The present invention relates to a welding bar according to the pre-characterizing part of the main claim.

Welding bars of the aforesaid type have been known for some time and are used, for example, in packaging machines adapted to form tubular packages containing one or more articles. Fig. 1 shows an example of these tubular packages 1 .

Generally, as shown schematically in Fig. 2, known packaging machines receive, at the inlet, an endless tubular element 4 already containing the articles 8 to be packaged, and is provided with a welding and dividing station 10 (also of known type), comprising for example rotating means 5 to which one or more welding bars 6, 7 are constrained in positions overlapping on one another (as shown in Fig. 2). The rotating means 5 and the welding bars 6A, B, 7A, B, as known to those skilled in the art, are structured and sized so that their outermost surfaces 9 and 10 come into contact with a predetermined frequency, in an operating position P (Fig. 2), and in this position the surfaces can transversely weld and divide the tubular element 4 into the desired packages 1 .

As is customary to those skilled in the art, the known packages are preferably made by starting with a single thin film folded so as to form a tubular element, generally they have a central area 1 A on their lower face in which the thin film that forms the package is of greater thickness with respect to the other areas 1 B and 1 C of the package; therefore transversely the packages do not have a uniform thickness.

For some time there has been the technical problem linked to producing packages in which the extreme transverse closing portions 1 D, 1 E (Fig. 1 ) of the package, effectively close the package without damaging the film of the package. In fact, it can occur that if the compression force exerted by the welding bars is too weak, the package is not closed correctly (for example it is not welded in the area of greater thickness) and, on the contrary, if this force is too great, the film of the package is damaged in this area of greater thickness.

To solve the technical problem above, there are known bars in which the two outer surfaces of the bars adapted to perform the welding are made of two materials with different elasticity (in this sense see, for example, US6230781 ). In another known solution a bearing made of an elastic material is inserted between a welding element and a body carrying this welding element (in this sense, see US6041580). Both these solutions complicate the assembly and the structure of the welding bars and in any case are not always able to solve the technical problem indicated above.

The object of the present invention is to produce a welding bar that is simple to assemble and that solves the technical problem linked to the fact of making appropriate welds also in the transverse segments of the packages of greater thickness.

These and other objects, that will be apparent to an expert skilled in the art, are achieved by a welding bar in conformity with the characterizing part of the main claim.

For a better understanding of the present invention, drawings are attached purely by way of non-limiting example, wherein:

Fig. 1 shows a schematic perspective bottom view of a customary package of the type in which the transverse closing areas have a variable thickness,

Fig. 2 shows a schematic and partial view of a welding and dividing station of a packaging machine,

Figs. 3A-3H show: a schematic perspective top view of a first embodiment of a welding bar according to the invention (Fig. 3A), a schematic front view (Fig. 3B), a schematic enlargement (Fig. 3C) of the detail of Fig. 3B identified by a dashed circle, a schematic partial lateral view (Fig. 3D), a schematic top view (Fig. 3E), a schematic partial cross sectional view (Fig. 3F) taken along the line FF of Fig. 3B, a schematic enlargement (Fig. 3G) of the detail of Fig. 3F identified by a dashed circle, a schematic longitudinal sectional view (Fig. 3H) taken along the line H-H of Fig. 3E;

Figs. 4A-H show: a schematic perspective top view of a second embodiment of a welding bar according to the invention (Fig. 4A), a schematic front view (Fig. 4B), a schematic enlargement (Fig. 4C) of the detail of Fig. 4B identified by a dashed circle, a schematic partial lateral view (Fig. 4D), a schematic top view (Fig. 4E), a schematic partial cross sectional view (Fig. 4F) taken along the line FF of Fig. 4B, a schematic enlargement (Fig. 4G) of the detail of Fig. 4F identified by a dashed circle, a schematic longitudinal sectional view (Fig. 4H) taken along the line H-H of Fig. 4E; Fig. 41 shows a schematic front view of a variant of the bar of Figs. 4A-H, Figs. 5A-L show: a schematic perspective top view of a third embodiment of a welding bar according to the invention (Fig. 5A), a schematic front view (Fig. 5B), a schematic enlargement (Fig. 5C) of the detail of Fig. 5B identified by a dashed circle, a schematic partial lateral view (Fig. 5D), a schematic top view (Fig. 5E), a schematic partial cross sectional view (Fig. 5F) taken along the line FF of Fig. 5B, a schematic enlargement (Fig. 5G) of the detail of Fig. 5F identified by a dashed circle, a schematic longitudinal sectional view (Fig. 5H) taken along the line H-H of Fig. 5E; a schematic partial cross sectional view (Fig. 51) taken along the line l-l of Fig. 5B, a schematic enlargement (Fig. 5J) of the detail of Fig. 51 identified by a dashed circle, a schematic partial cross sectional view (Fig. 5K) taken along the line KK of Fig. 5B, a schematic enlargement (Fig. 5L) of the detail of Fig. 5K identified by a dashed circle;

Figs. 6A-H show: a schematic perspective top view of a fourth embodiment of a welding bar according to the invention (Fig. 6A), a schematic front view (Fig. 6B), a schematic enlargement (Fig. 6C) of the detail of Fig. 6B identified by a dashed circle, a schematic partial lateral view (Fig. 6D), a schematic top view (Fig. 6E), a schematic partial cross sectional view (Fig. 6F) taken along the line FF of Fig. 6B, a schematic enlargement (Fig. 6G) of the detail of Fig. 6F identified by a dashed circle, a schematic longitudinal sectional view (Fig. 6H) taken along the line H-H of Fig. 6E.

