Method for plasma coating a component and extraction device

Abstract

Method for plasma coating a component (14), in which a coating plasma is generated by means of a plasma torch and applied to a coating surface of the component (14), wherein an extraction channel (20) open towards the coating surface is arranged adjacent to the component (14), through which excess coating plasma is extracted, and at least one replaceable cover plate (34, 36) is fixed inside the extraction channel (20), on which parts of the extracted coating plasma are deposited, characterized in that the cover plate (34, 36) is subjected to a vibration during the coating operation by means of an ultrasonic actuator (46) coupled to it, the frequency of which corresponds to one of its resonance frequencies.

Description

Field of invention

[0001] The invention relates to a method for plasma coating a component, in which a coating plasma is generated by means of a plasma torch and applied to a coating surface of the component, wherein an extraction channel open towards the coating surface is arranged adjacent to the component, through which excess coating plasma is extracted, and at least one replaceable cover plate is fixed inside the extraction channel, on which parts of the extracted coating plasma are deposited.

[0002] The invention further relates to an extraction device for extracting excess coating plasma during plasma coating of a component, in particular within the framework of a coating process of the type mentioned above. comprising an extraction duct with an air supply opening and an exhaust opening, between which an airflow can be generated, and with an intake opening arranged in the direction of flow between the air supply opening and the exhaust opening, wherein at least one replaceable cover plate is fixed inside the extraction duct. State of the art

[0003] Such a process and such an extraction device are known from DE 10 2017 213 360 A1. Plasma coating of components is widely used in industrial manufacturing. For example, the running surfaces of cylinders in aluminum crankcases for internal combustion engines are usually coated with a steel alloy applied using a low-pressure plasma process. For this purpose, a so-called plasma lance, at the tip of which is an angled plasma torch, is inserted axially into the cylinder bore of the crankcase and rotated around the axial direction, with the plasma torch being supplied with a carrier gas stream containing steel powder. The torch generates a plasma stream in which the steel powder melts and is propelled against the bore wall.With suitable axial and rotational control of the plasma lance, a uniform coating of the bore wall can be achieved to produce a high-quality cylinder running surface.

[0004] However, it is not possible to convert all of the plasma into running surface material; rather, a significant excess of plasma is generated. To prevent contamination, this excess plasma must be extracted from the cylinder bore. For this purpose, an extraction device, often referred to as a "process box," is provided, which essentially comprises a cuboid-shaped extraction channel. This channel rests with portions of one of its main surfaces on the cylinder bore inlet, with its wall perforated at this point by a suitably sized intake opening. One or two opposing end faces of the extraction channel are equipped with inlet and outlet openings, between which an airflow is established by means of a blower, usually an external one.According to the known laws of fluid dynamics, this airflow creates a negative pressure in the extraction duct, resulting in a bypass flow through the cylinder bore and the intake opening, by means of which excess plasma can be extracted from the cylinder bore into the extraction duct.

[0005] The annular section of the channel wall surrounding the intake opening acts as a masking plate for the surface area of ​​the crankcase surrounding the cylinder bore. It prevents the excess plasma from depositing on the cylinder bore and causing fouling. Instead, the deposits form on the masking plate. While efforts are made to minimize such deposits through flow optimization, this is not entirely possible in practice. Areas of the remaining channel wall near the intake opening are also affected by such fouling. Therefore, it has become standard practice to protect the areas most susceptible to fouling with replaceable cover plates or to design the corresponding wall sections themselves as such replaceable cover plates.If, during operation of the plasma coating system, the contamination reaches a level that is no longer tolerable for reasons of process stability, the cover plates can be replaced with fresh, clean ones without having to replace the entire extraction system or perform time-consuming cleaning. While replacing the cover plates reduces time and costs, an interruption of the coating system's operation is nevertheless unavoidable. Therefore, such maintenance work should ideally be required as infrequently as possible. Task

[0006] The object of the present invention is to further develop a coating process or a suction device of the generic type in such a way that the replacement of the cover plates is required less frequently. Description of the invention

[0007] This problem is solved in conjunction with the features of the preamble of claim 1 by subjecting the cover plate to a vibration during the coating operation by means of an ultrasonic actuator coupled to it, the frequency of which corresponds to one of its resonant frequencies.

