Solid bowl screw centrifuge screw with one screw flight

Description

Background of the invention

[0001] The invention relates to a solid-bowl screw centrifuge screw comprising a screw flight and a metallic screw hub serving as the base body. Furthermore, the invention relates to a manufacturing method for such a solid-bowl screw centrifuge screw.

[0002] Known solid-bowl screw centrifuge screws comprise a screw flight, which usually extends as a wound sheet metal outside a hollow cylindrical or tubular screw hub. The wound sheet metal protrudes radially outward from the screw hub at approximately a right angle to such an extent that the sheet metal or screw flight almost touches a surrounding drum. This drum, together with the screw, is one of the essential components of a solid-bowl screw centrifuge and rotates at high speeds during operation. Such a solid-bowl screw centrifuge screw is known, for example, from DE 12 97 034 B.

[0003] As the drum rotates, the rotating screw flight immerses itself in a phase mixture contained within the drum. From this phase mixture, the screw flight conveys a heavy, or denser, phase that separates radially outward from a light, or less dense, phase that collects radially inward. Depending on the application, the heavy phase often comprises particularly heavy solids such as soil, sand, and stones.

[0004] Especially with such heavy solids, in combination with the high rotation speeds during operation, the mechanical load on the screw and especially on the screw flight is enormous. Underlying task

[0005] The invention is based on the object of creating a particularly wear-resistant solid bowl screw centrifuge screw and a corresponding manufacturing method. Inventive solution

[0006] This object is achieved according to the invention with a solid bowl screw centrifuge screw comprising a screw flight and a metallic screw hub serving as a base body, in which the screw flight is produced by means of formative build-up welding.

[0007] By means of form-forming build-up welding, a screw flight is produced according to the invention, which is formed entirely from weld seams or weld layers. A first weld layer is applied helically around and onto a metallic screw hub serving as the base body. Chromium-nickel steels, duplex steels, and nickel-based steels are preferably used as the base material for the build-up welding according to the invention. A second weld layer is subsequently applied to the first weld layer, followed by a third weld layer to the second weld layer, and so on. The weld layers applied one after the other in this way form a helical surface of the screw flight, projecting radially from the screw hub on both sides. Such a helical surface produced by form-forming build-up welding is surprisingly so hard and strong that no further processing is required.This results in a particularly wear-resistant screw flight after just one step of build-up welding. Conventional screw flights formed from sheet metal generally require remachining on their flight surfaces and subsequent coating or hardening. In particular, wear layers are applied during this process. Such coating is significantly more expensive than the solution according to the invention, simply because of the additional processing steps required.

[0008] There is also a risk that such a layer will wear out during operation of the solid bowl screw centrifuge and, over time, become detached from the screw surface due to the friction that occurs.

[0009] In contrast, the solution according to the invention creates a screw flight whose material is not only very hard and strong, but also completely uniform. Designed in this way, the screw flight according to the invention exhibits particularly high and long-lasting wear resistance.

[0010] Alternatively, the spiral surface according to the invention can also be coated, making it even more wear-resistant. A coating with tungsten carbide creates an even harder surface in addition to the particularly wear-resistant weld surface. A tungsten carbide layer comprises the chemical elements tungsten and carbon, which form intercalated solid solutions. Carbon atoms are intercalated between the tungsten lattice sites. For the coating, fused tungsten carbide (WSC) in a matrix metal is preferably applied to the spiral surface using autogenous flame fusion welding.

[0011] According to the invention, the screw flight according to the invention is advantageously manufactured by welding with an active, reactive welding gas or with an inert welding gas as a formative build-up welding. Such welding processes are also referred to as MAG or MIG welding, or as welding with active gas or inert gas. Collectively, such processes are referred to as gas metal arc welding (GMAW). Such welding processes are defined in the standard EN ISO 4063: Processes 135 and 131.

[0012] Furthermore, according to the invention, a welding gas is preferably specifically selected from specific subgroups of welding gases. According to DIN EN ISO 14175, welding gases are divided into main groups I, M1, M2, M3, C, R, N, O, and Z. Of the welding gases in these main groups, only those welding gases that fall into main groups I, M1, M2, and N are preferably selected. Other welding gases are deliberately excluded according to the invention because, as has been shown according to the invention, these additional welding gases are not conducive to the solution sought according to the invention.

