DE29706168U1 - Device for strapping packages - Google Patents

Description

The invention relates to a device for strapping packages according to the preamble of claim 1.

Vibration welding using a vibrator driven at a high frequency is characterized in that the vibrator in the band closure area moves one of the two overlapping band sections into high-frequency vibrations relative to the other band section, which creates frictional heat that melts the contacting surfaces of the overlapping band sections so that they are bonded together by melting.

From DE 17 61 166 B1 it is known to let the vibrator oscillate in the longitudinal direction of the belt. Since the vibrator has to work against the belt tensile forces, it is possible to achieve

Postgiro office Credit- und Volksbank eGmbH Commerzbank AG VAT ID No. Eat Wuppertal-Barmen Wuppertal-Barmen VAT No. (Bank code 360 100 43) 445 04-431 (Bank code 330 600 98) 301 891 024 (Bank code 330 400 01) 4 034 S23 DE 121008676

Signode Bernpak GmbH

High tension forces cannot be achieved with packages that are only slightly compressible. Particularly high drive forces are also required on the vibrator. In addition, the arrangement is such that the tension in the loop is fully applied to the connection point of the overlapping belt sections, since the belt material is only clamped between the vibrator and grippers pressing against it from the other side of the belt. This type of belt closure is subject to a lot of wear.

In the device according to US 4,776,905, the overlapping band sections are pressed firmly together on one side next to the oscillator, and the oscillator moves the band section it is engaging transversely to the longitudinal direction of the band over the second band section pressed against it by a counterholder. Unlike the oscillation of the oscillator and the band end belonging to it in the longitudinal direction of the band, this transverse movement of the band leads to a very strong shear stress on the band section moved by the oscillator when the welded closure is produced. This can therefore easily tear off during the closure formation, especially at high band tensions.

In order to partially counteract this disadvantage, a button-shaped clamping body that can freely rotate around an axis perpendicular to the belt is arranged in the abutment plate next to the oscillator. However, this can only absorb the transverse oscillation movements of the belt to a very small extent, as it only absorbs rotating movements at a distance from the oscillator that moves linearly across the belt.

Signode Bernpak GmbH

can be carried out. Furthermore, with this friction welding device, the problem of a band tear is more likely to occur on the side of the oscillator facing away from the clamping device. Since no second band clamp is provided and due to the thermal stress on the band during closure formation, only low clamping forces can be achieved.

A further development of the subject matter of US 4,776,905 provides for the arrangement of the button-shaped band clamp, which can rotate freely about its longitudinal axis, to be pivotable about a distant axis. Such a clamp can follow the transverse band movement of the band end carried by the oscillator over a larger radius and therefore a little better, but still not optimally. Furthermore, the disadvantages mentioned for the subject matter of US 4,776,905 also apply here.

Furthermore, a friction welding device has become known from EP 0 605 759, for example, in which the vibrator vibrates neither in the longitudinal direction of the strip nor in the transverse direction of the strip, but is designed as a ring disk that rotates with an eccentric offset to an axis that is perpendicular to the strip surface. The strip section carried along by the vibrator is thus subjected to a wobbling or "wobbling" movement. A pressure piece that is only spring-loaded is integrated into the ring body of the vibrator in order to guide the strip ends in the effective range of the vibrator or to hold them against each other. In the corresponding device used in practice, there are two friction welding devices in front of and behind the strip in the direction of travel.

Signode Bernpak GmbH ,. ,. ,, , _{&phgr;# &iacgr;##&phgr;}

behind this vibration welding unit there are strap clamps which basically allow the strap to be closed under the tension of the strapped strap, but the strap is subjected to more or less strong loads in all directions in the closure area. In order to limit the shear stress that occurs on the strap sections, the strap clamps (not shown in EP 0 605 795 A1 but present in the machine in practice) are very far apart in front of and behind the vibration sealing unit in order to have long, freely movable strap sections available and to be able to exploit their stretch. However, this results in the disadvantage that small packages, e.g. bar material, cannot be strapped.

