STRETCHING DEVICE FOR STRETCHING A FILM MADE OF A SYNTHETIC MATERIAL Description
The present invention concerns a stretching device for stretching a film made of a synthetic material.
During the manufacture of a film made of a synthetic material, such as a film made of polypropylene, polyester or composed by any other thermoplastic material,
the film successively passes, after formation thereof, through a longitudinal stretching step and a transverse stretching step.
A stretching system, configured to stretch a film made of a synthetic material in the transverse direction, includes, in a known manner, a furnace allowing setting the temperature of the film during the stretching thereof in the transverse direction, and two stretching devices disposed on either side of the film.
More particularly, each stretching device includes:
- a guide rail extending at least partially into the furnace and including a first guide surface directed towards the film and a second guide surface opposite to the first guide surface,
- a plurality of clamps each intended to grasp the same longitudinal edge of the film, the clamps being configured to be guided in translation by the respective guide rail,
- a retaining rail extending along the respective guide rail, the retaining rail including a bearing surface directed towards the respective guide rail and a retaining surface opposite to the bearing surface,
- a plurality of retaining elements configured to be guided in translation by the retaining rail, and
- an endless chain including a series of links hingedly mounted relative to one another and first and second articulation elements hingedly connecting the links,
each clamp being hingedly mounted on a respective first articulation element and each retaining element being hingedly mounted on a respective second articulation element, the endless chain being configured to drive the respective clamps along the respective guide rail, and to drive the respective retaining elements along the respective retaining rail, the endless chain being also deformable between a first state in which the clamps are disposed proximate to one another, and a second state in which the clamps are away from one another.
Such a stretching system, for example known from US4807336, is suited for high production rates, even when this stretching system is configured to simultaneously ensure a stretching of the film in the transverse direction and a stretching of the film in the longitudinal direction.
However, in order to obtain a high longitudinal stretching ratio with such a stretching system, it is necessary to equip the endless chains of the stretching system with links having large lengths.
Yet, such a configuration of the stretching system induces a very large distance between two adjacent gripping areas of the film when each endless chain is in the second state and the clamps are away from one another.
For example, with clamps each having a 50 mm width and a longitudinal stretching with a ratio of 8, the distance between two adjacent gripping areas of the film will be 400 mm.
Consequently, such a distance between the clamps results in that the thickness of the film is not homogeneous at the level of the longitudinal edges of the latter, which requires a subsequent cutting of the film at the level of the longitudinal edges thereof, and therefore generates considerable product losses.
Furthermore, the use of links with large lengths requires large forces to displace each endless chain from the first state to the second state, which requires oversizing the drive devices (such as the transmission pulleys or the motors) of the endless chains, and therefore increases the bulk of the stretching system and the
— manufacturing costs of the latter.
In addition, the large forces applied on each endless chain to ensure their switch from the first state into the second state cause a clacking of each clamp against the respective guide rail during the sudden expansion of the links associated to said clamp, which generates a loud noise during the operation of the aforementioned stretching
— system.
The present invention aims at overcoming all or part of these drawbacks.
In particular, the technical problem at the origin of the invention consists in providing a stretching device that does not reguire any cutting of the produced film at the level of the longitudinal edges thereof after the stretching step, while limiting the noise generated by the stretching device during the operation thereof and the bulk of the stretching device.
To this end, the present invention concerns a stretching device for stretching a film made of a synthetic material, comprising:
- a guide rail including a first guide surface intended to be directed towards the film and a second guide surface opposite to the first guide surface,
- a plurality of first clamps and a plurality of second clamps each intended to grasp the same longitudinal edge of the film, the first and second clamps being disposed alternately along the guide rail and being configured to be guided by the guide rail, and
- a first endless chain connected to the first clamps and configured to drive the first clamps along the guide rail,
characterized in that the stretching device further comprises a second endless chain connected to the second clamps and configured to drive the second clamps along the guide rail, the first and second endless chains being distinct from each other such that the first clamps are not mechanically connected to the second endless chain and such that the second clamps are not mechanically connected to the first endless chain, and in that the first and second endless chains are deformable between a first state in which the first and second clamps are disposed proximate to one another, and a second state in which the first and second clamps are away from one another.
Such a configuration of the stretching device, and more particularly of the first and second endless chains, allows substantially limiting the distance between two adjacent gripping areas of the film when the first and second endless chains are in the second state and the first and second clamps are away from one another, and therefore ensuring a homogenous thickness of the film at the level of the longitudinal edges thereof.
Thus, the stretching device according to the present invention does not require any subsequent cutting of the film at the level of the longitudinal edges thereof.
Furthermore, the fact that the first and second clamps are disposed alternately along the guide rail and configured to be driven along the guide rail respectively by the first and second endless chains allows keeping a clearance between each pair of adjacent first clamps and a clearance between each pair of adjacent second clamps when the first and second endless chains are in the first state, and therefore ensuring a predetermined opening angle for each pair of adjacent links of the first and second endless chains when the first and second endless chains are in the first state.
