HVLP spray gun and integrated fluid nozzle therefor

An improved HVLP spray gun which operates from an air supply source and an improved nozzle therefor are disclosed. The HVLP gun has a fluid nozzle including a first, integral, laterally extending portion including pressure reduction orifices which are calibrated, relative to a fluid passage in the nozzle, so that the spray gun operates as an HVLP spray gun. The fluid nozzle includes a second laterally extending portion including a surface, against which atomization air impinges after exiting the calibrated pressure reduction orifices, and a plurality of longitudinally extending air distribution holes, wherein atomization air, after passing through the calibrated pressure reduction orifices, is directed radially outwardly in an expansion chamber where the low velocity air is pressure equalized before exiting through the air distribution holes and being directed within the air cap inwardly toward a fluid atomizing annulus. An improved air driven HVLP paint spray gun which is especially lightweight and can be used to spray all types of coating materials including corrosive waterborne paints is also disclosed. A spray gun having a reduced trigger force needed to activate the gun is also disclosed. It is preferred that the leading edge of the fluid tip is doubly tapered so as to introduce the pressurized air directly onto the exiting fluid stream, which produces finer atomization with lower air volume consumption.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the field of spray guns for the spray application 
of liquid coatings. More specifically, the invention primarily relates to 
improvements in spray guns of the type known as high volume, low pressure 
(hereafter, "HVLP") including a novel fluid nozzle assembly with integral 
pressure reduction and air volume control capabilities, an improved 
trigger fulcrum assembly, an improved construction based upon the use of 
components made of aluminum or of an aluminum alloy in place of components 
that have conventionally been made of stainless steel, and an exterior 
nozzle configuration which provides improved atomization. 
2. Description of the prior Art Compressed air spray guns are adjustable 
and are capable of producing finely atomized particles by using high 
pressure atomizing air or they can produce large atomized particles by 
using an appropriate cap and nozzle and employing HVLP air for the 
atomizing air at the gun cap. When guns are adjusted to high cap 
pressures, the paint is atomized into very small particles which results 
in smooth high gloss paint coatings such as are observed on automobiles. 
When many of the atomized particles are very small and light they can be 
blown past the target into the surrounding air by the high velocity of the 
surrounding atomizing air or merely drift into the surrounding ambient 
air. Transfer efficiencies, as a consequence, are poor and air pollution 
can also occur. The cost effectiveness of high pressure air atomizing has 
dropped drastically as the cost of paint has risen. 
HVLP atomizer guns were developed which expanded the low adjustment end of 
the standard conventional spray guns. These guns use baffles to reduce the 
incoming high pressure from air compressor lines in order to supply 
reduced cap air pressures and also use specially designed air caps and 
fluid nozzles to enhance this form of atomization. U.S. Pat. No. 5,209,405 
(Robinson et al.), the disclosure of which is hereby incorporated herein 
by reference, describes a separate removable baffle which acts as a 
pressure reduction means for atomizing air and pattern control air in 
combination. Yet other gun designs use some form of pressure reduction 
within a part of the gun body before the high pressure air reaches the 
spray head portion of the apparatus. This type of configuration is seen in 
U.S. Pat. No. 5,064,119 (Melette), where a variable adjustment of the 
atomizing air is accomplished by adjustment of an air valve stem located 
in the gun body air passage. The HVLP method of atomization produces a 
large distribution of medium and relatively large atomized particles 
which, partly due to the low velocity of the atomizing air exiting the 
spray cap assembly, will strike and attach themselves to the target being 
coated. This results in more of the atomized paint reaching and attaching 
to the target surface with higher transfer efficiencies, lower air 
pollution, and more efficient paint usage, but with somewhat coarser 
surface finishes. This type of gun has proven to be useful where high 
gloss surface finishes are not required. 
