CA1254030A - Particle spray gun - Google Patents
Particle spray gunInfo
- Publication number
- CA1254030A CA1254030A CA000506145A CA506145A CA1254030A CA 1254030 A CA1254030 A CA 1254030A CA 000506145 A CA000506145 A CA 000506145A CA 506145 A CA506145 A CA 506145A CA 1254030 A CA1254030 A CA 1254030A
- Authority
- CA
- Canada
- Prior art keywords
- particle
- electrode
- resistive
- electrostatic
- deflector
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
- B05B5/025—Discharge apparatus, e.g. electrostatic spray guns
- B05B5/053—Arrangements for supplying power, e.g. charging power
- B05B5/0533—Electrodes specially adapted therefor; Arrangements of electrodes
Landscapes
- Electrostatic Spraying Apparatus (AREA)
- Particle Formation And Scattering Control In Inkjet Printers (AREA)
- Coating By Spraying Or Casting (AREA)
Abstract
IMPROVED PARTICLE SPRAY GUN
ABSTRACT
An electrostatic particle spray gun having, in one preferred embodiment, a conical deflector of insulative material mounted in the nozzle in the particle path for forming a conical particle spray pattern. A resistive sheet connected to a high voltage electrostatic supply is sandwiched between the forward and rearward ends of the deflector, leaving only the perimeter of the sheet exposed at the periph-eral region of the conical deflector. The perimeter of the resistive sheet functions as a multi-point circular electrode for charging the particles such that improved coating transfer efficiencies are achieved. Also, because of the resistive nature of the resistive sheet, the sheet constitutes a resistor in the electrical current path between the center of the sheet where it connects to a high voltage terminal and the circular periphery of the sheet which serves as the multiple point charging electrode, thereby minimizing unsafe electrical discharges should the electrode inadvertently approach a grounded object.
Other embodiments of multi-point electrodes, for powder and/or atomized liquid coating applications, are also disclosed.
ABSTRACT
An electrostatic particle spray gun having, in one preferred embodiment, a conical deflector of insulative material mounted in the nozzle in the particle path for forming a conical particle spray pattern. A resistive sheet connected to a high voltage electrostatic supply is sandwiched between the forward and rearward ends of the deflector, leaving only the perimeter of the sheet exposed at the periph-eral region of the conical deflector. The perimeter of the resistive sheet functions as a multi-point circular electrode for charging the particles such that improved coating transfer efficiencies are achieved. Also, because of the resistive nature of the resistive sheet, the sheet constitutes a resistor in the electrical current path between the center of the sheet where it connects to a high voltage terminal and the circular periphery of the sheet which serves as the multiple point charging electrode, thereby minimizing unsafe electrical discharges should the electrode inadvertently approach a grounded object.
Other embodiments of multi-point electrodes, for powder and/or atomized liquid coating applications, are also disclosed.
Description
3~3 IMPROVED P~RTICLE SPRAY GUN
This invention relates to particle spray equipment and more particularly to an improved particle spray gun for electrostatically applying coating particles to an article to be coated.
Backqround of the Invention Coating applied electrostatically to an object to be coated can be either in the form of electrostatically charged solid particles, i.e., powder, or electrostatically charged liquid particles which have been atomized using a variety of well known LCM~jj .
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techniques or principlesp in~ludiny air impin~ement atomization, airless or hydrostatic pres~ure atomiza-~ion, and/or electrostatic atomiza~ion. This in~ntion iB useful wi~h both liquid and powder spray coating applications.
In the application of solid ~artic~laie coatings, such a~ p~wde~ed resins~ i~ ind~s*rial ~inishing applications, the particulat~ or pOW~
~ommonly conveyed to a spray device, often terme~ a ~gun", by air under pressure and is then sprayed ~rom an opening in ~he forward end, or nozzle, of -~he yun in the farm of a ~owde~-entrained ~ir ~tream which is projected along a path from the gun toward the o~ject ko be coated. In the ~rocess o~ spraying the coating 1~ particles frDm the gun, an electrical charge is preferahly imparted to the particles by an electxoae maintained at a high voltage which is mounted to the gun n~]e ~roximat~ tD the ~ath of the powder c~ating stream. The charged paxticles are ~hen electr~stati-- 20 cally attracted toward the object to be coated which is heId at electrical ground potential, enhanring the efficiency with which charyed particle~ sprayed ~rom the gun are deposited:on the ~arget article. ~f~er the article is coated,-it is generally conveyed ,~5 through an oven where the powder coating material is heated and fused onto the surface o~ the article to permanently bond it thereto.
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~ lectrostatic powder spray gun~ typically include a mechanical p~wder deflector moun*ed a* the ~ozzl~ end of the gun. In one ~re~erred form t~e deflector is in the shape of a cone and is disposed axially in the flow path of the pDwder b~ing sprayed from the g~n, defle~ting the powder into ~ onical ~pray patt~rn. ~ha~ is~ th~ deflector is Impacted by the powa~r coating material ~ein~ sprayed f~om the gu~
in the nozzle region and dire~ts th~ pDwder radially outwardly to form ~ conical spray patternO
Electros~atic liquid spray gun syst~ms cus'omlarily include a sourc~ of pressurized liquid which conveys the liquid coating to the gun via a hDse where it is ~mitted from ~he noz~l~ in a stream o~
1~ atomized particles. Atomization can ~e produ~d by impingement of the liquid~stream with ai~ in ~he region of the nozzle~ which is ~nown as air atomiza-tion. Plternative.y, the liqui~ coating c2n be ~.ighl~
pressllrized such that upon e~it f~om *he n~z~le atomization results, which is termed hydrostatic or airless atomization. In still other systems, th liquid is ~ubjected to electrostatic fo~ces which effectively atomi2e the liquid.
One of the o~jecti~es in the design ~f ~n
This invention relates to particle spray equipment and more particularly to an improved particle spray gun for electrostatically applying coating particles to an article to be coated.
Backqround of the Invention Coating applied electrostatically to an object to be coated can be either in the form of electrostatically charged solid particles, i.e., powder, or electrostatically charged liquid particles which have been atomized using a variety of well known LCM~jj .
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techniques or principlesp in~ludiny air impin~ement atomization, airless or hydrostatic pres~ure atomiza-~ion, and/or electrostatic atomiza~ion. This in~ntion iB useful wi~h both liquid and powder spray coating applications.
In the application of solid ~artic~laie coatings, such a~ p~wde~ed resins~ i~ ind~s*rial ~inishing applications, the particulat~ or pOW~
~ommonly conveyed to a spray device, often terme~ a ~gun", by air under pressure and is then sprayed ~rom an opening in ~he forward end, or nozzle, of -~he yun in the farm of a ~owde~-entrained ~ir ~tream which is projected along a path from the gun toward the o~ject ko be coated. In the ~rocess o~ spraying the coating 1~ particles frDm the gun, an electrical charge is preferahly imparted to the particles by an electxoae maintained at a high voltage which is mounted to the gun n~]e ~roximat~ tD the ~ath of the powder c~ating stream. The charged paxticles are ~hen electr~stati-- 20 cally attracted toward the object to be coated which is heId at electrical ground potential, enhanring the efficiency with which charyed particle~ sprayed ~rom the gun are deposited:on the ~arget article. ~f~er the article is coated,-it is generally conveyed ,~5 through an oven where the powder coating material is heated and fused onto the surface o~ the article to permanently bond it thereto.
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~ lectrostatic powder spray gun~ typically include a mechanical p~wder deflector moun*ed a* the ~ozzl~ end of the gun. In one ~re~erred form t~e deflector is in the shape of a cone and is disposed axially in the flow path of the pDwder b~ing sprayed from the g~n, defle~ting the powder into ~ onical ~pray patt~rn. ~ha~ is~ th~ deflector is Impacted by the powa~r coating material ~ein~ sprayed f~om the gu~
in the nozzle region and dire~ts th~ pDwder radially outwardly to form ~ conical spray patternO
Electros~atic liquid spray gun syst~ms cus'omlarily include a sourc~ of pressurized liquid which conveys the liquid coating to the gun via a hDse where it is ~mitted from ~he noz~l~ in a stream o~
1~ atomized particles. Atomization can ~e produ~d by impingement of the liquid~stream with ai~ in ~he region of the nozzle~ which is ~nown as air atomiza-tion. Plternative.y, the liqui~ coating c2n be ~.ighl~
pressllrized such that upon e~it f~om *he n~z~le atomization results, which is termed hydrostatic or airless atomization. In still other systems, th liquid is ~ubjected to electrostatic fo~ces which effectively atomi2e the liquid.
One of the o~jecti~es in the design ~f ~n
2~ electrostatic spray gun, either liquid or powder, is to maximize the~efficiency with which charged coating particles sprayed from ~he gun are deposited on the - article ~eing coated. This is called the "transfer
3~
~4--efficiency". It is generally believed ~y thos~
skilled in ~he ar* tha* transfer efficiency an ~2 increa~ed by increasing the charge vn the particles and/or by increasing the strength o~ the elec*rostatic i field between ~he gun and ~he aLrticle ~eing coated.
Accordingly, i* has ~een an objectiY~ of this invention ~o co~struct an electrostati~ spray gun which will ~oth increase the charge vn the particl~s 1~ and the strength o the electrostatic field between gun and article ~eing coated, and there~y ~rouide improved powder coating transfer efficiencyO This o~jective has been accomplished by pro~i~i~g a particle spray device, which has an opening from which a stream 1~ of particles i9 sprayea in a forward path toward an object to ~e electrostatically coated, with a multi-point electrode comprising a subs~antial num~er of closel~- sp2ced electro~e elemen*s locatea ~oxima~
the opening through which the particle stream pas~es.
2~ Energization o~ the multi-point electrode from a high voltage electrostatic supply results in the creation of A plurality of corona charging points proximate the particle stream, there~y enhancing coating transfer e f ~iC iency.
~ In one preferred embodime~t of a powder spray gun, a def lector is provided in the nozzle powder stream path which is constructed of electrical-~zs~
ly nonconductive material, and which has a~ a rear surfac~ upon which the forwardly directea pDwder ~tream Impinge~ ana as a ~esult ther~of b~c~
deflected intD the desired s~rel~m configuration, ~ a front surface facing the forward d-rectio~, nd c3 a subs~antial number o~ electrode elements circumferen-tially spac~d aro~nd the perimetex o~ t~e defle~tor which are ~o~nected tD ~ high vDltage source via associated resisti~e paths incorporatea in the de1ec-lD tor. These electrode elements collectively ~unctionas a multi-pDint electrode tD provide a pl~rality of corona charging points when the electrode is Pnergi2,ed.
In the one preferred embodiment descTibed above, the multi-pDint electrode is in the form of a 1~ fibrous resistive sheet constructed from a mateIial such ~s ~ilicor carbi~e, which is iDcorporated in the deflector between the front and rear surfaces thereo~
to define as its periphe.^~, which is proximate to the ~eflector periph~ry7 a large number of raaially : 20 ~rranged electrode elements which establish a plurali~y of corona charging points past which the de~lected powder stream passes to be electrostatically cha~ged as the powder particles are s~rayed from the gun~ In - this embodiment, in which the substantial number of 2~ radially arranged electrode elements ~ircum~erentially spaced around the de~lector periphery ~unction tD
establish a plurality of corona charging points, the .
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resistive sheet located radially inwardly o~ the electrode elements fune~ion~ as resis ive ~aths ; ~ incorporated in the deflector through which the electrode elements are energized from a suitable high voltage source~ While a silicon carbide material is preferred f~r use as the resis~ive sheet in this :- embodimen~l o*her ~ rous resistive material~ may also be suitable.
An important adva~tage o~ the foregoing embodiment of this inventi~n is that the peripheral edge of the silicon car~ide sheet includes the en~s of the many silicon car~ide fibers fonming the resistive sheet and these fiber ends form a multitude of radially arranged electrode elements which ~stablis~ ~ ~lurality of corona charging points which charge the ~owder particles-^as t~ley are sprayed. This deflecto~ struc ture is believed to both increase the charye trans-~erred to the powder particles, and to increase the str~ngth of the electrosta~ic field between the gun 2~ and the workpiece, to enhance coating transfer effi-ciency. Another advantage is that the deflector stxucture, particularly the resistive paths and ~lural circum~erentially-arranged electr~de el~ment~, is ~relatively inexpensiYe, easy to manufacture, and 2~ durable. It i~ also readily replacea~le shoul~ such become necessary. These attributes ~nha~ce the attxacti~eness of the g~n from a commercial standpoint.
