Control of Heat Input Characteristics of Plasma Arc by Constricted Nozzle Shape and its Effect

This paper describes a guide line to make low bevel angle cuts in plasma arc cutting by changing of only nozzle conditions ; nozzle shape, electrode tip position in the nozzle and torch height (standoff distance). The idea was deduced from the view point of that the kerf shape is influenced by the radial heat distribution pattern that was established in our another report. First, a new and easy evaluation technique is proposed to be estimated the radial heat distribution pattern with information of cutting speed and top kerf width. Then, the adaptability is examined with some experiments. Secondary, actual radial distribution patterns are experimentally observed at various nozzle conditions. As a result, it is concluded that high throat length, small nozzle convergent angle, long distance between electrode tip to nozzle inlet and low torch height conditions are useful to realize more square type of radial heat distribution pattern with plasma arc. Finally, the relationships between torch conditions and bevel angles are examined. Then, it is indicated that more square radial heat distribution condition is effective to obtain lower bevel angle cuts.