Note: Descriptions are shown in the official language in which they were submitted.
CA 02531672 2006-O1-06
WO 2005/005064 PCT/DK2004/000500
1
Jet spray tool
FIELD OF THE INVENTION
The present invention relates to a jet spray tool for treating surfaces,
especially clean-
ing surfaces using a carbon dioxide snow stream.
BACKGROUND OF THE INVENTION
Carbon dioxide snow jets or jets of pellets are known as cleaning means for
surfaces,
for example before further surface treatment. For example, such a system is
disclosed
in International patent application WO 01/76778 by Nielsen.
In International patent application WO 00/74897 by Werner and Zorn, a jet
spray tool
with a concentric dual nozzle system is disclosed. The dual nozzle system
produces a
supersonic stream of support gas for the ejected carbon dioxide snow. This
system is
complicated and expensive to produce.
Other complicated systems are disclosed in European patent application EP 332
356
by Kozo et al. and Japanese patent application JP 54015623 with publication
no. JP
55106538 by Yamauchi Hiroshi.
DESCRIPTION / SUMMARY OF THE INVENTION
It is the object of the invention to provide a novel jet spray tool which is
easy and
cheap to produce and yet reliable to use.
This object is achieved with a jet spray tool for frozen carbon dioxide
particles com-
prising a supply unit containing carbon dioxide gas under high pressure, for
example
40-60 bar, a jet nozzle connected to the supply unit for receiving pressurised
carbon
dioxide gas from the supply unit and for producing a jet of frozen carbon
dioxide par-
ticles due to the expansion of the gas when exiting the nozzle, and a
connection be-
°' ~~F~~~~ ~''
CA 02531672 2006-O1-06
WO 2005/005064 PCT/DK2004/000500
2
tween the supply unit and the jet nozzle for transporting the pressurised
carbon diox-
ide gas from the supply unit to the jet nozzle.
In the above stated prior art, liquid carbon dioxide is supplied to the carbon
dioxide
snow producing nozzle. However, this has led to rather complicated
arrangements.
In connection with the invention, it has surprisingly turned out, that carbon
dioxide in
gas form successfully can be used to produce frozen carbon dioxide at a nozzle
due to
the expansion of the pressurised gas. Typically such pressure is 40-60
atmospheres.
As experiments have indicated, an arrangement according to the invention, as
de-
scribed below, results in formation of a fast jet of carbon frozen dioxide
particles leav-
ing the nozzle. This jet behaves differently than typical snow jets known from
ar-
rangements, where liquid carbon dioxide is used. The effect has not yet been
fully
understood, but there are indications of frozen carbon particles in a
physical/chemical
phase that has not yet been observed foi° this kind of jet formation
but which has
proved to be very efficient for cleaning surfaces.
In practice, the supply unit may contain carbon dioxide gas and carbon dioxide
liquid.
However, to assure gas extraction and not liquid extraction, the connection is
con-
nected to the supply unit above the carbon dioxide liquid level in the supply
unit.
Thus, the connection may be connected to the supply unit at the uppermost
point of it.
In order to control the release of snow from the nozzle, a valve is located
between the
supply unit and the nozzle.
If the length of the connection is very long, it takes a substantial length of
time and
waste of carbon dioxide, until a carbon dioxide particle jet forms at the
nozzle. This is
a disadvantage for intermitted operation of a jet spray nozzle. Therefore, the
supply
unit should be near to the nozzle, for example at a distance less than 500
mrn, such
that the length of the connection is short. In a practical embodiment, the
applied dis-
tance between the extraction point of the supply unit and the nozzle has been
set to 70
CA 02531672 2006-O1-06
WO 2005/005064 PCT/DK2004/000500
3
mrri, which has been proven to be particularly useful. However, a length of
less than
200 mm can in certain instances be sufficient.
The rapid transport of gas from the intermediate chamber to the nozzle due to
the short
distance of the connection cools the nozzle so fast and efficient that a jet
can be
formed within less than a second after opening of the valve. Therefore, this
system is
easy to construct, cheap to produce and yet very reliable and precise even for
intermit-
tent jet application.
As a supply unit, a carbon dioxide bottle or tank can be used directly
connected to the
nozzle at a short distance. However, due to the short length of the connection
between
the supply and the nozzle, a large tank is disadvantageous near the nozzle.
