basic information about balancing machines_shimadzu

7/30/2019 Basic Information About Balancing Machines_SHIMADZU

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1. What is a dynamic balancing machine?

Dynamic balancing machines measure the size (magnitude) and angle(direction) of vibration.

There is no limit to the number of products that rotate.Using cars as an example, they consist of tires, shafts,flywheels, gears, and crankshafts, to name just a few.In our homes, we have a variety of equipment,including fans, vacuum cleaners, refrigeratorcompressors, video heads, DVD and CD systems, andcomputer hard drives. It would be impossible to countall the types of rotating objects and how many exist.

When these rotating parts or materials rotate, theygenerate centrifugal forces. Normally, the sum of thesecentrifugal forces equals zero, however, if they do not,that rotating object will generate vibration and noise.Dynamic balancing machines measure the amount andangle of this vibration

Rotation GeneratesVibration

2. What is dynamic unbalance?

Unbalance occurs when the center-of-gravity of a rotating object is notaligned with its center-of-rotation.

Unbalance is caused when the center of gravity is out ofalignment with the center of rotation. To correct theproblem, a weight of mass m must be attached to theopposite side of the rotating object. Given a rotor massM and radius R, the following relationship applies.

Units Used to Express Unbalance

In Terms of the Mass Eccentricity e : m, mm, cm

In Terms of Mass m : g, mg, g ,kg ...

In Terms of Mass x Radius (mR) : mg mm, mg cm, g mm, g cm, kg cm, ...


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3. What does "balancing" a rotor mean?

It means to reduce the amount of unbalance.

Unbalance refers to the center-of-gravity of the rotor being out of alignment with itscenter-of-rotation (eccentricity). If unbalanced, centrifugal forces will generate

vibration and noise during rotation. The world in which we live is overflowing with

rotating objects. In most homes, looking around many rooms you can find air

conditioners, forced air heaters, or fans, and sometimes even dehumidifiers,

humidifiers, or a video, CD or DVD player under the television. In the bathroom you

can find washing machine, drier, electric razor, n the kitchen ventilation fans,

refrigerators, microwave ovens and in a different room a computer and printer. All of

these consumer electronic products include internal rotating parts (motors). Outside

the home you see automobiles, which are a dense concentration of multiple rotating

objects, as are trains, ships, and aircraft. In manufacturing plants, you can find all

types of rotating machinery on a production line. At power plants there are rotating

turbines and generators. If all these items were not balanced properly, our lives

would undoubtedly be extremely noisy. Furthermore, generating vibration and noise

consumes energy, meaning energy is being wasted, which is counterproductive to

current efforts to save energy. Not only does vibration waste energy, it causes

bearings to wear more quickly and shortens the operating life of products. The

process of reducing the amount of unbalance in rotating items like these is called

balancing.

4. What is the difference between dynamic balancing (unbalance in two planes)

and static balancing (unbalance in one plane)?

Unbalance created by motion

Dynamic Unbalance

In general, unbalance can occur at any lateral (axial) position along the rotating


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body and with any magnitude. This unbalance is a combination of static unbalance

and couple unbalance and is called dynamic unbalance. The couple unbalance

component only appears when the object is rotated, so measuring dynamic

unbalance requires rotating the object. Dynamic unbalance must be corrected at two

locations in the axial direction (two-plane correction for two-plane unbalance). Put

simply, unbalance apparent when the object is perfectly still (no rotation) is called

static unbalance and unbalance that becomes apparent after an object begins to

rotate is called dynamic imbalance.

Unbalance Present With StaticStatic Unbalance

When a rotor is placed on smooth rails, the heavy side will turn to face downward.

The unbalance experienced when an object is static (not moving) is called static

unbalance. Static unbalance can be corrected using only one location (one-plane

correction for one-plane unbalance).

5. Why doesn't the sum of all centrifugal forces add up to zero?

The primary cause is an accumulation of error.

