EP0798214A1 - Device for stretchinga stretchable hood - Google Patents

Abstract

Horizontally movable stretch units (4) are positioned on a frame (5). Each unit has a stretch bracket (14) moving into the pre-opened end of the cap of stretch film. The stretch brackets each have stretch rollers parallel with the longitudinal axis (17) of the cap and mounted so as to rotate freely on their longitudinal axis (19). The rollers have a cylindrical outer surface and at least one roller has at least one back-tapered part between its two ends.

Description

The invention relates to a stretch device for biaxial stretching (ie for considerable stretching) of a stretch film hood formed from a side gusseted tube and consisting of a highly stretchable plastic film, for a packaging machine for wrapping a piece of piece goods with a stretch film hood, the undrawn size of which is considerably smaller than the stack size a plurality of horizontally movable stretch units arranged on a frame, each having a retractable stretch bracket in the pre-opened hood end and from their approximated retracted position via a spreading position in which the stretch bracket arranged in a corner of the hood each Open the hood without stretching and, in general, take up substantially the entire length of the hood, diagonally stretch the hood side walls into a spaced-apart pull-over position and move them together relative to the stack of items to be wrapped, the stretch bars being designed so that they cover the hood side walls When covering each case, impress vertical frictional forces on both sides of the relevant hood corner edge at a considerable distance from a hood corner, which are opposed to the relative movement of the film to the stretch bracket.

In particular, uniform, stackable piece goods, such as sacks filled with cement, are generally stacked on top of each other for storage and transport purposes by means of a so-called palletizer (generally on pallets) in such a way that cube-shaped or cuboid piece goods are stacked. However, the piece goods stack can also have other geometric shapes.

Various methods are known in which piece goods stacks are protected from environmental influences, in particular weather influences, during storage and transport, and to give them sufficient stack strength during implementation and transport, in which the piece goods stacks are firmly attached to at least their top and side surfaces Plastic film to be wrapped. In one of these processes, this takes place in that the piece goods stacks are fed one after the other to a packaging machine which covers them from above with a film hood.

Foil hoods are generally expediently formed from a so-called gusseted tube, which has two mutually parallel side surfaces and two V-shaped between it has folded-in side surfaces, all side surfaces running parallel and lying against one another in the stored state.

If the film hood consists of so-called shrink film, the circumference of the hose or hood is somewhat larger than the circumference of a stack to be wrapped. The hose or the hood is easily pre-opened at the free end, for example by suction devices, by moving the parallel side surfaces so far apart that receiving elements move into the pre-opened end and "stretch" the hood by spreading it apart, that is to say that it is (fully) free of expansion . In this spread-apart position (= pull-over position), there is a receiving element on the inside of the hood in each hood corner or corner edge. After covering the hood by means of these receiving elements, the film is shrunk onto the stack by applying heat.

If, on the other hand, the film hood consists of so-called stretch film, the circumference of the hose or the unstretched hood is considerably smaller than the circumference of the stack of items. The hoods must therefore be circumferentially stretched to a covering dimension such that they can be pulled over a stack of general cargo in the covering position. After covering, the hood then lies firmly against the stack under the permanent elastic stretch and ensures, among other things. for the desired stack strength.

This transverse stretching (generally referred to as transverse or horizontal stretching) is carried out by means of a stretch device integrated into the packaging machine, in that the pre-opened hood is positioned essentially centrally over the stack of stretch bars of the stretch device to be wrapped is picked up and first stretched by diagonally moving apart in a spreading position (still unstretched) so that their side faces each run essentially parallel to a side face of the stack to be wrapped. In this spread position, the hood side walls are thrown onto the stretch bracket. Since the hood circumference is considerably smaller than the stack circumference, the hood side walls are each offset inwards from the parallel stack side wall in the spread-out position. The hood is then stretched crosswise by moving the stretch bars diagonally apart into the pull-over position. This is done in such a way that the hood side walls each remain parallel to a side surface of the stack. The number of stretch units or the stirrups therefore corresponds to the number of side stacking edges. A stretch device therefore has four stretch brackets for enveloping cuboid or cube-shaped stacks.

