FR2535297A1 - Device for obtaining variable tangential differential velocities at various points of a deformable film. - Google Patents

Abstract

The invention relates to a drawing (stretching) device. This device is such that the tangential differential velocities VN can be varied at various points of a plane film 1 or deformable plane sheet, moving along at least one drawing (stretching) roller 3 which rotates about an axis XX, the film 1 or sheet moving in a direction perpendicular to the axis of rotation of the roller and bearing on a generatrix GN of the roller. The roller 3 has a rotation velocity N which is constant over time while the distance GNC between the bearing generatrix GN of the film and the axis C of rotation of the roller is variable over time. Application to the drawing (stretching) of plastic film.

Description

DEVICE FOR OBTAINING DIFFERENTIAL SPEEDS
TANGENTIAL VARIABLES IN VARIOUS POINTS OF ONE
MOVIE. DEFORMABLE.

The invention relates to a device for obtaining variable differential speeds at various points of a plane film or flat plate, in particular deformable and more harticulierement deformable elastically or plastically.

 In many industries, however, it is necessary to stretch sheet-shaped products, particularly in the textile or metallurgical industry, with a view to slimming or rolling these products. It is sometimes necessary to carry out pretensioning or prestressing of plastic, metallurgical or textile products. Finally, in the packaging industry, plastic films are stretched before being placed around palletised loads and retracted naturally or not.

In general, to perform these operations, it is necessary to obtain distinct speeds between two distinct points of the film. To do this, it is known to use two rollers, rotating about parallel axes, with a different speed of rotation. Thus, in general, the rotational speed of the downstream roll is greater than the rotational speed of the upstream roll. The variation of the angular speeds of the rotating rollers is obtained in particular by mechanical, electronic, hydraulic devices, by gearboxes, gears, etc. However, the known devices do not make it possible to vary the ratio of the tangential differential speeds of a value much greater than 1, for example up to 3.

In addition, in the case of wrapping pallets in the starting phase, it is not possible to obtain a gear ratio defférentjelles equal to 1 without using clutch devices.

The invention aims to overcome these disadvantages.

The invention relates to a device for obtaining variable tangential differential speeds at various points of a flat film or deformable flat plate, moving along at least one drawing roller rotating about an axis, the film or plate moving in a direction perpendicular to the axis of rotation of the roller, and supported on a generatrix of the drawing roller.

This device is characterized in that the roller has a rotation speed constant in time, while the distance between the support generator of the film and the axis of rotation of the roller is variable in time.

According to a first embodiment, the drawing roller is searched by a plurality of contiguous generators whose distance to the axis of rotation increases continuously in time, from the upstream generator on which the unstretched film arrives up to to the downstream generator that the stretched film leaves.

According to a second embodiment, the drawing roller is a deformable cylinder, in particular of circular base revolution, whose axis of rotation is offset with respect to the axis of revolution, the distance between the contingent generatrices augae, atal and continuously in time from the upstream generator on which the non-stretched film arrives until the downstream generator e stretched film leaves
The film is supported on the generator by means of at least one compression member exerting a pressure against the roller, in particular a support roller which moves in rotation on the arm as a function of the movement of the generator. support, the film being placed between the support member and the roller.

The relationship between the initial distance Po between the generator
o upstream and the axis of rotation and the final distance R1 between the downstream generator and the axis of rotation, is adjustable.

Finally, according to a third ~ ~ em embodiment, the film is driven by the rotation of two circular cylindrical rollers of revolution, parallel axes of rotation, the radius Ro upstream and the radius R1 downstream being variable in time. In addition, the draw ratio, more particularly the ratio of the tangential differential velocity V1 to a point of the downstream film after stretching and the tangential differential velocity Vo to a point of the upstream film, before drawing, is proportional to the ratio between the Ray
R1 of the downstream roll and the radius Ro of the upstream roll.

It is understood that the device. according to the invention provides significant advantages over known devices. In
effect, stretching is easily adjusted by either changing the position of
the axis of rotation with respect to the axis of revolution which modifies the distance between the generatrix on which the film rests and the axis of rotation of the roller, or by modifying the radii of the rollers relative to one another; to the other. Moreover, it is possible to use several rollers which, by varying their radius, make it possible to obtain variable differential speeds.

The following description, with reference to the accompanying drawings by way of non-limiting examples, will make it possible to understand how the invention can be put into practice.

