Note: Descriptions are shown in the official language in which they were submitted.
1 2193590
The present application relates to high build
coatings, such as plaster and stucco, and more particu-
larly to an apparatus for application of high build
coatings.
Many industries, such as the construction and
aerospace industries, have a need to apply high build
coatings. High build coatings are coatings with a fin-
ished thickness from about 0.060" to 2.000" and weights
ranging from approximately 2 lbs/cubic foot to 100
lbs/cubic foot. Plaster and stucco are examples of two
high build coatings which are frequently used in the
construction industry for aesthetic and structural pur-
poses, as well as for fireproofing. Plaster and stucco
coatings are mixtures of hydroscopic binders, fillers
and water. Plaster is typically an interior coating
based on gypsum, while stucco is traditionally an exte-
rior coating which is usually based on Portland cement,
but also has been made with other hydroscopic materials
such as gypsum. The fillers are typically materials
such as cork. vermiculite. glass fibers. styrofoam
beads. phenolic microballoons. glass microballoons. and
cellulose fibers.
Traditional application techniques required
manual mixing of the plaster and/or stucco in a barrel.
or pot with the mixed material being applied manually.
Manual application had many disadvantages including a
short pot-life of the material and the labor required
to apply the material.
Because thickness up to about 2.00" are regu-
larly required for high build coatings, spray systems
have been developed to apply high build coatings more
quickly than manual application allows. Prior art spray
systems generally include a bin or hopper for holding a
dry material which typically includes the hydroscopic
2 2193590
--
material and a filler, a nozzle for wetting the dry
material, a flexible conduit extending between the bin
and the nozzle and an apparatus for generating a motive
force to move the dry material from the bin or hopper
through the conduit and out the nozzle. The prior art
spray system may include two bins, one for holding the
hydroscopic binder and one for the filler material, and
a mixing device for combining the dry materials either
prior to entry into the conduit or along the conduit,
after entry.
Such prior art spray systems feed the dry
material to the nozzle, which then wets the dry mate-
rial, and ejects the wetted material onto the substrate
thereby coating it. Typically the dry material com-
prises the hydroscopic material and a filler. Proper-
ties of the coating deposited are dependent on water
control, the degree of wetting uniformity of the hydro-
scope material/filler distribution and filling timing.
One problem associated with typical prior art
spray systems stems from the means used to generate the
motive force. Two such means are a compressor and an
eductor connected to the bin. The compressor forces the
dry material out of the bin through the conduit and
nozzle using pressurized air. The eductor creates a low
pressure upstream of the eductor that draws the dry
material out of the bin.
The means for generating the motive force can
be placed at the upstream end of the conduit or the
downstream end of the conduit eductors and compressors
placed at the upstream end of the conduit if push the
dry material through the conduit. The problem with
pushing the dry material through the conduit is that
line losses are experienced, material separation
according to particle size occurs, and fall-out occurs.
3 2193590
All of which results in a non-uniform mixture passing
through the nozzle which consequently inhibits wetting
of the dry material and therefore decreases the proper-
ties of the coating.
To solve the problems of upstream eductors
and compressors, eductors have been.placed at the down-
stream end of the conduit, such as the granular mate-
rial emitting means shown in U.S. Patent No. 3,788,555.
The granular material emitting means comprises an elon-
gated, substantially tubular main body portion and an
elongated tubular branch portion. The axis of the bore
of the branch portion intersects the axis of the bore
of the main body portion at an acute angle of about 30
to about 800, with 30 to 60 being preferable. One end
of the bore of the branch portion is connected to a
suitable source or fluid under pressure and one end of
the tubular main body portion is connected to granular
material reservoir through a conduit. During operation,
the fluid under pressure flows through the branch por-
tion and the acute angle is sufficient to cause the
flow of the fluid to provide an area of reduced pres-
sure upstream of the junction between the bore of the
main body portion and the bore of the branch portion.
This reduced pressure tends to cause the granular mate-
rial to be withdrawn from the reservoir, entrained in
the fluid, and carried through the conduit to the main
body portion and out of the granular emitting means.
