Patent Description:
Depending on the material, the process of friction extrusion for metals according to prior art is conducted in either hot or cold variants which press a metallic billet with a hydraulic ram through a die. These processes demands high energy inputs both in terms of hydraulic rams and heating coils. Furthermore, in such processes if waste material is to be used for extrusion, it has to be carried out in a separate process to create a workable billet, whereas the present invention will process the waste directly in the (Friction Extrusion Unit) FEU.

The process of friction extrusion for plastic according to prior art is conducted as follows: Plastic pellets are gravity fed from a top mounted hopper into the barrel of the extruder where, under the action of an extrusion screw and heaters, it undergoes a thermomechanical transformation into continuous filament. Such an extruder apparatus is only suitable for polymers and additives such as colorants. UV inhibitors are mixed prior to the arriving at the hopper.

Known friction stir extrusion (FSE) according to the prior art works as follows: A rotating tool is used to produce heat and plastic deformation through friction between the tool itself and the chips to be recycled (into a hollow cylindrical chamber) by compacting, stirring and extruding the material. The length of the wire that can be produced in a single operation is very limited. Moreover, this technology is prone to vibrations and instability. <CIT> discloses a further known prior art.

It is an object of the invention to provide technology that allows to overcome the draw backs of the prior art.

This object is achieved by way of a waste fraction processing friction extruder unit of the above mentioned kind, wherein the diameter of the thread of the friction extruder screw essentially matches the inner diameter of the inner tube, and wherein the friction extruder screw has a shaft of conic shape, wherein the diameter of the conic shape of the shaft increases with increasing distance from the space for collecting waste fractions.

The present invention allows reuse of metal swarf as raw material otherwise considered as waste (circular economy). For instance in the metal forging industry, the swarf generated by milling of forged parts can be up to <NUM>% from the initial billet weight for titanium parts. It allows the use of self-generating friction energy as the main source to convert raw material into wire. The invention is suitable to extrude metal wire and/or polymeric filament. It can be used to manufacture coated wires and reinforced polymeric filaments.

Also, the invention allows merging the wire and filament post-extrusion processing step into one, making it flexible to handle metal or polymer.

Of course, the present invention is also suited to be fed with newly purchased/produced materials, already existent waste fractions or mixtures thereof.

Preferably, the outer tube has a cylindrical shape and is arranged coaxial with the inner tube, and wherein the end section of the outer tube is closed with a bottom element.

Advantageously, the end section of the outer tube is arranged on a lower end of the outer tube. Preferably, the waste fraction processing friction extruder unit further comprises an electric motor that is configured to rotate the friction extruder screw around its axis.

Advantageously, the diameter of the thread of the friction extruder screw is within a range of <NUM>% to <NUM>% of the inner diameter of the inner tube.

Preferably, the cone angle of the conic shape of the shaft is between <NUM>° and <NUM>°, in particular between <NUM>° and <NUM>°.

Preferably, the cone angle is essentially constant along the longitudinal extension of the shaft.

Preferably, the lead of the thread of the friction extruder screw is between <NUM> and <NUM>.

Advantageously, the longitudinal length of the friction extruder screw is between <NUM> and <NUM>.

Preferably, the friction extruder screw is hollow and comprises coaxial horizontal discs being distanced to another along the longitudinal axis of the screw and extending orthogonal to the longitudinal axis along the diameter of the conic shape of the shaft in order to increase the stiffness of the extruder screw.

Advantageously, the friction extruder screw is made of wear and temperature resistant metallic material such as stainless steel or Ni-based materials. Surface treatments to increase surface wear and corrosion resistant could be also applied.

Preferably, flanks of the thread of the friction extruder screw essentially extend orthogonally from the longitudinal axis of the friction extruder screw, and wherein preferably the flank angle of these flanks is zero.

Advantageously, each flank of the thread of the friction extruder screw comprises.

Preferably, at the end of broadened end section the upwards curved shape of the flank reduces the distance to the proximate upper flank between <NUM>% and <NUM>% when compared to the distance between the straight sections of the flanks.

Advantageously, the length of broadened end section amounts between <NUM>% to <NUM>%, in particular <NUM>% to <NUM>%, of the lead of the thread of the friction extruder screw.

