Optimal Abrasive Mass Flow Rate for Rock Erosion in AWJ Machining

Erosion process of the Abrasive Water Jet (AWJ) machining on a rock material depends on various parameters. A brittle rock material is removed predominantly by the deformation wear. Abrasive grains can enhance the machining since their hardness and therefore material removal is better than work of pure water. However, to this day, determination of an optimal dosage of the abrasive matter entering into the mixing chamber was rather neglected. Based on the laws of conservations of momentum and energy combined with some empirical facts, it is possible to derive an equation for erosion of the material and subsequently another relation that provides estimation of the optimal mass flow rate of an abrasive matter. The main equation for erosion consists of six experimental coefficients, for an intensive AWJ only four, describing the effectivity of the water jet k_w and abrasive jet k_a impacting the material. It seems that the energy that is used for erosion is very small and the ideal dosage of the abrasive material is approximately Ṁ_a ≈ ṁ_w·(1 − 2k_w/k_a), where Ṁ_a and ṁ_w are the abrasive and water mass flow rates. Such an equation could be used for setting of AWJ machines. The economical optimum (eo) for cutting is proposed via the relation eo = E/E_max − R/R_max, with the erosion E and its maximum value and the resistivity R and its maximum value.