An Improved Obturation for Pistons of Machines for Riveting Punching or Shearing Metal Plates, Driven by Gases Derived from Charges of Modern Smokeless Gunpowder.
Year: 1898

page_text: Date of Application, 20th Dec., 1898-Accepted, 11th Mar., 1899
An Improved Obturation for Pistons of Machines for Riveting
Punching, or Shearing Metal Plates, Driven by Gases Derived
from Charges of Modern Smokeless Gunpowder.
I. CARL BALTHASAR BENDER, of 51, Carson Road, West Dulwich, in the County
of Surrey, Civil Engineer, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement: -
This invention consists in providing elastic obturators or gas-checks of improved
design and arrangement for the pistons of machines which operate by the energy
contained in the gases derived from the explosion of charges of modern smokeless
gunpowder of such a nature as will leave practically no residue.
These gases have a strong tendency to escape through the least opening left
between the piston and the bore of the barrel or cylinder, and to cause scores.
My invention is intended to remedy this defect.
Of the figures accompanying the specification of my invention:
Fig. I is a longitudinal section and shows the obturators in a barrel composed
of a tube with breech-block screwed thereto.
Fig. II is also a longitudinal section showing the same obturators as applied to
a solid barrel.
Fig. III represents the obturators on a larger scale, and is likewise a longi-
tudinal section.
Fig. IV is an end-view of the secondary obturator.
Fig. V is a cross-section through the primary obturator.
The obturators, made of iron but preferably of steel, are cup-shaped.
The primary obturator (1,) is worked into the part of the piston next to the
powder-chamber A.
Into the hollow part of this obturator the gases are allowed to enter and by
their pressure to widen out the round wall of metal; and they press a more or
less considerable part thereof against the interior wall of the barrel.
The piston having already a good fit in the barrel the lateral movement of
the wall of the cup or bell is not great, namely about one fourhundredth part
of an inch on each side, and can even be reduced to mil.
The primary obturator may be turned or milled on a separate piece of the
piston suitably attached to-the remaining part thereof, for instance by cones
fitting snugly into each other.
Or the piston may be of one piece and the obturator formed on the end next
to the powder-chamber.
Fig. II by the dotted cross-sectional line m, n, o, P, q, exhibits a piston
consisting of two pieces; the one which is nearest to the powder-chamber contains
the primary obturator (1.)
*
Should this construction be adopted it will be essential that there is a suffi-
cient thickness of metal between line Po "and the bottom surface tu" of
the cup or bell.
The secondary obturator (2.) has a bearing plate S well fitting against the

page_text: bottom-surface of the barrel. This plate must have a considerable bearing sur-
face and thickness so that the gas-pressure will keep this obturator firmly in
position, that it may remain air tight, and that the plate may not be permanently
deformed.
Of the various strains set up in my obturators the most important are those
acting at tangents to circles which could be obtained by taking imaginary sections
at right angles to the axis, and also the longitudinal strains along planes parallel
to the axis and passing through the axis of the piston. (See the arrows of the
Figures V and III.)
One part of the gas-pressure causes the widening of those rings (Fig. V); the
remaining part of the pressure widens the mouth of the bell by setting up the
stresses in the direction of the length of the piston.
The tangential strains owing to the great thickness of metal are smallest
near "t" and " u"; and they are greatest at #20 where the metal-thickness
is least.
"
33
On the contrary the longitudinal strains in the neighbourhood of "-" are
nil, and they increase towards the bottom-surface of the cup.
"
These strains along 10-u "inside are tensions; and towards the outside they
turn into pressures; the maximum strains being inside at
u" where for this
reason the sharpness of the angle is reduced by rounding off the corner.
The metal thickness at "ut" being calculated, I draw for practical reasons
from "w" to "u" inside a straight line which on rotation around the axis of the
piston follows the interior conical surface.
The depth of the obturator is influenced by the diameter of the piston and by
the greater or lesser values of gas-pressures and by the degree of sensitiveness
demanded of the action of the obturator.
"
"
The angle of the line 10 u
with the axis of the piston may be one sixth,
and even less, of a right angle; and 1 make the metal at the edge about one
fiftieth of the diameter of the piston.
Obviously the intention is to give to the elastic cup-obturator such a sectional
form that a body of nearly uniform strength may be obtained. By the applica-
tion of this principle the greatest elastic deformation and thus the greatest effici-
ency and sensitiveness of the apparatus of obturation will be obtained, and its
durability will be enhanced.
Similar rules of design and metal-thicknesses apply to the secondary obturator,
only that this does not slide, that it is more easily replaced, and that its steel is
more easily hardened so that higher strains hence smaller dimensions are admis-
sible, and greater flexibility is obtained.
"
The secondary obturator (2,) fits into the primary obturator in such a manner
that the piston after its stroke returning towards its position near the bottom of
the barrel slides between a b" and the bore of the barrel, and is arrested by the
surface of the ring-shaped filling piece "TT" which butts against the bottom
surface of the barrel. The conical surface of the obturator as formed along
In case
""
line". น พ agrees with the conical surface of the secondary obturator.
of a separate breech-block the secondary obturator (2,) may be shrunk upon the
latter.
However the secondary obturator might also be made in one piece with the
breech-block but I prefer the separate plate for practical reasons.
If the barrel is made in one piece with the breech-block the secondary obturator
will have to be fitted to the bottom surface of the barrel.
The cylindrical surface a b" is recessed into the primary obturator and the
end-part ab of the secondary obturator is formed so as to fit well into its place
A wide space, facilitating manufacture, is left between the bell and the part of
the piston-metal remaining inside. This space is reduced again by the ring TT
This ring is intended to limit the air-space of the charge at will, and is made
to butt against the bottom-surface of the barrel in order that the piston may no
injure the secondary obturator.

page_text: It is intended that the primary obturator shall enter into the space between
the bore of the barrel and the secondary obturator with some elastic action, by
which the close contact between the two obturators is made still more secure.
There are shallow grooves gg" admitting the gases at once into the remain-
ing air-space of the bell.
The action of my system of obturation is this:
The piston being in its original position near the bottom of the barrel upon
firing the charge the gases will fill the air-spaces and press the secondary
obturator against the primary obturator. The ases likewise press the primary
obturator against the wall of the
1
1333
iton commences to move and,
wly moving, the gases make
since it is comparatively very heavy
the piston air tight before they can penetrate along a bw" behind the primary
obturator into the recess provided to receive as additional aid some stiff greasy
substance or wax injected through the screwed grease-hole H shown on the
a b" is made sufficiently
drawing. The way along the cylindrical surface
great so that when the gases at last can enter into the ring-shaped space behind
the primary obturator they are no longer able to escape from behind the piston.
As soon as the round edge of the primary obturator rests against the wall of the
barrel-bore the obturator becomes much stiffer than it was before.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what
claim is:
1. An elastic cup-obturator of practically uniform strength made into the piston,
moved within a cylinder by the gases of modern smokeless gun-powder, sub-
stantially as herein set forth and described.
2. A stationary obturator fixed to the bottom-plate of the cylinder, substantially
as and for the purpose herein described.
3. The filling piece "TT" for the purposes herein set forth.
4. A ring-shaped grease-space at the bottom of the barrel-bore and its grease-
hole H with its screw.
5. The combination of a stationary obturator with a sliding obturator sub-
stantially as and for the purpose herein set forth and described.
Dated this Twentieth day of December 1898.
CARL BALTHASAR DEADTH,
Applicant.