WO1991004149A1

WO1991004149A1 - Compacting scrap metal into briquettes

Info

Publication number: WO1991004149A1
Application number: PCT/GB1990/001439
Authority: WO
Inventors: Antonino Giorgio Cacace
Original assignee: Camborne Industries PLC
Current assignee: Camborne Industries PLC
Priority date: 1989-09-21
Filing date: 1990-09-19
Publication date: 1991-04-04
Anticipated expiration: 1992-03-21
Also published as: EP0501965A1; DE69020359T2; KR100212418B1; CA2066565A1; ATE123994T1; ZA907517B; ZA907515B; WO1991004148A1; EP0501965B1; AU6341390A; DE69020359D1; KR927003322A; DK0501965T3; AU6433190A; ES2078352T3; JPH05500635A; AU654469B2; JP2913213B2; CA2066565C

Abstract

A method is disclosed of forming a billet (30, 200, 300) comprising charges of swarf compacted cyclically into a number of briquettes (32, 202, 304) joined together. The billet may also comprise a tube (34, 204, 302) which forms a jacket around the briquettes. The briquettes are joined at interfaces which have complementary interengaging formations (206, 208, 306, 308). The formations may have frusto-conical shapes which are co-axial with the briquettes. Each interface may have a substantially flat annular peripheral portion (210, 310) normal to the longitudinal axis.

Description

COMPACTING SCRAP METAL INTO BRIQUETTES

FIELD OF THE INVENTION

This invention relates to the compaction of scrap metal, particularly but not necessarily exclusively the compaction of scrap metal swarf into briquettes for the purpose of recycling.

The term "swarf" comprehends the off cuts from machining operations in general and is intended to include the off cuts from turning, boring, shaping and milling operations on engineering steels. The fine off cuts from some stamping and punching operations may also be suitable.The term "engineering steel" is intended to describe those low alloy steels whi. are commonly subjected to machining operations including mild steel (a term which itself includes carbon steel), forging steel and axle or shaft steel all of which contain significant amounts of carbon.

DESCRIPTION OF PRIOR ART

In British patent #1313545 there is disclosed, inter alia, a process in which steel swarf is pressed into compact masses (which for convenience will be called "briquettes"). The briquettes are pressed together and jacketed in a closed tube, usually of steel or stainless steel. The billet so formed is then heated and worked by a process such as rolling into a finished or semi-finished product.

The forming of the briquettes may take place in a cavity die prior to being jacketed. Alternatively briquettes may be formed directly in the bore of the tube. In this case the tube is inserted in a supporting die during the compaction process and the bore of the tube serves as the cavity. In either case the compaction is carried out by means of a press having a ram which presses a quantity of the swarf previously inserted in the cavity into a briquette. The ram is then withdrawn and a new charge of swarf is inserted in the cavity. The ram is again inserted in the cavity to form a new briquette pressed up against the earlier formed briquette. The cycle is repeated until the cavity is substantially filled up with briquettes.

During the heating the oxides on the swarf inside the jacketing tube are reduced and during the working process the metal particles of which the briquettes are composed are consolidated into a unitary mass which are sintered to each other and to the jacket.

The reduction of oxides on the swarf occurs as a result of the combination thereof with carbon which is either introduced into the jacket or which diffuses out of the steel or other metal of which the swarf is composed. The jacketing tube serves to maintain reducing conditions within the billet. Attempts to produce an acceptable hot worked product from a billet of unjacketed swarf have been unsuccessful even when great care was taken to try to prevent atmospheric oxygen from getting to the hot billet.

The ram has an end face which comes into contact with the swarf in the cavity. In the rams which have been used up to the present time this face has been flat and perpendicular to the axis of the cavity. Consequently each briquette has effectively a pair of mutually parallel faces. Because they are formed one by contact with the end face of the ram and the other by contact with the flat end face of the adjacent briquette formed earlier in the cavity, these parallel faces are also flat and perpendicular to the axis of the cavity.

It has been found that the flat interface between adjacent briquettes results in a potential weakness. During subsequent hot rolling the action of the rolls has a tendency to separate the briquettes at the interfaces. This is shown in Figure 1 of the accompanying drawings which is a diagrammatic cross-sectional side view of a billet being rolled. The billet 10 comprises briquettes 12 in a tubular jacket 14. The billet is passing through rolls 16. The briquettes passing through the rolls are shown separating at the interface 18. The result of the separation is the formation of voids under the wall of the tube. The lack of contact with the hot solid mass of the briquettes causes rapid cooling of the tube at these points. As a result the tube necks during subsequent passes through the rolls as shown at 20 and eventually cracks ,

It is an object of the invention to reduce the incidence of this problem.

SUMMARY OF THE INVENTION

According to the invention there is provided a method of forming a billet comprising first and second briquettes of swarf which are joined at adjacent faces, characterised in that the adjacent faces are formed with complementary interengaging formations.

