DE10120995A1 - Solid bowl screw centrifuge with distributor - Google Patents

Abstract

The invention relates to a solid bowl screw centrifuge comprising a centrifuging chamber (19) having a rotating screw (1) and a likewise rotating drum (21) surrounding the centrifuging chamber (19), in addition to a distributor (15) which is preferably embodied as a tube and is used to introduce the material to be centrifuged (S) into the centrifuging chamber (19). Said distributor is oriented in a angular manner, especially perpendicularly, in relation to the central axis (A) of the screw (1). The material to be centrifuged is guided through an axially extending inflow tube (13) into the distributor (15). At least one wall (15a) of the distributor is provided with a surface structure consisting of projections (27) in such a way that the main part of the material to be centrifuged (S) which passes through the distributor must flow around at least one of the projections (27) on the at least one wall (15a) on the radial path from the inflow tube (13) to the centrifuging chamber (19).

Description

The invention relates to a solid bowl screw centrifuge, the following has: a rotating drum, which also has a centrifugal space with a enclosing rotating screw and a preferably designed as a tube Distributor for introducing centrifugal material into the centrifugal space, which is angled, especially special perpendicular to the central axis of the screw, the sluice dergut is passed through an axially extending feed pipe into the distributor.

In solid-bowl screw centrifuges, the centrifuged material should be on the peripheral ge speed of the screw at the diameter of the liquid level (surface) be accelerated in the screw channel. The relative speed be as small as possible when entering the centrifugal chamber (liquid surface).

Acceleration to the peripheral speed results in the distributor the screw on the liquid level diameter on the driver walls (des Distributor) a surface flow, the speed of which is strong with the radius increases, to a value that is approximately equal to the circumferential Ge speed of the screw at the liquid level diameter.  

From US 5,403,486 it is known to control the area of the centrifugal material supply the distributor in the broadest sense - a solid-bowl screw centrifuge with a larger number of outlet openings, which in different Win are aligned with each other. However, this solution is relatively expensive; in addition, no reduction in the relative speed is achieved.

From DE 12 93 089 it is also known to nozzle-like distributor openings in the Cover the centrifugal chamber with a baffle plate that deflects the centrifuged material, to reduce currents. This measure is sufficient for an effective reduction do not adorn swirls.

It is therefore the object of the invention to use the generic Continuing to develop a screw centrifuge such that the relative speed of the Centrifugal goods when entering the liquid surface on structurally simple Way is reduced.

The invention solves this problem by the subject matter of claims 1, 2 and 20th

Advantageous refinements are specified in the subclaims.

According to a first variant, at least one wall of the distributor is also included a surface structure of protrusions provided that the essential part of the centrifugal material flowing through the distributor on this at least one wall on the substantially radial and / or essentially in the direction of the Centrifugal force extending distance from the inlet pipe into the centrifugal chamber at least must flow around one of the projections.

According to a further variant, at least one wall of the distributor is provided with a Surface structure of at least two or more staggered radially to one another Provide rows of protrusions, the protrusions of the rows facing each other  other are axially offset that essentially no radial, free flow channels are formed on the wall.

These variants make it effective, yet simple and relative inexpensive way to ensure that at least the essential part, preferably but the entire centrifugal material, no longer in a direct, radial way out of the container can flow into the centrifugal chamber. The direction is here under "radial" to understand the distributor wall, in which the centrifugal material when turning the Distributor flow essentially into the centrifugal space by the centrifugal force wants d. H. the term "radial" can also be an axial component of motion and / or include a peripheral component. It is important that at least the we considerable part of the centrifugal material is not directly "in the direction of the centrifugal force" in the Spin chamber flows.

It is already known from DE PS 12 72 231, eini on the distributor wall to train ground (smashing) bodies. Best between these bodies hen, however, still direct paths radially into the centrifugal space, so that the liquid essentially not braked but with unchanged high radial speed the centrifugal space. The possibility of using Adv jump to reduce the relative speed of the centrifugal material Entry into the liquid surface in a structurally simple manner was here not recognized.

After a structurally particularly simple and yet particularly effective Variations are the projections as circular, diamond-shaped or in cross-section other square nubs formed.

