DE4424755A1 - Method for forming closures in packaging e.g. sausage skins - Google Patents

Abstract

The method uses a clip in the form of a symmetrical U-profile (4) with open end facing up, which forms part of a string of clips. One clip is separated from the string by the cutting edge (11) of the die (5) which engages with a horizontal flange of the profile. During cutting, the right hand and left hand horizontal flange of the U-profile are bent so that a point (Pos) is pushed to a position (P0B) and point (P0B) is pushed to a position (P1B) by a curved surface of the die. The radii over which the points are moved are determined from the material constants and the bending moments. The closed-up U-profile is finally compressed to grip the material being gripped.

Description

The invention relates to a method and an apparatus for Manufacture of tight closures on packaging containers, such as B. bags or hoses, by bending of Ver closing clips in the form of preferably open, symmetrical and U-shaped profiles with thin bars and under different thrust centers as well as arching resistances, the are connected to an endless band. From the so preceded Profiles are created using a tool consisting of egg a locking stamp and a die, the closures posed. The seal stamp is so against Movable die that he flanges one of the Profiles fed to the die bend against each other and to the web of the profile. Such facilities will be also as clip machines and those produced with these machines Closures are called clips and are particularly popular application for closing sausage casings. Because the U profiles fed from coherent strip material of the device before the closing process begins, first separated from each other by a cutting process the. The materials for the locking clips prove to be Metals, especially aluminum, are most appropriate.

Devices for the production of closures on ver Packing containers have been known since the 1960s has only been slightly improved since then. That this before The process inherent in the direction was developed by experts not yet recognized and for this reason could not be designed optimally. The well-known geometric Shapes of the closing tools are only based on empiri investigations. There were closing tools with one Stamp and a die realized with a relative great effort ultimately the desired result  Act. The causes do not lie theoretically thought optimal bending and bending process, which ultimately due to a high pressure, which is often the same The cause of the high heat pollution caused by the machine is must be balanced.

Because the forces during bending and kinking are not targeted act on the locking clip, the clip tries something like evading these forces, primarily sideways. In the DE PS 3940262 this deficiency is caused by milling a Groove in the capping tool that eliminates the width of the Locking clip corresponds. This makes it a lateral one Prevention of the locking clip prevents, but not the high pressure reduced. Other solutions aim to not the closing tool, but the geometry of the ver to change the closing brackets. It was an improvement the durability of the clips on the bag or hose achieved against slipping or opening, but not that essential deficiencies of the closing device already described ganges.

All known closing tools work according to the following Principle: A U-shaped bracket is inserted into the dimensions in batches trize moves and from the remaining rod-shaped material severed. The cutting edge is directly with the stamp connected, so that at the same time with the cutting a certain Bending of a horizontal flange is done. The Ver The width of the closing clip is reduced so far, that the U-shaped profile fits horizontally in the stamp and thus it is assigned to the stamp. Through this before the locking clip is already deformed asymmetrically and the subsequent bend is also asymmetrical. With the stamp, all flanges of the U-shaped profile (A horizontal flange is already cut through gear slightly bent and the other has a horizon tale initial position) bent until they meet bump.  

Now the stamp acts in a jerky manner with its stamping force F _S as a buckling force and the flanges buckle, ie both buckling and bending occur. The locking clip is now pressed to its final height and, depending on the position in the tool, more or less asymmetrically shaped, because all closed locking clips look different in the end result. Due to the strong pressing pressure (= stamping force F _S ), the material of the locking clips is strengthened and a cold extrusion takes place, so to speak. Despite many attempts to improve the result of the closing process, these had to remain unsuccessful without the complex analysis of all the physical laws underlying the process.

In the case of thin-walled open profiles, in connection with the bending, kinking and torsion as well as the thrust, in addition to the cross-sectional area and the center of gravity, other geometric cross-sectional sizes such as the second degree surface moments, the static surface moments, the arch resistance and the shear center (shear center) play a role. If the rod cross-section has axes of symmetry, then the center of thrust M lies on it ( FIG. 12). Here, the internal forces caused by the flange and web shear stresses can cause additional torsional stresses if the effective line of the resulting load (as a shear force) lies outside the shear center M. For the open profiles used as a clip, the distance of the shear center from the web center line should therefore be determined and then the acting forces (transverse forces, flange forces, web forces) and moments (torsional moment due to the flange forces, torsional moment caused by the web forces) should be determined.

The object of the invention is a method and a Vorrich device for the manufacture of closures on packaging containers by bending of symmetrical open profiles below to create different starting forms with which the Bending and buckling forces are reduced, the noise pollution  reduced and creates a firm and secure closure becomes.

