DE10048028A1 - Planetary gear extruder for processing plastic melts has a gap for melt outlet at the end between the inner teeth of the barrel and spindle end supporting ring - Google Patents

Abstract

A central spindle is surrounded by circulating planetary gear spindles(3) which mesh with the internal teeth of a bush(2) inside the extruder barrel(1) and the teeth on the central spindle. The ends of the spindles slide around a supporting ring(4) at the end of the spindles in the flow direction. Melt exits the housing through an outer gap between the supporting ring and the bush. An Independent claim is made for a process using planetary gear modules having >= 3 planetary spindles less than normal.

Description

The invention relates to a planetary roller extruder.

Extruders are used in particular for processing plastics. The Plastic is usually used in the form of granules and through the extruder plasticized and discharged into a nozzle that the plasticized plastic in a brings the desired shape.

In addition to plasticizing, the task of the extruder is to close the melt homogenize. In most cases, additives and additives have to be processed. That too can done in the extruder. In this case, the extruder has the task of adding additives to distribute evenly.

Extruders can also be found in the food industry and chemistry, among others Application.

Extruders come in different designs. Single screw extruders are known Twin screw extruder and planetary roller extruder.

Planetary roller extruders have an extreme in relation to the other extruders mentioned great plasticizing effect. This opens up the possibility to process raw materials that are in the other extruders cannot be used at all or can only be used poorly. Planetary roller extruder can also be used to significantly increase production output.

Planetary roller extruders have a revolving central spindle, thus meshing and revolving planetary spindles, which also have internal teeth in the surrounding housing comb. The surrounding housing has a double jacket in contemporary design. The Inner jacket is formed by a socket. Between the inner and outer jacket is the important cooling of the planetary roller extruder is provided.  

The socket is provided with the internal toothing. Comb it with the surrounding ones Planetary spindles. Insofar as we speak of an internally toothed housing in the following, this includes the training described above with a double jacket.

The planetary spindles do not require any guidance in the circumferential direction. Because of the interlocking ensures that the distance between the planetary spindles remains the same in the circumferential direction. It can be spoken of a self-guided tour.

External guidance is required in the axial direction, because the planetary spindles develop a more or less large pressure in the longitudinal direction. This pressure is the one Reaction pressure from the delivery effect of the planetary spindles. The print comes with a Thrust ring caught on which the planetary spindles slide.

The thrust ring is inevitably at the end of the planetary spindles. The thrust ring is also at the end of the extruder when the planetary spindles reach the end of the extruder. These can be planetary spindles that extend over the entire length of the extruder or over part of the extruder length. This can be the case with conventional extruders with a one-piece housing as well as with extruders with a multi-part housing as well as with multi-part extruders in modular design. The position of the thrust ring is different with a different arrangement of the planetary roller spindles. This results from the following:
The feed material is processed in different sections in each extruder. The various sections have already been mentioned at the beginning. It is possible to use the same extruder system for all extruder sections. Since the different systems have different properties, the use of planetary roller extruder sections is advantageous at least for certain feed materials and certain processes. This applies above all to the "Mixing and Cooling" process sections. The combination of different extruder systems can be realized inexpensively if a multi-part extruder housing is provided, in particular a housing with different sections. Then each section can be designed as desired, e.g. B. the section "feeding the material" as a single screw extruder section and the sections "mixing and cooling" as planetary roller extruder sections. The housing section for the single-screw extruder section is smooth on the inside. The housing section for the planetary roller extruder section has the associated toothing on the inside.

The single-screw extruder section includes a section on the one rotating in the housing Spindle with corresponding external toothing. The single screw section is through a sleeve or sleeve is formed which mates with the sleeves and sleeves of other sections in the described above sits on a common rod and is clamped.

The planetary roller extruder section includes the central spindle section and the Planetary roller spindles. The central spindle section is aligned with the Einschneckenspindelabschnitt. It forms a central spindle in the planetary system. The central spindle section is usually through different bushings or sleeves than in the single screw extruder section. The associated bushings and sleeves are seated with the bushings and sleeves of other sections, e.g. B. the single-screw extruder section, on the common rod and are clamped with the other bushings and sleeves The outer sleeve diameter or outer sleeve diameter of the The central spindle diameter is regularly different from that of the Einschneckenspindelabschnittes. In any case, the necessary space for those on the Central spindle section revolving planetary roller spindles are created.

