Hard-
Surfacing,
Building
Fusion
Welding
Carbon
Welding
Non-Ferrous
Metals
Heating
& Heat
Treating
Braze
Welding
Welding
Cast Iron
Welding
Ferrous
Metals
Brazing
&
Soldering
Equipment
Set-Up
Operation
Equipment
For
OXY-Acet
Structure
of
Steel
Mechanical
Properties
of Metals
Oxygen
&
Acetylene
OXY-Acet
Flame
Physical
Properties
of Metals
How Steels
Are
Classified
Expansion
&
Contraction
Prep
For
Welding
OXY-Acet
Welding
& Cutting
Safety
Practices
Manual
Cutting
Oxygen
Cutting By
Machine
Appendices
Testing
&
Inspecting
3
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It is this two-stage combustion process
which produces the well-defined inner cone in the oxy-acetylene flame. The
first stage of reaction takes place
at the boundary between the inner cone and the pale blue outer flame. The
second stage takes place in the outer
flame. If the proportion of acetylene supplied to the tip is increased, a white
”feather” appears around
the inner cone. This feather contains white-hot particles of carbon which, for
lack of sufficient
oxygen in the original mixture, cannot be oxidized to carbon monoxide at the inner
cone boundary. On the other
hand, if the proportion of oxygen fed to the tip is increased, the inner cone
will shorten noticeably and the noise
of the flame will increase. Flame
Adjustment For
most welding, a neutral flame is desired. Not even a skilled welder can distinguish
visually between a true neutral
flame and a slightly oxidizing flame. But anyone who
knows what to look for can tell the difference between a
neutral flame and a flame with a slight excess acetylene feather. Therefore, we
always adjust the flame to neutral from
the excess-acetylene side. We start with an excess of acetylene when we
light the torch and then increase the
flow of oxygen until the excess-acetylene feather just disappears. If the flame
is then too large for our purposes,
we reduce the oxygen flow first, to produce a feather, then cut back on the acetylene
flow until the feather
just disappears. Occasionally,
you will read instructions which call for a slight excess of oxygen, or a
slight excess of acetylene. Generally
speaking, such instructions imply that a slight excess of one gas cannot cause
trouble, but that a slight excess
of the other gas may. Unless otherwise defined, a slight
excess of acetylene means that you can just see a short
”feather”. A slight excess of oxygen means
that you’ve reduced the acetylene flow until the ”feather” has
disappeared, then reduced it a bit
more to cause a slight shortening of the inner cone. For
some operations, a substantial excess of acetylene is desired. The amount of excess
is then expressed numerically,
as ”2X”, ”3X”, or perhaps ”1-1/2X”. As shown in
Fig. 4-4, in a ”2X” excess acetylene flame the feather
(measured from the end of the torch
tip, not the end of the inner cone) is twice as long as the inner cone.
When a precise statement of amount
of excess oxygen is required, it is always expressed in terms of the
shortening of the inner cone from the
neutral flame length. Again, this is shown in Fig. 4-4.