DE 40 14 305 C2, from which the present invention is based, also deals with the problem of the disadvantageous consequences of band stress in a vibration welding area, in which the band sections to be joined overlap one another and in which a clamp is arranged in front of and behind this closure area, which only holds one band section. Here, the arrangement is such that the band clamp which acts on the band section which is acted upon by the vibrator is itself driven synchronously with the vibrator by a mechanical, active drive and moves parallel to the vibrator's vibrating movement, taking the band section with it, with this vibrating movement occurring at right angles to the longitudinal direction of the band.

Signode Bernpak GmbH

So that the driven clamping jaw can effectively take the strip section with it, it is pressed against a smooth abutment surface on the side facing away from the clamping jaw. On the one hand, this results in high friction forces and the resulting wear, and on the other hand, the smooth surface of the abutment naturally leads to lower clamping forces. Because the clamping jaw is actively driven, the mechanical complexity of the device is high.

Based on this, the invention is based on the object of creating a device for strapping packages using the friction welding process according to the preamble of patent claim 1, which allows a closure under high band tensile forces, which is also able to strap relatively small packaged goods with high band tension and in which complex additional drives for aggregate parts can be dispensed with.

The invention solves this problem with the features of claim 1 and is accordingly characterized in that the oscillator oscillates about an axis that runs through the movable clamping jaw and that the latter oscillates about the same axis in the same direction as the oscillator, but is only carried along by the oscillating band section.

Because the oscillator oscillates around an axis that runs through the movable clamping jaw, the oscillator performs a circular back and forth movement around this axis over a circle segment. Its movement

Signode Bernpak GmbH ^..^..^

The tension is oriented perpendicular to the longitudinal direction of the belt at only one point of the movement path, so that the belt section is subjected to significantly less shear stress. If the clamping jaw oscillates around the same axis in the same direction as the oscillator, no relative movements take place between the clamping jaw and the belt it holds. According to the invention, however, the clamping jaw is not driven, but is simply carried along by the oscillating belt section. 10

Carrying the clamping jaw in this sense was not provided for in the state of the art referred to so far.

According to a further embodiment of the invention, the clamping jaw is optimally guided along the vibrating belt section in synchronism with the vibrator, in particular when the abutment that interacts with the movable clamping jaw is a section of the vibrator itself. This results in the further advantage that all surfaces of the vibrator and clamping jaw that come into contact with belt surfaces can be designed to increase friction, i.e. in particular can be roughened or toothed, since there is no slippage between these contacting surfaces. The result of this is that the clamping jaw can exert very high clamping forces. In addition, a very simple design is achieved.

Oscillator and freely movable clamping jaw can be integrated in a particularly convenient way by attaching the oscillator to the end of a hollow shaft, which

Signode Bernpak GmbH

The movable clamping jaw is axially displaceable and rotatable.

According to a further embodiment of the invention, it is provided that the friction surface of the oscillator forms an angle of inclination with the opposite surface of an oscillator abutment, which opens away from the oscillation axis of the oscillator in the direction of the belt and has a magnitude of approximately 0.3° to 1.0°. This advantageously takes into account the different distances of belt sections from the oscillation center in coordination with the pressure forces that occur. Away from the oscillation axis, the pressure forces decrease continuously with increasing oscillation path in accordance with the angle of inclination. This achieves an extraordinarily even stress on the unit parts and the belt over the length of the closure produced and a completely homogeneous weld.

The oscillation angle of the oscillator is preferably small and is in the order of about 4° to 5°.

According to a further feature of the invention, the oscillator forms the head plate of the strapping unit facing the package, is attached to the end of the hollow shaft and from there protrudes freely into the strapping plane. Due to this design, the entire strapping unit can be swiveled out of the sealing area, which in a simple way releases the strap loop surrounding the package.

