Short Answer:

Dynamic balancing is the process of balancing a rotating body by ensuring that both the resultant centrifugal forces and the resultant couples (moments) acting on it are zero. It means that the body remains balanced even when it is rotating at high speed.

Dynamic balancing is used for rotors, turbines, crankshafts, and other parts rotating in more than one plane. It removes vibrations and uneven motion caused by unbalanced masses, making the machine run smoothly and safely during operation.

Detailed Explanation :

Dynamic Balancing

Dynamic balancing is an advanced form of balancing used in rotating machinery to ensure that both the unbalanced forces and couples are completely eliminated while the body is in motion. In simple words, dynamic balancing means that when a body is rotating, there are no unbalanced centrifugal forces or moments acting on it, allowing the system to run smoothly without vibration or noise.

Every rotating object produces centrifugal force due to its mass and speed. If the mass distribution of the rotating body is not uniform around the axis of rotation, these forces will not cancel each other and will cause vibration and stress on bearings and shafts. In such cases, balancing becomes necessary to correct the unequal mass distribution. While static balancing deals with unbalanced forces in a single plane, dynamic balancing deals with forces and couples in two or more planes.

In dynamic balancing, both the resultant force and the resultant couple should be zero. Mathematically,
ΣF = 0 and ΣM = 0,
where F represents the centrifugal forces and M represents the moments or couples.

Dynamic balancing is very important in machines that operate at high speeds, such as turbines, crankshafts, generators, and rotors. Even a small unbalance in these machines can lead to large vibrations, noise, and damage because of the high rotational speeds involved.

To understand the concept, imagine a rotor with two masses placed in different planes along a shaft. If these masses are not balanced, they produce centrifugal forces that act at different points, creating both a resultant force and a turning couple on the shaft. To achieve dynamic balancing, additional balancing masses are added in appropriate positions and planes so that both the forces and couples cancel each other.

In practical situations, dynamic balancing is performed using balancing machines that can measure vibration and unbalance while the rotor is rotating. The machine indicates the amount and position of unbalance in each plane. Based on this information, small correction weights are added or removed to achieve complete balance.

Importance of Dynamic Balancing:

Dynamic balancing plays a major role in improving the performance, efficiency, and safety of rotating machines. Some important advantages are:

1. Smooth Operation:
   It ensures smooth and vibration-free running of machines by removing both unbalanced forces and couples.
2. Reduced Wear and Tear:
   It decreases stress on bearings and other parts, which prevents mechanical wear and extends the life of components.
3. Increased Efficiency:
   Machines operate more efficiently when they are properly balanced, as less energy is wasted in overcoming vibrations.
4. Better Safety and Reliability:
   Dynamic balancing reduces the risk of sudden mechanical failure or accidents caused by excessive vibration.
5. Improved Product Quality:
   In manufacturing equipment like grinders and lathes, dynamic balancing ensures accurate and high-quality work by preventing vibration of the rotating tools.

Examples of Dynamic Balancing:

• Turbines and Generators: High-speed turbines and generators are dynamically balanced to prevent vibration and failure.
• Crankshafts: In engines, crankshafts are dynamically balanced to reduce shaking forces caused by reciprocating parts.
• Rotors and Fans: Industrial fans and rotors are balanced dynamically to maintain smooth airflow and efficient operation.
• Vehicle Wheels: At high speeds, car wheels are dynamically balanced to avoid shaking and improve driving comfort.

The process of dynamic balancing involves several steps. First, the rotor or rotating body is mounted on a balancing machine. The machine rotates the part and measures vibration at different points using sensors. The data obtained helps determine the location and amount of unbalance. Finally, weights are added or removed at specific positions to balance the rotor dynamically.

Modern balancing systems use electronic and computer-based equipment for accurate results. Laser or sensor-based methods can automatically detect unbalances and suggest the correction needed. This has made dynamic balancing fast, reliable, and highly precise.

Dynamic balancing is especially necessary for machines that rotate in multiple planes or at high speed, where even a small imbalance can cause large centrifugal forces. It not only increases efficiency but also ensures long service life and safety of mechanical systems.

Conclusion:

Dynamic balancing is the process of eliminating both unbalanced forces and couples from a rotating body to achieve smooth and vibration-free motion. It is essential for high-speed machinery like turbines, rotors, and crankshafts. Proper dynamic balancing improves performance, reduces wear and tear, increases safety, and enhances the overall reliability of mechanical systems.