[0001] The United states Government has contributed to the design and/or development of
the invention herein and, thereby, has acquired ownership of certain rights in the
invention.
CROSS-REFERENCE TO RELATED APPLICATION
[0002] Reference is made to a related application, Serial No. 07/ , filed of even date and
assigned to the same assignee as the present application. The related application
involves constructing a stabilizing fins for high velocity ammunition of an ablative,
warp resistant plastic material.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0003] The present invention is directed generally to a coating for protecting stabilizing
fins from thermal degradation and abrasion in high velocity artillery projectiles
and, more particularly, to achieving such protection by the addition of an ablative
coating applied as an overlayer for the protection of such fins.
2. Description of the Related Art
[0004] Very high velocity artillery projectiles are often provided with a rear fin assembly
in which a separate assembly having a plurality of stabilizing fins is attached to
the rear of the projectile to help control stability and attitude so that the projectile
will maintain proper aerodynamics in flight and guide the ordnance to the target along
a predetermined trajectory after it is fired. A multiple segment sabot assembly is
also typically provided surrounding a portion of the munition forward or the stabilizing
fins to engage the barrel or bore of the artillery piece or cannon to protect the
fins from unwanted contact with the barrel or bore and to properly guide the shell
along the barrel during firing. Just after the fired shell emerges from the barrel
of the cannon, the sabot separates into its segments and falls away from the projectile
leaving the stabilizing fins in full contact with the air. Such a discarding sabot
system is shown in Campoli, et al. U.S. Patent 4 187 783. To the extent knowledge
regarding the sabot system is required to better understand the present invention,
such information is deemed to be incorporated by reference herein.
[0005] The peak velocity of such projectiles is usually supersonic and may approach an air
speed of Mach V. At such speeds, the stabilizing fins are subjected to a great deal
of friction which, in turn, produces a great deal of heat and abrasion. The fin assemblies
are preferably fabricated from aluminum inasmuch as it has the required weight and
relative strength to properly balance the munition. Anodized aluminum functions fairly
well under the high heat and abrasion conditions as long as the layer of anodize on
the surface of the aluminum survives. However, under the extreme conditions created
by the explosion of the propellant, it is stripped off readily upon firing so that
the bare aluminum is exposed to the severe conditions of launch and high speed flight.
Under these conditions, the aluminum fins quickly suffer severe control surface damage
and, therefore, have heretofore proven unsatisfactory for this application. Attempts
to provide a thicker oxide coating on the aluminum fins have not proved successful.
[0006] Although steel fins have the strength and heat resistance to survive the high speed
friction, the relative added weight resulting from the metal change from aluminum
to the heavier steel puts more than the allowable stress on the penetrator of the
munition. For this reason, a steel fin assembly does not provide a suitable substitute
for the aluminum.
[0007] Studies are underway to determine if the majority of the damage to the fin is done
during the launch event or during the flight. It is generally believed at the present
time that the metal finish, chiefly aluminum oxide, is subjected to severe heat (several
hundred degrees Kelvin) and abrasion during the ignition and rapid combustion of the
propellant, during the launch of the projectile. Thus, if the metal finish could be
kept intact during the launch environment, that metal finish normally will be sufficient
to protect the surfaces of the fins during the remainder of the flight.
[0008] It is known that certain coatings utilizing silicone or siloxane polymer structures

can be used for the protection of rocket nozzles and other similar applications. Specifically,
a diphenyl methylvinyl-polysiloxane has been used which contains graphite and silicon
carbide fibers. Such materials, however, have not heretofore been applied to projectiles.
The materials have only been applied to stationary objects which do not have to produce
consistent aerodynamic characteristics.
[0009] Thus, there remains a need to protect the aluminum of the fins from the heat and
abrasion of high speed flight in a manner which does not significantly affect the
aerodynamic characteristics of the projectile.
[0010] It is a primary object of the invention to provide protection to the metal surface
at least during the launch event.
SUMMARY OF THE INVENTION
[0011] The present invention provides an ablative coating for the fins of cannon-fired,
high velocity munition projectiles of the class having stabilizing fins subject to
thermal degradation and abrasion loss upon firing. Such munitions generally have a
substantially ogive shaped nose, relatively elongated intermediate body and a plurality
of stabilizing fins attached to the rear portion of the body. The fins are preferably
made of aluminum or aluminum alloy and the ablative coating consists of a siloxane
polymer which becomes a protective ablative ceramic char when heated in the air and
which protects the aluminum fins to prevent thermal degradation and abrasion of the
control surfaces of the fins during shell firing and ablates during projectile flight.
The ablative coating may contain an amount of stabilizing fibers, such as carbon or
glass fibers, and is in the nature of a pliable, rubberized polysiloxane coating after
application. This helps protect the fin assembly during production and assembly of
the shell.
[0012] In the preferred embodiment, the ablative coating is in the form of a pasta including
the carbon and/or silicon carbide and/or glass fibers which is subsequently applied
from an hydrocarbon solution of the paste as by spraying. One such material is a paste
sold under the designation No. 93-104 by Dow Corning Corporation of Midland, Michigan.
Another material which does not contain the stabilizing fibers is available from General
Electric Corporation, Schenectady, New York, under the name TBS 758. It is further
contemplated that many other compounds of the silicone (siloxane) organosilicon oxide
polymer of the structure (I) in which the polymerized material takes on a plastic
or rubber-like property will provide the required protection by forming a protective
silica (Si0
2) coating when the maximum temperature for the polymer is exceeded.