In other variants, however, the projections have a meandering shape. Here, as well as after other versions, it is advantageous if the pre jumps are designed as sheets.  

According to a further variant, which is also to be considered independently, at least egg ne wall of the distributor with a circumferentially extending, stair provided pen-like surface structure, which also a braking, u. a. by Turbulence.

Exemplary embodiments are described in more detail below with reference to the drawing ben. It shows:

Figure 1 is a sectional view of a solid bowl screw centrifuge.

Fig. 2 shows the lead-in area of a distributor into a centrifugal chamber of a solid-bowl screw centrifuge;

Fig. 3 is a schematic representation of a section through the drum of Fig. 1;

FIGS. 4a-e show various cylindrical nubs assemblies;

Fig. 5-11 different structures of projections on the walls of United dividers;

Fig. 12 is a diagram illustrating the speeds of the centrifuged material.

Fig. 1 shows a solid-bowl screw centrifuge with a screw 1, which comprises a screw body 3, and here the screw body 3 helically surrounding screw blade 5. Between the screw flights x, x + 1,. , , is a screw channel 7 for conveying / transporting a centrifugal material to be processed.

The screw body 3 has in its rear region in FIG. 1 a cylindrical section 9 and in its adjoining region in FIG. 1, a front loading area gradually (alternatively: conically) tapering section 11 .

Centrifuged material S is passed through the centrally arranged inlet pipe 13 into a distributor 15 and from there through radial openings 17 in the distributor 15 into the centrifugal chamber 19 with the screw 1 and the drum 21 surrounding the screw 1 .

When the distributor 15 passes through and when it enters the centrifugal chamber 19 , the centrifuged material S is accelerated. The action of the centrifugal force causes the solid particles to settle on the drum wall in a very short time.

The screw 1 rotates at a slightly smaller or greater speed than the drum 21 and conveys the ejected solid F to the tapered section 11 from the drum 21 to the solids discharge 23 .

In contrast, the liquid L flows to the larger drum diameter at the rear end of the drum 21 and is drained there (overflow 25 ).

In the following, the structural design of the centrifugal material feed from the feed pipe 13 into the centrifugal chamber 19 - that is to say in particular the structure of the distributor 15 - will be considered in more detail.

For this purpose, reference is first made to FIG. 2.

FIG. 2 again shows the inlet pipe 13 , which projects into the distributor 15 , which here has an essentially rectangular cross section (perpendicular to the image plane of FIG. 2) or is essentially designed as a rectangular pipe. Alternative formations are of course conceivable, such as a design of the manifold as a tube construction from two intersecting rectangular tubes or as tubes which are not aligned perpendicular to the drum axis but at any angle to it. Furthermore, cross-sectional geometries deviating from a rectangular cross-section can also be realized.

The centrifugal material S entering the distributor 15 moves at the moment of exit from the inlet pipe 13 with the axial flow velocity in the inlet pipe 13 . When entering the distributor 15 , it is then taken along by the distributor 15 . The centrifugal material S thus rotates with the distributor 15 and, as a result of the centrifugal force in the distributor 15, moves essentially radially outward.

In the area of the openings 17 on the outer, radial edge of the distributor 15 , the centrifuged material has the absolute speed x (see FIG. 3) with which it leaves the distributor 15 (see also FIG. 3). The speed vector x has both a component u in the circumferential direction of the drum 21 and a component called v - relative speed. The relative speed v can contain a component in the radial direction as well as other components in other directions (e.g. axially).

In many products to be centrifuged, the relative speed component v should be as small as possible when the centrifugal material enters the centrifugal chamber 19 , for example in products which are relatively prone to foam formation or have sensitive structures which are not destroyed or damaged as in the prior art may be allowed (e.g. flocculants that should not be destroyed). The centrifugal material S should ideally only enter the centrifugal space with the circumferential rotational speed of the screw body 3 and without relative speed v (see also FIG. 12).

In order to reduce the relative speed v or in particular to prevent excessive acceleration in the radial direction, it is provided at least the walls 15 a, d of the distributor, which in the opposite ends of the distributor 15 essentially hold the centrifugal material during rotation take the distributor 15 with them - or additionally provide the side walls 15 b (or alternatively all the walls) of the distributor with a surface structure, which is formed in particular from directly on the wall 15 a, d or from at least one separate one the wall attachable sheet 29 can be formed projections 27 . A multi-layer arrangement of several sheets 29 lying one above the other with projections 27 can also be realized ( FIG. 3).

