DE102016117213A1 - Method and apparatus for extruding plastics - Google Patents

Abstract

In a method and a device for extruding plastics, preferably in connection with plastic extrusion granulation, the plastic heated to an extrusion temperature and extruded through one or more nozzles (7) of a nozzle head (1) is irradiated with electromagnetic radiation directly at the nozzle exit such that In the region of the nozzle outlet lingering plastic is heated to an elevated temperature, which is above the extrusion temperature, preferably above the decomposition temperature and optionally even above the combustion temperature of the plastic. At the same time, the nozzle head (1) can be irradiated with the electromagnetic radiation such that the inner wall surface of the nozzles (7) from the nozzle outlet to at least 5 mm into the nozzle head (1) heated to a temperature above the extrusion temperature and preferably below the Decomposition temperature of the plastic is. This serves to avoid plastic deposits on the nozzle outlet.

Description

The invention relates to a method and a device for extruding plastics, preferably in the form of thermoplastic plastic strands for the production of plastic granules. The method and the device can be used advantageously in particular in connection with plastic strand pelletizing plants.

In the plastic extrusion granulation thermoplastic material is extruded in the form of strands and transported via a cooling section to a granulator, in which the cooled strands are then pelletized into granules. The cooling section usually comprises cooling the strands by means of water either in a water bath or a water-purged channel.

Deposits in the form of a so-called "beard", which forms when extruding the plastic at the nozzle outlet of the individual nozzles of the nozzle head next to the actual plastic strand, prove to be problematic. If the beard tears off, there is a risk that it will come with the plastic strand to the granulator and into the granules.

To avoid this, such plastic deposits are usually burned at the nozzle exits by means of gas flames, which can be directed, for example, twice per minute for 10 seconds on the emerging from the nozzle plastic directly on the nozzle exit. For this purpose, a common flame is generated over the entire width of the nozzles usually arranged in a row by means of appropriate gas nozzles.

An alternative to this is in DE 10 2011 106 709 A1 described. Accordingly, the strands are at the exit from the perforated plate of a Anströmfluid impinged, which has a temperature of preferably 50 ° C to 80 ° C above the melting temperature of the plastic material. By heating the nozzle outlet of the plastic is prevented from attaching to the nozzle head. The exit velocity of the Anströmfluids is relatively high, preferably 150 m / s to 200 m / s to remove any deposits.

The energy input associated with the flow is high, in particular due to the need to heat the onflow fluid to the required high temperatures.

The object of the present invention is to propose an alternative for avoiding and / or removing plastic deposits arising at the nozzle exit of an extrusion die head.

This object is achieved by a method and an apparatus having the features of the appended independent claims. In dependent claims advantageous developments and refinements of the invention are given.

Accordingly, a method according to the invention provides for irradiating the plastic, which has been heated to an extrusion temperature and extruded through one or more nozzles of a nozzle head, with electromagnetic radiation directly at the nozzle outlet in such a way that plastic remaining in the region of the nozzle outlet is heated to an elevated temperature above that Extrusion temperature is. Accordingly, a device according to the invention comprises at least one source of electromagnetic radiation, which is set up to appropriately heat the plastic staying in the region of the nozzle outlet by means of electromagnetic radiation.

The heating of the accumulating at the nozzle exit plastic over the extrusion temperature is energetically efficient than first to heat a stream of air and to overheat the extruded plastic with the heated air flow. However, the invention does not exclude that plastic remnants are blown off from time to time by means of an air flow, which may also be hot, whereby this blow-off is preferably carried out in a pulse-like manner.

In particular, thermal radiation is used as electromagnetic radiation, preferably IR radiation. The IR radiation can advantageously be generated by means of one or more IR heating rods, which are arranged close to the nozzle outlet of the nozzle of the nozzle head. The distance is preferably 50 mm or less, more preferably 15 mm or less, and is in any case in the preferred range between 10 mm and 50 mm.

Alternatively, other electromagnetic radiation may also be used, for example laser radiation, since laser radiation can be used in a very targeted manner and with a high energy density. Particularly suitable laser radiation with long wavelengths, for example, the radiation of a CO ₂ laser, since thermoplastics usually absorb well without any additives long-wave radiation.

According to the invention, the use of the electromagnetic radiation can advantageously be used in two respects, namely on the one hand to remove unwanted plastic deposits and on the other hand to prevent such plastic deposits from ever forming, whereby both objectives can also be combined with one another.