In the foregoing form o~ the i~vention, the silicon carhide sheet has a cen~rally dispo~ed ~ig~
vol-tage texminal region remo~ fro~ *he edge thsreo~
for establishing an electrically resis~lve curren~
flow path through th~ sheet between the ~entral terminal region whereat high voltage i~ ~up~ d and the peripheral ~dge w~e~at co~Dna ~harginy ~i the powder particles occurs from *h,e many silicon c~rbid~
fiber ends. This resistive path cDnsti~ute~ a re~a-tively large xesistor and functions to minimizeignition h~zards due to inadvertent discharge of electrical energy capacitively s-~ored in the s~ray coating system of which the gun is a major ~omponent.
In another ~referred embodiment of this 1~ invention, the circumferentially spacea electro~e elements aroun~ the ~eflec*o} perimeter are in the ~orm of discrete, fixed electrodes in the f~r~. of electrically conductive needl~s or wires which project radially outwardly from the perimeter of the d~fl~c~or~
- 20 -~ach of the discrete electrDde~ is connected tD 2 high voltage source via a discrete resistor:embodied in the deflector. If desired, the radially disposed elec-trodes can be made fl~sh with the deflector peri~hery in lieu of projecting outwardly th~rerom, there~y reducing the likelihood of electrode dEmage.
In accordance with a still further, and also preferred, embodiment of the invention, the deflector : is provided with a.relatively narrow silicon carbide -- ~54~3V
ribbon or t~lread, which ~unction as cir~umf~entially arrang~d electrode el~ment~i ~ia disc~eet resist~ls embodied in the deflec~or ~hic~ are radially ~i~pose~
and cir~ferentially spaced within the defl~ctor~
I~ *he em~odiments of the i~vention utili~ing discreet xesistor~ embodied in the defl~ctor to interconnect ~he high voltage ~ource and ~he ~irc~m-~erentially ~paced el~trode elements on *he ~fle~to~
p~riphery, the resistors function tv minimize ignîtion hazards au~ to inadvertent elec~rical energy dis~
charges, thereby enhancing the safety oE the gun.
In accordance with a further aspect of the invention which can ~e advantageously incorporated into each of the f~reyoing emb~dIments, the nozzle 1~ lvcate~ at the forward end o~ t~e nonconduc~i~e ~un arrel is prvvided with an electrosta~ic shield. The shield is disposed outwardly and rearwardly of the pe~imeter of *he deflect~r whereat the corona c~arging points ar~ located which ~lectrost~$i~ally charg~ the 70 aeflected powder stream as it p~sses through the '' annular opening ~etween the nozzle and the conically-shape~ ae~lector which is axially disposed in the powder flow path. In a ~l~f~r~ed form, tne ~le~t~o-static shield is formed ~y flaring the end of ~he noz~le in the Iegion surrounding the forwara end of the conical deflector, particularly the perimet~
thereof, from which extend the corona charging points.
In practice, the electrostatic shield has ~een ~ollnd ~S~3~
to significantly improve the transfer efficiency when compared to a similarly-constructed spray device which does not have the electrostatic shield.
By way of background, and as an aid to understanding how the electrostatic shield of this invention enhances transfer efficiency, in a typical electrostatic spray gun of the type having an electrically-grounded handle or mounting member, the corona zone proximate the periphery of the deflector is approximately midway between the grounded gun handle or mounting member which is located rearwardly thereof and the electrically-grounded object being coated which is located forwardly thereof. By way of example, the distance between the grounded object being coated and the corona charging zone is approximately ten inches, which is approximately the same as the distance between the corona zone at the gun nozzl.e and the rearwardly-located electrically-grounded gun handle or mounting member. Without the electrostatic shielding outboard and behind the corona charging zone proximate the periphery of the deflector, the electrically-charged coating particles issuing from the gun nozzle are as close to the grounded article being coated as is the grounded gun handle or mounting member, with the result that some charged particles are electrostatically attracted to the grounded gun handle or mounting member, impairing the efficiency of the coating transfer process.
LCM:mls .~
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In addition, because the gun handle, or moun-ting hardward, provides an attraction to some of the charged particles, a corona current: path is set up be-tween the deflector and the grouncle~ handle which causes the available elec-trical energy for charging at the deflector to be reduced by parasitic discharge.
The reduction in available charging energy at the deflector, results in a corresponding reduc-tion in -transfer efficiency. Therefore, by inclusion of the electrostatic shield of this invention, the effect of the electrically-ground gun handle or mount in terms of attracting elec-trostatically-charged particles and of providin~ a parasitic curre~t leakage path is subs-tantially reduced, with the result that -transfer efficiency is significantly increased. This is a substantial improvement in transfer efficiency in comparison to -the result if the electrostatic shield-ing in the nozzle surrounding the deflector periphery is ommitted.
The electrosta-tic shield can be used advantageously with the guns, manual or automatic, which are designed -to spray coating par-ticles of ei-ther the atomized liquid or powder type.
In accordance with still other embodiments of the invention, the multi~point electrode is in the form of a disc with a sawtooth perimeter. The entire disc may be fabricated of resistive, semiconductive or conductive material. Al-ternatively~ the disc may be , -~
1~S~3~
of a comp~site construc~ion with an inner ci~cular section, ana an out~r annular ~ection with ~eeth at ~he peripheryO The inn~r and~Dr ~uter sec~ions ~ay ~e conductive, resistive, or semic:onductiYe solid sheet, fi~rous or mesh material~ In lieu of the inner circu-lar section, a series of electrical wires connected to ~he ~nnular section may ~e used to tr ns~ort high voltage to the toothea periphery thereof In ano~her form, the multi-point electrode 10 may be a disc-shaped mesh o~ conductive, semiconduc-tive, Dr resistiv~ wire, or nonc~nductive wir4 havinq a ~l~d~ing of conductive, semiconductive, ol resisti~e materialO
In another embodiment, use~ul in a powder gun ha~ing a deflector, the deflectDr is fabricated o~
..injection molded ~aterial containing.silicon carbide or other resistive fi.bers, particularly a* the per-.imeter thereof, which functiDn as multi-point elec-trodes. ~he deflecto~ may also include semicondllctive, 2D resistive~ or conductive material t~ tran~port ~he high voltage to the ~ilicon carbide ~ibers at the deflector perImeter~ Instead of silicon carbide fibers at the peliphery of.*he deflector, ~ multi -- point electrode could be provided by mounting a large .25 number of electrodes in ~he deflector ~erimeter to function as multiple elec*rodesO
:In any of the-aforementioned embodiments, it is desirable ~o pro~ide ~esis~ance s~fficiently close 3{~
to the multiple electrodes and in sufficient amount to avold unsafe elekrical discharges should electrical energy capacitively stored in the gun suddenly become discharged by -the approach of a grounded article to the multipoint electrode.
The multi-point electrode aspect of this invention, while described in connection with a powder gun having a deflector, is also useful in atomized liquid spray devices. In such devices the multi-point electrode is mounted in the nozzle region proximate the path of atomized liquid particles being emit-ted from the nozzle toward -the article -to be coated in much the sa~e manner that the multi-point electrode :is mounted in the deflector of a powder gun pro~imate the path oE the emitted powder particles.
These and other ojectives, advantages, and fe~-tur~sof-the invention will become more readily apparent from a de-tailed description of the invention taken in conjunction with the drawings in which:
Figure 1 is a side elevational view, partly in cross section, depicting the principal components of one embodimen-t of an electrostatic powder spray gun incorporating the invention;
Figure 2 is an enlarged side elevational view in cross section, showing the forward end of the powder gun of Figure 1, including the nozzle~ deflector, and powder-charging electrode.
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Figure 3 is a cross sPction 1 ~i~w along line 3~3 of FiguIe 1.
Figure 4 is a front e:le~i~nal view, o~ the nozzle of the gun of Figure 1, depictin~ the deflec~or partially cut-away to show the xesistive fibrous ~heet~
Figur~ ~ is B ~ont eLevational view of deflectr:r 7 incorporating radially outwardly ~rojec~in~
elec~rodes and discre~e resisiors, o~ another embodi men* o~ the invention.
Figure 6 is a sid~ elevational view of the de~lector of Figur~ ~.
Figure 7 is a front elevational view of a deflector, incorporating a silicon carbide ribbon or 1~ thread in the rim thereo~ ana discrete xesistors, o~ a . still u~t~er embodiment of the in~ention.
Figure 8 is a side elevational view of the deflectDr o~ ~igur~ 7.
Figure 9 is a ~ront elevational view of a multi-point electrode in the form of a sawtooth-edgea disc o~ uniform construction throughout.
Figure 10 is a front elevational view of a mu~ti-point ele~trode in tAe fDxm of a s~wtooth-edge~
disc o~ EOmpOsite construction~
Fig~re ll is a front ~levational view of a multi-point electrode in the form of a composite disc ~avlng an outer annular ia~ric~ mesh or screen section and an inner solid ci~cular section.
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Figure 12 is a front perspective view of the barrel of a spray device having a circular spray pattern, which uses a multi-point electrode to charge the coating particles.
Figure 13 is a front perspective view of the barrel of a spray device having a flat spray pattern, which uses a multi-point electrode to charge the coating particlesO
With reference to the figures, one preferred form of electrostatic spray gun incorporating the present invention is depicted. In the preferred embodiment of the spray device 10 is in the form of a gun having an electrically grounded conductive handl~ ll and a nonconductive or insulative barrel 12 which at its forward end terminates in a flared nozzle 14 having a central flared opening 15 from which projects a combined powder deflector and electrode charging assembly 16.
Except for the assembly 16, the preferred embodiment of the spray gun can be constructed in accordance with the teachings of United States Patent No. 4,634,058 entitled "Improved Powder Spray Gun", in the name of Thomas E. Hollstein, David E.
O'Ryan, and Joseph C. Waryu, assigned to the assignee of the present application.
LCM:jj ~2~ 3~3 ~ he ~arrel 12 includes an intern~l p~wder entry chamber 17 which at its rearward end com~unicates with a powder-entrained ~ess~ri.zed ai r s~pply hos~
13a via a port 13 in the barrel wall~ ~he int~rnal powaer entry chamber 17 at its fvrwaId end communicat~s with the nDzzl~ openi~g lS via a ta~ered bore 19 ~nd intermediate cham~er 21. A nonconductive mo~nting stub 22 for th~ de~lect~r an~ electrode assem~ly 1 extends axially ana Eorwardly ~rom a nonc~nductive spiaer 2~ locate~ within ~he in$ermediate cha~er 21.
Extending axially and reaYwardly from the ~pi~er 2~ is an electrically insulated conductive path ~9 incDrpor-ating a conductor 76 Ito ~e descri~ed) which extend~
through a stepped diameter bore 30a ~nd 30b wh~re i~
1~ makes an appropriate conne~tion with an insulated high ~oltage supply ca~le 26 which passes ~hrough the handle 11 exiting the butt thereof at 24 where it connects to a remote high voltag~ ele~trostatic power supply Inot shown).
The hanale 11 is provided with a m~vable trigger 34 which when activated supplies pressurized powder-entrained air to the pGwder entry cham~ex 17 . . Yia hose 13a~ Trigger 34 ~lso en2rgizes the remcte high voltage supply to provide high vol~age electro-2~ static power to an electrical conauctor 7D (l~ter described) which is axially di~posed within the powder deflector:.16. ~he conductor 7D is connected to the high voltaye supply by high voltage cable 24, 26 and the electrically insulat~d conductive ~ath ~9 whic~
passes through the mounting stu~ 22 and s~ider 2~.
The powder-en*rained air passes ~naer pres~ure from the entxy cham~er 17 successively through *he tap~red bore l9 and intermediate chamber 21 to the ~lared nozzle opening 15 wherea~ it is divert~d into a conical path and electros~atically charged ~y ~e electrode, to be de~cribed, incorporated in *he ~der deflector and electrode charging assembly 1~. The lD powder exits the nozzle opening in a generally conical pattern of elec*rostatically charged parti~les for impingement upon an electrically grounded articl4 (DDt shown) to be coated~
r~he powder deflector and elec rode ~harging assem~ly 167 considered in more detail in ~Dnnection with Fig. 2, is ~enerally conical in shap~ ~a~ing a circular flat front surface 40 and a conical rear ~: surface 42. ~ront surface 40 ~ould also be conv x Dl concave, i~ desired. A ~esistive sheet electrDde i~
the ~orllZ of a circular wafer or: disc 4~ is lc~cated iD
a boundary region between the frDnt and rear surfaces 40 and 42. The edge 46 of the resisti~e elec*rode sheet or disc 44 is ~re~erably flush:with the edges - 40' and 42' of the frcnt and rear surfaces 40 and 42.
