Powder gas guidance system for a coating system and method for operating a powder gas guidance system

Abstract

Powder gas conveying device (1) for a coating system (2), comprising at least the following components: - at least one conduit element (3) with a conduit wall (4) for conveying a powder (6) conveyed by means of a transport gas (5); - an enclosure (7) with an outer wall (8), wherein a pressure chamber (9) is formed between the outer wall (8) and the conduit wall (4); and - a pressure gas source (10) which is communicatively connected to the pressure chamber (9), wherein the pressure chamber (9) is filled with a gas (11) from the pressure gas source (10) at a monitored pressure, wherein a pressure sensor (12) is provided in the pressure chamber (9).

Description

The invention relates to a powder gas guidance device for a coating system, and to a method using such a powder gas guidance device for operating a powder gas guidance device. In cladding, powder from a powder source (for example, by means of a laser, such as high-speed laser cladding, in an embodiment known as EHLA [extremely high-speed laser cladding], for example as described in DE 10 2011 100 456 A1) or a corresponding other heat source is melted and applied to a surface to be coated. The powder is partially melted and bonds at the molecular level with a base material of the surface to be coated. After application, the coated surface has, for example, an improved property (e.g., increased abrasion resistance, corrosion resistance, and / or a defined surface roughness).To transport the powder from the powder source to the application point (i.e., the corresponding heat source), a conduit element (usually made of plastic or steel) is used. Within this element, the powder is carried along by the flow of a transport gas to the heat source. The powder particles rub (at least sporadically) against the inner wall of the conduit element. This leads to abrasion of the conduit element's wall, which can sometimes result in leaks. These leaks significantly alter the powder flow through the piping element. In one case, some of the powder escapes through a leak in the pipe wall, resulting in less powder being processed during application than intended. In another case, air is drawn in from the (external) environment, leading to an increased oxygen content in the (usually inert) transport gas. Consequently, the process parameters can change so drastically that the manufacturing result is unsatisfactory, for example, falling outside tolerances. This leads to the need for rework and / or scrap. US Patent 5,837,960 A relates to the laser production of articles from powders. Articles are formed from materials in particle form, with the materials being melted by a laser beam and deposited along a toolpath to create an article of the desired shape and dimensions. The toolpath and other parameters of the deposition process are determined using computer-aided design and manufacturing techniques. A controller, consisting of a digital computer, controls the movement of a deposition zone along the toolpath and provides control signals to adjust the functions of the device, such as the speed at which a deposition head, which delivers the laser beam and powder to the deposition zone, moves along the toolpath. This is related to the figure shown therein.1 mentions that the device comprises a chamber, wherein the process is carried out in the chamber under a protective gas atmosphere with a controlled pressure and / or gas composition. WO 2014 / 014 502 A1 concerns a powder gun that is configurable for supply by either a Venturi or a dilution phase pump. A selectively configurable spray gun may comprise a gun body that includes a selectable front section and a rear section. The rear section can be connected to one of two or more selectable front sections to configure the spray gun for operation with either a dilution phase or a dilution phase powder supply. The rear section may include a selectable powder flow path that can be connected at an inlet end to a source of dilution phase powder and at an outlet end to a selectable spray nozzle in the selectable front section, which may optionally include a diffuser. An adapter may be used to connect the rear section to a selectable spray nozzle or an air cap. Based on this, the present invention aims to overcome, at least partially, the disadvantages known from the prior art. The features of the invention are defined in the independent claims, for which advantageous embodiments are shown in the dependent claims. The features of the claims can be combined in any technically meaningful way, whereby the explanations in the following description and features from the figures, which comprise supplementary embodiments of the invention, can also be used. The invention relates to a powder gas conveying device for a coating system, comprising at least the following components: - at least one conduit element with a conduit wall for conveying powder conveyed by means of a transport gas; - an enclosure with an outer wall, wherein a pressure chamber is formed between the outer wall and the conduit wall; and - a pressure gas source, which is communicatively connected to the pressure