Package making – Methods – Applying a partial cover
Patent
1995-08-29
1998-08-25
Johnson, Linda
Package making
Methods
Applying a partial cover
53441, 53556, 53586, 53587, 53588, 2421604, 2424195, B65B 1302, B65B 5300
Patent
active
057972400
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method of wrapping loads in stretchable film, and to a machine and a film for implementing the method. More particularly, the invention relates to wrapping palletized loads, but it is not limited to that particular application insofar as it can be used for wrapping loads of articles brought together without a pallet.
BACKGROUND OF THE INVENTION
It is known that palletized or other loads can be wrapped in stretchable film by using a film, generally of polyethylene, that has a thickness lying in the range 12 microns to 150 microns and more generally in the range 20 microns to 30 microns, which film is paid out from a reel, and by performing two broad types of technique, that can be distinguished by the terms "winding" and "curtain-laying". In machines or installations which make use of the winding technique, a strip of film having a width of about 500 mm and reeled onto a card hub is installed around the load (palletized or otherwise) by making use of relative displacement between the load and moving equipment that carries the reel, with the load itself either being stationary or moving. In machines or installations that use the curtain-laying technique, a generally wider strip of film is placed across a path along which the load travels so as to form a "curtain" which is initially entrained by the load and which is subsequently closed over the load.
Examples of winding type installations are to be found in EP-096 635, whereas examples of curtain-laying installations are described in FR-2 281 275. Whatever the kind of wrapping installation used, the film is stretched in situ simultaneously or quasi-simultaneously with installation of the film itself, that is, either by tensioning the film between the load and a brake placed on the support for the film reel, or else by causing the film to run between rollers driven by motors at different circumferential speeds of rotation, as explained in the above-specified FR-2 281 275. In the winding technique, elongation of the film is limited to a value of about 80% to 100%, whereas in installations applying the curtain-laying technique, elongation can reach 200% or even more providing the loads (palletized or otherwise) are of appropriate shape, well centered on the machine, and the film-stretching device is particularly effective.
However, present machines are required to operate at high throughputs, and the speeds of rotation of a load to be wrapped, or of the reel going around the load, can reach values of about 40 revolutions per minute (rpm) to 50 rpm, but whatever kind of stretching device is implemented, such speeds prevent the film being paid out with satisfactory regularity.
Additionally, the stretching devices presently implemented on machines having motor-driven rollers require mechanisms that are relatively complex in order to obtain satisfactory results, thereby increasing the weight of the moving parts of wrapping machines so that in order to avoid rotating excessive masses, the supply reels of film are of limited weight, thereby narrowing the time the machine can operate without it being necessary to change its supply reels of non-stretched film. In addition, the paying out speeds of the film can change considerably over a short length of time, for example, from 10 meters per minute (m/min) to 200 m/min in a few tenths of a second, such that the resulting variations in elongation frequently give rise to the film rupturing, leading to operating incidents on the machine that reduce the productivity thereof, which productivity is also affected by the fact that the operators of the machines then generally slow them down or reduce the stretching percentage below that which could actually be obtained, with the result that more film-forming material is consumed.
In an attempt to mitigate the above drawbacks, and to enjoy the advantages associated with pre-stretching the wrapping film, FR-A-2 579 577 (which mentions the difficulties encountered in achieving full pre-stretching of the films which can be as much
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patent: 5027581 (1991-07-01), Kovacs
patent: 5307609 (1994-05-01), Kurata et al.
patent: 5458841 (1995-10-01), Shirrell
Jaconelli Georges
Martin-Cocher Jean-Paul
Johnson Linda
Newtec International
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