: 25 In a preferred form of the invention, the powder deflector and electrode charging assembly 16 is a composite:or sandwich assembly which in~ludes the intermediate resistive electrode disc:-44, a circular ~S~L~3~
insulating disc 40a having a diameter equal to that of the resistive electrode di~c 44, and a conical insulating section 42a the rearward surface of which constitutes the powder deflecting conical surface 42. The conical section 42a, resistive electrode disc 44, and disc 40a can be permanently assembled to form an integral unit utilizing commercially available adhesives. Alternativaly, the resistive sheet could be molded into the deflector.
In a preferred form of the invention the resistive electrode disc 44 is fabricated of nonwoven silicon carbide fabric embodying randomly oriented silicon carbide fibers or filaments in a resin matrix. The silicon carbide fibers or filaments from which the fabric is made have the physical and electrical characteristics of Nicalon fiber of the general type disclosed in United States Patent No. 4,100,233 and commercially available from Nippon Carbon Co., Ltd., Tokyo, Japan, and Dow Corning, Midland, Michigan. In a preferred embodiment the silicon carbide fibers are heat treated to provide a specific resistivity of 1 X 103 ohm-cm., and a fiber diameter in the approximate range oE 10-15 microns. The following publications of Nippon Carbon Co., Ltd., Tokyo, Japan, available from Dow Corning, Midland, Michigan, contain information on Nicalon fibers:
LCM:jj ,~'' ' .~ .
~5q~330 Nicalon Silicon Carbide Fiber, 12 payes;
Price Listing Effective 1-1-84, Nicalon Silicon Carbide Fiber Products Distributed by Dow Corning Corporation, 2 pages; and Industrialization of Silicon Carbide Fiber and Its Applications, by Jun-Ishi Tanaka, Executive Director, Nippon Carbon Co., Ltd., 11 pages.
Nicalon con-tinuous silicon carbide fiber, in one commercially available form, is physically charac-terized as follows:
Filament Diameter: 10-15 microns, Cross Section: round Density: 0.093 pounds/inch3 ~2.55 g/cm3), Tensile Strength: 360-470 ksi (250-300 kg/mm2), Tensile Modulus : 26-2g x 103 ksi (18-20 x 103 kq/mm2), and Coefficient of Thermal Expansion (parallel to Fiber): 3.1 x 10 6/oC.
The specific resistivity of Nicalon silicon carbide fiber which is uniform -throughou-t the fiber and independent of fiber flexure, can be varied by heat treating the fiber at differen-t temperatures subsequent to spinning. The variation in specific resistivity as a function of heat treating temperature can vary by a factor of approximately 104 from approxi-mately 102 ohm-cm to 106 ohm-cm.
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The Nicalon continuous silicon carbide fibers can be formed into woven abric, as well as nonwoven Eabric of random fiber orientation. In addi-tion, the resistive silicon carbide disc 44 can be fabricated of resin impregnated Nicalon fabric composite, glass Nicalon fabric composite and/or Nicalon fibers in a ceramic ma-trix.
The insulative fron-t disc 40a and insulative conical deflector 42a can be fabricated of a variety of nonconductive materials including glass-filled Teflon plastic, Delrin plastic, and the like.
~he d~flector/electrode assembly 16 is mounted to the s-tub 22 by the axial engagement of a reduced diameter sec-tion 22a at the forward end of the mountlng stub 22 and a blind hole or bore 64 formed in the rear central portion of -the conical deflector 42a.
The bore 64 and reduced diameter end 22a of the stub 22 are dimensioned -to provide a snug sliding fit therebetween.
As noted previously, electrostatic energy is trans-mitted from a remote power supply (not shown) to the resis-tive charging disc 44 via the cable 24, 26 and -the electrically insulated resistorized conductive path 29. Conductive path 29 includes an electrical conductor (or electrode) 70 which projec-ts axially from the end of the mounting stub 22 into a sui-tably provided axial passage in -the conical deflector section 42a to establish electrical contac-t wi-th the ~ 19 -;, .
~rc~
~Sg~l~3~
resis-tive disc 44. The conductor 70 is connected to the electrically conductive core of the cable 26 via a resistor 75 and electrical conductor 76 which consti-tute further elements of conduc-tive path 29, and which are in elec-trical series circuit arrangement between the conductor 70 and the conductive core of the high voltage cable 26.
In operation, when the trigger 34 is ac-ti-vated, powder-entrained pressurized air is introduced into -the internal powder en-try chamber 17 via the hose 13a whereupon it flows through the -tapered bore 19 into the intermediate chamber 21 where is passes through the spider 25 and impinges on the rear surEace 42 of the conical deflector 42a which causes -the path of -the powder to deflect and form a conical path as it exits the flared opening 15 of the nozzle 14 toward the ar-ticle or -target substrate to be coated (not shown).
Activation of the trigger 34 also energizes a remote power supply (not shown) -to cause high vol-tage electro-static energy to be supplied to the resistive charging disc 44 via the electrical pa-th previously described.
With the resistive charging disc 44 main-tained a-t a high electros-tatic voltaqe, such as 90 Kv, a corona discharge is produced at the multitude of resistive material fiber ends 46a located around the perime-ter 46 of the resistive charging disc ~4,causing electrostatic charge to be imparted -to the stream of powder as it exits the flared opening 15 of nozzle 14 subsequent to deflec-tion by the rear conical deflecting surface 42.
Experience has shown that higher coating transfer efficiencies canbe achieved with the electro-static spray coating gun of this invention. In practice, the number of corona points,as well as their precise loca-tion around the periphery 46 of -the resistive charging disc 44, is somewhat variable. At no load voltages of 90 Kv with a charging disc 44 having a diameter oE approximately 1 lJ2 inches and a thickness of approxi-mately 0.65 mm, anywhere between three and eight corona points have been observed to simul-taneouly occur at peripheral locations which are con-tinuously changing on a more or less random basis.
Con-tributing in a material manner to -transfer efficiency enhancement provided by the preferred embodimen-t depicted in Figures 1-4, as well as the other embodimen-ts herein described in more detail hereafter, is the flared configuration of -the nozzle 14 relative to the corona charging zone located proximate the edge 46 of the resistive electrode sheet 44. More particularly, -the nonconductive, flared outer portion of the nozzle 14, which is located outwardly and rear-wardly of the corona charging zone proximate perimeter 46, functions as an electrostatic shield which effectively shields electros-tatically-charged coating particles at the exit end of the nozzle from the electrically grounded handle 11, reducing the tendency of a parasi-tic leakage current ~r~
~2S~3~
to be set up between the deflector and the handle 11.
Were -the shielding omitted, the grounded hand 11 would tend to electrostatically at-tract the charged coating particles, set-ting up an undesirable leakage current, and thereby reducing the charging energy available at the deflector and the trans-fer efficiency.
This is particularly -true in view of the fact tha-t -the grounded handle is typically located at approximately the same dis-tance from the corona charging zone, albeit rearwardly thereof, as the object being coated which is electrically grounded and located forwardly of the gun nozzle. Tests have shown that removel of the portion of the flared nozzle 14 located radially beyond the perimeter 46 of -the deElector, which in turn eliminates the electrostatic shielding between the deflec-tor perimeter and the electrically-grounded handle 11, significantly reduces the -transfer efficiency.
While in the embodiment shown in Figures 1-4, the forward extrimity or lip 14a of the nozzle 14 is located slightly rearwardly rela-tive to -the edge 46 of the resistive electrode sheet 44 r the position of -the lip 14a relative to the electrode shee-t edge 46 can be varied, such as by locating -the flared nozzle mouth or lip 14a radially opposite the electrode sheet edge 46a or forwardly thereof (lef-twardly as viewed in Figure 2). Regardless of the exact location of flared nozzle mouth or lip 14a relative to the edge 46 oE the ~;~S4Q3~
resistive sheet 44, a-t least a portion of the noncon-ductive flared nozzle 14a must be located radially outwardly and rearwardly of the corona charging zone proximate edge 46 of resistive sheet 44 such that electrostatic shielding is provided between the electrostatic charging corona zone and -the electri-cally-grounded handle ll.
In the preferred embodimen-t, the electro~
s-tatic shield is described in connection with its use in a powder gun. As noted, it can also be used -to advantage in a liquid coa-tin~ gun wherein charged atomized paint par-ticles are pro~ima-te -the gun nozzle.
Because of the resistive nature oE the charging disc 44, the electrostatic spray gun oE this invention has been found to prevent igni-tion when subjected to standard ignition tests performed by Nordson Corporation, assignee of -the present applica-tion. In practice, -the disc 44 provides a resistance of l.0 Megohn - 1.5 Me~ohn when measured between the center which contacts conductor 70 and the periphery 46.
The composite or sandwich construction o~
the combined powder deflector and electrode charging assembly 16 is extremely durable and inexpensive, and yet is very effective both as a deflector and as an electrostatic charging electrode configuration.
If desired, the charging disc can be mounted on the fron-t surface 40, such that it faces forward -i rr~
3~
and ls exposed, ra-ther than be sandwiched between members ~IOa and 42a. However, the sandwich construc-tion is preferred.
In the embodimen-t of Figures 1-4, as described, the deflector 16 is principally fabricated of insulative sections 40a and 42a. If desired, -the deflector could be fabricated of resistive or semicon-ductive material, or possibly even conductive material, providing the multi-point electrode is located at the periphery thereof. With such a construction, suitable resistance is preferably provided in series with the multi-point electrode to avoid unsafe elec-trical discharges of electrical energy stored in the gun should the multi-point electrode be acc:identally grounded.
In accordance with the embodiment depicted in Figures 5 and 6, only the deflector assembly of which is shown, the nonconductive deflector 100 is seen to have the same general overall shape as the deflector of the embodimen-t of Figures 1-4. More particularly, the deflector 100 has a rear surface 102 against which the par-ticle-entrained air stream is directed in a generally axial (horizontally as viewed in Figure 6) direction as it exits from the nozzle of the gun in a forward (leftwardly as viewed in Figure 6~
direction. The deflector 100 also includes a generally circular flat front surface 104, which if desired could be either concave or convex. Embodied ,. ~ .
-irc~
-25~ 3~
in the deflector 100 and pr~j~cting radially outwardl~
from the periphery 106 theIe~f in a dir~cti~n ~rans-verse to the deflected path of th~ powder s~ream ~re plurality of electrode elements :ID8~ for e~ample~ in the form of electrically con~uct:ive wires o~ needles~
The electxode elements 108; o which there ~re six shown in the preferred embodime~t o~ Figures ~ and 6 although a lesser or greater ~umber can ~e used~ are circumferentially spaced at substantially equal intervals around the peri~hery 106 of the ~e~lector.
Resistive circuit paths in ~he ~Drm of discrete radially disposed resistors 112 interconnecting each of the elect.rodes 108 to a rentral, axially disposea electrical conductor 110 which c~nnects to a r~mote hiyh voltage source (not shown). The resistors 112, which are incorporated in the ~ody-of the.deflector between front and rear sur~aces 104 and 102, have a resistance, in the presently preferre2 embodiment, of, for example, 10 Megohms, alth~g~ ot~er ~esistance values may be used, if desired. In accoraance with variant of the embodiment actuaIly shown in Figures ~
and 6, the radially projecting electrodes 108 co~ld be made flush with the perimet~r lOS ~f the deflector 100, thereby avoiding the possibility o~ aamage *~ the electrodes.
In accordance with a still f~rther preferred embodiment of the invention depicted in:Fig~res 7 and 8, of which only the deflecto~ assembly is shown, an ~5~30 electrostatic spray gun is provided in which the nonconductive deflector 130 is seen to have the same overall configuration as the deflector 100 shown in the embodiment of Figures 5 and ~O More particularly, deflector 130 includes a front surface 134, a rear surface 132, and a perimeter 136. Like the deflector shown in Figures 5 and 6, the deflector 130 shown in Figures 7 and 8 incorporates in its body a plurali-ty of resistive circuit paths in -the form of radially disposed discrete resis-tors 142 which at their inner end have leads 142b which are connected in common to an axially disposed electrical conductor 144 which in -turn is connected to a remote high voltage source (not shown). The radially outward ends o~ resistors 142 have leads 142a which terminate in a circumferential groove 148 formed in the periphery 136 of -the deflector 130. Located in the groove 148 is a circumferentially-disposed silicon carbide thread or narrow ribbon 150.
The radially outboard ends of resis-tor leads 142a are electrically connected with their respectively proxi-mately located segments 130a of -the silicon carbi~e thread 150. If desiredr a resistive material other than silicon carbide can be used for the peripheral.ly located ribbon or thread 150.
In -the embodiment of Figures 5 and 6, corona charging takes place at the radially outboard ends of the electrodes 108 pas-t which the powder passes on its path -toward the object to be coated. In -the variant ` - 26 -jrc:l:
J3~
of the embodiment shown in Figures 5 and 6, wherein the electrodes 108 are flush wi-th -the perimeter 106 of the deflector 100, corona occurs at the point where the electrode joins the periphery 106 of the deflec-tor.
