Download Arc Welding

Arc Welding
Basic Safety
Warnings
• Welding can be safe when proper measures
are taken to protect yourself and others from
potential hazards.
• Understand and follow all warning labels
found on equipment and with all
consumables.
Potential Hazards
• Protect yourself and others from potential hazards
including:
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Fumes and Gases
Electric Shock
Arc Rays
Fire and Explosion Hazards
Noise
Hot objects
Welding Sparks
Fumes and
Gases
•Welding fumes can be harmful
to the welder causing
implications such as:
oIrritation of the
respiratory tract
oMetal fume fever
oSlightly increase the risk
of lung cancer
•Use enough ventilation,
exhaust at the arc, or both, to
keep fumes and gases from
your breathing zone and the
general area
•Use a respirator if needed or
required by the process.
•The ventilation system must be
on while welding at all times.
Electrical
Shock
•Electric shock can kill
•Do not touch live electrical
parts
Primary Voltage –208 240, 416 - 480 volt
input power
Secondary Voltage – 6
to 100 volts for welding
•Insulate yourself from work
and ground
•Follow all warnings on
welding equipment
•Wear insulated clothing
•Always shut off machinery
when done and roll the
cords up neatly
•Do not make repairs
yourself, alert your
instructor immediately!
U.V. Rays
•Welding will produce ultraviolet rays
that are harmful to the human eye and
skin. Proper protection is needed to
avoid bodily harm.
•Arc rays are ten times brighter than
the sun and can injure eyes and burn
skin
•Precaution must be taken to protect
your eyes and skin from UV radiation.
The welding arc is brighter than the
sun
•Wear correct eye and body protection
o10 shade helmet
oSafety Glasses under the
helmet
oGloves
oArm and Body Protection
Jacket
Shoulder Covers
Coveralls
Fire Hazards and Material Safety
• Welding sparks can cause fires and explosions
• Sparks and spatter from the welding arc can spray up
to 35 feet from your work
• Flammable materials should be removed from the
welding area or shielded from sparks and spatter
• Always clean painted materials
• All welding booths should be cleaned thoroughly
• Have a fire extinguisher ready
• Inspect area for fires 30 minutes after welding
• Watch for sharp metal edges
• Cool all welded metal in the water tank.
Ear Protection
• Loud noises can damage your hearing
• Keep loud noises at a safe level by using proper
hearing protection such as:
– Ear plugs
– Ear muffs
Protective
Clothing
•Welders must wear protective
clothing for
oProtection from sparks,
spatter and UV radiation
oInsulation from electric
shock
•Protective clothing includes …
oFire-proof clothing without
rolled sleeves, cuffs or frays
oWork boots
oWelding gloves, shirts
jackets, bibs, and fire-proof
pants
oWelding cap, helmet and
safety glasses
oEar protection – ear plugs
and muffs
oMost importantly safety
glasses are to be worn at all
times in the shop
Improper Protective Clothing
• List and describe
what is wrong
in this picture
Basic Electricity and Welding
Arc Welding
Basic Safety
Arc Welding Circuit and Concept
•The electricity flows from the power source,
through the electrode and across the arc,
through the base material to the work lead
and back to the power source.
Identify all the above parts for the arc welder,
describe the function of each part, and determine
each of the parts safety aspects.
Electrical
Concepts
DC -
DC +
•Voltage – The electrical potential
or pressure that causes current to
flow
oMeasured in Volts
•Current – The movement of
charged particles in a specific
direction
oMeasured in Amps
•Polarity
oDC- (Direct Current
Electrode Negative)
oDC+ (Direct Current
Electrode Positive)
oAC (Alternating Current)
•ALWAYS REMEMBER
THAT VOLTAGE WILL
HURT BUT AMPERAGE
CAN BE FATAL
AC
Electrical Lead
Condition
•Before starting an operation, always
check the condition of all electrical
leads.
•Cracked and worn leads can lead to
fatal shock.
•All electrode holders or “stingers”
should be in tack and not cracked or
missing pieces.
•All plugs and outlets should be in
tack. Never set-up a welder with a
broken plug or into a broken outlet.
Never operate a welder with splices
showing in the leads.
Shielded Metal Arc Welding
SMAW
SMAW Process
SMAW Key Parts
• Electrode Holder: Also known as the “stinger” Handle-like
tool that holds the electrode while welding.
– Never hold this part with your bare hand while welding.
• Ground Connection: Also known as the “workpiece
connection clamp” that connects to the work to complete
the electrical circuit
• Power Source: Where the welder plugs into
• Amperage Scale: Determines the amount of “heat” or
power the welder will operate at.
