Note: Descriptions are shown in the official language in which they were submitted.
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WINDING SYSTEM FOR USE IN PLASTIC FILMS PRODUCTION
LINES, IN PARTICULAR EXTENSIBLE PLASTIC FILMS, AND
METHOD FOR WINDING PLASTIC FILM REELS
The present invention refers to a winding system for
use in plastic films production lines, in particular
extensible plastic films, and to a method for winding
plastic film reels.
The extensible plastic films, also referred to as film
stretch, is a product widely used in the packaging
industry, representing the most common type of
packaging in Europe and in the United States.
There are several applications of such types of films
and they cover most of the products used commonly, both
for industrial and domestic purposes.
Plastic films differ according to their composition
which allows obtaining films with different
characteristics among which the toughness, elongation,
tensile strength, elastic memory, resistance to
perforation, and so on and so forth, thus meeting the
requirements of various applications.
Plastic films can be made up of three or more layers
made up for example from mixtures of linear low density
polyethylene (LLDPE), low and very low density
polyethylene (LDPE, VLDPE, ULDPE), metallocene-based
polyolefin (mLLDPE, mPP), ethylene-vinyl-acetate in
various percentages (EVA from 9% to 28%), polypropylene
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homopolymer, random or block copolymer, terpolymer (PP
homo, PP copo, PP ter) or biodegradable materials
(Mater-Bi, PLA).
Therefore, there are various formulations realised
through production lines having combinations of two or
more extruders with the aim of obtaining
stratifications capable of meeting the requirements of
the applications they are intended for.
Depending on the type and the thickness of the film
known are different types of applications, most
important among which are the food industries,
pharmaceutical industries, paper mills, brick and
ceramic industries, mechanical industry, large-scale
distributors, agricultural industry and domestic use.
Such wide variety of use implies an equally wide range
of type of films, both in terms of composition and
thickness, generally varying from 10 pm up to more than
100 pm, and also in terms of winding, which comes in
different shapes depending on the subsequent use the
film is intended for, that is depending on the
subsequent manual use, use in automatic machines, semi-
automatic machines and so on and so forth.
For example, in case of the film stretch type of reels
for industrial packaging, regardless of the
characteristics of the film in terms of mechanical
resistance and elongation to tear, used are particular
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automatic packaging machines, or "palletizers",
arranged on which are stretch reels of specifically
defined size and weight.
In particular, referred to for such type of application
are reels with an overall weight of 12.5 kg which are
wound on cardboard cores approximately weighing 1.25 kg
having an internal diameter of about 76 mm and have a
band width equivalent to about 500 mm.
In the same manner, the reels for manual use, with an
overall weight of about 2.5 kg and width of about 450
500 mm, on the other hand have cores with an internal
diameter equivalent to 50 mm and weight of about 0.5
0.6 kg, thus resulting easier to handle and use without
the help of machines.
Therefore, a serious concern facing the industry is
that of optimising the plastic films production lines
with the aim of obtaining the utmost efficiency of such
lines, automating them most possible to reduce
possibility of mistakes to the minimum, quickening the
production and simultaneously maintaining high
flexibility characteristics.
The flexibility of the lines, in particular, becomes
more and more important considering the fact that in
order to reduce the high storage logistics costs,
transport costs and so on and so forth, there is an
ever-growing tendency to produce, as a matter of fact,
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"just in time". Such production strategy is possible
only if the systems are capable of offering enough
flexibility to produce film reels classified according
to the type of film or winding, with very little waste
of time in particular during the procedures of
modifying the structure or material and during the
start-up procedures.
The plastic films production lines comprise extrusion,
cooling and winding systems made up of a variable
number of extruders, depending on the characteristics
intended to be imparted to the product, arranged
downstream of which are the winding systems which
receive the extruded and cooled film and wind it into
reels.
The extrusion and cooling part is not particularly
difficult in terms of flexibility, given that it is
based on technologies already consolidated over the
years.
However, considering the high costs of such part, there
arises the need to have high production volumes,
considering the fact that the final products have a
very low added value, thus implying the necessity to
rely on large scale production in order to attain
sufficient operating margins.
In order to attain such goal there arises the need to
produce plastic films at extremely high actual speeds,
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close to, if not exceeding, 500 m/min, also due to the
fact that use of materials such as linear polyethylene
allows reaching such speeds from an extrusion point of
view.
