Note: Descriptions are shown in the official language in which they were submitted.
B~CKGRO~lND OF TIIE INVENTION
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3 This invention relates to a method and apparatus for powder coating and
4 more specifically to a method and apparatus for eletroststic powder painting.
6 United States Patent No~ 4,228,961 discloses an electrvstatic powder painting
head in which clean gas from an outer chamber is fed to the surf~ce of a strip
7 electrode. A monopolar corona dischEIrge current flows between the strip electrode
8 and the needle electrode. The current charges the nir-powder mixture rnoving
9 through the centrQl powder ejection port. The clean gas on the periphery is used
1~ to keep the strip electrode clean or powder free thereby insuring ~ proper corona
11 discharge current. The clean air is not used to regulate or shape the air-powder
lZ mixture.
13 lJnited St~tes P~tent No. 4,235,381 discloses an electrostatic powder gun
14 having an auxili~ry compressed gas supply. The gas is passed to the nozzle and
ionized so that upon being discharged at the tip of the elpparatus it assists in1~ placing the final charge on the powder.
17 It is preferable in powder painting to provide means for regulating the area
18 of the paint particle stream, which in turn regulates the ultimate pattern size on
19 the work piece or target. Various prior art appar~tus and methods have beenused in powder painting. Prior art powder appar~tus having means to shape the
21 pattern size of the ejected powder included both mechanic~l types and vortex air
22 ~ypes. One meeharIical type prior ~rt shaping means included ~n exterior adjwsting
23 sleeve which was normally cylindric~l and was reciprocated into and out of the
24 powder patternO The sleeve deflected the pvwder purticles into ~ ~orward direction.
26 Often erosion of the sleeve and fusion of the powder on the interior surîace of
28 the sleeve became a major problem~
27 AnGther type of prior art mechanical shaping deviee included the pl~cing of
2~ a powder deflector in the center of the powde~air mixture and att~ching a rod
29 to the deflector. The rod normally exited the re~r of the pow~er gun. Pattern
3~;
adjustment was accomplished by moving the deflector closer to or further away
2 from the nozzle opening.
3 A prior art vortex air shaping means is shown in Fig. 5 of the present
4 drawings. A similar type vortex air structure is disclosed in United States P~tent
No. 3f940,Q61. Referring to Fig. 5, the prior art spray gun A has a central ~ir-8 powder passageway B, a centrally disposed diffuser C and a nozzle D. The nozzle
7 D defines a plurality of vortex air p~ssages E which are in communication with a
8 clean air chamber F. As the air-powder mixture, in the Fig. S ~un, moves around
9 the diffuser C, it is enga~ed by compressed vortex air from the passages E. The
vortex air strikes the air-powder mixture tangentially and causes the ai~powder
11 stream to assume a whirling movement. In this type of prior Qrt structure, as
12 the force of the tangential vo~tex air increases, the down stream area is increased.
13 When the vortex air force is reduced, the down stream area of the air-powder
14 mixture is reduced in eross sectional area.
Patent No. 3,964,683 discloses another prior art electrostatic spray apparatus
1~ for the deposition of powdered coating material. This patent is directed to a
17 pneumatic saftey interlock feature.
18
19 SVMMARY OF THE INVENTION
The present invention is a powder spray gun app~ratus whieh is normally ~
21 high voltage electrostatic type powder spray gun. The spr~y gun includes ~ remotely
22 controlled shaping feature, whereby the pattern size of the air-powder mixture
23 leaving the central region of the gun nozzle may be adjusted or regulated.
24 In a preferred form of the invention, a flared diffuser is positioned within
the nozzle assembly of a powder gun. A powder gunf according to the inllention,
æ~ may b~ either a manually operated gun or nn automatic gun. The flared diffuser
27 turns the air-powder mixture sharply outwardly.
28 A shaping air snnulus which is in communicQtion with a clean compressed
air supply is defined by the noz~le assembly. The shaping annulus is in the shape
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of a cylinder hRving its major axis p~rallel and normally coincidental with the
2 longitudinal axis of the central alr-powder passflgeway of the gun.
