Smaw

Charles Lu Andrew Tan Renz Raquion Emil Wang Derwin Li

FUNWELD EG

Shielded Metal Arc Welding Introduction: Shielded metal arc welding (SMAW), also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding or informally as stick welding, is a 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. 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: After the discovery of the electric arc in 1800 by Humphry Davy there was little development in electrical welding until Auguste de Méritens developed a carbon arc torch, patented in 1881Nikolay Benardos developed carbon arc welding, obtaining patents from 1887 showing a rudimentary electrode holder. In 1888 consumable metal electrode was invented by Nikolay Slavyanov. Later in 1890 C. L. Coffin received U.S. Patent 428,459 for his arc welding method that utilized a metal electrode. The process, like SMAW, deposited melted electrode metal into the weld as filler.

Characteristics of SMAW:      

Uses an 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 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: Shielded metal arc welding equipment typically consists of a constant current welding power supply and an electrode, with an electrode holder, a ground clamp, and welding cables (also known as welding leads) connecting the two.

Set Up and Operation: I.

Set Up A. The (+) should be plugged to the electrode holder and the ground (-) should be clamped to the work piece to obtain a complete circuit.

II.

Operation A. Guidelines i. Heat of electric arc brings work to be welded and consumable electrode to molten state ii. Heat intensity: as high at 9,000ºF at center iii. Thicker electrodes require larger current, hence, bigger amount of heat. iv. Follow recommendations of the electrode manufacturer when setting weld amperage B. Proper SMAW Operation i. Make sure workpiece is clean. ii. Place ground clamp as close to the weld as possible. iii. Observe proper arc length and electrode angle. iv. For best result, travel at a uniform speed, and feed the electrode downward at a constant rate as it melts. C. Arc Length i. Is the distance between the electrode and the workpiece. ii. Should be the same as the diameter of the electrode iii. 1/8” electrode should have an arc length of 1/8 inch (3mm) iv. Correct arc length would give a sharp, crackling sound. (like frying bacon) D. Striking An Arc i. Scratch Start Technique - Drag electrode across workpiece like striking a match; immediately lift electrode slightly after touching work. If arc goes out, electrode was lifted too high. If electrode sticks to workpiece, use a quick twist to free it. ii. Tapping Technique - Bring electrode straight down to workpiece; then lift slightly to start arc. If arc goes out, electrode was lifted too high. If electrode sticks to workpiece, use a quick twist to free it. E. Electrode Angle i. Groove Weld

ii. Fillet Weld

Welding Defects and Troubleshooting The most common quality problems associated with SMAW include porosity, excessive spatter, incomplete fusion, lack of penetration, excessive penetration, burn-through, waviness of bead and distortion. 1. Porosity is the state where small cavities or holes are developed resulting from gas pockets in weld metal. It is a serious concern since it can potentially weaken the weld. The possible causes of porosity are excessively long arc length, dirty workpiece and damp electrode. The corrective actions that can be undertaken are to reduce the arc length, remove all grease, oil, moisture, rust, paint, coatings, slag, and dirt from work surface before welding and use dry electrode. 2. Excessive spatter is the scattering of molten metal particles that cool to solid form near weld bead. It damages the appearance and increases cleaning costs. The possible causes are amperage too high for electrode and arc length too long or voltage too high. The corrective actions are to decrease amperage or select larger electrode and to reduce arc length or voltage. 3. Incomplete fusion is the failure of weld metal to fuse completely with base metal. The possible causes of incomplete fusion are insufficient heat input, improper welding technique and dirty workpiece. The corrective actions are to increase amperage and select larger electrode. 4. Lack of Penetration is the shallow fusion between weld metal and base metal. The possible causes are improper joint preparation, improper weld technique and insufficient heat input. The corrective actions are to reduce the thickness of the material, reduce travel speed and to select larger electrode and increase amperage. 5. Excessive Penetration happens when the weld metal melts through the base metal. The possible causes are excessive heat input and improper weld technique. The corrective actions are to select lower amperage and use smaller electrode and to adjust travel speed.

6. Burn-Through happens when weld metal completely melts through base metal resulting in holes where no metal remains. The possible cause is excessive heat input. The corrective actions are to select lower amperage, use smaller electrode and increase or maintain steady travel speed. 7. Waviness of Bead is the state where the weld metal is not parallel and does not cover joint formed by base metal. The possible cause is unsteady hand. The corrective actions are to use two hands and to practice. 8. Distortion is the contraction of weld metal during welding that forces base metal to move. The possible cause is excessive heat input. The corrective actions are to 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 and weld in small segments and allow cooling between welds.

