Department of Engineering
Design and Production
Lesson 12
Oxyfuel Gas Welding and Cutting
Professor Pedro Vilaça *
Materials Joining and NDT
* Contacts
Address: P.O. Box 14200, FI-00076 Aalto, Finland
Visiting address: Puumiehenkuja 3, Espoo
[email protected] ; Skype: fsweldone
February 2015
 OXYFUEL GAS WELDING (OFW) is a
manual process in which the metal
surfaces to be joined are melted
progressively by heat from a gas flame
and are caused to flow together and
solidify without the application of
pressure to the parts
 OFW can be applied with or without
filler metal
 The most important source of heat for
OFW is the oxyacetylene welding
(OAW)
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 Oxygen and fuel are stored in
separate cylinders
 The gas regulator attached to each
cylinder, whether fuel gas or
oxygen, controls the pressure at
which the gas flows to the welding
torch
 The mixed gases then pass
through the welding tip and
produce the flame at the exit end
of the torch tip
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 The equipment is versatile, low-cost, self-sufficient, and usually
portable
 It can be used for preheating, postheating, welding, braze
welding, and torch brazing, and it is readily converted into oxygen
cutting
 The process can be adapted to short production runs, field work,
repairs, and alterations
 The oxy-acetylene welding process (OAW) is by far the most
important, and probably the most versatile, of the oxy-fuel gas
welding (OFW) processes
 For welding applications the OAW is superceded by other
welding processes, e.g., the TIG welding process
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The gas acetylene (C2H2) is the most important fuel gas employed,
because it has the highest calorific (heat) value. Other
hydrocarbon gases are also used, e.g. Liquid Petroleum Gas
(LPG), Propane, etc.
deg C
Oxy-acetylene
3,100 to 3,300
Oxy-propane
2,500
Oxy-hydrogen
2,370
Oxy-coal-gas
2,200
Air-acetylene
2,460
Air-coal-gas
1,871
Air-propane
1,750
Table: Approximate Maximum Flame Temperatures
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Ratio: Oxygen versus Fuel gases for higher flame temperature
Ratio: Oxygen / fuel gas
Maximum temperature (ºC)
ACETYLENE
PROPANE
NATURAL GAS
HYDROGEN
1.1
4.5
1.5-2
0.22
3100
2820
2700
2400
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Chemical and physical characteristics of Oxygen and relevant fuel gases
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Chemical and physical characteristics of Oxygen and relevant fuel gases
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Ignition ranges of several fuel gases with mixture with air and oxygen
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 In practical applications the oxy-acetylene welding process (OAW)
is the only one applied in welding
•
Higher heat power density
•
Hotter for all the distances from the center of the flame
•
More reducing action
•
Easy to adjust with Oxygen
 The oxi-propane flame is more applied in brazing when temperature
and heat power should be lower
 Propane and butane are more safe to use fuel gases
 The propane, butane and natural gas allow greater autonomy as
they can be easily stored in large volumes.
