MetFab - Welding Fume Handbook - Flipbook - Page 17
7 Emission Rates: general factors
Many factors affect the rate at which
particulate fume and pollutant gases
are generated. The most important is
generally the choice of welding process,
but the welding current, voltage and
shielding gas are also important. This
guide looks at the effect of shielding
gases in greater detail in the sections
that follow.
The main job of welding engineers
and supervisors is generally to provide
a given level of weld quality at the
lowest cost, so the welding process
and conditions are often effectively
fixed. However, it is useful to be aware
of the health effects of different
welding processes, and to consider
choosing the process or the welding
conditions to minimise the risks where
possible. Indeed, in some cases it may
be appropriate to think about using
a metal joining technique other than
welding, or to avoid the need for joins
altogether.
In practice, most flexibility lies in the
choice of shielding gas for MIG/MAG,
TIG and FCAW work.
The welding process
Some processes inherently produce
more fume than others (Figure 4). The
largest amounts of particulate fume
occur in open-arc welding processes
where metal is transferred across the
arc: MMA, MIG/MAG and FCAW.
Although it is an open-arc process, TIG
welding does not produce significant
quantities of particulate fume because
metal is not transferred across the
arc. Submerged-arc welding generates
hardly any particulate fume.
40
40
Fume emission rate mg/s
35
30
25
20
15
10
10
10
10
MIMA Mild steel
4mm rod
FCAW Stainless steel
250A
5
5
0.1
TIG Stainless steel 220A
MAG Mild steel dip
MAG Mild steel spray
MIG Aluminium spray
Figure 4: Typical fume emission rates for different processes, materials and conditions
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