BOC Smootharc MMA 170, Руководство по эксплуатации, Страница: 14 / 36

14
Concave Fillet Weld
A fillet in which the contour of the weld is
below a straight line joining the toes of the
weld. It should be noted that a concave fillet
weld of a specified leg length has a throat
thickness less than the effective throat
thickness for that size fillet. This means that
when a concave fillet weld is used, the throat
thickness must not be less than the effective
measurement. This entails an increase in leg
length beyond the specified measurement.
Concave Fillet Weld
ACTUAL THROAT
EFFECTIVE THROAT
CONVEXITY
LEG
LENGH
THEORETICAL THROAT
CONCAVITY
ACTUAL THROAT
AND EFFECTIVE
THROAT
LEG
SIZE
SIZE LEG
THEORETICAL THROAT
The size of a fillet weld is affected by the
electrode size, welding speed or run length,
welding current and electrode angle. Welding
speed and run length have an important effect
on the size and shape of the fillet, and on the
tendency to undercut.
Insufficient speed causes the molten metal
to pile up behind the arc and eventually to
collapse. Conversely, excessive speed will
produce a narrow irregular run having poor
penetration, and where larger electrodes
and high currents are used, undercut is
likely to occur.
Fillet Weld Data
Nominal
Fillet Size
(mm) Minimum
Throat
Thickness
(mm) Plate
Thickness
(mm) Electrode
Size (mm)
5.0 3.5 5.0–6.3 3.2
6.3 4.5 6.3–12 4.0
8.0 5.5 8.0–12 & over 4.0
10.0 7.0 10 & over 4.0
Selection of welding current is important. If it is
too high the weld surface will be flattened, and
undercut accompanied by excessive spatter is
likely to occur. Alternatively, a current which is
too low will produce a rounded narrow bead
with poor penetration at the root. The first run
in the corner of a joint requires a suitably high
current to achieve maximum penetration at
the root. A short arc length is recommended
for fillet welding. The maximum size fillet which
should be attempted with one pass of a large
electrode is 8.0 mm. Efforts to obtain larger leg
lengths usually result in collapse of the metal
at the vertical plate and serious undercutting.
For large leg lengths multiple run fillets are
necessary. These are built up as shown below.
The angle of the electrode for various runs in
a downhand fillet weld is shown below.
Recommended Electrode Angles for
Fillet Welds
1st Run 2nd Run
3rd Run Multi-run Fillet