WO2018134018A1 - Continuous extrusion process for a metal-containing bulk material and metal-powder extrusion installation - Google Patents

Abstract

Continuous extrusion process for a metal-containing bulk material (13) for producing an extruded body, comprising the following steps: introducing the metal-containing bulk material (13) into a press channel (8) of a metal-powder extrusion installation (1), which is bounded by a rotating extrusion wheel (2) and pressing tool components, which comprise a running-in region having sealing plates (5, 6, 7) and comprise a deflecting region with a counter plate (11) and a feeding plate (10), feeding in the metal-containing bulk material (13) via a peripheral groove (3) of the rotating extrusion wheel (2) to the counter plate (11) and deflecting the compacted metal-containing bulk material (13) in the deflecting region through the feed plate (10), which has an opening, to a die (12), wherein at least one of the sealing plates (5, 6, 7) arranged in the running-in region is cooled by means of a cooling device. The invention also relates to a metal-powder extrusion installation that is suitable for carrying out the extrusion process according to the invention.

Description

 Continuous extrusion process for a metal-containing bulk material and metal powder extrusion plant

The invention relates to a continuous extrusion process for a metal-containing bulk material for producing an extruded body, comprising the following steps:

Introducing the metal-containing bulk material into a press channel of a metal powder extrusion press, which is delimited by a rotating extrusion wheel and press tool components, which comprise a gasket plate having an inlet region and a deflection region with a counter-holder and a feed plate,

 - Feeding the metal-containing bulk material via a circumferential groove of the rotating extrusion to the counter-holder and deflecting the compacted metal-containing bulk material in the deflection region through the opening having a feed plate to a die.

The term "metal-containing bulk material" used in this application includes, inter alia, metal-containing powders, powder mixtures, granules, and chips, and may also be mixtures of metal powders with ceramic fibers or particles, that is, composites.

Various methods have already been proposed for compacting a metal-containing bulk material.

Components made of powder metallurgy materials can be used for example in the automotive industry, aerospace engineering and general engineering. Continuous extrusion is a cost effective alternative to compact metal bulk materials, especially metal powders. Originally, this process, which is also referred to as the "conforming process", turned cast wire or wire rod made of aluminum or copper alloys into more complex geometries in a single step. Later Pressing processes have been developed to process granules or powders. It has been found that a stable process is difficult. An industrial use of such extrusion processes for metal-containing bulk materials therefore does not yet take place.

A conventional powder extruder suitable for the extrusion molding process comprises a rotary extrusion wheel with a circumferential groove and a stationary shoe comprising the feed plate arranged in the deflection region and the counter holder. At the opening having a feed plate, the die joins. The crimping tool components forming the lead-in area and the deflection area extend over approximately one quarter of the circumference of the extrusion wheel. The metal-containing bulk material, in particular a metal-containing powder, is drawn into the inlet region and the deflection region by friction in the case of a rotating extrusion wheel. The metal-containing powder is thereby accumulated and compacted on the counter-holder. The compacted powder is deflected at the anvil to the feed plate having the opening and to a die. The individual cold powder particles weld into a fully compacted strand due to shear forces without the powder particles melting. The friction and deformation forces that occur due to the rotation of the extrusion wheel generate the required temperatures and pressures for the continuous extrusion through the die.

In the dissertation Stadelmann, C: Extrusion of metal powders by continuous powder extrusion, Friedrich-Alexander-University Erlangen-Nürnberg, 2009, investigations are described in which metal powder mixtures are continuously pressed into a strand using a modified pressing system.

A similar continuous extrusion process is known from DE 10 2006 004 622 A1. WO 2008/003275 A1 describes a process for the production of molded parts from dispersion-hardened metal alloys.

Extrusion methods for metal powder mixtures are not yet implemented industrially, since usually no stable process control is possible. In the course of the extrusion process, powder adhesions occur in the area of the powder feed which clog the press channel and prevent a constant replenishment of the powder mixture. If the flow stress becomes too low during the extrusion process, complete compaction of the powder is not possible. It then builds on a sufficiently high pressure, which is required to completely weld particles of the metal-containing bulk material, in particular powder particles together.

