I. Core Definition: The Connecting Core of Power Grids
Power fitting bolts and nuts are specialized fasteners for power line hardware connections, differing from ordinary fasteners by requiring:
Mechanical strength: Withstand dynamic loads like conductor tension, wind vibration, ice loads
Electrical performance: Avoid corona discharge, maintain uniform electric field
Environmental resistance: Endure outdoor harsh conditions including UV, salt spray, temperature extremes
Per DL/T 764.4-2002 standard, their failure load must exceed ordinary bolts by ≥1.5 times.
II. Special Types: Innovative Designs for Power Applications
| Type | Features | Applications | Visual Identification |
|---|---|---|---|
| Ball-eye bolts | Spherical head avoids stress concentration | Insulator string to tower connection | Smooth hemispherical head |
| Wedge tension bolts | Self-locking wedge design, tighter under load | Tension clamp fixation | Tapered wedge tail |
| Double-nut bolts | Twin nuts lock against each other, vibration-proof | Jumper connections, vibrating equipment | Distinct double-nut structure |
| Hot-dip galvanized | Coating ≥86μm, 3000h salt spray resistance | Coastal, industrial areas | Silver-white with zinc spangle |
III. Technical Requirements: Beyond Ordinary Standards
III. Technical Requirements: Beyond Ordinary StandardsSpecial strength grades:
All power bolts ≥ Grade 8.8
Critical connections use 10.9 or 12.9 grade
Stringent anti-loosening:
Vibration test: ≤10% preload loss after 2000 cycles
Slip load: ≥1.5x nominal value
Superior corrosion resistance:
Hot-dip zinc: bolts ≥50μm, nuts ≥40μm
Salt spray test: ≥1000h no red rust
Installation convenience:
Standard wrench sizes (e.g., M16=24mm)
Anti-theft design: Special recesses require dedicated tools
IV. Materials & Processes: Specialized Manufacturing
Material selection:
Carbon steel Q235/Q345: General structures
Stainless steel 304/316: Coastal/corrosive environments
High-strength alloy steel: 35CrMo/42CrMo for critical loads
Surface treatments:
Hot-dip galvanizing: Most common, cost-effective
Dacromet: No hydrogen embrittlement, better corrosion resistance
Zinc penetration: High precision, suitable for high-strength bolts
Special processes:
Rolled threads: 30% stronger than cut threads due to continuous grain flow
Bulk heat treatment: Tempered to HRC28-32
V. Applications: Critical Connections Throughout the Grid
V. Applications: Critical Connections Throughout the GridTower connections:
Main member splicing: M20-M30 high-strength bolts
Crossarm installation: M16-M24 anti-loosening bolts
Ladder fixation: M12-M16 hot-dip galvanized bolts
Conductor connections:
Tension clamp fixation: Wedge bolts
Suspension clamp installation: U-bolts
Jumper connections: Double-nut anti-loosening bolts
Insulator connections:
Ball-eye assembly: Special spherical bolts
Socket-cap assembly: Unique neck design bolts
Distribution equipment:
Transformer platforms: Reinforced anchor bolts
Switchgear: Special bolts for conductive circuits
Epilogue
Power fitting bolts and nuts—these seemingly insignificant “small parts” are actually “critical joints” ensuring grid security. They silently endure mechanical tension, environmental erosion, and electrical challenges, using their steel bodies to safeguard stable grid connections. As power grid construction advances, these “steel joints” continue evolving with higher performance and smarter features, reliably supporting the transmission of electrical energy.
