APPARATUS AND METHOD FOR EXTRUSION

Introduction

The present invention relates to a method for extruding and a device for extrusion. The apparatus may be defined as an extrusion apparatus having a lay-out best described as two conventional continuous extrusion devices arranged in a series on a common axle for extrusion according to the invention. The novel apparatus may be arranged for recycling aluminium in the form of shredded material, or the mechanical alloying of solid feedstock, pellets or shredded material. The processing of the material takes place in the solid state. The feed material is subjected to a plurality of severe plastic deformation processes which in combination with heat generated from the deformation process and friction induced during the conveying of material within the apparatus results in the plasticization of the material. The purpose of the deformation process is to break down and dissipate an ubiquitously occurring surface aluminium oxide always formed on aluminium in the presence of oxygen. The purpose of the process is to create a solid product having sound mechanical properties and having an as uniform structure as possible. As the aluminium oxide layer does not bond as easily with aluminium as aluminium itself it is of importance to break down the continuous oxide layer so as for allowing aluminium-aluminium bonding to an as large extent as possible. Compacting powders in a continuous extrusion process is usually named a so- called Con-form process and elements of this background art are described in the patent literature mentioned below. However the methods and apparatus described in the background art seem not to be in widespread use, probably due to the insufficient material strength of the extrudate. A further explanation to this limited success of the background art seem to be connected to the substantially limited deformation imposed during the processes of the background art which may also explain the inferior material strength of the extrudate. The present invention comprises several steps some of which are known from the background art, each contributing to the deformation, but combined and improved in a novel and inventive manner through the use of the novel elements according to the invention. The plastic deformation exerted on the material through the method according to the invention substantially increases the relative deformation intensity of the processed material which may also be increased resulting in the material density approaching a theoretical maximum density. Background art

The underlying principles of the extrusion apparatus according to the invention are based on the first patent on Conform (continuous extrusion), GB1370894. This patent discloses a rotating wheel with a continuous circumferential groove forming three walls of a channel, or passage, and a stationary member, or shoe, forming the fourth side. Feed

material is fed into the circumferential groove for being extruded. This results in the channel having three driving surfaces and a stationary fourth surface, and thus a net of two surfaces aiding motion of the material, or work piece. A second stationary member, or abutment, entirely fills the channel, forcing the material, to flow plastically in a radial direction through a die or orifice in front of the second stationary member, or in a tangential direction through a die or orifice in the second stationary member.

An early apparatus of the background art is described in US patent 4061011 to Green et al named "Extrusion" and assigned to the UK Atomic Energy Authority. The patent relates to axial tube extrusion and is cited to describe a process and an apparatus for the production of a tube by continuous extrusion, in which material is fed into a passageway having a progressively decreasing cross-sectional area and being defined by a first member being rotatable relative to a second member, and a die ring co-operating with the first and second members to provide an annular extrusion path. The first member and the die ring form a major portion of the passageway. The relative movement thereinbetween causes material fed to the passageway to be drawn along the passageway by frictional drag and to be extruded as a tube through the annular extrusion path.

WO 9602335 discloses the use of multiple circumferential grooves being used in accordance with the basic patent GB1370894. However the purpose of the multiple groves according to WO 9602335 is to produce multiple products simultaneously, and not increase the deformation of the feed material.

US20020121121 and US5813270 also disclose the use of a plurality of circumferential grooves, however the purpose of having more than one circumferential groove as cited in the two patents is to increase the flow, or yield, of material through a die in a radial direction. That is, material is extruded from both grooves simultaneously, and combined through an extrusion die chamber, or pressure chamber, into one die serving both grooves in order to produce a product with a larger cross section than could be achieved with a single groove. This is in contrast to the application according to the present invention in which two or more circumferential grooves are arranged, where the purpose is to move the material from one groove in an axial direction to the next groove in order to increase the plastic deformation, or upsetting, exerted on the material.

US4227816A1 describes a multistage rotary processor for plastic and polymeric materials which are, or become viscous during the course of treatment. The apparatus comprises a plurality of processing passages arranged as circumferential grooves on a rotor within a housing, and in which auxiliary transfer passages are arranged statically within said housing for connecting said processing passages to transfer material. However, said transfer passages will be fixed with respect to the abutments protruding into the processing channels and will not allow significant mixing of material during the transfer of material from one

passage to another. The transfer of materials within said apparatus will thus be continuous and not discontinuous as in the present invention. The arrangement of auxiliary transfer channels in the housing will lengthen the required distance to be traversed by the material, thus increasing the pressure loss and energy consumption during the process without improving the throughput.

