Method and apparatus for making can bodies from sheets

Plane, rectangular sheets (10) are moved through between a driven bending roll (32) and a plurality of back-up rolls (34) and are bent round the bending roll (32) by these rolls and a plurality of pressure rolls (52, 56) disposed behind the bending roll (32) and back-up rolls (34). The almost completely rounded sheet (10) is bent resiliently away from the bending roll (32) by a deflecting member (62) as a result of which the front edge (10a) of the sheet is prevented from re-entering the gap between the bending roll (32) and the back-up rolls (34) before the rear edge (10b) of the sheet has travelled through this gap. Then the deflecting member (62) is moved back into its position of rest so that the front region of the sheet (10) springs back in the direction of the bending roll (32) and as a result is again gripped by the bending roll (32) and the back-up rolls (34) and moved through between them. When the front edge (10a) of the sheet (10) has reached the gap between the last two pressure rolls (56), all the pressure rolls (52, 56) are lifted. Then the sheet (10) is conveyed from a rounding station (31) to a positioning station (69). The sheet (10) continues to be rotated by the bending roll (32) until its front edge (10a) is arrested by catching levers (68). The rounded sheet (10) is now stripped axially off the bending roll (32).

The invention relates to a method of making sheets round, particularly for 
can bodies, each sheet having a front and a rear edge which are 
subsequently connected to one another, particularly welded, wherein each 
sheet travels, with its front edge leading, between a driven bending roll 
and a plurality of back-up rolls and, assisted by at least one additional 
shaping element disposed behind the bending roll, is bent round the 
bending roll, the sustantially completely rounded sheet being resiliently 
widened as a result of which the front edge is kept away from the bending 
roll and the back-up rolls while the rear edge travels through between 
them. The invention further relates to an apparatus for carrying out this 
method. 
In a known apparatus (DE-A 33 30 171) for carrying out such a method, 
following on a feed station consisting of two rolls and two slide members 
between which the sheets are fed is a preliminary bending station which 
likewise comprises a pair of rolls with one wedge-shaped bending member in 
front and one behind. Disposed behind that are two converging shaping 
members which are likewise wedge-shaped and which guide the sheets 
individually into a roll gap between an uppe and a lower bending roll. 
Disposed behind the roll gap is a further wedge-shaped shaping member 
which deflects each sheet downwards as it emerges from the roll gap so 
that it is laid round the lower bending roll. The lower one of the two 
shaping members disposed in front of the roll gap is hook-shaped so that 
it catches the front edge of the sheet and holds it while the rear portion 
of the sheet continues to run through between the bending rolls. As a 
result, the front edge of the sheet is prevented from re-entering the roll 
gap; the cylindrical sheet-metal member being formed widens out until the 
rear edge of the sheet has travelled through between the two bending rolls 
and then comes to a standstill bearing against the shaping member disposed 
behind the roll gap. Disposed below the shaping members are conveying 
pawls which finally push the cylindrical sheet-metal members axially away 
from the bending rolls into a guide with two grooves in which the front 
and rear edges of the sheet are guided in such a manner that they can be 
welded together behind it, overlapping one another. 
This known apparatus and the method which can be carried out thereby have 
generally useful results if the diameter of the fully rounded sheet-metal 
member or body is very great in relation to the thickness of the sheet and 
the requirements regarding the precise rounding of the sheet-metal member 
are not too high, particularly in the region of its front edge. 
With a relatively large thickness of sheet and/or relatively small diameter 
of the sheet-metal member, however, it becomes increasingly noticeable 
that the fully rounded sheet-metal members remain nearly plane in the 
region adjacent to their front edge and also to a certain extent in the 
region adjacent to their rear edge, but at least have a radius of 
curvature there which is considerably greater than the radius of the 
sheet-metal member as a whole. These inadequately rounded marginal regions 
can still be accepted in many cases if they are subsequently welded 
together with an overlap. Sometimes, however, difficulties arise even 
then; but such inadequatly rounded marginal regions have proved 
particularly disturbing in sheet-metal members, the front and rear edges 
of which are butt-welded together, for example by means of beam welding. 
