Screw of a solid bowl screw centrifuge

Abstract

The invention relates to a screw (30) of a solid bowl centrifuge (10), comprising a screw hub (32) extending along a longitudinal axis (12), and a screw flight (34) surrounding the screw hub; the screw hub (32) is provided with a lattice structure (56) in a section (36) of the longitudinal extension thereof.

Claims

1. A screw of a solid-bowl screw centrifuge, comprising: a screw hub (32) extending along a longitudinal axis (12); and a screw helix (34) surrounding the screw hub (32), wherein the screw hub (32) has a grid structure (56) in a portion (36) of a longitudinal extent of the screw hub (32), and wherein the grid structure (56) has at least one inclined strut (64) that extends oblique to the longitudinal axis (12) between two transverse discs (60).

2. The screw of a solid-bowl screw centrifuge claim 1, wherein the inclined strut (64) projects at its end into an adjacent transverse disc (60).

3. The screw of a solid-bowl screw centrifuge of claim 1 wherein the at least one inclined strut (64) comprises three inclined struts (64) equally spaced over the circumference of the screw hub (32).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a longitudinal section through a solid-bowl screw centrifuge according to the prior art.

(2) FIG. 2 shows a longitudinal section through a solid-bowl screw centrifuge according to the invention having a screw which is designed, in a portion of its longitudinal extent, with a grid structure.

(3) FIG. 3 shows a side view of the grid structure according to FIG. 2 with longitudinal bars, transverse discs and inclined struts.

(4) FIG. 4 shows the view according to FIG. 4 of the grid structure with the longitudinal bars omitted.

(5) FIG. 5 shows the section V-V according to FIG. 3 in an enlarged representation.

(6) FIG. 6 shows the section according to FIG. 5 with alternative longitudinal bars.

(7) FIG. 7 shows the section according to FIG. 5 in an alternative configuration.

DETAILED DESCRIPTION

(8) In the figures there is depicted a solid-bowl screw centrifuge 10 that extends substantially along a horizontal longitudinal axis 12. The solid-bowl screw centrifuge 10 has an outer housing 14, in which a drum 16 is mounted rotatably about the longitudinal axis 12. By rotating the drum 16 at a high rotational speed, a centrifugal force can be generated therein, by means of which a material to be clarified can be separated into a heavy and a light phase. For this purpose, the drum 16 is supported at a first drum bearing 18 and a second drum bearing 20.

(9) On the drum 16 there is formed an inlet 22 for the material to be clarified as well as an outlet 24 for the heavy phase and an outlet 26 for the light phase. To rotate the drum 16 there is provided a drive 28. The outlet 26 acts as an overflow for the light phase situated radially inwards in the drum 16, so that this phase flows out automatically there provided that a predetermined level, the so-called pond depth, is reached in the drum 16. In order to be able to discharge from the drum 16 the heavy phase situated radially outwards in the drum 16, a screw 30 is provided in the drum 16. The screw 30 is rotated by the drive 28 relative to the drum 16 and the material of the heavy phase is thereby discharged along a cone, formed on the drum 16, radially inwardly and thus to the outlet 24.

(10) For this purpose, the screw 30 has a screw hub 32 that extends along the longitudinal axis 12 and is surrounded radially outwards by a screw helix 34. The screw hub 32 thus serves to support the screw helix 34 in the radial direction, to transmit torque from the drive 28 to the screw helix 34 and in doing so to take up in particular tensile forces and shearing forces.

(11) For this purpose, the screw hub 32 has a cylindrical longitudinal portion 36 and an axially adjoining conical longitudinal portion 38. The screw hub is mounted rotatably by a first screw bearing 40 and a second screw bearing 42. As can be readily seen in FIG. 1, in a screw hub 32 according to the prior art, over its entire longitudinal extent, i.e. both in the cylindrical longitudinal portion 36 and in the conical longitudinal portion 38, its lateral surface 44 is designed substantially closed or covering the whole area by a metal plate or a tubular surface. Only where an inlet pipe 46 for supplying material to be clarified ends centrally in an inlet region 48 into the interior of the screw hub 32 are there provided individual openings 50 in the lateral surface 44, through which the material to be clarified can flow radially outwards. Furthermore, individual openings 50 are provided in the cylindrical portion of the screw hub 32 according to FIG. 1 surrounding the inlet pipe 46. Material that may unintentionally have gotten into the end of the inlet pipe 46 in this inner part of the screw hub 32 can flow out of this inner part radially outwards. Furthermore, a relatively large fluid-tight space 54 is situated in the interior of the screw hub 32 axially opposite the inlet pipe 46. This space is intended to prevent any material to be clarified from getting into the interior of the screw hub 32 at all. At the same time, however, this relatively large fluid-tight space 54 also causes large buoyancy forces if the screw hub 32 is to be immersed in the material to be clarified. With such a construction the screw hub 32 must not be permanently immersed in the material to be clarified.

