Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~ ~e~L cl~yQ~a on~tal ~ubes
The invention relates to a process for continuous application
of a protective layer to cover a longitudinal weld seam of
5 metal tubes on a welding machine with a welding arm, an
application arm connected to the welding arm, removable means
fQr the transport of the metal tubes lying and to end in an
axial direction and an application device for the protective
layer. The invention also relates to a process for the
10 performance and an application of the process.
Welding machines are known which have an application system
fitted "in line" which applies a protective strip to the
longitudinal weld seam of metal tubes, in particular
15 longitudinally welded tins and cans. In principle, these
differ by the application of a lacquer and a powder which are
processed in situ to give a seam-covering layer.
Depending on machine type, the lacquer is applied from above
20 or below, where the metal tube to be processed normally hangs
from an application arm or for application in the lower area
stands on a conveyor belt, and is transported in the
longitudinal direction of the application arm.
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25 The lacquer can be supplied without air at high pressure
through tubes of small diameter to the spray nozzle, atomised
with an air flow or in another variant applied with a wheel.
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The weld seam is covered with a wet lacquer, and the
resulting dry layer is around lO ~lm thick but relatively
porous in comparison with a white inner lacquer.
5 Furthermore, a dlsadvantage with the use of known lacyuer
application processes is that the tips o~ the butt and matrix
welded points are not covered with lacquer, as it flows off.
In other known application devices on welding machines, the
10 inner longitudinal weld seams of metal tubes are protected in
that a powder strip is applied in even thickness and melted
in situ. The rehardened layers are us-~ally around 30 - 60 ~m
thick and are essentially pore-free.
15 All lacquers and powders known to the specialist in this
application can be used.
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In particular ~or the cans used in the foodstuf~ industry, a
clean sterilization-resistant inner cover of the weld seam lS
20 extremely important. The food-resistance requirement means
~ that the protective layer must also resist hard mechanical
-~ stresses such as the application o~ beading or edging.
Tests for the application of sterilization-resistant "hot-
25 melts", as thermoplastic adhesives are known for short, which
also resist mechanical stress have previously failed in that
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they could not be applied with the technical means adapted to
the conditions.
The inventor has therefore faced the problem of creating a
5 process of the type described above and a device ~or its
performance which allows the use of hot-melt in a simple,
economic and effective manner. All undesirable dif~usion
processes to a filling, in particular food, should be
prevented.
With regard to the process, the task is solved according to
the invention in that a hot-melt mass is fed continuously
through the welding arm as a flexible hot-melt thread,
deflected in the application arm to the inside o~ the
15 longitudinal weld seam of the metal tube, pressed by the
` application device against the hot longitudinal weld seam,
melted and spread homogeneously over its width. Special and
more advanced design forms of the process are the subject of
the dependent patent claims.
The term "hot-melt thread" comprises also cords, wires,
strips, tapes, foils, films etc. and hot-melt masses which
are very long in comparison with their cross-section. In a
special design form, the term "hot-melt thread" also covers a
25 hot-melt piece or compact hot-melt powder without conveyor
medium passed through a flexible guide tube to the
application device. The term "in the application arm" also
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cover~ the ~pace present where applicable between the welding
arm and the application arm.
Simultaneously with the inner coating of the weld seam, a
5 second flexible also pre~erably cold hot-melt thread is
passed continuously to the outside of the longitudinal weld
ssam, pressed by a second application device against the hot
longitudinal weld seam, melted and/or spread homogeneously
over its width. This second hot-melt thread can have the
10 same chemical composition as the first applied internally.
The internal and external coating of a longitudinal weld
seam with a hot-melt layer has the essential advantage that
baking or drying ovens for lacquers with their high
requirements for space and energy can be eliminated.
The arrangement of the weld arm and application arms with the
coating device immediately behind each other has the further
advantage that the longitudinal weld seams of the metal tubes
~passing through are still very hot at the application head,
;20 usually still glowing faintly red. In particular with a low
layer thickness, these can give the metal tube enough
inherent warmth to melt one or both hot-melt threads on
contact and guarantee the required coating without the
provision of further heat. In addition, the still hot weld
25 seam gives a far better adhesion of the protective layer.
With insufficient heat transfer through the hot longitudinal
weld seam, in particular with greater layer thicknesses to be
applied and/or coating on both sides, additiorlal heat is
applied to one or both hot-melt threads in the area of the
application device by the application head being heated, for
example by inductive or resistance heating, a gas flame or a
5 radiator.
If a hot-melt thread, in the most common variant o~ the
design, is supplied and pressed in the ~irection of feed of
the metal tubes, with a corresponding design of the
10 application head, an automatic advance of a hot-melt thread
is possible, primarily on the outside. In particular with
heating of the application head and~or with a hot-melt thread
applied at a steeper angle to the longitudinal weld seam,
this is drawn by at least one additional drive element and
15 pushed towards the application device.
