EP1825016B1 - Method for coating a workpiece - Google Patents

Description

The invention relates to a method for coating a workpiece according to the preamble of patent claim 1.

Numerous methods for coating workpieces are known from the prior art. When so-called thermal spraying is a coating method in which a thermally active coating material is sprayed or sprayed onto a surface of a workpiece to be coated. Since almost all meltable coating materials can be used, coatings with different properties or functions such as thermal insulation, corrosion protection or wear protection can be realized by thermal spraying. In thermal spraying, there are virtually unlimited possible combinations between the material of the article or workpiece to be coated and the thermally active coating material to be used for the coating.

Depending on the heat source used, a distinction is made between various thermal spraying methods, namely, for example, plasma spraying, arc spraying, flame spraying or else high-speed flame spraying. Cold kinetic compaction is also a thermal spraying process. The selection of the corresponding thermal spraying method depends, for example, on the coating material, the desired properties of the coating and on the respective costs.

To provide, for example, a porous coating on the workpiece to be coated, it is already known, in addition to the actual coating material to apply a aggregate by thermal spraying on the workpiece to be coated, wherein the aggregate is decomposed or dissolved after the thermal spraying so to provide the porous coating. Thus, the decomposing aggregate leaves pores in the coating. The decomposition of the aggregate material is carried out in particular by a heat treatment of the coated workpiece. If no porosity is desired, the aggregate material can also remain in the layer and affect the properties of the layer, provided that it does not have a detrimental effect.

When coating workpieces with a thermal spraying process, quality control of the resulting coating takes place important role too. Only if the coating meets specified quality criteria, the coated workpiece can pass the quality control and optionally further processed. Since the aggregates, which are applied to the workpiece for providing, for example, a porous coating together with the coating material, can not be detected or detected by means of online quality control, destructive testing methods are randomly used according to the state of the art for quality control. On the one hand, a quality control destroying the workpiece is costly and time-consuming, on the other hand only random checks can be carried out.

DE-A-10244037 discloses a method for coating a workpiece by thermal spraying wherein the injection process is monitored and evaluated on-line. Properties of the spray jet (eg luminous intensity of the spray particles) are optically recorded and evaluated.

US-A-4327120 discloses a method for coating a workpiece by thermal spraying a coating material consisting of a mixture of a coating material and a UV-sensitive marker material.

On this basis, the present invention based on the problem to provide a novel method for coating a workpiece.

This problem is solved by a method for coating a workpiece according to claim 1. According to the invention, in addition to the coating material, a aggregate material is applied to the workpiece, in which or on which a fluorescent marker material is firmly bound, wherein the injection process is monitored online that at least the particles of the fluorescent marker material located in a spray jet are detected and evaluated.

For the purposes of the method according to the invention a coating material is used for coating a workpiece, in which or on which a fluorescent marker material is bound. The fluorescent marker material is recorded online during the injection process. In the production of, for example, porous coatings, the quality of the porous coating which sets up after the decomposition of the aggregate material can already be concluded during the injection process. This makes it possible for the first time to subject coatings produced by thermal spraying to comprehensive online quality control and thus to dispense with destructive test methods.

In the production of porous coatings, the aggregate material is decomposed after the injection process together with the fluorescent marker material, in particular by heat treatment of the coated workpiece.

Fig. 1

eine stark schematisierte Darstellung einer Vorrichtung zur Beschichtung eines Werkstücks zur Verdeutlichung des erfindungsgemäßen Verfahrens.

Preferred embodiments of the invention will become apparent from the dependent claims and the description below. An embodiment of the invention will be described, without being limited thereto, with reference to the drawing. Showing:

Fig. 1

a highly schematic representation of an apparatus for coating a workpiece to illustrate the method according to the invention.

Hereinafter, the present invention will be described with reference to FIG Fig. 1 described in more detail using the example of the preparation of a porous coating.

The invention relates to a method for coating a workpiece by means of thermal spraying. For this purpose, a coating material is applied to the workpiece together with a aggregate material by thermal spraying, namely sprayed or sprayed. After the thermal spraying operation, the aggregate is decomposed, in particular, by a heat treatment of the coated workpiece so as to provide a porous coating on the workpiece.

The invention will be described below for plasma spraying as a preferred thermal spraying process. However, the invention should not be limited to plasma spraying. Rather, the invention can also be used in other thermal spraying processes, for example in flame spraying, high-speed flame spraying, arc wire spraying or cold kinetic compaction.

