Cause of machine vibrations

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Cause Of Machine Vibrations


In our last blog we covered mechanical vibrations and now we would write about the factors that cause them.

Almost all machine vibration is due to one or more of these causes:

Repeating Forces

Let’s imagine a boat that is anchored in a bay. Waves are splashing at the sides of the boat, and as long as the waves act on the boat it would rock. The boat will continue to rock because the waves would be applying a repeating force on the boat.

Hence most machine vibration is due to repeating forces. Repeating forces such as these act on machine components and cause the machine to vibrate. Where does the repeating forces come from?

Repeating forces in machines are due to the rotation of imbalanced, misaligned, worn, or improperly driven machine components. Names of these four types of repeating forces are shown below:

Looseness

Looseness of machine parts leads to vibration. If parts become very loose, vibration that is normally of tolerable levels may become extreme and excessive.

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Resonance

The best example is a child swinging freely on a swing, without the child propelling himself or anyone pushing him. Observation says the child is swinging at a particular rate.

Machines also tend to oscillate at certain rates. The oscillation rate at which a machine tends to vibrate is called its natural oscillation rate. The natural oscillation rate of a machine is the vibration rate most obvious to the machine, that is, the rate at which the machine ‘chooses’ to vibrate.

Generally, the more complex the machine, the more natural oscillation rates it has.

What happens if a machine is ‘pushed’ by a repeating force? The machine will vibrate more and more strongly due to the repeating force encouraging the machine to vibrate at it’s natural rate. The machine will vibrate excessively, not only because it is doing so at a rate it ‘wants’ but also because it is receiving an external aid . A machine vibrating in such a manner is said to be experiencing resonance.

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