Welding clamp for hot welding and hot welding method

Abstract

The invention relates to a welding clamp for thermally welding a bag wall (1) made of plastic film to a welding region (2) of a mouth (3) made of plastic, comprising a clamp body (4) connected to a heat source, which clamp body (4) has a pressing surface (5) by means of which a surface region (1a) of the bag wall (1) to be welded is pressed against the welding region (2) of the mouth (3), which clamp body (4) is provided with a pressing element (6), in particular, a pressing element (6) is fixed to the caliper body (4), which pressing element (6) has a second pressing surface (7), which is adjacent to the first pressing surface (5) of the caliper body (4), and pressing a surface region (1b) of the bag wall (1), which is not welded but adjoins the surface region (1a) to be welded, against the welding region (2) of the mouth (3) or against the central longitudinal axis (12) of the pouring channel by means of the second pressing surface (7). The invention also relates to a method for thermally welding a bag wall (1) made of plastic film to a welding region (2) of a mouth (3) made of plastic.

Description

Technical Field

[0001] The invention relates to a welding pliers for thermally welding a bag wall made of plastic film to a welding region of a mouth made of plastic. The welding pliers comprise a pliers body which can be connected to a heat source and has a pressing surface with which the surface region of the bag wall to be welded can be pressed against the welding region of the mouth.

[0002] In particular, due to the thermal conductivity of the pliers body, which is preferably made of metal, the pressing surface of the pliers body can be heated indirectly by a heat source, in particular to a temperature above the melting point of the material of the wall and the welding area.

[0003] By pressing the wall against the welding area using the heated pressing surface, the wall and the welding area are heated, in particular to above their respective melting points, so that the two parts are integrally joined together at their mutually facing surfaces under the effect of the applied welding pressure.

[0004] The present invention also relates to a method for thermally welding a bag wall made of plastic film to a welding area of ​​a mouth made of plastic, in which method two oppositely placed welding pliers each have a pliers body connected to a heat source, and the two welding pliers are moved from opposite directions toward the welding area, wherein each pliers body has a pressing surface, by means of which the surface area to be welded of the bag wall located between the pressing surface and the welding area is pressed against the welding area of ​​the mouth. Background Art

[0005] The prior art discloses a bag packaging, in particular a so-called squeeze bag, in which a spout is welded between two oppositely disposed walls of the bag body, so that the contents of the bag can be removed through a pouring channel of the spout. The walls are preferably formed from corresponding film layers.

[0006] In the prior art, and preferably also in the present invention, such a spout comprises a pouring channel having a channel wall in the form of a spout connection section at a first end region, and a second end region surrounded by a weld region having two weld arms extending in opposite directions perpendicular to the channel axis of the pouring channel to respective ends, in particular extending away from the channel wall at the second end region. Each weld arm has a weld region, such as a plurality of rib elements, attached to the channel wall at the second end region and preferably spaced apart from one another along the channel axis. The weld regions comprise a first weld region extending between the channel wall and the end of the weld arm on a first weld side, and a second weld region extending between the channel wall and the end of the weld arm on a second weld side. The first and second weld regions converge toward the end of the weld arm. In one possible embodiment, the weld regions can extend at least partially in a straight or planar manner. In this case, an acute angle is formed between the straight-running regions of the first and second weld regions. However, the weld regions can also be curved.

[0007] This type of spout is known in the prior art, for example, as described in patent publication DE 10 2017 009 693 A1 by the same applicant. This spout is intended for welding between two walls, such as two film layers, of a packaging bag (particularly a film bag), for example, for food, particularly fluid food. Because the welding zones on the two welding arms converge, the weld area tapers from the channel axis toward the ends of the welding arms, particularly in a plane perpendicular to the channel axis. This shape is often referred to as a "boat shape."

[0008] The welding tongs apply welding energy from two oppositely disposed welding sides through corresponding walls of the bag body to the welding zone of the welding area, and weld the welding zone to the respective wall portions of the two welding sides.

[0009] The welding sides are thus two oppositely disposed sides of the welding region. The welding sides are located on either side of a plane formed by the channel axis and the ends of the two welding arms. In this case, the channel axis is the longitudinal axis of the pouring channel, which extends through the mouth.

[0010] This plane may also be called the front plane and corresponds to a plane parallel to the wall of the bag, in particular an unfilled bag.

