Device and method for forming a coating on an inner wall of a hollow cylindrical element

Abstract

Device for forming a coating on an inner wall of a hollow cylindrical element, in which a laser beam (2) emitted from a laser beam source is directed via an optical waveguide (3) onto an element (5) collimating the laser beam and onto a surface of a device inclined to the laser beam (2) at an angle in the range between 45° and 135° with respect to the optical axis of the laser beam. The reflecting element (6) is directed in the beam path behind the collimating element (5) and during the formation of the coating in the central longitudinal axis of the hollow cylindrical element (1), and a focusing element (7) is subsequently arranged in the beam path, focusing the laser beam (2) in the area of ​​the surface to be coated of the hollow cylindrical element (1), or the reflecting element (6) focuses the laser beam on its reflective surface in the area of ​​the surface to be coated, so that the laser beam (2) strikes the inner wall of the hollow cylindrical element (1) in an area where filler material can be supplied and a device is available with which a translational movement of the hollow cylindrical element (1) and the device or the reflecting element (6) can be achieved by means of a rotating relative movement of the hollow cylindrical element (1) and the device and a device (8) is provided on the optical waveguide (3) and the reflecting element (6) which is designed to support the device on the inner wall of the hollow cylindrical element and On the device (8), which is designed to support the device on the inner wall of the hollow cylindrical element (1), a counterweight (9) for mass compensation during a rotational movement is arranged on the side opposite the reflecting element (6) in the direction of the inner wall of the hollow cylindrical element.

Description

[0001] The invention relates to a device and a method for forming a coating on an inner wall of a hollow cylindrical element.

[0002] The invention can be used in all areas of industry where there is a requirement to coat pipes or cylinders from the inside: → General mechanical engineering / pipeline construction Chemical industry / petrochemical industry / pipeline construction → Turbine construction → Engine components of large machines (ships, railways, etc.) Hollow cylindrical components and pipelines must be resistant to corrosion and / or wear, depending on the desired performance characteristics or the fluid to be transported. For small pipe diameters, this is usually achieved by using high-alloy and thus corrosion-resistant materials. The resulting material-related additional costs only justify the effort of improving performance characteristics through internal coatings (e.g., nickel-carbide-silicon "Nikasil" coatings for the running surfaces of combustion engines) in special applications. The internal coating of small-diameter pipes is achieved using the following state-of-the-art processes: - galvanic coating processes thermal spraying (flame spraying, arc spraying, etc.) - physical vapor deposition (PVD coating)

[0003] For very large pipe diameters, electroplating and PVD coatings are not economically viable. Thermal spraying is one of the most established processes for coating large pipe diameters. Extreme high-speed laser cladding (EHLA) has been developed as a competing process. With theoretical process speeds of up to 500 m / min, the new process sets standards. The process is also extremely economical in terms of material efficiency, with achievable layer thicknesses starting from approximately 25 µm and a powder utilization rate of well over 80%. The disadvantage of this process is that, according to the current state of the art, only rotationally symmetrical components can be coated externally, which limits its application potential.To expand the application limits of the innovative EHLA process for the internal coating of pipes / cylindrical components with large cross-sections, new fields of application are to be generated. Of particular relevance here are pipes for the transport of hydrogen, for which low-strength seamless pipes (<350 MPa) are currently used to avoid hydrogen-induced embrittlement. For pipes with a diameter of over 1.2 m, the use of higher-strength pipes can drastically reduce material consumption, thus creating industrial interest in cost-effective technologies for the internal coating of such pipelines. In addition to corrosion protection, further application potential is seen in wear protection. This particularly applies to large-volume machinery, such as cylinder bores of ship engines or combustion chambers of aircraft turbines, power plants, etc.

[0004] There are currently no known solutions for internal coating using the EHLA process. A competing process for the internal coating of large-diameter pipes and cylinders (> 100 mm) is thermal spraying.

