Extruder for plastic granules

The invention relates to an extruder for plastic granulate according to the preamble of claim <b>1</b>,

In the extrusion process, plastic granules, in particular for a polymer, which is suitable for example for a spinning process, have generally the process steps drying, feeding, melting, degassing and land application are executed. In the conventional systems is the first process step of drying by a dryer realized, which is generally independent of the actual extrusion process in a continuously in a separate drying apparatus or discontinuously running process is carried out. The spin dry Granules is then fed to an extruder in which run the further steps to the application, the Degassing is directly dependent on the degree of drying of the granules.

In EP 0134977 B1, an extruder of the type mentioned is described. It forms a device for removing volatile Components of plastic material for molding by is conveyed and plasticized a plasticizing screw. This plasticizing screw is a heated cylinder arranged through which the particulate plastic material is received. The plasticizing screw consists of a real and plasticizing a thereto arranged upstream conveyor section. An upstream to this Plasticizing screw arranged additional auger conveys the material to be extruded in a suction channel, from which it in the Conveying section of the plasticizing screw falls. Since the cylinder in which the plasticizing screw works, is heated and then extruded to the Material through the work of the plasticating energy is supplied to escape volatile components, so that the granules also can be dried to some extent. These volatiles be via the suction line out of the cylinder, in which the plasticating works, dissipated. To ensure this removal, the screw conveyor and the plasticating screw are driven so that supplied only such a quantity of granules of the plasticating is that it in the region of the suction line, that is to say in the conveying section, is only partially filled.

With regard to the effectiveness of the drying of the pellets has the disadvantage this known device, among other things, that the granulate only is indirectly heated. Firstly occur by energy losses, and secondly an additional device is also necessary, which ensures a vacuum for sucking off the volatile components, what additional energy is required. Therefore, the known Device are only partially used for drying the granules. they is instead primarily for removing volatiles from a plastic material to be extruded.

In DE 44 28 867 A1, a machine is described and illustrated, for direct processing of uncrushed or coarse pre-shredded thermoplastic Moldings and semi-finished products used. Here are new products such as Cassette housing, office items, bags or semi-finished products such as granules, profiles and films are produced. In this known machine is a usual Extruder preceded by a catchment area in which the extruder screw a has markedly increased diameter. The uncrushed or roughly crushed thermoplastic moldings and semi-finished products are a Air or other flow into the intake region of the extruder screw sucked surrounding cylinder, characterized between the displacement elements of brought worm, compressed and conveyed to the downstream extruder. Since the air current for sucking the moldings and semi-finished products, a hot air stream may be a drying effect can be achieved, and the catchment area of the machine may be referred to as a drying chamber, in which as Conveying screw that part of the extruder screw is arranged, the Diameter is enlarged.

This known machine is not for melting plastic pellets provided, rather explicitly stated in DE 44 28 867 A1, that should be a final granules of this machine (column 1, lines 14 to 18, Summary). Granules could be on this machine can not process, because it in its small grain size in the cylinder wall of the catchment area would clog holes arranged for sucking in the air stream. The routing and dimensioning of the directed from top to bottom airflow aimed mainly thereafter, the lump moldings and semi-finished products to suck and compress. Therefore in case the functions of degassing and drying compromises, in particular a stronger warming of the material are avoided in the region of the screw conveyor.

It is therefore an object of the invention to provide an extruder of the type mentioned, is what carried in a compact design, which in addition to a drawing, Melting, degassing and application of plastic pellets also ensures the effective drying and which energy economically operable.

This object is in accordance with an extruder having the features Claim 1 dissolved. Expedient developments are defined in dependent Claims defined.

According to the invention, the extruder for plastic granulate which In particular, an appropriate for the spinning process the polymer be a Extruder screw to a plasticizing and conveying section, which in a heatable cylinder rotatable by a drive device is. Furthermore, the extruder is in an integrated unit two-stage design, wherein the extruder screw a screw conveyor is connected upstream, which is arranged in a drying chamber. These Auger conveys the plastic granules without compression to the extruder screw. According to the invention, the screw conveyor relative to the extruder screw a larger outer diameter. Preferred is moderation the feed screw with a greater cut displacer provided as the extruder screw. Furthermore, the auger is to Drying of the plastic granulate heatable. This configuration the conveyor screw is achieved that the screw conveyor a large heat-emitting surface forms that directly transfers the heat to the adjoining plastic pellets emits. The geometric configuration also permits long residence times of the granules inside the drying chamber, so that a uniform and very high level of dryness Plastic granulate is achieved. The displacer is here by one of the auger spiral orbiting scroll formed.