Figure 1 is a schematic view of a first embodiment.

Figure 2 is a schematic view of a second embodiment of the invention.

Fig. 3 is a perspective view of a third embodiment.

Figures 4A and 4B show the variation of the radii of the rollers respectively for miniumum stretching and for maximum stretching.

Figure 5 shows a first embodiment of a roll.

Figure 6 shows a second embodiment of a roll.

Figs. 7A and 7B show a first variant of the third embodiment with minimum draw (7A) and maximum draw (7B).

Figures 7C and 7D are schematic views from above on the one hand of the rollers and on the other hand control means of the bodies for expansion or contraction of the rollers.

FIGS. 8A, 8R show a second variant of this last embodiment of the invention, with minimum and maximum draw respectively.

The device according to the invention makes it possible to obtain variable tangential differential speeds at various points of a flat film or of a deformable flat plate, in particular an elastically or plastically deformable plastic film.

It is known that the elastic deformation is reversible and that the film, when no longer stretched back to its original position, while the plastic deformation is partially irreversible and the film when no longer stretched to a length final greater than its original length
Differential tangential velocity means the speed of the film which moves along at least one roller or is driven by the rotation of at least one roller rotating about an axis, the film moving in a direction perpendicular to the roller. axis of rotation of the roller and resting on a generatrix of the roller.

 According to the invention, the roll has a speed of rotation N which is constant in time, whereas the distance R between the support generator of the film and the axis of rotation of the roll is variable in time.

In Figure 1, there is shown a first embodiment of the invention. A film 1 reaches upstream in the drawing device 2 and leaves it downstream. The tangential velocity of the film 1 upstream being V, the speed
tangential of the film 1 downstream is equal to VN. The device 2 makes it possible to obtain differential tangential speeds
VN variables at various points of the film 1. This is flat and is shown in Figure 1, perpendicular to the plane of the figure. It is an elastically or plastically deformable film, preferably made of synthetic material. The length L between two points AB of the film upstream is
o less than the length LN between the same points AB of the film 1 downstream.

According to the invention, the device 2 allows the stretching of the film 1, that is to say that the segment AB of length L reaches
o progressively to length LN (Figure 1).

According to this first embodiment, the roll 3 is formed by a plurality of adjacent generators GB, ..., GN. The generators GN are rotated around C by a drive member 4, preferably at least two stars formed of flat circle sections placed at each end of the generators GN. The center of rotation C1 through which the axis of rotation of the star passes is offset relative to the center of rotation C of the drawing roller 3. The direction of rotation of the driving member 4 is the same as the direction of rotation of the drawing roller 3.The film 1 is driven by the rotation of at least one roller 3 rotating about an axis of rotation, perpendicular to the plane of the figure, of center C.The film 1 moves in a direction perpendicular to the axis of rotation of the drawing roller 3 and is supported on a generatrix GN of the roll 3, at a time tN.Thus, at the time to, the film 1 is based on the generator Go, its speed is VO, at time tl = to + AT, the film 1 is based on the generator G1, its speed is V1 = VO + # VO, at time tNZ the film is based on the generator GN, its speed VN = VO + z At 1 Preferably the increases in velocity A VN-1 are constant, but they can also vary. The drawing roller 3 rotates in the direction of the direction F1 and has an angular speed of rotation N constant in time, while the distance RN between the generatrix GNet support the axis of rotation of the drawing roller varies. More preferably, the distance C1Go>...> CLIN, and the distance between the axis of rotation of the drawing roller 3 and the generator G in
o upstream is less than the distance between the axis of rotation and the downstream NG generator. This CNG distance increases continuously in the upstream-downstream time. The initial distance GC upstream is equal to r, while the final distance downstream is equal to R.

The distance e between the center of rotation C of the drawing roller 3 and the center of rotation C1 of the driving member 4 is adjustable, which makes it possible to adjust the final tangential speed VN with respect to the tangential velocity Vo initial and therefore to adjust the draw ratio VN Vo
o
This draw ratio can be 2 or 3, in any case is much greater than 1 and can also be set to be less than 1.

The draw ratio can be made to be 1 when stretching a plastic film which is used for wrapping pallets. This draw ratio equal to 1 is necessary at the beginning of the wrapping, the film not having to be stretched. In this case the distance CCl is zero.

Thus, the invention makes it possible, by a relative displacement of the center C with respect to the center C1, to adjust the drawing ratio in a progressive manner.

