With all the bullets and shrapnel flying around Iraq nowadays, driving a military fuel tanker there can be a harrowing assignment. A new coating technology that can self-seal punctured fuel tanks may make that job at least a bit safer.
Developed by High Impact Technologies (HIT) and Rhino Linings USA, this new BattleJacket coating consists of three layers of sprayed on polyurethane elastomer. According to Russ Monk, HIT’s vice president of operations, the coating’s inner, outer and middle layers work together as a system to stop the leaks, fires and explosions caused when bullets or bomb fragments penetrate a fuel tank.
The self-sealing magic takes place in Battle Jacket’s middle layer. It contains a proprietary polymer additive that swells upon contact with hydrocarbons, such as gasoline or diesel fuel. This swelling plugs any bullet or bomb-fragment holes – but only with some help from the other two layers of urethane. “BattleJacket works as a constrained-layer system. The inner and outer layers are crucial to how the system functions,”Monk explains.
The inner layer’s role is to provide good adhesion to the metal tanks. “An intimate contact between the coating and the tank is important to stop the liquid fuel from working its way underneath the coating,” Monk says.
The outer layer’s role is more complex. As the middle layer swells after coming in contact with leaking fuel, the compressive force exerted by the outer layer ensures that the swelling is directed inward, plugging any punctures. Monk adds that this compression matters a great deal since the fuel exerts about 4 psi of force on the tank walls – because of its own weight and thermal expansion. The outer layer’s ability to exert a containment force on the inner layers is helped by the fact that the sprayed-on urethane shrinks by about a percent after its application. “So the whole tank is essentially under compression with the urethane stretched over it,” Monk says.
This urethane’s natural stretch also helps seal leaks in another way. Bullets or projectiles shot into the tank have to part the outer elastomeric outer layer, which partially springs back into shape once the bullet has passed through. “Even a large bullet leaves a hole about same diameter as a pencil,” Monk says.
HIT turned to Rhino Linings to find just the right urethane formulation to meet the strength and adhesion requirements. According to Ron LoPresto, Rhino’s industrial applications manager, the urethanes used for the BattleJacket coating have a Shore A hardness of 85, a tensile strength of 1,300 psi and an elongation of 350 percent. “The inner layer’s adhesion to steel is equal to the tensile strength of the urethane itself. On aluminum, the adhesion is only slightly less than the urethane’s tensile strength,” he says. BattleJacket is typically applied at thicknesses between 5/8- and 1-inch.
Rhino uses similar urethane formulations in its primary business – as a supplier of spray-on urethanes for pickup truck bed liners. The company also offers urethane coatings and linings for a variety of challenging industrial applications, including mining and foundry equipment. “These materials can hold up to a lot of abuse,” says LoPresto.
Over the past year, BattleJacket has been widely deployed on military tankers and other vehicles used in Iraq. Military uses, however, may be just the beginning for this technology. HIT, which has patents and patents pending on BattleJacket, also has related technologies in development. These include a self-sealing coating with a fire-resistant cap layer as well as versions that self-seal in the presence of industrial chemicals such as chlorine.
Monk says the technology, which won an innovation award from the Alliance of Polyurethane Industries, has already drawn interest as a way to protect civilian rail cars, stationary fuel tanks, and chemical process tanks. “The homeland security applications will probably exceed the military uses,” he predicts.
Developed by High Impact Technologies (HIT) and Rhino Linings USA, this new Battle-Jacket coating consists of three layers of sprayed on polyurethane elastomer. According to Russ Monk, HIT’s vice president of operations, the coating’s inner, outer and middle layers work together as a system to stop the leaks, fires and explosions caused when bullets or bomb fragments penetrate a fuel tank.
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