Short summary of the invention

The present invention is a solution to at least some of the abovementioned problems and comprises an apparatus for continuous extrusion of metals, said apparatus comprising * a cylindrical rotor comprising a first and a second circumferential groove, said rotor arranged for rotating in a housing covering said grooves,

* a feeder aperture in said housing arranged for feed material to be fed into said first groove, said first groove arranged for entraining by friction said feed material, said housing being provided with first and second shoe members arranged for tightly fitting over said first and said second groove,

* a first obstructing abutment arranged protruding from said housing into said first groove, said first abutment for upsetting and thereby increasing the pressure above a yield stress of said feed material to form plasticized material near said first abutment. The novel features provided by the invention comprises the following features: * one or more channels extending from said first groove to said second groove, said channels arranged in said rotor for allowing the flow of said plasticized material into said second groove,

* said second groove arranged for entraining by friction, and thus heating said material, towards a second obstructing abutment arranged protruding from said housing into said second groove for upsetting and increasing the pressure of said material to be extruded from said second groove through an extrusion die.

The present invention further discloses a corresponding method for continuous extrusion of metals, said method comprising feeding a feed material into a first circumferential groove in a rotating cylindrical rotor within a housing, said rotor being rotated with respect to said housing by means of a motor, said feed material being entrained by friction within said groove upon rotation of said rotor, said feed material being entrained towards a first obstructing abutment arranged protruding from said housing into said first groove, said feed material thereby being upset and subject to a pressure above a yield strength of said feed material thus forming a plasticized feed material. The novel and advantageous steps of the method according to the present invention comprise: said obstructing abutment diverting a flow of said plasticized material into channels arranged in said rotor,

said plasticized material flowing within said channels in a generally axial direction with respect to said rotor into a second circumferential groove arranged on said rotor, said plasticized material being entrained by friction from said second groove and entrained towards and against a second obstructing abutment arranged protruding into said second groove, said plasticized material being upset and diverted from said second groove canal through an extrusion die for the extrusion of said material as an extrudate.

The apparatus and method are advantageous in that the feed material may be more efficiently transferred from the first circumferential groove through shorter channels as compared to prior art and should improve material flow through the apparatus. Further, the partition of the plasticized material through multiple axially directed channels and entrainment with those channels in the circumferential directions and ejection into angularly distributed positions in said second circumferential groove both improves deformation and mixing of plasticized material before eventually extruding the plasticized material, improving the homogeneity, density and strength characteristics of the extruded material. Further advantageous features of the invention are disclosed in the adjoining dependent claims.

Figure captions

The herein enclosed figures are solely intended for illustration purposes and should not be construed to be limiting the invention which shall only be limited by the appended claims.

Fig. 1 illustrates a closed isometric view of the extrusion apparatus. A feeder aperture (6) and the flash outlet (13) may be seen substantially above a first groove (2). An extrusion outlet (11) may be seen arranged substantially above a second groove (3). Said first and second grooves (2, 3) are arranged in a rotor (1) within a housing (5), said rotor (1) being rotated in the direction as indicated by an arrow.

Fig. 2 is an isometric view illustrating said rotor (1) comprising said first and second groove (2,3) as well as transfer channels (9) in an axis-parallel direction between said first and second grove (2,3). Also shown is an annular (14) arranged for being arranged about said rotor (1). Said annular (14) may be arranged for being locked with respect to channels (9) by means of a series of rectangular grooves and abutments formed on the inner surface of said annular (14) being arranged for fitting to the channels (9) thus forming channel ceilings.

Fig. 3 illustrates a front elevation view of an upper portion of the housing (5) in which may be seen a feeder aperture (6) arranged for feeding feed material (20) into said first groove (2), a scraper abutment (12) arranged for removing feed material (20) having passed an obstructive abutment (7) in the lower portion of the housing (5), and displacing

said feed material (20) into a flash outlet (13) for removal from the extrusion apparatus. A second abutment (8) is arranged substantially above and protruding into a second groove

(3), said second abutment (8) arranged for upsetting and displacing plasticized material (21) through an extrusion die and into an extrusion outlet (10) for extrusion of the plasticized material (21) as an extrudate from the extrusion apparatus. Said scraper (12) is shown arranged on a first shoe member (16). The arrow indicates the rotation direction of the rotor

(1) within said housing (5).