The winding systems downstream of the extrusion and
cooling systems, must thus have a sufficient winding
capacity in such a manner to provide for the amount of
film produced over time.
Furthermore, the necessity to produce at high speeds
requires - in case of line production of reels of small
diameter for manual use, that is short in terms of
measurement - very frequent replacements ejecting the
full reel and inserting a new core within very few
seconds of time.
This requirement forcedly limits the production speed,
in that it conditions the entire extrusion process due
to the physical and mechanical constraints caused by
the movements adapted to perform the replacement cycle.
Therefore, in order to enhance the winding capacity in
line, the so called "jumbo" reels - that is reels with
a band equivalent to 500 mm but with an external
diameter up to 500 mm and above - have thus resulted
easier to wind, hence allowing overcoming the
abovementioned limits allowing a considerable
elongation of the times required to replace a reel.
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However, the winding of the film at high speeds,
implies the physiological presence of air trapped
between the turns, thus complicating the subsequent use
of the film itself and in any case representing a waste
of space during transport.
The low added value of such products leads to the cost
of transport having a highly considerable impact on the
production costs, thus also for such reason, alongside
the aforementioned practical reasons of usability of
the films, they require "hard" e and compact reels,
that is without air trapped between the turns.
In particular in case of a film stretch, the aspect of
the film itself, very sticky, implies contact winding,
that is "squeezing out" the reel against a motorised
cylinder which facilitates the ejection of the air
inevitably drawn by the film itself during its winding
motion around the reel core, which would otherwise
remain trapped between the wound turns.
However, the currently known systems performing contact
winding still do not offer satisfactory results when it
comes to the quality of the reels if wound at an
excessively high speed. Given that transport of air,
essentially due to the centripetal force of the
rotating rollers, is proportional to the speed squared,
such problem represents the greatest obstacle to
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obtaining a good winding in case of very fast systems
like the ones used for producing film stretch.
Furthermore, in such systems, during the replacement
step upon completing winding a reel, the cylinder which
facilitates the ejection of the drawn air is not
capable of acting on the reel, in such a manner that
during the winding of the end part of the film there is
an absorption of air which reduces the overall quality
of the reel.
A general object of the present invention is that of
overcoming the abovementioned drawbacks of the prior
art in an extremely simple, inexpensive and
particularly functional manner.
Another object of the present invention is that of
providing a winding system for use in plastic films
production lines capable of guaranteeing an ideal
quality of the wound reels though operating at high
production speeds.
A further object is that of providing a winding system
for use in plastic films production lines requiring
less amount of time for the steps of ejecting the full
reel and inserting a new core.
Last but not least, an object of the present invention
is that of conceiving a method for winding plastic film
reels capable of guaranteeing an ideal quality of the
wound reels though operating at extremely rapid cycles.
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Regarding the abovementioned objects, according to the
present invention, conceived was a winding system for
use in plastic films production lines and a method for
winding plastic film reels having the characteristics
outlined in the attached claims.
The structural and functional characteristics of the
present invention and its advantages with respect to
the known techniques shall be clearer and more evident
from an observation of the following description,
referring to the attached drawings, which show a
winding system for use in plastic films production
lines made according to the innovative principles of
the invention itself.
In the drawings:
- figure 1 shows a side view of a winding system
according to the present invention;
- figure 2 shows a sectional schematic view of the
winding system of figure 1;
- figures 3 to 7 show the various steps of the cycle
for winding and replacing the plastic film reels
according to the present invention.
Referring to the drawings, the winding system in
question is indicated in its entirety by 100.
The winding system 100 for use in plastic films
production lines comprises a star-shaped winder holder
10 constrained against which is a plurality of winders
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11-13 arranged around the same 10, each provided with a
reel core 16 wound around which is a reel 19 of plastic
film 18.
Preferably, the winders 11-13 are at least three so as
to be able to simultaneously perform the operations of
winding the reel, ejecting the full reels and inserting
the cores on which the new reels are to be wound.
In the case of the illustrated embodiment comprising
three winders 11-13, the arrangement around the star-
shaped winder holder 10 can be for example with pitches
respectively of 120 .
The winders 11-13 are preferably controlled by means of
alternating motors, for example controlled by an
inverter, and installed coaxially.
Furthermore, provided for at one end of the winders 11-
13 is a star-shaped flange 14 which holds the
tailstocks 15 which support the reel cores 16 of the
winders 11-13, which are preferably expansible.
