- Email: [email protected]
Conform and the recycling of non-ferrous scrap metals
Conservation 6 Recycling, Vol.2, pp.19- 29. Pergamon
Press Ltd. 1978. Printed
in Great Britain.
CONFORM AND THE RECYCLING OF NON-FERROUS SCRAP METALS* C. ETHERINGTON Springfields Nuclear Power Development Laboratories, United Kingdom Atomic Energy Authority, Springfields, Salwick, Preston, PR4 ORR, U.K. Abstract - There is a continuing search for more effective means for reprocessing scrap metals to return them once more into fully acceptable marketable products. Clean non-ferrous scrap arisings could be recycled directly if a means were available to metallurgically bond together the individual particles to produce a homogeneous product. Extrusion is a process which appears to have much to offer in this way, the generation of high pressures and the plastic deformation of the metal as it flows through the die ensures a homogeneous structure in the final product. A continuous extrusion process would offer environmental advantages and energy savings in eliminating the need for melting. The UKAEA Springfields Laboratories are currently developing a continuous rotary extrusion process known as Conform which has considerable potential for the direct recycling of scrap non-ferrous metal in various forms. The process uses mechanical friction both to feed stock up to an extrusion die and to generate the pressure necessary to extrude it through the die. This is accomplished in practice by the combination of a rotating grooved wheel with a stationary shoe arranged to overlap a portion of the wheel circumference. The shoe holds the die and the feedstock is carried along in the wheel groove as it rotates. This type of machine has been used to extrude both aluminium and copper particle feeds into solid products such as round wires, various shapes, and - in the case of aluminium - into tubing. These products have good mechanical properties and depending on the condition of the feed may have good electrical properties. The particle feeds have included powders, granules, machining, swarf, chopped wire, and chopped copper cathode. The Conform process is basically simple and offers the possibility of almost 100% yield. The machines are compact, easily operated and relatively cheap and the process offers the opportunity for considerable cost savings in recycling. Development work is continuing at the UKAEA laboratories and at the works of the licensed machine builders.
INTRODUCTION The recycling of scrap metal (secondary metal), both ferrous and non-ferrous, continues to be a most important factor in the effective management of the world’s finite resources and in the control of the environment. Scrap metal forms a very valuable source of supply particularly in countries which have no indigenous ores and careful husbandry and recycling can be important factors in the overall economic picture. The quantative aspects of the re-use of metals are regularly considered by various bodies and some figures for 1976[1] show that, worldwide, approximately 3 x lo6 tonnes of aluminium, 3.2 x IO6 tonnes of copper, 0.85 x lo6 tonnes of lead and 0.12 x lo6 tonnes of zinc are recovered. The actual amounts and percentages of the potential available vary from country to country, but the overall tonnages and volumes involved are considerable and will increase. Scrap has been categorised into three classes[2], the first two of which can be generdly characterised as ‘new scrap’. 1. Home - that lying entirely within the primary metal producing plant and recycled as a matter of routine in the overall operation and control of the plant. 2. Prompt industrial scrap - well-managed process scrap collected during the fabrication of productions; this can accurately be graded and identified as to metal purity, alloying etc.
*This paper was presented at the First World Recycling Congress, Basle, Switzerland, 6- 9 March 1978. 19
20
C. ETHERINGTON
3. Old scrap - as the term implies metal returned to the secondary smelters via scrap merchants with often no guarantee as to full identification and which will include arisings from products manufactured up to many decades previously, The current practice for recycling all three categories involves at least one melting stage within the processing route and while this is generally essential with category 3 scrap there could be something to be said for a direct recycling process, without melting, for some metals within the first two categories. Such a route would involve recycling secondary metal into usable ‘secondary metal products’. The purpose of this paper is to suggest for consideration a newly-developing metal forming process which could have considerable implications in the recycling of non-ferrous metals into secondary metal products.
