EP0734777A2 - Système d'ionisation électrostatique - Google Patents

Système d'ionisation électrostatique Download PDF

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Publication number
EP0734777A2
EP0734777A2 EP96301943A EP96301943A EP0734777A2 EP 0734777 A2 EP0734777 A2 EP 0734777A2 EP 96301943 A EP96301943 A EP 96301943A EP 96301943 A EP96301943 A EP 96301943A EP 0734777 A2 EP0734777 A2 EP 0734777A2
Authority
EP
European Patent Office
Prior art keywords
electrode
sprayer
needle
electrostatic
sharpened
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.)
Withdrawn
Application number
EP96301943A
Other languages
German (de)
English (en)
Other versions
EP0734777A3 (fr
Inventor
Yamin Ma
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Graco Inc
Original Assignee
Graco Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Graco Inc filed Critical Graco Inc
Publication of EP0734777A2 publication Critical patent/EP0734777A2/fr
Publication of EP0734777A3 publication Critical patent/EP0734777A3/fr
Withdrawn legal-status Critical Current

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    • 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
    • B05B5/0535—Electrodes specially adapted therefor; Arrangements of electrodes at least two electrodes having different potentials being held on the discharge apparatus, one of them being a charging electrode of the corona type located in the spray or close to it, and another being of the non-corona type located outside of the path for the material
    • 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
    • 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
    • B05B5/16—Arrangements for supplying liquids or other fluent material
    • B05B5/1608—Arrangements for supplying liquids or other fluent material the liquid or other fluent material being electrically conductive

