Quality Waterjet Newsletter – 09/08/2009
Safe Distance of Waterjets and Abrasive Suspension Jets Waterjets(WJ) and abrasive suspension jets
(ASJ) have been used for various field applications. Considerable number of
accidents have occurred that the jets hit the operator or nearby people.
Katakura’s paper* explored a scientific way to determine the injury-free
distance from the jets. A high pressure pump was used to generate pressure
of up to 69 Mpa. 60 Mpa
pressure was used for both the WJ and ASJ tests. Olivine sand was used as the
abrasive in the ASJ tests. Swine skin was used as a substitute material for
human skin in these tests.
Tensile testing was done to determine the tensile strength of the
swine skin to be 3-30 Mpa, similar to that of human
skin (3-13
Mpa). Frozen swine skin materials were defrosted
just before the experiment. Two layers of wire mesh were used to support the
swine skin sample to avoid backpressure upon penetration. The nozzle was mounted on a motion system that can
move parallel and perpendicular to the sample surface simultaneously. The
jets were aimed at the sheet of swine skin perpendicularly or at 45° or
135° angles. The nozzle moved from far to close, maintaining a
speed of about 1 cm/s at the direction parallel to the sample surface as well
as at the direction of the jet velocity. After being hit by the jets, the sample skins were
visually examined to identify the location of penetration, non-penetration
injury (depression or abrasion), or non-injury as well as the corresponding
standoff distance. The test results indicated that the safe standoff
distance based on the penetrating injury (SSD1) is about 50 cm for WJ and 70
cm for ASJ. The safe standoff distance based on the non-penetrating injury
(SSD2) is about 120 cm for WJ and 170 cm for ASJ. A sufficiently-safe
standoff distance was suggested to be 2.5 m for WJ and 3.5 m for ASJ, roughly
5 times of SSD1 and 2 times of SSD2. The effects of the traverse speed and
the incident angle appear to be small or negligible. The author concluded that this is a reproducible
method and the research effort will be continued. *Katakura, H. (2009) “Research on
the safety distance from a nozzle – measurement of safe standoff distances of
WJ and ASJ”, Proceedings of the 2009 American WJTA Conference and Expo,
August 18-20, |
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