A flashback is the burning of the gases within the
torch, and it is dangerous. It is usually caused by loose
connections, improper pressures, or overheating of the
torch. A shrill hissing or squealing noise accompanies a
flashback; and unless the gases are turned off
immediately, the flame may burn back through the hose
and regulators and cause great damage. The cause of a
flashback should always be determined, and the trouble
remedied before relighting the torch.
Fundamental Welding Techniques
The composition, thickness, shape, and position of
the metal to be welded govern the techniques to be
used. The fundamental techniques include holding the
torch, forehand welding, and backhand welding.
Figure 6-31.--Welding heavy plate.
HOLDING THE TORCH.--The proper method
composed of equal parts of the two pieces being
to use in holding the torch depends upon the thickness
welded. After the puddle appears, begin the movement
of the metal being welded. For light gauge metal, hold
of the tip in a semicircular or circular motion. This
the torch as shown in figure 6-30, with the hose draped
movement assures an even distribution of heat on both
over the wrist. For heavier work, hold the torch as
pieces of metal. The speed and motion of the torch are
shown in figure 6-31.
learned only by practice and experience.
Hold the torch so that the tip is in line with the joint
to be welded, and inclined between 30 and 60 from
FOREHAND WELDING.--Forehand (also
called "puddle welding" or "ripple welding") is the
the perpendicular. The exact angle depends upon the
oldest method of welding. The rod is kept ahead of the
type of weld to be made, the amount of preheating
tip in the direction in which the weld is being made.
necessary, and the thickness and type of metal. The
Point the flame in the direction of the weld, and hold the
thicker the metal, the more vertical the torch must be for
tip at an angle of about 45 to 60 to the plates (fig.
proper heat penetration. The white cone of the flame
6-32). This position of the flame preheats the edges you
should be held about 1/8 inch from the surface of the
are welding just ahead of the molten puddle. By moving
base metal.
the tip and welding rod back and forth in opposite
If the torch is held in the correct position, a small
semicircular paths, you balance the heat to melt the end
puddle of molten metal will form. The puddle should be
of the rod and the sidewalls of the joint into a uniformly
distributed molten puddle. As the flame passes the rod,
it melts off a short length of the rod and adds it to the
puddle. The motion of the torch distributes the molten
metal evenly to both edges of the joint and to the molten
Figure 6-30.--Welding light gauge metals.
Figure 6-32.--Forehand welding.
6-24
