Developing installation to increase cylindrical part surface hardness
The aim of the study is to develop an installation for increasing the hardness of the surface layer of cylindrical low-carbon steel components. An argon-arc welding apparatus was used as a plasma-arc source. The movements of the burner and the workpieces are provided by a numerical control to perform specific operations according to preprogramed commands, i.e. the unit operates during a work cycle according to a specially-designed program without operator intervention. Thus, the setup is designed for processing parts having complex geometric shapes to a given tolerance. For carburisation, a paste composed of graphite, sodium silicate (waterglass) and water was used. The waterglass is dissolved in water; then, after drying, a colloidal solution is formed with graphite powder. The layout of the installation was elaborated and the main components were selected. The installation comprises the following components: a personal computer for process control; a TIG 250P power source; a plasma arc source; guides fitted with mechanisms for ensuring the movement of tables and burners located on them; a table for affixing flat workpieces; a table equipped with a jaw chuck for securing and rotating cylindrical workpieces. The personal computer used to control the entire process of increasing hardness comprises a key element in the operation of the installation. The results of the study of workpiece samples following processing by means of the designed installation are presented. The installation provides a controlled process for heating the surface layer of a metal workpiece. A light-grey layer of increased hardness is observed on the surface of the hardened metal. The hardness of this layer achieves up to 50-55 HRC, while the roughness is in the range of 3-10 microns. Due to the high accuracy of the plasma carburisation process automated by means of the developed installation, it is possible to significantly reduce the carburisation time and ensure uniform quality properties of the carburised layers.