The projections 27 are distributed in such a way to the at least one wall 15 a of the Ver divider 15, that at least the predominant part of the in the distributor 15, a passing centrifuged S, but preferably more, on the radial outward path at least one - of the projections 27 must flow around ,

The at least one wall 15 a is also preferably provided with the projections 27 to ensure a sufficient "braking effect" in such a way that essentially no radial (or perpendicular to the outside send white) free flow paths 33 remain for the centrifuged material.

The projections 27 are preferably distributed over an area of 30 to 70% of the at least one wall 15 a of the distributor 15 .

The projections 27 are preferably also formed at least in the radially outer region of the distributor wall 15 a, d. This has the following advantage.

Since the centrifugal force is proportional to the square of the angular velocity and proportional to the radius r (F _z = mω ² r), it is immediately clear that the acceleration of the centrifugal material is greater in the outer, radial area of the distributor 15 than in the inner area, so that in the outer, radial region of the distributor 15 a, the braking effect of the projections 27 counteracts this acceleration particularly advantageously. For this reason, the projections 27 are preferably also formed up to the outer, radial edge of the distributor 15 or to the discharge opening 17 on the wall 15 a of the distributor 27 . The radially inner part of the distributor (z. B. the inner 30 or 50% of the wall surface of the wall 15 a), however, can be smooth, that is, formed without protrusion, without the "braking effect" is significantly reduced.

Since the centrifugal acceleration also increases with increasing radius, a variant of the invention has also proven to be particularly advantageous in which at least one or more wall (s) 15 a, d of the distributor or the plate 29 placed on the wall 15 a with the Projections 27 protrude radially beyond the edge of the opening 17 into the centrifugal space.

According to FIG. 2, the projections 27 as cylindrical studs 27 a, b - preferably of different diameters - formed which dung in holes 31 of the fixed Wan 15 a, z. B. are welded.

Alternative geometries are conceivable, such as triangular cross-sections, rectangular cross-sections te, diamonds, etc.

The projections 27 can also widen or taper away from the wall 15 a. Spherical shapes are also conceivable.

The extension of the projections 27 perpendicular to Verteilerwandung 15 a is selected so that at the particular preferred application (eg. As fruit juice production, etc.) and at a maximum throughput of material to be centrifuged, the projections 27 are at least high, as the liquid level at the wall 15 a. The projections are preferably approximately twice as high as the average liquid level.

The projections can alternatively also be designed as rods which pass through the distributor 15 from the wall 15 a to the opposite wall 15 d.

The knobs 27 can also be formed as stampings or in another way can be formed directly in one piece with the wall 15 a, d or the sheet 29 . This one-piece formation can be carried out further in the casting process or by milling the knob structure from a correspondingly thick wall plate.

According to FIG. 2, an inner, radial region of the wall 15 a protrusion is formed or nub-free. This inner, radial area is followed by a central, radial area with four rows of knobs 27 a aligned parallel to the drum axis A, each of which has a first diameter a. At the middle area, in turn, there is an outer area with three rows of knobs 27 b, which have a smaller diameter b in comparison to the diameter a and are also closer to one another, so that the runs between the knobs 27 b, oblique to the drum axis A aligned flow channels 33 are narrower than the broader b between the knobs 27 a remaining Strö mung channels 33 a.

The knobs 27 a, b are each arranged in rows, which are aligned parallel to the drum salmon A. The rows are arranged axially offset from one another by half the distance between two adjacent knobs 27 a, b in such a way that the centrifuged material S is prevented from flowing directly through in the radial direction. The axial distance d between the knobs 27 a, b is slightly larger than the diameter of the knobs 27 a, b. The distance between the centers of the knobs in ra dialer direction corresponds approximately to their diameter a, b.