Definitions

  • the present invention relates to an electrostatic charging system for atomizers and coating applicators; more particularly, the invention relates to an ionizing system adapted for use in connection with an electrostatic paint applicator. Moreover, it relates to a system wherein the paint is electrically conductive.
  • the electrostatic paint applicator may be either a hand-held spray gun or may be an automatic spray gun which is operable by remote control connections.
  • an ionizing electrode is placed in the vicinity of the spray gun spray orifice, the article to be painted is held at ground potential, and an electrostatic field is developed between the ionizing electrode and the article.
  • the distance between the two electrodes may be on the order of about one foot (30.48 cm) therefore, the voltage applied to the spray gun electrode must necessarily be quite high in order to develop an electrostatic field of sufficient intensity to create a large number of ion/particle interactions so as to develop a sufficient attractive force between the paint particles and the target.
  • electrostatic voltages on the order of 60,000-100,000 volts (60-100 kV) to the sprayer electrode in order to achieve a proper degree of efficiency in the spraying operation.
  • An ionizing current on the order of 50 microamps typically flows between the grounded article and the sprayer electrode.
  • Electrostatic systems of the foregoing type are frequently referred to as corona charging systems, because the field intensity creates a corona current from the electrode which ionizes the air in the vicinity, and the atomized paint particles which pass through the region of ionized air pick up the ionized charges and become more readily attracted to a grounded or neutral article to be coated.
  • the electrical field strength in the charging zone must be sufficiently intensive as to ionize the air in the vicinity of the electrode (in the charging zone) in order to create the corona current described above.
  • Electrostatic voltage charging systems can be utilized in connection with sprays whether the primary atomizing forces are created by pressurized air, hydraulic forces, or centrifugal forces. In each case, it is preferable that the ionizing electrode be placed at or proximate to the point where atomization occurs so as to cause the greatest number of atomized particles to pass through the ionizing field. Electrostatic ionizing systems can also be used with conductive or non-conductive paint; but in the case of conductive paint, the placement of the electrostatic ionizing electrode may have to be more carefully positioned so as to avoid developing a conductive path through the liquid paint column prior to the point of atomization.
  • the electrostatic electrode configuration most often used for satisfactory performance is a needle configuration, which permits a high intensity field to develop at the needle tip, wherein the needle is positioned at or proximate to the zone of atomization.
  • these needles are typically made from hardened steel material, frequently stainless steel, typically having a diameter of about 0.5 millimetres (mm) and projecting forwardly from the nozzle a distance sufficiently far to avoid electrical contact with the conductive paint column in the sprayer.
  • These needles are typically formed from wire material which is cut to length, and no attempt is made to provide a sharpened point on the needle. In some cases the needle end is rounded.
  • the voltage as applied to such needles is usually in the range of 60-100 kV, which develops a relatively high intensity electrostatic field in the vicinity of the needle, wherein the electrostatic field lines are formed between the needle and usually a grounded article to be painted.
  • the field gradient in volts per centimetre (V/cm) is determined by dividing the voltage applied to the needle by the distance in centimeters to the second electrode, usually the article, where the field is developed.
  • an electrostatic ionising system for use with a sprayer for emitting a pattern of atomised particles of otherwise conductive liquid, the system comprising: an electrode having a sharpened edge with a radius of curvature of less than 50 ⁇ m, which, in use, is positioned such that the sharpened edge is outside the pattern of atomised particles, and remote from the sprayer; and a further electrode which is formed as part of the sprayer; the sharpened electrode operable in conjunction with the further electrode such that a voltage differential can be developed therebetween to provide an electrostatic field and corona discharge for charging particles emitted through the field.
  • an electronic atomizer having an ionizing electrode operable in conjunction with a second electrode, with a voltage differential developed therebetween, for providing an electrostatic field and corona discharge for charging a pattern of conductive liquid particles emitted through the field by the sprayer, the improvement in an ionizing system comprising:
  • an electrostatic ionizing system for attachment to a sprayer proximate the atomizing nozzle which emits a pattern of atomized particles of otherwise conductive liquid, comprising:
  • an electrostatic sprayer having an ionizing needle operable in conjunction with a second grounded electrode, with a voltage differential developed therebetween, for providing an electrostatic field and corona discharge for charging liquid particles from an otherwise conductive liquid, emitted through the field by the sprayer, the improvement in an ionizing system comprising:
  • an electrostatic ionising system for attachment to an atomiser for emitting a pattern of atomised particles, the system comprising:
  • the ionising electrode is preferably positioned outside the particles emitted from the atomiser and the other electrode forms part of the atomiser.
  • the ionising electrode is preferably positioned proximate the pattern of particles and the other electrode is preferably positioned outside the pattern of particles, about 2.54 cm (1") from the ionising electrode.
  • the invention provides a construction which achieves a satisfactory field intensity E for electrostatic spraying of conductive liquids by controlling the geometry of the needle and by controlling the placement of the needle electrode relative to a second grounded electrode.
  • the needle diameter is selected to be less than about 250 micrometers ( ⁇ m)