RECYCLING
BY EXTRUSION
There is a continuing search for more effective means for collecting, segregating and reprocessing scrap metals to return them once more into use as fully acceptable, marketable products. Among the many factors to be considered in any new recycling route must be: 1. The capital cost and size of the plant involved. 2. The environmental aspects of its use - the control of emissions from metal processing plants is an ever more important and costly aspect of the business. 3. The overall operating requirements, costs and economic aspects - what are the potential savings of the route? What are the labour requirements; is skilled labour necessary? What other resources are required? 4. Effective metal yield - recycling routes currently involve melting stages and nonrecoverable losses occur in fumes, gases, oxides etc. that are formed. In the melting of fines very high losses can occur, perhaps as high as 30% with aluminium in some operations. The non-ferrous scrap arisings can vary from fine powder and swarf to large castings and fabrications. The more broken down arisings, typically powder, swarf, turnings, wire, foil etc. if clean and clearly categorised as new scrap, could be recycled directly if a means could be found to bond together metallurgically the individual particles and produce an homogeneous product. Extrusion is a process which appears to have much to offer in this way. High pressures can be generated ensuring the bonding together of the feed material and the final plastic deformation of the metal as it is forced to flow through the die should ensure a homogeneous structure in the final product. An extrusion route capable of continuous operation would have environmental advantages in eliminating the need for melting and could possibly show savings in overall energy usage as a once through process. The product would, however, be characterised as a secondary metal in that, for example, the oxide coating on each surface of the individual items of feed would be present in it. This may be one reason, together with the lack of continuity of operation, why conventional extrusion processes have not been adopted for recycling of clean scrap. However, many items manufactured today from what is basically a primary metal feed might equally well be made from recycled metal, particularly non-electrical components such as aluminium trim. The consistency of quality of the product would depend on the consistency of quality of the feed so that the route might be only applicable for home and prompt industrial scrap categories. The Advanced Metal Forming Group at the UKAEA Springfields Laboratories is currently developing a continuous extrusion process which appears to have considerable potential for application in the salvaging or direct recycling of scrap non-ferrous metal in various forms. This process, known as Conform[3], has been discussed in previous papers both by the inventor the
CONFORM AND THE RECYCLING OF NON-FERROUS SCRAP METALS
21
late D. Green, and by members of the development team[4 - 91. A manufacturing license for Conform machines has been granted by the UKAEA to a number of machinery manufacturers both in the U.K. and overseas[lO], and the process is currently attracting considerable world wide attention in the non-ferrous metals field both in its role as an extruder of conventional solid continuous feedstock, e.g. redraw rod, as well as its application to the extrusion of particulate feed.
THE CONFORM EXTRUSION
PROCESS
The Conform extrusion process has been discussed in detail in the papers quoted in the references. In essence, however, it uses mechanical friction both to continuously feed stock up to an extrusion die and to generate the pressure necessary to cause the metal to deform plastically and flow through the die. This is accomplished in practice by the combination of a rotating grooved thick disc or wheel with a stationary shoe, the shoe being arranged to overlap a portion of the wheel circumference. The normally rectangular groove is formed in the periphery of the wheel and forms three sides of a square section extrusion container (Fig. 1). The fourth Restraining
flxce
for wire output thrwgh dies
Feedstock
Section
x--x
Feedstock
Fig. 1. Diagrammatic arrangement of Conform continuous extruder.
side of the container is formed by tooling supported in the shoe and projecting a short way into the wheel groove. The ‘container’ so formed is closed at the die end by an abutment mounted in the shoe; this completely fills the cross-section of the groove. An extrusion die is located either in the abutment, or in the tooling adjacent to it. As the wheel rotates, the feedstock, which is an interference fit in the groove, is pulled forward by the friction existing between it and the groove walls. The feedstock moves under the stationary shoe tooling up to the abutment, and it is possible to generate sufficient frictional force to cause the feed, which might, typically, be round re-draw rod to yield, upset and flow to completely fill the cross-section of the groove over a short length in front of the abutment. Note that with three moving sides driving the feedstock forward and one stationary side - the shoe tooling - resisting forward motion, the net effect is of two sides driving forward assuming similar contact areas and frictional condi-
22
C. ETHERINGTON
tions obtaining on each contacting surface. Within the upset length the compressive stress in the billet builds up to a maximum in front of the die zone, each increment of grip length adding its own contribution to the stress in the material. The generation of compressive stresses which may be as high as, say, 1000 N/mm* (70 t/u-$) together with the associated temperature rise in the metal as it flows through the die zone (this may be as high as 450°C with copper) enables discrete lengths of material to be welded together and extruded as a continuous homogeneous product. The potential for this was demonstrated at a very early stage in the development of the process when short lengths of 6.35mm dia aluminium rod were fed into the experimental machine and were extruded into a continuous length of 2-mm dia wire. A similar demonstration was made shortly afterwards with copper rod. On examination, the product from these trials proved to have good mechanical properties, the joint zone exhibiting mechanical properties similar to the parent metal and the wire was capable of being drawn down to typically 0.4-mm dia without breakage. Green had, from its inception, foreseen the potential of his process to accept particulate feed and this aspect of its use is covered in the original patent, filed in 1971131. Since the process was principally conceived as a method for continuously working solid metal feed - typically redraw rod - and as being complementary to the non-ferrous continuous casting and rolling routes producing rod in large continuous coils, the development programme at Springfields has concentrated on this aspect of its use. Three experimental machines are operational in the laboratory and on each some demonstration trials with particulate feeds have been carried out. Figures 2 and 3 show the first experimental Conform machine to be built, the Mk 2A. This ‘Granule’ feed
r-45
Extrusion
Fig. 2. Mk 2A Conform machine, showing arrangement for granular feed.
was designed for extruding 6.35mm dia aluminium rods. When extruding with a particulate feed a hopper is used to feed the particles via a hole in the shoe and tooling so that they fall to the root of the wheel groove. As the wheel rotates the particles are carried forward to the abutment/die zone where they are compacted to fill the cross-section and as the compressive stress within the zone increases towards the abutment the individual particles begin to weld together into a homogenous mass. Final welding occurs under plastic flow conditions as the metal is forced to flow through the extrusion die forming a continuous product. The aluminium particulate feed material has included EC grade and alloyed fine powder and granules of a range of sizes, e.g. chopped scrap wire and clean machine chippings. These have been extruded
CONFORM AND THE RECYCLING OF NON-FERROUS SCRAP METALS
23
from a groove sized to accept 6.35-mm dia rods to round wire 2-mm and l-mm dia, i.e. through extrusion ratios of 13:l and 51:1, respectively. The homogeneity and ductility of the product has then been proved by mechanical, electrical and metallurgical inspection and by further drawing trials. Typical properties are given in Table 1. Table 1.