According to a second embodiment of the device according to the invention, the drawing roll is a cylinder 5 of revolution, preferably with a circular base, whose axis of rotation of the center C2 is offset with respect to the axis of revolution of the center C3. The drawing cylinder is deformable, preferably polyurethane. Thus, the distance between the contiguous generators Go, G1,..., GN increases continuously during the rotation (direction of the arrow F2), when the center of rotation is offset from the upstream side relative to the center of revolution. C3.

The film 1 is based on the generator GN, at a time tN the idler roller 7 causes the deformation of the support deformable cylinder 5 which moves by rotating around the center C3. The film is introduced downstream, on the side where the distance r = C2 GB between the center of rotation C2 and the generator Go is the weakest and goes upstream on the side where the distance R = C2 GN between the center of rotation C2 and the GN generator is the largest.

By adjusting the distance C2 C3, one adjusts the drawing ratio which can possibly be equal to 1 when C2 coincides with C3.

According to a third embodiment of the invention (FIGS. 3 to 8), the film 1 moves along two circular cylindrical rollers 7, 8, of rotation axis XX, parallel YY, the radius RO of the upstream cylinder 7 and the radius Rldu downstream cylinder 8 being variable in time.

The film 1 moves in a direction perpendicular to the axes XX, YY.

According to the invention, the tangential velocity Vo of the film 1 upstream is different from the tangential velocity V1 of the film 1 downstream.

The film 1, driven by the speed V1 can drive all the rollers 7 and 8. In another way the film 1 is driven at the speed V1 by the roller 8 driven by a motor 9.

According to the invention, the rollers 7,8 are rotated so that the ratio K of the rotation speed N1 of the cylinder 8 to the rotation speed N0 of the cylinder 7 is constant. Their direction of rotation is opposite. The cylinder 7 rotating in the direction of the arrow F3, the cylinder 8 rotates in the opposite direction (arrow F4).

So, if we call E the draw ratio of the film and if L
o is the length of a segment AB downstream and L1 the length of segment AB of film 1 upstream, one can write L1 ~
Lo
At time t, we have Lo = Vot and L1 = v1t.

L1 LU SEEN
o V0
But the tangential velocity is equal to the radius of the cylinder multiplied by the speed of rotation of the cylinder.

Thus, V1 = N1 R1 V = NR
oo
V1 = N1 R1 RE VO No Ro Ro
o No o
K is according to the invention is equal to N1
No.
By varying the radii R 1 and R 1 of the upstream 7 and downstream 8 cylinders, the ratio of the tagential speeds is varied.
Vo and V1.

The distance between a generator i at the center Co or C1 of rotation therefore varies with time, since the rays Ro and R1 are varied.

If R and R1 vary between limit values r and R, when
o
Where R1 = R and R = r, the draw ratio E is
o maximum.

Thus, E maxi = R and E min = r E max R.

r RE mini r
If we want to vary the stretch from 0 to 100%, F max = 2 r
r
R = about 113 mm, for example
r = about 80 mm
The average radius is about 97 mm.

If we want to vary the stretch from 0 to 200%, E max = 3
r = about 70 mm, for example E mini
R = about 123 mm and the average radius is about 97 mm.

If we want a draw ratio E equal to 1, it is necessary for the first case that K is equal to about 1.4 and in the second case equal to about 1.7. K ratios of rotation speeds of rollers are adjusted by means of a gear device 10.

According to the invention, the pre-stretching or variable stretching device comprises two drawing rollers 7, consisting of a plurality of curved longitudinal portions 11, forming the cylindrical surface of the roll. The two axes of rotation
XX, YY rollers are parallel.

Guide members 12 in radial translation portions 11 have the function of moving away or closer to the portions of the axes XX and YY of rotation. Rotational drive means 13 of the portions serve to rotate these portions 11 around the axes XX and YY and finally control means 14 have the function of actuating the guide members 12.

Preferably, the rotational drive means 13 are constituted by hubs 15 which provide the rotational drive portions 11 relative to the axis XX or YY which are fluted axes.The fluted axes pivot on bearings 16 .

The guide members 12 in radial translation portions 11 are constituted by ramps 17 which bear in grooves 18 formed in the hubs 15. Each cylinder 11 comprises at least two hubs 15. The hubs 15 of a cylinder 7 slide simultaneously along the fluted axis XX or YY.

