Balancing and Vibrations

7/31/2019 Balancing and Vibrations

1/16

HARDEEPSINH.G.RANA


2/16

INTRODUCTION TO BALANCING When a mass move in a circular path t experiences a

centripetal acceleration which generates a force and acts inthe inward directon.This force is known as centrifugal force

which is a disturbing force of the system . If the moving parts are not in complete balance, inertia

force are setup which may cause excessive noise , vibration

,wear and tear of the system.

If the resultant forces and couples between the machineframe and its foundation are zero , the machine is said tobe completely balanced


3/16

NEED OF BALANCING In a machine mainly two types of forces are acting, static

and inertia. Static forces are due to its own eight and steadyand uniform external load and inertia forces are due to

rotating and reciprocating parts of mechanical system. If these forces are not properly balanced, resultant

unblanced forces and couple act on the machine andtransmitted to machine frame and foundation affecting

effectiveness of the operation of machine. Balancing is required to minimize r completely eliminate

unbalanced forces in the mechanical system.


4/16

CAUSES OF UNBALANCE Faulty workmanship.

Non homogeneity of material.

Deformation /deflection in rotating parts.

Non symmetry in cast parts.


5/16

EFFECTS OF UNBALANCE Bending of shaft.

Extra load on bearing.

Wear and tear.Vibrations.

Fatigue due to variable loading because of periodicchange of line of action of centrifugal force.


6/16

TYPES OF BALANCING Static balancing

Dynamic balancing


7/16

STATIC BALANCINGA system of rotating masses is said to in static

balancing if the combined mass center of the systemlies on the axis of rotation.

If there is any unbalanced force in static system, thenit can be balanced by placing equivalent mass in theopposite direction in the plane.

Static balancing can be done manually by trial anderror or also done precisely by using balancingmachine.


8/16

DYNAMIC BALANCING When the rotating masses are not in the

same plane, the centrifugal forces inaddition to being out of balance, alsoform couple.

A system of rotating masses is indynamic balance when there does notexist any resultant centrifugal force as

well as resultant couple. Placing equivalent rotating mass at

suitable radius by trial and error tobalance the unbalanced centrifugalforce and disturbing couple is known asdynamic balancing.


9/16

VIBRATIONS


10/16

INTRODUCTON-VIBRATIONS Vibration is a mechanical phenomenon whereby oscillations occur

about an equilibrium point. The oscillations may be periodic such asthe motion of a pendulum or random such as the movement of a tire ona gravel road.

Vibration is occasionally "desirable". For example the motion of atuning fork, the reed in a woodwind instrument or harmonica, or thecone of a loudspeaker is desirable vibration, necessary for the correctfunctioning of the various devices.

More often, vibration is undesirable, wasting energy and creatingunwanted sound noise. For example, the vibrational motions ofengines, electric motors, or any mechanical device in operation aretypically unwanted. Such vibrations can be caused by imbalances in therotating parts, uneven friction, the meshing of gear teeth, etc. Carefuldesigns usually minimize unwanted vibrations.


11/16

DEFINATION The repeated motion during a period of time of a

system having a body with mass and elasticity isknown as vibrations


12/16

COMMON MECHANICAL SYSTEMS

WHICH VIBRATES

SPRING MASS SYSTEMSIMPLE PENDULUM

SIMPLY SUPPORTED BEAM

CANTILEVER BEAM

TORSIONAL PENDULUM


13/16

CAUSES OF VIBRATIONS Unbalance force produced in the machine.

Dry friction.

Loose fittings.

Incorrect alignment of the driving and driven shaft.

Vibrating waves.

Lack of isolation.

Lack of compact oil.

Excessive wind force on tall structures, over headtransmission lines.

Earthquake or accident or creation of sudden disturbingforces.


14/16

REMEDIES In order to remove or minimize vibrations, it is necessary to

study and analyze the vibrating systems thoroughly andfind the reasons causing vibrations.

Following remedies are taken:I. If the system is unbalanced, its proper balancing is

done and then only operated.

II. Use vibration dampers/ shock absorbers.

III. Make the structure rigid or use better materials ofconstruction.

IV. Use vibration isolator.

V. Isolate the noise.


15/16

Classification of vibrations

based onactuatingforce on body

based on stresses inducedin the supporting medium

free vibration forced vibraton

damped vibration Un damped vibration

longitudinal vibration

transverse vibration

torisonal vibration


16/16

THANK YOU

Documents

Balancing and Vibrations