[0013] Main Group I includes welding gases with 100 volume percent nominal argon (Subgroup 1), 100 volume percent nominal helium (Subgroup 2), and 0.5 to 95 volume percent nominal helium, with the remainder argon (Subgroup 3). These welding gases are completely inert.

[0014] Main group M1, subgroup 1 includes welding gases with 0.5 to 5.0 volume percent nominal carbon dioxide, 0.5 to 5.0 volume percent nominal hydrogen, and the balance argon or helium. These welding gases are slightly oxidizing and only slightly reducing. Main group M1, subgroup 2 includes welding gases with 0.5 to 5.0 volume percent nominal carbon dioxide, and the balance argon or helium. These welding gases are slightly oxidizing. Main group M1, subgroup 3 includes welding gases with 0.5 to 3.0 volume percent nominal oxygen, and the balance argon or helium. These welding gases are also slightly oxidizing. Main group M1, subgroup 4 includes welding gases with 0.5 to 5.0 volume percent nominal carbon dioxide, 0.5 to 3.0 volume percent nominal oxygen, and the balance argon or helium. These welding gases are also slightly oxidizing.

[0015] Main group M2, subgroup 0 includes welding gases with 5.0 to 15.0 volume percent nominal carbon dioxide and the remainder argon or helium. These welding gases have low oxidizing power. Main group M2, subgroup 1 includes welding gases with 15.0 to 25.0 volume percent nominal carbon dioxide and the remainder argon or helium. These welding gases also have low oxidizing power. Main group M2, subgroup 2 includes welding gases with 3.0 to 10.0 volume percent nominal oxygen and the remainder argon or helium. These welding gases also have low oxidizing power. Main group M2, subgroup 3 includes welding gases with 0.5 to 5.0 volume percent nominal carbon dioxide, 3.0 to 10.0 volume percent nominal oxygen and the remainder argon or helium. The main group M2, subgroup 4 includes welding gases with 5.0 to 15.0 volume percent nominal carbon dioxide, 0.5 to 3.0 volume percent nominal oxygen and the remainder argon or helium.Main group M2, subgroup 5 includes welding gases with 5.0 to 15.0 volume percent nominal carbon dioxide, 3.0 to 10.0 volume percent nominal oxygen, and the balance argon or helium. Main group M2, subgroup 6 includes welding gases with 15.0 to 25.0 volume percent nominal carbon dioxide, 0.5 to 3.0 volume percent nominal oxygen, and the balance argon or helium. Main group M2, subgroup 7 includes welding gases with 15.0 to 25.0 volume percent nominal carbon dioxide, 3.0 to 10.0 volume percent nominal oxygen, and the balance argon or helium. These welding gases are also comparatively low in oxidation.

[0016] Main group N, subgroup 1 includes welding gases with 100 volume percent nominal nitrogen. Main group N, subgroup 2 includes welding gases with 0.5 to 5.0 volume percent nominal nitrogen and the balance argon or helium. Main group N, subgroup 3 includes welding gases with 5.0 to 50.0 volume percent nominal nitrogen and the balance argon or helium. Main group N, subgroup 4 includes welding gases with 0.5 to 1.0 volume percent nominal hydrogen, 0.5 to 5.0 volume percent nominal nitrogen and the balance argon or helium. Main group N, subgroup 5 includes welding gases with 0.5 to 50.0 volume percent nominal hydrogen and the balance nitrogen. These welding gases are all inert, they are inert with high argon or helium content and they are only slightly reducing even with increasing hydrogen content.

[0017] In summary, the invention specifically selects welding gases that are inert, have low oxidizing and / or low reducing properties. As demonstrated by the invention, such a process enables the use of a low-oxidation weld bead and largely slag-free form-welding. This allows the weld seams or weld beads to be superimposed particularly well, ensuring a tight fit and a strong bond, as well as adhering to one another. Furthermore, a particularly fast welding speed can be achieved, enabling particularly short production times. The actual advantage of the fast welding speed is that the worm hub and previously applied weld beads are only slightly heated at specific points during welding. This results in minimal distortion or deformation.The particular advantage of the procedure according to the invention, however, is surprisingly that such build-up welding results in a particularly high wear resistance of the spiral surface produced thereby.

