Double Fold Self Locking Washer DIN25201 Double Stacked Wedge Lock Washer

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What is a Double Fold Self Locking Washer?

A Double Fold Self Locking Washer is a specialized type of washer designed to prevent loosening of fasteners due to vibration, thermal expansion, or dynamic loads. It features a unique double-folded design that creates spring tension when compressed between a nut and a surface, maintaining constant pressure and resisting rotational movement. Unlike standard washers, its locking mechanism does not rely on adhesives or external locking devices, making it a reliable mechanical solution for securing bolted joints.

Materials

Double fold self locking washers are manufactured from various materials to suit different environmental and mechanical requirements:

• Carbon Steel (Grade 8, 10, or 12.9) – High strength and durability for heavy-duty applications.

• Stainless Steel (A2/AISI 304, A4/AISI 316) – Corrosion-resistant, ideal for marine, chemical, and food-processing industries.

• Alloy Steel (4140, 4340) – Heat-treated for enhanced hardness and fatigue resistance.

• Phosphor Bronze (C51000, C52100) – Used in electrical applications due to its conductivity and anti-galling properties.

• Brass (C36000) – Suitable for low-friction and decorative applications.

• Titanium (Grade 2, Grade 5) – Lightweight yet strong, used in aerospace and medical devices.

Surface Treatments

To enhance performance and longevity, these washers undergo various surface treatments:

• Zinc Plating (Yellow/White Zinc) – Provides corrosion resistance and a smooth finish.

• Hot-Dip Galvanizing – Thick zinc coating for extreme environments.

• Black Oxide – Improves wear resistance and reduces light reflection.

• Cadmium Plating – High corrosion resistance (limited use due to environmental concerns).

• Passivation (for Stainless Steel) – Removes free iron particles to enhance corrosion resistance.

• Nickel Plating – Adds hardness and improves appearance.

Specifications

Double fold self locking washers come in a range of sizes and dimensions:

• Inner Diameter (ID): M3 to M36 (metric) or #4 to 1.5″ (imperial).

• Outer Diameter (OD): Varies based on application requirements.

• Thickness: Typically 0.5mm to 3mm, depending on material and load capacity.

• Locking Torque: Varies with material and design, usually between 5 Nm to 150 Nm.

• Standards: Compliant with DIN 6796, ISO 8750, and NASM 35338.

Applications

These washers are widely used in industries where vibration resistance is critical:

• Automotive & Aerospace: Engine mounts, landing gear, and transmission systems.

• Industrial Machinery: Pumps, compressors, and heavy equipment.

• Rail & Marine: Bolted joints in rail tracks and shipbuilding.

• Energy Sector: Wind turbines, oil rigs, and power generation systems.

• Electronics & Appliances: Securing components in high-vibration environments.

• Construction & Infrastructure: Bridges, steel frameworks, and seismic-resistant structures.

Excellent Case: Wind Turbine Blade Assembly

Challenge:

A leading wind turbine manufacturer faced persistent bolt loosening in rotor blade connections due to extreme wind-induced vibrations. Traditional locking methods (nylon inserts, thread lockers) failed under prolonged stress, leading to maintenance downtime and safety risks.

Solution:

The company switched to double fold self-locking washers (AISI 316 stainless steel, hot-dip galvanized) for all critical blade-hub fasteners. The washers provided:

• Persistent Spring Action: Maintained clamping force despite cyclic loads.

• Corrosion Resistance: Withstood harsh offshore conditions.

• No Chemical Degradation: Unlike thread lockers, they didn’t degrade under UV exposure.

Results:

• Zero Bolt Failures over a 5-year period.

• 50% Reduction in Maintenance Costs due to fewer retightening requirements.

• Increased Turbine Uptime by eliminating unscheduled repairs.

This case demonstrates how double fold self locking washers provide long-term reliability in high-stress, high-vibration applications.

Conclusion

The double fold self locking washer is an essential fastener for industries where vibration resistance is paramount. With diverse material options, surface treatments, and proven effectiveness in critical applications, it ensures secure, maintenance-free bolted joints. Whether in aerospace, energy, or heavy machinery, this washer delivers unmatched performance where traditional methods fall short.