Chaos of war resulting in
supply problems for Napoleons troops at the front prompted the development of
sterilizable
sheet metal packing in the
year 1810.
Chaos of war resulting in
supply problems with tin and its alloy (solder) for the tinplate can production
were
a decisive factor in 1943 for the development of a jointing technique for can
body production by means of
resistance welding.
Tin and lead became scarce commodities,
so that uncoated base material “blackplate” with lacquered
surface inevitably
became an alternative
to the popular hot-dipped tinplate. Under extreme
pressure
L. Schuler, Göppingen/ Germany
developed a semi-automatic carousel
welding
machine during the
Second
World War, similar in construction to their
existing soldering machine type BAX. The body jointing
edges
were
welded together with overlapping by means of a “moving roller” on a stationary copper
mandrel.
The
internal as well as external protection of
these black plate cans
was satisfactorily achieved through
heavy lacquer coats. Although this did not
retain the visual effect of the
tinplate, it did
guarantee the
provision of the required packing material.
obvious thing to take a closer look at the jointing technique “welding” for use in tinplate packing.
Mr. Dickmann, former Air Force officer from Ulm / Germany, equipped an old “bombed-out” spot-welding
machine with rollers an a Z-rail. Thus, he empirically developed a technology which made it possible to
shear off the tin oxide on the copper rolls by means of the cutting edges of the body ends, producing a
reasonable welding seam connection for those times. Manufacture with several semi-automatic machines
enable a more or less satisfactory production of aerosol cans which slowly established themselves on the
market during those years.
At this time, the management of the can factory Ernst
& Co., Küsnacht / Switzerland, saw the opportunity
to manufacture this new
can for the Swiss market. A welding machine “System Dickmann” was acquired in
1953. At the same time, the
writer
(then Assistant Manager at
Ernst & Co.) was instructed to study this
technology which was new for the
tinplate industry. It soon became apparent, that production with this
system could only be undertaken with specially trained staff, i.e. that a fundamental improvement
of this
technology was unavoidable.
With the knowledge of the known losses through long current- carrying distances from the transformer to
both welding rollers, an arrangement was chosen in accordance with figure 1.
It was possible to weld the
bottom seam indirectly with a roller transformer (loss almost 0) in accordance
with figure 2.
In addition to the external copper rollers, extensive
experiments were also made inside the cans with inert
electrode
materials
(tungsten rings).
The evaporation of the tin in the welding spot area led to a
non-electro
conductive oxide
layer on the welding rollers. Welding experiments
in a water bath, liquid tin bath as well
as inert gas dome were not
able to
improve the irregularities of the individual welding spots due to the
continuous build-up of tin oxide on the
welding rollers. These lengthy and
expensive experiments exhausted
the
provided budget and led to the discontinuation of the development program. Due
to the lack of necessary
funds, the writer was now limited to performing
principle experiments
using the existing equipment. Further
experiments were
conducted privately during spare time
with the
help of a company mechanic, electrician
and electronic engineer, but
they always failed due to the irregularity of the
welding through tin
oxide
diffusion in the electrode material. A well
known intermediate electrode system with copper
band could not
be realized due to lack of the necessary band material, so an experiment was made using stripped,
commercial electrical copper wire with a 1.5 mm² cross section. The welding seams immediately showed
the desired
irregularity, thus determining
that the realizable system for commercial tinplate welding had
been found.
with the experiment set-up resulted in such additional costs, that the writer regarded this type of system
as too expensive. In addition, the political trouble spots in Korea and Hungary resulted in high prices on
the raw material stock market, and the recycling of contaminated copper wire was not taken into
consideration in the calculation a this point in time. Due to the establishment of an own engineering
company, the financial means had to be invested in other developments which could be realized in
short-term returns. The mechanic and electrician participating in the experimental series applied for a
Swiss patent (figure 3) for this process at their own expense and subsequently sold it to SOUDRONIC
for 3'000.— Swiss Francs.
The detailed further development at various levels led
from round wire
► elliptical wire
► WIMA to today’s
SUPERWIMA system
(figure 4),
which, as
a well known fact, is widely used worldwide.
As an alternative to the wire system, Germann+Frei AG applied for a patent for a further concept in 1964.
The envisaged goal was to obtain an economical process at low electrode material costs. The usual seam
overlapping of 4 mm was divided into 2 mm on each end edge according to (figure 5).
The thin, and thus reasonably priced hard copper electrode discs required for the welding process, could be
arranged on solid contact plates directly above the welding transformer (figure 6).
An uniform, optimum welding
quality was achieved through the
continuous mechanical cleaning of the two
3 mm
thick
electrode discs of the
same diameter. The direct current modulation system used via capacitor
discharge
with integrated pressure controls via an oscillating
solenoid
permitted the welding of tinplate,
TFS,
as well as aluminium. A welding spot cadence of 800
spots per second could be achieved with this
system as early as 1966.
problem-free protective coating (as a result of the omission of a cutting edge inside the can), this
development was abandoned on the one hand, due to financial reasons and, on the other hand,
due to the poor appearance in the seam area.
in the seventies. The knowledge of the significant amounts of copper wire required for production, in
connection with recycling and high machine costs, again prompted the idea of breaking away from the
system using the intermediate electrode. As had already been performed in the experimental series at
Ernst & Co. / Switzerland, inert electrode materials such as tungsten, molybdenum and TZM-alloys were
used for the experiments during this development. Welding spot structures with a high degree of regularity
in the grain structure were achieved by optimizing the weld current, welding pressure and the high cooling
capacity in the welding rollers. The high seam quality with greatly limited welding parameter required,
could not be guaranteed with certainty over a time frame desired by the user of at least one work shift, even
with this inert electrode materials. This fact led to the discontinuation of the experimental series with theuse
in a production machine due to high costs.
After the laser
technology development in the armaments
industry found its way into the civilian sector
and was
used commercially in various
industrial groups, it seemed
the obvious thing to perform an experiment
for its use in the sheet
metal packing field.
prompted SAURIN in France, and an engineering team from the Stoffel Group in USA to use the laser
technique for butt welding rounded body blanks (figure 7), in the second half of the seventies.
The offer to develop the
mechanical part for the Stoffel Group’s system was declined by the writer on
the
basis
of his
knowledge of the problems to be expected. Extensive and
complicated experiment set-ups
were
unavoidable. In the
majority of today's
packing processes, sheet metal thickness of between
0.12 mm to 0.3 mm
are used,
and the focal
spot or focal line must be focused in the range of 0.1 mm to
0.2
mm to connect
the butt
jointing sheet metal edges.
The high demand on the
precision of jointing edges can hardly be realized using the conventional
cutting
technique
for
larger cans in the packing industry. The active
pressure lacking after the heat-up process
-
based
on physics – results
in a
reduction of the welding cross section by 20 to 30 % compared to the
sheet
metal
thickness. Due to
the lack of
jointing pressure, it is practically
unavoidable that the
homogeneity of the
welding
points is worse in
comparison to the laminated body blank material,
whereby
the jointing spot
represents the
weakest point of the
body with this technique. Development
expenditures
in double digit millions have not
achieved a commercially
usable
solution, and an application of this jointing
technology for the sheet metal
thickness used in the packing
industry is highly unlikely.
Presently, it appears that
technology is continuing in the same familiar manner. Not much is happening
as
there
are no alternatives. Experiments
are still being made to improve the existing welding process with
intermediate
electrodes.
However, the majority of the can manufacturers would
prefer a
more economical
solution.