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 Acetylene (C2H2) storing:
•
When under pressure of 203 kPa and above,
acetylene is unstable, and a slight shock can
cause it to explode, even in the absence of
oxygen or air
•
By dissolving purified and dried acetylene in liquid
acetone, a cylinder such as that shown in Figure
can be used to store about 7.79 m3 of acetylene
under a pressure of 1.7 MPa
•
The cylinders must be stored in an upright position
to keep the acetone from escaping during use
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•
The acetylene-acetone
Internal details of
dissolved-acetylene
cylinder
solution is in turn
absorbed by a porous
substance, such as
kapok, charcoal or
asbestos
•
The porous substance
must completely fill the
cylinder but, by virtue of
its porosity, it leaves
small spaces holding in
total a considerable
amount of liquid acetone
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Acetone is a chemical compound of hydrogen, oxygen and carbon
(CH2, CO, CH2). It is a liquid at room temperature with a pungent
smell (like nail varnish remover), boils at 56°C and is slightly
poisonous
•
It is inflammable and absorbs 25 times its own volume of acetylene
gas at atmospheric pressure. When the pressure is increased to
14 kg / cm2 it will absorb 370 times its own volume of acetylene
•
When acetylene gas is introduced into the cylinder, it is promptly
dissolved in the acetone, which in turn is contained in the tiny
pores or cells of the filling material
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•
Should disintegration of acetylene occur, it is localised by these tiny
pockets and so prevented from spreading to the remainder of the
acetylene in the cylinder
•
Not more than 20% of each cylinder’s gas capacity must be drawn off per
hour; otherwise acetone used to dissolve the acetylene in the cylinder
may be drawn out with the gas
•
In the high-pressure acetylene system the gas is stored in cylinders
having an average gas capacity of 3,398 to 6,230 litres
•
These cylinders may be used singly by individual welders, in which case
pressures of up to 1,05 kg/ cm 2 may be used at the blowpipe
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 Alternatively as a centralised manifold system feeding
multiple welding points, in which case, for safety reasons, the
line pressure is not allowed to exceed 0,63kg/cm2
•
The number of acetylene cylinders required on a manifold is
related to the total amount of acetylene required at any one
time.
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Manifold system on high-pressure acetylene supply line
Note: The oxy manifold may be basically the same or may be supplied for
liquid-oxygen evaporation plant.
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Manifolded supplies may be used for both acetylene and oxygen
cylinders, although where the oxygen consumption is high it is
more practical to use an oxygen generator/evaporator plant, the
oxygen being delivered and stored in the more compact liquid
form.
•
In each instance the gas is stored away from the workshop in a
special building designed to relevant safety requirements, the gas
is piped from the store to the supply points in the workshop.
•
The acetylene is conveyed in steel tubes (copper is not used
because of the danger of producing the explosive compound:
copper acetylide).
•
The line is protected by non-return valves and flash-back
arresters at each outlet. The cylinder is also protected by largecapacity flashback arresters.
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Oxygen cylinder
Acetylene cylinder
(Capacity, 220ft3 at 2 000 lb / in2, Weight 145 lb) (Capacity, 250ft3 at 250 lb / in2, Weight 215 lb)
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OXYFUEL GAS WELDING (OFW) STATION - Equipment
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1. Welding torch: efficient and light, producing a flame of the right shape
and temperature with controls that are easy to adjust allowing for the
quick and easy changing of nozzle tips, thus affording a wide range of
blowpipe power
2. Oxygen and acetylene gas regulators: to reduce the high pressure in a
gas storage cylinder to a lower working pressure, and at the same time
maintaining a steady supply, free from pressure fluctuations
3. Supplies of oxygen and acetylene gases, which must be safely stored in
cylinders and suitably piped to the welding areas
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4. Protection equipment, such as suitable colour-tinted
goggles, manufactured to the appropriate standard, e.g.
BS 679, and other protective clothing, such as chromeIeather gloves, aprons, etc
•
Filter glasses for goggles are invariably green, their main
function being to reduce the glare from the flame cone
and molten metal to a level comfortably acceptable to the
eyes of the welder, while also protecting the eyes from hot
sparks
•
They are produced in different densities or shades,
appropriate to light or heavy glare. Modern filters are
photo chromatic, i.e. they change shade automatically
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 Protection goggles
 Fire lighters
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5. Supplies of suitable filler rods in convenient diameters and lengths.
