[0001] The present invention refers to a device for the proper and free stacking of welded
bags in a welding machine, in particular said device avoids sticking between the welded
portions of the surfaces.
[0002] In the manufacturing process of bags, obtained from plastic tubular material or the
like, welded either at one end, the so called "open mouth" bags, or at both ends,
it has been more and more frequently used the operation of stacking said bags, coming
directly from the welding transverse bars, on a support provided with needles. In
fact, instead of providing transportation means to carry away the single bags, there
are provided suitable stacking supports having needles sufficiently thin to firmly
position the just welded bags.
[0003] Currently, because of the high working speeds of the modern welding machines for
thermoplastic materials, the weld lines, or more simply the weldings, along the transverse
direction (which have been executed on the bags or on the bag tubular material) are
still hot when the bags are stacked together. During said stacking phase on said needles,
said weldings, still hot, get in contact with each other during the stacking phase
and there is, easily, a gluing activity among the bags.
[0004] This fact causes several problems to the bag users since it is necessary to separate
one bag from the other along such glued areas.
[0005] The separation, besides causing an effective loss of time to the final user, might
cause the partial breaking of the welding. As a consequence, the bag or the bags involved
in such gluing, even though just locally, might not be utilised any more.
[0006] Further, a broken bag may not appear as such, but, when carrying a certain weight,
the welding breaks and the bag content falls down.
[0007] The conclusion is that a welding machine, without a suitable and proper solution
to the problem of accidental gluing of the bags along the transverse weld lines, will
not be sufficiently competitive.
[0008] In fact, such a machine should work at a lower rate of production in order to allow
the cooling of the bags while they are stacked together so that they do not stick
to each other.
[0009] An alternative solution to the low production rate has been obtained by realising
a support for the stacking of the welded bags which is movable back and forth along
the transport direction of the bags, i.e. back and forth horizontally in relation
to the bags which are progressively welded.
[0010] This fact leads to a stacking on the needle support with a displacement of the end
edges of the bags, i.e. a phase displacement thereof. This alternate positioning of
the edges and therefore of the displaced transverse weld lines of one bag in respect
to the preceding one as well as the next one, avoids the gluing between consecutive
bags.
[0011] However, such a solution requests the realisation of a special support swinging back
and forth in respect of each bag and of a special driving device able to act whenever
a bag is welded. Therefore, the support has to follow this quick succession of operations,
even in presence of significant inertial masses.
[0012] Further, the alternate motion run has to be adjusted according to the changes in
length of the bag which is being manufactured.
[0013] Therefore, the welding machine has to have a certain construction complexity downstream
of the welding system, i.e. in the stacking support area.
[0014] A purpose of the present invention is to find a solution that, besides solving the
previously shown and outlined technical problem will realise a welding machine as
simple as possible.
[0015] Another purpose is to realise a device that avoids a complicate construction, by
minimizing the masses and the elements in motion, and nonetheless able to fully reach
its required working features.
[0016] Another purpose is to reduce to the minimum all the necessary adjustments, even in
presence of a very simple assembly, therefore achieving a low construction and assembly
costs.
[0017] These and other purposes, according to the present invention, are attained by a device
for the proper and free stacking of welded bags in a welding machine, wherein the
welding machine comprises at least a pair of opposed rolls which feed a plastic tubular
material, an upper welding device and a lower welding device which cooperate to execute
the transverse welding of the plastic tubular material, a support for stacking the
welded bags as they come out from the two welding devices, said support is positioned
downstream of the welding devices and it carries needles on which the bags are steadily
positioned by means of a small upper press, characterised in that said device comprises
a driven transverse displacement element which acts on the single bag to be welded,
and causes the backing of one of the free front end of the bag, said displacement
element is positioned between the two welding devices and the support and it acts
every second bag, in order to displace one bag from the next one.
[0018] By means of a device according to the present invention, an embodiment is very easily
obtainable since it is made of elements suitable for a simple construction and assembly,
such elements are even commercially available.
[0019] Further, such a device is quickly adaptable to any kind of application.
[0020] Such a device has construction and drive advantages since it works every two bags.
[0021] Such a device will be easier to drive and it will work at lower speeds than the previous
devices.
[0022] Such a device will not require very sophisticated materials.
[0023] The functional and structural features and the advantages of a device according to
the invention will be better understood by way of a non limiting example, making reference
to the accompanying schematic drawing.
