Repair of damaged components and / or damaged sections of a solid shell screw centrifuge

Description

[0001] The invention relates to a method for repairing damaged components and / or damaged component sections of a solid-bowl screw centrifuge, according to claim 1.

[0002] Centrifuge screws of a solid-bowl screw centrifuge are typically based on a cylindrical or conical base and at least one screw helix. Such a screw helix is ​​often made of sheet metal. Due to wear, it is sometimes necessary to repair the screw helix of a centrifuge screw.

[0003] JP S56 73549 U discloses a method for mechanically measuring a screw helix. If deviations from a specified target value are found, the screw or individual component sections can be replaced.

[0004] From WO 2018 / 149454 A1 it is known to manufacture a screw hub using a form-giving build-up welding process.

[0005] German patent application DE 10 2014 222159 A1 discloses a repair method for a turbine blade of an aircraft engine, wherein this repair method is carried out in a process chamber of a device for the additive manufacturing of the component. The component area to be repaired is separated outside the device by means of a separation process.

[0006] In the event of a repair, it is usually necessary to completely remove the existing screw helix in several subtractive steps. A new screw helix is ​​then manufactured and wound onto the screw body. This type of repair process is essentially equivalent to manufacturing a new centrifuge screw.

[0007] The same applies to other components of a solid-bowl screw centrifuge. This can include any component of a solid-bowl screw centrifuge, including all rotor components, i.e., all components related to the centrifuge drum and screw. The repair methods known to date are extremely complex.

[0008] Furthermore, no methods are currently known that enable the repair of screw bodies or screw hubs formed from several individual parts, in particular from several rods and / or struts. Based on the foregoing, the object of the present invention is to provide a further developed method for repairing damaged components and / or damaged component sections of a solid-bowl screw centrifuge, wherein the repair method should be easy to carry out and, in particular, faster compared to previously known repair methods.

[0009] According to the invention, this problem is solved with regard to the method for repairing damaged components and / or damaged component sections of a solid-bowl screw centrifuge by the subject matter of claim 1. Advantageous and expedient embodiments of the repair method according to the invention are specified in the dependent claims.

[0010] The invention is based on the idea of ​​providing a method for repairing damaged components and / or damaged component sections of a solid-bowl screw centrifuge. The damaged components and / or damaged component sections are those components and / or component sections that are still attached to or inside the solid-bowl screw centrifuge and exhibit corresponding damage and / or wear.

[0011] The method according to the invention comprises the steps of claim 1.

[0012] The invention is thus based on the idea of ​​replacing the damaged component and / or component section by means of shape-giving additive material application. For this purpose, it is necessary in a preceding process step to determine the dimensions of a component and / or component section to be replaced in relation to neighboring components and / or component sections of the solid-wall screw centrifuge.

[0013] A component and / or component section to be replaced is defined as a component and / or component section that is no longer located in or on the solid-bowl screw centrifuge. This may be due to the fact that the component and / or component section has already detached itself from adjacent components and / or component sections of the solid-bowl screw centrifuge due to wear and tear. The procedure comprises step a), namely the removal of a damaged component and / or component section, with step a) occurring before step b).

[0014] In this case, the component and / or section to be replaced has not yet detached itself, or it is necessary to remove certain sections of a damaged component and / or a damaged component section.

[0015] For example, a damaged component may have already detached itself, but the detached edge may be such that further processing is necessary. For instance, part of a screw thread tip may have broken off from the screw thread. In such cases, the broken edge may not be suitable for replacing the screw thread tip by additive material deposition, so the broken edge itself is removed, creating a suitable edge area for the subsequent attachment of the damaged component to be replaced.

[0016] The removal in step a) is carried out using a thermal separation process.

[0017] In particular, in step a) removal can be carried out by means of laser cutting and / or plasma cutting.

[0018] Step a) is automated. This step can be performed using robots and / or machines.

[0019] In step a), a wear-resistant coating is removed, specifically a wear-resistant coating on a screw helix. Such a wear-resistant coating may be applied to the conveying surfaces of the screw helix. These coatings may consist of tungsten carbide compounds and / or chromium-cobalt compounds (Stellite) and / or hard metal plates and / or ceramic plates and / or a ceramic coating.

[0020] Preferably, after carrying out step a), it may be advantageous to remove any residues formed as a result of a thermal separation process before the further steps, in particular before step b).

[0021] In step b), a three-dimensional measurement is preferably carried out, in particular using a laser system. Specifically, the remaining adjacent component and / or the remaining adjacent component section is measured three-dimensionally using optical sensors.

