FR3065391A1 - FLEXIBLE FILM WELDING DEVICE HAVING HARD MATERIAL CONCENTRATOR WITHIN INDUCER - Google Patents

Abstract

The invention relates to a device for welding flexible materials (6) superimposed, comprising an induction jaw (2) equipped with an inductor with several parallel branches (10), and a jaw (4) provided for tightening the films (6) on the induction jaw (2), characterized in that the induction jaw (2) comprises between the inductor branches (10) an inner concentrator (14) made of a hard material having magnetic permeability and electrical resistivity.

Description

® FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY © Publication number:

(to be used only for reproduction orders)

©) National registration number

065 391

53378

COURBEVOIE

©) Int Cl ⁸ : B 29 C 65/74 (2017.01), B 29 C 65/02, B 65 B 51/10, B 26 D 7/27

A1 PATENT APPLICATION

©) Date of filing: 19.04.17. ©) Applicant (s): THIMONNIER Joint-stock company (30) Priority: simplified - FR. ©) Inventor (s): GUILLOT VICTOR, ROUMANET FRE- DERIC and VERDIER YANNICK. (43) Date of public availability of the request: 26.10.18 Bulletin 18/43. ©) List of documents cited in the report preliminary research: Refer to end of present booklet (©) References to other national documents ©) Holder (s): THIMONNIER Société par actions simpli- related: vision requested on 5/16/18 benefit trusted. from the filing date of 04/19/17 of the request initial n ° 17 1753378. ©) Extension request (s): @) Agent (s): CABINET GERMAIN & MAUREAU.

DEVICE FOR WELDING FLEXIBLE FILMS COMPRISING A HARD MATERIAL CONCENTRATOR WITHIN AN INDUCTOR.

FR 3,065,391 - A1 (iV) The invention relates to a device for welding flexible materials (6) superimposed, comprising an induction jaw (2) equipped with an inductor with several parallel branches (10), and a counter-jaw (4) provided for clamping the films (6) on the induction jaw (2), characterized in that the induction jaw (2) has an internal concentrator between the inductor branches (10) (14) made of a hard material having magnetic permeability and electrical resistivity.

i

The present invention relates to a device for welding flexible films, as well as to a welding method using such a device.

Complex flexible and laminated films, comprising a superposition of several materials each having specific functions, are commonly used to form sealed packages, in particular for packaging food products. The assembly of these flexible films by welding and cutting makes it possible in particular to produce sealed boxes or sachets.

Depending on the use, complex films have different qualities, such as mechanical resistance, or a barrier effect to avoid the diffusion of different molecules. These complex films comprise in particular layers of polypropylene "OPP" or of polyethylene terephthalate "PET", having rigidity and resistance to folding, of aluminum having an electrical conductivity allowing heating by induction, or of polyethylene " PE ”with good weldability.

A known type of welding and cutting device, presented in particular by documents US-A1-20050241277 and WO-A1-2016045967, comprises two jaws clamping together several superposed films. An induction jaw comprises an inductor with two parallel branches each forming an electrical conductor, arranged on each side of a cutting blade. The inductor may include a water cooling circuit to control the temperature.

A counter-jaw disposed opposite the induction jaw has two parallel bearing faces each receiving the support of an inductor. The jaw has a groove between these bearing faces allowing the cutting blade to advance freely, which then cuts the films during welding by a shearing effect. The groove may include an elastic material, coming to the surface of this groove or with a small shrinkage, mainly to improve the cut and avoid an accumulation of material in this groove.

An electric current of high frequency is applied to the inductor, in particular between 250 kHz and 1.5 MHz, generating a variable induced electric current within the conductive materials traversed by this magnetic flux, which heats them up by the Joule effect. This heating is thermally conducted to the materials to be welded.

For complex films comprising an electrical conduction layer, for example an aluminum layer, the electric currents generated in these layers locally heat the welding materials of these films, which causes the films to bond or merge together thanks to the clamping pressure applied by the jaws.

