Plant and method for the online recovery of trimmings in extrusion lines of film made of plastic material

Abstract

A plant and method for the online recovery of trimmings generated in an extrusion line of a plastic film includes a cutting apparatus configured to cut side portions, also called trimmings, from the plastic film made leaving a forming apparatus of the plastic film; a conveying apparatus, positioned downstream of the cutting apparatus, that conveys the trimmings; an extruder for treatment of the trimmings; and an apparatus dosing and feeding granules for forming the plastic film made in the extruder, the extruder and the apparatus dosing and feeding the granules being positioned upstream of the forming device. An apparatus for pre-treatment of the trimmings is provided at the inlet of the extruder and includes a shredder positioned coaxially with respect to the extruder.

Claims

1. A plant for online recovery of trimmings in an extrusion line of a film made of a plastic material (10), comprising: a cutting device (11) configured to cut trimmings shaped as side portions, from the film (10) made of the plastic material leaving a forming device (18) configured to form said film (10); a conveying apparatus (14) configured to convey said trimmings, said apparatus being positioned downstream of said cutting device (11); an extruder (16) configured to treat said trimmings; a dosing and feeding device (17) configured to dose and feed granules for formation of the film made in said extruder (16), said extruder (16) and said dosing and feeding device (17) being positioned upstream of said forming device (18); and a pre-treatment device (15) configured to pre-treat the trimmings of said film (10) conveyed to said pre-treatment device (15) by said conveying apparatus (14), said pre-treatment device being provided at an inlet of said extruder (16), said pre-treatment device (15) comprising a shredder positioned coaxially with respect to said extruder (16).

2. The plant according to claim 1, wherein said pre-treatment device (15) is a device configured to pre-chop and/or pre-grinding said trimmings.

3. The plant according to claim 1, wherein said pre-treatment device (15) is in line with the extruder, the dosing and feeding device and the forming device (16,17,18).

4. The plant according to claim 1, wherein said pre-treatment device (15) comprises a grinding mill or a densifier.

5. The plant according to claim 1, wherein said pre-treatment device (15) comprises the shredder directly connected to said extruder (16).

6. The plant according to claim 1, wherein an extrusion screw (28) of the extruder (16) is connected directly or coaxially with said shredder (29), said shredder (29) and said extrusion screw (28) being controlled by a same motor or by two different motors, said extruder (16) being provided with at least one inlet (31,32) for feeding the granules and/or the trimmings.

7. The plant according to claim 1, wherein said pre-treatment device (15) comprises a grinding mill (24) positioned on a feeding mouth of the extruder (16).

8. The plant according to claim 7, wherein said grinding mill (24) comprises a rotor bearing a plurality of rotating blades that impart a cutting action on the trimmings due to a second plurality of fixed blades, anchored directly to a structure of the extruder (16).

9. The plant according to claim 7, further comprising a fan (33) provided beneath the feeding mouth of said extruder (16), said fan being configured to suck ground trimmings in order to ensure a correct feeding to form said film made of the plastic material (10).

10. The plant according to claim 1, further comprising a pre-chopping device of the trimmings provided upstream of said pre-treatment device (15) of the trimmings.

11. A method of online recovery in an extrusion line of a film made of a plastic material (10), comprising: cutting, with a cutting device (11), trimmings, shaped as side portions, from the film (10) made of the plastic material leaving a forming device (18) of said film (10); conveying said trimmings leaving said cutting device (11); treating said trimmings inside an extruder (16); dosing and feeding granules for formation of the film made of the plastic material in said extruder (16), said extruder (16) and a dosing and feeding device (17) of the granules being upstream of said forming device (18), further comprising a step of pre-treating the trimmings obtained from cutting the side portions of said film (10) upstream of producing the film in the extruder (16).

12. The method according to claim 11, wherein the step of pre-treating comprises pre-chopping and/or pre-grinding said trimmings.

13. The method according to claim 11, wherein the step of pre-treating is performed in line with producing said film made of the plastic material (10).

Description

[0036] In the drawings:

[0037] FIG. 1 schematically illustrates a plant for the recovery of trimmings by re-granulation (or regeneration) in a specific extruder, said plant being produced according to the known art;

[0038] FIG. 2 schematically illustrates a plant for the recovery of trimmings by grinding the trimmings in a so-called mill and subsequent feeding into an extruder of the production line by means of suitable systems, said plant being produced according to the known art;

[0039] FIG. 3 schematically illustrates a trimming recovery plant according to the present invention;

[0040] FIG. 4 shows a shredder positioned directly and coaxially with respect to the extruder according to the present invention;

[0041] FIG. 5 illustrates a grinding mill applied orthogonally with respect to the movement direction of the melt in the extruder and in the feeding system of the extruder itself according to the present invention.

