The Bemidji daily pioneer. [volume] (Bemidji, Minn.) 1904-1971, 1917-04-12
The Various Processes That Produce
tho Conflicting Propsrtiss Necessary
In Thsss Modern ProjsetiIs Resisting
warship Jackets,

Xhe plate must be hard, glass hard,
resist penetration by heavy projec-
tiles moving at tremendous veloc1ties.
yet tough and fibrous enough to take
up the momentum without cracking or
distortion. Mechanically, then, the
plate must have an extremely hard
surface and a 6brous backing. These
requirements were attained in part by
the old compound armor. Molten steel
was poured on to q wrought iron plate
and cooled. The slab was then re-
heated, forged and rolled to the re-
}Quired dimensions. If the operations
were successfully carried out the line
Of demarcation was scarcely visible.
Recently a modification of this proc
ess was introduced to cheaper and
render less tedious the production of
armor. A layer Of hard steel was
/ poured into a cooled mold, the under
!. side quickly setting. On the still duid
or pasty surface a thick layer of soft
.asteel was poured. By careful man1pu-
Slation the union of the surfaces was
Almost complete. and 1t was impossi.
BILE to detect the break in composition
on viewing the fractured section. This
method Of manufacture was undoubt-
edly an improvement on the old COM
pound method.
The increasing size, velocity and
hardness Of modern armor piercing
projectiles have necessitated the intro
duction of the modern armor. The
process of manufacture essentially
consists in case hardening to depth
Of about two inches the surface OF
q homogeneous tough nickel chrome
steel. Special air or self hardening
nickel and more complex steels are
x2eed for lighter armor, gun shields
!. and cast armored structures.
The steel Is made in Siemens fur
naces and carefully cast into ingots
up to eighty tons In weight. These in
COTS are then stabbed under powerful
hydraulic presses $4,000 tons) or roll
ed direct to the required dimensions,
depending on the power Of the mills
and appliances. During the rolling
operation, which lasts about an hour,
the slab is reversed and inverted to at
tain uniformity of working, and scale
is removed by wood fagots and wa
ter Jets. After rolling the plate is
Ufually quenched.
The next operation is that of case
hardening, and in this two plates are
put face to face, separated by a layer
Of the carburizing reagent II 1t be
solid, or If gaseous hydrocarbons be
used the plates are slightly separated,
to allow free passage for the harden
ing gases, by bricks arranged In rows.
The plates are maintained at redness
in q car furnace for three weeks and
withdrawn after the hardening carbon
has penetrated to the required depth.
The plates are thus carburized and so
made capable of being hardened, but
they are not yet actually hard. At this
stage all holes are drilled and plugged,
and any bending or machining neces-
sary is carried out.
From this point onward the treat
ments differ. Some makers insist on
heating and quenching in oil or water
to remove any coarse structure that
may have been formed during the
long annealing while carburizing. The
next essential operation ia that Of
hardening, and this is usually car
Red out in one of two ways. Either
the plate is uniformly heated to the
hardening temperature and quenched
lby q series Of water jets playing on the
upper surface with sufficient force to
Sprevent the formation Of steam or by
4 process known as "diherential
quenching," by which the carburized
surface is heated to a temperature
from which it will harden and the
under side kept well below, so attaining
q gradual fall in temperature from the
top to the bottom. The whole plate Il
then immersed in water, the hotter sur
face alone being hardened, while the
bark Is toughened. Further mechanical
operations can be carried out only by
grinding or cutting with oxyacetylene,
- the plate has now undergone the
treatment comforting maximum hard
ness.
In resume, it will be noted that there
are three distinct operations in modern
methods of manufacture-the mechani.
cal working of the plate to the required
dimensions, the carburization Of the
surface, quenching the carburized
surface to harden it. These operations
call for exact manipulation, super
vision and control, for the skill Of the
engineer and metallurgist may be put
to the severest tests, not Of the labora-
fDfy or the testing machine, but out in
Ehe gray mists," when failure Of
unit may imperf the safety and CO
hesion Of the whole.-Chambers Jour-
nal.