The downstream eductor of the aforementioned
patent has the benefit of pulling the granular material
all the way up the conduit, thus no line losses, mate-
rial separation or fallout should be experienced. How-
ever, the downstream eductor above has two problems
with respect to applying high build coatings. The
granular material for use with the granular emitting
2193590
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device are perlite, clay, sand, talc, mica, calcium
carbonate, calcium silicate, glass beads, plastic
spheres and the like. These materials all weigh less
than the hydroscopic materials necessary to form high
build coatings; therefore, the motive force require-
ments necessary for the granular emitting means are
less than those necessary for forming high build
coatings.
Another problem associated with the spray
apparatus disclosed in the aforementioned patent is
that convergent nozzles are used to mix the granular
material with a plural component material, such as a
resin and a curing agent external to the spray appara-
tus. The use of convergent mixing external to the spray
apparatus is necessary in the Harrison patent because
the resin and curing agent turn from liquid to solid
upon contact with the atmosphere; therefore mixing out-
side the spray apparatus is necessary to prevent clog-
ging of the apparatus. However. it is desired that high
build materials be mixed within the nozzle in order to
optimize wetting and exercise greater control of pres-
sure, turbulence and impingement angles.
A need therefore exists for a spray apparatus
to apply coatings of hydroscopic material and filler,
which exerts sufficient motive force on dry material to
move it and which maintains this force throughout
length of conduit, while substantially uniformly wet-
ting the dry material within the nozzle.
The present application provides for a spray
system including a conveyance device which moves the
dry material through a conduit and uniformly wets the
dry material within a nozzle.
Various embodiments are described herein with
reference to the drawings wherein:
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Fig. 1, is a perspective view of one embodi-
ment of a spray system according to the present appli-
cation shown in the operating mode;
Fig. 2, is a perspective partially broken
away and partially in section view of the spray appara-
tus of Fig. 1; and
Fig. 3, is a front view of the spray appara-
tus of Fig. 1, shown in operative mode.
These figures are meant to be exemplary and
not to limit the generally broad scope of the present
invention as claimed.
A spray system for application of a wetted dry
material is provided, the spray system including: a
nozzle, the nozzle having a liquid inlet through which
a liquid enters and a conveyance device attached to the
nozzle. The conveyance device includes an outer enclo-
sure which has an air inlet through which a compressed
air enters and an inner enclosure disposed substan-
tially within the outer enclosure, the inner and outer
enclosure defining an air manifold therebetween. The
inner enclosure includes a longitudinally extending
inner bore and an array of bores disposed therethrough,
the array of bores providing fluid communication of the
compressed air between the air manifold and the inner
bore. Each of the bores in the array has an internal
diameter, the internal diameter being sufficient to
allow the compressed air to flow from the air manifold
through the inner bore, thereby producing a vacuum
within the inner bore. The vacuum produced is of suffi-
cient strength to transport a predetermined volume of
the dry material through the inner bore to the nozzle
where the dry material is wetted by the liquid, the
vacuum also being sufficient to propel the wetted dry
6 - 2193590
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material from the nozzle onto a substrate in order to
coat the substrate with the wetted dry material.
Referring now in specific detail to the draw-
ings, with like reference numerals identifying similar
or identical elements, referring initially to Fig. 1,
there is illustrated a perspective view of one embodi-
ment of a spray system 10 of the present application
shown in the operating mode. Spray system 10 applies
wetted dry material droplets 15 onto a substrate 16 in
the form of coating 14 and includes a spray apparatus
12 and a dry material feed assembly 18. Spray apparatus
12 preferably includes a nozzle 26 connected to a con-
veyance device 28. The dry material feed assembly 18
preferably includes a bin 20, which holds a dry mate-
rial 24, and a conduit 22 for delivering the dry mate-
rial from bin 20 to spray apparatus 12. As used herein,
the term "dry" material refers to any material utilized
with spray apparatus 12, prior to the material being
wetted by a liquid delivered through nozzle 26.
With continued reference to Fig. 1, nozzle 26
includes an aperture (not shown) connected to a liquid
inlet 30 for entry of a liquid into the nozzle, and
includes an outlet 32 through which the wetted dry
material droplets 15 exit. In the present embodiment
liquid delivery hose 40 connects the liquid inlet 30 to
a liquid supply 42.
