EP0451512B1 - Process for coating impeller blades - Google Patents

Description

The present invention relates to a method for coating blades according to the preamble of claim 1.

State of the art

For example, in the open gas turbine process, the air drawn in by the compressor also contains water vapor and solid and gaseous impurities. These have a negative impact due to erosion, pollution and corrosion. The deposits on the blades sometimes have a considerable concentration of corrosive components such as NaCl and KCl. In addition to high-temperature corrosion on the turbine blades, the salts also lead to increased pitting corrosion in the compressor area and to a complex chemical reduction in the strength of the blade material. At high air humidity, water vapor concentration occurs in the compressor inlet area, which explains the increased corrosion attack of the front rows of blades. In order to counteract this to some extent, blades of rotating thermal machines are often provided with protective layers. This is used both for steam and gas turbine blades and for compressor blades. The main thing is to increase resistance to corrosion and oxidizing attacks as well as erosion and wear (wear and tear). If, despite the surface treatment, the blades show damage whose degree could jeopardize operational safety, you proceed to
Removal of the blades: either they are replaced by new ones or reconditioned and reinstalled. This removal and installation is associated with relatively high costs and time. Furthermore, the actual state of the blading is only visible after a relatively long time, ie after pre-cleaning, so the decision as to whether or not reconditioning of the blades is feasible or already necessary can only be made much later. The disadvantages of this method are the great loss of time, the higher operating costs of the system, higher costs for revisions and the uncertainty about the question of the reconditionability of the blades. It is therefore no longer necessary to look for ways and means to remedy this. In this connection, a method has become known, according to which the entire bladed rotor is lifted out of the stator in order to be reconditioned in a separate system. The bladed rotors to be coated must be degreased in a suitable manner; if necessary, organic coatings applied earlier must be completely removed. The areas to be coated are then roughened by dry sandblasting with aluminum oxide and the metallic surface is activated. The zones that are not to be coated must be masked with suitable materials. Then the base layers are applied, whereby they have to be stoved on. This leads to a lengthy procedure: a sintering or baking process takes about 55 hours and has to be carried out on average four times. This sintering or baking process during coating consists of a heat treatment at approx. 350 degrees Celsius over a holding time of approx. 10-12 hours. In addition, quite large plants with a specific geometric configuration must be provided for carrying out the individual process steps, just think that during the sintering process the entire bladed part of the rotor must be enclosed by a furnace cover.

Object of the invention

The invention seeks to remedy this. The object of the invention is to propose a more rational method for reconditioning the blades in a method of the type mentioned at the outset in terms of the times required and the costs involved. The object of the invention is also to maximize the life of the coating by means of suitable methods and protective layers. This object is achieved with the method according to the characterizing part of claim 1.

The main advantages of the invention are that the bladed rotor does not have to be lifted out of its storage in the stator for the first process of reconditioning: the cleaning or protective layer removal can be done before the machine, ie the compressor, is actually switched off, i.e. during a Final phase of the operation ("on line"). A uniform loading of the blades to be treated is thus achieved, the efficiency of this cleaning process thus achieved, which ensures extensive removal of any protective layer that may be present, making an immediate decision about the reconditionability of the blades possible. This decision can be made after the machine has been switched off and the upper part of the stator has been removed. If, after an appropriate analysis of the condition of the blades, the decision is made to recondition them, it is sufficient to lift the bladed rotor from the storage and to place it on trestles, where the further process steps of the reconditioning can be carried out without the aid of a softened structure. This leads to low operating costs (overhaul costs), which is nothing to prevent periodic implementation of this type of treatment. This increases the operational safety of the system.

Another important advantage of the invention is that using a high-speed flame spraying method, the blades pretreated in the installed state are given a corresponding protective layer, preferably based on Si and Al, locally and as required, this coating method without heat treatment over long periods and can be carried out without the help of special additional systems. This simplifies the entire technical coating procedure, while the costs are approximately half lower than in the known processes. In addition, the service life of this type of coating is much longer than that of the layers currently used for this so-called complete coating. Since the pretreatment of the blades or the post-treatment after spraying on the protective layer for the life of the coating is of great importance, immediate corrections can be made, depending on the identified need. What is created in a very short time with low reconditioning costs by means of a process of high environmental compatibility is top-quality blading, which guarantees the operational safety of the system over a longer period of time.

Advantageous and expedient developments of the task solution according to the invention are characterized in the further claims.

Exemplary embodiments of the invention are shown schematically and explained in more detail below with reference to the drawing. All elements not necessary for the immediate understanding of the invention have been omitted. The direction of flow of the different media is indicated by arrows. Identical elements are provided with the same reference symbols in the various figures.

Fig. 1

eine Turbogruppe mit Aggregate für eine Vorbehandlungsstufe;

Fig. 2

eine Ansicht von Fig. 1 in der Ebene II-II;

Fig. 3

eine Reinigungsstufe bzw. Schutzschichtentfernung in einem schwingenden, erosivem Bad;

Fig. 4

eine Ansicht des Rotors gemäss Fig. 3 entlang der Ebene IV-IV;

Fig. 5

ein Schlussreinigungsverfahren mit Strahldüsen und

Fig. 6

eine Beschichtung der Schaufeln mit einem Hochgeschwindigkeits-Flammspritzverfahren.