With reference to Figs. 3A-H, these show a first embodiment of a welding bar 1 1 (FIG. 3A) according to the present invention, comprising an elongated body 16 having: at least one outer welding surface 12A, 12B (in the embodiment in the figures in question there are two outer surfaces) having, in cross sectional view (Figs. 3D, 3H-3J) and when the bar is in the resting position, an arched outline M1 and preferably a longitudinally or transversely serrated surface finish S1 , and at least one cavity 13A ,13B, 13C (in the embodiment of the figures in question there are three cavities) provided under at least one central longitudinal portion 14 (Fig. 3B) of said at least one welding surface 12A,12B and delimited at least by a first internal surface 15A (Figs. 3H-3J) closer to the outer welding surface 12A, 12B and by a second internal surface 15B opposite the first 15A.

According to the invention, the first internal surface 15 A has, in cross section, an arched outline M2 when the welding bar is in resting condition (as in Figs. 3H-3J). More in particular, the welding bar 1 1 , with the exception of the presence and of the structure of the cavity/cavities 13A-C, is a bar of substantially customary type for the expert skilled in the art and consequently will not be described in detail hereinafter.

The welding bar has an elongated and substantially parallelepiped shape, more precisely it comprises a base element 16A from which a welding element 18 branches off (Fig. 3A). The base element 16 is adapted to be constrained to customary movement means 5 (Fig. 2), for example to a rotating shaft 5A (Fig. 2), for example by means of constraining members passing through through holes 17A. The base element 16A also has further cavities 17B and holes 17C, 17D, 17E, of the conventional type for those skilled in the art, for example to house an electric resistor and/or sensors, adapted to heat and control the temperature of the welding surfaces 12A-B. The base element 16A has, for example, an arched lower surface 16B, preferably shaped as an arc of circle, front and rear surfaces 16B and C parallel to each other, lateral surfaces 16D and 16E also parallel to each other, and a flat upper surface 16F preferably perpendicular to the lateral and front and rear surfaces.

Above the base element 16A, the bar 1 1 has a welding element 18 comprising the two outer welding surfaces 12A-B and the cavities 13A-C. Advantageously, between the two outer welding surfaces 12A-B a longitudinal slot 18A (Fig. 3D) is provided, suitable to house a customary cutting member 9A (Fig. 2) or a customary stop member 10A (Fig. 2) for said cutting member. The slot 18A divides the welding element 18 into two welding bodies 18D and 18E that branch off from a base body 18 F.

The welding element 18 has customary threaded through holes 18B and 18C for housing the customary members (not represented) for adjusting the position of the cutting 9A and stop 10A members, with respect to the welding surfaces 12A-B, and for constraining said cutting and stop members in the adjusted position.

The welding element 18 has an elongated shape with front and rear walls 18H-G (Fig. 3E), preferably parallel to the corresponding front and rear walls 16B-C of the base element 16 and lateral walls 181-J, preferably parallel to the corresponding lateral walls 16D-E of the base element. As stated above, the two outer welding surfaces 12A, 12B have, in cross sectional view (Figs. 3D, 3H-3J) and when the bar is in a resting position, an arched outline M1 and preferably a longitudinally serrated surface finish S1 , S2.

The serrated surface finish S1 , S2 has (Fig. 3D) a plurality of raised elements 20A spaced by recessed elements 20B, all having the same parallel development at a longitudinal axis L (Fig. 3E) of the bar. The raised elements 20A advantageously have rounded apexes to avoid damaging the film of the package to be welded. The arched outline M1 of the outer welding surfaces 12A, 12B is represented by a line M1 tangent to the apexes of the raised elements 20A of the serrated finish S1 S2 (as shown in Fig. 3D).

Preferably, the arched outline of the outer welding surfaces 12A, 12B has the shape of an arc of circle, for example with radius of curvature ranging between 35 mm and 120 mm. Preferably, both the welding surfaces have the same arched outline, which lies in the same arc of circle with radius of curvature ranging between 35 mm and 120 mm.

Preferably, the welding surfaces have an outline increasing from the outside of the welding bodies 18E and 18D towards the inside so that the apex 20C (Fig. 3G) of the outermost raised element of the serrated surface finishes S1 , S2 is at a lower height H5 with respect to the height H6 of the apex 20D of the innermost raised element.

It has been found through experimentation that the aforesaid radii of curvature and amplitude of the arcs of circle ensure optimal welding results of the packages.

The welding bar 1 1 has three cavities 13A, 13B, 13C provided under at least one central portion 14 (Fig. 3B) of the two welding surfaces 12A, 12B and delimited by a first internal surface 15A (Fig. 3G) closer to the outer welding surface 12A, 12B and by a second internal surface 15B opposite the first 15A. According to the invention, the first internal surface 15A has, in cross section, an arched outline M2 when the welding bar is in resting condition (as in Fig. 3A).