chamber, wherein the pressure chamber is filled with a gas from the pressure gas source at a monitored pressure. Unless explicitly stated otherwise, ordinal numbers used in the preceding and following descriptions serve solely for unambiguous differentiation and do not indicate any order or ranking of the components referred to. An ordinal number greater than one does not necessarily imply the presence of another such component. The coating system is a device designed for coating with a powdered material supplied in situ via a delivery system. Examples of coating processes include laser spraying, thermal coating, and laser welding, for example, for cladding and / or high-speed laser cladding. For coating, for example, to modify surface properties, a welding filler material is supplied in powder form via the powder gas delivery system. The powder is partially melted, fully melted, and / or introduced into a melt pool within the surface to be coated by means of a heat source, thus bonding to the surface at the atomic level. The powder gas conveying device comprises at least one conduit element enclosed by a conduit wall and designed to guide the powder. The powder can be conveyed within the conduit wall by means of a transport gas and thus transported from one end of the conduit element (at a powder source) to the other end of the conduit element (at the heat source or the surface of a workpiece to be coated). The conduit element is, for example, designed as a flexible tube made of a plastic or rubber-like material. Alternatively or (in sections) additionally, the conduit element is made of a metal, preferably a material belonging to the tough metal alloys.It should be noted that the conduit element is preferably designed such that a predetermined service life or operating time can be achieved without any expected leakage. In one embodiment, the at least one conduit element is of conventional design. It should be noted that (in a given section) a single pipe element is located in a single associated pressure chamber. Alternatively, multiple pipe elements are located in the pressure chamber. Because leakage occurs rarely or only after a long operating period, and because the individual pipe elements are often subjected to a roughly uniform load (i.e., usage), replacing all pipe elements is advisable when a leak occurs in one or more of them. This avoids increasing the effort required for a common enclosure or even a single pressure chamber, and is therefore advantageous.It should be noted that with multiple pipe elements in which the same or different powder (or transport gas) and / or with different transport speed and / or transport pressure is conveyed, a leak in one of the pipe elements already results in insufficient process reliability, meaning that potentially only an unsatisfactory coating result can be achieved. It should also be noted that a piping element does not necessarily extend from a supplying powder source to a nozzle for dispensing the powder for the coating process. Alternatively, a piping system between the powder source and the nozzle may consist of multiple piping elements. For example, a rigid section, not designed for dynamic deformation, is initially provided between the associated powder source and an external connection of a coating system to a processing chamber or extending into the processing chamber. In one embodiment, this section is also multi-part. Subsequently, a section is provided that connects to a section fixed to a machine foundation and extends towards the nozzle, and this section is designed for dynamic deformation (for example, as an elastic hose).Finally, a rigid section not intended for dynamic deformation is preferably provided directly at the nozzle. In one embodiment, at least one suitable enclosure is provided for each of the sections. For example, an enclosure is flexible in a dynamically deformable section and rigid in a rigid section. It is proposed here that an enclosure for at least one conduit element of the powder gas delivery system is also included. A pressure chamber (sealed from the outside environment) is formed around at least one section of the conduit element by means of the outer wall of the enclosure, with the conduit wall acting as the inner wall. The pressure chamber is designed such that a pressure can be set independently of the current atmospheric pressure in the outside environment. In one embodiment, the outer wall is made of a pressure-resistant material (for the design pressures or pressure differential to the outside environment). For example, the outer wall is made of sheet metal or plastic. Alternatively or additionally, the outer wall is flexible, whereby a pressure change in the pressure chamber is visible from the outside via a change in volume or shape of the outer wall. In one embodiment, the pressure chamber completely encloses the pipe element, so that the inlet of the pipe element also forms the beginning of the pressure chamber. The same applies to the end of the pressure chamber and the outlet of the pipe element. Alternatively, the enclosure is provided in a section of the pipe element, for example, in an area that is difficult to access and / or not permanently or