Spray wand with spray fan control

A nozzle assembly (16), for spraying a liquid such as a urethane prepolymer on a substrate, has a liquid spray nozzle (28) with a center line (56). Air nozzles (30), with center lines (62) that are substantially parallel to the center line (56) of the liquid spray nozzle (28), are provided in the nozzle assembly (16) around the liquid spray nozzle. Air passing from the air nozzles (30) surrounds and encloses the liquid spray and decreases the size of the liquid spray fan pattern (58 or 70). The air spray nozzles (30) can be positioned in the nozzle assembly (16) to change the shape of the liquid spray fan pattern (58 or 70) as well as the size. Mixing of air and liquid is minimized by spraying air and liquid in parallel paths.

TECHNICAL FIELD 
The invention relates to the control of the size and shape of the spray fan 
from a nozzle on a spray wand and, more particularly, to a spray wand with 
a fluid spray nozzle and a plurality of gas nozzles that supply gas jets 
to control the size and shape of the fluid spray fan. 
BACKGROUND OF THE INVENTION 
Paint guns with a nozzle assembly having one central nozzle for a mixture 
of air and paint and other nozzles for air that change the shape of the 
paint spray fan are well known. The air nozzles direct air into the 
mixture of air and paint leaving the central nozzle. The air from the air 
nozzles mixes with the paint and air leaving the central nozzle and 
changes the shape of the paint spray fan. Adjustments are provided to vary 
the pressure of air supplied to the air nozzles and thereby adjust the 
size and shape of the paint spray fan. The nozzle assembly is generally 
rotatable relative to the nozzle assembly holder to change the orientation 
of the paint spray fan. Air nozzles that direct air against opposite sides 
of a stream of paint and air passing through a central nozzle reduce the 
width of the spray fan in one direction and spread the spray fan in 
another direction to create an oval spray fan. The dimensions of the oval 
spray fan can be changed by changing the pressure of the air supplied to 
the air nozzles. The volume of air mixed with paint can vary over a 
relatively wide range without adversely affecting a paint spray system. 
The orientation of the spray fan can be changed by rotating the nozzle 
assembly relative to a nozzle assembly holder. 
Nozzle assemblies are available with a central nozzle that sprays a resin 
and other nozzles which spray a catalyst into the resin and change the 
shape of the resin spray fan. The primary function of such nozzle 
assemblies is to mix the resin and the catalyst. These nozzle assemblies 
cannot make significant changes in the resin spray fan without adding too 
much or too little catalyst to the resin. To eliminate waste and reduce 
cost it is desirable to provide a correct quantity of catalyst to activate 
the resin. Excess catalyst sprayed into the resin will be wasted and 
spraying an inadequate quantity of a catalyst will result in incomplete 
activation of the resin. 
The mixture of a gas or liquid with a liquid sprayed from a primary nozzle 
is undesirable in some processes. When making a urethane foam, for 
example, by a reaction injection molding process, liquid urethane 
prepolymers are sprayed onto a substrate and then heat is applied in a 
mold to cure the polymer. A gas mixed with the liquid is undesirable. Such 
a gas can interfere with heat transferred during curing and may cause 
voids in the urethane foam. Current systems for spraying liquid urethane 
polymers on a substrate either apply the liquid through a nozzle with a 
small spray fan or apply liquid through a nozzle with a large spray fan. 
The spray fans are not adjustable during operation. Nozzles with a small 
spray fan take longer to apply a liquid urethane prepolymer. Nozzles with 
a relatively large spray fan over spray and waste material when spraying 
on small areas of a substrate. It is undesirable to apply a liquid 
prepolymer at a relatively slow rate on large flat areas of a substrate or 
to waste liquid polymer through over spray when applying a liquid 
prepolymer to a small area of a substrate. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a spray wand with an adjustable 
spray fan. 
Another object of the invention is to provide a spray wand having a liquid 
nozzle in combination with gas nozzles that adjust the size and shape of 
the liquid spray fan. 
A further object of the invention is to provide a spray wand with gas 
nozzles that adjust the size and shape of a liquid nozzle spray fan and 
minimize mixing of the gas and the liquid. 
The spray wand includes a nozzle assembly with a liquid nozzle for 
depositing a liquid such as urethane prepolymers on a substrate. The 
nozzle assembly also includes a plurality of gas nozzles that are adjacent 
to the liquid nozzle. The gas nozzles supply a ring of gas that surrounds 
and encloses the liquid spray. By increasing the quantity of gas 
surrounding the liquid spray, expansion of the liquid spray is decreased 
and the liquid spray fan is decreased in size. The volume of gas is 
controlled by controlling the pressure of gas supplied to the gas nozzles. 
