Abstract by S. Frei/2002

50 years of jointing technology „welding“ in the
packing industry

 

Mr. Siegfried Frei is owner and Managing Director of Frei AG in Wittenbach

near St. Gallen/Switzerland.
His company has been in existence for over 25 years and primarily manufactures
wet lacquer and powder seam coating systems as well as curing systems for
welded can bodies.

 

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
provisio
n of the required packing material.


When the economy in Europe started to normalize gradually at the beginning of the fifties, it seemed  the
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.


As early as 1954 the financial means were made available to build an automatic tinplate welding machine.
With the knowledge of the known losses  through long current- carrying distances from the transformer to
both welding roller
s, 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 mm
²
cross section. The welding seams immediately showed 
the desired irregularity, thus determining that the realizable system for commercial tinplate welding had
been
found.

However, calculations made with two auxiliary electrode wires for welding the can bodies in accordance
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.


Although the process represented an excellent  system due to the  reduced electrode costs and
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.


A patent for a further system with the objective  of “wireless welding” for tinplate was applied for in Germany
in the seventies. The knowledge of the significant amount
s 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.


The desire to eliminate the copper wire as intermediate electrode for reasons of cost and thus to save costs
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.