DEGASING EXTRUDER WITH A MULTI-SHELL UNIT AND METHOD FOR DEGASING POLYMER MELTING

Description

[0001] The invention relates to a degassing extruder with a multi-screw unit having the features of the preamble of claim 1 and to a method for degassing polymer melt therewith.

[0002] In the processing of polycondensates, especially polyesters, it is important to continuously remove the byproduct – usually water – in order to increase or at least maintain the polymer chain length and prevent further degradation of the molten polymer. This is particularly important in demanding manufacturing techniques such as the production of fine spun fibers, which require high polymer quality and, in particular, high intrinsic viscosity.

[0003] WO 2013 180 941 A1 describes a process for the production of Bulk Continuous Carpet Filament(Carpet-BCF) made from recycled polyester. The process involves splitting a stream of molten polymer into at least two individual streams. These individual streams are to be degassed separately by applying and maintaining a vacuum in separate extruders before being recombined into a single melt stream, which is then fed directly to a downstream spinning unit. However, splitting the process into multiple individual streams processed in parallel extruders results in significant equipment complexity in terms of cost, space requirements, synchronization, etc. As an embodiment of the process, a multi-shaft extruder is further described, which is intended to replicate the function of the multiple separate extruders in a single unit and which is designed to degas the separate melt streams independently of each other before they are recombined.A multi-rotation unit rotates around a central axis, within which several satellite screws are rotatably mounted. A housing with an opening connected to a vacuum pump is provided for degassing. While the division into separate partial melt streams offers the advantage over a single stream of increasing the polymer surface area available for gas exchange, the degassing of the individual melt streams, which are guided through the satellite screws, can only occur during the brief moment when, during the rotation of the multi-screw unit, the respective satellite screw with its partial melt stream passes the opening in the housing.It remains unclear how the continuous maintenance of a constant low pressure for degassing in each partial melt stream is to be maintained, although the associated satellite screw is only ever briefly moved through the opening of the casing and is then outside the influence of the vacuum for the remainder of the rotation.

[0004] WO2003 / 033240 A1 describes an MRS system comprising several satellite screws. This significantly increases the surface area of ​​the polymer melt and considerably improves melt quality. Crossflow across the rotor element, from one satellite screw to the next, is possible and desirable. The satellite screws are responsible for the majority of the polymer melt conveying, while a shallow screw rib on the rotor element contributes a smaller portion, primarily serving to surround the rotor element with melt, thus providing lubrication within the housing.

[0005] CN 101293397 A and CN 101837633 A each describe a multi-screw unit in which the satellite screws lie completely within the screw channel of the main screw web on the central rotor element. Therefore, they convey the polymer melt parallel to the core of the rotor element in a longitudinal direction via their webs. Because the satellite screws extend through the main screw webs with their entire cross-section, the melt is not only conveyed along the main screw web, but partial flows also occur that bridge the main screw. This counteracts the disturbance and long residence time in the area of ​​the suction opening that would promote degassing.

[0006] CN 1775506 A describes a multi-screw unit not designed for degassing. The satellite screws are each enclosed by the walls of a receiving groove on the central rotor element, with a predominant portion of their total cross-section. The screw flights on the satellite screws have a very low web height.

[0007] WO2016 / 081474A1 describes a degassing extruder that has a main rotor body in which several satellite screws are rotatably mounted. A vacuum is applied to remove gas bubbles contained in the polymer melt. The main rotor body has no screw web in the circumferential areas for the mounting grooves of the satellite screws.

[0008] WO2014183984A1 describes an extruder with a main rotor body in which several satellite screws are rotatably mounted. The satellite screws rotate in the same direction as the main rotor body. The extruder is designed and configured to incorporate as much blowing agent as possible into a polymer melt to obtain a polymer melt with a high gas content for the formation of a polymer foam. The main rotor body has a screw web in sections along its circumference for the mounting grooves of the satellite screws.

[0009] The object of the present invention is to provide a degassing extruder with which the quality of the polymer melt processed therein can be increased. In particular, a large polymer surface area should be generated and / or a high surface exchange in the polymer melt should be achieved as a prerequisite when the polymer melt passes through the extraction opening or even before it.

[0010] This problem is solved by degassing extruders with a multi-screw unit having the features of claim 1.