The shape of the liquid spray fan is determined primarily by the location 
of the gas nozzles. The shape of the liquid spray fan can also be changed 
by varying the quantity of gas supplied between individual gas nozzles. A 
gas nozzle which supplies a large quantity of gas will reduce the 
expansion of the liquid spray fan more than another gas nozzle which 
supplies a smaller quantity of gas in another location adjacent to the 
liquid spray fan. 
The gas nozzles each have a central axis that is parallel to the central 
axis of the liquid spray nozzle. By positioning the axies of the gas 
nozzles parallel to the axis of the liquid spray nozzle, turbulence 
between the gas and the liquid spray is minimized and the velocity 
difference between the liquid spray and the gas is minimized. Minimizing 
turbulence and velocity differences reduces mixing between the gas and the 
liquid spray that is surrounded by the gas. 
Other objects, advantages and novel features of the present invention will 
become apparent when the following detailed description of the preferred 
embodiment is considered in light of the drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The spray wand 10 is used for spraying liquid urethane prepolymers on a 
substrate. The substrate could, for example, be a portion of an automotive 
instrument panel. The substrate for an automotive instrument panel may 
have large flat areas as well as narrow strips. The liquid urethane 
prepolymer is sprayed on the substrate with a substantially uniform 
thickness. The substrate is placed in a mold and heated to cure the liquid 
urethane prepolymer and form a urethane foam polymer. The spray wand 10 
includes a liquid urethane prepolymer supply duct 12 and a compressed air 
supply duct 14 that is co-axial with the liquid urethane prepolymer supply 
duct. A nozzle assembly 16 is mounted in the delivery end of the spray 
wand 10. 
The air supply duct 14 is a pipe at the delivery end of the spray wand 10. 
The liquid urethane prepolymer supply duct 12 is pipe mounted in and 
co-axial with the air supply duct 14. The liquid urethane prepolymer 
supply duct 12 is held in a fixed position within the air supply duct 14 
by duct mounting rings 18 with multiple air passages 20. The discharge end 
22 of the liquid urethane prepolymer supply duct 12 is in the center of 
the air supply duct 14 and spaced from the discharge end 24 of the air 
supply duct. 
The nozzle assembly 16, as shown in the drawing, is a cylindrical body 26 
with a central liquid spray nozzle 28 and a plurality of air nozzles 30 
around the central liquid spray nozzle. The central liquid spray nozzle 28 
and the air nozzles 30 are orifices drilled through the cylindrical body 
26 as shown. The diameter of each orifice is chosen to provide the desired 
air or liquid flow. If desired, a separate nozzle could be inserted into 
bores through the cylindrical body 26. With separate nozzles, individual 
nozzles could be changed to change nozzle orifice size rather than 
changing the entire nozzle assembly 16. 
The cylindrical body 26 of the nozzle assembly 16 is telescopically 
received within the air supply duct 14. A threaded bore coaxial with one 
end of a liquid passage bore 25, in the center of the cylindrical body 26, 
receives and screws onto a threaded portion 32 of the discharge end 22 of 
the liquid urethane prepolymer supply duct 12. An O-ring 27 seals between 
the discharge end 24 of the air supply duct 14 and the cylindrical body 26 
of the nozzle assembly 16. A hexagon shaped portion 29 of the nozzle 
assembly 16 is engagable with a hand tool to tighten the nozzle assembly 
16 on the threaded portion 32 of the liquid urethane prepolymer supply 
duct 12. The passages that form the air nozzles 30 in the cylindrical body 
26 are connected to a groove 34 in the cylindrical body by radial passages 
36 as shown in FIGS. 1 and 3. The radial passages 36 and the groove 34 
allow air nozzles 30 to be bored any place within the cylindrical body 26 
and around the liquid passage bore 25. The groove 34 is within the air 
supply duct 14 and receives air from the air supply duct. The bores which 
form the central liquid spray nozzle 28 and the air nozzles 30 all pass 
through a flat surface 35 on the discharge end of the nozzle assembly 16. 