According to the first approach, the plastic remaining in the region of the nozzle outlet is heated by means of the electromagnetic radiation to a temperature which is not only above the extrusion temperature but above the decomposition temperature of the relevant plastic. As a result, plastic deposits are dissolved and do not get into the granules. If decomposition residues adhere to the plastic strands and thus get into the granules, these residues are so small and so small in dimension that they are irrelevant to the quality of the granules.

If - preferably - to avoid that it comes to flame formation, the elevated temperature is preferably on the one hand above the decomposition temperature but on the other hand below the combustion temperature of the plastic in question. The combustion or ignition temperature is in the vast majority of plastics about 50 ° C to 100 ° C above the respective decomposition temperature.

Alternatively, however, the elevated temperature may also be above the combustion temperature, so that flame formation intentionally occurs, as occurs in the prior art in the case of burning by means of gas flames. The risk that combustion residues could reach the granulate in relevant quantities with the plastic strands is not critical.

The electromagnetic radiation has no effect on the extruded plastic strands themselves, because the residence time of the plastic strands in the area exposed to the radiation is too short for the strand material to be appreciably heated by the radiation. However, in order to prevent the nozzle head from overheating itself, in particular in the first approach pursued here, in which the elevated temperature is above the decomposition temperature or optionally even above the combustion temperature of the plastic, it may be advantageous to use the irradiation only temporarily, in particular periodically.

According to the second approach, the addition or formation of a beard of the plastic in the nozzle exit area should not occur at all but should be suffocated as far as possible in the bud. This approach is based on the assumption that the beard already arises within the nozzle and is slowly pushed out of the nozzle. To counteract this, the nozzle head is irradiated immediately adjacent to the nozzle exit of the nozzles with the electronic radiation, in such a way that heats the inner wall surface of the nozzle from the nozzle outlet to at least 5 mm, preferably 10 mm into the nozzle head into a temperature, the is above the extrusion temperature and below the decomposition temperature of the respective extruded plastic. Preferably, the inner wall temperature is between 5 ° C and 20 ° C, more preferably between 10 ° C and 15 ° C above the extrusion temperature. When starting the system, the inside wall temperature can also be set to a temperature of approx. 25 ° C above the melt temperature (extrusion temperature) and shortly afterwards reduced to the abovementioned values. Although the nozzles are usually heated anyway, but with significantly lower temperatures for the particular purpose, when starting the extruder in the nozzles "frozen" plastic, ie plastic which has solidified by cooling, melt. This melting temperature is slightly above the melting temperature of the material, but well below the extrusion temperature. The extrusion temperature is the temperature that the plastic melt actually has, in other words the melt temperature. In the case of carbonate, for example, the melting temperature is 220 to 230 ° C, the melting temperature for melting frozen plastic in the nozzle of the nozzle head at about 250 ° C and the actual melt or extrusion temperature of the plastic material regularly well above 250 ° C.

By now according to the second approach, the inner wall surface of the nozzle is maintained at a temperature above the extrusion temperature and preferably below the decomposition temperature, the formation of a bar at the nozzle exit is counteracted from the outset.

By means of radiant heaters, especially IR heating rods, it is now very possible to use thermal radiation targeted. IR heaters can be easily conformed and, for example, as a heating coil, which at least partially surrounds the individual nozzles, be arranged along the row of nozzles and / or around individual nozzles.

Preferably means are provided whereby the radiation source can be displaced away from the nozzles and towards the nozzles to avoid collision with a scraper which is moved over the exit nozzles to initially exit the nozzles after the extruder start-up process strip off escaping plastic before the following plastic is fed to the granulator for pelleting. In that regard, it may be advantageous to temporarily move the radiation source out of the path of movement of the scraper. Also, for cleaning purposes and / or for adjusting the temperatures generated at the nozzles, it may be advantageous to move the radiation source away from the nozzles or closer to the nozzles.

Alternatively or additionally, a collision of the scraper with the radiation source can be prevented if the trajectory of the scraper between the radiation source and the nozzle head extends, so if there is a distance between the radiation source and the nozzle head, in which moves the scraper. According to another alternative, the scraper may advantageously be arranged to be movable between opposing radiation sources along a surface of the nozzle head (for example when the nozzles are arranged in series and one or more radiation sources are arranged on each side of the nozzle row).