easily visible (to the operator). To ensure a defined pressurization of the enclosure or pressure chamber, a pressurized gas source must be provided which is communicatively connected to the pressure chamber of the enclosure. In one embodiment, the pressurized gas source is a pump connected to the outside environment, which draws in ambient air and optionally compresses it so that it is introduced into the pressure chamber at a defined pressure. In an alternative embodiment, the pressurized gas source is a container with a compressed gas. In one embodiment, this gas differs from ambient air; preferably, the gas contains no oxygen. The compressed gas is, for example, an inert gas such as nitrogen, carbon dioxide, or a noble gas. In another embodiment, the gas is a mixture of several gases, preferably without oxygen to avoid an undesirable oxidation reaction, and particularly preferably without carbon dioxide to avoid recarbonization. It should be noted that in one embodiment, a coating process is to be interrupted if an unacceptably significant leakage occurs in at least one of the pipe elements. Alternatively or additionally, in one process configuration, the ingress of gas from the pressure chamber through the leakage into the pipe element is sufficiently negligible, so that at least one current coating process for one or more workpieces can still be completed with sufficient process reliability and coating quality, and the affected pipe element only needs to be replaced later. A predetermined pressure within the pressure chamber can be set and / or changed using the pressurized gas source. In one embodiment, the pressure is monitored in such a way that a closed control loop is formed (with or without a readable measurement output). Alternatively or additionally, the pressure is monitored such that a measurement value is output and any deviation can be adjusted externally (e.g., manually), for example, by means of a controllable, e.g., throttleable, valve. In another embodiment, this monitored pressure within the pressure chamber is kept constant by means of the pressurized gas source. For example, a regulator is arranged between the pressure chamber and the pressurized gas source, with the pressurized gas source being configured to maintain a constant pressure in the pressure chamber.The pressurized gas source and / or outlet maintains a constant (e.g., over-)pressure relative to the pressure of the transport gas, preferably regardless of the presence of a leak. In one embodiment, the pressure within the pressure chamber is selected to be equal to, or preferably higher than, the transport pressure. To prevent the powder from escaping the affected pipe element, the pressure in the pressure chamber is higher (e.g., by at least 1.5 times) than in the affected pipe element (in an undamaged state). In one embodiment, the pressure chamber is designed to detect leaks in at least one (enclosed) conduit element. In another embodiment, the pressure chamber is (solely or additionally) configured to prevent leaks in the at least one conduit element and the associated negative process effects, such as powder loss and / or changes (including increased or altered fluctuations) in the transport speed. A pressure chamber operated in this manner ensures consistent coating quality on a workpiece, even with a damaged conduit element. It is further proposed that a pressure sensor be provided in the pressure chamber. To maintain or adjust the desired (monitored) pressure within the pressure chamber, a high-precision monitoring system is proposed, such that a pressure sensor is located within the pressure chamber. In one embodiment, this pressure sensor is a mechanical manometer, and the pressure can be read from a scale located outside the pressure chamber and, if necessary, adjusted manually (at the pressurized gas source or an inlet valve). It should be noted that in another embodiment, pressure and / or flow measurement at or near the pressure source is sufficient, thus eliminating the need for a pressure sensor (or any other sensor for detecting changes) within the pressure chamber. In a preferred embodiment, the pressure sensor is an electronic pressure sensor or a pressure sensor with a digital or electrical output of the currently measured pressure within the pressure chamber, so that the pressure can be set automatically (i.e., controlled) or via a control panel. Here, the pressure sensor is connected to a control loop in which the pressurized gas source or a corresponding (inlet) valve is integrated. Thus, increasing the pressure by increasing the supply of gas from the pressurized gas source or decreasing the pressure in the pressure chamber by releasing the gas can be carried out automatically. For example, the pressure sensor is particularly easy to integrate into a control loop and / or usable for electronic documentation when designed as a piezoelectric or piezoresistive pressure sensor. In an advantageous embodiment of the powder gas guidance device, it is further proposed that the pressure chamber has an outlet and an inlet connected to the pressurized gas source. To maintain or bring the pressure chamber to a predetermined pressure, it is proposed here that