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What is ISFD Bearings, how it works?

What is the ISFD Bearings?
Integral squeeze film damper (ISFD) technology, a Flexure Pivot tilt pad journal bearing, provides precise stiffness and damping to increase the dynamic stability of the rotor/bearing system.

Reduce Dynamic Bearing Forces

ISFD technology reduces the dynamic load that is transmitted to the bearings, which reduces pedestal vibration and increases bearing life, particularly for rolling element bearings. For fluid film bearings, the technology can mitigate pivot wear and reduce babbitt fatigue.

Decrease Unbalance Sensitivity

ISFD technology helps reduce the sensitivity to unbalance, protecting impellers and seals from rubbing and increasing maintenance intervals.

Versatile Design

The ISFD design, manufactured through electrical discharge machining (EDM), can integrate the bearing and damper into one unit for a space-saving solution suitable for new and retrofit installations. ISFD technology can be used with tilt pad, Flexure Pivot tilt pad, fixed profile or rolling element bearings.

How It Works



 the flexibility of the spring allows for motion at the bearing location


squeeze film provides damping transferring energy from machine vibrations to the viscous fluid

a tilt pad flexure pivot bearing 

The ISFD design is manufactured through electrical discharge machining. Integral “S” shape springs connect an outer and inner ring, and a squeeze film damper land extends between each set of springs. Bearing pads are housed in the inner ring (Figure below). The unique design allows for high-precision control of concentricity, stiffness, and rotor positioning. It produces superior damping effectiveness by separating stiffness from damping.

 

Integral squeeze film damper (ISFD) technology, shown here as part of a Flexure Pivot tilt pad journal bearing, provides precise stiffness and damping to increase the dynamic stability of the rotor/bearing system.

This four-pad tilt pad journal bearing utilizes integral squeeze film damper technology.


While a conventional squeeze film damper (SFD) experiences a dynamic stiffness from the damper film that is dependent on amplitude and frequency, in the ISFD design, the stiffness is defined only by the springs. This allows for good predictability, and precise placement of critical speeds and rotor modes, regardless of vibration amplitudes and frequencies.

Whereas damping in a conventional SFD is generated by squeezing in the damper film and governed by circumferential film flow, the segmented ISFD design prevents circumferential flow and absorbs energy through the piston/dashpot effect. Flow resistance at the oil supply nozzle and end seals controls ISFD damping.

Both the stiffness and the damping of the ISFD design are optimized for the application through a rigorous rotordynamic analysis. For the steam turbine, because steam whirl was one of the root causes of the subsynchronous vibrations, the analysis of the ISFD solution paid careful attention to modeling destabilizing seal forces and stage forces.

A damped eigenvalue analysis without those forces showed a better stability margin by a factor of 12 with the ISFD design compared to the original bearings. With the destabilizing forces, the ISFD solution maintained a high stability margin. The combination of low stiffness and optimum damping at the bearing support is the key in transforming bending modes to more rigid body modes and improving the overall stability and damping ratio of the rotor/bearing system.

Typical Applications

  • Integrally geared compressors
  • Centrifugal compressors
  • Steam turbines
  • Gas turbines
  • Turboexpanders
  • Radial turbines
  • Supercritical CO2 power turbines
  • Generators
  • Motors
  • Overhung process equipment

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