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Centered cardan drive shaft: what are the causes of frictional vibration?

Views: 0     Author: Site Editor     Publish Time: 2022-07-27      Origin: Site

In the process of operation, the gap between the rotor and the stationary parts such as the steam seal disappears, leading to the contact between the moving and static parts and the resulting vibration is called friction vibration.

The volume and mass of large turbine rotor and cylinder are larger, so the compliance is larger. Due to the consideration of economy, the steam seal gap is controlled relatively small, so that the friction vibration occurs more frequently in this kind of unit.

Friction vibration is one of the common vibration faults of the unit, which is often severe and diverges quickly. If the thermal stress generated by static-static contact exceeds the yield limit of the material, it will also cause permanent bending of the rotor. A considerable part of rotor bending is caused by dynamic and static friction, and some shafting failure accidents are also directly or indirectly related to friction vibration. Therefore, it is very necessary to identify the characteristics of friction vibration and take correct countermeasures in time.

Rotor-stator contact most often occurs in shaft and diaphragm seals. Steam seal is a device for sealing steam. According to its position, it is divided into end steam seal (also known as shaft seal), baffle seal and blade seal. The end of the steam seal between the cylinder and the rotor, reduce steam leakage cylinder or air into the cylinder; Baffle steam seal in the rotor and baffle clearance outside, reduce steam leakage into the baffle; The end of the moving blade and the circumference of the wheel disc and the baffle body are arranged in the axial and radial direction of the steam blade is called the blade steam seal.

The rotor-stator contact between the seal and the diaphragm will cause the temperature asymmetry of the rotor and make the rotor thermal bending. However, the rotor - stator contact at the blade vapor seal has little effect on the rotor temperature and will not produce friction vibration.

In addition, the oil stop, bearing bush, generator end cover, sealing tile and other parts may be in contact with the rotor. The occurrence of dynamic and static contact is related to the reasons of structure, maintenance and operation.

Axle shaft with centered cardan: structural reasonsaxle shaft with centered cardan - xinsanming

1)Some low-pressure cylinders have low stiffness and are prone to deformation after filling with water, vacuuming and heating.

2) Longer steam seal section or close to mid-span rotor mid-span deflection position.

3)Steel seal or spring seal, this seal once the rubbing occurs, it is difficult to get out of contact.

4)Diaphragm deformation.

5)If the unit has high sensitivity, slight static and dynamic contact will be reflected in the vibration.

Single double cardan drive shaft: maintenance reasons

1) Improper adjustment of dynamic and static clearance.

Such as one-sided pursuit of economy, the gap will be improperly reduced, resulting in dynamic and static contact. For example, a 600MW unit cannot be fully delivered after production, the gap between the high and middle cylinders will be improperly reduced in maintenance, resulting in the boot cannot even reach 3000R /min. Later, the clearance of part of the shaft seal was reviewed, and it was found that some of the clearance was even zero.

The clearance value provided by the manufacturer is more for the consideration of unit economy. Static and dynamic contact cannot be completely avoided by adjusting the clearance value. For example, the installation clearance of the low-pressure cylinder separator steam seal is generally about 1mm, but the cylinder block subsidence can reach several millimeters in operation.

Because it is difficult to grasp the reasonable clearance in the installation, friction vibration is easy to occur after the start of the new machine and the overhaul of the unit.

2) The balance is unfavorable.

3)Cylinder deformation and deviation caused by the astringent sliding pin system.

Axle shaft with centered cardan: running causes

1)cylinder deviation or uneven foundation subsidence.

2) Change of steam temperature.

If the steam temperature changes too dramatically, it will cause deformation of the stationary parts. Therefore, the temperature change must be controlled within a reasonable range.

3)cylinder water intake and poor insulation.

Water entering the cylinder from the steam line or the extraction line will sharply cool the cylinder wall. The result is a large temperature difference between the upper and lower cylinders, causing the cylinder to "arch back" (bend). This will cause severe friction and pose a threat to the safety of the through part. Poor cylinder insulation can also cause cylinder deformation.

4) Rapid heating and cooling of exhaust cylinder.

Under low load and low steam flow, the exhaust cylinder is heated rapidly, which may cause cylinder deformation. If the sprinkler is not put in in time, friction may be caused.

5) Steam seal damage.

The drastic change of inlet temperature or water in the steam seal system will cause deformation or damage of the steam seal.

6)The heating machine is not sufficient. Start the machine when the rotor has large sway.

7)Violent vibration.

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Contact Us

  : +86 29 86033971
 : +86 29 86033972
  :  zhao.wanbao@dcsxsm.com
  : The Innovation Industrial Park, No.36, Jingwei Road ,Xi'an Economic and Technological Development Zone,Xi'an City,Shaanxi Province,China
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