Further advantageously, the device further comprises a guide device which serves to guide the extruded plastic during the start of the extruder from the subsequent transport path ("dissipative plate"), so that the extruded plastic does not reach the granulator during the start-up phase, or after Approaching the subsequent transport route zuzuleiten ("feeding plate"), so that the plastic passes only during the actual production phase to the granulator. For this purpose, the guide between a first position in which the extruded from the nozzle plastic falls by gravity on the guide and in which the guide is preferably rinsed with water, and a second position in which the extruded from the nozzle plastic on the Guide device falls past, relocatable. The scraper for stripping the emerging from the nozzle plastic is advantageously coupled to the guide, so that with the stripping of the plastic at the end of the starting process, the guide device moves in or out of the transport path of the extruded plastic, depending on whether it is an zuleitende or dissipative conducting device.

Further features and advantages of the invention will become apparent from the following description of embodiments according to the invention and further alternative embodiments in conjunction with the appended drawings, which show schematically:

1 a device for the extrusion of plastics with a guiding device,

2 a device for the extrusion of plastics with dissipative guide device,

3 a nozzle head in view from below for use with a device according to 1 or 2 .

4 the nozzle head off 3 in longitudinal cross-sectional view,

5 the nozzle head off 3 in cross-sectional view and

6 a variant of the nozzle head from the 3 to 5 in cross-sectional view.

1 shows a Kunststoffstranggranulieranlage with a nozzle head 1 an extruder C, from which plastic strands KS melt out and onto a guide device 2 meet, with the plastic strands KS a subsequent transport chute 3 be fed (leading feeder). The plastic strand pelletizer in 1 is shown in its operating phase, that is, the supplying guide 2 detects the plastic strands KS and directs them designed as an inclined, rigid groove transport device 3 to. The guiding device 2 is connected in a conventional manner to a water connection, and water (H ₂ O) flows over the surface of a plate 2 B (please refer 4 ) continue the gutter 3 down to a revolving conveyor belt 4 , wherein the water takes along the Kunststoffstrange KS. The cooling water is at the bottom of the gutter 3 essentially completely via a drainage device 5 deducted. The conveyor belt 4 serves as a temperature compensation path, so that the temperature profile homogenized over the cross section of the plastic strands before the plastic strands a granulator 50 be fed to the local granulation.

Instead of the circulating band 4 It is also possible to provide other assemblies for the treatment of the plastic strands. The circulating band 4 If necessary, it can also be completely eliminated or equipped with additional elements such as blowing nozzles or water spray nozzles.

The guiding device 2 can from the in 1 shown operating position in a start-up position, not shown, are preferably displaced in the direction perpendicular to the plane of the drawing. Each time you move from one position to the other position, the plastic strands become one in the following 3 to 6 Detector shown in detail 9 separated. If now in the case of in 1 shown Kunststoffstranggranulieranlage with zuleitender guide 2 the guiding device 2 is displaced perpendicular to the image plane, meet the ends of the following plastic strands automatically on the second, to a waste granulator 60 leading transport facility 10 , which is also designed as an inclined, rigid, wasserbespülte gutter. When then occupied, designated as the start position position of the guide 2 The plastic strands KS are thus directly in the waste granulator 60 granulated.

In 2 a corresponding Kunststoffstranggranulieranlage is shown, in which the guide device 2 However, is designed as a discharge guide. Shown is the Kunststoffstranggranulieranlage in this case in its start-up phase, that is, from the extruder 1 molten plastic strands KS impinge on the surface of the guide 2 on and are taken from the cooling water H ₂ O and the transport device 10 fed, the plastic strands in the example shown directly to the waste granulator 60 feeds.

Once the plastic strands KS have the desired consistency, the guide is 2 from her in 2 shown start-up position, preferably in a direction perpendicular to the image plane, wherein the plastic strands KS are simultaneously severed by means of a separating knife, again not shown in this figure. The ends of the following plastic strands fall then vertically down directly on the water-washed gutter 3 and, as related to above 1 explained, the production granulator 50 fed.

Both Kunststoffstranggranulieranlagen is furthermore common that they are a source 6 for electromagnetic radiation comprising one or more IR heating elements in these embodiments.

