ISO 6118:2006

Overview

ISO 6118:2006 - "Road vehicles - Elastomeric cups and seals for cylinders for hydraulic braking systems using a non‑petroleum base hydraulic brake fluid (service temperature 70 °C max.)" - specifies performance tests for moulded elastomeric brake cups and gland seals (60 mm diameter and smaller) used in hydraulic actuating cylinders on road vehicles. The standard focuses on functional performance and durability in contact with non‑petroleum base hydraulic brake fluids (as defined in ISO 4925) and does not set compound chemical composition, tensile strength or elongation limits. Disc brake seals are excluded.

Key topics and technical requirements

• Scope and applicability
  • Moulded cups and double‑lipped gland seals made from rubber, for use with ISO 4925 non‑petroleum brake fluids.
  • Service temperature range: −40 °C to +70 °C (note in standard).
• General requirements
  • Workmanship, marking (manufacturer identification; optional “ISO 6118” mark), packaging and sampling procedures.
• Core performance tests
  • Resistance to fluid at elevated temperature (70 °C): dimensional, volume and hardness changes after immersion; permitted volume and dimensional changes are specified (e.g., volume change up to +16%, lip diameter change limits).
  • Precipitation: maximum sediment permitted after centrifuging (specified value in standard).
  • Heat pressure stroking tests for wheel‑ and master‑cylinder seals: verify lip diameter retention, leakage, corrosion of pistons/bore, hardness change (≤ −10 IRHD allowed), and absence of excessive scoring, scuffing or blistering.
    • Wheel cylinder minimum lip excess over bore: ≤19.05 mm → 0.40 mm; >19.05–25.4 → 0.50 mm; >25.4–38.1 → 0.65 mm; >38.1–60 → 0.75 mm.
    • Master cylinder lip excess: ≤19.05 → 0.30 mm; >19.05–25.4 → 0.40 mm; >25.4–38.1 → 0.50 mm; >38.1–60 → 0.65 mm.
  • Low temperature performance: leakage and bend‑back recovery requirements.
  • Oven ageing: limits on hardness change (±5 IRHD) and condition of seals after ageing.
  • Corrosion and storage corrosion tests: permissible mass‑change limits for metal test strips and prohibitions on gelling, crystalline deposits or excessive corrosion.

Applications and users

• Relevant for: brake component manufacturers, OEMs, quality/validation engineers, test laboratories, suppliers of elastomeric seals and procurement/specification teams.
• Practical uses:
  • Verifying compatibility of brake seals with non‑petroleum hydraulic fluids.
  • Defining acceptance criteria during production control and type testing.
  • Guiding design and material selection for hydraulic brake actuators (wheel and master cylinders).

Related standards

• ISO 4925 - Specification of non‑petroleum‑base brake fluids
• ISO 4926 - Non‑petroleum base reference fluids (compatibility testing)
• ISO 188 - Accelerated ageing and heat resistance tests for rubber
• ISO 48 - Rubber hardness determination

Keywords: ISO 6118:2006, elastomeric cups, seals, hydraulic braking systems, non‑petroleum base hydraulic brake fluid, brake seal tests, wheel cylinder, master cylinder, corrosion, oven ageing, low temperature performance.