Transcription of VI Balance Grades - Vibration
1 Balance Grades :Electric Motor ExperienceVibration InstitutePiedmont Chapter 1412/01/2006 Clay Boyd, PECBM Acorn StreetDeer Park, NY 11729 Toll Free: 1-800-873-2352 Repairs Motor Repair Specification Balance Grades Initial Balance with Shop Balance Machine Final Balance with Motor AssembledMotor Repair Specification Work to be performed Acceptable Repair Practices Required Reporting Acceptance Criteria, includingBALANCE Grades Balance Grades are used to specify the allowable residualimbalance for rotating machinery. The ISO 1940 standard defines Balance Grades fordifferent classes of machinery. (Rigid Rotors Only*) Example: Balance Grade is recommended forSteam Turbines, Machine Tools and Small ElectricArmatures.* ISO 11342 defines the Balance quality requirements for rotors in a flexible stateBalance Grades :Sample ChartPermissibleResidualunbalanceperunit rotorweight(g*mm/g*1000)orPermissiblecgd isplacement(mm*1000)Service Speed (rpm) Grades A rotor balanced to will vibrate at mm/sec(Velocity) if freely suspended while rotating at servicespeed.
2 ( mm/sec = IPS)V(mm/sec) =2pe(mm)*RPM60sec/mine(mm) =Residual Imbalance (g-mm)Rotorweight(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, )Initial Balance with Shop Balance MachineIt is difficult if not impossible to achieve BalanceGrades or in a Balance machine onlyBalance 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 drivenInitial Balance with Shop Balance Machine : Roller Size ..the roller diameter should differ from the journaldiameter by at least 10%, and the roller speed shouldnever differ less than 60 rpm from the journal Fundamentals of Balancing, 2ndEd. 03/1983; SchenkTrebelFinal 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 readingsMotor 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 startFinal Balance with Motor AssembledFlexible or Rigid Rotor Large 2-pole motorsIn test runs at service speed, moving two testmasses from the end planes to the center plane,results in a Vibration change of less than 20%.
3 Fundamentals of Balancing, 2ndEd. 03/1983; SchenkTrebelGraphic: of startup heating60 HzTrial 1 (1:25 PM)1X Vibration BC 2C CBPM mils (ODE)Run2(ODE)Run3(ODE)Run4(ODE)Run5(ODE )Run6(ODE)Run1(DE)Run2(DE)Run3(DE)Run4(D E)Run5(DE)Run6(DE)Trial 2, 3, 4, (9:00 PM)As low as and After MOV Spectrum2 Year Overall TrendBalance Grades :Electric Motor ExperienceClay Boyd, PECBM AnalystQuestions?