According to one aspect of the invention the method includes the steps of inserting a first charge of swarf into a pressing cavity, causing a pressing head to press the first charge of swarf to form the first briquette with a back face which conforms to the shape of a working face of the pressing head which comes into contact with the swarf, inserting a second charge of swarf into the pressing cavity, and causing the pressing head to press the second charge of swarf against the back face of the first briquette to form the second briquette, characterised in that the back face of the first briquette and the front face of the second briquette are formed with complementary interengaging formations.

According to another aspect of the invention the billet comprises a metal jacket in which the swarf is pressed to form the briquettes.

In one form of the invention the formation in the back face of the first briquette comprises an annular recess. In an alternative form of the invention the formation comprises an axially projecting protuberance. In one aspect of the invention the briquettes and the said formation have a common axis of symmetry. Advantageously the said formation is substantially of frusto-conical shape.

In one aspect of the invention the back face has a substantially flat peripheral portion around the said formation the longitudinal axis of the briquette being normal to the peripheral portion. The angle at the imaginary apex of the frusto-conical shaped formation is advantageously between 30 and 120 degrees.

For round briquettes the frusto-conical shaped formation has a depth not greater than half of the diameter of the briquettes.

Further according to the invention there is provided a billet comprising first and second briquettes of swarf which are joined at adjacent faces, characterised in that the adjacent faces are formed with complementary interengaging formations.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further discussed with reference to the accompanying drawings in which:

Figure 2 is a cross-sectional side view of part of a billet being rolled;

Figure 3 is a side view of a nose piece mounted on the end of a ram;

Figure 4 is a cross-sectional side view of a second nose piece in the process of forming a billet;

Figure 5 is a cross-sectional side view of yet another nose piece; and

Figures 6 and 7 are cross-sectional side views of billets formed by rams with the nose pieces illustrated in Figures 3 and 5 respectively. DETAILED DESCRIPTION OF EXAMPLES SHOWN IN THE DRAWINGS

Referring first to Figure 2 there is shown a billet 30 comprising briquettes 32 (of, for example, mild steel shavings) jacketed in a tube 34 (again, by way of example, of mild steel or stainless steel).

The billet is being passed through rolls 36. In contrast to the briquettes 12 shown in Figure 1, the briquettes 32 have conical interfaces as indicated at 38. These conical interfaces are formed by the head of the ram (shown in dotted outline at 40) which is inserted in the tube and forms each briquette. The head of the ram has a conical end face 42. The apex 44 of the end face lies on the longitudinal axis 46 of the ram and projects away from the ram. Thus as each briquette is formed the end face 42 of the ram forms in the briquette an end face 48 which is an inversion of the shape of the end face 42. Moreover, during the formation of the briquette the shavings are pressed up against the end face 48 of the adjacent earlier formed briquette so that the two faces are formed with interlocking conical formations.

The fact that the interfaces between the briquettes are cone shaped has the result that the briquettes have less tendency to separate at the interfaces during rolling. This is believed to be on account of the fact that the forces applied by the rolls to the billet (shown schematically at 50) are less close to being parallel to the interfaces than is the case in the arrangement shown in Figure 1. Consequently the forces 50 have more of a compressing action than a shearing action at the interfaces.

The conical end face 42 can be formed integrally with the ram which would ordinarily be hardened by any well known hardening process. Alternatively the end face can be embodied in a nose piece of wear resistant material such as tungsten which is brazed on the end of the ram. In yet another alternative the nose piece can be demountably fixed on the end of the ram. In this case the nose piece can be replaced at much lower cost than the whole ram. The demountable nose piece can be fixed on the ram by means of a stud. One such stud is indicated in dotted outline at 86 and may be threaded at each end in opposite senses, one end being screwed into the nose piece and the other into the ram.

The conical shape of the end of the nose piece 40 is very suitable for forming briquettes having interfaces which have a diminished tendency to separate under the action of the rolls. However the shape of the nose piece 60 shown in Figure 3 is considered more suitable in practice. For this to be properly understood it is necessary first to note that the tubular jacket (shown at 62 in Figure 3) is mounted in the close fitting cavity 64 of a die 66 during the operation of forming the briquettes therein. Just as it is advantageous that the nose piece be made of wear resistant steel so it is advantageous to mount an annular collar 68 of wear resistant steel on the die, surrounding the entrance to the cavity 64. The collar has a central aperture 70 the diameter of which is substantially equal to the diameter of the bore of the tube 62. The nose piece is a close sliding fit in the aperture 70 and the bore of the tube. The provision of the collar prevents the die from wearing around the entrance to the cavity and also acts as a guide for the nose piece as it enters the bore of the tube. In fact in practice it has been found highly beneficial if the nose piece is capable of shearing shavings trapped between the periphery 72 of the end face 74 and the periphery of the aperture 70 as the nose piece approaches the aperture. This shearing action is most efficient if the end face 74 meets the cylindrical face 76 of the nose piece at a right angle, indicated at A. The periphery of the aperture 70 acts as a mating cutting edge. In the nose piece 60 the end face 74 is provided with what is essentially a frusto-conical portion 78 which is set in from the periphery 72. The portion 78 is symmetrical about the axis 80 of the nose piece. Thus end face 74 is provided with a modified conical portion and also, at its periphery, an annular portion 72 which is at right angles to the cylindrical face 76.

