Transcript 0061 welding

SUBMITTED BY-FAIZ
MOHD.ANSARI(ME-1)
1214340061(B-2)
IMS ENGINEERING COLLEGE
GHAZIABAD
TO KNOW ABOUT GAS WELDING
TO KNOW ABOUT ARC WELDING
TYPES OF ARC
WELDING(SMAW,TIG,MIG,SAW)
PRINCIPLES OF THESE TYPES OF
WELDING
Oxyacetylene Welding (OAW)
The oxyacetylene welding process
uses a combination of oxygen and
acetylene gas to provide a high
temperature flame.
Oxyacetylene Welding (OAW)
• OAW is a manual process in which the
welder must personally control the the torch
movement and filler rod application
• The term oxyfuel gas welding outfit refers
to all the equipment needed to weld.
• Cylinders contain oxygen and acetylene gas
at extremely high pressure.
Oxygen Cylinders
• Oxygen is stored within cylinders of various
sizes and pressures ranging from 20002640 PSI. (Pounds Per square inch)
• Oxygen cylinders are forged from solid
armor plate steel. No part of the cylinder
may be less than 1/4” thick.
• Cylinders are then tested to over 3,300 PSI
using a (NDE) hydrostatic pressure test.
Oxygen Cylinders
• Cylinders are regularly
re-tested using
hydrostatic (NDE)
while in service
• Cylinders are regularly
chemically cleaned
and annealed to relieve
“jobsite” stresses
created by handling .
Cylinder Transportation
• Never transport cylinders without the safety
caps in place
• Never transport with the regulators in place
• Never allow bottles to stand freely. Always
chain them to a secure cart or some other
object that cannot be toppled easily.
Pressure Regulators for
Cylinders
• Reduce high storage
cylinder pressure to
lower working
pressure.
• Most regulators have a
gauge for cylinder
pressure and working
pressure.
Pressure Regulators for
Cylinders
• Regulators are shut off
when the adjusting screw
is turn out completely.
• Regulators maintain a
constant torch pressure
although cylinder pressure
may vary
• Regulator diaphragms are
made of stainless steel
Regulator Hoses
• Hoses are are fabricated from
rubber
• Oxygen hoses are green in
color and have right hand
thread.
• Acetylene hoses are red in
color with left hand thread.
Check Valves &
Flashback Arrestors
• Check valves allow gas
flow in one direction only
• Flashback arrestors are
designed to eliminate the
possibility of an explosion
at the cylinder.
• Combination Check/
Flashback Valves can be
placed at the torch or
regulator.
Acetylene Gas
• Virtually all the acetylene distributed for welding and cutting
use is created by allowing calcium carbide (a man made product)
to react with water.
• The nice thing about the calcium carbide method of producing
acetylene is that it can be done on almost any scale desired.
Placed in tightly-sealed cans, calcium carbide keeps indefinitely.
For years, miners’ lamps produced acetylene by adding water, a
drop at a time, to lumps of carbide.
• Before acetylene in cylinders became available in almost every
community of appreciable size produced their own gas from
calcium carbide.
Acetylene Cylinders
• Acetylene is stored in cylinders specially designed
for this purpose only.
• Acetylene is extremely unstable in its pure form at
pressure above 15 PSI (Pounds per Square Inch)
• Acetone is also present within the cylinder to
stabilize the acetylene.
• Acetylene cylinders should always be stored in the
upright position to prevent the acetone form
escaping thus causing the acetylene to become
unstable.
Acetylene Cylinders
• Cylinders are filled with a
very porous substance
“monolithic filler” to help
prevent large pockets of
pure acetylene form
forming
• Cylinders have safety
(Fuse) plugs in the top and
bottom designed to melt at
212° F (100 °C)
Acetylene Valves
• Acetylene cylinder shut
off valves should only be
opened 1/4 to 1/2 turn
• This will allow the
cylinder to be closed
quickly in case of fire.
• Cylinder valve wrenches
should be left in place on
cylinders that do not
have a hand wheel.
Regulator Pressure Settings
• The maximum safe working pressure for
acetylene is 15 PSI !
Typical startup procedures
• Always use a flint and steel spark lighter to light the
oxygen acetylene flame.
• Never use a butane lighter to light the flame
Flame Settings
• There are three distinct types of oxy-acetylene
flames, usually termed:
– Neutral
– Carburizing (or “excess acetylene”)
– Oxidizing (or “excess oxygen” )
• The type of flame produced depends upon the
ratio of oxygen to acetylene in the gas mixture
which leaves the torch tip.
Pure Acetylene and Carburizing
Flame profiles
Neutral and Oxidizing Flame
Profiles
Flame definition
• The neutral flame (Fig. 4-1) is produced when the ratio of oxygen to
acetylene, in the mixture leaving the torch, is almost exactly one-toone. It’s termed ”neutral” because it will usually have no chemical
effect on the metal being welded. It will not oxidize the weld metal; it
will not cause an increase in the carbon content of the weld metal.
• The excess acetylene flame (Fig. 4-2), as its name implies, is created
when the proportion of acetylene in the mixture is higher than that
required to produce the neutral flame. Used on steel, it will cause an
increase in the carbon content of the weld metal.
• The oxidizing flame (Fig. 4-3) results from burning a mixture which
contains more oxygen than required for a neutral flame. It will oxidize
or ”burn” some of the metal being welded.