[0011] The approach according to the invention is precisely contrary to the prior art described above in the form of the so-called multi-rotation system and differs from it even in its terminology. The multi-screw unit according to the invention can also be described as a 'degassing monorotor extruder', since the conveying action is predominantly performed by the channels cut into the central (mono-)rotor element, and since the satellite screws improve the degassing effect without conveying independently.

[0012] The conveying action is achieved almost exclusively by at least one main screw web, which is formed on the outside of the rotor element. The main screw web is positioned so high above the core of the rotor element, or the channels between the webs are cut so deeply, that conveying is achieved solely by the main screw web. In contrast, the conveying effect of the satellite screws is significantly reduced or even negligible. Instead, the satellite screws serve to circulate, loosen, and mix the polymer melt. This is because the satellite screws are mounted as low as possible within the rotor shaft, thus largely eliminating or substantially reducing their conveying effect.

[0013] The advantages achieved with the invention consist not only of improved mixing and degassing. Furthermore, the shear of the polymer is reduced. The reduction of mechanical shear alone leads to improved melt quality. In addition, lower shear reduces the heat input into the melt, thus preventing overheating.

[0014] Because the satellite screw protrudes a large proportion of its surface area from the rotor element, the surface area of ​​the main screw is correspondingly increased. A larger surface area leads to greater dispersion and improves the degassing effect.

[0015] The height of the main worm web is preferably greater than the maximum channel depth of the receiving grooves. The height of the main worm web is preferably at least as high as the height of the worm web on the satellites, and in particular at least twice as high.

[0016] Preferably, the direction of rotation of the satellite elements with their screws is opposite to that of the rotor element with its main web, and the orientation of the satellite screw webs is opposite to that of the main screw web. If any conveying effect still emanates from the satellite screws, it is directed axially in the same direction as the conveying by the main screw web. Nevertheless, within the flights of the main screw, a counter-rotating relative movement occurs between the rotor element and the respective satellite screw, which improves the loosening of the conveyed melt and consequently its degassing. Design advantages include the fact that the satellite screws can be equipped at their ends with pinions that mesh directly with a toothed ring formed or attached to the rotor element.

[0017] Where the satellite screws pass through the main screw web, they are preferably enclosed for at least 70% of their circumference. This allows only minimal flow along the rotor element through the remaining gaps between the main screw web and the satellite screws. The conveying effect of the main screw web is maintained. In the section between adjacent parts of the main screw web, however, the satellite screws are significantly less enclosed by the receiving groove in which they are arranged and are at least half exposed. Therefore, they no longer form a conveying element as in an extruder, but primarily serve as mixing elements for the polymer melt.

[0018] In the context of the present invention, the 'enclosure degree' is defined as the ratio between the proportion of the circumference of the satellite mixing element which is shielded by walls of the rotor element and its main worm web, in relation to the total circumference.

[0019] With its large diameter and circumference, over which at least one nearly continuous main screw web runs, the rotor element offers a large surface area on which the melt stream spreads. This promotes, for example, the degassing of the polymer melt when it is guided past a vacuum-controlled extraction port in the housing. Furthermore, the screw flights located between adjacent sections of the main screw web carry a uniform melt stream instead of many individual streams. Due to the rotation of the rotor element, this uniform melt stream is repeatedly and precisely guided past the vacuum-controlled extraction port in the housing. Thus, there is a defined residence time within the vacuum zone.

[0020] According to the invention, as already explained, the satellite screws do not serve to convey individual molten streams, but rather are recessed within the screw channel of the rotor element, opening into the main screw channel to such an extent that they cause a circulation of those portions of the molten metal located at the bottom of the screw channel in the main screw web. The satellite screws thus loosen, mix, and relocate individual parts of an otherwise uniform molten stream flowing through the main screw channel, ensuring that the degassing effect of the vacuum is constantly present in the entire molten metal stream conveyed by the rotor element and not only in the outermost portions.

[0021] Even a single satellite screw improves the mixing and surface area of ​​the polymer melt. Preferably, at least three satellite screws are arranged on the rotor element at uniform angular intervals. The following considerations apply to the selection of the number of satellite screws: If the degassing extruder is primarily used for mixing several components or for homogenizing a single component, the mixing effect can be increased by increasing the number of satellite screws. If the focus is on degassing, the mixing effect influences the degassing efficiency. Increasing the number of satellite screws allows for a higher required partial pressure in the degassing chamber, i.e., a higher pressure within the vacuum zone.

