Application of Diamond Friction Shims in Wind Power Industry: Key Solution for Improving Bolted Connection Reliability and Maintenance Efficiency

Introduction

With the continuous growth of global wind power installed capacity, the reliability and maintenance efficiency of wind turbines have become core industry concerns. A typical onshore wind turbine contains thousands of bolted connection points, and offshore turbines have even more bolts. These connections carry load transfer for key components such as blades, hubs, main shafts, gearboxes, generators, and towers, and their connection reliability directly relates to the safe operation and design life of over 20 years.

Challenges in Wind Power Bolted Connections

1. Extreme Alternating Loads: Wind turbines withstand complex alternating loads during operation, including wind loads, gravity loads, inertial loads, and aeroelastic loads. The continuously changing amplitude and direction of these loads keep bolted connections in constant vibration and fatigue states.

2. Harsh Environmental Conditions: Offshore wind turbines face salt spray corrosion, high humidity, and temperature variations; onshore turbines must cope with sand, rain, snow, and extreme temperatures. These environmental factors accelerate corrosion and wear of bolts and connection surfaces.

3. Preload Decay: During long-term operation, bolt preload gradually decays due to connection surface embedding, material creep, and vibration relaxation. When preload drops below critical values, relative slippage occurs at connection surfaces, leading to bolt fatigue failure.

4. Maintenance Difficulties: Wind turbines are typically installed in remote areas or offshore, making high-altitude and offshore maintenance extremely costly. Regular inspection and retightening of bolted connections require significant manpower, resources, and time.

Common Failure Modes

1. Bolt Fatigue Fracture: The most severe failure mode. When relative slippage occurs at connection surfaces, bolt shanks experience additional bending and shear stresses, leading to fatigue fracture under alternating loads. Bolt fracture can cause major safety accidents such as blade shedding and tower collapse.

2. Connection Surface Slippage: When bolt preload is insufficient or friction coefficient is too low, connection surfaces slip under shear loads. Slippage not only causes bolt fatigue but also reduces connection accuracy and increases vibration.

3. Preload Relaxation: Due to embedding, creep, and vibration relaxation, bolt preload decays over time. Studies show that wind power bolt preload may drop by more than 20% in the first few months after commissioning, with some connection points requiring multiple retightening.

4. Corrosion Failure: In harsh environments, bolts and connection surfaces corrode, causing friction coefficient changes, cross-section weakening, and stress concentration, further reducing connection reliability.

Diamond Friction Shim Technology

Diamond friction shims are a new type of high-friction-coefficient connection element, with core technology in compositing a diamond particle coating on the metal shim surface. This unique structural design provides excellent anti-loosening and anti-slip performance in bolted connections.

Working Principle: When diamond friction shims are clamped between two connection surfaces, under bolt preload, diamond particles on the shim surface micro-embed into the metal surface layers of the upper and lower connection surfaces, forming a mechanical interlocking effect. This mechanical interlocking greatly increases the friction coefficient of connection surfaces, significantly enhancing anti-slip capability.

Technical Characteristics:

1. Ultra-high friction coefficient: 0.4+, 2-3 times that of ordinary flat shims

2. No damage to connection surfaces: micro-embedding depth of only several to tens of microns

3. Adaptive performance: works stably on steel, cast iron, aluminum alloy and other materials

4. Corrosion resistance: diamond coating has excellent chemical stability

5. Reusable: can be disassembled and reused under normal conditions

Key Applications in Wind Turbines

1. Blade-Hub Connection: Each blade typically uses dozens of high-strength bolts承受巨大的交变弯矩和离心力. Diamond friction shims effectively improve anti-slip capability and prevent bolt fatigue fracture.

2. Tower Flange Connection: Tower sections are connected by flanges with dozens or hundreds of bolts. Diamond friction shims significantly improve tower connection reliability and reduce high-altitude retightening operations.

3. Main Shaft-Gearbox Connection: Transmission system bolted connections withstand complex dynamic loads. Diamond friction shims improve connection stiffness and reduce vibration transmission.

4. Nacelle Base-Tower Connection: This connection carries the entire nacelle weight and aerodynamic loads. Diamond friction shims improve connection stability and reduce nacelle vibration.

5. Offshore Wind Foundation Connection: Offshore turbine foundations use大量螺栓连接, facing salt spray corrosion and wave loads. Diamond friction shims' high friction coefficient and corrosion resistance make them ideal for offshore applications.

Comparison with Traditional Solutions

Ordinary flat shims: friction coefficient 0.15-0.2, low anti-slip capability, poor preload retention

Spring washers: friction coefficient 0.15-0.2, elastic tension mechanism, not reusable, causes indentation damage

Double-stack self-locking washers: friction coefficient 0.2-0.3, inclined plane lifting mechanism, medium anti-slip, causes tooth mark damage

Diamond friction shims: friction coefficient 0.4-0.6, mechanical interlocking, high anti-slip, excellent preload retention, reusable, no substantial damage, excellent corrosion resistance

Case Studies

Case 1 - Onshore Wind Farm: 100 units of 2.5MW turbines, tower flange bolt preload decayed severely after 3 years, requiring annual high-altitude retightening at 8,000 RMB per unit. After试用 diamond friction shims on 20 units, preload decay rate dropped from 25% to below 8% over 2 years. Retightening cycle extended from 1 year to 3-5 years, saving approximately 5,000 RMB per unit annually.

Case 2 - Offshore Wind Project: 60 units of 6MW turbines, blade-hub connection bolts developed fatigue cracks after 1 year. After analysis, micro-slippage under strong wind loads caused additional bending stress. All subsequent units used diamond friction shims, and existing units were retrofitted. After 1 year monitoring, blade bolt preload retention exceeded 95%, with no new fatigue cracks.

Installation and Maintenance Guidelines

1. Connection surface treatment: Clean oil, rust, and impurities before installation

2. Preload control: Follow design requirements; recalculate installation torque based on actual friction coefficient

3. Installation sequence: Use symmetrical, step-by-step tightening for multi-bolt connections

4. Regular inspection: Check preload at 3, 6, and 12 months after commissioning, then annually

5. Disassembly and reuse: Protect diamond coating during disassembly; reusable if no明显 damage

6. Storage conditions: Store in dry, clean environment, avoid corrosive substances

Conclusion

Diamond friction shims provide an effective solution for improving bolted connection reliability in the wind power industry. With ultra-high friction coefficient, excellent anti-loosening performance, good corrosion resistance, and reusability, they have broad application prospects in blade connections, tower flanges, transmission systems, and other key components.

As the wind power industry moves toward larger capacity, offshore, and deep-sea directions, wind turbine bolted connections will face even greater challenges. DAOLER, as a professional diamond friction shim manufacturer, is committed to providing high-quality connection solutions for the wind power industry. Welcome wind turbine manufacturers, maintenance service providers, and component suppliers to contact us.