Two complex weld lines are obtained on complex films, each made in front of an inductor branch, and an intermediate section between these weld lines.

These devices performing welds mainly by direct induction, hardly weld films having no electrically conductive layer. Machines equipped with such a welding device cannot process a wide range of films, complex or not, which poses problems of flexibility of use and cost since other devices have to be used.

In addition, the absence of a rigid stop in front of the cutting blade makes it difficult to cut flexible films.

The object of the present invention is in particular to avoid these drawbacks of the prior art.

The invention provides for this purpose a device for welding superimposed flexible materials, comprising an induction jaw equipped with an inductor with several parallel branches, and a counter-jaw provided for clamping the films on the induction jaw, this device being remarkable in that the induction jaw comprises between the inductor branches an internal concentrator made of a hard material having a magnetic permeability and an electrical resistivity.

An advantage of this welding device is that the interior concentrator disposed between the branches of inductor, receiving the magnetic flux generated by this inductor, heats itself by its induced currents thanks to its electrical resistivity which makes it possible to add to induction welding delivered directly to the films, if they have a conductive layer, heating by thermal conduction coming from the interior concentrator between the inductor branches participating in the welding.

A welding of the films is obtained which can be continuous over the entire transverse distance between the inductor branches, without discontinuity between them.

In addition, it is possible in particular to weld films which do not contain an electrical conduction layer, which gives a much more versatile welding and cutting device making it possible to reduce production costs. Furthermore, the cutting of flexible films can be facilitated with the hard material of the interior concentrator on which a cutting blade fixed on the counter-jaw comes to bear.

The welding device according to the invention may further include one or more of the following characteristics, which can be combined with one another.

Advantageously, in the transverse direction, the interior concentrator fills all the space between the inductor branches.

In particular, in the longitudinal direction, the interior concentrator may include inserts having a different magnetic permeability or electrical resistivity.

Advantageously, the interior concentrator comprises a channel provided for circulation of water. We can thus regulate its maximum temperature, and heat it more quickly before a production.

Advantageously, the counter-jaw comprises at least one cutting blade aligned between two branches of inductor. In this way, welding and cutting of the superimposed materials is carried out in the same positions.

In this case, in a welding position, the cutting blades of the counter-jaw advantageously bear directly on the surfaces of the interior concentrator.

In this case, advantageously the surfaces of the interior concentrator receiving the support of the cutting blades comprise a material having a “Vickers” hardness greater than 170HV. The internal concentrator thus forms a stop allowing, by pressing the blade above, clean cuts of the flexible films.

The invention also relates to a method of welding superimposed films using a welding device comprising any one of the preceding characteristics, remarkable in that it simultaneously applies pressure on these films and induction heating.

In particular, the method can preheat the interior concentrator before induction welding, by circulating hot water in this concentrator.

Other characteristics and advantages of the invention will emerge on reading the description which follows, given solely by way of example, with reference to the following appended figures:

FIGS. 1 and 2 are cross-sectional views of the two jaws of a welding device according to the invention, presented successively tightened and loosened, along a cutting plane ll for the induction jaw and a cutting plane ll- ll for the counter jaw;

Figure 3 is a perspective view of the induction jaw having an inductor with two branches;

Figures 4 and 5 respectively show a cross-sectional view along the section plane IV-IV and a front view of the induction jaw;

Figure 6 is a front view of the counter jaw;

FIGS. 7 and 8 are graphs presenting the temperature of the different layers of a welded complex film as a function of the transverse distance, respectively for a welding device without an internal electrical resistive concentrator, and a device according to the invention;

Figure 9 shows in front view of the inductor according to a variant; and Figure 10 is a front view of a jaw having an inductor with four branches.

FIGS. 1 and 2 show an induction jaw 2 comprising a front clamping face 8 arranged opposite the front clamping face 8 of a cutting counter-jaw 4. For each jaw 2, 4 the front side is that of its tightening front face 8.