It is therefore the object of the invention to develop further a method of 
the type described at the beginning as well as an apparatus suitable for 
carrying out the method, in such a manner that the radius of curvature of 
the rounded sheet-metal member in the region of the front and rear edges 
coincides more precisely with the prescribed radius of curvature even when 
can bodies with a comparatively small diameter are produced from 
comparatively thick sheets. 
According to the invention, the problem is solved, so far as the method is 
concerned, in that, while the driven bending roll continues to rotate, the 
resiliently widened sheet is allowed to relax again and the front edge is 
again allowed to travel through between the bending roll and the back-up 
rolls, following on the rear edge. 
In contrast to the presupposed prior art, therefore, the front edge of the 
already largely rounded sheet-metal member is not finally caught in front 
of the roll gap which is formed between the bending roll and the back-up 
rolls and through which it has already travelled, but is held back until 
it can no longer come into an overlapping position with the rear marginal 
region of the sheet. As soon as the rear edge of the sheet has at least 
substantially travelled through between the bending roll and the back-up 
rolls, the sheet is released again in its front region so that it again 
travels through between the bending roll and backup rolls, more or less 
closely behind the rear edge, and in the course of this is given a radius 
of curvature which is better adapted to the diameter of the finished 
sheet-metal member. 
In a preferred way of carrying out the method according to the invention, 
in order to widen the sheet resiliently, its portion following on the 
front edge is moved away from the inner bending roll at least 
substantially counter to the entry direction. It would also be possible, 
however, to capture the front edge of the sheet in the known manner with a 
hook-shaped member provided this is so shaped and movable that it releases 
the front edge of the sheet in good time for the second passage between 
the bending roll and the back-up rolls. 
In the method according to the invention, the front edge--which has 
travelled through between the bending roll and the back-up rolls for the 
second time--of the fully rounded sheet can be caught after the 
displacement and the sheet can be pushed axially away from the bending 
roll into a guide in which the front and rear edges are brought into a 
position in which they are connected to one another, particularly welded. 
These method features--known apart from the second passage of the front 
edge of the sheet--can be further developed according to the invention in 
that the front edge is caught, following on the second passage between the 
bending roll and the back-up rolls, only after it has travelled, also 
through between at least one additional shaping element and the bending 
roll for the second time. As a result, the accuracy of shape of the 
rounded sheet is still further improved in the region adjacent to its 
front edge. 
The procedure last described can be perfected in that, beginning with the 
first passage of its front edge between the bending roll and the back-up 
rolls, the sheet is allowed to cover a distance of about 420.degree. to 
480.degree., preferably 440.degree. to 460.degree. round the bending roll, 
under the action of the at least one additional shaping element. 
Finally, it is an advantage if the sheet is then freed from the action of 
every additional shaping element, is moved from the rounding station into 
the positioning station, further rotated, and its front edge only caught 
after approximately two complete revolutions. In this manner, the rounded 
sheet can be brought particularly accurately into a defined position in 
which it can be prepared for further processing, particularly for the 
butt-welding of its front and rear edges. 
An apparatus which corresponds to the known one described in that it is 
equipped with a feed section for the feed of plane sheets, a bending roll 
and at least one additional shaping element disposed behind that, is 
particularly suitable for carrying out the method according to the 
invention. According to the invention, such an apparatus is further 
developed in that, in order to widen the partially rounded sheet, a 
deflecting member is provided which can be moved away from the bending 
roll at least substantially radially. 
In a preferred form of embodiment, the deflecting member has a 
sickle-shaped cross-section, is adapted, by its concave side, to the 
bending roll and bears at least approximately against it when it assumes 
its position of rest. During the rounding, the sheet can be moved over 
such a deflecting member, without disturbance, until its front edge has 
again approached so close to the roll gap between the bending roll and the 
back-up rolls that the front region of the sheet has to be deflected away 
from the bending roll by the movement provided for the deflecting member. 