the pressure chamber have an inlet and a (separate from the inlet) outlet for the gas providing the pressure. For example, the inlet and / or the outlet is each designed as a throttle valve, with the inlet being interposed between the pressure chamber and the pressurized gas source. Each separate pressure chamber then has its own valve to control the amount of gas flowing in. In one embodiment, a valve is a switching valve and / or a multi-way valve for a pressurized gas source serving multiple consumers, for example, several (separate) pressure chambers. In another embodiment, the pressurized gas source is the same source from which the transport gas for the at least one piping element is drawn. In an advantageous embodiment of the powder gas guidance device, it is further proposed that at least one flow sensor is provided for detecting a volume flow rate for the pressure chamber. As an alternative or in addition to the previously described pressure sensor in the pressure chamber, at least one flow sensor is proposed here. In one embodiment, the pressure chamber is a closed dead end in which the volume flow rate is zero with an intact pipe element and a perfectly sealed pressure chamber. However, if the pipe element is damaged, some of the gas flows from the pressure chamber into the pipe element, or vice versa, so that a volume flow rate can be detected by the flow sensor. This allows even the slightest changes to be detected with minimal technical effort. In one embodiment (as described above), a flow sensor is arranged at an inlet of the pressure chamber for gas supply, and another flow sensor is arranged at an outlet of the pressure chamber for gas discharge. In such an embodiment, for example, a continuous flow of gas through the pressure chamber is provided. In the event of a leak, a change in the volumetric flow rate through the pressure chamber is detected by means of the at least one flow sensor. For high accuracy and reliable specificity of the measurement, a flow sensor is arranged at an inlet, an outlet, or within the pressure chamber. In an advantageous embodiment of the powder gas guidance device, it is further proposed that the housing and the guide element are designed as a coaxial double line. In a coaxial twin-tube system, the tube element is partially enclosed by the pressure chamber (preferably over at least a large part of its spatial extent). Preferably, the entire tube element is enclosed by the pressure chamber from beginning to end. In one embodiment, the outer wall of the double conduit is made of a correspondingly thick and / or rigid plastic, preferably reinforced with a tensile-strength fiber material. In another embodiment, the pressure chamber is made of a pressure-resistant sheet metal. In yet another embodiment, the pressure chamber and its outer wall are made of a flexible material, preferably allowing the pressure chamber to move with the conduit element, which coaxially accommodates the conduit element inside. In an advantageous embodiment of the powder gas guidance device, it is further proposed that the outer wall of the enclosure be designed to be non-deformable under atmospheric pressure. With such a rigid outer wall, a defined pressure can be set over a defined volume or volume flow rate. In one embodiment, a conductor element is arranged inside a coating system and is exposed to powder spraying and / or the energy input of reflected laser light. The rigid outer wall then provides additional protection against damage to the conductor element. According to a further aspect, a method for operating a powder gas conveying device according to an embodiment as described above is proposed, comprising at least the following steps: a. pressurizing the enclosure with a gas at a predetermined pressure from the pressurized gas source; and b. conveying a powder from a powder source through the conveying element by means of a transport gas from a transport gas source, wherein the predetermined pressure, preferably atmospheric or higher, in the pressure chamber of the enclosure is greater than a transport pressure, preferably below atmospheric, within the conveying element. The powder gas supply system is designed to transport powder to a coating system, with the powder being supplied via the system. In a coating process incorporating the proposed method for operating the powder gas supply system, the powder is partially melted, completely melted, and / or introduced into a melt pool formed by the heat source onto a surface to be coated, thus bonding it to the surface at the atomic level. In the first step (a) of the procedure for operating the powder gas supply system, gas is introduced into the housing of the pressure chamber, i.e., between the piping element and the outer wall, by means of the pressurized gas source, or (by filling) adjusted to a defined pressure, so that the pressure chamber is pressurized to a predetermined pressure under monitoring. The gas is introduced into the housing, for example, via an inlet or outlet. Meanwhile (or after a predetermined pressure has been established in the pressure chamber), in step b, the powder is transported from a powder source through the conduit element by means of a transport