In addition, the associated housing sections of the planetary roller extruder section have a different housing diameter than the housing sections of the Einschneckenextruderabschnittes.

Depending on the arrangement of the planetary roller extruder section, the position of the Thrust ring on the extruder.

In the following, we only talk about thrust rings, although in an extruder several planetary roller modules for the thrust rings of the different modules Designations, e.g. B. thrust ring and intermediate thrust ring are common.

The thrust rings have different designs in conventional extruders; partly they are part of other components. Are popular with modular extruders separate rings that are installed between two modules. As above when addressed, the modules are identified by housing sections of a certain length. The extruder length required in each case is correspondingly large by putting them together Modules reached. The length of the planetary spindles corresponds essentially to the length of the Housing sections. As with other extruders with multiple housing sections, the the modular design, a common central spindle is provided for all modules. I.e. the Common central spindle extends through all housing sections / modules. How to the  described other extruders with several housing sections, it is also for the Modular design usual to assemble the central spindle from individual parts. To the Individual parts include bushings / sleeves that have the typical toothing of the central spindle have. Through the central opening of the bushes / sleeves, the rod with which the Bushings / sleeves are clamped to a central spindle.

The thrust rings usually clamped on the outside of the housing leave a gap Central spindle free. The melt flows through the gap. The design has changed extremely proven. This applies to both extruder production and Extruder operation.

The object of the invention is to improve the planetary roller extruder. there the invention has the extraordinarily proven previous design of the thrust rings in question posed. The invention turns to a more difficult and complex construction to gain procedural advantages. According to the invention, compared to conventional rings smaller rings used. These are rings that unite on the outside Leave the gap to the housing free (outer gap). The outer gap is preferably at least so large that the center of the planetary roller spindles is not in contact with the Have thrust ring. The outer gap can be chosen even larger, so that the Planetary roller spindles e.g. B. have only a minimal contact area with the thrust rings. The radial dimension of the contact surface is not the subject of the invention. It can do that for conventional thrust rings known radial dimension are adopted.

The invention of the outer gap has the great advantage of a significantly larger gap area with the same gap width compared to a conventional inner gap. As a result of the larger Gap area, with otherwise the same extruder design, creates a lower back pressure for the Melt. In addition, better flow conditions for the melt are formed. The Melt can flow more slowly. The flow path is cheaper.

The cooling surface on this flow path is cheaper. Therefore the invention additional advantages for use as a cooling extruder. It can be one one-piece or a multi-part extruder, in particular an extruder in Modular construction, act.  The thrust ring is optionally held by means of webs, which in turn are attached to the housing or are held between the housing sections. At least three are equally favorable distributed webs or more evenly distributed webs.

The thrust ring can also be held on the central spindle. It is possible to Thrust ring between the bushings / sleeves of the central spindle described above, clamp.

The thrust rings according to the invention can close when fastened to the housing slide on the central spindle or have a distance to the central spindle. Optionally, this can also be used to center the central spindle. With this Centering can prevent / reduce deflection of the central spindle. Though the planetary roller spindles support the central spindle. Nevertheless is in the frame of the play between the parts (central spindle / planetary roller spindles and inside toothed housing) can still evade. Evasion is all the more the more dangerous the smaller the number of planetary roller spindles. Already a little Dodging the central spindle can lead to uneven wear on the teeth or cause excessive partial wear. In extreme cases they can Skip planetary roller spindles. The result is an extreme overload of the Planetary roller extruder, possibly even a break.

Depending on the arrangement of the thrust rings, special shapes of the thrust rings may result. In a preferred application, a planetary roller extruder section is used for degassing the melt used.

All extruders have in common that in the melt or in the Feed / treatment material gaseous components can occur. It can be Trade components that were undesirable from the start. Such components can e.g. B. Be water. Some thermoplastics or fillers absorb water. Either have to these thermoplastics or fillers are pre-dried, or that in the extruder The resulting steam must be drawn off and degassed.

Gaseous components that are desired at the beginning and in the further processing Solvents, reaction accelerators or reaction inhibitors can be undesirable or inert gases. If there is no complete chemical conversion of these gases,  remains with monomeric, oligomeric degradation products and Decomposition products.