As such, plasma spraying is well known in the art. For example, the EP 0 851 720 B1 a plasmatron suitable for plasma spraying. For the sake of completeness, it should merely be noted that an arc is ignited during plasma spraying between a cathode and an anode of a non-illustrated plasmatron. This arc heats a plasma gas flowing through the plasmatron. The plasma gases used are, for example, argon, hydrogen, nitrogen, helium or mixtures of these gases. By heating the plasma gas, a plasma jet sets in, which can reach temperatures of up to 20,000 ° C in the core. The coating material used for coating is injected into the plasma jet using a carrier gas. Furthermore, this coating material to be used for the coating is accelerated to a high speed by the plasma jet. The accelerated in this way material is applied to the workpiece to be coated, namely sprayed.

To provide the porous coating, in addition to the coating material, an aggregate material is also sprayed onto the workpiece to be coated. In this case, a spray jet is formed, wherein the spray jet is formed on the one hand by the plasma jet and on the other by the particle beam of the coating material and aggregate material. The particles impinge with high thermal and kinetic energy on a surface of the workpiece to be coated and form a coating there. Depending on the parameters of the injection process, the desired properties of the coating are formed.

For the purposes of the present invention, a supplemental material is used in the thermal spraying, in which or on which a fluorescent marker material is tied. During thermal spraying, both the particles of the coating material and the particles of the marker material, which is firmly bound in or on the aggregate, are made to shine, so that the particles of the coating material and the particles of the marker material contained in the spray jet or particle beam collected and evaluated in the sense of online monitoring. The excitation of the fluorescent marker material and of the coating material can take place, for example, via the plasma jet. Alternatively, the excitation can be accomplished via a laser source, which excites the particles to glow.

In this context, it should be noted that marker materials are used which shine in a different wavelength range than the coating material. This makes it possible to distinguish in the particle beam, the particles of the coating material from the particles of the marker material and thus the aggregate material. As marker materials are used in particular laser dyes whose fluorescence is in the visible wavelength range. Particularly suitable as a laser dye rhodamine 6G, the fluorescence emission maximum is at about 560 nm. Rhodamine 6G can be firmly bound in organic aggregates, such as polyester, by, for example, diffusing Rhodamine 6G into polyester.

The monitoring and evaluation of the injection process takes place, as already mentioned, with the aid of online process control systems. The monitoring and evaluation of the injection process will be described below with reference to Fig. 1 explained. Fig. 1 shows a highly schematic of an adjusting during plasma spraying spray jet 10. The spray jet 10 is optically monitored by a camera 11 through an optical filter 12. The camera 11 is in the illustrated embodiment as a CCD camera educated. The optical filter can be embodied as a gray filter or color filter or bandpass filter. It is also possible to use a plurality of cameras and / or other process control systems, in particular a spectrometer for monitoring the injection process.

The image acquired by the camera 11 is supplied to an image processing system not shown in detail. In the image processing system, properties of the optically monitored spray jet are determined from the data acquired by the camera 11. The properties of the spray jet 10 determined from the optical monitoring of the spray jet are compared with predetermined desired values for these properties. If a deviation of the determined properties (actual values) of the spray jet from the predetermined values (nominal values) for the properties is detected, the process parameters for the plasma spraying are automatically adapted by a controller.

Of course, the method described here can also be used in combination with other methods for monitoring the spray jet, in particular the laser-induced fluorescence.

Finally, it should be noted that while the invention is preferably used in the production of porous coatings, it is not limited to this application. Rather, the invention can also be used in the production of solid coatings, in which case the aggregate material with the fluorescent marker material remains in the coating. Thus, for example, boron nitride (BN) or bentonite can be introduced as an additive in a massive coating, so as to form a predetermined breaking point in the coating. The boron nitride can be detected online during the coating by a fluorescent marker material bound to or in the boron nitride.

Claims (6)

1. A method for coating a workpiece, by which a coating material and an additional material are applied to the workpiece by thermal spraying, characterised in that a fluorescent marker material is permanently bound in or on the additional material, the spray process being monitored online in that at least the fluorescent marker material contained in the spray jet is detected and evaluated.
2. A method according to Claim 1, characterised in that after the spray process the additional material is decomposed, in particular by heat treatment of the coated workpiece, in order to produce the porous coating.
3. A method according to Claim 2, characterised in that after the spray process the additional material together with the fluorescent marker material is decomposed, in particular by heat treatment of the coated workpiece.
4. A method according to one or more of Claims 1 to 3, characterised in that an organic additional material, in particular polyester, is used as the additional material.
5. A method according to one or more of Claims 1 to 4, characterised in that a laser dye, in particular rhodamine 6G, is used as the fluorescent marker material.
6. A method according to one or more of Claims 1 to 5, characterised in that during the spray process the fluorescent marker material is excited to fluorescence and is detected with a camera.

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