The invention relates to a method for producing sacks from a fabric tube, in which
the flat fabric tube is fed out of a tube de-coiler or a tube-forming device, in which
the fabric tube is cut to length along a cutting line in order to obtain tubular sack
bodies which are open at both ends, wherein the fabric tube is cut to length in a
longitudinal transportation section, in which the fabric tube, 5 or the tubular sack
bodies, are transported in the longitudinal direction of the fabric tube.
The invention further relates to a device for carrying out this method.
10 The tubular bodies of a sack are usually formed from a tubular round material or a
flat material joined to a tube on the longitudinal edge. By this distinction, the
sacks are roughly divided into cushion-shaped or box-shaped. A cushion shape of
the sacks usually arises from finishing the bottoms with a textile seam or a welded
seam.
15
The fabric thus preferably consists of monoaxially stretched polymer tapes, in
particular polyolefin or polypropylene tapes. These tapes are produced by
stretching polymer, in particular polyolefin or polypropylene films, usually by
four to ten times, whereby the molecular chains are arranged in the longitudinal
20 direction of the tapes and are six to ten times stronger in this direction in
comparison to the original film. The width of the tapes is usually approx. 1.5 to 10
mm, the thickness 20 to 80 μm.
3
A method and a device of the kind named at the beginning are known, for
example, from WO 2010/086232 A1. One such device normally comprises firstly
a tube-forming device for producing and providing a tubular material. It can also
be only a tube de-coiler. This is generally able to be fitted with a material coil,
onto which tubular material is coiled. The material is removed 5 from this material
coil mostly continuously in longitudinal direction. During the sack producing
process by prior art machines, the fabric tube provided by the tube-forming device
or tube de-coiler is fed through a chisel edge device which separates the fabric
tube into individual tube pieces or tubular sack bodies. The tubular sack bodies
10 are passed on to a transportation device. By means of this transportation device,
the tubular sack bodies are carried to a station in which at least one open end of
the tube piece is sealed. The sealing is carried out, for example, by affixing a seam
in the perpendicular direction to the sack. Alternatively, the bottom can be folded
to obtain a rectangular bottom.
15
On the edges at the open ends of the sacks that come about during the cutting-tolength
procedure, there is, however, the danger of the tapes becoming detached, in
particular with sacks made of uncoated fabric. The tapes close to the edge,
running parallel to the cutting line, thus shift in the direction of the cutting line or
20 lose their parallelism and can consequently slip completely free from the fabric.
These occurrences are greatly disadvantageous for filling and further handling of
the sacks.
4
For this reason, the open ends of the sacks are usually manually folded and the
folded edge is connected to the fabric ply underneath, for example sewn up or
glued together, wherein a type of hem and thus a cleanly sealed edge are obtained
at the open ends of the sacks.
5
The disadvantage of this, however, is that this process of folding and connecting
requires a high expenditure of work and materials (sewing thread), as well as
causing a distinct loss of material from the sack material during the folding
process.
10
The present invention thus aims to avoid the disadvantages mentioned above. In
particular, the invention aims to automatize the production of a sack, as well as
minimise production costs and the material loss during production.
15 To achieve this object, the invention with a method of the kind named at the
beginning provides that a cutting line region of the fabric is treated on at least one
open end of the tubular sack bodies by heat input, before this open end is sealed.
The cutting line region of a sack body is an area formed as a strip, which extends
away from the cutting line in the longitudinal direction of the sack and preferably
20 substantially across the entire periphery of the fabric tube. A cutting line region is
thus on the side of the cutting line, i.e. on the edge of one of the two tubular sack
bodies produced by cutting to length, and a further cutting line region is on the
other side of the cutting line, i.e. on the edge of the other of the two tubular bag
5
bodies produced by cutting to length. In the scope of the invention, both cutting
line regions can be treated by heat input or alternatively only one of the two
cutting line regions.
Preferably, it takes place in such a way that the cutting 5 line region on the
respective edge of the tubular sack body is treated, said region consequently
forming the open end of the sack that enables it to be filled.
It is preferably provided that heat input takes places in the longitudinal
10 transportation section.
The heat input leads to the fabric tapes within the cutting line region being heated
up and the fabric tapes that cross over one another of the respective fabric ply
layers consequently joining to each other, such that detaching the tapes as
15 described above is effectively prevented. The heat treatment is constructed in such
a way that the fabric tapes are softened to the extent that they join with each other.
The heat input is thus carried out in such a way that only the fabric tapes crossing
one another of the respective fabric ply layers join to each other, wherein by
taking suitable measures the overlying fabric ply layers are prevented from
20 permanently connecting to one another because of the heat input. After heat
treatment, the treated cutting line region cools down again and the tapes harden.
