EP0032528B1 - Air flow system for the charging conductor in an electrostatic painting system - Google Patents

Air flow system for the charging conductor in an electrostatic painting system Download PDF

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Publication number
EP0032528B1
EP0032528B1 EP80106585A EP80106585A EP0032528B1 EP 0032528 B1 EP0032528 B1 EP 0032528B1 EP 80106585 A EP80106585 A EP 80106585A EP 80106585 A EP80106585 A EP 80106585A EP 0032528 B1 EP0032528 B1 EP 0032528B1
Authority
EP
European Patent Office
Prior art keywords
plenum
conductor
flow
air
charged conductor
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
Application number
EP80106585A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0032528A1 (en
Inventor
Thomas Jeffrey Richards
Robert Griffith Smead
Paul Julius Staebler
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.)
Caterpillar Inc
Original Assignee
Caterpillar Tractor Co
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 Caterpillar Tractor Co filed Critical Caterpillar Tractor Co
Publication of EP0032528A1 publication Critical patent/EP0032528A1/en
Application granted granted Critical
Publication of EP0032528B1 publication Critical patent/EP0032528B1/en
Expired legal-status Critical Current

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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
    • B05B5/08—Plant for applying liquids or other fluent materials to objects
    • B05B5/082—Plant for applying liquids or other fluent materials to objects characterised by means for supporting, holding or conveying the objects

