Prediction Equations Relating High Velocity Jet Cutting Performance to Stand Off Distance and Multipasses

A previously derived equation for continuous jet penetration of solids (1) is combined with empirical equation for jet spreading and velocity decay in air. These equations are used to study the effects of stand off distance and multipasses on cutting depth, volume removal and specific energy. Predicted trends are compared with limited published experimental data for wood, limestone and coal. Predicted cutting depths for single and multipass cutting are in reasonable agreement with measurements. Volume removal predictions are lower than measured values because other mechanisms such as brittle fracture and reverse jet flow not included in the present penetration model contribute to total material removal by widening of the kerf beyond the effective jet width. The equations confirm the existence of optimum stand off distance and the benefits of multipasses for certain combinations of jet, material and cutting speed parameters. Numerical values of the governing nondimensional groups for optimum performance are identified for conditions encountered in typical industrial applications.