[0022] Given a specific application, the number of satellite screws is determined, and the desired optimal pressure range for the process is achieved through a simple experiment by gradually applying a pressure from, for example, less than 0.1 mbar to over 1 bar, and analyzing the product treated in this way for several test stages.

[0023] The cross-sectional area in the main screw channel is selected relative to the nominal volume flow rate for the degassing extruder such that the cross-section is not completely filled during normal operation. Due to the low fill level, the suction effect of the vacuum can indirectly extend to all those circumferential areas of the rotor element that are not directly adjacent to the housing opening.

[0024] A key aspect of the invention is that the main screw web has only the smallest possible opening at the point where the satellite screws pass through it. Here, a larger proportion of the circumference of each satellite screw is enclosed by the cross-sectional areas of the rotor element, including the main screw web, than in the axial areas between.

[0025] If the degree of confinement of the satellite screw in the channels is 50% or less, this means that 180° or more of the circumference is exposed. A positive-locking guidance of the satellite screw in the receiving grooves is then not achieved in these areas. Therefore, the additional confinement of the satellite screw by the main screw web should be large enough to enclose more than 180° of the circumference, i.e., the degree of confinement should exceed 50%. Guidance is then necessarily provided by a sufficiently large confinement in the area of ​​the main screw web. Surprisingly, from a mechanical engineering perspective, guidance by the relatively short web sections is sufficient.

[0026] The enclosure of the satellite screws must either be greater than 50% in the receiving groove or, if this is not possible, at least greater than 50% where they pass through the main screw web. Preferably, the enclosure depth should be greater than 70% at at least one point along the axial path of the satellite screws. Together with the drive pinion, which is usually located at the rear end, this results in at least two bearing points for the positive-locking guidance of the satellite screws.

[0027] A large degree of enclosure at the points where the satellite screws pass through the main screw web is also advantageous because a small opening in the main screw web maintains the conveying effect of the main screw web. This means that the melt cannot develop significant cross-flows through small openings and must instead follow the course of the main screw web. In doing so, it is guided past the casing opening multiple times, thus improving degassing.

[0028] The following parameters must be adjusted for the degassing extruder according to the invention: Outer diameter of the rotor element, measured at the top edge of the main worm web; height of the main worm web above the rotor core; width of the main worm web; diameter of the pitch circle on the rotor element on which the at least one satellite worm is arranged, and diameter of the satellite worms and height of their satellite worm webs.

[0029] This results in the opening width or opening angle of the opening recess in the main screw web.

[0030] In multi-screw units with small nominal diameters and a correspondingly small number of 3 to 5 satellite screws, it is preferably provided that the core of the satellite screw, i.e., its central cross-sectional part without the outer satellite screw web, is positioned completely or almost completely within the circumference of the rotor core. This relationship results in the height of the satellite screw webs being approximately equal to the height of the main screw web and that the satellite screws do not restrict the conveying volume in the main screw web.

[0031] The sum of the diameter of the pitch circle and the diameter of the satellite worm webs must not exceed the outer diameter of the rotor element. This means that the worm webs of the satellite worms never extend radially beyond the upper edge of the main worm web. As a result, the gap between the outer edge of the main worm web and the housing recess can be kept very small.

[0032] On the other hand, the pitch circle and diameter of the satellite snails must be chosen so that the satellite snail webs extend sufficiently beyond the bottom of the snail passages in the main snail web to achieve their loosening effect.

[0033] Preferably, the arrangement is such that the satellite worms are enclosed by the flanks of the receiving groove with at least 40% and at most 70% of their circumference outside of those points where they are guided through the main worm web, and otherwise lie freely in the worm channel.

[0034] The difficulty lies in the fact that, as the channel depth increases, the satellite worms are no longer properly guided by the rim in the receiving grooves of the rotor element. The degree of rim engagement in the receiving grooves quickly drops below 60% when the pitch circle diameter is larger than the diameter of the rotor core. This is particularly necessary with larger rotor diameters because the size of the satellite worms and their web height are limited and cannot be increased proportionally to the diameter of the rotor core.