[0011] Typically, a detachable closure, such as a lid, is provided on one end region serving as the mouth connecting section (constituting its upper end region when the bag is in upright use). The closure is preferably fastened or fastenable to a threaded connection on the mouth connecting section and is detachable.

[0012] The second end region forming the welding area is the lower end region of the mouth during use as described above. The invention preferably relates to applying the method according to the invention to a mouth of the type described above and to using a mouth of the type described above in combination with welding tongs according to the invention.

[0013] When a welding clamp is applied to the welding area of ​​such a nozzle, the heated pressing surface of the clamp contacts the wall and heats it. As the clamp moves, the wall also moves toward the welding area of ​​the nozzle. This causes the heated surface area of ​​the wall to shift relative to the unheated surface area, and stretching occurs at the transition between the heated and unheated surface areas (which are not used for welding). This can lead to leakage in the wall after welding. Consequently, such leakage primarily occurs in the unwelded surface area directly adjacent to the welded surface area of ​​the wall. Summary of the Invention

[0014] Against this background, the object of the present invention is to develop a welding tongs of the type mentioned at the outset and a hot welding method in such a way that the stretching of the wall in the transition region between the welded surface region and the unwelded surface region of the wall is reduced, more preferably eliminated, and thus the risk of leakage is reduced, preferably eliminated.

[0015] This object is achieved in the following way: in a welding pliers of the type mentioned at the beginning of this article, a pressing element is arranged on the pliers body, in particular a pressing element is fixed to the pliers body, and the pressing element has a second pressing surface, which is adjacent to the first pressing surface of the pliers body and can be used to press the surface area of ​​the bag wall that is not welded but is adjacent to the surface area to be welded towards the welding area of ​​the mouth.

[0016] “Pressing surfaces” are understood to mean those surfaces of the welding tongs which, during the intended operation of the welding tongs, in particular when the welding tongs are moved towards the welding area of ​​the mouth, can be used to exert a force on the bag wall in order to move the wall area in contact with the respective pressing surface towards the welding area of ​​the mouth.

[0017] This object is achieved by the method mentioned at the beginning of this article, in which method a clamping element is arranged on the clamp body, in particular a clamping element is fixed to the clamp body, the clamping element having a second clamping surface, which is adjacent to the first clamping surface of the clamp body and by means of which a surface area of ​​the bag wall that is not welded but is adjacent to the surface area to be welded can be pressed towards the welding area of ​​the mouth.

[0018] Pressing the non-welding surface area of ​​the bag wall against the welding area of ​​the mouth should be understood as reducing the gap between at least the wall portion located outside the surface area to be welded and the welding area, i.e., the second pressing surface pushes the wall portion in this area forward, in particular towards the central plane of the mouth, around which the mouth is arranged and which contains the central longitudinal axis of the pouring channel extending through the mouth. This does not mean that this surface area is located directly opposite the welding area. Only the surface area of ​​the wall to be welded is brought into position directly opposite the welding area until it comes into contact with the welding area.

[0019] The surface area outside / adjacent to the surface area of ​​the wall to be welded (i.e. the surface area not welded to the welding area) is preferably located below the welding area, i.e. on the side of the welding area opposite to the pouring channel in the axial direction of extension of the pouring channel of the mouth, and / or next to the welding area in the radial direction of the extension direction of the pouring channel, in particular radially outside next to the radial outer end of the welding arm that tapers radially outward in the welding area.

[0020] Compared to the prior art, the present invention achieves the following effect: the welding clamp contacts not only the surface area of ​​the wall to be welded, but also the surface area not to be welded, and pushes them forward together during the movement. This prevents relative displacement between the surface area to be welded and the surface area not to be welded; in particular, these surface areas do not warp. Furthermore, the heated surface area is stretched at the transition to the surface area not to be welded, thus overcoming the aforementioned drawbacks.

[0021] Preferably, according to the method of the present invention, the temperature of the second pressing surface is kept lower than the temperature of the first pressing surface, in particular so that the temperature of the second pressing surface does not exceed the melting point temperature of the bag wall material and the welding area material to be welded, while the temperature of the first pressing surface is higher than the melting point temperature.

[0022] This can usually be achieved by cooling the pressure element and / or at least heating the pressure element to a lower degree than the pliers body.

[0023] According to the invention, for example, the pressing element or at least the second pressing surface can be made of a material having a lower thermal conductivity than the material of the pliers body.

