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UNIT: Oxy-Acetylene; Welding, Brazing, Cutting and Heating
LESSON: Oxy-Acetylene Welding (OAW)
RUNNING A BEAD WITH AND WITHOUT FILLER ROD
Standard B7.4
Know how to fusion-weld mild steel with and without filler rod by using the oxy-fuel system
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The Welding Flame
A chief advantage of theoxy-acetylene flame is itshigh operatingtemperatures.
This oxy-acetylene flamecan easily melt allcommon metals.
The proper mixture of
oxygen and acetyleneburns at 5,589 degreesFahrenheit, which makesit the hottest oxy-fuel gasflame.
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Types of Flames
Three types of flames can be
produced with the oxy-
acetylene torch: carburizing,
neutral, and oxidizing.
The operator must be able torecognize each type of flame
by its size, shape, and color.
The operator must also master
the adjustment of the oxygen
and acetylene hand valves on
the welding torch to produce
the desired flame.
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Carburizing Flame Flame contains more
acetylene than oxygen.
This flame is easy to recognizeby the outer flame, which has aslim bluish taper with anorange tip.
Inside this outer flame is ashorter, blue flame called theacetylene feather.
Flame has a lower temperature
than the neutral flame. Flames are sometimes used
for silver brazing, brazewelding, and soldering.
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Neutral Flame
The neutral flame is produced bya proper balance of oxygen and
acetylene.
It is approximately 5,589 degrees
Fahrenheit and is the most widely
used of the three types of flames.
As the flame is adjusted from a
carburizing flame to neutral flame
by adding more oxygen, the light
blue acetylene feather disappears.
At the same time, the brilliant
inner cone becomes slightly
shorter and more sharply defined.
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Neutral Flame - Cont.
When a neutral flame isdirected upon a steel surface,the metal melts slowly.
The molten metal does notboil and few sparks appear.
The neutral flame protectsthe molten steel fromoxidation, and the weld joint
is not burned.
Extremely strong welds areproduced from this flame.
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Oxidizing Flame
Flame contains moreoxygen than acetylene.
Is similar to the shape of the
neutral flame, however the
inner cone of the oxidizingflame is more pointed,
shorter, and purple.
The flame can also be
distinguished from theneutral flame by a loud
hissing sound caused by
the excess rush of oxygen.
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Oxidizing Flame Cont.
This flame has very littlepractical use in welding.
Its temperature may reach6,300 degrees Fahrenheit,but the oxides that form whenthe excess oxygen combineswith the molten metal causeproblems with the weld.
Such problems includebrittleness, weakness, andhardening around the weld.
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Characteristics of the
Three Welding Flames
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Holding the Torch
A torch may be held in either one of twoways, depending on which is the morecomfortable for you.
When welding light-gauge metal (under 14gauge), most operators prefer to grasp the
handle of the torch with the hose over theoutside of the wrist, in the same manner apencil ordinarily is held.
In the other grip, the torch is held like ahammer, with the fingers lightly curled
underneath.
In either case the torch should balanceeasily in the hand to avoid fatigue.
Pencil Grip Method
Hammer Grip Method
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Pushing a Puddle Hold the torch so the flame points in the
direction you are going to weld and at
an angle of about 45 degrees with thecompleted part of the weld.
If you are right handed, start the weld atthe right edge of the metal and bring theinner cone of the neutral flame to within
1/8 of the surface of the plate.
The left-handed person reverses thisdirection.
Hold the torch still until a pool of moltenmetal forms.
Then move (push) the puddle acrossthe plate.
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Pushing a Puddle Cont.
As the puddle travels forward, rotate
the torch to form a series ofoverlapping ovals or circles (forming a
bead)
Do not move the torch ahead of the
puddle, but slowly work forward, givingthe heat a chance to melt the metal.
If the flame is moved forward too
rapidly, the heat fails to penetrate far
enough and the metal does not melt
properly.
If the torch is kept in one spot too long,
the flame will burn a hole through the
metal.
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Laying a bead with filler rod
On some types of joints (outside cornerwelds) it is possible to weld the two piecesof metal without adding metal from a fillerrod.
The use of a filler rod requires coordinationof the two hands.
One hand must manipulate the torch to carrya puddle across the plate, while the otherhand must add the correct amount of fillerrod.
In most instances the use of a filler rod is
advisable because it builds up the weld,thereby adding strength to the joint.
The strength of a weld depends largely onthe skill with which the rod is blended, orinterfused, with the edges of the base metal.
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Selecting the filler rod
Filler rods come in a variety of sizesranging from 1/16 to 3/8 indiameter.
The size of rod to use will depend
largely upon the thickness of themetal being welded.
The general rule is to use a rod witha diameter equal to the thickness ofthe base metal.
In other words, if a 1/16 metal isbeing welded, a 1/16 diameter rodshould be used.
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Laying a bead with filler rod Cont.
The torch is held at an angle ofapproximately 45 degrees to the basemetal, hold the rod at approximately thesame angle as the torch but slant itaway from the torch.
Move the torch tip over the starting edgeand rotate the flame near the metal in acircular or semicircular motion until thebase metal melts into a small puddle.
Once a small pool of the base metal is
established, dip the tip of the rod in themolten pool.
ALWAYS DIP THE ROD IN THECENTER OF THE MOLTEN POOL.
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Laying a bead with filler rod Cont.
The molten puddle will melt the rodand add to the puddle, as the rodmelts in the pool, advance the torchforward.
Concentrate the flame on the base
metal and not on the rod.
Do not hold the rod above the pool. Ifyou do this the molten metal will fallthrough the air to the puddle.
When this happens it combines withthe oxygen in the air and part of itburns up, causing a weak, porousweld.
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Common Difficulties with Laying a
Bead with Filler Rod .
The beginner often experiences difficulty in
holding the welding rod steady which can
cause the rod to stick to the base metal
Instead of inserting the rod in the middle of
the puddle where the heat is sufficient tomelt it readily, a beginner generally inserts
the rod near the edge of the pool where the
temperature is lower. The heat at the edge is
not enough to melt the rod and the rod will
likely stick to the base metal.
If the rod sticks to the base metal, do not tryto jerk it loose.
Simply place the flame directly over the tip ofthe rod and the rod will be freedimmediately.
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Laying a bead with filler rod Cont.
The circular or semicircular
motion should be advanced
approximately 1/16 per
motion until the end of the
joint is reached.
Since the angle of the tip
flame is preheating the
metals ahead of the weld, the
last of weld is critical.
Slightly raise the welding tip
and increase the addition of
filler rod to insure a full
smooth weld.
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Bead with filler rod
Bead with Filler Rod
Push a Puddle (No filler rod)