The invention relates to an airfoil masking tool and use of the masking tool in a method of polishing the airfoil.
The demand for ever greater efficiency gains in gas turbine engines has lead to the demand for ultra-fine (low surface roughness) airfoils that have a surface roughness Ra in the region of 1 to 5 micro-inches. NASA has demonstrated that an industry-standard surface finished compressor rotor blade ultrapolished, also known by super finishing, super polishing, ultra finishing and high precision surface finishing, to a 5 micro-inch finish can produce an increase in engine efficiency of approximately 0.5%, William B. Roberts et al, The Effect of Ultrapolish on a Transonic Axial Rotor, ASME Turbo Expo 2005 International Gas Turbine and Aeroengine Congress Reno Nevada, Jun. 6 to 9, 2005.
It is widely known that media finishing processes, such as those recipes that are commonly provided with media finishing equipment sold by the Rosler, Sweco, Giant, Royson, etc., are able to polish most metal surfaces to achieve surface roughness Ra measurements in the region of 7 to 25 micro-inches. The media finishing process typically comprises a tub style, batch bowl, or a continuous flow-through vibratory finisher filled with hard ceramic media stones of various shapes, abrasive content and sizes, that is vibrated with an electric motor that spins an eccentric weight. Hard ceramic media is loaded into the bowl and the act of vibrating the bowl causes that media to flow in a directional manner and circulate around the bowl. Water and burnishing compounds are typically added to the bowl to assist in the polishing, and sometimes a paste or powder may also be added to accelerate the process. The articles that are to be polished are added to the bowl so that they flow around with the media. The parts can also be fixed in a stationary position in the bowl, but this is not typical. An example of a suitable polishing machine is shown in U.S. Pat. No. 6,261,154, which is incorporated herein by reference.
High energy finishing processes such as high energy tumbling or centrifugal finishing and drag-finishing are able to achieve lower surface finish conditions. However, the high energy nature of these processes can result in the loss of material at sharp edges which may harm the dimensions of the part.
When it comes to polishing close-toleranced parts such as gas turbine engine airfoils, the polishing process can be very aggressive on sharp radius edges and corners such as the leading and trailing edges of the airfoils and blade tip corners. Changes in the dimensions of the leading and trailing edges and blade tip corners can have a profoundly detrimental effect on the mechanical properties and aerodynamic efficiency of the airfoils. Thus, a process for super-polishing close-toleranced airfoils must be able to preserve the dimensions of these areas and possibly others.
An objective of the invention is to provide a super-polishing media process that will avoid altering close-toleranced dimensions of parts such as turbine blades.
Another objective is to provide an airfoil masking tool constructed to hold and protect parts of the airfoil during the polishing process.
The objectives can be obtained by a method of polishing an airfoil comprising:
The objectives can also be obtained by using an airfoil masking tool constructed to hold an airfoil during polishing comprising:
The invention will now be explained with reference to the attached non-limiting Figs.
As shown in
The rail of blades 12 or individual masking tools 7 can then be fitted onto a base plate 13 as shown in
Bladed discs or rotors 14, as shown in
Vane sectors 27, as shown in
The present invention can utilize any suitable polishing machine for mass finishing the surface of workpieces, in particular the airfoil masking tool holding the airfoil.
The tub 100 holds a finishing media which is generally designated by the dotted portions 112. The finishing media is a collection of small objects, usually selected to be uniform in shape, size, and composition, which strike a workpiece to be finished and carry out a polishing or abrading action upon it. The nature and type of finishing media selected for use with the invention is not critical to the invention, but exemplary media include natural stone, sand, porcelain, ceramic particles of various shapes and sizes, metal balls, certain natural organic media (e.g. walnut shells), or polymer-based materials or hybrid multi-component media (e.g. plastic or porcelain with embedded abrasive particles such as diamond). The individual pieces of the media are also referred to as “working bodies” to differentiate them from the workpieces being finished. In
The invention further comprises means for moving the media 112 in the tub 100 in a generally revolving motion that is indicated by the arrow 114 in
One embodiment of the invention is shown in
In addition to the two non-limiting examples of polishing machines disclosed herein, other polishing machines can be used. The invention is applicable to any polishing machine capable of adjusting the angle of the flow of the polishing media in relation to the workpiece being polished. By specifically aligning the airfoils and protecting the leading edge, trailing edge and tip, the exposed surfaces of the airfoils can be polished to higher degree. Preferred polishing machines are a tumbling machine, a high energy centrifugal barrel finishing machine or a drag finishing machine. A preferred medium is ceramic. The polishing machine should be constructed to flow the medium with or without an abrasive paste at desired flow angles against the exposed surfaces of the airfoils. Preferably, the flow angle is selected to provide a surface roughness Ra of less than 5 micro-inches. Examples of suitable flow angles are 50 to 0 degrees, more preferably 40 to 10 degrees, and most preferably 20 to 10 degrees, to the orientation of the leading edge/trailing edge chord axis of the airfoils.