The ramps 17 are capable of sliding radially in the grooves 18. Thus, the radius of the cylinders 7, 8 can vary by radial sliding of the ramps 17 in the grooves 18 and simultaneously axial sliding of the hubs 15.

Each cylindrical roller 7, 8 comprises at least one flange 19 providing end guidance of the portions 11. The stops 20 can slide radially with respect to the flange 19.

The device further comprises control means 14 of the guide members 12 in radial and axial translation.

The control means 14 are constituted by a double fork 21 pivoting about an axis 22 perpendicular to the axis of rotation XX, YY of the rollers 7, 8. The double fork 21 acts by means of a ring gear. support 22 placed at one end of the rotaion axis XY, YY of the rollers, on a ball stop 23.

Thus, when the double fork 21 leans on the side of the roller 7 upstream (Figure 7 A) it acts on the stop 23, which axially slides the hubs 15 of the cylinder 7 upstream. These are moved towards the end of the axis XX which does not comprise the abutment 23. The hubs 15 moving compress the return spring 24. The portions 11 and the ramps 17 are pressed on the sliding hubs 15 by means of circumferential springs 25 which are placed at each level of the ramps 17.

The hubs 15 moving along the axis XX push the portions 11 radially outward, which ensures the increase of the radius of the roller 7 which takes the value R.

On the contrary, the fork 21 is connected at its other end to the side of the downstream roller 8, the hubs 15 are in the reverse position of the hubs 15 of the cylinder 7 downstream. The return spring 24 pushes the sliding hubs and the control members to the position corresponding to the minimum radius value of the downstream roll 8 which takes the value r.

Gears 26 make it possible to adjust the speed of rotation of the upstream roll 7 with respect to the speed of rotation of the downstream roll.

In FIG. 7A, there is a radius R upstream and r downstream, the drawing ratio is minimum
On the contrary, by tilting in the opposite direction of the range 21 (Figure 7B), one obtains a radius r upstream and R downstream, the drawing ratio is maximum.

The pivoting of the fork 21 is controlled by a control member 27. This member can be as shown, a hydraulic cylinder, pneumatic or electric or a manual screw-nut system. Thus at each position of the pivot control member 27 of the fork 21 corresponds a value of the radii of the rollers 7 and 8, therefore a value of the coefficient of stretching. The positions of the member 27 can be controlled electrically, based on pre-established or proaramated setpoint values.

Another embodiment of the device according to the invention consists in placing the gear 8 on the side of the control means 14. The ramps 17 are integral with a shaft 28 concentric with the axis of rotation XX which comprises an abutment 29 on which supports the spring 24. The fork 21 pivoting compresses the spring 24, which causes the displacement of the hubs 15 axially in the direction of the arrow
F4, that is to say the direction of movement of the fork 21. The ramps 17 slide radially in the grooves 18, which causes the expansion of the downstream cylinder 7. In contrast, the upstream cylinder 8 is compressed.

 Preferably the portions 11 comprise on the outer surface a coating promoting adhesion.

In Figures 5 and 6, other embodiments of the rollers are shown. To the left of each figure is the half roll 30 of smaller radius and to the right is the half roll 31, larger radius.

The half-roll 30 is constituted, like the half roll 31 of portions 32, which are integral with radial elements 33 which are compressible. Preferably, they consist of an elastomer. These radial elements 33 are arranged between fixed radial partitions 34 and movable radial partitions 35 secured to a shaft 36 which can slide axially
When axial displacement of the shaft 36 is effected, the movable partitions 35 approaching the fixed partitions 35, the elastomeric element is compressed axially and deforms radially by pushing the portion 32 radially towards the stent. The radius of the roll increases. When the movable partitions 35 move away from the fixed partitions 34, the elastomeric element returns to its original shape. Preferably, the elastomeric elements are placed at each end of portions 11. In FIG. 6, the portions 11 are displaced by a hydraulic device. The displacement of the piston shaft 37 causes the support 38 to move the portion II,
the hydraulic fluid transferring the pressure between the piston shaft 37 and the support 38.

The hydraulic fluid is located in the chamber formed by the hollow shaft 39, the shaft 37 sliding axially and the support 38 sliding radially.