In the embodiment shown in Figures 7 and ~, wherein a silicon carbide thread or ribbon used, corona occurs at random locations around the surface of the -thread 150. If the thread 150 is fabricated of intertwined fibers of short length relative to the circumference of the deflector perimeter 106, corona willm~st probably occur where the fibers terminate since -the ends thereof 150a (see Figure 8) ~unction as electrodes -to form corona charging points. If the silicon carbide thread does not contain short lengths of fiber wi-th plural randomly located ends, corona will occur at randomly located points around the periphery of the silicon carbide -thread 150, the location of which points will change more or less continuously.
In the embodiment of Figures 7 and 8, the thread 150 in deflec-tor groove 148 is efEectively a continuous circular electrode comprised of six arcuate elec-trode elements or segments which are interconnec-ted end--to-end. The continuous circular electrode 130 functions in a manner analogous to -that of the periph-ery 46 of the disc-shaped resistive .sheet ~4 of Figures 1-4 which, in effect, a-t its periphery is also a continuous circular electrode comprising plural .~ - 27 -jrc~ s L~ f3 peripheral arcuate electrode elements or seyments connected end-to-end.
Instead of the silicon carbide resistive fabric 44 shown in Figures 1-4, the multi-point electrode can take the form of a sawtooth edge 200 on the periphery of a disc 202, as shown in Figure 9.
The disc may be fabricated of the same material throughout, such as a resistive, semiconductive, or conductive material. Alternatively, the disc 202' may be a composite having an annular outer section 203 with teeth 200' at the periphery, and an inner circular section 205, as shown in Figure 10. The inner section 205 and/or the outer section 203 may be resistive, semiconductive, or conductive.
Alternatively, disc 44, instead of being entirely of silicon carbide fabric, or other resistive material, as shown in Figuxe 4, could be of composite construction ac shown in Figure 11. More particularly, the resistive fabric 210 could be annular shaped, with the remainder of the disc 211 comprising an inner circular disc 212 of resistive, conductive, or semicon-ductive solid sheeting.
Also, instead of constructing the multi~point electrode of resistive fabric, as shown in Figure 4, such as silicon carbide fabric, the electrode could be constructed of screen or mesh, with the strands thereof being resistive, conductive, or semiconductive , .
~S~3C~
wire or nonconductive wire clad with re~istive, conductive, or semiconductive material.
Figure 12 depicts an insulative gun barrel 230 having a longitudinal circular cross-sectional bore 231 ~erminating in an opening 232 in face 233 from which is emitted coating pa:rticles. Located coaxially within the bore 231 is an insulative column 234, at the outer end of which a multi-point electrode 235 is mounted. Electrode 235 may alternati~ely be constructed like any of the electrode configurations or structures shown in Figures 4-11. In the E'ig. 12 embodiment, like Figs. 4-11, electrode 235 has a peripheral edge 235' which includes multiple electrodes projecting therefxom. The electrode 235 connects to a source of electrostatic voltage via an electrical conductor (not shown) located with column 234. The device of Figure 12 provides a circular spray pattern.
Figure 13 depicts an insulative barrel 240 having an upper rectangular cross-sectional longitudi-nal bore 241 and a lower rectangular cross-sectional longitudinal bore 242 separated by an insulative longitudinal column 243. Mounted on the outer end of column 243 is an electrode 244 having an upper multi-point electrode edge 244 and a lower multi-point electrode edge 245 for charging coating particles emitted from upper and lower bores 243 and 242, respectivel~. Electrode 244 is constructed similarly to electrode 235 of Figure 12. The electrode 244 ~25~3~
connects to a high voltage supply via an el~ctTical conductor (not shown) within column 243. Th~ ~m~odi-ment of Figure 13 provides a flat fan-shaped spray pattern.
The embodiments of Figures 5-13, li~e the embodiment of Figures 1-4, provide improved ~ransfer efficiency due to the multi-point electrode ro~figura-tion, and constitutes electrode assemblies which ~r~
inexpensive and simple in construction.
From the above disclosure of the geneIal pxinciples of the present invention and the ~receding detailed description of the preferred embodimients thereof, those skilled in the art will readily compre-hend the vari.ous modifications to which the p~esen*
invention is sus- ceptible. Therefore, I de~ire to ~e limited only by the scope of the following claims and equivalents thereof:
~4--efficiency". It is generally believed ~y thos~
skilled in ~he ar* tha* transfer efficiency an ~2 increa~ed by increasing the charge vn the particles and/or by increasing the strength o~ the elec*rostatic i field between ~he gun and ~he aLrticle ~eing coated.
Accordingly, i* has ~een an objectiY~ of this invention ~o co~struct an electrostati~ spray gun which will ~oth increase the charge vn the particl~s 1~ and the strength o the electrostatic field between gun and article ~eing coated, and there~y ~rouide improved powder coating transfer efficiencyO This o~jective has been accomplished by pro~i~i~g a particle spray device, which has an opening from which a stream 1~ of particles i9 sprayea in a forward path toward an object to ~e electrostatically coated, with a multi-point electrode comprising a subs~antial num~er of closel~- sp2ced electro~e elemen*s locatea ~oxima~
the opening through which the particle stream pas~es.
2~ Energization o~ the multi-point electrode from a high voltage electrostatic supply results in the creation of A plurality of corona charging points proximate the particle stream, there~y enhancing coating transfer e f ~iC iency.
~ In one preferred embodime~t of a powder spray gun, a def lector is provided in the nozzle powder stream path which is constructed of electrical-~zs~
ly nonconductive material, and which has a~ a rear surfac~ upon which the forwardly directea pDwder ~tream Impinge~ ana as a ~esult ther~of b~c~
deflected intD the desired s~rel~m configuration, ~ a front surface facing the forward d-rectio~, nd c3 a subs~antial number o~ electrode elements circumferen-tially spac~d aro~nd the perimetex o~ t~e defle~tor which are ~o~nected tD ~ high vDltage source via associated resisti~e paths incorporatea in the de1ec-lD tor. These electrode elements collectively ~unctionas a multi-pDint electrode tD provide a pl~rality of corona charging points when the electrode is Pnergi2,ed.
In the one preferred embodiment descTibed above, the multi-pDint electrode is in the form of a 1~ fibrous resistive sheet constructed from a mateIial such ~s ~ilicor carbi~e, which is iDcorporated in the deflector between the front and rear surfaces thereo~
to define as its periphe.^~, which is proximate to the ~eflector periph~ry7 a large number of raaially : 20 ~rranged electrode elements which establish a plurali~y of corona charging points past which the de~lected powder stream passes to be electrostatically cha~ged as the powder particles are s~rayed from the gun~ In - this embodiment, in which the substantial number of 2~ radially arranged electrode elements ~ircum~erentially spaced around the de~lector periphery ~unction tD
establish a plurality of corona charging points, the .
~2S9L~
resistive sheet located radially inwardly o~ the electrode elements fune~ion~ as resis ive ~aths ; ~ incorporated in the deflector through which the electrode elements are energized from a suitable high voltage source~ While a silicon carbide material is preferred f~r use as the resis~ive sheet in this :- embodimen~l o*her ~ rous resistive material~ may also be suitable.
An important adva~tage o~ the foregoing embodiment of this inventi~n is that the peripheral edge of the silicon car~ide sheet includes the en~s of the many silicon car~ide fibers fonming the resistive sheet and these fiber ends form a multitude of radially arranged electrode elements which ~stablis~ ~ ~lurality of corona charging points which charge the ~owder particles-^as t~ley are sprayed. This deflecto~ struc ture is believed to both increase the charye trans-~erred to the powder particles, and to increase the str~ngth of the electrosta~ic field between the gun 2~ and the workpiece, to enhance coating transfer effi-ciency. Another advantage is that the deflector stxucture, particularly the resistive paths and ~lural circum~erentially-arranged electr~de el~ment~, is ~relatively inexpensiYe, easy to manufacture, and 2~ durable. It i~ also readily replacea~le shoul~ such become necessary. These attributes ~nha~ce the attxacti~eness of the g~n from a commercial standpoint.
In the foregoing form o~ the i~vention, the silicon carhide sheet has a cen~rally dispo~ed ~ig~
vol-tage texminal region remo~ fro~ *he edge thsreo~
for establishing an electrically resis~lve curren~
flow path through th~ sheet between the ~entral terminal region whereat high voltage i~ ~up~ d and the peripheral ~dge w~e~at co~Dna ~harginy ~i the powder particles occurs from *h,e many silicon c~rbid~
fiber ends. This resistive path cDnsti~ute~ a re~a-tively large xesistor and functions to minimizeignition h~zards due to inadvertent discharge of electrical energy capacitively s-~ored in the s~ray coating system of which the gun is a major ~omponent.
In another ~referred embodiment of this 1~ invention, the circumferentially spacea electro~e elements aroun~ the ~eflec*o} perimeter are in the ~orm of discrete, fixed electrodes in the f~r~. of electrically conductive needl~s or wires which project radially outwardly from the perimeter of the d~fl~c~or~
- 20 -~ach of the discrete electrDde~ is connected tD 2 high voltage source via a discrete resistor:embodied in the deflector. If desired, the radially disposed elec-trodes can be made fl~sh with the deflector peri~hery in lieu of projecting outwardly th~rerom, there~y reducing the likelihood of electrode dEmage.
In accordance with a still further, and also preferred, embodiment of the invention, the deflector : is provided with a.relatively narrow silicon carbide -- ~54~3V
ribbon or t~lread, which ~unction as cir~umf~entially arrang~d electrode el~ment~i ~ia disc~eet resist~ls embodied in the deflec~or ~hic~ are radially ~i~pose~
and cir~ferentially spaced within the defl~ctor~
I~ *he em~odiments of the i~vention utili~ing discreet xesistor~ embodied in the defl~ctor to interconnect ~he high voltage ~ource and ~he ~irc~m-~erentially ~paced el~trode elements on *he ~fle~to~
p~riphery, the resistors function tv minimize ignîtion hazards au~ to inadvertent elec~rical energy dis~
charges, thereby enhancing the safety oE the gun.
In accordance with a further aspect of the invention which can ~e advantageously incorporated into each of the f~reyoing emb~dIments, the nozzle 1~ lvcate~ at the forward end o~ t~e nonconduc~i~e ~un arrel is prvvided with an electrosta~ic shield. The shield is disposed outwardly and rearwardly of the pe~imeter of *he deflect~r whereat the corona c~arging points ar~ located which ~lectrost~$i~ally charg~ the 70 aeflected powder stream as it p~sses through the '' annular opening ~etween the nozzle and the conically-shape~ ae~lector which is axially disposed in the powder flow path. In a ~l~f~r~ed form, tne ~le~t~o-static shield is formed ~y flaring the end of ~he noz~le in the Iegion surrounding the forwara end of the conical deflector, particularly the perimet~
thereof, from which extend the corona charging points.
In practice, the electrostatic shield has ~een ~ollnd ~S~3~
to significantly improve the transfer efficiency when compared to a similarly-constructed spray device which does not have the electrostatic shield.
By way of background, and as an aid to understanding how the electrostatic shield of this invention enhances transfer efficiency, in a typical electrostatic spray gun of the type having an electrically-grounded handle or mounting member, the corona zone proximate the periphery of the deflector is approximately midway between the grounded gun handle or mounting member which is located rearwardly thereof and the electrically-grounded object being coated which is located forwardly thereof. By way of example, the distance between the grounded object being coated and the corona charging zone is approximately ten inches, which is approximately the same as the distance between the corona zone at the gun nozzl.e and the rearwardly-located electrically-grounded gun handle or mounting member. Without the electrostatic shielding outboard and behind the corona charging zone proximate the periphery of the deflector, the electrically-charged coating particles issuing from the gun nozzle are as close to the grounded article being coated as is the grounded gun handle or mounting member, with the result that some charged particles are electrostatically attracted to the grounded gun handle or mounting member, impairing the efficiency of the coating transfer process.
LCM:mls .~
~5~3~
In addition, because the gun handle, or moun-ting hardward, provides an attraction to some of the charged particles, a corona current: path is set up be-tween the deflector and the grouncle~ handle which causes the available elec-trical energy for charging at the deflector to be reduced by parasitic discharge.
The reduction in available charging energy at the deflector, results in a corresponding reduc-tion in -transfer efficiency. Therefore, by inclusion of the electrostatic shield of this invention, the effect of the electrically-ground gun handle or mount in terms of attracting elec-trostatically-charged particles and of providin~ a parasitic curre~t leakage path is subs-tantially reduced, with the result that -transfer efficiency is significantly increased. This is a substantial improvement in transfer efficiency in comparison to -the result if the electrostatic shield-ing in the nozzle surrounding the deflector periphery is ommitted.