[0018] In an advantageous development of the invention, the welding gas has a nominal carbon dioxide content of less than 20 percent by volume. Such a low carbon dioxide content makes it possible, in particular, to advantageously process structural steels using pulse welding according to the invention. At the same time, a comparatively high burn-off of the welding wire is possible. This results in a high mass build-up during welding and a particularly fast operation. Preferably, the welding gas used is one with an oxygen content of less than the nominal volume percent. Such welding gases are particularly low in oxidation. Welding gases with a high argon content are also particularly inexpensive.

[0019] Particularly preferably, the inventive gas-shielded welding device is operated with a pulsed arc. Such a pulsed arc allows precise control of the melting of the welding wire on the gas-shielded welding device. Furthermore, the heat input into the workpiece can be deliberately kept particularly low, and temperature-induced deformation can be minimized.

[0020] The electrical welding current of such a pulsed arc welding system preferably has a base current of less than 200 amperes and a pulse current of greater than 200 amperes. Such welding currents are advantageous for particularly precise material build-up with a comparatively low deposition rate. The welding gas used is preferably a welding gas with a nominal 98% argon and 2% carbon dioxide by volume.

[0021] It is also particularly advantageous to operate the inventive gas-shielded welding device with a short arc, particularly a reduced-energy short arc. Such a process with a short arc is also referred to as a cold arc, i.e., a process with a particularly cold arc. To achieve a still highly molten arc, it is particularly advantageous to use an increased melting current pulse.

[0022] During build-up welding, it is also advantageous for the first weld layer to be wider than the second weld layer. This is achieved in particular by operating the gas-shielded welding device with a higher welding current during the application of the first weld layer than during the application of the at least one second weld layer. Alternatively, the first weld layer can be welded in an oscillating manner, with a slower welding speed or with a higher wire feed. With this procedure, the first weld layer is applied with a particularly thick or large mass deposit. The high-volume first weld layer is then overlaid by a second weld layer that has less volume and is therefore narrower. Together, this results in a rounded foot or shoulder on the base body of the workpiece, which has a low notch effect and thus high rigidity.

[0023] The inventive gas-shielded welding device is particularly advantageously operated with one welding wire, or advantageously two welding wires (twin welding process) with a diameter of 0.5 mm to 3.0 mm, preferably 1.0 mm to 1.6 mm. Surprisingly, such a welding wire diameter results in a high welding speed and, at the same time, particularly low thermally induced deformation. Individual welding layers or welding passes with a width of 6 to 7 mm are particularly preferred. A welding band with a rectangular cross-section is also particularly advantageous.

[0024] The base body of the workpiece according to the invention is preferably moved during the production of the metallic workpiece. During this movement, the workpiece is aligned at its welding location in such a way that an optimal position is achieved for the applied welding layer. The welding layer is particularly preferably applied to a horizontal surface. It is also advantageous if the welding layer is applied to a surface that slopes slightly upwards in the welding direction. The slope angle is preferably between 5° and 15°, advantageously between 7° and 10°. Accordingly, the base body is preferably moved in such a way that a horizontal welding surface or a welding surface that slopes upwards in the welding direction of the inert gas welding device is present at the welding location of the inert gas welding device.

[0025] In an advantageous development of the invention, the screw flight is designed with a flight pitch that varies in the longitudinal direction of the screw. By means of such a varying flight pitch, the speed of the material transport, in particular the transport of the heavy phase, can be adjusted as needed in the longitudinal direction of the screw. A low flight pitch improves material transport in the case of solids that are difficult to convey. Such a varying flight pitch, which is advantageous according to the invention, can be produced particularly quickly and easily by means of form-forming build-up welding, with high variability and low labor expenditure. Only different pitch ranges need to be entered into a data processing device controlling an automatic welding device.

[0026] Accordingly, the screw flight can be advantageously designed as a multi-start helix using form-forming build-up welding, which is quick, simple, and cost-effective to manufacture. Such a multi-start helix comprises several congruent screw lines or helices, which are offset from one another in their pitch. Such a multi-start helix can generate a large axial movement with comparatively little rotation. This allows for particularly fast material transport in the longitudinal direction of the screw flight.