[0035] In summary, the following geometric requirements arise with regard to the enclosure of the satellite worms according to the invention: Within the passages between the main screw flights, the degree of confinement by the receiving grooves should be less than 50% so that the satellite screws no longer exert a significant conveying effect and instead achieve better melt exchange around the circumference of the rotor. Within the passage through the main screw flight, the degree of confinement should be as large as possible to prevent longitudinal conveying not caused by the main screw flight. However, the degree of confinement at the main screw flight must in any case be greater than in the open areas of the passages. Either in the open areas of the passage or in the passage through the main screw flight, a degree of confinement of more than 50%, in particular at least 60%, must be achieved at at least one point to ensure positive mechanical guidance of the satellite screws in the rotor element.

[0036] In addition to these geometric relationships relating to the cross-section, the following applies to the consideration of the guidance of the screws on the rotor unit over the length: Over more than 70% of the length of the rotor element effective for degassing, the enclosure is provided by the rotor shaft core, and over more than 5% but less than 20% of the length, the enclosure is provided by the webs.

[0037] When considering the distribution of web width to thread width, the ratio should be at most 1:4 and preferably smaller, meaning the web width should occupy 20% of the screw pitch or less, in order to have as much conveying volume as possible available for melt conveying and degassing and to fill as little as possible with the main screw web.

[0038] When using the degassing extruder according to the invention for processing polymer melt, at least the following process steps are provided: Supplying a melt stream to the rotor element rotatably arranged in the housing recess, which has several rotatable satellite screws around its circumference; the drive is provided by an internal toothing in the housing recess with which the also toothed ends of the satellite screws are directly or indirectly engaged; spreading the melt stream over the circumference of the rotor element and onto the satellite screws by rotating the rotor element relative to the housing; conveying the polymer melt from the rotor element and from the satellite screws to at least one outlet channel.

[0039] In this process, the polymer melt distributed on the rotor element is conveyed along the length of the rotor element by means of at least one main screw web arranged on the outer circumference of the rotor element and loosened from the bottom of the channel by at least one satellite screw. If several satellite screws are present, this simultaneously results in the exchange of polymer melt between the adjacent satellite screws.

[0040] In this process, it is advantageous if the volume flow rate of the polymer melt supplied to the multi-screw unit and the volume flow rate discharged from it are coordinated such that the conveying volume enclosed between the adjacent sections of the main screw web, the outer surface of the rotor element, and the inner surface of the housing recess, or the conveying cross-section considered in the longitudinal section of the rotor element, is less than 100% filled with polymer melt, and in particular less than 80%. This reduction in the so-called fill level results in a large amount of free space being available to swirl the polymer melt through the satellite screws, increase the surface area, and intensify the mixing of adjacent portions of the melt stream.

[0041] The processing method using a degassing extruder according to the invention can be used to process, in particular, the following polymer melts: Polyester for various applications, in particular polyester in various fiber forms such as bulk continuous filament (BCF), which is suitable for carpet manufacturing. The polyester treated in a degassing extruder according to the invention can be directly introduced into a spinning process. Polyamide.

[0042] The invention is explained in more detail below with reference to the drawings. The figures show, in detail: Fig. 1 a degassing extruder in side view; Fig. 2 a rotor element in perspective view; Fig. 3 a section of a side view of a multi-screw unit; Fig. 4 a schematic development of the circumference of the rotor element; Fig. 5 the rotor element in section; Fig. 6 the rotor element of a third embodiment in section and Fig. 7 the rotor element of a third embodiment in section.

[0043] In Figure 1Figure 100 shows a degassing extruder in a side view. This extruder comprises, laterally adjacent to a housing 30, an inlet section 20, which is long in the illustrated embodiment. This inlet section has a rotating screw shaft 21 in an internal inlet channel. Furthermore, an outlet section 40 with an internal outlet channel, in which a rotating screw shaft 41 is also arranged, adjoins the housing 30 on the other side. The housing 30 is in Figure 1The diagram shows the side view of the housing, which has two adjacent openings 32 arranged within a common flange area 31, to which a vacuum extraction line can be attached. Parts of a multi-screw unit 10 are visible inside through the openings 32, with particular attention paid to the significantly increased thread depth or web height of a main screw web 12, which extends over the outer circumference of a rotor element 11, compared to the prior art.

[0044] Figure 2 Figure 11 shows the rotor element in a perspective view. A shaft core 15 is surrounded on its outer circumference by the main worm web 12. In addition, a total of eight receiving grooves 13 for satellite worms are formed on the outer circumference, each offset from the others by 45°. Fig. 2It is already apparent that a relatively large passage depth is provided for in the passage 18 formed in the main snail web 12.

