OXY-ACETYLENE CUTTING
AND WELDING
UNIT 23-24
I CAN
I can identify oxyacetylene equipment
 I can describe the safe startup, settings and
shutdown of the oxyacetylene equipment.
 I can explain the correct operating
procedure for brazing, heating and cutting.
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Oxy/Acetylene
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Fusion
– Process of joining two metals by fusioning (melting)
the adjoining surfaces.
– Move molten puddle back & forth between the metal.
Holds very little
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Brazing
– Process of joining two metals by fusioning (melting)
with a third metal bronze
– Brazing flame is 800 degree (F) or below.
– Base metal is not brought to molten stage.
THE FIRE TRIANGLE
TO PRODUCE FIRE, THREE THINGS MUST BE PRESENT AT THE
SAME TIME
The basic process that allows the oxy-acetylene equipment to work.
OXYGEN
HEAT
FUEL
Oxyfuel Gas Welding & Cutting
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Oxyfuel is a group of processes that use heat
generated as a result of the combustion of a
mixture of oxygen and a combustible gas.
Acetylene is the most commonly used in oxyfuel
processes. Propane is another good source of fuel.
The flexibility and mobility provided by oxyacetylene welding allow its use in all
metalworking industries.
Oxyfuel welding is primarily used for
maintenance, general fabrication, and repair work.
Chemicals Used
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Oxygen
– Colorless, odorless, tasteless gas
– Supports combustions & increase heat
– Produce by cooling air to a low temperature and turning it
into liquid where the oxygen is separate out.
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Acetylene
– Colorless, has a very distinctive odor
– Highly flammable
– Produce by mixing calcium carbide (coke + limestone burnt
together) and water yields acetylene and calcium hydroxide.
ADVANTAGES
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The relative cost of the equipment is low.
No electricity is required for this process.
Can be used for welding in all positions because no
electrical cables are required and the operator has
precise control of the process. This process is also
extremely portable.
Can be used on both thick and thin materials, which
makes it a very versatile process.
Very clean, producing no slag or spatter that must be
removed from the weld.
Produces high quality welds when done properly.
LIMITATIONS
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The materials that can be welded are limited
primarily to ferrous materials.
Creates a “Hot Zone”, fire hazard, because of the
sparks and flame generated in the welding process.
Requires the handling of high pressure gases. The
combination of oxygen with a fuel gas creates the
potential for flashbacks and backfires.
The process can often be slow when compared to
other types of welding processes.
Welding is limited to oxy-acetylene or oxyMAPP.
TIP HEIGHT
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This slide depicts cuts that have been made when the
cutting tip is too high or too low.
If the cutting tip height is too high, the top edge of the
cut is beaded or rounded. The cut face is not smooth
and often is only slightly beveled because the preheat
effectiveness is partially lost because the tip is held too
high. In this situation, the cutting speed is reduced
because of the danger of losing the cut.
If the cutting tip height is too low, the cut had grooves
and deep drag lines caused by an unstable cutting action.
In this case, part of the preheat cone burns inside the
kerf where normal gas expansion deflects the oxygen
cutting stream
CUTTING
The preheat flame performs four functions:
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To preheat the base metal to ignition temperature.
To maintain a protective shield around the cutting stream.
To maintain the reaction temperature.
To penetrate rust, scale, and other foreign properties on the base
metal.
CUTTING
Before cutting action can start, the steel
must be preheated to a bright cherry red.
 When the red spot appears, depress the
cutting oxygen lever slowly.
 Move steadily across base metal, keeping
the luminous inner cones approximately 1/8
inch above metal.
 While moving across the base metal, if
cutting stops, release the cutting lever,
preheat again and restart the cut.
 Use a smooth straight edge to steady and
guide torch movement, if necessary.
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Type of Flame
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Oxygen flame
– More oxygen is used than acetylene
– Used on torch cutting or heating.
– Flame is noisy
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Acetylene
– More acetylene than oxygen.
– Flame produces a black soot and is worthless
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Neutral
– Oxygen & acetylene same pressures
– Quiet flame
– Used on brazing.
FLAMES
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There are three basic flame types used in oxyfuel processes.
The neutral flame is used in most welding, brazing, soldering and
cutting because it does not carburize or burn the metal. A neutral
flame has a bright blue outer envelope with a sharp inner cone visible.