To keep the weight of the guns light so as to reduce operator fatigue, gun 
bodies are fabricated of aluminum but, because corrosive materials may be 
sprayed, it has been necessary to fabricate the fluid chambers of 
stainless steel, which increases the weight of these guns. This is 
exemplified in U.S. Pat. No. 4,537,357 (Culbertson et al.). This spray gun 
clearly claims a separate fluid section assembled at the front end of the 
device. U.S. Pat. No. 5,090,623 (Burns et al.) shows a corrosion resistant 
insert pressed into the gun body as well. Some gun bodies are fabricated 
from plastic to achieve weight reduction but they are not highly regarded 
due to their inability to withstand rough handling. Trigger pull is 
another important factor which can cause operator fatigue. There are 
minimal spring forces in spray guns which are required to return the fluid 
needle and the atomizing air valves to their closed position regardless of 
friction caused by packing seals and dried paint. Accordingly, most spray 
guns require high trigger force which can cause operator hand, wrist and 
finger fatigue. U.S. Pat. No. 5,236,129 (Grime et al.) makes claims to 
exceptionally light trigger forces based on the action of added internally 
designed pilot valves. 
Because air supplying equipment is used to provide air to all air atomizing 
guns and because the cost of operating this equipment must be factored 
into the total cost of painting, it is important to obtain efficient 
ratios of paint atomization to the amount of air used in order to achieve 
overall cost efficiency. 
SUMMARY OF THE INVENTION 
According to this invention an improved HVLP spray gun which operates from 
an air supply source is provided. The HVLP gun has a fluid nozzle 
including an integral laterally extending portion including pressure 
reduction orifices which are calibrated, relative to a fluid passage in 
the nozzle, so that the spray gun operates as an HVLP spray gun. 
Specifically, the pressure reduction orifices reduce the pressure of the 
atomizing air to a level of 10 PSI or less within the air cap chamber of 
the spray cap assembly of the gun. It is preferred that the laterally 
extending portion include a plurality of calibrated pressure reduction 
orifices to effect the required pressure reduction while allowing for the 
required high air volume needed to atomize the fluid stream exiting from 
the fluid nozzle. According to a further embodiment of this invention, the 
fluid nozzle includes a second laterally extending portion including a 
surface against which atomization air impinges after exiting the 
calibrated pressure reduction orifices. The second outwardly extending 
portion includes a plurality of longitudinally extending air distribution 
holes, preferably positioned radially outwardly from the location of the 
calibrated pressure reduction orifices so that atomization air, after 
passing through the pressure reduction orifices is directed radially 
outwardly in an expansion chamber between the first and second laterally 
extending portions of the fluid nozzle where the low velocity air is 
pressure equalized before exiting through the air distribution holes. 
After passing through the distribution holes, the evenly distributed high 
volume of low pressure air is directed within the air cap inwardly toward 
a fluid atomizing annulus created by a concentric hole in the air cap and 
an outer cylindrical concentric fluid nozzle surface from which the fluid 
to be atomized will exit. Confusion that a gun user normally feels about 
the use of most spray guns where there are multiple variables of separate 
spray caps, separate nozzles, and separate air pressure reduction baffles, 
all of which must be used in the proper combination in order to achieve 
desired atomization of paint, is eliminated by the HVLP spray gun of the 
present invention. 
It is preferred that the spray gun body be fabricated completely of 
aluminum. To make the surface of the aluminum sufficiently hard so that it 
will not become dented or scarred during handling, the gun body is first 
machined and then hard coat anodized. This process creates a deep oxide 
surface which is extremely hard and resistive to surface damage. Teflon 
material is then vacuumized into the depressions in the hexagonal oxide 
surface, thereby creating uniquely protective interior and external 
surfaces of the gun. The following advantages are the result of this 
unusual surface treatment of the spray gun: 1. The aluminum oxide surface 
is extremely hard and resists damage and blemishes caused by rough 
handling. 2. The impregnation of inert teflon into all oxide surfaces 
helps the surfaces to shed all fluid materials, thereby making the gun 
surface very easy to clean. 3. The oxide anodized base with the teflon 
impregnation creates an internal surface in the fluid passages which is 
impervious to waterborne paints and solvents, and to corrosive and 
abrasive fluids. 4. The surface treatment of this improved spray gun 
eliminates the need to use stainless steel inserts in order to withstand 
waterborne and abrasive fluids thereby reducing the weight of this spray 
gun embodiment. 5. Elimination of separately machined stainless steel 
inserts and the assembly of these inserts into the aluminum body as seen 
in most spray guns reduces the manufacturing cost of the spray gun 
according to the invention. 