The three cavities 13A-C are substantially identical and overlapping with respect to one another, preferably the distance P1 between one cavity and the other is the same, for example ranging between 0.3 mm and 10 mm and more preferably ranging between 0.3 mm and 2mm.

Hereinafter the shape of the first cavity 13A of the welding body 18E will be described, but the same considerations are also true for the other cavities 13B and 13C and for the cavities of the other welding body 18F.

Advantageously, the arched outline M2 (Fig. 3G) of the first internal surface 15A that delimits the first cavity 13A is substantially identical to the arched outline M1 of the corresponding outer welding surface 12A, B (in the present context substantially identical means that the difference between the two arched outlines is, for example, less than 5%).

Advantageously, the arched outline of the first internal surface 15A that delimits the first cavity 13A has the shape of an arc of circle, for example with radius of curvature ranging between 35 mm and 120 mm.

Advantageously, the arc of circle M2 (Fig. 3G) of the first internal surface 15A that delimits the first cavity 13A is substantially identical to the arc of circle M1 of the corresponding outer welding surface 12A, B (in the present context substantially identical means that the difference between the two arcs of circle is less than 5%). The second internal surface 15B that delimits the cavity 13A is preferably a surface having the same characteristics and the same shape as the first surface 15A. The two surfaces are spaced from each other by a constant segment P2, for example ranging between 0.3mm and 10 mm, which coincides with the height of the cavity 13A.

The cavity 13A closest to the welding surface 12A is preferably spaced from said welding surface, in the central portion 18C of the welding body, by a segment P3 (Fig. 3G) ranging between 0.3 mm and 10 mm.

Advantageously, the cavity 13A is a through cavity, i.e., it involves the entire thickness S (Fig. 3G) of the welding bodies 18E that end with the welding surfaces 12A, 12B. The cavities are therefore open and visible both at the outer wall 18H and at the internal wall 18J of the welding body 18E; at said walls the cavity comprises an outer 19A (Fig. 3A) and an internal 19B opening (partially visible in Fig. 3A)

Advantageously, the cavity 13A transversely has an outline increasing from the outside of the welding body 18E towards the inside of the body (i.e., from the outer wall 18H of the welding body 18E to the wall 18J (Fig. 3D) of the longitudinal central slot 18A of the welding element), so that the outermost point K1 (Fig. 3G) of the curvature of the first internal surface 15 is at a lower height H1 (with respect to a horizontal support plane O of the bar) with respect to the corresponding height H2 of the innermost point K2 of said first internal surface 15. Therefore, the outer 19A and internal 19B openings (Fig. 3A) are not at the same height, but the internal opening 19B is at a greater height with respect to the outer opening 19B. This transversely increasing outline of the cavity produces cavities that for each transverse section of the bar, copy in a substantially identical manner the transverse outline of the segment of the welding surface above, in this way it is possible to produce welding bars that for each transverse section thereof transversely have substantially uniform characteristics of elasticity.

Advantageously, the cavity 13A extends longitudinally not only at the central longitudinal portion 14 (Fig. 3B) of the two welding surfaces 12A, 12B but also in outermost longitudinal portions 14A, B (Fig. 3B) of these welding surfaces, adjacent to said central portion 14. By way of example, the central portion 14 has a length D1 (Fig. 3B) ranging between 10% and 70% of the total length D of the welding surfaces 12A, 12B, and the outermost portions, in which it is advantageous for the cavity to extend, have a length D2, D3 ranging between 10% and 70% of the total length D of the welding surfaces. According to a preferred embodiment, the cavities 13 A-C are not present only in extreme portions 14C and 14D of the welding surfaces 12 A-B, having a total length D4 D5 ranging between 1 % and 30% of the total length D of the welding surfaces.

Advantageously, the cavity 13A longitudinally has an arched outline M10 (Fig. 3B) and more preferably has the shape of an arc of circle.

Preferably, the cavity 13A has an outline increasing longitudinally from the ends 18M, 18N (Fig. 3B) of the welding body 18E towards a central segment 18P of the same body, so that the central longitudinal segment 13K (Fig. 3B) of the cavity 13 is also the segment of the cavity at the shortest distance from the corresponding most central segment 18P of the welding body 18 and of the welding surface 12B, whereas the extreme longitudinal segments 13M, 13N of the cavity are those at the greatest distance from the corresponding end segments 18M and 18N of the welding body 18 and of the welding surface 12B. It has been found through experimentation that the shape of the cavity 13A ensures that the welding surface is more elastic in its central portion 14 (Fig. 3) and less elastic in its outermost longitudinal portions 14A-B. The presence of the cavities 13A-C ensures that the welding surfaces 12A and 12B have variable elasticity, greater in their most central part 14 (Fig. 3E) and lower in the most extreme parts (14A-B). This variable elasticity allows optimal welding without damaging the packaging film, of packages 1 that transversely do not have a uniform thickness, and have, as shown in Fig. 1 , a central area 1 A in which the thin film that forms the package has a greater thickness with respect to the other areas 1 B and 1 C of the package. By ensuring that during the welding process the portion 1 A of greater thickness is located in the area 14 of the welding surface with greater elasticity, it has been found through experimentation that it is possible to obtain packages in which the transverse welds have no defects.

