Reduction of Heat Transfer to High Velocity Gun Barrels by Wear-Reducing Additives

In order to understand how wear-reducing additives such as TiO₂/wax and polyurethane foam liners reduce erosion, a series of gun firings was made in a 105 mm tank cannon equipped with thermocouples to measure the heat transferred to the gun barrel both in the presence and in the absence of the additives. Four thin thermocouples (0.13 mm diameter) were placed at different radial distances from the bore surface. Each thermocouple was placed at the same axial distance along the gun barrel. From the temperature distribution measured 100 milliseconds after propellant ignition, the total heat transferred in the gun barrel was determined. On the basis of single shot measurements, both the polyurethane foam and the TiO₂/wax liner reduced the heat transferred to the gun barrel by ten percent. Repeated firings with TiO₂/wax liners afforded steadily increasing reduction in heat transfer which was attributed to the formation of an insulating layer of TiO₂ and unreacted wax on the bore surface. This also accounts for the twenty-five fold increase in wear life of the M68 tank cannon firing rounds equipped with TiO₂/wax liners. This thermocouple technique is now used to design optimum weight and location of wear-reducing additives in other gun systems, since the efficacy of the wear-reducing liner can be deduced from a few shots.