gas from a transport gas source. The transport gas generates a transport pressure which, due to a pressure difference at opposite ends of the conduit element, creates a flow that entrains the powder and thus transports it through the conduit element. The powder source is, for example, one or more storage containers that hold the powder for a coating process. Preferably, the powder source includes a powder outlet distributor by means of which a defined flow rate of powder is provided, which is then entrained by the transport gas. In one embodiment, the powder in the powder source is already premixed, meaning it contains all the materials required for the coating. In an alternative embodiment, the powder is mixed from several powder sources, either before the nozzle in the area of ​​the powder gas guide or separately up to the nozzle. In both embodiments, the powder is then fed in situ to the heat source or the surface to be coated via the powder gas guide. Preferably, the predetermined pressure in the pressure chamber is higher than the transport pressure within the conduit element. This offers the advantage that, in the event of a leak in the conduit element, the powder cannot escape and the coating process can continue. Particularly preferably, the transport pressure is lower than the current or standardized atmospheric pressure, and the pressure within the pressure chamber is at least as high as the relevant atmospheric pressure. Furthermore, if the pressure in the pressure chamber is higher than that of the immediate surroundings, a compensatory measure against minimal (within tolerance) leaks in the outer wall of the enclosure is provided by reliably preventing the ingress of ambient air. In a further advantageous embodiment of the method, it is proposed that the gas for the pressure chamber is a gas inert for a coating process, preferably at least one gas component of the transport gas for the line element, and particularly preferably that the gas for the pressure chamber and the transport gas are identical. In this embodiment, the gas used in the pressure chamber is an inert gas that is sufficiently unreactive for the coating process or cannot participate in any reactions. Examples of such inert gases include nitrogen, carbon dioxide, or preferably a noble gas such as argon. This ensures that in the event of a leak in the piping element, no reactive gas enters the coating process and impairs or even renders the coating result unusable. In one embodiment, the inert gas in the pressure chamber is a gas that is also a component of the transport gas. While this does change the composition of the transport gas if gas from the pressure chamber enters due to a leak, the change is minimal enough to ensure safe process operation. Because leaks should be rare, using a less expensive gas in the pressure chamber (than is possible for a transport gas) can save costs. To keep the process and the coating system as simple as possible, this particularly preferred embodiment proposes that the gas for the pressure chamber and the transport gas be identical. That is, both the gas for the pressure chamber and the transport gas are inert gases. In one embodiment, a common pressurized gas source can then be used, whereby the gas consumption of such a pressure chamber is preferably almost negligible compared to the gas consumption during the coating process of the coating system. This also significantly reduces costs and the required installation space. However, it should be noted that in one embodiment, the pressure chamber is solely designed for leak detection, and continuing an ongoing coating process is not desired. For this purpose, it is sufficient if, for example, ambient air is maintained in the pressure chamber at a predetermined pressure. In this embodiment, the coating process is immediately terminated upon detection of a leak, and any (unsuitable) gas entering the leak and / or a non-negligible amount of powder escaping from the leak then has no further effect. In a further advantageous embodiment of the method, it is proposed that the pressure difference between the higher pressure in the pressure chamber and the transport pressure within the conduit element is 20% or less. In the case of an intact or only slightly damaged conduit element, in which the full conduit pressure is applied, a pressure differential of 20% [twenty percent] or less between the conduit pressure and the pressure within the pressure chamber is preferred, with the conduit pressure as the reference value (i.e., 100%). A small pressure differential ensures, on the one hand, that no powder escapes from a leak in the conduit element, while on the other hand preventing the process parameters (especially the transport speed and mixing, but also velocity fluctuations) from being excessively affected by gas penetrating from the pressure chamber. In an embodiment where the gas in the pressure chamber is not identical to the transport gas, the composition of the transport gas is also not excessively affected.Therefore, even in the event of a leak in a pipe element, the coating process can be carried out safely for a sufficient period of time. This period is sufficient, for example, until the