Anti-loosening for Connections in Rail Transit Braking Systems: High-Reliability Application Solution of Diamond Friction Shims

I. Reliability Requirements for Rail Transit Connections

Rail transit equipment imposes extremely high requirements on connection reliability, especially for critical components such as braking systems and bogies. When trains operate at high speeds, they are subjected to continuous vibration, impact loads and temperature fluctuations. Loosening of any connecting parts may endanger driving safety. As the last line of defense for train safety, the braking system has the highest priority for connection reliability.

Traditional anti-loosening methods face challenges in the rail transit sector: spring washers tend to suffer fatigue failure under high-frequency vibration; thread-locking adhesives may degrade under high temperatures in braking systems; increasing pre-tightening torque can lead to fatigue fracture of bolts. Featuring high friction, excellent wear resistance and wide temperature range, Diamond Friction Shims deliver a more reliable solution for critical rail transit connections.

II. Typical Application Positions in Rail Transit

1. Brake Caliper Connections The brake caliper is the core executive component of the braking system. Its mounting connection bears brake reaction force and continuous vibration. Loosening of caliper connections will cause variations in brake clearance and fluctuations in braking force, seriously impairing braking performance. Diamond Friction Shims increase the friction coefficient of mating surfaces, suppress micro-slip and ensure long-term stability of caliper mounting position.
2. Brake Disc Mounting Connections Connections between brake discs and wheels or axles withstand braking torque and thermal cycling loads. Loosening leads to brake disc runout and brake judder. High-friction shims stabilize bolt preload and reduce preload attenuation induced by thermal cycles.
3. Critical Bogie Connections The bogie serves as the running gear of the train and bears complex dynamic loads. Connections between the frame and axle boxes, suspension systems, traction devices and other assemblies have stringent anti-loosening requirements. Friction shims improve connection stiffness, reduce vibration transmission and extend the fatigue life of fasteners.
4. Traction Motor Connections Mounting connections of traction motors endure motor torque and vibration. Loosening causes motor misalignment and aggravated vibration. Ultra-thin friction shims improve connection reliability without modifying the original mounting structure.
5. Carbody-to-Bogie Connections Traction device and damper connections between carbody and bogie sustain heavy loads and alternating stresses. Connection reliability directly affects running smoothness. Diamond Friction Shims provide stable high-friction joints.

III. Advantages of Diamond Friction Shims for Rail Transit

DAOLER® Diamond Friction Shims adopt the Diamond Claw® interlocking technology, with the following benefits for rail transit applications:

1. Reliability under high-vibration environments A static friction coefficient of ≥0.6 is achieved via microscopic mechanical interlocking. The shims maintain stable connections under continuous train vibration and effectively restrain interfacial micro-slip and preload attenuation.
2. Excellent temperature resistance Braking systems operate at elevated temperatures, with temperatures near brake discs exceeding 150°C. DAOLER friction shims maintain stable performance across a wide temperature range from -40°C to 150°C, adapting to high-temperature conditions of braking systems.
3. High wear resistance & long service life Coating hardness ≥1000 HV; diamond particles have a Mohs hardness of 10. The shims sustain stable long-term performance under high-frequency vibration and fretting wear, with service life far exceeding conventional washers.
4. Direct replacement & upgrade Ultra-thin specifications starting from 0.1 mm can directly replace original flat washers. No modification to connection structures or bolt sizes is required, convenient for new vehicle manufacturing and retrofitting of in-service rolling stock.
5. No damage to mating surfaces The grain size and interlocking depth of diamond particles are precisely controlled. High friction is achieved without damaging precision-machined mating surfaces, protecting high-value rail transit components.
6. Corrosion resistance The nickel-phosphorus diamond composite coating delivers outstanding corrosion resistance, suitable for coastal environments with high salt spray and humidity.

IV. Application Outcomes

After applying Diamond Friction Shims to critical rail transit connections, the following results can be obtained:

• Preload attenuation rate of connections reduced by more than 70%, extending maintenance inspection intervals
• Stable mounting position of brake calipers, reduced brake clearance variation and more consistent braking performance
• Improved bogie connection stiffness, lower vibration level and enhanced riding smoothness
• Extended bolt fatigue life, mitigating risk of bolt fracture
• Reduced downtime for maintenance and improved train operational efficiency
• No need to increase pre-tightening torque or use thread-locking adhesives for simpler assembly and maintenance

V. Application Characteristics for High-Speed Rail and Urban Rail

High-speed rail applications High-speed trains run at speeds above 300 km/h with high vibration frequency and intensity, demanding the highest connection reliability. Diamond Friction Shims are recommended preferentially for critical connections of braking systems and bogies to secure connection safety under high-speed operation.

Metro / Urban rail applications Metro and urban rail trains feature frequent start-stop cycles and heavy-duty use of braking systems. Connection joints endure repeated impact loads. The high wear resistance and impact resistance of Diamond Friction Shims are particularly suited for such working conditions and reduce routine maintenance frequency.

Heavy-haul freight applications Heavy-haul freight trains have high axle loads and large load variations; connection joints bear high static and dynamic loads. High friction coefficient shims boost connection load capacity and guarantee connection reliability under heavy loads.

VI. Selection & Installation Guidelines

Selection Tips

• Select corresponding specifications according to load and vibration grade of the connection joint
• Verify 150°C temperature resistance for high-temperature positions in braking systems
• Choose salt-spray corrosion resistant models for coastal areas
• Prioritize ultra-thin specifications for precision connections
• Custom non-standard dimensions available

Installation Tips

• Clean mating surfaces before installation to remove grease, rust and burrs
• Place the friction shim between the two mating surfaces
• Tighten bolts following specified torque and sequence
• Carry out one preload inspection after the first operation
• Inspect in accordance with maintenance cycles; undamaged shims are reusable

VII. Conclusion

Anti-loosening reliability of critical rail transit connections is essential for safe train operation. Centered on DAOLER® Diamond Claw® interlocking technology, DAOLER® Diamond Friction Shims feature static friction coefficient ≥0.6, coating hardness ≥1000 HV and stable performance within -40°C ~150°C. They deliver an independently controllable, highly reliable connection solution for high-speed railways, metros and other rail transit equipment.