Advantageously, the welding bar described above is obtained by means of: conventional 3D printing techniques, with which a rough bar comprising the cavities 13A-C is produced, and subsequent customary finishing operations of the printed bar, with which, for example, the serrated welding surfaces 12A-B and/or the holes 17A-E and 18B-C and the longitudinal slot 18A are produced.

The bar is made of a metal material of customary type for producing "hot" welding bars (i.e., bars comprising an electric resistor), or of a plastic material of customary type for producing "cold" bars. Preferably, the bar according to the invention is made entirely of the same metal material or of the same plastic material. The bar could also be made of a metal/plastic composite material and also in this case it would be made entirely of said composite material. However, the various parts of which the bar is composed could also be made of two or more different materials, for example the base element 16 of the bar could be made of a plastic material and the welding element 18 of a metal material, or vice versa, with said two elements rigidly constrained to each other in a conventional manner for those skilled in the art. Likewise, the welding element 18 could in turn be made of different materials, for example with an upper layer thereof comprising the welding surface, made of a metal material and a lower layer thereof comprising the cavity/cavities made of a plastic material, or vice versa, and with said two layers rigidly constrained to each other in a conventional manner for those skilled in the art.

According to a first variant of the embodiment discussed above, a welding bar could have a smaller (for example one or two) or greater (for example ranging between four and ten) number of cavities identical to the cavities 13A-C discussed above.

It is also noted that the base body 16 and the welding body 18 that in the embodiment described above are made in one piece could also be made in two separate pieces connected to each other by means of customary constraining members (such as screws).

With reference to Figs. 4A-H, these show a second embodiment of a welding bar according to the invention; the technical characteristics in common with the bar of the first embodiment, described above with reference to Figs. 3A-H, will not be described again and will be indicated in Figs. 4A-H with the same numbers used for Figs. 3A-H, increased by 100.

The bar 1 1 1 of this second embodiment differs from the bar 1 1 described previously, essentially only for the shape of the cavity 1 13.

As for the bar described above, the arched outline M1 of the outer welding surfaces 1 12A, 1 12B is represented by a line M1 tangent to the apexes of the raised elements 120A of the serrated finish S1 (as shown in Fig. 4D).

Preferably, the arched outline of the outer welding surfaces 1 12A, 1 12B has the shape of an arc of circle, for example with radius of curvature ranging between 35 mm and 120 mm. Preferably, both the welding surfaces have the same arched outline, which lies in the same arc of circle with radius of curvature ranging between 35 mm and 120 mm.

Preferably, the welding surfaces have an outline increasing from the outside of the welding bodies 1 18E and 1 18D towards the inside so that the apex 120C (Fig. 4G) of the outermost raised element of the serrated surface finishes S1 is at a lower height H6 with respect to the height H5 of the apex 120D of the innermost raised element.

It has been found through experimentation that the aforesaid radii of curvature and amplitude of the arcs of circle ensure optimal welding results of the packages. The welding bar 1 1 1 has a cavity 1 13 provided under at least one central portion 1 14 (Fig. 4B) of the two welding surfaces 1 12A, 1 12B and delimited by a first internal surface 1 15A (Fig. 4G) closer to the outer welding surface 1 12A, 1 12B and by a second internal surface 1 15B opposite the first 1 15A. According to the invention, the first internal surface 1 15A has, in cross section, an arched outline M2 when the welding bar is in resting condition (as in Fig. 3A).

Advantageously, the arched outline M2 (Fig. 4G) of the first internal surface 1 15A that delimits the cavity 1 13 is substantially identical to the arched outline M1 of the corresponding outer welding surface 1 12A, B (in the present context substantially identical means that the difference between the two arched outlines is less than 5%).

Advantageously, the arched outline of the first internal surface 1 15A that delimits the cavity 1 13 has the shape of an arc of circle, for example with radius of curvature ranging between 35 mm and 120 mm.

Advantageously, the arc of circle M2 (Fig. 4G) of the first internal surface 1 15A that delimits the cavity 1 13 is substantially identical to the arc of circle M1 of the corresponding outer welding surface 1 12A, B (in the present context substantially identical means that the difference between the two arcs of circle is less than 5%). The second internal surface 1 15B that delimits the cavity 1 13 is preferably a surface having the same characteristics and the same shape as the first surface 1 15A. The two surfaces are spaced from each other by a constant segment P2, for example ranging between 0.3mm and 10 mm and more preferably ranging between 0.3mm and 2mm, which coincides with the height of the cavity 1 13.

The cavity 1 13 is preferably spaced from said welding surface 1 12A by a segment P3 (Fig. 4G) ranging between 0.5 mm and 10 mm.