Aluminium EC granules Powder Alloy granules Copper Dryflo chopped wire Alloy powder Chopped cathode at join
Typical properties of Conform recycled metals 0.1 Voproof stress (N/mm’)
UTS (N/mm’)
Elongation Vs)
Conductivity (Vo IACS)
95 185 230
170 284 325
7 6 1
45 56 -
338 114
432 247
7.8 28
97.4-98.5 89 loo.2
The second experimental machine to be built in the laboratory is used for the extrusion of copper. The Mk 2B as it is designated (Fig. 4) was originally designed for accepting S-mm dia
24
C. ETHERINGTON
and modified later for 9.5mm dia rod feed. Copper powder, chopped wire and bunched scrap cable in a continuous length (Figs. 5 and 6) have successfully been extruded into, typically, 2-mm dia round wire and also a rectangular section. The properties of typical products are given in Table 1, together with results obtained from extruding the chopped copper cathode fed into the machine in discrete lengths and extruded into wire. The latest machine designed and built at Springfields is the Mk 2D which is used for the extrusion of 9.5mm dia aluminium rod. The version of this design at Springfields has a vertical shaft and horizontal wheel so that the feeding of particulate material is more difficult, but the feeding of bunched wires and similar scrap is unaffected by this arrangement. Work has simultaneously been undertaken by the Conform machine licencees; for example, Fig. 7 illustrates the extrusion of aluminium wire from a powder feed on a Mk 2D type machine at the works of the Wanskuck Co. Providence, R.I. In this arrangement, the machine has been built with a horizontal shaft and vertical wheel to facilitate the feeding of granules and powders from a hopper. These nd hoc trials have demonstrated the feasibility of the process for the recycling of scrap materials and the conversion of particle feed in general into a continuous product. While in some instances the products have not been fully satisfactory and have exhibited blistering and occasional fold type defects, these can generally be associated with inadequate feeding of the
CONFORM
AND THE RECYCLING
Fig. 5. The extrusion
of copper
OF NON-FERROUS
strip from bunched
SCRAP
METALS
2-mm dia scrap ,wire. Discard
25
and tooling.
particles, and/or contamination of the feed, e.g. with cutting fluid in the case of machine swarf or insulation in the case of chopped cable. Figure 8 shows a transverse section of a 2-mm copper wire extruded from chopped copper wire produced by the Dryflo process showing typical oxide distribution patterns within the product. Further work is now necessary to investigate these processes in greater depth. There are many factors to be considered; for example, when recycling scrap wire the comparison must be made between a continuous stranded or bunched feed of wires with a chopped wire feed. Pretreatment of the feed needs to be considered to determine the purity required to meet the projected product properties. The compacting of fines and scrap into a rod form simply to improve the yield when remelting may be possible with a more contaminated feed than would be necessary for direct recycling to a finished product. The size and distribution of particles could have significant effects on the feeding, compaction and efficiency of throughput. The precornpaction of granules into the groove by the use of feed rollers and the use of screw feeders and vibration feed hoppers need to be investigated and overall production routes established for the various feed materials and products. Since Conform is an extrusion process a wide variety of product shapes and size, including tubing, are possible from the machine by simply changing the extrusion die. The type of product seems to be unaffected by the form of feed; shapes as well as rounds have been produced from granules and powders thus offering great flexibility to the potential user. Relating Conform to the four factors discussed earlier as requirements for a new process elicits the following indications: 1. Capital cost and size The Conform process is basically simple and such equipment should be cheaper than most metal recycling plant. The machines are compact units giving economy in factory floor space;
26
C. ETHERINGTON
Fig. 6. Discard removed from machine showing welding together of 12 strands of 2-mm dia copper wire to produce 7 X 3 mm rectangular strip.
the associated plant necessary will depend on the form of the feed material, but the product will normally be capable of being taken up on conventional equipment. 2. Environmental impact The Conform machine itself should have no adverse environmental effects. If the feed is in the form of fines then some form of shrouding may be necessary. Noise should not be a problem; the Conform unit itself is quiet in operation and the principle source of noise is the drive unit, whether electric or hydraulic. 3. Overall operating costs The Conform machine is basically a simple item of equipment and can be operated by semiskilled labour. Machine maintenance is straightforward, the principle skills being required in
CONFORM
Fig. 7. The extrusion
AND THE RECYCLING
of aluminium
OF NON-FERROUS
SCRAP
METALS
wire from powder feed. The wire can be seen exiting of Wanshuck Co., Providence, R.I., U.S.A.)
lower right.
