Shielded Metal Arc Welding TSM 233: Unit 5 Shielded Metal Arc Welding

What is SMAW? The SMAW process is accomplished by producing an electric arc between the base metal and a consumable flux-covered electrode.

What are the basic components of the SMAW process? Welder Leads Electrode holder Ground clamp Electrode

What are some specific safety precautions for SMAW? Produces intense ultra-violet rays. Need to use number 10 or 12 shade lens. U-V rays burn the outer layers of the skin/eyes. Electrical shock. Toxic fumes/smoke. Heat exposure.

How does the SMAW process produce heat? Volt –electrical pressure Amperage – amount of electricity Resistance – produces heat. Welder works at a lower voltage, pushes large amounts of electricity, across a gap. Voltage drops, amperage increases as the arc length decreases.

What are the key variables when SMAW? Type of metal, thickness, weld-ability. Type of weld, characteristics, position. Types of electrodes. Types of electrical current, amperage range. Welder (person) characteristics, speed, skill, electrode angles.

What are the different types of SMAW welders? Two basic types: Constant current – preset the amperage, used mostly for SMAW and GTAW (TIG) Constant potential (voltage), preset the voltage, GMAW (MIG) and FCAW (Flux Core)

AC –alternating current DC – direct current What are the characteristics of the different types of electrical current used for SMAW? AC –alternating current DC – direct current DCEN – electrode negative, straight polarity, greater deposit of metal and thinner metal. (electricity flows from the (-) negative pole to the positive (+) pole DCEP – reverse polarity, electrode positive, heat is greater at the metal, deeper penetration.

How are different types of electricity produced by the welders? AC is easier to get from electrical service, DC is easier to produce from a generator. Generators – produces the electricity, need an alternator to produce AC. To get DC from an alternator, convert the AC to DC. Static Converted power Transformer – very common, most lighter duty welders, changes the voltage/amperage. Rectifier – converts AC to DC. Inverter – converts the 60 mHz to High Frequency, 1000 – 50,000mHz., actually…. AC to DC to HFAC to Transformer to DC

Factors to consider when selecting SMAW welders. Input Voltage. Whether need AC and/or DC. Duty Cycle: the ratio of welding time to total time. Whether planning to also use the welder for GTAW.

How are welders classified? Welders are classified by their duty cycles for the rated output. Class I: 60%, 80% and 100% duty cycles. Class II: 30%, 40%, and 50% duty cycles. Class III: 20% duty cycle

What types of metals can we SMAW? Most all common metals, except Magnesium. Aluminum and Copper alloys are very difficult SMAW is still the most common, widely used type of welding process.

What to consider when selecting electrodes? type of base metal weld groove design required tensile strength position of the weld joint the rate of desired weld deposit the type of electrical current available

How do we identify the different types of electrodes? E – Electrode 60 – tensile strength in 1,000# 1 – position (1=all, 2=flat/horizontal only) 1 – special characteristics, flux, current.

What are some of the different types of electrodes? Low-Alloy Steel Covered Electrodes Low Hydrogen Electrodes Stainless Steel Electrodes Cast Iron Electrodes High Tensile Strength Electrodes Aluminum Electrodes Copper and Copper Alloy Electrodes Hard-facing/surfacing Electrodes

Low-Alloy Steel Covered Electrodes E6010 High cellulose, sodium DCEP E6011 High cellulose, potassium AC/DCEP E6012 High titania, sodium AC/DCEN E6013 High titania, potassium AC/DC E7014 Iron powder, titania AC/DC E7024 Iron powder, titania AC/DC Suffixes: A,B…G.

Low Hydrogen Electrodes E7015 Low hydrogen, sodium DCEP E7016 Low hydrogen, potassium AC/DCEP E7018 Low hydrogen, potassium, iron powder AC/DCEP E7028 Low hydrogen, potassium, iron powder AC/DCEP

Why use “stringer” type beads and “weave” type bead? Stringer Beads, welded with little side to side motion Weave beads use a deliberate side to side motion. Stringer beads: easier to perform generally a smoother finish. Less metal mass, therefore less potential distortion generally less penetration, less overall strength Weave beads: generally greater strength. More metal deposited Potentially deeper penetration. A “back and forth” forward motion is also often used to increase penetration and to help “freeze” the weld puddle An “in and out” motion is used to help freeze puddle, used for out-of-position welds, called a “whip” motion.

When should we groove the metal for welding? Grooving is used to help insure deeper weld penetration. Recommended when the base metals are equal to, or greater than twice the thickness of the electrode core wire diameter. Generally a 60 degree angle, not less than 45 degrees. Do not groove to a sharp point, leave a “root face” equal to the diameter of the electrode core wire. Use multiple passes: first pass is the “root pass” the last pass is a “wash pass” which uses a wide weave pattern to cover the pervious passes.

How do we store electrodes? Moisture and extreme temperature changes can harm/destroy electrodes. Store in a dry, air-tight environment. Commercial electrode storage cabinets are available, provide a warm, low humidity environment. Low hydrogen electrodes are very sensitive to moisture, and must be stored in a continuous dry environment. Heating electrodes in an oven above 212 degrees can help “dry” and restore electrodes.

What is “arc blow” and what can we do to reduce it? Arc Blow is caused by a distorted magnetic attraction of the electric arc to the base metal. The arc “curves” to one side. Or “jumps” from side to side in an inconsistent pattern. Generally a problem when using DC welding current Causes metal to be deposited to one side of the weld. How to control? Switch to AC. Move the ground clamp Use intermittent welds Use a weave pattern.

What is a weld “undercut” and what can we do to reduce it? Undercut is when the weld has a depressed area between the bead and base metal. Can be caused by: electrode side angle too high amperage poor weave pattern wrong type of electrode, too “hot” base metals are too dissimilar

Weld Heat Affected Zone

Types of Groove Welds

Welding Positions