The passage of compressed air for the pneumatic
expansion of the reel cores 16 is ensured by a rotating
seal installed in the support of the shaft of the same
16.
The tailstocks 15 are preferably provided with
pneumatic movement.
The star-shaped flange 14 is shaped in such a manner to
facilitate the passage of a core 17 wound around which
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shall be a film 18 upon the subsequent replacement and
a fully wound reel 19 of a film 18 respectively.
For such purpose, the flange 14 has a plurality of
cavities substantially of the same size as the section
of a reel core 16 and/or substantially of the same size
as the section of a full reel 19.
At a determined so-called angular winding position,
which in the illustrated embodiment corresponds to the
position in figure 3 in which the first winder 11 is
found, provided for is a suitable motorisation adapted
to control the winding of the film 18 at a determined
winding speed around the winder 11 which is at such
angular position.
Further provided at the angular winding position is a
drawing and pressure device 36 adapted to regulate the
tensioning of the film 18 during winding.
Such drawing and pressing device 36 comprises at least
one cylinder 20 which during the winding of the film 18
on the winder 11-13 is in contact with the respective
winder 11-13 and provides, along with a rubber roller
21, a device for drawing the film 18 itself. Such
cylinder 20 is connected to a pair of levers controlled
in movement through pneumatic pistons, preferably
provided with hydraulic breaking, and constrained to
rotate around a torsion axis 22.
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During the step of winding and replacing the reel, the
abovementioned device 36 has a rotational movement
around the axis 22 controlled by pneumatic pistons 23
with the aim of always maintaining the contact pressure
constant on the reel.
Furthermore, provided for at the winding position, is a
blade 24 for cutting the film 18 upon termination of
the step of winding an entire reel 19 of film.
The removal and reinsertion of the transverse cutting
blade 24 is controlled by a pair of pneumatic cylinders
25.
According to the present invention, associated to at
least the winder 11 arranged at the winding position
are special contact means 26 which maintain the contact
with the reel being wound constant, also during the
replacement step.
In such case, the contact means 26, during the
replacement step, follow the winder bearing the full
reel and, once the winding is definitely completed,
return to the winding position again.
In the illustrated preferred embodiment, each winder
11-13 is provided with special contact means 26-28
which follow the rotation movement of the related
winder 11-13 during the entire cycle, thus not
constantly requiring returning to the winding position
again. in such manner, it is not necessary to provide a
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special synchronisation between the movement of the
contact means 26-28 and the movement of the winders 11-
13.
According to a non-restrictive embodiment, the contact
means 26-28 are made up of an anodised and motorised
steel cylinder.
The constant contact with the reel is advantageously
provided for by means of a pneumatically controlled
lever mechanism with adjustable pressure.
In such manner, provided for is also a guide for the
last meters of the film, which otherwise, during the
replacement step in which the star-shaped winder holder
10 is rotated from the position in figure 3 to the
position in figure 4, would be without contact and thus
would cause the absorption of air.
Furthermore, the presence of a double opposite contact
on the same winder made by means of a contact cylinder
and the contact means 26-28 actually eliminates the
flexure phenomena to which the winder 11-13 would be
20 subjected in case of contact with a single cylinder.
Such cylinders of the contact means 26-28 are
preferably controlled, through a belt drive, by an
alternating motor controlled by an inverter. The final
drive occurs by means of a telescopic cardanic joint.
The abovementioned parts, just like the motorisations
of the winders 11-13, reel cores 16 and tailstocks 15,
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are installed on the star-shaped winder holder 10 which
rotates in a unidirectional manner. The rotation of the
star-shaped winder holder 10 is preferably controlled
by a gear motor 29 controlled by an inverter and
connected by means of a driving belt.
The control of the position of the star-shaped winder
holder 10 is ensured by an absolute encoder mounted in
axis with the gear motor 29, while the maintenance of
the position is provided for by a disk brake operated
pneumatically (not represented in the figure).
A distinctive characteristic of the winding system 100
according to the present invention consists in the fact
that the control and command part of all the parts
installed in the star-shaped winder holder 10 is
ensured by the apparatus installed on a rotating plate
coaxial to the star-element 10 itself.
Fixed on such plate are processing means such as for
example a PLC (programmable logic controller), motor
inverters and the required power parts, as well as the
regulation and control valves of the pneumatic cycle.
A collector with three phase rings, one of which is of
the mercury type for connecting with the processing
means of the line and one of the pneumatic power
supply, provide for supplying the star-shaped winder
holder 10.
