39.
What effect do oxides have in a finished weld?
a.
Causes the bond to be stronger
b.
Removes grease and oil from surface to be welded
c.
Seriously reduces the strength of the weld
40.
What should the approximate angle between the welding rod and the flame be?
a.
45
b.
90
c.
60
41.
What is the proper time to bring the welding rod under the flame during a
welding operation?
a.
Heat the base metal and welding rod at the same time
b.
Just before the base metal begins to melt
c.
After the base metal has formed a puddle
SECTION IV.
OXYGEN ACETYLENE CUTTING
18.
GENERAL.
a. If iron or steel is heated to its kindling temperature (not less than
1,600F), and then brought in contact with oxygen, it burns or oxidizes very
rapidly. The reaction of oxygen with the iron or steel forms iron oxide and gives
off considerable heat. This heat is sufficient to melt the oxide and some of the
base metal; consequently, more of the metal is exposed to the oxygen stream. This
reaction of oxygen and iron is utilized in the oxyacetylene cutting process. A
stream of oxygen is impinged on the metal surface, which has been heated to the
kindling temperature by the preheating flames at the torch tip. The hot metal
reacts with oxygen, generating more heat and melting, and the molten metal and
oxide are swept away by the rapidly moving stream of oxygen. The oxidation
reaction continues and furnishes heat for melting another layer of metal. The cut
progresses in this manner. The principle of the cutting process is shown in figure
13.
b. Theoretically, the heat created by the burning iron would be sufficient to
heat adjacent iron red hot so that the cut, once started, could be continued
indefinitely with oxygen only, as is done with the oxygen lance. In practice,
however, excessive heat absorption at the surface, caused by dirt, scale, or other
substances, makes it necessary to keep the preheating flames of the torch burning
throughout the operation.
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