In doing so, the heat input is not carried out in such a way that the respective open
end of the sack is sealed as a result. Rather, the sealing of the open end of the sack
6
body that has been treated by heat input within the scope of the invention takes
place in a subsequent, separate step.
The removal of the tapes is at least extensively prevented by the method
according to the invention, and it is not necessary to address 5 the detrimental
consequences of detaching the tapes by other process steps, such as a folding
method for example.
A preferred procedure provides that the heat input takes place by means of a
10 welding process. Welding is a method according to prior art and in this respect
inexpensive and easy to implement.
Particularly preferably, the welding process takes place by ultrasonic welding.
Alternatively, hot contact welding is also conceivable.
15
The welding process preferably produces one or more linear welded figure(s) or a
multiplicity of punctiform welded figures on the fabric tube. In doing so, the aim
is to treat the strip-formed cutting line region as much across the entire width of
the flat fabric tube as possible. The welding line(s) must not necessarily extend
20 uninterrupted across the whole width of the flat fabric tube, since by doing so
there is the danger of weakening the fabric material. Preferably, the welding
process thus produces a multiplicity of lines, dots or strips in the cutting line
region, separated from each other in the peripheral direction of the fabric tube.
7
It is preferably provided that the cutting line region has a width of at least 1 cm
measured away from the cutting line, and extends substantially over the entire
periphery of the fabric tube.
5
Particular preferably it is provided that the cutting line region starting from the
cutting line comprises at least 1 to 3 rows of fabric tapes that are parallel to the
cutting line and extend substantially over the entire periphery of the fabric tube.
10 A preferred procedure provides that the heat input takes place temporally before
or after the cutting to length. In doing so, for example, the region provided as a
cutting line region is initially treated by heat input and the cutting process carried
out only after the heating process. In one such sequence of the method steps, the
cutting to length can be carried out by means of cold cutting, with a knife for
15 example. In the opposite case, however, (firstly cutting to length, then heat input),
hot cutting, in particular with uncoated fabric, is preferred.
An alternative procedure provides that the heat input takes place at the same time
as or after the cutting to length.
20
Regardless of the temporal sequence of the cutting to length and the heat input in
the cutting line region, the heat input in the cutting to length preferably takes
place by means of devices different from one another. In particular, the heat input
8
during the cutting to length by means of a hot knife is not to be regarded as heat
input according to the invention because the effect to be achieved according to the
invention is not ensured by this means.
Furthermore, it is preferably provided that the overlying fabric 5 ply layers of the
flat tube are treated by heat input at the same time. Alternatively, the two fabric
ply layers can also be treated temporally one after another.
Regardless of whether the treatment of the two overlying fabric ply layers of the
10 flat tube takes place at the same time or one after another, the treatment of the two
fabric ply layers can take place by heat input in the same position or in two
different positions.
It is preferably provided that the overlying fabric ply layers of the flat tube are
15 spaced from one another by means of separating agents, in particular a separating
layer or an internally located tool, in order to prevent the overlying fabric ply
layers from connecting. The term internally located here means that the tool is
arranged inside the fabric tube.
20 A (hard) metal plate of preferably 0.3 – 2 mm thickness or a stainless steel band
or similar can be used as the internally located, preferably stationary, separating
layer. Alternatively, a film (made of polyamide or Teflon for example) is suitable
as a separating layer.
9
In the event of heat input by ultrasonic welding, the separating layer can fulfil a
double function, namely, on the one hand preventing the two fabric ply layers
from welding to one another, and on the other hand transferring the vibrations
produced by the sonotrode of the ultrasonic welding device, 5 such that the tapes
both within the upper tape fabric ply layer and within the lower tape fabric layer
are welded to one another. In this way, both fabric ply layers can be processed
with one single ultrasonic welding device. Essentially, the ultrasonic welding
device can have a sonotrode and an anvil.
10
Alternatively, the separating layer can be used as the counterpart, i.e. anvil, for at
least one sonotrode. In doing so, it is preferably provided that the separating layer
is formed as an anvil in order to work together with a sonotrode arranged outside
the fabric tube for the heat input.
15
Thus it is also possible to work with two sonotrodes (from above and below).
Furthermore it is possible to conduct the sonotrodes and/or the anvil flatly and to
provide the elevations on the intermediary layer (on one or both sides) responsible
for the welded figures.
20
If heat input takes place by means of a welding process, then it is preferably
provided that the welding is carried out without introducing additional materials,
such as adhesive.
10
A further preferred procedure provides that the line cutting regions of a sack
opening are treated by heat input and the other sack opening is sealed, for
example by sewing it up.
