Extruder for plastic granules

The invention relates to an extruder for plastic granulate according to the preamble of claim. 1

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

In EP 0134977 B1 an apparatus for removing volatile components from plastic material is described, which is fed and plasticized for molding by a plasticating screw. This plasticizing screw is a heated cylinder arranged through which the particulate plastic material is taken. The plasticizing screw is made of a proper plasticizing section and a thereto arranged upstream conveyor section. An upstream plasticating screw for this additional disposed auger conveys the material to be extruded in a suction channel, from which it falls into the conveying section of the plasticating screw. Since the cylinder in which the plasticating screw is working, is heated and as the material to be extruded is supplied through the work of the plasticating screw energy escaping volatile components, so that the granules can be dried also in some extent. These volatiles are via the suction line out of the cylinder, in which the plasticating screw operates dissipated. To aware afford this discharging, the conveyor screw and the plasticating screw are driven so that only such an amount is supplied to granules of the plasticating screw, that it is filled only partially in the area of ​​the suction line, that is to say in the conveying portion.

With regard to the effectiveness of the drying of the pellets, the disadvantage of this known device, inter alia in the fact that the granulate is only indirectly heated. Firstly occur by energy losses, and secondly an additional device is also required, which ensures a vacuum for sucking off the volatile constituents, for which additional energy is required. Therefore, the known device are only partially used for drying the granules. She is instead primarily for removing volatile constituents from a product to be extruded plastic material.

It is therefore an object of the invention to provide an extruder, which is designed in a compact design, ensuring which is featured with feeding, melting, degassing and application of plastic granules and the effective drying and which is energy-economical operation.

This object is achieved through an extruder having the features according to claim. 1 Expedient developments are defined in the dependent claims.

According to the invention Assigns the extruder for plastic granulate which can be a suitable for the spinning process the polymer particular, an extruder screw having a plasticizing and conveying section on which is rotatably disposed in a heated cylinder by a drive device. Furthermore, the extruder in an integrated constructional unit is formed in two stages, the extruder screw is preceded by a screw conveyor, which is arranged in a drying chamber. This auger conveys the plastic granules without compression to the extruder screw. According to the invention the screw conveyor relative to the extruder screw to a larger outer diameter. Preferred dimensions the screw conveyor is provided with a larger cut than displacing the extruder screw. Furthermore, the screw conveyor for drying the plastic granules is heatable. This embodiment of the screw conveyor is achieved that the screw forms a large heat-emitting surface that emits directly transfers the heat to the adjacent plastic granules. The geometric configuration also permits long residence times of the granules inside the drying chamber, so that a uniform and very high degree of drying of the plastic granulate is achieved. The displacement element is formed in this case by one on the conveyor screw spiral orbiting scroll.

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 decrease the conveying effect.

In a particularly advantageous embodiment of the invention, the screw conveyor is designed with several circumferentially arranged displacement elements. The displacement elements can be designed as blades, paddles, etc.. Such displacement elements lead to a very good mixing of plastic granules. Thus, the uniformity of drying within the granulate is further improved.

The drying effect in the drying chamber can be inventively improved by supplying a dry 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 granules are strongly mixed at low conveying effect, and in that in the region of the drying chamber by supplying a drying medium an active drying process is realized, it is possible to produce a dry granule what need in the further processing in the extruder substantially no degassing.

Thus, the drying process can be effectively implemented only as much granulate is fed via an inlet funnel this drying chamber, the space between the displacer of the screw conveyor and the drying chamber can still guarantee a reliable and intensive flowing around the material to be dried granules. Preferably, the drying medium is blown with a corresponding pressure in the drying chamber, so that, after it has passed through the drying process, is discharged via a Entweichleitung. To use the energy still contained in the drying medium further, the drying medium can be recykliert, where it has to be heated before it is re-injection into the drying chamber, as usual, that the loss of temperature of the drying medium is compensated as a result of heat loss to the granule.

According to a preferred embodiment, the screw conveyor of the drying chamber has a formed in the interior of its shaft channel, ie it is designed to be hollow, and with this channel is connected, is arranged between the displacement elements of exit holes through which the drying medium is the actual drying area between the displacement elements of the screw conveyor can be fed , Preferably, these exit holes are arranged radially around the circumference of the shaft of the auger between the displacer. Preferably they are arranged uniformly over the circumference. The particular advantage of this embodiment is that the screw conveyor is heated by the hot drying medium. Depending on the design of the channels can be dispensed with an electrical heating of the feed screw.

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

According to a further preferred embodiment, the extruder screw and the screw conveyor are arranged to one another such that the two augers are driven jointly by a drive device. Here, the transmission of the drive motion through a gear between the extruder screw and the feed screw can take place. This is particularly advantageous in order to realize arbitrary translations can. A particularly compact design is achieved in that the extruder screw and the feed screw are arranged on a common shaft.