• Polarity Switch: Setting that determines how the electrons
will flow during the welding process.
• On / Off Switch: Turns the welder on / off. Make sure the
switch function properly at all times.
SMAW Principles
• The American Welding Society defines SMAW
as Shielded Metal Arc Welding
• SMAW:
– Is commonly known as ‘Stick’ welding or manual
arc welding
– Is the most widely used arc welding process in the
world
– Can be used to weld most common metals and
alloys
SMAW Welding Circuit
• Current flows through the electrode cable, to the electrode
holder, through the electrode, and across the arc
• On the work side of the arc, the current flows through the
base material to the work clamp and back to the welding
machine
SMAW Process
Identify all the above segments for the SMAW process,
describe the function of each segment, and determine if any
safety aspects exist.
The Electrode
What is it?
• Is a consumable - it gets melted during the welding process
• Is composed of two parts
– Core Rod (Metal Filler)
 Carries welding current
 Becomes part of the weld
– Flux Coating
 Produces a shielding gas
 Can provide additional filler
 Forms a slag
Electrode
Classification
•Electrodes are classified
by a numbering system
•E6013
oE = Electrode
o60 or first two
numbers = Tensile
strength (thousands
of pounds
o1 or third number
= Welding position
o3 or fourth number
= Welding current
type and depth of
weld penetration.
Pictured above are E-7018 electrodes. Identify
what the tensile strength is for this electrode.
Electrode
Classification
Third Digit
•Third Digit
E_ _ 1 _ = Usable in
all directions
E_ _ 2 _ = Usable in
flat and horizontal
positions only
E_ _ 4 _ = Usable
for vertical down
only
Pictured above are E-6011 electrodes. Identify
what each digit resembles up to the third digit.
Electrode
Classification
Fourth Digit
•Fourth Digit
E_ _ _ 0 = DC reverse polarity
only
E_ _ _ 1 = AC and DC reverse
polarity
E_ _ _ 2 = AC and DC straight
polarity
E_ _ _ 3 = AC and DC
E_ _ _ 4 = AC and DC
E_ _ _ 5 = DC reverse polarity
E_ _ _ 6 = AC and DC reverse
polarity
E_ _ _ 8 = AC and DC reverse
polarity
Pictured above are E-6013 electrodes. Identify
what each digit resembles.
The Arc
•An arc occurs when the electrode comes
in contact with the work-piece and
completes the circuit … like turning on a
light!
•The electric arc is established in the space
between the end of the electrode and the
work
•The arc reaches temperatures of 10,000°F
which melts the electrode and base
material
•Don’t look at the arc without proper eye
protection.
•Wear proper body protection. The UV
rays will cause bodily harm.
Arc burning off the electrode
Weld Puddle
•As the core rod, flux
coating, and work pieces
heat up and melt, they
form a pool of molten
material called a weld
puddle
•The weld puddle is
what a welder watches
and manipulates while
welding
•Don’t touch the hot
puddle!!! The metal is
hot!!!
Shielding Gas
•A shielding gas is
formed when the flux
coating melts.
•This protects the weld
puddle from the
atmosphere preventing
contamination during
the molten state
•Don’t touch the
metal!!! The metal is
hot!!!
•Shielding gas can cause
bodily harm. Be sure
proper ventilation is
being used.
Shielding Gas
4
3
2
The shielding gas protects the molten puddle
from the atmosphere while stabilizing the arc
Solidified
Weldment
•As the molten weld
puddle solidifies, it
forms a joint or
connection between
two pieces of base
material
•When done properly on
steel, it results in a weld
stronger than the
surrounding base metal
•Don’t touch the
metal!!! The metal is
hot!!!
Slag
•Slag is a combination of the
flux coating and impurities
from the base metal that
float to the surface of the
weld.
•Slag quickly solidifies to
form a solid coating which
slows the cooling rate of the
weld
•The slag can be chipped
away and cleaned with a
wire brush when hard
•Don’t touch the metal!!!
The metal is hot!!!
•Slag can be dangerous
when being removed. Wear
the proper safety
protection.
This welder chips the slag off of a weld during
the repair of railroad tracks
Gas Metal Arc Welding
GMAW
“Mig”
GMAW Defined
• An arc welding process that uses an arc
between a continuous filler metal electrode
and the weld pool.
• The process uses a shielding gas that protects
the weld from contamination.
• Without using a shielding gas the weld
becomes pitted and contains no strength
value.