In order to increase the drying of the plastic granulate, it is advantageous if between the screw conveyor and the drying chamber an air gap is formed, so that the residence times of the granules significantly increase or the conveying effect reduced.

In a particularly advantageous embodiment of the invention, the screw conveyor is with a plurality of peripherally arranged displacement elements educated. Thereby, the displacement elements as paddles, paddle etc. executed. Such displacement elements lead to a very good mixing the plastic granules. Thus, the uniformity the drying within the granule further improved.

The drying effect in the drying chamber can be inventively improved by supplying a drying medium further with which the Plastic granulate is applied to the drying. Characterized in that the Displacement elements are arranged on the screw conveyor so that the Plastic granulate is heavily mixed with low conveying action, and characterized in that in the region of the drying chamber by supplying a Drying medium an active drying process is realized, it is possible to form a dry granulate, which in the further processing in the extruder requires essentially no degassing.

Thus, the drying process can be effectively realized, is a Inlet judge this drying chamber fed only as much granulate that the space between the displacing elements of the screw conveyor and Drying chamber still a reliable and intensive flowing around the to can provide dried granules. Preferably, the Drying medium with a corresponding excess pressure in the drying chamber blown, so that, after passing through the drying process has, is discharged via a Entweichleitung. To the drying medium to still use energy contained on, can the Drying medium recykliert, wherein prior to its re-blowing in the drying chamber again has to be heated to such an extent that the temperature loss of the drying medium as a result of heat transfer to the granulate is compensated.

According to a preferred embodiment has the feeding screw of the A drying chamber formed in the interior of their wave channel, ie it is hollow, and is connected to this channel, between the displacement elements arranged exit bores, via which the Drying medium the actual drying area between the displacement elements the auger fed. Preferably, these Exit holes radially around the circumference of the shaft of the screw conveyor arranged between the displacer. Preferably, they are on the Circumferentially arranged evenly. The particular advantage of this embodiment is that the feed screw by the hot drying medium is heated. Depending on the design of the channels, an electric Heating the feed screw omitted.

According to a further preferred embodiment, the drying medium introduced into the drying chamber so that it countercurrently is guided to the conveying direction of the plastic granules. Preferably is the drying medium hot air.

According to another preferred embodiment, the extruder screw and the screw conveyor arranged to each other that both Snails are driven together by a drive device. Here, the transmission of the drive motion through a gear take place between the extruder screw and the screw conveyor. This is particularly advantageous in order to realize any translations can. A particularly compact design is achieved in that the extruder screw and arranged the auger on a common shaft are.

A further advantage of such an extrusion apparatus according to the invention is that a very compact extruder can be achieved because both the drying chamber and the cylinder in an integrated unit are zusammenfaßbar.

According to a further preferred embodiment, the transition region between the diameter of the conveyor screw and the diameter the extruder screw substantially continuously formed. Under continuously in this context is essentially cone-shaped be understood. By such a tapered transition between different diameter ranges takes place a continuous and uniform filling of the extruder screw with the plastic pellets.

A particularly energy-economic development of the invention Extruder is then obtained when the drying medium essentially by means of a heat transfer device can be heated, in which the Energy is used, which at the compression of the plastic granulate in the extruder screw is released by this energy to the drying medium Gets transferred. The light emerging from the drying chamber drying medium or a portion thereof is preferably the heat transfer device supplied, whereby the energy loss of the Drying medium, which is due to energy transfer to the granules learns is compensated.