[0008] The problem is further solved in conjunction with the features of claim 5 by the fact that the cover plate is materially connected to a first end of a coupling nozzle, to the second, free end of which an ultrasonic actuator is coupled in a vibration-transmitting manner.

[0009] Preferred embodiments of the invention are the subject of the dependent patent claims.

[0010] The objective of the invention, unlike in the prior art, is not to further optimize the flow conditions to reduce the probability of contact between excess plasma and the cover plates, but rather (while potentially maintaining the same probability of contact) to reduce the probability of plasma components, in particular the (melted and possibly resolidified) steel powder, adhering to the contacting cover plates. This is achieved by setting the cover plates into a high-frequency vibration. For this purpose, each cover plate is connected to an ultrasonic actuator via vibration transmission, in particular ultrasound transmission. Such ultrasonic actuators, which operate, for example, on a piezoelectric basis, are commercially available. It has proven particularly effective to select a resonant frequency for the plate vibration that depends on the shape and material of the respective cover plate.It is known that a multitude of resonant frequencies can be excited, particularly in complexly shaped structures. In practice, the specific selection of a well-defined resonant frequency from among several high-frequency frequencies has proven unnecessary, as long as the chosen frequency lies in the ultrasonic range, preferably between 25 and 50 kHz, and particularly between 30 and 40 kHz.

[0011] It is of course known to those skilled in the art that crust-like deposits on sheet metal can be removed by high-frequency vibration excitation. However, this method relies primarily on the lack of elasticity of the soiling crust to break it up. The fact that the probability of individual soiling particles adhering to the sheet metal can also be reduced by high-frequency vibrations, thus preventing the formation of a soiling crust from the outset, is a surprising insight of the inventor. This is all the more remarkable since the present invention cannot draw on any apparent parallels to the cleaning of sheet metal in an ultrasonic bath. The cleaning effect of the ultrasonic bath is known to lie in the interaction between the oscillating bath fluid and the soiling particles already adhering to the sheet metal.However, in the present invention, the sheet metal, which is surrounded only by air, is itself excited to high-frequency vibrations.

[0012] Mechanically, this concept can be implemented as provided for in the invention by firmly connecting each cover plate to a coupling nozzle. This firm connection should be material-bonded, in particular by welding on a coupling nozzle. The coupling nozzle is particularly preferably designed as a coupling tube. The ultrasonic actuator is detachably fixed to the free end of the coupling nozzle, albeit in a vibration-transmitting manner, i.e., (at least also) force-fit. This can be achieved, for example, by means of a high-torque screw connection. In the particularly preferred case of a coupling nozzle designed as a coupling tube, the ultrasonic actuator can be screwed into an internal thread at the free end of the coupling tube.The detachability of the ultrasonic sensor's fixing is particularly advantageous with regard to replacing the cover plate, which – although significantly less frequently required as a result of the present invention – cannot be completely avoided.

[0013] Connecting the ultrasonic actuator to the cover plate via a coupling nozzle has the advantage that the ultrasonic actuator itself can be positioned virtually anywhere (depending on the shape of the coupling nozzle). In particular, it can be positioned at a location protected from the plasma flow. In a preferred embodiment of the invention, the ultrasonic actuator is arranged within the extraction duct between the cover plate and an inner wall of the extraction duct. This is advantageous because only the electrical connection cables of the ultrasonic actuator need to be routed through the duct wall.

[0014] In another embodiment of the invention, the coupling nozzle penetrates the channel wall to the outside, and the ultrasonic actuator is arranged outside the suction channel. While this requires a more complex, and preferably vibration-isolated, routing of the coupling nozzle through the channel wall, the protection of the ultrasonic actuator located outside the channel is significantly better than in the embodiment described above.

