Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD AND AN APPARATUS FOR MIXING A PROPELLENT GAS AND A
SLURRY
The present invention relates to a method and an apparatus for mixing a
compressed propellent gas and a slurry.
In particular the present of invention relates to a slurry, which contains a
binding agent, such as a cement slurry used for coating walls.
During the manufacture of walls and wall elements for buildings etc., the
conventional method is to apply grout or plaster or alternative cementitious
coating
on the walls or wall elements by spraying coating material on the walls. This
can
be done on both exterior end interior walls. The material is then in the form
of a
slurry, which contains a binding agent, normally cement-based or cementitious
as
mentioned above, and a filler such as sand for example. In order for the
slurry to
adhere to the wall surface, the wall surface is usually provided with some
type of
reinforcement. This increases both the adhesion of the slurry to the surface
and
enhances the mechanical strength of the resulting coating. The reinforcement
may
consist of a wire mesh net, woven glass fibre fabric etc. The reinforcement is
in-
stalled separately, and this is naturally a cost-increasing factor in the
process.
During the spraying of the slurry, special equipment is used. This equip-
2 o ment may consist of a mixer for mixing the slurry, a pipe or flexible hose
for trans-
porting the slurry to a mouthpiece where compressed air is added to the
slurry, a
compressed air source and a pump for the slurry. The compressed air is mixed
with the slurry at the outlet opening of the mouthpiece, where the compressed
air
is added via a separate channel on the outer perimeter of the mouthpiece, in
order
2 5 to achieve the spray effect.
As an alternative the slurry may be applied to the wall by means of a
manually driven apparatus including a container for the slurry and a manually
ope-
rated means for throwing and spreading the slurry onto the wall, mostly
including
some type of the shovel element. Also manual plastering equipment may be used,
3o e.g. trowels etc.
In the case of using the latter type of manual equipment, it is possible to
have a slurry that contains reinforcement elements, such as for example
fibres.
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2
However, the automatic equipment described above does not allow this
possibility,
since a slurry containing fibres will lead to congestion of the mouthpiece,
and the
frequent cleaning operations that are required will result in it not being
economi-
cally motivated to use automatic application equipment for fibre containing
slurry.
The purpose of the present invention is to solve the general problem of
obtaining a good mixture of a slurry and a propellent gas in any context when
such a mixture is used. It is also a purpose of the present invention to solve
the
above described problems in particular in connection with the coating of walls
with
a slurry containing reinforcement elements, such as fibres.
1 o The purpose of the present invention is achieved by the method including
the advantageous features stated in the characterizing portion of claim 1, as
well
as by an apparatus including the advantageous features stated in the
characteriz-
ing portion of claim 5.
According to the inventive method, the slurry is fed into the cavity, the pro-
pellent gas is added to the slurry inside the cavity, the resulting gas-added
slurry
is allowed to undergo a first expansion step while it is still inside said
cavity, before
it is allowed to exit from the cavity, and it undergoes a second expansion
step
while exiting from the cavity into the ambient air, whereby it is sprayed onto
a de-
sired object. By mixing the slurry and the propellent gas inside the cavity,
prior to
2 0 the spraying, a first expansion step can be achieved in the cavity,
offering a vol-
ume which is considerably larger than the relatively narrow passages available
when the expansion takes place in the opening of an ordinary mouthpiece. Con-
sequently, it will become possible to use a slurry mixed with particles or
elements
that are considerably larger than the filler elements, such as reinforcement
ele-
2 5 ments or elements used in view of obtaining a specific surface structure.
The expansion in two steps will occur since the propellent gas cannot ex-
pand directly to the external air pressure. This is due to the fact that the
slurry pre-
sent between the gas outlet and the gas/slurry outlet in the cavity will
function
more or less as a plug, and prevent an immediate complete expansion of the
gas.
