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Manual Metal Arc Welding Presentation


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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:

Arc Welding Safety 4 What are the principle hazards associated with SMAW? What can be done to manage the hazards associated with SMAW?

SMAW Process:

5 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.

What’s the purpose of slag?:

What’s the purpose of slag? 6


Equipment 7 Polarity switch Power cord Electrode holder Electrode Base metal Ground clamp G. Electrode lead H. Ground lead I. Amperage scale J. Amperage adjustment K. On/Off switch L. Welder case


8 Equipment

Six (6) Common SMAW Power Supplies:

Six (6) Common SMAW Power Supplies 9 Type Current Transformer Transformer with rectifier Generator Alternator Alternator with rectifier Inverter What welding current is available from each of these power supplies?

Initiating The Arc:

Initiating The Arc 10 List the six (6) steps for initiating the arc.

Brushing Method:

11 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 .

Tapping Method:

Tapping Method 12 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.

Five (5) Factors Controlling the Quality of SMAW Welds:

Five (5) Factors Controlling the Quality of SMAW Welds 13 Heat Electrode Electrode angle Arc length Speed of travel

1. Heat:

1. Heat 14 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? What are the characteristics of excessive heat when completing a SMAW joint? What are the characteristics of insufficient heat when completing a SMAW weld?

2. Electrodes:

2. Electrodes 15 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?

American Welding Society (AWS) Classification System:

American Welding Society (AWS) Classification System 16 The AWS system designates: tensile strength, weld position coating (flux) current. The primary difference in the performance of electrodes is the flux.

Arc Welding Electrode Flux:

Arc Welding Electrode Flux 17 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:

Seven (7) Classifications of Flux constituents 18 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, manganese, calcium fluoride and cellulose calcium carbonates, rutile, silica, talc nickel and iron powders, sodium, feldspar, clay, talc ferroalloys, ferrosilicon, iron powder manganese, iron, rutile, alumina, silica, calcium fluoride ferrow alloys, iron and nickel powders waterglass, mica organic binders

Electrode Performance Groups:

19 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:

20 Selecting Electrode Size What factors determine the optimum diameter of electrode that should be used? ROT: the diameter of the electrode should not exceed the thickness of the metal. Is it permissible to use more than one diameter of electrode to complete a joint? Yes Explain!

Electrode Storage:

21 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 under-bead cracking in alloy and medium carbon steels by reducing 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 does that mean? What is the primary source of hydrogen in the weld pool?

3. Electrode Angle:

22 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 = 15 o from vertical or 75 o from the work. Butt joint = 15 o from vertical or 75 o from the work. Lap joint = 45 o . T joint = 45 o . Corner = 15 o from vertical or 75 o from the work. What is the effect of incorrect travel angle?

Electrode Angle-cont…:

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

4. Arc Length:

4. Arc Length 24 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? What are the characteristics of a weld completed with insufficient arc length?

5. Speed of Travel:

5. Speed of Travel 25 The speed of travel is measured in inches per minute. What factors determine the best speed of travel?

5. Speed of Travel-cont…:

26 5. Speed of Travel-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 in 3 /min .)

5. Speed of Travel-cont…:

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

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