3 shows a nozzle head 1 as described in connection with the embodiments according to 1 and 2 can be used in a view from below. In this particular embodiment, the source becomes 6 formed for electromagnetic radiation by a single IR heating element, by means of a current or voltage source 8th is heated and emits electromagnetic radiation in the form of heat radiation, in particular IR radiation. The IR heating element 6 extends to both sides of a series of nozzles 7 of the nozzle head 1 from which extruded plastic at the extrusion temperature in the form of plastic strands KS exudes molten. The IR heating element 6 is near the nozzle exit of the nozzles 7 arranged so that the heat radiation at least that from the nozzles 7 leaking plastic reached directly at the nozzle exit. The distance of the IR heating element 6 from the nozzle outlets of the nozzles 7 and the temperature of the heating element 6 are chosen so that in the area of the nozzle exit lingering plastic is heated to an elevated temperature, which is above the extrusion temperature. The extrusion temperature is the temperature, averaged over the strand cross-section, of the extruded plastic at the nozzle exit of the nozzles 7 , also referred to as the melt temperature. Instead of a heating rod 6 can also use several heating elements 6 are used, for example, in each case one heating element to each side of the row of nozzles 7 or one heating element per nozzle. In particular, the heating element (s) can completely or at least partly surround the individual nozzles, as in FIG 3 shown where the heating element 6 as a heating coil at the row of nozzles 7 is guided along.

As previously mentioned, the electromagnetic radiation source serves 6 or the IR heating element to heat any remaining in the nozzle outlet plastic to a temperature above the extrusion temperature, said temperature is preferably above the decomposition temperature of the plastic. The decomposition residues of the plastic are so small in comparison to the total plastic throughput that they do not affect the quality of the plastic granules produced, as far as they even into the granulator 50 reach.

Alternatively, the temperature of plastic staying in the region of the nozzle outlet can even be heated above the combustion temperature of the plastic by means of the electromagnetic radiation source, although this is less preferred. The plastic burns then similar to the prior art when burning by means of a gas flame.

For energetic reasons, the electromagnetic radiation source 6 operated only temporarily, especially when the device is operated in the mode that the residing in the region of the nozzle outlet plastic is heated to a temperature above the combustion temperature of the plastic elevated temperature, so burned in this case only from time to time any plastic residues at the nozzle outlet become. Optionally, the decomposition or combustion residues may be blown away by a blowing device which may be cyclically operated (not shown in the figures).

By means of the electromagnetic radiation source 6 , In particular, also by means of the heating element specifically used here, the radiant energy can be introduced locally very targeted. According to a preferred variant, not only any plastic which lingers in the area of the nozzle outlet is heated to an elevated temperature above the extrusion temperature, but also the nozzle head 1 itself becomes immediately adjacent to the nozzle exit of the nozzles 7 irradiated with the electromagnetic radiation. The radiant energy is chosen so that the inner wall surface of the nozzles 7 from the respective nozzle outlet to at least 5 mm, preferably at least 10 mm, in the nozzle head 1 heated to a temperature which is above the extrusion temperature and below the decomposition temperature of the plastic. This will cause the formation of a plastic bar at the exit of the nozzles 7 counteracted.

As previously described in connection with the description of 1 and 2 mentioned, serves in the start-up phase of Kunststoffstranggranuliervorrichtung a scraper 9 In addition, the plastic strands generated in the start-up phase from the nozzle head 1 Separate before the subsequent plastic strands the granulator 50 be fed for granulation. To a collision of the scraper 9 with the electromagnetic radiation source 6 To avoid, may be provided, not shown in the figures, means with which the radiation source 6 from the nozzles 7 away and after the stripping process can be moved close to the nozzles again.

The 3 to 5 on the one hand, and 6 On the other hand, on the other hand, show two preferred embodiments, which such means for displacing the radiation source 6 can make dispensable. In the embodiment according to the 3 to 5 is a wiper 9 , which may be formed for example as a separating knife, for stripping the from the nozzles 7 emerging plastic strands provided between the radiation source 6 and the nozzle head 1 along a surface of the nozzle head 1 is movable. The direction of movement is in 3 indicated by two arrows. The scraper 9 is in turn about a holder 10 with the guide device 2 firmly coupled, as in the 4 and 5 is shown schematically in two orthogonal cross sections. Also in 4 is the direction of movement of the scraper 9 and the guide 2 indicated by two arrows. When the scraper 9 together with the guide device 2 from his in 4 shown position is moved to the left in a position in which the guide 2 below the nozzle head 1 is located, then during this movement from the nozzles 7 of the nozzle head 1 exiting plastic strands by means of the scraper 9 severed and the subsequent plastic strands fall onto a water-rinsed plate 2 B and be with the from the water supply 2a escaping water (H ₂ O) taken. The coupling of the scraper 9 with the guide device 2 over the holder 10 is well recognizable schematically in 5 shown.

