CVA Rotor Dynamics & Balancing

Question 1

What is a critical speed in rotor dynamics?

Accepted Answer

A rotational speed at which the shaft excitation frequency coincides with a rotor natural frequency

Answer

The maximum allowable operating speed of a machine

Answer

The speed at which bearing load capacity is exceeded

Answer

The minimum speed required for hydrodynamic lubrication

Question 2

What type of rotor unbalance causes a pure couple (moment) with no net centrifugal force?

Accepted Answer

Couple unbalance

Answer

Static unbalance

Answer

Dynamic unbalance

Answer

Overhung unbalance

Question 3

What is the vibration signature characteristic of rotor unbalance?

Accepted Answer

Dominant 1× running speed component, typically with consistent phase

Answer

Strong 2× running speed with high axial vibration

Answer

High-frequency random broadband noise

Answer

Sub-harmonic components at 0.5× running speed

Question 4

What is the influence coefficient method in rotor balancing?

Accepted Answer

A mathematical approach that determines correction weights by measuring the rotor response to known trial weights

Answer

A method to calculate critical speed from bearing stiffness

Answer

A technique for measuring shaft bow using proximity probes

Answer

A procedure for balancing flexible rotors at multiple planes simultaneously

Question 5

What is shaft bow, and how does it appear in a vibration spectrum?

Accepted Answer

Permanent or temporary curvature of a rotor shaft; produces 1× vibration that does not change with speed changes the way pure unbalance does

Answer

Axial bending of a shaft due to thermal gradients; appears as high axial 1× vibration

Answer

Excessive radial clearance in bearings; produces broadband noise

Answer

Torsional oscillation of the shaft; appears at gear mesh frequency

Question 6

In ISO 1940 balance quality grades, what does a higher G number indicate?

Accepted Answer

Looser balance tolerance allowing more residual unbalance

Answer

Tighter balance tolerance requiring more precision

Answer

Higher allowable vibration velocity

Answer

Greater rotor mass requiring larger correction weights