[0024] The effect of this is that, although the second pressing surface is also indirectly heated by the heating element through the pliers body, the temperature of the second pressing surface is lower than that of the first pressing surface due to the smaller heat flux transferred to the second pressing surface and the second pressing surface being preferably further from the heat source than the first pressing surface. The pressing element, or at least its second pressing surface, is preferably made of silicone. This material is thermally stable at the melting temperatures of conventional plastics and has a lower thermal conductivity than the material of the pliers body (for example, if the pliers body is preferably made of metal).

[0025] As an alternative or in addition to the above-described embodiment, it may be provided that the pressing element is indirectly fixed to the pliers body via at least one thermal insulation element made of a material having a lower thermal conductivity than the pliers body.

[0026] The function of the heat-insulating element is also that, although the second pressing surface is also indirectly heated by the heating element through the pliers body, because the heat flow transferred to the pressing element (i.e., the second pressing surface) through the heat-insulating element is small, and preferably, the distance between the second pressing surface and the heat source is also farther than the distance between the first pressing source and the heat source, the temperature of the second pressing surface is lower than that of the first pressing surface. When using a heat-insulating element, the thermal conductivity of the pressing element does not need to be lower than the thermal conductivity of the pliers body, and the pressing element can also be made of metal, for example. However, even in this case, the thermal conductivity of the pressing element is preferably lower than the thermal conductivity of the pliers body, and preferably, the pressing element is made of silicone.

[0027] In all possible embodiments, a preferred refinement of the invention is that a gap is formed in the welding jaws between the first and second pressing surfaces, in particular in which the bag wall does not come into contact with the welding jaws. This prevents heat transfer to the bag wall in this area, but the bag wall on either side of this area still moves due to the welding jaws and their two pressing surfaces, thus avoiding stress.

[0028] The gap is preferably formed by a spacer element disposed between the caliper body and the compression element, the spacer element having a surface area located rearward relative to the first and second compression surfaces. This spacer element may also simultaneously serve as the aforementioned thermal insulation element. Alternatively, the gap may be formed by chamfering or rounding at least one of the opposing edges of the first and second compression surfaces.

[0029] In all possible embodiments, the invention preferably further provides that the spacer element and / or the heat insulating element is formed of a material containing heat-resistant fibers, in particular glass fibers. "Heat-resistant" here particularly means that the material can withstand the temperatures on the clamp body without being damaged.

[0030] In all possible embodiments, the present invention can also preferably provide that the pressing element is arranged between two fixing plates, preferably, the fixing plates between the pressing element and the caliper body form the above-mentioned thermal insulation element and / or the spacer element.

[0031] For example, this allows a compression element, in particular one made of silicone, to be arranged between two fixing plates and fixed to the jaw body via the thermal insulation element on the side facing the jaw body. The fixing plates thus better ensure the required stability of the flexible compression element.

[0032] Typically, the pressing element can be fixed to the caliper body directly or indirectly via one of the aforementioned elements (insulating element, spacer element, fixing plate), for example by screws.

[0033] According to the present invention, in all possible embodiments, preferably, the first pressing surface is formed between two opposing surfaces of the caliper body in the thickness direction, and the second pressing surface is formed between two opposing surfaces of the pressing element in the thickness direction, and the two opposing surfaces of the caliper body and the two opposing surfaces of the pressing element are located in mutually parallel planes. This preferably allows the first pressing surface and / or the second pressing surface to be planar in the thickness direction at least in a major surface area.

[0034] In particular, the second pressing surface for the welding operation is constituted by a partial surface connecting two opposing surfaces, the partial surface extending in a direction perpendicular to the two surfaces.

[0035] In this arrangement, when the pouring channel is arranged vertically, the second pressing surface is located opposite the bag wall surface area, which is arranged next to the welding area of ​​the mouth and is on the side of the welding area opposite to the pouring channel, that is, the bag wall surface area is located below the welding area.

[0036] The pressure element and its pressure surface can also be fastened to the pliers body in such a way that the second pressure surface is located opposite the pocket wall surface area which is radially adjacent to the ends / tips of the welding arms mentioned in the introduction. The invention makes it possible to provide both arrangements of pressure elements on one welding pliers.

[0037] Particularly preferably, the first pressing surface and / or the second pressing surface is concave, in particular concave in a direction perpendicular to the thickness direction or in a cross section parallel to one of the oppositely arranged surfaces.