[0005] For example, a device for laser powder coating is known from DE 101 16 720 A1.

[0006] DE 10 2009 024 957 B3 concerns a modular system for deposition welding on internal surfaces of workpieces with a laser beam.

[0007] It is therefore an object of the invention to be able to reproducibly develop possibilities for the formation of surface coatings on inner walls of hollow cylindrical elements, which in particular have an inner diameter of less than 400 mm, with high productivity and good quality.

[0008] According to the invention, this object is achieved with a device having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in the dependent claims. Claim 9 defines a corresponding method.

[0009] In the device, a laser beam emitted by a laser beam source is directed via an optical fiber onto an element that collimates the laser beam. The laser beam is directed onto a surface of a reflective element that is inclined at an angle between 45° and 135° relative to the optical axis of the laser beam. The surface of the reflective element is arranged behind the collimating element in the beam path of the laser beam and, during coating formation, along the central longitudinal axis of the hollow cylindrical element.An element that focuses the laser beam in the area of ​​the surface of the hollow cylindrical element to be coated is then arranged in the beam path, or the reflective element is designed on its reflective surface to focus the laser beam in the area of ​​the surface to be coated, so that the laser beam strikes the inner wall of the hollow cylindrical element in an area in which additional material can be supplied.

[0010] Furthermore, a device is provided with which a translational movement of the hollow cylindrical element and the device can be achieved through a rotating relative movement of the hollow cylindrical element and the device or the reflective element. Alternatively, the hollow cylindrical element can rotate and perform a translational feed movement in the direction of its longitudinal axis, while the device itself remains stationary. However, the rotational and translational feed movements can also be achieved by the device alone, which should be the preferred variant. However, it is also possible to have both or one of these movements performed by the hollow cylindrical element and the device.

[0011] The device can be clamped centered or concentrically to the hollow cylindrical element and mounted there for rotation.

[0012] A device is provided, attached to, or connected to the optical waveguide and the reflective element, which is designed to support the device against the inner wall of the hollow cylindrical element. This allows a defined distance, in particular between the reflective element and / or a focusing element, to be maintained from the inner wall to be coated, and vibrations can be avoided or at least reduced.

[0013] Filler material can be supplied in the form of powder and / or wire using conventional conveying devices.

[0014] On the device designed to support the device on the inner wall of the hollow cylindrical element, a counterweight is arranged on the side opposite the reflective element, toward the inner wall of the hollow cylindrical element, to compensate for mass during a rotational movement, in particular to prevent the influence of imbalance. This is particularly advantageous at higher rotational speeds or rpm at which the device rotates. The mass of the counterweight should be selected such that it corresponds at least approximately to the mass of a device designed to support the device on the inner wall of the hollow cylindrical element and, if applicable, to a drive for the required feed movement(s).

[0015] In addition, a device for monitoring the surface area of ​​the inner wall of the hollow cylindrical element to be coated and / or the surface area already coated can be provided. This can be, for example, a camera or a similarly acting device that enables monitoring of a closed, sufficiently dense coating or the detection of coating defects. This device can also monitor the composition of the coating material, preferably with spatial resolution, either on its own or in addition to it, which can be achieved optically, for example, using spectral analysis.

[0016] The device designed to support the device against the inner wall of the hollow cylindrical element can include pressure rollers, cylinders, or skids that rest against the inner wall. This also has a beneficial effect on stability and maintaining optimal distances between the inner wall and the optical elements used to shape and align the laser beam.

[0017] The reflective element can also be pivoted about an axis aligned at an angle in the range of 45° to 135° relative to the longitudinal axis of the hollow cylindrical element. This makes it possible to reach a larger surface area while simultaneously reducing the translational displacement speed by scanning. This also makes it possible to coat hollow cylindrical elements with a different inner diameter while maintaining a suitable focus of the laser beam by pivoting the angle, which can be adapted to the resulting changes in distance between the reflective surface and the inner wall.