A hot-melt thread pushed between the application head and the
metal tubes approximately vertical to or even in the opposite
direction to the advance of the metal tubes can be pressed
20 against the hot longitudinal weld seam with generation of
friction heat, thus generating further heat.
In a special design form, the application device can he
- designed such that the flexible hot-melt thread melted
25 between the application head and the hot longitudinal weld
seam can where applicable be moved before application in a
rotation movement to eliminate any air inclusions. Thus air
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inclusions which have a negative effact in the protective
layer can be avoided.
In a first preferred variant o~ the material feed, the hot-
5 melt thread is unwound from a storage roll and passed through
the welding arm to the application device. Ths coatiny
process need be interrupted without special measures only
when the roll is finished and the hot-melt thread from the
next roll must be fed in. The end of the hot-melt thread of
10 one roll can for example be bonded e.g. by the attachment of
reserve loops to the start of the hot-melt thread of the
second roll, so as to guarantee a completely continuous
operation.
15 In another preferred variant, the flexible hot-melt thread is
generated in-line from a fluidised mass and then it is
continuously extruded or drawn for example. By the
attachment of reserve loops and by bonding the ends, ~ully
continuous operation is possible, even during any temporary
20 interruptions in the in-line production of hot-melt filament.
The process according to the invention with the essential
feature of the thread-like supply of hot-melt mass through
the welding arm to an application device has numerous
25 technical solutions which however all have as an object an
inner or an inner and an outer sealing of the longitudinal
weld seam of metal tubes.
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In tha application of the protective strip(s), the
longitudinal weld seam can be positioned not only on the kop
~ut also underneath or in any side position. This depends on
5 the position of the application devices, the arrangement of
the transport device and for "in-line" welding machines, the
alignment of the welding wire on the application devices. In
practice, the hot-melt strip is u~ually applied on the top
where the metal tubes are suspended on the transport device.
lO The metal tubes can be advanced further in axial direction
simply by an upper conveyor belt or preferably by two side
conveyor belts.
The hot-melt masses used according to the invention usually
15 ha~e a melting point in the range of lO0 to 300OC, including
those resistant to foodstuffs. The application heads are if
necessary controlled by sensors, brought to a corresponding
temperature and held there by programmed control.
20 The width of the hot-melt strips applied or sprayed on
differs according to the weld seam and in practice lies in a
range of 3 to 20 mm. The hot-melt strips become hard
immediately, with preferred layer thicknesses of lO to 150~1m,
in particular 20 - 50~lm, and the tips created during welding
25 do not press through as can be the case with the lacquer
coating process for example.
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With reference to the device, the task is solved according
to the inven-tion in that the welding arm ha~ at lea~t one
integral supply line for the flexible hot-melt thread, and
the application arm with at least one hollow chamber in the
5 area oE the coating has a melting head to apply the hot-~elt
thread to the inside of the longitudinal weld seam. Special
and more advanced forms of the device are the subject of
corresponding dependent claim~.
10 The application arm is connected in a known manner at one end
to the welding arm of the welding machine and at the other
end is preferably supported to move freely in an axial
direction.
15 The supply line for the hot-melt thread integrated into the
welding arm corresponds to the service channel in known
systems. These can be converted for operation according to
the invention without problem. The same supply line can also
be used for electrical lines or similar where the hot-melt
20 thread with a diameter of 2 - 6 mm for example allows. The
electrical lines or similar can also be arranged in another
supply line in the welding arm.
A large number of hot-melts are suitable for use according to
25 the invention, where foodstuff-resistant hot-melts are of
particular interest, for example based on polyester or epoxy
resinO
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In a preferred design form, the device according to the
invention also comprises an outer second application head to
apply a second flexible hot-melt thread on the outside
5 of the longitudinal seam. Like the inner first melt head,
the outer can also be suitably heated in a known manner, e.g.
by induction, ohmic resistance, a gas flame or a radiator.
One application head, either the inner or the outer, is
10 designed such that the corresponding weld seam cover can be
applied adjustable in the width or thickness by programmed
control. The term "application" here comprises rolling,
spreading or spraying on, where the application head
comprises the corresponding known means for performance, for
15 example a spreader, a scraper or a nozzle.
The pulling or pushing force exerted by the advancing metal
tube on the pressed hot-melt thread can be supported by a
drive element with a rotating or reciprocating movement which
20 is driven electrically, pneumatically or hydraulically. With
a feed of the flexible hot-melt thread vertical to or in the
opposite direction to the advance movement of the metal
tubes, this drive is essential, and the thread must not only
be pulled but also pushed to the application point.
At least the inner first hot-melt thread can be passed
through a flexible tube and protected by this. In the area
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of a drive el~ment, the flexible tube can also be opened so
that for example the torque o a drawiny roller can be
applied. This flexible tube can also be used for the supply,
without compressed air, of pelletised or powdery hot-melt
5 substance which reaches the application head as a single-
piece hot-melt thread and is melted.
