WELDING OPERATIONS I - OD1651 - LESSON 1/TASK 2
or impregnating a metal with carbon to strengthen it). This hard
surface extends to a depth of 1/5 to 1/4 of the outward facing
thickness of the armor on the tank or armored vehicle.
The
primary purpose of face hardened armor is to provide good
resistance against penetration from enemy projectiles. The inner
side is comparatively soft and has properties similar to those of
homogeneous armor.
As a matter of fact, the inside and outside
of face hardened armor plate has two different kinds of steel.
Face hardened steel up to 1/2 inch in thickness should be welded
from the soft side only.
c. Identification of Armor Plate.
A very important part of
welding lies in the welder having the ability to identify metal
products to be welded.
The following paragraphs describe two
simple but accurate tests that may be made in a field shop for
identifying armor plate.
(1) File Test. This type test is performed with the use of an
ordinary file found in the mechanics and welders tool sets.
(a) Homogeneous Armor. A file will bite into homogeneous armor
on both the outside and inside of the plate.
As the file is
drawn across either surface of the armor plate, the teeth on the
file will bite into the metal, making it necessary to apply force
to draw the file across the metal. This type test is performed
by applying the file only once or twice across the surface. The
armor protection qualities of the armor plate can be impaired by
repeated applications of the file; therefore, the number of
applications should be limited.
(b) Face Hardened Armor. In this type armor the file will bite
only into the soft side of face hardened armor plate.
When
applied across the face side (outside) of the armor plate, the
file will slip instead of biting into the metal.
But when the
file is applied to the reverse side (inside), the file will bite
as in homogeneous metal.
(2) Fracture Test.
Some metals can be quickly identified by
looking at the surface of the broken part or by studying the
chips produced with a hammer and chisel.
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