FIG. 8 is a schematic diagram showing the metering system for supplying 
liquid urethane prepolymer and air to a spray wand 10. The liquid urethane 
prepolymer is supplied by a reaction injection molding (RIM) metering 
system. The RIM metering system includes an isocyanate blend storage tank 
40 and a polyol blend storage tank 41. A high pressure pump 38 draws 
isocyanate from the isocyanate blend storage tank 40 through a pipe 43 and 
supplies isocyanate to a mixing head 45 through a pipe 47. A diverter 
valve 49 in the pipe 42 can divert isocyanate back to the isocyanate blend 
storage tank 40 through a return pipe 51. A mass flow meter 53 is provided 
in the pipe 47 to measure the flow rate of isocyanate to the mixing head 
45. A return line 55 is provided to return isocyanate to the isocyanate 
blend storage tank 40 when flow from the mixing head 45 to the spray wand 
10 is blocked. A high pressure pump 39 draws polyol from the polyol blend 
storage tank 41 through a pipe 57 and supplies polyol to the mixing head 
45 through a pipe 59. A diverter valve 61 in the pipe 59 can divert polyol 
back to the polyol blend storage tank 41 through a return pipe 63. A mass 
flow meter 65 is provided in the pipe 59 to measure the flow rate of 
polyol to the mixing head 45. A return line 67 is provided to return 
polyol to the polyol blend storage tank 41 when flow from the mixing head 
45 to the spray wand 10 is blocked. A prepolymer of mixed polyol and 
isocyanate are conveyed from the mixing head 45 to the spray wand 10 
through a liquid supply line 44. The prepolymer begins to react as soon as 
the isocyanate and the polyol mix in the mixing head 45. 
A flush block 69 with a solenoid operated valve 50 cuts off the supply of 
liquid from the mixing head 45 to the spray wand 10 when the desired 
amount of liquid urethane prepolymer has been dispensed through the spray 
wand. A flush valve in the flush block 69 opens, after the solenoid 
operated valve 50 closes, and the liquid supply line 44 and the spray wand 
10 are flushed. 
An air compressor 46 is connected to the compressed air supply duct 14 in 
the spray wand 10 by an air supply line 48. 
A solenoid operated valve 52 is provided in the air supply line 48 to 
control the flow of compressed air to the compressed air supply duct 14 
and to the air nozzles 30 at the discharge end of the spray wand 10. The 
solenoid operated valve 52 controls the pressure of the air supplied to 
the spray wand 10 to control the flow of air through the air nozzles 30 
and vary the flow of air as required. At least a portion of the liquid 
supply line 44 and the air supply line 48 are flexible lines that allow 
the spray wand 10 to move relative to the air compressor 46 and the liquid 
pump 38. The spray wand 10 will normally be attached to a computer 
controlled robot that moves the spray wand along a predetermined path 
relative to a substrate. A valve 71 can be provided in the spray wand 10 
to cut off and to start the flow of air and liquid from the spray wand. 
The valve 71 can be operated manually or by a solenoid. 
Liquid urethane prepolymers, supplied to a spray wand 10 under pressure by 
a liquid pump 38, is accelerated as it passes through a liquid spray 
nozzle 28. After passing through the liquid spray nozzle 28, the liquid 
tends to slow down and spread out following a path indicated by the arrows 
54 shown in FIG. 3. The spray fan from the liquid spray nozzle 28 will 
produce a circular pattern upon striking a substrate surface when the 
liquid spray nozzle has an orifice with a circular cross section and a 
center line 56 and when the surface of the substrate is perpendicular to 
the center line and no fluid passes through the air nozzles 30. 
The six air nozzles 30 spaced along two parallel spaced apart straight 
lines and around the central liquid spray nozzle 28 as shown in FIG. 2 
will produce the spray fan pattern shown in FIG. 4. The liquid urethane 
prepolymer spray fan pattern 58 is generally oval and is surrounded by air 
and an air spray fan pattern 60 that is generally oval with some 
irregularities. Each of the air nozzles 30 has a circular cross section 
and a center line 62. The center lines 62 of the air nozzles 30 are 
parallel to the center line 56 of the liquid spray nozzle 28. The passage 
of air through the air nozzles 30 tends to limit expansion of the spray 
fan 58 of the liquid urethane prepolymers. The passage of air through the 
air nozzles 30 also tends to maintain the speed at which the liquid 
urethane prepolymer is traveling when it leaves the liquid spray nozzle 
28. Compressed air as it leaves the air nozzles 30 moves along paths 
indicated by the arrow 64 in FIG. 1. The flow of liquid urethane 
prepolymer spray from the liquid spray nozzle 28 limits expansion of the 
air toward the center line 56 of the liquid spray nozzle. The flow of air 
through the air nozzles 30 tends to limit expansion of the liquid urethane 
prepolymer spray toward the center line 62 of the air nozzles 30. The 
velocity of the liquid urethane prepolymer spray decreases relatively 
slowly because the adjacent air is traveling in the same direction thereby 
reducing friction between the moving air and the liquid urethane 
prepolymer spray. The decreased cross-sectional area of the liquid 
urethane prepolymer spray, as a result of containment between streams of 
moving air passing through the air nozzles 30, reduces the volume of gas 
pushed by the liquid urethane prepolymer thereby further reducing the rate 
of deceleration of the liquid urethane prepolymer spray. 