The process according to the invention and the device for its
performance have the advantage not previously attainable
10 industrially that a hot melt layer can be applied to the
inside of a longitudinal weld seam of metal tubes adjacent to
the welding wire. Therefore firstly the heat transferr~d to
the metal tube during welding can now be used, and secondly
the longitudinal weld seams of the metal pipes are still
15 accurately aligned. The invention also offers the
possibility of applying a hot-melt protective layer to the
longitudinal weld seam internally and externally. The
resulting elimination of baking and drying ovens for lacquer
and similar, due to the far lower requirements for
20 investment~ space and energy, offers the filler the
possibility of producing his own cans to suit his production.
This in turn brings not only economic but also ecological
advantages that bulky transport of cans is no longer
required.
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The invention is explained in more detail using the design
examples shown in the drawing which are also subjects o~ the
dependent claims. The diagrams show:
- Fig. 1: a partial cross-section through a metal tube
in the area of the longitudinal weld seam
- Fig. 2: a partially cut-away view of a device for
continuous application of a hot-melt thread
- Fig. 3: a detailed representation with external
application of the hot-melt strip, and
- Fig. 4: a part view in axial direction with offset
conveyor belts.
A metal tube 10 partly shown in Fig. 1 has a longitudinal
weld seam 12 which is covered on the inside with a
longitudinal hot-melt strip 14 of polyesterO On the outside
20 runs a corresponding hot-melt strip 16.
In the device for continuous application of the hot-melt
strips to cover the inside ~Fig. 2) and optionally also the
outside of a longitudinal weld seam as in Fig. 3, the metal
25 tubes lying end to end have not been shown for the sake of
clarity. On welding arm 18 of a standard welding machine,
not shown, is arranged a welding wire 26 passing over a
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deflection roller 2~ in the area of face ~0. The welding arm
18 has for example a diameter of 60 mm and is particularly
suitable for welding metal tubes with a diameter of 65 to 200
mm. The diam~ter of the metal tube can therefore be not only
5 slightly but also very much larger than that of the welding
arm 1~. For smaller or larger metal tubes, a correspondingly
dimensioned welding arm 18 could be used.
Coaxially connected with welding arm 18 is an application arm
10 22 which consists for example of a steel tube. The
application arm 22 with the same longitudinal axis L as the
welding arm 18 is attached by fixing means 30.
The metal tubes 10, not shown (Fig. 1), joined together on
15 welding arm 18, run in-line to the application arm 22 where
they are advanced further by an endless conveyor belt 32
guided by two deflector rollers 34,36, one of which is the
drive roller. The conveyor belt 32 has a magnetic support
for the metal tubes and a variable speed drive. The
20 transport device 32,34,36 can be hinged up out of the way.
A hot-melt thread 28 is pressed by an application head 38 of
an application device 40 against the longitudinal weld seam
12 (Fig. 1) of a metal tube, not shown in Fig. 2, which is in
25 turn held down by conveyor belt 32. Under the effect of the
longitudinal weld seam still glowing faintly red and of the
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melting head 38, the hot-melt thread 28 mel-ts and thus forms
a reqular protective layer.
The continuously melting hot-melt thread, squeezed between
5 the hold-down metal tube and the application head, is
automatically pulled forward by the thrust of the advancing
metal tuhe. The hot~melt thread 28 is also in this case
passed over an additional drive element 42 which is arranged
in the application arm ~8 and driven electrically. The hot-
10 melt thread 28 is drawn through a supply line 44 in weldingarm 18 and passed over the rotating drive element 42 from
where it is pushed between the metal tube and the application
head 38.
15 Further details can be seen in the detailed representation in
Fig. 3 extended hy the outer application.
The hot-melt thread 28 does not completely fill the supply
line 44 integrated in the weldiny arm 18. Therefore
20 additional electrical lines 46 can also be passed through the
supply line 44` to an electric motor 48 with gearing 49 for
the drive element 42.
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The cold hot-melt thread 28 is passed throu~h the inner
25 chamber in the application arm 22 in the direction of the
drive element 42 and is partly guided and protected by a
flexible pipe 52.
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Above the metal tube is arranged an outer second application
device 54 with a second application head 56. An outer second
cold hot-melt thread 58 of the same chemical composition as
5 the inner first hot-melt thread 28 is passed between the
second application head 56 and the outside of the
longitudinal weld seam of the metal tube and there also
melted to form an outer hot-melt layer 16 on the longitudinal
weld seam 12.
With a device according to Fig. 3, a longitudinal weld-seam
can be coated internally and externally at the same time.
Fig. 4 shows that the metal tubes 10 are moved by two
15 conveyor belts 32 drawn to them magnetically. The conveyor
belts 32 are offset by an angle a of around goo to the
longitudinal axis L with an approximately vertical median.
The upper longitudinal weld seam 12 is generated by welding
wire 26 shown on the deflecting roller 24.