It shows:

Fig. 1

a turbo group with units for a pretreatment stage;

Fig. 2

a view of Figure 1 in the plane II-II.

Fig. 3

a cleaning stage or protective layer removal in a vibrating, erosive bath;

Fig. 4

a view of the rotor of Figure 3 along the plane IV-IV.

Fig. 5

a final cleaning process with jet nozzles and

Fig. 6

coating the blades with a high speed flame spraying process.

Description of the embodiments

1 shows a conventional gas turbine group 11, consisting essentially of a compressor part 11a, a combustion chamber 11b and a turbine part 11c. When pretreating the blades, a distinction must be made as to whether they were uncoated or coated in their original condition. Irrespective of this requirement, the blades are cleaned for the first time before the machine, ie the compressor, is switched off. In the case of coated blades, this cleaning is preferably based on erosion by means of a soft jet granulate. Of course, the cleaning of uncoated blades can only be carried out using an aqueous solvent, for example trichlorethylene. Through a centrally placed three-jet nozzle 1 (see also Fig. 2), which is in the intake duct of the compressor
acts, the cleaning agent (soft jet granulate, aqueous solution etc.) is injected into the air flow to the compressor over a certain period of time. The uniform and intensive action 12 on the compressor blades results in an efficient cleaning process for uncoated blades or a comprehensive removal of the old protective layer in coated blades. The cleaning process is repeated several times as needed. Since the soft jet granulate burns at temperatures of approx. 300 degrees Celsius, there are no problems with regard to disposal. When using an aqueous solution, these aspects must also be taken into account. The circuit relating to the multi-jet nozzle 1 consists of a ball valve 2, which is connected downstream of a mixing chamber 3 in the direction of flow of the cleaning agent and serves to regulate the quantity. The pressure in this mixing chamber 3 is represented by a manometer 7. A container 4 is provided upstream of the mixing chamber 3, in which, for example, a granulate is in stock, a sieve 5 and an inlet valve 6 each ensuring that the mixing chamber 3 is supplied with a homogeneous material. The required pressure in the container 4 is provided via an air supply line 10, a pressure reducing valve 8 and a main valve 9 in the air line being further aids of the circuit. Appropriate precautions can also be used to treat turbine blading.

If necessary, the blades are subjected to further cleaning or protective layer removal. This is done, as shown in FIGS. 3 and 4, by means of an oscillating, erosive bath 14. For this purpose, the bladed rotor 11a and 11c is removed from the stator and placed on trestles 13a and 13b in such a way that a certain part of the blading immersed in the bath 14. The individual are erosive by means of a vibration generator 15
Components of the bath 14 are excited to vibrate, whereupon the residual dirt or the residual protective layer on the blades is removed. Basically, all blade types of a rotor of a gas turbine group can be treated with it.

A final cleaning is carried out according to FIG. 5 with an industrial glass blasting agent 18. This final cleaning is based on erosion removal by the means mentioned, which can consist of glass. A certain part of the blading is covered with a special capsule 16; with simultaneous suction 19 of the injected agent, cleaning is accomplished using one or more jet nozzles 17.

• Abschleifen von allenfalls noch vorhandenen Lochfrassgrübchen an den meistbeanspruchten Stellen.
• Eine Rissprüfung der Schaufeln.
• Eine Masskontrolle der Schaufeln, falls diese einem Schleifprozess unterzogen wurden.
• Aufrauhen der Oberfläche durch Sandstrahlen.
• Vor der eigentlichen Beschichtung empfiehlt es sich, die Schaufeln auf ca. 80 Grad Celsius vorzuerwärmen, beispielsweise mittels Strahler.

Further process steps can be provided as required:

• Sand any pitting dimples that are still present at the most stressed areas.
• A check of the blades.
• A dimensional check of the blades if they have been subjected to a grinding process.
• Roughen the surface by sandblasting.
• Before the actual coating, it is advisable to preheat the blades to approx. 80 degrees Celsius, for example using a heater.

Figure 6 shows one way in which the high speed flame spraying process can be carried out. For this purpose, a sheath 16 accessible from the side is provided, which encircles a number of prepared blades. The protective layer is applied to the blades by means of a spray nozzle 20, it being readily possible to guide the jet nozzle 20 manually. A suction device 19 ensures that excess agent can be removed immediately from the area surrounding the blades.

• Zur Verringerung der Oberflächenrauhigkeit wird ein leichtes Ueberschleifen mit Schmirgeltuch und/oder Strahlen, beispielsweise mit Glasperlen.
• Zum Schutz der Grundschicht und zur weiteren Herabsetzung der Oberflächenrauhigkeit kann eine Lack-Deckschicht mit einer Farbspritzpistole aufgetragen werden. Bedingung ist, dass dieser Lack keine hohe und lange Einbrenntemperatur benötigt (kein Ofenbau). Dazu kann mindestens für die ersten Reihen des Kompressors, wo im Betrieb noch tiefere Temperaturen vorherrschen, ein Zweikomponenten-Lack verwendet werden.
  Ein Beispiel für eine solche Deckschicht kann ein Polyurethan-Reaktionslack auf Kunststoff-Basis sein.