[0018] A focusing element can also be designed or the surface contour of the reflecting surface of the reflecting element can be selected so that a rectangular focal spot geometry of the laser beam is achieved on the surface of the respective inner wall.

[0019] Advantageously, a telescopic mechanism can be provided on the device designed to support the fixture on the inner wall of the hollow cylindrical element. This allows the fixture to be used with different inner diameters of the hollow cylindrical element. Additionally, the telescopic mechanism can be equipped with a device for implementing adaptive distance control of the process with force or displacement control. The advantage is that both deviations in the shape of the hollow cylindrical element and deviations of the entire fixture relative to the hollow cylindrical element itself can be compensated for, thus reducing the accuracy requirements for centering the fixture inside the hollow cylindrical element.

[0020] A sensor capable of measuring distance is useful. This can be used to control the telescope mechanism or a collimating lens.

[0021] When machining hollow cylindrical elements with a small inner diameter (< 400 mm), a focusing element can also be arranged in the beam path of the laser beam in front of the reflecting element so that the already focused laser beam is redirected.

[0022] Instead of a moving focusing element by a telescopic arm of a telescopic mechanism, the distance control can also be realized by the movement of the collimating element by means of an adjustment mechanism.

[0023] The device for monitoring the surface area to be coated and / or the surface area already coated can be connected to an electronic control device designed to influence parameters such as the laser beam's orientation on the surface area to be coated, the relative movement of the laser beam's focal spot along the surface area to be coated, and / or a feed system for filler material. This allows for automated maintenance of the desired quality of the coating to be formed.

[0024] This enables adaptive control of the feed movements of the device inside the hollow cylindrical element. The underlying idea is that the feed rate can be calculated based on the contour of the coating already applied, thus ensuring constant coverage of the respective tracks with which the coating is successively applied. Furthermore, this or another device can be used to scan / probe / observe the surface of the inner wall to be coated in order to analyze the coating itself (quality assurance) and detect any defects, thus eliminating an additional quality assurance process step.

[0025] Likewise, when welding seam roots inside the hollow cylindrical element, the device for scanning / scanning / observing the inner wall surface can be used to locate the seam position (welding gap).

[0026] The invention will be explained in more detail below by way of example.

[0027] It shows: Fig. 1 a sectional view through a hollow cylindrical element with an example of a device according to the invention arranged in its interior.

[0028] In this case, a laser beam 2 emitted by a laser beam source (not shown) is coupled into an advantageously flexibly deformable optical waveguide 3, which, with a coupling element 4, directs the laser beam 2 onto a collimating element 5. The collimated laser beam 2 strikes a surface of a reflective element 6 that reflects the laser beam 2 and is thus deflected at an angle of preferably 90° or an angle in the range of 45° to 135° toward the inner wall of the hollow cylindrical element 1.

[0029] The laser beam 2 is guided through or between the device 8, which is designed to support the device on the inner wall of the hollow cylindrical element, in the direction of the respective inner wall of the hollow cylindrical element 1.

[0030] On this device 8, on the side opposite the reflective element 6, towards the inner wall of the hollow cylindrical element 1, a counterweight 9 is arranged to balance the mass during a rotational movement. In the example shown, a drive 10 is also present, with which at least the rotational movement of the elements for focusing and reflection, as well as of the support device 8, can be realized. A telescopic mechanism 11 is also present on the device 8. On its end face facing the inner wall of the hollow cylindrical element 1, there are additional pressure rollers 12 that are directly supported on the inner wall. A feed 13 for filler material is also arranged and designed there so that the filler material is conveyed into the area of ​​influence of the laser beam 2 and dosed in the desired amount in order to form the most continuous coating possible.

[0031] Also attached to the device 8 is a focusing optical element 7, with which the focal plane of the focused laser beam 2 can preferably be kept in the area of ​​the surface of the inner wall to be coated.