In realizing the object of the invention, according to the 1st Pa Tent claim regarding the process and the 3rd patent device, was determined by analyzing the Operations on known locking devices, which U-för Use profiles, an optimal method for symmetri bending bends found and in implementation of this procedure rens created a new tool as a device which from a sealing stamp, a die and a cutting edge exists, but a completely new one for the sealing stamp Geometry conditional.

According to the method, the horizontal and oblique flanges of the profile body are bent and kinked after the cutting. Various approaches (force or moment equation) can be used to analytically record the processes. It was found that the approach via the bending moment acting on the flanges is most suitable for calculating the deflection of the flanges of the profile body ( FIG. 1).

The deflection w _{B is} calculated from the equation

and the optimal bending radius r _B was introduced with the addition of a material and geometry-dependent correction factor (Jakob constant) j _B

determined.

For the analysis of the buckling process, it was necessary to find the most appropriate (correct) one for the solution of the task based on the moment relationship M _K = f (F _S , F _R ), of the possible Euler buckling cases. The two oblique flanges of the profile body are to be regarded as clamping in connection with its web and the free end of the flanges is loaded by an axial force (here the punch force F _S ) and at the same time a friction force F _R ≅ µ · acts on the roundness of the punch F _S.

If a carrier ( Fig. 2a), which corresponds to an oblique flange of the profile, deformed by the axial force F _S according to the United States according to Fig. 2b, F _R always forces a displacement of v = 0 on the floating bearing.

After a carrier part has been cut free, the bending moment M _{K is} calculated

M _K = Fv + F _R (1-z) = -EIv ′ ′

From which follows

The boundary conditions

lead to the coefficient determinant of unknowns A, B and

The associated eigenvalue is calculated

α1 = tan (α1)

to α1 = 4.49341
and the critical load is determined from this

and the deflection curve v (z) is the same

The optimal bending radius also results from the glide chung

with j _K as a material and geometry dependent constant (Jakob constant).

The final height of the closure is moved further towards the die by the closing die moving through further shaping (bending and kinking) and pressing according to the radii r _B and r _K according to the equations

and

reached.

Based on the optimum radii r _B and r _K determined by the method, these are to be transferred to the stamp of the closing tool. Since all processes take place symmetrically to an axis of symmetry in the middle of the profile to be deformed, different radii necessarily result.

As a key feature, the sealing ram therefore has two circular sections with a much larger radius r _B for bending the oblique flanges of the profile body and symmetrical to the axis of symmetry and a smaller radius r _K in its central area around the axis of symmetry for the bending . The length of the circular section for the smaller radius r _{K is} determined from the chord between points A and C, which runs at a distance b * from the apex B on the axis of symmetry. The distance b * is calculated from the equation

According to the width of the U-shaped profile, the Her position of the symmetry, which otherwise by the cutting a third radius r₀ would be affected introduced. The wedge angle of the cutting edge is expedient for this Approximately β = 45 ° and radius r₀ for guiding the profile by the stamp during cutting becomes a little bigger than chosen for the known tools.

The theory of bending and Buckling process explained in more detail and two execution examples play with U-profiles of different dimensions and shapes shown. Show it:

Fig. 1 A moment acting on a flange (beam) clamped on one side

Fig. 2a A one-sided clamped flange (beam), the sen free end is axially displaceably mounted

Fig. 2b The effect of the forces on the dargestell th in Fig. 2a flange (bar)

Fig. 3 shows the three essential Verformungsschrit te of the U-shaped profile

Fig. 4 The asymmetrical deformation of a U-profile according to the prior art

Fig. 5 representation of the bending process after Freischnei the U-profile using a profile with oblique flanges

Fig. 6 representation of the bending process after Freischnei the U-profile using a profile with oblique and vertical flange parts

Fig. 7 representation of the bending process using a profile with oblique flanges

Fig. 8 representation of the bending process using a profile with oblique and vertical flange parts

Fig. 9 representation of the kinetic closing curves for the profiles according to Fig. 5-8 derived from the theory of bending

Fig. 10 representation of the molding and pressing process on the basis of a profile with inclined and vertical flange parts

Fig. 11 geometry of the Verschließstempels with the determined from the analysis of the method radii

Fig. 12 representation of different locking rod profiles with thin webs

Fig. 13 representation of the arching resistance C _M as a function of the shear center coordinate d and under different locking rod profiles.

Fig. 1 describes the effect of a moment on one of the oblique flanges (with the clamping point A and the free end B) with the geometric dimensions of an oblique U-shaped profile (clip 1 ) at the point z = l₁ = 7.5 and a U-shaped profile with vertical and oblique flange parts (clip 2 ) at the point z = l₂ = 11.3.

From the beginning

and the area moment of inertia

with the cross-sectional dimensions b and h results in a Deflection of

at point B is x = ξ = 1, from which

follows.