Another advantage of such an extrusion device according to the invention is that a very compact extruder is 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 of the extruder screw is substantially continuously formed. Under continuous is to be understood in this context, substantially conical. By such a tapered transition between the 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 inventive extruder arises when the drying medium essentially be heated by means of a heat transfer device in which the energy is used, which is released during the compression of the plastic resin in the extruder screw, by this energy is transferred to the drying medium. The light exiting the drying chamber the drying medium or a portion thereof is preferably the heat transfer device supplied, whereby the energy loss of the drying medium which undergoes it by energy output to the granulate, is compensated for.

According to a still further preferred embodiment is arranged between the drying chamber and the cylinder of the extruder a metering device according to the invention, the passage cross-section for regulation of the residence time of the plastic granules in the drying chamber is changeable. Such, with respect to the passage cross variable dosing is that the drying chamber is readily adaptable to different levels of humidity to be dried granulate, without significant changes in the procedure with respect to temperature of the drying medium or amount must be made to the drying chamber supplied granulate allows , Preferably, the metering device is designed as a diaphragm whose passage cross section is regilierbar an adjustable slide.

According to a further preferred embodiment is still also the housing of the drying chamber heatable. This greater flexibility results in Verfährensdurchführung during drying, since the material to be dried granules from both the area of ​​the feed screw by the wall surrounding the screw conveyor undergoes itself over the drying medium as a corresponding power supply.

Since the plastic granulate is supplied when passing through the extruding work during the extrusion process, the internal energy is increased, whereby volatile constituents are expelled. Therefore, in another preferred embodiment of the invention in the wall of surrounding the extruder screw cylinder at least one outlet channel is provided for discharging vacant or forming gases. Depending on the type of gases they can be collected or discharged into the atmosphere.

The drying of the granules in the drying chamber is thus achieved by mechanical energy in the form of friction, heat transfer through the contact of the granular material to be dried to the surface of the screw as well as by heat transfer when flowing over the granules with the drying medium.

Apart from regulating the residence time of the medium to be dried in the drying chamber of the two-stage extruder by means of the metering equipment, metering can also be used to realize a relined operation of the extruder in the actual Extrudierstrufe.

Further advantages, features and possible applications of the present invention will now be explained by means of embodiments with reference to the drawings.

In the drawings:<dl id="dl0001" compact="compact"><dt>Fig. 1</dt><dd>a two-stage extruder with extruding and drying step according to the invention with a drive shaft of the joint of the side of the extruding step;</dd><dt>FIG. 2</dt><dd>An embodiment according to the invention with a drive for the screw conveyor 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 a continuous transition between the drying step and the extruding.</dd></dl>

In Fig. 1, an inventive two-stage extruder is shown having a 1 extruding stage and a drying stage 23. In the extruding step 1 an extruder screw 3 is rotatably disposed in a cylinder fifth The extruder screw 3 has on the inlet side with the inlet 12 to a conveyor section 21 and at the outlet end with the outlet of a plasticizing 22nd In the drying stage 23, a screw conveyor 4 is rotatably disposed in a housing thirteenth Between the screw conveyor 4 and the housing 13, a drying chamber 2 is formed. The screw conveyor 4 has a plurality of displacement elements 24 arranged on the periphery, which project into the drying chamber 2nd The displacement elements 24 can be, for example discs, paddles, blades or a group forming a helical worm gear.

Both the extruder screw 3 and the screw conveyor 4 are arranged on a common shaft. 7 Thus, the actual compression process may proceed in the extruding stage 1, the helical displacement element (screw) of the extruder screw 3 substantially up to the inner surface of the cylinder 5 is sufficient.

In the area of ​​the drying stage 23 is to be dried granules 18 that the drying chamber 2 is controlled preferably be fed from a collection hopper 17, merely circulated through the screw conveyor 4 and promoted, but not compressed. The height of the displacement elements 24 of the screw conveyor 4 is designed so that the outer diameter of the envelope is smaller than the inner diameter of the cylindrical housing 13 and define an air gap 26th By this radial annular space, an improved heat exchange between a heating medium 10 to be heated and the granules 18 is possible. Further characterized the residence time is increased. Serves as a heating medium, hot air 10 which is supplied via a channel 9 in the interior of the screw conveyor. 4 This inner channel 9 is formed on radial supply passages 8, which are guided between the displacement elements to the outer periphery of the screw conveyor 4, respectively. The so via the channel 9 supplied air flows through the ducts 8 into the region between the displacement elements, in which the granules deposited 18th

The flow rate of the drying medium 10 is chosen so that a more favorable heat exchange between the hot air and the granules is achieved. 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 the counter current process, the heated another part of it in the co-current process in the annulus.

It is also possible to supply the drying air together with the pellets 18 via the hopper 17 of the drying chamber the second In the drying chamber 2, supported in a bearing 20 screw conveyor 4 is provided with a heater 15th This heating device 15 may be an electrical heater, but it may also be formed as heating oil. It serves to achieve a higher flexibility of the drying stage 23rd In principle it is thus possible to obtain the drying of the pellets 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 with a heating device.

