An Improved Process for the Manufacture of Hard Faced Armour Plate.
Year: 1894

page_text: Date of Application, 24th Apr., 1894-Accepted, 14th July, 1894
An Improved Process for the Manufacture of Hard Faced Armour
Plate.
I, ALBERT AMMERMAN ACKERMAN, a Lieutenant in the United States Navy,
residing at No. 1916 G. Street, N.W. Washington, District of Columbia, United
States of America, do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement :-
My invention relates to an Improved Process for the Manufacture of Hard-
faced Armour Plates or other like Castings or Forgings, and is especially adapted
for use in hardening and toughening the surface of such plates.
It is well known that, other things being equal, the loss of heat of a solid °
body through radiation, varies with the area of the radiating surface; and also
that the increase of heat through absorption varies with the area of the surface
exposed to the heat rays; from this it follows that where two sides or faces of
a plate are of unequal surface, then the side having the greater surface is
capable of being more rapidly heated or cooled than the opposite side; thus
where one side of a plate is corrugated, gashed or pocketed and the other side
smooth, or comparatively smooth, the former side will absorb and radiate heat
more rapidly than the smooth side, and hence a desired temperature may be reached
on that side, and in these corrugations and openings earlier and with less expense
for fuel and labor than when, as in the case on the smooth side, the receiving
surface is smaller, and the section through which heat flows away into the body of
the plate is greater.
Again, where heated plates having parallel smooth faces are cooled in hardening
or tempering, the outer edges and corners of the plate cool more rapidly than the
central portion, producing an initial set of the outer positions and causing the
central portion as it cools to assume a stress due to its contraction within the fixed
bounds of the outer and colder portions. This produces inequalities in structural
strength in the plate and weakness in places. This may be avoided by so
increasing the area of radiating surface near the centre of the plate and muffling
the edges that the loss of heat may be approximately uniform all over the area of
the surfaces of the plate.
Again, it has been found, where armour plates have been heated to a high
temperature and then gradually cooled, the one face being cooled more rapidly
than the other, that the face cooling faster first assumes a set to which the entire
mass of material adapts itself; and that when the slower cooling portion becomes
rigid, the plate is buckled towards the side last cooling, thus producing not only a
deviation from the shape desired but by leaving unbalanced stresses in the plate,
decreases its resistance.
This may be avoided by constructing the plate with radiating surfaces so
arranged that, although the media into which the radiation takes place may differ,
the amount of heat radiated from each side of the plate may be practically the
Or this
same; and thus there may be no tendency of the plate to buckle.
tendency to buckle may be regulated by varying the surfaces. of the two sides of
the plate. Since the effect of these variations in the surface giving out or
absorbing heat will depend upon so many things in or around the furnace, the
dimensions and shape of the plate, etc., it will be impossible, at present, to lay
down any fixed rule, but the variations will probably have to be determined by
experiment in each particular instance.
°