According to a further preferred embodiment is between the drying chamber and the barrel of the extruder according to the invention a metering device arranged at the cross-section of the passage opening for regulating the residence time of the plastic granules in the drying chamber is changeable. Such, Metering variable passage opening allows to the drying chamber easily different moisture levels to be dried granules adaptable is without significant changes to the procedure in With respect to temperature of the drying medium or amount of the Drying chamber supplied granulate must be made. Preferably, the metering device is designed as a diaphragm whose passage opening can be regulated via an adjustable slide.

According to still another preferred embodiment is also the Housing the drying chamber heated. This results in a higher Flexibility in drying, because to be dried in the process implementation Granulate both the area of ​​the feed screw itself over the Drying medium as well as the wall surrounding the screw conveyor an appropriate power supply undergoes.

Since during the extrusion process the plastic granules as it passes through extruding the work is fed is increased its internal energy, whereby volatile constituents are expelled. Therefore, in a further preferred embodiment of the invention in the wall of the surrounding the extruder screw cylinder at least an outlet for Draining vacant or forming gases provided. Depending on the type the gases may be those collected or vented into the open air.

The drying of the granules in the drying chamber is thus carried mechanical energy in the form of friction, heat transfer via the contact of the granular material to be dried to the surface of the screw and by heat transfer during flow around the granule with reached the drying medium.

In addition to the regulation of the residence time of the material to be dried in the medium Drying chamber of the two-stage extruder by means of the metering device can also be used to this metering device, a relined to realize operation of the extruder in the actual Extrudierstrufe.

Further advantages, features and application possibilities of the present Invention will now by means of embodiments with reference explained in greater detail to the drawings.

In the drawings:<dl tsize="7" compact="compact"><dt>Fig. 1</dt><dd>a two-stage extruder having drying step and extruding according to the invention with a drive of the common shaft from the side of the extruding;</dd><dt>FIG. 2</dt><dd>An embodiment according to the invention with a drive for conveying screw and the extruder screw from the side of the drying step;</dd><dt>Fig. 3</dt><dd>An embodiment of the invention shown in FIG. 2, but with continuous transition between the drying step and the Extruding stage.</dd></dl>

In Fig. 1, an inventive two-stage extruder is shown, which an extruding step 1 and a drying stage 23 comprises. In the Extruding stage 1 is an extruder screw 3 rotatably in a cylinder 5 arranged. The extruder screw 3 has on the inlet side with the Inlet 12 a conveyor section 21 and on the outlet side to the outlet a plasticizing portion 22. In the drying stage 23 is a feed screw 4 is rotatably arranged in a housing thirteenth Between the Screw conveyor 4 and the housing 13 is a drying chamber 2 educated. The screw conveyor 4 has a plurality of peripheral displacement elements 24 are arranged, which project into the drying chamber 2nd The displacement elements 24 For example, disks, paddles, blades or be a helical gear forming screw.

Both the extruder screw 3 and the screw conveyor 4 are on a common shaft 7 arranged. Thus, the actual compression process can run in the extruding stage 1, extends the helical Displacer (screw) of the extruder screw 3 substantially to to the inner surface of the cylinder. 5

In the drying stage 23 is to be dried granules 18, which the drying chamber 2 preferably consists of a hopper 17 is controlled supplied, merely circulated through the screw conveyor 4 and promoted, but not compressed. The amount of displacement elements 24 of the screw conveyor 4 is so designed that the outside diameter of the Envelope is smaller than the inner diameter of the cylindrical Housing 13 and define an air gap 26th Through this radial Annular space is an improved heat exchange between a heating medium 10 and to be heated granules 18 possible. Furthermore, is characterized the residence time increases. The drying medium is hot air 10 which is supplied via a channel 9 in the interior of the screw conveyor. 4 This inner channel 9 is about radially trained supply channels 8, which between out the displacement elements to the outer periphery of the screw conveyor 4 are connected. The supplied so via the channel 9 drying medium flows through the 8 channels in the region between the displacement elements, in which to the granules 18 deposits.

The flow rate of the drying medium 10 is chosen so as that an effective heat exchange between the him and the Granulate is obtained. The outlet opening 16 for the drying medium is arranged approximately in the middle of the longitudinal extension of the drying chamber the second Thereby, a part of the granular material to be heated 18 in a countercurrent process, the other part of the co-current process in which Annulus heated.