In a second embodiment of the invention, the force required to pull the gun 
trigger is reduced. In most conventional spray guns, the fulcrum of the 
trigger is located well above the horizontal air passage near the top of 
the gun body barrel with considerable distance to the spring loaded needle 
connection point. The trigger fulcrum of this invention is located below 
the air passage section of the body, creating a lever advantage by placing 
the trigger pivot point close to the spring loaded fluid needle and air 
valve assembly contact point, which reduces the needle opening finger 
force on the trigger. It is preferred to further reduce the trigger pull 
force, and make it easier to operate a spray gun according to the 
invention, by providing roller bearings which are supported on and extend 
outwardly from the needle, perpendicular to its longitudinal axis. The 
rollers are engaged by a rear concave radial surface of the trigger 
contact area. As the trigger is pulled back, the rear curved surface of 
the trigger which makes contact with the rollers causes the rollers to 
rotate as the needle is moved backward against its spring force, thereby 
reducing the friction between the needle and trigger. 
In yet another embodiment of the present invention, there is a double taper 
provided on the front outer surface of a fluid exit tube of a fluid 
nozzle. Atomization air exits from an annulus contained within a hole in 
the front of an air cap which contains the fluid exiting tube 
concentrically at its center. Because the atomization air which causes the 
atomization of the fluid exiting the fluid tube moves generally 
horizontally along the outer front surface of the fluid tube, the taper on 
the front of the outer edge of the fluid tube causes a reduction of 
pressure at its tapered edge and consequently draws the atomizing air 
inwardly into the exiting fluid stream surface where the tapered edge on 
the fluid tube meets the fluid stream. Because the atomizing air is driven 
into the emerging fluid stream exactly at the point the fluid stream exits 
the fluid tube, atomization occurs very close to the front surface of the 
gun cap. This results in improved atomization as well as a reduction in 
the air volume required to cause the atomization. 
It is an object of this invention to provide an HVLP spray gun fluid nozzle 
with a fluid outlet and a laterally extending portion including pressure 
reduction orifices which are calibrated to the fluid outlet and operable 
to throttle high pressure air for atomizing a fluid stream exiting the 
nozzle under HVLP conditions. 
Accordingly, it is an object of this invention to provide an improved air 
atomizing spray gun which is lighter than most competitive types and which 
can be operated with less trigger pull, thereby reducing operator fatigue. 
It is another object of the invention to provide a spray gun whose interior 
and exterior surfaces are impervious to all types of destructive fluids, 
and are easily cleanable.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An HVLP fluid spray gun according to the invention is indicated generally 
at 10 in FIG. 1. The gun 10 includes a spray gun body 12 having a handle 
14 with a fitting 16 at the base of the handle for connection to a source 
of air. At the forward end of the gun, there is a spray head assembly 
indicated generally at 18 which includes an air cap retaining ring 20 and 
an air cap 22 which provides atomizing air through a passage 24 and 
pattern air through a passage 26. A fluid nozzle 28 is also a part of the 
spray head assembly 18. Fluid to be atomized is prevented from flowing 
through a passage 30 in the fluid nozzle 28 when the front portion of a 
needle 32 is in the position shown so that a tapered tip thereof closes 
the passage 30. When the needle 32 is withdrawn to the right from the 
position shown, fluid is free to flow through the passage 30 in the front 
end of the fluid nozzle 28. 