3 Compressed air which is discharged from the shaping air annulus impacts
4 the air-powder mixture with sufficient force to shape the downstream pattern
6 size. According to the present invention, increasing the nir pressure of the sir
discharged fron~ the shaping nir annulus increases the impact force and rsduces
7 the cross sectional area and the resulting p~ttern area of the ~i~powder mixture.
8 Decreasing the air pressure and impact force increnses the resulting pattern
9 ~rea. It has been found that this novel method results in greater transfer
efficiencies p~rticularly when large patterns are required.
11 Accordingly, it is an object of the present invention to provide a powder
12 painting method and apparatus resulting in greater transfer ef~iciencies.
13 Another object of the invention is to provide an electrostatic powder coating
14 apparatus having a remotely controlled air-powder shaping me~ns.
Another object of the present invention is to provide an electrostatic powder
1~ apparatus in which mechanical movable components are not used to vary the
.7 powder p~ttern size.
18 Another object of the present invention is to proYide ~n improved eleeerostatic
~ g powder apparatus in which shaping air is utilized during the less frequent times
when a reduced p~ttern size is an operational requirement.
~1 Other objects and advantages of the invention will become apparent f~rn2æ the following detailed àescription, with reference being made to the ~ccompanying
23 drawings.
24 BRIEF I)ESCRIPTION OF THE DR WINGS
Fig. 1 is an elevational view of an electrostatic powder apparatus for the
8~ deposition of a powder material on a wcrkpiece in accordance with a preferred
27 embodiment of the invention.
~8 Fig. 2 is ~n exploded YieW showing individual major components of the
29 apparatus of Fig. 1;
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35;
Fig. 3 is a ~ragmentary cross-section~l view of the apparatus of Fig, 1,
2 shown on an enlarged scale;
3 Fig. 4 is a cross-sectional view taken along line 4-4 of Fig. 3; and4 Fig. 5 is a fragmentary, cross-sectional view, similar ~o Fig. 37 and showing
a prior art electrostatic handgun having a vortex air shaping device.
DESCRIPTION OF THE PREFERRED EMBODIMENT
7 Referring to Figs. 1 and 2 a handgun 1;0 for the electrostfltic deposition of
8 a powdered coating material, such as paint, is shown. It is understood that the
9 handgun l0 is only one embodiment of the present inventionO The present invention
may be used in automatic painting apparatus rather than in the manual handgun
1 1 shown.
12 The handgun l0 incluàes a gun body ll and a barrel 12 haYlng a front se~tion
13. Referring to Figs. 2 and 3, an electrode holder 15, mounting an electrode 1614 is received by the front section 13. A nozzle assembly l8 includes an inner nozzle
member 19 and an outer nozzle member 20 whieh are press fit together.
1~ The noz~le assembly 18 defines a cylindrical recess 2~ which recelves a
17 diffuser 23. As best shown in Fig. 4, the diffuser 23 includes legs 24 which engag~
18 the cylindrical recess 22 in a seated position. During normal operation, the diffuser
1g 23 does not move longitudinally with respect to the longitudinal axis 27 of the
~0 barrel 12. The diffuser 23 includes a flared end 28. Referring to Fig. 39 the
21 handgun l0 includes a cylindrieal powder tube 29 which mates with a cylindrical
~2 recess 30 which is defined by the electrode holder 15. The recess 30 discharges
23 into a powdel passageway 31 which is defined by the nozzle assembly 18. During
24 operation, an air powder mixture is pumped through the aligned passageways
defined by the tube 29, the cylindrical recess 30 and the passageway 31 As tlhe
2~3 air powder mixture moves along the longitudinal axis 279 the diffuser 23 ~nd its
27 flared end 28 deflect the air powder mixture sharply angularly outwardly into a
28 ~rusto-conical shape.
29
The gun 10 includcs a power supply circuit, gener~lly indic~ted as 33 and
2 having a current limiting resistor 34. The power supply circuit 33 includes biu~ing
3 springs 35 and 36 which are in electrical communication with the electrode 16.
4 The present handgun 10 includes safety valving me~ns generally indicated
by the reference number 40. The safety valving means 40 senses air pressure at
the face 41. The safety valving means 40 shuts off both the powder supply and
7 the electrical power as soon as the nozzle ~ssembly 18 is loos~ned or removed
8 frorn the gun 10.