  • the needle tip is sharpened to have a tip radius of curvature less than about 50 micrometers ( ⁇ m).
  • the needle is positioned to be relatively near the atomization zone for the particular spray gun to which it is applied.
  • the electrostatic system will develop an ionizing current in the range of 20-80 microamp ( ⁇ a) with an applied voltage in the range of 50-80 kV.
  • FIG. 1 shows an isometric view of a typical electrostatic sprayer in conjunction with the present invention.
  • the electrostatic sprayer 10 has a manually-operable trigger 14 for spraying liquid delivered through delivery tube 16 through a spray nozzle 12.
  • the electrostatic high voltage is either developed internally by a high voltage supply in the sprayer, or delivered to sprayer 10 via a cable 15 which ultimately places a high voltage on needle 20.
  • the atomized spray is ejected from an orifice at the front of nozzle 12 and is shaped into a spray pattern 24.
  • the particles forming the spray pattern 24 are respectively ionized by the electrostatic field through which they pass as they are emitted from the orifice in the spray nozzle 12.
  • This invention is primarily directed to a sprayer for spraying particles of liquid, which liquid is electrically conductive. Therefore, a column of the liquid will conduct electricity in much the same manner as an electrical wire. Spraying such liquids under electrostatic field conditions requires extreme care in the design of the equipment in order to avoid short circuiting the electrostatic high voltage directly to ground in cases where the liquid column flowing to the sprayer is grounded. In some cases in the prior art, the sprayer and its associated components have all been isolated from ground; and therefore, attain a voltage level equal to the electrostatic high voltage. In the present case, the sprayer and its associated equipment is maintained at ground potential; and therefore, isolation must be maintained between the high voltage components and the sprayer and its associated conductive liquid column.
  • the needle 20 is placed at the forward end of an insulated rod 25, and voltage isolating a conductor through the insulated rod 25 to contact the conductor in cable 15.
  • the needle 20 is spaced away from the front of nozzle 12 by a distance of approximately 4-5 inches to provide the requisite voltage isolation needed for this application.
  • the electrostatic high voltage emitted at the tip of needle 20 is always placed into the atomization zone, i.e. the zone where liquid particles pass but not in the zone where a liquid column is present.
  • An important realization of the present invention is the discovery of the improved ionizing system which can produce a highly efficient coating process without contaminating the electrode by coating it with the sprayed material.
  • a higher intensity field causes higher electron emissions from the tip, which in turn generates an increased number of ions via a stronger corona current, to increase the charge accumulation on liquid droplets passing through the ionization zone, even though the tip is outside the atomization zone.
  • the spacing of the voltage electrode and the grounded electrode creates a very highly intense ionizing zone, and when this ionizing zone is positioned in or close to the zone of atomization the number of droplets which accumulate higher charges is also increased.
  • the net result with about 20-80 kV applied to the needle electrode of the present invention, produces a droplet charge accumulation equivalent to a conventional isolated electrostatic system, using comparable voltages.
  • the corona current produced by the improved ionizing system can range from 50-100 microamperes (50-100 ⁇ A), and can produce a heating effect at the point of emanation from the sharpened tip or edge. Therefore, it is important that a material having a relatively high melting point be selected for the needle construction.
  • FIG 2 shows an enlarged partial elevation view of a typical needle as known in the prior art.
  • a needle is typically formed of a hardened steel such as stainless steel, and the diameter D 1 is usually about 0.5 mm.
  • Figure 3 shows an enlarged partial elevation view of the needle of the present invention which is preferably formed of an alloy having a high melting point, preferably above 2,300° Celsius (°C).
  • a preferred material for forming needle 20 is tungsten, which has a melting point of 3,410°C.
  • Needle 20 has a diameter of D 1 , which is preferably less than about 250 micrometers ( ⁇ m). Needle 20 is sharpened to a point having a radius of curvature "R". Radius "R" is less than 50 ⁇ m and is preferably less than 25 ⁇ m.
  • the high voltage supply to the electrostatic needle of the sprayer shown in the preferred embodiment is approximately 40-80 kV.
  • This voltage will create a stable corona current at least in the range of 20-80 microamps ( ⁇ A) wherein the entire corona current flows from the extremely sharpened tip of the electrostatic needle.
  • This relatively high corona current put together with the sharpened needle point tends to create heat in the vicinity of the needle point; and therefore, it is important that the needle be made from a material which has a high melting point in order to maintain the sharpness of the needle point when heated.
  • the preferred material for use in connection with this invention is tungsten, although carbon, osmium and rhenium also have melting points in excess of 3,000° C.
  • the magnitude of high voltage which must be applied to the needle in the present invention is determined by a number of factors including the type of liquid material being sprayed, the distance between the needle and the spray nozzle, the distance between the needle and the article to be sprayed, the velocity of the sprayed particles through the atomization zone and environmental factors such as humidity and temperature. It is preferred that the high voltage applied to the sprayer of the present invention be adjustable so as to enable the operator to select the electrostatic voltage value which best suits the particular operating conditions in circumstances.
  • the electrostatic ionizing field will be developed between the needle and the grounded sprayer and also between the needle and the grounded article to be coated.
EP96301943A 1995-03-28 1996-03-21 Système d'ionisation électrostatique Withdrawn EP0734777A3 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US41205395A 1995-03-28 1995-03-28
US412053 1995-03-28

