Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ATOMISATION NOZZLE WITH ROTATING ANNULAR GAP
The invention relates to an atomizing nozzle, with a first f low
channel of annular cross section for the guidance of a medium
to be atomized, which flow channel is circumscribed by two
walls spaced radially apart from one another and opens into an
annular nozzle orifice, and with a second flow channel for
guiding a gaseous spray medium, which f low channel encircles
the first f low channel and likewise opens into an annular noz-
zle orifice.
An atomizing nozzle of this type is known, for example, from
DE 197 49 071 A1. Atomizing nozzles of this type serve for
spraying a medium to be atomized, usually a liquid, sometimes
also a powder, with the aid of a gaseous spray medium.
In this context, the medium to be atomized is transported under
pressure through the annular or gap-like flow channel to a
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This first annular flow channel is encircled by a second like-
wise annular flow channel, and the likewise opens into, adja-
cent to the first flow channel, in an annular or gap-Like noz-
zle orifice.
Depending on how the mouth head of the nozzle is designed, such
nozzles spray axially or laterally to a greater or lesser ex-
tent away from the axial axis, with an increasingly larger
spray angle, in this case with spray angles of up to 180° and
with a looping angle of 360° around the mouth head.
Such nozzles are in widespread use in devices for the treatment
of particulate material, for example for the granulation or
coating of these particles. In granulation, a tacky liquid is
sprayed, which serves for sticking together the particles into
larger agglomerates, that is to say the desired granulates.
In coating, a covering layer is sprayed onto the surface.
Such devices are used, above all, in the pharmaceutical indus-
try, where tablet ingredients which are produced as fine-dust
powders are granulated into handable powders capable of being
pressed, for example, into a tablet.
In coating, pellets or finished granulates or even whole tab-
lets are provided with an outer covering layer.
Depending on the configuration of the device, the nozzles spray
vertically upwards, that is to say are designed as upright
nozzles, spray at an inclination or are directed horizontally
or even, in many instances, vertically from the top downwards.
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By means of atomizing nozzles of this type, suspensions, dis-
persions or solutions can be sprayed, and these can also be
employed in what are known as hot-melt methods in which wax
melts or hard grease are processed under thermal influence.
In order to achieve as fine a spraying as possible, the annular
flow channels operate with liquid cross sections which are in
the region < 0.25 mm.
In the practical use of such spray nozzles, then, it was found
that, with some kind of suspensions or dispersions, partial
blockages of the small liquid cross section occur due to undis-
solved solid fractions.
This can also be observed especially when these solid fractions
are of a fibrous or crystalline nature.
Taking the example of the abovementioned nozzle with a spray
angle of 180° or a looping angle of 360°, the nozzle head
sprays a spray cone in the form of a plane spray pat. If block-
ages occur then, no medium to be atomized emerges in certain
circumferential regions of the annular gap. This has extremely
adverse effects on the treatment result which is to be achieved
by means of an apparatus in which such an atomizing nozzle is
arranged.
In a fluidized-bed coater, for example, the material to be
treated is swirled or moved around the nozzle, so that, in a
nozzle spraying unequally along the circumference because of
blockages, an irregular treatment result is obtained.
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However, it is precisely the aim, in this technology, to achie-
ve as uniform a treatment result as possible, for example to
obtain granulates within a very narrow grain-size range or
covering layers with as equal a covering thickness as possible.
The object of the present invention is, therefore, to develop
further an atomizing nozzle of the type mentioned in the intro-
channelion, to the effect that even medium to be sprayed which
tend to cause blockages can be atomized uniformly.
The object is achieved, according to the invention, in that the
walls circumscribing the first flow channel are rotatable rela-
tive to one another about a nozzle longitudinal axis.