Conveyance device 28 includes a dry material inlet 34
connected to conduit 22 and a dry material outlet 36.
Dry material outlet 36 is located downstream of dry
material inlet 34 and is connected to nozzle 26. The
conveyance device 28 further includes an aperture (not
shown) connected to an air inlet 38 for entry of a com-
pressed air into the conveyance device. Air inlet 38 is
connected to an air hose 4-4 at one end thereof: the air
7 - 2193590
hose connecting the air inlet 38 to an air supply 46.
The air supply 46 used is a conventional industrial air
compressor capable of producing between about 125 to
150 psig air. The compressor should be designed for
continuous operation, therefore, the compressor should
have active cooling and lubrication. The preferred air
compressors offer air-cooling and moisture removal from
the compressed air through blow-down and desiccation
with point-of-use filters to further remove moisture
and oil vapors from the compressed air. Two such com-
pressors are manufactured by Ingersall-Rand and by
Champion Corp., under the names HP-100 and HRA 30-12
respectively. The conveyance device 28 provides uniform
conveyance of the dry material 24 from bin 20 to the
dry material inlet 34, mixing currents (not shown) to
aid in production of wetted dry material droplets 15,
and uniform discharge of the wetted dry material drop-
lets 15 from the outlet 32.
With continuing reference to Fig. 1, dry
material feed assembly 18 includes conduit 22 which is
connected at a first end to conveyance device 28 and is
connected at a second end, opposite the first end, to
bin 20. Conduit 22 is preferably connected at its first
end to an inner enclosure 62 of conveyance apparatus 28
by a stub extension (not shown). The conduit, stub
extension and inner enclosure all have complementary
inner and outer diameters to aid in the delivery of dry
material from the conduit to the conveyance device.
Alternatively, conduit 22 may be connected to inner
enclosure 62 by a screw fitting, by machined recesses
that accept thin sleeves which form protruding stubs or
any other conventional attachment method. Conduit 22 is
connected at its second end to bin 20. The conduit is
preferably connected to bin 20 by a hose clamp fitting,
$ - 2193590
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but alternately may be connected in any manner which
will provide communication between the bin and conduit
without leakage of dry material and which will not
reduce the inside diameter of the conduit so as to
create a check point.
The bin 20 or hopper to hold the dry material
24 preferably includes sloped side walls and a mechani-
cal agitator (not shown) to break-up any dry material
which may become caked or stuck together, prior to the
dry material entering conduit 22. The sloped walls
preferably are angled at about 60 to about 70 in
order to minimize channeling of the dry material 24
while maximizing the useful volume of the dry materiel.
In addition to having sloped side walls the bin 20 also
preferably feeds to a single screw or twin screw dis-
charge which provides a reasonably uniform discharge of
the dry material from the bin 20 to conduit 22. The
mechanical agitator, the bin 20 and the single or twin
screw discharge are all conventional designs, readily
available to one skilled in the art from a variety of
sources including Acrison, Inc of Moonachie, NJ.
With continuing reference to Fig. 1, conduit
22 is preferably flexible and includes a relatively
smooth bore (not shown) disposed therethrough. In the
present embodiment, the inner diameter of the bore is
preferably in the range of 1 to 2 inches, with approxi-
mately 1.625 inches especially preferred. The diameter
of the bore is determined by several factors including,
but not limited to, the type of material to be trans-
ported. the ability of the air compressor to provide
sufficient air volume and pressure to transport the
material and the cost to do so.
Conduit 22 may be constructed from a variety
of thermoplastic materials, as long as the material
9 2193590
utilized provides sufficient strength to preclude col-
lapse of the conduit under the vacuum which is utilized
for conveyance of the dry material 24 from the bin 20
to the nozzle 26. The preferred conduit material is
also low in cost since this element can be subject to
high wear. Preferred conduit materials include, but are
not limited to, clear, fiber reinforced polyethylene,
polybutylene or polybutadiene tubing. Various other
materials may be employed, depending upon the prefer-
ence of the designer. Some factors to consider during
selection are functionality, cost, ease of manufacture
durability and the type material to be coated onto the
substrate.
