Fastener Fundamentals: The "Bonds" of The Mechanical World

I. Fastener Fundamentals: The "Bonds" of the Mechanical World

Definition: Any mechanical component (e.g., bolts, nuts, rivets) used to join two or more objects through friction or deformation.
Core Functions:

• Shear Resistance: Prevents transverse slippage

• Tensile Resistance: Withstands axial separation forces

• Sealing/Insulation: Special designs prevent leaks/electrical conduction

II. Four Primary Fastener Types (Illustrated)

1. Bolts & Nuts (Most Common Pair)

• Bolt: Rod-shaped body with external threads, featuring drive structures (hex/internal hex)

• Nut: Internal-threaded counterpart, typically hexagonal

• Key Parameters:

• Strength Class: e.g., 8.8 (bolt tensile strength: 800MPa; yield ratio: 0.8)

• Thread Specification: Metric M6/M8/M10; Imperial 1/4"-20 (1/4" diameter, 20 TPI)

2. Screws (Self-Tapping/Machine)

• Self-Tapping Screws: Cutting tips for direct insertion into thin metal/plastic (no pre-drilling)

• Metal sheets (≤2mm): Type AB point

• Wood: Coarse twin threads

• Concrete: Nylon anchor sleeves

• Material Compatibility:

• Machine Screws: Require pre-threaded holes (common in precision equipment)

3. Rivets (Permanent Joints)

• Working Principle: Tail deformation forms "mushroom head" locking

• Evolution:
  Solid rivets (hammered) → Blind rivets (pop-rivet gun) → Explosive rivets

• Innovations:

• Explosive Rivets: Internal charge expands for hermetic sealing (aerospace)

• Shape-Memory Rivets: Heat-activated self-locking

4. Washers (Force Directors)

III. Anti-Loosening Technologies: Defeating Vibration

Mechanical Locking

• Double Nutting: Jam nut creates opposing forces (low cost, adds height)

• Cotter Pins: Cross-pinning through bolt holes (truck wheel hubs)

• Castle Nuts: Slotted nut + cotter pin (aircraft landing gear)

Chemical Locking

• Threadlockers: Anaerobic adhesives fill thread gaps, cure into plastic

• Low (purple): Hand-removable

• High (red): Requires 260°C heat for removal

• Strength Grades:

Structural Locking

• Wedge Threads: Asymmetric angles (30°/45°) tighten under vibration

• All-Metal Lock Nuts: Top-section deformation creates radial pressure

IV. Material Science: Cast Iron to Composites

Top 3 Surface Treatments:

• Galvanizing: Sacrificial anode protection (white/color zinc)

• Dacromet®: Zinc-aluminum flakes + chromate (1000h+ salt spray resistance)

• Nitriding: Surface hardness HRC60 (5× wear resistance)

V. Cutting-Edge Innovations: Smart Fasteners

1. Strain-Sensing Bolts:

• Embedded fiber optics monitor preload in real-time (wind turbine towers)

2. Self-Healing Coatings:

• Microencapsulated corrosion inhibitors repair scratches

3. Shape-Memory Washers:

• Nitinol alloy compensates for thermal relaxation

VI. Selection Protocol: 4-Step Avoidance Guide

1. Determine Strength: Calculate load (shear/tension) + 1.5× safety factor

2. Assess Environment:

• Coastal → 316 stainless + PTFE coating

• Chemical → Hastelloy C-276

3. Prevent Galvanic Corrosion:

• Aluminum + steel → Insulating sleeves mandatory

4. Match Tools:

• Electronics → Torque screwdriver (±3% accuracy)

• Heavy structures → Hydraulic wrench (3000Nm+)

Knowledge Extension:

• Historical Note: First metal bolts appeared in Leonardo da Vinci’s 15th-century sketches; standardized by Joseph Whitworth in 1841

• Extreme Application: ISS uses Grade 12.9 titanium bolts surviving -180°C to 200°C thermal cycling

Fasteners—though small—are the "metallic bonds" upholding modern civilization. From 0.6mm screws in smartphones to M64 anchor bolts in the Three Gorges Dam, they silently guard the integrity of human engineering.

This version preserves all technical details while optimizing terminology for global engineering audiences. Let me know if you need version adjustments for specific regions (e.g., ASME vs. ISO standards).