SMAW Hazards: 1. 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. The input power circuit and machine internal circuits are also live when power is on. In semiautomatic or automatic wire welding, the wire, wire reel, drive roll housing, and all metal parts touching the welding wire are electrically live. Incorrectly installed or improperly grounded equipment is a hazard.  

Do not touch live electrical parts. Wear dry, hole-free insulating gloves and body protection.
D Insulate yourself from work and ground using dry insulating mats or covers big enough to prevent any physical contact with the work or ground.

2. Hot parts can burn  Do not touch hot parts bare handed. Allow cooling period before working on equipment.  To handle hot parts, use proper tools and/or wear heavy, insulated welding gloves and clothing to prevent burns. 3. Fumes and Gases can be hazardous  Welding produces fumes and gases. Breathing these fumes and gases can be hazardous to your health.  Keep your head out of the fumes. Do not breathe the fumes.
D If inside, ventilate the area and/or use local forced ventilation at the arc to remove welding fumes and gases.  If ventilation is poor, wear an approved air-supplied respirator.  Work in a confined space only if it is well ventilated, or while wearing an air-supplied respirator. Always have a trained watch- person nearby. Welding fumes and gases can displace air and lower the oxygen level causing injury or death. Be sure the breathing air is safe.

4. 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. Accidental contact of electrode to metal objects can cause sparks, explosion, overheating, or fire. Check and be sure the area is safe before doing any welding.     

Remove all flammables within 35 ft (10.7 m) of the welding arc. If this is not possible, tightly cover them with approved covers. Do not weld where flying sparks can strike flammable material. Protect yourself and others from flying sparks and hot metal. Be alert that welding sparks and hot materials from welding can easily go through small cracks and openings to adjacent areas. Watch for fire, and keep a fire extinguisher nearby.

5. 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. 

Wear an approved welding helmet fitted with a proper shade of filter lenses to protect your face and eyes from arc rays and sparks when welding or watching

6. Electric and magnetic fields (EMF) can affect Implanted Medical Devices  Wearers of Pacemakers and other Implanted Medical Devices should keep away.  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. 7. Overuse can cause overheating  Allow cooling period; follow rated duty cycle.  Reduce current or reduce duty cycle before starting to weld again.  Do not block or filter airflow to unit. 8. Arc welding can cause interference  Electromagnetic energy can interfere with sensitive electronic equipment such as computers and computer-driven equipment such as robots.  Be sure all equipment in the welding area is electromagnetically compatible.  To reduce possible interference, keep weld cables as short as possible, close together, and down low, such as on the floor.  Locate welding operation 100 meters from any sensitive elec- tronic equipment.  Be sure this welding machine is installed and grounded according to this manual.

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.  Do not weld around combustible or flammable materials.  Do not pick up hot metal with the hands. (NOTE) Use a pair of pliers  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.  Stand on dry footing when welding.  Keep area around welder clean.  Keep tools and metals in proper location.

Advantages of SMAW: 1. Cheap - This type of welding is considerably cheap compared to other welding machines. 2. Versatile - It’s versatile because of the simplicity of the process and operation. 3. Simple - It’s simple because all you need is the machine and electrode to be able to operate. 4. Portable - The machine of SMAW is considerably smaller when compared to other welding machines. 5. Less sensitive to wind - The arc is less sensitive to wind which would come in handy when operated in an open space facility.

6. Welds in almost any position - The SMAW welds in almost any position which would come in handy because some welding processes are limited to certain degrees. 7. Electrode available to match properties and strength of metals - Various electrodes can be chosen in order to match the properties of the two pieces of metals being welded together.

Disadvantages of SMAW: 1. Smoke is hazardous to the health - Since the smoke released by SMAW is hazardous to the health, good ventilation is required to keep the welder safe. 2. Weld depends on the user’s skill - The weld depends on the user’s skill, therefore a beginner may not be able to make a good weld. 3. Need to remove slag immediately after - The slag absorbs moisture, so removing it immediately is recommended so the metal doesn’t absorb moisture. 4. Doesn’t weld softer metals - SMAW generated a huge amount of heat and may burn through softer metals. 5. Low productivity - SMAW takes time for the electrode to weld into the work piece so it has a low productivity rate.

References:     

Cary, H., Helzer, S., Jeffus, L., Weman, K. (n.d.). SMAW. (PDF document). Retrieved from: google.com. (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 http://en.wikipedia.org/wiki/Shielded_metal_arc_welding