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    Dynamic Balancing

    Uploaded by

    Nitesh Asthana
    The document discusses unbalance in rotors and how it causes vibration. It defines unbalance as an uneven mass distribution about the rotor's axis of rotation. As the rotor spins, the extra mass exerts a centrifugal force that varies based on the radius and angular velocity. There are three types of unbalance: static, couple, and combined. Balancing machines work by measuring the centrifugal forces caused by unbalances in different planes and determining weights needed to counteract the total unbalance.

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    Dynamic Balancing

    Uploaded by

    Nitesh Asthana
    130 views7 pages
    The document discusses unbalance in rotors and how it causes vibration. It defines unbalance as an uneven mass distribution about the rotor's axis of rotation. As the rotor spins, the extra mass exerts a centrifugal force that varies based on the radius and angular velocity. There are three types of unbalance: static, couple, and combined. Balancing machines work by measuring the centrifugal forces caused by unbalances in different planes and determining weights needed to counteract the total unbalance.

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    The document discusses unbalance in rotors and how it causes vibration. It defines unbalance as an uneven mass distribution about the rotor's axis of rotation. As the rotor spins, the extra mass exerts a centrifugal force that varies based on the radius and angular velocity. There are three types of unbalance: static, couple, and combined. Balancing machines work by measuring the centrifugal forces caused by unbalances in different planes and determining weights needed to counteract the total unbalance.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as DOC, PDF, TXT or read online from Scribd
    Download as doc, pdf, or txt
    130 views7 pages

    Dynamic Balancing

    Uploaded by

    Nitesh Asthana
    The document discusses unbalance in rotors and how it causes vibration. It defines unbalance as an uneven mass distribution about the rotor's axis of rotation. As the rotor spins, the extra mass exerts a centrifugal force that varies based on the radius and angular velocity. There are three types of unbalance: static, couple, and combined. Balancing machines work by measuring the centrifugal forces caused by unbalances in different planes and determining weights needed to counteract the total unbalance.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as DOC, PDF, TXT or read online from Scribd
    Download as doc, pdf, or txt
    of 7

    UNBALANCE

    Any rotor with an uneven distribution of mass about its axis of rotation has an unbalance. Figure shows a rotor with an unbalance caused by an extra mass m. A similar effect is created by out of centre machining, non uniform windings in armatures, blades of different sizes on rotors, internal flaws in casting, uneven density of material etc.

    When rotor rotates, the extra mass m exerts a centrifugal force. This centrifugal force moves around with the rotating mass and causes deformation to the shaft and vibration to the system. Since excessive vibrations are objectionable, we try to reduce them and are done by reducing Unbalance.

    UNBALANCE AND CENTRIFUGAL FORCE


    The unbalance U of the rotor is given by: U = m.r m = unbalance mass. r = Radius at which this mass is located. It is seen that unbalance U is independent of speed and it exists even when the rotor is stationary. When the unbalanced rotor rotates, the centrifugal force is given by: F = mv = mr = U v = Linear velocity = Angular Velocity This is clear that the centrifugal force F is directly proportional to the unbalance U hence we can reduce this force and therefore vibration by reducing unbalance.

    TYPES OF UNBALANCE
    There are three types of unbalance: Static Unbalance Couple Unbalance Combined Unbalance STATIC UNBALANCE The unbalance existing in only one side of the rotor is called Static unbalance or force unbalance. COUPLE UNBALANCE In this type of unbalance two equal weights are present in two different planes (Plane One and Plane Two). One weight is at the top and other at the bottom (180 from each other). This type of unbalance is also referred to as Dynamic unbalance.

    When the rotor is rotated, two equal forces are produced which constitute a couple and give rise to vibrations. Even though this forces are equal and are opposite in direction they do not cancel each other as they are axially displaced. COMBINED UNBALANCE The two type of unbalance discussed exists only in theory. In actual practice a large number of static and couple unbalances exist simultaneously in the rotor.

    DESCRIPTION OF UNBALANCE
    It must be noted here that besides the amount of unbalance it is also necessary to know the location of the unbalance. This is generally expressed as the angle at which the unbalance is located. From figure, Unbalance in left Plane = 12 cm g at 135 Unbalance in Right Plane = 24 cm g at 30

    PRINCIPLE OF BALANCING MACHINE


    When the rotor is rotated each unbalance on it gives rise to a centrifugal force as shown in figure.

    The rotor under consideration is a rigid body; each force can be resolved in two planes. For example resolving the force F in the left plane and the right plane we get: F resolved in left plane = 0.8 F F resolved in right plane = 0.2 F After resolving all the forces shown in the figure the result obtained is shown in the figure.

    The above example is not the most general case but it illustrates that the total unbalance of a rigid rotor can be represented by two weights (or unbalances) in any two planes required. The Dynamic Balancing machine operates on the above principle. The rotor to be balanced is placed on to the work supporting carriages of the balancing machine and rotated. The centrifugal forces created due to the unbalances act on the carriages and are measured. These two forces give total unbalance of the rotor in planes in which we have carriages. While measuring the unbalance we have to ensure that the rotor is rotated about its normal axis of rotation. If we rotated the rotor in any other plane or about any other axis, spurious unbalance shall be created by the displaced mass of the rotor. The simplest method is to rotate rotor while supporting it on its bearing surface.

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