Advantageously, the cavity 1 13 is a through cavity, i.e., it involves the entire thickness S (Fig. 4G) of the welding bodies 1 18E, F that end with the welding surfaces 1 12A, 12B. The cavity 1 13 is therefore open and visible both at the outer 1 18H, 1 18G and internal 1 18 J walls of the welding bodies 1 18E, 1 18F; at said walls the cavity comprises an outer 1 19A (Fig. 4A) and an internal 1 19B opening (partially visible in Fig. 4A).

The cavity 1 13 has a plurality of transverse walls 121 A, B (Fig. 4H) that connects the first 1 15A and the second 1 15B surface of the cavity to each other. These transverse walls are suitable to act as elastic elements and to allow differentiated bending of the welding surfaces 1 12A, B: i.e., bending to a greater extent in the central part 1 14 (Fig. 4B) of said surfaces (where the film of the packages, having greater thickness, is to be welded) and to a lesser extent in the parts 1 14A, B adjacent to said central part. This differentiated elasticity allows optimal welding without damaging the packaging film, of packages 1 that transversely do not have the same thickness. It has been found through experimentation that it is possible to obtain packages in which the transverse welds have no defects.

According to a preferred embodiment, the transverse walls 121 A, B have an inclined outline with respect to a horizontal plane forming an angle Z1 , Z2 (Fig. 4H) ranging between 10° and 60°. Moreover, the transverse walls 121 A, B have symmetrical inclinations with respect to a vertical central axis L3 (Fig. 4H), so that the walls inclined to the right and to the left of this axis have identical but opposite inclinations (Fig. 4H).

Advantageously, the distance F1 between the most central transverse walls 121 B' and 121 A' is greater than the distance F2 between the other transverse walls 121 A and B adjacent to each other (Fig. 4H); for example:

1 %F1 <=F2=< 80%F1

Advantageously, the thickness S1 (Fig. 4C) of the transverse walls 121 A and B is constant and ranging between 0.3 mm and 10mm, more preferably ranging between 0.5mm and 1 mm.

The transverse walls 121 A and B divide the cavity 1 13 into a plurality of sub- cavities: a central sub-cavity 1 13E (Fig. 4H), and lateral sub-cavities 1 13F.

Advantageously, the cavity 1 13 transversely has an outline increasing from the outside of the welding body 1 18E towards the inside of the body (i.e., from the outer wall 1 18H of the welding body 1 18E to the wall 1 18 J (Fig. 4F) of the longitudinal central slot 1 18A of the welding element), so that the outermost point K1 (Fig. 4G ) of the curvature of the first internal surface 1 15 is at a lower height H1 (with respect to a horizontal support plane O of the bar) with respect to the corresponding height H2 of the innermost K2 of said first internal surface 1 15. Therefore, the outer 1 19A and internal 19B openings (Fig. 4A) are not at the same height, but the internal opening 1 19B is at a greater height with respect to the outer opening 1 19B. This transversely increasing outline of the cavity provides cavities that for each transverse section of the bar, copy in a substantially identical manner the transverse outline of the segment of the welding surface above, in this way it is possible to produce welding bars that for each transverse section thereof transversely have substantially uniform characteristics of elasticity.

Advantageously, the cavity 1 13 longitudinally has a rectilinear outline parallel to that of the welding surfaces 1 12A and B.

Advantageously, the cavity 1 13 extends for the entire length of the welding surface.

The presence of the cavity 1 13 and in particular the presence of the inclined transverse walls 121 A and B of the cavity, ensure that the welding surfaces 1 12A and B have a variable elasticity, greater in their most central part 1 14 (Fig. 4b) and lower in the most extreme parts (1 14A-B), allowing packages with variable thickness, greater in the centre and lower in the lateral parts of the package, to be welded without defects.

Advantageously, the welding bar described above is obtained by means of: conventional 3D printing techniques, with which a rough bar comprising the cavity 1 13 is produced, and subsequent customary finishing operations of the printed bar, with which, for example, the serrated welding surfaces 1 12A-B and/or the holes 1 17A-D and 1 18B-C, as well as the longitudinal slot 1 18A, are produced. The bar can be made of the same materials and with the same combinations of materials indicated with reference to the first embodiment of the invention.

According to a first variant of the embodiment discussed above, a welding bar could have a greater number of cavities 1 13 substantially identical and overlapping with respect to one another, for example spaced from one another by a segment ranging between 0.3 mm and 10 mm, more preferably between 0.3 mm and 5 mm. Fig. 4I shows a bar 1 1 1 ' that is a further variant of the embodiment of Figs. 4A-H, the cavity 1 13' of this variant has the same shape and dimensions as the cavity 1 13 described previously and therefore will not be further describe hereunder; however, the transverse walls 121 ' are not inclined but have a perpendicular outline with respect to a horizontal surface.

Advantageously, the distance between the transverse walls 121 ' is constant and for example ranging between 1 mm and 10mm.

Advantageously, the thickness of the transverse walls 121 ' is constant and ranging between 0.3 mm and 1 mm, more preferably ranging between 0.3mm and 0.5mm. It is also noted that the base body 1 16 and the welding body 1 18 that in the embodiment described above are made in one piece could also be made in two separate pieces connected to each other by means of customary constraining members (such as screws). With reference to Figs. 5A-L, these show a third embodiment of a welding bar according to the invention, the technical characteristics in common with the bar of the first and second embodiments, previously described with reference to Figs. 3A-H and 4A-H, will not be described again and will be indicated in Figs. 5A-H with the same numbers used for Figs. 3A-H and 4A-H, but increased by 100 (Figs. 3A- H) or 200 (Figs. 4A-H).