A supply air passage or chamber 36 extends through the handle 14. In the 
position shown, an air valve 40 prevents the flow of air from the supply 
air passage 36. The air valve 40 is carried by a needle actuating assembly 
indicated generally at 42, which is moveable to the rear of the gun 10, 
i.e., to the right in FIG. 1, when the lower end of a trigger 44, which is 
pinned to the body 12 as indicated at 46, is moved toward the handle 14, 
causing a concave rear portion of the trigger 44 to contact a roller 
bearing 48 which is pinned to the needle 32 and to the needle actuating 
assembly 42 as indicated at 50, and move the needle 32 and the assembly 42 
to the right, opening the passage 30 of the fluid nozzle 28 and the air 
valve 40, and compressing a spring 52. When the pressure on the trigger 44 
is released, the spring 52 causes the needle 32 and the needle actuating 
assembly 42 to return to the position shown. So long as the lower part of 
the trigger 44 is held in a position closer to the handle 14 than that 
shown, the air valve 40 is open, and the needle 32 no longer prevents the 
flow of fluid through the passage 30 from the interior of the fluid nozzle 
28. 
When the trigger 44 is moved toward the handle 14, pressurized air which 
enters the air passage 36 can flow through the air valve 40 into a first 
chamber 54, from which fan or pattern air can flow into a second chamber 
56 and then into the passage 26 and through air pattern holes 58, 
compressing the normally circular atomized fluid stream emitted from the 
fluid outlet passage 30 of the nozzle 28, into a narrow straight line 
pattern. Fan air volume, which controls the size of the narrow atomized 
fluid pattern, can be adjusted by moving a fan adjusting needle 60 in or 
out of the second chamber 56 by rotating the needle 60 clockwise or 
counterclockwise. 
Atomizing air exits the first chamber 54 through apertures 62 located 
before the fan air adjustment needle 60 lowers the air pressure in the fan 
air cavity 56 and, consequently, the pressure of atomizing air is 
unaffected by the fan air adjustment. The atomizing air flows into and 
through a third chamber 64, then into and through fluid nozzle pressure 
reduction orifices 66 (see, also, FIGS. 2 and 3), into a fourth, pressure 
equalizing chamber 68, through air distribution holes 70, into the 
atomizing air passage 24, sometimes referred to hereinafter as a fifth 
chamber, and then through an atomizing air annulus 72 where it atomizes 
exiting fluid from the fluid outlet passage 30 of the fluid nozzle 28. 
Atomizing air also flows from the passage 24 through holes 73. 
FIG. 2 shows the spray head assembly 18 of the fluid spray gun 10, 
including the air cap 22, the fluid nozzle 28 and the air cap retaining 
ring 20 mounted on the front portion of the gun body 12. When the gun is 
in operation, fluid under pressure enters a gun body fluid inlet 74 from 
which it flows into a cavity 76 of the fluid nozzle 28, which is 
threadably engaged with the body 12, as indicated at 78. Since the needle 
32 is withdrawn to the right during operation of the gun 10, the fluid 
which enters the cavity 76 flows through the opening or fluid outlet 
passage 30 of the nozzle 28 and is atomized by air which flows through the 
apertures 62, and through the third chamber 64, the fluid nozzle pressure 
reduction orifices 66, the fourth, pressure equalizing, chamber 68, the 
distribution holes 70, and into the atomizing air passage or fifth chamber 
24, and then through the atomizing annulus 72 to atomize fluid leaving 
nozzle 28. Atomizing air leaving the annulus 72 flows along a first 
tapered portion 79 of the nozzle 28 and past a tapered forward end 80 of 
the nozzle 28. The tapered forward end 80 is more severely tapered than 
the first tapered portion 79. There is a pressure reduction as a 
consequence of atomization air flowing past the intersection 81 of the 
first tapered portion 79 and the tapered end 80. Air moves inwardly as a 
consequence of the reduced pressure, causing it to impinge upon and cause 
effective atomization of the fluid leaving the opening 30 of the fluid 
nozzle 28. 
