Lincoln Electric IM10067 CENTURY AC120 - Manual (Page 13)

B-3 OPERATION B-3
NOTE: When welding on thin plate, you will find that
you will have to increase the welding speed, whereas
when welding on heavy plate, it is necessary to go
more slowly in order to get good penetration.
COMMON METALS
Most metals found around the home are low carbon
steel, sometimes referred to as mild steel. Typical
items made with this type of steel include most sheet
metal, plate, pipe and rolled shapes such as chan-
nels and angle irons. This type of steel can usually
be easily welded without special precautions.
Regardless of the type of metal being welded, in
order to get a quality weld, it is important that the
metal is free of oil, paint, rust or other contaminants.
Joint Types and Positions
Five types of welding joints are: Butt joint, Fillet joint,
Lap joint, Edge joint and Corner joint see Figure B.5.
Of these, the Butt joint and Fillet joint are the two
most common welds.
Butt Joints
Butt joints are the most widely used welds. Place two
plates side by side.
Tack the plates at both ends, otherwise the heat will
cause the plates to move apart. (See FIGURE B.6):
CENTURY® AC 120
FIGURE B.5
FIGURE B.6
Butt joint Lap joint Edge joint Fillet joint Corner joint
Butt joint
Lap joint
Edge joint Fillet joint Corner joint
Lower your headshield or hold the hand shield in front
of your face. Scratch the electrode slowly over the
metal and you will see sparks flying. While scratching,
lift the electrode 1/8" (3.2mm) and the arc is estab-
lished.
NOTE: If you stop moving the electrode while
scratching, the electrode will stick.
NOTE: Most beginners try to strike the arc by a fast
jabbing motion down on the plate. Result: They either
stick or their motion is so fast that they break the arc
immediately.
3. The Correct Arc Length
The arc length is the distance from the tip of the
electrode core wire to the base metal.
Once the arc has been established, maintaining the
correct arc length becomes extremely important. The
arc should be short, approximately 1/16 to 1/8" (1.6 to
3.2mm) long. As the electrode burns off the electrode
must be fed to the work to maintain correct arc
length.
The easiest way to tell whether the arc has the cor-
rect length is by listening to its sound. A nice, short
arc has a distinctive, “crackling” sound, very much
like eggs frying in a pan. The incorrect, long arc has a
hollow, blowing or hissing sound.
4. The Correct Welding Speed
The important thing to watch while welding is the
puddle of molten metal right behind the arc. Do
NOT watch the arc itself. It is the appearance of
the puddle and the ridge where the molten puddle
solidifies that indicate correct welding speed. The
ridge should be approximately 3/8" (9.5mm) behind
the electrode as shown in Figure B.4.
Most beginners tend to weld too fast, resulting in a
thin, uneven, “wormy” looking bead. They are not
watching the molten metal.
IMPORTANT: For general welding it is not necessary
to weave the arc; neither forwards and backwards nor
sideways. Weld along at a steady pace. You will find
it easier.
FIGURE B.4