Glossary

Balance Tolerance

The amount of imbalance which is allowed at the designated balance speed. Imbalance is expressed in ounce-inches (for example, 2 oz. in. is 1 ounce imbalance on a 2 inch radius, or 2 ounce imbalance on a 1 inch radius).

Critical Speed

The speed at which harmonic vibration occurs in a rotating body as a result of its center of gravity being slightly removed from the body's true center.

Dead Shaft Roll

A roll with internal bearings which allow it to rotate around a stationary shaft. Dead shaft rolls traditionally have less inertia than live shaft rolls.

Idler Roll

A web-driven roll whose primary purpose is to help carry, support or redirect the web as it moves.

Live Shaft Roll

A roll with journals which allow the roll to rotate on externally mounted bearings. They are ideal for high temperature or high loading applications.

Nominal Diameter (Nom Dia)

Dimension that comes from the original diameter of stock tubing before it is machined. Machined tubing is always slightly less than the Nominal Diameter listed.

PLI

The net load that the roll encounters, usually the result of web tension, web width and wrap angle.

Runout (Circular)

Full indicator movement as measured around the circumference of a roll at any given point along the length of the body.

Sealed Bearings

Bearings which are tightly enclosed with contacting seals between the inner and outer race to keep out contaminants. Resulting friction is usually greater than that of a shielded bearing.

Shielded Bearings

Bearings which are not sealed, but enclosed with non-contacting shields, resulting in a very low friction bearing.

Surface Finish

A number which designates the smothness of a surface in Ra (roughness average).

Straightness

A tolerance which controls the diameter variation of a roll, especially important when roll diameter tolerance is not tight.

T.I.R.

Total Indicator Reading.