[0027] According to the invention, the screw flight is preferably further provided with a balancing weight, which is also manufactured by means of form-forming build-up welding. With at least one such balancing weight, uneven mass distributions and structural imbalances on the screw flight and the connected screw hub can be compensated. The individual balancing weight can be welded onto the screw flight with particular precision in terms of location and size. Furthermore, the balancing weight welded in this way is particularly stable thanks to the integral weld deposit on the screw flight. The balancing effort is thus significantly reduced. Such a stable and precisely positioned arrangement of the individual balancing weight is of great advantage, particularly at the high rotational speeds prevailing during operation of solid bowl screw centrifuges.An imbalance and the resulting vibrations would otherwise have a significantly greater impact on almost all components.

[0028] Furthermore, it is advantageous to provide the screw flight according to the invention with at least one through-opening, which is also produced by means of shape-giving build-up welding. Such a through-opening enables a significantly faster and more energy-efficient removal of the lighter, radially inner phase compared to removal by means of a screw flight without a through-opening. Without a through-opening, the radially inner, light phase must flow along all turns of the screw flight against a transport direction of the radially outer, heavy phase. This path along the turns is considerably longer compared to a path that the light phase has to travel when passing through at least one through-opening. According to the invention, such a through-opening can preferably already have been recessed within the flight surface during the shape-giving build-up welding of the screw flight.The screw flight can be manufactured particularly quickly and cost-effectively in just one step.

[0029] Furthermore, it is advantageous to design the screw flight according to the invention with a profiled flight cross-sectional area. Such a profiled flight cross-sectional area can be manufactured particularly easily in a wide variety of shapes, depending on individual requirements, using form-giving build-up welding. The flight cross-sectional area is designed as a flight root at its radially inner end adjacent to the flight hub, in particular thickened and / or with a rounding, bevel, or chamfer. Designed in this way, the light phase running along it during operation can flow away in an energy-saving manner without significant flow resistance. A flight neck adjoining the flight root is preferably designed to taper radially outwards with an angle of attack or an inclination, in particular tapering.This allows the movement of material flowing along the central area of ​​the spiral cross-sectional area to be enhanced, similar to a blade surface, thus saving additional energy. A spiral head located radially outwardly adjacent to the spiral neck is preferably designed with a clearing edge and / or an additional coating. The clearing edge allows the heavy phase located radially outwardly of the drum to be particularly comprehensively collected and expelled from the drum. The additional coating can protect this particularly heavily loaded area of ​​the spiral against abrasion, particularly from sand and debris.

[0030] Furthermore, according to the invention, a damming disk in the form of a baffle disk, immersion disk or flotate disk is advantageously formed on the screw flight, which is also produced by means of form-giving build-up welding. A disk produced in this way can be attached particularly stably, simply and cost-effectively, in particular to the associated screw hub. The damming disk is preferably attached to the screw hub where no spiral blade is arranged. Particularly preferably, the damming disk is located on a conical section of the screw hub, after which only the heavy phase is to be transported away in the discharge direction of the heavy phase. The damming disk ends with its diameter radially further inwards than the drum and thus serves as a weir to prevent further transport of the radially inner, lighter phase in the discharge direction of the heavy phase.

[0031] According to the invention, a scraper is also advantageously formed on the screw flight, which is also manufactured by means of form-forming build-up welding. This type of scraper is also particularly cost-effective in production and particularly stable during operation. Such a scraper must be particularly stable and able to withstand high forces. Its function, located at an end region of the screw flight in the discharge direction of the heavy phase, is to remove the heavy phase, particularly solids.