It is also possible, the drying medium together with the granules 18 supplied via the funnel 17 of the drying chamber. 2 In the area the drying chamber 2 is supported in a bearing 20 auger 4 provided with a heater 15th This heater 15 may be an electrical heater, but it can also as an oil heater be formed. It serves a higher flexibility of the drying step achieving 23rd In principle, it is thus possible drying of the granules 18 by supplying a drying medium 10 and / or by Providing the screw conveyor 4 with a heating device 15 and / or the Housing 13 of the drying chamber 2 in addition to a heater to achieve.

is in the transition area of ​​the drying chamber 2 to the cylinder 5 a metering means 11 disposed in the form of a diaphragm. This diaphragm with respect to the passage opening 25 adjustable, as indicated by the double arrow is indicated. For this purpose, a slide 29 is adjusted. By regulation the passage opening 25 of the diaphragm 11, it is possible, the residence time the granules 18 in the first processing stage of the extruder to vary, so an individual degree of drying of the granules, which is dependent on the polymer, is adjustable. The area in the drying chamber 2 uncompressed granular 18 passes through the passage opening 25 to the inlet 12 in the extruding stage 1. Compressing by means of the extruder screw 3 is to be extruded medium further heated, whereby volatile depending on the degree of drying ingredients are released. These volatiles could via an outlet opening 14 escape; they are there, according to their type and composition collected or released into the atmosphere. is the end of the extruding stage 1 a radially directed outlet 19 is provided through which the full extruded plastic pellets exiting.

In the described embodiment, the drying medium 10 is on the side of the drying stage 2 the inner axial channel 9 of the screw conveyor 4, respectively. Therefore, the drive unit 6 is for the common Shaft 7 of the extruder screw 3 and the screw conveyor 4 on the side of the Extruding unit 1 arranged.

In Fig. 2 is another embodiment of the inventive extruder represented essentially the embodiment of FIG. 1 corresponds. In contrast to the extruder of FIG. 1 is the supply of the drying medium 10 in the past in the screw conveyor channel 4 9 via a radial channel guide through the housing block of the drying chamber 2 out. is at such a supply of the drying medium 9 it is possible, the drive means 6 for the conveyor screw 4 and the Extruder screw 3 still on the side of the drying stage 23 to arrange. The heating means of the screw conveyor 4 is not shown in Fig. 2. In this embodiment, the screw conveyor 4 and the Extruder screw 3 formed by two shafts, the transmission by means of a 27 are coupled together. Here, the screw conveyor 4 and the Extruder screw operated at different speeds, the by the gear ratio of the transmission 27 and the drive means 6 determined. The auger 3 is on one side by a Bearing 20 mounted in the housing 13 of the drying chamber. 2 The extruder screw 3 is supported on the inner wall of the cylinder 5 in the extruding 1 from.

The outlet channel 16 for the drying medium 10 from the drying chamber 2 is arranged in the vicinity of the granulate feed hopper 17th This substantially complete counterflow principle to be heated or realized to be dried granules 18 by the drying medium 10 opposite to the conveying direction of the conveyor screw 4 passes. The advantage of Counter current process is in manner known per se in an improved Heat transfer from the drying medium 10 to the granule 18th

Due to the arrangement of the drive motor 6 on the side of the Drying stage 2 it is possible, an axially arranged outlet opening 19 provide from the extruding. 1 This structural form may therefore continue the measures required to achieve reduction of the extrusion process Energy expenditure contribute because of the discharge of the completely extruded Plastic granules without additional deflection at the end of the extruding 1 takes place.