According to FIG. 2, the knobs 27 have a diameter that gradually decreases radially outwards. The flow channels 33 are also smaller or narrower. This design causes the centrifugal material to brake more radially from the inside outwards, ie it counteracts the increasing acceleration due to the increasing centrifugal force. The distance to be covered for the centrifuged material S becomes longer by the knobs 27 a, b.

FIGS. 4 to 10 show further variants of nubs structures.

According to Fig. 4a the rows of studs 27 are arranged in each case offset by a diameter of the nubs to one another, wherein the distance between the center points or center axes of the cylindrical studs 27 corresponds to each row a in each of the diam ser d of the studs 27 a.

From Fig. 4a through FIG. 4d, the axial offset of the rows of knobs is reduced relative to each other, respectively. In a direction oblique to the drum axis A there are flow channels 33 which become narrower and become narrower outward. These can also be avoided entirely if the diameter of the knobs 27 a, b as in FIG. 2 or the offset of the rows of knobs is varied from row to row or is further reduced (see FIG. 4e). A wide range of flow characteristics can be achieved through a suitable design of the knobs.

It is conceivable to produce the knobs using pot cutters. For the pimples are Various materials, such as steel, cast iron or even plastics, are conceivable. art Fabric has the advantage that the knobs are slightly flexible or movable, which the Braking effect can increase.

Fig. 4e shows a variant in which the knobs of a row have such a small distance from each other that with an axial offset of the rows of knobs by half the distance between two adjacent knobs no perpendicular to the Mittelach se A of the centrifuge, linear flow channels 33 remain.

According to FIG. 5, the projections are diamond-shaped. The connecting lines of the tips of the diamonds 227 are perpendicular and parallel to the central axis A of the centrifuge. The tips of the diamonds 227 also point in rows in the various diamonds, with flow channels 33 remaining between the diamonds 227 in an oblique or inclined direction to the central axis. The flow channels 33 or diamonds 227 can be z. B. produce by a milling process.

Fig. 6a shows a variant of the invention, in which instead of rows of knobs at least two rows of sheet metal strips 127 are attached to the wall 15 a of the distributor.

These sheet metal strips 127 are each directed at an angle to the central axis A of the centrifuge and are so close to one another in mutually opposed rows offset that again no flow channels remain in the radial direction on the distributor wall but a strong deflection and braking he follows. The angle here is approximately 30 °. The smaller the angle to the central axis, the higher the speed must be so that no deposits form on the sheet metal. The angle could also decrease towards the outside, possibly up to the value 0.

The metal strips 127 could also not be perpendicular to the screw body, but could be formed and / or arranged at any angle (see FIG. 6b) and / or in an L or U or T shape (see for example FIGS. 6c and 6d) , In places with high speed the angle to the central axis should be larger than in places with lower speed.

A variant shows Fig. 7. A first, very flat sheet 127 leads to strong braking from a labyrinth arrangement 128 from further, bent sheets 127 , which is designed so that again no radial flow is possible.

According to FIG. 8, the projections have a meandering type. The zigzag-like meanders 327 intermesh in such a way that in turn no through-flow channels ra dial remain outside in the distributor 15 .

According to FIG. 9 to 11 a kind of step-like surface structure (Stufenkonstrukti on 427) is a shaft of the distributor reali Siert in the manifold 15 and to the walls 15. Both in Fig. 9 and in Fig. 10, the liquid flow must flow via "steps" in the circumferential direction. Again, the effect is optimal if the step construction extends into the liquid level.

According to FIG. 9, the stepped contour is made of a plurality of sheets 428; alternatively, the contour can also be formed from a workpiece (e.g. milled).

The sheets 428 have an angled cross-section, ie they each consist of a section 428 a which runs essentially parallel to the distributor wall and an angled section 428 b which, for example, has an inclination of approximately 30 ° to the vertical on the distributor wall.

The section 428 a of the first plate 428 , which runs essentially parallel to the distributor wall, is placed directly on the distributor wall. The parallel to the distributor wall 428 a sections of the following sheets 428 are each attached to the rear of the angled sections 428 b of the previous sheet, so that a kind of swirling space is created between the successive sheets 428 .

This arrangement has the following advantages.

If the liquid jet strikes from one stage or a plate 428 to the next stage or the next plate 428 , it is directed (in FIG. 9 to the left and right) in the direction of flow and counter to this in different directions and swirls, which in turn causes a braking effect.

