WO2002078854A1 - Dispositif destine au revetement electrostatique avec une fente double pour emission de poudre, notamment au revetement de bobines metalliques - Google Patents

Dispositif destine au revetement electrostatique avec une fente double pour emission de poudre, notamment au revetement de bobines metalliques Download PDF

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Publication number
WO2002078854A1
WO2002078854A1 PCT/IB2002/001013 IB0201013W WO02078854A1 WO 2002078854 A1 WO2002078854 A1 WO 2002078854A1 IB 0201013 W IB0201013 W IB 0201013W WO 02078854 A1 WO02078854 A1 WO 02078854A1
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WO
WIPO (PCT)
Prior art keywords
powder
previous
emission
electrode
venturi
Prior art date
Application number
PCT/IB2002/001013
Other languages
English (en)
Inventor
Ines Urbani
Giovanni Bortolato
Original Assignee
Ines Urbani
Giovanni Bortolato
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 Ines Urbani, Giovanni Bortolato filed Critical Ines Urbani
Publication of WO2002078854A1 publication Critical patent/WO2002078854A1/fr

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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
    • B05B5/025—Discharge apparatus, e.g. electrostatic spray guns
    • B05B5/03—Discharge apparatus, e.g. electrostatic spray guns characterised by the use of gas, e.g. electrostatically assisted pneumatic spraying
    • B05B5/032—Discharge apparatus, e.g. electrostatic spray guns characterised by the use of gas, e.g. electrostatically assisted pneumatic spraying for spraying particulate materials
    • 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
    • B05B5/14—Plant for applying liquids or other fluent materials to objects specially adapted for coating continuously moving elongated bodies, e.g. wires, strips, pipes
    • 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
    • B05B5/1683—Arrangements for supplying liquids or other fluent material specially adapted for particulate materials
    • 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
    • B05B5/1691—Apparatus to be carried on or by a person or with a container fixed to the discharge device
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B1/00—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means
    • B05B1/02—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to produce a jet, spray, or other discharge of particular shape or nature, e.g. in single drops, or having an outlet of particular shape
    • B05B1/04—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to produce a jet, spray, or other discharge of particular shape or nature, e.g. in single drops, or having an outlet of particular shape in flat form, e.g. fan-like, sheet-like
    • B05B1/044—Slits, i.e. narrow openings defined by two straight and parallel lips; Elongated outlets for producing very wide discharges, e.g. fluid curtains
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B1/00—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means
    • B05B1/14—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means with multiple outlet openings; with strainers in or outside the outlet opening