completion of the current coating process on a workpiece, or until a scheduled operational break (e.g., due to a change in powder composition). In an advantageous embodiment of the method, it is further proposed that pressure fluctuations detected by a pressure sensor of a powder gas guidance device according to an embodiment as described above and / or flow fluctuations detected by at least one flow sensor of a powder gas guidance device according to an embodiment as described above are displayed and / or recorded in the pressure chamber, preferably synchronized to a coating process and automatically documented by computer. Pressure fluctuations or deviations from a predetermined pressure in the pressure chamber of the enclosure are related to a leak in the affected pipe element. This results in an inconsistent and / or reduced powder flow rate. Consequently, (at least in the case of a significant leak) the desired surface coating quality can no longer be reliably achieved. Pressure fluctuations are therefore an indicator of an unsafe process, which in some cases can only be determined through extensive follow-up testing. The same applies to flow rate fluctuations or deviations from a predetermined flow rate (possibly even a predetermined flow rate of zero). For monitoring a coating process, it is advantageous for an operator or a system control unit if pressure and / or flow fluctuations are displayed (preferably electronically), allowing for external intervention. In one embodiment, it is important that such deviations are recorded. For example, a fluctuation might have occurred due to a very small leak that reseals itself (repeatedly or permanently). This could trigger a dedicated quality inspection for the affected workpiece or even a specific area of ​​a workpiece, thus revealing even difficult-to-detect defects and / or enabling case-by-case sampling or supplementation with such cases. In a preferred embodiment, pressure or flow fluctuations are detected and documented synchronously with the coating process, so that the detected fluctuations can be clearly attributed to the processes involved in the coating process. By detecting and synchronously documenting these fluctuations, a specific follow-up inspection of the coated surfaces is thus possible. This means that not all coated components, or even an entire component, need to be inspected, but only a well-defined area of ​​the component, determined by the synchronized detection; specifically, only those components where such a fluctuation has been detected and documented. The invention described above is explained in detail below against the relevant technical background with reference to the accompanying drawings, which show preferred embodiments. The invention is in no way limited by the purely schematic drawings, it should be noted that the drawings are not dimensionally accurate and are not suitable for defining dimensional relationships. Figure 1 shows a powder gas guidance device with a conduit element in a pressure chamber; Figure 2 shows the powder gas guidance device according to Figure 1 with a leakage in a conduit element in a pressure chamber; Figure 3 shows a micrograph of three surface coatings of workpieces after a coating process; and Figure 4 shows a coating system with a clamped brake disc. Figure 1 shows a schematic sectional view of a powder gas conveying device 1 with a conduit element 3 in a pressure chamber 9, where the conduit element 3 is shown without leakage 21. The powder gas conveying device 1 comprises a conduit element 3 enclosed by a conduit wall 4 and equipped with a transport gas 5 to convey a powder 6 (in the direction of the arrow shown). The powder 6 can be conveyed within the conduit wall 4 by means of the transport gas 5 from a transport gas source 19 (not shown in detail here, for example, a pressurized gas container) and thus transported from one end of the conduit element 3 at a powder source 18 (also not shown in detail, for example, a powder container) to the other end of the conduit element 3 at the heat source 39 or the surface of a workpiece 30 to be coated (compare, for example, Figure 4). The conduit element 3 is arranged within the housing 7. For example, this is a schematic representation of an embodiment as a double conduit 17, in which the conduit element 3 is centered and surrounded by a housing 7 (or enclosing conduit) forming a pressure chamber 9. Thus, a gas sheath is formed between the conduit wall 4 and the outer wall 8 of the pressure chamber 9. The outer wall 8 of the housing 7 forms the inner wall of at least a section of the conduit element 3 shown here, with the conduit wall 4 as its inner wall, creating the pressure chamber 9 (which is sealed off from the external environment 40). The pressure chamber 9 is designed such that a pressure can be set, preferably independently of the current atmospheric pressure in the external environment 40. To set a desired pressure, the pressurized gas source 10 is connected to the pressure chamber 9 via an inlet 13.The pressurized gas source 10 is also not shown in detail here; for example, a pressurized gas container, preferably the same pressurized gas container as the one for the transport gas 5. For