Oxy acetylene fuel cutting occurs when oxygen is directed to heated metal resulting in the metal burning or oxidizing away. Oxygen is required to support any burning process. Oxygen is not flammable by itself, however, it increases the speed and force with which burning takes place. When combined with acetylene, the flame becomes hotter and combustion is faster.
An oxyfuel torch can be fitted with cutting attachments instead of using a welding head. The cutting attachments can be used to cut steel approximately 6 inches thick.
Oxyfuel cutting operations can use gasses such as oxygen, acetylene, MAPP, natural gas and propane.
Oxyacetylene Equipment Check List Includes:
Oxygen/Acetylene welding hose
Single-purpose oxyfuel cutting torch
Cylinders and cart
Flash arrestor and check vales (protective equipment)
Flint lighter to ignite torch
Oxy Acetylene Cutting Equipment
Oxy Acetylene Cutting Torch
Oxy Acetylene Torch Styles
The cutting torch (see figure 5-12 below),
like the welding torch, has a tube for oxygen and one for acetylene. In
addition, there is a tube for high pressure oxygen, along with a
cutting tip or nozzle.
Oxy-actyelene Cutting Torch Diagram - Figure 5-12
Tip: The tip (see figure 5-13)
is provided with a center hole through which a jet of pure oxygen
passes. Mixed oxygen and acetylene gas pass through holes surrounding the
center holes for the preheating flames. The number of orifices for
oxy-acetlylene flames ranges from 2 to 6, depending on the purpose for
which the tip is used.
Oxyactylene Cutting Tip Diagram
Torch Control: The cutting torch is controlled by a trigger or
lever operated valve. The cutting torch is furnished with
interchangeable tips for cutting steel from less than 1/4 in. (6.4 mm)
to more than 12.0 in. (304.8 mm) in thickness.
A cutting attachment fitted to a welding torch in place of the welding tip is shown in figure 5-14.
Welding Torch Cutting Attachment - figure 5-14
In order to make uniformly clean cuts on steel plate,
motor driven cutting machines are used to support and guide the cutting
torch. Straight line cutting or beveling is accomplished by guiding the
machine along a straight line on steel tracks. Arcs and circles are cut
by guiding the machine with a radius rod pivoted about a central point.
Typical cutting machines in operation are shown in figure 5-15 and figure 5-16.
Cutting Machine Bevel
Welder using an oxyfuel cutting machine to make a circular bevel
Oxyfuel Machine for Making Multiple Simultaneous Cuts - Figure 5-16
Oxyfuel Cutting Tip Styles
There is a wide variety of cutting tip styles and
sizes available to suit various types of work. The thickness of the
material to be cut generally governs the selection of the tip. The
cutting oxygen pressure, cutting speed, and preheating intensity should
be controlled to produce narrow, parallel sided kerfs.
Cuts that are
improperly made will produce ragged, irregular edges with adhering slag
at the bottom of the plates. Table 5-3 identifies cutting tip numbers, gas pressures, and hand-cutting speeds
used for cutting mild steel up to 12 in. (304.8 mm) thick.
Oxyactylene Cutting Information - Table 5-3
(1) Various manufacturers do not adhere to the numbering of tips as set forth in this table; therefore, some tips may carry different identification numbers.
Operation of Oxy acetylene Cutting Equipment
Flame Cutting Steel Plate
Diagram a: Example of steel plate flame cutting with an oxyfuel cutting torch nozzle. Diagram b: flame-cut plate cross-section with drag lines
Oxygen Acetylene Welding Cutting Torch Video
Oxyfuel Operating Steps:
Here are the operating steps for oxyfuel cutting:
a. Attach the required cutting tip to the torch and adjust the oxygen and acetylene pressures in accordance with table 5-3 above.
The oxygen and acetylene gas pressure settings listed
are only approximate. In actual use, pressures should be set to effect
the best metal cut.
Adjust the preheating flame to neutral.
Hold the torch so that the cutting oxygen lever or trigger can be
operated with one hand. Use the other hand to steady and maintain the
position of the torch head to the work. Keep the flame at a 90 degree
angle to work in the direction of travel. The inner cones of the
preheating flames should be about 1/16 in. (1.6 mm) above the end of the
line to be cut. Hold this position until the spot has been raised to a
bright red heat, and then slowly open the cutting oxygen valve.
If the cut has been started properly, a shower of sparks will fall
from the opposite side of the work. Move the torch at a speed which
will allow the cut to continue penetrating the work. A good cut will be
clean and narrow.
When cutting billets, round bars, or heavy sections, time and gas
are saved if a burr is raised with a chisel at the point where the cut
is to start. This small portion will heat quickly and cutting will start
immediately. A welding rod can be used to start a cut on heavy
sections. When used, it is called a starting rod.
Oxyacetylene Cutting Hose
Two hoses are built into one (siamesed). Green hose is used for oxygen, red for acetylene, black for any inert air or gas
General requirements include (follow manufacturers directions):
Always check for tight hose connections and leaks
Blow out the cylinder value
Do not stand behind or in front of regulator when opening the cylinder value
First turn on cylinder value and then adjust the regulator pressure screw
Slowly open the cylinder valve
Purge any oxygen and acetylene passages
Make sure mixing know is off before lighting torch
Light the acetylene
Never use with grease or oil. Do not handle with greasy gloves or oily hands. Oil and grease can become explosive in hte presence of oxygen!
Do not substitute oxygen for air
Keep the work area clean
Note that oxyacetylene becomes unstable above 15 PSI, do not use above this level (oxygen max is 40 psi)
Do not pick up materials with gloves after cutting