Definitions

  • the present invention relates to a device for electrostatic painting in general, but with particular reference to its application to metal coils, which allows an increase in both the production and uniformity of the thickness of the paint deposited on the surfaces.
  • the powder has a higher concentration in the centre of the projection axis and a lower concentration at the edges.
  • the powder has a higher concentration in the centre of the projection axis and a lower concentration at the edges.
  • metal coils having a width of one meter, which are to be painted at a operating speed of 20 meters / minute, with a surface powder coating thickness of 50 microns, at least 2 kg of powder deposited per minute are normally necessary.
  • Current electrostatic systems are only able, theo- retically, due to the known charge limits of powder, to deposit only 60% of the powder emitted and each has a projection capacity of a weight quantity of 250-300 gr. per minute. In order to paint 20 metres a minute, it is therefore necessary to use a set of at least twenty spray-guns.
  • the powder is conveyed to each spray-gun by means of a pipe (63) called diffuser pipe, connected to a Venturi-type pump (65) fed by compressed air from the pipe (66), at a pressure regulated by means of a reducer valve, with pressure reading applied by a pressure gauge, Figure 4A.
  • the pumps suck the powder through a pipe which draws from an appropriate tank (64) of fluidified powder by air charged through the pipe (62) (fluid bed), Figure 4A.
  • the flow-rate of each spray-gun must be individually established by regulating the air pressure of its Venturi pump and a further regulation of compressed air, called powder dilution air. If the flow-rate of the powder sent to the spray-gun must be increased, the quantity of air of its Venturi pump must be increased, i.e. we must increase its pressure and consequently also increase its discharge rate from the ejector.
  • Another known problem relates to having to place the spray-guns on a line which is such as to cover, with pow- der emission cones, the total width of the arrival surface.
  • the deposition is influenced by the electrostatic charge supplied to the powder due to corona discharge
  • the low efficiency ratio is due to the geometry of the emission electrode which is generally positioned co- axially to the centre, in the terminal part, of the outlet pipe of the powder. Under these geometrical condi- tions, the current, discharged from the electrode, is limited, as known for repulsion, by the electric charge with the same sign acquired by the powder which flows around it.
  • the only way of enhancing the charge is to increase the voltage of the electrode to raise the quantity of current discharged. As known, a rise in the voltage causes a harmful increase in the electric field near the surface to be painted.
  • the increase in the electric field induces undesired effects on the surface covered by the powder deposited, once baked and polymerized such as: a) orange-peel surface effect, b) surface with a pin-holes effect, c) separation of the particle-size of the powder with differences in colour.
  • the geometrical shape of the electric field, gener- ated by the electrodes of the spray-guns (53) is repre- sented by a number of lines of force (57) , proportional to the intensity of the field, Figure 2B, which extend from the electrodes (52) and terminate in general points of the surface.
  • the projected image of the lines of force (57) of the surface electric fields has a certain value on the vertical of the individual point-electrode increasing where the fields cross with each other (59) , Figure 2B.
  • electrostatically charged powder is deposited, it follows the lines of force of the electric field and consequently the thickness of the deposit has in turn maximums and minimums .
  • At least twenty spray-guns should be used, with twenty Venturi pumps, forty pressure regulators, forty reading manometers, ten double electronic air pressure control centers (61), Figure 4A, pipes (66) and a high electric voltage of the spray-guns, cables (60) .
  • the aim of the invention is to overcome the solve the problems described above, achieving the following objectives : a) Reduction to one or two projectors installed for painting, b) Reduction in the number of Venturi diffuser pumps of the powder itself, c) Reduction in the diffuser regulation systems of the powder, d) Linear discharge and a uniform density of the powder to obtain emission without cross-points, e) Geometry of the electrode so that the electric field near the surface is uniform and without discontinuity points, f) Emission of electrons from the electrode to have a uniform and non-dispersed formation of ions for the optimum charging of the powder, g) Reduction in the number of electrostatic generators necessary for charging the powder, h) Increasing the surface painted within the time unit, thus increasing production with a considerable eco- nomic advantage.
  • the device of the invention consists of a rectangular tank (16) Figure 1A represented in section, containing two porous septa inside (7) and (13) which divide it into three superimposed chambers (4), (5) and (6) .
  • the rubber socket (11) on one side of the container (19) serves for the inlet pipe (41) of the powder from a general feeding tank (46) , aspirated by means of a single Venturi pump (44) with a high flow-rate, Figure 4B.
  • the compressed air is fed into the chambers (6) and (4) by means of inner pipes (24) and (10), holed (14) and connected at the T-shaped socket (43), with pipes (42), (45) and with the air intake pipe (40) , Figure 4B.
  • the air passes through the porous septa (7), (13) and fluidizes the powder which enters the chamber (5) through the pipe (41), Figure 4B.
  • the septum (15) vertically separates the chamber (5) into two sub-chambers (21) and (20) .
  • the septum (15) is at a suitable distance from the porous septum (7), in order to allow the enter- ing powder (which once fluidified behaves as a liquid) to occupy the two chambers (21) and (20) acting as communicating vessels, Figures 1A and IB.
  • the chamber (20) which, after a period of time, must integrate the quantity of powder sent through the pump (44), has a larger volume than the chamber (21).
  • a Venturi-shaped ejection profile of the powder (17) has been adopted, partly situated in the lid (12) and partly in the block (18), whose length is slightly higher than that of the metallic coil to be painted.
  • Two superimposed longitudinal slits (19) and (3) are situated in this ejector block (18) by means of the septum (8) for the projection of the powder.
  • the emission of the powder takes place both as a result of the pressure of the air sent through the porous septa (7) and (13) into the chamber (20) , and also by means of the diffused air pressure of the Venturi pump (44) into the same chamber (20) which also communicates with the chamber (21) where the powder is pushed out through the slits (19) and (3), Figure 1A, to paint the coil.
  • This consists of a metallic pipe (1), with reference to Figure 3A, having a length which is slightly higher than that of the emitter with a slit (37) figure 3B, in section, longitudinal with an opening of about 100°.
  • Two plugs, made of an electrically insulating plastic material, (33) and (34) are inserted at the ends of the milled pipe (1) figure 3A.
  • a screw connection (31) for inserting the high voltage cable (39), coming from the voltage multiplier bridge (36) , fed to the electronic control center (40), figure 3C.
  • the high voltage cable (39) is regulated so as to make contact with the plate (38) to which an electrically conductive metal wire (2) acting as electrode, is attached, which is connected to the other end plug (34) where it is kept under stress by the spring (35) with the possibility of regulating the stress by means of the screw (32) .
  • the electrode in this case is a wire, and therefore has a continuous geometry
  • the electric field, dashed lines (58), Figure 2C, generated thereby, close to the surface of the coil also has the advantage of having the same continuity and uniformity, eliminating the maximum and minimum points which were formed, as specified above, with the use of several projectors.
  • both the quantity of powder emitted from the projector and the electrode current must be increased, as there would otherwise be a large quantity of powder which could not be sufficiently charged for adhering to the coil.
  • the quantity of current absorbed by the powder emitted, with respect to the total amount, is about 0.5%. It can therefore be deduced that there is a very high dispersion of ions generated by the corona discharge and only a minimum fraction of these contributes to charging the powder.
  • the device of the invention has been designed so that the emission of ions (68) takes place in a single direction through the slit (37) towards the flow of powder (69) projected from the emitter, decreasing the dispersion, Figure 3D.
  • the electrons emitted by the wire (2) ionize the molecules of air present in the space between the walls (30) of the pipe (1) and the wire itself, creating an electric charge of the same sign.
  • the pipe is immersed in the electric field due to the voltage present on the wire and its electric potential is conse- quently slightly lower than that of the feeding of the wire itself, due to its minimum distance from the wire.
  • the electric charge, generated inside the pipe (1) by the electrode (2) is attracted towards the walls (30) as their electric potential is lower, Figure 4D.
  • the new charges (68) therefore only have the possibility of exiting from the slit (37) situated in the direction of the ejection outlet of the powder (69), crossing the flow and consequently electrically charging it.
  • edges (67) of the slit are at a voltage of the same electric sign as the ions generated by the electrode, but as a result of their edges, due to known physical effects, they produce a strong electric field and consequently have a repulsion effect on the same ions, forcing them to be discharged in a fine linear beam at the centre of the slit (37) , in the direction of the powder without being dispersed in the environment, Figure 3D.
  • a further advantage lies in the installation of the device of the invention on a plane attached to it (25) , also connected to another supporting planee (27) by means of four anti-vibration supports (28) and (26) .
  • a pneumatic or mechanical vibrator (29) is installed on the surface (25) , which guarantees the necessary vibration for obtaining the best results for a clean emission and uniform deposit, Figure IB. It can be clearly seen how the device of the invention, although extremely simple in its construction and running, provides a considerable improvement to the surface finishing, a saving in the installation and operating costs, but at the same time also has the possibility of increasing the production within the time unit, thanks to its high emission capacity and electric charge of the powder.