In tumbling machines having two side vibration motors, one can be set at 0 to 50 degrees, and more preferably +10 to 40 degrees, and more preferably +10 to 20 degrees and the other side motor at 0 to −50 degrees, and more preferably −10 to −40 degrees, and more preferably −10 to −20 degrees. However the motor orientation can be altered to change the flow angle of media as necessary such that the flow angle is within 50 to 0 degrees and more preferably 40 to 10 degrees, more preferably 30 to 10 and most preferably 20 to 10 degrees at the desired angle to the orientation of the leading edge/trailing edge chord axis of the airfoils.
Bladed discs or rotors 14, as shown in
A preferred medium for polishing metallic airfoils comprises ceramic media, such as the RCP porcelain non-abrasive polishing stones that can be acquired from Rösler along with a Rösler RPP6279 abrasive paste. However, these media are usually not suitable for polishing airfoils that are coated with an erosion resistant coating such as BalckGold®. Surprisingly, a method that was found to produce a surface finish to levels below 4 μin was a medium comprising diamond paste. The paste used to polish the BlackGold® coating was comprised of a one-micron diamond powder with a gum that serves to keep the diamond powder on the surface of the ceramic media and a water soluble oil, commonly used in metallographic polishing, that assists in the acceleration of the polishing process.
Preferably the polishing paste comprises a polishing media and a carrier. The polishing media can be any media suitable for polishing an airfoil. Examples of suitable media include, but are not limited to, ceramic and diamond. Any suitable carrier for the media can be used. Preferred carriers comprise gum, water and oil.
A preferred polishing paste comprises the following components:
Examples of suitable polishing paste compositions comprise:
Water in the range of 3 to 10 L, preferably 4 to 7 L and more preferably 4 to 5 L; and
The invention is also suitable for fine adjustments to a structure of the airfoil or other desired workpiece. For example, the polishing can be conducted to remove a desired portion of the airfoil to change or alter a dimension or shape of the airfoil. For example, the airfoil can be machined or cast into a desired shape and then fine adjustments to the shape can be performed at the same time as polishing, by controlling the flow of media over the surface of the part such that the action of the media is more heavily concentrated in the area where a dimensional adjustment is required. The surface of any desired portion of the airfoil can be removed at the same time as polishing. This method is suitable for controlled removal of material ranging from 1 micron up to one millimeter in thickness of material from the airfoil.
The polishing method will be further described with reference to the following non-limiting examples.
The process for the super-finishing of parts such as turbine blades comprises of the following components:
1. Tumbling Machine
2. Ceramic Media
3. An Abrasive Paste
4. Stationary Fixed Parts
The Walter Trowal MV-25 tumbling machine is equipped with three vibrator motors; two on the side and one on the base. The two side motors can be oriented individually about 360 degrees. In the present example, the two side motors were set to 10 degrees from the horizontal; one at +10 degrees and the other at −10 degrees.
During operation the three motors were set to 100% power. The media flows in one direction, for example generally from the leading edge to trailing edge of the airfoils, and every 14 minutes the medium flow was reversed automatically by the machine so that the medium flow direction was generally from trailing edge to leading edge and then from leading edge to trailing edge. This cycle was repeated for 5 to 5½ hours. Longer or shorter time periods can be used as required to achieve the required surface finish.
Once the polishing run was completed the media parts were rinsed with water and a 2-5% by volume of a burnishing compound (brand name Rosier FC120) for 45 minutes to an hour. At this point the process was complete and the polished parts were removed from the media. The surface roughness Ra was less than 5 micro-inches.
The same process as Example 1 was used to super polish airfoils that were first coated with an erosion resistant coating, MDS Coating Technologies' BlackGold® coating. The erosion resistant coating was applied to the airfoils and once polished according to the present invention to a surface finish (Ra) of less than 4 μin. The surface finish retention of the coated and polished surface was compared to an uncoated surface having a surface finish (Ra) of less than 4 μin by subjecting the polished coated and uncoated surfaces to erosion using Arizona road dust as the abrasive media.
The abrasive paste for polishing coated gas turbine blades (Example 1, Item 3) is:
While the claimed invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one of ordinary skill in the art that various changes and modifications can be made to the claimed invention without departing from the spirit and scope thereof.
This application claims priority to U.S. provisional patent application Ser. Nos. 61/870,980, filed Aug. 28, 2013; 61/907,207, filed Nov. 21, 2013; 61/913,439, filed Dec. 9, 2013; and 62/001,425, filed May 21, 2014, the complete disclosures of which are incorporated herein by reference.
Filing Document | Filing Date | Country | Kind |
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PCT/CA2014/000628 | 8/18/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2015/027310 | 3/5/2015 | WO | A |
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Entry |
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William B. Roberts et al, The Effect of Ultrapolish on a Transonic Axial Rotor, ASME Turbo Expo 2005 International Gas Turbine and Aeroengine Congress Reno Nevada, Jun. 6 to 9, 2005, pp. 1-7. |
International Search Report issued in PCT/CA2014/000628 dated Oct. 27, 2014, pp. 1-4. |
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Number | Date | Country | |
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20160184959 A1 | Jun 2016 | US |
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62001425 | May 2014 | US | |
61913439 | Dec 2013 | US | |
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61870980 | Aug 2013 | US |