Transcript Document

Oxyfuel Cutting
and Welding
8609-A
Instructional Materials Service
Texas A&M University
Introduction
• Oxyfuel: the process of combining pure
oxygen with a combustible fuel gas to
produce a flame
• Can be used for welding, brazing, cutting,
and heating metals
• Oxygen & fuel gases are stored under
pressure in cylinders and are released as
individual gases through valves, regulators,
and hoses.
– Mixed as they flow through torch assemblies
– Burn as they are discharged through special tips
• Fuel gases:
– Propane, natural gas, propylene & acetylene
– Vary in their chemical composition
– React with the metal in different ways
• Factors to consider in selecting a gas:
– Availability & cost
– Welding process or operation to be performed
– Thickness of metal & type of welded joint to be
produced
– Physical properties of metals
– Chemical properties of metals
Propane (C3H)
• Supplied in a liquid form under positive
pressure, which varies with temperature
• Most oxyfuel cutting torches can use LP
gas, but special hoses and cutting tips
are required.
• Readily available in most areas
• Due to cost, propane cutting is heavily
used in the metal recycling industry.
Propylene (C3H6)
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Has been used for approximately 30 years
Stable in both liquid and gas states
Economical
Produces little slag
Has a high heat value
Does not have the withdrawal pressure
limitations that are necessary with
acetylene
• Approximately 5% propylene, 87% propane
& traces of other gases
Acetylene (C2H2)
• Most widely used fuel gas for welding
and cutting applications
• Produces a clean weld and a
controllable flame
• Less stable and more expensive than
other fuel gases
• Performs most functions well and is
widely available
Compressed Natural Gas (CH4)
• Adaptable for cutting, soldering,
brazing, and preheating
• A water seal or blowback valve to
prevent backfiring into the gas supply
line must protect the natural gas
source.
Facts About Oxygen (O2)
• Odorless, colorless, tasteless & heavier
than air
• Makes up about 20% of the atmosphere
• Will not burn by itself
• Produced commercially by causing air to liquefy
• Compressed into steel cylinders at 1,800 to
2,400 pounds per in2 (psi)
• Supports combustion and is explosive if
handled improperly
• Cylinder sizes = 80 to 244 ft3
Facts About Acetylene (C2H2)
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Colorless, but has a very distinct odor
Highly combustible
Cylinder sizes = 60 to 300 ft3
Cylinder contains a porous substance saturated
with liquid acetone
• Acetylene is pumped into the cylinder,
displacing some of the acetone
• Not under extremely high pressure
– Full cylinder is pressurized to approximately 250 psi
• May not be withdrawn at a rate higher than
15 psi
Functions of Oxyfuel Heat
• Oxyfuel cutting of mild carbon steel heats the metal to
rekindling temperature (1,400oF to 1,800oF), then
oxidizes and blows the slag from the cut with a stream
of pure oxygen.
• Oxyfuel welding fuses two pieces of metal by heating
them to the melting point with a combustible mixture
of oxygen and fuel gas.
– Can be done with or without the use of a welding rod
– Brazing: the joining of metals by adding bronze filler
– Soft and hard solders (lead & silver alloys) are the filler
materials used in soldering.
• The oxyfuel flame is also used to bend, shape,
preheat, stress relieve, post-heat & temper metal.
Assembly of the Oxyfuel Rig
A. Secure the oxygen and fuel gas cylinders
to a wall, a special cylinder cart, or a
special rack if transported to job sites in a
truck.
B. Remove the valve protection caps and
wipe off any dirt accumulation with a
clean, dry cloth (free from oil or grease).
C. Slightly open (crack) both cylinders to
make sure they do not stick and to blow
out any dirt or dust lodged in the valve.
Close the valves.
D. Check all valves, connections, and soft
plugs for leaks with mild soapy water and
a clean brush.
E. Attach the regulators to the cylinders
pointing toward the sky to prevent
someone from getting in front of the
regulator.
