Note: Descriptions are shown in the official language in which they were submitted.
~17725Q
SURFACE TREATMENT NOZZLE AND METHOD AND DEVICE FOR
SURFACE TREATMENT USING SUCH A NOZZLE.
The present invention concerns a surface
treatment nozzle, as well as a method and a device
for surface treatment utilizing such a nozzle, for
example for stripping one or more layers of paint or
another coating provided on a surface, such as the
outside surface of a plane.
In particular, the present invention relates
to a surface treatment nozzle intended for projecting
solid particles carried in a gas stream under
pressure, this nozzle being provided with a single
inlet for receiving the solid particles mixed to the
gas stream under pressure and a single outlet to
project the solid particles, the outlet having the
shape of an elongated slot which has a longitudinal
axis and extend along this longitudinal axis between
two ends, the nozzle including a channel having, in
the direction of flow of the solid particles, first a
converging section which communicates with the inlet
of the nozzle, then a divergent section which opens
outside the nozzle through the outlet slot and which
has along its entire length a section of a shape which
is flattened parallel to said outlet slot, the
diverging section additionally having two lateral
edges which extend along said diverging section each
up to an end of the outlet slot.
A nozzle of this type is disclosed in the
document GB-A-2 191 127.
This known nozzle however has the
disadvantage that the efficiency of the surface
treatment is not equally distributed along the entire
width of the nozzle, this efficiency being high at the
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center of the nozzle and low along the sides of the
nozzle jet.
Thus, during stripping operations for
example, when such a surface treatment nozzle is moved
above a surface which is covered with paint while
projecting solid particles, it leaves behind it a
stripped mark in the form of a band whose median line
has undergone a high stripping, due to the fact that
it has been exposed for a long time to the stripping
operation and that it has received the solid particles
with higher energy, and whose sides are little or
badly stripped, due to the fact that they have been
exposed for a short time to the projected solid
particles and that they have received solid particles
projected with lower energy.
This disadvantage requires:
- either to move the surface treatment
nozzle at a speed which is sufficiently low for the
sides of the stripped mark to be suitably stripped,
which slows down the stripping process and may
additionally damage the surface which carries paint at
the center of the stripped mark, if this surface is
sensitive to attacks, for example if this surface is
made of a composite material or an undercoat which is
deposited on a solid material,
- either to redo the edges of the marks
already stripped, to suitably strip these edges, which
also slows down the stripping process.
Moreover, the nozzle disclosed in the
document mentioned above presents a section
discontinuity which may result in a rapid wear of the
nozzle and which produces turbulences which also
disturb the efficiency of the stripping operation,
such as when the nozzle is used at important gas
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speeds, and in particular supersonic speeds in the
diverging section.
The present invention aims for example to
overcome these disadvantages.
For this purpose, according to the
invention, a surface treatment nozzle of the type
mentioned above is essentially characterized in that
the channel has progressing variations of
cross-section along its entire length, in that the
converging section has a downstream end which has a
cross-section which is flattened parallel to the
outlet slot, and in that the diverging section has, at
least towards the outlet slot, two lateral parts of
widened cross-section respectively in the vicinity of
the two lateral edges, these two lateral parts of
widened cross-section being separated by at least one
part of narrower cross-section.
Thus, when the surface treatment nozzle
according to the invention is moved above a surface,
for example perpendicularly to its outlet slot, by
projecting solid particles on this surface, this
nozzle leaves behind it a treated mark in which all
the points have received particles which have
substantially the same kinetic energy and have been
exposed to said particles during a substantially
identical period. Consequently, the surface treatment
is of the same quality along the entire width of the
treated mark.
With the surface treatment nozzle according
to the invention, it is for example possible to strip
a layer of paint which covers an underlying surface
made of an undercoating, a composite material or
another material without in no way deteriorating said
underlying surface.
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According to advantageous embodiments,
either or all the following provisions may be
additionally used:
- the converging section has an upstream end
which has a circular cross-section;
- the diverging section includes,
substantially along its entire length, said two
lateral parts of widened cross-section;
- the diverging section has, at least in the
vicinity of its outlet slot, a central part of widened
cross-section which is separated from each lateral
part of widened cross-section by a part of narrower
cross-section, so as to further optimize the
equalization of the kinetic energy of the particles
which are projected by the nozzle along the entire
width of the outlet slot,
It is also an object of the present
invention to provide a device for a surface treatment
including a nozzle as defined above and feeding means
to send at the inlet of the nozzle the solid particles
mixed with the gas stream under pressure, with a
sufficient flow rate to enable the gas stream to be
supersonic in the diverging section.