There are many factors than can cause dynamic unbalance.

For formed or machined parts, potential causes include:

Variations in the specific weight of materials

Shape is not symmetric with respect to the center axisVariations in forming, machining or other processes

For part assemblies, potential causes include:

Variations in assembly process

Variations in the mass of individual parts

Variations in placement

6. How accurately can unbalance be measured?

In terms of eccentric distance, in the range of thousandths of a micron.


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Assuming a cylindrical rotor 50 mm in diameter and weighing 300 grams, for

example, model DBM-SGF-03 could measure a 0.6 mg weight attached to the

rotor perimeter. In comparison, one grain of rice weighs about 20 mg. This

means it can detect an unbalance equivalent to 1/33 of a grain of rice on the

surface of a 300 g workpiece roughly the weight of a filled small-beverage can.

This list is intended to provide simple explanations for some of the more commonly used dynbalancing terminology.

Terminology

1. Dynamic Unbalance 2. Static Unbalance

3. Couple Unbalance 4. Vertical Dynamic BalancingMachine

5. Horizontal Dynamic BalancingMachine

6. Soft Type Dynamic BalancingMachine

7. Hard Type Dynamic Balancing 8. Dynamic Unbalance
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Machine

9. Balancing 10. One-Plane Balancing

11. Two-Plane Balancing 12. Composite Unbalance

13. Mass Eccentricity(Distance to Center-of-Gravity)

1. Dynamic Unbalance

Dynamic unbalance is the unbalancethat occurs during rotation.

For more information, see BasicInformation About Balancing Machines

2. Static Unbalance

Static unbalance is the vector synthesis of lateral unbalance. It isthe unbalance that causes a rotor to rotate by gravity when placedon smooth rails.

For more information, see Basic Information About Balancingmachines

3. Couple UnbalanceCouple unbalance is the amountof unbalance remaining aftercorrecting static unbalance ofrotor. It consists of multipleunbalance vectors of equalmagnitude, located laterally apartand oriented 180 degrees inopposite directions.

4. Vertical Dynamic Balancing Machine

Dynamic balancing machine that measures a rotor

VG VG2

P
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5. Horizontal Dynamic Balancing Machine

Dynamic balancing machine that measures a rotor

SGB SGF

HGB HGJ

6. Soft Type Dynamic Balancing Machine

Dynamic balanceing machine using flexible bearing housings formeasurements at rotational speeds (frequency) higher than thenatural frequency of the unit which uses the bearings.

SGB SGF

7. Hard Type Dynamic Balancing Machine

Dynamic balancing machine using rigid bearing housings formeasurements at rotational speeds lower than the naturalfrequency of the unit which uses the bearings.

HGB HGJ

8. Dynamic Unbalance

Dynamic unbalance refers to thecenter of gravity being out ofalignment with the center ofrotation.

For more information, seeBasic Information AboutBalancing machines

e: Mass Eccentricity (distance [
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g] to center of gravity)

M: Mass of a Rotor (kg)

R: Radius of a Rotor (mm)

m: Mass of a Weight (g)P

9. Balancing

Balancing is the process ofreducing the amount ofunbalance of a rotatingobject.


e: Mass Eccentricity (distance

[ g] to center of gravity)

M: Mass of a Rotor (kg)

R: Radius of a Rotor (mm)

m: Mass of a Weight (g)

10. One-Plane Balancing

Process of measuring dynamic unbalancein only one plane in order to measure

static unbalance, which is one type ofunbalance, or correct the unbalance,especially in thin rotors.

11. Two-Plane Balancing

Process of measuring dynamicunbalance in two planes tocorrect one type of dynamicunbalance often found longerrotors.

12. Composite Unbalance

Dynamic unbalance calculatedby combining two lateral planesby vector synthesis.
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13. Mass Eccentricity (distance to center of gravity)

Refers to center of rotation being

out of alignment. The distance towhich it is out of alignment iscalled the distance to the centerof gravity.

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