Although the stretch brackets retracted into the pre-opened hood end are intended to stretch the hood side walls across their entire height, their extension in the direction of the hood longitudinal axis is generally considerably smaller than the hood length in order to reduce the required height. Therefore, the hood side walls before the cross stretching of the hood are reefed onto the stretch bars by reefing means, so that the hood side walls are then taken up in folds by the stretch bars. The reefing devices generally consist essentially of a driven reefing roller with a horizontal axis, which can be moved from the outside to the relevant stretch bracket after it has come into contact with the inside of the hood, so that the hood side walls at the same time Approaching all reefing rollers on their respective stirrups and correspondingly driving the reefing rollers are to be thrown completely onto the stretching stirrups.

As has already been briefly stated, hoods are generally not supplied to the packaging machine in the finished state, but rather are formed in / from it, in each case from a section of a gusseted tube, which is stored in the packaging machine in the folded-up state, rolled up into a roll, and with its free end is fed to a hood forming device of the packaging machine. In the hood-forming device, the end of the hose is generally pre-opened (generally by suction devices or wedge plates) so that the hose can be received at its end by receiving elements, which are generally the stretch brackets of the stretching device, so that the hood after its completion does not need to be handed over to the stretch device first. The hood is formed by placing a cross weld seam at a distance from the end of the hose and separating the section provided with the cross weld seam and forming the hood from the hose supply.

The unstretched circumference of stretch film hoods is generally chosen to be at least 10-20% smaller than the circumference of the stack of piece goods to be wrapped, so that a corresponding transverse stretch (transverse stretch) of 10-20% occurs in the finished loading units. In the meantime, however, stretch films have already been made available or are in development, which allow even larger elongations of up to 50% and more.

Even with a view to an all-round uniform stack strength, it is highly desirable that the hood side walls of the finished loading units are stretched substantially uniformly. Not only for this, it is also highly desirable that a stretch film hood is stretched evenly evenly before being pulled over the stack on the stretch brackets and is not prevented from this by friction on the stretch brackets, since in such cases there is not only very different stretching the hood side walls but can also come within a hood side wall, so that, if necessary, greatly expanded hood side wall sections are overstretched, while the expansion potential of other hood side wall sections, which on the other hand are considerably less stretched, is not used.

In addition, it has proven to be extremely useful to create a high stacking strength if the stretch film hoods are not only stretched crosswise in the finished loading units, but are additionally provided with a longitudinal stretch in the longitudinal direction of the hood, so that a biaxial stretching state is present. This longitudinal stretching of the hood expediently takes place when the hood which has already been stretched crosswise is pulled over the stack. In this regard, reference is made to DE-PS 39 18 311.

When developing the stretch hood technology and thus the development of suitable stretch devices, the stretch bars were initially designed as rod-shaped or finger-shaped elements that protrude from the stretch frame with a longitudinal axis running parallel to the longitudinal axis of the hood or into one after / after entering the open hood end such position are pivotable (see DE 37 07 877 A1, for example). It lies down when moving apart of the stretch units from their approximated retracted position into their pull-apart position from each other, the inner side of the hood against an outer circumferential section of each stretch finger and, when the hood side walls are stretched, is pressed against the stretch fingers with increasing pressure. The frictional forces thus created between the film and the stretch brackets may have the consequence that no stretch compensation can take place during cross-stretching between adjacent hood side walls if the hood side walls adjacent to a stretch bracket are stretched to different extents when the stretch units are moved apart, since the frictional forces prevent that the film can slide over the stretch bar to create an expansion compensation. Different stretching of adjacent hood side walls occurs, however, if the stretch bars from their spreading position, in which the hood (generally reefed) has been picked up by them, are not moved into the pull-over position in such a way that the mutual distance between adjacent reefing bars varies as a percentage enlarged in the same way so that the area spanned by the stretch brackets is enlarged geometrically similar. A different method of stretching stirrups is, for example, expedient or necessary if the stretching stirrups span a surface in their spread position that is not geometrically similar to the cross-sectional area of the stack (in plan view) and the respective distance between the hood side walls and the adjacent one Side wall of the piece goods stack in the pull-over position should be essentially the same size. If, however, there are significantly different transverse expansions of the hood side walls when the hood is stretched across, overstretching can occur. These strains are also the same when covering the stack with the hood not necessarily completely out, so that an uneven transverse expansion of the hood side walls can remain in the finished loading unit.

