Extra Long Bolt

Extra-Long Hex Bolts (Extended Hex Head Bolts): Overview

Material:

• Common materials:
  • Carbon steel (Grade 8.8, 10.9) for high tensile strength.
  • Stainless steel (304/316) for corrosion resistance in marine or chemical environments.
  • Alloy steel (ASTM A325/A490) for structural applications.
• Surface treatments: Zinc plating, hot-dip galvanizing, Dacromet coating, or Xylan® coating for enhanced corrosion and wear resistance.

Manufacturing Process:

1. Cold Heading: Forms the hex head and partially threads the shank from steel wire.
2. Thread Rolling: Precision rolling of full or partial threads (metric/SAE) using high-pressure dies.
3. Heat Treatment: Quenching and tempering (for high-grade steel) to achieve required hardness (HRC 22-34) and tensile strength.
4. Surface Finishing: Electroplating or hot-dip coating applied uniformly across the extended length.
5. Straightening: Ensures bolt straightness via mechanical adjustment to meet tolerance standards.

Key Production Considerations:

• Length-to-diameter ratio: Maintains structural integrity during manufacturing and prevents bending.
• Thread consistency: Critical for long bolts to avoid misalignment during installation.
• Coating uniformity: Prevents corrosion over extended surfaces; automated dipping for long bolts.
• Straightness tolerance: ≤1mm per meter to ensure proper fit in pre-drilled holes.

Applications:

• Structural engineering: Bridges, skyscraper frameworks, and wind turbine foundations.
• Heavy machinery: Securing bases of presses, turbines, and mining equipment.
• Marine/offshore: Shipbuilding, oil rigs, and coastal infrastructure.
• Energy sector: Transmission towers, pipeline supports, and nuclear plant components.
• Transportation: Rail tracks, cargo container lashing, and aerospace assemblies.

Installation:

1. Pre-drilling: Drill holes matching bolt diameter and depth (1.5x bolt diameter for steel).
2. Alignment: Insert bolt through aligned components; use alignment pins for multi-layer structures.
3. Torque application:
   • Turn-of-nut method: Tighten to snug tight, then rotate 1/2-3/4 turns for preload.
   • Calibrated wrench: Apply specified torque (e.g., 400 Nm for M30 Grade 10.9).
4. Load distribution: Use hardened washers under the nut and head to prevent embedment.
5. Inspection: Verify bolt tension via ultrasonic testing or torque audits for critical joints.

Note:

• Corrosion prevention: Apply anti-seize compound on threads for stainless steel in salty environments.
• Vibration resistance: Pair with lock nuts or thread-locking adhesives in dynamic applications.
• Reuse limits: Discard bolts with stretched threads, cracks, or coating damage.