Balance measurement overview

About the relationship between vibration and unbalance

When you rotate a pump, blower, blower, fan, etc., is the vibration larger than when it was newly installed and is it noisy?

When machining with a machine tool such as a grinding machine, machining center, or lathe,is the vibration increased or the machining accuracy deteriorated if the rotation speed is increased?

They may be due to imbalances in rotating bodies such as impellers, grinding wheel, chuck, etc.

What is unbalance?

Imbalance occurs if the center of a rotary body is not on the axis.
Rotation under the unbalanced condition will generate the centrifugal force.
The centrifugal force varies in proportion to the square of the rotation speed.
If the rotation speed becomes twice, the centrifugal force will become four times.
The centrifugal force will bend the rotation axis, the rotary body will become eccentric, which will cause large vibration to the machine.


There are 2 types of unbalance:

①Static unbalance

Unbalance occurred while being stationary.

②Dynamic unbalance

Unbalance occurred while in rotation

What causes the unbalance?

①Uneven mass distribution of rotating equipment

⇒There will be uneven mass distribution of rotating equipment, such as when distribution of abrasive grains of grinding stone becomes uneven or cast product develops cavities in the manufacturing process.

②A position shift when fitting rotating equipment to axis

⇒There will be a position shift between the rotation center and the axis center, as the hole diameter of rotating equipment does not completely equal the axis diameter.

③Assembly tolerance of rotating equipment

⇒The rotation center will come off the axis such as when there is a key way for installation or assembling rotating equipment with multiple components has generated a position shift.

④Uneven mass distribution caused by thinning or abrasion of rotating equipment such as grinding wheel or endmill

⇒Grinding wheel or endmill, even if it's balanced initially, can lose the balance gradually due to thinning or abrasion while being used.

⑤Fixation of foreign substances on impeller

⇒Imbalance can be caused by foreign substances fixed on impeller of blower or others depending on its use environment.
The heavier such foreign substances are, the more likely it will cause imbalance.

How does the unbalance affect?

Rotation under the unbalanced condition will generate the centrifugal force and the rotation axis will be bent, which will cause large vibration to the rotating equipment.
Vibration will lead to the followings:

①Deterioration of processing accuracy

Vibration prevents tool from uniformly contacting the processing surface, which can generate chatter marks.

②Shortening of tool life

Vibration will increase the dressing frequency on grinding stone or put more load on endmill or cutting tool, which will shorten the tool life.

③Damage on machine

Vibration will put stress on the bearing particularly, which may need to be replaced at some point.

What does it need to do to adjust the balance?

Shift the rotation center to the axis so as to stop the vibration.
Add weight of the yellow square at the point in axial symmetry with the pink circled point of imbalance, as shown in the illustration below.
The rotation center will shift to the axis, which will stop the vibration.

What does it need to do to adjust the balance?

What kind of rotating equipment needs balance adjustment?

Rotation can cause vibration due to the imbalance. To use the equipment efficiently for a long duration, it’s essential to adjust the balance.
The lower the rotation speed is, the less the centrifugal force is. The higher the rotation speed is, the more the centrifugal force is, and that will cause high level vibration.

Here are examples of many products which require balance adjustment: Blower, pump, undercarriage components of car or train (hub, flywheel, drum brake, disc brake), shaft, roller, machine tool (grinding machine, machining center) , grinding wheel, centrifugal separator, rotary crusher, air conditioner outdoor unit, spindle

How does it calculate the balancing weight and its angle?

There are 2 kinds of calculation method for dynamic or static imbalance:

1、How to adjust the dynamic imbalance

The unbalanced amount has a close relationship with the vibration level.
The more the unbalanced amount is, the higher the vibration level becomes.
Considering their proportional relationship, reducing the vibration will lose the unbalanced amount. (in case of rotary body with high hardness)

  • For OHMIYA Industry's products, the weight and position of the balance correction weight are calculated by the following method.
  • ①Vibration level measured while in rotation in the initial state
  • ②Vibration level measured while in rotation with temporary weight attached
  • ③Balancing weight and its angle are to be calculated from the temporary weight and its angle and the change amount from 1) to 2).

The device equipped with the above measuring functions is commonly called "Field Balancer."
Also called dynamic balancer, field balancing machine, portable balance measuring machine, etc.
OHMIYA Industry's has a lineup of measuring machines called Myself-1 type TII that measures the balance state and calculates the unbalanced weight and phase angle required for balance correction with high accuracy.

Omiya Kogyo also has a lineup of systems that automatically perform everything from balance measurement to correction.
The system consists of a control unit that performs calculations necessary for correction based on the measurement results,and a head unit that receives the results and performs balancing.
You can attach it to the device you want to balance and operate the controller directly to balance it,or you can operate it from the external device side.

2、How to adjust the static imbalance

OHMIYA Industry's measuring device is based on the original center alignment and three-point measuring system.
After installing a subject rotary body to the measuring device, the center will be aligned, the weight distribution will be measured,and the unbalanced amount and its angle will be calculated.

Measurement while the subject is stationary will bring high precision performance.
Many of our clients have introduced our measuring device for automobile parts (hub, drum brake, disc brake),impeller of blower or pump, grinding wheel, or other products.

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