Improvements in the Manufacture of Face-hardened Armour.
Year: 1895

page_text: Date of Application, 13th Feb., 1895-Accepted, 6th Apr., 1895
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Face-hardened Armour.
I, ALBERT AMMERMAN ACKERMAN, a Lieutenant in the United States Navy,
attached to the Bureau of Ordnance of the Navy Department of the United
States at Washington in the District of Columbia, United States of America, and
residing at 1908 Sunderland Place in the said City, do hereby declare the nature
of my invention, and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement :-
This invention relates to improvements in the manufacture of face hardened
In the manufacture of case
armour whereby its resistance is greatly increased.
hardened and other armour intended to resist attack by the destruction of the
projectile before great penetration is effected, it is the practice at present to harden
but one face, that exposed to the attack. This is effected in various ways, chiefly,
however, by supercarburizing (either with or without the impregnation of other
elements, such as chromium, nickel, &c.) that face and rendering it more susceptible
to hardening when the heated plate is chilled than the body of the plate.
Now it has been my experience that the increased resistance of face hardened
plates is not, as generally supposed, due to the breaking up of the projectile
from the point on the hard face, but to the arrest of the projectile after it has
achieved a certain penetration, and the resistance of the plate over a greater area
is felt.
The hard face and tough underlying layers have great tenacity and resist flow.
Being unable to flow or evade the projectile point, they are carried in with and
before it, the jagged fragments scoring and cutting the ogival and impeding its
progress. In addition the rigid face being unable to bulge or give way, the
displaced metal, can move only towards the back of the plate, and even then not
before the back of the plate bulges to give it room. The advance of the projectile
is resisted therefore by the entire thickness of the plate before any penetration
whatever can be effected.
Now it is the custom in the manufacture of face hardened armour whether
merely cast or forged, to leave the central body and back of the plate relatively
soft, even going so far in some cases as to decarburize it, this, with the intention of
thereby preventing cracks and of forming an extensible band which will hold the
hard face together no matter how shattered it may be by impacts. It is found, in
consequence, that above a certain point, an increase in thickness of such a plate
consisting only of the addition of soft metal, in itself very little, if any more
resisting than wrought iron, gives an increase of resistance incommensurate with
the increased cost and risk of manufacture, as well as the great size and weight of
the plate. It is also apparent that the soft back, by permitting the formation of a
back bulge allows the easier displacement of the metal in the body of the plate by
the advancing projectile. At the same time, from the very nature of the metal
the energy required to form a crack of any depth and that required to produce a
through crack, differ by no great amount, so that but little is gained. Especially
is this the case when it is considered that the thicker plates are of comparatively
small extent and therefore very subject to cracking when attacked by large calibres,
or when the body of the plate is hard and strong.
It is, therefore, proposed to stiffen or harden the backs of plates above a certain
thickness, say 12" by supercarburization followed by chilling preferably to a less
depth than the face, and thereby prevent the formation of a back bulge. This

page_text: would require the penetrating projectile to carry before it a frustum of a cone,
the base of which, composed of extremely tough and hard material of great extent,
must be forced bodily, as a projectile, through backing and supporting structure
before perforation can be effected.
It is evident that if the whole face, edges, and back of the plate were hardened
it would be impossible to bolt the armour in position or machine the edges so as to
make good butts and joints or make fastenings to its face. I have, therefore,
devised certain novel means for controlling and limiting the hardening of super-
carburized and homogeneous plates wherever it is desired to keep them soft for
machining after treatment.
It has been the custom for some years in cementing armour plates and other
castings and forgings, to protect from carburization the edges which may require
fitting after hardening, as well as certain areas in the face of the plate, intended
for port-holes, sight-holes, bolt and rivet-holes where it may be necessary to drill
after the plate is hardened and in position on the ship or elsewhere. The object of
so doing is to keep the carbon at so low a point in these localities that the metal
will not harden when chilled after cementation, and thus will not become impossible
to machine.
This protection has hitherto been secured by,-first, superimposing metallie
frames or shapes either in cementing or hardening, or both. These are expensive
and inefficient, since the shapes fit irregularly and expansion permits the carbon
gases, whether supplied from a reservoir or generated by heat from carbonaceous
matter in contact with the plate to leak beneath them in cementing, as well as the
chilling medium in hardening; second, by superimposing inert material in
cementing, such as sand, clay and silicious compounds. The second method is also
unsatisfactory, as this inert material permits the carbon gases to seep through; or
by baking and rising, or cracking away, exposes the surface to the carburizing
agents.
