Method and apparatus for making a can body

A method of making a can body is provided. The method comprises forming a ferromagnetic metal blank into a can body preform having adjacent confronting side edges whose edge faces are spaced, magnetizing the confronting edges to have a reverse polarity to each other, so that the confronting edge faces be attracted to each other and brought into abutting relationship to form an abutting portion, and joining the abutting portion. An apparatus for making a can body according to the method is also provided.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for making a can 
body, more particularly to a method and apparatus for making a can body by 
jointing the side edges of a can body preform formed from a ferromagnetic 
metal sheet such as tinplate. 
A can body having a side joint usually has been manufactured by forming a 
can body preform having an overlapped portion by overlapping the opposite 
edges of a metal blank of such as tinplate, and then welding or bonding 
with an adhesive the overlapped portion. The can body of this type has a 
step along the side joint, and thus is disadvantageous in that it is 
difficult to mend satisfactorily the joint with lacquers or the like and 
ensure hermetic sealability of the double-seamed portions of a can formed 
by double seaming top and bottom ends to the can body. 
An art of making a can body by joining, preferably laser beam welding, the 
confronting side edges in edge-to-edge relationship without overlap is 
proposed in U.S. Pat. No. 4,152,573. In case of joining, particularly 
welding of this type, it is necessary to joining or welding the 
confronting edges in such abutting relationship that the edge faces 
thereof are in close contact with each other without substantial gap and 
step therebetween along the whole length, so as to obtain a joint or weld 
which has a thickness substantially equal to that of the metal sheet and 
is free of the step and pinholes. 
It is, however, very difficult to bring the confronting edge faces of a 
relatively thin metal sheet blank of such as tinplate, usually of 0.15 to 
0.25 mm thick into the above-mentioned abutting relationship. 
Accordingly, in the aforementioned prior art the confronting side edges are 
clamped by means of two longitudinal parallel vices which are pressed 
together with clamping screws, so as to ensure the abutting relationship 
free of the gap and the step, that is, to avoid the possibility of 
creating pinholes and a surplus thickness at the weld. 
This type of butt-joining or butt-welding is poor in productivity and 
unsuitable to a high speed production of the can body such as several 
hundreds can bodies per minute, since the confronting edges of the 
respective can body preform must be clamped by screwing, which is 
time-consuming. 
SUMMARY OF THE INVENTION 
The invention relates to a method and apparatus for making a can body by 
joining the confronting side edges of a can body preform formed of a 
ferromagnetic metal sheet in abutting relationship which is suitable to 
high speed production. 
According to the invention there is provided a method of making a can body 
comprising: forming a ferromagnetic metal blank into a can body preform 
having adjacent confronting side edges whose edge faces are spaced, 
magnetizing the confronting edges to have a reverse polarity to each 
other, so that the confronting edge faces be attracted to each other and 
brought into abutting relationship to form an abutting portion, and 
joining the abutting portion. The joining may be preferably laser beam 
welding. 
According to the invention, further there is provided an apparatus for 
making a can body comprising: a mandrel along which a can body preform 
having side edges is transferred, the can body preformed being formed from 
a ferromagnetic metal blank, means for allowing the side edges to confront 
adjacently to each other while the can body preform is transferred, a 
magnet which is disposed at the downstream side of the means for allowing 
the side edges to confront and adjacent a portion of the can body preform 
opposite to the side edges with respect to an axis of the mandrel, so as 
to magnetize the confronting side edges to reverse polarity to each other 
and attract the side edges to each other, whereby the confronting side 
edges are brought into abutting relationship to form an abutting portion, 
and means for joining the abutting portion. The means for joining may be a 
laser beam radiation means which is disposed opposite to the abutting 
portion to form an autogenous weld. 