A significant further disadvantage of these finger-like reefing brackets is that when the stack is pulled over the width of the hood side walls, a satisfactory longitudinal stretch of the hood's side walls cannot be achieved, since finger-like reefing brackets rest essentially only in a line (almost punctiform in plan view) on the hood, so that when pulling only in the corners of the hood in the longitudinal direction of friction forces act on it, which can produce a longitudinal expansion in the corner areas when the hood slides off the stretch bars when pulled over, but not in the areas between the adjacent stretch bars Hood side walls. At least, with such finger-like stretch brackets of the hood, no vertical forces can be impressed, which also cause a considerable longitudinal stretch in the central region of a hood side wall.

From DE-PS 1 938 960 a spreading device for (unexpanded) spreading ("spreading") a shrink film hood formed from a gusseted tube is known, the circumference of which is greater than the circumference of the stack of articles to be wrapped. This spreading device generally consists of four finger-like vertical rods, which are each arranged at the free end of a horizontally pivotable lever articulated on a lifting frame, are moved together in an approached retracted position into the pre-opened hose or hood end (by suction devices), and then synchronously to be pivoted outwards each under the hood in a corner edge of the hood, stretch the hood in the extended position (unstretched). Since the spreader bars come into contact with the film on an unfolded hood side wall before reaching the pull-over position and move relative to the film when the bonnet side walls are appropriately lengthened, and since this relative movement should be prevented by frictional forces between the spreader bars and film , The spreader bars can optionally be designed as rollers rotatably mounted about their longitudinal axis.

Apart from the fact that this shrink hood expansion device is particularly suitable for large transverse expansions of e.g. 50% is therefore not suitable as a stretch device for stretch film hoods, because the maximum transverse expansion that can be achieved is limited by the length of the lever, it would also be unsuitable for this if the finger-like pick-up rollers could not be swiveled between the retracted and extended positions, but could be moved diagonally. There would then be a stretch compensation between adjacent hood side walls when stretching, but the hood side walls - as with firmly arranged finger-like receiving elements - would only be subjected to vertical forces when the hood was pulled over directly and adjacent to the hood corner edges, so that a satisfactory vertical stretch could not be achieved , especially since the roll diameter must be relatively small so that the distance between the hood side walls and the stack can be kept as small as possible.

One therefore has finger-like stretch brackets with one at their free end facing away from the frame (In the top view) L- or C-shaped stretch bracket section extending at right angles from the finger-shaped section, in order in this way to have a contact surface between the stretch bracket and film available when the hood is pulled over the stack extends considerably larger circumferential section of the hood and thus also impresses vertical forces generated by friction into the film at a corresponding distance from the respective hood corner. Although with such (in the side view T-shaped) stretch brackets a satisfactory longitudinal stretch can be achieved in the hood side walls when the stack is pulled over, it has been shown that, especially with large transverse stretches and the like. Large internal tensions of the hood can be difficult when pulling on, because the film material below the transverse stretch bracket sections, which is only supported there by the finger-like stretch bracket sections, pull inwards due to the elastic restoring forces that occur during cross stretching and therefore not optimal when the hood is pulled over slide off the stretch bars, but can be pinched if necessary.

Also, due to the frictional forces, the film lying on the horizontal stretch bracket sections cannot stretch, at least not in the same way, during cross stretching as the film sections not acted upon by the stretch bars, so that the latter may be overstretched in sections.

DE 90 06 374 U1 has therefore also proposed, as it were, shell-shaped stretch bars which are designed at their upper end in exactly the same way as the previously discussed stretch bars, but differ from them in that they cover their entire length Height L- or C-shaped, so that the film rests on them over a large area, cannot pull inward in the area of the stretch bracket and therefore slides freely from the stretch bracket when the hood is pulled over the stack of items.