The cross-sectional dimensions for clip 1 with b₁ = 4 mm and h₁ = 1.25 mm and for clip 2 with b₂ = 5 mm and h₂ = 2 mm result in bending radii

Fig. 2a and Fig. 2b shows an inclined flange as a beam clamped on one side, the free end of which is axially displaceably mounted and Fig. 2b shows the effect of the forces on the beam shown in Fig. 2a to illustrate the buckling process. From the calculation of the critical load

and the deflection course

results for the calculation of the optimal radius r _K for the buckling

From Fig. 3, the three essential deformation steps egg nes U-shaped profile with a left 1 and a right horizontal flange 1 ', a left 2 and a right oblique flange 2 ' and a web 3 can be seen. The partial pictures represent a) the cutting and kinking of the left horizontal flange, b) the bending of the oblique flanges and c) the kinking and pressing until the finished clip closure.

Fig. 4 shows the asymmetrical deformation of a U-profile 4 according to the prior art. Due to the radius r of the punch 5 being too small, the clip is pressed with the sheath 11 into the die (not shown) and into the radius r of the punch 5 with rx during the cutting process, and thereby by a few degrees Φ from its position symmetrical to the center of gravity coordinate. e.g. Φ = 4 °) rotated. It is easy to see that all other bending and kinking processes must inevitably run asymmetrically.

In FIG. 5, the bending operation after the cutting free of the U-profile 4 with the cutting edge 11, which is disposed on the plunger 5, shown at the interface 12 using the example of a smaller profile with inclined flanges. Fig. 5 shows the left oblique flange of the profile 4 after the cutting process a and after the bending process b. It can be seen that when cutting with a known device, the point P _{0B of} a flange edge of the U-profile 4 _first moves to the point P _0B and a bending of the left oblique flange from the point P _0B to the point P _1B on a circular path by friction of the point P _0B at a curvature of the closing _punch 5 , the radius r _{B of} the circular path through the equation

is determined and is determined by the geometry of the locking die. The deflection is indicated with w _B.

In Fig. 6, the conditions are shown on a slightly larger profile 4 with oblique and vertical flange parts. Again, the bending process takes place according to the same ratios as in Fig. 5, only that the size of the radius, determined according to the equation

must be another.

The bending buckling process of a profile 4 with oblique flanges is shown schematically in FIG. 7. The point P _1B now moves on a circular path with the radius due to the stamp force F _S and the friction force F _R

to point P _1K .

Fig. 8 shows the analogous process for the profile 4 with an oblique and a vertical flange portion. However, the point P _1B moves through the buckling process in the opposite direction to the point P _1K .

The optimal design of the radii for the closing stamp can be seen in FIG. 9. They were derived from the kinetic closing curves according to Fig. 5-8 on the basis of the theory of bending. Fig. 9 shows the strictly symmetrical process, a) for the profile with the oblique flanges and b) with the profile with the oblique and vertical flange parts. The different radii r _B for the bend and r _K for the kink can be seen.

The last process step is outlined in FIG. 10. With it by further shaping (bending and kinking) and pressing the profile 4 according to the equations

and

the final height of the closure is reached by the closing punch, which is shown in FIG. 10 only by its radii r _B and r _K , moving further towards the die (not shown).

In Fig. 11, the geometry of the Verschließstempels 5 r after the device having the ermittel th from the analysis of the method radii _B and R _K shown. The die (not shown) facing surface of the sealing die 5 has a curved surface about a symmetrical axis 6 in the middle of the sealing die 5 , which surface is symmetrical about the symmetry axis 6 from a central curved region 7 with the radius

and a left 8 and a right curved edge region 8 'with the radius

put together. The central curved region 7 extends from point A to point C and the chord thus formed has a distance b * to the apex C of the curvature 7 . The left curved surface 8 carries at its end a Ge cutting edge 9 and the right curved surface 8 'has an extension 10 with the radius r₀, which serves to symmetrize the profile 4 after the cutting process with the cutting edge 11 and the die (not shown) has a shape corresponding to receiving the profile 4 , but with a lower height than the profile 4 .

The open symmetric profiles with thin webs used and usable in the process have different shear centers d and arching resistances C _M. A comparison of the different profiles shown in Fig. 12 shows that at the center of thrust the square open profile ( Fig. 12c) followed by the triangular profile ( Fig. 12b), the right corner profile ( Fig. 12a) and the circular profile ( Fig. 12d ) has the best value. In the case of arch resistance, it follows that the rectangular profile gives the best value, followed by the triangular profile in the closed state (ie as a closed profile with a slot). FIG. 13 shows these facts in a diagram in the dependency C _M = f (d, type of profile). The rectangular profile ( FIG. 12a) seems to be the cheapest solution for all applications when summarized from FIG. 12 and FIG. 13.

