"Why balancing is required in rotating parts is it done on reciprocating pats like piston etc "?

Answer 1

Unbalance is caused by the displacement of the mass centerline from the rotor's axis by an eccentricity in the distribution of the rotor mass. In simpler terms, due to centrifugal force, the "heavy" point of a rotor exceeds the centrifugal force exerted by the light side of the rotor and pulls the entire rotor in the direction of the heavy point. Balancing is the correction of this phenomena by the removal or addition of mass to the component to compensate for centerline error.
There are two general forms of balancing: "Static" and "Dynamic". Static balancing involves installing the component into a balancing machine and measuring the "heavy" point in relation to the centerline, while the part is rotating. If the required balance correction is at a single axial point on the rotor the balance is said to be "Single-Plane". Single plane balancing is adequate for rotors which are short in length, such as pulleys and fans.
Dynamic or "Dual-Plane" balancing is required for components or assemblies of significant length. Rotors with some axial length can have two "heavy" points at opposing ends of the component, acting independently on the mass center line. In order to balance the component, both planes must be corrected for center line error. Dynamic balancing is required for components such as shafts and multi-rotor assemblies.

An important consideration in the design and manufacture of any high speed rotating equipment is balance of each component and assembly. Unbalance in high speed rotating components can cause noise, component wear, excessive vibration, and reduction in bearing life. Balancing, which "is the process of attempting to improve the mass distribution of a body so that it rotates in its bearings without unbalanced centrifugal forces”1 is critical to the performance of any high speed equipment. It increases the performance of the equipment by reducing the wear & power wasted. Vibration in an engine regardless of its source, is detrimental to power, performance and longevity. Vibration is wasted energy and it can be greatly reduced by balancing all the rotating and reciprocating parts to finer tolerances than traditionally found in common practice.
In the process of balancing in an engine , the individual parts are weight matched. These include the pistons, rods and rings. There is not much you can do to the rings or rod bearings so, other than just setting up the "File-Fit" rings before balancing; all you do is to balance the piston. The PISTONS are weight-matched, but the "material removal" machining is done either under the piston pin boss with a special offset cutter, or it is done by drilling holes (very carefully) on the surface of the pin boss. You do this to both piston bosses, sharing the material loss. You DO NOT want to remove the material off only one side.
Another way of doing balance is adding counter weight.
In accordance with the accepted formula, 100 percent of the weight of rotating parts and 50 percent of the weight of reciprocating parts are used to calculate the total counter weight.The revolving weights can be counterbalanced by weights attached to the wheel to which they belong, while the reciprocating weights can only be balanced in one direction by adding weights to the driving wheels as all weights added after the revolving parts are balanced overbalance the wheel vertically exactly to the same extent that they tend to balance the reciprocating parts horizontally. This overbalance exerts a sudden pressure or hammer blow upon the rail directly proportional to its weight and to the square of its velocity.

Answer 2

A Gram of Weight As RPM Goes Up Turns Into Pounds which Will Cause Vibration. Same Goes For Rods And Pistons. If You Wiegh Them All Out Evenly (both rod ends) So That They All Match, Your Engine Runs Smooth And Gains Power Because It Isn't Trying To Pull It's Self Apart It's Kind Of Like An Unbalanced Tire. The Faster You Go The Worse It Gets, But If You Balance It You Get A Nice Smooth Ride And Speed Is No Problem

Answer 3

Stick a lump of pasticine (not too big!) on a ceiling fan and you'll see why balancing is needed. In a machine like an engine, things are turning much faster, and so the consequences of an imbalance are more severe. Vibration and even failure could be a result.
Balancing reciprocating parts is also important. In an engine, the mass of the piston (and conrod) going up and down needs to be balanced, otherwise there will be a lot of vibration. Usually this is done by using the mass of the other pistons. As one goes up, another goes down, and the imbalance is cancelled. Sit on a large capacity single cylinder motorcycle and you'll feel what unbalanced vibration is like!
Unfortunately, it's not quite as simple as that if you want to cancel out ALL the vibration in an engine. Extra balancing shafts are often needed. These are usually shafts driven off the main crankshaft, with offset masses positioned so that they rotate and cancel out the vibration from the pistons.

Answer 4

Balancing Of Rotating Masses

Answer 5

Try turning a hammer by the holding the edge and after that try it holding the center of gravity. Feel the difference? That is the same thats felt by the bearings.

If the Nett force on the bearings is not zero (i.e center of gravity of the system is not on the rotating axis) the bearings could break free.
Imagine a jet propeller going off suddenly. (That could happen if a single tooth on it breaks away)

Read more about rotor balancing and Torque.

Answer 6

Out of balance forces produce loads on bearings and vibration

Answer 7

Dissipation of harmonic energies produced in mid-band power curve.