It is also an object of the present
25 invention to provide a surface treatment device
including a nozzle such as defined above and
positioning means for moving the nozzle essentially in
translation along a treatment surface,
It is also an object of the present
invention to provide a process of surface treatment by
projection of solid particles carried in a gas stream
under pressure, in which:
. the particles are projected by means of a
nozzle such as defined above,
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. the nozzle is supplied with the mixture of
solid particles in the gas stream under pressure at a
flow rate which is sufficient to enable the gas stream
to be supersonic in the diverging section,
. the longitudinal axis of the outlet slot
is disposed substantially parallel to the treatment
surface,
. and the nozzle is moved essentially by
translation along a direction which is parallel to the
treatment surface, and which may possibly be
substantially perpendicular to the longitudinal axis
of the outlet slot of the nozzle.
This process may be used for example for
stripping surfaces.
For example, the projected particles may be
particles based on starch or plastic material
products.
The process of surface treatment according
to the invention is particularly adapted for stripping
a surface with a very precise outline or which is
sensitive to attacks, for example the outside surface
of a plane.
Other characteristics and advantages of the
invention will appear during the following description
of some embodiments, given by way of non-limiting
examples, with reference to the annexed drawings.
In the drawings:
- Figure 1 is a cross-section view of a
nozzle for surface treatment according to an
embodiment of the invention, the cross-section being
taken along line I-I of Figures 2 and 3,
- Figure 2 is a view in elevation from the
rear of the nozzle of Figure 1,
- Figure 3 is a view in elevation taken from
the front part of the nozzle of Figure 1,
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- Figure 3A is a view similar to Figure 3,
of a variant of the nozzle of Figures 1 to 3,
- Figure 4 is a partial perspective view of
the nozzle of Figures 1 to 3, in operation,
- and Figure 5 is a schematic view of a
device for a surface treatment including a nozzle such
as the one of Figures 1 to 3.
The surface treatment nozzle of Figures 1 to
3 includes a central channel which extends
longitudinally between an inlet opening 3 and an
outlet opening 4.
The inlet opening 3 of the channel includes
a housing 31 which is adapted to receive an end of a
feeding duct which feeds up to the channel of the
nozzle a gas stream under pressure carrying solid
particles with possibly liquid droplets. This
housing 31~ strictly speaking, does not constitute a
part of the central channel of the nozzle, since it is
not in contact with the gas stream under pressure nor
with the solid particles which are carried by this gas
stream.
From housing 31~ the central channel of the
nozzle includes, in the direction of flow of the solid
particles, first a converging section 6, then a
diverging section 7.
The inlet opening 3 of the nozzle has a
circular cross-section, and the converging section 6
has a cross-section which varies continuously between
a circular cross-section at its upstream end, and a
flattened cross-section, for example elliptical, at
its downstream end, i.e. at the level of neck 5 which
separates converging section 6 from diverging section
7. Thus, converging section 6 is progressively
flattened between its upstream end and its downstream
end.
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On the other hand, the opening of outlet 4
of the nozzle is an elongated slot, and the diverging
section 7 has on the other hand a cross-section which
is flattened parallel to the outlet slot 4.
More specifically, in the specific example
which is illustrated in the drawings, the diverging
section 7 has, in the vicinity of neck 5, an
elliptical cross-section which corresponds exactly to
the cross-section of the upstream end of converging
section 6.
This elliptical cross-section is
progressively modified towards outlet slot 4 by
slightly widening in the direction of the longitudinal
axis 12 of the outlet slot, up to a given width 1 at
the level of the outlet slot, and by increasing the
thickness in the vicinity of the lateral edges 71 of
the diverging section 7, until forming widened lateral
parts 41 f thickness e at the level of the ends of
outlet slot 4.
The ratio l/e may for example be higher than
2.
Possibly, as illustrated in Figure 4,
diverging section 7 could eventually also include a
progressive widening at its center, until also forming
a widened part 42 at the center of outlet slot 4, this
central widened part being separated from the lateral
widened parts 41 by means of parts of narrower
cross-section.