The invention also can provide a new method of producing welding and additive manufacturing (AM) wires, as well as polymeric filament for 3D printing using friction energy to convert metal swarf, or polymeric pellets, into continuous wire or filament rods. <FIG> shows the processing stages that can fulfil the new method by utilizing the friction extruder unit according to the invention. The friction energy entailed in the process will generate heat which will be reutilised to assist the upstream drawing stages. Notwithstanding, for higher temperature materials a heating unit can be added for better formability in the drawing stages. Subsequently, the metallic wire or polymeric filament undergo through a series of drawing stages to reduce diameter and tailor final mechanical properties of the rod extruded by the FEU into the final product. i.e. fine wire or filament spooled in a drum. At this stage, the wire or filament is ready to be commercialised as welding wire or polymeric filament for welding and AM purposes.

The task of transforming the metallic waste related to subtractive manufacturing, (i. milling, grinding, drilling, etc.) into continuous wire or filament, thus eliminating waste and enabling the continual use of metallic swarf and recycled polymer.

This is made possible using friction as the energy source to promote metal dynamic recrystallisation or polymeric softening or remelting. ln a preferable configuration, the metallic wire or polymeric filament are produced with a vertically arranged extrusion setup. The machine can be composed essentially of two concentric cylindrical tubes, where the outer one is the reservoir for metallic swarf or polymeric pellets and the inner one is the actual core of the machine. The latter can be composed by a conical friction extruder screw driven in a rotational motion by a motor (e.g. hydraulic, e/electrical, etc.) bolted inside the top section of the inner cylinder, an top of the extruder screw. The metal swarf or polymeric pellets will be forced by the conical friction extruder screw to move in an upward motion. With the increase in thread lead the volume decreases as a result of the conically shaped shaft. The decrease in volume will result in a significant change in pressure, friction and consequently temperature. The combined effect of these three contributions will promote the dynamic recrystallization, viscoplastic flow in the case of metallic wire extrusion, and gradual softening or melting of the polymer pellets for filament extrusion. Finally, viscoplastic metal or melted polymer are extruded in a continuous wire or filament through a nozzle positioned at the same height as the last screw thread. The metallic wire extrusion can take place in solid state regime, i. bellow the melting temperature of the swarf material, and in polymeric filament extrusion such temperature is surpassed. The use of possible different die geometries for producing solid or hollow wires and filaments, allows the fabrication of co-extruded wires. For instance a premanufactured metal/ wire can be coated with extruded meta/ or polymer (e.g., providing functionality or protection). In the case of polymer filaments, continuous fibre reinforcement can be directly added during friction extrusion.

In the following, exemplary features of the friction extruder screw are explained:
One probable material candidate to produce the screw is Stainless Steel (e.g. <NUM>) along with a nitriding process to harden the screw surface against abrasion, hence wear.

Rotational Speed (RPM) - the table below summarises preferred rotational speed enabling sufficient energy to process metallic and polymeric materials in dependence of the material. The proposed values were based on existing literature of other friction based and extrusion processes. Processable materials are also mentioned.

Most polymer extruders possess heating coils, providing an additional amount of energy to promote melting. The present idea for a machine set up focuses more on the use of frictional energy, thus the lack of heating units are compensated with a comparably higher rotational speed.

Working temperatures - The temperature range that ensures dynamics recrystallisation for metals, and melting for polymers, of relevant material types for to be used in present invention are presented in the table below.

In the following, in order to further demonstrate the present invention, illustrative and non-restrictive embodiments are discussed, as shown in the drawings, which show:.

In the following figures identical reference signs refer to identical features unless expressly depicted otherwise.

<FIG> shows a perspective view of a waste fraction processing friction extruder unit <NUM> according to the invention. The waste fraction processing friction extruder unit <NUM> comprises a receptacle <NUM> for receiving fragments of metallic or polymeric waste fractions <NUM>. The receptacle <NUM> comprises an outer tube 2a, said outer tube 2a being closed at an end section 2a' defining a space 2b (see in particular <FIG>) for collecting waste fractions <NUM> entered into the receptacle <NUM>.

The friction extruder unit <NUM> further comprises an extrusion device <NUM>. As can be seen from the exploded view of <FIG> said extrusion device <NUM> comprises a cylindrically shaped inner tube 4a, said inner tube 4a having a longitudinal axis x and an inner diameter di (see <FIG>), a friction extruder screw 4b that is coaxially arranged within the inner tube 4a, and an extrusion nozzle 4c connected to the inner tube 4a. The friction extruder screw 4b extends at least until to the extrusion nozzle 4c, said extrusion nozzle 4c being configured to receive material transferred by the friction extruder screw 4b towards the nozzle 4c and to shape, from said material, a continuous wire 5a or filament 5b.