27
(By courtesy
the manufacture of tools and dies. The principle cost savings will come if the marketplace will accept products made directly from recycled scrap. While it is very difficult to arrive at actual costs, some figures might be quoted at this stage for consideration. It apparently costs around 15 e!per kg (7 L per lb) to convert scrap copper wire back into rod by the conventional wire bar route. This rod has then to be worked to give the finished product, e.g. rectangular strip. The current on-cost of producing rectangular copper strip directly from redraw rod by Conform can be estimated at about 17e per kg (8 rt per lb); this latter figure will be very slightly different if the feed were in a particle form or were bunched wires. There seems
28
C. ETHERINGTON
Fig. 8. Transverse section of 2-mm dia copper wire extruded from Dryflo feed (X 37.5).
to be a possibility of considerable savings here between the established route and a notional new route for the manufacture of, for example, copper earthing tape. Similarly, with aluminium, redraw rod currently costs around U.S. $1.1 per kg (50 G!per lb) to buy and scrap is selling at only 33L per kg (15 I per lb). There is potential for savings here, in the manufacture of products such as furniture or luggage trim as well as the possibility of higher grade products such as tubing. 4. Effective metal yield Conform offers the possibility of an almost 100% yield depending on the condition of the feed. The quantity of ‘waste’ metal produced in the process is that which extrudes through the running clearances between wheel and tooling, normally amounting to no more than 3% of the total throughput. This metal can immediately be fed back into the machine so there would be no loss. The discard left when the machine is stopped at the end of a run is approximately the upset length - typically 25 mm in a 9.5mm wide groove - and this may be left in for the next start-up, when it will act as a lead for the following period of operation. The simplicity of concept and compactness of the equipment should make it attractive for the consideration of its use within existing production and fabrication plants where scrap arisings are currently fed back into the secondary metal industry for re-melting. In the aluminium field the arisings from the manufacture of products from sheet wire, rod and foil as well as some of the arisings from extrusion plants could well be recycled directly through a Conform machine.
CONFORM AND THE RECYCLING OF NON-FERROUS SCRAP METALS
29
FUTURE DEVELOPMENTS Many non-ferrous metals and alloys have been successfully extruded by Conform from solid rod feedstock including aluminium, copper, lead, silver, zinc and a number of alloys. With all of these there appears to be very good prospects for the direct recycling by Conform of scrap arisings. The feed may be either as particles or in a more massive form. The Conform machines operating to date (September 1977) have all been designed principally to accept re-draw rod up to 9.5-mm dia and, therefore, their ability to accept particulate feed is limited to particle sizes which will readily enter and be compacted in a 9.5-mm wide groove. Larger machines with groove sizes up to 25-mm wide are currently in design and manufacture and these should enable a much wider range of particle sizes to be handled. To meet the requirements for the recycling of old scrap which may be of unknown quality and new inhouse scrap which may be in too massive a form for direct feeding to Conform or even for granulating, e.g. extrusion press discards, melting is still going to be a necessary requirement. Consideration could then be given to the possibility of converting the molten metal directly into either powder or shot for direct feeding into Conform without the necessity for casting into billets for subsequent rolling or extruding. In this context it is interesting to note in Table 1 the high strength obtained in wires extruded directly from aluminium powder feed, with no subsequent treatment. A powder route opens up the opportunity for mixed metal feeds and for fibre strengthened products. Alternatively, the molten metal might be poured directly into a large Conform wheel where solidification would take effect as the metal is carried to the dlie for continuous extrusions. [5]. The advent of the Conform process opens up the possibility of an alternative economic and environmentally acceptable route for the reconversion of scrap non-ferrous metal into usable product, and with continuing development further novel aspects of the process may emerge. Acknowledgements - The author wishes to acknowledge the assistance of his colleagues in the Advanced Metal Forming Group of the UK&A Springfields Laboratories in the preparation of this paper and the Laboratory and UKAEA Northern Group Management for permission to publish it.
REFERENCES 1. World Bureau of Metal Statistics (August 1977). 2. M. B. J. Bever, The significance of scrap in western economies, Lecture to the Univ. of Nottingham. Short course on reclamation and recycling of metals (March 1976). 3. D. Green, Improvements in or relating to extrusion, U.K. Patent 1370894 (Filed March 1971). 4. D. Green, The continuous extrusion forming of wire sections, J. Inst. Metals 100, 295- 300 (1972). 5. C. Etherington, Conform - A new concept for the continuous extrusion of metals, ASME 73-WA/PT-2 (November 1973). 6. C. Etherington, The UKAEA conform method of continuous extrusion, ZWMA Conference, New Developments in Wire Technology, Amsterdam (1976). 7. E. Hunter, Continuous extrusion by the Conform process, Sot. Manufacturing Eng. Conf., Chicago SME MF76-407 (June 1976). 8. D. J. Marsh, Extrusion of copper by the conform continuous extrusion process, 18th Znt. Machine Tool Design and Research Conf., London (September 1977). 9. J. A. Pardoe, The Conform continuous extrusion process - development experience with non-ferrous metals, Wire Association Conf., Boston (October 1977). 10. Licensees: U.K.-Babcock Wire Equipment Co., Bolton; Marshall Richards Barcro Ltd., Crook, Co. Durham. U.S.A.-Wanshuck Co., Providence, R.I. Japan-Sumitomo Heavy Industries, Niihama.
