After a brief history of plasma arc cutting (PAC) is given, its types and abilities are discussed. Experimental data (unfortunately, little is available) on plasma parameters are reviewed. The status of contemporary understanding of the process involved in PAC is presented. The main emphasis is on those processes that determine the technological abilities of the method. Along with the existing theories reviewed, we propose qualitative hypotheses on some of these processes. Among them are: dependence of the cyclic cathode erosion on the rate of current increase, double arcing and the role of insulating inclusions at the nozzle orifice on double arcing, dross formation and the shape of the kerf.
The variation of piercing hole depth with time was obtained for the following metal-gas combinations: carbon steel-oxygen, carbon steel-nitrogen and aluminium-nitrogen. It was shown that hole depth initially decreases rapidly after the arc strikes the plate and then the deepening speed slows down. A simple model to describe cavity growth during piercing is proposed. Assuming rapid evacuation of the molten metal layer, the model treats the jet as a heat source only. Approximate solution of the heat conduction equation made it possible to describe deepening of the cavity in accordance with experimental data. Comparison of the calculated cavity depth with experimental points allowed the fraction of the total arc power which is consumed by the piercing process to be estimated. This fraction is 30-70% for the metal-plasma gas combinations that were studied. The possible reasons for there being a thickness limit in piercing are also discussed.
When cutting metal with plasma arc cutting, the walls of the cut are narrower at the bottom than at the top. This lack of squareness increases as the cutting speed increases. A model of this phenomenon, affecting cut quality, is suggested. A thin liquid layer, which separates the plasma from the solid metal to be melted, plays a key role in the suggested model. This layer decreases heat transfer from the plasma to the solid metal; the decrease is more pronounced the higher the speed and the thicker the liquid metal layer. Since the layer is thicker at the bottom of the cut, the heat transfer effectiveness is lower at the bottom.The decrease in heat transfer effectiveness is compensated by the narrowness of the cut. The suggested model allows one to calculate the profile of the cut. The result of the calculations of the cutting speeds for plates of various thicknesses, at which the squareness of the cut is acceptable, agrees well with the speeds recommended by manufacturers.The second effect considered in the paper is the deflection of the plasma jet from the vertical at a high cutting speed. A qualitative explanation of this phenomenon is given.We believe the considerations of this paper are pertinent to other types of cutting with moving heat sources.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.