These arrangements allow considerably limiting the forces that shall be applied on the first and second endless chains to deform them from the first state into the second state, which substantially reduces the manufacturing costs of a stretching system equipped with the stretching device according to the present invention and also the noise generated during the operation of the stretching device according to the present invention.
The stretching device may further have one or more of the following features, considered alone or in combination.
According to an embodiment of the invention, the first endless chain and the second endless chain are nested within one another, i.e. are imbricated within one another.
According to an embodiment of the invention, the first endless chain includes first primary links and second primary links disposed alternately along the first endless chain and hingedly mounted relative to one another, and first articulation elements and second articulation elements disposed alternately along the first endless chain and about which the first and second primary links are hingedly mounted, each first clamp being mounted on a respective first articulation element, and wherein the second endless chain includes first secondary links and second secondary links disposed alternately along the second endless chain and hingedly mounted relative to one another, and first articulation members and second articulation members disposed alternately along the second endless chain and about which the first and second secondary links are hingedly mounted, each second clamp being mounted on a respective first articulation member.
According to an embodiment of the invention, the first and second primary links of the first endless chain and the first and second secondary links of the second endless chain are nested within one another.
According to an embodiment of the invention, the first and second primary links of the first endless chain are not mechanically coupled, that is to say mechanically connected, to the first and second secondary links of the second endless chain.
According to an embodiment of the invention, the first and second articulation elements extend substantially vertically, and the first and second articulation members extend substantially vertically.
According to an embodiment of the invention, each first clamp includes a first running roller configured to roll over an upper surface of the guide rail, and each second clamp includes a second running roller configured to roll over the upper surface of the guide rail.
Advantageously, the first primary running roller of each first clamp has a substantially horizontal axis of rotation, and the second running roller of each second clamp has a substantially horizontal axis of rotation.
According to an embodiment of the invention, the first clamps are substantially identical to the second clamps.
According to another embodiment of the invention, the first clamps are different from the second clamps.
According to an embodiment of the invention, the first articulation members are substantially identical to the first articulation elements, and the second articulation members are substantially identical to the second articulation elements.
According to an embodiment of the invention, the first articulation members are different from the first articulation elements, and the second articulation members are different from the second articulation elements.
According to an embodiment of the invention, each first clamp includes a primary guide roller configured to cooperate with the first guide surface of the guide rail, and each second clamp includes a secondary guide roller configured to cooperate with the first guide surface of the guide rail.
5 According to an embodiment of the invention, each primary guide roller has a substantially vertical axis of rotation, and each secondary guide roller has a substantially vertical axis of rotation.
According to an embodiment of the invention, the primary guide rollers of the first clamps and the secondary guide rollers of the second clamps extend substantially in the same plane of extension.
According to an embodiment of the invention, each first clamp is located opposite a respective second articulation member, and each second clamp is located opposite a respective second articulation element.
According to an embodiment of the invention, each articulation element carries at least one first bearing roller configured to cooperate with the second guide surface of the guide rail, and each first articulation member carries at least one second bearing roller configured to cooperate with the second guide surface of the guide rail.
According to an embodiment of the invention, the at least one first bearing roller has a substantially vertical axis of rotation, and the at least one second bearing roller has a substantially vertical axis of rotation.
According to an embodiment of the invention, each first articulation element carries a first upper bearing roller and a first lower bearing roller which are shifted vertically and which are configured to cooperate with the second guide surface of the guide rail, and each first articulation member carries a second upper bearing roller and a second lower bearing roller which are shifted vertically and which are configured to cooperate with the second guide surface of the guide rail.
According to an embodiment of the invention, the primary guide rollers, the secondary guide rollers, the first upper bearing rollers and the second upper bearing rollers extend substantially in the same plane of extension.
According to an embodiment of the invention, the stretching device further includes:
- a retaining rail extending along the guide rail, the retaining rail including a bearing surface directed towards the guide rail and a retaining surface opposite to the bearing surface, and
- a plurality of first retaining elements and a plurality of second retaining elements disposed alternately along the retaining rail and configured to be guided by the retaining rail, each first retaining element being mounted on a respective second articulation element of the first endless chain and being configured to be driven by the first endless chain along the retaining rail, each second retaining element being mounted on a respective second articulation member of the second endless chain and being configured to be driven by the second endless chain along the retaining rail.
According to an embodiment of the invention, the first retaining elements are substantially identical to the second retaining elements.
According to an embodiment of the invention, each first clamp is configured to abut against a respective second retaining element when the first and second endless chains are in the second state, and each second clamp is configured to abut against a respective first retaining element when the first and second endless chains are in the second state.
These arrangements allow stabilizing the first and second clamps when the first and second endless chains are in the second state, and in particular after release of the film by the first and second clamps (for example when these reach a transmission pulley).
According to an embodiment of the invention, each first clamp includes a first planar stop surface configured to abut against a second planar stop surface provided on the respective second retaining element when the first and second endless chains are in the second state, and each second clamp includes a planar primary stop surface configured to abut against a planar secondary stop surface provided on the respective first retaining element when the first and second endless chains are in the second state.
According to an embodiment of the invention, each first retaining element includes a primary retaining roller configured to cooperate with the retaining surface of the retaining rail, and each second retaining element includes a secondary retaining roller configured to cooperate with the retaining surface of the retaining rail.