Definitions

  • This invention relates generally to an electrostatic painting system and more particularly to an air flow system for preventing deposition of paint on a charged conductor used to charge an article isolated from ground, being painted in an electrostatic painting system.
  • Electrostatic painting systems are known in which the articles painted are electrically charged. See for instance US-A-4 158 344.
  • articles are carried through a painting zone by a conveyor with the articles and article carriers isolated from electrical ground.
  • a charged conductor extends along the conveyor path.
  • a charge collector on the article carrier is spaced from the charged conductor and an electric charge is transferred to the carrier and thus to the article supported therefrom.
  • the electric potential on the conductor may be of the order of 75 kV to 100 kV.
  • An undesirable discharge or arcing may occur from the charged conductor. This condition is aggravated by the presence of dirt, paint particles or the like. It is known to enclose the charged conductor in a housing and to blow air through the housing thus minimizing the build-up of charged particles.
  • the air flow around the charged conductor is turbulent or nonuniform. Outside air, which may contain paint particles, is drawn into the enclosure. Swirls or eddies form allowing charged paint particles and other contaminants to enter the field of the charged conductor and to be deposited on the conductor and on the supporting structure therefor. This causes undesirable coating of the charged conductor and inhibits ionization of the air surrounding the conductor and charge transfer to the charge collector on the article carrier. The voltage gradient between the conductor and the collector may become excessive in the absence of ionization of the air and disruptive sparking may occur. Conversely, if the air around the conductor is contained, the concentration of ionized particles may become excessive, lowering the resistance to ground and causing an undesirable current flow to the collector or to ground.
  • the present invention is directed to overcoming one or more of the problems as set forth above.
  • an improved air flow system includes a blower, means defining a plenum chamber extending along the length of the charged conductor, means for directing a flow of air from the blower through the plenum chamber and a perforate wall between the plenum chamber and the charged conductor, a flow of air being directed through the perforate wall and outward from the wall across the charged conductor.
  • the uniform flow of air across the charged conductor prevents the paint particles from depositing on the conductor and avoids the problems noted above.
  • the uniformity of flow is characterized by freedom from swirls and eddies so that paint particles are not drawn to localized areas of the conductor.
  • the invention enables operation of a coating system for an extended period of time without need to clean the charged conductor.
  • Fig. 1 The painting installation of Fig. 1 has an overhead conveyor with a conveyor track 10 and wheeled article carriers 11 which are drawn along the conveyor track as by a chain, not shown.
  • a depending carrier member 12 supports a rack 13 from which articles 14, which are to be painted, are suspended.
  • the conveyor 10 passes through a coating zone within a paint booth defined by walls, including a top wall 15 and front wall 16, and end and rear walls which are not shown.
  • a paint gun 17 provides a source of particulate paint and is spaced from the path of article travel, adjacent the front of the paint booth.
  • the paint gun is preferably triggered on as articles to be painted pass through the painting booth.
  • the gun may be fixed or may be reciprocated laterally and vertically as indicated by arrows 18, 19 if such movement is desirable to deposit an adequate coating on the articles.
  • the paint gun is electrically charged, as to a negative potential of the order of 25 kV and the articles to be coated are charged with a positive potential of the order of 75-100 kV.
  • the articles to be coated, and the article carriers have a charge transferred thereto from a charged conductor, here shown as a wire 22 which extends along the path of travel of the article carriers in the coating zone within the paint booth.
  • a disc- shaped charge collector 23 mounted at an intermediate point on carrier member 12 travels in close proximity to the charged conductor and acquires a charge therefrom which is conductively coupled through the carrier and rack to the articles 14.
  • the conveyor 10 is electrically grounded and the upper portion of carrier member 12 includes an isolation resistor so that the charge transferred to the collector 23 is not immediately dissipated to ground.
  • paint particles In the system described some of the paint particles have a negative charge, others have a positive charge and some are uncharged. There is a tendency for the paint particles, and particularly those which have a negative charge, opposite to that of the positively charged conductor, to be attracted to and deposit on the conductor or its supporting structure. This reduces charge transfer to collector 23 and promotes sparking as discussed above.
  • a flow of air is directed across the charged conductor 22 counteracting the electrostatic force attracting the paint particles toward the conductor. This greatly reduces the deposition of paint particles on the conductor and minimizes the arcing problem.
  • the air flow is essentially unidirectional along the length of the conductor although the velocity may not be the same at all points. It is important that the air flow across the conductor be free of swirls and eddies which may draw the paint particles to some sections of the charged conductor rather than keeping them away.
  • the charged conductor 22 is mounted on posts 24 of an insulating material which extend generally horizontally from a plate (wall) 25 also of insulating material. At each end of the coating zone, the charged conductor 22 is supported by insulating plates 27, 28 which have an arcuate configuration with a scalloped edge. The conductor extends along the arcuate scalloped edge so that the spacing between the conductor and charge collector 23 gradually decreases as the article carrier enters the coating zone and increases as the carrier leaves the coating zone. This affords a gradual build-up of the particle potential at entry and avoids an abrupt field termination at the exit.
  • the scalloped edges of plates 27, 28 support conductor 22 on a series of knife edges minimizing conductor contact with the supporting surface. This is desirable as contact between the conductor and a surface reduces ionization of air around the conductor and the charge transfer to collector 23.
  • the charged conductor 22 is connected at one end to a source of high voltage, not shown.
  • a blower 30 is located outside the paint booth, as above top wall 15.
  • Intake air for the blower may be filtered room air or may be filtered, temperature and humidity controlled air from the spray booth makeup plenum, not shown.
  • the blower discharge is connected through conduits or ducts 31, 32 with each end of a plenum chamber 33 extending the length of the charged conductor. Dampers 34, 35 are adjusted to balance the air flow to each end of the plenum.
  • the chamber is defined by top and bottom walls 36, 37, rear wall 38 and wall 25 which is between the plenum and the charged conductor and which is perforated or porous to allow air to flow therethrough.
  • the walls of the plenum are all of insulating material.
  • the charged conductor 22 and the plenum chamber 33 are oriented in the paint booth so that the chamber is physically located between the paint gun 17 and the conductor.
  • the only paint particles which approach the charged wire are those which are mechanically projected beyond the articles 14 and are not otherwise dissipated.
  • the air flows out through a plurality of slots 40 in wall 25 and across the charged conductor.
  • the cross sectional area of plenum 33 is tapered, becoming smaller as the distance from the conduits 31, 32 increases so that the rate of air flow outwardly across the charged conductor is substantially uniform from one end to the other.
  • the direction of air flow within the plenum is parallel with the longitudinal extent of charged conductor 22 and the wall surface. The air flow must change direction to pass from the plenum through the slots.
  • a section 25a of wall 25 extends across a chord of the curved end portion of conductor 22.
  • a baffle 42 in the plenum directs a portion of the air flow along wall section 25a so that there is an adequate air flow across the plate 28 and the portion of the conductor which is supported thereon.
  • the plenum wall 25 shown in Figs. 1, 2 and 3 has two rows of slots 40 therein. One row is above charged conductor 22 and the other row is below. The ends of the slots are staggered to minimize air flow variations.
  • FIG. 4 An alternate form of the perforate wall is illustrated in Fig. 4.
  • the wall 44 rather than having slots, has holes 45 formed therein which are of such a size and spacing that they afford a flow factor of the order of 50%. In other words, roughly one-half the surface area of wall 44 is solid and the other half is open.
  • top and bottom walls 36, 37 of plenum 33 extend beyond wall 25 and charged conductor 22. This restricts the flow of air preventing its expansion and reduction in velocity until it is at a point beyond the charged conductor.
  • the charged conductor 22 is 28.5 mm (1-1/8 inch) from the surface of wall 25, and the edge of lower plate 37 is 67 mm (2-5/8 inch) outside the conductor.
  • the velocity of air flow needed to minimize deposition of charged paint particles on the conductor depends on factors such as the charge on the particles, their mass and diameter and the charge on the conductor. In one system a flow velocity in the range of 2 to 3 m/s (400 to 600 ft/min) across the wire has been found satisfactory.
  • Articles 14 are transported by conveyor 10 and article carriers 11 through the painting zone defined by the booth. As the articles enter the booth, charge collector 23 approaches charged conductor 22 and an electric charge is induced on the carrier and the articles. Paint particles from gun 17 are attracted to and deposited on the articles.
  • the air flow from blower 30 is directed to the tapered plenum 33 and distributed uniformly along the length of charged conductor 22 through perforate wall 25. The air flow outwardly across the conductor prevents paint particles and other contaminants from depositing on the conductor.

