Fundamentals Of Vibrations

Fundamentals Of Vibrations

• Introduction :

                  Vibrations occur where there are rotating or moving parts in a machinery. Apart from the machinery itself, the surrounding structure also faces the vibration hazard because of this vibrating machinery.

                   The common examples are locomotives, diesel engines mounted on unsound foundations, whirling of shafts, etc.

The main causes of vibration are as follows:

1. Unbalanced forces in the machine: These forces are produced from within the machine itself.
2. Dry friction between the two mating parts: This produces what are known as self excited vibration.
3. External excitation's: These excitation's may be periodic, random, or the nature of an impact produced external to the vibrating system.
4. Earthquakes: These are responsible for the failure of many buildings, dams, etc.
5. Winds: These may cause the vibration of transmission and telephone lines under certain conditions. 

• Effects:

                   The effects of vibration are excessive stresses, undesirable noise, looseness of parts and partial or complete failure of parts. In spite of these harmful effects, the vibration phenomenon does have some uses also, e.g. in musical instruments, vibrating screens, shakers, stress relieving etc. 

                                   

• Elimination or Reduction of vibrations: 

                 The elimination or reduction of the undesirable vibrations can be obtained by one or more of the following methods.

        1. Removing the causes of vibrations.

        2. Putting the screens if noise is objectionable.

        3. Placing the machinery on proper isolators.

        4. Using shock absorbers.

        5. Using dynamic vibration absorbers.