A disadvantage of this stretch bracket is, however, that the film is prevented during cross stretching due to the resulting frictional forces from stretching in their contact areas on the stretch bars in the same way as the film sections running between adjacent stretch bars. This is particularly disadvantageous if film material with a very high degree of stretch is used and this is used, i.e. the hood circumference is doubled when stretching, for example, and if the circumferential section of the hood acted upon by the reefing brackets in relation to the distance between two adjacent stretch brackets is relatively large. If, however, essentially only the foil sections lying between adjacent reefing brackets are stretched during transverse stretching, overstretching can occur there.

The present invention has for its object to improve a stretch device of the type described in particular in that the hood is stretched iw evenly over its entire circumference in the cross-stretched pull-over position even with extremely high transverse stretches, and that you nevertheless achieve a satisfactory one Vertical stretches at a considerable distance from the hood corners or corner edges should be impressed when the vertical brackets are pulled over, while at the same time it is to be ensured that the hood easily slides off the stretch brackets.

The solution to this problem is, according to the invention, that the stretch brackets each have a plurality of stretch rollers which are freely rotatable about their longitudinal axis and which are arranged parallel to the longitudinal axis of the hood and have a substantially cylindrical lateral surface, which are arranged such that they essentially mirror-symmetrically when the hood is stretched and pulled over a middle reference plane running parallel to their longitudinal axes through the relevant hood corner abuts the hood.

In a configuration with only one stretch roller per stretch unit, it could no longer occur that the hood side walls are stretched to different extents in the cross-stretched pull-over position of the hood, but with such a design of the hood, vertical forces would only be impressed in the corners do not lead to a satisfactory vertical stretch of the hood side walls (in the middle area). This can only be achieved with optimal transverse expansion compensation if the stirrups each have several stretch rollers.

At least some of the cylindrically shaped stretch rollers can be provided with at least one groove-like undercut, into which the hood, which is usually attached to the stretch bracket before the stretching, fits into it, so that these undercuts, as it were, form abutments for the film, by means of which when Excess additional longitudinal forces are to be impressed into the hood side walls without the film being adversely affected as in the prior art, in particular if the transitions of the undercuts to the lateral surface are rounded and the depth of these undercuts - depending on the film material - is not chosen too large. Undercuts of stretch bars are known per se from DE 39 18 311 C2, but not for finger-like stretch elements (here: stretch rollers), but only between a finger-like stretch bar section and a stretch bar section running transversely to this.

In the stretch device according to the invention, too, the hood can be seen to easily hit the stretch bracket by means of a suitable reefing device.

Preferred embodiments of the present invention are described in the subclaims.

Fig. 1

eine Draufsicht auf eine erfindungsgemäße Stretcheinrichtung, deren vier Stretcheinheiten sich in der Aufspreizstellung befinden;

Fig. 2

eine Darstellung gemäß Fig. 1, wobei sich die Stretcheinheiten in der Überziehstellung be finden;

Fig. 3

eine teilweise geschnittene, vergrößerte Seitenansicht der Darstellung gemäß Fig. 2 in Richtung der Schnittlinie III-III in Fig. 2 gesehen;

Fig. 4

eine teilweise Draufsicht auf die Darstellung gemäß Fig. 3 in Richtung des Pfeiles IV in Fig. 3 gesehen;

Fig. 5

eine Seitenansicht einer Stretcheinheit in Richtung des Pfeiles V in Fig. 4 gesehen in vergrößerter Darstellung;

Fig. 6

eine Schnittdarstellung durch die Darstellung gemäß Fig. 5 in Richtung der Schnittlinie VI-VI in Fig. 5 gesehen;

Fig. 7

eine Draufsicht auf die Darstellung gemäß Fig. 5 in Richtung des Pfeiles VII in Fig. 5 gesehen;

Fig. 8

eine Fig. 5 entsprechende Darstellung einer Variante einer Stretcheinheit;

Fig. 9

einen Schnitt durch die Darstellung gemäß Fig. 8 in Richtung der Schnittlinie IX-IX in Fig. 8 gesehen; und

Fig. 10

eine Draufsicht auf die Darstellung gemäß Fig. 8 in Richtung des Pfeiles X in Fig. 8 gesehen.

The invention is explained below using exemplary embodiments with reference to a drawing. It shows:

Fig. 1

a plan view of a stretch device according to the invention, the four stretch units are in the spread position;

Fig. 2

a representation of Figure 1, wherein the stretch units are in the pull-over position be.