According to an embodiment of the invention, the primary retaining roller of each first retaining element has a substantially vertical axis of rotation, and the secondary retaining roller of each second retaining element has a substantially vertical axis of rotation.
According to an embodiment of the invention, each primary retaining roller is arranged so as to be retained by the guide rail so as to apply a retaining force on the respective second articulation element, and each secondary retaining roller is arranged so as to be retained by the guide rail so as to apply a retaining force on the respective second articulation member.
According to an embodiment of the invention, each second articulation element carries at least one primary bearing roller configured to cooperate with the bearing surface of the retaining rail, each second articulation member carries at least one secondary bearing roller configured to cooperate with the bearing surface of the retaining rail.
According to an embodiment of the invention, the at least one primary bearing roller has a substantially vertical axis of rotation, and the at least one secondary bearing roller has a substantially vertical axis of rotation.
According to an embodiment of the invention, each second articulation element carries an upper primary bearing roller and a lower primary bearing roller which are shifted vertically and which are configured to cooperate with the bearing surface of the retaining rail, and each second articulation member carries an upper secondary bearing roller and a lower secondary bearing roller which are shifted vertically and which are configured to cooperate with the bearing surface of the retaining rail.
According to an embodiment of the invention, the primary retaining rollers, the secondary retaining rollers, the upper primary bearing rollers and the upper secondary bearing rollers extend substantially in the same plane of extension.
According to an embodiment of the invention, the retaining rail includes a first rail portion which extends substantially parallel to the guide rail and which is spaced apart from the guide rail by a first distance, and a second rail portion which extends substantially parallel to the guide rail and which is spaced apart from the guide rail by a second distance which is different from the first distance, the second rail portion being located downstream of the first rail portion, and wherein the retaining rail is configured such that a displacement of the first and second retaining elements from the first rail portion to the second rail portion causes a deformation of the first and second endless chains between the first and second states.
According to an embodiment of the invention, the retaining rail includes a transition portion connecting the first rail portion and the second rail portion.
Advantageously, the transition portion forms an inclined ramp.
According to an embodiment of the invention, the second distance is smaller than the first distance, and the retaining rail is configured such that a displacement of the first and second retaining elements from the first rail portion to the second rail portion causes a deformation of the first and second endless chains from the first state to the second state so as to impart a longitudinal stretching of the film.
According to an embodiment of the invention, the second distance is larger than the first distance, and the retaining rail is configured such that a displacement of the first and second retaining elements from the first rail portion to the second rail portion causes a deformation of the first and second endless chains from the second state to the first state so as to impart a longitudinal relaxation of the film.
According to an embodiment of the invention, the first and second articulation elements belonging to the first endless chain are distinct and mechanically separate from the first and second articulation members belonging to the second endless chain.
According to an embodiment of the invention, each first articulation element is located opposite a respective second articulation member and is spaced apart from the respective second articulation member by a separation distance which varies depending on the state occupied by the first and second endless chains, and each second articulation element is located opposite a respective first articulation member and is spaced apart from the respective first articulation member by a spacing distance
— which varies depending on the state occupied by the first and second endless chains.
According to an embodiment of the invention, the separation distance is equal to a first separation value when the first and second endless chains are in the first state and is also equal to a second separation value when the first and second endless chains are in the second state, the second separation value being smaller than the first separation value.
According to an embodiment of the invention, the spacing distance is equal to a first spacing value when the first and second endless chains are in the first state and is also equal to a second spacing value when the first and second endless chains are in the second state, the second spacing value being smaller than the first spacing value.
According to an embodiment of the invention, the transition portion is configured to reduce the retaining force applied on each second articulation element and on each second articulation member in order to deform the first and second endless chains in the second state.
According to an embodiment of the invention, the transition portion is configured to increase the retaining force applied on each second articulation element and on each second articulation member in order to deform the first and second endless chains in the first state.
According to an embodiment of the invention, each first retaining element includes a primary running roller configured to roll over an upper surface of the retaining rail, and each second retaining element includes a secondary running roller configured to roll over the upper surface of the retaining rail.
Advantageously, the primary running roller of each first retaining element has a substantially horizontal axis of rotation, and the secondary running roller of each second retaining element has a substantially horizontal axis of rotation.
According to an embodiment of the invention, the stretching device further includes a plurality of additional first retaining elements and a plurality of additional second retaining elements disposed alternately along the retaining rail and configured to be guided by the retaining rail, each additional first retaining element being mounted on a respective second articulation element of the first endless chain and being shifted vertically with respect to the first retaining element mounted on the respective second articulation element, each additional second retaining element being mounted on a respective second articulation member of the endless chain and being shifted vertically with respect to the second retaining element mounted on the respective second articulation member, each additional first retaining element and each additional second retaining element being configured to be driven respectively by the first endless chain and the second endless chain along the retaining rail.
According to an embodiment of the invention, the additional first retaining elements are substantially identical to the additional second retaining elements.
