Experimental studies of natural material-based coatings for thermal protection of metallic surfaces

Heat transfer studies have been conducted for cooling systems with coatings made of natural materials, depending on the parameters of the detonation flame of a thermal tool and the thermophysical properties of natural materials. Cooling systems with porous coatings of mineral media powders (quartzites, granites, teschenites, tuffs, marbles) had been developed, which were applied on a metal surface at temperatures up to (2500 ÷ 3500) °C and flow rates up to 2500 m/s by hot flames emanating from combustion chambers and nozzles. The holography and high-speed filming method has been used in the studies. The cost impact per one thermal tool is at least 200–300 dollars. The phenomenon of spin detonation of a flame at an oxidant excess coefficient of less than one has been recorded; the spraying process was intensified by 2 to 6 times. The coatings have shown high reliability compared to other boosted systems. The maximum specific heat flows on the coating are (from 2 to 20 × 10⁶ W/m²) and the oscillation frequency are up to 200 Hz. The overheating range of the coating was 20 ÷ 75 K. The thermodynamic characteristics of thermal tools have been established in the model and experimentally; the granulometric composition of materials has been obtained; the hydrodynamic operating modes of the burners have been selected (fuel combustion method, jet length, jet angle). The flight time of the particles, the optimal thickness of the coatings, the diameter of the powder, and the limiting compression and tensile stresses of the coating have been determined. Dependences of displacements for coatings under thermal influence have been obtained, which is important for diagnostics and forecasting of plants and prolongation of service life.