Influence of plasma torch design on cutting quality during precision air-plasma cutting of metal

Optical interferometry and metallographic analysis were used to study structure of cutting seams obtained after 09G2S steel cutting by PMVR-5 plasma torch. These plasma torches have a number of design features in the system of gas-dynamic stabilization of plasma arc. It is shown that application of new plasma torch allows obtaining higher quality of cutting 09G2S steel of medium thickness with high productivity and lower energy costs. Metallographic analysis has shown that qualitative composition of the cut surface structure is almost the same, so priority criteria for comparative quality analysis are parameters of surface microgeometry. Evaluation of this parameter shows high quality of cutting almost along the entire length of a cut, since the influence of technological features of plasma arc cut into the metal affects at a distance of less than 0.3 mm from the edge of the sheet. The use of additional methods of gas-dynamic stabilization in PMVR -5.2 plasma torch (feed symmetry with a double swirl system of plasma-forming gas) allows to achieve additional advantages in terms of surface quality compared to PMVR -5.1. A number of features that affects quality of cut when cutting metals of different thicknesses for welding, is noted depending on the angle of inclination of plasma torch during cutting. Estimates of the surface layer hardness indicate minimal deviations from the requirements of GAZPROM Standard 2-2.4-083 (instructions on welding technologies in the construction and repair of field and main gas pipelines), which allows further use of cutting seams obtained by studied plasma torches for welding without removing zones of thermal influence. Thus, application of new plasma torches makes possible precision finishing plasma cutting of metals, including production of welded joints.