GB2043517A - An apparatus for use in the production of cans - Google Patents

Abstract

An apparatus for use in the production of cans, especially those shaped by stretching a sheet metal, the edge region of the can so produced requiring trimming and annealing treatment to facilitate forming an edge flange, comprises can retainers (6a) which are rotatable at an adjustable speed about the axis of the can retained thereon and a laser beam (33) for effecting at least the trimming treatment. The laser beam is directed at the region (56) of the cans (8) where trimming is to be effected and a displaceable protective gas hood (48) comprising an inner (50) and an outer (49) portion, which in use overlaps the edge (47) of the can to be treated is provided with a window (58) through which the laser beam passes. The table 1 may be rotated past the laser or a separate laser is provided for each can, a mirror 34 deflecting the beam during loading etc. The area 57 may be annealed by an electrical induction heater 9 or by laser beams 61 parallel to the 'sharp' cutting beams 60. <IMAGE>

Description

SPECIFICATION Apparatus for use in the production of cans The present invention relates to an apparatus for use in the production of cans, especially cans formed from sheet metal part by stretching or drawing, in which the edge region of the can is trimmed and simultaneously annealed by means of a laser beam prior to an edge flange being produced.

An apparatus for trimming the edges of cans is known which comprises a clamping device which temporarily retains the can, a drive device being provided for rotating the can about its major axis. Instead of a conventional mechanical cutting tool, which tool is displaced towards the tin to remove excess metal, a laser beam generator, preferably continuously operating, is located at the minimum spacing from the can wall compatible with unobstructed continuous operation. By this means the edge region of the can is trimmed and simultaneously the adjacent edge region of the can wall is affected by the beam so that the production of an edge flange therefrom is facilitated. In this known arrangement, a carbon dioxide laser beam generator is used which produces a coherent beam having a width of 0.05 mm. The cutting speed, if the generator output is 425 W, is 0.25 m/s.

It has been known for some time that tubes, pipes and cylindrical bodies can be trimmed with a laser beam. However, when producing cans by drawing a cup-shaped sheet metal part, the hardness of the sheet metal material increases substantially after cold work-hardening. This is particularly true of sheets made of rimmed cast steel. Thus, the deformation behaviour of all types of sheet metal used for producing cans is critical, particularly if the edging flange is formed after the drawing operation but without any prior drawing-in of the edge. This is because the stretching or drawing of the material to beyond its nominal diameter caused by such forming, subjects the sheet metal to considerable stress. Similar problems arise in can bodies having a longitudinal seam, particularly if they are made from lower quality sheet metal.Such lower quality sheet metal is frequently unable to stand up to this deformation without the risk of damage.

Furthermore, high demands must be met in the trimming of the tin body, particularly with regard to the neatness and the accuracy of the trimming.

Very accurate and neatly trimmed edges may be produced using a laser beam. Nevertheless, treatment of the edge of the can, to improve its shaping properties, necessitates monitoring of the treatment conditions and adjustment thereof to ensure that the appropriate treatment is effected.

The present invention seeks to provide an apparatus of the type described hereinbefore in which simultaneous trimming and annealing treatments of the edge region of the can may be effected simply and reliably, whilst permitting the treatment conditions to be accurately monitored and controlled but not impairing the high operating speed which can be attained by utilising a laser beam is not impaired.

According to the present invention, there is provided an apparatus for use in the production of cans, more especially in the production of cans which are shaped by stretching a cuplike sheet metal component, the edge region of the can so produced requiring simultaneous trimming and annealing treatment to permit an edge flange, the apparatus comprising retaining members for the cans, which retaining members are rotatable at an adjustable speed about the axis of the can retained thereon, the retaining members being displaceable through a treatment zone, and a laser beam system including a laser beam source producing a laser beam for effecting at least the trimming treatment, said source directing said laser into the region of the cans where trimming is to be effected wherein a displaceable protective gas hood comprising an inner and an outer portion, the hood, in use, overlapping the edge of the can to be treated, the hood being provided with a window around its circumference aligned with the laser beam and permitting the laser beam to pass therethrough.

By so doing, not only is the region of the can wall to be treated and swept by a cloud of protective gas, but other wall regions not requiring treatment are protected by the gas hood. The hood may comprise an inner and outer portion which define, between them, a gap into which the protective gas is passed.