[0013] The ablative coating is normally applied as by spraying from an hydrocarbon solution
to a thickness in the range of from about 0.005" to about 0.050". However, much thicker
layers of up to 1.0 inches can be used for some applications where more initial protection
is required. The coating containing the carbon or glass fibers, imparts a wrinkled
texture to the external surface of the fins. This texture has not been found to adversely
affect the performance of the projectile when fired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In the drawings:
Figure 1 is a view, partially in section, of an artillery round of the type which
may incorporate the coated fins in accordance with the invention;
Figure 2 is a side elevational view of stabilizing fin assembly in accordance with
the invention; and
Figures 3A and 3B are views depicting a fin from the assembly shown in Figure 2.
DETAILED DESCRIPTION
[0015] Figure 1 depicts, partially in section, a typical cannon-fired high velocity munition
round showing generally at 10. It includes a large caliber cartridge case 11 which
may be alloy or stainless steel and having a primer 12 utilized to fire an internal
charge of smokeless propellant which, in turn, launches the projectile 13 along and
out of the barrel in a well known manner. The projectile 13 has a generally ogive
shaped nose 14, a central body portion 15 and a rear or tail portion 16. A stabilizing
fin assembly shown generally at 17 is attached as by threads (not shown) to the end
of the tail section 16 at 18. The stabilizing fin assembly includes a plurality of
aerodynamic guidance stabilizing fins 19 arranged symmetrically about a central member
20. While other numbers of fins can be used in accordance with munition design standards,
the illustrative embodiment includes six such fins, four of which are visible in the
view depicted. As better seen in Figures 2, 3A and 3B, the fins are provided with
a textured coating as best soon at 21 in Figure 3B.
[0016] As is well known, a great deal of heat and pressure and abrasion are associated with
the rapid combustion or explosion of the propellant charge during the firing of the
shell which launches the projectile of interest along the barrel and into its flight
trajectory. As discussed above, the initial firing of the shell removes the anodize
from the aluminum fins and that event, plus the high velocity friction, destroys the
usefulness of the fins.
[0017] The coating 21 is applied to the anodized surface of the aluminum fin assembly prior
to its being attached to the munition projectile which is subsequently assembled to
the cartridge case 11. The ablative coating is usually in the form of a paste including
the carbon and/or silicon carbide and/or glass fibers which is subsequently applied
to the control surfaces from an hydrocarbon solution of the paste as by spraying.
The coating can also be painted on, or the fin assembly can be dipped in the mixture,
if desired, or the material may be molded in place on the fin.
[0018] One such material is a paste sold under the designation No. 93-104 by Dow Corning
Corporation of Midland, Michigan. Another material which does not contain the stabilizing
fibers is available from General Electric Corporation, Schenectady, New York, under
the name TBS 758. It is further contemplated that many other compounds of the silicone
(siloxane) organosilicon oxide polymer of the structure (I) in which the polymerized
material takes on a plastic or rubber-like property will provide the required protection
by forming a protective silica (Si0
2) coating when the powder is ignited.
[0019] The ablative coating is normally applied as to a thickness in the range of from about
0.005" to about 0.050". A much heavier coating of up to about 1.0 inches in thickness
can be used, if desired, however. The coating containing the carbon or glass fibers,
imparts a wrinkled texture to the external surface of the fins.
[0020] When an artillery shell containing a projectile of the class employing a finned projectile
in which the fin assembly is coated in accordance with the present invention, the
silicon based organic polymer forms a silicon dioxide based ceramic char which is
strengthened by the presence of the various fibers. The char insulates the anodize
from the firing environment and, after launch, ablates and flakes off leaving the
anodized control surfaces to provide the desired ballistic characteristics during
the flight of the projectile. In this manner, the coating imparts the protection to
the metal surface when required during the firing of the shell and thereafter allows
the full flight control of the projectile by restoring the metal control surfaces.
[0021] This invention has been described in thin application in considerable detail in order
to comply with the Patent Statutes and to provide those skilled in the art with the
information needed to apply the novel principles and to construct and use such specialized
components as are required. However, it is to be further understood that the invention
can be carried out by specifically different equipment and devices and that various
modifications both as to equipment and procedure details can be accomplished without
departing from the scope of the invention itself.
1. A cannon-fired high velocity munition projectile having a aerodynamic nose, a selectively
elongated intermediate body rearward of the nose and a plurality of stabilizing fins
attached to the rear portion of the body, characterized by comprising:
an ablative coating on the fins to prevent thermal degradation and abrasion of the
fins during shell firing and projectile flights; and
wherein the ablative coating consists of a siloxane polymer which becomes a protective
ablative ceramic char when heated in air.
2. The projectile of claim 1 wherein the fins are fabricated from material selected
from aluminum or aluminum alloys.
3. The projectile of claim 1 wherein the ablative coating further contains a amount
of stabilizing fibers selected from carbon fibers, silicon carbide fibers and glass
fibers.
4. The projectile of claim 2 wherein the ablative coating further contains a amount
of stabilizing fibers selected from carbon fibers, silicon carbide fibers and glass
fibers.
5. The projectile of claim 1 wherein the ablative coating is applied by spraying from
a hydrocarbon solution of the coating.
6. The projectile of claim 3 wherein the ablative coating is applied by spraying from
a hydrocarbon solution of the coating.
7. The projectile of the claim 2 wherein the ablative coating is applied by spraying
from a hydrocarbon solution of the coating.
8. The projectile of any of claims 2, 4, 6 or 7 wherein the ablative coating has a
thickness in the rage from about 0.005" to about 1.0".
9. The projectile of claim 3 wherein the ablative coating consists substantially of
diphenyl-methyl vinyl siloxane.