Landscapes

  • Electrostatic Spraying Apparatus (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
  • Details Or Accessories Of Spraying Plant Or Apparatus (AREA)
EP80106585A 1980-01-18 1980-10-27 Air flow system for the charging conductor in an electrostatic painting system Expired EP0032528B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
PCT/US1980/000047 WO1981001967A1 (en) 1980-01-18 1980-01-18 Air flow system for charged conductor
WOPCT/US80/00047 1980-01-18

Publications (2)

Publication Number Publication Date
EP0032528A1 EP0032528A1 (en) 1981-07-29
EP0032528B1 true EP0032528B1 (en) 1984-03-28

Family

ID=22154158

Family Applications (1)

Application Number Title Priority Date Filing Date
EP80106585A Expired EP0032528B1 (en) 1980-01-18 1980-10-27 Air flow system for the charging conductor in an electrostatic painting system

Country Status (4)

Country Link
EP (1) EP0032528B1 (enrdf_load_stackoverflow)
JP (1) JPS56501872A (enrdf_load_stackoverflow)
DE (1) DE3067285D1 (enrdf_load_stackoverflow)
WO (1) WO1981001967A1 (enrdf_load_stackoverflow)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE961333C (de) * 1951-10-25 1957-04-04 Metallgesellschaft Ag Verfahren und Einrichtung zur Oberflaechenbehandlung im elektrostatischen Feld, beispielsweise zum Lackieren von Gegenstaenden
US3563203A (en) * 1969-06-11 1971-02-16 Purex Corp Ltd Spray chamber apparatus having protected conveyor means
US3749229A (en) * 1971-02-18 1973-07-31 Ilg Ind Inc Method and apparatus for protecting chain conveyor
CH560558A5 (en) * 1973-10-31 1975-04-15 Elfag Holding Electrostatic spray coater booth - air curtain over inwall leads out to blower suction-side outlet
WO1979000267A1 (en) * 1977-11-09 1979-05-17 Caterpillar Tractor Co Electrostatic coating system
WO1980001361A1 (en) * 1978-12-28 1980-03-20 Protectaire Syst Protected conveyor system

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB798111A (en) * 1956-03-15 1958-07-16 Printing Packaging And Allied Preventing or reducing mist formation from oils, printing inks, etc
US3296999A (en) * 1963-11-27 1967-01-10 Continental Can Co Apparatus for shielding pail open tops while spraying body exteriors
US3478969A (en) * 1966-03-09 1969-11-18 Frederick J Lund Pneumatic precipitating powder applying apparatus
US3690289A (en) * 1971-07-22 1972-09-12 Charles A Frank Vapor treatment hood
CH564376A5 (en) * 1974-02-01 1975-07-31 Elfag Holding Electrostatic powder coating chamber with protected wall - non-turbulent air curtain blown in through microporous surface
CH581503A5 (en) * 1975-01-31 1976-11-15 Gema Ag Electrostatic powder coating tunnel with cleaning system - has tunnel made of wire screens, cleaned from outside by travelling air blast

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE961333C (de) * 1951-10-25 1957-04-04 Metallgesellschaft Ag Verfahren und Einrichtung zur Oberflaechenbehandlung im elektrostatischen Feld, beispielsweise zum Lackieren von Gegenstaenden
US3563203A (en) * 1969-06-11 1971-02-16 Purex Corp Ltd Spray chamber apparatus having protected conveyor means
US3749229A (en) * 1971-02-18 1973-07-31 Ilg Ind Inc Method and apparatus for protecting chain conveyor
CH560558A5 (en) * 1973-10-31 1975-04-15 Elfag Holding Electrostatic spray coater booth - air curtain over inwall leads out to blower suction-side outlet
WO1979000267A1 (en) * 1977-11-09 1979-05-17 Caterpillar Tractor Co Electrostatic coating system
WO1980001361A1 (en) * 1978-12-28 1980-03-20 Protectaire Syst Protected conveyor system

Also Published As

Publication number Publication date
WO1981001967A1 (en) 1981-07-23
JPS56501872A (enrdf_load_stackoverflow) 1981-12-24
EP0032528A1 (en) 1981-07-29
DE3067285D1 (en) 1984-05-03

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