone TC of the screw extruder. z According to an aspect of the present invention, the feeding system may apply conventional feeder technology, such as a screw feeder, and a load cell to obtain an accurate feeding rate and mixing ratio.

[0057] As the material enters the conveying and conditioning zone, it needs to be uniformly merged with the compressed material further ahead (in the direction of extrusion) in the screw channel.

[0058] According to an aspect of the present invention, pre-treatment of the input material is beneficial to achieve a stable steady-state process.

[0059] For example, an optional debinding step can be included to reduce gas generation as the input material is heated towards the "active zone", thereby minimizing the length variation that occurs due to adhesion friction, which can result from gas generation causing delamination between the process material and internal surfaces or between the compressed mass of the input material itself.

[0060] However, it has been experienced that highly contaminated material can be fed into the system.

[0061] Additionally, increasing the bulk density of the feed material through pre-treatment has been observed to facilitate improved system capacity. It is believed that a denser feed material requires less axial length to be compressed toward the "active zone." That is, it is assumed that LPC ∝ Δρ, where LPC is the axial length over which pre-compression toward the active zone occurs, and Δρ is the change in bulk density from the feed state to a fully dense billet ahead of the screw.

[0062] Control and utilization of surface friction conditions (Ts manipulation) To ensure friction between the material being processed and the surrounding surfaces (including screws, tools, liners, and pre-chamber areas), it may be beneficial according to aspects of the present invention to manipulate the friction of the surrounding surfaces by coating, roughness, or temperature to allow for optimal design.

[0063] FIG. 5 discloses a screw extruder with the following zones (from right to left): Fz, TCz, CPz, Ez

[0064] FIG. 6 shows the preferred shape of the compressed material in the CPz screw extruder.

[0065] FIG. 7 shows a situation where the majority of the compressed material occurs at the end of the screw, creating high torque and axial loads on the device.

[0066] Figure 8 shows a schematic diagram of the heat and cooling control of a screw extruder. The length of the CPz is considered to be very important. It can be correlated with and monitored by torque and temperature measurements along the axial position. In other words, the length of the CPz can be controlled by the ratio of cooling / heating and feed / rotation speed. As the CPz increases, more deformation heat is generated. Therefore, torque can be used as a parameter to set / adjust / regulate the cooling and heating output or the feed rate and / or rotation speed during steady state.

[0067] Figure 9 discloses details of the liner construction that promotes adhesive friction in the desired area, which is typically the CPz portion of the device, since that is where adhesive friction occurs. The liner L also provides a galling-resistant surface in another area where adhesive friction is less likely to occur, which is typically the TCz portion of the device.

[0068] 10 further discloses in more detail how the process occurring within the screw extruder can be further monitored and controlled. For example, water cooling can be increased to prevent heat transfer backward within the device. Additionally, heat breaks can be implemented, for example in the liner, to promote temperature rise at the front of the device and prevent temperature rise at the rear.

[0069] Selected portions of the liner can also be coated to reduce heat generation and reduce the risk of sticking.

Claims

1. 1. An apparatus for continuous extrusion of highly viscous materials, particularly materials containing metals such as aluminum, magnesium, titanium, copper, nickel, zinc and alloys thereof, comprising an Archimedes screw (12) rotatably mounted within a liner (L) of a screw housing or vessel (11) having an inlet (Fo) for feeding the material to be extruded, an extrusion zone (Ez) having an extrusion die assembly for forming the shape of the desired extruded product (7), and comprising a feeding zone (Fz) for the material, a conveying and conditioning zone (TCz) for the material, and a compression and pressure development zone (CPz) for the material, wherein the compressed material formed in the compression and pressure development zone (PCz) and the compressed plug of material in the extrusion zone (Ez) are constrained against rigid body rotation so that the required compression and extrusion pressures are obtained. The device is characterized in that it comprises means for controlling and regulating the temperature of the material within a set range of temperatures before it is extruded into the product (7), and the compression pressure in the extrusion chamber is controlled within a set range of pressures.

2. the rotation of the Archimedes screw is provided by a motor (M) with torque and / or speed control; Torque and / or speed are monitored and applied to adjust the compression pressure in the extrusion chamber based on an algorithm that calculates torque and / or speed based on the recorded pressure in the extrusion chamber. and 10. The apparatus of claim 1.

3. further comprising an upstream preparation / mixing zone PMz for processing the material, 3. The device according to claim 1 or 2.

4. The feed zone Fz includes a means for controlling the temperature of the feed material to a specific predetermined temperature. An apparatus according to any one of claims 1 to 3.

5. the conveying and conditioning zone TCz includes means for controlling the temperature of the material to a specific predetermined temperature; An apparatus according to any one of claims 1 to 4.

6. The Archimedes screw is a double-flight screw. An apparatus according to any one of claims 1 to 5.

7. A method for continuous extrusion of highly viscous materials, particularly metals such as aluminum, magnesium, titanium, copper, nickel, zinc and their alloys, carried out in an apparatus comprising an Archimedes screw (12) rotatably mounted in a liner (L) of a screw housing or vessel (11) provided with a feed opening (Fo) for feeding the material to be extruded, an extrusion zone (Ez) and an extrusion die assembly for forming the shape of the desired extruded product (7), preparing a feed material and feeding it from a feed zone Fz through said feed opening Fo and into a conveying and conditioning zone TCz for further pre-compressing said material and conveying it into a compression and pressure generation zone CPz forming part of an extrusion zone Ez, thus obtaining a predetermined compression and extrusion pressure; In a method further comprising: the temperature of the material in the extrusion zone Ez is controlled and regulated to a set range temperature and the compression pressure in the extrusion chamber is controlled within a set range pressure before the material is extruded to form the product (7).

8. the pressure of the material in the extrusion zone Ez is controlled and adjusted to a set pressure range before the material is extruded to form the product (7), The method of claim 7.

9. wherein the rotation of the Archimedes screw is provided by a motor with torque and / or speed control, and the torque and / or speed are monitored and controlled to regulate the compression pressure in the extrusion chamber. The method of claim 8.

10. The feed zone Fz includes a means for controlling the temperature of the feed material to a specific predetermined temperature. The method of claim 7.

11. The conveying zone Tz includes a means for controlling the temperature of the material to a specific predetermined temperature. The method of claim 7.

12. Before processing the material, a pre-analysis and classification of the material is carried out in order to adjust one or more process parameters of the device. The method of claim 7.

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