As a high-performance self-locking fastener complying with the German industrial standard DIN 25201, the Double Fold Self-Locking Washer is engineered with a unique double-folded structure to deliver reliable anti-loosening performance in dynamic load scenarios. Available in carbon steel and stainless steel variants, it is widely applied across industrial, automotive, and infrastructure sectors. This introduction details its design features, performance metrics, application guidelines, and compliance specifications.
Core Structural Characteristics
The washer adopts a symmetrical double-folded configuration, consisting of two annular metal sheets folded along the central axis to form a pre-compressed elastic gap. Key structural parameters comply with DIN 25201: the fold angle is standardized at 15°-20°, the elastic gap width ranges from 0.2mm to 1.8mm (varies by size), and the inner diameter features a smooth chamfer (C0.3-C1.0) to avoid thread damage during installation. Additionally, the outer edge is designed with a deburred finish to prevent scratches on connected components.
Self-Locking Mechanism
- Preloaded Elastic Locking: The double-folded structure stores elastic potential energy during installation. When the bolt/nut is tightened, the folded sheets exert continuous axial preload on the connection interface, maintaining stable clamping force and resisting loosening caused by vibration or thermal expansion/contraction.
- Wedge Effect: The inclined contact surface between the folded layers generates a wedge effect under lateral forces. This converts the loosening torque into axial clamping force, forming a "self-reinforcing" anti-loosening loop.
- Multi-Point Contact Friction: The double-layer structure creates two independent friction interfaces (washer-bolt head and washer-workpiece). Compared with single-layer washers, the total friction coefficient is increased by 40%-60%, significantly enhancing anti-loosening durability.
Base Material Specifications
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Material Type
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Grade/Alloy
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Key Properties
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Compliance with DIN 25201
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Typical Application Scenarios
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Carbon Steel
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C1018, C1045
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Tensile strength ≥ 600 MPa, Hardness HV 280-350, Good formability
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Clause 4.1 Material Requirements
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General industrial machinery, non-corrosive indoor equipment
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Stainless Steel
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AISI 304 (1.4301), AISI 316 (1.4401)
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Corrosion resistance (salt spray test ≥ 5000h for 316), Tensile strength ≥ 550 MPa
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Clause 4.2 Corrosion Resistance Requirements
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Marine equipment, food processing machinery, chemical pipelines
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Surface Treatments
- Carbon Steel Variants: Zinc Plating (Yellow/White): Corrosion resistance ≥ 200h salt spray (DIN 50021), cost-effective for general environments.
- Phosphating + Oil Coating: Enhances friction coefficient (μ ≥ 0.35) and anti-rust performance, suitable for high-torque connections.
- Dacromet Coating: Environmentally friendly, corrosion resistance ≥ 1000h salt spray, compliant with RoHS standards.
Stainless Steel Variants: Passivation Treatment: Removes surface oxide film, improves corrosion resistance and surface gloss (DIN EN ISO 15730).
Electropolishing: Reduces surface roughness (Ra ≤ 0.8μm), suitable for high-cleanliness applications (e.g., pharmaceutical equipment).
Standard
DIN 25201 specifies the technical requirements for double fold self-locking washers, including dimensional tolerances, material composition, mechanical properties, corrosion resistance testing, and marking requirements. All our products undergo third-party testing to meet Class A dimensional accuracy (tolerance ±0.05mm for key dimensions) and pass the dynamic anti-loosening test (500,000 vibration cycles without loosening).
Key Specifications
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Item
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Carbon Steel (C1045)
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Stainless Steel (316)
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Test Standard (DIN 25201)
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Size Range (Inner Diameter)
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M3 - M30
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M3 - M24
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Clause 5.1 Dimensional Tolerances
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Hardness
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HV 300 - 380
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HV 220 - 280
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Clause 6.2 Hardness Test
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Elastic Recovery Rate
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≥ 85%
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≥ 80%
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Clause 6.3 Elasticity Test
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Anti-Loosening Performance
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No loosening after 500,000 vibration cycles
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No loosening after 500,000 vibration cycles
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Clause 6.4 Dynamic Test
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Application Fields
- Industrial Machinery: Gearboxes, motors, pumps, and compressors—where continuous vibration requires long-term anti-loosening reliability.
- Automotive Industry: Chassis components (suspension brackets), engine accessories (water pumps, alternators), and transmission systems—compliant with automotive-grade fatigue resistance requirements.
- Infrastructure & Construction: Steel structure connections for bridges, wind turbine towers, and building steel frames—resistant to outdoor environmental corrosion and temperature fluctuations.
- Home Appliances & Electronics: Washing machines (motor mounts), air conditioners (compressor brackets), and power distribution cabinets—ensuring stable operation under cyclic loads.
- Specialty Industries: Marine equipment, chemical reactors, and pharmaceutical machinery (stainless steel variants)—meeting strict corrosion resistance and cleanliness standards.