The electrosta-tic shield can be used advantageously with the guns, manual or automatic, which are designed -to spray coating par-ticles of ei-ther the atomized liquid or powder type.
In accordance with still other embodiments of the invention, the multi~point electrode is in the form of a disc with a sawtooth perimeter. The entire disc may be fabricated of resistive, semiconductive or conductive material. Al-ternatively~ the disc may be , -~
1~S~3~
of a comp~site construc~ion with an inner ci~cular section, ana an out~r annular ~ection with ~eeth at ~he peripheryO The inn~r and~Dr ~uter sec~ions ~ay ~e conductive, resistive, or semic:onductiYe solid sheet, fi~rous or mesh material~ In lieu of the inner circu-lar section, a series of electrical wires connected to ~he ~nnular section may ~e used to tr ns~ort high voltage to the toothea periphery thereof In ano~her form, the multi-point electrode 10 may be a disc-shaped mesh o~ conductive, semiconduc-tive, Dr resistiv~ wire, or nonc~nductive wir4 havinq a ~l~d~ing of conductive, semiconductive, ol resisti~e materialO
In another embodiment, use~ul in a powder gun ha~ing a deflector, the deflectDr is fabricated o~
..injection molded ~aterial containing.silicon carbide or other resistive fi.bers, particularly a* the per-.imeter thereof, which functiDn as multi-point elec-trodes. ~he deflecto~ may also include semicondllctive, 2D resistive~ or conductive material t~ tran~port ~he high voltage to the ~ilicon carbide ~ibers at the deflector perImeter~ Instead of silicon carbide fibers at the peliphery of.*he deflector, ~ multi -- point electrode could be provided by mounting a large .25 number of electrodes in ~he deflector ~erimeter to function as multiple elec*rodesO
:In any of the-aforementioned embodiments, it is desirable ~o pro~ide ~esis~ance s~fficiently close 3{~
to the multiple electrodes and in sufficient amount to avold unsafe elekrical discharges should electrical energy capacitively stored in the gun suddenly become discharged by -the approach of a grounded article to the multipoint electrode.
The multi-point electrode aspect of this invention, while described in connection with a powder gun having a deflector, is also useful in atomized liquid spray devices. In such devices the multi-point electrode is mounted in the nozzle region proximate the path of atomized liquid particles being emit-ted from the nozzle toward -the article -to be coated in much the sa~e manner that the multi-point electrode :is mounted in the deflector of a powder gun pro~imate the path oE the emitted powder particles.
These and other ojectives, advantages, and fe~-tur~sof-the invention will become more readily apparent from a de-tailed description of the invention taken in conjunction with the drawings in which:
Figure 1 is a side elevational view, partly in cross section, depicting the principal components of one embodimen-t of an electrostatic powder spray gun incorporating the invention;
Figure 2 is an enlarged side elevational view in cross section, showing the forward end of the powder gun of Figure 1, including the nozzle~ deflector, and powder-charging electrode.
jrc~
~5~3~
Figure 3 is a cross sPction 1 ~i~w along line 3~3 of FiguIe 1.
Figure 4 is a front e:le~i~nal view, o~ the nozzle of the gun of Figure 1, depictin~ the deflec~or partially cut-away to show the xesistive fibrous ~heet~
Figur~ ~ is B ~ont eLevational view of deflectr:r 7 incorporating radially outwardly ~rojec~in~
elec~rodes and discre~e resisiors, o~ another embodi men* o~ the invention.
Figure 6 is a sid~ elevational view of the de~lector of Figur~ ~.
Figure 7 is a front elevational view of a deflector, incorporating a silicon carbide ribbon or 1~ thread in the rim thereo~ ana discrete xesistors, o~ a . still u~t~er embodiment of the in~ention.
Figure 8 is a side elevational view of the deflectDr o~ ~igur~ 7.
Figure 9 is a ~ront elevational view of a multi-point electrode in the form of a sawtooth-edgea disc o~ uniform construction throughout.
Figure 10 is a front elevational view of a mu~ti-point ele~trode in tAe fDxm of a s~wtooth-edge~
disc o~ EOmpOsite construction~
Fig~re ll is a front ~levational view of a multi-point electrode in the form of a composite disc ~avlng an outer annular ia~ric~ mesh or screen section and an inner solid ci~cular section.
~54~3~
Figure 12 is a front perspective view of the barrel of a spray device having a circular spray pattern, which uses a multi-point electrode to charge the coating particles.
Figure 13 is a front perspective view of the barrel of a spray device having a flat spray pattern, which uses a multi-point electrode to charge the coating particlesO
With reference to the figures, one preferred form of electrostatic spray gun incorporating the present invention is depicted. In the preferred embodiment of the spray device 10 is in the form of a gun having an electrically grounded conductive handl~ ll and a nonconductive or insulative barrel 12 which at its forward end terminates in a flared nozzle 14 having a central flared opening 15 from which projects a combined powder deflector and electrode charging assembly 16.
Except for the assembly 16, the preferred embodiment of the spray gun can be constructed in accordance with the teachings of United States Patent No. 4,634,058 entitled "Improved Powder Spray Gun", in the name of Thomas E. Hollstein, David E.
O'Ryan, and Joseph C. Waryu, assigned to the assignee of the present application.
LCM:jj ~2~ 3~3 ~ he ~arrel 12 includes an intern~l p~wder entry chamber 17 which at its rearward end com~unicates with a powder-entrained ~ess~ri.zed ai r s~pply hos~
13a via a port 13 in the barrel wall~ ~he int~rnal powaer entry chamber 17 at its fvrwaId end communicat~s with the nDzzl~ openi~g lS via a ta~ered bore 19 ~nd intermediate cham~er 21. A nonconductive mo~nting stub 22 for th~ de~lect~r an~ electrode assem~ly 1 extends axially ana Eorwardly ~rom a nonc~nductive spiaer 2~ locate~ within ~he in$ermediate cha~er 21.
Extending axially and reaYwardly from the ~pi~er 2~ is an electrically insulated conductive path ~9 incDrpor-ating a conductor 76 Ito ~e descri~ed) which extend~
through a stepped diameter bore 30a ~nd 30b wh~re i~
1~ makes an appropriate conne~tion with an insulated high ~oltage supply ca~le 26 which passes ~hrough the handle 11 exiting the butt thereof at 24 where it connects to a remote high voltag~ ele~trostatic power supply Inot shown).
The hanale 11 is provided with a m~vable trigger 34 which when activated supplies pressurized powder-entrained air to the pGwder entry cham~ex 17 . . Yia hose 13a~ Trigger 34 ~lso en2rgizes the remcte high voltage supply to provide high vol~age electro-2~ static power to an electrical conauctor 7D (l~ter described) which is axially di~posed within the powder deflector:.16. ~he conductor 7D is connected to the high voltaye supply by high voltage cable 24, 26 and the electrically insulat~d conductive ~ath ~9 whic~
passes through the mounting stu~ 22 and s~ider 2~.
The powder-en*rained air passes ~naer pres~ure from the entxy cham~er 17 successively through *he tap~red bore l9 and intermediate chamber 21 to the ~lared nozzle opening 15 wherea~ it is divert~d into a conical path and electros~atically charged ~y ~e electrode, to be de~cribed, incorporated in *he ~der deflector and electrode charging assembly 1~. The lD powder exits the nozzle opening in a generally conical pattern of elec*rostatically charged parti~les for impingement upon an electrically grounded articl4 (DDt shown) to be coated~
r~he powder deflector and elec rode ~harging assem~ly 167 considered in more detail in ~Dnnection with Fig. 2, is ~enerally conical in shap~ ~a~ing a circular flat front surface 40 and a conical rear ~: surface 42. ~ront surface 40 ~ould also be conv x Dl concave, i~ desired. A ~esistive sheet electrDde i~
the ~orllZ of a circular wafer or: disc 4~ is lc~cated iD
a boundary region between the frDnt and rear surfaces 40 and 42. The edge 46 of the resisti~e elec*rode sheet or disc 44 is ~re~erably flush:with the edges - 40' and 42' of the frcnt and rear surfaces 40 and 42.
: 25 In a preferred form of the invention, the powder deflector and electrode charging assembly 16 is a composite:or sandwich assembly which in~ludes the intermediate resistive electrode disc:-44, a circular ~S~L~3~
insulating disc 40a having a diameter equal to that of the resistive electrode di~c 44, and a conical insulating section 42a the rearward surface of which constitutes the powder deflecting conical surface 42. The conical section 42a, resistive electrode disc 44, and disc 40a can be permanently assembled to form an integral unit utilizing commercially available adhesives. Alternativaly, the resistive sheet could be molded into the deflector.
In a preferred form of the invention the resistive electrode disc 44 is fabricated of nonwoven silicon carbide fabric embodying randomly oriented silicon carbide fibers or filaments in a resin matrix. The silicon carbide fibers or filaments from which the fabric is made have the physical and electrical characteristics of Nicalon fiber of the general type disclosed in United States Patent No. 4,100,233 and commercially available from Nippon Carbon Co., Ltd., Tokyo, Japan, and Dow Corning, Midland, Michigan. In a preferred embodiment the silicon carbide fibers are heat treated to provide a specific resistivity of 1 X 103 ohm-cm., and a fiber diameter in the approximate range oE 10-15 microns. The following publications of Nippon Carbon Co., Ltd., Tokyo, Japan, available from Dow Corning, Midland, Michigan, contain information on Nicalon fibers:
LCM:jj ,~'' ' .~ .
~5q~330 Nicalon Silicon Carbide Fiber, 12 payes;
Price Listing Effective 1-1-84, Nicalon Silicon Carbide Fiber Products Distributed by Dow Corning Corporation, 2 pages; and Industrialization of Silicon Carbide Fiber and Its Applications, by Jun-Ishi Tanaka, Executive Director, Nippon Carbon Co., Ltd., 11 pages.
Nicalon con-tinuous silicon carbide fiber, in one commercially available form, is physically charac-terized as follows:
Filament Diameter: 10-15 microns, Cross Section: round Density: 0.093 pounds/inch3 ~2.55 g/cm3), Tensile Strength: 360-470 ksi (250-300 kg/mm2), Tensile Modulus : 26-2g x 103 ksi (18-20 x 103 kq/mm2), and Coefficient of Thermal Expansion (parallel to Fiber): 3.1 x 10 6/oC.
The specific resistivity of Nicalon silicon carbide fiber which is uniform -throughou-t the fiber and independent of fiber flexure, can be varied by heat treating the fiber at differen-t temperatures subsequent to spinning. The variation in specific resistivity as a function of heat treating temperature can vary by a factor of approximately 104 from approxi-mately 102 ohm-cm to 106 ohm-cm.
~ ~ .
~ZS~6?3~
The Nicalon continuous silicon carbide fibers can be formed into woven abric, as well as nonwoven Eabric of random fiber orientation. In addi-tion, the resistive silicon carbide disc 44 can be fabricated of resin impregnated Nicalon fabric composite, glass Nicalon fabric composite and/or Nicalon fibers in a ceramic ma-trix.
The insulative fron-t disc 40a and insulative conical deflector 42a can be fabricated of a variety of nonconductive materials including glass-filled Teflon plastic, Delrin plastic, and the like.
~he d~flector/electrode assembly 16 is mounted to the s-tub 22 by the axial engagement of a reduced diameter sec-tion 22a at the forward end of the mountlng stub 22 and a blind hole or bore 64 formed in the rear central portion of -the conical deflector 42a.
The bore 64 and reduced diameter end 22a of the stub 22 are dimensioned -to provide a snug sliding fit therebetween.
As noted previously, electrostatic energy is trans-mitted from a remote power supply (not shown) to the resis-tive charging disc 44 via the cable 24, 26 and -the electrically insulated resistorized conductive path 29. Conductive path 29 includes an electrical conductor (or electrode) 70 which projec-ts axially from the end of the mounting stub 22 into a sui-tably provided axial passage in -the conical deflector section 42a to establish electrical contac-t wi-th the ~ 19 -;, .
~rc~
~Sg~l~3~
resis-tive disc 44. The conductor 70 is connected to the electrically conductive core of the cable 26 via a resistor 75 and electrical conductor 76 which consti-tute further elements of conduc-tive path 29, and which are in elec-trical series circuit arrangement between the conductor 70 and the conductive core of the high voltage cable 26.
In operation, when the trigger 34 is ac-ti-vated, powder-entrained pressurized air is introduced into -the internal powder en-try chamber 17 via the hose 13a whereupon it flows through the -tapered bore 19 into the intermediate chamber 21 where is passes through the spider 25 and impinges on the rear surEace 42 of the conical deflector 42a which causes -the path of -the powder to deflect and form a conical path as it exits the flared opening 15 of the nozzle 14 toward the ar-ticle or -target substrate to be coated (not shown).