Press Ltd. 1978. Printed
in Great Britain.
CONFORM AND THE RECYCLING OF NON-FERROUS SCRAP METALS* C. ETHERINGTON Springfields Nuclear Power Development Laboratories, United Kingdom Atomic Energy Authority, Springfields, Salwick, Preston, PR4 ORR, U.K. Abstract - There is a continuing search for more effective means for reprocessing scrap metals to return them once more into fully acceptable marketable products. Clean non-ferrous scrap arisings could be recycled directly if a means were available to metallurgically bond together the individual particles to produce a homogeneous product. Extrusion is a process which appears to have much to offer in this way, the generation of high pressures and the plastic deformation of the metal as it flows through the die ensures a homogeneous structure in the final product. A continuous extrusion process would offer environmental advantages and energy savings in eliminating the need for melting. The UKAEA Springfields Laboratories are currently developing a continuous rotary extrusion process known as Conform which has considerable potential for the direct recycling of scrap non-ferrous metal in various forms. The process uses mechanical friction both to feed stock up to an extrusion die and to generate the pressure necessary to extrude it through the die. This is accomplished in practice by the combination of a rotating grooved wheel with a stationary shoe arranged to overlap a portion of the wheel circumference. The shoe holds the die and the feedstock is carried along in the wheel groove as it rotates. This type of machine has been used to extrude both aluminium and copper particle feeds into solid products such as round wires, various shapes, and - in the case of aluminium - into tubing. These products have good mechanical properties and depending on the condition of the feed may have good electrical properties. The particle feeds have included powders, granules, machining, swarf, chopped wire, and chopped copper cathode. The Conform process is basically simple and offers the possibility of almost 100% yield. The machines are compact, easily operated and relatively cheap and the process offers the opportunity for considerable cost savings in recycling. Development work is continuing at the UKAEA laboratories and at the works of the licensed machine builders.
INTRODUCTION The recycling of scrap metal (secondary metal), both ferrous and non-ferrous, continues to be a most important factor in the effective management of the world’s finite resources and in the control of the environment. Scrap metal forms a very valuable source of supply particularly in countries which have no indigenous ores and careful husbandry and recycling can be important factors in the overall economic picture. The quantative aspects of the re-use of metals are regularly considered by various bodies and some figures for 1976[1] show that, worldwide, approximately 3 x lo6 tonnes of aluminium, 3.2 x IO6 tonnes of copper, 0.85 x lo6 tonnes of lead and 0.12 x lo6 tonnes of zinc are recovered. The actual amounts and percentages of the potential available vary from country to country, but the overall tonnages and volumes involved are considerable and will increase. Scrap has been categorised into three classes[2], the first two of which can be generdly characterised as ‘new scrap’. 1. Home - that lying entirely within the primary metal producing plant and recycled as a matter of routine in the overall operation and control of the plant. 2. Prompt industrial scrap - well-managed process scrap collected during the fabrication of productions; this can accurately be graded and identified as to metal purity, alloying etc.
*This paper was presented at the First World Recycling Congress, Basle, Switzerland, 6- 9 March 1978. 19
20
C. ETHERINGTON
3. Old scrap - as the term implies metal returned to the secondary smelters via scrap merchants with often no guarantee as to full identification and which will include arisings from products manufactured up to many decades previously, The current practice for recycling all three categories involves at least one melting stage within the processing route and while this is generally essential with category 3 scrap there could be something to be said for a direct recycling process, without melting, for some metals within the first two categories. Such a route would involve recycling secondary metal into usable ‘secondary metal products’. The purpose of this paper is to suggest for consideration a newly-developing metal forming process which could have considerable implications in the recycling of non-ferrous metals into secondary metal products.
RECYCLING
BY EXTRUSION
There is a continuing search for more effective means for collecting, segregating and reprocessing scrap metals to return them once more into use as fully acceptable, marketable products. Among the many factors to be considered in any new recycling route must be: 1. The capital cost and size of the plant involved. 2. The environmental aspects of its use - the control of emissions from metal processing plants is an ever more important and costly aspect of the business. 3. The overall operating requirements, costs and economic aspects - what are the potential savings of the route? What are the labour requirements; is skilled labour necessary? What other resources are required? 4. Effective metal yield - recycling routes currently involve melting stages and nonrecoverable losses occur in fumes, gases, oxides etc. that are formed. In the melting of fines very high losses can occur, perhaps as high as 30% with aluminium in some operations. The non-ferrous scrap arisings can vary from fine powder and swarf to large castings and fabrications. The more broken down arisings, typically powder, swarf, turnings, wire, foil etc. if clean and clearly categorised as new scrap, could be recycled directly if a means could be found to bond together metallurgically the individual particles and produce an homogeneous product. Extrusion is a process which appears to have much to offer in this way. High pressures can be generated ensuring the bonding together of the feed material and the final plastic deformation of the metal as it is forced to flow through the die should ensure a homogeneous structure in the final product. An extrusion route capable of continuous operation would have environmental advantages in eliminating the need for melting and could possibly show savings in overall energy usage as a once through process. The product would, however, be characterised as a secondary metal in that, for example, the oxide coating on each surface of the individual items of feed would be present in it. This may be one reason, together with the lack of continuity of operation, why conventional extrusion processes have not been adopted for recycling of clean scrap. However, many items manufactured today from what is basically a primary metal feed might equally well be made from recycled metal, particularly non-electrical components such as aluminium trim. The consistency of quality of the product would depend on the consistency of quality of the feed so that the route might be only applicable for home and prompt industrial scrap categories. The Advanced Metal Forming Group at the UKAEA Springfields Laboratories is currently developing a continuous extrusion process which appears to have considerable potential for application in the salvaging or direct recycling of scrap non-ferrous metal in various forms. This process, known as Conform[3], has been discussed in previous papers both by the inventor the
CONFORM AND THE RECYCLING OF NON-FERROUS SCRAP METALS
21
late D. Green, and by members of the development team[4 - 91. A manufacturing license for Conform machines has been granted by the UKAEA to a number of machinery manufacturers both in the U.K. and overseas[lO], and the process is currently attracting considerable world wide attention in the non-ferrous metals field both in its role as an extruder of conventional solid continuous feedstock, e.g. redraw rod, as well as its application to the extrusion of particulate feed.
