Fishplate Welding Process and Quality Control
- What requirements apply to fish plate welding groove preparation?
Use mechanical machining or flame cutting to create V-grooves with 60±5° angle, 1-2mm root face, and 2-3mm gap. Grind surfaces to remove oxide and oil (Ra≤25μm) for Q345B fish plates to ensure good fusion.
- How does welding current affect fish plate weld quality?
Insufficient current causes shallow penetration; excessive current overheats the weld. For E5015 electrodes, use 160-180A current and 22-24V voltage to achieve ≥8mm penetration without softening the heat-affected zone.
- How to detect internal weld defects via non-destructive testing?
Ultrasonic testing (UT) detects internal cracks and porosity with Φ2×40-12dB sensitivity; magnetic particle testing (MT) finds surface/near-surface defects. Critical lines require 100% inspection per GB/T 11345, with defects ≤Class III.
- What role does post-weld heat treatment play in fish plate performance?
Post-weld tempering at 600-650℃ for 2 hours reduces residual stress by >80% and improves HAZ toughness. Treated welds achieve impact energy ≥47J, vs. 25J untreated.
- How do material differences between fish plates and rails affect welding?
For Q345B fish plates and U71Mn rails, use E5016 electrodes (≥500MPa tensile strength), preheat to 100-150℃, and cool slowly to prevent cracks from coefficient mismatch.