It is considered that the width of the peripheral portion 72 which Is at right angles to the cylindrical face need not be more than about 1/8 of the diameter of the end face. In the example illustrated the width is 4 mm, the diameter of the end face being a 97.7 mm.

The end face 74 should be radiused where the frusto-conical portion 78 meets the peripheral portion 72 and also at the extremity 84 of the frusto-conical face 82. This not only prevents stress raisers from occurring in the nose piece in use but also sharp edges in the frusto- conical portion 78 can cause the nose piece to be wedged into the shavings being compacted causing difficulties in retracting the ram. This is thought to take place due to the elasticity of the shavings. Radii of as little as 6mm have been found adequate. However, in the example illustrated, the radius at the junction of the annular portion 72 and the frusto-conical face 82 is about 12 mm and the radius at the extremity 84 is about 25 mm.

For the same reason the face 82 should not be too close to being right circular cylindrical. It is considered that the angle at the (imaginary) apex of the frusto-conical face 82 should be between 30 and 120 (indicated by the angle B). In the example illustrated angle B is 90°.

It is considered that the axial length of the frusto-conical portion 78 should not be more than about half the diameter of the nose piece and is best between 0.2 and 0.5 thereof. In the example illustrated in Figure 3 the axial length is about 30 mm. A nose piece 90 with a frusto-conical portion 92 having an axial length approximately equal to the diameter of the nose piece is shown in Figure 4, inserted in a tube and in the process of compacting a mass of shavings into a briquette. As the free end of the frusto-conical portion 92 enters the inversely shaped recess 94 in the face of the earlier formed briquette 96 shavings located therebetween begin to be compacted. These shavings (indicated at 98) ultimately become so densely compacted that the advance of the nose piece into the tube is stopped. There is in this case a possibility that there will be shavings located deep in the recess 94 (indicated at 100) and/or between the densely compacted shavings 98 and the peripheral portion 72 of the nose piece (indicated at 102) which will be less compacted than the shavings 98. In an extreme case the shavings 100, 102 may not be compacted at all and there could even be voids in those regions. Such a void is indicated at 106. A briquette composed of unevenly compacted shavings or incorporating voids results in a poor quality end product and may also result in failure of the billet during rolling.

Despite the disadvantages associated with the nose piece 90 it may in some circumstances be useful under carefully controlled conditions. In Figure 5 there is shown a nose piece 110 having an end face 116 in which there is formed a recess 112 rather than a protuberance. The recess 112 is again substantially frusto-conical. The end face has a peripheral portion 114 which is at right angles to the cylindrical face 122. It will be clear that the face of a briquette formed by the nose piece 110 will have a protuberance (rather than a recess) which projects towards the nose piece. A possible disadvantage of the nose piece 110 is that the forces applied thereto by the shavings during compaction, especially at the conical face 118 of the recess 112, will have radial components which may tend to force the zone of the nose piece surrounding the conical face outwardly. This may cause the nose piece 110 to fail due to fatigue at locations such as those indicated at 120.

Another advantage of using a nose-piece with a protuberance rather than a recess in the end face is that the nose piece with a protuberance is likely to produce a briquette in which the density of the swarf will be greater at the centre of the briquette than at the periphery thereof. A highly compressed smooth surface at the periphery of a briquette is less likely to result in satisfactory interlocking between adjacent briquettes at the periphery thereof. This is important as it is this area which undergoes the greatest shearing stress during subsequent hot rolling.

A billet 200 is shown in Figure 6 comprising briquettes 202 formed by a press having two rams with nose pieces 60 is illustrated in Figure 3. The rams are mounted in axial alignment with the tube 204 mounted in a supporting die located between the rams. The rams are advanced cyclically into both ends of the tube at the same time. A predetermined quantity of swarf is fed into each end of the tube between each cycle of the press. In the first cycle a first briquette 202a is formed in the longitudinal centre of the tube. Thereafter two briquettes are formed, one by each ram, in each cycle. The nose piece forms a frusto-conical recess 206 in the front face of each briquette which interlocks with a complementary protuberance 208 in the back face of the adjacent briquette. The protuberance is formed by the swarf which fills up the recess in the process of being compacted. The annular face 72 of the nose piece forms a complementary annular face 210 around the periphery of the front face. The recess 206 and the protuberance 208 are surfaces of revolution having an axis of symmetry coincident with the longitudinal axis 212 of the billet. The face 210 is normal to the axis 212.

