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WATER JET CONFERENCE - Waterjet Technology Association

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energy it effects an increase in mechanical specific energy. Hence, a compromise must<br />

be found for every cutting condition. For the most efficient cutting at a selected speed the<br />

jet should not penetrate the rock surface deeper than the mechanical tools.<br />

At a constant waterjet pressure and constant stand-off distance, the jet penetration<br />

depth increases directly with increase in nozzle diameter; more so at higher pressures.<br />

Because increasing nozzle diameter causes an increase in jet penetration depth, the tool<br />

forces are reduced as a result. Three nozzles have performed equally well at a constant<br />

stand-off/nozzle diameter ratio. The optimum nozzle diameter is dependent both on the<br />

type of mechanical tool with which it is to be used and on the location of the nozzle with<br />

respect to the tool tip. Also, on desired pressure range and available power. Power<br />

requirements for water jet cutting increase with the first power of pressure and second<br />

power of nozzle diameter. Therefore, the nozzle diameter should be selected such that it<br />

will cost less to penetrate to a required depth. This necessitates the use of smaller<br />

diameter nozzles whenever practicable.<br />

A large rock cutting rig is presently being modified to increase the cutting speed<br />

to lm/s to permit a more detailed investigation of this promising rock excavation system.<br />

REFERENCES<br />

1. Altinoluk. S., 1981, Ph.D Thesis, Univ. Newcastle upon Tyne, U.K.<br />

2. Cooley, W.C., 1970, Correlation of data on erosion and breakage of rock by high<br />

pressure water Jet. Proc. 12th Symp. on Rock Mechanics,pp.653-65.<br />

3. Harris, H.D., Mellor, M., 1974, Cutting rocks with water jets. Int. J. Rock Mech. and<br />

Min.Sci. and Geotech. Abstr., Vol.ll, pp. 343-58.<br />

4. Plumpton. N. A. and Tomlin M.G., 1982, The development of a water jet system to<br />

improve the performance of a Boom Type Roadheader, Proc. 6th Int. Symp. on Jet<br />

Cutting <strong>Technology</strong>, Paper Gl, pp.267-82, Guildford, Il.K.<br />

5. Summers, D.A., Lehnhoff, T.F., 1977, Water jet drilling in sandstone and granite.<br />

Proc. 18th. Symp. on Rock Mech.<br />

6. Tecen, O., 1982, High Pressure <strong>Waterjet</strong> Assisted Drag Tool cutting of rock<br />

materials. Ph D. Thesis, Univ. Newcastle upon Tyne, U.K.<br />

373

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