Tool assembly for making transverse seams in packaging web

Abstract: The application relates to a tool assembly (1) for use in a flow wrap packaging machine. The tools (4, 5) are provided at both ends with followers (8, 13; 34, 35), one follower (13, 35) being mounted on a bearing around a crank (12). The followers are able to roll over curved discs (16, 17) positioned eccentrically, whilst the tools are guided along guide rods (19, 20). The plain bearings (21, 30; 22, 31) of diametrically opposed tools (4, 5) can be linked to one another so that the followers (8, 13; 34, 35) are in close abutting contact with the bearing surfaces of the curved discs (16, 17) even at high speeds of rotation. The construction according to the present invention results in a very lightweight and easily accessible tool assembly.

Description: The present invention relates to a tool assembly for making a transverse seam in packaging formed from a continuous web of film material. More specific, the present invention relates to a tool assembly according to the preamble of claim 1. A tool assembly according to the preamble of claim 1 is disclosed by EP-A-226.693. Figure 3 of this publication discloses a transverse seal station having an upper seal claw holder driven around a central axis. This seal claw holder is provided with a crank such that the guide rollers are positioned at a material distance. Upon unrolling of the guide rollers along curved plates, slides are displaced along guide bars. A further tool assembly is disclosed in Netherlands Laid Open Application NL-A 7 703 794. This tool assembly is used in flow wrap packaging machines with which bag-shaped packaging is formed from a continuous film web by making longitudinal and transverse seams in the film material. After making a longitudinal seam, the film web is sealed and cut off between the successive products with the aid of the tool assembly. The known tool assembly comprises two tools located opposite one another which are attached to a rotary tool mounting that is driven in such a way that the orientation of the tool is constantly towards the film web and that, in a sealing position, the tools move horizontally at the speed of the film web. The tool position is varied with respect to the central rotary shaft by moving the tool up and down along a guide rod by means of plain bearings. The position of the tool along the guide rod is determined by a curved track along which the tool mounting is rotated and against which the tool bears via a follower rolling over the curved track. The curved track has a shape such that at the location of the film web the tool moves only horizontally at the speed of the film. The known installation has the disadvantage that the moving parts are of relatively heavy construction, with the result that the working capacity is limited. Furthermore, because of the multiplicity of components, the known installation takes up a relatively large amount of space so that use of multiple tool pairs is difficult to implement, as a result of which only limited adaptation to different product formats is possible. Furthermore, the known follower is enclosed between two curved tracks, with a certain play. The direction of rotation of the follower changes depending on the bearing surface over which the follower rolls. One aim of the present invention is to provide a tool assembly that is relatively lightweight and takes up relatively little space and with which a high sealing pressure can be achieved when forming a transverse seam. A further aim is to provide a tool assembly that can easily be adapted to different product formats. To this end the tool assembly according to the present invention is characterised in that the positioning shafts at each end of a tool are mounted in a respective plain bearing that is movable along a respective guide rod, wherein the guide rod is rotatable, close to the second end of the tool, about a second rotary shaft which is a distance away from the central rotary shaft, which distance corresponds to the distance between the first and second positioning shafts. By using the followers on either side of the tool, which followers are mounted on bearings about shafts offset with respect to one another, a fixed tool orientation is obtained without complex transmissions being required for this. As a result the tool assembly can be of lightweight construction, so that the forces of inertia remain restricted and a high working capacity becomes possible. By placing the positioning shafts apart in the vertical direction, skewing of the tools in the horizontal path when the tools are subjected to force (during sealing) is prevented. As a result of the space-saving construction of the tool assembly according to the present invention it is possible to place multiple tool pairs around the central rotary shaft. Furthermore, a tool can be dismantled easily, for example for maintenance or for adaptation to a different product format, by shifting the plain bearings of the guide rods or by dismantling the guide rods. After the tools have been dismantled, the cam discs or curved discs can also be easily