[0032] The invention further relates to a manufacturing method of a solid bowl screw centrifuge screw, in which the screw flight is manufactured by means of formative build-up welding. Brief description of the drawings

[0033] In the following, exemplary embodiments of the inventive solution are explained in more detail with reference to the attached schematic drawings. It shows: Fig. 1 a first part of a longitudinal section of a solid bowl screw centrifuge screw according to the invention, Fig. 2 a second part of the longitudinal section according to Fig. 1 , Fig. 3 a side view of section III according to Fig. 1 , Fig. 4 the detail IV according to Fig. 1 in an enlarged view, Fig. 5 the top view V according to Fig. 2 , Fig. 6Variants of detail VI according to Fig. 2 , Fig. 7a first variant of view VII according to Fig. 5 , Fig. 8a second variant of view VII according to Fig. 5 , Fig. 9a third variant of view VII according to Fig. 5 and Fig. 10 a fourth variant of view VII according to Fig. 5 . Detailed description of the embodiment

[0034] In the Fig. 1 to 10 A screw 10 of a solid-bowl screw centrifuge is shown, which is to be manufactured as the workpiece mentioned here. The screw 10 has an axis of rotation 12 that defines an axial direction 14 and a radial direction 16.

[0035] The screw 10 is surrounded by a drum 18 and serves to discharge a heavy phase from a phase mixture (not shown) in the axial direction 14 within the drum 18. The screw 10 is designed with a central screw hub 20 and a screw flight 22 helically surrounding it.

[0036] Furthermore, a shielding gas welding device 24 is provided, by means of which the screw flight 22 is produced in a shaping build-up welding.

[0037] For this purpose, a first weld layer 26 is applied to the screw hub 20 using the inert gas welding device 24, followed by a second weld layer 28. Further second weld layers are applied in this manner, one above the other. This creates a flat, helical element or a spiral surface that forms the screw flight 22.

[0038] During the production of the screw flight 22 by means of build-up welding, the worm hub 20 serves as a first base body and is moved during production. In particular, the worm hub 20 is rotated about its axis of rotation 12, while simultaneously the gas-shielded welding device 24 is moved in the axial direction 14 and gradually raised in the radial direction 16.

[0039] The gas-shielded welding device 24 comprises a welding wire 30 and is operated in the MIG / MAG process with a welding gas 32. In this case, the welding gas 32 is selected from one of the subgroups of main groups I, M1, M2, or N of the DIN EN ISO 14175 standard and has a nominal carbon dioxide content of less than 20 percent by volume and a nominal oxygen content of less than 3 percent by volume. An arc 34, which in this case is implemented as a pulsed arc, is generated by the gas-shielded welding device 24.

[0040] In this way, the screw flight 22 can be designed particularly simply and cost-effectively, with low distortion and at the same time, with exceptional wear resistance. In particular, a multi-start flight can also be easily manufactured. The screw flight 22 can also be designed with a flight pitch 36 that varies in the axial direction 14 or in the longitudinal direction of the screw 10, i.e., has different sizes.

[0041] Furthermore, a balancing weight 38 can be simultaneously produced on the screw flight 22 by means of formative buildup welding. The balancing weight 38 can be individually and precisely dimensioned using individual weld points and / or larger accumulations of weld material. This significantly reduces the balancing effort.

[0042] Furthermore, the screw flight 22 can be provided with various through holes 40 very easily and without machining processes because it is manufactured by shaping build-up welding.

[0043] A dam-up disc 42 is also fabricated on the screw flight 22 by means of form-forming build-up welding. The disc 42 can function as a dam-up disc, but also as an immersion disc or flotate disc.

[0044] In addition, a reamer 44 is formed on the screw flight 22 at its end region on the screw hub 22 by means of the forming build-up welding.

[0045] A transition 46 from the worm hub 20 to the worm helix 22 is formed as a rounded, chamfered, or beveled portion by means of the formative build-up welding. For this purpose, the first weld layer 26, as shown in Fig. 4 is illustrated, is made wider than the second welding layer 28 arranged above it. The wider welding layer 26 is produced in particular with a higher welding current, a pendulum welding process or a lower welding feed.

[0046] A lateral helix surface 48 of the screw flight 22 was mechanically reworked by build-up welding after its manufacture. However, such rework is not mandatory. Furthermore, a wear-resistant coating 50 made of tungsten carbide was optionally applied to the helix surface 48. This coating was also applied as a single layer by build-up welding using the inert gas welding device 24.

[0047] The screw flight 22 has a flight cross-sectional area 52 according to the Fig. 6 advantageously profiled in various variants. The spiral cross-sectional surface 52 has a spiral root 54 radially inward, a spiral neck 56 radially further outward, and a spiral head 58 radially outward.