Fig. 3

seen a partially sectioned, enlarged side view of the illustration of Figure 2 in the direction of section line III-III in Fig. 2.

Fig. 4

a partial top view of the illustration of Figure 3 seen in the direction of arrow IV in Fig. 3.

Fig. 5

a side view of a stretch unit in the direction of arrow V in Figure 4 seen in an enlarged view.

Fig. 6

a sectional view through the representation of Figure 5 seen in the direction of section line VI-VI in Fig. 5.

Fig. 7

a plan view of the representation of Figure 5 seen in the direction of arrow VII in Fig. 5.

Fig. 8

a representation corresponding to FIG. 5 of a variant of a stretch unit;

Fig. 9

seen a section through the representation of Figure 8 in the direction of section line IX-IX in Fig. 8. and

Fig. 10

seen in the direction of arrow X in FIG. 8.

1 shows a stretch device, denoted overall by 1, for the biaxial stretching of a stretch film hood 2 indicated by a dotted line. The stretch device 1 is part of a packaging machine for wrapping a piece of packaged goods in each case with a stretch film hood 2, the unstretched circumference of which is considerably smaller than the stack circumference. Such a piece goods stack 3 is indicated in Fig. 1 with a dash-dotted line (in plan view). It is recognizable that the piece goods stack 3 has a substantially square base. It is cube-shaped or cuboid.

The stretching device 1 has four stretching units 4, which are arranged on a frame 5, which is denoted overall by 5 and extends in a horizontal plane, and which is designed as a lifting frame and can be moved vertically on stands 6 of the packaging machine (not shown in detail). The frame 5 is initially arranged above the piece goods stack 3 and has an outer frame 7 and two double traverses 9 movable in the direction of the double arrow 8 relative to the latter, which can be moved synchronously in opposite directions by means of a drive 10 'via a chain drive 11' in the direction of the double arrow 8 .

On each double traverse 9, two stretch units 4 are arranged, or the like by means of a drive 10 via chain drives 11. in the longitudinal direction of the double traverses 9 and thus the double arrow 12 can be moved synchronously. The arrangement and control is made such that the stretch units 4 are moved synchronously in the opposite direction from the position shown in FIG. 1 in the direction of arrow 12 when the double traverses 9 perform an opposite, synchronous extension movement in the direction of arrow 8, whereby the respective speeds are adjusted so that each of the four stretch units 4 moves relative to the space on its longitudinal central axis 13.

Each stretch unit 4 has a stretch bracket generally designated 14, this designation in Regarding the terminology common in practice, although each stretch bracket 14 consists of several elements, as will be explained in more detail below. The stretch brackets 14 of all the stretch units 4 can be retracted into the open end of a pre-opened hood 2 fed from above to the open end of the stretch device 1 in a retracted position in which the stretch units 4 are moved even further than shown in FIG. 1. After the stretch brackets 14 have been moved into the hood, the stretch units 4 are first moved apart into the spread-apart position shown in FIG. 1, in which the stretch brackets 14 stretch the lower end of the hood completely, without already stretching the hood 2. In this position, the hood side walls are raised by means of reefing devices, denoted overall by 15, onto the stretch bracket 14, as is indicated in the left part of FIG. 3 and will be described further below. The stretch bars 14 are to be explained beforehand, in particular with reference to the enlarged representations according to FIGS. 3 to 7.

The stretch bracket 14 of each stretch unit 4 has five stretch rollers 16 (= 16.1,..., 16.5) arranged parallel to the longitudinal axis 17 of the hood, which are freely rotatable about their respective longitudinal axis 19 on a horizontal base plate 18 of the stretch unit 4 concerned. The stretch rollers 16 are arranged mirror-symmetrically to a central reference plane 20 running parallel to their longitudinal axes 19 (see FIG. 7), into which the longitudinal central axis 13 of the stretch unit 4 also falls. The stretch rollers 16 each have an at least substantially cylindrical lateral surface 16 ', the stretch rollers 16.1, 16.2, 16.4 and 16.5 arranged at a distance from the reference plane 20 each having circumferential grooves Undercuts 21 are provided, which merge with rounded edges 22 into the cylindrical outer surface 16 '.