THE CONFORM EXTRUSION
PROCESS
The Conform extrusion process has been discussed in detail in the papers quoted in the references. In essence, however, it uses mechanical friction both to continuously feed stock up to an extrusion die and to generate the pressure necessary to cause the metal to deform plastically and flow through the die. This is accomplished in practice by the combination of a rotating grooved thick disc or wheel with a stationary shoe, the shoe being arranged to overlap a portion of the wheel circumference. The normally rectangular groove is formed in the periphery of the wheel and forms three sides of a square section extrusion container (Fig. 1). The fourth Restraining
flxce
for wire output thrwgh dies
Feedstock
Section
x--x
Feedstock
Fig. 1. Diagrammatic arrangement of Conform continuous extruder.
side of the container is formed by tooling supported in the shoe and projecting a short way into the wheel groove. The ‘container’ so formed is closed at the die end by an abutment mounted in the shoe; this completely fills the cross-section of the groove. An extrusion die is located either in the abutment, or in the tooling adjacent to it. As the wheel rotates, the feedstock, which is an interference fit in the groove, is pulled forward by the friction existing between it and the groove walls. The feedstock moves under the stationary shoe tooling up to the abutment, and it is possible to generate sufficient frictional force to cause the feed, which might, typically, be round re-draw rod to yield, upset and flow to completely fill the cross-section of the groove over a short length in front of the abutment. Note that with three moving sides driving the feedstock forward and one stationary side - the shoe tooling - resisting forward motion, the net effect is of two sides driving forward assuming similar contact areas and frictional condi-
22
C. ETHERINGTON
tions obtaining on each contacting surface. Within the upset length the compressive stress in the billet builds up to a maximum in front of the die zone, each increment of grip length adding its own contribution to the stress in the material. The generation of compressive stresses which may be as high as, say, 1000 N/mm* (70 t/u-$) together with the associated temperature rise in the metal as it flows through the die zone (this may be as high as 450°C with copper) enables discrete lengths of material to be welded together and extruded as a continuous homogeneous product. The potential for this was demonstrated at a very early stage in the development of the process when short lengths of 6.35mm dia aluminium rod were fed into the experimental machine and were extruded into a continuous length of 2-mm dia wire. A similar demonstration was made shortly afterwards with copper rod. On examination, the product from these trials proved to have good mechanical properties, the joint zone exhibiting mechanical properties similar to the parent metal and the wire was capable of being drawn down to typically 0.4-mm dia without breakage. Green had, from its inception, foreseen the potential of his process to accept particulate feed and this aspect of its use is covered in the original patent, filed in 1971131. Since the process was principally conceived as a method for continuously working solid metal feed - typically redraw rod - and as being complementary to the non-ferrous continuous casting and rolling routes producing rod in large continuous coils, the development programme at Springfields has concentrated on this aspect of its use. Three experimental machines are operational in the laboratory and on each some demonstration trials with particulate feeds have been carried out. Figures 2 and 3 show the first experimental Conform machine to be built, the Mk 2A. This ‘Granule’ feed
r-45
Extrusion
Fig. 2. Mk 2A Conform machine, showing arrangement for granular feed.
was designed for extruding 6.35mm dia aluminium rods. When extruding with a particulate feed a hopper is used to feed the particles via a hole in the shoe and tooling so that they fall to the root of the wheel groove. As the wheel rotates the particles are carried forward to the abutment/die zone where they are compacted to fill the cross-section and as the compressive stress within the zone increases towards the abutment the individual particles begin to weld together into a homogenous mass. Final welding occurs under plastic flow conditions as the metal is forced to flow through the extrusion die forming a continuous product. The aluminium particulate feed material has included EC grade and alloyed fine powder and granules of a range of sizes, e.g. chopped scrap wire and clean machine chippings. These have been extruded
CONFORM AND THE RECYCLING OF NON-FERROUS SCRAP METALS
23
from a groove sized to accept 6.35-mm dia rods to round wire 2-mm and l-mm dia, i.e. through extrusion ratios of 13:l and 51:1, respectively. The homogeneity and ductility of the product has then been proved by mechanical, electrical and metallurgical inspection and by further drawing trials. Typical properties are given in Table 1. Table 1.