The pressure reduction orifices 66 extend through a first, laterally 
extending portion of the nozzle 28. The orifices 66 are calibrated to 
reduce the pressure of atomization air as it passes through the orifices 
66 so that air causes atomization of a fluid stream exiting the fluid 
outlet passage 30 under HVLP conditions. Excellent results have been 
achieved, in the case where the fluid outlet passage 30 had a diameter of 
0.042 inch (1.10 mm), with three pressure reduction orifices 66, evenly 
spaced around the nozzle 28, each having a diameter of 0.055 inch (1.40 
mm). It is preferred that there be at least three pressure reduction 
orifices and that the be evenly spaced around the nozzle 28. A differently 
sized fluid outlet passage 30 will require a different arrangement or size 
of pressure reduction orifices in order that the nozzle will produce HVLP 
atomization of an exiting fluid. In any case, the present invention 
integrates these calibrated pressure reduction orifices with a given fluid 
outlet passage in a single nozzle, thereby eliminating the need for 
operators to mix and match fluid nozzles with air pressure reduction 
baffles according to the prior art. 
Air passing through the pressure reduction orifices 66, into the fourth 
chamber 68, is directed onto a solid portion of a second, laterally 
extending portion of the nozzle 28. As a consequence, the atomization air 
flows radially outwardly in the fourth, pressure equalization chamber 68, 
before passing through the distribution holes. Excellent results have been 
achieved in the specific embodiment described in the preceding paragraph 
where there are 12 air distribution holes, equally spaced around the 
second laterally extending portion of the nozzle 28, each having a 
diameter of 0.090 inch (2.29 mm). 
The gun body 10 is formed from one piece of aluminum which is machined 
prior to being hard coat anodized. After the hard coat anodizing, the body 
is subjected to a teflon impregnation process. The anodizing is 
sufficiently deep in the aluminum that it produces a hard, porous aluminum 
oxide surface; the teflon impregnation fills the pores, reducing porosity 
and making it resistant to damage by corrosive fluids. Because of the 
hardness of the anodized aluminum surface, it is also resistant to damage 
by abusive handling. All of the surfaces of the fluid spray gun 10, 
interior and exterior, are preferably subjected to hard coat anodizing and 
then to teflon impregnation, but the anodizing and teflon impregnation are 
particularly important on the surfaces which enclose the body fluid inlet 
74, the surfaces which enclose the cavity 76 and the passage 30 of the 
fluid nozzle 28, the needle 32 and the surfaces which enclose a cavity 82 
in the body 12 through which a fluid to be atomized must flow between the 
cavity 74 and the cavity 76. All of these surfaces come into contact with 
the fluid being atomized. Because they are hard coat anodized and teflon 
impregnated there is no need for stainless steel in the components where 
steel was previously considered to be necessary, particularly in the fluid 
inlet cavity 74. The teflon surface sheds all types of paints and fluids 
that are used in fluid air guns, offering a lubricous surface which is 
easy to maintain and clean. Nimet Industries, Inc., 2424 North Foundation 
Drive, South Bend, Ind. 46628 does hard coat anodizing or hard coat 
anodizing and teflon impregnation on a custom basis; the machined aluminum 
or aluminum alloy parts for a fluid spray gun according to the invention 
which require hard coat anodizing and teflon impregnation can be shipped 
to the indicated company for the required processing. 
It will be apparent to those skilled in the art that various changes and 
modifications can be made to the preferred embodiments of the invention 
that have been described without departing from the spirit and scope of 
the invention as defined in the attached claims. It will also be apparent 
that the invention is in various improvements to a fluid spray gun of the 
type that is operated from a source of high pressure air and uses a high 
volume low pressure flow of air or a high pressure flow from a cap that is 
releasably attached to and is part of a spray head assembly at the forward 
end of a gun body for fluid atomization and for pattern shaping of a fluid 
discharged from a nozzle that, except for a protruding tip, is inside the 
air-directing cap, and is releasably attached to the gun body, and that 
the spray gun is one having: 
(a) a fluid-inlet for receiving, from a source, fluid to be sprayed, and to 
deliver the fluid to the interior of the nozzle, 
(b) a supply-air passage for receiving high pressure air from a source, 
(c) a first chamber in the gun body operably associated to receive high 
pressure air from the first-air chamber, 
(d) a second chamber in the spray head assembly operably associated to 
receive pattern shaping air from the first chamber, 
(e) a needle that is resiliently urged into the interior of the nozzle to 
prevent the flow of fluid therefrom, 
(f) a valve that is resiliently urged toward a closed position where it 
prevents the flow of high pressure air from the supply-air passage to the 
first chamber, and 
(g) a trigger pinned to the gun body and operably associated with an 
actuator to withdraw the needle from the interior of the nozzle and to 
open the valve so that it does not prevent the flow of high pressure air 
from the supply-air passage to the first chamber. 