Shielded Metal Arc Welding
(SMAW)
• Manual arc welding
– Heat for welding generated by electric arc
established between flux-covered consumable
metal rod (electrode) and work
• Called stick electrode welding
• Combustion and decomposition of electrode
creases gaseous shield
– Protects electrode tip, weld puddle, arc, and
highly heated work from atmospheric
contamination
• Additional shielding provided by covering of molten
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slag (flux)
•Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
•American Welding Society
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•Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
SMAW Operating Principles
• Sets up electric circuit
– Includes welding machine, work, electric cables,
electrode holder and electrodes, and a work
clamp
• Heat of electric arc brings work to be welded
and consumable electrode to molten state
– Heat intense: as high at 9,000ºF at center
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•Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Welding Process
• Electric arc started by striking work with
electrode
• Heat of arc melts electrode and surface of
base metal
• Tiny globules of molten metal form on tip
of electrode and transferred by arc into
molten pool on work surface
• After weld started, arc moved along work
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SMAW Operating Principle
•American Welding Society
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•Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Introduction to practical
application of wire feed welding
MIG – Metal Inert Gas Welding
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•
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May be called GMAW (Gas Metal Arc Welding)
Avoid cutting in drafty or windy conditions
Molten pool is shielded by the inert gas envelope
Joints are stronger, more ductile, and more
corrosion resistant
• Flux center wire has slag; Solid wire has no slag,
thus eliminating slag inclusion
• Welded metal does not readily distort
REQUIREMWNTS FOR MIG
• Power Supply
• Gas Supply
• Wire feeder
• Gun and Whip
• Process
MIG Machine Operation
• Wire is fed at a pre-set rate
• Gas flows at about 35 cubic feet per hour
and is directed around the welding wire for
shielding
Advantages
 Welding can be done in all
positions
 High rates of metal deposition
 Excellent filling ability for
poor-fit joints
 High weld Quality
 No electrode stub loss
 Less distortion due to narrow,
deep weld profile
 Easier process to learn and
use
Disadvantages
 Welding power source
expensive
 Shielding gas expensive
 Higher electrode wire cost
 Most machines require threephase input power
 Not as versatile as SMAW for
maintenance
 Welding cast iron
 Cutting
 Carbon arc torch
applications
TIG Welding Introduction
Background
►What is TIG?
 Tungsten Inert Gas
►Also referred to as GTAW
 Gas Shielded Tungsten Welding
►In TIG welding, a tungsten electrode heats
the metal you are welding and gas (most
typically Argon) protects the weld from
airborne contaminants
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Background
►TIG welding uses a non-consumable
tungsten
►Filler metal, when required, is added by
hand
►Shielding gas protects the weld and
tungsten
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Inert Gases for Shielding
• Argon
– Cheap – comes from air
– Heavier than air – blankets
weld well
– Provides clean welding of
Aluminum and Magnesium
– Best with AC
• Helium
–
–
–
–
–
–
Arc voltage is greater
Hotter arc
Deeper Penetration
Fast Speed
Less Distortion
May spatter more than
Argon
• Carbon Dioxide
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–
–
–
–
Cooling effect
Low cost
Produces Spatter
Deep penetration
Not same inert
characteristics as Argon and
Helium
Advantages
• Welds more metals and
metal alloys than any
other process
• High quality and
precision
• Pin point control
• Aesthetic weld beads
• No sparks or spatter
• No flux or slag
• No smoke or fumes
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Disadvantages
► Lower filler metal deposition
rates
► Good hand-eye coordination
a required skill
► Brighter UV rays than other
processes
► Slower travel speeds than
other processes
► Equipment costs tend to be
higher than other processes
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Safety
►Electric shock can kill.
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Always wear dry insulating gloves
Insulate yourself from work and ground
Do not touch live electrical parts
Keep all panels and covers securely in place
►Fumes and gases can be hazardous to your health.
 Keep your head out of the fumes
 Ventilate area, or use breathing device
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Safety
►Welding can cause fire or explosion.
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Do not weld near flammable material
Watch for fire; keep extinguisher nearby
Do not locate unit over combustible surfaces
Do not weld on closed containers
►Arc rays can burn eyes and skin; Noise can damage
hearing.
 Wear welding helmet with correct shade of filter
 Wear correct eye, ear, and body protection
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SUBMERGED ARCH WELDING
•WELD ARC IS SHIELDED BY GRANULAR FLUX
• FLUX CONSIST OF SILICA,MgO,CaF2
•FLUX IS FED IN WELD ZONE BY GRAVITY FLOW
THROUGH A NOZZLE
•IN THIS CONSUMABLE ELECTRODE IS USED
PURPOSE OF USING FLUX
•THICK LAYER OF FLUX COMPLETEL
COVERS THE METAL
•THUS, PREVENTS SPATTERS AND SPARKS
• SUPPRESSES UV RADIATIONS
•IT ALSO ACTS AS A THERMAL INSULATOR
•THUS, PROMOTING DEEP PENETRATION
OF HEAT INTO THE WORKPIECE
SPECIFICATIONS FOR SAW
•RANGE OF CURRENT – 300 TO 2000A
•VOLTAGE SUPPLY REQUIRED – 440V
•CONSUMABLE ELECTRODE IS A BARE
ROUND COIL OF 1.5mm-10mm IN
DIAMETRE FED THROUGH WELDED GUN
ADVANTAGES OF SAW
•UNUSED FLUX CAN BE RECOVERSD
•IT CAN BE USED TO WELD VARIETY OF CARBON
& ALLOY STEELS
•THE QUALITY OF WELD PRODUCE IS HIGH
•
•THE WELD HAS GOOD TOUGHNESS,DUCTILITY
AND UNIFORMITY OF PROPERTIES