Other forms of embodiment of the deflecting member are, however, also 
conceivable. Thus the deflecting member could be formed by a sector of the 
bending roll itself, which could be extended radially, or by an 
electromagnet which is disposed outside the region where the sheet is 
rounded round the bending roll and which, in the magnetized state, 
attracts the front region of the partially rounded sheet. 
Regardless of how the deflecting member is formed in detail, an 
advantageous further development of the invention consists in that at 
least one additional shaping element disposed behind the bending roll or 
back-up rolls is resiliently supported at least substantially radially 
with respect to the bending roll and comprises a pressure roll. As a 
result, it is possible to exert considerable forces, which are radial with 
respect to the bending roll, on the sheet without an appreciable 
resistance being opposed to its movement round the bending roll. 
Behind the bending roll and the back-up rolls, a plurality of pressure 
rolls, which are resilient in various directions which are at least 
substantially radial with respect to the bending roll, are preferably 
disposed on a common carrier which is adjustable, as a whole, towards the 
bending roll and away from it.

The apparatus illustrated serves the purpose of making plane, rectangular 
sheets 10 of tin plate with a thickness of 0.3 mm for example, into round 
can bodies with a diameter of 40 mm for example. The sheets 10 each have a 
front edge 10a and a rear edge 10b which, after the rounding, should be 
disposed parallel to one another with slight spacing; the rounding should 
extend as uniformly as possible as far as these two edges 10a and 10b. 
The apparatus illustrated has a feed section 12 with a loading station 14 
in which the sheets 10 are inserted individually. Extending below the 
loading station 14 is the upper strand of a conveyor chain 16 which can be 
driven step-by-step by a drive shaft 18 and comprises pusher dogs 10 at 
intervals corresponding to the length of the sheets 10. Extending from the 
loading station 14 are parallel guide rails 22 which guide the sheets 10 
at both sides as well as at the top and bottom, as far as a roll gap 
between two horizontal conveying rolls 24 and 26 disposed vertically one 
above the other. The upper conveying roll 26 is mounted on a vertically 
adjustable conveying-roll carrier 28 which is resiliently preloaded 
downwards. Both conveying rolls 24 and 26 can be driven by a motor, not 
illustrated, through a gearbox 30 to which the drive shaft 18 is also 
connected. 
Disposed behind the conveying rolls 24 and 26 are a bending roll 32 and a 
plurality of back-up rolls 34, the axes of rotation of which are likewise 
disposed horizontally and parallel to one another but in such a manner 
that the plane defined by the axes converges upwards with the vertical 
plane in which the axes of rotation of the two conveying rolls 24 and 26 
lie. The bending roll 32 is called a bending roll because the sheet 10 is 
rolled round it; this bending roll 32, like the lower conveying roll 24, 
is mounted in a fixed position and can be driven in rotation, in the same 
direction as this, from the gearbox 30. The outer back-up rolls 34 have a 
considerably smaller diameter than the bending roll 32 and are mounted on 
a roll carrier 36 which is adjustable radially with respect to the bending 
roll 32, according to the characteristics of the sheet 10, particularly 
the sheet thickness. 
Behind the bending roll 32 and the back-up rolls 34, a carrier 38 is guided 
on a stationary guide 40 which extends horizontally and transversely to 
the bending roll 32 and the back-up rolls 34. The carrier 38 is preloaded 
by a spring 42 which tends to pull it away from the inner bending roll 32; 
this spring 42 is counteracted by eccentrics 44 which are secured to a 
shaft 46 driven from the gearbox 30 and each of which can roll on a roller 
48 mounted on the carrier 38. Pivotally mounted on the carrier 38 is a 
shaping element 50 on which a pressure roll 52 is mounted coaxially. The 
shaping element 50 is adjustable and is resiliently preloaded in such a 
manner that the pressure roll 52 tends to roll on the bending roll 32. 