The moving air from the air nozzles 30 is moving in substantially the same 
direction as the liquid urethane prepolymer spray because the center lines 
62 of the air nozzles 30 are parallel to the center line 56 of the liquid 
spray nozzle 28. This reduces turbulence between the liquid urethane 
prepolymer spray and the surrounding air. By reducing turbulence mixing of 
air with liquid urethane prepolymers spray is reduced. Air mixed with a 
liquid urethane prepolymers can reduce heat transfer and interfere with 
curing of the urethane foam polymer. 
Air nozzles 30 arranged in a circle around a liquid spray nozzle 28, as 
shown in FIG. 5 will produce a substantially circular liquid prepolymer 
spray fan pattern. The liquid prepolymer spray fan that results from 
passing compressed air through air nozzles 30 arranged in a circle with a 
liquid spray nozzle 28 in the center of the circle will be smaller in 
diameter than the spray fan of the liquid spray nozzle 28 when compressed 
air is not supplied to the air nozzles. The size of the liquid spray fan 
can be varied by changing the pressure of the air supplied to the air 
nozzles 30. 
The air nozzle assembly 16 with four air nozzles 30 located on each side of 
the liquid spray nozzle 28 along a semi circular path as shown in FIG. 6 
will produce a liquid spray fan pattern 70 and an air spray fan pattern 72 
as shown in FIG. 7. Such a spray fan may provide a uniform layer of liquid 
urethane prepolymers on a pipe or other convex surface. 
The spray wand 10 will, during operation, cover large areas with a layer of 
liquid urethane prepolymers quickly without a supply of compressed air to 
the air nozzles 30. Compressed air can be supplied to the air nozzles 30 
to reduce the size of the liquid urethane prepolymer spray fan pattern 58 
or 70 when a small area or strip of the substrate is to be covered. 
Reducing the size of the spray fan 58 will reduce the amount of over spray 
and thereby reduce the quantity of liquid urethane prepolymers required. 
Arranging the air nozzles 30, in a desired pattern, will vary the shape of 
the spray fan and the spray fan pattern 58 to provide uniform application 
of the liquid prepolymers. 
There are a number of modifications that can be made to the spray wand 10 
to obtain the desired distribution of liquid urethane prepolymers on a 
substrate. The location of the air nozzles has been mentioned above. 
Changes in the pressure of air supplied to the air nozzles has also been 
mentioned. In addition to the location of the air nozzles 30 and changes 
in the air pressure, it would be possible to provide air nozzles with 
different size orifices in one nozzle assembly. It would also be possible 
to supply air to some air nozzles 30 at one pressure and to supply air to 
other nozzles 30 in the same nozzle assembly 16 at a different pressure. 
The center lines 62 of the orifices of the air nozzles 30 should be 
parallel to the center line 56 of the central liquid spray nozzle 28 to 
reduce mixing of air and liquid urethane prepolymer spray. The angle of 
the center lines 62 of the orifices in the air nozzles 30 can be angled 
toward or away from the center line 56 of the central liquid spray nozzle 
28 up to five degrees with minimal mixing of air with the liquid spray. 
The change in the angle of the center line of the air nozzles can further 
change the size and shape of the spray fan of the liquid urethane 
prepolymers. 
The spray wand 10 has been described above in use with a liquid urethane 
prepolymer. The spray wand 10 can be used with other materials to produce 
foams and other products. The spray wand 10 can be useful in processes in 
which it is desired to limit mixing of one spray material with other spray 
materials and to vary the size or shape of a liquid spray fan. 
The spirit and scope of the present invention are limited only by the terms 
of the appended claims.