These are usually from 1,2mm to 4,8mm in diameter and 1mm in length
6. Certain other equipment, such as flexible, high-pressure rubber hoses,
coloured red for fuel gas and black for oxygen, with properly designed
connections, threaded left-hand for fuel gas and right-hand for oxygen, to
prevent accidental exchange
•
Also, safety devices, such as flash-back arresters, or hydraulic backpressure valves. Equipment such as refractory-surfaced work tables,
gas economizers, etc are desirable but cannot be regarded as
absolutely essential
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 Safety/security devices
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 Although individual designs from different manufacturers vary to
some extent in appearance and performance, welding torches
are of two main types, namely low-pressure and highpressure
Essential features of high-and low-pressure blowpipes
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Features of low-pressure with injector blowpipe
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 Types of torches/burners architecture
Features of high-pressure with no injector blowpipe
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•
The high pressure blowpipe is lighter and simpler. In operation
it is less troublesome since it does not suffer from backfires to the
same extent
•
It does not need an injector, so that the gases are fed to the torch
at equal pressures, and when the flame setting is neutral, in
equal proportions
•
To change the power of the blowpipe, it is only necessary to
change the nozzle tip size and increase or decrease the gas
pressures appropriately
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 Selecting a filler rod diameter
•
The following working formulae may be used:
 For butt welds up to t=4,8mm then D = t / 2
 For vee welds up to t=6,4mm then D = t / 2 + 0,8mm
Where: D is the rod diameter and t the plate thickness.
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 Selecting a filler rod diameter (cont.)
•
The diameter of the welding rod can considerably affect the ease of
welding and the weld quality
•
Too large a rod is slow to melt and can chill or freeze the weld pool,
leading to lack of fusion, cold laps and other defects
•
Too small a rod melts too fast and other metal tends to drop through
the joint. The rod must then be fed into the joint more rapidly,
requiring extra dexterity on the part of the operator
•
Quite a small increase in rod diameter greatly increases the total
available volume of weld metal, because V is proportional to D2,
where V is the volume of weld metal, and D the rod diameter
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 Procedure for adding a filler rod into the weld pool
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 Fluxes:
•
A flux prevents the oxidation of molten metal. The flux (material) is
fusible and non metallic
•
During welding, flux chemically reacts with the oxides and a slag is
formed that floats to and covers the top of the molten puddle of metal
and thus helps keep out atmospheric oxygen and other gases
•
Except for lead, zinc, and some precious metals, OFW of nonferrous
metals, cast irons, and stainless steels generally requires a flux
•
In welding carbon steel, the gas flame shields the weld adequately, and
no flux is required
•
Adjustment for correct flame atmosphere is important, but the absence of
flux results in one less variable to control
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 The maximum temperature of the oxy-acetylene flame is
3,100 to 3,300 °C and the centre of this heat concentration is
just off the extreme tip of the white cone. Combustion is
recognised as taking place in two main stages of combustion
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 Types of Flames in OAW
•
In oxy-acetylene welding the character of the flame is most important. Certain
technical terms must be learned in this connection
•
When the acetylene and oxygen are in equal proportions the resultant flame is
said to be neutral; when there is an excess of oxygen the flame is said to be
oxidising; and if more acetylene is present than oxygen the flame is said
to be carburising, or reducing
•
A reducing flame is on that, because of its need for oxygen will reduce surface
oxides, such as iron oxide. A strictly neutral setting is correct, but the slightest
excess of acetylene may keep oxidation to a minimum, particularly when welding
stainless steels
•
For example, non-ferrous alloys and carbon steels may require a reducing flame,
while zinc-bearing materials may need an oxidising flame
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 Three types of flame setting: mixture ratio
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1. Oxygen and acetylene (O2 and C2H2), in equal proportions by
volume, burn in the inner white cone. In the cone two separate
reactions take place, the oxygen combining with the carbon of the
acetylene to form carbon monoxide (CO), while the hydrogen (H2) is
liberated.
2. Upon passing into the outer envelope of the flame two more separate
reactions take place as combustion is completed. The carbon
monoxide takes up oxygen from the atmosphere, and as a result of
burning forms carbon dioxide (CO2). The hydrogen also burns with
oxygen from the atmosphere to form water vapour (H2O).
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•
While the quantities of acetylene and oxygen taken from the supply
are equal, something like two and a half times as much oxygen is
actually consumed, the balance being taken from the surrounding
air.
•
The combustion products are the reason for maintaining good
ventilation in gas welding bays, together with the fact that the flame
itself uses large quantities of oxygen from the air.
