IMPROVEMENTS IN THE CONSTRUCTION OF ORDNANCE
Year: 1879

page_text: PROVISIONAL SPECIFICATION left by Charles William Siemens at the Office
of the Commissioners of Patents on the 20th February 1879.
CHARLES WILLIAM SIEMENS, of No. 12, Queen Anne's Gate, Westminster, in the
County of Middlesex. "IMPROVEMENTS IN THE CONSTRUCTION OF ORDNANCE."
The method now generally adopted of constructing heavy guns consists of forty-
fying a tube of steel by means of coiled rings of wrought iron shrunk on, the gun
being farther strengthened at the breech end by two or more such rings. Though
serviceable guns can be thus produced, it is not possible by this method to obtain
the greatest amount of strength and permanency from the material employed. The
shrinkage strain of each ring is uncertain in amount, and falls in a greater measure
upon the inner metal than on the outer metal of cach ring. The rings moreover
being made of iron, while the inner tube is of the superior material steel, it follows
that when the internal pressure exceeds certain limits the iron rings will be the first
to undergo permanent distortion at their inner circumferences, so as to slacken their
grip at the inner tube, and afterwards, by dint of repeated efforts, the rings will
cease to support the tube, which in its turn must yield to the disruptive strain of
the explosion.
My Invention relates to means of remedying these defects, either by special
arrangement of material or preparation thereof, or by both combined, as I will
now describe. Instead of making the inner tube of the harder and more elastic
material, I use in its construction a yielding but very uniform material, such
as very mild steel; and instead of making the supporting rings of the softer
material, I employ for these a more elastic and stronger material, such as
steel of a medium temper. Where there are several tiers of supporting rings I
make the outer rings of a harder steel than the inner, so as to be capable of sus-
taining the greater strain without suffering deformation. Farther, in order to
avoid the undue strain to which solid hoops, whether of steel or of iron, are sub-
jected by the action of internal pressure, straining them more near their inner than
their outer circumferences, I subject each such ring or hoop to a preliminary
operation, which puts it into such a condition that the strains produced by great
internal pressure are nearly balanced. For this purpose I heat the ring of steel or
iron, preferably in a gas furnace, to a uniformn temperature, to be determined by
experience, according to the relation of the internal and external diameters. While
the ring remains in the furnace, or while it is protected against external loss of
heat, its internal surface is subjected to a sudden cooling action capable of being

page_text: regulated at will. The effect of this is that the metal near the interior surface of
the ring, though cooled, is prevented by the hot metal surrounding it from under-
going material contraction circumferentially. Contraction must therefore take
place chiefly in the direction of the thickness, the internal diameter remaining
nearly the same as when the ring was entirely heated. By continuing for a time
the cooling action, the interior cooled, and what may be termed the set portion, will
extend to such a depth as to resist the subsequent effort of the external portions to
contract in the direction of the diameter as they gradually cool; and thus the inner
portions of the ring when it is entirely cooled will be in a condition of compressive
strain, while the outer portions will be in tension, the change from the maximum
compressive to the maximum tensile strain being gradual from the internal to the
external surface of the ring. When a ring or hoop thus prepared is subjected to
great internal pressure, the compressive strain already acting on its interior portion
assists in contending against the bursting strain at the expense of the outer portion
of the ring, which in this manner is made to receive its due proportion of the total
bursting strain. The degree of heat to which the ring is subjected when the
internal refrigeration is applied should be such that the external tension produced
will cause the bursting strain to be equally distributed throughout the mass just
before the elastic limit of the material is reached. When this uniformity of strain
is attained the ring will be of maximum strength, that is to say, it will resist the
greatest amount of internal strain that the material is capable of sustaining.
Instead of constructing a gun of an inner tubo fortified by a series of separate
rings or hoops, I also construct the gun of only two principal parts, namely, an
inner tube and an outer body. The inner tube may in this case be only a thin
lining of mild or yielding steel, whilst the outer body is a tube of dimension and
strength sufficient, when prepared as above described, to resist the entire pressure
of explosion. The tube being in this case of varying thickness, the cooling applied
to its interior surface has to be varied in duration and degree. This can be dono
by covering the internal surface of the heated tube with a protecting sheet or tubo
of unequal thickness before the water or other refrigerating agent is applied. In
order to fix tho rings or the outer body of the gun upon the inner lining tube they
may be bored out a little taper and forced on the tube, which is turned externally
to a taper corresponding to that of the rings or body after they have been subjected
to the cooling action, after which the chase of the gun can be bored true and rifled
in the usual manner. Otherwise the rings or body after the cooling treatment may
be heated to a moderate temperature and placed on the tube, so as to have a slight
shrinkage thereon sufficient only to produce fair metallic contact, the chase being
afterwards bored and finished. The construction above described may obviously be
applied to either breech loading or muzzle loading guns.