standoff distance: distance from nozzle to target, islands: regions of the target where the coating has not been removed from the substrate after waterjet cleaning,.
N95-18996 1994
_
NASA/ASI_ESUMMERFACULTYFELLOWSHIPPROGRAM
MARSHALL THE
DESIGN
Prepared
OF
SPACE
UNIVERSITY
HIGH
FLIGHT OF
PRESSURE
ALABAMA
WATERJET
Andre
By:
CENTER
NOZZLES
P. Mazzoleni
Academic
Rank:
Assistant
Institution
and Department:
Texas
Professor
Christian University
Department
of Engineering
NASA/MSFC:
MSFC
Laboratory: Division:
Materials
Branch:
Process
Colleague:
Eutiquio
and Processes
Fabrication
XXIX
Services
Automation
Martinez
Division and Modeling
C_/,//
_" "_
'
'
Introduction The
Hydroblast
Research
of high
pressure
various
substrates.
such
(e.g.
enables the
the
waterjet This
have
report
at MSFC
affect
study
studies
of a large of material
research
project high
nozzle but
spray
depleting
cleaning
method
has
which
(ODC)
to be
a viable
cleaning
such
and
involves
the
controlled.
as incomplete
damage
use from
chemicals
is robotically
problems
the
coatings
proven
of waterjet
not cleaned)
conducted
consisted
pressure
things
involved
thermal
use ozone
waterjet
area,
is used to investigate
and
to the
This coverage
substrate
from
observed.
The
such
often
water
cleaning
been
nozzle
by the
author
of identifying
water
as stripping
computer
of different
pressure
of "islands"
multijet,
operation
pressure
Center
adhesive
[4, 5]. A popular
high
summarizes
in 1994.
of rotating, The
rapid
formation
Flight
grease,
of cleaning
High
use of solvents multijet,
Space
paint,
methods
solvents.
to the
use of a rotating, method
to strip
Current
as chlorinated
alternative
Cell at Marshall
waterjets
nozzles, rate,
and investigating
and
distance
an extensive
and
Faculty
the
how particular
standoff
simulations,
as a Summer
basic
designs
literature
review,
properties
and
completeness
Fellow modes
of
of coverage.
and
experimental
designs.
Definitions Since
there
is no widespread
define
here
the
terms
used
substrate:
material
which
needs
to be removed
from
substrate,
nozzle:
attached
multijet
orifice
nozzle,
is moved
target
is on a rotating
coating
has
amount
of time
not
been
Factors
Affecting for
pressure This
information
either
through
and
the
increases
concern dwell
water
the
pressure is not and
path
as the
cleaning
of this
likely, dwell
time
- is usually
on surface
of nozzle,
sweep
rate:
rate
at which of the
waterjet
rate
cleaning,
a particular
nozzle target
dwell
region
is moved
over
on
at which
(as is the case when
regions
the
the
effect and
paper
and
hence
integrity
the
rotates, where
time:
of the
the the
target,
the target.
distance,
to be removed.
so that
impact
and
decreases XXIX-1
of the with
coating
will be assumed
be adjusted
The
water
the
coating target
standoff
water
to be
this information,
on the
increased
substrate.
of standoff
Given
damaged.
of the
the
experiment.
dwell
time
to target
of orifices
to be cleaned
can
to be removed
Requirements
to know
through
material
orifices
nozzle
is maintaining
substrate
impinges,
or other
are several
past
nozzle
waterjet
we
- there
orifice,
with
Cleaning
focus
and
after
production,
for material
waterjets
velocity:
contact
we need
on the
or more
pressure
islands:
substrate
cleaning
material, time
is not
in pressure
the
in waterjet
theory,
substrate
angular to target,
is in continuous of the
name
for waterjet
is moved
nozzle
Waterjet
a particular and
distance,
width
grease
placement
or target
from
which
paint,
of an individual
nozzle
from
removed
a waterjet
width:
Thus,
target,
distance
stripping
Of paramount
to the turntable),
distance:
high
configuration: structure
upon
with
generic
final exit device
orifice
parallel
coating:
of waterjet
object
coated
for delivering
orifice:
terminology
target:
usually
via waterjet,
the internal
nozzle
regarding
paper:
cleaned,
device
arm,
geometry:
standoff
in this
to be
to a robotic
a single
convention
known, standoff
is removed
increases distance.
with It may
,
7
be necessaryto make severalpassesoverthe target in order to removethe coating without damaging the substrate. This can alsobe accomplishedvia overlapfrom multiple jets. Another important constraint is the time required to clean the target. This will be a function of the stripping width, the sweeprate and the number of passesnecessaryfor cleaning. Standoff distance will be constrainedby the geometryof the target. For a perfectly flat plate, there is no constraint on possiblestandoff distance.If there are protrusions,however, such as bolts or ridges, then this will limit the possiblestandoff distances,unlessthe robot to which the nozzle is attached is equipped with the meansto adjust to variations in the target geometry. Factors
Affecting
Waterjet
To maximize
waterjet
eliminate
production
The
the
coverage
standoff Jet
aspect
distance and
performance,
of coating
of waterjet
is determined the
internal
and have
by the
to have
complete
the largest
possible
will be a function
of the
geometry
Performance
it desirable
"islands", cleaning
will be a function
compactness
orifices,
cleaning
Cleaning
compactness
way
in which
of each
the
of the
coverage, standoff
orifice
i.e. distance.
configuration.
of the
jet
issuing
water
is delivered
from
to The
each
to the
orifice.
individual
orifice.
Coverage The main factors affecting orifices on the nozzle. The
angular
of orifices pump,
there
number
velocity
increases. of orifices
derive given
to the
a formula exit,
nozzle
for the
maximum and
v = exit
Pa -- atmospheric
orifice
velocity
pressure,
there
of orifices
of orifices
that
decreasing
the
limit
on the
number
of orifices
exit diameter.
p -- density
exit
diameter
can
of water
diameter
and
as the
number
with
each
an unlimited
of each
of the
orifice,
orifice.)
be placed
but
Below,
on a nozzle
we for a
A = cross sectional
of orifice,
n = number
of these
associated
(In theory,
Let F = flow rate,
d -- exit
placement down
rate
diameter that
the
goes
flow
can be added.
a lower
of waterjet,
and
for full coverage
is a maximum
by simply
place
number
necessary
since
can be added
pressure
are the
number
considerations
flow rate,
of orifice
of the However,
is a limit
manufacturing
coverage
p -
pump
of orifices.
area
pressure,
Then
F = nvA.
r----------------"
But
A = 7rd2/4
and
from
a modification
of Bernoulli's
law we have
v = c_/_,
where
V
c_ is an experimentally between
0.9 and
c_ = 1. Thus (i.e.
Once
nozzle
by radial Fig. la.
--
the
4F
7rd 2 V
2(p-pa)
-- 50in3/sec,
number
called
/___2_.__
•
the
p = 36,000
of orifices
for
velocity
coefficient
For a conservative
the
psi, and nozzle
which
assessment
d -- .019in,
is chosen,
the
is usually
of n, we set
we have effect
n < 6.36
of different
can be studied.
In studying the
constant
[4]. So, n
