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Shielded Metal Arc Welding. Safe practices when Arc Welding Don’t stand in water Don’t stand in water Discard frayed cords and wires Discard frayed cords.

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Presentation on theme: "Shielded Metal Arc Welding. Safe practices when Arc Welding Don’t stand in water Don’t stand in water Discard frayed cords and wires Discard frayed cords."— Presentation transcript:

1 Shielded Metal Arc Welding

2 Safe practices when Arc Welding Don’t stand in water Don’t stand in water Discard frayed cords and wires Discard frayed cords and wires Keep flammable liquids away from heat Keep flammable liquids away from heat Don’t look at the arc with out a number 10 lens. Don’t look at the arc with out a number 10 lens.

3 Dress Code Wear properly fitted clothes. Wear properly fitted clothes. When welding, sleeves should be buttoned and gloves should be worn. When welding, sleeves should be buttoned and gloves should be worn. Wear boots or high top; Tightly laced shoes. Wear boots or high top; Tightly laced shoes. Do not wear loose clothing, shirt tails, and unbuttoned sleeves around power equipment. Do not wear loose clothing, shirt tails, and unbuttoned sleeves around power equipment. Do not wear clothes that you do not want to get dirty. Do not wear clothes that you do not want to get dirty.

4 The Arc When electrons jump through the air When electrons jump through the air When the pressure overcomes resistance When the pressure overcomes resistance V=A X R V=A X R

5

6 Parts of the Arc Arc stream Arc stream  Vaporized metal  Appears yellow  Liquid metal  Appears green Arc flame Arc flame  Natural gases surrounding arc stream  Pale red

7 Arc Control Length Length Angle Angle

8 Reverse Polarity (DCEP) Electrode positive Electrode positive Better penetrated welds Better penetrated welds

9 Straight Polarity (DCEN) Electrode Negative Electrode Negative Used when a high rate of filler metal is required. Used when a high rate of filler metal is required. EXX2X Electrodes EXX2X Electrodes

10 Alternating Current Stops and starts Stops and starts  Must have enough voltage restart arc Good penetration Good penetration Less expensive Less expensive

11 Classification of Steel Electrodes Electrode designated by “E” followed by a 4- or 5- digit number Electrode designated by “E” followed by a 4- or 5- digit number First two or three digits - minimum tensile strength as-welded deposited weld metal expressed in thousands of pounds per square inch (1000psi) First two or three digits - minimum tensile strength as-welded deposited weld metal expressed in thousands of pounds per square inch (1000psi)  E-60xx - 60,000psi TS  E-120xx - 120,000 psi TS

12 Classification of Steel Electrodes Third or fourth digit refers to the welding position. Third or fourth digit refers to the welding position.  E-xx1x - all positions  E-xx2x - flat and horizontal fillet positions  E-xx3x - flat position only

13 Classification cont. The fourth or fifth and last digit indicates the type of welding current and the type of flux covering The fourth or fifth and last digit indicates the type of welding current and the type of flux covering  E-xx10 - DC reverse polarity (electrode positive) only (cellulose sodium).  E-xx11 - AC or DC reverse polarity (cellulose potassium ) Fast freeze, cutting  E-xx13 - AC or DC straight polarity (titania potassium)

14 Factors of Electrode Selection Type of metal to be welded Type of metal to be welded Thickness of metal Thickness of metal Position of weld Position of weld Type of power (DC or AC) Type of power (DC or AC) Cleanliness of metal Cleanliness of metal Weld bead appearance desired Weld bead appearance desired

15 Flux Improves the performance in handling, storage and operation of the electrode Improves the performance in handling, storage and operation of the electrode Floats out impurities Floats out impurities Directs arc stream (stabilizer) Directs arc stream (stabilizer) Insulator Insulator Prevents oxidation (slag or gas) Prevents oxidation (slag or gas) Holds in heat Holds in heat Iron-powder improves striking ability and increases metal deposition rate Iron-powder improves striking ability and increases metal deposition rate

16 Striking the Arc Pecking Pecking  Touching  Touching electrode to the base metal and moving away to proper arc distance. Moving electrode in a vertical motion.  Can  Can start precisely where the weld is to be. Scratching  Moving electrode across base metal then moving electrode away to the proper arc distance.  Dose not work good in tight places

17 Common Striking Problems Sticking Sticking  Lift electrode and metal  Break electrode from metal  Remove electrode from clamp Arc is extinguished  The electrode is moved to far away from the base metal after the arc is struck.

18 Arc Length Longer arc Longer arc  Increases Resistance  Increases Voltage  Decreases Current  Decreases filler consumption Shorter arc  Decreases Resistance  Decreases Voltage  Increases Current  Increases filler consumption

19 Arc Length Should be no more then ¼ inch Should be no more then ¼ inch The sound of the arc should sound like eggs frying The sound of the arc should sound like eggs frying

20 Bead Width Stringer bead Stringer bead  Only motion is in the direction of travel  About 3 times the width of the electrode  With 1/8 inch electrode should be 3/8 inch Weaving bead  Motion side to side as well as forward  About 6 times the width of the electrode  With 1/8 inch electrode should be 3/4 inch

21 Stringer Bead

22 Weaving Bead

23 Electrode Angle Should be 15° to 20° tipped forward in the direction of travel Should be 15° to 20° tipped forward in the direction of travel Stringer bead should be at 90° from the base metal Stringer bead should be at 90° from the base metal

24 Travel Speed Bead width Bead width Bullet-nose-shaped ripples Bullet-nose-shaped ripples

25

26 Restarting Strike ark 3/8 inch in front of previous weld Strike ark 3/8 inch in front of previous weld Move back to crater Move back to crater Move forward to finish weld Move forward to finish weld

27 Restarting


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