In practice billet comprises a jacketing tube which is typically of 89 mm internal diameter, 6 mm wall thickness and 100 or 200 cm long. Typically there would be about twenty four briquettes 202 in each metre length of tube after compacting. The tube can be mild steel or stainless steel. In the latter case mild steel end pieces, indicated at 204a, may be welded to the ends of the tube before it is filled with briquettes. One advantage of using these end pieces, the remains of which which are cut off and discarded after the billet has been heated and rolled into a finished product, is to reduce the cost of the billet. The end pieces also promote better product quality and assist the entry of the billet into the rolls. Billets provided with the end pieces are more fully discussed in the applicant's PCT patent application entitled "Recycling Scrap Metal".

Figure 7 is an illustration, similar to Figure 6 of a billet 300 comprising a tube 302 filled with billets 304 using a press having two rams provided with nose pieces 110 as shown in Figure 5. The nose piece forms a frusto-conical protuberance 306 in the front face of each briquette which interlocks with a complementary recess 308 in the back face of the adjacent briquette. The annular face 114 of the nose piece forms a complementary annular face 310 around the periphery of the front face. The recess 308 and the protuberance 306 are surfaces of revolution having an axis of symmetry coincident with the longitudinal axis 312 of the billet. The face 310 is normal to the axis 312.

The invention may be employed to form a billet comprising briquettes prior to insertion in a jacket; for example the billet may be formed by pressing swarf into briquettes in a split cavity die. Improved cohesion between adjacent briquettes has the result that a greater degree of hot working or reduction from a larger diameter to finished size can be achieved more rapidly. Production time is reduced and smaller final sizes can be rolled. Furthermore strength requirements of the jacket are reduced enabling, for example, a larger range of tubing to be used. In the case of a billet formed prior to jacketing, greater cohesion between briquettes results in a billet which can sustain a far greater degree of rough handling before it will break up. It is also possible to produce a longer billet than has heretofore been the case.

The manner of further processing and working the billets formed by the use of the present invention will be fully understood by reference to the aforementioned British patent #1313545.

The invention may usefully be applied to briquettes made up of swarf composed of engineering steels and also suitable high alloy steels such as stainless steel.

It is not intended that the scope of a patent granted in pursuance of the application of which this specification forms a part should exclude modifications and/or improvements which are within the spirit of the invention as defined in the claims appended hereto or be limited by details of the embodiments described and/or illustrated further than is necessary to distinguish the invention from the prior art.

Claims

1.

A method of forming a billet [30, 200, 300] comprising first and second briquettes [32, 202, 304] of swarf which are joined at adjacent faces, characterised in that the adjacent faces are formed with complementary interengaging formations [206, 208, 306, 308].

2.

A method according to claim 1, including the steps of inserting a first charge of swarf into a pressing cavity, causing a pressing head to press the first charge of swarf to form the first briquette with a back face which conforms to the shape of a working face [42, 74, 116] of the pressing head which comes into contact with the swarf, inserting a second charge of swarf into the pressing cavity, and causing the pressing head to press the second charge of swarf against the back face of the first briquette to form the second briquette, characterised in that the back face of the first briquette and the front face of the second briquette are formed with complementary interengaging formations [206, 208, 306, 308].

3. A method according to claim 1 or claim 2, characterised in that the billet comprises a jacket [34, 204, 302] in which the swarf is pressed to form the briquettes.

A method according to claim 2 or claim 3, characterised in that the formation in the back face of the first briquette comprises an annular recess [206].

5.

A method according to claim 2 or claim 3, characterised in that the formation in the back face of the first briquette comprises an axially projecting protuberance [306].

6.

A method according to claim 4 or claim 5, characterised in that the briquettes and the said formation in the back face have a common axis of symmetry [46, 212, 3123.

7.

A method according to any one of claims 4 to 6, characterised in that the said formation [48, 206, 306] in the back face is substantially of frusto-conical shape.

8. A method according to claim 6, characterised in that said formation is surrounded by a substantially flat peripheral portion [210, 310] of the back face, the briquettes having a longitudinal axis [212, 312] which is normal to the peripheral portion.

9. A method according to claim 7 or claim 8, characterised in that the angle of the imaginary apex of the frusto-conical shaped formation is between 30 and 120 degrees.

10.

A method according to any one of claims 7 to 9, characterised in that the briquettes are round in cross section and the frusto-conical shaped formation has a depth not greater than half of the diameter of the briquette.

11.

A billet [30, 200, 300] comprising at least two briquettes [32, 202, 304] of swarf which are joined at adjacent faces, characterised in that it is formed by a method according to any one of claims 1 to 9.