exchanged, in order to adapt the shape of the bearing surfaces to the working capacity and the product format. In one embodiment of the tool assembly according to the present invention, the guide rods have two plain bearings on either side of the respective rotary shafts of the guide rods, which plain bearings are movable along the guide rods and each bear via a follower on diametrically opposed positions of the respective bearing surface and are linked to one another via coupling elements. By means of the diametrically opposed followers, each tool is positioned in two radial directions with respect to the curved track, so that contact of the followers with the track at high speeds of rotation is always guaranteed. Compared with the known method of using spring loading to guarantee that the followers are in contact with the bearing surfaces, the construction according to the invention offers the advantage that drive forces for rotation of the tools can remain restricted. Preferably, there is a tool connected to the plain bearings on each side of the rotary shaft, so that two tools are rotated over the bearing surfaces of the curved track per pair of diametrically opposed followers. It is pointed out that EP-A 0 738 582 discloses a tool assembly with which four tools with followers are rotated over an internal and an external curved track, such that the followers are enclosed between the curved tracks. The tools are held in a fixed orientation by means of a planetary gear system. The known installation is relatively heavy because of its multiplicity of components and is relatively complex. Close abutting contact of the followers of the tools by connecting two diametrically opposed tools to one another is not shown in this publication. Furthermore, the known followers are mounted on bearings in a large disc on which the tools are also mounted, with the result that the disc is relatively heavy. Moreover, the radius of the track of the tool heads changes during the sealing path so that guiding of the tools is necessary. Such a guide is expensive and relatively vulnerable, partly because of the thermal expansion and contraction which is caused by the heated tools. In a further embodiment of the tool assembly according to the present invention, a second pair of guide rods is located transversely to the first pair of guide rods, so that one or more further tools are movable along the second pair of guide rods. The further tools bear on the bearing surfaces via their followers. By using the relatively open construction according to the present invention, four or six tools can be rotated around the curved tracks, so that a very high working capacity can be obtained. The tools can have been provided with a cutting element that is movable in a slot in the tool and is operated by a stationary pressure element which engages on the cutting element when the tool is in the sealing position and pushes said cutting element beyond the bottom edge of the tool. In a tool unit having an upper and a lower tool assembly according to the invention, wherein the drive mechanisms of the tool units have each been provided with a drive shaft with a toothed element, a drive element in the form of a closed loop is placed around the toothed elements. By driving the upper and the lower tool unit by means of a single toothed belt or chain, the tools are rotated in opposing directions in a manner which produces little noise, without play and without the need to use lubricants. A further embodiment of a tool unit having an upper and a lower tool assembly, each with a rotary tool, is characterised in that the upper tool assembly is hingeably connected to the lower tool assembly at a hinge point located on one side of a separation plane. By this means it is possible to open up an entire tool group at the hinge point, so that the tools are easily accessible for cleaning and maintenance. The upper and the lower tool assembly can also have been connected via an elastic hinge so as to provide for an accurately determined small mutual displacement. The invention will be explained in more detail with reference to the appended drawing, in which: Figure 1 shows a cross-sectional view of a tool unit with four upper and lower tool assemblies according to the present invention, Figure 2 shows a plan view, partially in cross-section, of the tool unit according to Figure 1, and Figure 3 shows a side view, partially in cross-section, of the tool unit according to Figure 1. Figure 1 shows a tool unit 1 for making transverse seams in a flow wrap packaging installation with an upper tool assembly 2 and a lower tool assembly 3. The upper tool assembly 2 comprises four tools, two tools 4, 5 of which are shown in Figure 1. Tool 5 is in the sealing position, in which it is in contact with the tool 6 of the lower tool assembly 3. The tool 4 is provided at its first end 7 with a follower 8 that is rotatably mounted on a bearing around a first positioning shaft 9. The tool 4 is rotatably connected at the second end 11 thereof to a second follower 13 via a crank 12. The follower 13 is rotatably mounted on a bearing around a second