[0022] In step c), a CMT ®< welding (cold metal transfer) and / or a pulsed arc welding and / or a thermal spraying process is carried out.

[0023] The build-up welding process is particularly preferably carried out with a short arc, especially a reduced-energy short arc. Such a short-arc process is also known as cold arc welding.

[0024] In particular, it is possible to use an arc wire process and / or an arc powder process and / or a laser wire process and / or a laser powder process to perform a shaping additive material application. In other words, the material to be applied can be in powder form and / or as a wire, which is heated by means of an arc and / or a laser.

[0025] Build-up welding is preferably carried out in such a way that several weld layers applied one after the other form the component or component section to be replaced. A first weld layer is applied to an adjacent component and / or component section. Further weld layers are preferably applied to this first weld layer. The welding gas is particularly preferably selected from one of the subgroups of main groups I, M1, M2 or N of the standard DIN EN ISO 14175.

[0026] Welding is preferably carried out using active, reactive welding gas or inert welding gas. Such a welding process can also be referred to as MAG or MIG welding, or as welding with active or inert gas. These welding processes are collectively known as metal inert gas welding (MIG / MAG).

[0027] Main group I comprises welding gases with 100% nominal argon by volume (subgroup 1), 100% nominal helium by volume (subgroup 2), and 0.5 to 95% nominal helium by volume with the remainder being argon (subgroup 3). These welding gases are completely inert.

[0028] Main group M1, subgroup 1 comprises welding gases with 0.5 to 5.0% nominal carbon dioxide by volume, 0.5 to 5.0% nominal hydrogen by volume, and the remainder being argon or helium. These welding gases are slightly oxidizing and only slightly reducing. Main group M1, subgroup 2 comprises welding gases with 0.5 to 5.0% nominal carbon dioxide by volume, and the remainder being argon or helium. These welding gases are also slightly oxidizing.

[0029] Main group M1, subgroup 3 comprises welding gases with 0.5 to 3.0% nominal oxygen by volume and the remainder being argon or helium. These welding gases are also low oxidizing. Main group M1, subgroup 4 comprises welding gases with 0.5 to 5.0% nominal carbon dioxide by volume, 0.5 to 3.0% nominal oxygen by volume, and the remainder being argon or helium. These welding gases are also low oxidizing.

[0030] Main group M2, subgroup 0 comprises welding gases with 5.0 to 15.0 volume percent nominal carbon dioxide and the remainder being argon or helium. These welding gases are only slightly oxidizing. Main group M2, subgroup 1 comprises welding gases with 15.0 to 25.0 volume percent nominal carbon dioxide and the remainder being argon or helium. These welding gases are also only slightly oxidizing. Main group M2, subgroup 2 comprises welding gases with 3.0 to 10.0 volume percent nominal oxygen and the remainder being argon or helium. These welding gases are also still only slightly oxidizing. Main group M2, subgroup 3 comprises 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 being argon or helium. Main group M2, subgroup 4 comprises 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 comprises welding gases with 5.0 to 15.0 by volume nominal carbon dioxide, 3.0 to 10.0 by volume nominal oxygen, and the remainder argon or helium. Main group M2, subgroup 6 comprises welding gases with 15.0 to 25.0 by volume nominal carbon dioxide, 0.5 to 3.0 by volume nominal oxygen, and the remainder argon or helium. Main group M2, subgroup 7 comprises welding gases with 15.0 to 25.0 by volume nominal carbon dioxide, 3.0 to 10.0 by volume nominal oxygen, and the remainder argon or helium. These welding gases are also relatively low-oxidizing.

[0031] Main group N, subgroup 1 comprises welding gases with 100% nominal nitrogen by volume. Main group N, subgroup 2 comprises welding gases with 0.5 to 5.0% nominal nitrogen by volume and the remainder being argon or helium. Main group N, subgroup 3 comprises welding gases with 5.0 to 50.0% nominal nitrogen by volume and the remainder being argon or helium. Main group N, subgroup 4 comprises welding gases with 0.5 to 1.0% nominal hydrogen by volume, 0.5 to 5.0% nominal nitrogen by volume and the remainder being argon or helium. Main group N, subgroup 5 comprises welding gases with 0.5 to 50.0% nominal hydrogen by volume and the remainder being nitrogen. These welding gases are all relatively unreactive; they are inert with high argon or helium content and exhibit only slight reducing properties even with increasing hydrogen content.

