EP0796151B1 - Method and apparatus for electrostatically painting parts made of dielectric or low-conductivity material - Google Patents

Abstract

PCT No. PCT/FR95/01284 Sec. 371 Date May 2, 1997 Sec. 102(e) Date May 2, 1997 PCT Filed Oct. 4, 1995 PCT Pub. No. WO96/11063 PCT Pub. Date Apr. 18, 1996A method for painting a parts made of dielectric or low-conductivity material using a paint spraying unit including a chamber connected to both a paint outlet and to a paint supply. At least one electrode is mechanically and electrically connected to the part. An electrostatic field is generated between the electrode and the paint spraying unit. Paint is fed from the paint supply through the chamber to the outlet. The paint is electrically charged. The paint is sprayed onto the part to be painted. The outer surface of the electrode used includes at least one jagged portion for engaging the part to be painted. The jagged portion is the location of a peak electrostatic effect.

Description

The present invention relates to a painting process parts made of dielectric material or weakly conductor, an electrode for painting installation by electrostatic path of parts made of dielectric material or weakly conductive and a paint installation of parts made of dielectric or weakly conductive materials.

The present invention is particularly applicable to wood and furniture industries.

Currently known wood painting processes consist of sanding a wooden panel, covering it with a filling bottom, allow to dry, shell this bottom then apply a liquid paint, to dry the paint and to repeat these three operations several times, until seven times. The edges of the panel are processed independently and both sides must be treated several times. The whole process therefore takes two days and a half (simple gloss) to four days (forms complex with moldings, knockouts and grooves). Moreover, liquid paints cannot be guaranteed in stability for more than a few years. The range of color is necessarily very limited. Finally, the layers of paint must perform a counterbalance, i.e. that the number of layers must be substantially equal on the two flat faces of each panel, failing what, said panel is veiled.

Other wood panel finishing processes consist of depositing a layer of melamine paper or laminate or veneer of natural essence on the faces of the wooden panel. Complex forms are then difficult to achieve, if not impossible, using the process of manufacturing itself. Coatings and their connection to the mass of the wood offer mechanical qualities against impacts generally limited.

Finally, a last method consists in applying under press and hot, on one side and the four edges, a colored plastic film and different structure. This process is called thermoforming. This method does can fully cover a panel at one time. In addition, the edges of the face against facing reveal the thermoformed film. The choice of color is also very limited here.

Document JP 57194 074 discloses an electrode according to the preamble of claim 1, for weakly electrostatic painting of a room conductive, this electrode being intended to be affixed to one of the large faces of the part to be painted, the other large face of the part being intended to receive a coat of paint. This electrode by covering one of the large faces of the part prohibits the affixing of paint on all the faces of the part in a single operation. This electrode is provided with tips anchor crossing the part right through according to its thickness to come to the contact of the deposited paint and allow the evacuation of charges electrostatic.

Document DE-A-3 724 804 discloses a painting installation by electrostatic path including in particular spray guns paint and a device for transporting the part to be painted under the spray guns painting. This transport device consists of a plurality of drums spokes, the spokes of these drums by rotation of the latter being successively intended to support the part to be painted. These ray drums are connected to an electrical ground and are electrically conductive. The room paint is previously coated with a conductive layer, this layer constituent electrode. The spokes provide electrical continuity between this layer and the electrical ground of the installation. These rays cannot penetrate the room to be painted otherwise the bead formed around the penetration hole would destroy electrical continuity.

The present invention intends to remedy these drawbacks by proposing a new electrode for electrostatic installation.

The electrode according to the invention for installation of painting by way electrostatic of parts made of dielectric material, or weakly conductive, intended to come into contact with the part to be painted and to be connected to one of the two poles of an electrical voltage source fitted to the installation, which installation includes a gun comprising in the passage section of the paint an electrode connected to the other pole of the voltage source said gun being subjected to electrically charge the paint and spray it onto the part to be painted, characterized in that it has on its external surface angular regions joined by hollow regions, said regions angular and the said hollow regions being intended to come at least in part in the part to be painted, said angular regions being the seat of the so-called peak electrostatic effect, said peak effect causing a significant deformation of the field lines, allowing simultaneous deposition on all sides of the part without moving the gun

The description which follows, made with reference to the attached drawings in a explanatory and in no way limitative aim makes it possible to better understand the advantages, aims and characteristics of the invention.

Figure 1 shows a block diagram of operations according to the method of the present invention.

