CAN BASE REFORMING

Abstract: A method and apparatus for reforming the base profile of a can by using the difference in rotational speed of concentric shafts (A, B) to move a roller (5) radially into contact with the can base. A cam (10) is fixed to one (B) of the shafts and a pair of cam followers (12, 14) is mounted on a support block (6) which is connected to the other shaft (A) via linear bearings (7, 8). The support block also carries the reform roller and causes it to rotate around the can base. (Figure 5)

Description: CAN BASE REFORMING This invention relates to a method and apparatus for reforming the base of a container. In particular, but not exclusively, it relates to a method and apparatus for reforming the base profile of a can having a one-piece can body used for packaging carbonated beverages . Such so-called "beverage cans" typically comprise a side wall, a transition region and a base including a stand bead, an annular inner wall and a substantially dome-shaped centre panel. When such beverage cans are manufactured on a bodymaker, the base formed by the dome station usually has a radially inwardly tapering inner wall for ease of removal from the domer. However, in recent years it has become common practice to reshape this inner wall at least to a vertical profile or, more usefully, to a negative angle, or a hooked or beaded profile. The benefits of reforming the base profile have been demonstrated in terms of limiting dome growth and increasing dome reversal pressure. When the can is pressurised, the dome will "grow" outwards, pushing the metal around the stand diameter so that the stand bead will roll out and the can height will increase. Dome growth is thus a particular problem when the can needs to withstand pasteurisation pressures, such as is the case when the product is beer, for example. Dome reversal pressure is the pressure at which internal pressure from a carbonated beverage, for example, will cause the dome- shaped centre panel to reverse its shape completely from externally concave to externally convex. Although the principles of base profile reforming are well-known, apparatus which has been available in order to carry out the reforming process has not been found to be entirely satisfactory. External base profile reforming which is carried out by applying radially inward pressure to the transition region of the can is well-established but has problems in terms of defining the final shape which is achieved and/or tool removal where a negative angle is formed by pressing the inner annular wall onto a shaped chuck. Internal base profile reforming involves the direct application of a roll against the inner wall so as to reform part or all of that wall to a specific new profile. Internal base profile reforming tooling which is currently available uses complex mechanisms which have a very high rate of wear. This wear is particularly costly in terms of replacement tool parts and, if components are not replaced, will lead to variability in the very profile which is critical to the can's performance. Furthermore, because the tooling is complex, there are typically adjustments which need to be made in the factory to maintain consistency of the reformed profile. This invention seeks to provide a solution to these problems which may be used for both internal and external base profile reforming. According to the present invention, there is provided an apparatus for reforming the base profile of a can, the apparatus comprising: a roller for forming a desired new profile on the can base; and first and second concentric shafts, the first shaft rotating the roller relative to the can, and the second shaft actuating the roller to move radially to engage the can when there is a speed differential between the shafts. Typically, the shafts rotate in the same direction. Since the apparatus uses continuous rotation in the same direction instead of forward and back as in known base reforming apparatus, the mechanism is very simple. By using full rotation, there is no setting required by the factory and the reformed profile is more consistent and the apparatus exhibits less wear. Preferably, the apparatus further comprises a cam or an eccentric for actuating the roller to move radially. The cam or eccentric may be fixed to the second shaft and one or more cam followers may be mounted on the first shaft. Such mounting may be directly or indirectly. In a preferred embodiment, the cam follower or followers is/are fixed to a support block which is attached to the first shaft via linear bearings. Typically, the apparatus is one of a plurality of base profile reforming apparatus each of which is fixed at stations around a rotatable turret machine. In one embodiment, the first shaft rotates +/- two rotations relative to the second shaft in one machine rotation. For example, the first shaft may rotate at six times machine speed and the second shaft may rotate at four times machine speed, or vice versa . It should be appreciated, however, that the actual machine speed is not relevant to the invention. What is essential to the radial movement of the roller is the differential speed between the two shafts . The cam is shaped to control the radial movement of the roller so that there is no need for a separate end stop component, for example. The apparatus may be used for either internal or external base profile reforming. According to another aspect of the present invention, there is provided a method of reshaping the base profile of a can, the method comprising: providing a roller for forming a desired new profile on the can base; providing first and second concentric shafts; rotating the roller relative to the can by means of the first shaft; actuating the roller to move radially to engage the can by driving the first and second shafts at different speeds. A preferred embodiment of the invention will now be described, by way of example only, with reference to the drawings, in which: Figure 1 is a side section of internal base profile reforming apparatus; Figure 2 is a side section of the apparatus of figure 1, at right angles to the side section of figure 1; Figure 3 is enlargement III of figure 1; Figure 4 is a transverse section through the line IV-IV on figure 3; Figure 5 is a trnasverse section through the lije V- V on figure 3; and Figure 6 is a 180° timing layout of a turret machine showing the apparatus at 30° positions around the turret. Figures 1 to 5 show an apparatus for internal base profile reforming of a beverage can having a domed base. The apparatus comprises a base support 1 for supporting a can (not shown) and a profiled roller 5 for reforming the internal base profile. Shafts A and B are concentric, a support block 6 holding the reform roller 5 and being joined to the end of shaft A by linear bearings 7, 8. For simplicity, the drawings show the linear bearings as linear ball bearings. Alternative bearings such as crossed roller bearings may be ideally used. A cam 10 is mounted on inner shaft B and rotates between cam followers 12, 14 which are in turn mounted on the support block 6. Concentric shafts A and B are connected to gears A' and B' respectively. The apparatus is surrounded by a housing 9. Profiled roller 5 is rotated about the can centre by shaft A and gear A to reform the internal base profile. In this example, the can remains stationary, although this is not essential to the invention. In use, gears A' and B' drive shafts A and B respectively to rotate. Typically shafts A and B will rotate in the same direction but at different speeds. Since the cam 10 is fixed to shaft B, cam 10 rotates at the same rotational speed as shaft B. Rotation of shaft A will cause linear bearings 7, 8, support block 6, cam followers 12, 14 and reform roller 5 to rotate at the same speed as shaft A. However, cam followers 12, 14 will also move radially according to their position on the cam. The outer races 7 of the linear bearings are attached to the end of the shaft A so that since shaft A rotates, the support block 6 has a combined motion of rotation due to the rotation of shaft A, and radial movement when the cam followers move around the cam profile. If shafts A and B rotate at the same rate, there will be no radial movement of the cam followers (or the reform roller) . Where there is a difference in the rotational speeds of the shafts, this speed differential will result in the cam followers moving around and thereby following the cam profile. Linear bearings 7, 8 allow for radial movement of the support block according to the cam shape. This leads to radial movement of the reform roller into contact with the can base. This radial movement of the cam followers due to their position on the cam is shown in figure 6, in which the shaft B (and cam) is rotating at four times machine speed and shaft A (with the cam followers) is rotating at six times machine speed. In contrast with prior art base profile reformers, the reformed can shape is set in the tooling. There is therefore no factory setting to be made. Continuous rotation of the shafts and rolling rather than sliding contact reduces wear in comparison with known base profile reformers. Further simplification of the cam design can be made by adding compliance to either or both cam followers. Typically spring loading of the return cam follower against the cam is appropriate. Although this example uses a cam and cam followers, clearly an eccentric, being a specific type of cam, could be used within the scope of the invention. Furthermore, it is anticipated that the invention will also be used for external reforming of the base profile. Finally, the simplicity of the design of this invention make it ideal for combining with other can forming processes, for example die necking. This would avoid the need for two separate stations, one for the necking and another for the base reforming.