Activation of the trigger 34 also energizes a remote power supply (not shown) -to cause high vol-tage electro-static energy to be supplied to the resistive charging disc 44 via the electrical pa-th previously described.
With the resistive charging disc 44 main-tained a-t a high electros-tatic voltaqe, such as 90 Kv, a corona discharge is produced at the multitude of resistive material fiber ends 46a located around the perime-ter 46 of the resistive charging disc ~4,causing electrostatic charge to be imparted -to the stream of powder as it exits the flared opening 15 of nozzle 14 subsequent to deflec-tion by the rear conical deflecting surface 42.
Experience has shown that higher coating transfer efficiencies canbe achieved with the electro-static spray coating gun of this invention. In practice, the number of corona points,as well as their precise loca-tion around the periphery 46 of -the resistive charging disc 44, is somewhat variable. At no load voltages of 90 Kv with a charging disc 44 having a diameter oE approximately 1 lJ2 inches and a thickness of approxi-mately 0.65 mm, anywhere between three and eight corona points have been observed to simul-taneouly occur at peripheral locations which are con-tinuously changing on a more or less random basis.
Con-tributing in a material manner to -transfer efficiency enhancement provided by the preferred embodimen-t depicted in Figures 1-4, as well as the other embodimen-ts herein described in more detail hereafter, is the flared configuration of -the nozzle 14 relative to the corona charging zone located proximate the edge 46 of the resistive electrode sheet 44. More particularly, -the nonconductive, flared outer portion of the nozzle 14, which is located outwardly and rear-wardly of the corona charging zone proximate perimeter 46, functions as an electrostatic shield which effectively shields electros-tatically-charged coating particles at the exit end of the nozzle from the electrically grounded handle 11, reducing the tendency of a parasi-tic leakage current ~r~
~2S~3~
to be set up between the deflector and the handle 11.
Were -the shielding omitted, the grounded hand 11 would tend to electrostatically at-tract the charged coating particles, set-ting up an undesirable leakage current, and thereby reducing the charging energy available at the deflector and the trans-fer efficiency.
This is particularly -true in view of the fact tha-t -the grounded handle is typically located at approximately the same dis-tance from the corona charging zone, albeit rearwardly thereof, as the object being coated which is electrically grounded and located forwardly of the gun nozzle. Tests have shown that removel of the portion of the flared nozzle 14 located radially beyond the perimeter 46 of -the deElector, which in turn eliminates the electrostatic shielding between the deflec-tor perimeter and the electrically-grounded handle 11, significantly reduces the -transfer efficiency.
While in the embodiment shown in Figures 1-4, the forward extrimity or lip 14a of the nozzle 14 is located slightly rearwardly rela-tive to -the edge 46 of the resistive electrode sheet 44 r the position of -the lip 14a relative to the electrode shee-t edge 46 can be varied, such as by locating -the flared nozzle mouth or lip 14a radially opposite the electrode sheet edge 46a or forwardly thereof (lef-twardly as viewed in Figure 2). Regardless of the exact location of flared nozzle mouth or lip 14a relative to the edge 46 oE the ~;~S4Q3~
resistive sheet 44, a-t least a portion of the noncon-ductive flared nozzle 14a must be located radially outwardly and rearwardly of the corona charging zone proximate edge 46 of resistive sheet 44 such that electrostatic shielding is provided between the electrostatic charging corona zone and -the electri-cally-grounded handle ll.
In the preferred embodimen-t, the electro~
s-tatic shield is described in connection with its use in a powder gun. As noted, it can also be used -to advantage in a liquid coa-tin~ gun wherein charged atomized paint par-ticles are pro~ima-te -the gun nozzle.
Because of the resistive nature oE the charging disc 44, the electrostatic spray gun oE this invention has been found to prevent igni-tion when subjected to standard ignition tests performed by Nordson Corporation, assignee of -the present applica-tion. In practice, -the disc 44 provides a resistance of l.0 Megohn - 1.5 Me~ohn when measured between the center which contacts conductor 70 and the periphery 46.
The composite or sandwich construction o~
the combined powder deflector and electrode charging assembly 16 is extremely durable and inexpensive, and yet is very effective both as a deflector and as an electrostatic charging electrode configuration.
If desired, the charging disc can be mounted on the fron-t surface 40, such that it faces forward -i rr~
3~
and ls exposed, ra-ther than be sandwiched between members ~IOa and 42a. However, the sandwich construc-tion is preferred.
In the embodimen-t of Figures 1-4, as described, the deflector 16 is principally fabricated of insulative sections 40a and 42a. If desired, -the deflector could be fabricated of resistive or semicon-ductive material, or possibly even conductive material, providing the multi-point electrode is located at the periphery thereof. With such a construction, suitable resistance is preferably provided in series with the multi-point electrode to avoid unsafe elec-trical discharges of electrical energy stored in the gun should the multi-point electrode be acc:identally grounded.
In accordance with the embodiment depicted in Figures 5 and 6, only the deflector assembly of which is shown, the nonconductive deflector 100 is seen to have the same general overall shape as the deflector of the embodimen-t of Figures 1-4. More particularly, the deflector 100 has a rear surface 102 against which the par-ticle-entrained air stream is directed in a generally axial (horizontally as viewed in Figure 6) direction as it exits from the nozzle of the gun in a forward (leftwardly as viewed in Figure 6~
direction. The deflector 100 also includes a generally circular flat front surface 104, which if desired could be either concave or convex. Embodied ,. ~ .
-irc~
-25~ 3~
in the deflector 100 and pr~j~cting radially outwardl~
from the periphery 106 theIe~f in a dir~cti~n ~rans-verse to the deflected path of th~ powder s~ream ~re plurality of electrode elements :ID8~ for e~ample~ in the form of electrically con~uct:ive wires o~ needles~
The electxode elements 108; o which there ~re six shown in the preferred embodime~t o~ Figures ~ and 6 although a lesser or greater ~umber can ~e used~ are circumferentially spaced at substantially equal intervals around the peri~hery 106 of the ~e~lector.
Resistive circuit paths in ~he ~Drm of discrete radially disposed resistors 112 interconnecting each of the elect.rodes 108 to a rentral, axially disposea electrical conductor 110 which c~nnects to a r~mote hiyh voltage source (not shown). The resistors 112, which are incorporated in the ~ody-of the.deflector between front and rear sur~aces 104 and 102, have a resistance, in the presently preferre2 embodiment, of, for example, 10 Megohms, alth~g~ ot~er ~esistance values may be used, if desired. In accoraance with variant of the embodiment actuaIly shown in Figures ~
and 6, the radially projecting electrodes 108 co~ld be made flush with the perimet~r lOS ~f the deflector 100, thereby avoiding the possibility o~ aamage *~ the electrodes.
In accordance with a still f~rther preferred embodiment of the invention depicted in:Fig~res 7 and 8, of which only the deflecto~ assembly is shown, an ~5~30 electrostatic spray gun is provided in which the nonconductive deflector 130 is seen to have the same overall configuration as the deflector 100 shown in the embodiment of Figures 5 and ~O More particularly, deflector 130 includes a front surface 134, a rear surface 132, and a perimeter 136. Like the deflector shown in Figures 5 and 6, the deflector 130 shown in Figures 7 and 8 incorporates in its body a plurali-ty of resistive circuit paths in -the form of radially disposed discrete resis-tors 142 which at their inner end have leads 142b which are connected in common to an axially disposed electrical conductor 144 which in -turn is connected to a remote high voltage source (not shown). The radially outward ends o~ resistors 142 have leads 142a which terminate in a circumferential groove 148 formed in the periphery 136 of -the deflector 130. Located in the groove 148 is a circumferentially-disposed silicon carbide thread or narrow ribbon 150.
The radially outboard ends of resis-tor leads 142a are electrically connected with their respectively proxi-mately located segments 130a of -the silicon carbi~e thread 150. If desiredr a resistive material other than silicon carbide can be used for the peripheral.ly located ribbon or thread 150.
In -the embodiment of Figures 5 and 6, corona charging takes place at the radially outboard ends of the electrodes 108 pas-t which the powder passes on its path -toward the object to be coated. In -the variant ` - 26 -jrc:l:
J3~
of the embodiment shown in Figures 5 and 6, wherein the electrodes 108 are flush wi-th -the perimeter 106 of the deflector 100, corona occurs at the point where the electrode joins the periphery 106 of the deflec-tor.
In the embodiment shown in Figures 7 and ~, wherein a silicon carbide thread or ribbon used, corona occurs at random locations around the surface of the -thread 150. If the thread 150 is fabricated of intertwined fibers of short length relative to the circumference of the deflector perimeter 106, corona willm~st probably occur where the fibers terminate since -the ends thereof 150a (see Figure 8) ~unction as electrodes -to form corona charging points. If the silicon carbide thread does not contain short lengths of fiber wi-th plural randomly located ends, corona will occur at randomly located points around the periphery of the silicon carbide -thread 150, the location of which points will change more or less continuously.
In the embodiment of Figures 7 and 8, the thread 150 in deflec-tor groove 148 is efEectively a continuous circular electrode comprised of six arcuate elec-trode elements or segments which are interconnec-ted end--to-end. The continuous circular electrode 130 functions in a manner analogous to -that of the periph-ery 46 of the disc-shaped resistive .sheet ~4 of Figures 1-4 which, in effect, a-t its periphery is also a continuous circular electrode comprising plural .~ - 27 -jrc~ s L~ f3 peripheral arcuate electrode elements or seyments connected end-to-end.
Instead of the silicon carbide resistive fabric 44 shown in Figures 1-4, the multi-point electrode can take the form of a sawtooth edge 200 on the periphery of a disc 202, as shown in Figure 9.
The disc may be fabricated of the same material throughout, such as a resistive, semiconductive, or conductive material. Alternatively, the disc 202' may be a composite having an annular outer section 203 with teeth 200' at the periphery, and an inner circular section 205, as shown in Figure 10. The inner section 205 and/or the outer section 203 may be resistive, semiconductive, or conductive.
Alternatively, disc 44, instead of being entirely of silicon carbide fabric, or other resistive material, as shown in Figuxe 4, could be of composite construction ac shown in Figure 11. More particularly, the resistive fabric 210 could be annular shaped, with the remainder of the disc 211 comprising an inner circular disc 212 of resistive, conductive, or semicon-ductive solid sheeting.
Also, instead of constructing the multi~point electrode of resistive fabric, as shown in Figure 4, such as silicon carbide fabric, the electrode could be constructed of screen or mesh, with the strands thereof being resistive, conductive, or semiconductive , .
~S~3C~
wire or nonconductive wire clad with re~istive, conductive, or semiconductive material.
Figure 12 depicts an insulative gun barrel 230 having a longitudinal circular cross-sectional bore 231 ~erminating in an opening 232 in face 233 from which is emitted coating pa:rticles. Located coaxially within the bore 231 is an insulative column 234, at the outer end of which a multi-point electrode 235 is mounted. Electrode 235 may alternati~ely be constructed like any of the electrode configurations or structures shown in Figures 4-11. In the E'ig. 12 embodiment, like Figs. 4-11, electrode 235 has a peripheral edge 235' which includes multiple electrodes projecting therefxom. The electrode 235 connects to a source of electrostatic voltage via an electrical conductor (not shown) located with column 234. The device of Figure 12 provides a circular spray pattern.
Figure 13 depicts an insulative barrel 240 having an upper rectangular cross-sectional longitudi-nal bore 241 and a lower rectangular cross-sectional longitudinal bore 242 separated by an insulative longitudinal column 243. Mounted on the outer end of column 243 is an electrode 244 having an upper multi-point electrode edge 244 and a lower multi-point electrode edge 245 for charging coating particles emitted from upper and lower bores 243 and 242, respectivel~. Electrode 244 is constructed similarly to electrode 235 of Figure 12. The electrode 244 ~25~3~
connects to a high voltage supply via an el~ctTical conductor (not shown) within column 243. Th~ ~m~odi-ment of Figure 13 provides a flat fan-shaped spray pattern.
The embodiments of Figures 5-13, li~e the embodiment of Figures 1-4, provide improved ~ransfer efficiency due to the multi-point electrode ro~figura-tion, and constitutes electrode assemblies which ~r~
inexpensive and simple in construction.