Therefore,
in a further embodiment, the carbon dioxide tank may be located at a larger
distance
and be connected to the supply unit for supply of carbon dioxide from the tank
to the
supply unit as an intermediate chamber close to the jet nozzle. This is
especially useful
where the distance between the carbon dioxide tank and the supply unit is much
longer
than the distance between the supply unit and the jet nozzle, for example more
than an
order of magnitude larger.
In experiments for cleaning surface, the internal volume of the intermediate
chamber
was about 50 cubic centimetres, and depending of the need, it is proposed to
use a
volume of the order of between 5 ccm and 500 ccm.
In the supply unit as an intermediate chamber, carbon dioxide is received and
stored
before further use at the nozzlee There may be stored carbon dioxide liquid in
the in-
termediate chamber together with carbon dioxide gas for extraction.
It may in some circumstances be an advantage that the intermediate chamber and
the
gas therein are cooled during the storage time, which in most circumstances is
rela-
tively short. For this cooling, the intermediate chamber has an opening into
atmos-
phere for exhaust of carbon dioxide, which causes cooling.
CA 02531672 2006-O1-06
WO 2005/005064 PCT/DK2004/000500
4
A. typical nozzle that has been used with success is tubular and comprises a
lateral
groove across the exit hole at the front end of the nozzle.
As an extra. feature, the jet spray tool according to the invention may
comprise pre-
y cooling arrangement for precooling the jet nozzle before ejection of a jet
of frozen
carbon dioxide particles, for, example in the form of snow, from the nozzle.
Such a
precooling can be accomplished by, for instance, by a Peltier cooling element
in ther-
mal contact with the nozzle or by a container with liquid Helium in thermal
contact
with at least part of the nozzle. In this case, the nozzle can be precooled to
a tempera-
tore of at least below =40°C and preferably to the boiling temperature
of liquid carbon
dioxide.
SHORT DESCRIPTION OF THE DRAWINGS
The invention will be explained in more detail with reference to the drawing,
where
FIG. 1 is a diagram of the jet spray system with the spray tool,
FIG. 2 is a sketch of a possible embodiment of the nozzle,
FIG. 3 is a micrograph of an aluminium surface,
FIG. 4 shows two micrographs in connection with a first cleaning process of an
alu-
minium surface using a slit nozzle with 0.8 mm size,
FIG. 5 shows two micrographs in connection with a second cleaning process of
an
aluminium surface using a slit nozzle with 1.1 mm size,
FIG. 6 shows two micrographs in connection with a third cleaning process of an
alu-
minium surface using a nozzle with a round exit hole with a diameter of 1.2
DETAILED DESCRIPTION l PREFERRED EMBODIMENT
Fig. 1 is a diagram of the jet spray system with a jet spray tool according to
the inven-
tion. The jet spray system 1 comprises a storage tank 2 for carbon dioxide
liquid and
gas, typically at a pressure of 40-60 atmospheres. The storage tank 2 is
connected to a
nozzle arrangement 9 with a nozzle 10, through which a jet of frozen
carbon,dioxide
particles 11 is ejected when carbon dioxide gas is supplied under high
pressure. The
CA 02531672 2006-O1-06
WO 2005/005064 PCT/DK2004/000500
connection 4, 6, 8 between the storage tank 2 and the nozzle 10 can be
accomplished
by stiff and/or flexible tubing that generally is used for this kind of
arrangements. The
carbon dioxide supply from the storage tank can be controlled by a valve 3.
5 Inserted between the storage tank 2 and the nozzle 10 is an intermediate
chamber 5,
where carbon dioxide supplied from the storage tank 2 can be stored for rapid
extrac-
tion. From the intermediate chamber, carbon dioxide gas can be supplied to the
nozzle
through the tubing 6, 8 when valve 7 is opened, where the extraction of carbon
dioxide
from the intermediate chamber 5 through the tubing 6 is above the liquid level
18 in
the intermediate chamber in order to assure gas extraction. Alternatively, the
extrac-
tion can be from the top of the intermediate chamber in order always to assure
gas
extraction. As the intermediate chamber is only 70 mm from the nozzle, the
supply of
carbon dioxide gas to the nozzle from the intermediate chamber 5 is rapid
enough to
cause a fast cooling of the nozzle resulting in a formation of a carbon
dioxide particle
jet after a very short initial phase of cooling of less than a second. This is
very suited .
for sequential spraying with time scales in the order of few seconds. The
intermediate
chamber 5 further comprises an opening 17 into atmosphere.
