What is machine vibration
Machine vibration can be described as the back and forth movement of a machine or machine components. Any component which oscillates or moves back and forth is vibrating, machine components can vibrate over large or small distances, quickly or slowly and with or without perceptible sound or heat. Machine vibration can lead to machine damage. By watching and listening to machine vibration we can sometimes determine the severity of the vibration. Some kind of machine vibration is rough, others are noticeable, or negligible. The two most important root cause of machine vibration is amplitude and frequency amplitude describes the severity of the vibrations and frequency describes the oscillation rate of vibration.
What is vibration
Vibration can be described as the oscillation or repetitive motion of an object around an equilibrium position. The equilibrium position is the position the object will attain when the force acting on it is zero and this type of vibration is called “whole-body motion” in which all parts of the body will move together in the same direction at any point in time.
What is complex vibration
Vibration is the motion resulting from an oscillating force and for a linear mechanical system, the vibrating frequency is the same as the forcing frequency if there are several forcing frequencies that occur at the same time then the result will be the sum of all the vibration at each frequency. In this kind of situation, the waveform of the vibration will be very complex.
A complex waveform is created by the combination of the low and high-frequency vibration, in cases like this it is easy to find the frequencies and amplitudes of the two components by examining the waveform, but most of the vibration signals are complex than this and is extremely difficult to interpret.
What causes machine vibration
Mostly all vibrations are caused in machines because of one or more of these causes
Repeating force, Looseness, and resonance
Repeating forces in machines are mostly because of the rotation of the unbalanced, misaligned, worn, or improperly driven machine components.
Unbalanced machine components contain ‘heavy spots’ which will exert a repeating force on a machine when it is rotated. Unbalance can be caused by matching errors, non-uniform material density, variation in bolt sizes and air cavities in cast parts…
Misaligned machine components create bending moments which when rotated exerts a repeating force on the machine. Misalignment can also be caused by inaccurate assembly, uneven floors, thermal expansion, distortions due to fastening torque, and improper mounting of couplings
A repeated force will be exerted on machines when a worn machine component is in a running state and it is because of the rubbing of the uneven worn surfaces. Wear in roller bearings, gears, and belts are due to improper mounting, poor lubrication, and overloading.
Improperly driven machine components will exert a repeating force on the machine because of intermittent power supply, pumps receiving air in pulses is an example
Looseness of machine part will make the machine vibrate, if machine parts become loose then the tolerable level vibrations could become excessive. Looseness can create vibrations in rotating and non-rotating machinery. Looseness can be caused by excessive bearing clearness, loose mounting bolts, mismatched parts, and corrosion.
Machines will vibrate at certain oscillation rate and the rate at which the machine vibrate is called natural oscillation rate. Most machines will have more than one natural oscillation rate. If the machine is pushed by a repeating force that matches the rate of the machines natural oscillation then the machine will vibrate vigorously and excessively and a machine that vibrates in such a way can be said to be experiencing resonance.