Transcription of VI Balance Grades
1 Balance Grades : Electric Motor Experience Vibration Institute Piedmont Chapter 14. 12/01/2006. Clay Boyd, PE. CBM Analyst 704-382-3608. References Schenck Trebel Corporation 535 Acorn Street Deer Park, NY 11729. Toll Free: 1-800-873-2352. Motor Repairs Motor Repair Specification Balance Grades Initial Balance with Shop Balance Machine Final Balance with Motor Assembled Motor Repair Specification Work to be performed Acceptable Repair Practices Required Reporting Acceptance Criteria, including Balance grade . Balance Grades Balance Grades are used to specify the allowable residual imbalance for rotating machinery.
2 The ISO 1940 standard defines Balance Grades for different classes of machinery. (Rigid Rotors Only*). Example: Balance grade is recommended for Steam Turbines, Machine Tools and Small Electric Armatures. * ISO 11342 defines the Balance quality requirements for rotors in a flexible state Balance Grades : Sample Chart Permissible Residual unbalance per unit rotor weight (g*mm/g*1000) or Permissible cg displacement (mm*1000). Service Speed (rpm). Balance Grades A rotor balanced to will vibrate at mm/sec (Velocity) if freely suspended while rotating at service speed.
3 ( mm/sec = IPS). V(mm/sec) = 2pe(mm)*RPM. 60sec/min e(mm) = Residual Imbalance (g-mm). Rotor weight(g). Balance Grades Balance grade is a function of Rotor Mass (lbm, Kg, g). Service speed (rpm). Residual imbalance (g-in, oz-in, lb-in, g-mm ). Initial Balance with Shop Balance Machine It is difficult if not impossible to achieve Balance Grades or in a Balance machine only Balance Grades and have special requirements. The rotor must be mounted in its own service bearings No end drive (for Balance machines). The rotor must be mounted in its own housing and bearings Must be run under normal service conditions: Load, Self driven Initial Balance with Shop Balance Machine : Roller Size the roller diameter should differ from the journal diameter by at least 10%, and the roller speed should never differ less than 60 rpm from the journal speed.
4 Fundamentals of Balancing, 2nd Ed. 03/1983; Schenk Trebel Final Balance with Motor Assembled Motor Setup Flexible or Rigid Rotor Large 2-pole motors Effect of startup heating Interference of 60 Hz electrical vibration on unloaded 2- pole Motor phase readings Final Balance with Motor Assembled Motor Setup Motor on Solid Base Elevate on shims at base bolt locations Shim to eliminate soft foot Secure with bolts or clamps Lubricate bearings Monitor vibration from the first start Flexible or Rigid Rotor Large 2-pole motors In test runs at service speed.
5 Moving two test masses from the end planes to the center plane, results in a vibration change of less than 20%. Fundamentals of Balancing, 2nd Ed. 03/1983; Schenk Trebel Graphic: Effect of startup heating 60 Hz Trial 1 (1:25 PM). Trial 2, 3, 4, 5 6 (9:00 PM). 1X Vibration BC 2C CBPM. mils pk-pk 5. 4. 3. Run1(ODE). 2. Run2(ODE). Run3(ODE). Run4(ODE). 1. Run5(ODE). Run6(ODE). Run1(DE). 5. 4. 3. 2. 1. 1. 2. 3. 4. 5. Run2(DE). Run3(DE). 1. Run4(DE). Run5(DE). Run6(DE). 2. 3. As low as reasonably achievable. 4. 5. Before and After MOV Spectrum 2 Year Overall Trend Questions?
6 Balance Grades : Electric Motor Experience Clay Boyd, PE. CBM Analyst