Fig. 4 illustrates a front elevation view of a lower portion of said housing (5), comprising a first shoe member (16) onto which is arranged a first abutment (7) arranged for upsetting and displacing feed material (20) within said first groove (2) axially through channels (6) towards said second groove (3) shown in Fig. 2. As before, the arrow indicates the rotation direction of the rotor (1) within said housing (5).

Fig. 5 illustrates an isometric view of the upper portion of said housing (5) as seen from a position below the housing interface split plane. Further to the elements shown in Fig. 3 may be seen a first and a second bearing seat (18, 19) in which may be arranged bearings

(not shown) for said rotor (1) shown in Fig. 2.

Fig. 6 illustrates an isometric view of the corresponding lower portion of said housing

(5) as seen from a position above the housing interface plane. Further to the elements shown in Fig. 4 may be seen an annulus arranged for holding the annular (14) shown in Fig. 2. Fig. 7 is a simplified surface map view of a cylindrical surface of the rotor (1) with grooves and channels, showing abutments and potential material flow patterns within said extrusion apparatus.

Description of preferred embodiments of the invention. Referring firstly to Fig. 1 of the drawings in which is shown an isometric view of an assembled extrusion apparatus according to the invention. The apparatus according to the invention comprises a housing (5) in which is arranged a cylindrical rotor (1) comprising a first and a second circumferential groove (2,3) in which said rotor (1) is arranged for rotating within said housing (5). Motor means should be connected and arranged for driving said rotor (1) in a desired rotation direction. The housing (5) comprises a feeder aperture (6) arranged for feeding feed material (20) into said first groove (2). The housing (5) is arranged for fitting tightly over said first and second groove (2, 3), preferably by means of respective first and second shoe members (16,17) protruding slightly into the axial bore from within said housing (5) and tightly fitting onto the grooves (2,3). As the rotor (1) is rotated, the feeder material (20) is entrained by the rotor due to friction within said groove (2) towards a first obstructive abutment (7) arranged protruding from said housing (5) into said first groove (2). As described in GB1370894 the rotor (1) with the continuous first circumferential groove (2)

forms three walls of a channel, or passage, and a stationary member, or shoe (16), forms the fourth side. This results in the channel having three driving surfaces and a stationary fourth surface, and thus a net of two surfaces aiding motion of the material.

As the feed material (20) is entrained it will eventually be upset against the obstructive abutment (7), the pressure upon the feed material (20) increases, and as the feed material (20) is additionally heated due to the friction within the first groove (2), the effect is to increase the pressure upon the material above a yield strength of the feed material (20) thus plasticizing the feed material (20). By the pressure force, the plasticized material (21) is forced into channels (9) extending from said first groove (2) to said second groove (3) arranged for allowing the flow of material from said first groove (2) to said second groove (3). As the plasticized material (21) is forced into said second groove (3) it is again entrained by the rotor (1) due to friction along the rotation direction of the rotor (1). A second obstructive abutment (8) is arranged protruding from the housing (5) into said second circumferential groove (3), and in which said second obstructing abutment (8) is arranged for upsetting and thus increasing the pressure upon said plasticized material (21) within said second groove (3) so as for even further compacting the material (21). An extrusion die (10) is arranged in the near proximity of said second obstructive abutment (8) and is arranged for allowing the extrusion of said plasticized material (21) as extrudate (22) through an extrusion outlet (11) in the housing (5). Said first and second obstructive abutments (7, 8) may advantageously be formed as axially inward directed protuberances on respective first and second shoe members (16,17).

The extrusion direction may be either radial or tangential, both directions being more or less in an axis-perpendicular plane with respect to the rotor (1), according to two separate preferred embodiments of the invention. The extrusion die (10) may also be arranged so as for allowing the extrudate (22) to be forced through e.g. a ring-shaped axis parallel die having a shape as a tube or for allowing the extrusion of multiple extrudate elements or any other extrusion configuration as will be obvious to a person skilled in the art.

