Organic coating removal by single particle impact

grantor: University of TorontoOrganic coatings are often removed using solvents that create waste which is difficult and expensive to dispose of. For this reason, mechanical coating removal techniques such as blast cleaning are of increasing interest. The impact of single particles with two typical coating/substrate systems was examined in detail as an important first step to understanding the fundamental mechanisms which govern the removal of organic coatings by blast cleaning. A gas gun capable of launching single particles at speeds of up to 120 m/s and a high-speed photographic setup capable of measuring inbound and rebound particle velocities were constructed in order to characterise impact behaviour with respect to energy loss. The impact sites were photographed and the amount of coating removal was determined using image analysis. Coating removal for a typical alkyd enamel on a pretreated steel substrate was found to be due to impact-induced buckling delamination of the coating. An analytical technique based on the coupling of a novel post-buckling analysis with an existing strain energy release rate analysis was developed with the purpose of predicting the amount of coating removed when a single particle was launched, at a given velocity, against a coated substrate. Predictions of delamination size using this model were obtained for a wide variety of incident velocities, particle sizes, and coating thicknesses, and comparison with measured delamination size revealed good agreement. A second coating system, consisting of a typical aerospace urethane coating with an epoxy primer applied to an aluminum substrate, was found to be eroded, and an existing rigid-plastic erosion theory developed for semi-infinite targets and spherical particles was modified to include elastic effects and shown to predict crater size well. A general rigid-plastic analysis was then developed in which the size of an impact crater, particle rebound velocity and energy loss could be predicted for an incident particle of any size, shape, and density, impacting at any angle of attack and in any orientation. Finally, a parametric study in the case of symmetric particles of arbitrary angularity revealed interesting trends with respect to coating removal.Ph.D