Pitted GMAW Weldment
Weld is Pitted from improper
flow of shielding gas
GMAW Safety Points
• Fumes and Gases can be dangerous
– Keep your head out of the fumes
– Use enough ventilation, exhaust at the arc, or both, to keep
fumes and gases from your breathing zone and the general area
– Local exhaust and mechanical ventilation can be used without
reducing weld quality
• Electric Shock can kill – to receive a shock your body must touch
the electrode and work or ground at the same time
– Do not touch the electrode or metal parts of the electrode
holder with skin or wet clothing
– Keep dry insulation between your body and the metal being
welded or ground
– The coil of wire is ‘electrically hot’ when the trigger is pulled
GMAW Safety Points (Continued)
• REMEMBER – Gas Cylinders require SPECIAL
safety precautions
– Cylinders must be secured in an upright position
– Cylinders should be located in an area away from arc
welding, cutting, heat, sparks, and flame
– Shut off the gas cylinder when finished.
– Our Lab uses a 75% argon and 25% carbon dioxide or
90% argon 10% carbon dioxide mix for shielding gas.
– Don’t bleed or purge the lines after an operation. This
gas will not combust / burn.
GMAW
Process
•During the GMAW
process, a solid metal
wire is fed through a
welding gun and
becomes the filler
material
•Instead of a flux, a
shielding gas is used to
protect the molten
puddle from the
atmosphere which
results in a weld
without slag
GMAW Process (Continued)
• Three things happen when the GMAW gun trigger is pulled:
– The wire electrode begins to feed
– The circuit becomes electrically ‘hot’
– Shielding gas flows through the gun and out the nozzle
• Current flows from the power source through the gun cable,
gun, contact tip to the wire and across the arc.
• On the other side of the arc, current flows through the base
metal to the work cable and back to the power source
• Shielding gas flows through the gun and out the nozzle
GMAW Parts
GMAW Key Parts
• Gun Housing: Holds or houses the welding wire liner, gas
line, and trigger in one piece
• Conductor Tube: The angled part of the gun that the wire
and shielding gas flow through during the weld operation
• Gas Diffuser: Disperses the shielding gas onto the
weldment
• Contact Tip: The part where the welding wire runs
through. Different sized tips accommodate different
sized wire.
• Nozzle: The cover for the end of the gun that keeps
spatter from sticking to the contact tip and gas diffuser
and plugging the gun up.
GMAW Process
Welding Tip: Generally, drag on thin sheet
metal and push on thicker materials
Shielding Gas
Solidified Weld Metal
Arc
Electrode
Puddle
GMAW Electrode
• A GMAW electrode is:
– A metal wire
– Fed through the gun by the wire feeder
– Measured by its diameter
GMAW electrodes are commonly
packaged on spools, reels and coils
ranging from 1lb to 1000lbs
GMAW Arc
• An electric arc occurs in the gas filled space
between the electrode wire and the work
piece
Electric arcs can generate
temperatures up to 10,000°F
GMAW Weld
Puddle
•As the wire
electrode and work
piece heat up and
melt, they form a
pool of molten
material called a
weld puddle
•This is what the
welder watches
and manipulates
while welding
Shielding Gas
•GMAW welding
requires a
shielding gas to
protect the weld
puddle
•Shielding gas is
usually CO2,
argon, or a
mixture of both
Final Weld
•The welder
“lays a bead” of
molten metal
that quickly
solidifies into a
weld
•The resulting
weld is slag free
Weld Examples
• GOAL - Make Good Welds
• Eliminate Porosity
Eliminate Ropey Convex bead
Eliminate Excessive Spatter
OXY ACETYLENE
SET-UP
Terms and Definitions
• Backfire: A short pop of the torch flame
followed by extinguishing of the flame or
continued burning of the gases.
• Flashback: when the torch flame moves into
or beyond the mixing chamber.
• Preheating: Heating prior to a welding or
cutting operation
Equipment Required
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Oxygen cylinder
Acetylene cylinder
Pressure regulators
Two hoses encased together
Welding torch with tips
Welding goggles and safety glasses
Striker
Check valves to prevent flashback
Acetylene Regulator
Oxygen Regulator
Typical Torch
Torch Parts
Striker
Cutting Tip
Welding and Heating Tips
Check Valves
Safety Rules for Oxy-Acetylene Workplace
• Keep the work area free of grease, oil, and
flammable materials
• Cool or quench hot metal and extinguish all
sparks before leaving. Sparks can travel up to
35 feet.