Referring now to Fig. 2, there is illustrated
a perspective view partially broken away and partially
in section of the spray apparatus 12. Nozzle 26 further
includes connector 48 attached to dry material outlet
36 of conveyance apparatus 28. Connector 48 includes an
upstream first section 50 adjacent the dry material
outlet 36, a downstream second section 52 adjacent out-
let 32, and a nozzle ring 54 welded therebetween. In
the present embodiment first section, second section
and the nozzle ring are preferably cylindrical and
define a longitudinal axis "X" as shown in Fig. 2.
Alternatively, connector 48 may be formed as a single
member and may also be formed in a variety of shapes.
Nozzle ring 54 preferably includes a plurality or cir-
cumferentially disposed injection hole. represented by
the injection hole 55. The injection holes are most
preferably distributed in a plane perpendicular to the
longitudinal axis "X", at an equal radial distance from
the longitudinal axis in order to maximize wetting of
the dry material.
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Nozzle 26 further includes a liquid enclosure
56 spaced apart from nozzle ring 54. Liquid enclosure
56 is preferably circumferentially disposed about the
nozzle ring and partially disposed about first and sec-
ond sections 50 and 52 adjacent the nozzle ring. The
liquid enclosure 56 defines a liquid manifold 58 dis-
posed between the liquid enclosure and the nozzle ring.
Liquid enclosure 56 is preferably fitted about connec-
tor 48 by an interference fit and the seams are prefer-
10 ably sealed by foil or putty to prevent leakage through
the liquid manifold 58. However, any method can be used
to join these elements provided that the liquid does
not leak through the liquid manifold 58.
With continuing reference to Fig. 2, the con-
veyance device 28 further includes an outer enclosure
60 substantially disposed about inner enclosure 62
thereby providing essentially an airtight air manifold
64 between the outer and inner enclosures. In the pre-
sent embodiment, the outer and the inner enclosures are
preferably cylindrical and are made of aluminum,
although other shapes and materials may be utilized.
Aluminum is the preferred material because it is inex-
pensive, easy to drill, easy to machine and facilitates
attachment of the two enclosures by welding. Other
materials that may be used are plastic. steel or any
high strength low wear alloys with or without ceramic
liners.
In the embodiment of Fig. 2. inner enclosure
62 includes an elongated tubular member 66 which has a
longitudinally extending inner bore 68 disposed there-
through, bore 68 defining a longitudinal axis "Y", such
that dry material inlet 34 and the dry material outlet
36 are spaced apart along the longitudinal axis "Y". In
the present embodiment inner bore 68 has a continuous
2 fi 935g0
- 11 -
diameter. Inner enclosure 62 further includes an array
of bores, represented by bore 74, disposed through
tubular member 66, about the circumference thereof in
a random pattern. The array of bores extends substan-
tially along the length of inner enclosure 62 the
length being represented in the present embodiment as
La. Bores 74 provide fluid communication of the com-
pressed air between the air manifold 64 and the inner
bore 68 as represented by the air flow arrow "Fa".
Air manifold 64 functions to evenly distrib-
ute the compressed air to all of the bores; dampens any
fluctuations in air flow due to pressure surges, dry
material surges or plugged bores; functions to provide
uniform distribution of the vacuum, as described fur-
ther below, and uniform mixing within the inner bore.
Each of the bores 74 includes an internal
diameter "d", and is disposed at an angle a with
respect to the longitudinal axis Y. The internal diame-
ter d must be sufficient to allow the compressed air to
flow from the air manifold 64 through bores 74, into
inner bore 68 and out the dry material outlet 36,
thereby producing a vacuum sufficient to transport a
predetermined volume of the dry material to the nozzle
outlet at a predetermined velocity, otherwise known as
through put. In addition. the vacuum must also be suf-
ficient to propel the dry material and the liquid from
the nozzle onto the substrate (not shown). Bore angle
a provides directional flow of the dry material toward
the dry material outlet and is preferably angled to
create mixing currents as the dry material is moved
toward the dry material outlet 36. In the present
embodiment the directional flow of the dry material is
illustrated by the dry material flow arrow Fd. The mix-
12 - 2 i 93590
-
ing currents, or vortex effect, is represented by the
flow line Fv.
