EP0484958A2

EP0484958A2 - Protective coating for projectile fins

Info

Publication number: EP0484958A2
Application number: EP91119054A
Authority: EP
Inventors: F. Joseph Walker; Mark P. Jones; Loren J. Walensky
Original assignee: Alliant Techsystems Inc
Current assignee: Northrop Grumman Innovation Systems LLC
Priority date: 1990-11-09
Filing date: 1991-11-08
Publication date: 1992-05-13
Also published as: KR920010250A; EP0484958A3

Abstract

An ablative coating is provided on the stabilizing fins of a cannon-fired high velocity munition projectile to prevent thermal degradation and abrasion of the fins during shell firing and projectile flight. The ablative coating consists preferably or a siloxane polymer which becomes a protective ablative ceramic char when heated in air.

Description

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

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

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

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.
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.
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.
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.
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.
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.
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

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.
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 (Si0₂) coating when the maximum temperature for the polymer is exceeded.
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

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

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.
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.
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.
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 (Si0₂) coating when the powder is ignited.
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.
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.
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.

Claims

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.