[0032] In this example, a device 14 is provided, which enables monitoring of the surface area of ​​the inner wall of the hollow cylindrical element 1 that is to be coated and / or has already been coated. In this example, the device 14 is arranged on the side of the device that is adjacent to the surface of the inner wall of the hollow cylindrical element 1 on which a coating is being or can be formed at the same time, thereby enabling monitoring of already coated or not yet coated surface areas. With this arrangement, the actual coating process cannot be monitored simultaneously.

[0033] The system described can achieve various advantages: → Welding of weld roots inside pipes / cylinders → Internal coating of pipes → Adaptive machining process to reduce component accuracy requirements → Possibility of integrated quality assurance → Development of new technologies for the internal coating of pipes / cylinders

[0034] Use of materials for coating that could not previously be processed.

Claims

[1] Device for forming a coating on an inner wall of a hollow cylindrical element, in which a laser beam (2) emitted by a laser beam source is directed via an optical waveguide (3) onto an element (5) collimating the laser beam and onto a surface of a hollow cylindrical element which is inclined at an angle in the range between 45 ° and 135 ° with respect to the optical axis of the laser beam reflecting element (6) which is arranged in the beam path behind the collimating element (5) and during the formation of the coating in the central longitudinal axis of the hollow cylindrical element (1) and in the beam path following thereto an element (7) focusing the laser beam (2) in the area of the surface of the hollow cylindrical element (1) to be coated is arranged or the reflecting element (6) on its reflecting surface focuses the laser beam in the area of the surface to be coated in the area of the surface to be coated, so that the laser beam (2) strikes the inner wall of the hollow cylindrical element (1) in an area in which additional material can be supplied and a device is provided with which a translational movement of the hollow cylindrical element (1) and the device can be achieved by a rotating relative movement of the hollow cylindrical element (1) and the device or the reflecting element (6) and a device (8) is provided on the optical waveguide (3) and the reflecting element (6) which is designed to support the device on the inner wall of the hollow cylindrical element and on the device (8) which is designed to support the device on the inner wall of the hollow cylindrical element (1), a counterweight (9) for mass compensation during a rotational movement is arranged on the side opposite the reflecting element (6) in the direction of the inner wall of the hollow cylindrical element. [2] Device according to the preceding claim, characterized bythat a device (14) for monitoring the surface area to be coated and / or the already coated surface area of the inner wall of the hollow cylindrical element (1) is provided. [3] Device according to one of the preceding claims, characterized by that the device (8) designed to support the device on the inner wall of the hollow cylindrical element (1) has pressure rollers, cylinders or runners (12) supported on the inner wall. [4] Device according to one of the preceding claims, characterized by that the reflective element (6) is pivotable about an axis aligned at an angle in the range 45°-135° with respect to the longitudinal axis of the hollow cylindrical element (1). [5] Device according to one of the preceding claims, characterized bythat on the device (8) which is designed to support the device on the inner wall of the hollow cylindrical element (1), there is a telescopic mechanism (11) which is equipped with a force-displacement control for an adaptive distance control. [6] Device according to one of claims 2 to 5, characterized bythat the device (14) for monitoring the surface area to be coated and / or the surface area already coated is connected to an electronic control device which is designed to influence parameters with which the laser beam (2) is directed onto the surface area to be coated, the relative movement of the focal spot of the laser beam (2) and the surface area to be coated and / or a feed (13) for additional material, wherein the device is a camera or a similarly acting element with which a closed, sufficiently dense coating can be monitored or coating defects can be detected. [7] Device according to one of claims 2 to 6, characterized by that the device (14) can be used to monitor the spatially resolved composition of the coating material. [8] Device according to one of the preceding claims 2 to 6, characterized bythat the feed can be controlled as a function of the real-time monitoring by a device (14) of the surface area to be coated and / or the already coated surface area of the inner wall of the hollow cylindrical element (1) of the coating. [9] A method for forming a coating on an inner wall of a hollow cylindrical element, in which a device according to one of the preceding claims is used.

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