The bar 21 1 of this second embodiment differs from the bar 1 1 previously described essentially only for the shape of the cavity 213.

As for the bar previously described, the arched outline M1 of the outer welding surfaces 212A, 212B is represented by a line M1 tangent to the apexes of the raised elements 220A of the serrated finish S1 (as shown in Fig. 5D).

Preferably, the arched outline of the outer welding surfaces 212A, 212B have the shape of an arc of circle, for example with radius of curvature ranging between 35 mm and 120 mm. Preferably, both the welding surfaces have the same arched outline, which lies in the same arc of circle with radius of curvature ranging between 35 mm and 120 mm.

Preferably, the welding surfaces have an outline increasing from the outside of the welding bodies 218E and 218D towards the inside so that the apex 220C (Fig. 4G) of the outermost raised element of the serrated surface finishes S1 is at a lower height H5 with respect to the height H6 of the apex 220D of the innermost raised element.

It has been found through experimentation that the aforesaid radii of curvature and amplitude of the arcs of circle ensure optimal welding results of the packages. The welding bar 21 1 has three cavities 213A, 213B, 213C (Fig. 5C), indicated as a whole with the reference 213, provided under at least one central portion 14 (Fig. 5B) of the two welding surfaces 212A, 212B; each cavity is delimited by a first internal surface 215A (Fig. 5G) closer to the outer welding surface 212A, 212B and by a second internal surface 215B opposite the first 215A. According to the invention, the first internal surface 215A has, in cross section, an arched outline M2 (Fig. 5G) when the welding bar is in resting condition (as in Fig. 5A).

The three cavities 213A-C are substantially identical and overlapping with respect to one another; preferably the distance P1 (Fig. 5J) between one cavity and the other is the same, for example ranging between 0.3mm and 10 mm and more preferably ranging between 0.3 mm and 2 mm.

Hereunder the shape of the first cavity 213A of the welding body 218E will be described, but the same considerations are also true for the other cavities 213B and 213C and for the cavities of the other welding body 218F.

Advantageously, the arched outline M2 (Fig. 5G) of the first internal surface 215A that delimits the first cavity 213A is substantially identical to the arched outline M1 of the corresponding outer welding surface 212A, B (in the present context substantially identical means that the difference between the two arched outlines is less than 5%).

Advantageously, the arched outline of the first internal surface 215A that delimits the first cavity 213A has the shape of an arc of circle, for example with radius of curvature ranging between 35 mm and 120 mm.

Advantageously, the arc of circle M2 (Fig. 5G) of the first internal surface 215A that delimits the first cavity 213A is substantially identical to the arc of circle M1 of the corresponding outer welding surface 212A, B (in the present context substantially identical means that the difference between the two arcs of circle is less than 5%).

The second internal surface 215B that delimits the cavity 213A is preferably a surface having the same characteristics and the same shape as the first surface 215A. The two surfaces are spaced from each other by a constant segment P2 (Fig. 5G), for example ranging between 0.3mm and 10 mm and more preferably ranging between 0.3 mm and 2mm, which coincides with the height of the cavity 213A.

The cavity 213A closest to the welding surface 212A is preferably spaced from said welding surface, in the central portion 218C of the welding body, by a segment P3 (Fig. 5G) ranging between 0.3 mm and 10 mm.

Advantageously, the cavity 213A is a through cavity, i.e. involves the whole thickness S (Fig. 5G) of the welding bodies 218E that end with the welding surfaces 212A, 212B. The cavities are therefore open and visible both at the outer wall 218H and at the internal wall 218J of the welding body 218E; at said walls the cavity comprises outer openings 219A (Fig. 5C) and an internal opening 219B

(partially visible in Fig. 5A)

Advantageously, the cavity 213A transversely has an outline increasing from the outside of the welding body 218E towards the inside of the body (i.e., from the outer wall 218H of the welding body 218E to the wall 218J (Fig. 5D) of the longitudinal central slot 218A of the welding element), so that the outermost point K1 (Fig. 5G) of the curvature of the first internal surface 215 is located at a lower height H1 (with respect to a horizontal support plane O of the bar) with respect to the corresponding height H2 of the innermost point K2 of said first internal surface 215. Therefore, the outer 219A and internal 219B openings (Fig. 3A) are not at the same height, but the internal opening 219B is at a greater height with respect to the outer opening 219B. This transversely increasing outline of the cavity provides cavities that for each transverse section of the bar, copy in a substantially identical manner the transverse outline of the segment of the welding surface above; in this way it is possible to produce welding bars that for each transverse section thereof transversely have substantially uniform characteristics of elasticity.