It was found that, in such a configuration of the gap-forming
walls, a centrifugal and radial, that is to say toroidal move-
ment is established in the annular gap. The medium to be atom-
ized, conveyed through the annular gap in the axial direction,
is moreover also set, by the walls rotating relative to one
another, in a rotating movement which results in the abovemen-
tioned toroidal movement. If, then, media tending to cause
blockages or also entraining even smaller solid lumps are gui-
ded through such a flow channel, the rotary configuration of
the liquid gap results in some comminution of such solid lumps
which would otherwise lead to a blockage of the liquid gap in
the case of stationary walls. Virtually a kind of self-cleaning
effect is achieved by means of the rotary configuration, so
that the medium to be atomized ultimately leaves the annular
nozzle orifice, uniformly distributed circumferentially.
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In a further embodiment of the invention, moreover, the two
walls are axially displaceable relative to one another, with
the result that the gap width of the nozzle orifice of the
first annular flow channel can be varied.
This measure, then, has the considerable advantage that it is
possible, by virtue of the axial moveability, to vary the gap
width of the nozzle orifice of the first flow channel and, in
particular, even to close this nozzle orifice. If the nozzle is
not in use or is temporarily not in use, the nozzle orifice is
closed, so that no dirt enters or no blockages occur due to
drying-out or the like in the region of the nozzle orifice.
An essential and considerable advantage of this axial displace-
ability is also that a self-regulation of the width of the
annular gap takes place over a certain bandwidth.
Conventional annular gaps in such atomizing nozzles have a
width of 0.1 to about 0.25 mm, and it is desirable to have the
capability of expelling 1 to 5 grams of medium to be sprayed
per millimetre of length of the gap.
Depending on the nature of the medium to be sprayed, then, the
axial moveability makes it possible for the gap height to be
set automatically. When a specific medium with a specific pres-
sure is led through the first flow channel, intrinsic proper-
ties, for example, in the case of a liquid, its viscosity and,
in the case of emulsions, their flowability and stickiness,
exert a considerable influence on what quantity per millimetre
of length of the gap can pass through. In other words, there
are liquids which can be expelled relatively simply through
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such a gap, whereas others require a somewhat wider gap for the
same outflow quantity.
It was found, in practical use, that, of course within a cer-
tain determined range, the gap width is set automatically to an
optimum value in the case of given boundary conditions, that is
to say the nozzle virtually regulates itself.
The initially mentioned possibility of closing the nozzle mouth
of the first flow channel in the state of rest can be achieved
in a simple way, for example in the case of an upright nozzle,
in that the at least one moveable wall sinks due to gravity and
the closing movement thereby takes place.
In the case of angled, horizontal or even suspended nozzles,
this movement may take place by means of a spring force or
other mechanisms.
In a further embodiment of the invention, conveying elements,
which control a movement of the medium to be atomized which is
transported to the nozzle orifice, are arranged at least on one
of the walls rotatable relative to one another.
The provision of these conveying elements has the considerable
advantage that, by virtue of the conveying elements, the tor-
oidal movement formed by the axial transport direction and by
the rotating walls is, on the one hand, guided in a focussed
manner arid also additionally promoted.
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In addition, these conveying elements may also serve as me-
chanical means for transporting in a focussed manner and, if
necessary, comminuting any entrained solid lumps.
In a embodiment of the invention, one wall is designed to be
stationary and the other wall to be rotatable.
This measure has the advantage in structural terms that only
one of the two walls has to be moved, and, accordingly, corre-
sponding drive members have to be present for only one of these
walls.
In a further embodiment of the invention, one wall is station-
ary and the other wall is axially displaceable.
This, too, results again in the advantage of the simple struc-
tural configuration of the additional axial displaceability of
the walls relative to one another.
In a further embodiment, that wall which is rotatable is also
at the same time axially displaceable.
This measure has the advantage in structural terms that the
measures both of rotatability and of axial displaceability can
be implemented in connection with a single wall.
In a further embodiment of the invention, the control of the
axial displaceability is carried out by means of the conveyed
medium to be atomized itself.
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This measure makes it possible to have the already abovemen-
tioned self-regulating effect of the gap width of the nozzle
orifice of the first flow channel.
In a further embodiment of the invention, the axial displace-
ability is designed in such a way that, in the state of rest,
the nozzle orifice of the first flow channel is closed.
