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Sub merged arc welding
- 1. SUB-MERGED ARC WELDING CAUSES AND CURES OF COMMON DEFECTS
- 2. Types of common defects • Blow Hole • Undercut • Slag Inclusion • Incomplete Penetration • Crack • Distortion • Bum-Up • Arc Blow • Pit • Over Lap
- 3. Why-Blow Hole • Wet, unclean surface or damaged electrode. • Base metal surface covered with oil, rust etc. • Over travel • Overcurrent • Excessive arc length • Too thick base metal or too fast cooling rate.
- 4. How to do avoid Blow Hole • Properly maintain and store electrode. • Properly clean base metal before weld. • Reduce travel speed • Use proper welding current. • Maintain proper arc • Proceed proper pre-heating.
- 5. Why-Undercut • Welding current too high • Improper stick electrode. • Excessively long arc length • Improper manipulation. • Unclean base metal. • Base metal is overheated.
- 6. How to avoid Undercut • Reduce welding current. • Properly choose stick size and type. • Properly maintain arc length • Use proper electrode angles and pause at each side of weld bead when using a weaving technique. • Properly clean base metal surface. • Use smaller electrode size.
- 7. Why-Slag Inclusion • Incomplete slag removal from previous bead. • Too low welding current. • Too slow travel speed. • Too large weaving width. • Improper groove shape.
- 8. How to avoid Slag Inclusion • Completely remove slag from previous bead. • Use higher welding current. • Use higher travel speed. • Reduce weaving width • Properly modify groove angle and root gap.
- 9. Why-Incomplete Penetration • Improper electrode • Too low welding current • Too fast or slow travel speed • Improper grooving and fixturing
- 10. How to avoid Incomplete Penetration • Select the electrode with better penetration. • Use proper welding current. • Properly adjust travel speed • Increase groove angle and root map. Moreover reduce root face.
- 11. Why-Crack • Bad electrode quality or damp electrode. • Too strong restraint for groove. • Base metal with too high sulphur content • Without preheating or post heating
- 12. How to avoid Crack • Use proper electrode and be ware of drying. • Modify groove design, beware of welding sequence and proceed PWHT. • Avoid using improper base metal • Proceed preheating or PWHT
- 13. Why-Distortion • Excessive layers or faulty joint preparation • Improper bead sequence • Improper set-up and fixture • Excessive weld size • Over- heating of base metal.
- 14. How to avoid Distortion • Tack weld parts with allowance for distrotion. • Use proper bead sequencing • Tack or clamp part sequence • Make welds to specify size
- 15. Why-Bum-Up • Too large welding current when groove welding • Too large root gap caused by improper grovee shape.
- 16. How to avoid Bum-Up • Reduce welding current. • Reduce root gap.
- 17. Why-Arc Blow • Unstable magnetic field during welding. • Excessive mahnetism in part or fixture.
- 18. How to avoid Arc Blow • Use AC current • Reduce welding current and arc length. • Change location of thr work connection on workpiece.
- 19. Why-Pit • Improper electrode • Damp electrode • Too fast base metal cooling rate • Unclean electrode and segregation of base metal • Too high carbon and manganese content for weld metal
- 20. How to avoid Pit • Use proper electrode • Use dried electrode • Reduce travel speed and proceed preheating and post heating • Use good low hydrogen type electrode.
- 21. Why-Over Lap • Too low welding current • Too slow travel speed
- 22. What to do for • Properly use welding current. • Properly use travel speed.
- 23. THANK YOU BY KEERTHIVASAN. R 2018229036