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FERROUS AND NONFERROUS METALS THAT CAN BE WELDED BY
OAW:
(a) - Match base metal ; (b) - No Flux required
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 Combustion with other fuel gases
 Acetylene: 2 C2H2+5 O2=4 CO2+2 H2O
 Propane: C3H8+5 O2=3 CO2+4 H2O
 Natural Gas: CH4+2 O2=CO2+2 H2O
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 Flame Setting: Influence of the Speed of Flow
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 Lighting a blowpipe
•
The correct pressures, as recommended for the appropriate nozzle,
should first be set, initially the fuel gas by opening slightly the blowpipe
acetylene valve and regulating it to the correct pressure by the
pressure-regulator screw
•
This procedure is repeated for the oxygen supply, the oxygen valve
then being closed. The fuel gas is turned on, ignited and adjusted so
that the flame just ceases to form soot but is not blown away from the
nozzle tip
•
The oxygen is now turned on at the blowpipe valve and adjusted until
the acetylene feather just disappears, to obtain a neutral flame setting
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 Lighting a blowpipe (cont.)
•
Each nozzle size will impose the flame conditions at the neutral setting
ranging from a soft quiet flame to a hard or harsh flame. The average
gas velocity is (approximately) 182,88 m / sec
•
To extinguish the flame, the fuel gas should be turned off first, followed
by the oxygen. In the event of backfires with either design of torch, the
fuel gas should be turned off first to prevent the internal temperatures
from being destructively high and damaging the blow-pipe body
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 Welding techniques
The usual techniques in oxy-acetylene welding are:
•
the leftward (push technique)
•
the rightward (pull technique)
•
(of rather less prominence are variations, such as) the all-position
rightward technique and Linde welding
For all descriptive purposes it is assumed that the operator is right
handed: should he be left handed, it is only necessary to interchange
the words 'right' and 'left' and 'rightward' and 'leftward'
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 When plate exceeds 6-4 mm, the combined power of the two
blowpipes is much higher than using a single blowpipe to weld an
equal thickness, even if employing the rightward technique
•
This means not only that less metal is needed, but also that the
operators are subjected to less physical discomfort and fatigue
•
Whether the weld calls for one operator or two, the weld can be
completed with a single pass without any need for multi-passes
•
Welding speed overall is much higher, and the consumption of gas
and filler rod is lower, up to about 50% saving, where the plate is
over 6,4 mm thick, than with the down-hand leftward or rightward
technique
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 Combined power of the two blowpipes (cont.)
•
Advantages are obvious from the point of view of both the
economies and the quality and soundness of the weld deposit
•
Absence of heavy oxide scale and smaller tendency to distort
because of uneven heating or weld-metal distribution is another
advantage
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 Some useful data will be found in Tables 1 to 6
Table 1 - Tack welds
Thickness of plate
6,4 mm
9,5 mm
12,7 mm
Dimensions of tack
12,7 mm long
19,1 mm long
25,4 mm long
152 mm
229 mm
305 mm
3,2 mm bare
3,2 mm
3,2 to 4,0 mm
Distance apart of tacks
Distance between
edges after tacking
Size and form of tack weld
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Table 2 - Welding rate in relation to plate thickness
Plate thickness
Welding rate
Leftward method
Rightward method
m/h
mm
mm
6,1 to 7,6
0,8, 2,4
-
7,6 to 9,1
1,6
-
5,5 to 6,1
3,2
-
4,6 to 5,5
4,0
-
3,7 to 4,6
4,8
4,8
3,0 to 3,7
-
6,4
2,1 to 2,4
-
7,9
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Table 2 - Welding rate in relation to plate thickness (continued)
Plate thickness
Welding rate
Leftward method
Rightward method
m/h
mm
mm
1,8 to 2,1
-
9,5
1,4 to 1,5
-
12,7
1,1 to 1,3
-
15,9
0,9 to 1,0
-
19,1
0,6 to 0,7
-
25,4
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Table 7 - Nozzle power in relation to plate or tube wall thickness
Plate or tube wall thickness Power of blowpipe (volume of acetylene per hour)
mm
litres
6,4
1,133 to 1274
7,9
1,274 to 1,416
9,5
1,416 to 1,557
11,1
1,472 to 1,614
