ISO 6971:2002

Overview

ISO 6971:2002 specifies the characteristics, dimensions and testing requirements for cranked-link drag chains of welded construction, together with their attachments and sprockets, for conveying bulk materials. The standard ensures interchangeability of complete chains and individual links for repair and maintenance, covers sprockets with 5 to 20 teeth, and defines five attachment types used with these conveyor chains.

Key topics and requirements

• Scope and applicability
  • Chains intended for bulk material conveyors; sprockets 5–20 teeth.
  • Chains of welded-steel cranked-link (also called “offset sidebar” in the USA).
• Interchangeability and designation
  • Standardized chain dimensions and a WD prefix designation for welded designs to permit cross-manufacturer replacements.
• Dimensions and tolerances
  • Detailed dimensional limits for pitch, barrel shape, plate and pin dimensions, and clearances to ensure compatibility with sprockets and attachments.
• Tensile strength and testing
  • Minimum tensile strength given as a comparative figure; tensile testing procedures specified (destructive test on a chain sample of at least three pitches).
• Length accuracy and measurement
  • Finished-chain measurement procedure and nominal reference length (approx. 3 048 mm) with specified measuring forces.
• Attachments
  • Five attachment types defined: C1, C3, C4, RR, and wing, with required geometrical dimensions so attachments fit standardized chain links.
• Sprocket geometry
  • Pitch circle diameter, tip and root diameters, measuring-pin diameter, tooth-gap form, rim profile, pitch-line clearance and tolerances; measurement over measuring pins for inspection.
• Marking
  • Manufacturer name/trademark and ISO chain number marking required; markings must not be obscured by attachments.
• Normative reference
  • ISO 286-2 (limits and fits for holes and shafts) is referenced for tolerance grades.

Applications and who uses it

ISO 6971 is used by:

• Conveyor and mechanical design engineers specifying chain-driven bulk-material conveyors (mining, cement, grain handling, ports).
• Chain and sprocket manufacturers for product design and quality control.
• Maintenance teams and procurement professionals to source interchangeable replacement chains and attachments.
• Plant operators and OEMs ensuring safe, reliable material handling systems and minimizing downtime through standardized spare parts.

Practical benefits include simplified spare-part inventories, predictable chain/sprocket engagement, and clearer procurement specifications for welded cranked-link conveyor chains.

Related standards

• ISO 286-2 - ISO system of limits and fits (referenced for dimensional tolerances)
• Prepared by ISO/TC 100 (Chains and chain wheels for power transmission and conveyors)

Keywords: ISO 6971, cranked-link drag chains, welded construction, conveyor chains, attachments (C1 C3 C4 RR wing), sprockets, interchangeability, tensile strength, pitch circle diameter.