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WATER JET CONFERENCE - Waterjet Technology Association

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Figure 23. Removing baked enamel from a sheet of aluminum.<br />

(Nozzle diameter = 0.254 mm, pressure 138 MPa, Traverse speed = 28 cm/sec)<br />

NAME: Andrew F. Conn<br />

COMPANY: Tracor Hydronautics<br />

DISCUSSION<br />

QUESTION: "In your tests for removal of baked enamel from aluminum siding, your<br />

optimum X/d (standoff: X = 10.2 cm, nozzle dia.: d = 0.254 mm) was 402. At this<br />

distance, would you agree that the erosive mechanism was droplet impingement, and not<br />

a steady erosive jet (l/2 pv2) mechanism?"<br />

ANSWER: The authors do not agree The erosive mechanism is not due to droplet<br />

impingement. The width of the paint removed increases because the cross sectional area<br />

of the jet increases due to aerodynamic drag. The coherent length of a good jet can persist<br />

up to a distance of 2000 nozzle diameters. In any case, if the erosion was due to droplet<br />

impingement, the width of the paint removed would be irregular (random patches), not<br />

clean as shown in the photograph of the paper<br />

NAME: Steve Sugino<br />

COMPANY: Sugino Machine Limited<br />

QUESTION: "When you cut the frozen fish or fish fillet, didn't you have any problem of<br />

dehydration on its surface? What was the cutting condition?"<br />

ANSWER: No, we did not find any dehydration problems. Frozen samples of fish were<br />

stored in a deep freezer prior to testing They were cut immediately after removing them<br />

from the freezer. At the feed rates involved, dehydration would be a problem. If anything,<br />

softening of the top layers of the tissue due to defrosting would be a problem, but only a<br />

minor one.<br />

317

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