[0015] As explained, the core of the invention is to subject the cover plate to high-frequency vibration. However, the rest of the extraction duct should preferably not be subjected to vibrations that would place a significant mechanical load, particularly on the connection points of different elements. Therefore, in a further development of the invention, the cover plate is mounted in a vibration-isolated manner from the duct wall. This can be achieved, for example, by means of rubber-elastic buffers installed as spacers between the cover plate and the inner wall of the extraction duct.

[0016] Alternatively, and particularly relevant for the cover plate serving as a masking plate in a process box, it can be designed to form a vibration-isolated component of the channel wall. In other words, this embodiment makes a portion of the channel wall itself replaceable. Such a masking plate, which has the intake opening of the extraction channel at its center, rests directly on the crankcase and exposes only the opening of the cylinder bore to be coated, while covering the surrounding crankcase surface against excess plasma. The vibration-isolated integration into the rest of the channel wall can be achieved, for example, by means of a rubber-elastic sealing ring encircling the edge of the masking plate.

[0017] As explained, despite the reduction in contamination achieved according to the invention, the adhesion of plasma components to the cover plates cannot be completely prevented. Over time, a layer of contamination will therefore grow on them. This alters the vibration-related properties of the cover plate, which can lead to a shift in its resonant frequencies. However, if the ultrasonic actuator is operated constantly at the frequency corresponding to the selected resonant frequency of the clean cover plate, while the actual resonant frequency shifts, the efficiency of the method according to the invention suffers. The cover plate is no longer excited at its resonant frequency.In a further development of the invention, it is therefore provided that the resonant frequency of the cover plate is checked at specific times during the coating process and, if a change within a predetermined tolerance range is detected, the ultrasonic actuator is readjusted accordingly. This ensures that the cover plate is not excited, or at least only for short periods, outside its resonant frequency. The contamination prevention according to the invention is therefore always highly efficient.

[0018] This approach can also be used for monitoring the contamination of the cover plate. As explained, the resonant frequency shifts depending on the (increasing) contamination. The shift of the resonant frequency relative to a given reference point, e.g., the resonant frequency of the clean plate, can therefore be used as a measure of the current contamination of the plate. In a particularly preferred embodiment of the invention, the resonant frequency of the cover plate is checked before and / or at specific times during the coating process, and a contamination warning is issued if a change outside a predetermined tolerance range is detected. The tolerance ranges within which readjustment occurs and outside which a contamination warning is issued can be the same or different.

[0019] The aforementioned verification of the resonance frequency is preferably carried out by varying the frequency of the ultrasonic actuator within a predetermined range, measuring the electrical power consumption of the ultrasonic actuator, and determining the frequency corresponding to the highest power consumption as the current resonance frequency. This frequency is then compared to the previously assumed resonance frequency, e.g., the frequency determined in the preceding resonance determination. The resonance frequency of the cover plate is characterized by a particularly low reactive component in the corresponding vibration. Consequently, a particularly high mechanical power can be coupled into a vibration mode. This manifests itself through a correspondingly high power consumption of the ultrasonic actuator.Therefore, the current power consumption of the actuator can be used as a measure of the currently achieved proximity to the resonance frequency.

[0020] Further details and advantages of the invention will become apparent from the following, specific description and the drawings. List of characters

[0021] They show: Fig. 1 a schematic, partially cut-away perspective view of a plasma coating system with extraction device according to the invention, Fig. 2 a schematic side view of the plasma coating system of Fig. 1 without plasma lance. Detailed description of preferred embodiments

[0022] Identical reference symbols in the figures indicate identical or analogous elements.

[0023] Fig. Figure 1 shows a highly schematic, partially cutaway, perspective view of a plasma coating system 10 for plasma coating the inner walls of cylinder bores 12 of a crankcase 14 for the internal combustion engine of a motor vehicle. A plasma lance 16 is provided for the coating process. This lance immerses into the cylinder bores 12 and has a plasma torch (not shown) at its tip. Coating material, in particular steel powder, is fed to the torch in a manner not shown.