According to an embodiment of the invention, each additional first retaining element includes an additional primary retaining roller configured to cooperate with the retaining surface of the retaining rail, and each additional second retaining element includes an additional secondary retaining roller configured to cooperate with the retaining surface of the retaining rail.
According to an embodiment of the invention, the additional primary retaining roller of each additional first retaining element has a substantially vertical axis of rotation, and the additional secondary retaining roller of each additional second retaining element has a substantially vertical axis of rotation.
According to an embodiment of the invention, each additional first retaining element includes an additional primary running roller configured to roll over a lower surface of the retaining rail, and each additional second retaining element includes an additional secondary running roller configured to roll over the lower surface of the retaining rail.
Advantageously, the additional primary running roller of each additional first retaining element has a substantially horizontal axis of rotation, and the additional secondary running roller of each additional second retaining element has a substantially horizontal axis of rotation.
According to an embodiment of the invention, the additional primary retaining rollers, the additional secondary retaining rollers, the lower primary bearing rollers and the lower secondary bearing rollers extend substantially in the same plane of extension.
According to an embodiment of the invention, the stretching device further includes a plurality of first guide elements and a plurality of second guide elements disposed alternately along the guide rail and configured to be guided by the guide rail, each first guide element being mounted on a respective first articulation element of the first endless chain and being shifted vertically with respect to the first clamp mounted on the respective first articulation element, each second guide element being mounted on a respective first articulation member of the second endless chain and being shifted vertically with respect to the second clamp mounted on the respective first articulation member, each first guide element and each second guide element being configured to be driven respectively by the first endless chain and the second endless chain along the guide rail.
According to an embodiment of the invention, the first guide elements are substantially identical to the second guide elements.
According to an embodiment of the invention, each first guide element includes an additional primary guide roller configured to cooperate with the first guide surface of the guide rail, and each second guide element includes an additional secondary guide roller configured to cooperate with the first guide surface of the guide rail.
According to an embodiment of the invention, the additional primary guide roller of each first guide element has a substantially vertical axis of rotation, and the additional secondary guide roller of each second guide element has a substantially vertical axis of rotation.
According to an embodiment of the invention, each first guide element includes an additional first running roller configured to roll over a lower surface of the guide rail,
and each second guide element includes an additional second running roller configured to roll over the lower surface of the guide rail.
Advantageously, the additional first running roller of each first guide element has a substantially horizontal axis of rotation, and the additional second running roller of each second guide element has a substantially horizontal axis of rotation.
According to an embodiment of the invention, the additional primary guide rollers, the additional secondary guide rollers the first lower bearing rollers and the second lower bearing rollers extend substantially in the same plane of extension.
According to an embodiment of the invention, each first guide element is configured to abut against a respective additional second retaining element when the first and second endless chains are in the second state, and each second guide element is configured to abut against a respective additional first retaining element when the first and second endless chains in the second state.
According to an embodiment of the invention, the first and second endless chains are configured such that the first and second clamps bear against one another when the first and second endless chains are in the first state.
According to an embodiment of the invention, the first and second endless chains are configured such that the first and second retaining elements bear against one another when the first and second endless chains are in the first state.
According to an embodiment of the invention, the first and second endless chains are configured such that the additional first and second retaining elements bear against one another when the first and second endless chains are in the first state.
According to an embodiment of the invention, the first and second endless chains are configured such that the first and second guide elements bear against one another when the first and second endless chains are in the first state.
According to an embodiment of the invention, each first clamp includes a first clamp body and two first lateral support pads which are disposed on either side of the respective first clamp body and which are shifted along the guide rail, and each second clamp includes a second clamp body and two second lateral support pads which are disposed on either side of the respective second clamp body and which are shifted along the guide rail, the first and second endless chains being configured such that, when the first and second endless chains are in the first state, each first lateral support pad bears against a second lateral support pad of an adjacent second clamp.
According to an embodiment of the invention, each first lateral support pad includes a first planar bearing surface which is configured to cooperate with a second planar bearing surface on the respective second lateral support pad.
Advantageously, the first and second planar bearing surfaces extend substantially perpendicular to the guide rail.
According to an embodiment of the invention, each first retaining element includes a first support body and two additional first lateral support pads which are disposed on either side of the respective first support body and which are shifted along the retaining rail, and each second retaining element includes a second support body and two additional second lateral support pads which are disposed on either side of the respective second support body and which are shifted along the retaining rail, the first and second endless chains being configured such that, when the first and second endless chains are in the first state, each additional first lateral support pad bears against an additional second lateral support pad of an adjacent second retaining element.
According to an embodiment of the invention, the first and second clamps are substantially aligned along the guide rail.
According to an embodiment of the invention, the first and second retaining elements are substantially aligned along the guide rail.
The present invention further concerns a stretching system for stretching a film made of a synthetic material at least in a transverse direction, comprising two stretching devices according to the present invention disposed on either side of the film, the first and second clamps of one of the stretching devices being arranged so as to grasp a first longitudinal edge of the film and the first and second clamps of the other one amongst the stretching devices being arranged so as to grasp a second longitudinal edge of the film.