The protective gas double hood does not rotate relative to the laser beam, and the window formed therein constantly faces the laser beam. The can, however, is rotated at speeds in excess of 200 r.p.m., preferably at a speed of not less than 500 r..p.m. Accordingly, within the protective gas hood, an extremely stable protective cloud of gas is produced on both the outer and inner surfaces of the can body, the stability and reliability of which is not disturbed even in the region of the window. On the other hand, the laser beam can pass in an unobstructed manner through the protective gas hood onto the edge of the can, so that the trimming and, more importantly, the annealing or edge treatment can be accurately and reliably monitored and the conditions adjusted. The can is also screened against the action of the ambient atmosphere.

Thus, a laser beam may, if desired, be used only for trimming the edge of the tin, whilst the annealing treatment may be effected by means of an induction heating device. Prefera bly, however, both the trimming and the annealing treatments are effected by means of the laser beam.

Preferably, the hood is non-rotatable and is displaceable through the treatment zone with the retaining members, the window in the hood having a width in a direction parallel to the can axis corresponding to the width of the region of the can to be annealed and extending arcuately in the circumferential direction on each side of the laser beam through an angle of between 30 and 60 . By means of such dimensioning of the window in the circumferential direction, the action of the laser beam may be controlled, particularly with regard to the simultaneous continuously progressive movement of the retaining members through the path of the laser beam.If the can is continuously displaced through the beam and simultaneously rotated about its own axis, circumferential regions of the can are first impinged upon by the beam at points remote from the focus of the beam. When the laser beam or, if provided, the laser beam optical system is located so as to be focussed in the region of the protective gas atmosphere, the laser beam only acts in these regions to provide heating but not cutting. The cutting effect does occur until a portion of the can periphery passes the focal point of the laser. If the retaining members pass quickly through the focus, the cutting occurs only momentarily. However, this short length of time, in combination with the high speed of rotation of the tin about its own axis suffices to effect trimming all around the can.Immediately after this, the laser beam begins to impact the more remote circumferential regions of the can thereby losing its cutting action, but maintaining the heating effect on the edge of the can. On account of the setting of the laser beam optical system in the manner described, it is desired that the cutting effect by means of the laser beam is caused to occur only in the region of the minimum metal thickness.

It is, however, advantageous to produce the laser beam from a bundle of the beams and the laser beam optical system which, for example, is adapted with a zoom-like variable focal point position, to be so adjusted that one or more beams are focussed in the region of impact of the laser beam on the can wall, whilst one or more further beams above and below this focussed beam have their focal point elsewhere. These latter beams are therefore not sharply focussed on the can and therefore-produce only a heating effect.

It is also possible for several laser beams to be used simultaneously in order so to trim and/or treat a plurality of cans simultaneously. To improve the stability of the protective gas cloud, it is expedient for the axis of the can to extend vertically.

For continuous operation of the laser, it has been proved advantageous to arrange a pivotal, rotary or otherwise displaceable mirror between the retaining members and the laser beam source, which mirror is controlled in dependence upon the movement of the cans.

The mirror directs the laser beam only for a short period of time towards the window of the protective gas hood whilst a can is passing the treatment region and is use, for the remainder of the time, to deflect the beam into an ineffective direction.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows, schematically, a perspective view of an apparatus for use in the production of cans in accordance with the present invention.

Figure 2 is a somewhat simplified vertical section through an individual treatment device forming part of an apparatus in accordance with the present invention; Figure 3 shows a detail of part of a can showing the manner of trimming thereof; Figure 4 is a sectional, somewhat simplified view of part of a modified embodiment of the apparatus of Fig. 1; Figure 5 shows a vertical section through a hood forming part of an apparatus in accordance with the present invention, the hood having cooling devices associated therewith; and Figure 6 shows a cross-sectional view of part of the hood shown in Fig. 5, on an enlarged scale relative thereto.

In Fig. 1, there is shown a turntable 1 which may be rotated continuously or intermittently. The turntable 1 is rotated about the axis 2 in the direction of the arrow 3 preferably at a constant speed but possibly intermittently.