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Lastly, the removal of the full reels 19 is performed
by a mechanical arm 30 which slides on a linear guide
31 controlled by a gear motor 32.
Analogously, insertion of the cores 17 occurs by means
of a ring 33 which slides on a second linear guide 34,
also controlled by a gear motor 35.
The operation of the winding system 100 is as follows.
During the normal winding, the film 18 is wound on the
winder 11 which is arranged at the winding position,
that is in contact with the drawing and pressure device
36 (figure 3).
At the end of said first step, that is when the film
reel 19 is completed (figure 4), the so-called
replacement step is performed, wherein a second winder
12 is initially started up at a peripheral speed
slightly higher with respect to the winding one.
Subsequently, the star-shaped winder holder 10 rotates
for a predetermined angular portion, for example 120
clockwise with reference to the implementation, moving
the second winder 12 to the winding position (figure
5).
As observable in the figures, during the entire
operation the contact means 26 corresponding to the
first winder 11 never lose contact with the winder
itself, thus constantly guaranteeing the "squeezing
out" of the air between the turns.
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The rotation speed of the star-shaped winder holder 10,
summed with the peripheral speed of the winder 11,
leads to further tensioning of the film 18.
Such rotation further moves the film 18 to the cutting
position where the blade 24 (figure 6) intervenes,
without the risk of the film 18 being lost during the
passage from the first winder 11 to the second 12.
For such purpose, the film 18 is also precharged by
means of an electrostatic discharge thus being
attracted towards the core 17 of the reel core 16 of
the winder 12 without requiring glues or adhesives.
In order to avoid the dragging of the film 18 against
the contact means 27 relative to the second winder 12,
the same means 27 are provided with a housing or anti-
adherent cover (not shown) which allows the film 18 to
slide without hindrance.
Upon termination of the cutting step, the contact means
27 relative to the second winder 12 are arranged in
contact with the corresponding reel core 16, and where
they remain up to the subsequent replacement cycle.
On the other hand, in case the contact means 26-28 are
single and common to all the winders 11-13, upon
termination of the step of winding the end of the cut
film 18, the contact means 26-28 oscillate backwards
thus returning to the winding position and in contact
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with the reel being wound on the second winder 12
shortly after the start of such step.
Once terminated the winding of the cut end, the star-
shaped flange 14 removes the tailstocks 15 that support
the reel cores 16 relative to the winders 13 and 11, in
such a manner to be able to insert a new core 17 on the
third winder 13 and simultaneously eject the reels 19
wound on the first winder 11 (figure 7).
The operations of ejecting the full reel 19 and
inserting the new core 17 occur simultaneously by means
of special mechanical actuators 30 and 33 which operate
at high speeds.
Thus, the winding system 100 according to the present
invention is capable of considerably reducing the
replacement times and thus obtain production speeds
when winding reels for manual use similar to the
production speeds for "jumbo" reels.
Due to the optimisation of the abovementioned
operations, the operating cycle generally lasts for
about 15 seconds.
The entire process herein described is performed within
very short periods of times and thus it is required
that the control occurs by means of a particularly
sensitive control and management device.
According to the points outlined above with reference
to the figures, it is clear how a winding system for
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use in plastic films production lines according to the
points outlined above is particularly useful and
advantageous.
Thus, with the winding system described it is possible
to produce ideal quality plastic film reels in a rapid
manner
It is thus possible to produce reels extremely short in
size also due to the short periods of time required for
the operations of ejecting the full reels and inserting
the new cores which, in the described system, may occur
simultaneously.
Such winding system can be prepared both for winding
reels with an internal core equivalent to 50 mm, that
is reels for manual use, and for winding reels on cores
of 76 mm, that is reels for use in automatic machines,
thus offering a high degree of flexibility.
The winding system can also be used on production lines
having a multiple finished band measuring 1 metre
according to a chequered disposition of the winding
devices, which thus also allows the simultaneous
production of reels on 50 mm reel cores and reels on 76
mm reel cores, further increasing the flexibility of
the production lines, due to the possibility of
differentiating the final result of the work without
adjusting any parameter of the line.
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Obviously, the winding system for use in plastic films
production lines according to the invention can be
implemented differently with respect to the
implementation described and illustrated strictly for
exemplifying and non-limiting purposes.
Therefore, the scope of protection of the present
invention is delimited by the attached claims.