positioning shaft 14. The first positioning shaft 9 and the second positioning shaft 14 are located parallel to one another some distance (d) apart. The followers 8, 13 bear against curved discs 16, 17. The axis of the curved disc 16 is coincident with a central rotary shaft 18 about which the tools 4 and 5 and the positioning shaft 9 are rotated. The second curved disc 17 is positioned eccentrically with respect to the curved disc 16. The axis of the second curved disc 17 is coincident with a second rotary shaft 25 about which the follower 13 and the positioning shaft 14 are rotated. The second rotary shaft 25 is located a distance (d) away from the central rotary shaft (18), the distance (d) corresponding to the distance between the first positioning shaft 9 and the second positioning shaft 14 of the tool 4. As a result of the eccentric positioning of the curved discs 16, 17 and the mutually offset positions of the positioning shafts 9, 14, the orientation of the tool 4 remains constant on rotation of the tool 4 about the central rotary shaft 18, the followers 8, 13 rolling over the bearing surfaces of the curved discs 16, 17. As shown in Figure 3, the curved track 16 comprises a flat bottom section 16', so that in the sealing region, in which the tools move parallel to the film web, the tools 5, 6 in contact with the web are pushed against one another under a constant force. As a result of the rolling of the followers 8, 13 along the curved tracks 16, 17, the distance of the tool 4 from the central rotary shaft 18 is varied, whilst the position of the tool remains constant. The radial movement of the tool 4 with respect to the central rotary shaft 18 is guided along guide rods 19, 20. The tool 4 is vertically displaceable over the guide rods 19, 20 via plain bearings 21, 22. The plain bearings 21, 22 are rotatable about the positioning shafts 9 and 14, respectively. The guide rods 19, 20 are fixed in blocks 23, 24. The block 23 is driven around the central rotary shaft 18 via a toothed belt and toothed pulley 26. The block 24 and the guide rod 20 are driven around the second rotary shaft 25 via a toothed pulley 27. The construction according to the present invention is very lightweight and open so that various pairs of guide rods 19, 19' (for example 2, 3 or 4 pairs) can be used crosswise, as is clear from Figure 3. Maintenance of the tools and adjustments to the product format by adding or removing tools is very simple since these can easily be dismantled by uncoupling the plain bearings 21, 22 from the guide rods 19, 20 or by detaching the guide rods 19, 20 from the blocks 23, 24. As can clearly be seen from Figure 3, the plain bearings 30, 31 of the tool 5, which is located diametrically opposite tool 4, are linked to the plain bearings 21, 22 via coupling rods 32, 33. By means of the mutual coupling of the plain bearings 21, 30; 22, 31 it is guaranteed that the followers 8, 13 of the upper tool 4 and the followers 34, 35 of the lower tool 5 are in close abutting contact with the curved discs 16, 17, even at high speeds of rotation at which centrifugal forces force the followers radially away from the curved discs 16, 17. As can be seen from Figure 2, the tool 4 has a slot 37 in which a cutting element is accommodated such that it is movable up and down. The cutting element is provided with two projections 38, 39 which in the sealing position of the tool can be brought into engagement with rollers 40, 41 which are attached via arms 42, 43 to the central rotary shaft 25. As a result of the engagement of the rollers 40, 41 on the projections 38, 39 the cutting element is pushed out below the sealing surface of the tool 4 so that the film clamped beneath the tool is cut through. As shown in Figure 3, the upper tool assembly 2 and the lower tool assembly 3 are driven by a single toothed belt 46 which is fed in a closed loop around the toothed pulleys 26, 26' via two guide pulleys 47, 48. Gears could also be used instead of the toothed belt drive. As shown in Figure 3, the upper tool assembly 2 and the lower tool assembly 3 are hingeable with respect to one another along a separation plane 50. The tool assemblies 2, 3 are connected to one another at one side of the separation plane 50 via a hinge 51. In the embodiment under discussion the hinge 51 is formed by a flexible metal connection between the upper tool assembly 2 and the lower tool assembly 3. The elastic hinge 51 is made from an elastic aluminium alloy and is ideal for movements with a short stroke and displacement with high accuracy. A hinge in the form of a hinge pin at point 51 is also possible. The spacing between the upper tool assembly 2 and the lower tool assembly 3, and thus the sealing pressure between the tools 5, 6, can be adjusted by means of a compression spring 52 which presses the upper tool assembly 2 against the lower tool assembly 3. The slit width of the gap at the separation plane 50 is determined by a sleeve 54 positioned eccentrically with respect to a post 55. The slit width between the upper tool assembly 2 and the lower tool assembly 3 can be accurately adjusted by rotation of the sleeve 54.