The turntable 1 carries, adjacent its periphery a plurality of spidles 4, the spindles forming a ring. Each spinle 4 may be driven about its axis 5 in the direction of the arrow 6 at a speed which is adjustable by means of drive devices, not shown. This speed is preferably adjustable within the range of 200 to 300 r.p.m. and is expediently 500 r.p.m. Each spindle 4 carries at its upper end, a clamping plate 6a which receives the base of a drawn can body 8. The plate 6a may, as shown, be provided with suitable centering and clamping devices 7 which may be magnetic. It is essential that the axis 8a of each can body 8 is aligned as accurately as possible with the axis 5 of the spindle 4 on which it is mounted and is reliably retained in this aligned position.

In the embodiment shown in Fig. 1, a zone of incandescence 9 for the treatment of the tin edges is provided. As shown, the zone of incandescence 9 is formed by the inductor loop 10 of a high frequency inductive heating device. The inductor loop 10 is supported on a frame external to the turntable. Thus, the outwardly projecting ends 15 and 16 of the loop may be connected to a high frequency source indicated generally at 17.

The inductor loop comprises substantially two loop sections 11 and 12 which are arcuate and extend horizontally parallel to each other. At their ends, these sections are interconnected by vault-like outlet and inlet end pieces 13 and 14. The dimensions of the zone of incandenscence 9 are determined by the length of the parallel arc sections 11 and 12. The length 18 is expediently not less than the inter-axial spacing of two adjacent spindles 4, so that at lest one can body is located in the zone of incandescence at any one time. The length 18 may, however, be substantially greater than this so that, for example, ten tins may be located simultaneously in the zone of incandescence.

The speed of rotation of the turntable 1 is desirably adapted to the rate of rotation of the spindles 4.

The edge region of each tin, whilst passing through the zone of incandescence 9, is in a protective gas cloud. For this purpose, gas hoods, as shown, in the form of glass hoods 20, are provided. These are axially aligned with the rotary plate. The protective gas hoods may be connected in pairs, or, as shown, individually connected via conduits 21, 22 to a gas source. In a continuous treatment process, the protective hoods travel through the zone of incandescence with the spindles.

Details of a preferred embodiment of a protective gas hood are shown in Figs. 2, 5 and 6. In Fig. 2, there is shown a protective gas hood 48 which comprises an inner hood 50 and an outer hood 49, having an annular gap 51 defined therebetween. This annular gap 51, when the hood is lowered into its position of use, accommodates the edge 47 of a can to be trimmed as well as the edge region of the can 57 including the trimming line 56. It is desirable if the protective gas atmosphere extends downwardly beyond the region 57 to be annealed. The outer hood portion 49 of the hood 48 has a centrally disposed gas inlet 52 having a connection portion 53 leading to a gas source. The protective gas thus extends over the end face of the can, over its entire periphery.This gas distribution is improved by the fact that the can 45 rotates, at a comparatively high speed, about its axis 46 and rotates the protective gas in the gap 51 relative to the stationary hood 48. The distribution of the gas over the outer and inner circumferential surfaces of the can body is thus reliably achieved. Thus, rotating protective gas clouds are formed which slowly pass through an annular gap formed on the lower edge of the internal and external surfaces as indicated by the arrows 54 and 55. The free edges of the hood portions 49, 50 are aerodynamically formed that no external air is induced into the hood.

The protective gas hood 83 shown in Figs.

5 and 6 is similarly constructed, although the connection of the annular gap 84 between the two hood portions to the supply conduit is not shown. It is, however, immediately apparent from these two Figures that the gap has an enlarged cross-section at the lower, gas outlet edge. This facilitates the entry of the edge 85 of the can into the gap 84 when the hood is lowered onto a can.

The hood 83 is expediently cooled. A certain amount of cooling is effected by the protective gas itself. The outer surface of the hood may also be cooled by means of a blower, not shown, which directs a cooling air flow against the outside of the hood. Additional forced cooling may be achieved by providing devices 86 and/or 87 (see Fig. 5) which can be annular. The cooling device 87 is located on the internal surface of the hood.

In Fig. 5, a shank 88 of the inductor loop is shown. The hood 83, by virtue of its indirect mounting on the turntable, travels along the length of this shank 88, slightly spaced apart therefrom, during continuous operation. In the region adjacent the shank 88, the outer wall 89 of the hood is of substantially reduced thickness so as to obtain the minimum spacing between the shank 88 of the loop and the rotating can body 85. In its circumferential regions which do not face the induction loop, the protective gas hood, as shown in Fig. 6, may additionally be provided with cooling ribs 90 to supplement the cooling effect of, for example, an external blower. Since both cooling and heating effects are produced it is desirable to use a heat pump arrangement in which the heat extracted during the cooling process is employed to pre heat the cans.