[0038] In this case, the welding area can preferably be partially surrounded by the first pressing surface, in particular on one side of the central longitudinal axis of the pouring channel, preferably at least 170 degrees around the central longitudinal axis. Thus, the two oppositely arranged welding jaws can respectively surround the welding area from both sides after being moved relative to each other.

[0039] In this embodiment, according to the present invention, preferably, the first pressing surface and / or the second pressing surface can be concave, and the concave shape is realized in that each pressing surface includes two partial surfaces, in particular two respectively flat partial surfaces, which form an angle greater than 90 degrees, preferably greater than 100 degrees, and preferably transition to each other in a transition area, in particular transition in a continuous manner, preferably with a rounded transition.

[0040] The flat part surface preferably lies in a plane parallel to the central longitudinal axis of the pouring channel.

[0041] In the matching combination of the nozzle and the welding clamp, the angle formed between the taper angle of the welding arm in the welding area and the partial surface of the first pressing surface is matched to each other, so that the partial surface is in full contact with the welding area on the welding arm in the welding area. The angle formed between the partial surfaces is preferably 180 degrees minus the taper angle of the welding arm.

[0042] According to the present invention, preferably, the second pressing surface can be moved so that it is partially located in front of and / or behind the first pressing surface, in particular, when the pressing surface extends symmetrically from the inside to the outside, the outer surface area of ​​the second pressing surface moves in front relative to the outer surface area of ​​the first pressing surface, and the inner surface area of ​​the second pressing surface moves behind relative to the inner surface area of ​​the first pressing surface.

[0043] Particularly for this purpose, but also for other reasons, according to the invention the angle formed between the partial surfaces of the second pressing surface is preferably smaller than the angle formed between the partial surfaces of the first pressing surface.

[0044] It is further preferred, in particular in order to obtain the aforementioned "in front / behind" effect, that the first pressing surface and the second pressing surface each form a concave groove, in particular in a cross section parallel to the oppositely arranged surfaces, each concave groove having a groove bottom surrounded by two opposite groove edges, the groove bottoms of the two pressing surfaces and / or the groove edges of the two pressing surfaces not being aligned with each other or being misaligned with each other, in particular when viewed in the correct, intended direction of movement of the welding clamp during the welding operation.

[0045] The groove bottom preferably includes or is preferably the region where the partial surfaces transition into each other. The groove edge is preferably the region where the pressing surface (ie its two partial surfaces) extends upwards from the groove bottom and rises.

[0046] According to the present invention, preferably, the groove edge of the second pressing surface protrudes outward relative to the groove edge of the first pressing surface, in particular protrudes toward the welding area, and / or the groove bottom of the second pressing surface is set backward relative to the groove bottom of the first pressing surface, in particular set backward relative to the movement direction of the welding clamp toward the welding area.

[0047] It is further preferred that the groove edges of the second pressing surface (particularly viewed from the gap between the groove edges) form a more slender platform than the groove edges of the first pressing surface, and in particular the second pressing surface protrudes outwards beyond the first pressing surface.

[0048] In this context, "outward" means extending from the groove bottom to beyond the groove edge. Each pressing surface preferably extends from the groove bottom via a portion of the surface to the highest point of the groove edge, in particular until the groove edge drops outward again. Thus, the groove edge of the second pressing surface preferably begins to drop outward further back than the groove edge of the first pressing surface.

[0049] It is further preferred that the concave first pressing surface and / or the concave second pressing surface are symmetrical with respect to a central plane, in particular parallel to the thickness direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The accompanying drawings show a comparison between the present invention and the prior art, wherein Figures 1 and 2 show the prior art, and Figures 3 to 6 show embodiments of the present invention. DETAILED DESCRIPTION

[0051] FIG1 schematically shows the initial stage of thermal welding of the bag wall 1 to the welding area 2 of the mouth 3. The upper area of ​​the mouth 3 is provided with a pouring channel which is closed by the lid and extends around the central longitudinal axis 12, which transitions to the welding area 2 located below the lid. In this respect, Figure 1B The weld region 2 can be designed in a boat shape, which is a common design in the art. As in the prior art and the present invention, the weld region is formed by two weld arms that extend radially outward from the central longitudinal axis 12 in opposite directions and, in this example, taper outward from the central longitudinal axis, particularly in a plane perpendicular to the central longitudinal axis 12. The radially outward surfaces of the weld arms constitute the weld surface of the weld region 2, to which the bag wall is welded.