(12) Consequently, a pond depth 52 of this solid-bowl screw centrifuge 10 according to the prior art is substantially limited by the outer radius or the outer diameter of the screw hub 32 to a relatively large radius or diameter.

(13) Illustrated in FIGS. 2 to 7 are exemplary embodiments of solid-bowl screw centrifuges 10 that make it possible and that also are provided for permanently immersing the screw hub 32 in the material to be clarified. In this solid-bowl screw centrifuge the associated screw hub 32 is designed in the cylindrical longitudinal portion 36 and specifically exclusively in this portion with a grid structure 56.

(14) The grid structure 56 in the present case is designed by means of twelve longitudinal bars 58 that are arranged over the circumference of the screw hub 32 in the longitudinal direction thereof, i.e. distributed parallel to the longitudinal axis 12 at equal spacings. The preferred number, according to the invention, of longitudinal bars 58 lies between eight and sixteen, in particular between ten and fourteen. The longitudinal bars 58 form radially outwards in each case a bearing surface for the screw helix 34 and are supported radially inwards on transverse discs 60. The longitudinal bars 58 extend over the transverse discs 60 which are oriented transversely to the longitudinal axis 12 and thus form an inner support for the longitudinal bars 58. The transverse discs 60 are designed, radially inwards by means of a central open 62, hollow in the form of an annular disc, so that in particular also the inlet pipe 46 can extend through them.

(15) Between each two transverse discs 60 there extend between two and six inclined struts 64. In the exemplary embodiment according to FIGS. 5 and 6, there are three inclined struts 64, and, in the exemplary embodiment according to FIG. 7, there are four inclined struts 64. These inclined struts 64 are inclined with respect to the longitudinal axis at an angle of between 30 and 40, preferably between 33 and 37, in the present case 35, and at their ends are each bevelled and welded to the adjacent transverse disc 60. The respective inclined strut 64 preferably projects into a recess (not shown) on the transverse disc 60. By means of this recess the inclined strut 64 is advantageously coupled in a form-fitting manner to the transverse disc 60 and for the assembly of the grid structure, which given the required low dimensional tolerances is quite difficult, can be positioned easier and more precisely.

(16) In addition to the longitudinal bars 58 and inclined struts 64 which in FIGS. 5 and 7 are each of round and solid form in cross-section, various advantageous cross-sectional shapes 66 for the longitudinal bars 58 are illustrated in FIG. 6. A hexagonal shape is advantageous in view of a uniform bending moment distribution and furthermore an outflow of material from radially inwards to radially outwards. A rectangular shape is advantageous in view of the two bending moments of different size in the radial direction and in the circumferential direction which are thereby achieved. A triangular shape is advantageous because a wide radially outer area for the screw helix 34 results and yet material can easily flow out from inside towards the outside. With regard to these properties, a semi-circular shape is a good compromise, since semi-circular material can be obtained far more cost-effectively. By means of a hollow shape, in particular a circular tube shape, high bending moments with low material requirement and low weight can be achieved. A square shape is inexpensive to obtain and is advantageous precisely when two of the corners are aligned in the radial direction. The diagonal bending moment axes of this shape are then also advantageously used. By means of a T-shape a wide contact surface for the screw hub 32 can also be provided radially outwards.

(17) In conclusion, it should be noted that all the features which have been mentioned in the application documents and in particular in the dependent claims, despite their formal dependence on one or more specific claims, should also be accorded independent protection individually or in an any arbitrary combination.

LIST OF REFERENCE NUMERALS

(18) 10 solid-bowl screw centrifuge 12 longitudinal axis 14 outer housing 16 drum 18 first drum bearing 20 second drum bearing 22 inlet for material to be clarified 24 outlet for heavy phase 26 outlet for light phase 28 drive 30 screw 32 screw hub 34 screw helix 36 cylindrical longitudinal portion 38 conical longitudinal portion 40 first screw bearing 42 second screw bearing 44 closed lateral surface 46 inlet pipe 48 inlet region 50 opening in the lateral surface 52 pond depth 54 fluid-tight space 56 grid structure 58 longitudinal bar 60 transverse disc in the shape of an annular disc 62 central opening 64 inclined strut 66 cross-sectional shape of the longitudinal bars