[0045] This is particularly evident in Figure 3 Figure 1 shows a section of a side view of the multi-screw unit 10, specifically the forward end in the direction of flow, which transitions into the discharge screw 41 at a transition cone 42. Only immediately upstream of the transition cone 42 does the rotor element 11 have a shallow channel 14.1. In the remaining areas to the right of this channel, the channel 14 is significantly deeper, with the channel depth measured radially from the outer circumference of the main screw web 12 to the outer circumference of the shaft ring 15.

[0046] The diameter of the rotor element 11 is denoted by D; t denotes the pitch of the main screw web 12, where the pitch t is generally given as a dimensionless number that indicates the relationship between the axial distance of the web segments at the same angular position relative to the diameter D. The thread pitch is then the measurable distance from one web edge to the next on the main screw web, measured at the same angular position, and is calculated as the product of diameter D and pitch t. The width of the threads 14 is therefore determined as the difference between the thread pitch D*t and a web width d.

[0047] A slope of t=1 according to this definition means that the axial distance, measured at the same angular position on the circumference, from one screw web leading edge to the next, is equal to the diameter. For the purpose of polymer degassing, t < D, so that the residence time of the polymer melt is long and the effect of gas extraction can be effective. Furthermore, in Figure 3 It is clearly visible that the main screw web 12 has a counter-rotating orientation to the satellite screw webs 17. The rotor element 11 and the satellite screws 16 rotate in opposite directions because they are interlocked and directly engaged with each other.

[0048] The features of the invention described in relation to the degree of enclosure of the satellite worms 16 are importantly related to further features described in the Figure 2The visible longitudinal course of the rotor element is related. Compared to the prior art, the enlarged enclosure of the cross-section of the satellite screws 16 leads to a self-cleaning effect in a multi-screw unit equipped with the multi-screw unit 10 of the invention, since the main screw web 12 scrapes along the inner walls of the housing recess over its entire length and circumference, thus removing any adhering polymer residues.

[0049] The degree of edging of the satellite screws 16 provided according to the invention accordingly results in the interruptions in the main screw web 12 being short enough to ensure the aforementioned self-cleaning effect. This relationship is illustrated by the Figure 4 and 5 explained.

[0050] Figure 5Figure 1 shows a cross-section of the rotor element 11. The main screw web 12, interrupted for each of the eight receiving grooves 13, has an opening recess 12.1 above each receiving groove 13. The upper receiving groove 13 is shown empty. The solid thick line characterizes the degree of enclosure of the satellite screws 16 within the passages 14, i.e., in the axial areas between parallel sections of the main screw web 12. The dashed line at the receiving groove 13 to the right characterizes the degree of enclosure at the points where the satellite screws 16 pass through the main screw web 12.

[0051] Figure 4Figure 1 shows a schematic development of the outer circumference of the rotor element 11 with the main screw web 12 and opening recesses 12.1 for a satellite screw. The bore diameter, or outer diameter D, of the main screw web 12 is predetermined based on factors such as the desired throughput of the extruder or the viscosity of the polymer being processed. The outer diameter D is therefore considered a constant for the further design of the multi-screw unit. The length of the circumference is derived from this: U = D ⋅ π

[0052] The opening width x of the opening recess 12.1 is determined by the opening angle α (see Fig. 5 ) certainly: x = α D 2

[0053] The functional requirement regarding the self-cleaning effect of the multi-screw unit 10 stipulates that there must be a slight overlap in the axial direction between the edges 12.2 and 12.3, which define the opening recess 12.1; this is in Figure 4 marked as overlap zone 12.4.

[0054] For the calculation, it is essential that edges 12.2 and 12.3 are at least axially at the same height to prevent an axial gap, because in the event of a gap, the area of ​​the inner wall of the housing recess swept over by this section of the rotor element could not be cleaned.

[0055] This results in the following for the web width d of the main worm web 12 in relation to the opening angle α (see Figure 5 ) and the following relationship applies to the slope t: d = ∝ ⋅ D ⋅ t 2 π

[0056] The web width d should be as small as possible so that the conveying volume of the channels 14 between the sections of the main screw web 12, determined by the channel width and web height, is as large as possible. As already explained above, the ratio of web width d to channel width should be chosen as follows: d D ⋅ t − d ≤ 1 4

[0057] With respect to the slope t, the following results for the web width d: d ≤ D ⋅ t 5

[0058] Based on the aforementioned web width limitation of 20% of the slope, the opening angle α is: ∝ ≤ 2 π 5

[0059] Further details of the multi-screw unit 10 according to the invention can be seen from the sectional views in the following figures.

