From the inspection results, the 40th forged steel meets its corresponding mechanical properties, and only the section shrinkage does not meet the (standard) technical requirements, but the 40th forged steel can not meet the stress of the 85t weight of the rotor and the large shaft flange. Claim. This is one of the reasons why the rotor coupling bolts appear to be de-weld and fractured. Secondly, there are problems with the installation process during construction. When we checked the bolts for No.1, No.2, and No.3 machines, we found that the external force applied when removing the coupling bolts for No. 1 and No. 2 machines is obviously better than the force of removing the No. 3 coupling bolts. To be large (in the case of using the same disassembly tool, the length of the tool arm is the same), which proves that in the installation of the rotor coupling bolt, it may not be strictly in accordance with the construction process requirements.
We have done tests on this, and inspected No. 4, No. 5, No. 10 and No. 12 of the original rotor coupling bolts of Unit 2 on the No. 2 machine. It was found that the elongation values â€‹â€‹of No. 4, No. 10 and No. 12 did not meet the design tensile value requirements. Finally, the vibration of the turbine operating under different working conditions is different. The de-welding fracture of the rotor coupling bolt also has different degrees of influence or even damage.
In the design and selection of the hydro-generator, the force of the unit under five working conditions should be analyzed and calculated in detail to take the maximum value as the design value. The drainage condition (that is, the force of the unit before the water filling) and the water filling condition (that is, the force under the hydrostatic condition before the operation after the water is filled) have no effect on the rotor coupling bolt.
Under normal operating conditions (ie, the unit is subjected to full load during normal operation), the unit is under stress and should not affect or destroy the rotor coupling bolts. However, when the unit is under load, the flow is not due to the flow. Uniform, there are flogs and impacts, the horizontal vibration of the water guide and the vertical vibration of the runner shell increase with the increase of the load, resulting in strong vibration and noise of the unit in the high load region. This also has a certain negative impact on the desoldering fracture of the rotor coupling bolt. Under full load conditions, the unit produces severe vibration and noise. Measures to solve the problem There are major safety hazards in the phenomenon of de-welding and fracture of the rotor coupling bolts of No.1, No.2 and No.3 units. In order to ensure the safe operation of the hydro-generator, the 35CrM was decided after discussion by the expert group.
The round steel material replaces the original 40 forged steel. The mechanical properties of 35CrMo were tested with the cooperation of quality supervision and inspection stations. The test results show that 35CrMo is used as a rotor coupling bolt to meet the design requirements of the manufacturer, and to ensure that the rotor coupling bolt no longer breaks.
Concluding remarks Guangxi Guiping Hydropower Plant replaced the rotor coupling bolts of No. 1, No. 2 and No. 3 units, which solved a very hidden and significant safety hazard. From the time of replacement to the present, no faults or accidents have been discovered in one year. The unit is in good operating condition. In short, the safety and reliability of the unit have been greatly improved after replacing the new rotor coupling bolts. 35CrMo material can meet the manufacturer's design requirements for rotor coupling bolts.
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