[0052] Figure 1A and Figure 1BThe starting position of the jaws 4 of the welding tongs, which can be heated by a heating element 14, is shown from different directions. Only one of the two jaws 4 is shown, which are arranged opposite each other around a central longitudinal axis and are preferably moved simultaneously in the direction indicated by the arrows toward the central longitudinal axis (i.e. toward the welding region 2), pressing the bag wall 1 toward the welding region 2 in the process.

[0053] This causes the wall area 1a to be welded to come into contact with the pressing surface 5 of the pliers 4 and to be heated. In both the prior art and the present invention, the arrangement of the welding pliers / pliers 4 and the bag wall 1 relative to the mouth 3 is mirror-symmetrical relative to a plane containing the central longitudinal axis 12 and the ends of the welding arms.

[0054] from Figure 1A and Figure 1B It can be seen that the non-welded wall area 1b is adjacent to the welded surface area 1a, in particular directly adjacent, and is in contact neither with the pressing surface 5 of the caliper body 4 nor with any other component guiding this surface area.

[0055] Figure 2A and Figure 2B The problem associated with this is shown, in particular, that an excessive relative movement occurs between the two surface areas 1a and 1b, since only the area to be welded is pressed towards the welding area 2, i.e. towards the central longitudinal axis 12, while the adjacent non-welded areas 1b, in particular those that lag behind said movement, are not pressed towards the welding area 2. As a result, the heated surface area to be welded 1a is stretched at the transition to the non-welded surface area 1b, thereby weakening the bag, which may lead to the subsequent production of bags. Figure 2A and Figure 2B Leakage occurs in the corresponding area circled in the figure.

[0056] The present invention solves the problem shown in Figures 1 and 2. The solution is to provide a pressing element 6 on the pliers body 4, which is particularly fixed to the pliers body 4, for example by screws. The pressing element 6 has a second pressing surface 7, which is adjacent to the first pressing surface 5 of the pliers body 4. By means of this second pressing surface 7, the surface area 1b of the bag wall 1 that is not welded but is adjacent to the surface area 1a to be welded can also be pressed towards the welding area 2 of the mouth 3, that is, towards the central longitudinal axis 12 of the pouring channel.

[0057] Figure 3A and Figure 3B Shown with Figure 1A and Figure 1B The starting position of the clamp body 4 of the present invention is compared with the starting position of the prior art shown. Figure 4A and Figure 4B Shown with Figure 2Aand Figure 2B The end position of the clamp body 4 according to the present invention is shown compared to the end position of the prior art.

[0058] As can be seen from the figure, the second pressing surface 7 provided by the pressing element 6 acts on the surface area 1b that is not welded but is adjacent, in particular directly adjacent, to the area to be welded 1a, thereby ensuring that there is no relative movement, or no excessive relative movement, between the surface areas 1a and 1b. This can reduce or even completely avoid stretching and weakening of the heated surface area 1a at the transition to the surface area 1b.

[0059] Advantageously, this is facilitated by maintaining the second pressing surface 7 of the pressing element 6 at a lower temperature than the first pressing surface 5 of the jaws 4 , in particular below the melting point of the material of the welding area 2 and the bag wall 1 .

[0060] This can be achieved by using a compression element 6 made of a material having a lower thermal conductivity than the pliers body 4, or by indirectly securing the compression element to the pliers body 4 via a thermally insulating element 8 having a lower thermal conductivity than the material of the pliers body 4. The compression element 6 is preferably made of silicone. Metal or other plastics may also be used.

[0061] Compared to the material of the caliper body 4, the compression element 6 and / or the insulation element 8 have a lower thermal conductivity, resulting in a much lower heat flow from the heat source 14 to the second compression surface 7 than from the heat source 14 to the first compression surface. Cooling by ambient air is sufficient to keep the temperature of the second compression source 7 lower than that of the first compression surface. Alternatively, in all possible embodiments, the compression element 6 can also be actively cooled.

[0062] 3 and 4 show that a plurality of pressing elements 6 may be used, the second pressing surfaces 7 of which abut against the first pressing surface 5 in different directions / directions. Figure 3A and Figure 4A The shown pressing element 6 is located immediately adjacent to / below the caliper body 4 in the axial direction of the central longitudinal axis 12 ; Figure 3B and Figure 4B The shown pressing element 6 is at least substantially located radially adjacent to the caliper body 4, ie radially outside the ends of the welding arms. Both types of pressing elements 6 can be used simultaneously.