Volatile constituents in the melt are often more than 3 to 4% by weight and, in extruded polymers, may usually not exceed 0.2% by weight. There are various reasons that compel degassing. This includes:
Improve product quality, avoid health damage
Reduction of costs
Prevent chemical degradation
Implementation of further process steps.

Different devices are available for degassing. Degassing is usually carried out on the extruder. First, a degassing zone is defined on the extruder. The following zones are known for the extruder:
Feed zone, compression zone, first plasticization and homogenization zone and decompression zone, second plasticization and homogenization or dispersion zone, cooling zone, discharge zone. The designation of the different zones explains their function. In this way, the feed material is drawn into the extruder in the feed zone and compressed in the compression zone. In the plasticization zone, the material is plasticized, in the homogenization zone, the material is homogenized in the dispersion zone, additives are distributed in the material, in the cooling zone, cooling, etc.

The above zoning applies to single screw extruders or Twin-screw extruder. In the case of planetary roller extruders, the Plasticization and homogenization zone combined.

Various solutions are offered for degassing. All solutions are based on the fact that Volatile components dissolved in the melt are released by reducing the pressure. The Pressure drop can occur to ambient pressure or to a pressure above it. The gas inevitably then releases from the melt. The gas bubbles can then subtracted from.

In cascade extruder systems or tandem extruder systems, the degassing mostly takes place between the primary part and the secondary part. With the cascade extruder systems produced with one extruder (primary extruder) and then into another  Transfer extruder (secondary extruder), the transfer preferably is determined by gravity. I.e. the melt falls from the primary extruder into the Secondary extruder feed opening. The handover is often used for degassing. It is convenient to enclose the handover and with a suitable vacuum apply.

In tandem systems, a transfer from the primary extruder to the secondary extruder is under Pressure provided. The pressure is only essential for degassing at the transfer point reduced compared to the existing operating pressure.

At the transfer points described above, the thrust ring can take the form of a Have disc. In this form, the extruder is on to the intended outer gap Exit end closed. The same effect can be achieved with an annular thrust ring can be achieved by sliding on the central spindle. An escape of Melt between the teeth of the central spindle z. B. can be prevented by the Central spindle is cut free in front of the thrust ring. To put it simply, it is Gearing has been removed by cutting free. The toothing can also in the Leak the area.

A central spindle end formed in this way can be enclosed by the thrust ring. The thrust ring acts as a centering on the central spindle in the form described above. In the case of a thrust ring in the form of a disk, the melt escapes from the Central spindle excluded. The central spindle can also be mounted on the disc take place, e.g. B. by grasping the disc with a hub in the central spindle end. At a outer circumference of the central spindle is again a free cutting of the central spindle favorable.

Degassing is also still possible if in the trained as a primary extruder Planetary roller extruder there is a low pressure. The pressure is still so high that one Relaxation of the melt can occur after exiting through the outer gap.

The melt then only has a low pressure, if necessary the melt is even depressurized. The melt is then returned to the necessary pressure in the secondary extruder brought to their further processing. A pressure build-up by means of a intermediate pump provided.

The degassing can also take place in the primary extruder designed as a planetary roller extruder additionally or only backwards. In this case, the melt occurs with low pressure or, if necessary, depressurized through the outer gap of the primary extruder.  

During the reverse degassing in the planetary roller extruder, the melt in the in The direction of flow of the melt in the front extruder area is relaxed and gas is drawn off. For this purpose, appropriate metering of the amount of melt ensures that at least in the front extruder area, a melt-free cavity sufficient for degassing consists. The melt-free cavity is at least 10%, preferably at least 30%, at most 90% and preferably at most 70% of the cavity in the melt-free Planetary roller extruder. This cavity is defined by the interior of the interior toothed planetary roller extruder housing, through the central spindle and through the Planetary spindles.

The degassing can also be supported in that the secondary extruder as 4 Planetary roller extruder is designed. Then the gas is extracted at the transfer point between the primary extruder and the secondary extruder that the melt is not only at the Transfer point but continues to be degassed backwards from the secondary extruder.

