Smaw

Shielded Metal Arc Welding By: Charles Lu Derwin Li Andrew Tan Renz Raquion Emil Wang

Shielded Metal Arc Welding Also known as: 

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Manual Metal Arc Welding (MMAW) Flux shielded arc welding Stick welding

 Manual

arc welding process that uses a consumable electrode coated in flux to lay the weld.  An electric current, in the form of either alternating current or direct current from a welding power supply, is used to form an electric arc between the electrode and the metals to be joined.  As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination.

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Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's most popular welding processes. It dominates other welding processes in the maintenance and repair industry, and though flux-cored arc welding is growing in popularity, SMAW continues to be used extensively in the construction of steel structures and in industrial fabrication. The process is used primarily to weld iron and steels (including stainless steel) but aluminium, nickel and copper alloys can also be welded with this method.

Development  1800

– Henry Davy – electric arc  1881 – Auguste de Meritens – carbon torch  1887 – Nikolay Benardos – electrode holder  1888 – Nikolay Slavyanov – metal electrode  1890 – C.L. Coffin – welding using electrode

Characteristics of SMAW  Uses

a electrode rod that is quickly consumed,  Uses equipment that is simple, inexpensive, and highly portable,  Uses an electrode that provides and regulates its own flux,

Characteristics of SMAW  Provides

all position flexibility,  Is less sensitive to wind or drafts,  Yields a weld with a variable quality and appearance based on operator skill,

EQUIPMENTS

Power Supply

Electrode

SMAW Set-Up and Operation

SMAW Set-Up

SMAW Operation

Striking An Arc: Scratch Start Technique

Striking An Arc: Tapping Technique

Guidelines:  Heat

of electric arc brings work to be welded and consumable electrode to molten state 

Heat intensity: as high at 9,000ºF at center

 Thicker

electrodes requires larger current, hence, bigger amount of heat.  Follow recommendations of the electrode manufacturer when setting weld amperage

Proper SMAW Operation  Make

sure workpiece is clean.  Place ground clamp as close to the weld as possible.  Observe proper arc length and electrode angle.  For best result, travel at a uniform speed, and feed the electrode downward at a constant rate as it melts.

Arc Length  Is

the distance between the electrode and the workpiece.  Should be the same as the diameter of the electrode 

1/8” electrode should have an arc length of 1/8 inch (3mm)

 Correct

arc length would give a sharp, crackling sound. (like frying bacon)

Electrode Angle for Groove Welds

Electrode Angle for Fillet Welds

Welding Defects and Troubleshooting

Porosity  small

cavities or holes resulting from gas pockets in weld metal.  can potentially weaken the weld Possible causes

Corrective actions

Arc length too long.

Reduce arc length.

Dirty workpiece.

Remove all grease, oil, moisture, rust, paint, coatings, slag, and dirt from work surface before welding.

Damp electrode.

Use dry electrode.

Excessive Spatter  scattering

of molten metal particles that cool to solid form near weld bead.  damages its appearance and increases cleaning costs Possible Causes

Corrective Actions

Amperage too high for electrode.

Decrease amperage or select larger electrode.

Arc length too long or voltage too high.

Reduce arc length or voltage.

Incomplete Fusion 

failure of weld metal to fuse completely with base metal.

Possible Causes

Corrective Actions

Insufficient heat input.

Increase amperage. Select larger electrode.

Improper welding technique.

* Adjust work angle or widen groove to access bottom during welding. * Momentarily hold arc on groove side walls when using weaving technique. * Keep arc on leading edge of weld puddle.

Dirty workpiece.

Remove all grease, oil, moisture, rust, paint, coatings, slag, and dirt from work surface before welding.

Lack Of Penetration  Shallow

fusion between weld metal and base metal.

Possible Causes

Corrective Actions

Improper joint preparation.

Material too thick. Joint preparation and design must provide access to bottom of groove.

Improper weld technique.

* Keep arc on leading edge of weld puddle. * Reduce travel speed.

Insufficient heat input. Increase amperage. Select larger electrode.

Excessive Penetration  weld

metal melting through base metal and hanging underneath weld.

