A short insight to governing of steam turbines.This will be more useful and mean more to Power Plant professionals and for those who are beginners or trainees in the Thermal Power Plants.Descrição completa
MANUFACTURING OF STEAM TURBINE BLADE A visit to “Quality profiles pvt ltd, patancheru” was carried out and information regarding manufacturing blade was collected. After that we manufactured blade according to specifications with the help technician overthere on CNC 3AXIS MACHINE.
CNC INTRODUCTION •
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In order to meet the increasing demand to manufacture complicated components of high accuracy in large quantities, sophisticated technological equipment and machinery have been developed. The design and construction of Computer Numerically Controlled (CNC) machines differs greatly from that of conventional machine tools. This difference arises from the requirements of higher performance levels. The control of a machine tool by means of stored information through the computer is known as Computer Numerically Controlled. The information stored in the computer can be read by automatic means and converted into electrical signals, which operate the electrically controlled servo systems. Computer Numerically Control can be applied to milling machines, Lathe machines, Grinding machines, Boring machines, Flame cutters, Drilling machines etc.
MANUFACTURING PROCESS The different processes followed in the manufacture of steam turbine blade on cnc 3axis machine as follows 1. RAW MATERIAL PROCUREMENT: The steam turbine blade material is procured as per the design specification. The material is inspected dimensionally and all the mechanical and chemical analysis are made as per the specification.
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2. LENGTH CUTTING: The material is cut to length by keeping machining allowance at both ends either by Band Saw or by Power Hack Saw. 3. THICKNESS MILLING: The material is clamped in a vice or fixture and thickness is milled on both sides by keeping n allowance of 0.5mm on both sides for grinding. This operation is done either by horizontal milling machining or by vertical milling machine.
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4. THICKNESS GRINDING: The milled bars are deburred and kept on a magnetic chuck of the segemental surface grinding machine. 5 to 10 blades are kept each time depending on the size and ground each side to maintain the dimension. The tolerance on the grinding dimensions would be +/‐ 0.05 mm and parallarith should be with in 0.02 mm. 5. RHOMBOID MILLING: The ground blade bars are milled to rhomboid shape with an angle given in the process by clamping in a ficture on both sides with an allowance of 0.5mm on both side. This is done on the horizontal milling machines.
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6. RHOMBOID GRINDING: The milled bars are deburred and kept on magnetic chuck of the surface grinder and grinding is done on both sides and the tolerance should be +/‐ 0.05 mm. The surface must be with in 8 microns. 7. FACING AND SIZE MILLING: The ground blades are faced on the root side to maintain perpendicularity. This is very important as the blade is held on this face while in assembly. Then on other side size milling is done to maintain the total length of blades as per the drawing.
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8. ROOT MILLING: Clamp the blade in a vice or ficture and machine the root on both sides as per drawing keeping an allowance for root radius. Do not machine 2 blade as these are used for locking purpose. This operation is done on horizontal milling machine. 9. ROOT RADIUS MILLING: Clamp the blade in a vice or fixture and machine the root radius as per drawing by CNC M aching center. This operation is done on CNC Vertical machining center by CNC Program.
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10. WIDTH MILLING: The profile width is done on both sides on horizontal milling machine as per the drawing. 11. CONVEX MILLING: The milling is done on convex side by a CNC machining center. The CNC Program is developed based on the profile coordinates and then loaded into the CNC system of the machine.
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12. CONCAVE MILLING: The profile milling is done on concave side by a CNC machining center. The CNC Program is developed based on the profile coordinate and then loaded in to the CNC system of the machine. 13. TAPER MILLING: The taper milling is done on a horizontal milling machine by putting in a fixture specially made. The taper is calculated from sine values and machined accordingly.
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14. TAPER GRINDING: The taper grinding is done on a surface grinding machione and ensure the angle with in the given tolerance in the diagram. Also surface finish must be with in 8 microns. 15. FITTING AND POLISHING: The blades are deburred and rounded off on the inlet side and then polished on blade polishing machine.
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CONCLUSION •
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As we understood that the efficiency and reliability of a steam turbine depends on the proper design of blades. The reliability of moving blades is to be ensured upon proper design selection of material. In blade profile where as in impulse the entire heats drop occurs in stationary blades. The fork root has higher load carrying capacity than T‐root. Different milling cutters are used to finish the operation on the blade. The growth for the steam turbines are very high and demand for blades is growing.
