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WATER JET CONFERENCE - Waterjet Technology Association

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NAME: John E. Wolgamott<br />

COMPANY: Stone Age, Inc.<br />

DISCUSSION<br />

QUESTION:"Why did you choose to place the jet in front of the pick? I found in my<br />

earlier work at the Colorado School of Mines that this location suffered greatly because<br />

of disruption to the jet by the generated chips from the pick action. Aiming the jet from<br />

behind the pick avoids this problem, allowed lower jet pressures to be effective, and had<br />

a dramatic effect on lowering the normal force required to keep the pick cutting in the<br />

rock.<br />

ANSWER: There were a number of reasons for placing the jet in front and not behind<br />

the tool, namely:<br />

• at the time of the study this was the obvious position, hypothesised by many to be<br />

desirable;<br />

• this position in conjunction with a tool mounted on a modified metal planer,<br />

presented both least technical difficulty and allowed for both easy and flexible<br />

variation of stand-off distance and lead-on distance.<br />

• you will appreciate the large number of variables involved in linear hydrid cutting,<br />

and the jet in front offered the most progressive experimental program within the<br />

philosophy of the pilot study.<br />

• The study looked at effects of speed, stand-off distance, various lead-on and offset<br />

geometries for the nozzle, nozzle diameter, water pressure, depth of cut and rock<br />

type, and their effects on specific energy, cutting and normal forces, jet<br />

penetration, hydraulic specific energy for a point attack tool, for both single and<br />

multiple passes<br />

However, this is not to say that any other jet position is to be ignored.<br />

Indeed, we plan in our present work on a much larger linear rig cutting at 1 m/s<br />

with commercial tools, to change jet position, and we believe that the jet impinging from<br />

behind the tool may well prove effective in reducing forces, especially the critical normal<br />

force at these speeds. We also feel that any jet impinging in this way may well display an<br />

advantage in coal cutting by cooling the path of the tool, and so preventing the incidence<br />

of frictional ignition in potential methane environments.<br />

We hope, in due course, to have the opportunity of presenting the results of our<br />

present research.<br />

380

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