Since the metal sheets 428 are offset from one another, the liquid jet moves somewhat counter to the direction of rotation (to the right in FIGS. 9 and 10, arrow P3) along the dashed line.

When it hits, the liquid is divided in the direction of rotation and counter to the direction of rotation (arrows P1, P2). This division and the swirling of the jet ensure a particularly advantageous braking effect. The braking effect is composed here, as it were, of the effect of the oblique sections of the metal sheets 428 and the shadow effect of the eddies (arrow P2).

Fig. 10 differs from Fig. 9 not only in that the step construction 427 was realized in one piece from a cast or milled part, but in that the step construction is designed such that the section 429 a of the steps running essentially parallel to the distributor wall 429 connects to the ends of the angled sections 429 b of the previous stage, so that there is no swirling space between the successive stages.

An alternative to FIGS. 9 and 10 is shown in FIG. 11. In this figure, a type of "waterfall brake inflow" is realized. A type of step contour 427 is also implemented here; however, the individual steps 430 are here again formed by rows of projections 431 running essentially parallel to the drum axis, or rows of grooves 432 are milled into a plate. The rows of grooves 432 in turn have an angled cross-section, that is to say they each consist of a section 432 a running essentially parallel to the distributor wall and an angled section 432 b which, for example, has an inclination of approximately 30 ° to the vertical on the distributor wall , The sections 432 a of the rows of grooves which essentially run parallel to the distributor wall are essentially flush with one another, ie they lie in one plane, which makes the manufacture cheaper compared to the variant in FIG. 10 (less waste during milling or less casting material required) , It is advantageous in the example shown here that the oblique section 432 b has an angle of approximately 30 ° to the vertical on the distributor wall and that the impingement of the liquid jet on the next step is also at an angle of z. B. 30 °.

LIST OF REFERENCE NUMBERS

1

slug

3

screw body

5

screw blade

7

screw channel

9

cylindrical section

11

tapered section

13

inlet pipe

15

distributor

15

ad walls

17

discharge

19

centrifugal chamber

21

drum

23

solids

25

overflow

27

projections

27

a, b pimples

29

sheet

31

drilling

33

flow channels

127

metal strip

128

labyrinth arrangement

227

diamonds

327

meander

427

stage design

428

sheets

428

a, b sections

429

stages

430

stages

431

projections

432

rows of grooves

432

a, b sections
A drum axis
S centrifuged goods
a, b diameter: knobs
d Distance: nubs axially
x, x + 1,. , , screw flights
S centrifuged goods
F solid
L liquid
r radius
α, α1 angle of inclination
P1-P3 arrows

Claims (27)