From the above disclosure of the geneIal pxinciples of the present invention and the ~receding detailed description of the preferred embodimients thereof, those skilled in the art will readily compre-hend the vari.ous modifications to which the p~esen*
invention is sus- ceptible. Therefore, I de~ire to ~e limited only by the scope of the following claims and equivalents thereof:
Claims (64)
1. An electrostatic spray coating system comprising:
a high voltage electrostatic supply for providing electrostatic voltages;
a particle spray device having a particle spraying opening therein from which a stream of particles is sprayed in a path in a forward direction toward an article to be electrostatically coated;
a particle deflector constructed of elec-trically nonconductive material located in said particle path for deflecting said particle stream, said deflector having a) a rear surface upon which said particle stream impinges and as a result thereof becomes deflected, and b) a front surface facing in said forward direction, a resistive sheet located between said front and rear surfaces having a peripheral edge at its outer limits for effectively providing a plurality of corona charging points past which said deflected particle stream passes in its path toward said article to be coated, said resistive sheet having a high voltage terminal region located remote from said peripheral edge for establishing an electrically resistive current path through said sheet between said terminal region and said peripheral edge for the purpose of minimizing shock and ignition hazards due to inadvertent discharge of electrical energy capaci-tively stored in said system; and an electrical path interconnecting said high voltage supply and said terminal region of said resistive sheet to facilitate the production of corona discharges at said peripheral edge of said resistive sheet for electrostatically charging said deflected steam as it flows in proximity thereto in its path toward said article to be coated.
a high voltage electrostatic supply for providing electrostatic voltages;
a particle spray device having a particle spraying opening therein from which a stream of particles is sprayed in a path in a forward direction toward an article to be electrostatically coated;
a particle deflector constructed of elec-trically nonconductive material located in said particle path for deflecting said particle stream, said deflector having a) a rear surface upon which said particle stream impinges and as a result thereof becomes deflected, and b) a front surface facing in said forward direction, a resistive sheet located between said front and rear surfaces having a peripheral edge at its outer limits for effectively providing a plurality of corona charging points past which said deflected particle stream passes in its path toward said article to be coated, said resistive sheet having a high voltage terminal region located remote from said peripheral edge for establishing an electrically resistive current path through said sheet between said terminal region and said peripheral edge for the purpose of minimizing shock and ignition hazards due to inadvertent discharge of electrical energy capaci-tively stored in said system; and an electrical path interconnecting said high voltage supply and said terminal region of said resistive sheet to facilitate the production of corona discharges at said peripheral edge of said resistive sheet for electrostatically charging said deflected steam as it flows in proximity thereto in its path toward said article to be coated.
2. The electrostatic spray system of claim 1 wherein said rear surface is conical and wherein said resistive sheet is circular such that its peripheral edge effectively defines a circular multi-point particle-charging electrode.
3. The electrostatic spray system of claim 1 wherein said deflector has a periphery, and wherein said peripheral edge of said sheet is exposed in the region of the periphery of said deflector.
4. The electrostatic spray system of claim 1 wherein said defector has a periphery, and wherein said peripheral edge of said sheet is substantially flush with the periphery of said deflector.
5. The electrostatic spray system of claim 1 wherein said deflector is comprised of rear and front sections, and wherein said resistive sheet is substan-tially flat and is sandwiched between said front and rear sections.
6. The electrostatic spray system of claim 5 wherein said deflector has a periphery, and wherein said peripheral edge of said sheet is exposed in the region of said deflector periphery.
7. The electrostatic system of claim 6 wherein said peripheral edge of said sheet is substantially flush with said deflector periphery.
8. The electrostatic system of claim 1 wherein said electrical path includes an electrical conductor projecting forwardly through said rear surface of said deflector along the axis thereof into electrical contact with said terminal region of said resistive sheet.
9. The electrostatic spray system of claim 1 wherein said resistive sheet consists substantially of fibrous resistive materials.
10. The electrostatic spray system of claim 1 wherein said resistive sheet is comprised substantially of silicon carbide filaments.
11. The electrostatic spray system of claim 1 wherein said resistive sheet comprises nonwoven fabric consisting substantially of randomly oriented silicon carbide filaments and a bonding agent.
12. An electrostatic spray coating system comprising:
a high voltage electrostatic supply for providing electrostatic voltages;
a particle spray device having a particle-spraying opening therein from which a stream of particles is sprayed in a path in a forward direction toward an article to be electrostatically coated;
a particle deflector constructed of elec-trically nonconductive material located in said particle path for deflecting said particle stream, said deflector having a surface upon which said particle stream impinges and as a result thereof becomes deflected;
a resistive sheet electrode having a periphery proximate said deflector surface past which said deflected particle stream passes to be electro-statically charged in its path toward said article to be coated, said resistive sheet electrode having a high voltage terminal region located remote from said periphery for establishing an electrically resistive current path from said terminal through said resistive sheet electrode to said periphery for minimizing shock and ignition hazards due to inadvertent discharge of electrical energy capacitively stored in said system;
and an electrical path interconnecting said high voltage supply and said terminal region of said resistive sheet electrode to facilitate the production of a corona discharges at said electrode periphery for electrostatically charging said deflected steam as it flows in proximity thereto in its path toward said article to be coated.
a high voltage electrostatic supply for providing electrostatic voltages;
a particle spray device having a particle-spraying opening therein from which a stream of particles is sprayed in a path in a forward direction toward an article to be electrostatically coated;
a particle deflector constructed of elec-trically nonconductive material located in said particle path for deflecting said particle stream, said deflector having a surface upon which said particle stream impinges and as a result thereof becomes deflected;
a resistive sheet electrode having a periphery proximate said deflector surface past which said deflected particle stream passes to be electro-statically charged in its path toward said article to be coated, said resistive sheet electrode having a high voltage terminal region located remote from said periphery for establishing an electrically resistive current path from said terminal through said resistive sheet electrode to said periphery for minimizing shock and ignition hazards due to inadvertent discharge of electrical energy capacitively stored in said system;
and an electrical path interconnecting said high voltage supply and said terminal region of said resistive sheet electrode to facilitate the production of a corona discharges at said electrode periphery for electrostatically charging said deflected steam as it flows in proximity thereto in its path toward said article to be coated.
13. The electrostatic spray system of claim 12 wherein said resistive sheet electrode consists substantially of silicon carbide filaments.
14. The electrostatic spray system of claim 12 wherein said resistive sheet electrode comprises fabric consisting substantially of silicon carbide filaments.
15. The electrostatic spray system of claim 12 wherein said resistive sheet electrode comprises nonwoven fabric consisting substantially of randomly oriented silicon carbide filaments and a bonding agent.
16. A particle deflector and charging assembly for use with an electrostatic spray system having a high voltage electrostatic supply for providing electrostatic voltages, and a particle spray device having a particle-spraying opening therein from which a stream of particles is sprayed in a path in a forward direction toward an article to be electro-statically coated, said particle deflector and charging assembly comprising the combination of;
a particle deflector constructed of elec-trically nonconductive material located in said particle path for deflecting said particle stream, said deflector having a) a rear surface upon which said particle stream impinges and as a result thereof becomes deflected, and b) a front surface facing in said forward direction, a resistive sheet located between said front and rear surfaces having a peripheral edge at its outer limits defining a multiple point electrode past which said deflected particle stream passes to be electrostatically charged in its path toward said article to be coated, said resistive sheet having a high voltage terminal region located remote from said peripheral edge for establishing an electrically resistive current path through said sheet between said terminal region and said peripheral edge for the purpose of minimizing shock and ignition hazards due to inadvertent discharge of electrical energy capacitively stored in said system, said terminal region being connectable to said high voltage supply to facilitate the production of a corona discharge at said peripheral edge of said sheet for electro-statically charging said deflected stream as it flows in proximity thereto in its path toward said article to be coated.
a particle deflector constructed of elec-trically nonconductive material located in said particle path for deflecting said particle stream, said deflector having a) a rear surface upon which said particle stream impinges and as a result thereof becomes deflected, and b) a front surface facing in said forward direction, a resistive sheet located between said front and rear surfaces having a peripheral edge at its outer limits defining a multiple point electrode past which said deflected particle stream passes to be electrostatically charged in its path toward said article to be coated, said resistive sheet having a high voltage terminal region located remote from said peripheral edge for establishing an electrically resistive current path through said sheet between said terminal region and said peripheral edge for the purpose of minimizing shock and ignition hazards due to inadvertent discharge of electrical energy capacitively stored in said system, said terminal region being connectable to said high voltage supply to facilitate the production of a corona discharge at said peripheral edge of said sheet for electro-statically charging said deflected stream as it flows in proximity thereto in its path toward said article to be coated.
17. The particle deflector and charging assembly of claim 16 wherein said resistive sheet consists substantially of silicon carbide filaments.
18. The particle deflector and charging assembly of claim 16 wherein said resistive sheet comprises fabric consisting substantially of silicon carbide filaments.
19. The particle deflector and charging assembly of claim 16 wherein said resistive sheet comprises nonwoven fabric consisting substantially of randomly oriented silicon carbide filaments and a bonding agent.
20. An electrostatic spray coating apparatus comprising:
a particle spray device having a particle-spraying opening therein from which a stream of particles is sprayed in a path in a forward direction toward an article to be electrostatically coated;
a particle deflector constructed of elec-trically nonconductive material located in said particle path for deflecting said particle stream, said deflector having a surface upon which said particle stream impinges and as a result thereof becomes deflected;
a plurality of electrode elements proximate said deflector surface past which said deflected particle stream passes to be electrostatically charged in its path toward said article to be coated, an electrical terminal associated with said deflector which is connectable to a source of high voltage, said terminal being remotely located relative to said plurality of electrode elements, and a plurality of resistive circuit paths incorporated in said deflector which are each con-nected between said terminal and a different one of said plurality of electrode elements, said resistive paths facilitating both energization of said electrode elements when said terminal is connected to a high voltage source and minimizing shock and ignition hazards due to inadvertent discharge of electrical energy capacitively stored in said spray coating apparatus.
a particle spray device having a particle-spraying opening therein from which a stream of particles is sprayed in a path in a forward direction toward an article to be electrostatically coated;
a particle deflector constructed of elec-trically nonconductive material located in said particle path for deflecting said particle stream, said deflector having a surface upon which said particle stream impinges and as a result thereof becomes deflected;
a plurality of electrode elements proximate said deflector surface past which said deflected particle stream passes to be electrostatically charged in its path toward said article to be coated, an electrical terminal associated with said deflector which is connectable to a source of high voltage, said terminal being remotely located relative to said plurality of electrode elements, and a plurality of resistive circuit paths incorporated in said deflector which are each con-nected between said terminal and a different one of said plurality of electrode elements, said resistive paths facilitating both energization of said electrode elements when said terminal is connected to a high voltage source and minimizing shock and ignition hazards due to inadvertent discharge of electrical energy capacitively stored in said spray coating apparatus.
21. The apparatus of Claim 20 wherein said electrode elements are each discrete electrical conductors having an outer end extending outwardly from said deflector transversely to said deflected particle stream and an inner end connected to a different one of said resistive circuit path.
22. The apparatus of Claim 20 wherein each said electrode element is a discrete electrical conductor incorporated in said deflector having an outer end terminating proximate said deflector surface and an inner end connected to a different one of said resistive paths.
23. The apparatus of Claim 20 wherein said plurality of electrode elements collectively comprise serially connected segments of a single continuous electrode mounted to said deflector generally parallel to said deflector surface and transverse to said deflected particle stream, and wherein each of said resistive paths connect to different ones of said segments.
24. The apparatus of Claim 23 wherein said continuous electrode consists substantially of a fibrous resistive material.
25. The apparatus of claim 24 wherein said fibrous resistive material comprises silicon carbide filaments.
26. The apparatus of claim 20 wherein said resistive circuit paths each comprises a discrete resistor.
27. The apparatus of claim 21 wherein said resistive circuit paths each comprises a discrete resistor.
28. The apparatus of claim 22 wherein said resistive circuit paths each comprises a discrete resistor.
29. The apparatus of claim 23 wherein said resistive circuit paths each comprises a discrete resistor.
30. The apparatus of claim 24 wherein said resistive circuit paths each comprises a discrete resistor.
31. The apparatus of claim 24 wherein said fibrous resistive material includes filaments having ends projecting outwardly therefrom whereat corona can occur when said continuous fibrous resistive electrode is energized from a high voltage source via said resistive circuit paths.
32. The apparatus of claim 25 wherein said fibrous resistive material includes filaments having ends projecting outwardly therefrom whereat corona can occur when said continuous fibrous resistive electrode is energized from a high voltage source via said resistive circuit paths.
33. The electrostatic spray system of claim 9 wherein said fibrous resistive sheet includes fila-ments having ends projecting outwardly therefrom at the periphery of said sheet whereat said corona discharges occur.
34. The elctrostatic spray system of claim 10 wherein said silicon carbide filaments include ends projecting outwardly therefrom at the periphery of said sheet whereat said corona discharges occur.
35. The system of claim 13 wherein said silicon carbide filaments include ends projecting outwardly therefrom at the periphery or said sheet whereat said corona discharges occur.
