Balance Grades as per ISO 1940

8/13/2019 Balance Grades as per ISO 1940

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References

Schenck Trebel Corporation

535 Acorn Street

Deer Park, NY 11729

Toll Free: 1-800-873-2352

http://www.schenck-usa.com

http://www.mpta.org/MPTABalancingPrimer.pdf

http://www.irdbalancing.com/downloads/TechPaper1BalQualityReqmts.pdf


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Motor Repairs

Motor Repair Specification

Balance Grades

Initial Balance with Shop Balance Machine

Final Balance with Motor Assembled


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Motor Repair Specification

Work to be performed

Acceptable Repair Practices

Required Reporting

Acceptance Criteria, including BALANCE GRADE.


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Balance 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 G2.5 is recommended forSteam Turbines, Machine Tools and Small ElectricArmatures.

* ISO 11342 defines the balance quality requirements for rotors in a flexible state


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Balance Grades

A rotor balanced to G2.5 will vibrate at 2.5 mm/sec

(Velocity) if freely suspended while rotating at service

speed. (2.5 mm/sec = 0.10 IPS)

V(mm/sec) = 2pe(mm)*RPM

60sec/min

e(mm) = Residual Imbalance (g-mm)

Rotor weight(g)


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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)


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Initial Balance with Shop Balance Machine

It is difficult if not impossible to achieve Balance

Grades G1.0 or G0.4 in a balance machine only


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Balance Grades G1.0 and G0.4 have special requirements.

G1.0

The rotor must be mounted in its own service bearings

No end drive (for balance machines)

G0.4

The rotor must be mounted in its own housing and bearings

Must be run under normal service conditions: Load,Temperature..

Self driven


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Initial Balance with Shop Balance Machine : Roller Size

the roller diameter should differ from the journaldiameter by at least 10%, and the roller speed should

never differ less than 60 rpm from the journal speed. p.54 Fundamentals of Balancing, 2nd Ed. 03/1983; Schenk Trebel


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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


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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



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Flexible or Rigid Rotor Large 2-pole motors

In test runs at service speed, moving two test

masses from the end planes to the center plane,

results in a vibration change of less than 20%.pp.21-22 Fundamentals of Balancing, 2nd Ed. 03/1983; Schenk Trebel

Graphic: http://www.schenck-usa.com/lib_101_types_unbal.asp


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Effect of startup heating


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60 Hz


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Trial 1 (1:25 PM)


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1X Vibration BC 2C CBPMmils pk-pk

5.

4.

3.

2.

1.

1.

2.

3.

4.

5.

5. 4. 3. 2. 1. 1. 2. 3. 4. 5.

Run1(ODE)Run2(ODE)

Run3(ODE)

Run4(ODE)

Run5(ODE)

Run6(ODE)

Run1(DE)

Run2(DE)

Run3(DE)

Run4(DE)

Run5(DE)

Run6(DE)

Trial 2, 3, 4, 5 6 (9:00 PM)

As low as reasonably

achievable.


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Before and After MOV Spectrum


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2 Year Overall Trend


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Balance Grades:

Electric Motor Experience

Clay Boyd, PE

CBM Analyst

Questions?

Documents

Balance Grades as per ISO 1940