Airfoil machine components polishing method
A polishing method is described for polishing a machine component comprising at least one airfoil portion comprised of a suction side, a pressure side, a leading edge and a trailing edge. The method provides for arranging the machine component in a container and constraining the machine component to the container. A polishing mixture is added in the container, and the container is caused to vibrate together with the machine component constrained thereto, thereby generating a polishing mixture flow along the airfoil portion until a final arithmetic average roughness is achieved.
1. A method for polishing a machine component, the method comprising:
arranging a machine component in a container and constraining the machine component to the container, the machine component comprising at least one airfoil portion comprised of a suction side, a pressure side, a leading edge, and a trailing edge;
adding a polishing mixture in the container, the polishing mixture containing at least abrasive powder, a liquid and metal particles; and
vibrating the container and the machine component constrained thereto, thereby generating a polishing mixture flow along a surface of the airfoil portion until a final arithmetic average roughness equal to or less than 0.3 μm is achieved on at least a portion of the airfoil portion surface, wherein the dimension and shape of the airfoil portion in contact with the polishing mixture flow is substantially unaltered.
2. The method of claim 1 , wherein a final arithmetic average roughness achieved is equal to or less than 0.2 μm.
3. The method of claim 1 , wherein a final arithmetic average roughness achieved is equal to or less than 0.17 μm.
4. The method of claim 1 , further comprising selecting a vibration frequency of the container and the machine component, wherein the selected vibration frequency causes the metal particles advancing along the airfoil portion to adhere to a surface of the airfoil portion while abrasive particles of the abrasive powder are trapped between the airfoil portion and the metal particles.
5. The method of claim 1 , wherein the metal particles have substantially planar surfaces, and wherein the metal particles are advanced by vibration along the airfoil portion with the planar surfaces thereof in contact with the airfoil portion.
6. The method of claim 1 , further comprising, prior to arranging the machine component in the container, subjecting the surface of the machine component to shot peening treatment.
7. The method of claim 1 , wherein the step of generating a flow of the polishing mixture along the airfoil portion comprises advancing the metal particles of the polishing mixture along the pressure side and the suction side of the airfoil portion.
8. The method of claim 1 , wherein the machine component is a blade or bucket of an axial turbomachine, having a root and a tip, wherein the airfoil portion extends between the root and the tip, an airfoil chord being defined between the trailing edge and the leading edge in each position of the airfoil portion from the root to the tip, and wherein a length of the chord is maintained substantially unaltered during the step of vibrating the machine component until a final arithmetic average roughness of 0.3 μm or less is achieved.
9. The method of claim 8 , wherein the final arithmetic average roughness is 0.17 μm or less.
10. The method of claim 8 , wherein during the step of vibrating the machine component the chord length is varied by less than 0.05%.
11. The method of claim 8 , wherein during the step of vibrating the machine component the chord length is reduced by not more than 0.1 mm.
12. The method of claim 11 , wherein during the step of vibrating the thickness of the blades of the impeller is reduced by less than 0.5% on average.
13. The method of claim 11 , wherein during the step of vibrating the thickness of the blades of the impeller is reduced by not more than 0.1 mm.
14. The method of claim 11 , wherein during the step of vibrating the machine component the diameter of the central drive-shaft receiving bore is varied by less than 0.05%.
15. The method of claim 11 , wherein the impeller comprises a shroud comprised of an impeller eye; the impeller eye has an outer surface with at least one cylindrical outer surface portion; and during the step of vibrating the machine component, the diameter of the cylindrical outer surface portion remains substantially unaltered when the final arithmetic average roughness achieved on an inner surface of the vanes is equal to or less than 0.3 μm.
16. The method of claim 15 , wherein during the step of vibrating the machine component a diameter of the cylindrical outer surface portion is varied by less than 0.01%.
17. The method of claim 15 , wherein the hub, the shroud and adjacent impeller blades define flow vanes therebetween, each flow vane having an outlet aperture at the trailing edges of the blades, and wherein during the step of vibrating a axial dimension of the outlet apertures varies on average less than 0.05%.
18. The method of claim 11 , wherein the impeller is an un-shrouded impeller and wherein the method further comprises the step of applying an impeller closure, closing the vanes along tips of the blades before adding the polishing mixture in the container.
19. The method of claim 1 , wherein the machine component is a turbomachine impeller comprising a hub with a central drive-shaft receiving bore and a plurality of blades arranged on the hub around the drive-shaft receiving bore, vanes being defined between adjacent blades, each vane having an inlet and an outlet, each blade having a leading edge at the inlet and a trailing edge at the outlet of adjacent vanes, and wherein vibrating the machine component causes the polishing mixture flow to circulate in the vanes.
20. The method of claim 19 , wherein during the step of vibrating the machine component an inner diameter of the central drive-shaft receiving bore remains substantially unaltered when the final arithmetic average roughness achieved on the inner surface of the vanes is equal to or less than 0.3 μm.
21. The method of claim 1 , wherein the metal particles comprise metal chips.
22. The method of claim 1 , wherein the metal particles comprise copper particles.
23. The method of claim 1 , wherein the abrasive powder is aluminum oxide, ceramic or a combination thereof.
24. The method of claim 1 , wherein the liquid comprises water.
25. The method of claim 24 , wherein the liquid comprises water and a polishing medium.
26. The method of claim 1 , wherein the polishing mixture has the following composition by weight:
metal particles 90-98%
abrasive powder 0.05-0.4%
liquid 3-10%.
27. The method of claim 1 , wherein the step of vibrating the container and the machine component constrained thereto lasts between 5 and 8 hours.
28. The method of claim 1 , wherein the step of vibrating the container and the machine component constrained thereto lasts between 1.5 and 10 hours.