Publications (2)

Publication Number Publication Date
EP0734777A2 true EP0734777A2 (fr) 1996-10-02
EP0734777A3 EP0734777A3 (fr) 1997-08-20

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EP96301943A Withdrawn EP0734777A3 (fr) 1995-03-28 1996-03-21 Système d'ionisation électrostatique

Country Status (2)

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EP (1) EP0734777A3 (fr)
JP (1) JPH08266949A (fr)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009114295A1 (fr) 2008-03-10 2009-09-17 Illinois Tool Works Inc. Procédé et appareil permettant la retenue d’accessoires extrêmement serrés dans une résine moulée ou un boîtier en polymère
WO2009114296A1 (fr) 2008-03-10 2009-09-17 Illinois Tool Works Inc. Commande de la température dans un atomiseur de matériau de revêtement à air comprimé et à assistance électrostatique
WO2009114322A1 (fr) 2008-03-10 2009-09-17 Illinois Tool Works Inc. Source électrique étanche pour la pulvérisation électrostatique à commande pneumatique et dispositif de distribution
WO2009114276A1 (fr) 2008-03-10 2009-09-17 Illinois Tool Works Inc. Configuration de carte de circuits imprimés pour pistolet de pulvérisation à air comprimé et à assistance électrostatique
USD608858S1 (en) 2008-03-10 2010-01-26 Illinois Tool Works Inc. Coating material dispensing device
US7926748B2 (en) 2008-03-10 2011-04-19 Illinois Tool Works Inc. Generator for air-powered electrostatically aided coating dispensing device
US8770496B2 (en) 2008-03-10 2014-07-08 Finishing Brands Holdings Inc. Circuit for displaying the relative voltage at the output electrode of an electrostatically aided coating material atomizer
EP2946839A4 (fr) * 2013-01-15 2016-09-07 Sumitomo Chemical Co Atomiseur électrostatique
CN108554663A (zh) * 2018-06-27 2018-09-21 湖北金稽山机械科技有限公司 一种加厚粉体材料成型装置
CN110042337A (zh) * 2019-05-28 2019-07-23 沈阳理工大学 一种氩气保护微束电弧喷涂枪

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2959353A (en) * 1954-10-04 1960-11-08 Gen Motors Corp Electrostatic charger apparatus
FR2224212A1 (fr) * 1973-04-06 1974-10-31 Mueller Ernst Kg
FR2304411A1 (fr) * 1975-03-21 1976-10-15 Redelec Systeme d'electrodes de charge electrostatique pour projection de poudres ou liquides pulverises
US4079894A (en) * 1976-07-14 1978-03-21 Nordson Corporation Electrostatic spray coating gun
US4219864A (en) * 1977-04-04 1980-08-26 Eltex-Elektronik H. Grunenfelder El. Ing. Device and method for moistening and/or discharging electrically insulating objects and materials
US4343828A (en) * 1980-12-24 1982-08-10 Caterpillar Tractor Co. Electrodynamic painting system and method
US4744513A (en) * 1982-10-21 1988-05-17 Basf Farben & Faser Ag Device and process for the electrostatic coating of articles with fluids
EP0469775A1 (fr) * 1990-08-01 1992-02-05 Hughes Aircraft Company Appareil et méthode de déposition électrostatique de peinture
WO1994018011A1 (fr) * 1993-02-12 1994-08-18 Tonejet Corporation Pty Ltd. Procede et appareil de production de gouttelettes
US5344676A (en) * 1992-10-23 1994-09-06 The Board Of Trustees Of The University Of Illinois Method and apparatus for producing nanodrops and nanoparticles and thin film deposits therefrom