Reference list

α function of the stamp and the bending strength

β wedge angle (cutting edge)
ξ coordinate (for x)
Φ Inclination angle with an inclined bending and kinking position
µ coefficient of friction
A equation coefficient
b flange width
B equation coefficient
b * Distance of the tendon from the apex of the curvature of the closing punch
C _M warp resistance
d Distance of the shear center from the center line of the profile
E modulus of elasticity
F _K critical buckling force
F _R friction force
F _S stamp force
h flange thickness
I area moment of inertia
j _B Jakob constant for bending
j _K Jakob constant for buckling
l flange length
M thrust center
M _B bending moment
M _K buckling moment
r₀ sliding radius (at the beginning of the bending process)
r _B bending radius
r _K bending radius
v displacement (general)
v ′ ′ curvature of the flanges (2nd derivative of the displacement)
v ′ slope of the flanges (1st derivative of the displacement)
w deflection
w _B deflection at the free end of the profile.

Claims (5)

1. Process for the manufacture of closures on packaging containers by bending open symmetrical profiles, which are U-shaped, with more or less rounded corners and geometric figures with thin webs and different thrust centers and arch resistance, are formed and essentially from a left and a right horizontal flange, a left and a right oblique, straight or curved flange and a web, and the bending buckling is carried out by a tool, which is composed of a closure stamp, a die and a cutting edge, characterized in that

• a) a symmetrically shaped, upwardly open profile ( 4 ), one of a plurality of similar profiles ( 4 ) to composite endless band, the die is fed and through the cutting edge ( 11 ) on the left horizontal flange ( 1 ) of the open top Profile ( 4 ) is cut off the tape,
• b) during the cutting, the left ( 1 ) and right ( 1 ′) horizontal flange is angled by moving point P _0S to point P _0B both left and right and bending the oblique flanges ( 2 , 2 ′) from point P _0B to point P _1B on a circular path by friction of point P _0B on a curvature of the closing _die ( 5 ), the radius of the circular path being achieved by the equation is determined and is determined by the geometry of the closing punch ( 5 ),
• c) at the same time for cutting the left horizontal flange ( 1 ) and bending the left oblique flange ( 2 ) the right horizontal flange ( 1 ') is angled symmetrically to the left horizontal flange ( 1 ) by the movement of the closing punch ( 5 ) and the right oblique flange ( 2 ′) moves symmetrically to the left oblique flange ( 2 ) in the opposite direction to the axis of symmetry ( 6 ) of the profile ( 4 ),
• d) when the point P _{1B of} the two oblique flanges ( 2 , 2 ') of the profile ( 4 ) by the further movement of the closing die ( 5 ) against the die, the kinking process begins by the point P _1B being on a circular path moved towards the point P _1K , the radius of the circular path by the equation is determined and is determined by the geometry of the sealing die ( 5 ) and
• c) the final height of the closure, by further shaping (bending and kinking) and pressing the profile ( 4 ) according to the equations and is achieved by moving the wear stamp ( 5 ) towards the die.

2. The method according to claim 1, characterized in that when using differently shaped, open symmetrical profiles ( 4 ) with thin webs and different thrust center points and arching resistances one, according to the underlying theory, optimization of the thrust point and the arching resistance depending on the Geometry, kinematics and kinetics of the deformation process takes place. 3. Device for the production of closures on packaging containers by symmetrical bending of open profiles which are U-shaped, with more or less rounded corners with thin webs and different thrust centers as well as arching resistances, and are essentially composed of a left and a right one horizontal flange, a left and a right oblique, straight or curved flange and a web, and the bending buckling is carried out by a tool which is composed of a closing punch, a die and a cutting edge, characterized in that the die surface facing the Verschließstempels (5), has an about a extending in the middle of the Verschließstempels (5) axis of symmetry (6), curved surface which extends symmetrically relative to the symmetry axis of a central curved portion (7) with the radius and a left ( 8 ) and a right ( 8 ') curvature edge region with the radius composed, the right curved surface ( 8 ') has an extension ( 10 ) with the radius r₀, which serves to symmetrize the pro fils ( 4 ) after the cutting process and the die ei ne for receiving the profile ( 4 ) corresponding, but with has a lower height than the profile ( 4 ). 4. The device according to claim 3, characterized in that a cutting edge ( 11 ) is arranged on the side of the closing punch ( 5 ) and connected thereto, and a counter-cutting edge ( 9 ) is attached to the die in opposition to this cutting edge ( 11 ). 5. The device according to claim 4, characterized in that the cutting edge ( 11 ) has a wedge angle of approximately 45 °.