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Ⅴ. What is peripheral velocity?

Maximum Operating Speed

“Peripheral velocity” is the speed that a point in the circumference moves per second. “Maximum operating speed” is the highest peripheral velocity for ensuring safe operation; in no circumstances should the speed be exceeded. (Safety and hygiene regulations, article 119)

Maximum Operating Speed is marked on each product.
*Manufacturer of grinding wheel should mark the maximum operating speed on the wheel which is over 3 inch. (Standards of grinding machines in Japan laws)

Peripheral velocity and RPM(Round Per Minute)

Peripheral velocity: The speed that a point in the circumference moves per second (Unit: m/s, m/min)
RPM: The number of times that a point in the circumference rotates per minute (Unit: min-1)

Assuming there is a point in the circumference, when this point moves 72m (4,300m per minute) per second, the peripheral velocity of wheel is 72m/s (4,300m/min). The number of rotations when wheel moves 72m/s is calculated according to the following equation.


Peripheral velocity of grinding wheels

The table below shows peripheral velocity that is converted to kilometer per hour for easy reference.
The careless operation is the common cause of serious accidents. Always pay attention to the safety.

Grinding wheels Maximum operating speed
Kilometers per hour
Resinoid flat grinding wheels 50 180
Cut off wheel 72 259
Resinoid depressed center wheels 72 259
Resinoid depressed center wheels for high speed 80 288

Burst peripheral velocity

The biggest factor affecting safety is the internal stress caused by centrifugal force.
Excessive speed will produce internal stress exceeding its strength which can result in a wheel breakage. The excessive speed is called “bursting peripheral velocity” and safety degree is established based on the bursting peripheral velocity.

The maximum operating speed is calculated by dividing the bursting peripheral velocity by a fixed safety factor. The safety factor for manual "center depressed wheel" and "cut off wheel" is "2.0".
NRS has been conducting a random bursting test on our products (center depressed wheels and cut off wheels); make sure that the actual bursting peripheral velocity is more than double of the maximum operating speed for ensuring safety.
It's the user's responsibility to not exceed these maximum operating speeds.

Peripheral velocity

Basic Knowledge of Grinding Wheel