Plasma cutting of concrete: Heat propagation and molten material removal from the kerf

Abstract

An experimental investigation of heat propagation in the case of plasma cutting of concrete is reported. The experiments were carried out by using a high-enthalpy nitrogen plasma jet generated in a dc vortex-stabilized nontransferred arc torch. Concrete plates of different thicknesses up to 52 mm and with and without steel reinforcement were used. The plates were placed horizontally while cutting. The heat conduction losses inside the material were estimated by comparing thermocouple measurements and theoretical temperatures obtained with an analytical model of the heat propagation in the material. The influence of the molten concrete layer that separates the plasma to the solid material due to the high viscosity of the liquid concrete was accounted for. The power losses below the material in the extinguishing plasma have also been determined from calorimetric measurements. For different plate thicknesses and cutting velocities, a complete power balance of the process is performed with the calculation of the cutting efficiency on the basis of various relevant power terms. In addition, the hydrodynamics of the molten concrete layer in the kerf is analyzed. For a mean power level of 11.2 kW and a nitrogen gas flow rate of 25 Nl/min, the torch is able to cut a concrete plate of 52 mm in thickness with a speed of 20 mm/min and a whole efficiency of about 30%. The viscosity force is the main limiting factor on the cutting velocity in thick plates.