[0042] With reference to FIG. 3: [0043] reference number 10 indicates a film (of any type) complete with trimmings; [0044] reference number 11 indicates a device for cutting the trimmings (which, as is known, can have various embodiments); [0045] reference number 12 indicates the film net of trimmings; [0046] reference number 13 indicates a device for winding or in any case for collecting the film produced; [0047] reference number 14 indicates a device for conveying the trimmings (which, as is known, can have various embodiments); [0048] reference number 15 indicates a device for the pre-treatment of the trimmings (chopping or grinding); [0049] reference number 16 indicates an extruder for treating said trimmings; [0050] reference number 17 indicates a device for dosing and feeding the granules into said extruder; [0051] reference number 18 indicates a device for forming the film (produced according to a known embodiment).

[0052] According to the present invention, the plant for the on-line recovery of trimmings in extrusion lines of plastic material 10 comprises: [0053] a device 11 for cutting side portions, so-called trimmings, from a film 10 of plastic material leaving a device 18 for forming said film 10; [0054] means 14 for conveying said trimmings positioned downstream of said cutting device 11; [0055] an extruder 16 for treating said trimmings; [0056] a device 17 for dosing and feeding granules for the formation of the plastic film in said extruder 16, said extruder 16 and said device 17 for dosing and feeding granules being positioned upstream of said device 18 for the formation of said film 10.

[0057] Said pre-treatment device 15 is provided in combination with said extruder 16.

[0058] In an embodiment, at the inlet of said extruder 16, a pre-treatment device 15 of the trimmings is provided, obtained by cutting side portions of said film 10 and conveyed to said pre-treatment device 15 by said conveying means 14.

[0059] According to the present invention, said pre-treatment device 15 is a pre-chopping and/or pre-grinding device for said trimmings.

[0060] Said pre-treatment device 15 is in line with the devices 16,17,18 for the production of said plastic material 10.

[0061] As illustrated in FIG. 3, said pre-chopping or pre-grinding device 15 of the continuous trimming is provided before it enters the extruder 16.

[0062] The presence of said device 15 essentially creates the possibility of guaranteeing an adequate constancy of feeding of the extruder, which obviously proves to be strongly influenced by the considerable difference in density that is found between the virgin granule (whose feeding must in any case be guaranteed independently) and the trimming.

[0063] More specifically, for production lines in which the quantity of trimming is significant, this pre-chopping or pre-grinding device 15 is important, as the percentage ratio between the quantity of trimming fed and the granule dosed in the extruder can be high.

[0064] For applications typically (but not exclusively) on lines that use the so-called cast technology, in fact, the percentage of trimming can reach very significant levels; in this case, in order to ensure a correct feeding of the extruder (or to the extruders) destined for the recovery of the trimming, it is preferable to pre-chop or pre-grind said continuous trimmings, so as to considerably increase their density with respect to that of the granule.

[0065] This pre-chopping or pre-grinding device 15 can have the most varied construction forms, as it can be represented by a real grinding mill or by a so-called densifier, or again by a shredder, the latter solution preferably, but not exclusively, providing for its positioning coaxially with the extruder itself, so as to provide not only for the chopping of the trimming, but also for conveying (or forcing) it into the extruder 16.

[0066] The pre-chopping or pre-grinding device 15 can be directly or indirectly connected to the extruder 16. In the case of an indirect connection, the two devices are separate, whereas in the case of a direct connection, the two devices form a single element.

[0067] In particular, this latter solution is particularly suitable for the purpose, as it allows a further compacting of the whole, at the same time guaranteeing an efficient feeding constancy.

[0068] In this case, the shredder is generally composed as represented in FIG. 4, which illustrates an extrusion screw 28 directly and coaxially connected to the so-called shredder 29, which can be rotated by the same motor 30 or by two different motors.

[0069] An inlet 31 is therefore present for feeding the trimming (possibly already pre-chopped by means of a multi-cutter system), conveyed by any transporting means 14, and simultaneously also an inlet 32 for the feeding of the granule, which can take place either by gravity (i.e. directly applying a storage hopper in correspondence with said inlet 32) or by means of a dosage screw.

[0070] Finally, the granule can also be fed directly, again by means of a storage hopper, from the mouth of the inlet 31 of the trimming, so as to also ensure a certain pre-mixing of these two elements.

[0071] In any case, the common feature of the above-mentioned pre-chopping or pre-grinding devices 15 is to allow a considerable increase in the apparent density of the trimming, so as to allow its direct feeding into the extruder 16, without the risk of creating bridges in the feeding and therefore having the possibility of obtaining a correct hydraulic seal on the mouth of the extruder 16, without the need for using particular or sophisticated forcing systems, and above all completely eliminating problems linked to the transporting and treatment of the dust inevitably produced in this phase.

[0072] According to a further embodiment, a real grinding mill, of the type described above, can be applied on the feeding mouth of the extruder 16.

[0073] Said grinding mill 24 comprises a rotor equipped with a series of rotating blades which impart a cutting action on the trimming, thanks to the presence of a second series of fixed blades anchored directly to the structure of the extruder 16.