[0024] The plasma lance 16 passes through a so-called process box 18, which essentially forms an approximately cuboid-shaped extraction duct 20. The extraction duct 20 has an air inlet 22 with a skirt 24 on one end face of the cuboid. On the opposite end face, the extraction duct 20 has an exhaust air inlet 26. As indicated by the flow arrows 28, a continuous airflow between the air inlet 22 and the exhaust air inlet 26 can be generated by means of a blower (not shown). A further opening, namely the intake inlet 30, is located in the base of the extraction duct 20. The plasma lance 16 passes through this inlet, as well as through a corresponding opening 32 in the ceiling, and through the process box 18.In the illustrated embodiment, the intake opening 30 is located in the center of a masking plate 34, which is interchangeably fixed in the channel base and rests on the crankcase 14 during operation of the plasma coating system 10. The masking plate's surface seals against the common volume of the extraction channel 20 and the cylinder bore 12. Furthermore, the side walls of the extraction channel 20 in the area of ​​the plasma lance 16 are lined with replaceable sacrificial plates 36.

[0025] During the coating process, in which coating plasma is expelled from the tip of the plasma lance 16 into the cylinder bore 12, excess plasma that does not adhere to the walls of the cylinder bore 12 is drawn into the extraction duct 20 by the airflow and carried away. Because the masking plate 34 seals against the edge of the cylinder bore 12, this excess plasma cannot reach the surface of the crankcase 14. Instead, excess plasma not carried away by the airflow 28 contacts the surface of the masking plate 34. The same applies to the sacrificial plates 36, which serve to protect the duct walls. The masking plate 34 and sacrificial plates 36 are also referred to collectively here as cover plates 34, 36.

[0026] Tubular coupling nozzles 38 are welded to the cover plates 34, 36, wherein in Fig. 1 only the corresponding weld points 40 are recognizable.

[0027] Fig. Figure 2 shows a highly schematic side view of the plasma coating system 10. Fig. Figure 1 shows the exhaust opening 26, but without the coating lance 16. In the illustrated embodiment, the masking plate 34 is designed as a component of the duct floor, which is vibrationally decoupled and interchangeably connected to the rest of the duct wall via a rubber-elastic sealing ring 42. The sacrificial plates 36 are also vibrationally decoupled and interchangeably fixed to the duct wall via rubber-elastic buffers 44. As mentioned above, all cover plates 34, 36 are welded to a tubular coupling nozzle 38 on their outer surface. The further arrangement of the coupling nozzles 38 is shown in Figure 1. Fig. 2 three different variants: Since the masking plate 34 is an integral part of the channel wall itself in the illustrated embodiment, the coupling nozzle 38 welded to it lies completely outside the extraction channel 20. The one attached to the Fig. The two coupling nozzles 38 welded to the left-hand sacrificial plate 36, however, penetrate the channel wall from the inside, where the sacrificial plate 36 is located, to the outside. The one attached to the Fig.The coupling nozzles 38 welded to the sacrificial plate 36 shown on the right ultimately run entirely within the space between the sacrificial plate 36 and the channel wall, thus lying completely inside the channel. In each case, an ultrasonic actuator 46 is fixed to the free end of the respective coupling nozzle 38 in a vibration-transmitting and replaceable manner, preferably by means of a force-fit connection using a screw. Depending on the specific design of the coupling nozzle and its routing, the ultrasonic actuator is located inside or outside the process box 18, but in any case is protected against the plasma flow.

[0028] Energizing the ultrasonic actuator 46 leads to the coupling of a high-frequency vibration via the respective coupling nozzle 38 into the associated cover plate 34, 36, whereby, however, the mechanical vibration generated in the cover plate 34, 36 is not transmitted to the rest of the channel wall or other elements of the plasma coating system 10 due to the vibration decoupling via the rubber-elastic sealing ring 42 or the rubber-elastic buffers 44.

[0029] As explained in detail in the general description, this vibration excitation of the cover plates 34, 36 has the effect that excess plasma coming into contact with the cover plates 34, 36 adheres to them less readily, so that these cover plates 34, 36 become soiled much more slowly than would be the case with non-vibrationally excited cover plates 34, 36. The skilled person will know how to adjust the specific parameterization of the vibration excitation, in particular with regard to frequency and power, taking into account the specific material and shape of the cover plates 34, 36 and their vibration decoupling. For this purpose, simple, manageable test series will be required in each individual case. In the plasma coating systems 10 operated by the applicant, frequencies in the range between 25 and 50 kHz, in particular between 30 and 40 kHz at a power of 20-50 watts, have proven effective.