5
With sacks that are to receive an inner layer made of polymer film, in particular
polyolefin or polypropylene film, on their inside, a preferred procedure provides
that the film is positioned on the inside of the fabric tube before the heat input step
and an edge of the film is connected to the fabric in the cutting line region by
10 means of the heat input step.
If a sack is to be produced with gusseted folding, it is preferably provided that
firstly the heat input is carried out, then the gusseted folding is produced and
finally the cutting to length takes place. By gusseted folding, the provision of one
15 or more folds in the side of the sack, meaning the edges running in the
longitudinal direction of the tubular sack bodies, is to be understood, whereby a
substantially rectangular shaped sack can be produced.
As has already been mentioned, the invention is preferably used for sacks whose
20 fabric consists of monoaxially stretched polymer tapes, in particular polyolefin
and polypropylene tapes. The fabric can be essentially coated or uncoated.
However, the advantages of the invention have an effect particularly with
uncoated fabric, since above all such fabrics have a tendency to fray. In cases of
11
coating, this can consist of a thin layer of polypropylene or a mixture of
polypropylene and polyethylene.
To achieve the object underlying the invention, the invention further proposes a
device for producing sacks from a fabric tube, comprising a tube 5 de-coiler or tubeforming
device, a cutting device, to which a flat fabric tube can be supplied from
the tube de-coiler or the tube-forming device in the tube longitudinal direction and
from which, through the cutting to length of the fabric tube, the tubular sack
bodies obtained are able to be led away, and a sack sealing device for sealing at
10 least one open end of the sack body, wherein the device comprises at least one
heat input device for treating at least at least one cutting line region of the tubular
sack bodies by heat input, wherein the heat input device is arranged in the
transport direction in front of the sack sealing device.
15 A preferred development provides that separating agents, in particular a separating
layer or an internally located tool, for spacing apart the overlying fabric ply layers
of the flat tube are assigned to the at least one heat input device.
Furthermore it is preferably provided that the at least one heat input device is
20 formed as a welding device.
12
A preferred device provides that the welding device is a hot contact welding
device, wherein the internally located tool is formed as the counterpart for at least
one welding stamp of the hot contact device.
Another preferred embodiment provides that the welding device 5 is an ultrasonic
welding device, wherein the internally located separating agent is formed as a
vibration transferring agent.
Furthermore it is preferably provided that the heat input device is designed as an
10 independent unit to the cutting device. Alternatively, it can be provided that the at
least one heat input device and the cutting device form a unit.
In a preferred embodiment it is provided that the at least one heat input device is
arranged before the cutting device in the transportation direction of the fabric
15 tube.
The invention is subsequently explained in further detail by using an exemplary
embodiment depicted in the drawings. In these, Fig. 1 shows a schematic top view
of the device according to the invention, Fig. 2 a sectional view along the line II-II
20 of Fig. 1 and Fig. 3 an alternative formation of the welding device.
It can be seen in Fig. 1 that a fabric tube 1 of the device is led in the direction of
arrow 2 and is transported inside the device at the same time in the direction of
13
arrow 2. In step S1, the fabric ply layers of the fabric tube 1 are spaced apart by
means of an internally located, i.e. arranged between the fabric ply layers of the
fabric tube 1, tool 3. In step S2, the fabric ply layers that are now spaced apart
from one another in cutting line region indicated by 6, are at the same time heated
up by a welding stamp 4 situated above and a welding stamp 5 situated below 5 of a
hot contact welding device, such that welding of the overlying fabric tapes occurs.
In the welding process, the tool 3 situated inside prevents the two fabric ply layers
of the flat tube from welding together. In step S3 the fabric tube 1 is now cut to
length along the provided cutting line 8 by a cutting device that is not depicted, in
10 order to obtain a sack body 7.
In step S4 the sack bodies 7 that have been further transported transversely in the
direction of arrow 9 are further processed, for example sealed at one end. An
exemplary, completed sack is depicted by 10, which has a heat treated cutting line
15 region 6 according to the invention on the open side and an end region sealed in
the conventional way on the other side.
In Fig. 1 the steps S2, S3 and S4 are depicted by means of tube sections in
different feeding positions. The feeding of the fabric tube 1 or the sack body 7 in
20 the direction of the arrow 2 or 9 thus takes place at intervals, wherein in the
pauses between the individual feeding intervals, steps S2 and S3, and S4 where
necessary, are carried out simultaneously. Thus, while welding takes place in step
14
S2, a section already provided with a welding cutting line region 6 and further
transported of the fabric tube is cut to length at the same time in step S3.
