Investigation of Residue and Coating Stoichiometry on 120-mm Combustible Cartridge Cases
Abstract : An investigation was conducted to determine the cause of coating residue found in the test gun chambers during qualification firing of 120-mm combustible cartridge case (CCC) ammunition for the MlAl/A2 main battle tank. The CCC is coated with a clear epoxy- polyamide topcoat and a highly pigmented aluminum epoxy basecoat. A laboratory analysis was performed on actual residues; parts of the CCC retain samples of actual coatings and laboratory control samples. Since there are six different resins used in this two-component coating system, production errors and deviations from correct mixing prior to application could have caused the residue. Any variation from the specified stoichiometry could also result in films with lower cross-link densities and lower glass transition temperatures (Tg). Rounds fired at 120 C have more residues than identical rounds fired at ambient temperature; additional weeks of cure lower the amounts of residue. A differential screening calorimeter (DSC) analysis of the various samples revealed that a suspect lot of ammunition with higher levels of residue had lower Tg values. Fourier-transform infrared (FTIR) was effective in monitoring the degree of cure of the epoxy coating system. Analyzing the residue from actual firings showed similar features. Koenig hardness values showed variations caused by dry film thickness, but also showed insignificant changes caused by transformations in the stoichiometry of the clear topcoat from 52.5 to 45 phr (pounds per hundred of resin).
Thermal characterization of polymeric materials
Thermoanalytical instrumentation, techniques and methodology, P.K. Gallagher the basis of thermal analysis, B. Wunderlich thermoplastic polymers, R.P. Chartoff polymer blends and block copolymers, H.E. Bair and A. Hale elastomers, A.K. Sircar thermosets, R.B. Prime fibres, M. Jaffe, J.D. Menczel, and W.E. Bessy films, M. Jaffe, J.D. Menczel, and W.E. Bessy thermal characterization of composites, R.J. Morgan thermal analysis of additives in polymers, H.E. Bair.
Modulated differential scanning calorimetry: isothermal cure and vitrification of thermosetting systems
Abstract Modulated differential scanning calorimetry (MDSC) is used to study simultaneously the evolution of heat flow and heat capacity for the isothermal cure of thermosetting systems. A stepwise decrease in the heat capacity is observed. For the organic resins studied, it is shown that the glass transition temperature of the curing resin reaches the cure temperature at half of the decrease in heat capacity. Vitrification, the isothermal transition from a rubbery or liquid state to a glassy state, and the corresponding vitrification time can thus be measured in a single experiment. A mobility factor is proposed which is based directly on the observed heat capacity evolution. This mobility factor is compared to the diffusion factor which is calculated from the modelled rate of reaction and the decrease in the rate of reaction at vitrification. For the amine-cured and the anhydride-cured epoxies studied, both factors coincide and thus the mobility factor can be proposed as a direct measurement of the diffusion factor. In contrast, the rate of reaction of the low-temperature formation of an inorganic polymer glass (IPG) is (nearly) uninfluenced by the vitrification process. The conversion increases long after vitrification and a glass transition temperature largely above the cure temperature can be reached. In this case, the diffusion and mobility factors do not coincide. MDSC is shown to be a promising technique to study in more detail the effect of polymer microstructure and reaction mechanism on the interrelation between vitrification and the decrease in the rate of reaction due to mobility restrictions.