The conditions described above also apply if the primary extruder only ends up with is provided with a planetary roller extruder section or the secondary extruder only at the beginning is provided with a planetary roller extruder section.

Between the sections of an extruder is also the use of the invention Thrust rings cheap. This also applies if at the transition from an extruder section in withdraw the other section of melt from the extruder and connect it is fed back to the extruder. This also applies to degassing by deducting the Gases on the thrust rings. The melt drawdown can have different reasons, e.g. B. the above-mentioned degassing or only the interposition of a pump Pressure increase.

The degassing can also take place on the thrust ring without melt removal. For this purpose, a pressure drop is provided in the flow direction behind the thrust ring.

The lower pressure is achieved through a zone of low pressure. That can e.g. B. by interrupting the teeth of the planetary spindles. An area without Pressure effect can be achieved in that the planetary spindles have no teeth in the zone own or that a volume expansion arises from the fact that the planetary spindles in start some distance from the thrust ring. The distance depends on the diameter.  

The diameter of the pitch circle diameter of the internal teeth of the housing is one Planetary roller extruder called. The distance can be up to 200 mm and in extreme cases more be. It is advantageous if not all planetary spindles have the distance and at least one of the planet spindles has a small distance, e.g. B. at most 10 mm. That serves to keep the vent opening in the thrust ring clear. An unwanted one Material build-up in front of the degassing opening is prevented.

The planetary spindles are alternately short / long. It also comes other even or uneven changes of "short" and "long" into consideration, e.g. B. short-short-long.

The pressure drop in front of and behind the thrust ring is essential for degassing Importance. The pressure gradient is preferably increased by changing the passage gap the thrust ring. The passage gap preferably runs conically. The Gap adjustment can be achieved by adjusting the central spindle in the axial direction become. The axial adjustment of the central spindle can be hydraulic or mechanical respectively. Both adjustments can be continuously, so that the pressure drop is also is infinitely variable. In practice, the optimal central spindle positions are for everyone Material and quickly found for every operating condition of the extruder.

Optionally, a gradual adjustment is also provided.

For the degassing, it may be sufficient if only openings are present through that the released gas can escape.

By applying suction, the degassing performance is increased significantly. The degassing is preferably carried out through the thrust ring into a vacuum dome. The vacuum dome has a considerable volume. There is a vacuum at the vacuum dome created. The large volume of the cathedral contributes to the operational safety of the degassing and Selectivity of the degassing.

The degassing acts beyond the immediate space behind the thrust ring and also into the material gripped by the spindles and pushed in the conveying direction until the compression of the material prevents further degassing. It is particularly beneficial for degassing if the number of planetary spindles is lower than normal. The number of planet spindles depends on the diameter. The pitch circle diameter of the internal toothing on the housing of the planetary roller extruder is designated by diameter. The normal planet spindle numbers depending on the diameter and the spindle length are shown below:

According to the invention, at least 3 planetary spindles are preferably used for degassing less than the number of normal spindles used.

This results in a relatively large distance between the planet spindles, in which the Degas material for a relatively long time.

With regard to this material, as long as degassing is still taking place, a shape is created backward degassing because the gas is related to the extruder's output is pulled backwards.

A multi-stage degassing is optionally available.

Particularly favorable conditions result when a vertical extruder is used. In the vertical extruder is formed by the gravity of the Melt / feed material / material to be treated behind the thrust ring is very degassing conducive cavity by ensuring at the same time through appropriate extruder throughput is that the inflowing melt / feed / treatment material does not close the cavity fills. The gas has the least resistance in the vertical arrangement Escape from the melt and from the extruder.

In the drawing, an embodiment of the invention is shown.

In the exemplary embodiment, PVC granulate is converted into a PVC melt using an extruder won.

1 denotes a cylindrical extruder housing for a planetary roller extruder section. The housing 1 is lined with a socket 2 which is provided with teeth on the inside. With the teeth of bushing 2, mesh 6 planetary roller spindles 3 . The planetary roller spindles also mesh with a central spindle, not shown. The central spindle has a conventional drive.

The planetary roller spindles 3 are held in the axial direction by a thrust ring 4 in the form of a disk. The planetary roller spindles 3 slide along the disc.

There is an outer gap between the thrust ring 4 and the bushing 2 through which the melt exits.