Other objects and advantages of the invention will be apparent from the 
following description and the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
Referring to FIG. 1, a tubular can body preform 1 is formed from a 
rectangular blank of a ferromagnetic metal sheet such as black plate, a 
surface treated steel sheet, e.g. tinplate, tinfree steel, very-thinly 
nickel plated steel sheet and the like by means of a roll forming machine 
(not shown) or the like located at the left of a mandrel 8. The can body 
preform 1 whose confronting side edges 2a, 2b are spaced is pushed its 
rear edge surface by a finger 10 of a feed bar 9, and transferred one 
after another in the direction shown by arrow A along the mandrel 8. A 
stationary laser beam gun 11 is disposed below the downstream portion of 
the mandrel 8 so as to direct a laser beam 16 upwardly. 
Along the lower end of the upstream portion of the mandrel 8, as best shown 
in FIG. 2, is disposed a guide bar 12 through which the side edges 2a, 2b 
of the can body preform 1 are guided. The guide bar 12 is formed with a 
pair of confronting horizontal grooves 13a and 13b through which the side 
edges 2a and 2b pass respectively. Along both the sides of the upstream 
portion of the mandrel 8 are disposed pushing means 15 for pushing the 
sides of the can body preform 1 against the mandrel 8 which pushing means 
is biased radially, inwardly by means of a spring 14. 
The can body preform 1, with both the sides pushed by the pushing means 15 
and the side edges 2a and 2b passing through the grooves 2a and 2b, 
respectively, and thus forming a gap 3 therebetween, is transferred toward 
the laser beam gun 11 along the upstream portion of the mandrel 8. 
As shown in FIG. 1 and FIG. 3, an elongated permanent magnet 4 is disposed 
above the portion of the mandrel 8 between the downstream end 12a of the 
guide bar 12 and the laser beam gun 11, such that it may magnetize the 
side edges 2a and 2b to a polarity reverse to each other, and thus attract 
the confronting edge faces 2a.sub.1 and 2b.sub.1 to each other against the 
elastic counter-force of the can body preform 1 until the edge faces 
2a.sub.1 and 2b.sub.1 is abutted, that is, in edge-to-edge relationship. 
The magnet 4 may be an electromagnet. 
In case of FIG. 3, the magnet 4 is disposed adjacent the can body preform 1 
such that it extends in the direction of the axis of the preform 1 along 
the opposite side to the gap 3 with respect to the axis, and the south 
pole and the north pole are positioned above the side edges 2a and 2b, 
respectively. 
As shown in FIG. 4, the can body preform 1, after having left the guide bar 
12, is formed with lines of magnetic force 5, thus the side edges 2a and 
2b are magnetized to the north pole and the south pole, respectively, and 
while moving in the direction shown by arrow A, the adjacent confronting 
edge faces 2a.sub.1 and 2b.sub.1 which have been spaced through the gap 3, 
are attracted to each other and abutted. Thus the edge faces 2a.sub.1 and 
2b.sub.1 forms an abutting portion 6, as shown in the can body preform 1 
of dotted lines in FIG. 4, at the upstream side of the laser beam gun 11. 
The abutting portion 6 along the whole length has no substantial gap in 
accordance with the finishing degree of the edge faces, that is, perfectly 
no gap in case of mirror finishing, and no substantial step since the side 
edges 2a and 2b form common inner and outer curved surfaces along their 
inner surfaces and outer surfaces, respectively. 
The abutting portion 6 then is radiated with a laser beam 16 by means of 
the laser beam gun 11, and melt and solidified preferably in an innert gas 
atmosphere to form an autogenous weld 17, and a welded can body 18 is 
made. The weld 17 will have no defects such as pinhole and no step with 
the thickness substantially same as that of the metal sheet blank. The 
invention is suitable to high speed production, since the confronting side 
edges are automatically brought into edge-to-edge relationship as soon as 
the can body preform enters the magnetic field of the magnet. 
The invention is not limited to the embodiment described and illustrated 
which have been given by way of example only. For example, joining may be 
done by applying an adhesive, soldering, brazing or the like.