F. The regulators, safety check valves, and
hoses should be tightened securely with a
wrench.
G. Do Not use a wrench to attach the
welding tip or cutting attachment to the
torch.
Oxyfuel Equipment
• Designed with several built-in safety
precautions:
– Oxygen hoses are usually green.
– Fuel gas hoses are red.
– All oxygen connections and cylinders have righthand threads.
– All fuel gas connections and cylinders have lefthand threads.
– Fuel gas fittings have a “V” notch cut around
the the outside of the connectors.
– Oxygen fittings and connectors are smooth.
• Cylinders:
– Two
• Regulators:
– Two sets
– Two stage regulators are the
safest to use.
• Hoses:
– Color-coded & specifically
designed based on use
– Type R: designed specifically
for acetylene use
– Type T: approved for all fuel
gases
• Safety Check Valves:
– Two sets recommended
– Attach between regulators and hoses and
between hoses and torch to prevent reverse
flow of the gases and flame that could cause
hose fires, regulator ruptures, and cylinder fires
• Torch Handle:
– Regulated by two valves
– Often equipped with internal reverse flow check
valves
• Cutting Attachment:
– Regulated by preheat oxygen control valve
– Operated by depressing the cutting oxygen
lever
Torch Butt
Cutting Attachment
• Cutting Tips:
– 3 to 8 preheat orifices and 1 oxygencutting orifice
– Drill size determines tip size
– Propane tip is a 2-piece tip with at least 6
preheat orifices
• Welding Tip:
– 1 orifice for gas mixture
– Size is determined by drill size of orifice
Safety Precautions
• Keep oil and grease away from all parts of the
oxyfuel apparatus.
• Secure the cylinders in an upright position so
they cannot be overturned.
• Face the regulator gauges toward the sky
making it impossible to stand in front of them.
• Store and use oxyfuel units in well ventilated
areas adequately separated from other
activities.
• Acetylene pressure in the lines should NEVER
exceed 15 psi.
• Open the acetylene cylinder valve ¼ to ½
turns; if it is the wheel type, open all the way.
• Use an approved spark lighter to light the
torch; never use matches or cigarette lighters.
• NEVER use oxygen to operate pneumatic
tools, blow out lines, inflate tires, or dust off
clothing.
• NEVER hang clothing on cylinders, running the
risk of saturating them with oxygen and
acetylene.
• DO NOT convert an acetylene regulator to an
oxygen regulator or vice versa.
• Slowly open the oxygen cylinder valve to
prevent a sudden surge of pressure.
• Release or loosen the regulator adjusting
screw before opening a cylinder valve.
• DO NOT walk with a lighted torch or lay
down a lighted torch.
• Purge hoses before attaching the torch
• Repair hoses with proper hose splices,
not friction tape. NEVER use a leaking
hose.
• Test for leaks with soap and water, not
matches.
• If valves on cylinders are faulty or too
tight, notify the supplier; undue force
would be dangerous.
• Keep a fire extinguisher handy at all times.
• Dress properly and wear eye protection.
• Prevent heat and sparks from getting to
cylinders and hoses.
• DO NOT strike an arc on a cylinder or hit a
cylinder with a metal object.
• NEVER use a cylinder as a ground in an
electrical circuit.
• NEVER guess; get the correct
information from a qualified person.
• Mark, isolate, or otherwise designate
empty cylinders.
• Oxygen and fuel gas cylinders (either
full or empty) MUST be stored
separately in accordance with safety
and fire codes.
Set-Up Procedure for
Oxyfuel Torch Nozzle
1. Check torch body for closed valves.
2. Check regulator for loose regulator adjusting
screw.
3. Open acetylene cylinder valve ¼ to ½ turn
(wheel-type valves one turn) maximum.
4. Turn acetylene regulator adjusting screw to
desired working pressure.
5. Open oxygen cylinder valve completely.
6. Turn oxygen regulator adjusting screw to
desired working pressure.