9 Referring to Fig. 3, a compressed air chamber 42 is defined by the front
section 13 of the handgun~ The clean air supplied to this charnber normally ranges
ll between 0 psig and 40 psig. The nozzle assembly 18 defines an annular shaping
12 air cavity 43 which discharges~through a shaping air annulus 44. The air annulus
1~ 44 is preferably between .1)05 inches wide and .025 inches wide"Nith the preferable
14 width in the present embodiment being .015 inches. The shaping air annulus 44
extends in a direction parallel to the longitudinal axis 27. When shaping air is1~ discharged through the air annulus 44 it is discharged along a cylindrical path
17 which has its major axis coinciding with the longitudinal axis 27. Referring to
18 Fig. 39 the shaping air pnth P intersects the frust~conical air powder path S. A
19 plane r which is perpendicular to both the longitudinal axis a7 and the pnth P
intersects the ~rust~conical air-powder path S and defines an acute angle R,
2} which in the present embodiment Is 23o However, the angle R may vary7 norrnally
22 falling between 15 ar~d 30 , with a preferQble range between 20 Qnd 25.
~3 A plurality Gf circumferentially spaced holes 46 are defined by the inner
24 member 1g of the nozzle assembly 18 and are in communication with the shaping
air cavity 43. The other end of the holes 46 are in communication with an ~nnular
2~ air chambel 47 which in turn communicates with the compressed ~ir chamber 42
~7 through passageways, one of which is indicated by dashed lines at 4~ Therefore,
28 the air cavity 43 is in full communication with the compressed air chamber 42
29 through the holes 46, the annular chamber 47 and the passageways 48.
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When using an automatic system9 the air pressure within the compressed
2 air chamber 42 and consequently the shaping air cavity 43 is regulated at a remote
3 location. It is not necessary to manually adjust a rod or manually adjust the
longitudinal positioning of a deflector mechanism to shape the ai~powder mixturebeing discharged from the gun.
In the present embodiment, the air pressure in the chamber 42 and cavity
7 43 is adjusted between 0 psig and 40 psig. As the air-powder mixture passes8 through the powder tube 29 and is deflected outwardly in the frust~conical shape
9 along the path S, the shaping air is discharged from the shaping air annulus 44
into the cylindrical path P. The shaping air intersects the frusto-conical path S
11 arld impacts the air-powder mixture. The impact force drives the air-powdermixture into patterns of a sm~ller area as the air pressure is increased. If the13 air pressure is decreased, the downstream pattern size incl eases with the maximum
~ 4 pattern size being present when the air pressure reaches û psig. It has been âound
that the transfer efficiencies, particularily in the larger pattern sizes is greatly
1~ improved by the prescnt method and apparatus.
17 Transfer efîiciency is the amount Qf powder placed upon the workpiece
18 compared to the amourlt of powder passing through the spray apparatus. The
19 following test results, while not represented as covering all prior art app~ratus
nor covering all parameters of operation, indicate that e~t the largest pattern
21 slze, where many industrial powder painting operations occur the apparatus,22 according to the present invention (shown in Fig. 3 and identified as "DeVilbiss
23 FLo~) has a signifieantly higher transfer efficiency.
24
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27
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29
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MAXIMUM
TRANSFER EFFECTIV~ ~LOW
TESr GUN EFF5CIENCY PATTERN RATE
DeVilbiss FL. 91% 19 in. 2ao gr./min.
3 DeVilbiss Standard 81% 15.5 in. 200 gr./min.
EHP-504
4 N 84% 19 in. 200 gr./min.
G 78% 16 in. 200 gr./min.
The DeVilbiss Standard EHP-504 apparatus is the prior art apparatus, which
7 uses vortex air for shaping the pattern size. This apparatus is shown in ~ig. 4.
8 The "N~' unit uses replaceable diffusers having different diameters to ad~ust
g pattern size.
lQ The "GI' unit uses a diffuser which is movable along the longitudinal axis of
ll the nozæle to vary the pattern size.
12 During operation, the electrode 16, in the present embodiment, electro-
statically charges the particles being discharged from the gun 10.
14 It will be appreciated that although a single preferred embodiment of the
improved method and apparatus has been described, various modifications and
l~ changes may be made without departing from the spirit and scope of the invention
17 hereinafter claimedO
18
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2~1
23
24
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27
28
2g
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