Signode Bernpak GmbH

· 1

The means for controlling this can also be very simple. In this regard, the features of claims 8 to 10 are important. A particularly significant advantage is that the drive shaft forms a central drive, via which all stroke-controlled functional parts of the band closure unit can be controlled in a timed manner.

Furthermore, the invention is best understood from the following explanation using an embodiment shown in the drawings. In the drawings:

Fig. 1 a strapping machine in schematic view,

Fig. 2 is a schematic representation of the band sealing unit in a first position after the band surrounding a package has been inserted,

Fig. 3 shows a view of the sealing unit corresponding to Fig. 2 with the strap loop tightened around the package,

Fig. 4 is an enlarged view of only the closure area of the device compared to Fig. 3, with

For clarification, all surface roughenings are not shown.

Fig. 5 shows a schematic cross section through the operating position of Figs. 3 and 4,

Locking unit in the area of the oscillator,

Signode Bernpak GmbH

Fig. 6 an enlarged view to explain the geometry and function of the oscillator and clamping jaw, and

Fig. 7 shows a representation corresponding to Fig. 4 of the unit position at the end of a working cycle.

A strapping machine in its entirety is designated 10 in Fig. 1. On its machine frame 11 there is an essentially closed strap guide channel 12 through which and around a package 13 indicated by dotted lines a thermoplastic synthetic strap 14 is fed to a strap sealing unit 15. The task of this is to weld overlapping end sections of the strap 14 guided around the package 13 together by means of friction welding through the action of heat.

The band 14 is stored outside the machine frame 11 on a rotatably mounted band reel (drum 55). First, the band 14 runs through a pair of rollers 16 on the machine input side, which have two rollers that engage with opposing band surfaces in a frictional manner, which are tensioned towards one another and thus held against the band 14 with pressure. The motor drive of this pair of rollers 16 conveys the band 14 into a band storage unit 17, which stores a length of band 14 without tension as is required at least for the subsequent strapping and for the distance of the band 14 to the sealing unit 15.

Signode Bernpak GmbH .. ..

-10-2 '<"·

A second pair of rollers 18 is arranged following the belt storage device 17 in the belt feed direction. The two rollers of this pair of rollers 18 also drive the belt 14 with friction. This pair of rollers 18 is driven reversibly, because it serves on the one hand to feed the belt 14 into the belt guide channel 12 and, with the opposite drive direction, on the other hand to retract the belt 14 and tighten it around the package 13. In the latter sense, the pair of rollers 18 is a so-called "low tension tensioning device".

In the tape feed direction, the weft and retraction roller pair 18 is followed by a "high tension tensioning device" using a tensioning drum 19, which is the subject of another patent application and is not of further importance here. This tensioning drum 19 is followed by a special tape clamp 20 and a guide channel 21, through which the tape 14 takes its way to the tape closure unit 15.

Fig. 2 illustrates details of the tape closure unit 15. According to this illustration, the tape 14 was fed to the tape closure unit 15 by means of the weft roller pair 18 through the tension drum 19 and through the tape guide 21 until the leading tape end 14' ran against a so-called weft switch 23.

On its way there, the free leading tape end 14' has passed through a separator slot 24 in a first tape clamp 25 and then through a separator 26 serving to guide the tape within a so-called

Signode Bernpak GmbH ,

-11-5

"Welding clamp" 27. The two separator slots serve to keep the band sections in their common overlapping area (initially) away from each other and to enable unhindered cutting of the lower band section.

The actuation of the insertion switch 23 by the leading, free strap end 14' signals the machine's starting position to the machine control and practically carries out a 'reset'. This starting position is characterized by the fact that a strappable section of the strap 14 is already held ready within the strap guide channel 12 (Fig. 1).

The strapping process itself then begins when the machine command is initiated by pressing a button after a package 13 has been placed in the channel 12. The pair of rollers 18 receives the command to reverse the drive and pulls back the strap 14, which begins to tighten around the package 13 in accordance with the friction forces exerted by the pair of rollers 18, because the first strap clamp 25 presses the front strap section 14' against the underside of the head plate 22.

