A flat suspension element consisting of multiple high-strength steel cords encapsulated in a polyurethane jacket, used in place of conventional wire ropes in modern gearless traction elevator systems.
Full Definition
Coated steel belts (also marketed as SteelFlex, AraFlex, or Aramid/Steel composite belts depending on manufacturer) were pioneered by Otis (Gen2 system) and now supplied by multiple manufacturers including Wittur and Pfeifer. The belt's flat cross-section allows the sheave diameter to be reduced to 75–100 mm (versus 400–700 mm for wire rope sheaves), enabling more compact, energy-efficient gearless machines. Minimum breaking force and safety factor requirements are specified in EN 81-20 Section 9.2 (safety factor ≥16 for coated belts vs ≥12 for wire ropes). The polyurethane jacket protects the steel cords from corrosion and provides the traction interface with the sheave (coefficient of friction μ ≈ 0.25–0.35 for PU on steel). Belt life is typically 10–15 years; condition monitoring uses magnetic flux leakage (MFL) testers to detect broken cords without removing the belt. Rope equaliser units are replaced by belt tension equalisation clips or wedge terminations.
