How is balancing achieved in machines?

Short Answer:

Balancing in machines is achieved by adjusting the distribution of mass in rotating or reciprocating components so that the resultant centrifugal forces and moments are eliminated or reduced to a safe level. This process ensures that the center of gravity of the system coincides with its axis of rotation.

In simple terms, balancing is done by adding or removing small amounts of mass at specific positions on the rotating body. It reduces vibration, noise, and wear, allowing the machine to operate smoothly, efficiently, and safely without generating unbalanced forces.

Detailed Explanation :

Balancing in Machines

In mechanical systems, many components such as shafts, flywheels, rotors, and reciprocating parts rotate or move at high speeds. If the mass of these parts is not evenly distributed, it creates unbalanced centrifugal forces and couples, which cause vibration, noise, and excessive bearing loads. To prevent these harmful effects, balancing is performed.

Balancing in machines means adjusting or redistributing the mass of rotating or reciprocating parts so that the resultant dynamic forces and moments acting on them are zero. In other words, the system should not produce any unwanted vibration or oscillation while running. Proper balancing increases machine efficiency, enhances safety, and extends the service life of mechanical components.

  1. Meaning of Balancing

Balancing is the process of making the center of gravity (C.G.) of the rotating body coincide with the axis of rotation. When this condition is achieved, the rotor is said to be perfectly balanced, and no centrifugal force acts on the bearings or supporting structures.

In real-life conditions, perfect balance is difficult to achieve due to manufacturing tolerances and uneven material distribution. Therefore, balancing aims to reduce unbalance to an acceptable level rather than eliminate it entirely.

  1. Principle of Balancing

The principle of balancing is based on the centrifugal force developed during rotation. When a mass  rotates at radius  with angular velocity , the centrifugal force acting on it is:

If several masses are rotating in different planes, the resultant of these forces and the couples produced by them must be zero to achieve complete balance.

Hence, the condition for balancing is:

where  is the distance between the planes of rotation.
When both these conditions are satisfied, the system is said to be dynamically balanced.

  1. Methods of Achieving Balancing in Machines

Balancing in machines can be achieved using two main methods — static balancing and dynamic balancing — depending on the type of unbalance and motion of the component.

  1. Static Balancing
  • Definition: Static balancing is done when the center of gravity of a stationary rotating body lies on the axis of rotation.
  • Purpose: To remove unbalanced forces acting when the component is at rest.
  • Method:
    1. The component (such as a wheel or pulley) is mounted on low-friction supports.
    2. The heavy point naturally moves to the bottom.
    3. To balance it, a counterweight is added exactly opposite to the heavy point or some material is removed from the heavy side.
    4. The process is repeated until the body remains stationary in any angular position.

Static balancing ensures smooth rotation at low speeds and is commonly used for flywheels, fan blades, pulleys, and grinding wheels.

  1. Dynamic Balancing
  • Definition: Dynamic balancing is achieved when both the unbalanced forces and the unbalanced couples acting on a rotating body are eliminated.
  • Purpose: To ensure balance during actual rotation, especially for high-speed rotors or shafts.
  • Method:
    1. The rotor is placed in a dynamic balancing machine and rotated at operating speed.
    2. Sensors measure the vibration amplitude and phase angle of unbalance.
    3. Using these measurements, the location and amount of correction mass are calculated.
    4. Small weights are added or material is removed in two or more planes to counteract the unbalance.
    5. The process continues until the resultant vibration is within acceptable limits.

Dynamic balancing is essential for high-speed components such as turbine rotors, compressors, crankshafts, and electric motor rotors.

  1. Balancing of Reciprocating Parts

In addition to rotating parts, reciprocating components like pistons and connecting rods in internal combustion engines also cause unbalanced forces due to their back-and-forth motion.

  • These forces are partially balanced by adding counterweights on the crankshaft opposite to the reciprocating mass.
  • Complete balancing of reciprocating parts is not possible, but partial balancing minimizes the resulting vibrations.
  • Multi-cylinder engines are designed in such a way that the forces from different pistons cancel each other, achieving better overall balance.
  1. Equipment Used for Balancing

Different tools and machines are used to achieve balancing in practical applications, such as:

  1. Static balancing machine: Uses knife-edge supports or rollers for balancing light parts.
  2. Dynamic balancing machine: Uses sensors, rotating shafts, and electronic detectors to measure unbalance precisely.
  3. Field balancing kits: Used to balance large machines on-site without dismantling, using vibration analysis equipment.
  1. Importance of Balancing in Machines

Balancing is a critical aspect of machine design and maintenance. It provides multiple advantages:

  1. Reduced Vibration: Prevents excessive oscillations that cause mechanical damage.
  2. Increased Bearing Life: Reduces uneven loading on bearings, leading to longer service life.
  3. Improved Efficiency: Minimizes power loss due to vibration and friction.
  4. Enhanced Safety: Prevents component failure or accidents caused by excessive centrifugal forces.
  5. Noise Reduction: Reduces mechanical noise in rotating systems.
  6. Extended Machine Life: Decreases wear and tear on all rotating parts.
  1. Examples of Balancing in Machines

Balancing is applied in almost every rotating system, such as:

  • Automobiles: Balancing of wheels, crankshafts, and flywheels.
  • Turbines and Compressors: To prevent vibration at high speeds.
  • Electric Motors and Generators: To ensure smooth operation of rotors.
  • Fans and Blowers: To reduce noise and increase performance.
  • Industrial Machines: To maintain accuracy and prevent fatigue failure.
  1. Steps Involved in Achieving Balancing
  1. Detect the unbalance: Measure vibration amplitude and phase.
  2. Calculate correction mass: Determine the magnitude and position of the counterweight.
  3. Apply correction: Add or remove weight as required.
  4. Recheck balance: Run the machine again to verify vibration reduction.

These steps are repeated until the vibration levels are within safe operational limits.

Conclusion:

Balancing in machines is achieved by redistributing or adding corrective masses so that the centrifugal forces and moments produced during rotation are eliminated. It is carried out either statically or dynamically depending on the type of unbalance. Proper balancing minimizes vibration, reduces bearing loads, improves efficiency, and ensures the long-term reliability and safety of machines. It is, therefore, a vital process in the design, manufacture, and maintenance of all rotating and reciprocating mechanical systems.