The middle stretch roller 16.3 is shortened compared to the other stretch rollers because a reef roller 24 rotatably mounted on a reefing bracket 23 with an axis of rotation 24 ′ running transversely to the longitudinal axes 19 of the stretch rollers 16 'is arranged in its area, which will be explained further below. The upper section 23 'of the reefing bracket 23 clearly forms part of the stretch bracket 14.

1, in which the open lower end portion of the hood bears against the stretch rollers 16 and the upper portion 23 'of the reefing bracket 23, they become particularly good in FIG. 3 recognizable reefing devices 15 each move up to the assigned stretch bracket 14, so that their reefing roll 15 'is to be thrown onto the reefing roll 24 by pressing the film in between onto the stretching bracket 14 if the reefing rolls are driven in the direction of arrow 25 by a drive of the reefing device 15 until the hood cover rests on the top of the stretch bracket 14.

The stretch units 4 are then moved from the spread position shown in FIG. 1 relative to the shirred hood 2 spanned by the stretch brackets 14 in the direction of their longitudinal central axis 13 into their pull-over position (see FIG. 2), the stretch brackets 14 opening the hood side walls stretch a covering dimension (see dotted line in FIG. 2), in which the hood circumference is larger than the stack circumference and the Stretch bracket 14 with its inside a sufficiently large distance from the stack 3, which allows a safe covering of the hood 2 over the stack 3.

In this state, the lifting frame 5 is lowered on the stands 6, the hood cover 2 'laying on the upper side of the stack 3 and serving as an abutment when the stack 3 is pulled over, against which the stretch fingers 14 follow the hood side walls when the lifting frame 5 is lowered pull down so that the side walls of the hood are stretched vertically at the same time, that is, provided with a longitudinal stretch.

Although the hood side walls are stretched extraordinarily strongly when stretching, as can be seen from a comparison of FIGS. 1 and 2, and the stretch bracket 14 in the receiving position (FIG. 1) lies against the film at approximately 50% of the hood circumference, it obviously cannot In addition, essentially only the film sections stretched freely between the adjacent stretch brackets 14 are stretched, since the stretch rollers 16 can rotate freely when the stretching of the film sections leading away from them on both sides and thus the forces acting there become differently large, until there is a balance of forces and thus an expansion compensation. This ensures that the hood side walls are each stretched substantially uniformly over their entire width. However, this does not yet ensure that adjacent hood side walls are stretched evenly in the pull-over state, since the hood 2 is stretched at its corner regions, inter alia, by the fixed upper sections 23 'of the reefing bracket 23, from which it is no longer unimpeded can slide along if a considerable amount of pressure and thus a correspondingly high frictional force has occurred due to considerable transverse expansion. In order to ensure a largely uniform expansion of all hood side walls, according to the stretch bracket design shown in FIGS. 8 to 10, the reef bracket 23 is offset inwards and provided on its upper side with further short stretch rollers 16.6 and 16.7, so that the film when stretching in the area of Stretch bracket 14 rests overall on stretch rollers 16 and therefore uniform stretching is ensured over the entire hood circumference. Since the outer stretch rollers 16.1, 16.5 of each stretch bracket 14 are arranged at a considerable distance from the respective hood corner edge, vertical forces are also impressed into the film there, so that a satisfactory vertical stretch can occur.

With reference to FIG. 7 as an example, reference should also be made to the fact that, in the exemplary embodiment according to FIGS. 5 to 7, the rollers 16.1 and 16.2 or 16.4 and 16.5 lying outside the reference plane 20 are arranged such that the hood 2 is the outermost stretch rollers 16.1 and 16.5 is affected, but is not redirected by them. Although such an arrangement is also expedient, the stretch rollers 16 are preferably arranged in such a way that a certain deflection of the film takes place on each stretch roller 16, i.e. in such a way that a first tangent T1 applied from the outside to the outside of two adjacent stretch rollers 16.1, 16.2 the side facing the stretch rollers 16 in a top view with a second tangent T2 includes an angle α of less than 180 °, which from the outside from the outside of one of these two stretch rollers (here the stretch roller 16.2) to the outside of the other adjacent stretch roller 16.3 is laid. The critical angle at which the stretch rollers are still effective is clearly 180 °. This angle is preferably smaller than the critical angle.

