Upgrading a CVD unit for chrome carbide deposition on the inner surfaces of the fuel injector nozzle body of a diesel engine

Abstract

Fuel injector nozzle parts tend to wear out due to abrasive particles of quartz and aluminum oxide penetrating into the fuel. The hardness of quartz abrasive particles exceeds the hardness of work surfaces in 1.4 times, and that of aluminum oxide – in 2.7 times. Strengthening one part of the fuel injector nozzle does not increase the service life sufficiently, so it is necessary to harden both parts of the precision pair. The CVD method is the most promising technology of wear-resistant coating deposition on steel machine parts. It produces carbide-chrome coating with microhardness up to 19 GPa (in vacuum conditions of 100 to 0.001 Pa) at temperatures above 200°C. The analysis of available devices and the review of patents of known solutions on the coating deposition from a steam phase have shown the impossibility of using these devices for restoration of the nozzle body. In this respect, the author developed a new reactor design and a scheme of the CVD unit for the coating deposition on the inner hard-to-reach surfaces of the nozzle body. The developed CVD unit takes into account the factors affecting chromium carbide deposition: thermodynamic conditions, reagent feed, deposition duration, unit parameters, adhesion and coating properties. The CVD unit upgrade results in making chromium carbide coating on the inner surfaces of the nozzle sprayer body, achieving thermodynamic equilibrium of chemical reaction of chromium hexacarbonyl decomposition at temperatures below 200°C (below the low tempering level of 18Х2Н4ВА, 12Х2Н4А and 40ХН2МА steel), and ensuring a controlled supply of a reaction medium to hard-to-reach areas, where refractory metal coatings are formed.