6 shows in contrast a second embodiment. Instead of the wiper 9 between the radiation source 6 and the nozzle head 1 move along, is the scraper 9 here between radiation sources 6 concerning the nozzles 7 face each other along the surface of the nozzle head 1 movable. This arrangement allows the radiation source 6 even closer to the surface of the nozzle head 1 to arrange.

The following table shows typical extrusion temperatures and decomposition temperatures of common plastics. The combustion or ignition temperature is in most plastics about 50-100 ° C above the decomposition temperature. It should be noted that the decomposition is not exclusively temperature dependent. Even at lower temperatures and correspondingly long time, plastics can decompose. Some plastics (eg, PET, PA) are hygroscopic, and in the presence of H ₂ O (steam), at elevated temperature, a reversal of the condensation reaction, ie, molecular chain degradation, occurs. plastic Extrusion temperature [° C] Decomposition temperature [° C] LDPE 180-200 > 340 HPPE 210-240 > 340 LLDPE 190-230 > 340 PP 190-240 > 330 PC 260-290 > 350 PET 260-280 > 300 PA6 240-260 > 300 PS 180-220 > 300 PMMA 180-240 > 280

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102011106709 A1 [0005]

Claims (15)

Process for extruding plastics, preferably in the form of plastic strands (KS) for the production of granules, comprising the following steps: - extruding the plastic heated to an extrusion temperature through one or more nozzles ( 7 ) of a nozzle head ( 1 ) and - irradiating the from the nozzles ( 7 ) exiting plastic directly at the nozzle exit with electromagnetic radiation such that in the region of the nozzle outlet lingering plastic is heated to an elevated temperature, which is above the extrusion temperature. The method of claim 1, wherein the elevated temperature is above the decomposition temperature of the plastic, preferably below the combustion temperature of the plastic. The method of claim 1 or 2, wherein the electromagnetic radiation heat radiation, preferably IR radiation, more preferably by means of one or more IR heating elements ( 6 ) is generated IR radiation. Method according to one of claims 1 to 3, wherein the irradiation takes place only temporarily. Method according to one of claims 1 to 4, wherein also the nozzle head ( 1 ) immediately adjacent to the nozzle exit of the nozzles ( 7 ) is irradiated with the electromagnetic radiation. The method of claim 5, wherein the irradiation of the nozzle head is such that the inner wall surface of the nozzle ( 7 ) from the nozzle outlet to at least 5 mm, preferably at least 10 mm, into the nozzle head ( 1 ) is heated to a temperature which is above the extrusion temperature and preferably below the decomposition temperature of the plastic. Device for the extrusion of plastics, preferably in the form of plastic strands (KS) for the production of granules, comprising: - a nozzle head ( 1 ) with one or more nozzles ( 7 ) for extruding molten plastic and - at least one source ( 6 ) for electromagnetic radiation, which is adapted to heat in the region of the nozzle outlet lingering plastic by means of electromagnetic radiation. Apparatus according to claim 7, wherein the radiation source ( 6 ) comprises one or more IR heating elements. Apparatus according to claim 7 or 8, wherein the nozzles ( 7 ) of the nozzle head ( 1 ) in at least one row and the radiation source ( 6 ) on both sides of the row of nozzles ( 7 ) are arranged. Device according to one of claims 7 to 9, wherein the radiation source ( 6 ) the individual nozzles ( 7 ) at least partially encloses. Device according to one of claims 1 to 10, comprising means for displacing the radiation source from the nozzles ( 7 ) away and to the nozzles ( 7 ). Device according to one of claims 7 to 11, wherein a scraper ( 9 ) for stripping from the nozzles ( 7 ) leaving plastic is provided between the radiation source ( 6 ) and the nozzle head ( 1 ) along a surface of the nozzle head ( 1 ) is movable. Device according to one of claims 7 to 11, wherein a scraper ( 9 ) for stripping from the nozzles ( 7 ) leaving plastic is provided between radiation sources ( 6 ) with respect to the nozzles ( 7 ) are opposed to each other along a surface of the nozzle head ( 1 ) is movable. Device according to one of claims 7 to 13, comprising a guide device ( 2 ) between a first position in which the from the nozzles ( 7 ) extruded plastic due to gravity on the guide device ( 2 ) and in which the guiding device ( 2 ) is preferably rinsed with liquid (H ₂ O), and a second position, in which the from the nozzles ( 7 ) extruded plastic on the guide device ( 2 ) falls past, is relocatable. Device according to claim 14, comprising one with the guide device ( 2 ) coupled scrapers ( 9 ) for stripping from the nozzles ( 7 ) leaking plastic.

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