Reference list

1

Stretch device

2nd

(Stretch film) hood

2 '

Hood cover

3rd

General cargo stacks

4th

Stretch units

5

frame

6

Stand

7

Outer frame

8th

arrow

9

Dcppeltraversen

10.10 '

drive

11.11 '

Chain drive

12th

arrow

13

Longitudinal center axis (of 4)

14

Stretch bar

15

Reefing equipment

15 '

Reef roll (of 15)

16

Stretch rolls

16 '

Lateral surface

17th

Hood longitudinal axis

18th

Base plate (of 4)

19th

Longitudinal axis (from 16)

20th

Reference plane

21

Undercuts

22

Edges (of 21)

23

Reefing bracket

23 '

upper section (of 23)

24th

Reef role

24 '

Axis of rotation (of 24)

25th

arrow

Claims (10)

Stretch device (1) for biaxially stretching a stretch film hood (2) formed from a side gusseted tube and made of highly stretchable plastic film, for a packaging machine for wrapping a piece of packaged goods (3) in each case with a stretch film hood (2) whose unstretched circumference is considerably smaller than the stack circumference , with a plurality of stretch units (4) horizontally displaceably arranged on a frame (5), each in the pre-opened hood end have retractable stretch brackets (14) and from their approximated retracted position via a spreading position, in which the stretch brackets (14) arranged in each corner of the hood (2) stretch the hood (2) without stretching and, in general, in a reefed manner substantially over their entire length , diagonally stretching the hood side walls in a pull-apart position that is distant from each other and in this jointly relative to the stack of items (3) to be wrapped in each case, the stretch bars (14) being designed so that they each pull away from the hood side walls at a considerable distance Inject a vertical cornering force on a hood corner on both sides of the relevant hood corner edge, which counteracts the relative movement of the film to the stretch bracket (14), characterized in that the stretch bracket (14) each has a plurality of freely rotatable bearings parallel to the longitudinal axis (17) of the longitudinal axis (19). arranged street have etch rolls (16.1, ..., 16.7) with an essentially cylindrical lateral surface (16 ') which are arranged such that when the hood (2) is stretched and pulled transversely, they are essentially mirror-symmetrical to one parallel to their longitudinal axes (19) rest against the hood (2) through the central reference plane (20) running through the hood corner in question. Stretch device according to claim 1, characterized in that at least one stretch roller (16) is provided with at least one circumferential undercut (21) arranged between its two ends. Stretch device according to claim 2, characterized in that several / all stretch rollers (16.1, ... 16.7) are provided with at least one undercut (21). Stretch device according to claim 2 or 3, characterized in that the transitions between an undercut (21) and the lateral surface (16 ') are rounded. Stretch device according to one or more of the preceding claims, characterized in that the stretch rollers (16.1, ... 16.7) of a stretch unit (4) are each arranged directly adjacent to one another. Stretch device according to one or more of the preceding claims, characterized in that the stretch rollers (16) of a stretch bracket (14) are at least partially arranged such that a first tangent (T ₁ ) applied to the outside of two adjacent stretch rollers (for example 16.1, 16.2) on the side facing the stretch rollers (16) in a plan view with a second tangent (T ₂ ) which is placed from the outside of one (16.2) of these two stretch rollers (16.1, 16.2) to the outside of the other stretch roller (16.3) adjacent to them , encloses an angle (α) of at most 180 °. Stretch device according to claim 6, characterized in that the angle (α) enclosed by the two tangents (T ₁ , T ₂ ) is less than 180 °. Stretch device according to claim 1, characterized in that the longitudinal axis (19) of a further stretch roller (16.3) is arranged in the reference plane (20). Stretch device according to one or more of the preceding claims, characterized in that between two stretch rollers (16.2, 16.4) of a stretch unit (4) a reefing bracket (23) provided with a reefing roller (24) is arranged. Stretch device according to Claim 9, characterized in that at least one further stretch roller (16.6, 16.7) is arranged on the reefing bracket (23) and projects outward beyond the reefing bracket (23).

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