The present invention relates to method for repairing a turbomachine component by laser-cladding.
The increasing use of turbomachines to the operational limits requires the development of specific repair technologies designed to reproduce conditions close to those of new parts. Both rotating and non-rotating parts are subject to damages due to erosion and/or to wear.
For example, steam turbine shafts are often damaged in coupling areas at shaft ends and in journal bearing areas. On centrifugal compressor shafts the same situation occurs for bearing journals and for the shaft ends, while very often during compressor overhaul; impellers are found with the sealing area worn out. Other rotary or stationary parts can be damaged as well, such as steam turbine blades, centrifugal compressor cases, or gas turbine rotors.
In the above field, conventional repairing techniques, such as electric arc or microplasm deposit welding, show a plurality of disadvantages, i.e., in particular, high heating and cooling rates and low melting volumes. As an alternative, repairing methods by laser surfacing are known. Advantages of the latter over alternative surfacing processes include:
Among laser surfacing methods, laser cladding is generally known. Laser cladding uses a laser beam to fuse a cladding material having desired properties into the base material of a component whose surface is to be repaired. Laser cladding offers the possibility to create surface layers with superior properties in terms of pureness, homogeneity, hardness, bonding, and microstructure.
Laser cladding repairing methods are already used to repair stationary components, as described in US20100287754, or to deposit small volumes of cladding material, as described in US20090057275.
To repair larger and thicker damaged areas and/or surfaces of rotary components, the method parameters have to be properly tuned in order to optimally restore the aspect and properties of the damaged components. In particular, it has to be solved the conflict between the demand of achieving a good metallurgical bond, necessary to rebuild damaged parts, and avoiding mixture between the coating and the base material in order to have desired coating properties on the surface. In general, the right correlation between all the variables of the process has to be found.
It would be therefore desirable to provide an improved laser cladding method which permits to find such a correlation in an easy and reproducible way for each turbomachine component to be repaired, in order to avoid the inconveniencies of the known prior arts.
According to a first embodiment, the present invention accomplish such an object by providing a method for repairing a turbomachine component comprising the steps of:
According to a further advantageous feature of the first embodiment, the step of setting up the laser cladding machine includes the sub-steps of:
According to a further advantageous feature of the first embodiment, the plurality of geometric data includes:
With respect to other known repairing methods, the solution of the present invention allows to:
In a second embodiment, the present invention provides a mobile apparatus for repairing a turbomachine component comprising a turning machine and a laser cladding device of the type including a laser device for creating a laser beam and a powder feeder device for blowing a metal powder towards said laser beam, characterized in that said laser cladding device is fixable to a tool station of said turning machine.
The same advantages described above with reference to the first embodiment of the present invention are accomplished by this second embodiment. In addition, the latter embodiment permits to perform the method of the present invention directly on site, without requiring the whole turbomachine or the components to be repaired to be moved away.
Other object feature and advantages of the present invention will become evident from the following description of the embodiments of the invention taken in conjunction with the following drawings, wherein:
With reference to the attached
The method 1 comprises a first step 50 of setting up a laser cladding machine 100 (i.e. an “apparatus”), including a laser beam device 101 (i.e. a “laser cladding device”) and a powder feeder.
The laser beam device 101 is of a conventional type, for example Rofin YAG laser, 2.2 kW or IPG fiberlaser, 2.2 kW. In general, for the purposes of the present invention, other laser beam devices can be used provided that a uniform power density is reached in order to obtain an acceptable uniform temperature distribution and consistent clad properties over the width of the laser track.
With reference to
With reference to
The tool station 111, grinder 115 and post-welding heat treatment station 116 are movable parallel to the guides 110 in various configurations, as detailed further above.
The laser cladding machine 100 is also configurable in order to be completely housed in a limited volume V, suitable for transportation by truck, in particular a standard shipping container.
The first step 50 of setting up the laser cladding machine includes a first sub-step 51 of identifying a set of laser cladding process parameters.
The process parameters, with relevant ranges, include:
The powder type is chose among Inconel 625, Stellite 21 or ASTM A 322 type 4140.