12,7
1,557 to 1,699
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 Linde Technique
•
The Linde welding process is a special one basically used for the butt
welding of steel tubes at a temperature below the melting point of the
parent metal
•
When carbon is added to steel the melting points is lowered; e.g. a 0,8%
carbon steel has a lower melting point than a 0,2% carbon steel
•
When a carburising (or excess acetylene) flame is played on the surface
of mild steel, the steel at high temperature absorbs carbon on its surface
and the surface sweats because its melting point is lowered
•
The rightward technique is used, the flame being set with an excess
acetylene feather about one and a half times as long as the standard
neutral cone
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•
Nozzles larger than normal are used (Table 7) and special doublenozzle blowpipes allow pre-heating of the vee and increased welding
speed
Preheating the Vee
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The filler rod may also be of a larger diameter than usual (Table
8), as the blowpipe flame is played upon this more than upon the
joint walls
•
Normal-carbon mild-steel rod is unsuitable, and must be replaced
by one containing suitable proportions of silicon and manganese
•
Linde welding is at its best for materials, tubes, etc over 6,4 mm
thick; the joint edges should have a 70° included-angle vee with
clean oxide and scale-free surfaces
•
The welding should be carried out in the flat position, tubes being
rotated to achieve this. Tack welds should be about three times
the parent-metal thickness in length and taper formed
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•
As welding approaches completion, particularly on a tube, special
precautions become necessary. About 12,7 mm from the end of the run,
the blowpipe is adjusted to give a smaller neutral flame
•
This is now played on the original start of the weld, which is reheated
for about 50mm until red hot. The original start and finish are then fused
together at the root of the joint without adding filler wire
•
After fusion has been achieved, filler rod is again introduced to
complete the weld reinforcement. Tables 9 and 10 indicate the high
speeds which can be obtained by the Linde welding technique
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Table 9 - Welding rate in relation to thickness
Plate or tube wall thickness
Rate of welding
mm
m/h
6,4
4,6 to 4,9
7,9
4,0 to 4,6
9,5
3,7 to 4,0
11,1
3,0 to 3.4
12,7
2,7 to 3,0
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Plate or tube wall
thickness
Outside diameter
mm 152
mm 203
mm 254
mm 305
mm 457
mm
min
min
6,4
6,25
8
min
min
min
10
12,50
18
7,9
6,75
10,50
12
14
20
9,5
7,50
11,50
13,50
15,50
24
11,1
9
12,50
15
18,50
27,50
12,7
10,50
14
17
21
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Table 10 - Average time for butt pipe joint for different outside diameters of
pipe
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Department of Engineering
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Lesson 12a
Oxyfuel Gas Cutting
Professor Pedro Vilaça *
Materials Joining and NDT
* Contacts
Address: P.O. Box 14200, FI-00076 Aalto, Finland
Visiting address: Puumiehenkuja 3, Espoo
[email protected] ; Skype: fsweldone
February 2015
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Introduction to Material Cutting Technologies
General Classification
Cutting Technologies, include:
 Sectional cutting (e.g. beveling)
 Drilling
 Marking
 Removing partial layer from
surface
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Introduction to Material Cutting Technologies
Applicability Analysis of Cutting for Beveling
Welding Joint preparation (1/2):
Welding Joint
Process
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Introduction to Material Cutting Technologies
Applicability Analysis of Cutting for Beveling
Welding Joint preparation (2/2):
Welding Joint
Process
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Fundaments of OXYFUEL GAS CUTTING (OFC):
 A group of cutting processes that use controlled chemical reactions to remove
preheated metal by rapid oxidation in a stream of pure oxygen.
 A fuel gas/oxygen flame heats the workpiece to ignition temperature, and a
stream of pure oxygen feeds the cutting (oxidizing) action.
 The OFC process, which is also referred to as burning or flame cutting, can cut
carbon and low-alloy steel plates of virtually any thickness.