• Don’t leave torches, or hot metal where
someone will pick them up
• Never carry matches or lighters into any work
area
Pressure Gauge Failure
Cracked Acetylene Hose
Improper Storage of Tanks
Oxygen/
Acetylene
Cutting
Torch
Stored on
Unsafe
Cart
Oxygen/ Acetylene Cutting Torch Stored in
Flammable Liquids Cabinet
Regulator Parts
Pressure regulators reduce the supply pressure, indicated by the
high pressure gauge to suitable working pressure, indicated by the
low pressure gauge. By turning the adjusting screw, proper
working pressures can be achieved.
Personal Safety
• Shirts
– keep collar and sleeves buttoned to keep out sparks.
Avoid wearing shirts with pockets.
• Pants or Coveralls
– no cuffs and come over shoe tops
• Shoes
– leather, cover entire foot
• Gloves
– Leather, never use to pick up metal
• Safety Glasses
– worn under helmets and goggles and all times.
Eye Protection
• Wear safety glasses at all times
• Wear welding goggles or a face shield with a
lens no. 4-6 while using torch equipment
– when in doubt start with too dark of a lens and
then switch to a lighter one.
Color Codes
• Green = Oxygen
• Red = Acetylene
Pressure Regulating Valves
• Each regulator has two gauges mounted on a
single manifold. One indicates cylinder
pressure and the other indicates working
pressure for the torch.
• Each regulator has an adjusting screw or Tscrew, so pressure to the torch can be quickly
controlled by turning the screw righty-tighty
to increases pressure and left-loosey to
decrease pressure.
Regulator Attachment
– Acetylene connectors have a V-groove left handed
thread
– Oxygen connectors have a plain surface right
handed thread
PSI Settings
• Acetylene = 15 psi. max
– Over 15 psi. can be fatal
– Our regulators in the NCWHS lab will be set at 10
psi. max.
• Oxygen = 40 psi. max
– Over 40 psi. will dilute the heat of the flame
– Our regulators in the NCWHS lab will be set at 30
psi. max.
Torch Parts
• Torch body is the part of the torch that is held
like a pencil. It contains two needle valves to
control the flow of gas
• The welding head contains a mixer, mixing
throat, and the welding tip
Types of Flames
• Oxidizing
– Excess oxygen with no feather, makes hissing
sound. Sounds like an angry snake.
– Least used for anything
• Neutral
– Burns equal amounts of oxygen and acetylene and
has a clear edged inner cone
– Most used
Types of Flames
• Carburizing
– Excess acetylene with an acetylene feather two to
three times the length of the inner cone
– While burning it will produce a heavy black smoke
flame
– Used some in hardsurfacing, adds carbon to metal
Operation Safety
• 1. Before you start make sure personal safety
is followed.
• 2. Make sure you have had instruction
• 3. Release adjusting screw on regulators
before opening valves
• 4. Stand on the opposite side of the regulator
when opening a valve
• 5. Open cylinder valve slowly, oxygen first all
the way open acetylene just a quarter of a
turn
Operation Safety (II)
• 6. Do not use or compress acetylene at pressures higher
than 15 psi.
• 7. Set working pressures as desired.
– Acetylene: 10 psi for NCWHS lab
– Oxygen: 30 psi for NCWHS lab
• 8. Light acetylene first
9. Never use oil on regulators or any equipment
– If oil mixes or touches the acetylene it will combust
• 10. Do not use compressed air as a substitute for oxygen
• 11. Keep heat, flames, and sparks away from
combustibles.
• 12. Keep hoses out of sparks or spatter to prevent leaks
Safety Lighting the Torch
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•
•
Check the torch valves to make sure they are closed
Open the oxygen tank valve full open
Open the acetylene tank valve ¼ turn
Turn on the oxygen knob on the torch body
– This is located next to the acetylene knob
• Turn the acetylene gas on no more than ¼ turn
• Strike and light
• Mix oxygen into the flame with the mixing knob on the torch
body. While mixing you want to create a neutral flame. Press
down on the cutting lever also to make sure the flame does
not jump.
– The mixing knob is located half-way up the torch body next to the
cutting lever
Shutting down the unit
• Shut down the flame by turning off the acetylene knob
on the torch body.
• Close the oxygen mixing knob located half-way up the
torch body
• Shut off the tanks by closing the tank valves
• Open the acetylene to purge or bleed the line
• When both gauges read zero, close the valve
• Open the oxygen valve
• When both gauges read zero, close the valve
• Release pressure on the regulators by turning adjusting
screw left or T-screw (out). DO NOT remove the T-screw
• Coil hoses and put tools away