Abstract

L'invention concerne un dispositif de peinture en poudre électrostatique comprenant (1) un distributeur de poudre doté d'une sortie linéaire (3, 9) et d'un diffuseur plat (17), (2) une chambre (20, 21) d'absorption des turbulences provoquées par une pompe du diffuseur, (3) deux septa poreux situés face à face (7, 13) dans la chambre (20, 21), et (4) au moins un appareil vibrant.
PCT/IB2002/001013 2001-03-28 2002-03-26 Dispositif destine au revetement electrostatique avec une fente double pour emission de poudre, notamment au revetement de bobines metalliques WO2002078854A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITMI01A000654 2001-03-28
IT2001MI000654A ITMI20010654A1 (it) 2001-03-28 2001-03-28 Dispositivo per verniciatura elettrostatica ad emissione lineare di polvere attraverso una doppia fenditura di qualsivoglia lunghezza per us

Publications (1)

Publication Number Publication Date
WO2002078854A1 true WO2002078854A1 (fr) 2002-10-10

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PCT/IB2002/001013 WO2002078854A1 (fr) 2001-03-28 2002-03-26 Dispositif destine au revetement electrostatique avec une fente double pour emission de poudre, notamment au revetement de bobines metalliques

Country Status (2)

Country Link
IT (1) ITMI20010654A1 (fr)
WO (1) WO2002078854A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7626602B2 (en) * 2006-09-15 2009-12-01 Mcshane Robert J Apparatus for electrostatic coating

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4688518A (en) * 1985-03-08 1987-08-25 Gabriele Missier Powder distributor for electrostatic painting
EP0800868A1 (fr) * 1996-04-10 1997-10-15 ABB Research Ltd. Système de dispersion pour un pulvérisateur de poudre
US5800876A (en) * 1996-02-20 1998-09-01 Abb Research Ltd Method and device for controlling the outflow of a fluidized solid from a container
WO2001085353A1 (fr) * 2000-05-10 2001-11-15 Paolo Checcucci Equipement pour peinture electrostatique a buse de venturi

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4688518A (en) * 1985-03-08 1987-08-25 Gabriele Missier Powder distributor for electrostatic painting
US5800876A (en) * 1996-02-20 1998-09-01 Abb Research Ltd Method and device for controlling the outflow of a fluidized solid from a container
EP0800868A1 (fr) * 1996-04-10 1997-10-15 ABB Research Ltd. Système de dispersion pour un pulvérisateur de poudre
WO2001085353A1 (fr) * 2000-05-10 2001-11-15 Paolo Checcucci Equipement pour peinture electrostatique a buse de venturi

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7626602B2 (en) * 2006-09-15 2009-12-01 Mcshane Robert J Apparatus for electrostatic coating
US8269807B2 (en) 2006-09-15 2012-09-18 Mcshane Robert J Apparatus for electrostatic coating

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Publication number Publication date
ITMI20010654A0 (it) 2001-03-28
ITMI20010654A1 (it) 2002-09-28

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