The Effect of Feedstock Particle Size on the Heat Transfer Rates and Properties of Thermally Sprayed Polymer Coatings

SummaryA heat transfer analysis has been undertaken to predict the temperature profiles of in-flight polymer particles in a plasma jet. It shows that the development of large temperature gradients below the surface of particles during plasma spraying is a distinctive characteristic of polymers and is primarily due to their low rate of internal heat conduction relative to that of metals and ceramics. The large temperature gradients together with the low decomposition temperatures result in a kinetic difficulty in achieving complete melting of in-flight polymer particles despite their low melting temperatures. The theoretical analysis indicates that a suitable balance between maximizing the degree of melting and minimizing degradation can be achieved by control of the feedstock particle size. The experimental results are consistent with the theoretical predictions and show that size control provides an appreciable improvement in the density, tensile properties and wear resistance of polyamide coatings.