Aluminium EC granules Powder Alloy granules Copper Dryflo chopped wire Alloy powder Chopped cathode at join
Typical properties of Conform recycled metals 0.1 Voproof stress (N/mm’)
UTS (N/mm’)
Elongation Vs)
Conductivity (Vo IACS)
95 185 230
170 284 325
7 6 1
45 56 -
338 114
432 247
7.8 28
97.4-98.5 89 loo.2
The second experimental machine to be built in the laboratory is used for the extrusion of copper. The Mk 2B as it is designated (Fig. 4) was originally designed for accepting S-mm dia
24
C. ETHERINGTON
and modified later for 9.5mm dia rod feed. Copper powder, chopped wire and bunched scrap cable in a continuous length (Figs. 5 and 6) have successfully been extruded into, typically, 2-mm dia round wire and also a rectangular section. The properties of typical products are given in Table 1, together with results obtained from extruding the chopped copper cathode fed into the machine in discrete lengths and extruded into wire. The latest machine designed and built at Springfields is the Mk 2D which is used for the extrusion of 9.5mm dia aluminium rod. The version of this design at Springfields has a vertical shaft and horizontal wheel so that the feeding of particulate material is more difficult, but the feeding of bunched wires and similar scrap is unaffected by this arrangement. Work has simultaneously been undertaken by the Conform machine licencees; for example, Fig. 7 illustrates the extrusion of aluminium wire from a powder feed on a Mk 2D type machine at the works of the Wanskuck Co. Providence, R.I. In this arrangement, the machine has been built with a horizontal shaft and vertical wheel to facilitate the feeding of granules and powders from a hopper. These nd hoc trials have demonstrated the feasibility of the process for the recycling of scrap materials and the conversion of particle feed in general into a continuous product. While in some instances the products have not been fully satisfactory and have exhibited blistering and occasional fold type defects, these can generally be associated with inadequate feeding of the
CONFORM
AND THE RECYCLING
Fig. 5. The extrusion
of copper
OF NON-FERROUS
strip from bunched
SCRAP
METALS
2-mm dia scrap ,wire. Discard
25
and tooling.
particles, and/or contamination of the feed, e.g. with cutting fluid in the case of machine swarf or insulation in the case of chopped cable. Figure 8 shows a transverse section of a 2-mm copper wire extruded from chopped copper wire produced by the Dryflo process showing typical oxide distribution patterns within the product. Further work is now necessary to investigate these processes in greater depth. There are many factors to be considered; for example, when recycling scrap wire the comparison must be made between a continuous stranded or bunched feed of wires with a chopped wire feed. Pretreatment of the feed needs to be considered to determine the purity required to meet the projected product properties. The compacting of fines and scrap into a rod form simply to improve the yield when remelting may be possible with a more contaminated feed than would be necessary for direct recycling to a finished product. The size and distribution of particles could have significant effects on the feeding, compaction and efficiency of throughput. The precornpaction of granules into the groove by the use of feed rollers and the use of screw feeders and vibration feed hoppers need to be investigated and overall production routes established for the various feed materials and products. Since Conform is an extrusion process a wide variety of product shapes and size, including tubing, are possible from the machine by simply changing the extrusion die. The type of product seems to be unaffected by the form of feed; shapes as well as rounds have been produced from granules and powders thus offering great flexibility to the potential user. Relating Conform to the four factors discussed earlier as requirements for a new process elicits the following indications: 1. Capital cost and size The Conform process is basically simple and such equipment should be cheaper than most metal recycling plant. The machines are compact units giving economy in factory floor space;
26
C. ETHERINGTON
Fig. 6. Discard removed from machine showing welding together of 12 strands of 2-mm dia copper wire to produce 7 X 3 mm rectangular strip.
the associated plant necessary will depend on the form of the feed material, but the product will normally be capable of being taken up on conventional equipment. 2. Environmental impact The Conform machine itself should have no adverse environmental effects. If the feed is in the form of fines then some form of shrouding may be necessary. Noise should not be a problem; the Conform unit itself is quiet in operation and the principle source of noise is the drive unit, whether electric or hydraulic. 3. Overall operating costs The Conform machine is basically a simple item of equipment and can be operated by semiskilled labour. Machine maintenance is straightforward, the principle skills being required in
CONFORM
Fig. 7. The extrusion
AND THE RECYCLING
of aluminium
OF NON-FERROUS
SCRAP
METALS
wire from powder feed. The wire can be seen exiting of Wanshuck Co., Providence, R.I., U.S.A.)
lower right.