The front faces 8 receive between them two superimposed films 6 running in a direction indicated by the arrow T, intended to be clamped then welded to a certain width, and at the same time cut in the middle of this width by a cutting blade 30 arranged in a median plane of symmetry P. Subsequently the outer sides are defined with respect to the median plane P.

Figures 1, 2, 3, 4 and 5 show the induction jaw 2 comprising a body 16 elongated in a longitudinal direction, supporting on each side of the median plane P an inductor branch 10 of square section, forming an electrical conductor comprising a contact face aligned on the front clamping face 8 of this jaw.

Each inductor branch 10 of the two-branch inductor receives outward an external magnetic field concentrator 12 comprising a return coming from behind this inductor.

An internal magnetic field concentrator 14 having in this example a high magnetic permeability, disposed in the median plane P comprises a tab fitted between the two inductor branches 10 and between the two external concentrators 12, then behind these external concentrators a wider rectangular section with a longitudinal water circulation hole.

The internal concentrator 14 is formed by a steel having a high “Vickers” hardness, in particular greater than 170HV.

The tongue of the internal concentrator 14 is interrupted in the longitudinal direction in the middle of the induction jaw 2 (cf. FIG. 4), and on each side of this jaw, by inserts 22 making it possible to locally modify the current density induced on film 6 to the right of these inserts.

The various concentrators 12, 14 are formed from a material with electrical resistivity or high magnetic permeability. The material of the interior concentrator 14 may in particular have a higher magnetic permeability than that of the exterior concentrators 12.

Preferably for the internal concentrator 14, the magnetic permeability or the electrical resistivity is higher in front of the zones where the necessary melting energies are greater, in particular in the zones of overlap of a greater number of films 6, in order to promote its heating.

Figures 1, 2, and 6 show the counter-jaw 4 comprising an elongated body 32 comprising on the front side a cutting blade 30 disposed in the median plane P, which is clamped by a support 34 disposed below this plane, maintained by screws 36 on the elongated body. The front edge of the cutting blade 30 slightly protrudes from the front face 8 of the counter-jaw 4.

The counter-jaw 4 has on its front face 8 on each side of the cutting blade 30 a bar 38 held by clamping screws 40, which clamps the films 6 on the induction jaw 2.

Each inductor branch 10, the internal concentrator 14 and the counter-jaw 4 each have a longitudinal bore forming a conduit receiving a circulation of water to limit their heating from iron losses from magnetic materials, losses from induced currents not transmitted to the materials soldering, related to the efficiency of magnetic coupling, and losses by thermal conduction.

The operation of the welding device according to the invention is as follows. After having clamped at least two films 6 between the two jaws 2, 4, a high frequency current is delivered in the inductor 10. A variable magnetic field is obtained generating electric currents causing internal heating by its inductive current in the inductor 10, by currents induced in the internal concentrator 14 if it is conductive, and in the conductive layer of complex films 6 if they have one.

The internal concentrator 14 transmits by contact on the films 6 between the inductor arms 10, a high temperature on the surface of these films allowing with the clamping pressure exerted at this location, bonding or welding in this area. This welding is said to be by thermal pulse because it is caused by the external application of heat to the materials of the films 6, coming from contact with the internal concentrator 14 giving thermal conduction.

The external concentrators 12 have an average magnetic permeability in order to limit their iron losses, which also makes it possible to delimit the weld in a precise manner beyond each branch of inductor 10.

Figures 7 and 8 show, as a function of the distance from the median plane P, expressed in meters, the temperature reached by the layers of a complex film 6 expressed in degrees Celsius, presented by a first curve for the aluminum layer 50, by a second curve for the polyethylene layer 52 and by a third curve for the polypropylene layer 54. The ambient temperature is far from the median plane P is 22 °.

FIG. 7 shows on each side of the median plane P a temperature peak 56 for the three layers, formed just at the level of each inductor branch 10. In the absence of an internal concentrator, between the two inductor branches 10 the temperature of the three layers increases slightly to reach 30 °.