Claims (15)

1.- Device for obtaining tangential differential speeds VN variable at various points of a film (1) planar or deformable flat plate, moving along at least one drawing roller (3) rotating around a axis XX, the film (1) or plate moving in a direction perpendicular to the axis of rotation of the roller, and resting on a generatrix GN of the roller, characterized in that the roller (3) has a rotational speed N constant in the  time, while the GNC1 distance between the support generator GN of the film and the axis Cl rotation of the roller is variable in time. 2.- Device according to claim 1, characterized in that the drawing roller (3) is formed by a plurality of contiguous GN generators whose distance to the axis of rotation of the drawing roller (3) increases by continuous way in time from the upstream generator Go on which reaches the unstretched film to the downstream generator GN that stretched film leaves. 3.- Device according to claim 1, characterized in that the drawing roller (3) is a cylinder (5) of revolution, in particular circular base, the axis of rotation C2 is offset from the axis of revolution C3, the distance between contiguous generators GN increasing continuously over time from the upstream generator GB on which the unstretched film reaches the downstream generator G N that the stretched film leaves. 4.- Device according to any one of claims 1 to 3, characterized in that the film (1) is supported on the generator by means of at least one con-oression member (7) exerting pressure against the roller (3), in particular a support roller, this member rotating as a function of the displacement of the support generatrix GN, the film (1) being placed between the support member (7) and the roller (5) . 5.- Device according to any one of claims 1 to 4, characterized in that the ratio between the initial distance r between the upstream generator G and the axis of  o C2 rotation and the final distance R between the downstream generator GN and the axis of rotation C2, is adjustable. 6.- Device according to claim 1, characterized by the  the film travels along at least two circular cylindrical revolution rollers (7, 8) rotating about parallel axes of rotation (XX, YY), the radius Ro of the upstream cylinder (7) and the radius R1 of the downstream cylinder (8) being variable in time, the ratio of the rotation speeds N1 / NU of the cylinders being constant. 7.- Device according to claim 6, characterized in that the drawing ratio more particularly the ratio of the tangential differential velocity V1 at a point of the downstream film after drawing and the tangential differential velocity V at a point of the film upstream , before stretching,  o is proportional to the ratio between the radius R1 of the downstream roll (8) and the radius Ro of the upstream roll (7). 8.- Device according to any one of claims 6 and 7, characterized in that one varies the drawing ratio E by simultaneously varying the radius R1 and the radius Ro between two limit values r and R. 9.- Device according to any one of claims 6 to 8, characterized in that the drawing ratio varies from 0 to 100%, the R and R1 rays ranging between r = 80 mm  About 0 and R = about 113 nm. 10.- Device according to any one of claims 6 to 9, characterized in that the drawing ratio varies between 0 and 200%, the rays Ro and R1 between r = 70 mm and R = 123 rd about. 11.- Device according to any one of claims 6 to 10, characterized in that the boundaries between which varies the drawing ratio E are adjustable by adjusting the ratio of the rotational speeds of the rollers. 12.- Device according to any one of claims 1 and 2, characterized in that it comprises a cylindrical surface (3) preferably center of revolution C whose generatrices are driven in rotation around C1 by a body of (4), the distance between the axis of rotation C1 of the bearing generatrices resting on the cylindrical surface (3) and the axis of rotation C of the cylindrical surface being adjustable. 13.- Device according to claims 4 and 5, characterized in that the ratio of the distance R and the distance  o R1 is adjustable by the displacement of the axis of rotation of the roller (3). 14.- Device according to any one of claims 6 to 11, characterized in that it comprises  two rollers (7,8) consisting of a plurality of longitudinal portions (11) forming the cylindrical surface of the roll,  two axes of parallel rotations (XX, YY) of the rollers,  - Guide members (12) in radial translation of the portions (11),  - Rotational drive means (13) portions  control means (14) for guiding members  (12) in radial translation. 15.- Device according to claim 14, characterized in that the rotary drive means (13) consist of hubs (15) sliding simultaneously along the axis of rotation, and the translation guide members. radial being constituted by rare (17) sliding radially in grooves (18) formed in the hubs (15) 16.- Device according to claim 15, characterized in that the control means (14) of the guide members ( 12) in radial translation are constituted by a double fork (21) pivoting about an axis (22) perpendicular to the axis of rotation of the rollers and acting by means of a bearing ring (23a) placed at one end of the axis of rotation of the rollers on a stop (23) ball, which causes the simultaneous movement and in opposite directions of the hubs (15) of each roller, (7,8) the pivoting of the fork (21) ) being controlled by a control member (27) , a particular cylinder.