Materials of this supposed inert nature are also dangerous on account of unnoticed
impurities which may flux with the highly carburized steel at the border of the
protection, causing deep holes to be scored and fused in the surface of the plate.
The result is that after the application of either of these methods there is no
certainty that the metal will not have taken up sufficient carbon in these localities
to render it quite impossible to. machine after the hardening process has been
completed.
The methods of preventing the hardening of these spaces by delaying the
abstraction of heat in the subsequent operation of chilling the heated plate through
the application of red hot bars or guards of metal to those localities it is intended
shall remain soft, are also uncertain and disadvantageous on account of their
requiring that much additional heat to be abstracted through the remaining
unprotected surface, and thereby delay and moderate, if not altogether prevent its
hardening.
The method by which I accomplish the desired result is by providing over the
portions of the plate to be protected from the carburization a coating of material
which will oxidize or decarbonize the carbon gases which may seep through it
before they reach the face of the plate. The decarburizing material to consist of
a metallic oxide paint capable of reduction by the carbon gases, mixed and
stiffened with asbestos, clay, or other refractory material intended to serve as a
dilutent and moderator of the oxide. Over this material the usual inert material
may be placed so that the only carbon gases having access to it will be scanty and
attenuated. In addition to this these parts so protected may also be covered with
a non-conducting or partially non-conducting substance during the operation of
hardening. The preferred method of so doing is before the spray or cooling
medium is brought to play upon the heated plate, asbestos boards of appropriate.
shape to the port-holes, lines of rivet-holes, fitting ends of the plate, etc., are
firmly pressed upon it preventing the contact of the cooling medium and preventing
heat radiation over these areas which it is not desired to chill. These asbest s

page_text: boards are not intended to act as a dam preventing the flow of the cooling medium
over certain areas which are cooled by radiation as in certain processes of saw
tempering, where the hardness and toughness of metal is shaded from the teeth to
the back, but is for the purpose of retaining the heat as long as possible over the
areas in contact with them and permitting the freest abstraction of heat elsewhere.
It is found that their use will prevent the hardening of even a fully carburized
surface.
The metal with which we propose to deal in the surface of armour plates is
capable of hardening by air cooling, and this process is especially applicable to
armour having a composition in the original plate which is susceptible to hardening
even without supercarburization as chrome and high per cent. nickel steel. This it
would be found impossible to do by means of dams and edge and corner guards
which may act as dams and prevent the rapid flowing off of the cooling medium
after it has absorbed sufficient heat to reduce its chilling properties.
I have found that to a certain degree the desired result may be accomplished in
cementation by leaving on the scale, which forms on the plate in its various
heatings, over the parts to be protected from the action of the carbon gases, and by
removing the scale from all of the parts of the plate as above mentioned to be
subsequently hardened. This scale, being an oxide of iron is reduced to metallic
iron by the carbonic oxide gas, which gas is converted into carbon di-oxide, which
has little or no effect in carburizing the plate.
This scale is also left in position over these localities while hardening the plate
subsequent to cementation, when through its being a poor heat conductor the
abstraction of heat is delayed on those parts, especially, if further prevented by
covering them with artificial non-conducting material such as the asbestos boards
mentioned above. Since this scale forms unevenly, varies largely with different
conditions, and is occasionally cracked away we would prefer in cementation to
grade the coating of the decarburizing agent to the conditions required.
In this manner, a decarburizing material will be brought closely into contact
with the surface of the metal, baking to it when heated. This material will not
only require to be reduced before the gases can reach the plate, but on account of
its large percentage of oxygen, and its compact nature, the gases will be much
attenuated, nearly inert, and long delayed before reaching the true surface. In
addition, where through lack of knowledge of the exact location of the desired
soft strips, before cementation, it has been impossible to wholly exclude the carbon
from a space required to be machined after hardening, and also as an additional
precaution to prevent hardening, when the carbarized spaces have been correctly
located, it is proposed to protect these areas in hardening from contact with the
chilling medium by means of non-conducting material such as boards lined with
asbestos firmly pressed to the plate.
I am aware that a certain decarburization takes place on the back of cementel
plates where they happen to be bedded in sand, presumably inert, but containing
some oxide, and where the metal is inaccessible to the carbon.
The intention of this invention is not to grade the carbon throughout the
thickness of the plate, as in the case above mentioned, but is to prevent the access
of the carbon to certain localities or to render it inert before it reaches them.
