Yoshito Umeda

Efficiency Improvement of Vacuum Carburizing by Using Natural Gas

Acetylene and ethylene are frequently used in vacuum carburizing in Japan. In this study the natural gas which is available from the lifeline is applied to vacuum carburizing. The gas composition inside the furnace was analyzed by the gas chromatography in order to examine the carbon infiltration mechanism. Unsaturated hydrocarbon gases (such as acetylene and ethylene) are generated from the natural gas. The effect of acetylene concentration in the furnace on the carbon infiltration rate was investigated. The carbon amount which infiltrates into the steel increases, as acetylene concentration in furnace increases. It is possible that carbon concentration of specimen surface increases to the cementite precipitation concentration in the short term, when natural gas flow rate increases in the initial carburizing stage. After that, carbon concentration of specimen surface does not decrease, even if the natural gas flow decreases, because carbon atoms which are consumed for diffusion to inside are sufficiently supplied. By using this method, inhibition of soot generation, reduction of process gas and shortening of the carburizing period are possible. The carbon concentration profile of the vacuum carburized specimen was compared with the simulation.

Characteristics of Combustion of Rich-Lean Burner Controlled Boundary Region between Rich and Lean Flames (2nd Report, Effects of Mixture and Air Supplied into Boundary Region on Practical Combustion Region)

Effects of the velocity and the air ratio of the mixture and the air supplied into the boundary region between the rich and lean flames on the characteristics of the rich-lean combustion were investigated in order to develop a new type of a domestic boiling water heater and a warm heater with low emission of NOx and high TDR. The characteristics of flame stabilization of the rich-lean combustion are improved even under the condition of the practical combustion when the stoichiometric, lean mixture and the air are supplied into the boundary region between the rich and lean flames. The stable combustion is achieved under the condition of 1.34 times of the normal load combustion by ontrolling the boundary region. The emission of NOx is decreased when the air is suplied into the boundary region between the rich and lean flames. Especially, the effects of NOx reduction are noticeable under the conditions of low load combustion. Therefore, it is possible to prevent combustion oscillation and combustion noise with low frequencies from occurring, and to develop the new type of burners with high performance of high TDR and further low emission of NOx by supplying the mixture and the air into the boundary region between the rich and lean flames in the rich-lean combustion.