[0030] Regarding the inventive method and the preferred method for operating a plasma coating system according to the figures, reference is made to the explanation in the general part of the description.

[0031] Naturally, the embodiments discussed in the detailed description and shown in the figures represent only illustrative examples of the present invention. In light of this disclosure, a wide range of variations is available to the person skilled in the art. Reference symbol list 10 Plasma coating system 12 cylinder bore 14 Component / Crankcase 16 Plasma lance 18 Process Box 20 extraction channel 22 Air intake opening 24 apron 26 Exhaust opening 28 Flow / Flow arrow 30 Intake opening 32 Ceiling opening 34 Cover plate / masking plate 36 Cover plate / sacrificial plate 38 coupling nozzles 40 welding points 42 rubber-elastic sealing ring 44 rubber-elastic buffers 46 Ultrasound actuator QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102017213360 A1

[0003]

Claims

[1] Method for plasma coating a component (14) in which a coating plasma is generated by means of a plasma torch and applied to a coating surface of the component (14), wherein an extraction channel (20) open towards the coating surface is arranged adjacent to the component (14), through which excess coating plasma is extracted, and at least one replaceable cover plate (34, 36) is fixed inside the extraction channel (20), on which parts of the extracted coating plasma are deposited, characterized by , that the cover plate (34, 36) is subjected to a vibration during the coating operation by means of an ultrasonic actuator (46) coupled to it, the frequency of which corresponds to one of its resonant frequencies. [2] Method according to claim 1, characterized by, that before and / or at given times during the coating operation the resonance frequency of the cover plate (34, 36) is checked and if a change is detected within a specified tolerance range the ultrasonic actuator (46) is readjusted accordingly. [3] Method according to any of the preceding claims, characterized by , that before and / or at given times during the coating operation the resonance frequency of the cover plate (34, 36) is checked and a contamination warning is issued if a change outside a specified tolerance range is detected. [4] Method according to any of the preceding claims, characterized by, that to check the resonance frequency the frequency of the ultrasonic actuator (46) is varied within a specified variation interval, the electrical power consumption of the ultrasonic actuator (46) is measured and the frequency corresponding to the highest power consumption is determined as the current resonance frequency and compared with the frequency previously assumed to be the resonance frequency. [5] Extraction device for extracting excess coating plasma during plasma coating of a component (14), in particular within the framework of a method according to one of the preceding claims, comprising an extraction duct (20) with an air supply opening (22) and an exhaust air opening (26), between which an airflow (28) can be generated, and with an intake opening (30) arranged in the direction of flow between the air supply opening (22) and the exhaust air opening (26), wherein at least one replaceable cover plate (34, 36) is fixed inside the extraction duct (20), characterized by , that the cover plate (34, 36) is materially connected to a first end of a coupling nozzle (38), to the second, free end of which an ultrasonic actuator (46) is coupled in a vibration-transmitting manner. [6] Extraction device according to claim 5, characterized by , that the coupling nozzle (38) is designed as a coupling tube. [7] Extraction device according to one of claims 5 to 6, characterized by , that the ultrasonic actuator (46) is arranged between the cover plate (34, 36) and an inner wall of the extraction duct (20). [8] Extraction device according to one of claims 5 to 6, characterized by , that the coupling nozzle (38) penetrates the channel wall to the outside and the ultrasonic actuator (46) is arranged outside the suction channel (20). [9] Extraction device according to any one of claims 5 to 8, characterized by , that the cover plate (34, 36) is mounted in a vibration-isolated manner from the channel wall. [10] Extraction device according to any one of claims 5 to 8, characterized by , that the cover plate (34, 36) forms a component of the channel wall which is mounted in a vibration-isolated manner from the rest of the channel wall.

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