In the transition area from the drying chamber 2 to the cylinder 5 a metering device 11 is arranged in the form of a diaphragm. This diaphragm with respect to the passage opening 25 set, which is indicated by the double arrow. For this purpose, a slide 29 is adjusted. By regulating the passage opening 25 of the diaphragm 11, it is possible to vary the residence time of the pellets 18 in the first processing stage of the extruder, whereby an individual degree of drying of the granules, which is dependent on the polymer, is adjustable. The non-compressed in the area of ​​the drying chamber 2 granulate 18 passes through the passage opening 25 to the inlet 12 in the extruding stage 1. By the compressing means of the extruder screw 3 to be extruded medium is further heated, whereby volatile components are released depending on the degree of drying. These volatiles could exit via an outlet opening 14; they are there collected depending on their type and composition or into the open. At the end of the extruding stage 1 a radially directed outlet 19 is provided through which the exits completely extruded plastic pellets.

In the described embodiment, the drying medium 10 is the inner duct 9 of the screw conveyor 4 is supplied axially on the side of the drying step, the second Therefore, the drive unit 6 is arranged on the common shaft 7 of the extruder screw 3 and the screw conveyor 4 on the side of the extruding unit first

In Fig. 2, another embodiment of the extruder according to the invention, which essentially corresponds to the embodiment of FIG. 1. In contrast to the extruder of FIG. 1, the supply of the drying medium 10 in the past in the screw conveyor channel 4 is guided 9 via a radial channel guide through the housing block of the drying chamber 2. With such a supply of the drying medium 9, it is possible to use the driving means 6 for the conveyor screw 4 and the extruder screw 3 still to be arranged on the side of the drying stage 23rd 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 are formed by two shafts which are coupled together by means of a transmission 27th Here, the screw conveyor 4 and the extruder screw can be operated at different rotational speeds, which are determined by the gear ratio of the transmission 27 and the drive means 6th The screw conveyor 3 is supported on one side by a bearing 20 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 first

The outlet channel 10 for the drying medium from the drying chamber 2 is arranged in the vicinity of the granulate feed hopper 17th Thereby a substantially complete counterflow principle for the material to be heated or to be dried granules 18 is realized by the drying medium 10 flows against the conveying direction of the conveyor screw. 4 The advantage of the countercurrent procedure is in manner known per se in an improved heat transfer from the drying medium 10 to the granular 18th

Due to the arrangement of the drive motor 6 on the side of the drying stage 2, it is possible to provide an axially arranged outlet opening 19 from the extruding first This structural design can help to reduce the time necessary for the extrusion energy expenditure thus continue, since the discharge of the completely extruded plastic granulate is no additional deflection at the end of the extruding. 1

In Fig. 3, a further embodiment of the invention is shown, which the embodiment of 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 a larger diameter and the 3 the extruder screw of the extruding stage 1 with a smaller diameter, a substantially continuous transition is provided. The continuous transition is realized in the form of a cone-shaped, that is funnel-shaped inlet 12th

From a filler neck 17 the plastic granulate reaches 18 directly into the drying chamber 2. in the drying chamber 2 is hollow auger is supplied with hot drying air 10, which is guided via radial channels formed 8 in the helical gears to the outside to the material to be dried plastic pellets. The uniform pitch of the screw and through the annular space between the outer periphery of the screw and the inner periphery of the housing 13, the granulate is 18 merely conveyed in the drying chamber 2, but not compacted. During this promotion, the granules 18 is dried accordingly. Since the outlet channel 16 is arranged for the drying medium from the drying stage 2 in the region of the entry of the granules 18, a counter-current principle in the heating of the granular material 18 by the hot air in the drying stage 2 is almost realized.

The dried granules 18 is guided via the inlet 12 to the cylinder 5 with the extruder screw third A dosage of the granulate is achieved here by a trained end of the drying chamber 2, paragraph 28, which envelops the displacer of the screw conveyor 4 with no air gap. Thus enters a 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 stage 1. At the bottom, that is downstream third of the extruding stage 1 could be an outlet channel 14 released for 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 granulate is axially realized because the driving of the common shaft 7 for the extruder screw 3 and the screw conveyor 4 on the side of the drying chamber 2 through the common drive unit 6 is realized. In this arrangement, the cylinder 5 and the drying chamber 2 also are incorporated in a common housing thirteenth

The described embodiments have in common that the drying chamber 2 and the feed screw are 4 runs with a larger diameter, while the diameter of the compression portion, ie, the cylinder 5 with the extruder screw 3 is running low. Furthermore, an annular air gap 26 is formed between the screw conveyor 4 and the housing 13, so that high residence times are achieved, which are up to 1 hour in the range of about 20 minutes. The screw conveyor 4 also has wide cut or mounted with a correspondingly large incision on the periphery of displacement elements 24, in order to have a large heat-emitting surface for drying the granules.

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

LIST OF REFERENCE NUMBERS

<dl id="dl0002" 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>airstream</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>