7. Crack acetylene torch valve and light
the torch, open acetylene torch valve
until soot disappears.
8. Open oxygen torch valve to adjust to
neutral flame; no acetylene feather
and sharp inner cone
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When welding, the ratio of oxygen to
acetylene is approximately 1:1.
Oxygen and acetylene settings will vary
depending on the attachment tip and
thickness of metal to cut or weld.
Types of Oxyfuel Flames
Shutdown Procedure
for Torch Nozzle
1. Turn off acetylene valve on torch butt.
NEVER turn off oxygen first.
2. Turn off oxygen valve on torch butt.
3. Close acetylene cylinder valve.
4. Bleed acetylene hose by opening
acetylene torch valve; close valve.
5. Back acetylene regulator adjusting screw
until loose.
6. Close oxygen cylinder valve.
7. Bleed oxygen hose by opening oxygen
torch valve; close valve.
8. Back oxygen regulator adjusting screw
until loose.
9. Recheck valves for closure, roll up hoses.
10. If rig is not to be used for some time,
remove the regulators and put the
safety caps back on the cylinders.
11. NEVER leave equipment under
pressure 24 hours a day.
Cutting Metals
• Metal to be cut should be clean, marked with a
punch or soapstone, and placed in a suitable
position for cutting.
• DO NOT cut over a concrete floor.
• Use a container or special cutting table device
to catch the molten metal.
• Oxyfuel cutting is limited to ferrous metals.
• Steels with a high tungsten or chromium
content or stainless steel cannot be cut with
oxyfuel.
• Cast iron is more difficult to cut than steel.
– An excess fuel flame is used
– More oxygen pressure is needed
Steps to Follow in Making a Cut
1. Hold blowpipe perpendicular to surface of
metal unless bevels are to be cut
– Hold the flame inner cone about 1/16 to 1/8 inch
above the plate.
– Proper distance away from plate will prevent
metal from sticking to the tip
– Hold tip so that two preheat holes are in line with
the cut
2. Hold torch at edge of metal until metal begins
to melt
– Top of torch may be slanted toward the cut &
changed to a vertical position as cut progresses
3. Press down slowly on the cutting
oxygen lever until cutting valve is
completely open
– When the cut is through the metal, move
torch along mark
4. Tilt torch tip toward direction of cut on
thin metal
– It should be held in a vertical position on
thick metal
5. Move torch slowly along surface or
oxygen stream will not pass
completely through thick metal
– To restart the cut, release cutting lever
and reheat metal again before pressing
cutting level
– Losing the cut may cause irregular edges.
6. When beveling plate edges or cutting
at an angle, lean the tip at the desired
angle and hold the torch parallel to
the work.
Correct Cut
Notice that the top edge
is square and that the
drag lines show a slight
curve.
Oxygen Pressure Too
Low
Produces a cut with
rough surface, makes it
difficult to hold cut and
results in slow speed
with too much lag.
Speed Too Fast
Produces a rough
cut with pronounced
drag line very
similar to too low
oxygen pressure.
Oxygen Pressure
Too High
Produces a rough
surface, melts down
top edge and
wastes oxygen.
Too Much Acetylene in
Preheats
Reduces cutting speed
approximately 25%.
Forms carbon deposits on
cut surface and wastes
acetylene.
Correct Cut
Here the factors of tip
size, pressures and speed
are correct…results in
square top edge and
uniform narrow kerf.
Preheats Too Heavy
Top edge is melted
down, kerf irregular
and excess gas is
consumed by the
preheat flame.
Preheats Too Small
Wastes time as
maximum speed
cannot be obtained.
Low cutting speed
results in gouges at
bottom edge of cut.
Oversize Tip
Produces a kerf which
is too wide, causing
not only a waste of
plate but also a waste
of both gases.
Undersize Tip
Inefficient cut
because piece will not
drop when end is
reached as slag has
not cleared the kerf
and cutting time will
be excessive.