[0063] Figures 3 and 4 also show a gap 9 between the compression element 6 and the jaw body 4. This gap can be formed by an insulating element 8 or a spacer element 10 located between the compression element and the jaw body. The gap 9 can also be formed completely or partially by chamfering or rounding the opposing edges of the compression element 6 and the jaw body 4. In the gap area 9, the bag wall 1 does not come into contact with any compression surface, so the degree of heating in this area is lower.

[0064] In the embodiments of FIG. 3 and FIG. 4 , according to the present invention, the Figure 3B and Figure 4B The pressing element provided at the end of the welding arm is provided, and only one pressing element 6 is provided, such as Figure 3A and Figure 4A As shown, in particular, the pressing element is in contact with the unwelded surface area 1 b below the weld region 2 in the axial direction of the axis 12 .

[0065] Figure 5 6 show different views of a particularly preferred embodiment of the welding pliers according to the invention, wherein the heat source on the pliers body 4 is not shown. Generally, the heat source 14 can be fastened to the surface of the pliers body 4 not occupied by the pressing element 6.

[0066] Figure 5 Figure 6 shows that the clamping element 6 is a flat element or plate-like structure, whose large surfaces are spaced apart in the thickness direction and are parallel to the opposite surfaces 4a and 4b of the pliers body 4. The opposite surfaces 4a and 4b of the pliers body 4 are also spaced apart in the thickness direction thereof, and a first clamping surface 5 that exceeds the thickness is formed between the opposite surfaces.

[0067] The first pressing surface 5 and the second pressing surface 7 each form a concave groove, at least in a cross-sectional plane parallel to the surfaces 4a and 4b. The concave grooves have groove bottoms 5c and 7c, respectively, and corresponding groove edges 5d and 7d. Each concave groove extends outward from the groove bottoms 5c and 7c to the groove edges 5d and 7d, respectively. Partial surfaces 5a, 5b, and 7a, 7b of the first pressing surface 5 and the second pressing surface 7 are located between the groove bottoms 5c and 7c and the groove edges 5d and 7d, respectively.

[0068] Especially if Figure 6A and Figure 6B As shown, each concave groove is preferably mirror-symmetrical with respect to a plane passing through the groove bottom and perpendicular to surfaces 4a and 4b. The concave groove of the first pressing surface 5 preferably completely matches the outer shape of the welding area 2 of the mouth, so that the bag wall 1 can be pressed against the welding area in the area to be welded. In essence, the concave groove of the first pressing surface 5 can correspond to the negative shape of one of the two opposing welding surfaces of the welding area 2.

[0069] The concave grooves of the second pressing surface 7 may be identical to the concave grooves of the first pressing surface 5 in a cross section in a plane parallel to the surfaces 4a and 4b, but are preferably different.

[0070] Figure 6A and Figure 6BIt is clearly shown that the angle α1 formed between the partial surfaces 5 a and 5 b of the first pressing surface 5 is greater than the angle α2 formed between the partial surfaces 7 a and 7 b of the second pressing surface 7 .

[0071] The invention further provides that the groove bottom 7c of the second pressing surface 7 is set back relative to the groove bottom 5c of the first pressing surface 5, in particular relative to the direction of movement of the welding tongs toward the welding region 2, which is indicated here by the arrow 15. Thus, during the welding operation, the groove bottom 7c is located behind the profiled bottom 5c in the direction of movement 15.

[0072] Furthermore, it is provided that the groove edge 7d of the second pressing surface 7 projects forward relative to the groove edge 5d of the first pressing surface 5, in particular towards the welding region 2. Thus, during the welding operation, the groove edge 7d is located ahead of the groove edge 5d in the direction of movement 15.

[0073] In addition, the groove edges 7d of the second pressing surface 7 form a platform portion 7e that is longer than the groove edges 5d of the first pressing surface 5, especially when viewed from the gap direction between the groove edges 7d, and especially the second pressing surface 7 protrudes outward beyond the first pressing surface 5.