According to an embodiment of the invention, the stretching system is configured to stretch the film made of a synthetic material at least in a longitudinal direction, and for example in a transverse direction and in a longitudinal direction.
According to an embodiment of the invention, the stretching system is also configured to achieve a longitudinal relaxation of the film made of a synthetic material, for example after stretching of the latter.
According to an embodiment of the invention, the stretching system includes a furnace, and the guide rails of the two stretching devices extend at least partially into the furnace.
According to an embodiment of the invention, the guide rails of the two stretching devices diverge away from one another in a first area of the stretching system.
According to an embodiment of the invention, the guide rails of the two stretching devices extend substantially parallel to one another in a second area of the stretching system located downstream of the first area of the stretching system.
According to an embodiment of the invention, the second rail portion of the each retaining rail is located at least partially in the first area of the stretching system.
These arrangements allow ensuring a longitudinal stretching or a longitudinal relaxation of the film simultaneously with a transverse stretching of the film.
According to an embodiment of the invention, the transition portion of each retaining rail is located at least partially in the second area of the stretching system.
These arrangements allow ensuring a longitudinal stretching or a longitudinal relaxation of the film after a transverse stretching of the film.
Anyway, the invention will be better understood using the following description with reference to the appended schematic drawings representing, as a non-limiting example, an embodiment of this stretching system.
Figure 1 is an overview of a plant for producing a film made of a synthetic material.
Figure 2 is a partial perspective view of a stretching device belonging to the production plant of Figure 1 showing first and second endless chains of the stretching device in a first state. Figure 3 is a partial perspective view of the stretching device of Figure 2 showing the first and second endless chains of the stretching device in a second state. Figure 4 is a partial side view of the stretching device of Figure 2. Figure 5 is a cross-sectional view of the stretching device of Figure 2. Figure 6 is a partial top view of the stretching device of Figure 2, showing the first and second endless chains in the first state. Figure 7 is a partial top view of the stretching device of Figure 2, showing the first and second endless chains in an intermediate state. Figure 8 is a partial top view of the stretching device of Figure 2, showing the first and second endless chains in the second state. Figure 9 is a partial perspective view of the stretching device of Figure 2, showing more particularly a transmission pulley of the stretching device. Figure 10 is a partial top view of the stretching device of Figure 2. Figure 11 is a partial top view of a guide rail and of a retaining rail belonging to the stretching device of Figure 2. Figure 1 represents a production plant 2 for the production of a film 3 made of a synthetic material having two substantially parallel longitudinal edges 4. The production plant 2 successively includes : - a system 5 for feeding the synthetic material 6, - an extruder 7 fed with synthetic material by the feed system 5, and comprising an extrusion die 8, - a casting drum 9 which is disposed under the extrusion die 8 and over which the film 3 is formed by pouring the synthetic material 6 in the molten state, - a longitudinal stretching system 11 for stretching the film 3 in the longitudinal direction, the longitudinal stretching system 11 including for example rolls 12 with a speed differential to convey and stretch the film 3, and - a stretching system 13 for stretching the film 3 at least in the transverse direction. The stretching system 13 includes a furnace (not represented in the figures) allowing setting the temperature of the film 3 during the stretching thereof in the transverse direction, and two stretching devices 14 disposed on either side of the film
3. More particularly, as shown in Figures 2 to 10, each stretching device 14 includes:
- a guide rail 15 extending at least partially into the furnace and including a first guide surface 15.1 directed towards the film 3 and a second guide surface 15.2 opposite to the first guide surface 15.1,
- a plurality of first clamps 16 and a plurality of second clamps 17 each intended to grasp a corresponding longitudinal edge 4 of the film 3, the first and second clamps 16, 17 being disposed alternately along the respective guide rail 15 and being configured to be guided in translation by the respective guide rail 15,
- a retaining guide 18 extending along the respective guide rail 15, the retaining rail 18 including a bearing surface 18.1 directed towards the respective guide rail 15 and a retaining surface 18.2 opposite to the bearing surface 18.1,
- a plurality of first retaining elements 19 and a plurality of second retaining elements 21 disposed alternately along the retaining rail 18 and configured to be guided in translation by the retaining rail 18,
- a first endless chain 22 configured to drive the first clamps 16 along the respective guide rail 15, and to drive the respective first retaining elements 19 along the respective retaining rail 18,
- a second endless chain 23 configured to drive the second clamps 17 along the respective guide rail 15, and to drive the respective second guide elements 21 along the respective retaining rail 18.
The first and second endless chains 22, 23 of each stretching device 14 are nested within one another, and are deformable between a first state (cf.
Figures 2 and 6) in which the first and second clamps 16, 17 are disposed proximate to one another, and for example bearing against one another, and a second state (cf.
Figures 3 and 8) in which the first and second clamps 16, 17 are away from one another.
As reflected in Figure 1, the guide rails 15 of the two stretching devices 14 diverge away from one another in a first area A1 of the stretching system 13 located in the furnace, and extend substantially parallel to one another in a second area A2 of the stretching system 13 located downstream of the first area A1 of the stretching system 13, and which may be located either within or outside the furnace.