[0032] In summary, welding gases that are inert, low-oxidizing, and / or low-reducing are preferably selected. With such a process, form-giving build-up welding can be performed with a low-oxidation weld bead and largely without slag. This is particularly advantageous for layering weld beads. Furthermore, a particularly fast welding rate can be used. This initially enables very short repair times. However, the real advantage of a fast welding rate lies in the fact that the component and / or component section being replaced is only heated minimally at specific points during welding, resulting in minimal distortion or deformation.

[0033] The advantage of the preferred method, however, lies in the fact that such build-up welding results in a particularly high wear resistance of the surface produced.

[0034] According to this embodiment of the repair method according to the invention, subsequent remuneration, in particular the application of wear layers, can be dispensed with.

[0035] For example, the welding gas has a nominal carbon dioxide content of less than 20% by volume. Such a low carbon dioxide content makes it possible, in particular, to process structural steels using pulse welding. 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 working time. Furthermore, welding gases with a nominal oxygen content of less than 3% by volume are preferably used. Such welding gases are particularly low-oxidizing. Welding gases with a high argon content are also particularly cost-effective.

[0036] In one embodiment of the invention, a gas-shielded welding device is operated with a pulsed arc. Such a pulsed arc allows for precise control of the welding wire melting rate at the gas-shielded welding device. Furthermore, the heat input into the component being replaced and / or the component section being replaced can be kept particularly low. This minimizes temperature-induced deformations. The electric welding current of such a pulsed arc welding device 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 comparatively low melting rates. A welding gas with a nominal argon content of 98% by volume and a nominal carbon dioxide content of 2% by volume is advantageously used.

[0037] Furthermore, it is particularly advantageous to operate a shielding gas welding system with a short arc, especially a reduced-energy short arc. Such a short-arc process is also known as cold arc welding, meaning a process with a particularly cold arc. To achieve a still high-melting arc, it is especially advantageous to use an increased melting current pulse.

[0038] In a build-up welding process, the first weld layer can be thicker than the second weld layer. This is achieved in particular by operating a shielding gas welding machine with a higher welding current during the application of the first weld layer than during the application of the second and subsequent weld layers.

[0039] Alternatively, the first weld layer can be welded using a pendulum motion, with a slower welding speed or a higher wire feed rate. This method results in a particularly thick or substantial first weld layer. This high-volume first weld layer is then overlaid by a second weld layer, which has a lower volume and is therefore thinner. This allows for the formation of a rounded base or shoulder on the base of a component, exhibiting low stress concentration and thus high stiffness.

[0040] A gas-shielded welding device is particularly advantageously operated with one welding wire, or advantageously also two welding wires (twin welding process) with a diameter of 0.5 mm to 3.0 mm, preferably from 1.0 mm to 1.6 mm.

[0041] Surprisingly, this welding wire diameter results in a high welding speed and, at the same time, particularly low thermally induced deformation. Individual weld layers or passes with a width of 6 to 7 mm are especially preferred.

[0042] A welding strip with a rectangular cross-section is particularly advantageous.

[0043] The base body of a component and / or component section to be replaced can preferably be moved during the repair. This movement aligns the component and / or component section at its welding point in such a way as to achieve an optimal position for the applied weld layer. The weld layer is particularly preferably applied to a horizontal surface.

[0044] It is also advantageous if the weld 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°. The base body is preferably moved accordingly such that a horizontal weld surface or a weld surface that slopes upwards in the welding direction of the shielding gas welding device is present at the welding point of the shielding gas welding device.

[0045] Applying a weld layer to a surface that slopes slightly upwards in the welding direction offers particular advantages. It makes it possible to optimally replicate the pre-incline of a screw thread, i.e., the pre-incline of a screw helix. In other words, the inventive method allows for the particularly accurate reproduction of an existing pre-incline of a screw helix in components and / or component sections to be replaced.

[0046] The component and / or component section produced by form-giving additive material deposition, in particular by build-up welding, can have exactly the same forward tilt as the previously existing component and / or component section that was replaced by the method according to the invention. Subsequent balancing effort with regard to the repaired solid-wall screw centrifuge, in particular the centrifuge screw, is significantly minimized.

[0047] Furthermore, due to the method according to the invention, it is possible to simplify a balancing process when repairing damaged components and / or damaged component sections of a solid-jacket screw centrifuge.