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Fundaments of OXYFUEL GAS CUTTING (OFC):
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Fundaments of OXYFUEL GAS CUTTING (OFC):
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Introduction to Material Cutting Technologies
Analysis of Cutting for Beveling
Geometrical characteristics of edges after cutting:
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Chemical Reaction in Iron Combustion, by Oxidation at Ignition Temperature:
1st- Fe + O = FeO +
267 kJ ( 64 kcal )
2nd- 3Fe + 2O2 =Fe3 O4 + 1120
3rd- 2Fe + 1.5 O2 = Fe2O3
kJ ( 266 kcal )
+ 825 kJ ( 190 kcal )
The products (oxides / slag) from the chemical reactions are:
 50% FeO ; 40% Fe2 O3 ; 10% Fe
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Note 1: In 1776, the French scientist Lavoisier conducted an experiment showing
that introducing a small slot of red-hot iron into a bottle containing oxygen it burned
continually: Lavoisier proved that the iron is fuel.
Note 2: The ignition temperature does not depend on the oxygen pressure. A carbon
steel foil ignites in oxygen according to the Semenov-Frank-Kamenetskii mechanism
at an initial surface temperature not lower than 1233 K.
The Iron (Fe) presents significant Advantages for OFC:
 Burns in Oxygen at Ignition Temperature.
 The combustion is highly exothermic.
 Ignition Temp. < Slag Fusion Temp < Base Material Fusion
Temperature
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
CRITERIA: Suitability of Materials for Flame Cutting (OFC)
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Equipment of OXYFUEL GAS CUTTING (OFC):
 The simplest equipment consists of two cylinders (one for oxygen and one for
the fuel gas, typically acetylene), gas flow regulators and gages, gas supply
hoses, and a cutting torch with a set of exchangeable cutting tips.
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Oxyfuel Gas Cutting Torch for Manual and Automatic Operation:
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Oxyfuel Gas Cutting TIPS for Several Operations:
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Fundaments of OXYFUEL GAS CUTTING (OFC):
 The OFC equipment manually operated is portable and inexpensive.
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Fundaments of OXYFUEL GAS CUTTING (OFC):
 Manual Cutting
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Fundaments of OXYFUEL GAS CUTTING (OFC):
 Cutting machines, employing one or several cutting torches guided by solid
template pantographs, optical line tracers, numerical controls, or computers,
improve production rates and provide superior cut quality.
 Machine cutting is important for profile cutting--the cutting of regular and
irregular shapes from flat stock.
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Fundaments of OXYFUEL GAS CUTTING (OFC):
 Machine Cutting
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Application of OFC in Beveling:
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Application of OFC in Beveling:
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Cutting Of Oxidation Resistant Metals:
 With oxidation-resistant materials, either a chemical flux or metal powder is
added to the oxygen stream to promote the exothermic reaction.
Basics Of Powder Cutting:
 In the powder cutting process, a finely divided "iron rich" powder is introduced
into the reaction zone.
 This iron powder, because of its finely divided state, combines rapidly with the
Oxygen stream and increases the temperature of the reaction, resulting in an
increase in the fluidity of the refractory oxides.
 A clean surface is exposed to cutting oxygen stream, and cut progresses
through the metal. The quality of the cut is slightly inferior to that of oxygen cut
low carbon steel.
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Basics Equipment for Powder Cutting:
 In the normal cutting nozzle is surrounded by a powder nozzle which introduces
the powder which in turn is fed from a powder dispenser.
 The medium of carrying the powder to the nozzle is compressed air or nitrogen.
 The "fluid" oxides are now removed by a combined melting and fluxing
operation and to a certain extent by the eroding action of the iron particles
themselves.
 The intense heat generated by the powder eliminates the preheating of
Oxidation Resistant Metals, and therefore "flying starts" can be made
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Basics Equipment for Powder Cutting:
Figure: Multi-jet
powder nozzle
Figure: Single tube
powder feed
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Cutting Of Oxidation Resistant Metals: Stainless Steel
 When certain alloys are added to Stainless Steel, they become oxidation
resistant rendering them unsuitable for cutting by means of the normal oxy-fuel
process.