From the foregoing it will be seen that this invention consists not only in
retarding, in diluting with inert carbon di-oxide, and in diminishing in quantity the
carbonic oxide gases that may eventually reach the plate through the protecting
material; but the said invention also consists in actually decarburizing the metal
itself, thereby rendering it certain that in the time required for cementation the
said localities of the plate will not be carburized to such an extent as to render its
hardening possible in the subsequent operation of chilling.
The scale in the one case, and the asbestos or clay mixed in with the metallic
oxides in the other case will also form a non-conducting medium which should not
be removed prior to the process of chilling; and thus those parts of the plate are
shielded from the direct action of the chilling medium, keeping the said parts softer

page_text: than the contiguous parts which are chilled. In addition to the above scale and
protective material employed in cementation being left in hardening on these spaces,
they are further covered with non-conducting material which prevents access of the
chilling medium.
I have also devised certain improved methods and apparatus intended to control
and limit the depth of hardening, as distinguished from the toughening effect, as
well as rendering the hardness more uniform and severe over the surface than is
possible with the methods employed at present. The chilling of the metal being
made uniform and regular, its grain and toughness is not only improved, but the
equal abstraction of heat from opposite sides of the plate permits its contraction to
take place without leaving it stressed or warped. This is of especial importance in
thick plates which frequently crack under treatment although so gently sprayed as
to insufficiently harden the surface.
The present method of hardening is to force a cooling fluid through openings in
pipes opposed to the faces of the plate, in order to break up and allow the escape
of a non-conducting film of steam or heated fluid that may lodge upon the surface
of the plate. These openings are about one-eightieth of an inch in area and spaced
one for about every two square inches of plate. There is, therefore, a large area
of 18ths of an inch out of every 2 inches which is cooled by the convection of an
already partially heated fluid. This leads to irregularities and a much slower and
less uniform rate of cooling than is desirable.
It is also apparent that if the number of jets or their pressure be increased, there
will be such a volume of fluid delivered upon the plate that it will dam up forming
a steam or hot fluid cushion, which will baffle and heat the jets before they reach
the plate.
To obviate this I propose to atomize or minutely subdivide the spray so that each
minute portion of the plate will receive directly its quota of cooling fluid. At the
same time the volume of fluid employed on any part of the plate will be no greater
than that which can be utilized in cooling that part, any increase being obviously
an impediment to the contact of the spray.
It is the custom, at present, to harden armour right out or at least into a great
depth. This has serious disadvantages as the elastic limit over a large part of the
thickness of the plate approaches its failing point so closely that a crack initiated
on the surface is apt to extend through. This practice also prohibits the use of a
strong body or one likely to harden to a great depth, so that face hardening
is limited to plates of an essentially weak body and back. Now at any instant
the maximum hardening effect having penetrated to a desired depth fixed by the
thickness of the plate, and the surface having acquired the temperature of the
cooling medium, it is known that the temperature towards the interior increases at
a very rapid rate, while the loss of heat is also smaller than near the surface.
This is due to the diminished conductivity and increased specific heat of the metal
at the higher temperature. If at this time the spray be reduced, stopped entirely,
or warm water or steam be turned upon the plate instead, a change of temperatures
due to the tendency to equalise the heat in the interior of the plate will take place.
This will be manifested by a rise in temperature of the exterior of the plate and
a slower reduction of it further in, corresponding to annealing rather than chilling.
If the cold spray be now turned upon the plate again before the exterior of the
plate has become sufficiently warm to lose its hardness or take a temper, for
example as soon as steam begins again to form upon it the interior distribution of
heat will again be changed. And in this manner, by repeating the operation,
without reducing the hardness of a certain depth of the exterior, the metal below
it may be tempered and annealed rather than rendered hard and brittle. It will
also be apparent that in this way the distortion of the plate may be minimized.
We are aware that a method is employed of tempering plates by stopping the
spray in chilling and starting it again when the surface has reached a temperature
sufficiently high to melt scraps of soft alloy. But it is evident that in this case the
exterior of the plate is intended to be tempered, this we desire to avoid.
The

page_text: exterior is to be made as hard as possible but that hardness is to be limited to a
predetermined depth, below which the plate is to be tempered and toughened for
a distance, and then merely annealed at the heart. Our process is after hardening
the surface, to abstract the remaining heat in such a manner as to prevent chilling
the body of the plate, and in this manner we propose to face harden plates of
a much stronger body and of a composition more susceptible to hardening than can
now be manufactured.