The transported during the supply of the metal-containing bulk material flow per wheel revolution is reduced by the given bulk density. The strand exit speeds therefore differ significantly from those with wire feed. This in turn causes longer residence times of the metal-containing, partially compacted bulk material in the pressure channel of the die, so that the risk of adhesions and thus pressing errors is higher on the sealing plates and on the die.

The invention is therefore based on the object to provide a continuous extrusion process for a metal-containing bulk material, which allows a stable process management.

In order to achieve this object, it is provided according to the invention in an extrusion process of the type mentioned in the introduction that at least one of the sealing plates arranged in the inlet region is cooled by means of a cooling device. Surprisingly, it has been found that a stable process can be ensured by controlled temperature control of press tool components in the form of cooling. This is surprising since one would first assume that heating would be beneficial for a stable process. It could be assumed that the powder flows more easily due to rearrangement and that less heat is generated by plastic deformation (adiabatic heating). The lower internal heat generation would actually have to be compensated by more heating. Instead, it has surprisingly been found in tests that a targeted, graded tempering in the form of cooling of at least one sealing plate has a process-stabilizing effect. By cooling provided according to the invention, an extruded body can be produced in a continuous process with high quality. It has been found that by cooling the inlet region of the press channel, powder adhering to the gasket plates can be avoided. This ensures a continuous powder feed and a uniform pressure build-up.

In the area of the counter-holder, cooling of the pressing-tool components, in particular of the feeding plate, causes a sufficiently high pressing pressure to be built up, which leads to break-up of oxide skins and welding of metal particles of the metal-containing bulk material. In an extrusion process in which a wire is fed, however, a cooling in the area of the counter-holder would cause high compression pressures and increased chip formation, which may hinder or stop the entire process. In the method according to the invention, it is preferred that at least one pressing tool component arranged in the deflection region, namely the feed plate and / or the counter holder, is or are cooled by means of or by means of the cooling device. The pressing tool components form a pressing channel with the extrusion wheel. The anvil deflects the flow of material through the feed plate to the die. By inventively provided

Cooling, buildup of the metal powder mixture can be avoided, the unstable process conditions and lead to press errors. In addition, sufficiently large pressures are generated.

The extrusion process according to the invention can be carried out on a metal powder extrusion press with one or more, in particular two or three, sealing plates arranged in the circumferential direction.

In the method according to the invention, it is preferred that in the processing of copper or a copper alloy, a sealing plate is cooled to a temperature between 80 ° C and 130 ° C. This cooling ensures that powder adhesions are avoided and that a sufficiently high pressure is built up.

Similarly, it can be provided in the extrusion process according to the invention, that in the processing of aluminum or an aluminum alloy, a gasket is cooled to a temperature between 50 ° C and 100 ° C. In contrast, occur in conventional methods that are performed without cooling, temperatures between about 300 ° C and 330 ° C. Preferably, in the extrusion process according to the invention, at least the middle sealing plate is cooled in the case of a metal powder extrusion press having three sealing plates. Of course, it is also possible that the first and / or the third sealing plate (seen in the circumferential direction) is cooled or become. In addition, all three sealing plates can be cooled. If there are two sealing plates, one of the two sealing plates or alternatively both can be cooled.

Thus, in the method according to the invention, it is possible to cool both one or more sealing plates as pressing tool components arranged in the inlet region and also the feed plate and / or the counter holder as pressing tool components arranged in the deflection region. The respectively cooled die components are selected in a process-optimizing manner, whereby the inlet area and optionally also in the deflection area can be set specifically a desired temperature profile.

In the extrusion molding method according to the invention, it is also possible that during the processing of copper or a copper alloy, at least one pressing tool component arranged in the deflection region, in particular the feed plate, is cooled to a temperature between 310 ° C. and 380 ° C. In contrast, temperatures of more than 440 ° C. occur during a process without cooling.

Similarly, when processing aluminum or an aluminum alloy, it may be provided that at least one pressing tool component arranged in the deflection region, in particular the feed plate, is cooled to a temperature between 340 ° C. and 420 ° C.

In addition to the cooling of one or more pressing tool components, it is also possible to cool the anvil. Preferably, in the processing of copper or a copper alloy, the anvil is cooled to a temperature between 340 ° C and 430 ° C. On the other hand, in the extrusion process of the present invention, in the processing of aluminum or an aluminum alloy, the counter-holder can be cooled to a temperature between 300 ° C and 380 ° C.