According to the invention, said channels (9) extend generally in or on said rotor (1), leading from said first groove (2) to said second groove (3). Advantageously this creates a short transfer path of plasticized material (21) from said first to said second groove (2, 3) incurring less pressure loss compared to channels in the housing (5). A further advantage of the invention is that the plasticized material (21) entrained by channels (9) passing the abutments will partition and mix the plasticized material (21) to a considerable degree, providing a higher degree of mixing and deformation of the material superior to background art. In a particularly preferred embodiment of the invention said channels (9) are arranged generally axial-parallel in said rotor (1) and may be formed by axially directed rectangular grooves between the first and second ring-shaped grooves (2, 3) as shown in fig. 2. Using a

configuration as shown in Fig.2 it may be advantageous to cover said axially directed grooves by means of an annular (14) in which said annular (14) may have a configuration as inwardly toothed wheel in which said teeth are arranged for fitting into the grooves thus forming a groove roof and also locking said annular (14) to prevent it from rotating with respect to the rotor (1).

In an alternative preferred embodiment of the invention, the channels (9) may be formed as bores in the rotor (1) in the rotor shaft between said first and said second circumferential groove (2,3).

The main intended application of the apparatus according to the invention is for the compacting and extruding of aluminium, in which the aluminium may be in the form of powders or shredded material. Aluminium reacts with atmospheric oxygen to form aluminium oxides which are hard and do not bond well with pure aluminium metal matrix. Thus it is of utmost importance that the aluminium oxides are as widely dispersed in the extrudate matrix as possible, so as to allow for the compacting of the powder or shredded material to have a density as near the theoretical maximal density of the metal as possible. Although the background art provides numerous examples of extruding apparatus, none is known for the inventors that addresses this problem. The arrangement of grooves or channels (9) formed in the rotor and arranged between said first and said second circumferential groove (2, 3) provides a solution to this problem, as is explained below. Feeding aluminium scrap metal or aluminium particles into an apparatus according to the invention, the ubiquitously existing surface oxide is broken down into fine discrete particles and dispersed in the aluminium matrix. In more detail: aluminium oxide has a low ductility when compared to aluminium. Furthermore the ductility of aluminium increases appreciably with increasing temperature, while the ductility of aluminium -oxide is relatively unaffected by temperature. The effect of this is that the brittle surface oxide layer is broken into discrete so-called islands or flakes of oxide as the underlying aluminium is deformed. As more deformation is progressively introduced, the oxide islands are broken down into smaller fragments and are gradually dispersed in the aluminium matrix. With sufficient deformation, the oxide particles can attain a size similar to that of particles in the aluminium matrix originating from alloy constituents, and may actually add to the strength of the material. If, however, the deformation of the material is insufficient and the surface oxide remains in the material as relatively large islands or flakes, they create an internal crack, or a zone without bonding, inside the material, as the oxide once created will not further bond to an adjacent existing internal aluminium surface. This latter effect may have a considerable negative effect on the mechanical properties of the material. Some oxidation may anyhow take place inside the machine, and a thin, more ductile surface oxide layer will be created as the material emerges into the second groove. However, the amount of deformation created as the

material is forced along the second groove (3) and the upsetting before the second abutment (8) is sufficient to deform also this newly formed thin surface oxide layer. Thus the amount of deformation created as material is passed through the machine ensures complete aluminium-aluminium bonding even in the presence of a thick initial surface oxide layer. It should further be noted that the pressure profile within said first groove (2) may be more or less stable during the extrusion process. As the feed material (20) is subject to a pressure exceeding a yield strength of the material, it will become plasticized material (21) and begin to flow through said channels (9) alleviating the pressure on the remaining material (21) remaining ahead within the groove (2). Thus the process as a whole will be a more or less steady state process, and the pressure profile in the groove (2) be more or less consistent over time. This will also be valid for the second groove (3), although the material (21) will not backflow through said channels (9) as long as the feeding of feed material (20) and thus pressure in the first groove (2) is maintained.