As shown in Fig. 2, the protective gas hood 48 has a circumferentially extending window 58 formed in the outer hood portion 49. This window is located at a level which, in use, coincides with the trimming line 56. Its dimension in a direction parallel to the axis 46 of the can is determined by the task to be carried out by the laser beam 59. If the laser beam is to be used only for severing along the trimming line 56, then an axial dimension of the window 58 sufficient to allow passage to the "sharp" laser beam 60 used for trimming is all that is required.

In such a case, and as is shown in Fig. 4, the circumferential dimension of the window for the "sharp" laser beam 76 need only be an arc subtending an angle of about 30 .

Instead of annealing the edge region with an induction loop as is shown in Fig. 1, the annealing may also be effected utilising laser beams. It should be noted that the laser beam is "sharp" only at the focal point of the optical system for the beam. In other words, the energy is available at this point so that a clean cut occurs. If, on the other hand, the focal point of the optical system is at a point spaced from the wall of the can, the laser beam can produce a heating effect on the wall of the can to a limited extent. As shown in Fig. 4, it is assumed that the cans 72 are continuously displaced in the direction of the arrow 71 by means of the turntable 70 and are simultaneously rotated about their axes 72a in the direction of the arrow 73 at a relatively high speed.The laser beam 76 is assumed, in Fig. 4, to extend in the direction of the arrow 82 and is directed against the axis of rotation of the turntable 70 in the position of the can shown therein. The direction of the beam coincides with the connecting line joining the optical system 75, the axis 72a of the tin and the axis of the turntable.

Accordingly, at the point of impact 72b of the laser beam 76 on the can, trimming or severing of the sheet metal occurs at the portion of the can wall nearest the laser source, which point is the focal point of the optical system.

The high energy of the laser beam, will, nevertheless, still cause a cutting in the angular region 80 which subtends an angle of about 30 at the axis of rotation of the can.

On the other hand, the can moves in the direction of the arrow 71 and, in reaching the position shown in Fig. 4, the laser beam first impacts the circumferential position 72c leading in the direction of rotation. This position is somewhat distant from the focal point of the laser beam so that the laser beam only produces a limited heating effect in this region.

The heating effect increases with the progressive travel of the can 72 in the direction of the arrow 71 and reaches its maximum value when the point 72b passes the laser beam. If the progressive travel is continued, the heating effect diminishes until the point 72d passes the laser beam. In practice, the laser beam should only exhibit a punctiform cutting effect. As shown in Fig. 3, due to the rotation of the can 62 about its axis 66, this cutting effect, should extend along the trimming line 64. However, the can region 57 requiring annealing has a significant axial dimension. It is therefore necessary either to provide separate laser beams for trimming and for annealing or, as is shown in Fig. 2, to provide a bundle of laser beams 59.The bundle of laser beams comprises a "sharp beam" 60 and a "non-sharp" beam 61, the sharp beam being directed against the trimming line 56 and the non-sharp beam 61 being directed against the region 57 of the can to be annealed. The laser beam 76 shown in Fig. 4 may also be of this type.

Such a laser beam may also be used if the cans, their spindles and hoods during the trimming and annealing treatment are not moved by the turntable and the can is rotated at high speed about its own axis. In such a case, the laser beams may bs used to effect trimming and annealing of the edge region.

During such stationary operation it is expedient to provide a plurality of annealing and trimming zones operating simultaneously, each of which has a separate laser beam device, so that a large number, say sixteen, cans may be trimmed and annealed simultaneously. During the time in which the treated cans are removed and replaced by untreated cans, the laser beam is deflected by a mirror 34 shown in Fig. 1.

In Fig. 1, there is shown a laser beam source 30, an optical system 31, and a laser beam 33, which beam is directed along the radius 32 towards the axis of rotation 2 of the turntable 1. Laterally of the laser beam, the deflecting mirror 34 is pivotably mounted about an axis 35. The mirror has a vane fixedly secured thereto which is arranged in the angular region of two air jet nozzles 38 directed towards one another. The air jet nozzles 38 are connected alternately, by means of a valve control device 39, 40 to a source of compressed air. This permits the mirror to be pivoted extremely rapidly, with great sensitivity, into and out of the path of the laser beam 33. Stops 36 and 37 limit the pivotal movement of the mirror.