30 To continue, due to the expansion of the mixture in two steps, the slur-
ry/gas mixture leaving the mouthpiece will have a conical shape and the slurry
will
be finely "atomized", thus achieving a superior spray effect. The slurry can
thus be
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3
sprayed in thin layers, which improves the drying process and decreases the
risk
for cracking. In addition, this has the advantage that a certain evaporation
takes
place, which also reduces the time required for drying.
The inventive apparatus, according to the present invention, includes a
cavity surrounded by a cavity wall and in which cavity the propellent gas and
the
slurry are mixed, further containing an inlet opening in the cavity wall for
feeding
the slurry into the cavity, means for feeding the propellent gas into the
cavity,
whereby the slurry is brought to a first expansion step inside the cavity by
the add-
ing of the propellent gas to the slurry, and further including means for
spraying the
1 o gas and slurry mixture onto a desired object, during a second expansion
step. The
advantages achieved by this apparatus correspond to the advantages above,
mentioned in connection with the inventive method.
Advantageously, the slurry contains a binding agent, preferably a hydrau-
lic binding agent, for example cement, and also a filler, such as sand,
cinder, fly
ash etc. The slurry may also contain reinforcement elements, which may be or-
ganic or inorganic. Examples of such elements are vegetable fibres in the form
of
soaked cutter shavings, straw, chaff, strips of corrugated cardboard or paper,
etc.
The slurry may also contain particles or elements, which gives the coating
surface a certain structure, such as sand particles or gravel, plastic
granules, etc.
2 o Advantageously, the means for feeding the propellent gas into the cavity
include a tube connected to a gas source, and which is inserted through the
wall
of the cavity and is moveable inside the cavity, and has a gas outlet opening
in-
side the cavity. In a preferred embodiment, the tube is moveable in different
posi-
tions inside the cavity. These positions are chosen depending on the
properties of
the slurry fed into the cavity. Preferably, the apparatus also includes means
for
adjusting the position of the tube inside the cavity.
Further features and advantages will become apparent from the depend-
ent claims.
The present invention will now be described in further detail, with refer-
3 o ence to different embodiments, given by way of example only, illustrated
in the
appended schematic drawings, in which:
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Figure 1 shows a side view, partially in cross section, of a first embodiment
of
an apparatus according to the present invention:
Figure 2 shows a side view, partially in cross section, of a second embodi-
ment of the apparatus, according to the present invention,
Figure 3 shows a side view, partially in cross section, of the second embodi-
ment;
Figure 4 shows a side view, partially in cross section, of the second embodi-
ment;
Figure 5 shows a side view, partially in cross section, of a third embodiment
of
1 o the apparatus, according to the present invention; and
Figure 6 shows a side view, partially in cross section, of a fifth embodiment
of
the apparatus, according to the present invention.
In the first embodiment of the apparatus illustrated in figure 1, the appara-
tus comprises a cavity 1 into which a slurry is fed through a inlet opening 3
and
propellent gas is fed into the cavity via a gas feeding means 5. The gas
feeding
means comprises a tube 6 inserted through the wall 8 of the cavity and having
an
outlet opening inside the cavity. The tube is connected to a compressed
propellent
gas source, not illustrated. The slurry inlet opening 3 is located at the
bottom of a
funnel shaped container 10, into which the slurry is fed. The slurry itself
has al-
e o ready been previously mixed in a separate mixer. The cavity 1 has an
outlet open-
ing 4 for the gas and slurry mixture. In the illustrated first embodiment the
gas/slur-
ry outlet opening is designed as a mouthpiece with an essentially cone-shaped
design. This outlet for the gas/slurry mixture, or spray outlet, has an
opening with
an area (SOA) in relation to the area of the gas outlet opening (GOA) which
pref-
2 5 erably is in the interval of 10 to 30 times the latter.
