Ensuring the reliability and performance of brake lines is critical in the automotive industry. In this Q&A with expert Jeff Andrasik, we will explore the core aspects of brake line testing, the relevant standards, and the techniques employed for robust validation.

What are the main considerations for testing automotive brake lines?

The primary considerations for testing automotive brake lines revolve around durability and performance under a wide range of operational and environmental conditions. This includes resistance to extreme temperatures (both high and low), pressure integrity, fatigue life under dynamic conditions (flexing and vibration), chemical compatibility with brake fluids and oils, and resistance to environmental degradation like ozone and corrosion. In addition, the physical integrity of the hose and its end fittings, including their adhesion and retention capabilities, is vital. The ultimate goal is to validate that the brake line will maintain its structural and functional integrity throughout the vehicle's lifespan, preventing leaks, bursts, or performance degradation that could compromise braking effectiveness.

Which standards are most commonly used for brake line testing in the automotive market?

The Federal Motor Vehicle Safety Standard (FMVSS) 106 is the most commonly used standard for hydraulic brake hoses, brake hose assemblies, and brake tubing in the automotive market. This standard specifies comprehensive performance and design requirements to reduce brake system failures. Adherence to FMVSS 106 is mandatory for brake lines used in vehicles manufactured for sale in the United States. While FMVSS 106 is central, other regional or manufacturer-specific standards and internal validation protocols may also be applied to ensure compliance with specific vehicle platforms or performance targets.

What are some of the key testing techniques applied to brake hoses?

A variety of testing techniques are applied to brake hoses to ensure their compliance and reliability. These include:

• Constriction Testing: A pre-test to ensure the internal diameter is not restricted.
• High and Low Temperature Resistance Tests: Evaluating material integrity and crack formation after exposure to extreme temperatures.
• Oil and Brake Fluid Compatibility Tests: Assessing material swelling and degradation when exposed to automotive fluids.
• Ozone Resistance Tests (Static & Dynamic): Accelerated aging tests to determine resistance to atmospheric ozone, including vibration to simulate real-world conditions.
• Length Change and Volumetric Expansion Tests: Measuring dimensional stability under pressure.
• Adhesion Test: Determining the bond strength between layers of the hose and its reinforcement.
• Flex Strength and Whip Tests: Simulating dynamic flexing and vibration experienced during vehicle operation to assess fatigue life.
• End Fitting Corrosion Test: Evaluating the corrosion resistance of metal end fittings to prevent leaks or structural failure.
• Burst Strength Testing: Applying hydrostatic pressure to the point of failure to determine maximum pressure resistance.
• Tensile Strength Test: Measuring the force required to pull the hose apart or separate it from its end fittings.
• High Temperature Impulse Test: Cyclically loading pressure at elevated temperatures to accelerate aging and identify weaknesses in crimp or end fitting connections.

What testing techniques are specifically used for brake tubing, and how do they differ from hose testing?

While some methods overlap, testing techniques for rigid brake tubing differ due to their inherent structural properties. For air brake tubes, key tests include:

• High Temperature Conditioning & Collapse Resistance Test: Assessing dimensional stability and resistance to collapse after prolonged exposure to elevated temperatures.
• Boiling Water Conditioning & Tensile Strength Test: Evaluating the tube's strength after exposure to hot water, simulating environmental effects.
• Thermal Conditioning and Tensile Strength Test: Similar to boiling water, but involving temperature cycling.
• Vibration Resistance Test: Subjecting tubes to constant air pressure and vibration at various temperatures to check for leaks and fatigue.
• End Fitting Retention Test: Verifying the leak-free integrity of fittings under pressure.
• End Fitting Serviceability Test: Ensuring the fitting maintains integrity after multiple assembly and disassembly cycles, simulating maintenance scenarios.

The primary difference lies in the emphasis on flexibility for hoses versus rigidity and connection integrity for tubes, reflecting their respective roles in the brake system.

Regardless of your brake line type or application, the experts at Smithers can assist with developing a thorough validation program customized to your needs and goals. Our team has supported many tier suppliers and OEM programs. Contact us today to get started!