SMAW Welding

Definition Shield Metal Arc Welding is an arc welding process that uses a consumable electrode to initiate the arc and provide the filler material.

Arc Welding Safety What are the principle hazards associated with SMAW? What can be done to manage the hazards associated with SMAW? Hot metal. Harmful rays Fire Burns Explosion tripping/falling _______ Use appropriate PPE Inspect equipment Pliers shaded lens welding apparel

What’s the purpose of slag? SMAW Process The arc temperature over 9,000 oF melts the base metal, the wire core and the coating on the electrode. The high temperature causes some of the ingredients in the flux to form a gaseous shield. The electric energy is provided by a power source. As the weld cools slag forms on top of the weld puddle. The slag contains the impurities that were in the weld pool and it retards the cooling rate. What’s the purpose of slag?

Equipment Polarity switch Power cord Electrode holder Electrode Base metal Ground clamp Electrode lead Ground lead Amperage scale Amperage adjustment On/Off switch Welder case

Six (6) Common SMAW Power Supplies What welding current is available from each of these power supplies? Type Current Transformer Transformer with rectifier Generator Alternator Alternator with rectifier Inverter Transformer Ac Transformer-rectifier AC & DC Generator DC Alternator AC Alternator-rectifier AC and DC Inverter AC and DC

Initiating The Arc List the six (6) steps for initiating the arc. Select the best electrode Set the welder current Turn on welder Warn bystanders Lower helmet Start arc (two methods) Brushing Tapping

Brushing Method Hold end of electrode about 1/4 - 1/2 inch above the surface. Lower helmet Gently brush surface of the metal with the end of the electrode. When arc starts, lift electrode 1/8 inch. If electrode sticks, twist it back and forth. If it does not break loose, release electrode from electrode holder. Do not shut off the welder with the electrode stuck to the metal. Burn out the switch Why?

Tapping Method Set up welder Hold the electrode at the travel angle and 1/4 - 1/2 inch above the metal. Quickly lower the electrode until it touches the metal and then lift it 1/8 inch. Recommended method for E7018 electrode because the flux must be broken off before the arc will start.

Five (5) Factors Controlling the Quality of SMAW Welds Heat Electrode Electrode angle Arc length Speed of travel

Five (5) Factors 1. Heat The arc welder must produce sufficient heat (BTU’s) to melt the electrode and the base metal to the desired depth. How is the amount of heat at the weld controlled? What factors determine the amount of heat required for a weld? Adjusting the amperage Thickness of the metal Type of joint, Electrode type Electrode diameter Weld position

Five (5) Factors 1. Heat – cont. What are the characteristics of excessive heat when completing a SMAW joint? What are the characteristics of insufficient heat when completing a SMAW weld? Electrode easier to start Excessive penetration (burn through) Excessive bead width Excessive splatter Electrode overheating Hard to start Reduced penetration Narrow bead Coarse ripples

Five (5) Factors 2. Electrodes What are the two (2) primary requirements for an SMAW electrode? What metals can be welding with the SMAW process? How are SMAW electrodes classified? Must be compatible with base metal Must be correct size. Carbon steels Low alloy steels Corrosion resisting steels Cast irons Aluminum and alloys Copper and alloys Nickel and alloys American Welding Society system and grouping

American Welding Society (AWS) Classification System The AWS system designates: tensile strength, weld position coating (flux) current. The primary difference in the performance of electrodes is the flux. Manufactures may and do use their own numbering system and sell electrodes that do not use the AWS system.

Arc Welding Electrode Flux Flux: A material used during arc welding, brazing or braze welding to clean the surfaces of the joint chemically, to prevent atmospheric oxidation and to reduce impurities and/or float them to the surface. (British Standard 499) SMAW fluxes are naturally occurring minerals. The quality, and cost, of the flux is directly related to the amount of resources the manufacture invests purifying the minerals for the flux.

Seven (7) Classifications of Flux constituents calcium, manganese, calcium fluoride and cellulose Protection from atmospheric contamination & slag formers Fluxing agents Arc initiators and stabilizers Deoxidizes Physical properties of the flux Fillers and metallic additions Binders and flux strength improvers calcium carbonates, rutile, silica, talc nickel and iron powders, sodium, feldspar, clay, talc ferroalloys, ferrosilicon, iron powder manganese, iron, rutile, alumina, silica, calcium fluoride waterglass, mica organic binders ferrow alloys, iron and nickel powders

Electrode Performance Groups Fast-freeze Mild steel Quick solidification of weld pool Deep penetrating Recommended for out of position welds Deep penetrating arc Fast-fill Highest deposition rate Stable arc Thick flux Flat position and horizontal laps only Fill-freeze General purpose electrodes Characteristics of fast-freeze and fast-fill Low hydrogen Welding characteristics of fill-freeze Designed for medium carbon and alloy steels

Selecting Electrode Size What factors determine the optimum diameter of electrode that should be used? Is it permissible to use more than one diameter of electrode to complete a joint? Yes Explain! thickness of the base metal, welding position capacity of the welding power supply Small diameter for route pass—larger for filler passes. ROT: the diameter of the electrode should not exceed the thickness of the metal.