It is preferred that the bore angle a be
less than 90 degrees because if the bore angle is too
large, the directional guidance and the vortex effect
will be reduced, consequently, reducing the discharge
rate from the nozzle and the turbulence of the flow Fv.
Likewise, if the angle is too small the effectiveness
of the directional guidance and the efficiency of mix-
ing and discharge will be dampened. Therefore, it is
preferred that the bore angle be between about 15 and
45 and it is most preferred that the bore angle be
about 30 .
The number of bores will vary depending on
the desired through put. For example, a through put of
approximately 12 cu. ft/hr requires approximately 56
bores. Likewise, the spacing of the bores also depends
on the desired through put. The bores are preferably
disposed in a random pattern, for maximization at the
vortex effect which facilitates wetting of the dry
material as described hereinbelow.
With continued reference to Fig. 2 outer
enclosure 60 is connected to air inlet 38. upstream
from nozzle 26. It is preferred that the inlet be posi-
tioned non-orthogonal with respect to the longitudinal
axis Y so that tangential entry of the compressed air
into the air manifold 64 is provided. Thus. the air
inlet is preferably disposed at an angle (D with
respect to the longitudinal axis "Y". In the present
embodiment (D is approximately 35 to 45 degrees.
Referring now to Fig. 3, there is illustrated
a front view of the spray apparatus 12 of the present
application, shown in operative mode. Injection holes
55 extend through nozzle ring 54 and create a liquid
13 - 2193590
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screen 78 when the liquid flows through the injection
holes 55, the liquid screen extending across the cross-
sectional area of the nozzle ring 54. In the present
embodiment there are 14 injection holes, with a separa-
tion angle of approximately 25 between each of the
holes which is appropriate for connector 48 which, in
the present embodiment has an inner diameter of about
1" to about 2. 5" . The number and optimum placement of
the injection holes would depend on the diameter, type
of dry material, flow rate of the liquid, flow rate of
dry material, and liquid pressure. The injection hole
size should, however, be small enough to produce
desired discharge stream characteristics of the wetted
material to a first order, or acceptable, degree of
satisfaction. In this embodiment the injection holes
are round, however other shapes may be used with dif-
ferent results. Liquid screen 78 provides for a high-
velocity of impingement of the liquid with the dry
material, creates very fine streams of the liquid and
enough misting to insure that all of the dry material
is at least wetted prior to ejection. Ideally the mix-
ing regime is turbulent whereas the discharge stream of
material has more laminar flow characteristics.
The operation of spray apparatus 12 will now
be described with reference to Figs. 1-3. Spray appara-
tus 12 can be held by an operator or the spray appara-
tus can be mounted using conventional mounting methods
to move in the x-y plane on a pedestal robot of the
type known by those of ordinary skill in the art. The
substrate 16 to be coated may be any one of a variety
of substrates having a variety of surface roughness.
Surface roughness refers to the peak to valley heights
and the average distance or period of the peak to
valley transition on the substrate surface, and is
14 - 2 1935 90
-
preferred in the present application to improve adhe-
sion of the coating to the substrate. The preferred
substrate has a surface roughness in the range of
approximately .005" to .125", peak to valley surface
roughness, as is known in the art. Some examples of
substrates with which the system can be utilized
include, but are not limited to, cinder blocks, poured
concrete, chicken wire, rough stone, plywood, straw
bales, styrofoam, stacked tires, cellulose batting, and
rough-backed fiberglass composite. Regardless of the
substrate utilized, the orientation of the substrate
may be horizontal, vertical, overhead or somewhere in
between.
The dry material selected preferably has a
specific gravity in the range of about 0.25 (as for
cork/cellulose) to abut 8.00 (as for ceramics/metals),
The particle size of the dry material can range from 25
microns to 0.25 inches depending on the specific grav-
ity of the dry material, the length of' the conduit,
and the motive pneumatic power provided by the air sup-
ply. In the present embodiment a cement filler mixture
is used as the dry material, however a gypsum/filler
mixture can also be utilized.