27
(By courtesy
the manufacture of tools and dies. The principle cost savings will come if the marketplace will accept products made directly from recycled scrap. While it is very difficult to arrive at actual costs, some figures might be quoted at this stage for consideration. It apparently costs around 15 e!per kg (7 L per lb) to convert scrap copper wire back into rod by the conventional wire bar route. This rod has then to be worked to give the finished product, e.g. rectangular strip. The current on-cost of producing rectangular copper strip directly from redraw rod by Conform can be estimated at about 17e per kg (8 rt per lb); this latter figure will be very slightly different if the feed were in a particle form or were bunched wires. There seems
28
C. ETHERINGTON
Fig. 8. Transverse section of 2-mm dia copper wire extruded from Dryflo feed (X 37.5).
to be a possibility of considerable savings here between the established route and a notional new route for the manufacture of, for example, copper earthing tape. Similarly, with aluminium, redraw rod currently costs around U.S. $1.1 per kg (50 G!per lb) to buy and scrap is selling at only 33L per kg (15 I per lb). There is potential for savings here, in the manufacture of products such as furniture or luggage trim as well as the possibility of higher grade products such as tubing. 4. Effective metal yield Conform offers the possibility of an almost 100% yield depending on the condition of the feed. The quantity of ‘waste’ metal produced in the process is that which extrudes through the running clearances between wheel and tooling, normally amounting to no more than 3% of the total throughput. This metal can immediately be fed back into the machine so there would be no loss. The discard left when the machine is stopped at the end of a run is approximately the upset length - typically 25 mm in a 9.5mm wide groove - and this may be left in for the next start-up, when it will act as a lead for the following period of operation. The simplicity of concept and compactness of the equipment should make it attractive for the consideration of its use within existing production and fabrication plants where scrap arisings are currently fed back into the secondary metal industry for re-melting. In the aluminium field the arisings from the manufacture of products from sheet wire, rod and foil as well as some of the arisings from extrusion plants could well be recycled directly through a Conform machine.
CONFORM AND THE RECYCLING OF NON-FERROUS SCRAP METALS
29
FUTURE DEVELOPMENTS Many non-ferrous metals and alloys have been successfully extruded by Conform from solid rod feedstock including aluminium, copper, lead, silver, zinc and a number of alloys. With all of these there appears to be very good prospects for the direct recycling by Conform of scrap arisings. The feed may be either as particles or in a more massive form. The Conform machines operating to date (September 1977) have all been designed principally to accept re-draw rod up to 9.5-mm dia and, therefore, their ability to accept particulate feed is limited to particle sizes which will readily enter and be compacted in a 9.5-mm wide groove. Larger machines with groove sizes up to 25-mm wide are currently in design and manufacture and these should enable a much wider range of particle sizes to be handled. To meet the requirements for the recycling of old scrap which may be of unknown quality and new inhouse scrap which may be in too massive a form for direct feeding to Conform or even for granulating, e.g. extrusion press discards, melting is still going to be a necessary requirement. Consideration could then be given to the possibility of converting the molten metal directly into either powder or shot for direct feeding into Conform without the necessity for casting into billets for subsequent rolling or extruding. In this context it is interesting to note in Table 1 the high strength obtained in wires extruded directly from aluminium powder feed, with no subsequent treatment. A powder route opens up the opportunity for mixed metal feeds and for fibre strengthened products. Alternatively, the molten metal might be poured directly into a large Conform wheel where solidification would take effect as the metal is carried to the dlie for continuous extrusions. [5]. The advent of the Conform process opens up the possibility of an alternative economic and environmentally acceptable route for the reconversion of scrap non-ferrous metal into usable product, and with continuing development further novel aspects of the process may emerge. Acknowledgements - The author wishes to acknowledge the assistance of his colleagues in the Advanced Metal Forming Group of the UK&A Springfields Laboratories in the preparation of this paper and the Laboratory and UKAEA Northern Group Management for permission to publish it.
REFERENCES 1. World Bureau of Metal Statistics (August 1977). 2. M. B. J. Bever, The significance of scrap in western economies, Lecture to the Univ. of Nottingham. Short course on reclamation and recycling of metals (March 1976). 3. D. Green, Improvements in or relating to extrusion, U.K. Patent 1370894 (Filed March 1971). 4. D. Green, The continuous extrusion forming of wire sections, J. Inst. Metals 100, 295- 300 (1972). 5. C. Etherington, Conform - A new concept for the continuous extrusion of metals, ASME 73-WA/PT-2 (November 1973). 6. C. Etherington, The UKAEA conform method of continuous extrusion, ZWMA Conference, New Developments in Wire Technology, Amsterdam (1976). 7. E. Hunter, Continuous extrusion by the Conform process, Sot. Manufacturing Eng. Conf., Chicago SME MF76-407 (June 1976). 8. D. J. Marsh, Extrusion of copper by the conform continuous extrusion process, 18th Znt. Machine Tool Design and Research Conf., London (September 1977). 9. J. A. Pardoe, The Conform continuous extrusion process - development experience with non-ferrous metals, Wire Association Conf., Boston (October 1977). 10. Licensees: U.K.-Babcock Wire Equipment Co., Bolton; Marshall Richards Barcro Ltd., Crook, Co. Durham. U.S.A.-Wanshuck Co., Providence, R.I. Japan-Sumitomo Heavy Industries, Niihama.