Preparation of the surface of measurement paths of eddy-current sensors of relative vibrations by the SND method.
Rotor is the most important component of each rotary machine such as: turbogenerator, compressor, turbine, blower, pump. There is a tendency in the industry to monitor rotor operation by measuring relative vibrations using an eddy current sensor and a control & recording system. The measurements include analysis of mechanical and electrical disturbances caused by imperfections of the surface of rotor bearing journals.
Electromagnetic distortions (so called electrical runout) are the result of variable magnetic intensity at different zones of the rotor, stresses in the top layer, and non-homogeneities of metallographic structure. The runout can be reduced by demagnetization.
Mechanical distortions (so called mechanical runout) are the result of faults in shape and location as well as unevenness of bearing journal surface. Excessive runout interferes in the readings of relative vibration measuring sensors and should be minimized. That can be done by reducing the mechanical component of the runout. Journal surfaces should have low roughness, no scratches or cavities, possibly uniform metallographic structure, and uniform stresses in the top layer.
Masz – ZAP obtains such properties as a result of a diamond-tip burnishing operation (Polish abbreviation: SND) performed in accordance with the recommendations of the standard API 617 for rotors having the following parameters:
- max. diameter: 660 mm
- overall length: 2000 mm
- max. weight: 500 kg.
Description of the SND method:
During an SND operation, a rounded tip of the tool (a diamond bead) is moved across the surface being processed and, at the same time, pressed against that surface with appropriate force, thus causing plastic deformation of and smoothing out surface distortions, plus a small increase in the hardness of the top layers. The surface quality obtained is tested by measuring overall runout runout-u) using a 3300XL Bently Nevada measuring kit consisting of a measuring probe and a proximitor. The results are recorded using a digital oscilloscope.