According to the embodiment represented in the figures, each guide rail 15 has a substantially rectangular section, and each retaining rail 18 also has a substantially rectangular section.
As shown in particular in Figures 5 to 8, each first endless chain 22 includes first primary links 25 and second primary links 26 disposed alternately along the first endless chain 22 and hingedly mounted relative to one another, and also first articulation elements 27 and second articulation elements 28 disposed alternately along the first endless chain 22 and about which the first and second primary links 25,
26 are hingedly mounted.
The first and second articulation elements 27, 28 extend substantially vertically.
Each first clamp 16 includes a first clamp body 29 hingedly mounted on a respective first articulation element 27, and a gripping finger 31 pivotally mounted on the first clamp body 29 and configured to grasp the film 3. Each first clamp 16 further includes a primary guide roller 32 having a substantially vertical axis of rotation and configured to cooperate with the first guide surface 15.1 of the guide rail 15, and a first running roller 33 having a substantially horizontal axis of rotation and configured to roll over an upper surface 15.3 of the guide rail 15. Each first retaining element 19 includes a first support body 34 hingedly mounted on a respective second articulation element 28, and a primary retaining roller 35 having a substantially vertical axis of rotation and configured to cooperate with the retaining surface 18.2 of the retaining rail 18. Each primary retaining roller 35 is arranged to be retained by the guide rail 18 so as to apply a retaining force on the respective second articulation element 28. Each first retaining element 19 further includes a primary running roller 36 having a substantially horizontal axis of rotation and configured to roll over an upper surface 18.3 of the retaining rail 18. As shown in particular in Figures 5 to 8, each second endless chain 23 includes first secondary links 37 and second secondary links 38 disposed alternately along the second endless chain 23 and hingedly mounted relative to one another, and also first articulation members 39 and second articulation members 41 disposed alternately along the second endless chain 23 and about which the first and second secondary links 37, 38 are hingedly mounted.
Advantageously, the first and second articulation members 39, 41 extend substantially vertically, and the first and second primary links 25, 26 of the first endless chain 22 and the first and second secondary links 37, 38 of the second endless chain 23 are nested within one another.
Each second clamp 17 includes a second clamp body 42 hingedly mounted on a respective first articulation member 39, and a gripping finger 43 pivotally mounted on the second clamp body 42 and configured to grasp the film 3. Each second clamp 17 further includes a secondary guide roller 44 having a substantially vertical axis of rotation and configured to cooperate with the first guide surface 15.1 of the guide rail 15, and a second running roller 45 having a substantially horizontal axis of rotation and configured to roll over the upper surface 15.3 of the guide rail 15. Each second retaining element 21 includes a second support body 46 hingedly mounted on a respective second articulation member 41, and a secondary retaining roller 47 having a substantially vertical axis of rotation and configured to cooperate with the retaining surface 18.2 of the retaining rail 18. Each secondary retaining roller 47 is arranged so as to be retained by the guide rail 18 so as to apply a retaining force on the respective second articulation member 41. Each second retaining element 21 further includes a secondary running roller 48 having a substantially horizontal axis of rotation and configured to roll over the upper surface 18.3 of the retaining rail 18.
Advantageously, each first clamp 16 is located opposite a respective second articulation member 41, and is configured to abut against a respective second retaining element 21 when the first and second endless chains 22, 23 are in the second state, whereas each second clamp 17 is located opposite a respective second articulation element 28, and is configured to abut against a respective first retaining element 19 when the first and second endless chains 22, 23 are in the second state.
According to the embodiment represented in the figures, the first clamp body 29 of each first clamp 16 includes a first planar stop surface S11 configured to abut against a second planar stop surface S12 provided on the second support body 46 of the respective second retaining element 21 when the first and second endless belts 22, 23 are in the second state, and the second clamp body 42 of each clamp 17 includes a planar primary stop surface S21 configured to abut against a planar secondary stop surface S22 provided on the first support body 34 of the respective first retaining element 19 when the first and second endless chains 22, 23 are in the second state.
The first planar stop surface S11, the second planar stop surface S12, the planar primary stop surface S21 and the planar secondary stop surface S22 extend substantially parallel to the respective guide rail 15. Advantageously, the first and second endless chains 22, 23 of each stretching device 14 are also configured such that the first and second retaining elements 19, 21 bear against one another when the first and second endless chains 22, 23 are in the — first state.
According to the embodiment represented in the figures, each first articulation element 27 carries a first upper bearing roller 49 and a first lower bearing roller 51 which are shifted vertically and which are configured to cooperate with the second guide surface 15.2 of the guide rail 15. Advantageously, each of the first upper and lower bearing rollers 49, 51 has a substantially vertical axis of rotation.
Each second articulation element 28 also carries an upper primary bearing roller 52 and a lower primary bearing roller 53 which are shifted vertically and which are configured to cooperate with the bearing surface 18.1 of the retaining rail 18. Advantageously, each of the upper and lower primary bearing rollers 52, 53 has a substantially vertical axis of rotation.