This measure makes it possible, in an extremely simple way in
structural terms, to have the initially mentioned closing of
the nozzle orifice of the first flow channel, this taking place
exactly when no medium to be atomized is led through the first
f low channel.
In a further embodiment of the invention, the axial displace-
ability takes place counter to a return force which moves the
displaceable wall or displaceable walls into the closing posi-
tion of the nozzle orifice.
As already mentioned, gravity may be utilized as the return
force, so that, in the case of upright nozzles, the one move-
able wall is moved into the closing position due to gravity as
a result of displacement relative to the other.
If gravity is not sufficient or not capable of executing this
movement, this may take place by means of other control ele-
ments, for example by means of springs or other elements.
In a further embodiment of the invention, the axial displace-
ability of the walls is designed in such a way that, in the
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state of rest, the nozzle orifice of the second flow channel is
also closed.
This measure has the advantage that both nozzle orifices are
closed in the state of rest.
This not only has the already mentioned advantage that no dirt
can enter the nozzle, but also has the advantage that residual
medium quantities possibly still present in the flow channels
do not emerge, so that, for example during transport or de-
mounting, such residual quantities then do not emerge and cause
soiling.
In a further embodiment of the invention, the rotatable wall
carries, on the outside of a head of an atomizing nozzle, a
fan, by means of which the head can be freed of any adherent
substances in the region of the nozzle orifice.
A problem which repeatedly arises is the soiling of the mouth
head due to an usually uncontrolled secondary air movement
which occurs in the region surrounding the liquid gap or spray
gap. Owing to the high blow-out velocity, vacuum regions are
formed which re-attract stray liquid droplets just sprayed and
deposit them on the mouth head. This consequently then results
there in an agglomeration or a gradual build-up of dried-on
solids from the sprayed liquid.
The provision of the fan in this case makes it possible to keep
these critical regions free of such adherent substances. The
rotatability according to the invention of the wall therefore
can not only be utilized to provide optimum conditions inside
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the nozzle, but this rotating movement can at the same time be
utilized to prevent substances from adhering to the outside of
the head.
In a preferred embodiment of the invention, one wall is de-
signed as the outside of a central spindle which is rotatable.
This measure has the structural advantage that the rotating
wall is produced by a structurally simple means, to be precise
the central spindle.
In a further embodiment of the invention, the conveying ele-
ments are designed as rotor portions.
This measure has the advantage that an especially uniform pro-
motion of the movement of the medium to be sprayed is thereby
possible.
If the rotor portions are formed on the outside of the above-
mentioned central spindle, this is extremely simple to imple-
ment in structural terms and especially favourable and focussed
conveyance can be achieved. The length and number of the rotor
portions, that is to say the number of conveying wheels and
their cross-sectional shape, may additionally be varied, so
that particularly difficult media to be sprayed can addition-
ally be dealt with.
In a further embodiment of the invention, the spindle is driven
via a pneumatically operable motor.
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This measure has the advantage in structural terms that a gase-
ous medium for spraying the medium to be sprayed is led through
such a spraying nozzle in any case, that is to say the latter
is connected to a source of spray air, usually compressed air.
Parts of this air may therefore also be utilized at the same
time for operating the motor which ensures the rotary movement
between the walls.
In a further preferred embodiment, the spindle is plugged onto
a drive journal which allows some axial moveability of the
spindle.
This measure has the particular advantage in structural terms
that, as a result of these dimensions, the spindle is both
rotatable and to some extent axially moveable.
The degree of moveability may be limited, for example, by means
of a connecting crosspin which runs in a long hole in the drive
journal.
In a further preferred embodiment of the invention, the fan is
seated on the head of the spindle.
The advantage of this measure is that this advantageous design
is at the same time also implemented on the central spindle.
It goes without saying that the features mentioned above and
those yet to be explained below can be used not only in the
combinations specified, but also in other combinations or alo-
ne, without departing from the scope of the invention.