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2959353A (en) * 1954-10-04 1960-11-08 Gen Motors Corp Electrostatic charger apparatus
FR2224212A1 (fr) * 1973-04-06 1974-10-31 Mueller Ernst Kg
FR2304411A1 (fr) * 1975-03-21 1976-10-15 Redelec Systeme d'electrodes de charge electrostatique pour projection de poudres ou liquides pulverises
US4079894A (en) * 1976-07-14 1978-03-21 Nordson Corporation Electrostatic spray coating gun
US4219864A (en) * 1977-04-04 1980-08-26 Eltex-Elektronik H. Grunenfelder El. Ing. Device and method for moistening and/or discharging electrically insulating objects and materials
US4343828A (en) * 1980-12-24 1982-08-10 Caterpillar Tractor Co. Electrodynamic painting system and method
US4744513A (en) * 1982-10-21 1988-05-17 Basf Farben & Faser Ag Device and process for the electrostatic coating of articles with fluids
EP0469775A1 (fr) * 1990-08-01 1992-02-05 Hughes Aircraft Company Appareil et méthode de déposition électrostatique de peinture
US5344676A (en) * 1992-10-23 1994-09-06 The Board Of Trustees Of The University Of Illinois Method and apparatus for producing nanodrops and nanoparticles and thin film deposits therefrom
WO1994018011A1 (fr) * 1993-02-12 1994-08-18 Tonejet Corporation Pty Ltd. Procede et appareil de production de gouttelettes

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009114295A1 (fr) 2008-03-10 2009-09-17 Illinois Tool Works Inc. Procédé et appareil permettant la retenue d’accessoires extrêmement serrés dans une résine moulée ou un boîtier en polymère
WO2009114296A1 (fr) 2008-03-10 2009-09-17 Illinois Tool Works Inc. Commande de la température dans un atomiseur de matériau de revêtement à air comprimé et à assistance électrostatique
WO2009114322A1 (fr) 2008-03-10 2009-09-17 Illinois Tool Works Inc. Source électrique étanche pour la pulvérisation électrostatique à commande pneumatique et dispositif de distribution
WO2009114276A1 (fr) 2008-03-10 2009-09-17 Illinois Tool Works Inc. Configuration de carte de circuits imprimés pour pistolet de pulvérisation à air comprimé et à assistance électrostatique
USD608858S1 (en) 2008-03-10 2010-01-26 Illinois Tool Works Inc. Coating material dispensing device
US7926748B2 (en) 2008-03-10 2011-04-19 Illinois Tool Works Inc. Generator for air-powered electrostatically aided coating dispensing device
US7988075B2 (en) 2008-03-10 2011-08-02 Illinois Tool Works Inc. Circuit board configuration for air-powered electrostatically aided coating material atomizer
US8016213B2 (en) 2008-03-10 2011-09-13 Illinois Tool Works Inc. Controlling temperature in air-powered electrostatically aided coating material atomizer
US8496194B2 (en) 2008-03-10 2013-07-30 Finishing Brands Holdings Inc. Method and apparatus for retaining highly torqued fittings in molded resin or polymer housing
US8590817B2 (en) 2008-03-10 2013-11-26 Illinois Tool Works Inc. Sealed electrical source for air-powered electrostatic atomizing and dispensing device
US8770496B2 (en) 2008-03-10 2014-07-08 Finishing Brands Holdings Inc. Circuit for displaying the relative voltage at the output electrode of an electrostatically aided coating material atomizer
EP2946839A4 (fr) * 2013-01-15 2016-09-07 Sumitomo Chemical Co Atomiseur électrostatique
US9764341B2 (en) 2013-01-15 2017-09-19 Sumitomo Chemical Company, Limited Electrostatic atomizer
CN108554663A (zh) * 2018-06-27 2018-09-21 湖北金稽山机械科技有限公司 一种加厚粉体材料成型装置
CN110042337A (zh) * 2019-05-28 2019-07-23 沈阳理工大学 一种氩气保护微束电弧喷涂枪

Also Published As

Publication number Publication date
JPH08266949A (ja) 1996-10-15
EP0734777A3 (fr) 1997-08-20

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