example, the pressurized gas source 10 maintains a constant pressure (e.g., an overpressure compared to the transport pressure) inside the piping element 3. This pressure is, for example, measurable, preferably adjustable, by means of a pressure sensor 12 in the pressure chamber 9. To measure the volumetric flow rate at the inlet 13, an inlet-side flow sensor 15 is arranged in this embodiment (purely optionally). To also measure the volumetric flow rate at an outlet 14 (purely optionally), an outlet-side flow sensor 16 is also arranged at the outlet 14 in this embodiment (but independently of such a measurement at the inlet 13). In such an embodiment, for example, a continuous flow of gas 11 through the pressure chamber 9 is provided. In the event of a leak 21 in the piping element 3, a change in the volumetric flow rate through the pressure chamber 9 is detected by means of the at least one flow sensor 15, 16. With the two flow sensors 15, 16, a differential measurement is possible, and thus a conclusion can be drawn about the proportion of gas 11 flowing into or out of the piping element 3. In one embodiment, the housing 7 is a separate component through which a conductor element 3 is drawn. Alternatively, the housing 7 comprises a separate conductor element 3 to which an incoming and a outgoing conductor element 3 are connected via terminals 20. In Fig. 2, the powder gas guidance system 1 from Fig. 1 is shown in the same schematic sectional view with a leakage 21 in a conduit element 3 within a pressure chamber 9, where the conduit element 3 shown here has a leakage 21. Due to the leakage 21, the mass flow rate of the powder 6 is disrupted. Without the enclosure 7 proposed here, the mass flow rate of the powder 6 is not constant and / or is reduced in the event of a leakage 21. Consequently, a desired quality of a surface coating 22 can no longer be reliably achieved (at least in the case of a significant leakage 21). Pressure fluctuations, which are an indicator of an unreliable process, can be detected by means of the pressure sensor 12 in the pressure chamber 9 and / or the flow sensors. With the method for operating the powder gas control device 1, the monitored pressure in the pressure chamber 9 is preferably higher than the transport pressure within the piping element 3. This has the advantage that, in the event of a leak 21 in the piping element 3, the powder 6 cannot escape from the piping element 3 (or only in a negligible amount), and the coating process in the coating system 2 can continue. In an embodiment in which the gas 11 in the pressure chamber 9, which enters the piping element 3 via the leak 21, is sufficiently similar (preferably identical) to the transport gas 5, sufficient process reliability is also ensured even in the presence of a leak 21. Figure 3 shows a micrograph of three (superimposed) sections of a surface coating 22 on three workpieces 30 after a coating process. The surface coatings 22 shown here each represent a surface coating 22 on a treatment surface 26 of a substrate material 38 of the workpiece 30. The substrate material 38 is, for example, a lamellar gray cast iron. The illustration has a scale 23, for example, 1 mm [one millimeter]. In the central micrograph (B) shown, it is clearly visible that the surface coating 22 breaks off or is incomplete approximately in the middle of the workpiece 30. During the application of the surface coating 22 shown there, a leakage 21 occurred in the coating process, so that not enough powder 6 could be supplied to the heat source 39 or to the treatment surface 26 to be coated.The topmost micrograph (A) shows a coating without such interference. The bottommost micrograph (C) shows a coating with a leakage 21 but with an enclosure 7 and a pressure chamber 9 as described previously. The result is similar to the topmost micrograph (A) and is within the manufacturing tolerances. By detecting and documenting leaks 21 in the pipe element 3, such defective coatings can be more easily identified or precisely sorted out in a subsequent quality control check. In one embodiment, the detection and documentation of pressure fluctuations or flow rate fluctuations due to leaks 21 in the pipe element 3 is synchronized with the coating process, so that the detected fluctuations can be clearly attributed to the processes in the coating process. Figure 4 shows a coating system 2 with a brake disc 31 clamped in a tool chuck 34. The brake disc 31 is the workpiece 30 to be coated by the coating system 2. For this purpose, the brake disc 31 has a treatment surface 26 (shown as the upper surface) and an opposing back surface 37 (shown as the lower surface). In the state shown, a surface coating 22 (see Figure 3) can be applied to the treatment surface 26. The brake disc 31 is held in a precisely positioned position in the tool chuck 34 for this purpose. In this embodiment, the tool chuck 34 is, for example, a clamping chuck with a rigid axis of rotation 32, and the brake disc 31 is aligned coaxially with the axis of rotation 32. The axis of rotation 32 is thus oriented perpendicular to the treatment surface 26.In the illustrated embodiment, the tool chuck 34 is optionally driven by a rotary drive 33, so