Aftertreatment of the sprayed blades usually comprises the following process steps:

• To reduce the surface roughness, light sanding with emery cloth and / or blasting, for example with glass beads.
• To protect the base layer and to further reduce the surface roughness, a top coat of paint can be applied with a paint spray gun. The condition is that this varnish does not require a high and long baking temperature (no oven construction). For this, a two-component paint can be used at least for the first rows of the compressor, where temperatures are even lower during operation.
  An example of such a top layer can be a polyurethane reaction lacquer based on plastic.

• 1. Eine Schutzschicht besteht aus 6 bis 15 Gew.-% Si, Rest Aluminium;
• 2. Eine andere Schutzschicht besteht aus Rein-Aluminium
• 3. Eine andere Schutzschicht besteht aus 80 Gew.-% Al, 5 bis 15 Gew.-% Si, Rest Cu, Mn, Mg, Ni.

Regarding the quality of the protective layer, it can be said that conventional compressor coatings very often show a low resistance to erosion. Since such galvanic protective layers only work if they are present in the metal-layer-electrolyte system, a locally eroded layer is reduced in its protective effect.
The protective layer based on aluminum used here is an active corrosion protection layer, the composition of which preferably looks as follows:

• 1. A protective layer consists of 6 to 15 wt .-% Si, balance aluminum;
• 2. Another protective layer consists of pure aluminum
• 3. Another protective layer consists of 80 wt .-% Al, 5 to 15 wt .-% Si, balance Cu, Mn, Mg, Ni.

The chemical structure of the above protective layers as well the application process (high-speed flame spraying process) also described above provides a less erosion-sensitive "sacrificial anode" layer, which actively protects the base material against corrosion. The application process, which is a high-energy coating process, provides well-adhering and erosion-resistant protective layers which have the desired electrical connection to the base material without further protective layer-specific aftertreatment. The proposed protective layers can additionally be provided with a cover layer. This protective layer can be black, for example. Such a dirt-repellent cover layer enables ice to be more easily recognized on the blades by means of ice detectors. The high-speed flame spraying process, which runs at a particle speed of at least 300 m / s, represents an optimal interlocking of the coating with the base material of the blades. Even with a thicker protective layer, it is ensured that the coating does not flake off. This can be explained by the fact that when the powder particles impact, the high kinetic energy creates residual compressive stresses in the previously sprayed layer. The maximized resistance to erosion is due to the fact that the layers used here have a very high hardness. The method proposed here results in the oxide content of the layer being lower than in the case of protective layers sprayed in air. This means that the layer is cleaner, which is why it oxidizes less quickly, with oxidation only occurring on the surface at most. Because the protective layers are very dense, their porosity is below 0.5%. Destruction by corrosion can practically be ruled out: In the salt spray test according to DIN 50021, a commercially available ceramic aluminum layer was compared with a protective layer with the above composition and with the above methods. The results have fully confirmed the above statement. In a fatigue process, an analogous Ver carried out immediately :. It was found that the load up to the first fatigue crack in the blade was 20% higher in the case of blades coated according to the above composition and method than in the comparison blades. This means that the safety of the blades against fatigue fracture could be increased.
Based on the advantages listed and the results after several thousand hours of operation in a compressor in a plant close to the sea, the service life of the active protective layer was improved by 50%.

Claims (8)

1. Process for coating blades of a rotating thermal machine having a compressor, characterised in that the blades undergo a first cleaning process, in the operating state of the thermal machine, by means of an agent mixed in with the air stream to the compressor, in that the blades undergo a preparation process for the subsequent coating stage, after opening the machine in the stationary state, and in that the blades are coated in the stationary state with a protective coating by means of a high-speed flame spraying process, which sprays the protective coating particles onto the surface of the base material at at least a velocity of 300 m/s.
2. Process according to Claim 1, characterised in that the blades are treated in a vibrating erosive bath in the preparation process before the application of the protective coating.
3. Process according to Claim 1, characterised in that the blades undergo in the stationary state, after the application of the protective coating, an after-treatment to reduce the surface roughness and/or to apply a top coating.
4. Process according to Claim 1, characterised in that the protective coating applied by means of a high-speed flame spraying process consists of 6-15% by weight Si, the remainder Al.
5. Process according to Claim 1, characterised in that the protective coating applied by means of a high-speed flame spraying process consists of Al.
6. Process according to Claim 1, characterised in that the protective coating applied by means of a high-speed flame spraying process consists of 80% by weight Al, 5-15% by weight Si, the remainder Cu, Mn, Mg, Ni.
7. Process according to Claim 1, characterised in that the agent mixed in with the air stream for cleaning the blades consists of soft-blasting granules.
8. Process according to Claim 3, characterised in that the top coating consists of a plastic-based polyurethane reaction lacquer.

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