It will also be apparent that one of the improvements is a longitudinally 
extending nozzle member which extends through an opening in the cap and 
has exterior walls spaced from the walls of the cap which surround the 
opening and form therewith a passage for the flow of air from the supply 
air chamber to the first chamber, the exterior of said nozzle member 
having first and second spaced, laterally extending portions. The improved 
gun further comprises a third chamber, a fourth chamber and means for 
delivering high pressure air from the first chamber to the third chamber. 
The first, laterally extending portion of the nozzle separates the third 
chamber from the fourth chamber and has at least one pressure reduction 
orifice through which air can flow from the third chamber to the fourth 
chamber. The second laterally extending portion of the nozzle separates 
the fourth chamber from a fifth camber which is between the nozzle and the 
walls of the cap. At least one air distribution orifice is provided in the 
second laterally extending portion of the nozzle, through which air can 
flow from the fourth chamber to the fifth chamber. The at least one 
pressure reduction orifice is calibrated to reduce the pressure of air 
passing therethrough to that required for atomization of a fluid stream 
flowing out of the nozzle under HVLP conditions. The nozzle shown in the 
drawings and described with reference thereto has an exterior surface 
which is a surface of revolution around the axis of the nozzle. Such an 
exterior surface is preferred, at least for the portion of the nozzle 
which cooperates with the cap to form the air annulus through which air 
flows from the fifth chamber 24. 
According to others of the improvements, all of the components of the gun 
are composed of aluminum or of an aluminum alloy; all of the surfaces of 
the components of the gun are hard coat anodized; and all of the hard coat 
anodized surfaces of the components of the gun are impregnated with 
teflon. 
The invention is also an improvement to such a spray gun where the body 
additionally has a structurally integral, downwardly extending handle at 
its rear end, is one where the trigger is pinned to the body adjacent the 
lower surface thereof below the first chamber and forward of the gun 
handle. 
According to another improvement, there are bearing shafts that are 
structurally integral with the needle and extend therefrom in opposite 
directions in a plane that is perpendicular to the axis of the needle, 
there is a bearing with a rolling bearing surface mounted on each of said 
bearing shafts, and the trigger has a concave contact surface on which the 
bearing surfaces of the bearings roll as the needle is withdrawn from and 
returned to its position where it prevents the flow of fluid from the 
nozzle. 
The invention is also a longitudinally extending fluid nozzle for a spray 
gun which has a fluid inlet end that is threaded for engagement with the 
fluid cavity of a spray gun body, a fluid outlet end, an interior passage 
extending from the inlet end through the outlet end, and an exterior 
surface between the inlet end and the outlet end having a central portion 
that is a surface of revolution about an axis of the nozzle. The surface 
of revolution has first and second radially enlarged flanges separated 
from one another longitudinally of the nozzle, the first of the flanges 
being nearer the inlet end of the nozzle and having a smaller diameter 
than the second of the flanges which is nearer the outlet end. There are a 
plurality of bores extending through both of the flanges, the axes of the 
bores in each flange being substantially equidistant from the axis of the 
nozzle, and the axes of the bores through the second of the flanges being 
farther from the axis of the nozzle than are the axes of the bores through 
the first of the flanges. The bores in the first flange constitute 
pressure reduction orifices which are calibrated to reduce the pressure of 
air passing therethrough to that required for atomization, under HVLP 
conditions, of a fluid stream flowing, out of the nozzle. A preferred 
nozzle as described in the previous sentence is one wherein the exterior 
surface of the nozzle, adjacent the outlet end, is a surface of revolution 
which has such a uniform taper such that the exterior diameter of the 
nozzle is substantially equal to the interior diameter thereof at the 
discharge end.