FIG. 8 also presents a main temperature peak 56 for the aluminum layer 50 and the polyethylene layer 52, formed at each inductor branch 10, with a temperature remaining high between these branches. For the polypropylene layer 54 there is over the entire width of the main peaks 56 and between these peaks, a minimum temperature of 80 ° comprising two secondary peaks 58 close to the median plane P.

Temperatures are obtained well for complex films 6 allowing homogeneously over the entire width between the inductor branches 10, bonding or welding of plastics.

It will be noted that it is also possible, with a welding device according to the invention, to carry out the operations presented in FIG. 7 not comprising any welding or bonding between the branches of inductor 10, with a simple exchange of the internal concentrator 14 to replace it. by another concentrator having a lower electrical resistivity, making it possible to reduce its induced currents and therefore its temperature.

In addition, just after the heating and the fusion of the welding materials of the films 6, the cutting blade 30 comes to press on the internal concentrator 14 having a high mechanical hardness to avoid wear, which constitutes a stop allowing a sharper cut than the shearing. formed by the devices according to the prior art, and delivering less waste.

The thermal regulation of the various components thanks to the water circuits makes it possible to improve the efficiency of the welding carried out by thermal impulse at the level of the interior concentrator 14. In fact it is possible with these circulations of water to preheat the interior concentrator 14 , saving welding time for this part, in particular at the start of the welding cycles.

FIG. 9 presents a front view of an induction jaw 2, comprising two inductor branches 10 as well as an interior concentrator 14 forming in the longitudinal direction a curvature. The counter-jaw 4 disposed opposite has a cutting blade 30 having the same curvature, so as to come in the axis of the median plane P.

A similar, continuous weld is obtained between the two inductor arms 10, making it possible to follow, on films 6, a weld and cutting contour which is curved.

FIG. 10 presents a front view of an induction jaw 2, comprising an inductor 10 with four parallel branches, and an internal concentrator 14 disposed between all the inductor branches comprising three zones in the transverse direction.

The internal concentrator 14 is a hard electric resistive material with magnetic permeability. The part of the internal concentrator 14 in the median plane P receiving the support of the cutting blade 30, is made of a material with high hardness. A wider weld is thus obtained, with the need for a material of the inner concentrator 14 with high hardness only in line with the cutting blade 30.

Claims (9)

1. Device for welding flexible materials (6) superimposed, comprising an induction jaw (2) equipped with an inductor with several parallel branches (10), and a counter-jaw (4) provided for clamping the films (6 ) on the induction jaw (2), characterized in that the induction jaw (2) comprises between the inductor branches (10) an internal concentrator (14) made of a hard material having magnetic permeability and a electrical resistivity. 2. Welding device according to claim 1, characterized in that in the transverse direction, the interior concentrator (14) fills all the space between the inductor branches (10). 3. Welding device according to any one of the preceding claims, characterized in that in the longitudinal direction the internal concentrator (14) has inserts (22) having a different magnetic permeability or electrical resistivity. 4. Welding device according to any one of the preceding claims, characterized in that the interior concentrator (14) has a channel provided for circulation of water. 5. Welding device according to any one of the preceding claims, characterized in that the counter-jaw (4) comprises at least one cutting blade (30) aligned between two inductor branches (10). 6. Welding device according to claim 5, characterized in that in a welding position the cutting blades (30) of the counter-jaw (4) come to bear directly on the surfaces of the interior concentrator (14). 7. Welding device according to claim 6, characterized in that the surfaces of the interior concentrator (14) receiving the support of the cutting blades (30), comprise a material having a "Vickers" hardness greater than 170HV. 8. A method of welding overlapping films (6) using a welding device according to any one of the preceding claims, characterized in that it simultaneously applies pressure to these films (6) and induction heating. 9. A welding method according to claim 8, characterized in that it performs a preheating of the interior concentrator (14) before induction welding, by a circulation of hot water in this concentrator. 2/4 3/4 4/4