Full definition
A pulley equipped with raised lateral edges (flanges) on one or both sides of the belt running surface, preventing the belt from walking off the pulley during operation. Essential in applications with inherent lateral belt forces: vertical shaft drives, high-vibration environments, drives with frequent start-stops or reversals, and conveyors with off-center loading. For timing belt pulleys, a flange on at least one side of the wider pulley is standard per ISO 13050 (flanged pulleys are designated with "F" suffix). Flange height: typically 1.5-6 mm above the belt surface depending on belt width and speed. Material: same as pulley body (cast iron, steel, or aluminum) with smooth inner face to avoid belt edge damage. In flat belt drives, flanges are used on the non-crowned pulley. Excessive belt contact with flanges indicates misalignment and must be corrected rather than relying on the flanges as a fix.