[0048] The spiral cross-sectional area 52 is according to the two variants in Fig. 6top left in radial direction 16 tapering radially outwards. According to a variant in Fig. 6 top middle and two variants in Fig. 6 At the bottom right, the profiled spiral cross-sectional surface 52 has a spiral head 58 which is thickened in the axial direction 14.

[0049] In several variants, a clearing edge 60 which is inclined axially towards the clearing direction and which carries the coating 50 is formed on the spiral head 58.

[0050] According to three variants in Fig. 6 At the top center, the spiral cross-sectional area 52 has a first support web 62 and a second support web 64, with the support webs 62 and 64 being largely radially aligned. A free space 66 is located in the axial direction 14 between the support webs 62 and 64. This creates a lightweight yet structurally particularly stable construction.

[0051] A through-opening 68 passes through at least one of the support webs 62 and 64 and is located in particular in the second support web 64 facing away from a clearing side 70 of the screw flight 22.

[0052] According to variants in Fig. 6 At the top right and bottom left, the profiled spiral cross-sectional surface 52 has a first section 72 extending in the radial direction 16 and a second section 74 inclined relative to the radial direction 16. An angle of attack 76 or an inclination of this second section 74 is preferably between 10° and 40°, in particular between 15° and 20°.

[0053] According to several variants in Fig. 6 At the top and bottom, the profiled spiral cross-sectional surface 52 has a third section 78 which, viewed in cross section, is curved in the shape of a bowl.

[0054] The worm hub 20 has also been manufactured at least partially by means of shaping build-up welding with the inert gas welding device 24.

[0055] The worm hub 20 has a Fig. 1 On the far left, it has a cylindrical, first longitudinal section 80, which serves as the second base body for the build-up welding. Accordingly, the longitudinal section 80 itself was not manufactured by build-up welding, but rather conventionally as a tube, which was further turned and milled.

[0056] A first bearing support 82 for the screw 10 has been formed on the longitudinal section 80 by turning or turning processes.

[0057] The longitudinal section 80 is followed on the worm hub 20 in the direction of the rotation axis 10 by a frustoconical, second longitudinal section 84, which is produced by means of formative buildup welding. In this case, an annular first weld layer 86 is first applied to the longitudinal section 84, followed by a second weld layer 88 and numerous additional second weld layers in the direction of the rotation axis 12 or opposite the axial direction 14.

[0058] During such build-up welding, the first longitudinal section 80 has been moved and in particular rotated, wherein the inert gas welding device 24 is then moved counter to the axial direction 14, but otherwise only slightly moved radially in order to form the truncated cone shape.

[0059] The second longitudinal section 84 is followed, opposite to the axial direction 14, by a cylindrical, third longitudinal section 92, which is essentially tubular and manufactured in a conventional manner. The longitudinal section 92 can also advantageously be manufactured by build-up welding and, in particular, can be designed in a grid-like manner. Located on the longitudinal section 92 is an inlet chamber 94, into which the phase mixture to be clarified is to be introduced. This inlet chamber 94 is particularly advantageously manufactured by form-forming build-up welding because individually designed flow surfaces can then be formed on it.

[0060] Furthermore, outlet openings 96, which are to be produced in the longitudinal section 92 in the region of the inlet chamber 94, can advantageously be formed by means of build-up welding.

[0061] In the area of ​​the longitudinal section 92, an inlet pipe 98 is located radially inward or concentrically to the axis of rotation 12. This inlet pipe 98 is also advantageously manufactured by means of formative build-up welding, so that special flow and guide surfaces can also be specifically formed on it.

[0062] In the Fig. 7 to 10 various embodiments of through-openings 40 in the respective associated screw flight 22 with associated screw hub 20 are shown.

[0063] The individual through-opening 40 has Fig. 7 It has a particularly wide section in the radial center in the circumferential direction. This section allows a middle layer of the phase mixture to be clarified to pass through the screw flight 22.

[0064] According to Fig. 8Several through-openings 40 are arranged at two different radii in the radial direction 16. The radially outer through-openings 40 have a greater width in the circumferential direction than the radially inner through-openings. This embodiment also allows material from a circumferential layer that is to be clarified to a specific extent to pass through the screw flight 22.

