Obtaining powders with particle shape near to spherical by water atomization of melts

Abstract

Abstract. Problem. Recently, there is a tendency to increase volumes of use of spherical powders. But due to high cost of spherical powders obtained by conventional technologies, improvement of current more economical methods of its production is interesting. Goal. The goal is to substantiate formation of metal powders of spherical shape (or near to it) at high-pressure water atomization with use of swirl jet. Methodology. On the basis of results of atomization of medium-carbon ferromanganese with use of modified annular hydraulic nozzle and wellknown literature data, conditions for spheroidization of metal drops at atomization «in spout» are analyzed. By mathematical modelling method the semiempirical equation for definition of average median size of powder particles is deduced. Results. Using the example of atomization of ferromanganese, possibility of obtaining powders with particle shape near to spherical by water atomization is confirmed. The model of atomization is proposed. It is shown that impact is carried out by water, but through thin gas layer, without direct contact of water and metal. Thickness of gas layer is important. At optimal parameters of atomization solidification time of drops increases, that is favourable for obtaining particles of spherical shape or near to it. Originality. Model of water atomization of melts «in spout» is proposed. Conditions needed to form particles of spherical or spheroidal shape during water atomization are substantiated. Engineering equation to determine median size of powder particles is obtained. Practical value. Described technology is promising to produce metal powders with particles of spherical shape or near to it. Use of obtained powders of ferromanganese for coating of welding electrodes demonstrated the advantage over ground powders such as elimination of swelling coating during production of electrodes, better plastic strength of coating, and higher impact strength of welded seam at negative temperatures.