[0048] When repairing damaged components and / or sections of a solid-bowl screw centrifuge, calculations regarding the required balancing sections can be performed simultaneously. Therefore, it is no longer necessary, as was previously the case, to apply visible and / or individual balancing weights to components and / or sections of a solid-bowl screw centrifuge. Instead, it is possible to calculate and determine the weights of the components and / or sections to be replaced during the repair process itself, thus eliminating the need for additional balancing weights. Methods for applying balancing weights, particularly welding, are no longer required.

[0049] Furthermore, when repairing damaged components and / or damaged component sections of a solid-bowl screw centrifuge, it is possible, thanks to the method according to the invention, to achieve a higher strength of a replaced component and / or a replaced component section. The increased strength is particularly noticeable in comparison to the previously damaged component and / or component section.

[0050] Accordingly, the inventive method makes it possible not only to repair a damaged component and / or a damaged component section, but also to simultaneously produce a new component and / or a new component section with improved strength. A component and / or a component section produced using a form-giving additive material deposition exhibits higher strength than, for example, a component produced conventionally by sheet metal or metalworking.

[0051] The method according to the invention has the additional advantage that the component and / or component section to be replaced can be reproduced with extreme precision. The replaced component and / or component section produced by means of shape-giving additive material deposition can be manufactured with tighter tolerances than is possible with conventional repair methods.

[0052] The method according to the invention further has the advantage that the component and / or component section to be replaced can be designed in a topologically optimized manner. It is possible to perform an intermediate step between step b) and step c).

[0053] As an intermediate step, a geometrically optimized component / component section can be determined. The component and / or component section to be manufactured can, for example, have a geometry that includes at least one cavity and / or recess. With the help of cavities and / or recesses, weight and / or material savings can be achieved, for example. Until now, it has not been possible to simultaneously perform optimizations on the component / component section while repairing a damaged component and / or component section.

[0054] The method according to the invention also has the advantage that the component and / or component section to be replaced can be manufactured from a material that does not correspond to the material of adjacent components and / or component sections of the solid-bowl screw centrifuge. If it is determined that the fatigue of the component and / or component section to be replaced is due to the previous material selection, a different material can be used to repair the damaged component and / or component section. The use of different materials is surprisingly feasible when applying a form-giving additive material deposition process, particularly when using a build-up welding process.

[0055] It is possible to combine several different processes for shape-defining additive material application. For example, a component and / or a component section to be replaced may first be manufactured using weld overlay and then subjected to a thermal spraying process.

[0056] The dimensions recorded in step b) are preferably sent as data to a device for carrying out step c) and used for controlling and / or regulating step c). Therefore, it is possible to automate the additive material application based on the dimensions recorded in step b) and stored as data.

[0057] According to the invention, prior to step a), the damaged component and / or the damaged component section is captured three-dimensionally. Based on such capture of the damaged component and / or the damaged component section, the damaged component and / or a damaged component section can then be automatically removed in step a).

[0058] The capture, especially the three-dimensional capture, can be done using a 3D scan, as is possible, for example, with a laser system.

[0059] In the context of shape-giving additive material application, the material being applied can be in the form of wire or powder.

[0060] The method according to the invention preferably comprises a step d), which is carried out particularly after step c). In step d), a final surface treatment is performed. The surface treatment can be carried out, for example, by means of a grinding process. The final surface treatment or surface finishing can also be carried out fully automatically.

[0061] In a preferred embodiment of the invention, a section of a screw helix of a centrifuge screw is repaired using the method according to the invention.

[0062] A solid-wall screw centrifuge is also disclosed. The solid-wall screw centrifuge is characterized in that at least one component and / or a component section is repaired by means of a method according to the invention.

[0063] In other words, the disclosed solid-bowl screw centrifuge comprises at least one replaced component and / or component section manufactured by means of form-giving additive material deposition. The components and / or component sections manufactured in this way exhibit improved mechanical properties compared to the prior art. Among other things, the yield strength and the elongation at break of these components and / or component sections are improved. Due to controlled heat input in the repair process according to the invention, a fine-grained microstructure is formed in the material.

[0064] Using the method according to the invention, repairs can be carried out within a short time. Furthermore, a high degree of automation can be achieved. Due to the at least partially automated execution of individual process steps, high repeatability is also possible. In addition, customer requirements can be implemented in a customized manner.

[0065] Due to the inventive method for repairing damaged components and / or damaged component sections of solid-bowl screw centrifuges, the section-by-section restoration of damaged sections is possible, thus resulting in material savings and resource conservation compared to known repair methods. A significant reduction in the amount of material used can be achieved through precise, shape-giving additive material application.

[0066] The invention will be explained in more detail below using exemplary embodiments with reference to the attached schematic drawings.