Neck 5 between converging section 6 and
diverging section 7 consists of the line of
intersection between the inner surfaces of said
converging and diverging sections, so that the central
channel of the nozzle contains no discontinuity in
cross-section, i.e. no surface forming a sharp
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obstacle to the flow of compressed gas or a sharp
widening.
Moreover, the channel of the nozzle
preferably includes a non-angular cross-section, even
at the level of the lateral edges 71 f converging
section 7, where the cross-section of the channel has
a small radius of curvature.
The surface treatment nozzle of the
invention may be manufactured in different manners. In
the particular example illustrated in the drawings,
this nozzle is made by molding two pieces 11 et 12, of
a metallic material of high hardness, these two pieces
being assembled according to a joint plane 13 which is
parallel to longitudinal axis 12 of outlet slot 4, by
means of screws 2.
When the surface treatment nozzle of the
invention is in operation, solid particles are brought
in a stream of compressed gas, for example compressed
air under 2 to 3 bars, at the inlet of converging
section 6.
This gas flow loaded with solid particles is
accelerated in converging section 6, and in general
becomes sonic at the level of neck 5, then is
supersonic immediately downstream, so that it
continues to be accelerated in diverging section 7.
For treating a surface 8, for example for
stripping an outside surface of a plane, nozzle 1 is
placed above surface 8, so that the longitudinal axis
12 of outlet slot 4 of the nozzle be disposed parallel
to said surface 8. While solid particles are projected
on surface 8 to strip the latter, i.e. for example to
remove paint which covers said surface 8, nozzle 1 is
moved essentially in translation according to
direction 9, (in one way or thè other) parallel to
surface 8 and in general, but not exclusively,
f ~1772~0
perpendicularly to longitudinal axis 12 of outlet slot
4.
The movement of nozzle 1 may possibly
include oscillations which are parallel to surface 8
and perpendicular to direction 9, however nozzle 1 is
then always moved in translation, i.e. with its axis
12 always in the same direction.
In addition to its translation movement, it
goes without saying that the nozzle may sometimes
undergo movements causing a rotation of its axis 12,
for example during repositioning operations.
Thus, the movement of surface treatment
nozzle 1 produces a stripped mark 10 which is suitably
treated along its entire width, without any attack of
the underlying material of surface 8 at the center of
mark 10.
Preferably, and for example when the
treatment surface 8 should preserve a shape which is
extremely precise or is formed of a delicate material
(composite material or undercoating for example~, the
projected particles may for example be particles based
on plastic material products or starch products, for
example particles of wheat starch.
The surface treatment nozzle 1 according to
the invention may for example be used in surface
treatment device 20 illustrated in Figure 5.
This device includes a working head 21
constituting an enclosure which is open towards the
treatment surface 8, and the outlet of nozzle 1 opens
inside this enclosure.
The working head 21 is kept applied against
surface 8, or in the vicinity of surface 8, and it is
also moved along surface 8 by means of a positioning
system 22 which may be of any known type.
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In the illustrated example, positioning
system 22 includes a guiding beam 23 which may be kept
fixed during the operation of nozzle 1, a carriage 24
moveable along guiding beam 23, a robotized
articulated arm 25 which is fixed to carriage 24, and
compressed air hydraulic cylinders 26 which maintain
working head 21 against surface 8.
Possibly, guiding beam 23 may be mounted at
the end of an articulated arrow carried by a vehicle
(not illustrated).
Inlet 3 of nozzle 1 is supplied with
compressed gas, for example compressed air, loaded
with solid particles, by means of a feeding duct 30
which is connected on the one hand to a compressor 31,
and on the other hand to a feeding hopper 32
containing a supply of solid particles.
Preferably, working head 21 is also
connected to a section duct 33 to collect solid
particles after their projection, this section duct 33
being connected to a suction turbine 34 by means of a
collecting hopper 35 which receives the sucked solid
particles.
The solid particles which have been
collected in hopper 35 may be recycled towards feeding
hopper 32, in which case they preferably pass through
a system of separation 36 which may for example
separate by sieving the particles which are too large
or too small, by centrifugation for the particles
which are too heavy, and possibly by magnetizing for
the metallic particles, to send these separated
particles to reject 37. Separation system 36 may
additionally receive new solid particles from a supply
38.
Preferably, compressor 31 supplies nozzle 1
with a gas flow rate which is sufficient to ensure
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that the flow of gas in nozzle 1 is sonic at the level
of neck 5 and supersonic in the diverging section 7.