To produce a clean accurately trimmed edge, the best results are obtained using a high energy laser beam. With a high energy laser beam, it is possible to direct the laser beam directly against the trimming line. If a lower energy laser beam is used, a hole of relatively large diameter is produced at the outset of the trimming operation.

In such a case, it is expedient to proceed in a manner described with reference to Fig. 3.

The laser beam is first directed against a point 67 in the end region 63 of the can to be severed, which point is axially spaced from the trimming line 64. On commencement of the cutting operation, a hole 67 is produced in the can 62.

The can is then raised a short distance 68, whereupon the laser beam cuts open the sheet metal to the trimming line 64. Subsequent rotation of the can causes a neat trim to be effected along the trimming line 64. In practice the tin 62 is already rotating so that the cut line 68 is, in practice, a helical line which tangentially merges into the trimming line 64.

The circumferential dimension of the aperture in the protective hood 74 (Fig. 4) to provide simultaneous annealing and cutting must be larger than is necessary merely for trimming using a combined laser beam 76.

This angle 81 is expediently 1 20', that is to say, an arc of 60 on either side of the laser beam.

The control of the pivotal movement of the mirror 34 can be effected with the pneumatic switch 39, 40. Switching may be effected within one-tenth of a second. The deflection of the laser beam is, however, only necessary when the production line has stopped or is being used intermittently. An example of this latter case is when with the pivotal axis of the can is fixedly secured to a frame during the treatment with the laser beam.

Since cans generally have relatively thin wall thicknesses, relatively weak lasers of, for example 150 W, per station may be used.

The cutting speed of the laser with conventional thin sheet metal is about 90 m/min., which is substantially greater than the cutting speed of conventional mechanical trimming devices.

With intermittent operation, it is possible to simultaneously trim and anneal sixteen cans at a time. Even allowing for locating the cans in the working position and lowering and raising the protective gas hoods as well as the actual cutting and annealing operation. Some 650 cans/min may be treated in this manner.

The laser is therefore constantly on since during the change-over of cans it is deflected by the mirror 34.

Claims (9)

1. An apparatus for use in the production of cans, more especially in the production of cans which are shaped by stretching a cuplike sheet metal component, the edge region of the can so produced requiring simultaneous trimming and annealing treatment to permit an edge flange, the apparatus comprising retaining members for the cans, which retaining members are rotatable at an adjustable speed about the axis of the can retained thereon, the retaining members being displaceable through a treatment zone, and a laser beam system including a laser beam source producing a laser beam for effecting at least the trimming treatment, said source directing said laser into the region of the cans where trimming is to be effected wherein a displaceable protective gas hood comprising an inner and an outer portion, the hood, in use overlapping the edge of the can to be treated, the hood being provided with a window around its circumference aligned with the laser beam and permitting the laser beam to pass therethrough.

2. An apparatus as claimed in claim 1 wherein the laser is continuously operating.

3. An apparatus as claimed in claim 1 or 2 wherein the hood is non-rotatable and is displaceable through the treatment zone with the retaining members, the window in the hood having a width in a direction parallel to the can axis corresponding to the width of the region of the can to be annealed and extending arcuately in the circumferential direction on each side of the laser beam through an angle of between 30 and 60t.

4. An apparatus as claimed in claim 1, 2 or 3 wherein a mirror is interposed between the protective gas hood and the laser beam source, the mirror being pivotable or displaceable so as to deflect the beam from the window of the hood.

5. An apparatus as claimed in any preceding claim wherein the laser beam comprises a bundle of sharp and beam portions which are focussed at the point of impingement of the beam on the can body and further beam portions which are not so focussed.

6. An apparatus as claimed in any preceding claim wherein a laser beam optical system is associated with the laser beam source, the optical system being so located with respect to the protective gas hood that the focal point of the laser is located in the region of the protective gas cloud on a line connecting the can axis to the laser beam source.

7. An apparatus as claimed in any one of claims 1 to 5 wherein the retaining members and the laser beam source are displaceable relative to one another in the direction of the can axis from an initial position by a predetermined section to a region of the edging line.

8. An apparatus as claimed in claim 1 wherein the annealing is effected by means of the laser beam.

9. An apparatus for use in the production of cans constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.