High temperature composite projectile barrel

Abstract

A composite projectile barrel is disclosed comprising a polymer matrix composite outer shell that accommodates higher temperature loading. In one embodiment, the invention comprises an outer shell fabricated from carbon fibers and polyimide resin having a glass transition temperature greater than 500° F. In another embodiment, the resin mixture includes a plurality of sizes of aluminum particles, between about 0.1 microns and 10.0 microns in diameter and of approximately spherical shape, as a thermal conductive additive.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to two Provisional patent application No. 61 / 871,154 filed Aug. 28, 2013 and No. 61 / 873,771 filed Sep. 4, 2013. The entire disclosures of both provisional applications are hereby incorporated by reference and relied upon.BACKGROUND OF THE INVENTION[0002]Users have long desired lighter gun systems that remain durable and reliable. It is known to substitute relatively strong but lightweight materials—such as unreinforced and reinforced polymers, continuous glass fiber or carbon fiber composites—for various portions of the gun commonly fabricated from steel, aluminum, or other metals. Attention has focused on gun barrels, which constitute a large percentage of a gun's weight. It is known, for example, to fabricate a gun barrel having a steel inner liner surrounded by a carbon fiber reinforced polymer matrix composite (PMC) outer shell, incorporating a resin. This combination lightens the gun while retaining g...

AI Technical Summary

Benefits of technology

The patent describes a new type of composite barrel for a projectile that can withstand higher temperatures. It is made of a polymer matrix composite that has a high glass transition temperature. The barrel also has an inner liner and an outer shell, and the outer shell is made of a thermally conductive material to facilitate heat transfer. The technical effect is that this new design of the barrel can withstand higher temperatures, which means it can handle more powerful projectiles without being damaged.

Problems solved by technology

When a composite barrel is subjected to high heat from rapid or prolonged firing, however, they are usually less durable than solid steel barrels.

Even with the addition of thermally conductive chopped carbon pitch, however, rapidly firing a gun fitted with a carbon fiber composite barrel may cause barrel temperatures to significantly exceed the use-temperature capability of epoxy resins.

At the Tg, the PMC softens significantly and the mechanical integrity of the composite barrel is compromised.

As the barrel is heated to even higher temperatures irreversible thermal decomposition of the cured epoxy matrix occurs and barrel structural integrity is further compromised.

Because all of these thermally conductive additives tend to strongly increase the viscosity of the resin, however, higher concentrations of the thermally conductive additive make the resin mixture more viscous, inhibiting complete coating of the carbon fiber tow with resin and making manufacturing more difficult and less consistent.

Additionally, high loadings of conductive additives generally diminish the mechanical properties (e.g., strength) of the composite.

Other resins having higher glass transition temperatures than epoxy exist, but they are generally more difficult to process and manufacture PMC articles with and are significantly more expensive than epoxies.

Although cured polyimide resins have superior thermal performance as compared to epoxy resins, many have relatively high toxicity from the solvents and monomers used in their manufacture.

The RP46 resin, however, at high enough solids concentration for manufacturing PMCs is semi-solid at room temperature; its high viscosity makes it very difficult to work with when “wet” winding fiber filament tows.

Another obstacle to using polyimide resins such as the P2SI® 635LM resin in filament winding applications relates to processing difficulties to cure a freshly-wound barrel.

When curing a wound gun barrel that inherently has minimal part “edges”, however, it has proven difficult to remove the volatile products and gasses because they tend to become trapped between the continual filament windings.

This problem is compounded when utilizing the higher viscosity polyimide resins.

Despite the advantages of using a polyimide resin to wrap a thin cylinder such as a small caliber gun barrel, use of polyimide resins for PMCs—even with alternative composite manufacturing techniques such prepreg, towpreg, and resin transfer infusion—has been substantially confined to flat or relatively large radius carbon fiber sheets or panels.

PEEK is significantly more expensive than epoxies.

Further, the glass transition temperature of PEEK is only about 290° F., with (even more costly) higher-temperature formulations exhibiting glass transition at about 315° F. These glass transition temperatures are still lower than desirable in a rapid-fire weapon.

When a PMC is used as an outer shell for a barrel, solving the heat problem is difficult because most heat must be conducted radially to the outside surface of the barrel and ambient atmosphere, through the composite shell, requiring heat to transfer through resin and transversely across individual fibers.

At the micro level (i.e., the scale of the fiber diameter, approximately 10 microns), significant obstacles to transferring heat from the hot steel inner barrel through the PMC are the lower thermal conductivity of the resin between the fibers, heat transfer resistance at the polymer matrix-fiber interface, and heat transfer resistance at the polymer additive particle interface.

However, the interstitial space is not uniform; the space may range from, for example, from about <1 micron to about 50 microns.

Therefore, effective quantities of particles sized small enough to occupy the smaller interstitial spaces will tend to make the resin mixture too viscous, and may locally weaken the matrix if / where the smaller additive particles “clump” in the larger interstitial spaces.

On the other hand, if the thermally conductive material particles are sized too large, larger than available interstitial spaces, they will not fit into the smaller interstitial spaces, thus displacing the continuous reinforcing fibers.

This results in lower composite fiber volume fraction, compromised mechanical properties, and lower thermal conductivity throughout the PMC.

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