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The invention is described and explained in more detail below
with reference to some selected exemplary embodiments, in con-
junction with the accompanying drawings in which:
Fig. 1 shows, partially in longitudinal section, a side view
of a first embodiment of an atomizing nozzle accord-
ing to the invention,
Fig. la shows an enlarged view of the region circumscribed by
a circle at top right in Fig. 1,
Fig. 2 shows a side view, rotated through 90°, of the atom-
izing nozzle of Fig. 1,
Fig. 3 shows an illustration corresponding to the sectional
illustration of Fig. 1, of a further embodiment of an
atomizing nozzle with a fan attached to the head, and
Fig. 4 shows a top view of the end face of the head of the
atomizing nozzle of Fig. 3.
An atomizing nozzle illustrated in Fig. 1 and 2 is designated
as a whole by the reference numeral 10.
The atomizing nozzle 10 has an approximately bar-shaped nozzle
body 12, to one end of which, the lower end in the illustration
of Fig. 1 and 2, a motor 14 is flanged.
A first flow channel 16 which is annular or takes the form of
an annular gap is formed in the nozzle body 12.
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This first flow channel 16 is delimited on the inside by an
inner wall 18 which is the outside 20 of a central spindle 22.
The spindle 22 is plugged onto an upright angular drive journal
24 of the motor 14 and, for this purpose, has at its lower end
a corresponding slot 26.
As a result, on the one hand, a rotationally fixed connection
between the motor 14 and the spindle 22 is afforded, that is to
say, when the motor 14 is in operation, the spindle 22 rotates
about its longitudinal mid-axis 70 which is also at the same
time the longitudinal mid-axis of the atomizing nozzle 10.
The plug connection is, moreover, such that some axial move-
ability of the spindle 22 is afforded, the meaning and purpose
of this being described later in connection with the type of
operation.
The axial displaceability or the limitation of the amount of
axial movement can be provided in that the drive journal has
cut out in it a vertical long hole which receives a crosspin
which is inserted in the radial bore of the spindle 22 in the
region of the slot 26.
The first flow channel 16 is delimited on the outside by an
outer wall 30 which is formed by an inside of a continuous
central bore or orifice 34 in the nozzle body 12. Both the
spindle 22 and the nozzle body 12 widen, opposite the motor 14,
in a trumpet-like manner in a widening 36 and a widening 38
respectively, as is evident especially also from Fig. la.
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An approximately horizontally oriented nozzle orifice 40 in the
form of an annular gap 42 running around through 360° is there-
fore formed.
The width of the annular gap 42 can be varied on account of the
axial displaceability of the spindle 22, the variation being in
the range of between 0.1 mm and 0.25 mm.
As is evident especially from Fig. 2, the ffirst f low channel 16
is connected to a lateral connection piece 44, so that, via
this connection piece 44, a medium to be atomized, for example
a liquid 45, can be fed into the first flow channel 16, can be
transported through the first flow channel 16 and can emerge
via the annular gap 42. The transport and conveyance of this
liquid 45 is also additionally promoted by conveying elements
48 in the form of two rotor portions 46 and 46' on the outside
22 of the spindle 22, the height of a rotor being such that the
latter corresponds approximately to the gap width of the ffirst
flow channel 16 inside the atomizing nozzle 10.
In the shown embodiment, the profile of the rotor 46 is such
the latter bears approximately over its area against the inside
32 of the central orifice 34, other profiles, for example
rounded or pointed rotor profiles, of course, also being possi-
ble.
In order to atomize finely the liquid or the medium to be atom-
ized, which may also be a powder, which emerges through the
annular gap 42, a second flow channel 50 is provided.
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This second flow channel 50 encircles the first inner flow
channel 16 and opens into a codirectional widening 52 in a
nozzle orifice 54 which is likewise in the form of an annular
gap 56. The annular gap 56 is arranged in such a way that it is
directly adjacent to the annular gap 42, directly below the
first annular gap 42 in the shown embodiment of the upright
atomizing nozzle 10. The second flow channel 50 is delimited on
the inside by the nozzle body 12 and on its outside by a ro-
tatable sleeve 58. The sleeve 58 is screwed into the nozzle
body 12 via a thread 60.