If the package 13 is to be subjected to a higher band tension than the "Low Tension" roller pair 18 can impart to the band 14, the "High Tension" tensioning drum 19 rotates into the band tensioning process and thereby tightens the band with a strong tensile stress.

Such a tightened belt state is shown in Fig. 3, which also shows that the separator 26

Signode Bernpak GmbH

(Fig. 2) has been swung out sideways from its operating position there, whereupon the welding clamp 27 and a second band clamp 41 arranged outside next to it have been moved upwards, which now also holds the band 14 here.

A cutting blade 46 attached to the welding clamp 27

has cut off the length of strapping required for strapping from the strap supply. The strap 14, which is tightened around the package 13, is now in the welding position to form a strap closure.

This position is - as shown in Fig. 4, which shows the essential functional parts larger than Fig. 3 - primarily characterized by the fact that the front end of the band is held by the clamping jaw 25' of the first band clamp 25 in cooperation with the head plate 22 on one side of the closure formation zone, while the clamping jaw 41' of the band clamp 41 presses the other end of the band 14" on the other side of the band closure zone against a clamping abutment 42. Each clamping jaw 25' and 41' therefore only holds one band section, and the overlapping band sections 43 and 44, which are to be connected to one another, are located in the band closure zone in between. The band closure zone is kept free from band tensile forces resulting from the strapping.

The head plate 22 is also a vibrator and is driven to oscillate around a vertical axis designated 29. The oscillation axis 29 is also the central axis of the band clamp 25 with clamping jaw 25', which can rotate freely around this axis.

Signode Bernpak GmbH

is. Specifically, the arrangement is such that the bearing shaft 30 of the band clamp 25 is guided into a hollow shaft 31. As shown in Fig. 5 and Fig. 7, the hollow shaft 31 is connected to the oscillator head plate 22 in a movement-unitary manner.

The oscillator 22 is driven by a motor 33 flanged to a bearing block 32, which drives an oscillating fork 35 via an eccentric shaft 34, to which the hollow shaft 31 is connected in a rotationally fixed manner. The oscillator 22 thus carries out oscillating movements around the vertical axis 29. This is shown in Fig. 6, with one end position of the oscillating movement shown in solid lines and the other in dotted lines. Shown is a top view of the oscillator 22, which has been partially broken away to make the clamping jaw 25' of the band clamp 25 underneath visible.

The oscillation movement of the oscillator 22 leads to the belt section 43, which the oscillator 22 engages, being moved back and forth over a circular sector relative to the opposite belt section 44 held by the welding clamp 27, which leads to frictional heat and thus to the softening of the surfaces of the overlapping belt sections facing each other. The oscillation angle is kept small at around 4° to 5°, which helps protect the belt and the components and also reduces wear and noise.

Signode Bernpak GmbH

For the optimal distribution of the pressure forces that occur during the friction welding process, the surface 28 acting on the band section 44 is inclined by an angle w to the lower surface 22 of the oscillator, which acts on the band section 43. The angle w, whose vertex lies in or near the oscillation axis 29, opens outwards from there across the clamping section. The angle of inclination w, which is approximately 0.7°, achieves a balance between the friction path and the pressure force in such a way that the force becomes slightly smaller with increasing oscillation path, i.e. in the direction of the opening angle w. This also contributes significantly to the low wear and noise of the device and to homogeneous welding.

The band section 43 moved in an oscillating manner by the oscillator 22 is also pressed against the underside of the oscillator 22 by the clamping jaw 25' of the first band clamp 25, so that the band section 43 driven in an oscillating manner by the oscillator 22 takes with it the clamping jaw 25' of the band clamp 25, which is guided in a rotationally movable manner in the hollow shaft 31 of the oscillator 22. As a result, the shear forces acting on the band section 43 are kept so low that they cannot have any damaging effects on a secure closure, which can also take place under high band tension.