DESCRIPTION OF THE DRAWINGS.
The accompanying drawings illustrate diagrammatically the operation of the
hereindescribed invention ;-
Fig. 1 represents a section through a plate and the adjacent media, the plate
being shewn in section along the line ax of Fig. 2, and the purpose being to keep
the centre and edges of the plate soft.
Fig. 2 represents a plan view of the plate shewn in section in Fig. 1, representing
a plate intended for use in the wake of a port-hole.
Fig. 3 represents a similar section to that shewn in Fig. 1, except that the edges
and two strips for drilling rivet-holes are to be kept soft, the section in said figure
being along the line y y of Fig. 4.
the
Fig. 4 represents a plan view of the plate shewn in section in Fig. 3.
Fig. 5 represents a sectional view showing diagrammatically means for chilling
plate shewn in Figs. 1 and 2.
Fig. 6 is a sectional view showing diagrammatically a tapered plate for side
arinour with means for chilling the same on both sides.
Fig. 7 represents an end view of a spraying apparatus for use in chilling and
tempering plates.
Fig. 8 represents a plan view of the same.
Fig. 9 represents a detailed view of one of the spraying pipes, parts being broken
away, and
Fig. 10 represents a cross-section along the line z z of Fig. 9.
A represents a mass of inert material which is applied in the ordinary way.
B represents the plate under treatment, and 6 the softer portions of the surface
thereof.
Crepresents the carburizing material.
D represents the decarburizing material.
E represents the scale which may or may not be left over the portions of the plate
to be kept soft.
F represents the board divisions which may be employed as shewn in Fig. 1, or
may be omitted as shewn in Fig. 3.
In the chilling apparatus shewn in Fig. 5, the plate B rests on the frame H
and is wedged in place with the wedges K, which bear against the boards M faced
with asbestos m, for keeping the ends of the plate from becoming chilled.
The part of the plate to be cut away for the port-hole is covered with an asbestos-
faced board M' weighted down by weights m¹.
N and N represent sources of water supply for the sprays n, from the jets n' on
the branch pipes n.
In the form of chilling apparatus shewn in Fig. 6, the plate B is wedged in the
frame H', as described with reference to Fig. 5, but is supported upon asbestos
pads Q on tracks R, transverse to the iron beams P, set across the frame H'.
The plate is sprayed on from the top and bottom as before.
In this case, the location of bolt holes on the back as well as the edges of the plate
is kept soft.
In the spraying apparatus shewn in Figs. 7 to 10, S and S¹ represent two
revoluble supply pipes receiving their supply of water, steam, or other fluid, from
the flexible curved pipes S and S' connected with the reservoir S which reservoir is
supplied with hot or cold water, steam, or the like by the pipes S7 and S³ controlled
by the valves s' and as shewn in Fig. 9.

page_text: Each of these pipes S and S' is provided with a plurality of delivery pipes S³,
preferably crossing each other as shewn in Fig. 7, and extending the full length of
the plate to be treated.
These pipes S are perforated as at 82 and are enclosed in the pipes S³ which are
slotted along the elements thereof next to the plate, the said slotted portion being
covered with a wire gauze s whereby minute subdivision of the flu'd sprayed on the
plate is obtained.
The pipes S³ terminate in the stiffening plates U, to which lifts V are attached
to take the weight off the ends of the pipes S³ when they are filled with water.
The pipes S and S', with the branch pipes S2 and S3 are revolved by means of
the hand-levers S which engage, by means of the pins so in the holes t of the
sector T, whereby the said pipes may be set at any desired angle.
In Fig. 7 the full lines indicate the position of the pipes and levers for spraying
on the curved plate, and the dotted lines indicate the position for spraying on a
flat plate.
The pipes S and S¹ may be connected together by collars and straps if
desired, or each may be pivoted independent of the other.
There should preferably be duplicate spraying apparatus, similar to that
hereindescribed, the one for one side of the plate, and the other for the other
side whereby both sides of the plate may be chilled or tempered at the same
time.
It is our purpose to spray over the plate cold water, hot water, steam, oil, or
any other hot or cold fluid that may be suitable for chilling or tempering the
plate.
Atomizers may be used in connection with the hereindescribed apparatus, if
desired.
It is obvious that various modifications of the hereindescribed process and
apparatus may be made which could be used without the departing from the spirit
of our invention.