Guided on the carrier 38 for displacement substantially radially with 
respect to the inner bending roll 32 are two further shaping elements 54 
on which pressure rolls 56 are mounted, the diameter of which corresponds 
substantially to that of the back-up rolls 34 and is considerably smaller 
than the diameter of the pressure rolls 52. The shaping elements 54 are 
likewise adjustably preloaded in such a manner that the pressure rolls 56 
tend to roll on the bending roll 32. 
Secured to the drive shaft 18 is a cam plate 58 which controls a bell-crank 
lever 60. Secured to the bell-crank lever 60 is the one end of an 
elongated deflecting member 62 of sickle-shaped cross-section which is 
disposed parallel to the bending roll 32. In FIGS. 2 and 4, the deflecting 
member 62 is illustrated in a position of rest in which it bears at least 
approximately against the peripheral surface of the bending roll 32; as 
shown in FIG. 3, the deflecting member 62 can be moved out of this 
position of rest, substantially radially away from the bending roll 32, in 
the direction of the lower conveying roll 24. 
Also controlled by the cam plate 58, according to FIG. 1, is a pivotable 
bearing block 64 on which a back-up roller 66 is mounted to support the 
bending roll 32. 
According to FIG. 1, a group of hook-shaped catching levers 68 is mounted 
for pivoting about a stationary pin 70, substantially opposite the back-up 
roller 66 with respect to the bending roll 32. The catching levers are 
controlled by cam plates 72 which are secured to the shaft 46. 
Constructed parallel to the axis of the bending roll 32 and below it is a 
removal section 74 on which pivotable catches 76 can be moved backwards 
and forwards. Likewise disposed parallel to the axis of the bending roll 
34 and in axial continuation thereof, adjacent to the observer in FIG. 1, 
is a guide 78 which has a groove 80 and 82 respectively in each of its two 
sides and as a result has a substantially Z-shaped section. 
The apparatus described works as follows: 
During each working cycle of the apparatus, a sheet 10 is conveyed from the 
loading station 14 to the conveying rolls 24, 26 and gripped by these. 
During the next working cycle, the sheet 10 is conveyed by the conveying 
rolls 24, 26 to the bending roll 32 and the back-up rolls 34, is gripped 
by the pressure roll 52 and is bent round the bending roll 32. In the 
course of this, the deflecting member 62 at first assumes the position of 
rest illustrated in FIG. 2, in which the sheet 10 runs onto the deflecting 
member 62 during the rounding. Immediately afterwards, the deflecting 
member 62 is moved out of its position of rest as shown in FIG. 2 into its 
position remote from the bending roll 32 as shown in FIG. 3. As a result, 
the front edge 10a of the sheet 10 is prevented from striking against the 
rear region of the sheet and entering, together with this, the gap between 
the bending roll 32 and the back-up rolls 34. As soon as the rear edge 10b 
of the sheet 10 has travelled through the gap between the bending roll 32 
and the back-up rolls 34 during continued rotation of the bending roll 32, 
however, the deflecting member 62 is moved back into its position of rest 
so that now the front edge 10a of the sheet 10 re-enters the gap between 
the bending roll 32 and the back-up rolls 34 and travels through this as 
well as through the gap between the bending roll 32 and the first pressure 
roll 52. 
When the front edge 10a has reached the gap between the two pressure rolls 
56, the operation of rounding is regarded as terminated and the carrier 38 
is moved away from the bending roll 32 so that all the pressure rolls 52 
and 56 lose contact with the sheet 10 as shown in FIG. 4. The sheet 10 is 
then pushed from a rounding station 31 into a positioning station 69 by a 
catch 76. As a result of continued drive of the bending roll 32, the sheet 
10 then continues to be rotated until the hook-shaped catching levers 68 
engage in the gap which has remained open between front edge 10a and rear 
edge 10b of the sheet. As a result, the rotation of the sheet is ended and 
at the same time the back-up roller 66 is moved away from the bending roll 
32 so that the sheet can now be pushed by one of the catches 76 axially 
away from the bending roll into the guide 78, the front edge 10a entering 
the groove 80 and the rear edge 10b entering the groove 82.