The cavity 213A has a plurality of transverse walls 221 (Fig. 5C) that connects the first 215A and the second 215B surface of the cavity to each other. These transverse walls are suitable to act as elements for transmitting and concentrating the force F (Fig. 5C) applied to specific portions of the welding surface over said walls 221 , and are adapted to transmit a corresponding force F1 to the cavity below. This particular shape of the cavities is particularly useful when the portion of package to be welded does not have a single central segment of greater thickness but also has further segments of greater thickness at the sides of said central segment. Ultimately, the bar according to the present embodiment allows a differentiated bending of the welding surfaces 212A, B: i.e., bending to a greater extent in the parts of said surfaces in which a segment of the package having greater thickness is to be welded. This differentiated elasticity allows optimal welding without damaging the packaging film, of packages 1 that transversely do not have a uniform thickness. It has been found through experimentation that it is possible to obtain packages in which the transverse welds have no defects.

According to a preferred embodiment, the transverse walls 221 A, B have a perpendicular outline with respect to a horizontal plane, and therefore are similar to transverse columns.

Advantageously, the distance between the transverse walls 221 (Fig. 5C) is constant. Advantageously, the thickness S1 (Fig. 5C) of the transverse walls 221 is constant and ranges between 0.3mm and 10mm, more preferably ranges between 0.5mm and 1 mm.

The transverse walls 221 divide the cavities 213A-C into a plurality of sub-cavities 213A'-C all identical to one another, although these sub cavities could, in a variant not represented, also have different dimensions to one another, for example greater at the central part of the welding surfaces.

Advantageously, the cavity 213A longitudinally has a rectilinear outline parallel to that of the welding surfaces 212A and B.

Advantageously, the cavity 213A extends longitudinally not only at the central longitudinal portion 214 (Fig. 5B) of the two welding surfaces 212A, 212B but also in outermost longitudinal portions 214A, B (Fig. 5B) of these welding surfaces, adjacent to said central portion 214.

Advantageously, the cavity 213 A does not extend also in the most extreme segments 214D and 214C of the two welding surfaces 214A and B; these end segments without cavities have, for example, a length having a total length D4 D5 ranging between 1 % and 30% of the total length D of the welding surfaces.

Advantageously, the welding bar described above is obtained by means of: conventional 3D printing techniques, with which a rough bar comprising the cavities 213 is produced, and subsequent customary finishing operations of the printed bar, with which, for example, the serrated welding surfaces 212A-B and/or the holes 217A-D and 218B-C and the longitudinal slot 218A are produced.

The bar can be made of the same materials and of the same combination of materials indicated with reference to the first embodiment of the invention.

According to a first variant of the embodiment discussed above, a welding bar could have a smaller (for example two) or larger (for example ranging between four and ten) number of cavities, identical to the cavities 213A-C discussed above. According to a further variant, to increase the elasticity at the central part 214 of the welding surfaces 212A and B the length V (Fig. 5C) of the sub-cavities 213A'- C could be greater with respect to the similar length of the sub-cavities provided in the parts 214 A and B of the welding surfaces, adjacent to said central part.

It should also be noted that the base body 216 and the welding body 218 that in the embodiment described above are made in one piece could also be made in two separate pieces connected to each other by means of customary constraining members (such as screws).

With reference to Figs. 6A-H these show a fourth embodiment of a welding bar according to the invention; the technical characteristics in common with the bar of the first, second and third embodiments, described above with reference to Figs. 3-5A-H, will not be described again and will be indicated in Figs. 6A-H with the same numbers used for Figs. 3A-H, 4A-H, 5A-L increased by 100 (Figs. 3A-H), 200 (Figs. 4A-H) or 300 (Figs. 5A-L).

The bar 31 1 of this fourth embodiment differs from the bars previously described essentially only for the shape of the cavity 313.

As for the bar previously described, the arched outline M1 of the outer welding surfaces 312A, 312B is represented by a line M1 tangent to the apexes of the raised elements 320A of the serrated finish S1 (as shown in Fig. 6D).

Preferably, the arched outline of the outer welding surfaces 312A, 312B has the shape of an arc of circle, for example with radius of curvature ranging between 35 mm and 120 mm. Preferably, both the welding surfaces have the same arched outline, which lies in the same arc of circle with radius of curvature ranging between 35 mm and 120 mm.

Preferably, the welding surfaces have an outline increasing from the outside of the welding bodies 318E and 318D towards the inside so that the apex 320C (Fig. 6G) of the outermost raised element of the serrated surface finishes S1 is at a lower height H6 with respect to the height H5 of the apex 320D of the innermost raised element.

It has been found through experimentation that the aforesaid radii of curvature and amplitude of the arcs of circle ensure optimal welding results of the packages.

The welding bar 31 1 has a cavity 313 provided under at least one central portion 314 (Fig. 6B) of the two welding surfaces 312A, 312B and delimited by a first internal surface 315A (Fig. 6G) closer to the outer welding surface 312A, 312B and by a second internal surface 315B opposite the first 315A. According to the invention, the first internal surface 315A has, in cross section, an arched outline M2 when the welding bar is in resting condition (as in Fig. 6A).

Advantageously, the arched outline M2 (Fig. 6G) of the first internal surface 315A that delimits the cavity 313 is substantially identical to the arched outline M1 of the corresponding outer welding surface 312A, B (in the present context substantially identical means that the difference between the two arched outlines is less than 5%).