Figure 2 shows a schematic view of a painting installation provided with an electrode according to the invention and intended for the implementation of the method according to the invention.

Figure 3 shows a sectional view of a first embodiment of the electrode according to the present invention.

FIG. 4 represents a front view of the electrode according to FIG. 3.

Figure 5 shows a sectional view of a second mode of realization of the electrode according to the present invention.

FIG. 6 represents a front view according to FIG. 5.

Figure 7 shows, in section, an electric field generated by an electrode according to the present invention.

Figure 8 shows in perspective another form for producing an electrode according to the invention.

Figure 9 shows schematically, view of above, a painting installation baking oven according to the present invention.

In FIG. 1, the process object of the present invention to a particular example, that of wood furnishings. This furniture wood can be M.D.F (medium density fiber), i.e. wood made from from citrus fruit compressed under high pressure. This wood can also be of agglomerate, and more generally all type of natural or blended wood used in industry furniture. The piece to paint, as we can see in particular in FIG. 2 may be in the form a polygonal contour panel, for example rectangular or square.

In Figure 1 are shown a cut and put in shape 1, a hole 2, a sanding and a protection 3 of edges, a sanding 4 of the whole piece, a attachment of electrode 5, application of voltage 6 to electrode, applying a voltage 7 to the paint, a projection 8 of paint, a low flux cooking 9, high flux cooking 10, cutting 11 of margins and an application 12 of varnish.

The cutting and shaping 1 is of known type. She includes both rectangle cutting and rounding edges and possibly knocking and grooving, for example. It consists in giving the room its shape definitive. The other operations concern the state of surface of this room. The wood used must preferably have a humidity of 8 to 12 percent.

Drilling 2 consists of making a first hole in the part in such a way that the placement of the electrode can be done without popping the room. This drilling will advantageously blind and in the case where the part to be painted consists of a panel, will be made so that its median axis of symmetry is perpendicular to the two large faces of the panel.

The drilling 2 of electrodes is carried out either in a area which will then be machined, either in an area which will be eliminated by cutting margins. Preferably, the 2 electrode hole is then used, for example for the installation of hinges or hinges or any other mechanical elements involved in assembling the panels of a piece of furniture. In the case where the electrode is affixed to the part to be painted the drilling is not carried out. This piercing is also not performed if the shape of the electrode allows it to be forcefully inserted into the room without danger of bursting of the latter.

The edge protection 3 of the panel is a characteristic operation of the present invention. The edges of the piece of wood are sanded, for example with a grain of 400 for the M.D.F., with a grain of 220 for the chipboard, then covered with a blocking primer, consisting for example of wood pulp based on barium or a polyurethane varnish. This operation therefore consists in closing the pores of the wood or in fill in the rough edges of the wood. This protection 3 of edges also has a drying phase which can last a few hours. It allows pieces of wood to undergo then heaters, i.e. high cooking temperature.

Sanding 4 is also one of the operations features of the present invention. The sanding is an action to prepare the above surface the application of a product. Sanding disappears in surface fibers, impurities, traces of fat, scratches. This sanding is carried out according to the method of present invention with a grain greater than 300 and preferably 400. This grain generally corresponds to a particular sanding operation, called ginning, because of the fineness of the grain used. This sanding is made on all the surfaces to be painted in the room. The fineness of the grain allows the wood fibers not to be open so that the heating of the wood, during cooking operations 9 and 10, does not cause significant bubbling or degassing. So the surface finish of the paint is not altered. In the case of a panel the sanding is carried out on all sides of the latter.

The attachment of electrode 5 consists in fixing mechanically and therefore electrically the electrode to the part to be painted. Depending on the preferred form of realization the electrode is introduced, preferably in force, in the hole drilled during drilling 2. Hanging can be done by pushing in or by screwing for example. The electrode has projections straight or curved or acute angles. The electrode therefore has concave parts. This operation is the main feature of the invention because of the shape of the electrode which favors the appearance of a field electric spherical or flattened around the electrode when it is connected to a voltage source.

The application 6 of voltage on the electrode consists in electrically connect the electrode to a voltage source electric. Usage generally prefers that this tension be zero. Preferably, the electrode is connected by an electric cable or a metal support to said source of tension.

Applying tension to paint 7 is also of known type. It consists of electrically charging a solid paint powder, for example polyester powder with a sign voltage opposite to that which charges the part, said voltage being delivered by the source of voltage to which the electrode is connected.

In this way, the equipotential lines are spread around the room and one of them is practically identical to the volume of the room. It is notable that the effect tip applies to the part and as a result, the corners are painted in the same way as the rest of the piece, if not better.