[0060] In Figure 5 The multi-screw unit 10 is shown in section, specifically in the area of ​​line IV-IV in Figure 3A pitch circle 19, which defines the position of the centers of the receiving grooves 13 and satellite augers 16, has a diameter approximately the same as the diameter of the shaft core 15 of the rotor element 11. A portion of the core cross-section of the satellite augers 16 projects beyond the circumference of the rotor shaft core 15. This is necessary, on the one hand, to limit the size of the satellite augers 16 so that they do not exert a significant conveying effect, and on the other hand, to allow the satellite auger webs 17 to extend to the outer edge of the main auger web 12, or at least very close to it. Such a wide radial extension of the satellite auger webs 17 outwards is chosen so that the proportions of the openings in the main auger web that are not covered by the projected cross-sectional area of ​​the satellite augers and their webs 17 remain small.The resulting degree of enclosure E G1 of the satellite snails 16 in the passage is represented by an arc line drawn in bold. In this example, it is less than 50%. The passage depth of passage 14 in the main snail web 12 is denoted by T G1. At the same time, in . Fig. 4 It is evident that the proportion of the opening in the main snail web 12, which is not covered again by the projected area of ​​the satellite snail 16, remains small.

[0061] Figure 5 shows a very similar representation of a 10' multi-screw unit as in Fig. 4 The outer diameter of the main screw web 12', the outer diameter of the satellite screws 16' and the pitch circle 19', on which receiving grooves 13' and satellite screws 16' are arranged, are each identical, for example according to Figure 4In contrast, the passage 14' formed in the main screw web 12' has a greater passage depth T G2 > T G1, which consequently reduces the diameter of the rotor shaft core 15'. The degree of confinement E G2 in passage 14', characterized by the bold arc line, also decreases, while the degree of confinement E S2 of the satellite screw 16' remains constant as it passes through the main screw web 12'.

[0062] On the shaft core 15" which is in Figure 7In the multi-screw unit 10" shown, five round receiving grooves 13" are milled into it, arranged at 72° intervals on a common pitch circle 19". In this example, the pitch circle 19" is smaller than the diameter of the shaft core 15". This ensures that the cross-sections of the respective core areas of the satellite screws 16" lie almost completely within the circumference of the rotor shaft core 15"; that is, the conveying volume in the passage 14" in the main screw web 12" is almost completely maintained and is hardly restricted by the satellite screws 16".

[0063] The flanks of the receiving grooves 13" formed in the rotor shaft core 11" each extend over more than 180°, achieving a degree of enclosure exceeding 50%. This ensures that the satellite screws 16" are positively locked in the receiving grooves 13". The remaining portion of their circumference of the satellite screws 16" lies open within the passage 14" in the main screw web 12". The satellite screw webs 17" of the satellite screws 16" can thus effectively loosen the melt from the bottom of the passage 14". Since the satellite screw webs 17" extend to the outer circumference of the main screw webs 12" and rotate in the opposite direction, the circulation is particularly efficient.

Claims

1. Degassing extruder (100) having a multi-screw unit (10; 10'; 10"), at least comprising: - a housing (30), having ∘ an inlet region (20) with an inlet opening, ∘ an inner housing recess with a suction opening (32) extending as far as the outside, ∘ an outlet region (40) with an outlet opening; - the multi-screw unit (10; 10'; 10"), which is rotatably arranged in the housing recess and at least comprises: ∘ a rotor element (11; 11'; 11") and ∘ at least one rotationally driven satellite screw (16; 16'), which is mounted in a receiving groove (13; 13'; 13") on the rotor element (11; 11'; 11"), which receiving groove (13; 13'; 13") extends at least along part of the length of the multi-screw unit (10; 10'; 10"), characterized in that the rotor element (11; 11'; 11") has at least one main screw flight (12; 12'; 12") which extends over the outer circumference of a rotor shaft core (15; 15'; 15"), and in that at least in the region of the suction opening (32): - the main screw flight (12; 12'; 12") above the receiving groove (13; 13'; 13") has a respective opening recess (12.1) for passing through the satellite screw (16; 16'); - the circumference of the satellite screw (16; 16') in the channels (14, 14.1) formed by the main screw flight (12; 12'; 12") is enclosed to an extent of at least 40% and at most 70% in the receiving groove (13; 13'; 13") in the rotor shaft core (15; 15'; 15") and - the degree of enclosure of the cross section of the satellite screw (16; 16') within the main screw flight (12; 12'; 12") is greater than in the channels (14; 14'; 14") outside of this and is at most 95%.