In Fig. 3, a further embodiment of the invention is shown, which the embodiment shown in FIG. 2 corresponds essentially, but in which in the area between the drying chamber 2 and the Cylinder 5, that is, the auger 4 of the drying chamber 2 with larger diameter and the extruder screw 3 of the extruding stage 1 provided a smaller diameter, a substantially continuous transition is. The continuous transition is in the form of a cone-shaped, realized that the funnel-shaped inlet 12th

From a filler neck 17 the plastic granules 18 passes directly into the Drying chamber 2. The hollow formed in the drying chamber 2 Auger is supplied with hot drying medium 10, which on radial channels formed in the helical passages 8 to the outside to the led to be dried plastic pellets. The uniform Pitch of the screw and through the annular space between the outer circumference of the screw and the inner periphery of the housing 13, the granules 18 only conveyed in the drying chamber 2, but not compacted. During this promotion, the granules 18 is dried accordingly. There the outlet channel 16 for the drying medium from the drying stage 2 is arranged in the region of the entry of the granules 18, is a counter-current principle, during heating of the granular material 18 by the drying medium in the drying stage 2 is almost realized.

The dried granules 18 is over the inlet 12 to the cylinder 5 the extruder screw 3 out. A dosage of the granules is in this case by a trained end of the drying chamber 2, paragraph 28 reached, the displacing element of the screw conveyor 4 without an air gap wrapped. Thus one passes through the incision of the screw conveyor 4 predetermined amount of granules continuously for extruder screw 3. The Compression and the other extrusion then take place in the extruding 1. In the lower, that is downstream third of the extruding 1 could be an outlet channel 14 for free by the extrusion process Volatile constituents are provided, if the degree of drying of the Granules requires. The outlet 19 for the finished extruded plastic pellets is realized axially, as the drive of the common shaft 7 for the extruder screw 3 and the screw conveyor 4 on the side of the is drying chamber 2 realized by the common drive unit. 6 In this arrangement also, the cylinder 5 and the drying chamber 2 incorporated in a common housing thirteenth

The described embodiments have in common that the drying chamber 2 and the screw conveyor 4 with a larger diameter are performed while the diameter of the compression portion, the ie the cylinder 5 with the extruder screw 3 is running low. Furthermore, it is an intermediate of the conveyor screw 4 and the housing 13 annular air gap 26 is formed so that high residence achieved are lying up to 1 hour in the range of about 20 minutes. The Screw conveyor 4 has also correspondingly low-cut or large incision at the periphery Inappropriate displacing 24 in order a large heat-emitting surface for drying the granulate to have.

Moreover, in the described embodiments, the axial Expansions of the drying chamber 2 and the cylinder respectively almost same run. However, it is also possible that the drying section made longer, the compression section is performed on the other hand is shorter. This differs depending on the degree of dryness to be obtained or to the polymer used and, moreover, to be achieved after the Degree of compression. In addition, it is also possible that both stages with are formed almost the same diameter, but the worm in each case different slopes have. In the drying chamber 2 is in such an embodiment, the pitch of the screw in the substantially constant while it is variable in the compression zone. Preferably, in the compression zone is a decreasing channel depth provided.

LIST OF REFERENCE NUMBERS

<dl tsize="3" compact="compact"><dt>1</dt><dd>extruding</dd><dt>2</dt><dd>drying chamber</dd><dt>3</dt><dd>extruder screw</dd><dt>4</dt><dd>auger</dd><dt>5</dt><dd>cylinder</dd><dt>6</dt><dd>drive means</dd><dt>7</dt><dd>wave</dd><dt>8th</dt><dd>Channels, outlet bore</dd><dt>9</dt><dd>channel</dd><dt>10</dt><dd>drying medium</dd><dt>11</dt><dd>metering</dd><dt>12</dt><dd>Inlet</dd><dt>13</dt><dd>housing</dd><dt>14</dt><dd>outlet opening</dd><dt>15</dt><dd>heater</dd><dt>16</dt><dd>outlet channel</dd><dt>17</dt><dd>hopper</dd><dt>18</dt><dd>Plastic granulate</dd><dt>19</dt><dd>outlet</dd><dt>20</dt><dd>warehouse</dd><dt>21</dt><dd>conveyor section</dd><dt>22</dt><dd>plasticizing</dd><dt>23</dt><dd>drying stage</dd><dt>24</dt><dd>displacer</dd><dt>25</dt><dd>Passage opening</dd><dt>26</dt><dd>air gap</dd><dt>27</dt><dd>gear </dd><dt>28</dt><dd>paragraph</dd><dt>29</dt><dd>pusher</dd></dl>