The paint projection 8 is of known type and is usually performed by an electrostatic spray gun painting. It's propelling air, static electricity and the electric field created between the electrode and the pistol that cause the powder to move paint towards the part to be painted. This pistol paint electrostatic is connected to the source of voltage and is subject to electrically charging the painting whatever the positive or negative polarity.

The projection of paint is carried out by scanning but the powder paint deposited forms a single layer.

Low flux cooking 9 is carried out in the first part of an oven, the part in which the painted parts are introduced. The air flow hot, which comes from the bottom of the oven is braked by a mechanical protection. Thus, the thermal shock is limited as well as the mixing of air which could disturb uniformity of paint deposition. This is limited to one very short duration of two to four minutes, for which the paint begins to adhere to the support.

High flux cooking 10 is of known type. She has place in the rest of the oven. The two types of cooking are made for example in a gas oven but it goes without saying that any other type of oven suitable for this function may be used.

Finally, in the case of parts sold in the form of panels, cutting 11 of margins allows both bring the part to the required dimensions and eliminate the electrode hole 2.

The application 12 of varnish is of known type, for example curtain, cylinder, automatic spraying or manual.

• l'utilisation d'une électrode qui comporte des saillies droites ou courbes ou des angles aigus et qui favorise ainsi l'apparition d'un champ électrique sphérique ou aplati autour de l'électrode lorsque celle-ci est reliée à une source de tension.
• le ponçage effectué avec un grain supérieur à 300 et préférentiellement de 400, correspondant aussi à une opération appelée égrenage. Ce ponçage améliore la rugosité de surface sans ouvrir de voies au débullage au moment de la cuisson.
• la protection des chants 3 qui sont recouverts de pâte à bois que l'on peut diluer ou de vernis de polyuréthanne. Cette opération consiste donc à obturer les pores du bois ou encore à remplir les aspérités du bois. Cette protection des chants comporte aussi une phase de séchage qui peut durer quelques heures.

It is understood from the description of Figure 1 that the characteristic steps of the process are in order of decreasing importance.

• the use of an electrode which has straight or curved projections or acute angles and which thus favors the appearance of a spherical or flattened electric field around the electrode when the latter is connected to a voltage source.
• sanding done with a grain greater than 300 and preferably 400, also corresponding to an operation called ginning. This sanding improves the surface roughness without opening any channels for boiling during baking.
• the protection of the edges 3 which are covered with wood pulp which can be diluted or with polyurethane varnish. This operation therefore consists of closing the pores of the wood or even filling the roughness of the wood. This edge protection also includes a drying phase which can last a few hours.

In FIG. 1, the process object of the present invention to a particular example, that of wood furnishings. However, other examples could have be used, for example, that of plaster, that of earthy materials, bricks, P.V.C, tiles and more generally of all slightly conductive materials.

The process can also be applied according to the present invention to cardboard products made at from shredded products mixed with glue urea formaldehyde and hot compressed. Products shredded can be cartons lined with a sheet aluminum.

It should be noted that the paint can be metallized and / or metallize the part or any other surface effect, like grained, hammered effects, structured and smooth.

The products produced according to the process described in Figure 1 have successfully tested for resistance to shocks with ball of 110 grams, for qualification of lacquer and varnish paints, adhesion tests by checkering on varnish or lacquer, resistance tests from scratches, burns from cigarettes, stains from household and food products.

According to a first variant, the method comprises a varnishing phase by applying colorless varnish to drying with ultraviolet radiation having a variable brightness between 25 and 100 percent, depending on the choice of the user without ginning the support. The grammage per square meter preferably reaches 90 to 160 grams with a precision and homogeneity of 10 grams.

According to a second variant, the method comprises a varnishing phase by applying a varnish polyurethane with traditional drying or wood pulp diluted with conventional drying.

According to these two variants, the application methods can be, for example, by robot, by curtain, by spray gun or manually.

Figure 2 shows schematically a painting installation according to the invention.

In Figure 2 are shown a gun 13, a workpiece 16, electrode 17, support electrode 18 and a voltage source 19, paint 20, a spray of paint 21, a compressor 45 and a tank of powder coating 46 constituting paint reserve 20.

