EXERCISE
42.
The thickness of the material to be cut governs the selection of a cutting
tip. What size tip would be used to cut a plate 3/4 of an inch thick?
a.
No 2
b.
No 1
c.
No 3
43.
After the metal is sufficiently heated, how high is the torch raised from the
metal to pierce a hole ?
a.
1/4 inch
b.
1/8 inch
c.
1/2 inch
44.
When cutting billets, round bars, or heavy sections with a cutting torch, what
can be done to save time and gas?
a.
Raise a bur with a chisel at the start of the cut
b.
Use an extra large tip
c.
Preheat material to a dull red color
SECTION V.
BRAZING
21. GENERAL. Brazing is a group of welding processes in which fusion is
produced by heating to a suitable temperature above 800F; also, by using a
nonferrous filler metal having a melting point below that of the base metals.
Filler metal is distributed between the closely fitted surfaces of the joint by
capillary attraction. Torch brazing will be the only process covered in this
section. Other types of brazing processes are shown across the top portion of
figure 1 of this lesson.
22.
PRINCIPLES.
a. Brazing and hard soldering. Brazing is not a true welding operation, but
a method for joining metals. The oxyacetylene welding torch is frequently used in
brazing operations where the brazing material is in the form of spelter. It is
also effective in hard-soldering fittings to copper pipe that is to be used at
temperatures where soft solder ordinarily would not be satisfactory, for conditions
where greater joint strength than that provided by soft solder is needed, or for
corrosion-resistant joints.
b. Metallurgy of braze welding.
(1) The bond between two plates which have been brazed together, in most
cases, will produce an adherence stronger than the base metal itself.
(2) It has been found that three distinct forces act to maintain adherence.
(a) Tinning - A clean metal surface will receive a thin film of molten
metal of low surface tension. The bond thus produced depends on the action of the
molecular forces at the interface between the copper alloy brazing material and the
base metal,
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