According to the embodiment represented in the figures, each first articulation member 39 also carries a second upper bearing roller 54 and a second lower bearing roller 55 which are shifted vertically and which are configured to cooperate with the second guide surface 15.2 of the guide rail 15. Advantageously, each of the upper and lower second bearing rollers 54, 55 has a substantially vertical axis of rotation. Each second articulation member 41 also carries an upper secondary bearing roller 56 and a lower secondary bearing roller 57 which are shifted vertically and which are configured to cooperate with the bearing surface 18.1 of the retaining rail 18. Advantageously, each of the upper and lower secondary bearing rollers 56, 57 has a substantially vertical axis of rotation. Each stretching device 14 further includes a plurality of additional first retaining element 58 and a plurality of additional second retaining elements 59 disposed alternately along the retaining rail 18 and configured to be guided by the retaining rail
18. Each additional first retaining element 58 and each additional second retaining element 59 is configured to be driven respectively by the respective first and second endless chains 22, 23 along the retaining rail 18. Each additional first retaining element 58 is mounted on a respective second articulation element 28 of the first endless chain 22 and is shifted vertically with respect to the first retaining element 19 mounted on the respective second articulation element
28. Advantageously, each additional first retaining element 58 includes an additional primary retaining roller 61 which has a substantially vertical axis of rotation and which is configured to cooperate with the retaining surface 18.2 of the retaining rail 18, and also an additional primary running roller 62 which has a substantially horizontal axis of rotation and which is configured to roll over a lower surface 18.4 of the retaining rail
18. Each additional second retaining element 59 is mounted on a respective second articulation member 41 of the respective second endless chain 23 and is shifted vertically with respect to the second retaining element 21 mounted on the respective second articulation member 41. Advantageously, each additional second retaining member 59 includes an additional secondary retaining roller 63 having a substantially vertical axis of rotation and configured to cooperate with the retaining surface 18.2 of the retaining rail 18, and also an additional secondary running roller 64 having a substantially horizontal axis of rotation and configured to roll over the lower surface
18.4 of the retaining rail 18. Each stretching device 14 further includes a plurality of first guide elements 65 and a plurality of second guide elements 66 disposed alternately along the guide rail 15 and configured to be guided by the guide rail 15. Each first guide element 65 and each second guide element 66 are configured to be driven respectively by the respective first and second endless chains 22, 23 along the respective guide rail 15.
Each first guide element 65 is mounted on a respective first articulation element 27 of the respective first endless chain 22 and is shifted vertically with respect to the first clamp 16 mounted on the respective first articulation element 27. Advantageously, each first guide element 65 includes an additional primary guide roller 67 which has a substantially vertical axis of rotation and which is configured to cooperate with the first guide surface 15.1 of the respective guide rail 15, and also an additional first running roller 68 which has a substantially horizontal axis of rotation and which is configured to roll over a lower surface 15.4 of the respective guide rail 15. Each second guide element 66 is mounted on a respective first articulation member 39 of the respective second endless chain 22 and is shifted vertically with respect to the second clamp 17 mounted on the respective first articulation member
39. Advantageously, each second guide element 66 includes an additional secondary guide roller 69 which has a substantially vertical axis of rotation and which is configured to cooperate with the first guide surface 15.1 of the respective guide rail 15, and also an additional second running roller 71 which has a substantially horizontal axis of rotation and which is configured to roll over the lower surface 15.4 of the respective guide rail 15. According to the embodiment represented in the figures, the primary guide rollers 32, the secondary guide rollers 44, the primary retaining rollers 35, the secondary retaining rollers 47, the first upper bearing rollers 49, the second upper bearing rollers 54, the upper primary bearing rollers 52 and the upper secondary bearing rollers 56 extend substantially in the same plane of extension. According to the embodiment represented in the figures, the additional primary guide rollers 67, the additional secondary guide rollers 69, the first lower bearing rollers 51, the second lower bearing rollers 55, the additional primary retaining rollers 61, the additional secondary retaining rollers 63, the lower primary bearing rollers 53 and the lower secondary bearing rollers 57 extend substantially in the same plane of extension. According to the embodiment represented in the figures, each first guide element 65 is configured to abut against a respective additional second retaining element 59 when the respective first and second endless chains 22, 23 are in the second state, and each second guide element 66 is configured to abut against a respective additional first retaining element 58 when the respective first and second endless chains 22, 23 are in the second state. Advantageously, the first and second endless chains 22, 23 of each stretching device 14 are configured such that the respective additional first and second retaining elements 58, 59 bear against one another when the first and second endless chains 22, 23 are in the first state, and such that the first and second guide elements 65, 66 bear against one another when the first and second endless chains 22, 23 are in the first state.
According to the embodiment represented in the figures, each first clamp 16 further includes two first lateral support pads 72 which are disposed on either side of the respective first clamp body 29 and which are shifted along the guide rail 15, and each second clamp 17 includes two second lateral support pads 73 which are disposed on either side of the respective second clamp body 42 and which are shifted along the guide rail 15. The first and second endless chains 22, 23 of each stretching device 14 are configured such that, when the first and second endless chains 22, 23 are in the first state, each first lateral support pad 72 bears against a second lateral support pad 73 of an adjacent second clamp 17.
