Thermal Cutting
1
Definition
A group of processes that use heat to sever metals by
melting or by chemical reaction of oxygen with the metal at
elevated temperatures
2
A Group of Processes
What are the two common thermal cutting processes?
3
Oxyfuel Cutting
4
Definition
A group of processes used to sever or
remove metals by high temperature
exothermic reaction of oxygen with the base
metal.
(Welding Handbook, 5th ed.)
What is an exothermic reaction?
5
Oxyfuel Cutting Principles
What is the source of the heat?
How hot is the flame?
How does the process work?
Will compressed air work
instead of oxygen?
Why is acetylene the preferred
fuel gas for thermal cutting?
6
Principles-cont.
What type of flame should you use when cutting
with oxyacetylene torch?
What determines the working pressure for the
acetylene and oxygen?
7
Principles-cont.
Victor cutting pressure chart
Thickness (inch)
1/8
1/4
1/2
3/4
1-1/2
2-1/2
3
Tip Size
000
00
0
1
2
3
4
Drill Size
70
66
59
56
53
50
45
20-25
20-25
20-25
30-35
35-45
40-50
40-50
3-5
3-5
3-5
3-5
3-7
4-10
5-10
Oxygen Pressure
Fuel Pressure
8
OxyFuel Cutting Equipment
What is the difference between a cutting attachment and a cutting torch?
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Cutting Attachment
A.Oxygen lever
B.Oxygen cutting valve
C.Oxygen tube
D.Attachment head
E.Nozzle nut
F.Cutting nozzle
G.Preheat orifices
H.Cutting orifice
I.
J.
K.
L.
M.
N.
O.
Preheat Oxygen & acetylene
Mixing chamber
Cutting attachment
Preheat oxygen valve
Preheat acetylene
O-rings
Attachment nut
10
OxyFuel Cutting
Flame
Identify the neutral flame and
explain how to tell the difference
between the three types of flames?
C
A
B
11
OxyFuel Cutting-cont.
Organize the following step for
completing an oxyacetylene cut in the
correct order.
A. Fully depress cutting lever quickly.
B. Heat the metal until a spot is
cherry red.
C. Move torch across the surface of
the metal.
D. Hold the torch on the edge of the metal with the tips of the
inner cones about 1/8 inch from the surface.
12
Four (4) Factors Which Control Quality of Cut
1.
2.
3.
4.
Preheat
Clearance
Speed
Pressure
What are the indications of
excessive preheat?
How can you determine if a cut was
completed with excessive or insufficient
clearance?
What are the results of excessive or insufficient speed of travel?
How can you tell if the oxygen pressure was set correct?
13
Piercing Steel
What hazard can occur when piercing
metal with an oxyacetylene torch that isn’t
usually present when cutting?
Organize the following steps required to
pierce a hole in the correct sequence.
A. Raise torch 1/2 inch or more above metal.
B. Preheat spot until cherry red.
C. Once cut breaks through, lower torch and complete the cut.
D. Depress cutting lever and simultaneously start torch movement
E. Check to insure heat cherry read all the way through
14
Cutting Pipe
The first step in cutting pipe is piercing the pipe.
After the pipe is pierced two different methods can be used.
– Pipe 3 inch diameter and less: cut 90o to the left and right, keeping
the torch at the same angle. Rotate the pipe 180o and repeat.
– Pipe > 3 inch diameter: cut in quadrants rotating the angle of the
torch to stay perpendicular to the surface of the pipe or rotate the
pipe.
15
Plasma Arc Cutting
16
Definition
In the plasma arc cutting process compressed air is forced
through a small orifice at high speed. At the same time an
electrical arc is completed from the electrode in the torch
to the metal which converts the gas to a plasma.
The plasma has sufficient heat and velocity to blow the
molten metal from the cut.
17
Plasma Arc Cutting
Why was the plasma arc cutting method developed, oxyacetylene
cutting was already available?
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Plasma Arc Cutting--cont.
A. Electrode
B. Compressed air
C. Nozzle
D. Plasma
E. Standoff
F. Base metal
19
Plasma Arc Cutting--cont.
Stand off
– All plasma arc torches require a
distance between the nozzle opening
and the metal.
– This is called the stand off.
Insufficient Stand off
– Excessive heat on cutting tip
– Accelerated erosion of cutting orifice
Excessive Stand off
– Reduced heat at cut
– Reduced quality of cut
Check owners manual on piercing. Most plasma
arc torches must start from an edge or have
limited piercing capabilities.
20
Questions?
21