page_text: Again, in the Harvey and kindred processes, where elements or compounds are
caused by means of heat to impregnate by occlusion of gases or otherwise, the
surface of armour plates, the penetration of these foreign substances extends only
to a limited distance from the surface, and varies in percentage to a certain extent
inversely as the depth therefrom; now if by deep cuts, corrugations, or pockets,
the area of the surfaces is increased, then the amount of material exposed to these
hardening and toughening agents is increased; and if these projections or corru-
gations be rolled or pressed down afterwards to form a smooth surface, then the
depth of material so treated under that surface will be increased approximately
in proportion to the comparative areas of the surfaces before and after rolling,
with the addition that the surface percentage may be carried in as far as desired
which is of vital importance when the process is applied to thick plates. Moreover,
where a given thickness of impregnated material is desired, the time necessary
for carrying out the process will be shortened in proportion to the increased area
of exposed surface.
This is very important as the time required for treating a thin armour plate
under the Harvey process is ordinarily from ten days to three weeks and for a
thick plate much longer, thus entailing great expense for fuel and labor in
maintaining the amount of heat required. My process also diminishes the serious
scaling in such processes of cementation or conversion, both by decreasing the
time and by permitting the same effects to be obtained at a lower temperature.
Thus, in the latter case, extending the life of the furnace, obviating the risks
and actual damages attending the long maintainance of great masses of metal
at high temperatures, and decreasing necessary repairs.
In order to permit good welds in case the corrugations or ridges are rolled
down as well as to avoid in all cases the intrusion of a film of non-conducting
material between the face of the plate and the heating or cooling agencies which
may be employed in subsequent operations of hardening or tempering it will
usually be found necessary to remove the coating of scale and unabsorbed carbon
which may adhere to the face of the plate after treatment by exposure to an
oxidising flame sand blast blows of a hammer in conjunction with a spray of
water on the treated surface or any other of the ordinary and recognized methods
of scaling forgings and castings suitable for the purpose.
Since the higher percentage of graphitic carbon renders that part of the plate
softer at the same high temperature these carburized corrugations or projections
are readily rolled or pressed down into a smooth surface without danger of
overheating the plate. In fact the sharpness of their angles may be reduced
in the cementation furnace by raising the temperature a few hours before end of
process.
ว
In addition work done on the plate will be concentrated on this corrugated
surface due to its greater softness, thus improving that surface which is exposed to
greater strains, and which in the unworked surfaces of other processes, is known
to be lowered in quality and toughness by the heterogeneous mixture of graphitic
carbon, especially when long exposed to a very high temperature.
Moreover, by this means, the percentage and extent of carburization may be
controlled by the shape and dimensions of the ridges or corrugations; that is,
when these ridges are made narrow and deep, the percentage of carbon will be
high, while the depth of its penetration will be comparatively slight. By
introducing other shapes, the gradation of carbon from the carburized to the
uncarburized portion of the plate may be made more or less abrupt, superficial,
or deep; and in this way a high carburizing and hence great hardening effect
may be extended deeply into the plate, without permitting the loss of toughness
to lower the quality of a large depth of plate. This applies particularly to the
case of thick plates, and also where carburizing is applied directly to the ingot
on which these ridges are provided, the metal in this case being subjected to
an annealing process, as it were, while the carburizing is being carried on.
The ingot will not only be benefited by the annealing process, but the specific

page_text: gravity of the metal being less than in the forged metal, the process will be more
rapid and by means of the enlargements of surface as herein described, the
carburizing or Harveyizing in any form may be carried to any desired depth
without rendering the back of the plate brittle through loss of carbon and
subsequent oxidation, or the central portions less tough through becoming too high
in carbon.
I am aware that chisellings, ridges, or pockets of sharp contour cannot be pressed
down into the plate without leaving seams or imperfect welds of slight depth, but
these I regard as immaterial, experience having shown that defects such as cracks,
pockets, tapped holes, &c., from one to two inches deep, if confined to the hard-face
and not iudicating a strained condition of the more ductile back do not reduce the
resistance of the plate. In the case of narrow gashes or chisellings, therefore, it
is not essential to close them at all, although that may be done by edging up the
plate, or by raising the temperature of the plate in the cementation furnace for a
few hours towards the close of the process, in order to soften the highly carburized
film, and to cause the lips of the gashes to flow together. In this way the
distortion due to forging down and extending one surface more than the other is
obviated.
DESCRIPTION OF THE DRAWINGS.
My invention will be more clearly understood after reference to the accompanying
drawings, in which :-
Figs. 1 and 2 represent cross-sections of plates having one side or face smooth and
the other face corrugated or dentated.
Fig. 3 represents a cross-section of an armour plate that has its front face
indented with compound corrugations.
The shaded portion of the said plate indicates the depth to which the carburizing
of said plate would extend.
Fig. 4 represents a cross-section of the same plate shown in Fig. 3, after the
corrugations are rolled down; the carburized portion of the plate being represented
by shade lines.
Fig. 5 represents a cross-section of a carburized indented plate, the carburization
being shown in shaded lines.
When rolled out flat this plate would resemble that shown in Fig. 4.
Fig. 6 represents a front view of a plate having its radiating or absorbing surface
increased by a plurality of grooves or hatchings crossing each other in the face of
the plate;
Figs. 7, 8, 9 and 10 represent plates having the surface indented with gashes or
chisellings, which are shown regularly disposed but may be made irregularly on the
face of the plate if desired.
Fig. 11 represents a front view of a plate provided with a number of elliptical
grooves in the face thereof, the said grooves being spaced further apart towards
the outer edges of the plate whereby the radiating surfaces of the center of the
plate may be increased, and the plate may be caused to cool more uniformly.
Fig. 12 is similar in every respect to Fig. 6, except that the elliptical grooves
are replaced by coarse indentations or chisellings, which are deeper and more
frequent near the center of the plate than towards the edges thereof, whereby
greater uniformity in the cooling of the plate is obtained.
Figs. 13 and 14 represent cross-sections of hollow cylindrical bodies having their
radiating interior surfaces largely increased by indentations such as are shown.
The tendency of hollow cylinders constructed in these shapes would be to facilitate
the transmission of heat from without and to retard the transmission of heat from
within. This construction would rather be of advantage for water tubes for boilers
than for armour however.
It will be evident that forgings or castings of this shape might be carburized
from both sides and thus completely. through.