The die of the metal powder extrusion plant is not cooled. Instead, it is heated to a temperature between 370 ° C and 420 ° C during processing of copper or a copper alloy. When processing aluminum or an aluminum alloy, the die is heated to a temperature between 400 ° C and 430 ° C. The specified temperature ranges are given by way of example for alloys containing copper or aluminum as the main constituent. The process control, in particular the temperature control must in each case depending on used alloy can be adjusted. Other influencing factors include the particle size of the metallic bulk material, the particle roughness, the oxide content of the particles and the particle shape. If one of these factors is changed, the pressing behavior also changes, so that the temperature control must be adjusted. The temperature range suitable for the processing is also dependent on the rotational speed of the extrusion wheel and its diameter and thus on the rotational speed.

In addition, the invention relates to a metal powder extrusion plant, which is designed for continuous extrusion of a metal-containing bulk material, with a pressing channel, which is delimited by an extrusion wheel and pressing tool components comprising a sealing plates having inlet region and a deflection region with a counter-holder and a feed plate. The metal powder extrusion system according to the invention is characterized in that it has a cooling device with which at least one of the sealing plates arranged in the inlet region can be cooled.

A preferred development of the metal powder extrusion press according to the invention provides that it comprises a controller, which is designed to cool at least one sealing plate to a predetermined temperature. Preferably, the controller is also adapted to cool the feed plate and / or the anvil.

It may also be provided that the cooling device of the metal powder extrusion press according to the invention comprises integrated, in the sealing plates integrated, can flow through a cooling medium cooling channels. Analog can also have the feed plate and the counter-holder corresponding cooling channels.

The invention will be explained below with reference to an embodiment with reference to the drawings. The drawings are schematic representations and show: 1 is a sectional view of a metal powder extrusion press according to the invention in the region of the press channel in carrying out the method according to the invention, and FIG. 2 is an enlarged view of FIG. 1 in the region of the press channel.

Fig. 1 shows the essential components of a metal powder extrusion plant 1, which is suitable for the production of extruded bodies from a metal powder mixture by an extrusion process.

The metal powder extrusion press 1 comprises a rotating extrusion wheel 2 which has a peripheral groove 3 on its outside. The extrusion wheel 2 is driven at a fixed speed by a drive motor (not shown).

On a stationary tool shoe 4 sealing plates 5, 6, 7 are arranged side by side along a circular segment-shaped path. The sealing plates 5, 6, 7 together with the extrusion wheel 2 form a press channel 8. A metal powder mixture is introduced into the press channel 8 via a feed 9 which is tubular in this exemplary embodiment. As best seen in the enlarged view of FIG. 2, the die components in the deflection area comprise a feed plate 10 with an opening for the bonded metallic bulk material 13. In carrying out the extrusion process, the compacted metallic bulk material flows through the opening to a die , In the deflection region and a counter-holder 1 1 is arranged, which causes a deflection of the already almost completely compacted metallic bulk material 13 by about 90 °. After passing through the opening of the feed plate 10, the almost completely compacted metallic bulk material 13 passes into a die 12, by which the outer contour of the extruded body produced is determined. Alternative embodiments are also possible in which a female die is the inner contour or both the inner contour and the outer contour of the extruded body Are defined. The die 12 may, for example, have a circular, rectangular or more complex cross section.

