Effects of Focus Geometry on the Hard Rock‐Cutting Performance of an Abrasive Waterjet

Abstract

Abrasive waterjets are being increasingly used in civil engineering for rock and concrete cutting, particularly for the demolition or repair of old structures. The energy of an abrasive waterjet is primarily provided by the accelerated abrasive. The momentum transfer during mixing and acceleration determines the abrasive velocity, which affects the cutting performance. Meanwhile, the geometry of the focus at which mixing occurs influences the momentum transfer efficiency. In this study, the effects of the focus geometry on the optimum abrasive flow rate (AFR) and momentum transfer characteristics in hard rock cutting were investigated. Experiments were conducted using granite specimens to test the AFR under different focus geometry conditions such as diameter and length. The results show that the focus geometry significantly affects the maximum cutting depth and optimum AFR. The maximum cutting energy was analyzed based on the cutting efficiency of a single abrasive particle. In addition, the momentum transfer parameter (MTP) was evaluated from the empirical relationship between the maximum energy and the cutting depth for granitic rocks. Accordingly, a model for estimating the MTP based on the AFR was developed. It is expected that the results of this study can be employed for the optimization of waterjet rock cutting.

Performance and Reuse of Steel Shot in Abrasive Waterjet Cutting of Granite

“…The momentum of the high-velocity water flow ( ṁ w × v w ) is transferred to the momentum of the abrasive ( ṁ a × v a ). This transfer continues until the terminal velocity ( v t ) of water and abrasive becomes equal (Cha et al 2020;Momber and Kovacevic 2012): where ṁ w is the water flow rate, v w,o is the velocity of water at the pump, v w is the velocity of water during acceleration, ṁ a is the abrasive flow rate, and v a is the velocity of abrasive during acceleration. The abrasive acceleration and mixing efficiency are expressed in terms of a momentum transfer parameter ( t ) that is affected by the abrasive flow rate, and determines the terminal velocity (Cha et al 2020;Momber and Kovacevic 1995;Oh and Cho 2015):…”

Simple Approach for Evaluation of Abrasive Mixing Efficiency for Abrasive Waterjet Rock Cutting

“…The cutting energy of an abrasive waterjet is a function of the AFR, and the system design determines its characteristics [12,13]. The optimum AFR is a function of the impact frequency, the terminal velocity, and the kinetic energy of the abrasive through the relationship between the mixing efficiency and energy [14,15]. Meanwhile, optimizing the focus shape improves the mixing efficiency, where the momentum of the water is transferred to the abrasive [16].…”

“…Analysis of variance on the effects of the focus and orifice has shown that 98% of the cutting width and roughness results from the focus diameter and the AFR [18,25,26]. The abrasive mixing efficiency is the characteristic that is the most strongly affected by the AFR, and the larger the focus diameter, the higher the optimum AFR [15]. Moreover, the larger focus diameter reduces the energy that accelerates the abrasive [27].…”

Orthogonal Experiment on the Surface Quality of Carbon Fiber Reinforced Plastic Cut by Abrasive Water Jet

“…To sum up, the previous studies have shown that the cutting quality and depth of the AWJ on the CFRP depend heavily on process parameters like jet pressure, cutting speed, and abradant flow rate. However, there is little report on the surface morphology or roughness on the cutting plane [15][16][17][18][19]. To make up the gap, this paper carries out orthogonal experiment to disclose the impacts of the AWJ cutting speed and the CFRP thickness on the surface roughness on the cutting plane, and to reveal the variation of surface roughness with cutting depths.…”