[0074] An example of this grinding mill is illustrated in FIG. 5, which also illustrates, in addition to the mill 24 and relative grid 25, a possible fan 33 positioned below the extruder 16 and specifically below the extruder 16 and in correspondence with the feeding inlet of the mill 24 to the extruder 16. The fan 33 is suitable for sucking the ground trimming and preventing it from creating a bridge which prevents a correct feeding. Said fan 33, when present, has the particular function of preventing the ground material from remaining too long in correspondence with the grid 25. This would in fact lead to an overheating of the material with the formation of a molten layer which would block the passage holes of said grid 25.

[0075] The presence of a fan 33, on the other hand, which acts as a sucker in said position, avoids the overheating of the ground material and has no contraindications as there is no presence of melt in the feeding area of the extruder 16 but only, possibly, granule in the solid state, obviously in addition to the ground material coming from the mill 24.

[0076] FIG. 5 shows in particular the movement direction of the molten mass with the arrow, and the outlet point of the same from the extruder, which can be connected to a filter-change system, to a die or to whatever else is necessary, not shown in the figure.

[0077] The object of the present invention also relates to a method for the online recovery of trimmings in extrusion lines of film made of plastic material 10.

[0078] Said method, according to the present invention, comprises the following steps: [0079] cutting, by means of a cutting device 11, side portions, so-called trimmings, from a film 10 made of plastic material leaving a device 18 for the formation of said film 10; [0080] conveying said trimmings leaving said cutting device 11; [0081] treating said trimmings inside an extruder 16; [0082] dosing and feeding granules for the formation of the film made of plastic material in said extruder 16, said extruder 16 and the device 17 for the dosage and feeding of granules positioned upstream of said device 18 for the formation of said film 10,
the pre-treatment step of the trimmings obtained from cutting side portions of said film 10 is provided in combination with the production of the film in the extruder 16.

[0083] In particular, the pre-treatment step consists of the pre-chopping and/or pre-grinding of said trimmings.

[0084] As described above, the pre-treatment step is in line with the steps for the production of said film made of plastic material 10.

[0085] The plant object of the present invention appears as extremely compact and above all completely eliminates the limits and defects of the two plants previously analyzed, i.e.:

[0086] a) With respect to regeneration, the energy consumption is practically zero, as the power used for the reprocessing of the trimmings is spent directly for the production of part of the finished product, and not for a semi-finished product (i.e. the granule) which is then subsequently re-extruded; the only additional energy consumption with respect to a common extruder is represented by the conveying system of the trimmings and by the pre-grinder, but in both cases these are power values used well below those present in the two known plants described above and illustrated in FIGS. 1 and 2.

b) With respect to regeneration, no additional operator is required, as the extruder 16 is an integral part of the production line, for which one or more operators are already destined.
c) With respect to regeneration, there is no risk of degradation of the material, which is reprocessed only once and therefore does not significantly change its chemical-physical characteristics, making it completely similar from this point of view to the recovery system with a grinding mill.
d) With respect to regeneration, as there is no need to cool the granule produced (as, thanks to the present invention, there is no production of granules from trimmings), there is no need for an independent cooling system and possible subsequent drying.
e) With respect to regeneration, there is no problem with the overall dimensions of the plant, as this is incorporated by the production line, which does not significantly change its overall dimensions in plan or raised views.
f) With respect to regeneration, there is no risk of supply irregularity, as the more constant the production of the entire extrusion line, the more constant the quantity of trimming is, and in any case even in the event of undesired or unavoidable variations, there is the possibility of compensating the missing flow-rate with a dosage of granule (device 17 illustrated in FIG. 3). Furthermore, the presence of a pre-grinding or pre-chopping device 15 completely solves this problem.
g) With respect to the recovery of fluff, there is no generation of dust as, due to the plant conformation, there is no need for conveying the broken or ground trimming, which is charged directly into the extruder 16.
h) With respect to the recovery of fluff, there is no need to create any hydraulic seal on the mouth of the extruder 16, as the trimming is substantially pushed into the same by the same chopping or grinding device 15.
i) With respect to the recovery of fluff, the feeding constancy derives specifically from the fact that, as there is no type of conveying of the chopped or ground trimming from the chopping or grinding device to the extruder, there is no possibility of creating any type of accumulation or stagnation, therefore the constancy of the flow-rate is nevertheless guaranteed.
j) With respect to the recovery of fluff, the overall dimensions are substantially zero, since, as already stated, the extruder 16 which recovers the trimming is an integral part of the production line and consequently does not require the addition of any other type of plant or device, apart from the primary conveying device of the trimming, which in any case represents a truly negligible encumbrance with respect to the rest of the extrusion line, of whatever type it may be.

[0087] The objectives of the invention mentioned in the preamble of the description have thus been achieved.

[0088] The protection scope of the present invention is defined by the enclosed claims.