 With stainless steel and non-ferrous metals, the oxide formed when the jet of
oxygen is impinged on to the heated plate, has a higher melting point than the
material itself, and this forms a film on the surface of the metal which prevents
any further oxidation.
 Before the introduction of powder cutting, stainless steel had to be cut by
mechanical means which is expensive and very slow and when these high costs
are added to the cost of an already expensive material, the final costs of
products become prohibitive.
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Cutting Of Oxidation Resistant Metals: Cast Iron and High Alloy Steels
 Some cast irons and high alloy steels may be cut in a manner similar to stainless
steel. However, when cutting high alloy and tool steels, it is advisable to preheat
to avoid cracking which may result from local heating.
 Gray cast irons are almost impossible to cut due to lamellar graphic form of the
carbon content.
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Introduction to Material Cutting Technologies
Oxyfuel Gas Cutting (OFC)
Cutting Of Oxidation Resistant Metals: Copper and Copper Alloys
 When "cutting" copper and copper alloys, powder cutting appears to be a
"melting action", coupled with the eroding action of the high velocity particles of
iron powder rather than a true oxygen cutting action.
 The main problem with copper is its high thermal conductivity. The rapid
dissipation of heat through the metal being cut poses problems due to the large
amount of heat required to maintain the high temperature to allow the cut to
progress.
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1. Correct Conditions
Appearance of cut
Remarks
Sharp top edge
Smooth surface, drag lines barely visible
A very light scale of oxide easily removed
Square face
Sharp bottom edge
The very light drag lines should be
almost vertical for profile cutting. For
straight cutting a drag of up to 10%
would be permissible
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2. Speed Too Slow
Appearance of cut
Remarks
Melted and rounded top edge
Lower part of the cut face fluted or gouged
very irregularly
Bottom edge rough
Heavy scale on cut face which is difficult to
remove
The bad gouging in the lower half of
the cut is caused by molten steel
scouring the cut surface and the hot
metal and slag which congeals on the
underside is always difficult to remove.
Secondary cause of this condition is
oxygen pressure being too low
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3. Speed Too Fast
Appearance of cut
Remarks
Top edge not sharp and may be beaded
Undercutting at top of cut face
Drag lines have excessive backward
drag
Slightly rounded bottom edge
The excessive backward drag of the cut
line would result in the cut not being
completely severed at the end. The
occasional gouging or fluting along the
cut indicates that the oxygen pressure is
too low for the speed, but possibly not
too low for a normal speed. In other
words, if the speed was dropped and
the oxygen pressure maintained, a
perfectly good cut would result
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4. Nozzle Too High Above Work
Appearance of cut
Remarks
Excessive melting and rounding of top
edge
Undercut at top of cut face with lower
part square and sharp bottom corner
The melting at the top edge is due to
heat spread each side of the cut and the
undercutting is caused by the oxygen
stream being above the work so that it
spreads or trends to “bell out” as it
traverses down the kerf
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5. Nozzle Too Low
Appearance of cut
Remarks
Top edge slightly rounded and heavily
beaded
Cut face usually square with fairly sharp
bottom corner
Having a nozzle too low does not usually
spoil the cut face unduly, but will badly
burn the top corner. Very often it retards
the oxidation reaction and makes it
appear that the cut has been done too
slowly
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6. Pressure Of Cutting Oxygen Too
High
Remarks
Appearance of cut
Regular bead along top edge. Kerf
wider at top edge with undercutting of
face just below
Probably the commonest fault in cutting,
causing rounding of the top part of the cut
face through turbulence within the oxygen
stream which is set at too high pressure.
On thinner material it may cause a taper
cut which sometimes leads to the
incorrect supposition that the cutter is
incorrectly mounted in relation to the
plate.
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7. Preheat Flame Too Large
Appearance of cut
Remarks
Rounded top edge with melted metal
falling into kerf
Cut face generally smooth, but tapered
from top to bottom
Excessive tightly adhering slag
This is the easiest and most obvious
condition to correct. Providing other
conditions are normal, the appearance is
of a clean but heavily oxidised face
combined with very heavy rounding at
the top edge
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