The gun 13 is adapted to orient the jet of paint 21 electrically charged to room 16. It is of known type. This pistol has an internal chamber formed in a projection cannon and in relation to a part with a paint outlet hole provided in end of the barrel and secondly with the reserve of painting 46 through a conduit. The painting in powder form is powered by compressed air at across the chamber from the reserve 46 towards the orifice paint outlet. In the gun chamber is provided an electrode, not shown, connected electrically via the waterfall gun electronics, to the positive pole of the electric voltage 19. The other pole of the voltage source 19 is electrically connected to electrode 17 or directly either indirectly through the support 18. Between electrode 17 and gun electrode is therefore established an electrostatic field which can be negative or positive depending on the choice of waterfall electronic. The paint charges electrically when his passage in the room by coming near or at gun electrode contact. Preferably the source of electric voltage supplied between its terminals a potential difference of several tens of kilovolts.

The part to be painted 16 is in the spraying operation of paint 8 of the process described in FIG. 1. It therefore has already been sanded with a grain greater than three hundred and his songs may have their blocked edges.

The compressor 45 injects compressed air into the powdering tank 46 according to known techniques in order to thin the paint in this tank. The fluidized paint is then sprayed.

The electrode support 18 is adapted to mechanically support the electrode 17 and the part 16 and to electrically connect one of the electrical terminals of the voltage source 19 to the electrode 17.
The electrode 17 promotes the appearance of a spherical or flattened electrical song around it when it is connected to a voltage source. The electrode 17 is conductive, has angular regions such as for example straight or curved projections or acute angles. Thus the electrode 17 has concave parts. It is electrically connected to an electrical ground and to part 16. To this electrical ground will be connected the negative pole of the voltage source 19. It also serves as a support for part 16.

Each projection that the electrode may include, according to a plane normal to the surface of said electrode, may have a triangular cross section or trapezoidal or any other form presenting distance from said surface a region of strong curvature.

Each projection can form a pin or be longiform and develop in the latter case so straight on the surface of the electrode or so curve for example in a helical circle or other curve.

The electrode may include a core, the projection (s) being formed on the external surface of the core and being able to develop radially with respect to the latter. An electrode with core is intended to be inserted into a hole previously made in the part to be painted.
Such an electrode when it is mechanically and electrically connected to a part in the form of a polygonal contour panel, all the external surfaces of which are to be painted, is preferably introduced into the panel in the thickness direction of this latest. The longitudinal axis of the electrode core is therefore perpendicular to the two large faces of the panel.

The core may have a cross section polygonal but preferably the cross section of this nucleus is circular. This core will be cylindrical or else in shape conical. The protrusions of an electrode with core cylindrical or conical can each develop according to one of the generators of the cylindrical or conical surface external of the nucleus or else curved on this external surface for example in helix, in circle and other. The protrusions of an electrode with a cylindrical core or conical may also be constituted by pins which will develop radially from the core.

Figure 3 shows a sectional view of a mode preferential embodiment of the electrode object of the present invention. Figure 4 shows a front view of the same embodiment of the electrode. This electrode consisting of a cylindrical core, is provided with a external thread and at least one longitudinal groove extending along a generatrix of the nucleus through the thread.

In Figure 3 and in Figure 4 are shown a part 16, an electrode 17 with a cylindrical core having an external thread 22, 23, 24, 25, at least one groove, a recess 28, an internal thread 29, a face before 30 and a rod 32. Preferably the electrode is provided with two diametrically opposite grooves 26, 27. The electrode can be fitted with a larger number grooves which preferably will be discarded regularly from each other. Furthermore it is specify that the length of the electrode is suitable for the thickness of the product to be painted.

The part 16 was pierced with a hole whose diameter is substantially equal to the bottom diameter of the external threads 22, 23, 24 and 25 and whose depth is substantially equal to or greater than the length re-entering the electrode in the panel.

External thread 22, 23, 24, 25 and both grooves 26, 27 are formed in a single thread of which the step for example is of the order of a millimeter. Each piece of thread 22, 23, 24 and 25 is therefore substantially equal to but less than half a step from a propeller stopping to grooves 26 and 27. The electrode 17 therefore comprises curved and helical projections and acute angles.

The recess 28 of cylindrical shape crosses through in part the electrode along the longitudinal median axis of the core of the latter.

The electrode as shown in Figure 3 does not has no shoulder but alternatively it can be equipped with a shoulder to limit penetration into the Exhibit 16.

The internal thread 29 or internal thread is produced in the recess 28 over the entire length of the latter.

