SHIELDED METAL ARC WELDING

PROCESS

Arc melts base metal and end of electrode.

Melted electrode crosses arc and is deposited in the weld pool to form weld bead.

Protective covering of electrode is melted which forms gas that protects weld from Oxygen & Nitrogen.

Slag is formed

DANGERS

Arc- heat, light, molten metal. Infrared & ultraviolet light

Surrounding area- clear area of combustible materials

Electrical Hazards- do not service welding machines, do not use near water

Ventilation- remove smoke and fumes, keep head out of fumes

TERMINOLOGY

Crater- depression at the end of a weld

DC- current that flows in only one direction

Flux- Material used to prevent oxides

Arc blow- arc wanders from intended course. Caused by magnetism

TERMINOLOGY

Reversed polarity- arrangement of arc welding leads where wok is negative pole and electrode is the positive pole

Straight polarity- arrangement of arc welding leads where work is the positive pole & electrode is the negative pole

EQUIPMENT

• Power source- constant

• Work clamp

• Electrode clamp

• Lead

EQUIPMENT

EQUIPMENT SET-UP

Protective equipment

Prepare machine

• Connect ground

• Set voltage

• Turn on machine

• Put electrode in holder

MACHINE SETTINGS

DC electrode negative (straight polarity)

105-110 amps

STRIKING THE ARC

• Can use a motion like a match

• Vertical tapping

If electrode gets stuck, break loose by quick twisting motion.

TECHNIQUE

Goal: Weld should be two electrode diameters wide

Arc length: one electrode diameter

Should sound like frying.

Similar to MIG welding. Slow circles! SLOW.

Work on uniformity

After completing weld you must clean with a chipping hammer and wire brush

TIPS

Hold electrode nearly vertical

Reverse direction of travel at end of bead to fill crater

Remove slag before doing another bead

TROUBLESHOOTING

Arc too long- uneven crackling sound, spatter, bead too wide

Arc too short- buzzing sound, electrode sticks to work, narrow bead

Travel speed too low- large bead, warped plate

Travel speed too fast- bead too narrow

ADVANTAGES

• Simple

• Cheap upfront cost

• Low cost

• Great penetration

• Change quickly between applications

• Many applications- electrode choices

• Mobile

• All positions

• Outdoors

DISADVANTAGES

• Doesn’t deposit as much metal as GMAW

• Frequent stops/starts (electrode length)

• Lacks efficiency- electrode stubs

• More difficult

• Time- slag removal

READING ELECTRODES