Claims: CLAIMS 1. An apparatus for reforming the base profile of a can, the apparatus comprising: a roller for forming a desired new profile on the can base; and first and second concentric shafts, the first shaft rotating the roller relative to the can, and the second shaft actuating the roller to move radially to engage the can when there is a speed differential between the two shafts . 2. An apparatus according to claim 1, further comprising a cam or an eccentric for actuating the roller to move radially. 3. An apparatus according to claim 2 , in which the shafts rotate in the same direction. 4. An apparatus according to claim 2 or 3 , in which the cam or eccentric is fixed to the second shaft and one or more cam followers are mounted on the first shaft. 5. An apparatus according to claim 4, in which the cam follower or followers is/are mounted on the first shaft via linear bearings . 6. An apparatus according to any one of claims 1 to 5 , in which the apparatus is one of a plurality of base profile reforming apparatus each of which is fixed at stations around a rotatable turret machine. 7. An apparatus according to claim 6, in which the first shaft rotates +/- an integer number of rotations relative to the second shaft in one machine rotation. 8. A method of reshaping the base profile of a can, the method comprising: providing a roller for forming a desired new profile on the can base; providing first and second concentric shafts; rotating the roller relative to the can by means of the first shaft; actuating the roller to move radially to engage the can by driving the first and second shafts at different speeds .

Inventors: DVORAK JAN, GOLDING RICHARD MARK ORLANDO, DVORAK, JAN, GOLDING, RICHARD,MARK,ORLANDO
Applicants: CROWN CORK & SEAL TECH CORP, DVORAK JAN, GOLDING RICHARD MARK ORLANDO, METAL BOX PLC, CARNAUDMETALBOX PLC, CROWN CORK & SEAL TECHNOLOGIES CORPORATION, DVORAK, JAN, GOLDING, RICHARD,MARK,ORLANDO
Application year: 2001
Main classification: B21D51
IPC codes: B21D22, B21D51