To produce an extruded body, metallic bulk material in the form of a metal powder mixture is introduced via the feed 9. In the present embodiment, the metal powder mixture is a copper alloy. The powder particles pass into the pressing channel 8, which is formed on the one hand by the groove 3 of the extrusion wheel 2 and on the other hand by the sealing plates 5, 6, 7 as pressing tool components. When passing through the press channel 8, the metal powder mixture is compacted. The pressure generated when passing through the press channel 8 causes the metallic powder particles to be compacted. In the region of the counter-holder 1 1, a reversal of the konnpaktierten metal powder mixture 13 by 90 °. Subsequently, the compacted metal powder mixture 13 is extruded through the die 12. In order to ensure a stable process, it is essential that the sealing plates 5, 6, 7 are cooled. The fact that a cooling of the sealing plates 5, 6, 7 and thus a cooling of the metal powder mixture 13 to be compacted is required is surprising since it has hitherto been assumed that the heat produced during the compacting makes it easier to flow the metal powder mixture. Experiments have shown, however, that at high process temperatures caused by the compaction in the pressure channel 8, there is a low yield stress. It then builds on a sufficiently high pressure, which completely welded together the metallic powder particles. Therefore, the sealing plates 5, 6, 7 are respectively cooled graded by associated cooling means. A cooling device comprises in a sealing plate 5, 6, 7 integrated cooling channels, which are flowed through by a cooling medium. In the illustrated embodiment, water serves as a cooling medium. By means of the cooled sealing plates 5, 6, 7, resulting heat is removed in a controlled manner during the compaction of the metal powder mixture 13. In addition, the feed plate 10 is associated with cooling means having cooling channels to cool the feed plate 10. In contrast, the die 12 is not cooled. Instead, it is associated with a heater (not shown). In addition, alternative embodiments are possible in which the die is optionally cooled. In this case, the inlet region upstream of the extrusion chamber, an antechamber or a spacer ring arranged in front of the die can be cooled.

Along the sealing plates temperature sensors are arranged, which are formed as a thermocouple and in the component to be cooled, d. H. either in a sealing plate 5, 6, 7 or in the feed plate 10, are integrated. The Diehl o tion plate 5 has a cooling channel 15. The sealing plate 6 has a

 Cooling channel 16 on. The sealing plate 7 has a cooling channel 17. In the sealing plate 5, a temperature sensor 18 is integrated. The sealing plates 6, 7 have corresponding temperature sensors 19, 20. A temperature sensor 21 is integrated in the feed plate 10, which has a cooling channel 22. The cooling channels 15 15, 16, 17, 22 of the sealing plates 5, 6, 7 and the feed plate 10 each form a separate cooling circuit. Each cooling circuit includes a pump through which the cooling fluid is circulated. The temperature sensors 18, 19, 20, 21 are connected via lines not shown with a controller 14. By means of the temperature sensors, a control of the cooling process is carried out by the controller 14. In this way, the sealing plates 5, 6, 7 and the feed plate 10 can be controlled individually and separately to set a specific temperature or temperature range in each section of the pressing channel 8. Each sealing plate 5, 6, 7 and the feed plate 10 is assigned a separate control loop. By controlled cooling, a stable quasi-stationary state can be generated, so that the extrusion process can be carried out continuously.

The choice of a suitable temperature range depends on the metal powder mixture to be processed. For copper or copper alloys, the second sealing plate 6 is cooled in this embodiment to a temperature of 80 ° C to 140 ° C. The adjacent sealing plates 5 and 7 can be cooled to a lower or higher temperature. The feed plate 10 is opened a temperature between 320 ° C and 380 ° C cooled. The counter-holder 1 1 is cooled to a temperature between 360 ° C and 430 ° C. The die 12 is heated to a temperature between 350 ° C and 450 ° C. For the processing of aluminum, ie pure aluminum, and aluminum alloys, for example, the following temperatures have been found to be suitable:

The second sealing plate 6 is cooled to a temperature between 40 ° C and 100 ° C. The feed plate 10 is cooled to a temperature between 340 ° C and 430 ° C. The counter-holder 1 1 is cooled to a temperature between 310 ° C and 380 ° C. The die is heated to a temperature between 380 ° C and 450 ° C. The temperatures given are to be understood as examples which have to be adapted depending on the metallic bulk material used, the powder characteristics (particle size, particle shape, particle surface, mixing ratio of several components). The temperature of the die must be adapted to the metallic bulk material to be processed and the profile to be produced (cross-sectional area, multiple perforations, expansion behavior).

When carrying out the extrusion process, heating of the sealing plates 5, 6, 7 is prevented by the targeted cooling. This results in the advantages of a lower tool load, no loss of the required pressing pressure and a significantly improved intake behavior of the added metal powder mixture.

Another effect of the cooling in the intake area of the press channel 8 is that the temperature in the extrusion area on the die 12 remains constant. A heating of the die 12 is required, in particular for small cross sections of the extruded body, since otherwise the pressing pressure becomes so great that the compacted material does not flow through the die 12 but laterally on the side Counterholder 1 1 is squeezed out over as chip. In this undesired case, the temperatures at the feed plate 10 and at the anvil 1 1 are significantly higher than at the die 12. However, if this temperature difference is compensated by heating the die 12 and cooling the feed plate 10, the desired extrusion through the die takes place 12th

The continuous extrusion process for metallic bulk material enables the production of an extruded body with high and uniform quality.