After the band closure has been made in the manner described, the band clamps 25 and 41 as well as the welding clamp 27 move downwards again with respect to the drawings, and all stroke-controlled devices of the closure unit, in particular the oscillator

Signode Bernpak GmbH .. .. .* . ··.···.

22 and the band clamp 25 integrated into it are swung sideways out of the band closure plane. This is shown in Fig. 7, in which the separator 26 can also be seen which has already been swung out in the opposite direction.

The moving functional parts are controlled centrally via a control shaft 45 with a control cam 47 for the stroke-controlled strap clamp 25, a control cam 48 for the welding clamp 27 and a control cam 49 for the second strap clamp 41. As a result of the swiveling out of the unit parts, the strapped package can be removed from the machine table particularly easily.

Claims (10)

Signode Bernpak GmbH , - 16 4 Expectations 1 . Device for strapping packages with a thermoplastic band, which is fed from a band supply into a band guide channel surrounding the package and through this is fed to a band sealing unit, which connects overlapping band sections in the band strapping plane by means of friction welding, wherein a clamping jaw is provided in front of and behind the overlapping area for pressing a band section against an abutment and in the overlapping area of the band sections an oscillator driven in oscillation parallel to the band plane causes the band section facing it to vibrate relative to the other in high-frequency vibrations that generate frictional heat and thereby welds the band sections together, and wherein the clamping jaw of the band section on which the oscillator acts is arranged to be movable in and against at least one direction parallel to the band plane, characterized in that the oscillator (22) oscillates about an axis (29) which runs through the movable clamping jaw (25') and that this is rotatable about the same axis (29) oscillates in the same direction as the oscillator (22), but is only carried along by the oscillating belt section (43). 2. Device according to claim 1, characterized in that the abutment cooperating with the movable clamping jaw (25') is a section of the oscillator (22) itself. Signode Bernpak GmbH 3. Device according to claim 1 or 2, characterized in that the oscillator (22) is attached to the end of a hollow shaft (31) which supports the movable clamping jaw (25') in an axially displaceable and rotationally movable manner. 4. Device according to one of claims 1 to 3, characterized in that the friction surface (22a) of the oscillator (22) is in contact with the surface opposite it (28) of an oscillator abutment (welding clamp 27) encloses an angle of inclination (w) which opens in the direction of the belt, pointing away from the oscillation axis (29) of the oscillator (22). 5. Device according to claim 4, characterized in that the angle of inclination (w) has a magnitude of about 0.3° to 1.0°. 6. Device according to claim 1 or one of the following, characterized in that the oscillation angle of the vibrator (22) has a magnitude of approximately 4° to 5°. 7. Device according to claim 1 or one of the following, in particular according to claim 3, characterized in that the oscillator (22) forms the head plate of the strapping unit (15) facing the package (13), is attached to the end of the hollow shaft (31) and from there projects freely into the strapping plane on one side. Signode Bernpak GmbH - 18 4 8. Device according to claim 1 or one of the following, characterized in that the movable strap clamp (25) associated with the oscillator (22) has a shaft (30) which passes through the hollow shaft (31) and which forms the plunger for its stroke control, which can be acted upon at the front by a control surface as part of a control element such as a cam (47) or cam disk, which control element is attached to a drive shaft (45) extending parallel to the strapping plane. 9. Device according to claim 8, characterized in that the drive shaft (45) carries control elements (47; 48; 49) for all stroke-controlled functional parts of the band closure unit and thus forms a central drive. 10. Device according to claim 8 or 9, characterized in that the stroke-controlled band sealing unit parts such as band clamps (25, 41), band cutting knives (46) and oscillating abutments (27) as well as the stroke-fixed functional parts interacting with them such as oscillators (22) and clamping abutments (42) are guided or held in a common carrier (50) which is pivotally mounted about the axis of the central drive shaft (45) and can be pivoted by means of additional control surfaces moved by it in such a way that the band sealing unit (15) as a whole can be temporarily controlled out of the band strapping plane.