Having thus particularly ascertained and described the nature of my said inven-
tion, what I claim as new is :—
1. An armour plate having both faces thereof hardened and the interior portion
in a relative soft state, substantially as and for the purposes hereindescribed.
2. There hereindescribed method of regulating the hardening of one or both
of the faces of an armour plate, substantially as and for the purposes herein set
forth.
3. The spraying apparatus substantially as hereindescribed as shewn in Figs. 7
to 10 of the drawings hereunto annexed.
4. In the manufacture of armour plates, the method of controlling and limiting
the hardness of the face or faces of the plate, which consists, in the operation of
supercarburization, of providing on the surface of those portions which it is desired
to retain soft, a coating of material adapted to oxidize the carbon in the carbon
gases of cementation; and in exposing to the action of the said gases the remaining
portions of the plate, substantially as described.
5. In the manufacture of armour plates, the method of controlling and limiting
the hardness of the face or faces of the plate, which consists, in the operation of
supercarburization, of providing on the surface of those portions which it is desired
to retain soft, a coating of material adapted to oxidize the carbon in the carbon
gases of cementation; in exposing to the action of the said gases the remaining
portions of the plate; and, in the subsequent operation of hardening by chilling the
heated plate, covering the said locations which it is desired to retain in a soft
condition with a layer of non-conducting material, substantially as described.
6. In the manufacture of armour plates, the method of controlling and limiting
the bardness of the face or faces of the plate, which consists in the operation of
supercarburization, of providing on the surface of those portions which it is desired
to retain soft, a coating composed of a mixture of inert material and material

page_text: adapted to oxidize the carbon in the carbon gases of cementation, and in exposing
to the action of the said gases the remaining portions of the plate, substantially as
described.
7. In the manufacture of armour plates, the method of controlling and limiting
the hardness of the face or faces of the plate, which consists in the operation
of supercarburization, of providing on the surface of those portions which it is
desired to retain soft, a coating composed of a mixture of inert material and
material adapted to oxidize the carbon in the carbon gases of cementation; in
exposing to the action of the said gases the remaining portions of the plate; and, in
the subsequent operation of hardening by chilling the heated plate, covering the
said locations which it is desired to retain in a soft condition with a layer of
non-conducting material, substantially as described.
8. In the manufacture of armour plates, the method of controlling and limiting
the hardness of the face, or faces of the plate, which consists, in the operation of
supercarburization, of providing or leaving on the surface of those portions which
it is desired to retain soft, a coating of metallic oxide capable of oxidizing the
carbon in the carbon gases of cementation, and in exposing to the action of the said
gases the remaining portions of the plate, substantially as described.
9. In the manufacture of armour plates, the method of controlling and limiting
the hardness of the face or faces of the plate, which consists, in the operation
of supercarburization, of providing or leaving on the surface of those portions
which it is desired to retain soft, a coating of metallic oxide capable of oxidizing the
carbon in the carbon gases of cementation; in exposing to the action of the said
gases the remaining portions of the plate; and, in the subsequent operation of
hardening by chilling the heated plate, covering the said locations which it is
desired to retain in a soft condition with a layer of non-conducting material,
substantially as described.
10. In the manufacture of armour plates, the method of controlling and limiting
the hardness of the face, or faces of the plate, which consists, in the operation of
supercarburization, of providing on the surface of those portions which it is desired
to retain soft, a coating consisting of a mixture of inert material and metallic oxide
capable of oxidizing the carbon in the carbon gases of cementation, and in
exposing to the action of the said gases the remaining portions of the plate,
substantially as described.
11. In the manufacture of armour plates, the method of controlling and limiting
the hardness of the face or faces of the plate, which consists, in the operation of
supercarburization, of providing on the surface of those portions which it is desired
to retain soft, a coating composed of a mixture of inert material and metallic oxide
capable of oxidizing the carbon in the carbon gases of cementation; in exposing to
the action of the said gases the remaining portions of the plate; and, in the
subsequent operation of hardening by chilling the heated plate covering the said
locations which it is desired to retain in a soft condition with a layer of
non-conducting material, substantially as described.
12. The method of controlling and limiting the hardening of armour plates of any
description by retaining the scale in position over parts it is desired to retain in
their soft condition and covering these surfaces with a comparatively non-conducting
material in the operation of hardening by chilling the heated plate, substantially as
and for the purposes described.
T
11
10.1 1
1408
TONGUE & BIRKBECK,
Southampton Buildings, Chancery Lane, London, W.C.,.
Agents for the Applicant.