The metal rod 32 allows the insertion of the electrode 17 in the part 16 by its geometry and the connection of electrical connectors to electrode 17. The rod 32 is preferably cylindrical and has a thread at the end to engage, by this end, screwed into the internal thread 29 of the electrode 17. This rod 32 will provide electrical and mechanical connection of the electrode to the electrode holder 18. This rod can also constitute electrode support.

The shape of the electrode 17 presented in FIGS. 3 and 4 is preferably inserted by screwing. Thanks to the presence of grooves, the electrode according to this form of realization is self-tapping and its screwing in the hole performs tapping of the latter. So the projections under form of net that this electrode penetrates in all in the material of the panel and are therefore intimate contact with the part which is conducive to improving both electrical and mechanical connection with this last.

Preferably, the insertion depth of the electrode 17 in the hole made by drilling the part 16 is substantially greater than half the thickness of the part 16 and substantially less than said thickness.

Figure 5 shows a sectional view of a second embodiment of the electrode object of the present invention.

FIG. 6 represents a front view of the electrode presented in figure 5.

In FIGS. 5 and 6 are shown a part 16, an electrode 17 having a core on the surface cylindrical with straight projections external longitudinal 33 separated by recesses 34 longitudinal, a recess 35, a shoulder 31 and a rod 32. This electrode has a cylindrical core.

The external longitudinal straight protrusions 33 and the hollow 34 form a prism with a polygonal base, for example star shaped. The recess 35 crosses right through the electrode and is formed along the longitudinal axis of the core of the latter. The shoulder 31 and the rod 32 end threaded have the same characteristics and functions as in Figures 3 and 4.

The shape of the electrode 17 presented in FIGS. 5 and 6 is preferably forced into a hole previously provided in the panel. The electrode 17 therefore has straight protrusions and sharp angles.

Other forms of electrodes conform to the spirit of the invention, such as, for example, wood screws, threaded rods, or any other element.

An electrode can also be provided. in the form of a plate of reduced thickness and of polygonal outline for example, the projections being formed on at least one of the faces of said plate. A such electrode can be force-fitted into the panel of wood without prior drilling of the latter or well being inserted into the hole provided to receive this electrode or be affixed to one of the faces of the part. The projections provided for this electrode in the form of a plate may be spikes of the longiform bosses and other. The projections will always each have a cross section of triangular shape, trapezoidal shape and other forms likely to be the seat of an effect so-called electrostatic.

The plate may form a succession of projections and hollow, so this plate will be wavy. The ripples of the plate may be triangular in shape. The tall faces of the corrugations may be smooth or else present protrusions like those previously described.

Figure 7 shows, in section, an electric field generated by a device which is the subject of the present invention.

In figure 7 are shown lines of equipotential 36, 37 and 38 generated by the setting under voltage in the air of the inserted part of the electrodes 17.

These equipotential lines 36, 37 and 38 are ellipticals and, in space, their surface is ellipsoidal.

It is understood that when the electrode 17 is inserted in room 16, the field lines take shape even more flattened and one of them is substantially identical to the shape of part 16. This is due to the dielectricity of the material constituting the part 16 or its slight conductivity.

Figure 8 shows a paint baking oven according to the present invention.

In FIG. 8 are represented an oven 39, an area coin entry area 40, a coin exit area 41, a high-flow heating zone 42, a hot air inlet 43 with protection 44.

The oven 39 has the parts inlet zone 40 which is, for example, at one end and the parts outlet zone 41 which is, at the other end of the oven. Between these two zones there is an intermediate zone 42 In this oven (39) the first heating or baking phase takes place with reduced air movement speeds compared to the following heating or baking phases so that the paint can gel before the part reaches the area with strong air movement. The first heating phase is carried out in the air intake zone while the following phase is carried out in the rest of the oven, ie in zones 42 and 41. It should be noted that the entire oven volume is at uniform temperature.
The high-flow heating region 42 includes the zones 42 and 41. According to a preferred embodiment, the oven is provided over its entire extent with air intake orifices, the air intake being effected by the bottom and the orifices being distributed in the zones 40, 41, and 42. So that the movement of air is reduced in the air intake zone, the latter is provided with a screen 44 constituted by a removable wall placed on the bottom of the zone 40 in order to hide the air intake orifices of the latter. According to this method and this heating device, the parts 16 undergo first of all cooking without thermal shock or air mixing, these two events being able to deteriorate the paints produced on the surface of the parts 16 which are still in the form of powder. solid deposited on the surface of the parts 16.

It should be noted that the temperatures and durations of cooking are those recommended for paints powder used, the wood being able, once protected on its songs and knockouts by a blocking primer, withstand high temperatures without expansion thermal.