Referring now to Figs 2 and 3, the liquid
supply for the present embodiment provides water with a
viscosity of 1 cps to produce a cement or coating. Any
other liquid with a comparable viscosity can be used
with the nozzle 26 of this embodiment. The water in the
present embodiment is flowed at a pressure in the range
of approximately 20 to 65 psig, so that as the water
passes through the liquid screen 78 a combination of
turbulent diverging streams and mist is created. Water
flows from liquid supply 42 through delivery hose 40
into liquid manifold 58 of nozzle 26, described above.
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The liquid manifold 58 aids in evening out pressure
variations for each of the injection holes 55, by being
completely filled with liquid during operation. The
water pressure should be monitored by using a flow
meter or actual measurements to ensure that adequate
water flow for proper impingement/wetting of the dry
material occurs.
Referring now to Figs. 1 and 2, air flows
from the air supply 46 through the air hose 44 and
through the air inlet 38 and into the air manifold 64.
The air pressure at the inlet 38 is dependent on the
specific gravity of the dry material used, the coating
rate (i.e. rate at which a particular area is covered
at a certain thickness) and the relative standoff dis-
tance S, between the nozzle and the substrate. In the
present embodiment the working range for the stand-off
distance is approximately 12 to about 30 inches. Alter-
nate stand-off distances are acceptable as long as a
uniform spray pattern cross-section is achieved with
acceptable taper of the coating thickness at the outer
extremities. Reduced thickness at the periphery is to
be expected but should be within acceptable limits as
established for the particular application, as is
known in the art.
If the air pressure at the air inlet is too
strong there can be dramatic divergence of the powder
when it leaves the nozzle outlet, thus causing poor
adhesion to the substrate and excess scatter in the
work area. Conversely, if the air pressure at the air
inlet is too weak then there will be an insufficient
vacuum created for the transfer of the dry material
from the bin 20 to the dry material outlet 36. Thus,
the air pressure should minimize divergence while pro-
ducing a sufficient vacuum to achieve an acceptable
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flow rate. The nominal pressure range from the air sup-
ply to the air inlet is about 25 psig to about 110
psig. Pressure in the air manifold preferably ranges
from 10 psig to about 50 psig.
The air from the air inlet 38 enters the air
manifold 64 at a velocity that is dependent on the
pressure at the air inlet, the diameter of the air
inlet and the total cross-sectional area of the air
manifold. The air velocity should be sufficient to
create a back-pressure in the air manifold which
increases airflow out of the manifold, such velocity
resulting in a rise in the air manifold dynamic pres-
sure. The air velocity should also be fast enough to
create a sufficient vacuum to transport the dry mate-
rial. In the present embodiment the air velocity is in
the range of approximately 50 to 500 feet per second
which is sufficient to achieve the aforementioned
effects.
The air flows from the air inlet 38, into the
air manifold 64, through bores 74, into the inner bore
68 and out the dry material outlet 36. The air flow
from the air inlet which has a diameter of approxi-
mately .45" to about .50" through the small diameter
bores 74 which are all angled in the same direction as
shown in Fig. 2, creates a low pressure area behind the
air entering the inner bore 68 which in turn creates
the vacuum within the inner bore 68 that effectively
draws the dry material from the bin 20 up the conduit
22 and into the conveyance device 28. The vacuum
achieved by the air flow is weak about 5-15 inches of
water or 0.4-1.2 inches of Mercury; however, this is
strong enough to draw the dry material because of the
pressure differential between the bin and the conduit
and the entraining current of the air. If the length of
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the conduit increases the air volume and/or velocity
will have to increase to create the same vacuum due to
line losses and the mass in the line.
The dry material, once it flows into the dry
material inlet 34, flows adjacent the bores 60. The dry
material flow Fd increases in velocity or accelerates,
along La and swirls because of the vortex effect cre-
ated by the angle a of the bores, as described above.
The swirling created by the vortex effect Fv separates
the dry material particles, consequently aiding in wet-
ting of the dry material, because it increases the dry
material surface exposed to the liquid downstream. The
pressure at the dry material inlet in the present
embodiment is about 26-27Hg. Alternate pressure at the
dry material inlet are possible as long as a satisfac-
tory coating is achieved.
