Gas-Dynamic Specifications of Glow Discharge During Ion Nitriding Process

Abstract

Ion-plasma nitriding in glow discharge is a widely used method of surface hardening in the industrialized countries of the world and it is the most modern and technological type of surface hardening of machine parts, molds, dies and cutting tools. However there is no detailed review in the literature of technical characteristics and operation of a gas-vacuum part in ion nitriding units and it does not allow estimating electric power consumption for operation of a gas-vacuum system while assessing efficiency of the given equipment. The paper considers problems pertaining to relationship of gas-dynamic parameters of the nitriding process (pressure and gas flow rate) and energy characteristics of the glow discharge (current density, discharge voltage) during ion nitriding at industrial plants and their impact on the process. Calculation-practical modeling of a vacuum system for an ion nitriding installation shows that it is advisable to use vacuum units which represent consistently connected forevacuum and two-rotor pumps in order to ensure independent control of a pumping speed and flow rate of the gas mixture. Such approach makes it possible to carry out nitriding processes in a wide range of pressures with the possibility to provide high plasma gas rates at a low pressure, in particular, when processing large areas. The paper has revealed temperature interrelations, chamber pressure and glow discharge current density that ensure its existence in the abnormal form. It has been shown that at lower operational pressure during the process, higher degree of discharge abnormality can be provided at uniform temperature of the batch. Due to this it is possible to attain higher temperature similarity which ensures uniformity of a nitrided layer on all parts of the batch.