Electrode Storage Electrodes are damaged by rough treatment, temperature extremes and moisture. The should be kept in their original container until used. They should be stored in a heated cabinet that maintains them at a constant temperature. The storage of low hydrogen electrodes is very critical. Designed to reduce underbead cracking in alloy and medium carbon steels by reducing the the amount of hydrogen in the weld pool. The flux is hydroscopic-- Moisture in the flux also causes excessive gasses to develop in the weld pool and causes a defect in the weld called worm holes. What is the primary source of hydrogen in the weld pool? What does that mean? Water attracts moisture (H2O).

Five (5) Factors 3. Electrode Angle Two angles are important: Travel Work The travel angle is the angle of the electrode parallel to the joint. The correct travel angle must be used for each joint. Beads = 15o from vertical or 75o from the work. Butt joint = 15o from vertical or 75o from the work. Lap joint = 45o. T joint = 45o. Corner = 15o from vertical or 75o from the work. Excessive—poor puddle geometry Insufficient—reduced penetration, tall narrow bead What is the effect of incorrect travel angle?

Five (5) Factors Electrode Angle-cont. The work angle is the angle of the electrode perpendicular to the joint. The appropriate angle must be used for each joint. Beads = 90o Butt joint = 90o Lap joint = 45o T joint = 45o Corner = 90o Can you think of a situation where the travel angle should be modified? When completing a joint with metal of different thickness.

Five (5) Factors 4. Arc Length The arc length is the distance from the metal part of the electrode to the weld puddle. The best arc length is not a fixed distance, but should be approximately equal to the diameter of the electrode. What are the characteristics of a weld completed with excessive arc length? Excessive length Excessive spatter Reduced penetration Poor quality weld Electrode sticks Narrow weld What are the characteristics of a weld completed with insufficient arc length?

Five (5) Factors 5. Speed of Travel The speed of travel is measured in inches per minute. What factors determine the best speed of travel? The size of the joint, The type of electrode The size of the electrode The current setting on the machine Deposition rate of the electrode (cubic inches per minute)

Five (5) Factors 5. Speed-cont. The ideal speed can be calculated using the volume of the joint and the deposition rate of the electrode. Step one: determine the area of the weld. (Assuming 1/16 inch penetration.) Step Two: knowing the deposition rate of the electrode, determine the welding speed. (Deposition rate = 2.5 in3/min.)

Five (5) Factors 5. Speed-cont. The correct welding speed is indicated by the shape of the ripples. Too slow = excessive width, excessive penetration Too fast = narrower width, elongated ripple pattern, shallow penetration. Recommended = width 2-3 times diameter of electrode, uniform ripple pattern, full penetration.

SMAW Joints

Square Groove A butt joint can be completed with a groove welded on metal up to 1/8 inch thick with a single pass on one side, with no root opening. Electrode manipulation should only be used to prevent burning through.

Square Groove Thicker Metal A groove weld on metal up to 1/4 inch thick can be welded with a single pass on one side but, if possible, it should be completed with a single pass on both sides. Metal this thick requires a root opening to achieve adequate penetration. Electrode manipulation will reduce penetration.

Single V Groove Weld Butt joints on metal greater than 1/4 inch thick require joint preparation. Note that the groove does not extend all the way. A short distance, called the root face, is left undisturbed. Several different combinations of passes can be used to complete this joint. What determines that amount of joint preparation that must be done before welding? The purpose of the joint preparation is to compensate for not having sufficient amperage and electrode diameter. Note: this is the principle use of pattern beads.

T-Joints

Information In a T-joint the two welding surfaces are at an angle close to 90 degrees from each other. The welding side and number of passes uses depends on the thickness of the metal, the welding access and capacity of the power supply. Common joints include. Plane T T with joint gap Single preparation Double preparation

Plane T-Joint The plane T joint is very useful for thin metal. Can be completed at angles other than 90 degrees. Can be completed with metal of different thickness. The work angle must be changed to direct more heat to the thicker piece.

T-joint--Thicker Metal When the metal thickness exceeds 1/8 inch the recommendation is to gap the joint. Improves penetration May not be necessary if larger diameter electrode is used and sufficient amperage is available. The need for a joint gap varies with the type of electrode, but should not exceed 1/8 inch.

T-joint Single Single Bevel As with other joints, thicker metal must have joint preparation to achieve full penetration with smaller diameter electrodes. Several different preparations can be used. A popular one is the bevel. A bevel can be completed by grinding or cutting. The bevel joint can be completed with electrode manipulation or no electrode manipulation. When when electrode manipulation is used to fill the joint, the first pass should be a straight bead with no manipulation.

T-joint Double Bevel The double bevel T-joint is recommended for metal 1/2 inch thick and thicker. The root passes should be with not manipulation, but the filler passes can be completed with either straight beads or patterns beads. Alternating sides reduces distortion.

Weld Defects

Common SMAW Defects Hot cracks Undercutting Slag inclusions Porosity Caused by excessive contraction of the metal as it cools. Excessive bead size May also be found at the root of the weld. Slag inclusions Long arc Incomplete removal of slag on multipass welds. Undercutting improper welding parameters; particularly the travel speed and arc voltage. Porosity Atmospheric contamination or excess gas in the weld pool.

SMAW Weld Defects-cont. Incomplete fusion Toe cracks Microcracks Underbead cracks Toe Cracks Excessive heat and rapid cooling. Underbead cracks Excessive hydrogen in weld pool Microcracks Caused by stresses as weld cools. Incomplete fusion Incorrect welding parameters or welding techniques.

Questions