LIST OF REFERENCE NUMBERS

1 metal powder extrusion plant

2 extrusion wheel

3 groove

 4 tool shoe

 5, 6, 7 sealing plate

 8 pressing channel

 9 feeder

10 feed plate

 1 1 counterholder

 12 matrix

 13 metal powder mixture

 14 controllers

15, 16, 17 cooling channel

 18, 19, 20, 21 temperature sensor

 22 cooling channel

Claims

claims 1 . Continuous extrusion process for a metal-containing bulk material (13) for producing an extruded body, comprising the following steps: - Introducing the metal-containing bulk material (13) in a press channel (8) of a metal powder extrusion press (1), which is bounded by a rotating extrusion wheel (2) and pressing tool components, a sealing plates (5, 6, 7) having inlet region and a deflection region comprising a counter-holder (11) and a feed plate (10), - Feeding of the metal-containing bulk material (13) via a circumferential groove (3) of the rotating extrusion wheel (2) to the counter-holder (1 1) and deflecting the compacted metal-containing bulk material (13) in the deflection region through the opening having a feed plate (10) to a Die (12), characterized in that at least one of the arranged in the inlet region sealing plates (5, 6, 7) is cooled by means of a cooling device. 2. Extrusion method according to claim 1, characterized in that at least one arranged in the deflection area pressing tool component, namely the feed plate (10) and / or the counter-holder (1 1), is cooled by means of or by means of the cooling device or. 3. extrusion process according to claim 1 or 2, characterized in that a metal powder extrusion press (1) with two or three circumferentially arranged sealing plates (5, 6, 7) is used. 4. extrusion process according to one of the preceding claims, characterized in that in the processing of copper or a copper alloy, a sealing plate (5, 6, 7) is cooled to a temperature between 80 ° C and 130 ° C. 5. Extrusion method according to one of the preceding claims, characterized in that in the processing of aluminum or an aluminum alloy, a sealing plate (5, 6, 7) is cooled to a temperature between 50 ° C and 100 ° C. 6. extrusion process according to claim 4 or 5, characterized in that at a three sealing plates (5, 6, 7) having metal powder extrusion press system (1) at least the middle sealing plate (6) is cooled. 7. extrusion process according to one of the preceding claims, characterized in that in the processing of copper or a copper alloy, the feed plate (10) is cooled to a temperature between 310 ° C and 380 ° C. 8. Extrusion method according to one of the preceding claims, characterized in that in the processing of aluminum or an aluminum alloy, the feed plate (10) is cooled to a temperature between 340 ° C and 420 ° C. 9. extrusion process according to one of the preceding claims, characterized in that in the processing of copper or a copper alloy, the counter-holder (1 1) is cooled to a temperature between 340 ° C and 430 ° C. 10. extrusion process according to one of the preceding claims, characterized in that in the processing of aluminum or an aluminum alloy, the counter-holder (1 1) is cooled to a temperature between 300 ° C and 380 ° C. 1 1. Extrusion method according to one of the preceding claims, characterized in that the die (12) in the processing of copper or a Copper alloy is heated to a temperature between 370 ° C and 420 ° C and in the processing of aluminum or an aluminum alloy to a temperature between 400 ° C and 430 ° C. 12. metal powder extrusion plant (1), which is designed for the continuous extrusion of a metal-containing bulk material (13), with a pressing channel (8) which is delimited by an extrusion wheel (2) and pressing tool components having a sealing plates (5, 6, 7) Inlet region and a deflection region with a counter-holder (11) and a feed plate (10), characterized in that the metal powder extrusion plant (1) has a cooling device with which at least one of the sealing plates (5, 6, 7) arranged in the inlet region is coolable. 13. Metal powder extrusion plant according to claim 12, characterized marked, that it comprises a controller (14) which is adapted to at least one sealing plate (5, 6, 7) to cool to a predetermined temperature. 14. Metal powder extrusion plant according to claim 12 or 13, characterized in that the cooling device in the sealing plates (5, 6, 7) integrated eng- integrated, can flow through a cooling medium cooling channels.