Winding – tensioning – or guiding – Tension control or brake
Reexamination Certificate
1999-07-23
2001-01-09
Walsh, Donald P. (Department: 3653)
Winding, tensioning, or guiding
Tension control or brake
C425S066000, C053S441000
Reexamination Certificate
active
06170776
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an outer wrapping film, to a device for prior stretching of the film and suitable for use in prior stretching such an outer wrapping film, and to a method of outer wrapping that uses such a film. The prior stretching advantageously includes a step of paying out the film from a feed reel, a stretching step, and a step of winding the stretched film onto a mandrel or a take-up reel, prior to subsequent use.
BACKGROUND OF THE INVENTION
A helical wrapping technique that is conventionally used only by simple machines operating at a low rate of throughput, stretches a film directly on a palletized load in the form of a rectangular parallelepiped. The film is taken from a vertical axis reel fitted with a brake. One end of the film is initially fixed to the load, after which the load is caused to rotate about a vertical axis. The reel is braked in such a manner as to cause the film to be stretched by the desired amount.
Unfortunately, since the load is not circularly cylindrical, but generally forms a rectangular parallelepiped, the radial distance to be covered with the film varies with respect to the particular portion or region of the load being wrapped, so that rotating the load at a constant angular velocity while applying a constant braking force causes the film to be elongated in a non-uniform manner. Also, immediately after stretching, the stretchable film is subject to relaxation which leads, over a period of approximately 48 hours, to a drop in its resilient return force that is substantially equal to 50%. Thus, with a machine of this type, there is a limit set by the stretching forces that can be withstood by the load, whereas the resilient forces that subsequently provide cohesion to the load during handling and transport are significantly lower. These factors have led to the above type of machine being abandoned in favor of wrapping machines including a pre-stretching device comprising a plurality of motor-driven rollers operating at different peripheral speeds. At the outlet from the rollers of the pre-stretching device, the film is wrapped without tension, or preferably under low tension, on the load to be wrapped, as explained with reference to FIG.
1
.
In patent application No. 92/10254 (published under No. FR 2 695 102), the Applicant describes a method of wrapping a load in a previously-stretched film, with the film being put into place only after a period has elapsed to allow the film to relax while still under tension. As explained below with reference to
FIG. 2
, that patent application indicates that it is thus possible to achieve an improvement with respect to residual elongation, after the film has relaxed, thereby making it possible to consume less film.
In patent application No. 92/10254 (published under No. FR 2 695 102), the Applicant describes the optimum way of using a previously-stretched film with relaxation under a high level of tension.
However, films relaxed under a high level of tension are not suitable for all types of wrapping. Firstly, they exert a large constriction force on the film reel, which force can, in some cases, be great enough to destroy such a reel. It is thus necessary to use reels that are very strong in compression, for example, those made of steel. Such reels are expensive and, in most cases, must be reused. The return of empty reels gives rise to non-negligible costs. Also, because of its elastic memory, the film placed around a load exerts a constriction force which has a value that is substantially equal to half the value of the tension under which the film was relaxed. Thus, some loads are too fragile or too compressible to withstand the constriction forces exerted by a film that has been relaxed under a high level of tension. Further, films relaxed under a high level of tension are rather stiff, are not very resilient, and they are often fragile. In some cases, such films present a high risk of being punctured, in particular at the corners of the pallet.
WO 89/06594 describes a device for producing thin films that takes best advantage of the production capacities of an extruder. A relatively thick film is initially extruded and its area can be increased by stretching.
In that document, it is desired to release the force in the film as much as possible prior to relaxation in order to wind the film around a load with a force that is as low as possible.
OBJECTS OF THE INVENTION
Consequently, an object of the present invention is to provide an outer wrapping film that exerts a controlled constriction force on its storage reel.
Another object of the present invention is to provide an outer wrapping film which has suitable for exerting a moderate force on the wrapped load.
It is also an object of the present invention to provide an outer wrapping film which has good mechanical properties, in particular a film that is resilient, and that withstands friction and puncturing.
It is also an object of the present invention to provide an outer wrapping film which has suitable for being deposited around a load with a tension which is lower than the tension that it subsequently exerts on the load in order to ensure cohesion thereof.
It is also an object of the present invention to provide a film which is able to be adapted to the mechanical characteristics of the goods forming the load to be wrapped.
SUMMARY OF THE INVENTION
The foregoing and other objects are achieved by a film of the present invention which has been previously stretched under large tension, released, and then wound upon a reel under moderate tension under which the film is relaxed.
In accordance with a first variant implementation of the method of the present invention for preparing the film, tension in the film is released immediately after the stretching step. As soon as it reaches the desired elongation, the released film is wound under moderate tension on a storage reel on which it subsequently relaxes. In accordance with a second implementation of the method of the present invention for preparing the film, the film is maintained under tension for a short period of time before the tension in the film is released and it is wound onto a reel. For example, a film that has been stretched and that is being maintained under tension is caused to follow a path between deflection rollers so as to release the film somewhat later after it has been stretched. Depending on the constriction force exerted, the film is wound onto a mandrel made of cardboard, of plastic material, of steel, or of some other material.
The invention mainly provides a wrapping film that is subjected to stretching, under a tension lying in the range of 10 N/mm
2
to 20 N/mm
2
, of its initial cross-section, to winding, and to relaxation on a take-up mandrel or reel under tension lying in the range of 10% to 90% of the stretching tension.
The invention also provides a film subjected to winding and relaxation under tension lying in the range of 10% to 50% of the stretching tension.
The invention also provides a film, wherein, after the stretching operation and before release, it has been subjected to partial relaxation at the stretching tension for a period of time lying in the range of 0.1 s to 10 s.
The invention also provides a reel of film, comprising a film of the invention wound onto a cardboard hub.
The invention also provides a reel of film comprising a plastic material film of the invention wound on a hub.
The invention also provides a film stretching machine including means for stretching a stretchable film, guide means for guiding the film, and winding means for winding the stretched film on a storage reel, the machine including means for partially releasing the tension in the film after stretching and before winding onto the storage reel.
The invention also provides a machine, wherein the stretching means and the means for partially releasing the tension comprise motor-driven rollers, and wherein the different peripheral speeds of the outlet rollers of the stretching means compared with the speed of the roller of the means for p
Jaconelli Georges
Martin-Cocher Jean-Paul
Rivera William A.
Schwartz & Weinrieb
Thimon, S.A.
Walsh Donald P.
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