Steps to Follow When
Piercing Holes
1. Hold blowpipe tip perpendicular to
the surface until a spot on the
surface begins to melt
2. Raise torch until tip is about 1/2”
from the surface and slowly press
the lever as torch is raised
3. Move tip to one side of the heated
area so that the slag can be blown
out
4. Move inner cone within about 1/8”
from the surface and make the cut
on the inside edge of the hole
5. To facilitate the cutting of a hole in
thick metal, drill a hole 1/4” in
diameter or larger and start the
piercing in this hole.
Care of Oxyfuel Tips
• Tips frequently become spattered with metal or
other materials that may cause inferior work.
• To clean tips:
– Rub emery cloth, steel wool, or the file on a tip
cleaner to clean and square the tip point.
– Insert the correct size cleaner into each orifice.
Push in and pull out; do not twist or bend the
cleaner.
– Open oxygen slightly during this procedure to blow
out foreign particles.
– Care should be taken not to damage the threads
and seats of the tips.
Preparing Metal for Welding
• Free the metal from oil, paint, grease,
dirt, rust, and other foreign material.
Heat the metal with the torch, and then
clean with a wire brush.
• Thick metal should be beveled with a
grinder or torch.
• Align the plates to be welded and tack
weld them to prevent warping.
Proper Welding Tip Positions
• The blowpipe can be held like a hammer when
standing or like a pencil when sitting.
• The tip and welding rod should be held at a 45o
angle to the work surface.
• The inner cone flame should be 1/16” to 1/8”
above the metal.
• Preheating the metal is very important in
making a successful weld; therefore, the flame
should be moved in the direction of the weld,
and the cone should stay inside the puddle.
Oxyfuel Welding Procedures
• One of the most important steps in learning to
weld with oxyfuel is to carry a molten puddle of
metal along the line or seam of parts to be
joined.
• Forming & running the bead:
– Flame held at starting point until a bright round
pool (1/4” to 3/8” in diameter) is formed
– Welding speed should be adapted to maintain a
uniform puddle width.
– Inner cone held 1/16” to 1/8” above surface
– Slow speed: flame burns a hole through the metal
– Fast speed: bead will be irregular and narrow
– Most common movement pattern for fusion
welding is the circular motion
– Zigzag motion is best when using a filler
rod
– Torch should be held at about 45o to the
surface
– Welding rod should be held at 45o, but
slanted away from the torch tip
– Rod diameter should be equal to the
thickness of the metal
– Torch may be held so tip is pointed in
direction of weld (forehand welding) or tip
pointed toward weld (backhand welding)
Types of Welded Joints
• Most are either butt joints or fillet joints
• Butt welding:
– Two pieces of metal are butted together
and welded, with or without beveling
• Fillet welding:
– Metal pieces are joined together forming
an angle
Welding Cast Iron
• Usually done with a bronze rod,
unless the color of the base
metal must be matched
• Cast iron rods require higher
preheating than bronze rods.
• Practice procedure for welding cast
iron:
– Select the correct flux.
– Clean and bevel the edges of the stock.
– Use a 3/16” rod with a neutral flame and
tack the ends together.
– Heat the rod tip to a red-colored heat and
dip it in the flux, then dip the tip into the
molten puddle of cast iron.
– Weld in the same manner as fusion
welding on mild steel. Dip the hot tip of
the rod in flux from time to time. If
bubbles appear, add more flux.
• Practice Procedure for Braze Welding:
– Does not require extremely high welding
temperature
– Clean surface to be welded
– Bevel and align edges of the metal
– Use neutral flame and heat the end of the rod
and dip into the flux
– Heat the area to be welded to a dull red and
tack ends
– Apply flux from rod on heated area, then pass
rod into flame and deposit a small amount of
bronze at the intervals until the weld is
complete.
– Add flux from time to time.
Hardsurfacing
• Application of an all alloy material to
another metal for the purpose of
reducing wear
• Procedure:
– Thoroughly clean the metal before applying
alloy.
– Place the material to be hardsurfaced in a
flat position.