The thrust ring 4 is held on the housing 1 with three webs 5 distributed uniformly on the circumference.

Claims (27)

1.Extruder for the production and / or processing of plastic materials, in particular melt, wherein the extruder is designed at least in sections as a planetary roller extruder and has a central spindle, revolving planetary roller spindles and an internally toothed housing as well as a thrust ring behind the planetary roller spindles in the flow direction of the melt , the planetary roller spindles with their toothing both with the toothing of the central spindle and with the. Comb the internal teeth of the housing and the planetary roller spindles slide along the thrust ring, characterized in that the thrust ring forms an outer gap. 2. Extruder according to claim 1, characterized in that the thrust ring in the housing or is held in the central spindle. 3. Extruder according to claim 2, characterized by webs as a holder. 4. Extruder according to claim 2 or 3 characterized by a clamping between Housing sections or between the bushings or sleeves of the central spindle. 5. Extruder according to one of claims 1 to 4, characterized by centering the central spindle by means of the thrust ring. 6. Extruder according to one of claims 2 to 5, characterized by a free cut or the teeth run out in the area of the central spindle and / or through a Number of webs of 3 or more and / or by an even distribution of the webs. 7. Extruder according to one of claims 2 to 6, characterized in that in the housing held thrust ring closes and at the same time slides on the central spindle.   8. Extruder according to one of claims 1 to 7, characterized by a disc-shaped thrust ring at the end of an extruder. 9. Extruder according to claim 8, characterized in that the disc-shaped thrust ring grips with a hub centering in the end of the central spindle or with a collar grips the end of the central spindle. 10. Extruder according to one of claims 1 to 9, characterized by a pressure drop Melt after exiting the outer gap and by subsequent degassing. 11. Extruder according to claim 10, characterized in that the melt outlet through the outer gap in a cascade arrangement at the transfer of the melt from Primary extruder is provided for the secondary extruder. 12. Extruder according to claim 10, characterized in that the melt outlet through the outer gap in a tandem arrangement at the transfer of the melt from Primary extruder is provided for the secondary extruder. 13. Extruder according to claim 10, characterized in that the thrust ring in one Extruder is arranged between two extruder sections. 14. Extruder according to claim 13, characterized in that the melt for degassing withdrawn from the extruder and fed again after the degassing or that the degassing in the planetary roller extruder section by a gas vent on or in Thrust ring is carried out. 15. Extruder according to one of claims 11, 12, 14, characterized in that in Melt flow after degassing a pump for pressure build-up is provided. 16. Extruder according to claim 14, characterized by a pressure drop for the Degassing in the subsequent extruder section.   17. Extruder according to claim 16, characterized by a lower conveying effect in Direction of delivery behind the thrust ring and / or an increase in Void volume. 18. Extruder according to claim 17, characterized by a following the thrust ring Planetary roller extruder section, in which planetary spindles also in the degassing area broken teeth or in the planetary spindles without teeth in the degassing area or are provided in the planetary spindles, which leave a cavity. 19. Extruder according to claim 18, characterized in that the melt-free cavity in Extruder at least 10% and at most 90%, preferably at least 30% and preferably at most 70% of the total void volume in the Planetary roller extruder section is. 20. Extruder according to one of claims 17 to 19, characterized in that the Planetary roller spindles all or individually the same or different distance from that Have a drain ring. 21. Extruder according to claim 20, characterized by using at least one Planet spindle with a distance of at most 10 mm and / or at least one Planet spindle with a larger distance. 22. Extruder according to claim 21, characterized by using a distance of up to 200 mm and / or changing lengths of the planetary spindles 23. Extruder according to one of claims 14 to 22, characterized in that the gas in Direction of conveyance of the extruder is withdrawn at the back of the thrust ring. 24. extender according to one of claims 14 to 23, characterized by a connected vacuum dome for degassing. 25. Extruder according to one of claims 14 to 24, characterized by a vertical arrangement of the extruder.   26. The method according to any one of claims 1 to 25, characterized by the use of planetary roller extruder modules with a number of planetary spindles which is at least 3 less than the number of normal planetary spindles. 27. The method according to any one of claims 1 to 26, characterized by cooling and / or heating the modules in the degassing area.