With the increase of the number of power plants and the continuous improvement of the capacity and parameters of single machine, the maintenance and overhaul of units become more and more complicated and important. Generator rotor, as the heart component of steam turbine generator set, has high running precision, high running speed and high manufacturing cost. Once damaged, it will directly lead to the decline or even paralysis of the whole unit. Thermal spraying, argon arc welding, mounter, brush plating and other processes have been used for repair [2], but the actual effect after repair is not ideal.
In this paper, DZ- 1400 electric spark surfacing equipment developed and produced by Institute of Surface Engineering Technology of China Academy of Agricultural Sciences is used to repair the worn shaft diameter of generator rotor sealing section, and satisfactory results and successful experience are obtained. Up to now, nearly 20 worn rotor shafts have been repaired, and the longest running time after repair is more than two and a half years. Practice has proved that the electric spark surfacing technology has played an important role in the repair of power station components, resulting in huge economic and social benefits. 3. 1 sample preparation
50mm 10mm According to the common materials of rotor shaft diameter, 35CrMoA is selected as the sample matrix material, and Inconel high alloy covered electrode with the size of 25mm6.0mm is used for surfacing covered electrode. The chemical composition is shown in Table 2.
13. The choice of surfacing covered electrode material is subject to the requirements of the factory: the hardness of surfacing layer is consistent with the matrix, and it has self-lubrication, self-polishing, cavitation resistance and high alloy content.
Turning, brush plating, repair, electric spark surfacing and 1. And the machining accuracy is high.
1. Suitable for field treatment.
Low cost.
3. Ensure the original design size.
1. Suitable for field treatment.
4. High efficiency.
1. Site construction
The period is short.
3. Ensure the original size.
4. High adhesive strength.
⒌ Minimum residual stress ⒈ Reduction of shaft diameter.
4. Tiles need to be repackaged, and the interchangeability of parts is poor.
[13] The cycle is long, the cost is high, and the field treatment is difficult.
1. Low adhesive strength.
The coating thickness is limited.
3. The copper coating has poor wear resistance and is easy to form galvanic corrosion.
1. The interlayer porosity of the patch is high.
2. Low adhesive strength-low efficiency
Table 2 Composition of surfacing covered electrode
Nickel-chromium-iron-molybdenum-manganese-silicon others
70 14 4.5-7.8 0.5 bar
[13] 2 test analysis
Use sandpaper and copper wire brush to remove the oxide on the sample surface, and then use acetone solution to clean the oil on the sample surface. Fasten the sample matrix with the grounding wire of the electric spark surfacing machine, and surfacing on the surface of the sample, with the surfacing thickness of 65438 0 mm.
3000), it can be known that:' After the electric spark surfacing, the cross section of the surfacing layer is obtained by wire cutting method, and the metallographic sample is prepared. Fig. 5 is a metallographic photograph of the cross section of the surfacing layer (
(1) The surfacing layer has no welding defects such as blowholes, oxide slag inclusion and cracks.
⑵ The grain size of surfacing layer and parent metal transition layer is fine and there is no tendency to grow up.
⑶ The microstructure of surfacing layer is extremely fine columnar crystal structure, which proves that surfacing layer has good corrosion resistance and wear resistance.
︳︱︱︱︱︱︱︱︱︱
The microhardness measurement of the matrix shows that the average hardness of surfacing layer and heat affected zone is HV220, which is very close to the matrix hardness. Theater influence zone Tm. This not only proves that the surfacing layer with good metallurgical combination with the base metal can be obtained by EDM surfacing, but also shows that the heat affected zone of surfacing is extremely narrow and the welding residual stress can be ignored. Figure 6 shows the surfacing layer. Fig. 5 shows the energy spectrum analysis of Ni and Cr elements in the surfacing layer. After measurement, the thickness of HAZ of electric spark surfacing is only 10.
3. Results
M), the hardness of surfacing layer is consistent with that of matrix. The above analysis results meet the requirements of power station for repairing the shaft diameter of motor rotor. Figures 7 and 8 show the diameter of the repaired generator rotor shaft. M test shows that Inconel alloy is surfacing by electric spark surfacing, and the surfacing layer is metallurgically bonded with the base metal without welding defects. The heat affected zone after welding is extremely narrow (when the surfacing layer reaches 1mm, the heat affected zone is only 0.011. The electric spark surfacing layer and the base metal are metallurgically combined, so the heat affected zone of surfacing is extremely narrow and the residual stress can be ignored.
4. Repairing the damage of the key parts of the power plant by using the electric spark surfacing technology, which can be operated online and has a simple process. After repair welding, the machining amount is small, reducing the downtime.
13. The electric spark surfacing technology has a broad application prospect in power plants, which contains huge economic and social benefits.
refer to
[1] Electric Power Reliability Management Center, National Manual for Large Units [M],1998,4
[2] Prospect of power station welding technology [C], Proceedings of the 60th anniversary academic report of China Electrical Engineering Society
[3]Williams A, D, Humphries J.L Selected Papers of the15th International Thermal Spraying Conference (1998, ITSC).