As is evident especially from Fig. 2, the sleeve 58 is provided
on its outside with a scaling 62.
Consequently, by the sleeve 58 being rotated, the gap width of
the annular gap 54 can be varied.
The second flow channel 52 is connected to the exterior via a
radially projecting connection piece 64, via which a gaseous
medium in the form of spray air 65 is introduced into the noz-
zle body 12.
The motor 14 is designed as a pneumatically operated motor,
that is to say compressed air 67 is introduced through an inlet
66 and this compressed air 67 is discharged again through an
outlet 68.
During operation, the motor 14 is controlled and driven by the
abovementioned compressed air, so that the spindle 22 rotates.
The rotational speed is governed by the respective application
of the medium to be sprayed and may be in the range of 1 to
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1 000 revolutions per minute. A medium to be sprayed, for exam-
ple a tacky liquid to be sprayed for granulation, is conveyed
by the connection piece 44 and is expressed via the annular gap
42. The liquid may also consist of an externally melted sub-
stance.
This expressed liquid is sprayed in a fine mist by means of the
spray air 65 emerging from the second flow channel 50 or from
the nozzle orifice 54 of the latter, the spray air usually
being under a pressure of 0.5 to 5.0 bar.
This gives rise to a correspondingly horizontally oriented
spray pat or corresponding spray cone, as indicated by the
reference numeral 75 in Fig. 2.
As mentioned, the gap width of the annular gap 56 from which
the spray air emerges can be varied by means of the rotatable
sleeve 58.
The gap width of the annular gap 42 from which the liquid 45 to
be sprayed emerges is regulated automatically owing to the
axial moveability of the spindle 22 , on the one hand by means
of the predetermined liquid pressure of the liquid to be spray-
ed and additionally, to some extent, by virtue of the intrinsic
properties of the liquid, that is to say its viscosity or its
nature as an emulsion, slurry or powder mixture.
If, as shown in Fig. 1, the atomizing nozzle 10 is designed as
an upright nozzle and medium to be sprayed is no longer sup-
plied, the spindle 22 sinks down due to gravity and at the same
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time automatically closes the annular gap 42 or the first f low
channel 46, as indicated in Fig. la by the double arrow.
It may be gathered from Fig. 1 that the spindle 22 is closed
off on its outside via an approximately mushroom-shaped head
80.
In practical use, it was found, as indicated in Fig. 2, that,
in a region 88 of the outer edge of the head 80, certain prob-
lem zones exist, in which sprayed particles or even solid par-
ticles whirling around in a fluidized-bed device gradually
settle. This region is indicated in Fig. 2 by the reference
numeral 88.
Figs. 3 and 4 illustrate a design variant which, as regards the
configuration of the atomizing nozzle as such, is identical to
the embodiment described in connection with Fig. 1 and 2.
A fan 82 is additionally mounted on the outside of the head 80.
This fan 82 has a plurality of rearwardly curved centrifugal
fan blades 84 which suck in air out of an axial tube 86 and, as
is evident especially in the top view of Fig. 4 from the arrow
89, blow out this air radially. As a result, the critical re-
gion designated by the reference numeral 88 in Fig. 2 is
continuously blown free, so that no undesirable adherences or
accumulations of solid or liquid particles occur.
This air additionally blown out by the fan 82 may additionally
be utilized to accompany the spray cone 75, illustrated in
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Fig. 2, on its top side, that is to say either to control this,
additionally swirl it or utilize it for other purposes.
Depending on where the air sucked in by the axial tube 86
originates, this air may also be utilized as a "microclimate",
for example in the form of hot air, in order to keep the liquid
droplets supplied as a melt as long as possible in the melted
state, so that those particles which are to be sprayed by the
spray nozzle are coated with still liquid particles even at
some distance from the nuzzle.
In the embodiment described above, one wall, to be precise the
outer wall 30, of the first flow channel 16 was stationary, and
the inner wall 18, to be precise the outside 20 of the spindle
22, was rotatable.
It is also conceivable for this to be carried out kinematically
in reverse or else, if appropriate, for both walls to be set in
rotational movement.
