Rolled edge in cans

An unrollable rolled edge in cans containing a product under pressure wherein a flat edge of the can is turned outwardly orthogonally and rolled within a rolled edge in which the radius of the rolled portion is less than the length of the flat edge confined therein in a plane passing through the axis of the can.

The process for forming an aerosol can in which the rolled edge is unable 
to unroll comprises a reducing operation, known per se, for providing the 
opening of the can with the required diameter, turning back the free edge 
of the can orthogonally in relation to the wall of the can to form a 
stable flange, turning the flat flange back in a second operation to give 
it a frustoconical form and then rolling it in a final operation in a 
manner whereby it is situated within the rolled edge and its profile 
remains straight in a plane passing through the axis of the can. 
The rolled edge, thus formed, cannot be unrolled despite extremely high 
internal pressures. 
The invention is applicable to any pressurized can having a rolled edge in 
which the free end is provided with a straight profile that militates 
against unrolling. The length of this straight portion of the profile is 
preferably greater than the internal radius of the rolled part so as to 
resist unrolling. 
The invention also relates to the apparatus employed and, more 
particularly, to the punch which turns the straight edge back along a 
frustoconical surface, having, as its axis, the axis of the can. This tool 
comprises a neck of triangular profile having one side parallel to the 
vertical wall of the reduced-diameter opening. The angle at the apex of 
the profile of the neck portion is preferably about 35.degree.. 
Referring now to the drawings, the can 1, shown in FIG. 1, has already 
undergone the forming operation which reduced the internal diameter of the 
edge 2 to the required value, for example, 38.1 mm. The edge 2 has also 
been evened out by means of the rotary grinding tool 3, carrying a milling 
cutter mounted about a centering spigot 4. 
The first operation, according to the invention (FIG. 2) comprises turning 
outwardly the upper edge portion 5 of the can 1 into a plane substantially 
perpendicular to the axis of the can 1. 
This operation is carried out by means of the tool 6 which comprises a 
centering spigot 7 dimensioned to be received within the open top of the 
can 1, a ring 8 of larger cross sectional dimension than the open end of 
the top of the can 1, and a curvilinear neck portion 9 joining the 
underside of the ring 8 to the vertical wall of the spigot 7. The spigot 7 
is used accurately to center the can 1 with respect to the tool 6. Towards 
the end of the downward stroke of the tool 6, the edge 2 of the can 1, 
about the open upper end, is deflected outwardly by the neck 9 and follows 
the underside of the ring 8 to extend radially substantially 
perpendicularly from the spigot wall 7. 
FIG. 3 shows the result of this operation in detail. A flange 5 of linear 
profile is formed to extend generally in the plane perpendicular to the 
axis of the can 1. The width of the flange can be varied, amounting to 
approximately 2.5 mm in the illustrated modification. 
The second operation (FIG. 4) is carried out with a different tool 10 which 
essentially provides a cavity 11 of triangular profile for forming the 
neck. To facilitate machining, the tool 10 is made up of several 
components interfitted one with another. In particular it comprises a 
center spigot 12, dimensioned to correspond with the spigot 7 and having 
an axially disposed side wall, and a hollow punch 13 having a central bore 
13.sup.a dimensioned to receive the spigot in sliding relation and 
terminating in an inner wall extending outwardly at an oblique angle with 
the axis of the tool, such as at an angle of about 35.degree. in the 
illustrated modification. 
Upon descent of the tool in the direction toards the can 1, the outwardly 
extending flange portion 5 is engaged by the outer wall 14 of the 
triangular section to turn the flanged portion downwardly at a 
corresponding angle, without changing the shape of its profile. The 
flanged portion thus defines a frustoconical section extending at an angle 
of 35.degree. with the vertical wall of the can (FIG. 5) and which is 
integrally joined to the can via a curvilinear section. 
The tool 15, used for the third operation (FIG. 6), which provides the 
described portion of the can with its final shape, is somewhat more 
elaborate. The central section 16 comprises a terminal portion 17 which 
acts as a centering spigot and which terminates at its upper end with an 
annular, curvilinear, outwardly extending concave neck forming portion 18 
of substantially semi-circular section, facing downwardly in the axial 
direction, the inner wall of which merges smoothly with the outer wall of 
the spigot 17, and having a diameter equal to the external diameter of the 
rolled edge of the can. The central portion 16 is entirely surrounded by a 
matrix 19 mounted for relative axial displacement relative to the central 
portion and to the tool holder 20. Means are provided constantly to urge 
the matrix 19 in the direction towards the inoperative-extended position. 
In the illustrated modification, such means comprises a coil spring 21 
confined in a compressed state within a cavity, with one end of the coil 
spring in engagement with the tool holder 20 while the other bears against 
the back side of the matrix 19. In operative position, the matrix 19 is 
situated in an advanced position under the action of the several springs 
21. 
In response to movement of the tool assembly from inoperative position to 
operative position, the tool holder 20 descends and the matrix 19, the 
bore of which corresponds to the reduced-diameter shoulder of the can, 
comes into contact with the can to effect the desired centered relation, 
thus forestalling any possible deformation during the rest of the 
operation. For this purpose, the cavity portion of the matrix is formed at 
its upper end with an inwardly offset portion which corresponds to the 
contour of the can adjacent its upper edge, thereby to provide a backup 
support for the can during the subsequent shaping operation. As the tool 
holder 20 continues to descend, the springs 21 will be compressed until 
the neck 18 of the terminal portion 17 comes into contact with the top 22 
of the edge of the can 1. Thereafter, the pressure of the tool 15 causes 
the vertical portion of the edge to be rolled from this apex line 22, in a 
manner known per se, to form a rolled portion having a radius which is 
less than the length of the linear flanged portion 5 which undergoes a 
rotation of more than 180.degree., while its linear profile remains 
unchanged. 
After this transformation, the vertical part surrounding the opening of the 
blank 1 at the beginning of the cycle has become enclosed within the 
rolled edge of the can (FIGS. 6 and 7). The width of the flange is 
preferably slightly greater than the internal radius of the rolled portion 
in which it is enclosed thereby to prevent the edge from being unrolled, 
despite the considerable force applied to the valve from within. 
Apart from the application described above, the process of the invention 
has application in other structures wherein it is desired to prevent a 
rolled edge from being unrolled. 
It will be understood that changes may be made in the details of 
construction, arrangement and operation without departing from the spirit 
of the invention, especially as defined in the following claims.