A nozzle arrangement 9 that can be used in a system according to the invention
is i1-
lustrated in Fig. 2. The nozzle arrangement 9 is connected to the tubing 8 by
a stan-
dard connection, for example a threaded fitting 13. The nozzle arrangement 9
com-
prises a tubular nozzle 10 with a simple jet exit hole 16 inserted into a
nozzle holder
14 fastened to the tube fitting 13. This nozzle arrangement 9 with the nozzle
10 is very
simple in nature, though still providing a satisfactory jet 11 of carbon
dioxide parti
cles.
An improvement of the jet formation has been observed for nozzles 10 that are
pro-
vided with a lateral groove 15 across the front end of the nozzle 10 with the
ejection
hole 16, which is shown in an enlarged head-on perspective in Fig. 2b.
In the following, some experimental results are presented which are achieved
with an
arrangement according to the invention.
CA 02531672 2006-O1-06
WO 2005/005064 PCT/DK2004/000500
6
In FIG. 3, a micrograph of an aluminium surface is shown without a surface
treatment
with a jet tool. The width of the image is 1 micrometer. Three pieces of
aluminium
have been treated with three different jet tool nozzles in an arrangement
according to
the invention. The results are shown in FIG. 4, 5 and 6 for three different
dies. For
each of FIG. 4, 5, and 6, the right image shows an untreated part of the
surface and the
left image shows a corresponding surface treated with a carbon dioxide jet
according
to the invention. Beware that the width of the right images is 1 micrometer,
whereas
the left images have a width of 0.5 micrometer.
The dies used for FIG. 4 and 5 had slit formed nozzle holes with widths of 0.8
and 1.1
mm, respectively, whereas the die used for FIG. 6 had a circular nozzle exit
hole with
a diameter of 1.2 mm. Useful nozzle exit hole sizes have .been tested
primarily in the
range of 0; 8 to 3 mm. Nozzles with hole diameters of up to 10 mm have been
used,
however, the amount of carbon dioxide for a jet cleaning process increases
largely for
such large nozzles.
The form of the nozzle exit hole or holes depend on the desired use. For
example, a
nozzle has been used with a central hole formed as a slit and two side round
holes. The
distances from the nozzle to the probe were typically 15-25 mm and the gas
pressure
60 bar.
As can be seen from FIG. 4, 5 and 6 in mutual comparison, the result in FIG. 6
is more
pronounced than the other two results. As the crystals on the aluminium
surface were
distinctively smaller, a higher surface tension was achieved resulting in a
more smooth
glue layer on the surface.
In the experiment, where aluminium pieces afterwards were glued together, it
turned
out that the strength of the glue after the jet tool treatment as shown in
FIG. 6 was
comparable to the strength of glue after initial cleaning with isopropanol
(IPA) which
is the normal way used in industry. For steel and aluminium surfaces,
strengths of
more than 19 MPa were achieved. This is a great advantage, because cleaning
with
CA 02531672 2006-O1-06
WO 2005/005064 PCT/DK2004/000500
7
alcohol implies high costs and is environmentally disadvantageous. Thus, by
the in-
vention, a simple way with low costs has been found to substitute the
undesired use of
IPA in cleaning processes of surfaces, for example metal surfaces such as
aluminium
surfaces or steel surfaces.
Cleaning with IPA resulted in surfaces with approximately 2-3% of chemical rem-
nants on the surface. In contrast, the cleaning with the carbon dioxide
particle jet
yielded a much cleaner surface, where the amount of remnants was less than 0.1
making this method highly useful for surfaces where the cleaning is critical.
The jet from the nozzle has been observed to behave differently than normal
snow jets
from prior art nozzles. Also, supply of liquid carbon dioxide to the nozzle
did not lead
to successful results. This indicates that the expansion of the highly
pressurised gas
leads to a special phase of carbon dioxide which has not yet been completely
under-
stood.
A nozzle according to the invention may comprise a central stop in front of
the nozzle
exit hole. This would result in a hollow conical jet which is suited for
cleaning of sur-
faces, where certain areas of the surface should not be hit by the jet. Such
surfaces
may be printed circuit boards with delicate electronic components.