In the sectional view according to Fig. 2, the internally located tool 3 can be more
easily seen. The internally located tool 3 comprises two rollers 5 12 which space the
two fabric ply layers 13 and 14 of the fabric tube 1 apart from one another. The
internally located tool 3 further comprises a plate 15 that is connected to the
rollers 12 in the transport direction 2, which is formed as the counterpart to the
welding stamps 4 and 5 in the heat input region.
10
The sectional view according to Fig. 3 corresponds substantially to the sectional
view according to Fig. 2, with the difference that an ultrasonic welding device is
now provided for the heat input. The ultrasonic welding device comprises a
stationary anvil 16 and a sonotrode 17. Thus, the plate 15 of the internally located
15 tool 3 serves as the vibration transferrer in order to transfer the vibrations applied
to the upper fabric ply layer 14 to the lower fabric ply layer 13, such that both the
tapes that cross over one another of the upper fabric ply layer 14 and the tapes of
the lower fabric ply layer 14 that cross over one another are at the same time
joined or welded to one another.

Claims:
1. Method for producing sacks from a fabric tube, in which the flat fabric
tube is fed out of a tube de-coiler or a tube-forming device of a cutting
device, in which the fabric tube is cut to length along a cutting line in
order to obtain tubular sack bodies which are open at 5 both ends, wherein
the fabric tube is cut to length in a longitudinal transport step in which the
fabric tube, or the tubular sack bodies, are transported in the longitudinal
direction of the fabric tube, characterised in that a cutting line region of the
fabric is treated by heat input on at least one open end of the tubular sack
10 bodies by means of a welding process, before sealing this open end,
wherein the welding process is carried out temporally before cutting to
length or at the same time as cutting to length and is carried out in such a
way that only the small, crossing fabric tapes of the respective fabric layer
are connected to each other.
15 2. Method according to claim 1, characterised in that the welding process is
carried out by ultrasonic welding.
3. Method according to claim 1 or 2, characterised in that the welding
process produces one or more linear or strip welding piece(s) on the fabric
tube.
20 4. Method according to claim 1 or 2, characterised in that the welding
process produces a multiplicity of punctiform welding pieces on the fabric
tube.
16
5. Method according to one of claims 1 to 4, characterised in that the cutting
line region measured away from the cutting line has a width of at least
1cm and preferably extends substantially over the entire periphery of the
fabric tube.
6. Method according to one of claims 1 to 5, characterised 5 in that the cutting
line region starting from the cutting line comprises at least one to three
rows of small fabric tape that are parallel to the cutting line and preferably
extend substantially over the entire periphery of the fabric tube.
7. Method according to one of claims 1 to 6, characterised in that the
10 overlying fabric layers of the fabric tube are treated by the welding process
at the same time.
8. Method according to one of claims 1 to 7, characterised in that overlying
fabric layers of the fabric tube are spaced apart from one another by means
of separating agents, in particular a separating layer or an internally
15 located tool, in order to prevent overlying fabric layers from connecting to
one another.
9. Method according to one of claims 1 to 8, characterised in that the cutting
line regions of a sack opening is treated by the welding process and the
other sack opening is sealed by sewing, for example.
20 10. Method according to one of claims 1 to 9, characterised in that the fabric
consists of monoaxially stretched small polymer tapes, in particular
polyolefin or polypropylene tapes.
17
11. Method according to one of claims 1 to 10, characterised in that a film is
positioned inside the fabric tube before the welding process and one edge
of the film is connected to the fabric in the cutting line region by the
welding process.
12. Method according to one of claims 1 to 11, characterised 5 in that fabric is
cut to length after the welding process and this is carried out by means of
cold cutting.
13. Device for producing sacks from a fabric tube, in particular for carrying
out the method according to one of claims 1 to 12, the device comprising a
10 tube de-coiler device or tube-forming device, a cutting device, the fabric
tube being a flat fabric tube from the de-coiler or tube forming device that
can be supplied in the longitudinal direction of the fabric tube and enable
tubular sack bodies obtained by cutting the fabric tube to length to be
guided away, and a sack sealing device for sealing at least one open end of
15 the sack bodies, characterised in that the device comprises at least one
welding device for treating at least one cutting line (8) of the tubular sack
bodies (7) by heat input, wherein the welding device is arranged in front of
the sack sealing device, wherein the at least one welding device and the
cutting device form a unit or the at least one welding device is arranged in
20 front of the cutting device in the transport direction of the fabric tube (1),
and separating agents, in particular a separating layer or an internally
located tool (3), are assigned to the at least one welding device during the
18
welding process, to space the fabric layers (13, 14) of the fabric tube (1)
lying on top of each other apart from one another.
14. Device according to claim 13, characterised in that the at least one welding
device is formed as an ultrasonic welding device.
15. Device according to claim 14, characterised in that the 5 internally located
separating agent is formed as a means of vibration transfer.