– Heat a small section of the area with an
excess acetylene flame until the metal
begins to sweat.
– Touch the tip of the alloy rod to the surface
and melt enough of the rod to form an
alloy cover 1/16” thick and a desirable
width without heating the base metal to a
melting point.
– Maintain the hardsurfacing temperature in
front of the path on the hard metal. Add
just enough rod to the metal to maintain a
uniform thickness and width.
– Hardsurfaced metal should be allowed to
cool slowly. Dry lime serves as a good
cover for cooling metal.
– Be sure to follow recommendations of the
manufacturer of the hardsurfacing rods.
American Welding
Society Certification
• The American Welding Society (AWS) is
the professional organization
responsible for setting standards for the
certification of weldors.
• 1st step in becoming a highly skilled
craftsman is to certify as an Entry Level
Weldor
• Certification process for Entry Level Weldor
consists of:
– A Practical Knowledge Test:
• Welding/cutting theory
• Welding/cutting inspection & testing
• Skill-related vocabulary
• Metal identification
• Welding variables
• Electrical fundamentals
• Welding symbol interpretation
• Fabrication principles & practices
• Safety
• Requires a minimum passing grade of 75%, with a
minimum score of 90% on safety-related questions
– A Performance Test:
• Reading welding symbols
• Following written procedures
• Cutting parts to proper specifications
• Fitting parts correctly
• Performing specific welding techniques
• Prepare test coupon by oxyfuel (OFC) and
plasma-arc cutting (PAC)
– Includes both cutting straight lines and
piercing holes
Checking for Cylinder Leaks
• Standard acetylene cylinder contains from 90 to
154 ft3, stored in a porous filler saturated with
acetone
• Cylinders are filled under pressure and may
develop leaks around the valve stem or in the
“soft plugs”
• An acetylene cylinder leaking for an entire
weekend into a closed facility can become a
tragedy of significant proportions.
– Sparks from electrical switches or pilot lights on
forced-air heaters can provide the necessary
ignition source.
•
•
To guard against fire damage, a good
practice is to check acetylene cylinders for
leaks when delivered.
Materials:
– Small paintbrush
– One-quart container
– One pint liquid soap, or a soap and water
solution
•
Procedure:
1. Lay acetylene cylinder on its side and “paint”
the soft plugs with the soap solution. A leak
here will cause bubbles to form.
2. Stand the cylinder upright and paint the soft plugs
on the shoulders of the bottle. DO NOT try to
stop leaks in or around soft plugs—call the dealer
and have the cylinder replaced!!
3. Paint the regulator receptacle or main opening
before attaching the regulator. If the bottle shows
a leak now, this means that the main valve seat is
damaged and leaking, regardless of how tightly
the cylinder valve is closed.
4. Paint the main valve stem around the ring nut at
the top of the valve. If a leak is present here,
stop the leak by tightening the ring nut with an
adjustable wrench.
5. Attach the regulator to the cylinder and open
the cylinder valve; paint the regulator ring nut
and repaint the cylinder valve stem.
6. Ask the distributor that any leaking bottles be
replaced at their cost.
•
Oxygen cylinders can be checked in the
same manner EXCEPT:
– A commercial leak detector liquid such as
“SnoopTM” should be used (BEST IDEA).
OR
– A non-petroleum based liquid detergent must
be used (such as IvoryTM liquid).
– Remember, oxygen cylinders are pressurized
to about 2,200 lbs. psi.
Acknowledgements
Kirk Edney, Curriculum Specialist, Instructional Materials Service,
edited and reviewed this PowerPoint presentation.
Kristie Weller, Undergraduate Technician, Instructional Materials
Service, organized and developed the information used in this
PowerPoint presentation.
All Rights Reserved
Reproduction or redistribution of all, or part,
of this presentation without written
permission is prohibited.
Instructional Materials Service
Texas A&M University
2588 TAMUS
College Station, Texas 77843-2588
http://www-ims.tamu.edu
2007