Effect of Change in Energy and Momentum Levels on the Rock Removal Rate in Indiana Limestone

An investigation is made into the effects of water jet pressure, nozzle diameter, traverse speed of the nozzle over the rock surface and the number of times the jet passes over the same area on the penetration of a water jet into Indiana limestone. The effectiveness of the cut is judged on the depth of cut established and the specific energy of rock removal. Pressure is varied in the range from 550 to 3,400 bars at nozzle diameters from 0.58 to 25.4 mm. For pressures above 1,720 bars and nozzle diameters over 1.016 mm. the jet is produced through a single shot water cannon, modified from a 90 mm field piece. At pressures and nozzle diameters below these bounds the jet is generated by a 1,720 bar capacity triplex pump providing a continuous flow through the nozzle. Rock traverse speed is controlled through differential gearing on a lathe to lie in the range from 0 to 1.54 m/min. for the pump experiments. In the experimentation with the Water cannon a theoretical traverse speed is calculated, and used in the comparisons, based on the time taken to penetrate 5 cm. of the limestone. 1. INTRODUCTION Indiana limestone is fine grained, sedimentary rock also commonly known as Salem limestone. By reason of its granular structure water jet cutting of the material is confined to the area of rock directly located under the jet impact point and it is not possible to establish consistent kerf removal between successive jet cuts by water jet action alone, as can be established for the crystalline rocks such as marble and granite. It has been shown (Ref. 1) that little extra energy is required to remove ribs of material left between two successive jet passes. It would therefore seem advantageous to design a cutting machine where the water jets cut channels in the rock face, in which channels roller cutters would run to pry the ribs remaining away from the face.