[0065] In Fig. 9 An embodiment is shown in which the through-openings 40 are wider radially on the inside than radially on the outside. This width difference in the circumferential direction is designed in steps. With this embodiment, more material can pass through the screw flight 22 when it has reached the radius of the step toward the inside.

[0066] Fig. 10Finally, FIG. 1 shows an embodiment in which the through-openings 40 are designed as straight slots inclined obliquely to the radial direction 16. When material passes through them, such slots result in mixing and thus in the breaking up of the material to be clarified. List of reference symbols

[0067] 10Screw 12Rotation axis 14Axial direction 16Radial direction 18Drum 20Screw hub 22Screw flight 24Inert gas welding device 26First welding layer of the screw flight 28Second welding layer of the screw flight 30Weld seam 32Welding gas 34Arc 36Flight pitch 38Balancing weight 40Through opening 42Disk 44Raker 46Transition 48Flight surface 50Coating 52Flight cross-sectional area 54Flight base 56Flight neck 58Flight head 60Raking edge 62First support web 64Second support web 66Free space 68Through opening 70Raking side 72First section of the flight cross-sectional area 74Second section of the Spiral cross-sectional area 76Angle of attack 78Third section of the spiral cross-sectional area 80First longitudinal section of the screw hub 82First bearing support 84Second longitudinal section of the screw hub 86First weld layer on the screw hub 88Second weld layer on the screw hub 92Third longitudinal section of the screw hub 94Inlet chamber 96Exit opening 98Inlet pipe

Claims

1. A solid-bowl centrifuge screw (10) comprising a screw flight (22) and a metallic screw hub (20) serving as base body, characterized in that the screw flight (22) is produced by means of shaping build-up welding and is formed completely of welding layers (26, 28), wherein a first welding layer (26) is helically applied around and to the metallic screw hub (20) serving as base body, wherein a second welding layer (28) is subsequently applied to the first welding layer (26), a third welding layer is subsequently applied to the second welding layer (28) and so forth, wherein the welding layers (26, 28) applied in such a way one after the other and one on top of the other, protrude radially from the screw hub (20) building a helical surface (48) of the screw flight (22) on both sides.

2. The solid bowl centrifuge screw according to claim 1, characterized in that the screw flight (22) is designed with a flight pitch (36), which varies in the longitudinal direction of the screw (10).

3. The solid bowl centrifuge screw according to claim 1 or 2, characterized in that the screw flight (22) is designed as a multiple thread flight.

4. The solid bowl centrifuge screw according to one of claims 1 to 3, characterized in that the screw flight (22) is provided with a balance weight (38), which is likewise produced by means of shaping build-up welding.

5. The solid bowl centrifuge screw according to one of claims 1 to 4, characterized in that the screw flight (22) is provided with at least one passage opening (40), which is likewise produced by means of shaping build-up welding.

6. The solid bowl centrifuge screw according to one of claims 1 to 5, characterized in that the screw flight (22) is designed with a profiled cross-sectional flight surface (52).

7. The solid bowl centrifuge screw according to one of claims 1 to 6, characterized in that a disk (42) having a damming effect, which is likewise produced by means of shaping build-up welding, is formed on the screw flight (22).

8. The solid bowl centrifuge screw according to one of claims 1 to 7, characterized in that a scraper (44), which is likewise produced by means of shaping build-up welding, is formed on the screw flight (22).

9. A production method of a solid-bowl centrifuge screw (10), comprising a screw flight (22) and a metallic screw hub (20) serving as base body, characterized in that the screw flight (22) is produced by means of shaping build-up welding and is formed completely of welding layers (26; 28), wherein a first welding layer (26) is helically applied around and to the metallic screw hub (20) serving as base body, wherein a second welding layer (28) is subsequently applied to the first welding layer (26), a third welding layer is subsequently applied to the second welding layer (28) and so forth, wherein the welding layers (26; 28) applied in such a way one after the other and one on top of the other, protrude radially from the screw hub (20) building a helical surface (48) of the screw flight (22) on both sides.

10. The production method according to claim 9, characterized in that a first welding layer (26) as well as a second welding layer (28), which is applied to the first welding layer (26), are created during the build-up welding by means of a welding apparatus (24), and the first welding layer (26) is formed to be wider than the second welding layer (28) during the application.