It is called a neutral flame because there is an approximate one-to-one
mixture of acetylene and oxygen. This results in a flame that is
chemically neutral. The brilliant white cone should be approximately
1/16” to ¾” long, depending on the welding tip size.
Any variation from the one-to-one oxygen-acetylene mixture will alter
the flame characteristics. When excess oxygen is forced into the
oxyacetylene mixture, the resulting flame is said to be oxidizing The
oxidizing flame has excess oxygen beyond the neutral flame. It is pale
blue in color without the clearly defined inner cone and characterized
by a hissing sound. An oxidizing flame is sometimes used for brazing.
The carburizing or reducing flame is caused by excess acetylene and is
characterized by a feather flame that contracts towards the welding tip
and inner cone. A carburizing flame can be identified by observing
the existence of three flame zones instead of the usual two found in the
neutral flame. The end of the brilliant white cone is not as well defined
and is surrounded by an intermediate white cone, that has a feathery
edge in addition to the bluish outer envelope.
Equipment
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Cylinder Sizes
– Oxygen—green color cylinder
» Sizes—244, 122, or 80 cubic feet.
– Acetylene—red color cylinder
» Sizes—300, 100 or 60 cubic feet
» Contains acetone which absorbs large amounts of acetylene without
changing the nature of the gas.
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Cylinder Pressure (Full pressurize cylinders)
– Oxygen—2200 psi at 70 degree244 cubic feet
– Acetylene—250 psi at 70 degree100 cubic feet.
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Operating Pressure (NEVER ADJUST ACETYLENE ABOVE 15 PSI)
– Cutting—5 parts oxygen to 1 part acetylene
» Setting—35 oxygen, 7 acetylene
– Brazing—1 part oxygen to 1 part acetylene
» Setting 3 oxygen, 3 acetylene
Cylinders
Acetylene Bottle
Oxygen Bottle
Equipment II
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Cylinder Valve
– Oxygen & acetylene valves—open all the way.
» Allows the gases to flow one way—out.
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Gages
– 1st gage will show the pressure in the cylinders
» Oxygen 0 to 4000 psi; Acetylene 0 to 400 psi
– 2nd gage will show the working line pressure.
» Oxygen 0 to 100 psi; Acetylene 0 to 30 (Never go above 15 psi)
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Regulators
– Used to adjust the line pressure.
– Double stage regulators.
– Turn regulator knob clockwise to increase pressure.
NOZZLES
Regulators
Equipment III
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Nuts
– Acetylene nuts are grooved—counter threads.
» Turn counter clockwise to tighten
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Torch body
– Two passages for the gases to travel.
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Hoses
– Acetylene—red; Oxygen—green
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Brazing tips
– Numbered 0—15; Larger the number the larger the hole.
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Cutting tips
– Have 4 preheat orifices (holes)
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Oxygen Pre-Heat Valve
– Adjusts your flame
Brazing Head Setup
Torch Head Setup
Cutting Tip
Safety Concerns
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Lens—Use a number 5 lens.
– Used to see the hot metal from the cold
metal.
Acetylene Adjustment
– Never go above 15 psi working pressure.
Check for leaks.
– Use non-organic soap and water. Brush soap
and water on connection and see if bubbles
form. If bubbles appear—fix.
Use long sleeve, long pants, close toe shoes,
leather gloves.
Backfire—tip is too close to metal, causes the
flame to blow out. Caused by overheating,
wrong pressure.
Flashback—flame goes into torch head, makes
a shrill hissing noise. Cause—hose leak. Shut
off acetylene, check and fix.
SUMMARY
Most popular gases for heating, cutting,
welding metal are acetylene & propane.
 Acetylene is shut off first followed by
oxygen.
 3-types of flames – oxidizing flame(excess
oxygen) hottest flame; carbonizing
flame(excess acetylene) cooler flame;
neutral flame(correct balance of
acetylene/oxy
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SUMMARY
Check leaks with soapy water.
 NEVER!!! NEVER use oil or oily
substance around oxygen regulators,
fittings, etc.
 Slag is an insulator rather than steel. Will
not cut.
 Clearance prevents bevel cuts(distance
between tip and base metal.
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SUMMARY
Oxygen must be 99.5% pure to support the
combustion of iron.
 Cutting or heating galvanized metal creates
a toxic fume.
 Prevent Backfire(tip to close to work, dirty
tip, tip overheating) & flashback(leakage)
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