2. Degassing extruder (100) according to Claim 1, characterized in that the degree of enclosure of the cross section of the satellite screw (16; 16') at least in one of the axial zones within the main screw flight (12; 12'; 12") or in the channels (14; 14'; 14") outside the main screw flight (12; 12'; 12") is greater than 50% in each case.

3. Degassing extruder (100) according to Claim 1 or 2, characterized in that the flight of the satellite screw (16; 16') reaches as far as the outer circumference of the at least one main screw flight (12; 12'; 12").

4. Degassing extruder (100) according to one of Claims 1 to 3, characterized in that the centre axes of the satellite screws (16; 16') are arranged on a pitch circle which is smaller than the diameter of the rotor shaft core (15; 15'; 15").

5. Degassing extruder according to Claim 4, characterized in that more than 80% of the cross section of the shaft core of the satellite screws (16; 16') is arranged within the circumference of the rotor shaft core (15; 15'; 15").

6. Degassing extruder according to one of the preceding claims, characterized in that formed on the rotor element (11; 11'; 11") are at least three receiving grooves (13; 13'; 13"), in each of which a satellite screw (16; 16') is rotatably mounted.

7. Degassing extruder according to one of the preceding claims, characterized in that the channel depth (TG1, TG2) of the main screw flight (12; 12'; 12") is greater than the maximum channel depth of the receiving grooves (13; 13'; 13").

8. Degassing extruder according to one of the preceding claims, characterized in that the satellite screws (16; 16') are driven in rotation in the opposite direction to the direction of rotation of the rotor element (11; 11'; 11") and have an orientation which is opposite to the main screw flight (12; 12'; 12").

9. Degassing extruder according to one of the preceding claims, characterized in that the diameter D and the pitch t of the main screw flight (12; 12'; 12") and the respective opening width x of the opening recess (12.1) are coordinated to one another in such a way that the inner wall of the housing recess is passed over completely by the main screw flight (12; 12'; 12") when the rotor element (11) is rotating.

10. Degassing extruder according to one of the preceding claims, characterized in that the ratio of the flight width d of the main screw flight (12; 12'; 12") to the channel width of the channel (14; 14'; 14") is less than 1:4.

11. Method for processing a polymer melt by means of a degassing extruder (100) according to one of the preceding claims, comprising at least the following steps: - feeding a melt stream to the rotor element (11; 11'; 11") rotatably arranged in the housing recess and having at least one rotatably mounted satellite screw (16; 16'); - surface-area distribution of the melt stream on the circumference of the rotor element (11; 11'; 11") and the at least one satellite screw (16; 16'); - discharging the polymer melt from the rotor element (11; 11'; 11") and from the satellite screw (16; 16') to at least one outlet channel, - degassing the polymer melt by applying a vacuum to the suction opening (32); characterized in - that the polymer melt distributed on the rotor element (11; 11'; 11") is conveyed over the length of the rotor element (11; 11'; 11") by means of at least one main screw flight (12; 12'; 12") arranged on the outer circumference of the rotor element (11; 11'; 11") and wherein, to loosen up the melt conveyed in the channels (14; 14'; 14") of the main screw flight (12; 12'; 12"), at least one satellite screw (16; 16') which is arranged in receiving grooves (13; 13'; 13") on the outer circumference of the rotor element (11; 11'; 11") is used; - that the volumetric flow of the polymer melt fed to the multi-screw unit (10) and the volumetric flow discharged therefrom are coordinated to one another in such a way that the conveying volume enclosed between the adjacent portions of the main screw flight (12; 12'; 12"), the outer side of the rotor element (11; 11'; 11") and the inner side of the housing recess is filled to an extent of less than 100% with polymer melt.

12. Method according to Claim 11, characterized in that during the degassing, the conveying volume available in the channels (14; 14'; 14") is filled to an extent of less than 80% with polymer melt.