The inner tube 4a extends from the space 2b for collecting waste fractions <NUM>, and wherein the friction extruder screw 4b extends within the inner tube 4a into the space 2b for collecting waste fractions <NUM>.

The diameter dth (see <FIG>) of the thread of the friction extruder screw 4b essentially matches the inner diameter dit (see <FIG>) of the inner tube 4a. Preferably, the diameter dth of the thread of the friction extruder screw 4b is within a range of <NUM>% to <NUM>% of the inner diameter dit of the inner tube 4a. The friction extruder screw 4b has a shaft 4b' of conic shape, wherein the diameter ds of the conic shape of the shaft 4b' increases with increasing distance from the space 2b for collecting waste fractions <NUM>.

As can be seen from <FIG>, the outer tube 2a has a cylindrical shape and is arranged coaxially with the inner tube 4a, and wherein the end section 2a' of the outer tube 2a is closed with a bottom element 2a". <FIG> shows that this bottom element 2a" can also be made out of two connectable pieces.

Regarding <FIG>, reference sign <NUM> depicts a coupling for connecting the screw 4b to an electric motor <NUM> by using the bolts <NUM>. Reference sign <NUM> refers to a top cover. The screw 4b is connected with a ball bearing <NUM> to facilitate smooth rotation. The electric motor <NUM> that is configured to rotate the friction extruder screw 4b around its axis x.

As can be seen in <FIG>, the end section 2a' of the outer tube 2a is arranged on a lower end of the outer tube 2a.

<FIG> shows an upper section of the screw 4b. <FIG> shows a lower section of the screw 4b. The cone angle α of the conic shape of the shaft 4b' is preferably between <NUM>° and <NUM>°, in particular between <NUM>° and <NUM>°.

Preferably, the cone angle α is essentially constant along the longitudinal extension of the shaft 4b'.

<FIG> shows that the lead h of the thread of the friction extruder screw 4b. Preferably, this lease h is between <NUM> and <NUM>. Please note that all the dimensioning specifications shown in <FIG> are in the unit "mm" and are only exemplary and non-restrictive.

The longitudinal length L of the friction extruder screw 4b is preferably between <NUM> and <NUM>.

The friction extruder screw 4b is preferably hollow and comprises coaxial horizontal discs 4b" (see <FIG>) being distanced to another along the longitudinal axis x of the screw 4b and extending orthogonal to the longitudinal axis x along the diameter of the conic shape of the shaft 4b' in order to increase the stiffness of the extruder screw 4b. Preferably, the flanks 4b‴ of the thread of the friction extruder screw 4b essentially extend orthogonally from the longitudinal axis x of the friction extruder screw 4b, and wherein preferably the flank angle of these flanks is zero.

Claim 1:
Waste fraction processing friction extruder unit (<NUM>) comprising
- a receptacle (<NUM>) for receiving fragments of metallic or polymeric waste fractions (<NUM>), said receptacle (<NUM>) comprising an outer tube (2a), said outer tube (2a) being closed at an end section (2a') defining a space (2b) for collecting waste fractions (<NUM>) entered into the receptacle (<NUM>), and
- an extrusion device (<NUM>), said extrusion device (<NUM>) comprising
* a cylindrically shaped inner tube (4a), said inner tube (4a) having a longitudinal axis (x) and an inner diameter (di),
* a friction extruder screw (4b) that is coaxially arranged within the inner tube (4a), and
* an extrusion nozzle (4c) connected to the inner tube (4a), wherein the friction extruder screw (4b) extends at least until to the extrusion nozzle (4c), said extrusion nozzle (4c) being configured to receive material transferred by the friction extruder screw (4b) towards the nozzle (4c) and to shape, from said material, a continuous wire (5a) or filament (5b),
wherein the inner tube (4a) extends from the space (2b) for collecting waste fractions (<NUM>), and wherein the friction extruder screw (4b) extends within the inner tube (4a) into the space (2b) for collecting waste fractions (<NUM>),
characterized in that
the diameter (dth) of the thread of the friction extruder screw (4b) essentially matches the inner diameter (dit) of the inner tube (4a), and wherein the friction extruder screw (4b) has a shaft (4b') of conic shape, wherein the diameter (ds) of the conic shape of the shaft (4b') increases with increasing distance from the space (2b) for collecting waste fractions (<NUM>).