[0067] It shows: Fig. 1a and 1b a component in a damaged state; Fig. 2 a component with component sections to be replaced; and Fig. 3 a repaired component with replaced component sections.

[0068] In the following, the same reference numbers are used for identical and equivalent parts.

[0069] In the Fig. 1a-3 The steps of a method according to the invention for repairing a damaged centrifuge screw 10 are shown by way of example. This serves only as an example. It is possible that further and / or other components of a solid-bowl screw centrifuge can be repaired using the same method steps.

[0070] The Fig. 1a shows a front view of a centrifuge screw 10 with a screw body 15 and a screw helix 18.

[0071] In Fig. 1b The centrifuge screw is shown section by section in a longitudinal section. It can be seen that the screw helix 18 has damaged component sections 20 at the helix tip. Here, individual sections have broken off or been torn from the screw helix 18. According to the invention, these damaged component sections 20 are to be repaired.

[0072] In the illustrated example, the screw body 15 is formed from a solid cylindrical element. It is possible to repair damaged component sections of such a screw body 15 using the method according to the invention.

[0073] In a further embodiment not shown, the screw body or screw hub 15 can be formed from several rods and / or struts, wherein individual rods and / or struts can be repaired or completely replaced using the method according to the invention.

[0074] As in Fig. 2 As shown, the damaged component section 20 is first prepared. The in Fig. 1a The depicted demolition edge 16 is prepared for both damaged component sections 20. Thus, further parts of a damaged component section 20 are initially removed. This corresponds to step a) according to the invention.

[0075] This straightening of the demolition edge 16 is necessary, among other things, to simplify and control the form-giving additive material application. In Fig. 2 Thus, two component sections 30 to be replaced are shown. These must first be recorded. In step b), the dimensions of the component sections 30 to be replaced are recorded in relation to adjacent components or, in this case, in relation to the remaining screw helix 18.

[0076] These recorded measurements are stored as data. In step c) (here Fig. 3 ) the damaged and meanwhile completely removed component section is replaced by a specified additive material application.

[0077] In a preferred embodiment of the invention, this is achieved by means of build-up welding, in particular by means of build-up welding with an energy-reduced short arc. Fig. 3Individual welds 41 and 42 are visible. Welds 41 are the first weld applied to the adjacent component section, namely the section with the still existing screw helix 18. Subsequently, further welds 42 are applied to these initial welds 41. After completion of process step c), all applied welds 41 and 42 form a completely replaced component section 40.

[0078] After performing process step c), a grinding process is preferably carried out. This grinding process, which can also be called smoothing, is particularly useful for producing a precise finishing edge 45. When designing or assembling a solid-bowl screw centrifuge, it is especially important to maintain a defined gap between the inner wall of the drum and the screw helix.

[0079] The wear-resistant coating can, for example, be applied to the screw helix in the form of individual plates.

[0080] The replaced component sections 40 exhibit good mechanical properties with regard to yield strength and elongation at break. This is due to the controlled heat input during the repair process and the resulting fine-grained microstructure. Reference symbol list

[0081] 10 Centrifuge screw 15 Screw body 16 Break-off edge 18 Screw helix 19 Helix tip 20 Damaged component section 30 Component section to be replaced 40 Replaced component section 41 First weld 42 Further weld 45 End edge

Claims

1. A method for repairing damaged components and / or damaged component portions (20) of a solid bowl centrifuge, characterized by the steps: a) removing the damaged component and / or the damaged component portion (20), namely of a wear protection coating of a screw flight, wherein step a) takes place prior to step b), wherein the removing takes place in an automated manner by means of a thermal separating process, b) capturing the dimensions of a component to be replaced and / or of a component portion (30) to be replaced in relation to adjacent components and / or component portions (18) of the solid bowl centrifuge; c) replacing the damaged component and / or the damaged component portion (20) by means of forming additive material application, by way of carrying out cold metal transfer welding and / or pulsed-arc welding and / or a thermal spraying process, wherein a three-dimensional capturing of the damaged component and / or of the damaged component portion (20) takes place prior to step a).

2. The method according to one of the preceding claims, characterized in that a three-dimensional measuring, in particular by means of a laser system, takes place in step b)3. The method according to one of the preceding claims, characterized in that the dimensions captured in step b) are sent as data to a device for performing step c) and are used for controlling step c).

4. The method according to one of the preceding claims, characterized in that at least one portion (20) of a screw flight (18) of a centrifugal screw (10) is repaired.