Development of equipment and technology for precision air-plasma cutting of plate steel

The authors have investigated the structure of cutting seams obtained after cutting steel 09G2S with a new narrow-jet plasma torch of PMVR-5.3 type which has a number of design features in gas dynamic stabilization system (GDS) of plasma arc. To increase the efficiency of GDS in PMVR-5.3 plasma torch, a symmetrical input of plasma-forming gas (PFG) into the flow division system and a gas-dynamic flow stabilizer using two (forming and stabilizing) swirlers with a variable number of swirl channels were used. It is shown that the achieved advantage in GDS efficiency makes it possible to obtain high cutting quality of steel 09G2S with thickness of 40 mm with high productivity and lower energy costs. Analytical methods have proved a high degree of cutting precision of the new torch– a small cut width, no melting and rounding of the upper edge, as well as a grate in the cut lower part and splashes in the cut upper part, almost zero angular deviation, minimum values of the surface microrelief and width of the thermal impact zone. Metallographic analysis and determination of hardness showed the presence of three subzones in the thermal impact zone with significant structural changes in two of them. A number of factors were noted influencing the revealed changes in the structure formation, as well as changes in the elemental composition of the cutting seam surface layer revealed during the X-ray spectral analysis. Attention is drawn to the surface microrelief after plasma cutting, which in all quality indicators is commensurate with machining of the surface after milling and corresponds to the second class of quality in terms of surface cleanliness. It was proved that the use of the new narrow-jet plasma torch allows high-quality cutting of plate steel in thickness range up to 40 mm or more. However, welding of blanks without pre-machining can be carried out with a cutting thickness of no more than 20 mm.

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