THERMAL CUTTING SKILLS
(SCQF LEVEL5)
MODULE No : F5F1 11
OXY-FUEL GAS GOUGING SKILLS
COURSE INFORMATION
Oxy-fuel Gouging
Oxy-fuel or flame gouging offers fabricators a quick and efficient method of
removing metal. It can be at least four times quicker than cold chipping
operations. The process is particularly attractive because of its low noise,
ease of handling, and ability to be used in all positions.
Process description
Flame gouging is a variant of conventional oxyfuel gas welding. Oxygen and a
fuel gas are used to produce a high temperature flame for melting the steel.
When gouging, the steel is locally heated to a temperature above the 'ignition'
temperature (typically 900deg.C) and a jet of oxygen is used to melt the metal
- a chemical reaction between pure oxygen and hot metal. This jet is also
used to blow away molten metal and slag. It should be noted that compared
with oxyfuel cutting, slag is not blown through the material, but remains on the
top surface of the workpiece.
The gouging nozzle is designed to supply a relatively large volume of oxygen
through the gouging jet. This can be as much as 300 litre/min through a 6mm
orifice nozzle. In oxyacetylene gouging, equal quantities of oxygen and
acetylene are used to set a near-neutral preheating flame. The oxygen jet flow
rate determines the depth and width of the gouge. Typical operating
parameters (gas pressures and flow rates) for achieving a range of gouge
sizes (depth and width) can be seen in the Table.
Typical operating data for manual oxyacetylene flame gouging
Gouge
dimension Gas pressure
Gas consumption
s
Nozzle
Travel
orifice
speed
dia.(m Widt Dept
(mm/mi
Acetyle
Oxyge
Preheat Oxygen
m)
n)
h
h Acetyle
ne
n
(Litre/mi (Litre/mi
(mm (mm ne (Bar)
(Litre/mi
(Bar)
n)
n)
)
)
n)
3
6-8
3-9
0.48
4.2
15
22
62
600
5
810
6-12 0.48
5.2
29
31
158
1000
6.5
1013
1013
5.5
36
43
276
1200
0.55
When the preheating flame and oxygen jet are correctly set, the gouge has a
uniform profile and its surfaces are smooth with a dull blue colour.
Operating techniques
The depth of the gouge is determined principally by the speed and angle of
the torch. To cut a deep groove the angle of the torch is stepped up (this
increases the impingement angle of the oxygen jet) and gouging speed is
reduced. To produce a shallow groove, the torch is less steeply angled, see
above, and speed is increased. Wide grooves can be produced by weaving
the torch. The contour of the groove is dependent upon the size of the nozzle
and the operating parameters. If the cutting oxygen pressure is too low,
gouging progresses with a washing action, leaving smooth ripples in the
bottom of the groove. If the cutting oxygen pressure is too high, the cut
advances ahead of the molten pool - this will disrupt the gouging operation
especially when making shallow grooves.
There are four basic flame gouging techniques which are used in the following
types of application.
Progressive gouging
This technique is used to produce uniform grooves. Gouging is conducted in
either a continuous or progressive manner. Applications include removal of an
unfused root area on the reverse side of a welded joint, part-shaping a steel
forging, complete removal of a weld deposit and preparing plate edges for
welding.
Spot gouging
Spot gouging produces a deep narrow U-shaped groove over a relatively
short length. The process is ideally suited to removal of localised areas such
as isolated weld imperfections. Experienced operators are able to observe
any imperfections during gouging. These appear as dark or light spots/streaks
within the molten pool (reaction zone).
Back-step gouging
Once the material has reached ignition temperature, the oxygen stream is
introduced and the torch moved in a backward movement for a distance of 1520mm. The oxygen is shut off and the torch moved forward a distance of 2530mm before restarting the gouging operation. This technique is favoured for
removal of local imperfections which may be deeply embedded in the base
plate.
Deep gouging
It is sometimes necessary to produce a long deep gouge. Such operations are
completed using the deep gouging technique, which is basically a
combination of progressive and spot gouging.
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