that the workpiece 30 can be rotated about the axis of rotation 32. Preferably, the workpiece 30 can be positioned with repeatable coordinate accuracy by the rotary drive 33 according to a coordinate system. As shown, a coating unit 27 of the coating system 2 is positioned above the workpiece 30. The coating unit 27 has a coating axis 29 (here optionally aligned parallel to the axis of rotation 32), and a processing cone 28 is provided coaxially with the coating axis 29. The processing cone 28 is connected to the powder gas guide unit 1 (see Fig. 1) and contains a powder 6 supplied in a conical shape by a transport gas 5. This powder is fed as a heat source 39 (preferably in a protective gas atmosphere provided by the transport gas 5) at a focal point of a multi-beam, preferably conical, laser beam. The coating unit 27 shown is therefore designed for ultra-precise, high-speed coating.The coating unit 27 (here purely optional) is movable radially relative to the workpiece 30 about the axis of rotation 32 along a feed axis 24 in a desired feed direction 36. In addition, the coating unit 27 (here purely optional) is adjustable axially about the axis of rotation 32, for example, solely for adjusting a height and / or for adjusting the distance with increasing application in a multi-layer coating process. Furthermore, the coating device here (purely optionally) includes a measuring unit 25, which is configured to record a height profile of the treatment surface 26 and / or the applied coating. The measuring unit 25 measures a changing distance and / or temperature along a measuring axis 35. With the powder gas guidance device shown here, a leak in a line element can be easily detected. Reference symbol list 1 Powder gas guide system 2 Coating system 3 Conduit element 4 Conduit wall 5 Transport gas 6 Powder 7 Enclosure 8 Outer wall 9 Pressure chamber 10 Compressed gas source 11 Gas 12 Pressure sensor 13 Inlet 14 Outlet 15 Inlet-side flow sensor 16 Outlet-side flow sensor 17 Double line 18 Powder source 19 Transport gas source 20 Connections 21 Leakage 22 Surface coating 23 Scale 24 Feed axis 25 Measuring unit 26 Treatment surface 27 Coating unit 28 Machining cone 29 Coating axis 30 Workpiece 31 Brake disc 32 Rotation axis 33 Rotation drive 34 Tool chuck 35 Measuring axis 36 Feed direction 37 Back side 38 Carrier material 39 Heat source 40 External environment

Claims

Powder gas conveying device (1) for a coating system (2), comprising at least the following components: - at least one conduit element (3) with a conduit wall (4) for conveying a powder (6) conveyed by means of a transport gas (5); - an enclosure (7) with an outer wall (8), wherein a pressure chamber (9) is formed between the outer wall (8) and the conduit wall (4); and - a pressure gas source (10) which is communicatively connected to the pressure chamber (9), wherein the pressure chamber (9) is filled with a gas (11) from the pressure gas source (10) at a monitored pressure, wherein a pressure sensor (12) is provided in the pressure chamber (9). Powder gas guidance device (1) according to claim 1, wherein the pressure chamber (9) has an outlet (14) and an inlet (13) communicating with the pressure gas source (10). Powder gas guidance device (1) according to one of the preceding claims, wherein at least one flow sensor (15,16) is provided for detecting a volume flow rate for the pressure chamber (9). Powder gas guidance device (1) according to one of the preceding claims, wherein the housing (7) and the guide element (3) are designed as a coaxial double line (17). Powder gas guidance device (1) according to one of the preceding claims, wherein the outer wall (8) of the housing (7) is designed to be non-deformable under atmospheric pressure. A method for operating a powder gas conveying device (1) according to one of the preceding claims, comprising at least the following steps: a. pressurizing the enclosure (7) with a gas (11) at a predetermined pressure from the pressurized gas source (10); and b. conveying a powder (6) from a powder source (18) through the conveying element (3) by means of a transport gas (5) from a transport gas source (19), wherein the predetermined pressure in the pressure chamber (9) of the enclosure (7) is greater than a transport pressure within the conveying element (3). Method according to claim 6, wherein the gas (11) for the pressure chamber (9) is an inert gas (11) for a coating process. Method according to claim 6 or claim 7, wherein the pressure difference between the greater pressure in the pressure chamber (9) and the transport pressure within the conduit element (3) is 20% or less. Method according to any one of claims 6 to 8, wherein pressure fluctuations detected by a pressure sensor (12) of a powder gas guidance device (1) and / or flow fluctuations detected by at least one flow sensor (15, 16) of a powder gas guidance device (1) according to claim 3 are displayed and / or recorded in the pressure chamber (9). The method according to claim 9, wherein pressure fluctuations and / or flow fluctuations are automatically documented by computer in a synchronized manner during the course of a coating process.

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