Balanceamento de polias: é sempre necessário?

Pulley balancing: is it always necessary?

balancing the pulleys

When a pulley rotates, centrifugal forces act on the pulley, and if its mass is not evenly distributed around the axis of rotation – that is, if it is unbalanced – these centrifugal forces will also become unbalanced and cause the pulley to vibrate. (Uneven mass distribution may be due to imperfections in the finish or inconsistencies in the material structure.)

Pulley vibrations can be transferred to support bearings and other machine components, causing premature or even catastrophic failures. This is why pulleys used in belt drive systems almost always undergo some type of balancing.

Static balancing

Virtually all pulleys undergo static balancing, also known as “single plane balancing,” after production. This method ensures that the weight of the pulley is distributed equally around its center of rotation. As the name suggests, static balancing can be performed while the object is at rest and is relatively easy to demonstrate through a simple experiment.

Turn the pulley by hand and let it rest on its own. It marks the point at the bottom of the center of the pulley. Spin again and let it rest. If it stops at the same point in the bottom center, your weight is not balanced: the pulley is heaviest at that point.

Correcting this is typically done by one of two methods: removing mass from the “heavy” point (which is usually accomplished by drilling a small hole in the pulley) or adding mass to a point 180 degrees from the “heavy” point.

Static balancing is typically sufficient for pulleys traveling at 6,500 ft/min (33 m/s) or less. For speeds higher than this or when the pulley diameter is less than 7 to 10 times the visible width, dynamic balancing is recommended.

Dynamic balancing

Dynamic balancing, also known as “two-plane balancing,” goes one step further than static balancing and ensures that the pulley's center of mass is on the same axis as its center of rotation. It is possible for a pulley to be statically balanced but dynamically unbalanced (although the reverse is not true), so dynamic balance must be measured as the pulley rotates.

Because it involves forces in two planes, dynamic balancing requires the addition of mass in two planes to neutralize imbalances and avoid vibrations in the pulleys.

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