[0074] Figure 5 As shown in the structure of FIG6 , the pressure element 6 can preferably be fixed between two fixing plates 11, in particular, fixing plates made of heat-resistant fiber (e.g., fiberglass). This is particularly advantageous when the pressure element is made of other less robust materials (e.g., silicone). These fixing plates 11 can even provide thermal insulation relative to the caliper body 4. The fixing plates 11 preferably also have a groove, which preferably has the same contour as the groove of the first pressure surface 5, i.e., the same contour as the groove of the first pressure surface in a plane parallel to the surfaces 4a, 4b. However, it is more preferred that the groove of the fixing plates be set back parallel to the groove of the first pressure surface, in particular, set back relative to the direction of movement 15 toward the central longitudinal axis 12. The bottom of the groove of the fixing plates 11 can be flush with the bottom 7c of the groove of the pressure element 6, in particular, at least at its deepest point. In this case, the unit consisting of the pressure element 6 and the two surrounding fixing plates 11 is indirectly fixed to the caliper body 4 via the thermal insulation element 8. This ensures a sufficient cooling effect on the second pressure surface 7.

[0075] Preferably, when the method is implemented, the temperature of the first pressing surface is generally higher than 190 degrees Celsius, while the temperature of the second pressing surface is lower than 190 degrees Celsius, preferably lower than 170 degrees Celsius, in particular lower than 150 degrees Celsius. Preferably, the temperature of the first pressing surface is at least substantially uniform over the entire surface, while the temperature of the second pressing surface 7 decreases gradually in a direction away from the first pressing surface 5.

Claims

1. A welding pliers for thermally welding a bag wall (1) made of plastic film to a welding area (2) of a mouthpiece (3) made of plastic, the welding pliers comprising a pliers body (4) connected to a heat source, the pliers body (4) having a pressing surface (5), by which the surface area (1a) of the bag wall (1) to be welded is pressed against the welding area (2) of the mouthpiece (3), characterized in that The clamp body (4) is provided with a pressing element (6), in particular, the clamp body (4) is fixed with a pressing element (6), the pressing element (6) having a second pressing surface (7), the second pressing surface (7) being adjacent to the first pressing surface (5) of the clamp body (4), and through the second pressing surface (7), a surface area (1b) of the bag wall (1) that is not welded but adjacent to the surface area (1a) to be welded is pressed toward the welding area (2) of the mouth (3) or toward the central longitudinal axis (12) of the pouring channel.

2. The welding tongs according to claim 1, characterized in that The pressing element (6) or at least the second pressing surface (7) is made of a material having a lower thermal conductivity relative to the material of the pliers body (4).

3. Welding tongs according to any one of the preceding claims, characterized in that The pressing element (6) is indirectly fixed to the caliper body (4) via at least one thermally insulating element (8), which is made of a material with a lower thermal conductivity relative to the material of the caliper body (4).

4. Welding tongs according to any one of the preceding claims, characterized in that A gap (9) is formed between the first pressing surface (5) and the second pressing surface (7), in particular a gap is formed so that the bag wall (1) does not come into contact with the welding clamp.

5. The welding tongs according to claim 4, characterized in that: The gap (9) is formed by a spacer element (10) arranged between the pliers body (4) and the pressing element (6), and the spacer element (10) has a surface area that is set back relative to the first pressing surface (5) and the second pressing surface (7), in particular, the spacer element (10) also constitutes the insulating element (8) according to claim 3, or at least one of the opposite edges of the first pressing surface (5) and the second pressing surface (7) is formed with a chamfer or a rounded corner.

6. Welding tongs according to any one of the preceding claims 3 to 5, characterized in that The spacer element (10) and / or the insulation element (8) are formed from a material containing heat-resistant fibers, in particular glass fibers.

7. Welding tongs according to any one of the preceding claims, characterized in that The pressing element (6) is arranged between two fixing plates (11), preferably, the fixing plate (11) located between the pressing element (6) and the caliper body (4) forms an insulating element (8) according to claim 3 and / or a spacing element (10) according to claim 5.

8. Welding tongs according to any one of the preceding claims, characterized in that The first pressing surface (5) is formed between two opposite surfaces of the caliper body (4) in the thickness direction of the caliper body (4), and the second pressing surface (7) is formed between two opposite surfaces of the pressing element (6) in the thickness direction of the caliper body (4), and the two opposite surfaces of the caliper body (4) and the two opposite surfaces of the pressing element (6) are located in planes parallel to each other.

9. Welding tongs according to any one of the preceding claims, characterized in that The first pressing surface (5) and / or the second pressing surface (7) are planar in the thickness direction at least in a major surface area.

