Arc Welding Metals and Welding. Precautions and Safe Practices Relatively safe compared to other forms of welding 4 areas of concern during arc welding.
Post on 16-Dec-2015
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- Arc Welding Metals and Welding
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- Precautions and Safe Practices Relatively safe compared to other forms of welding 4 areas of concern during arc welding Shock- Fire Burns- Fumes Light Heat
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- Prevention of Shock Use a wooden grating on concrete floors Rubber soled shoes are best Danger of shock is increased with higher temperature and humidity - perspiration Disconnect power before repairing Qualified electrician should complete maintenance and repairs Make sure the machine is grounded Ground clamp paint, rust, grease will prevent solid ground
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- Prevention of Shock Use special welding cables with high quality insulation Repair solid dont use tape Keep in good condition free of grease, oil, out of water, ditches, etc. Electrode holders and cables should be fully insulated Turn main switch to welder off when leaving the work area Follow usual precautions in handling electric power
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- Prevention of Light Burns Eyes Helmet or hand shield with a minimum shade of no. 10 lens is required (see table on 159-160) Wear safety glasses also Completely screen equipment for arc glare Locate jobs in special rooms or booths Avoid accidental contact on the part of others Skin Completely cover body UV Light will cause sunburn type burn
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- Prevention of Heat Burns Clothing Completely cover body Sparks and heat Cotton clothing is preferred with leather shoes and gloves Mark hot metal to prevent others from coming in contact with welded pieces Pick up hot metal with pliers or tongues, not gloves or hands Dont hand hot metal to instructor or TAs
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- Prevention of Fire Clothing Stand while Arc welding Dont roll cuffs Keep free of oil, grease, etc. Sweatshirts turned inside out Do not weld near flammable materials Proper fire extinguishing equipment should be stationed near welding operations
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- Prevention of Fumes Exposure Exhaust systems or breathing apparatus should be provided when welding inside Fumes from electrode flux non-toxic Fumes from paint lead content - toxic Fumes from metal coating Zinc (galvanized), Aluminum - toxic Carbon monoxide Carbon dioxide Dust
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- General Safety Good housekeeping Keep area clean Electrode stubs Slag on concrete floor Cables hung up Tools put away Good workmanship in making sound welds is essential to that others may not be injured due to failure of welded parts
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- Stick Electrode Welding Operation of a miniature electric furnace between the grounded base metal and the electrode Arc temperature is about 11,000 F Molten metal must be protected from the air by a gaseous shield and/or slag shield Machine settings and operators manipulations determine size and shape of bead
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- Successful Arc Welding depends upon: Correct metal identification Metal properties vary Correct electrode selection Depends on metal type, thickness and position of weld Correct amperage Depends upon electrode type, size, position, and metal thickness Influence burn off rate and affect arc length and speed of travel
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- Successful Arc Welding depends upon: Proper Arc length Influences the amount of heat during the weld Correct speed of travel Determines the width of bead and indirectly the strength of the weld Angle of electrode Determines the bead shape and controls slag and gas inclusions
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- AC/DC Alternating Current electrons change direction every 1/120 of a second (60 cycles per second) Rapid reversal causes the welding heat to be evenly distributed on both the work and the electrode Direct Current flow of electrons in one direction Electrode Negative (DC Straight) electrode is negative and the work is positive (high electrode melting rate) Electrode Positive (DC Reverse) electrode positive and work is negative (produces the best welding arc characteristics)
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- Electrode Selection Early arc welding done with bare, low carbon steel wire electrodes on DC welders Early 1930s flux coated electrodes Exhaustive research into chemical and physical properties and chemical combinations American Welding Society (AWS) has classified electrodes to allow for wide choices for many applications
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- Classification of Electrodes Classified according to filler metal specifications by AWS and ASTM (American Society for Testing Materials) Lincoln, AIRCO, Hobart, etc. will all be the same Based upon four factors: Minimum tensile strength of the as-welded deposited weld metal Type of covering Welding position Type of welding current (AC, DC+, DC-)
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- Classification of Steel Electrodes 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) E-60xx - 60,000psi TS E-120xx - 120,000 psi TS
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- Classification of Steel Electrodes 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
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- Classification cont. 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) Pg. 161
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- Factors of Electrode Selection Type of metal to be welded Thickness of metal Position of weld Type of power (DC or AC) Cleanliness of metal Weld bead appearance desired
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- Electrode storage Store electrodes in protected place Avoid cracking or chipping flux by bending or striking Store in dry place Aluminum and low hydrogen (E7018) should be stored in a closed container Old refrigerator works well Low hydrogen electrodes may be re-dried at 300 F for non-x-ray welds
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- Function of Flux Improves the performance in handling, storage and operation of the electrode Floats out impurities Directs arc stream (stabilizer) Insulator Prevents oxidation (slag or gas) Holds in heat Iron-powder improves striking ability and increases metal deposition rate (E7024)
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- Selecting the Electrode for the Job Fast-Freeze-electrodes - deposits a weld that solidifies or freezes rapidly - E6010, E6011. Fast-Fill - deposits metal rapidly - E7018, E6024, E6027. Fill-Freeze - characteristics between fast- freeze and fast-fill - E6012, E6013, E6014.
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- Amperage Setting Influences the rate of metal deposition Influences the speed of welding Bead should be 2x the diameter of the electrode wire Type of electrode influences amp. setting Unusual to select the proper setting on the first try For steel, start at 90 amps and adjust from there Actual amperage is greatly influenced by arc length
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- Striking the Arc Peck Method DC welders Contact the plate with downward motion Scratch Method AC or DC welders Contact by sweeping motion
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- Angle of Electrode Arc has a definite directional force Flat welding Perpendicular from side to side Tilted in direction of travel about 15
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- Angle of Electrode by Position Tee and Lap 45 side; 15-20 lead 6011, 6013, 7024 Horizontal 5-10 side; 15-20 lead 6013, 6011 Overhead 90 side; 10-15 lead 6011 Vertical up 90 side; 0-5 slant 6011 Vertical down 90 side; 10-15 lead 6013
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- Proper Arc Length Arc welding involves unavoidable changes of arc length Must be controlled as much as possible Arc length influences: Actual amperage (heat) Appearance of a bead Arc length should be equal to the diameter of the wire in the electrode (1/8) Tighter arc will give even penetration, metal deposition, a strong bead, and less spatter
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- Proper Arc Length Long arc results in: Large globules melting Wavering arc Wide spatter and irregular bead Short arc results in: Electrode sticks Poor penetration Convex bead Clag inclusions Irregular bead Use short length for vertical welds
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- Speed of Travel Movement of electrode forward and downward Travel speed influences: Bead width Penetration General shape of the bead Use a uniform speed Both hands on the electrode holder Operator comfort Bead should be about twice the diameter of the electrode wire
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- Read the Bead
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- Controlling distortion (Volume changes of expansion followed by contraction during cooling) Do not overweld. Avoid continuous welds. Consider chain intermittent Or staggered intermittent Use fewer beads (passes).
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- Controlling distortion cont. Use 60 0 included angle on edge prepared joints. Weld near the neutral axis. Use back-step welding. Use wedging.
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