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 elec ⁇ trostatic painting system and more particularly to an air flow system for preventing deposition of paint on a charged conductor used to charge an article iso ⁇ lated from ground, being painted in an electrostatic painting system.
• Electrostatic painting systems are known in which the articles painted are electrically charged.
• articles are carried through a painting zone by a conveyor with the articles and article car ⁇ riers isolated from electrical ground.
• a charged conductor extends along the con ⁇ veyor path.
• a charge collector on the article car ⁇ rier is spaced from the charged conductor and an electric charge is transferred to the carrier and thus to the article supported therefrom.
• the elec ⁇ tric potential on the conductor may be of the order of 75 kV to 100 kV.
• An undesirable discharge or arc ⁇ ing may occur from the charged conductor. This condi- tion is aggravated by the presence of dirt, paint particles or the like.
• the present invention is directed to over ⁇ coming one or more of the problems as set forth above.
• an im ⁇ proved air flow system includes a blower, means defin- ing 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 deposit ⁇ ing 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 is a diagrammatic perspective of a painting installation illustrating the invention
• Fig. 2 is an enlarged fragmentary section taken generally along line 2-2 of Fig. 1;
• Fig. 3 is an enlarged section taken along line 3-3 of Fig. 1;
• Fig. 4 is a fragmentary elevation illus- trating an alternate form of perforate wall.
• Fig. 1 The painting installation of Fig. 1 has an overhead conveyor with a conveyor track 10 and wheeled article carriers 11 which are drav 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 i ⁇ , and end and rear walls which are not shown.
• a paint gun 17 provides a source of particulate paint and is spaced fron 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 paint ⁇ ing booth.
• the gun may be fixed or may be recipro ⁇ cated 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 ex ⁇ tends 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 there ⁇ from which is conductively coupled through the carrier and rack to the articles 14.
• the conveyor 10 is elec ⁇ trically grounded and the upper portion of carrier member 12 includes an isolation resistor so that the charge transferred to the collector 23 is not imme ⁇ diately dissipated to ground. In the system described some of the paint particles have a negative charge, others have a posi ⁇ tive charge and some are uncharged.
• a flow of air is directed across the charged conductor 22 coun ⁇ teracting 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 25 also of insulating mate ⁇ rial. 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 scal ⁇ loped 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 conduc- tor 22 on a series of knife edges minimizing conductor contact with the supporting surface. This is desir ⁇ able 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 be ⁇ tween the plenum and the charged conductor and which is perforated or porous to allow air to flow there- through.
• the walls of the plenum are all of insulat- ing material.
• the charged conductor 22 and the ple ⁇ num 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, becom ⁇ ing smaller as the distance from the conduits 31, 32 increases so that the rate of air flow outwardly a'cross 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 ade- quate 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. 2 An alternate form of the perforate wall is illustrated in Fig. 2.
• 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 25 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 be ⁇ yond 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 48 mm (2-5/8 inch) out ⁇ side 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 conduc ⁇ tor. 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 de ⁇ fined by the booth. As the articles enter the booth, charge collector 23 approaches charged conductor 22

Landscapes

• Electrostatic Spraying Apparatus (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Details Or Accessories Of Spraying Plant Or Apparatus (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=22154158

Family Applications (1)

Country Status (4)

Citations (7)

Family Cites Families (5)

• 1980
  • 1980-01-18 JP JP50094780A patent/JPS56501872A/ja active Pending
  • 1980-01-18 WO PCT/US1980/000047 patent/WO1981001967A1/en unknown
  • 1980-10-27 EP EP80106585A patent/EP0032528B1/en not_active Expired
  • 1980-10-27 DE DE8080106585T patent/DE3067285D1/de not_active Expired

Patent Citations (7)

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