The above parameters have to be correctly tuned depending on the type and geometry of the component to be repaired, on the specific laser cladding machine which is used to perform the repairing operations and on the environment, for example room temperature and humidity.
For example the latter has influence on the choice of powder mesh. First tentative values are defined first sub-step 51 in the first sub-step 51 by applying the procedure which follows, based on relations A1, A2, A3, A4.
Energy density is defined as
E=PS·It, (A1)
where
PS=PL/Aw (A2)
is the specific power and
It=dS/v (A3)
is the interaction time process. Aw and dS are, respectively, welding area and spot welding diameter, depending on the geometry of the region to be repaired and of the laser cladding device 101, for example optics, i.e. lenses and focal length of the laser cladding device.
By combining together the above relations A1, A2 and A3, the following expression for E is obtained:
E=(PL·ds)/(Aw·v) (A4)
In the above, the PL, ds, Aw, and v have to be tuned in order to limit the energy density between 110 and 120 J/mm2. Scanning speed v is to tuned between 2 and 10 mm/s, in order to avoid high thermal residual stresses.
The first step 50 of setting up the laser cladding machine includes a second sub-step 52 of identifying a sample, for example a cylinder of the same material of the component to be repaired.
In a third sub-step 53 of the first step 50, a first layer is welded on the sample by the laser cladding machine 100 after imposing a set of the above laser cladding process parameters.
In a fourth sub-step 54 of the first step 50, a plurality of geometric data of the first layer is compared with a respective plurality of reference data ranges.
Geometric data includes:
Reference data ranges are:
If the plurality of geometric data is within the specified ranges, the first step 50 of the method 1 continues with fifth sub-step 55 of welding a plurality of further layers on the sample by the laser cladding machine 100.
In a sixth sub-step 56, the plurality of further layers is tested by micrographic inspection, including examining inter-run porosity, wherein the reference parameter is an overlap parameter defined as clad width percentage of overlap.
If the plurality of geometric data are outside the plurality of reference data ranges, the first step 50 of setting up the laser cladding machine 100 includes the further sub-step of modifying said set of laser cladding process parameters. For example, if the angle α is greater than said respective angle range than the powder rate is reduced. In general all parameters are inter-correlated, therefore a correct set have to be defined considering all of them. After changing the process parameters the third and fourth sub-step 53, 54 are repeated.
In order to carry out the set-up of the laser cladding machine 100, in particular the laser beam device 101, one or (typically) more accessories are used; the laser cladding machine 100 is advantageously provided and shipped with these accessories.
The method 1 comprises a second step 70 of inspecting the turbomachine component to be repaired.
After the second step 70, the method 1 includes a group 10 of repairing steps 11, 12, 13, 14. The group of repairing steps 11, 12, 13, 14 includes:
The final step 15 comprises:
At the end of the method 1, the step 15 is followed by a further step 40 of finally checking the turbomachine component C, including a dimensional and geometric check 41 and a balancing sub-step 42, by using the balancing device 104.
In an embodiment 1a (
In the case that preliminary checks of the second step 70 identify that disassembly of the rotary shaft is required, method 1a continues with a disassembly step by which the impellers are disassembled from the shaft and with a group 10b of repairing steps, including the same steps of the group 10a. Differently from the group 10a, the group of steps 10b is applied on the shaft. At the end the final step 15 of testing the impellers and the repaired shaft are again assembled.
Both groups of steps 10a and 10b are in the end followed by the step 40 of finally checking the turbomachine component C, including first the balancing sub-step 42, performed for example by using the balancing device 104, and then the dimensional and geometric check 41.
In another embodiment 1b (
The group of steps 10 is in the end followed by the step 40 of finally checking the turbomachine component C, including first the balancing sub-step 42, performed by rotating the impeller till overspeed conditions are reached, and final geometric check 41.
In general, many other turbomachine components can be repaired with the method of the present invention by using a laser cladding machine as above described.
In all cases it is essential that the laser cladding process parameters are correctly defined by correctly applying the set up step 50, thus allowing to accomplish the object and advantages cited above.
This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspects, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application.
Number | Date | Country | Kind |
---|---|---|---|
CO2012A000041 | Sep 2012 | IT | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/EP2013/068279 | 9/4/2013 | WO | 00 |