[0024] In fact, the drawing shows a schematic front elevation view of a device according
to the invention which is applied to a welding machine for the production of welded
bags, shown in its welding arrangement. In the drawing, a full line indicates an extended
bag, without the intervention of the device of the present invention; meanwhile a
chain (dash and dot) line indicates a bag on which an intervention is performed by
the device of the present invention.
[0025] With reference to the drawing, a possible embodiment of a portion of the welding
machine is shown (indicated by reference numeral 11), wherein a tubular material 12
is fed, having a flattened shape and being devoted to the bag production.
[0026] The type of the welding machine is of no relevance for the application of this invention,
since this new device is built so that it can be applied to any welding machine, even
to existing and already working machines.
[0027] The welding machine 11 generally comprises a pair of opposed rolls 13 which feed
the material 12, nozzles 14 associated to such rolls to feed air in order to maintain
the material fed through the rolls 13 in a flat position.
[0028] An upper welding device 15 and a lower welding device 16 cooperate to execute the
transverse welding of the tubular material and said devices have a cutting blade 17
which works between two weld lines realised by the welding devices when they engage.
[0029] A swivel 18 is positioned downstream of the two welding devices 15 and 16 , said
swivel, by means of transverse bars 19, moves downward the welded bag ends. Further
downstream, a support 20 is positioned in order to stack the welded bags 21, 21' coming
out from the welding devices 15 and 16. The support 20 carries needles 22 (just one
is shown) whereon the bags 21, 21' are steadily positioned by means of a small upper
press 23.
[0030] The bags 21 are indicated by a full line and the bags 21' are indicated by a chain
line.
[0031] Some of the bags 21, 21' lay on a table or on a similar element 24 and some of the
bags are hanged to and dangle from the needles 22 of the support 20, moved downward
thanks also to the action of the bars 19 of the swivel 18. According to the present
invention, a specific device is positioned between the two welding devices 15 and
16 and the support 20 for the stacking of the welded bags 21, 21' in order to realise
the proper and free stacking of welded bags in a welding machine.
[0032] In fact, this device avoids the gluing of consecutive bags along the still hot weld
lines. In particular, a pushing element 25 will be provided and it will be driven
downward or upward, being positioned above or below a bag 21', by means of an actuator
26, as a cylinder or the like. In fact, the pushing element 25 pushes only the bags
21', indicated by a chain line, which have to be displaced in respect to the bags
21 which are stacked without any displacement.
[0033] The pushing element 25, shaped as a plate or as a roll, works as a transverse displacement
element of the single bag 21' to be welded, and said element 25 pushes an intermediate
area of the bag and causes the backing of the free front end 27 of the bag positioned
on the table 24.
[0034] The needles 22 of the support 20 penetrate into the bag 21' in a displaced position,
towards the center of the bag, in respect to the penetration area of the preceding
bag 21. In this way, when the bag 21' welded also in its back free end 28, is released
by the two welding devices 15 and 16, this end falls downward below the corresponding
end of the preceding bag 21.
[0035] It is understood that the device according to the present invention will have to
work every two bags in order to displace two consecutive bags.
[0036] According to this simple arrangement, the problem, due to the accidental gluing along
the weld lines of two consecutive bags welded at high speed, is solved.
[0037] It is therefore evident that, according to the present invention, a new and innovative
technical solution to the problem of the gluing between the weld lines of consecutive
bags has been found in a simple and easy way.
1. A device for the proper and free stacking of welded bags in a welding machine (11),
wherein said welding machine comprises at least a pair of opposed rolls (13) which
feed a plastic tubular material (12), an upper welding device (15) and a lower welding
device (16) which cooperate to execute the transverse welding of the plastic tubular
material (12), a support (20) for stacking the welded bags (21, 21') as they come
out from the two welding devices (15, 16), such support (20) is positioned downstream
of the welding devices and it carries needles (22) on which the bags (21, 21') are
steadily positioned by means of a small upper press (23), characterised in that said
device comprises a driven transverse displacement element (25) which acts on the single
bag (21') to be welded, and causes the backing of one of the free front end (27) of
the bag, said displacement element (25) is positioned between the two welding devices
(15, 16) and the support (20) and it acts every second bag, in order to displace one
bag from the next one (21, 21').
2. A device according to claim 1, characterised in that said displacement element is
a pushing element (25), driven by a corresponding actuator (26).
3. A device according to claim 1, characterised in that close to said displacement element
(25) there is a swivel device (18) which, by means of transverse bars (19) moves downward
the welded back ends (28) of said bags (21, 21').
4. A device according to claim 1, characterised in that said transverse displacement
element (25) is movable upward.
5. A device according to claim 1, characterised in that said transverse displacement
element (25) is movable downward.