36. The assembly of claim 17 wherein said silicon carbide filaments include ends projecting outwardly therefrom at the periphery of said sheet whereat said corona discharges occur.
37. The electrostatic spray system of claim 1 wherein said resistive sheet comprises woven silicon carbide filaments.
38. The electrostatic spray system of claim 1 wherein said resistive sheet comprises woven resistive filaments.
39. The system of claim 1 wherein said spray device includes a) an electrically nonconductive barrel having a nozzle in which said particle spraying opening is located and b) an electrically conductive section located remote from said nozzle;
means connected to said electrically conduc-tive section of said spray device for maintaining said electrically conductive section at an electrostatic voltage substantially different than the voltage of said corona charging points or at ground potential, and an electrostatic shield located between said corona charging points and said electrically conductive section to electrostatically shield electrostatically charged particles in the region of said nozzle form said electrically conductive section.
means connected to said electrically conduc-tive section of said spray device for maintaining said electrically conductive section at an electrostatic voltage substantially different than the voltage of said corona charging points or at ground potential, and an electrostatic shield located between said corona charging points and said electrically conductive section to electrostatically shield electrostatically charged particles in the region of said nozzle form said electrically conductive section.
40. The system of claim 39 wherein said electro-static shield is incorporated in said nozzle.
41. The system of claim 39 wherein said nozzle is outwardly and forwardly flared to provide, in the region of said charged particles proximate said particle-spraying opening, a portion thereof which is located outwardly and rearwardly of said corona charging points, thereby defining said electrostatic shield.
42. The system of claim 12 wherein said spray device includes a) an electrically nonconductive barrel having a nozzle in which said particle spraying opening is located and b) an electrically conductive section located remote from said nozzle, means connected to said electrically conduc-tive section of said spray device for maintaining said electrically conductive section at an electrostatic voltage substantially different than the voltage of said electrode periphery or at ground potential, and an electrostatic shield located between said electrode periphery and said electrically conductive section to electrostatically shield electrostatically charged particles in the region of said nozzle from said electrically conductive section.
43. The system of claim 42 wherein said electro-static shield is incorporated in said nozzle.
44. The system of claim 42 wherein said nozzle is outwardly and forwardly flared to provide, in the region of said charged particles proximate said particle-spraying opening, a portion thereof which is located outwardly and rearwardly of said electrode periphery, thereby defining said electrostatic shield.
45. The apparatus of claim 20 wherein said spray device includes a) an electrically nonconductive barrel having a nozzle in which said particle spraying opening is located and b) an electrically conductive section located remote from said nozzle, means connected to said electrically conduc-tive section of said spray device for maintaining said electrically conductive section at an electrostatic voltage substantially different than the voltage of said electrode elements or at ground potential, and an electrostatic shield located between said electrode elements and said electrically conductive section to electrostatically shield electrostatically charged particles in the region of said nozzle from said electrically conductive section.
46. The apparatus of claim 45 wherein said electrostatic shield is incorporated in said nozzle.
47. The apparatus of claim 45 wherein said nozzle is outwardly and forwardly flared to provide, in the region of said charged coating proximate said particle-spraying opening, a portion thereof which is located outwardly and rearwardly of said electrode elements, thereby defining said electrostatic shield.
48. An electrostatic spray coating apparatus com-prising:
a particle spray device having a particle-spraying opening therein from which a stream of part-icles is sprayed in a path in a forward direction toward an article to be electrostatically coated;
a multipoint electrode comprising a substantial number of closely spaced electrode elements located im-mediately proximate, but not extending significantly in-to, said opening through which said particle stream passes to be electrostatically charged in its path toward said article to be coated, said electrode elements being con-nectable to an electrostatic voltage source for establish-ing a plurality of corona charging points to enhance trans-fer efficiency.
a particle spray device having a particle-spraying opening therein from which a stream of part-icles is sprayed in a path in a forward direction toward an article to be electrostatically coated;
a multipoint electrode comprising a substantial number of closely spaced electrode elements located im-mediately proximate, but not extending significantly in-to, said opening through which said particle stream passes to be electrostatically charged in its path toward said article to be coated, said electrode elements being con-nectable to an electrostatic voltage source for establish-ing a plurality of corona charging points to enhance trans-fer efficiency.
49. The apparatus of claim 48 wherein the multipoint electrode includes silicon carbide fabric having a per-ipheral edge defining said plurality of spaced electrode points.
50. The apparatus of claim 48 wherein the multipoint electrode includes resistive sheet having a peripheral edge defining said subtantial number of closely spaced electrode points.
51. The apparatus of claim 4, wherein the multipoint electrode includes mesh having a peripheral edge defining said substantial number of closely spaced electrode points.
52. The apparatus of claim 51 wherein the mesh is resistive.
53. The apparatus of claim 48 wherein the multipoint electrode includes a sheet having a toothed peripheral edge defining said substantial number of closely spaced electrode points.
54. The apparatus of claim 53 wherein said sheet is a composite including a) an outer section on which said teeth are formed, and b) an inner section connect-able to a source of high voltage which is more electri-cally resistive than said outer section.
55. The apparatus of claim 48 wherein the multipoint electrode includes a semiconductive sheet having a peripheral edge defining said substantial number of closely spaced electrode points.
56. The system of claim 1 wherein said spray de-vice includes a) an electrically nonconductive barrel having a nozzle in which said particle spraying opening is located and b) a rear section located remote from said nozzle; and an electrostatic shield extending laterally be-yond and rearwardly of said corona charging points to electrostatically shield electrostatically charged part-icles in the region of said nozzle from sources of electrostatic potential different from that of said electrode located rearwardly and/or laterally relative to said corona charging points.
57. The system of claim 56 wherein said electro-static shield is incorporated in said nozzle.
58. The system of claim 56 wherein said nozzle is outwardly and forwardly flared to provide, in the region of said charged particles proximate said particle-spraying opening, a portion thereof which is located outwardly and rearwardly of said corona charging points, thereby de-fining said electrostatic shield.
59. The system of claim 12 wherein said spray device includes a) an electrically nonconductive barrel having a nozzle in which said particle spraying opening is located and b) a rear section located remote from said nozzle, and an electrostatic shield extending laterally beyond and rearwardly of said electrode periphery to electro-statically shield electrostatically charged particles in the region of said nozzle from sources of electrostatic poten-tial different from that of said electrode located rearward-ly and/or laterally of said electrode periphery.
60. The system of claim 59 wherein said electrostatic shield is incorporated in said nozzle.
61. The system of claim 59 wherein said nozzle is out-wardly and forwardly flared to provide, in the region of said charged particles proximate said particle-spraying opening, a portion thereof which is located outwardly and rearwardly of said electrode periphery, thereby defining said electro-static shield.
62. The apparatus of claim 20 wherein said spray device includes a) an electrically nonconductive barrel having a nozzle in which said particle spraying opening is located and b) a rear section located remote from said nozzle, and an electrostatic shield extending laterally beyond and rearwardly of said corona charging points to electrostati-cally shield electrostatically charged particles in the re-gion of said nozzle from sources of electrostatic potential different from that of said electrode elements located rear-wardly and/or laterally relative to said electrode elements.
63. The apparatus of claim 62 wherein said electrostatic shield is incorporated in said nozzle.
64. The apparatus of claim 62 wherein said nozzle is outwardly and forwardly flared to provide, in the region of said charged coating proximate said particle-spraying opening, a portion thereof which is located out-wardly and rearwardly of said electrode elements, there-by defining said electrostatic shield.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US72439285A | 1985-04-18 | 1985-04-18 | |
| US724,392 | 1985-04-18 | ||
| US79135285A | 1985-10-25 | 1985-10-25 | |
| US791,352 | 1985-10-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1254030A true CA1254030A (en) | 1989-05-16 |
Family
ID=27110970
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000506145A Expired CA1254030A (en) | 1985-04-18 | 1986-04-09 | Particle spray gun |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0203694B1 (en) |
| JP (1) | JPH0724794B2 (en) |
| KR (1) | KR940006020B1 (en) |
| AU (1) | AU580147B2 (en) |
| CA (1) | CA1254030A (en) |
| DE (1) | DE3664185D1 (en) |
| DK (1) | DK175486A (en) |
| IN (1) | IN166961B (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4819879A (en) * | 1985-10-25 | 1989-04-11 | Nordson Corporation | Particle spray gun |
| ES2019888B3 (en) * | 1986-03-13 | 1991-07-16 | Ransburg-Gema Ag | ELECTROSTATIC SPRAYER FOR COATING POWDERS. |
| FR2620354B2 (en) * | 1987-02-12 | 1990-01-05 | Sames Sa | DEVICE FOR ELECTROSTATIC PROJECTION OF POWDERED PRODUCT |
| US4784331A (en) * | 1987-05-27 | 1988-11-15 | Nordson Corporation | Electrostatic spray gun device and cable assembly |
| US4811898A (en) * | 1987-09-21 | 1989-03-14 | Nordson Corporation | Electrostatic powder spray gun with adjustable deflector and electrostatic shield |
| WO1991006376A1 (en) * | 1989-11-06 | 1991-05-16 | Frederick David Haig | Spray gun with corona and tubular electrodes |
| EP0978319B1 (en) * | 1998-08-07 | 2000-09-20 | ABB Research Ltd. | Powder spray device with external and internal charging |
| US20040256503A1 (en) * | 2003-05-08 | 2004-12-23 | Young Roy Earl | Shielded electrode |
| DE102011055660B4 (en) * | 2011-11-23 | 2013-09-05 | P+S Pulverbeschichtungs- Und Staubfilteranlagen Gmbh | Method for applying powder by means of a powder spray gun and powder spray gun for carrying out the method |
| CN111495617B (en) * | 2019-12-12 | 2024-08-02 | 中冶京诚工程技术有限公司 | Nozzle for powder spraying device and powder spraying device |
| WO2023232199A2 (en) * | 2022-06-03 | 2023-12-07 | P+S Pulverbeschichtungs- Und Staubfilteranlagen Gmbh | Method for applying powder and powder spray nozzle for carrying out the method |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR92033E (en) * | 1967-03-22 | 1968-09-13 | Sames Mach Electrostat | New and improved device for electrostatic powder coating of objects |
| US3327948A (en) * | 1964-07-07 | 1967-06-27 | Cosmic Inc | Method of electrostatic coating including velocity reduction |
| FR2172612A5 (en) * | 1972-02-18 | 1973-09-28 | Air Ind | |
| US4027050A (en) * | 1975-07-10 | 1977-05-31 | Frederic David Haig | Method and apparatus for electrostatic coating |
| CH598871A5 (en) * | 1975-07-29 | 1978-05-12 | Air Ind | |
| US4627903A (en) * | 1982-07-26 | 1986-12-09 | Exxon Research & Engineering Company | Electrode for an electrostatic atomizing device |
| DE3412694A1 (en) * | 1983-04-07 | 1984-10-11 | Kopperschmidt-Mueller GmbH & Co KG, 7057 Winnenden | METHOD AND DEVICE FOR ELECTROSTATICALLY SPRAYING ON POWDER PARTICLES ON A SURFACE TO BE COATED |
| JPS6053355U (en) * | 1983-09-21 | 1985-04-15 | トリニティ工業株式会社 | electrostatic painting equipment |
-
1986
- 1986-04-09 CA CA000506145A patent/CA1254030A/en not_active Expired
- 1986-04-09 AU AU55790/86A patent/AU580147B2/en not_active Ceased
- 1986-04-11 IN IN329/DEL/86A patent/IN166961B/en unknown
- 1986-04-15 DE DE8686302813T patent/DE3664185D1/en not_active Expired
- 1986-04-15 EP EP86302813A patent/EP0203694B1/en not_active Expired
- 1986-04-17 DK DK175486A patent/DK175486A/en not_active Application Discontinuation
- 1986-04-18 KR KR1019860003001A patent/KR940006020B1/en not_active IP Right Cessation
- 1986-04-18 JP JP8842486A patent/JPH0724794B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0203694A3 (en) | 1987-01-07 |
| DE3664185D1 (en) | 1989-08-10 |
| EP0203694A2 (en) | 1986-12-03 |
| DK175486D0 (en) | 1986-04-17 |
| IN166961B (en) | 1990-08-11 |
| AU5579086A (en) | 1986-10-23 |
| AU580147B2 (en) | 1989-01-05 |
| EP0203694B1 (en) | 1989-07-05 |
| KR940006020B1 (en) | 1994-07-02 |
| JPH0724794B2 (en) | 1995-03-22 |
| KR860007968A (en) | 1986-11-10 |
| DK175486A (en) | 1986-10-19 |
| JPS6297654A (en) | 1987-05-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |