Helical screw conveyor unit, screw shaft, screw press and method for providing a screw shaft

Description

Technical area

[0001] The present invention relates to a spiral screw conveyor unit according to the preamble of claim 1.

[0002] The present invention further relates to a screw shaft, in other words a conveyor screw, according to the preamble of claim 6.

[0003] The present invention further relates to a screw press according to the preamble of claim 14.

[0004] Finally, the present invention relates to a method for providing a worm shaft according to the preamble of claim 15. State of the art

[0005] The general structure of a screw shaft for use in a screw press and a screw press for dewatering a suspension is described, for example, in the documents EP 1 072 574 A2, US 2017 / 08778 A1 and EP 2 792 739 A1.

[0006] Document EP 1 072 574 A2 discloses a fermentation plant with a fermenter and a dewatering device as a cylindrical screw conveyor. This screw conveyor extends along a linear axis. As shown in the Figures 1 to 3 As shown, the spiral elements form a solid unit with the worm shaft.

[0007] US 2017 / 08778 A1 discloses a screw press for dewatering an aqueous suspension of organic material. The device comprises a press chamber in which a press screw with spiral elements winds helically and is mounted for rotation about its longitudinal axis. To allow simple and quick maintenance of the screw press, US 2017 / 08778 A1 teaches the provision of multi-part, upwardly pivoting screen baskets, which allow easy access to the press chamber and screen changes by a single person.

[0008] Document EP 2 792 739 A1 discloses a twin-screw shaft in a compression chamber, such as those used in cell disruption extruders. The helical screw conveyor units have so-called clearing tines on the adjacent screw shafts.

[0009] Anaerobic digestion (A[naerobic]D[igestion]) is a bioprocess that enables the energetic utilization of organic residues, especially green waste, by converting them into biogas. The substrate is digested under anaerobic conditions in a fermenter. A digestate containing the waste materials is mixed with liquid, and the resulting digestate suspension is fermented anaerobically in a fermenter.

[0010] The digestate produced during the fermentation of the fermentation material suspension is dewatered using a screw press, separating the press water to produce a press cake with a higher dry matter content than the digestate. After the substrate leaves the fermenter, it is separated into solid and liquid digestate by a screw press.

[0011] Essentially, a screw press consists of an internal screw shaft with helically wound spiral elements and a screen drum or screen cylinder enclosing the screw shaft. The digestate to be dewatered is pumped into the screen drum via a digestate inlet. The screw shaft rotates, conveying the digestate toward a press cake outlet, where there is a resistance, such as a counterpressure cone, against which the digestate is pressed. The press water drains off via a press water outlet.

[0012] The further the digestate is transported forward, i.e., toward the resistance, the greater the volume reduction and the higher the pressure on the digestate. This forces even more liquid out of the digestate, which runs off as press water. The dewatered press cake leaves the screw press via a press cake discharge.

[0013] During operation of the screw press, the spiral elements wear out over time. This wear occurs more rapidly the more pressure the spiral elements exert on the digestate, and is particularly severe in the front area of the screw shaft, closest to the press cake discharge. Wear shifts the pressing point backward, reducing the amount of water drained from the digestate. Worn spiral elements must therefore be serviced or replaced.

[0014] As in the Figures 2 and 3As shown in US 2017 / 08778 A1, the spiral elements are usually firmly connected to the shaft of the worm shaft, for example, by welding. If individual spiral elements wear out, extensive welding work must be performed or the entire worm shaft must be replaced.

[0015] EP 0098 340 A1 discloses a screw pump for conveying solid and granular material. To ensure that the particularly worn end sections of the screw flight are arranged in a replaceable manner, replaceable sleeves are provided in the end section, which can be pulled axially off the screw shaft. To replace the sleeves, the screw shaft must be removed from the screw pump.

[0016] Furthermore, GB 859 416 A discloses a screw conveyor with replaceable screw elements that can be attached as sleeves. To enable the removal of individual sections of the screw shaft for maintenance and repair work, the screw shaft is constructed from several matching sleeve-like longitudinal sections. These longitudinal sections are releasably attached to the shaft of the screw shaft by means of semicircular, clamp-like bearings. After loosening the bearings, the sleeve-like longitudinal sections can be pulled axially away from the shaft of the screw shaft. For this, the screw shaft must be removed from its bearing on at least one side.

[0017] To avoid the laborious removal and repair of screw conveyor blades after they wear out, which involves welding, the document CN 212 831 025 U teaches how to attach the blades to the shaft using a groove and screws. The blades are separate paddle-like elements that are screwed to the shaft independently of one another. Description of the present invention: task, solution, advantages

[0018] The invention is based on the object of further developing a helical screw conveyor unit of the type mentioned above, a worm shaft of the type mentioned above, a screw press of the type mentioned above, and a method of the type mentioned above such that the helical screw conveyor unit can be serviced with minimal maintenance effort. In particular, the helical screw conveyor unit designed as a replacement element for a helix should be replaceable without having to remove the worm shaft from its bearing. Furthermore, the maintenance costs of the worm shaft should be reduced.

[0019] This object is achieved by a helical screw conveyor unit having the features specified in claim 1, by a worm shaft having the features specified in claim 6, by a screw press having the features specified in claim 14, and by a method having the features specified in claim 15. Advantageous embodiments and expedient further developments of the present invention are characterized in the respective dependent claims.

[0020] The invention is therefore based on the fact that the helical screw conveyor unit can be mounted radially interchangeably on a fastening area of the worm shaft shaft. The helical screw conveyor unit can thus be mounted as a replaceable spare part on a rotatably mounted worm shaft of a screw press. The present invention thus enables quick replacement of the helical screw conveyor unit because, due to the radial opening of the base body of the helical screw conveyor unit designed to accommodate the shaft, it can be mounted radially interchangeably on the shaft and can be replaced even if the shaft is mounted at its axial ends in at least one pivot bearing.

[0021] In this context, "radial" refers to a direction perpendicular to the longitudinal axis (L) of the worm shaft shaft or the base body of the worm shaft. Radial interchangeability thus enables efficient replacement of the reversing elements without removing the worm shaft from its bearings, resulting in long operating times.

[0022] The shaft of the worm shaft is a rod-shaped element for transmitting rotary motion. The helical screw conveyor unit can be mounted as a detachable spare part on the fastening area of the shaft. The helical screw conveyor unit is thus advantageously designed to be detachably mounted on a fastening area of a worm shaft as described above. Furthermore, the worm shaft is advantageously suitable for installation in a screw press of the type described above.

[0023] For releasably securing the base body of the helical element to the fastening area, the helical screw conveyor unit has at least one fastening element. Advantageously, the fastening element of the helical screw conveyor units of the type described above can be releasably connected to the fastening means, in particular to the fastening structure, of the worm shaft of the type described above.

[0024] In an advantageous embodiment, the base body is a foot element of the spiral element, which is arranged on the radially inner region of the spiral element. The fastening element is designed to releasably fasten the foot element to the fastening region. The fluff element can be placed on the fastening region like a foot, and the spiral element extends outward from the foot element.

[0025] In order to attach the spiral element to the worm shaft in a simple, radially detachable manner, the fastening element can, in its position of use, extend radially into a support area of the shaft designed to support the spiral screw conveyor unit and can fasten the foot element resting on the fastening area to the support area.

[0026] In an advantageous embodiment, the support region of the shaft has at least two spiral elements, with each spiral element being assigned at least one fastening element, and the fastening elements of the adjacent spiral elements being arranged both axially and radially offset from one another. The fastening element is preferably a cylinder head screw, and the fastening means is a thread. Alternatively, the fastening element can also interact with the fastening means in the manner of a releasable snap closure.

[0027] Preferably, the inner surface of the base body of the helical screw conveyor unit of the type described above is designed to rest, in particular to bear, on the fastening region of the worm shaft of the type described above. In other words, the fastening region is associated with a region of the worm shaft that is designed to support the base body of the helical screw conveyor unit.

[0028] In order to make replacing the helical screw conveyor unit on the worm shaft particularly easy, the inner surface of the base body is advantageously shaped such that, when the inner surface of the base body rests on the fastening area of the worm shaft, the alignment of the helical element of the helical screw conveyor unit on the worm shaft is defined and radial mobility of the base body on the worm shaft is at least limited. Thus, the inner surface of the base body and the fastening area advantageously have a shape or structure which interact and prevent radial slippage or rotational movement of the helical screw conveyor unit about the shaft. Radial rotational movement of the helical screw conveyor unit about the shaft is already prevented by the interaction of the shape or structure of the fastening area with the shape or structure of the inner surface of the base body.The fastening means then serves for further or additional fixation. As described in more detail below, this fastening, achieved by means of a shape or structure, can be achieved, for example, by means of a square-like shape of the fastening area. The fastening area is designed for releasably fastening the fastening element of the helical screw conveyor unit and is assigned to a support area of the worm shaft shaft designed to support the helical screw conveyor unit. The fastening area has at least one fastening means, such as a fastening structure. Advantageously, the support area has at least two fastening areas, so that advantageously at least two helical screw conveyor units of the type described above can be releasably fastened to the support area of the worm shaft.

[0029] Advantageously, the worm shaft therefore has at least two helical screw conveyor units. The fastening regions of the support region are preferably designed such that adjacent helical screw conveyor units are each arranged axially and radially offset from one another, for example offset in a mirror-image manner. In this advantageous exemplary embodiment, the worm shaft has at least two helical elements arranged axially and radially offset from one another. Accordingly, the support region has at least two fastening regions arranged axially and radially offset from one another. Advantageously, in this exemplary embodiment, the fastening elements of the adjacent helical screw conveyor units are also arranged axially and radially offset from one another, for example offset by 90 degrees, approximately perpendicular to one another.

[0030] The spiral elements have a partial spiral turn, for example, a quarter to half a spiral turn. Several adjacent spiral elements together result in a spiral, helical, or screw-like spiral turn. Several spiral turns together result in the screw-like, helical, or spiral-like wound spiral of the screw shaft. Since the spiral elements are interchangeable in the present invention, an increased material output of these spiral elements can be accepted compared to a screw shaft known from the prior art with non-detachable spiral elements, and the resistance of the screw press can be increased; for example, the counterpressure cone can be enlarged or lengthened to provide greater force for dewatering the digestate.

[0031] The base body of the helical screw conveyor unit has a radial opening. The fastening area can be passed through this opening in a radial direction, i.e., in a direction perpendicular to the longitudinal axis (L) of the base body, and positioned on the inner surface of the base body. In other words, the support area can be passed through the opening and accommodated in a cavity surrounded by the concave base body.

[0032] The fastening element is preferably designed to provide a positive connection between the base body and the support area or shaft body element of the shaft, for example, a screw, such as a cylinder head screw. Alternatively, the fastening element could also be designed to provide a snap connection or a clamp connection.

[0033] In order to be able to arrange the base body supported on the support area, the inner surface of the base body is designed to be complementary to the fastening area and the outer side of the base body is concavely curved and runs, preferably in a half-shell or semicircular shape, around the longitudinal axis.

[0034] The fastening region has at least one support surface designed to support the base body, in particular the inner surface of the base body. To prevent the base body from slipping on the support surface, the inner surface of the lateral surface of the base body advantageously has at least one contour designed to arrange the base body in a fixed position on the fastening region and is advantageously designed to complement the fastening region or the support surface of the fastening region. The contour of the inner surface of the base body of the helical screw conveyor unit is preferably U-shaped or N-shaped in cross-section.

[0035] The helical screw conveyor unit on the screw shaft can be replaced particularly quickly and easily if the helical element is shaped in such a way that, by resting the inner surface of the base body on the fastening area of the screw shaft, the helical element is aligned in such a way that it at least essentially continues the course of the helically or spirally wound helix of the screw shaft.

[0036] To prevent radial slippage of the base body on the shaft, the inner surface of the lateral surface can be rectangular, curved, bent, or stepped, for example. For example, the fastening area can be U-shaped in cross-section and the inner surface of the base body can be N-shaped in cross-section, or vice versa.

[0037] The support area of the shaft can be designed as a square, at least in the area of the fastening area. Alternatively, the fastening area can be formed by at least one recess or at least one groove in the otherwise cylindrical support area. For example, the fastening area can be a U-shaped or N-shaped recess in the otherwise cylindrical support area. To prevent the helical screw conveyor units from slipping on the fastening area, the latter advantageously has a square seat.

[0038] The spiral element comprises a portion or section of a spiral turn, preferably half a spiral turn. Alternatively, it can also comprise, for example, a third of a spiral turn or a quarter of a spiral turn. The spiral screw conveyor unit comprises at least one spiral unit, preferably several, for example, four, spiral units arranged side by side. For a precise connection, spiral elements of the spiral screw conveyor unit arranged side by side can be welded and ground together.

[0039] Advantageously, the fastening element extends radially through the support area in its use position and projects into the base body or through the base body of at least one helical screw conveyor unit arranged on the support area. Particularly preferably, the fastening element projects into the base body of a helical screw conveyor unit at its end exiting the support area. This allows the fastening element to be only partially released to replace the helical screw conveyor unit, for example, only released from the base body of the helical screw conveyor unit while still remaining attached to the support area. This prevents the fastening element from becoming lost.

[0040] The worm shaft advantageously has at least one helical screw conveyor element according to the type described above, wherein the helical screw conveyor element can be detachably fastened to the fastening region.

[0041] In addition to the helical screw conveyor element, the shaft can further comprise a cylindrical shaft body extending along the longitudinal axis with at least one shaft body helix wound helically around the shaft body. The fastening area of the support area, which also extends along the longitudinal axis, has a smaller cross-sectional diameter than the cylindrical shaft body. This allows the helical screw conveyor unit to be arranged on the support area such that the upper side of its outer surface is flush with the cylindrical shaft body.

[0042] Advantageously, the support area is arranged eccentrically, particularly in a region near the end, for example, at the terminal, of the cylindrical shaft body. Thus, the screw shaft can be arranged in a screw press such that the at least one replaceable spiral element is located in the front area of the screw press, closest to the press cake discharge. Replacing only the front spiral, which is most affected by wear, allows for simple, quick, and low-cost maintenance of the screw shaft.

[0043] In an advantageous embodiment of the method of the present invention, the screw shaft is maintained by at least one fastening means which fastens a first helical screw conveyor unit to the fastening region is released, the first helical screw conveyor unit is removed from the worm shaft, a further helical screw conveyor unit is arranged on the fastening region and is detachably fastened to the fastening region by means of a fastening means assigned to this further helical screw conveyor unit.

[0044] Finally, the present invention relates to the use of at least one screw shaft of the type described above in a screw press of the type described above for separating solid and liquid fermentation residues from biogenic residues, in particular green materials, treated by means of a fermenter. Short description of the drawings

[0045] As already discussed above, there are various possibilities for advantageously embodying and developing the teaching of the present invention. For this purpose, reference is made, on the one hand, to the claims subordinate to claim 1 and claim 6. On the other hand, further embodiments, features and advantages of the present invention are described below, inter alia, with reference to the Figures 1 to 7 illustrated embodiment is explained in more detail.

[0046] It shows: Fig. 1 shows a perspective view of a longitudinal section of a first embodiment of a worm shaft according to the present invention, with a helical screw conveyor unit according to the present invention that can be detachably arranged thereon and is replaceable according to the method of the present invention; Fig. 2 shows a longitudinal section of the worm shaft from Figure 1 ; Fig. 3a side view of the worm shaft from Figure 1; Fig. 4 a detailed view of the front area of the worm shaft from Figure 2 ; Fig. 5 a cross-section of the spiral screw conveyor unit from Figure 1 along the Figure 3 shown line BB; Fig. 6in exploded view the worm shaft from Figure 1 ; and Fig. 7 an embodiment of a screw press according to the present invention with the screw shaft from Figure 1 .

[0047] Identical or similar designs, elements or features are not included in the Fig. 1 to 7 provided with identical reference symbols. Best way of carrying out the invention

[0048] Figure 1shows an embodiment of a helical screw conveyor unit 100 for a worm shaft 200. The helical screw conveyor unit 100 has a base body 10 extending along a longitudinal axis L. The base body has two end regions that extend perpendicular to the longitudinal axis, in other words, opposite each other in the direction of the longitudinal axis. The end regions 12, 14 are connected to one another by a lateral surface, with at least one helically wound helical element 30 being arranged around an upper side 16 or outer surface of the lateral surface.

[0049] In the Figures 1 to 3 In the embodiment shown, the worm shaft 200 has several, for example two, spiral elements 30. To ensure a precise connection of the spiral elements 30, they can be welded and ground together.

[0050] The at least one spiral element 30 has a partial, in particular a quarter to a half, spiral turn. The base body is concavely curved, i.e., arched inward, and has a radial opening 20. In other words, the base body is hollow and extends in an arc around the longitudinal axis L. Preferably, the base body extends in a partially circular shape, for example, like a half-shell, around the longitudinal axis L.

[0051] The helical screw conveyor unit 100 is designed for replaceable installation in a screw shaft 200, preferably in a screw shaft 200 of a screw press 300 designed for dewatering digestate obtained by anaerobic fermentation of organic material.

[0052] Figure 6shows an exploded view of the worm shaft 200. This has four helical screw conveyor units 100, which together form two rotating helices. Adjacent helical screw conveyor units 100 are arranged radially offset by 180 degrees, i.e., mirror-image, to one another. For releasably fastening the base body 100 to the fastening areas 40 of the support area 210, the helical screw conveyor units each have two cylinder heads 34. The fastening areas 40 are shaped like a partial square or rectangular. The areas of the support area 210 opposite the helical screw conveyor units 100 or the fastening areas 40 are designed as filler bodies. These protect and stabilize the support area 210. These filler bodies can be firmly connected to the support area 210, for example, formed integrally with the support area 210, or can be releasably attached to the support area 210.The packings are concavely bent around the longitudinal axis L.

[0053] As in Figure 7 As shown, the screw press 300 has an internal screw shaft 200 with outwardly extending helically wound spiral elements 30, 210 and a screening drum 340 enclosing the screw shaft 200. The screening drum 340 can have pivoting screening shells, allowing easy access to the screw shaft and quick replacement of screening and wear parts.

[0054] For interchangeable installation in a worm shaft 200, the spiral screw conveyor unit 100 on the lateral surface of the base body 10 an inner surface 18 designed to receive a support region 210 of a shaft 230, and at least one fastening element 34 designed to releasably fasten the inner surface 18 to the support region 210.

[0055] The spiral screw conveyor unit 100 is therefore a detachably attachable or replaceable element for a worm shaft 200.

[0056] In an embodiment of the present invention, not shown here, the worm shaft 200 may comprise exclusively replaceable spiral elements 30. Alternatively, as shown in the Figures 1 to 7 shown, it is possible to design only a partial area, for example a front area of the screw shaft 200 close to a press cake discharge 350 in the position of use, as an exchangeable spiral screw conveyor unit 100.

[0057] The Figures 1 to 7The worm shaft shown has, in addition to the replaceable helical screw conveyor unit 100, a shaft 230 with a cylindrical shaft body and with a shaft body helix 240 wound helically around the shaft 230. In the region of the cylindrical shaft body, the shaft body helix 240 is permanently connected to the shaft 230, for example, formed integrally with the shaft 230 or welded to the shaft 230.

[0058] The support region 210 of the helical screw conveyor unit 100 can be permanently connected to the cylindrical shaft body, for example, by welding, such as a root weld 232. Alternatively, the support region 210 can also be formed integrally with the cylindrical shaft body of the shaft 230.

[0059] The spiral screw conveyor units 100 are arranged such that the spiral elements 30 continue the course of the shaft body spiral 240 of the cylindrical shaft body and form a common shaft body spiral unit with them.

[0060] The base body 10 of the spiral screw conveyor unit 100 is concavely curved. REVISED SHEET (RULE 91) ISA / EP

[0061] The base body can be designed such that, in the use position of the worm shaft 200, the support area 210 is completely enclosed by the base bodies of the helical screw conveyor units 100 arranged on the support area 210 (not shown). For example, two helical screw conveyor units 100 designed as half-shells can each completely enclose the shaft body element 210.

[0062] Alternatively, the base body 10 can be a foot element 32 of the spiral element 30, which is arranged on the radially inner region of the spiral element 30 and can be arranged interchangeably in a fastening region 40 of the support region 210 designed as a groove.

[0063] In the Figures 1 to 7 In the embodiment shown, the spiral frequency of the spiral elements 30 is identical to the spiral frequency of the shaft body spiral 240. However, the spiral frequency, or the pitch of the spiral elements 30, could also increase compared to the spiral frequency of the shaft body spiral 240.

[0064] To ensure the screw shaft 200 can be rotatably mounted in the screw press 300, the screw press 300 has at least one pivot bearing 250. To relieve the gearing of the screw press 300 from radial and axial forces, the screw shaft 200 can be supported by two bearings. This enables a longer service life of the screw press 300.

[0065] A preferred material for the helical screw conveyor unit 100 of the type set out above and for the worm shaft 200 of the type set out above is steel. List of reference symbols

[0066] 10Base body, in particular foot element of the spiral element 30 12First end region of the base body, in particular first end region of the base body extending perpendicular to the longitudinal axis 14Second end region of the base body, in particular second end region of the base body extending perpendicular to the longitudinal axis 16Top side, in particular outer side, of the lateral surface of the base body 10 18Inner side of the lateral surface of the base body 10 20Radial or concave opening of the base body 10 30Helix element of the spiral screw conveyor unit 100 34Fastening element of the spiral element 30 40Fastening area, in particular U-shaped fastening area, square or receiving groove, of the base body 10 42Filling body 100Helix screw conveyor unit 200Screw shaft or conveyor screw or press screw, in particular rod-shaped screw shaft with helical or spiral wound spiral elements 240,30 210Shaft body element or support area of the worm shaft shaft 230 designed to support the base body 10 of the helical screw conveyor unit 100, in particular shaft support area or support area of the shaft 230 of the worm shaft 200 212Fastening means, in particular thread, of the shaft body element 210 230Shaft or rod-shaped base body of the worm shaft 200, in particular with a cylindrical shaft body and support area designed to support the base body 10 of the helical screw conveyor unit 100 210 232Weld seam, in particular root weld, for connecting the cylindrical shaft body 230 to the base body 10 240Spiral or helical or screw-like wound shaft body helix or helix element of the worm shaft 200 250Rotary bearing (cf. , Figure 4 ) 300Screw press 340Screen drum 350Press cake discharge 360Digestate inlet 370Resistance, especially counterpressure cone LLongitudinal axis

Claims

1. Helical screw conveyor unit (100) configured as an exchangeable element for a helicoidally or spirally winding helix (240) of a worm shaft (200), having a main body (10) extending along a longitudinal axis (L), the main body (10) having two axial end regions (12, 14) and a lateral surface that connects the end regions (12, 14) to one another, at least one helicoidally winding helix element (30) being arranged on a top side (16) of the lateral surface and extending radially outward away from the top side (16), characterized in that - the top side (16) of the lateral surface is concavely curved in shell-like form about the longitudinal axis (L), and the main body (10) has a radial opening (20), the radial opening (20) being configured such that a fastening region (40) of a shank (230) of the worm shaft (200) can be led through the opening (20) in a direction perpendicular to the longitudinal axis (L) and can be arranged in a cavity formed by the main body (10), - the helix element (30) has at most one half of one helix turn, - the lateral surface of the main body (10) has an inner surface (18) configured for being seated on the fastening region (40), and - the helical screw conveyor unit (100) has at least one fastening element (34) configured for detachably fastening the main body (10) to the fastening region (40).

2. Helical screw conveyor unit as claimed in claim 1, characterized in that the main body (10) runs in the shape of a semicircle or in the shape of a half-shell about the longitudinal axis (L), in particular is configured as a half-shell, and the helix element (30) has one half of one helix turn.