10. Welding tongs according to any one of the preceding claims, characterized in that The first pressing surface (5) and / or the second pressing surface (7) are concave, in particular concave in a direction perpendicular to the thickness direction or in a cross section parallel to one of the oppositely arranged surfaces, preferably, the welding area (2) is partially surrounded by the first pressing surface (5), in particular surrounded on one side of the central longitudinal axis of the pouring channel, preferably surrounded by at least 170 degrees around the central longitudinal axis.

11. The welding tongs according to claim 10, characterized in that The first pressing surface (5) and / or the second pressing surface (7) is concave, and the concave shape is realized in that each pressing surface (5, 7) comprises two partial surfaces (5a, 5b, 7a, 7b), in particular comprises two respectively flat partial surfaces (5a, 5b, 7a, 7b), and the two partial surfaces form an angle (α) greater than 90 degrees, preferably greater than 100 degrees, and preferably transition into each other in a transition area, in particular transition in a continuous manner, preferably with a rounded transition.

12. The welding tongs according to claim 10 or 11, characterized in that: An angle (α2) formed between partial surfaces (7a, 7b) of the second pressing surface (7) is smaller than an angle (α1) formed between partial surfaces (5a, 5b) of the first pressing surface (5).

13. Welding tongs according to any one of the preceding claims 10 to 12, characterized in that The concave first pressing surface (5) and / or the concave second pressing surface (7) are symmetrical about a central plane (13) which is particularly parallel to the thickness direction.

14. Welding tongs according to any one of the preceding claims 10 to 13, characterized in that The first pressing surface (5) and the second pressing surface (7) each form a concave groove, in particular a concave groove in a cross section parallel to the oppositely arranged surfaces, each concave groove having a groove bottom (5c, 7c) surrounded by two opposite groove edges (5d, 7d), the groove bottoms (5c, 7c) of the two pressing surfaces (5, 7) and / or the groove edges (5d, 7d) of the two pressing surfaces (5, 7) not being aligned with each other or being misaligned with each other, in particular not being aligned with each other or being misaligned with each other when viewed in the correct, intended direction of movement of the welding tongs during the welding operation.

15. The welding tongs according to claim 14, characterized in that The groove edge (7d) of the second pressing surface (7) protrudes outward relative to the groove edge (5d) of the first pressing surface (5), in particular, protrudes toward the welding area (2), and / or the groove bottom (7c) of the second pressing surface (7) is set back relative to the groove bottom (5c) of the first pressing surface (5), in particular, set back relative to the movement direction of the welding clamp toward the welding area (2).

16. The welding tongs according to claim 14 or 15, characterized in that The groove edges (7d) of the second pressing surface (7), particularly when viewed from the gap direction between the groove edges (7d), form a platform (7e) that is more slender than the groove edges (5d) of the first pressing surface (5), and particularly the second pressing surface (7) protrudes outward beyond the first pressing surface (5).

17. A method for thermally welding a bag wall (1) made of plastic film to a welding area (2) of a mouthpiece (3) made of plastic, wherein two oppositely arranged welding tongs are moved from opposite directions toward the welding area (2), each welding tongs having a tong body (4) connected to a heat source (14), each tong body (4) having a pressing surface (5), by which the surface area (1a) of the bag wall (1) to be welded, located between the pressing surface (5) and the welding area (2), is pressed against the welding area (2) of the mouthpiece (3), characterized in that A pressing element (6) is provided on the pliers body (4), in particular a pressing element (6) is fixed on the pliers body (4), the pressing element (6) having a second pressing surface (7), the second pressing surface (7) being adjacent to the first pressing surface (5) of the pliers body (4), and a surface area (1b) of the bag wall (1) which is not welded but is adjacent to the surface area (1a) to be welded is pressed toward the welding area (2) of the mouth (3) or toward the central longitudinal axis (12) of the pouring channel via the second pressing surface (7).

18. The method according to claim 17, characterized in that The second pressing surface (7) is maintained at a temperature lower than the temperature of the first pressing surface (5).

19. The method according to claim 17 or 18, characterized in that The second pressing surface (7) is moved so that the second pressing surface (7) is partially located before and / or after the first pressing surface (5), in particular, when the pressing surfaces (5, 7) extend symmetrically from the inside to the outside, the outer surface area of ​​the second pressing surface (7) moves in front relative to the outer surface area of ​​the first pressing surface (5), and the inner surface area of ​​the second pressing surface (7) moves behind relative to the inner surface area of ​​the first pressing surface (5).

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