Possible Causes

Corrective Actions

Excessive heat input.

Select lower amperage. Use smaller electrode.

Improper weld technique.

Adjust travel speed.

Burn-Through  weld

metal melting completely through base metal resulting in holes where no metal remains.

Possible Causes

Corrective Actions

Excessive heat input.

Select lower amperage. Use smaller electrode. Increase and/or maintain steady travel speed.

Waviness Of Bead  weld

metal that is not parallel and does not cover joint formed by base metal. Possible Causes

Corrective Actions

Unsteady hand.

Use two hands. Practice technique.

Distortion  contraction

of weld metal during welding that forces base metal to move.

Possible Causes Corrective Actions Excessive heat input.

* Use restraint (clamp) to hold base metal in position. * Make tack welds along joint before starting welding operation. * Select lower amperage for electrode. * Increase travel speed. * Weld in small segments and allow cooling between welds.

Good

Amps too low

Amps too high

Arc Length too short

Arc length Travel speed too too long slow

Travel speed too fast

Hazards & Safety Precautions

Hazards 

Electric Shock can kill

Touching live electrical parts can cause fatal shocks or severe burns. The electrode and work circuit is electrically live whenever the output is on. 

Hot parts can burn

Do not touch hot parts bare handed. Allow cooling period before working on equipment.

Hazards 

Fumes and Gases can be hazardous

Welding produces fumes and gases. Breathing these fumes and gases can be hazardous to your health.

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Welding can cause fire or explosion

Welding on closed containers, such as tanks, drums, or pipes, can cause them to blow up. Sparks can fly off from the welding arc. The flying sparks, hot workpiece, and hot equipment can cause fires and burns.

Hazards 

Arc rays can burn eyes and skin.

Arc rays from the welding process produce intense visible and invisible (ultraviolet and infrared) rays that can burn eyes and skin. Sparks fly off from the weld. 

Electric and magnetic fields (EMF) can affect Implanted Medical Devices.

Implanted Medical Device wearers should consult their doctor and the device manufacturer before going near arc welding, spot welding, gouging, plasma arc cutting, or induction heating operations.

Hazards 

Overuse can cause overheating

Allow cooling period. Reduce current or reduce duty cycle before starting to weld again. Do not block or filter airflow to unit. 

Arc welding can cause interference.

Electromagnetic energy can interfere with sensitive electronic equipment such as computers and computerdriven equipment such as robots.

Safety precautions      

Cover all skin to prevent Radiation burns Cover hair to prevent sparks setting hair on fire Wear ear plugs to protect from noise and burning ear drums with sparks Never look at the arc with the naked eye. Wear safety glasses at all times Do not strike an arc or weld until you are sure those in the vicinity have protective equipment or will look in the other direction.

Safety precautions  

Do not weld around combustible or flammable materials. Do not pick up hot metal with the hands. (NOTE) Use a pair of pliers

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Do not weld in confined places without ventilation Always turn off main switch or disconnect plug when checking over a welder. Do not leave electrode holder on the welding table or in contact with grounded metal. Do not use worn or frayed cables.

Safety precautions  Stand  Keep  Keep

on dry footing when welding. area around welder clean.

tools and metals in proper location.

Advantages and Disadvantages of SMAW

Advantages  Cheap  Versatile  Simple

 Portable  Less

sensitive to wind  Welds in almost any position  Electrode available to match properties and strength of metals

Disadvantages  Smoke

is hazardous to the health  Weld depends on the user’s skill  Need to remove slag immediately after  Doesn’t weld softer metals  Low productivity

Reference(s):     

Cary, H., Helzer, S., Jeffus, L., Weman, K. (n.d.). SMAW. (PDF document). Retrieved from: google.com. http://en.wikipedia.org/wiki/Shielded_metal_arc_welding (2013). Guidelines For Shielded Metal Arc Welding (SMAW). (PDF document). Retrieved from: www.MillerWelds.com EWF. (n.d.). Manual Metal Arc welding. (PDF document). Retrieved from: google.com. Sacks, Bohnart. (n.d.). Shielded Metal Arc Welding Principles. (PPT document). Retrieved from: google.com