Advantageously, each first retaining element 19 includes two additional first lateral support pads 74 which are disposed on either side of the respective first support body 34 and which are shifted along the respective retaining rail 18, and each second retaining element 21 includes two additional second lateral support pads 75 which are disposed on either side of the respective second support body 46 and which are shifted along the respective retaining rail 18. The first and second endless chains 22, 23 of each stretching device 14 are configured such that, when the first and second endless chains 22, 23 are in the first state, each additional first lateral support pad 74 bears against an additional second lateral support pad 75 of an adjacent second retaining element 21.
Similarly, the first and second guide elements 65, 66 and the additional first and second retaining elements 58, 59 may be provided with support pads.
As shown in Figure 11, each retaining rail 18 includes a first rail portion 181 which extends substantially parallel to the respective guide rail 15 and which is spaced apart from the respective guide rail 15 by a first distance D1, and a second rail portion 182 which is located downstream of the first rail portion 181 and which extends substantially parallel to the respective guide rail 15, the second rail portion 182 being spaced apart from the respective guide rail 15 by a second distance D2 which is different from the first distance D1. Each retaining rail 18 further includes a transition portion 183 connecting the respective first and second rail portions 181, 182. Advantageously, each transition portion 183 forms an inclined ramp.
More particularly, each retaining rail 18 is configured such that a displacement of the first and second retaining elements 19, 21 from the first rail portion 181 to the second rail portion 182 causes a deformation of the respective first and second endless chains 22, 23 between the first and second states.
Advantageously, the transition portion 183 of each retaining rail 18 is located in the first area A1 of the stretching system 13. These arrangements allow ensuring a deformation of the first and second endless chains between the first and second states in the first area A1 of the stretching system 13, and therefore ensuring a longitudinal stretching or a longitudinal relaxation of the film 3 simultaneously with a transverse stretching of the latter.
The operation of the stretching system 13 will now be described while considering that the second distance D2 separating each second rail portion 182 and the respective guide rail 15 is smaller than the first distance D1 separating each first rail portion 181 and the respective guide rail 15.
At the time the film 3 comes into the stretching system 13, the longitudinal edges 4 of the film 3 are grasped respectively by the first and second clamps 16, 17 of each stretching device 14. The first and second clamps 16, 17, driven by the first endless chains 22, 23, convey the film 3 along the guide rails 15. In the first area A1 of the stretching system 13, the film 3, having reached an appropriate stretching temperature, is stretched in the transverse direction by the divergence of the guide rails 15, and hence by the continuous increase of the spacing between the first and second clamps 16, 17 of one of the stretching devices 14 and the first and second clamps 16, 17 of the other one amongst the stretching devices 14.
When the first and second retaining elements 19, 21 of each stretching device 14 reach the transition portion 183 and the second rail portion 182 of the respective retaining rail 18, the upper and lower primary bearing rollers 52, 53 carried by each second articulation element 28 and the upper and lower secondary bearing rollers 56, 57 carried by each second articulation member 41 are urged towards the respective guide rail 15 by the transition portion 183 and the second rail portion 182 of the respective retaining rail 18, which causes a displacement of the second articulation elements 28 and of the second articulation members 41 towards the respective guide rail 15. This displacement of the second articulation elements 28 and of the second articulation members 41 results in increasing the pitch of each of the first and second endless chains 22, 23 and in bringing the first and second clamps 16, 17 of each stretching device 14 away from one another.
Thus, these arrangements allow ensuring a longitudinal stretching of the film 3 simultaneously with the transverse stretching thereof.
The operation of the stretching system 13 will now be described while considering that the second distance D2 separating each second rail portion 182 and the respective guide rail 15 is larger than the first distance D1 separating each first rail portion 181 and the respective guide rail 15.
When the first and second retaining elements 19, 21 of each stretching device 14 reach the transition portion 183 and the second rail portion 182 of the respective retaining rail 18, the primary and secondary retaining rollers 35, 47 carried by the first and second retaining elements 19, 21 are urged away from the respective guide rail
15 by the transition portion 183 and the second rail portion 182 of the respective retaining rail 18, which causes a displacement of the second articulation elements 28 and of the second articulation members 41 away from the respective guide rail 15. This displacement of the second articulation elements 28 and of the second articulation members 41 results in reducing the pitch of each of the first and second endless chains
22,23 and in bringing the first and second clamps 16, 17 of each stretching device 14 close to one another.
Thus, these arrangements allow ensuring a longitudinal relaxation of the film 3 simultaneously with the transverse stretching thereof.
According to a variant of the invention, the guide rails 15 may have, in the second area A2 of the stretching system 13, a portion over which the guide rails 15 converge towards one another so as to enable a transverse relaxation of the film simultaneously with the longitudinal relaxation thereof.
It goes without saying that the invention is not limited to the sole embodiment of this stretching system, described hereinabove as example but it comprises, on the contrary, all variants thereof.
Thus, in particular, the stretching device may include third clamps each disposed between a respective first clamp and a respective second clamp, and a third endless chain connected to the third clamps and configured to drive the third clamps along the guide rail.
The stretching device may also include more than three types of clamps and more than three endless chains.