The method and the device described in the present invention apply equally to the painting of parts particle board, compressed wood, particle board coated with polyvinyl film, for example smooth P.V.C. or imitation of natural essence, in wood M.D.F. gross or smooth or coated with smooth P.V.C. or imitation petrol natural, or natural gas veneer.

It should be noted that the electrode can be a element of the finished product and for this reason is not removed from the panel. This electrode which in this case constitutes insert can be used later as a point anchor for the panel.

Claims (19)

1. An electrode (17) for an installation for electrostatic painting of workpieces made of dielectric or low-conductivity material, designed to come into contact with the workpiece (16) to be painted and to be connected to one of the two poles of an electric voltage source (19) with which the installation is equipped, which installation comprises a gun (13) comprising, in the paint passage section, an electrode connected to the other pole of the voltage source (19), said gun (13) being responsible for charging the paint electrically and projecting it onto the workpiece to be painted, characterised in that it comprises on its outer surface angular regions linked by recessed regions, said angular regions and said recessed regions being intended at least partially to enter the workpiece to be painted, said angular regions being the seat of the electrostatic effect known as the peak effect, said peak effect causing considerable deformation of the field lines, allowing simultaneous deposition on all the faces of the workpiece (16) without moving the gun (13).
2. An electrode (17) according to claim 1, characterised in that the angular regions take the form of projections (22), (23), (24), (25), (33).
3. An electrode (17) according to claim 2, characterised in that it comprises a core, the projection(s) (22), (23), (24), (25), (33) being formed on the outer surface of the core.
4. An electrode (17) according to claim 3, characterised in that each projection (33) is elongate and extends in rectilinear manner.
5. An electrode (17) according to any one of claims 2 to 4, characterised in that it has an elongate core of circular cross-section, the projection(s) (22, (23), (24), (25) extending helically over the outer surface of the core.
6. An electrode (17) according to claim 5, characterised in that it consists of a cylindrical core provided with an external thread (22), (23), (24), (25) and at least one longitudinal channel (26), (27) extending along a generating line of the core, through the thread.
7. An electrode (17) according to claim 1, characterised in that it takes the form of a plate, the projection(s) being formed on at least one of the faces of said plate.
8. An electrode (17) according to claim 1, characterised in that it takes the form of a corrugated plate.
9. An electrode (17) according to claim 8, characterised in that the corrugations of the plate are triangular.
10. An electrode (17) according to claims 2 and 9, characterised in that the plate comprises projections on at least one of its faces.
11. A process for painting a workpiece (16) of dielectric or low-conductivity material, in which a means (13) for projecting paint (20) is used which comprises a chamber connected on the one hand with a paint outlet opening and on the other hand with a paint reservoir (46), characterised in that it consists in:

    connecting mechanically and electrically to the workpiece (16) at least one electrode (17) according to any one of the preceding claims,

    creating an electrostatic field between the electrode (17) and the paint projecting means (13) by applying an electric potential difference between the electrode (17) and another electrode accommodated in the chamber of the projecting means (13),

    propelling the paint from the reservoir (46) to the outlet opening by passage through the chamber,

    electrically charging said paint (20),

    and projecting said paint towards the workpiece (16) to be painted.
12. A painting process according to claim 11, characterised in that it consists in using solid paint in powder form.
13. A painting process according to claim 11 or claim 12, characterised in that it consists in introducing the electrode (17) into the body of the workpiece (16).
14. A painting process according to claim 11 or claim 12, characterised in that it consists in affixing the electrode (17) to at least one of the outer faces of the workpiece (16) to be painted.
15. A painting process according to any one of claims 11 to 14, characterised in that, before the paint is applied, the workpiece surfaces to be painted are cleaned.
16. A process according to claim 15, characterised in that, prior to the projection of solid paint, the edges of the workpieces and the recesses have their roughness filled by the application of a surfacer.
17. A process according to any one of claims 11 to 16, characterised in that it comprises passage through an oven (39), in which low-flux baking proceeds at air displacement speeds which are reduced relative to the following heating stages.
18. An installation for electrostatic painting of workpieces (16) made of dielectric or low-conductivity material for performing the process according to any one of claims 11 to 17, characterised in that it is equipped with at least one electrode (17) according to any one of claims 1 to 10.
19. An installation according to claim 18, characterised in that it comprises an oven (39) in which low-flux baking proceeds at air displacement speeds which are reduced relative to the following heating stages.

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