M.M.A [SMAW]

M.M.A [SMAW] :

Power source is preferred in site work is diesel [or] petrol driven generator.

Power source :

• Open circuit voltage 50 to 90 v.
• Voltage 20 to 30 v
• Ampere [or] current 30-350Amps.

Current [ amperage] :

• Current low : poor fusion, penetration.
• Current high: excessive penetration, burn through.
• Ocv should not exceed 100 v & usually in 50-90 v if exceed to reduce risk of fatality; electronic equipment may damage.
• Arc blow : the deflection of the arc from its normal path due to magnetic forces.

 

TRAVEL SPEED HIGH                                              TRAVEL SPEED LOW

1) Low current         .                                     1) High current.

2) Low heat input.                                           2) High heat input.

3) High hardness.                                            3) Low toughness.

4) Poor weld profile.                                        4) Over lap.

5) Lack of penetration &                                   5) excessive penetration.

Fusion.

6) PG down position [vertical].                           6) PF vertical up position.

7) Under cut.                                                  7) Burn through.

8) Difficult to slag removal.                               8) Wide weld bead counter.

9) Linear misalignment.                                    9) Spattern.

Rutile:

1. Electrode titanium oxide {rutile}.
2. Power source AC & DC, all positions.
3. Horizontal and vertical, PB position [fillet joint].
4. Low OCV 50 V.
5. Slag is viscous.
6. Hydrogen content >15 ml/100gm.
7. Medium [moderate] weld metal mechanical properties.
8.  Electrode E-6013.

Basic:

1. Electrode calcium carbonate & calcium fluoride.
2. Power source is only DC, all positions.
3. Vertical & horizontal, PD position [fillet joint] over head.
4. Backing is required: 1hr 350°c mother oven [or] backing oven.

2hr 150°c holding oven.

4hr 70°c portable [or] quivers oven.

1. Low hydrogen weld metal.
2. Hydrogen level <5 ml/100gm.
3. Good mechanical properties.
4. Electrode E-7018.

Cellulosic:

1. Electrode is cellulosic.
2. Power source is DC.
3. PG position; vertical down.
4. Stove pipe welding technique.
5. Cross country pipe line root should be done by cellulosic, hot pass by basic electrode.
6. High hydrogen level >25 ml/100gm.
7. High hydrogen content.
8. Electrode E-6010.

Typical defects:

1. • Slag inclusion.
   • Arc strikes.
   • Porosity.
   • Under cut.
   • Shape defects, [overlap, excessive root penetration  …etc.,]