Gas exchange in d-gun’s devices for coating spraying

Abstract

The main requirements for detonation gas installations (DGI) for coating deposition are explosion safety and environmental friendliness, stable operation and high productivity, etc. In the technological application of gas detonation, it is necessary to solve the problems of fast and high-quality mixing of mixture components, reliable initiation of detonation, cooling of installations, taking into account the limits detonation, strength and weight of devices, etc. The stages of the DGI operating cycle, including the processes of gas exchange in the detonation combustion chambers, ensuring their filling with a fresh combustible mixture and powder with the previous displacement of residual combustion products, determine the initial state of the fresh charge, which affects the intensity and the nature of the physicochemical transformations occurring in the powder particles, and thus the conditions for the formation of coatings. This article is devoted to the systematization and analysis of the principles of organizing gas exchange in the working combustion chambers of detonation-gas installations for spraying coatings, including the analysis and systematization of the designs of detonation-gas installations for spraying coatings operating with various structures of the working cycle, with the identification of concepts and patterns of gas exchange in working combustion chambers. The main gas exchange schemes include the following: with the ejection of residual combustion products by a purge gas or a combustible mixture component; with the ejection of residual combustion products with a fresh combustible mixture; with pumping out of residual products of combustion; combined gas exchange with pumping and purge of residual combustion products; with transverse movement of gases; with a variable composition of the fresh combustible mixture. According to the method of removing residual gases, one should distinguish between: blowing the barrel with inert gases and subsequent supply (pushing out the inert gas) with a fresh combustible mixture of gases; blowing the barrel with air or oxygen, followed by the supply of a fresh combustible mixture; supply of a fresh combustible mixture with its direct ejection of combustion products; supply of a fresh combustible mixture with its direct ejection of combustion products through an intermediate gas plug of short length; pumping out residual gases from the barrel to create a rarefaction (vacuum) with subsequent filling with a fresh combustible mixture of gases; combination of purging (pushing out) of residual gases with pumping out. In the direction of the flow of a fresh combustible mixture, its supply is distinguished: in the direction of the outflow of combustion products; towards the direction of the outflow of combustion products; across the direction of the outflow of combustion products; a combination of the above methods. According to the place where the fresh combustible mixture is introduced into the barrel, its supply is distinguished: at the closed end; at the open end; in the middle part of the barrel; simultaneously along the entire length of the barrel; a combination of the above methods. Gas exchange schemes with different gas supply cycles are considered.