Claims: Tool assembly (2, 3) for making a transverse seam in packaging formed from a continuous web of film material, comprising: a tool (4), rotatable about a central rotary shaft (18), having a longitudinal axis and having, at a first end (7), a follower (8) that is fixed to the tool (4) and is rotatable around a first positioning shaft (9), a stationary bearing surface (16) having a closed contour on which the follower (8) bears, a guide rod (19) which is rotatable together with the tool (4) about the central rotary shaft (18), the tool (4) being connected to the guide rod (19) via a plain bearing (21) that is movable along the guide rod (19), and a drive mechanism (26, 26') for rotating the tool (4), the follower (8) and the guide rod (19) about the central rotary shaft (18), in which the tool is connected at a second end (11) to a second follower (13) that is rotatable about a second positioning shaft (14) which is parallel to the first positioning shaft and which is located a predetermined distance (d) away from the first positioning shaft (9), a second bearing surface (17) which is parallel to the first bearing surface (16) and on which the second follower (13) bears being provided close to the second end (11) of the tool (4), characterised in that the positioning shafts (9, 14) at each end (7, 11) of a tool are mounted in a respective plain bearing (21, 22) that is movable along a respective guide rod (19, 20), wherein the guide rod (20) is rotatable, close to the second end (11) of the tool (4), about a second rotary shaft (25) which is a distance (d) away from the central rotary shaft (18), which distance (d) corresponds to the distance between the first and second positioning shafts (9, 14). Tool assembly (2, 3) according to Claim 1, characterised in that the guide rods (19, 20) have two plain bearings (21, 30; 22, 31) on either side of the respective rotary shafts (18, 25) of the guide rods, which plain bearings are movable along the guide rods and each bear via a follower (8, 34; 13, 35) on diametrically opposed positions of the respective bearing surface (16, 17) and are linked to one another via coupling elements (32, 33). Tool assembly (2, 3) according to Claim 2, characterised in that a tool (4, 5) is connected to the plain bearings (21, 22; 30, 31) on each side of the rotary shafts (18, 25). Tool assembly (1) according to Claim 1, 2, or 3, characterised in that at least a second pair of guide rods (19') is located transversely to the first pair of guide rods (19, 20), over which second pair of guide rods (19') one or more further tools are movable, which further tools bear on the bearing surfaces (16, 17) via their followers. Tool assembly (2, 3) according to one of the preceding claims, characterised in that the bearing surfaces (16, 17) are provided, in a sealing position of the tools, with an essentially flattened section (16') to provide a predetermined compressive force of the tool (5) on a tool (6) located opposite in the sealing position. Tool assembly (2, 3) according to one of the preceding claims, characterised in that at least one tool (4) is provided with a central slot (37) and a cutting element (38, 39) movable in the slot, wherein a pressure element (40, 41) is provided that, in the sealing position of the tool (4), engages on the cutting element (38, 39) and that pushes the latter out of the slot (37). Tool assembly (2, 3) according to Claim 6, characterised in that the pressure element (40, 41) is arranged on a pressure arm (42, 43) extending transversely to rotary shaft (18, 25). Tool unit (1) comprising an upper and a lower tool assembly (2, 3) according to one of the preceding claims, characterised in that the drive mechanisms of the upper and the lower tool assembly are each provided with a drive shaft with a toothed element (26, 26') fixed thereto, one drive element (46) being placed in the form of a closed loop around the toothed elements of the upper and the lower tool assembly (2, 3). Tool unit (1) according to Claim 8, characterised in that the drive element (46) is guided along a top side of the top toothed element (26) to a first return element (47) located below the bottom toothed element and from there is guided to a top side of the bottom toothed element (26') and via a second return element (48) to the top toothed element (26). Tool unit (1) comprising an upper and a lower tool assembly (2, 3) according to one of Claims 1 to 7, characterised in that the upper tool assembly (2) is joined at a hinge point (51) to the lower tool assembly (3) on a first side of a separation plane (50) between the upper tool assembly (2) and the lower tool assembly (3). Tool unit (1) according to Claim 10, characterised in that the hinge point (51) is formed by a connection, made of an elastic material, between the upper and the lower tool assembly (2, 3). Tool unit (1) according to Claim 10 or 11, wherein the lower tool assembly (3) is joined, at a second side located opposite the first side of the separation plane (50), to the upper tool assembly (2) via a spring element (52).

Inventors: BRAAKMAN HERMAN WICHERT THEODO, BRAAKMAN, HERMAN WICHERT THEODOOR
Applicants: KLOECKNER HAENSEL TEVOPHARM, KLOECKNER HAENSEL TEVOPHARM B.V.
Application year: 2000
Main classification: B65B51
IPC codes: B65B51