The accelerated and separated dry material
particles are drawn through the dry material outlet 36
and into the nozzle 26. Referring to Figs. 2 and 3, the
dry material flows through the liquid screen 78 created
by the flow of the liquid through holes 55 and the
nozzle ring 54. As the material flows out of the nozzle
outlet it emerges as a uniform stream of wetted dry
material droplets 15 with sufficient velocity to
provide good "splat" formation on impact with the sub-
strate, i.e. sufficient flattening of the coating drop-
lets as they impact the substrate, with minimum
rebound. The formation of the wetted dry material drop-
lets occurs as the dry material is mixed with the water
at the liquid screen and in the turbulent flow immedi-
ately downstream of the nozzle outlet 36. The wetted
dry material droplets are hydroscopic particles of dry
material that have surface adsorbed the liquid. These
wetted dry material droplets will adsorb the liquid and
18 - 2193590
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contact the substrate 16. The combination of velocity
of the wetted dry material droplets and standoff com-
bined to adhere the droplets to the substrate forming
the coating 14. In time the coating cures to form
concrete.
Wetting of the droplets can be modified and
improved by adjusting the surface to volume ratio of
the dry material to the liquid, water impingement,
duration of exposure to the liquid between the liquid
screen and substrate and by adjusting the turbulence
within the inner chamber and at the nozzle outlet.
The dry material to water ratio is carefully
monitored by a flow meter and controlled by operator
controlled valves in order to obtain the desired wetted
droplets and hence properties of the concrete, (i.e
compressive strength and density). Proper mixing is
verified by product testing, but is assumed based on
consumption (retention) of the materials converged as a
unit mass (minimum waste). The amount of waste will
increase as the mixture ratio deviates above or below
the nominal. This waste is generated by material bounc-
ing off or sloughing off the substrate which indicates
a less than desirable mixture. On a vertical surface
the adherence and build rate indicate the quality of
mixing. In addition to the above, there may also be on
line control provided by either a flow controller, a
motion controller, a thickness monitor or the like.
Thickness building occurs by transversing the
substrate in a sweeping horizontal or vertical motion.
The rate of thickness building will vary with the mate-
rials used. For example, on a vertical surface with a
standoff of 24 inches and a swath, or width, of about
4" a cork/cement mixture was sprayed at 4 feet per
second with a thickness per pass of 0.125" and a
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transfer efficiency of about 80% (i.e. coating stick-
ing). This yielded a deposition rate of approximately
48 sq. feet per minute at a thickness of 0.125" or 12
sq. feet per minute at a thickness of 0.5".
The spray system of the present application
as described hereinabove provides for uniform convey-
ance of the dry material because the motive force cre-
ated by the vacuum to move the dry material is substan-
tially equal throughout the conduit. In addition, a
conveyance device is provided which improves wetting of
the dry material by creating a vortex effect which
separates the dry material in an inexpensive manner,
without moving parts. The present apparatus also elimi-
nates concerns of pot-life, waste and product uniform-
ity by wetting the dry material close to the nozzle
outlet.
Another advantage of the present system is
that it utilizes a relatively low vacuum because the
point of wetting is located downstream, therefore the
conveyance device moves the dry powder not a more vis-
cous and adherent liquid/powder mixture that would
require a stronger vacuum.
Other advantages of the present apparatus
include inexpensive construction, ease of manufacture,
ease of use and cleaning, highly adjustable spray
rates, ease of control of water-to-cement ratio, uni-
form coating thickness and greater deposition rates. In
addition, strength of cement product, decreasing
rebound and ability to blend many dry materials with
conveyance device.
While a particular invention has been
described with reference to illustrated embodiment,
this description is not meant to be construed in a lim-
iting sense. It is understood that although the present
-20- 2193590
invention has been described in a preferred embodiment,
various modifications of the illustrative embodiment,
as well as additional embodiments of the invention,
will be apparent to persons skilled in the art upon
reference of this description without departing from
the spirit and scope of the invention, as recited in
the claims appended hereto. It is therefore contem-
plated that the appended claims will cover any such
modification or embodiments that fall within the true
scope of the invention.