3. Helical screw conveyor unit as claimed in claim 1 or 2, characterized in that the inner surface (18) of the main body (10) is shaped such that, as a result of the inner surface (18) of the main body (10) being seated on the fastening region (40) of the worm shaft (200), the orientation of the helix element (30) of the helical screw conveyor unit (100) on the worm shaft (200) is defined, and radial mobility of the main body (10) on the worm shaft (200) is at least restricted.

4. Helical screw conveyor unit as claimed in claim 3, characterized in that, for the orientation of the helix element (30) on the worm shaft (200), the inner surface (18) of the lateral surface has a contour of complementary shape with respect to the fastening region (40) of the shank (230).

5. Helical screw conveyor unit as claimed in claim 2 or 3, characterized in that the helix element (30) is shaped such that, as a result of the inner surface (18) of the main body (10) being seated on the fastening region (40) of the worm shaft (200), the helix element (30) is at least substantially oriented so as to continue the course of the helicoidally or spirally winding helix (240) of the worm shaft (200).

6. Worm shaft (200) for use in a worm extruder (300), having a shank (230) which extends along a longitudinal axis (L) and which has a helicoidally or spirally winding helix (240), characterized by at least one helical screw conveyor unit (100) as claimed in at least one of claims 1 to 5, and at least one fastening means (212) configured for detachably fastening the fastening element (34).

7. Worm shaft as claimed in claim 6, characterized in that the fastening means (212) is configured to interact with the fastening element (34) of the helical screw conveyor unit (100) such that the helical screw conveyor unit (100) is detachably fastenable to the fastening region (40) of the worm shaft (200).

8. Worm shaft (200) as claimed in claim 6 or 7, characterized in that the fastening region (40) of the worm shaft (200) is shaped such that a radial movement of the main body (10) seated on the fastening region (40) is at least restricted.

9. Worm shaft (200) as claimed in at least one of claims 6 to 8, characterized by at least two fastening regions (40) which are formed by at least one recess or at least one groove of the otherwise cylindrical shaft body element (210) and which are arranged so as to be radially and axially offset with respect to one another.

10. Worm shaft (200) as claimed in at least one of claims 6 to 9, characterized in that the shank (230) has a cylindrical shaft body and the fastening region (40), the fastening region (40) being assigned to a support region (210), configured for supporting the main body (10) of the helical screw conveyor unit (100), of the shank (230) and having a cross-sectional diameter smaller than that of the cylindrical shaft body.

11. Worm shaft (200) as claimed in claim 10, characterized in that the support region (210) is arranged eccentrically, in particular on a near-terminal region, for example on a terminal region, of the shank (230).

12. Worm shaft as claimed in claim 10 or 11, characterized in that the support region (210) has at least two helical screw conveyor units (100) configured as claimed in at least one of claims 1 to 5, the helical screw conveyor units (100) being arranged such that the helical elements (30) of the helical screw conveyor units (100) continue the course of the shaft body helix (240) of the cylindrical shaft body and, with this, form a common shaft body helix unit.

13. Worm shaft as claimed in at least one of claims 10 to 12, characterized in that the worm shaft has at least two helical screw conveyor units (100) which are in each case arranged adjacent to one another and together form one full helix turn that fully encircles the shank (230) once.

14. Worm extruder (300) for dewatering a suspension, in particular for dewatering digestate obtained by anaerobic digestion of organic material, having an extruder chamber in which a worm shaft (200) having a helicoidally winding helix element is mounted (250) so as to be rotatable about its longitudinal axis (L), characterized in that the worm shaft (200) is configured as claimed in at least one of claims 6 to 13, the shank (230) of the worm shaft (200) having at least two helical screw conveyor units (100), in particular being encased by at least two helical screw conveyor units (100), and the helical screw conveyor units (100) being configured as claimed in at least one of claims 1 to 5.

15. Method for providing a worm shaft (200) configured for use in a worm extruder (300), characterized in that - a helical screw conveyor unit (100) configured as claimed in at least one of claims 1 to 5 is arranged on the fastening region (40) and - is detachably fastened to the fastening region (40) by means of the fastening element (34) assigned to said helical screw conveyor unit (100).