The tube 6 is moveable in such a way that it can adopt different positions
within the cavity. This is more clearly illustrated in figures 2-4. The
opening of the
tube is directed towards the gas/slurry outlet 4. The tube can in fact also be
re-
movable, in order to facilitate cleaning of the tube and the outlet opening of
the
3 o tube.
A second embodiment of the apparatus according to the present invention
is illustrated in figures 2-4. This embodiment mainly differs from the first
embodi-
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ment in that the slurry is not fed into the cavity via a funnel-shaped
container. In-
stead, the slurry is fed by means of a tube or pipe 20 directly connected to
the
cavity 1 by means of an inlet opening 13. The tube 20 preferably has the same
di-
ameter as the diameter of the cavity 11. The means for feeding the propellent
gas
5 15 into the cavity 20 comprise a tube 16 inserted through an opening in the
cavity
wall 18. The tube is moveable and can adopt different positions inside the
cavity,
as illustrated in figure 3 and figure 4. In the position adopted by the gas
inlet tube
illustrated in figure 3, the apparatus is particularly suitable for a slurry
containing
fibres or other reinforcement elements. As can be seen, this position is a
position
1 o where the tube 16 is in a rearward position, i.e. with its outlet
relatively close to the
cavity wall. The gas fed into the cavity 11 mixes with the slurry fed into the
cavity
via the inlet 13 and the gas/slurry mixture undergoes an essentially cone-
shaped,
first, partial expansion step, illustrated by the cone 22. The mixture is then
pro-
pelled towards the outlet of the cavity 14, where it undergoes a second
expansion
step, illustrated by the cone 23 in figure 3.
Figure 4 illustrates the apparatus according to the second embodiment
when it is adapted to a slurry, which contains little or no fibre. For this
purpose the
gas inlet tube 16 is inserted further inside the cavity 11, i.e. with its
outlet further
forward, in the direction towards the outlet for the gas/slurry mixture, then
the po-
t o sition illustrated in figure 3. Also in this case, the slurry and the gas
are mixed in
an essentially cone-shaped expansion, illustrated by the cone 32. This is also
a
partial expansion, in a first expansion step. The mixture is then directed
towards
the outlet of the cavity, where it undergoes a second expansion illustrated by
the
cone with the reference number 33. It is during the second expansion that the
2 5 slurry is sprayed onto the surface, which is to be coated by the slurry
material.
A third embodiment is illustrated in figure 5. This only differs from the em-
bodiment in figure 4, in that the outlet opening 34 for the gas and slurry
mixture
has a much less accentuated conical form. This allows for the spraying of a
slurry
containing much larger reinforcement particles or other particles or fibres.
This
30 slurry is fed into the cavity 31 via a tube 40 with the same diameter as
the cavity,
and the gas is fed into the cavity 31 by means of a feeding device 35,
designed as
a tube 36. In this figure is also illustrated means for controlling the feed
of the pro-
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pellent gas into the cavity. Said control means may comprise a valve, not
illus-
trated, and a pressure gauge 39. By controlling the gas flow and the gas
pressure
it is possible to control the flow of slurry through the cavity, as well as
the charac-
teristics of the spray jet. For example, if the pressure is too high, the
impact veloc-
ity of the spray against the surface will be too high, which will result in
that larger
particles in the slurry will bounce off the surface. The pressure must also be
adapted to the friction of the slurry within the cavity. The gas pressure
inside the
tube may be in the interval 150 kPa - 700 kPa, preferably approximately 200
kPa.
In the fourth embodiment illustrated in figure 6, the outlet opening of the
l0 cavity 51 is not cone-shaped. Instead it has essentially the same diameter
as the
cavity itself and it also has essentially the same area as the slurry inlet
opening 40
of the cavity. The gas feeding means 45 are arranged in an opening in the
cavity
wall, in a way similar to what has been described above.
The present invention shall not be considered as limited to the embodi-
ments above, given by the way of example only, but may be varied and modified
in numerous ways by the persons skilled in the art, within the scope of the ap-
pended patent claims.