page_text: Fig. 1 represents a cross-section o1 & stellated body enclosing a cynnaricar
chamber.
Armour for conning towers, smoke stacks, and the like might be readily
carburized while approximately in this shape and then forged down to a cylindrical
exterior thus giving greater depth to the carburized surface than where cylindrical
bodies are so treated.
Fig. 16 illustrates a combination of the types shown in Figs. 14 and 15, and
represents a steel casting or forging readily adapted for carburization from both
sides or all the way through.
Fig. 17 represents a cross-section of a steel plate corrugated on both sides, and
adapted to be carburized on either or both sides, and to radiate heat as readily
from one side as from the other; and
Figs. 18 and 19 represent cross-sections of plates unevenly indented upon opposite
sides and adapted to radiate heat faster from one side than from the other. These
various figures represent types of either castings or forgings on which these
increased surfaces have been provided in any convenient way. These castings or
forgings are treated by any of the hereindescribed processes, and may be then
either left with the ridges or gashes intact, or may be forged to an approximately
smooth surface.
The depth of the indentations may not be nearly as deep, relatively, as is shown
in the drawings, but the larger the increase of surface the more pronounced will be
the effect.
It will be evident, while I have particularly described the advantages of my
invention with regard to the carburization, that it is equally applicable to those
processes wherein chromium, nickel, nitrogen, phosphorus and other elements or
compounds are introduced into the metal; and it is also applicable to all processes
of cementation, conversion, case hardening, tempering, and annealing.
From the foregoing it will be seen that my invention consists in so varying the
area of surface on one or both sides of the plate or mass of material to be subjected
to heat or chemical treatment, that the mass may be more readily affected by
thermal or chemical agents.
Having now particularly ascertained and described the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The hereindescribed process for hardening the face of armour plates, sub-
stantially as described.
2. In the manufacture of armour plates, the method of treating the plate or ingot
which consists in providing on one of the faces thereof a plurality of grooves,
pockets, gashes or corrugations, in heating the surface so increased in contact with
a chemical agent, such as carbon, chromium, nickel, nitrogen, phosphorus or other
elements or compounds, adapted to harden the face of the plate, and in removing
the un-absorbed portion of the hardening agent from the plate, as set forth.
3. In the manufacture of armour plates the method of treating the plate or ingot,
which consists in providing on one of the faces thereof, a plurality of grooves,
pockets, gashes, corrugations, in heating the surface so increased in contact with a
chemical agent adapted to harden the face of the plate, in removing the
unabsorbed portion of the hardening agent from the plate, and in forging, rolling,
or pressing the projections down to an approximately smooth surface, as set forth.
4. In the manufacture of armour plates, the method of treating the plate or
ingot, which consists in providing on one of the faces thereof a plurality of grooves,
pockets, gashes, or corrugations, in heating the surface so increased in contact with
a carburizing agent and in removing the unabsorbed portion of the carburizing
agent from the plate, substantially as described.
5. In the manufacture of armour plates, the method of treating the plate or
ingot, which consists in providing ou one of the faces thereof, a plurality of grooves

page_text: pockets, gashes, or corrugations, in heating the surface so increased in contact with
a carburizing agent, in removing the unabsorbed portion of the carburizing agent
from the plate, and in forging, rolling or pressing the projections down to an
approximately smooth surface.
Dated this 24th day of April 1894
TONGUE & BIRKBECK,
34, Southampton Buildings, Chancery Lane, London, W.C.,
Agents for the Applicant.