Advantageously, the arched outline of the first internal surface 315A that delimits the cavity 313 has the shape of an arc of circle, for example with radius of curvature ranging between 35 mm and 120 mm.

Advantageously, the arc of circle M2 (Fig. 6G) of the first internal surface 315A that delimits the cavity 313 is substantially identical to the arc of circle M1 of the corresponding outer welding surface 312A, B (in the present context substantially identical means that the difference between the two arcs of circle is less than 10%).

The second internal surface 315B that delimits the cavity 313 is preferably a surface having the same characteristics and the same shape as the first surface 315A. The two surfaces are spaced from each other by a constant segment P2 (Fig. 6G), for example ranging between 0.3 mm and 10 mm and more preferably ranging between 0.3mm and 2mm, which coincides with the height of the cavity 313.

The cavity 313 is preferably spaced from said welding surface 312A by a segment P3 (Figs. 6G and 6C) ranging between 0.3 mm and 10 mm.

Advantageously, the cavity 313 is a through cavity i.e. involves the entire thickness S (Fig. 6G) of the welding bodies 318E, F that end with the welding surfaces 312A, 312B. The cavity 313 is therefore open and visible both at the outer walls 318H, 318G and at the internal walls 318J of the welding bodies 318E, 318F; at said walls the cavity comprises an outer 319A (Fig. 4A) and an internal 319B opening (partially visible in Figs. 6A and 6C).

Advantageously, the cavity 313 transversely has an outline increasing from the outside of the welding body 318E towards the inside of the body (i.e., from the outer wall 318H of the welding body 318E to the wall 318J (Fig. 6F) of the longitudinal central slot 318A of the welding element), so that the outermost point K1 (Fig. 6G) of the curvature of the first internal surface 315 is at a lower height H1 (with respect to a horizontal support plane O of the bar) with respect to the corresponding height H2 of the innermost point K2 of said first internal surface 315. Therefore, the outer 319A and internal 319B openings (Figs. 6A and 6C) are not at the same height, but the internal opening 31 9B is at a greater height with respect to the outer opening 319B. This transversely increasing outline of the cavity provides cavities that for each transverse section of the bar, copy in a substantially identical manner the transverse outline of the segment of the welding surface above; in this way it is possible to produce welding bars that for each transverse section thereof transversely have substantially uniform characteristics of elasticity.

Advantageously, the cavity 313 extends longitudinally not only at the central longitudinal portion 314 (Fig. 6B) of the two welding surfaces 312A, 312B but also in outermost longitudinal portions 314A, B (Fig. 6B) of these welding surfaces, adjacent to said central portion 314. According to a preferred embodiment, the cavity 313 A-C does not extend also in extreme portions 314C and 314D of the welding surfaces 312 A-B, having a total length D4, D5 ranging between 1 % and 30% of the total length D of the welding surfaces.

Advantageously, the cavity 1 13 longitudinally has a regular wavy outline, parallel to that of the welding surfaces 312A and B (the term parallel means that the lines L6, I7, Fig. 6C passing through the apexes of the waves of the cavity are parallel to the corresponding lines of the welding surfaces).

By way of example, the amplitude J2 (Fig. 6C) of the wavy cavity is, for example, ranges between 0.6 mm and 20 mm and the period J1 of the wave ranges between 1 mm and 30mm.

This particular structure of the cavities is particularly useful when the portion of package to be welded does not have a single central segment of greater thickness but also has further segments of greater thickness at the sides of said central segment. Ultimately, the bar according to the present embodiment allows differentiated bending of the welding surfaces 212 A, B: i.e., bending to a greater extent in the parts of said surfaces in which a segment of packaging film having greater thickness is to be welded. This differentiated elasticity allows optimal welding without damaging the packaging film, packages that transversely do not have the same thickness. It has been found through experimentation that it is possible to obtain packages in which the transverse welds have no defects.

Advantageously, the welding bar described above is obtained by means of: conventional 3D printing techniques, with which a rough bar comprising the cavity 313 is produced, and subsequent customary finishing operations of the printed bar, with which for example the serrated welding surfaces 312A-B and/or the holes 317A-D and 18B-C and the longitudinal slot 318A are produced.

The bar can be made of the same materials and with the same combinations of materials indicated with reference to the first embodiment of the invention.

According to a first variant of the embodiment discussed above, a welding bar could have a two or more wavy cavities identical to those described above and, for example, spaced from one another by a segment ranging between 0.3 mm and 10 mm.

It is also noted that the base body 316 and the welding body 318, that in the embodiment previously described, are made in one piece could also be made in two separate pieces connected to each other by means of customary constraining members (such as screws).

Finally, it must be stressed that the embodiments illustrated herein have been provided purely by way of example and that numerous further variants are possible, all falling within the same inventive concept expressed in the main claim. Hence, for example, the bars that have always been described herein as bars suitable to be associated with rotating movement means could be associated with movement means suitable to move them closer together with a linear motion and/or bars with a single welding surface not interrupted by a longitudinal slot for housing a cutting or stop element.