As the first obstructing abutment (7) is fixed with respect to said housing (5), according to of the invention, the plasticized material (21) will flow into successive channels or grooves (9) rotating with the rotor (1). The plasticized material (21) will form material partitions that experience a retention time for each partition within said channels (9) before being forced into said second groove (3) by the inflow of additional plasticized material (21) in the channel (9). Thus plasticized material (21) may pass from several angular positions of said first groove (2) to several other angular positions of said second groove (3), improving the degree of deformation and mixing of said plasticized material (21) in said second groove (3). Plasticized material (21) residing in a channel (9) passing the first abutment (7) will be intermittently cut-off from the pressure in the first groove (2), and will experience to be brought along parts of one more turn for subsequently being subject to an increasing pressure and eventually being fed and mixed into other portions of plasticized material (21) residing in said second circular groove (3) This will also contribute to improved mixing as compared to the background art. As the plasticized material (21) is forced into the second groove (3), the material (21) will be sheared out of the channels (9) in portions, and will be mixed with material already present within said second groove (3). This will ensure the additional mixing of the plasticized material (21) and further increasing the uniformity, strength and density of the resulting extrudate (22) up to and towards the theoretical density limit.

In a further preferred embodiment of the invention it has proved advantageous to arrange a scraper (12) extending from said housing (5) into said first groove (2) in which said scraper (12) is arranged for at least partially removing feeder material (20) from said first groove (2) into a flash outlet aperture (13). Although every effort is made to ensure that the entirety of the feed material (20) is extruded, this has during model tests proven to be

difficult, and thus to avoid partial blocking of said first circumferential groove (2) it is beneficial to remove said non-extruded feed material (20) from said groove (2). As is evident, the removed feed material (20) may be reused at a later stage.

Said scraper (12) may advantageously be arranged on a wall abutment, in which said wall abutment is arranged for hindering the backflow of material from the second groove (3) in the vicinity ahead of said second obstructive abutment (8) and back into said channels (9). As the pressure near said second abutment (8), which, in a preferred embodiment of the invention, is arranged near the angular position of said scraper (12), may exceed the pressure within said channels (9), it is of importance to mechanically block the backflow of material from said second groove (3) into said first groove (2), and this may be accomplished by forming the scraper abutment as an arch formed wall above said first groove (2) near to and ahead of the angular position of said extrusion die (10). This is clearly shown in figs. 3 and 5. Although some backflow from said second groove (3) to said first groove (2) may take place despite said scraper and wall abutment (12), this may be of minor importance, and the material having flowed through the channels (9) will either be removed by said scraper (12), or be fed back into the second groove (3) by being diverted by the first abutment (7). In a preferred embodiment of the invention, said scraper and wall abutment (12) forms a protuberance on said first shoe member (16).

Further scrapers (12', 12",...) may also be arranged protruding into said second groove (3) or intermediate grooves (2',2",...) for the removal of remaining material from said grooves (2',2",.--,3) as will be evident to a person skilled in the art.

As mentioned the feed material (20) is preferably aluminium in the form of shredded material or powders. However, any metallic compound that will turn plasticized under pressure and elevated temperature may advantageously be used in the extruder as will be evident to a person skilled in the art. Of course, the rotor and housing material must remain non-plasticizable under the pressure and temperature conditions of which the feed material becomes plasticized and flows.

In a further advantageous embodiment of the invention, the housing (5) may comprise two or more separate parts, preferably an upper and a lower (51, 52) complimentary part, joined by bolts or other attaching devices for the increased serviceability and facilitated tooling of the apparatus.

In a particularly preferred embodiment according to the invention, one or more further intermediate circumferential grooves (2',2",...) connected by said channels (9) and possible similarly arranged auxiliary channels (9 ¹ ), are arranged on said rotor (1), between said first and said second circumferential groove (2, 3). Said one or more further intermediate circumferential grooves (2',2",...) are provided with respective obstructive abutments protruding from the housing (5), the abutments arranged for the stepwise transportation

through said channels (9) and possibly auxiliary channels (9 ¹ ) of the so far transferred plasticized material (21) from said first circumferential grove (2) further towards said second and final circumferential groove (3). The increased number of steps allows for the improved mixing of the plasticized material (21) before the extrusion and may thus further improve the material properties of the extrudate (22)

In an alternative embodiment the apparatus according to the invention, said first abutment (7) may comprises multiple escarpments arranged in a step-wise arrangement progressing inwardly in a radial direction in said first groove (2), so as for upsetting the feed material (20) in a step-wise manner along the path of the entrained feed material (20).