1. Solid bowl screw centrifuge, which has the following:
a rotating drum ( 21 ) which surrounds a centrifugal space ( 19 ) with a screw ( 1 ) which also rotates,
a distributor ( 15 ), preferably in the form of a tube, for introducing centrifugal material (S) into the centrifugal chamber ( 19 ), which is angled, in particular perpendicular, to the central axis (A) of the screw ( 1 ),
wherein the centrifuged material is passed through an axially extending feed pipe ( 13 ) into the distributor ( 15 ), characterized in that at least one wall ( 15 a) of the distributor is provided with a surface structure made of projections ( 27 ) that the essential Part of the centrifugal material flowing through the distributor (S) on this at least one wall ( 15 a) on the substantially radial and / or substantially in the direction of the centrifugal force extending distance from the inlet pipe ( 13 ) in the centrifugal space ( 19 ) at least one of the Projections ( 27 ) must flow around. 2. Solid bowl screw centrifuge, in particular according to claim 1, characterized in that the at least one wall ( 15 a) of the distributor with at least two or more radially offset rows of the projections ( 27 ) is provided, wherein the projections ( 27 ) Rows are axially offset from one another in such a way that essentially no radial and / or substantially in the direction of the centrifugal force flow channels are formed on the wall ( 15 a). 3. solid bowl screw centrifuge according to claim 1 or 2, characterized in that the projections are formed as cross-sectionally circular, diamond-shaped or other-angular knobs ( 27 ). 4. solid bowl screw centrifuge according to claim 1 or 2, characterized in that the projections ( 227 ) have a meandering shape. 5. Solid bowl screw centrifuge according to claim 1 or 2, characterized in that the projections ( 127 ) are designed as sheet metal strips and / or are produced by welding, milling or the like. 6. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the sheet metal strips ( 127 ) are each angled - before preferably 30 ° - to the central axis (A) of the centrifuge and are of the kind closely lined up, in particular in mutually angular rows, that no flow channels remain in the radial direction on the distributor wall. 7. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the angle (α) preferably between the sheet metal strips ( 127 ) and the central axis (A) decrease with increasing radius of the distributor ( 15 ) or with increasing distance to the drum axis , 8. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the sheet metal strips ( 127 ) form a labyrinth to the centrifugal space. 9. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the knobs ( 27 ) from the wall of the distributor ( 15 ) from tapering or widening or circular or ku gel-like or constant in diameter have a contour. 10. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the knobs ( 27 ) are integrally formed with the wall ( 15 a) or the sheet ( 29 ). 11. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the knobs ( 27 ) are welded into bores in the sheet metal ( 29 ) or the wall ( 15 a). 12. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the knobs ( 27 ) have such a height we substantially perpendicular to the wall ( 15 a) that at maximum throughput of centrifugal material (S) the liquid level on the wall ( 15 a) is lower than the height of the knobs. 13. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the diameter and / or the distance of the knobs ( 27 ) decreases radially outwards. 14. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the diameter and / or the distance of the knobs ( 27 ) is constant radially outwards. 15. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the projections provided with the wall ( 15 a) or the plate ( 29 ) on the wall together with the projections over the peripheral wall of the screw body into the centrifugal chamber ( 19 ) a stretch. 16. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the projections ( 27 ) are formed at least in the outer, ra dialen area of the distributor ( 15 ). 17. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the surface structure with the projections ( 27 ) covers at least 40% of the area of the wall ( 15 a). 18. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that in the distributor ( 15 ) on the at least one wall ( 15 a) several superimposed layers of plates provided with the projections are arranged so that the distributor by flowing centrifugal material flow is divided into several parts. 19. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the projections ( 27 ) and / or the sheet metal, cast or plastic or rubber receiving the cracks are available. 20. Solid bowl screw centrifuge, which has the following:
a rotating drum ( 21 ) which surrounds a centrifugal space ( 19 ) with a screw ( 1 ) which also rotates,
a distributor ( 15 ), preferably in the form of a tube, for introducing centrifugal material (S) into the centrifugal chamber ( 19 ), which is oriented at an angle, in particular perpendicular, to the central axis (A) of the screw ( 1 ),
the centrifuged material being fed into the distributor ( 15 ) through an axially extending feed pipe ( 13 ),
characterized in that at least one wall ( 15 a) of the distributor is provided with a step-like surface structure extending in the circumferential direction - step structure ( 427 ). 21. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the step construction ( 427 ) consists of a plurality of sheets ( 428 ) lying on / against one another in the circumferential direction. 22. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the step construction ( 427 ) consists of a one-piece metal or plastic body. 23. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the plates ( 428 ) have an angled cross-section and each consist of a section substantially parallel to the distributor section ( 428 a) and an angled section ( 428 b) , 24. Solid bowl screw centrifuge according to one of the preceding claims, characterized in
that the section ( 428 a) of the first plate ( 428 ) extending essentially parallel to the distributor wall is placed directly on the distributor wall and
that the parallel to the distributor wall ( 428 a) extending sections of the following sheets ( 428 ) are each brought to the rear of the angled sections ( 428 b) of the previous sheets, so that a swirl space is formed between the successive sheets ( 428 ). 25. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the step construction is designed in such a way that the section ( 429 a) of each step ( 429 ) running essentially parallel to the distributor wall is in each case at the end of the angled section ( 429 b ) the previous stage. 26. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the individual steps ( 430 ) are formed by rows of grooves ( 432 ) which run parallel to the drum axis and which preferably have an angular cross section. 27. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the respective substantially parallel to the Ver partition wall sections ( 432 a) of the rows of grooves ( 432 ) are essentially in one plane.