Unbalance is the most common rotor system malfunction. Its primary symptom is 1X vibration, which, when excessive, can lead to fatigue of machine components. In extreme cases, it can cause wear in bearings or internal rubs that can damage seals and degrade machine performance.
The primary symptorn of unbalance is 1X vibration. Unbalance can produce high rotor and casing vibration, and it can produce vibration in foundation and piping systems. 1X vibration can also contribute to stress cycling in rotors, which can lead to eventual fatigue failure. Unbalance - induced vibration can also cause internal rubs in machinery, especially when passing through resonances.
Diagnosis of unbalance can be complicated by the fact that many different malfunctions can produce 1X vibration. Mechanical and electrical runout, rotor bow, thermal bow, electrical noise, coupling problems, shaft cracks, loose rotating parts, trapped debris or fluids, rub, decreasing foundation spring stiffness, and various electric motor problems can all produce 1X or near 1X vibration. Because so many malfunctions can masquerade, as unbalance, the machinery diagnostician should be careful to establish unbalance as the root cause before balancing a machine. A loose rotating part can cause an intermittent or continuous change in 1X vibration.
Unbalancing rotatary generates vibration forces resulting in high stresses in the shaft and bearings. Measurement of these forces can give valuable input in accessing the reliability of such systems. This experiment shows the vibration forces generated due to a selector unbalance and RPM. The vibration force due to unbalance vary with respect to the speed of the rotor and the unbalance quantity.