EP0303541A1 - Spraying installation for a coating product, e.g. for a water soluble paint - Google Patents

Abstract

Installation for spraying a coating product, in particular a conductive water-soluble paint. …<??>The installation comprises a colour-changing unit (11) connected by a distribution circuit (12) to a spraying device (13); an intermediate reservoir (41) capable of being disconnected from the colour-changing unit consists of a pipe section of the circuit (12), which section can be connected to a pressurised reservoir (44) of rinsing product in order to permit the pushing of the injected paint into the said intermediate reservoir. …<??>Application to the painting of bodywork elements in the automotive industry. …<IMAGE>…

Description

The invention relates to an installation for spraying a coating product, in particular a conductive coating product, such as a water-soluble paint or a metallized paint, applied electrostatically; it relates more particularly to a new arrangement making it possible to rapidly ensure changes to such products. The invention finds its preferred field of application in the fields where the objects to be covered follow one another along the same projection location and where any two consecutive objects must generally be covered by coating products of different colors. Such operating constraints imposing extremely rapid color change cycles are encountered in particular in the automotive industry for painting bodywork elements. The invention is more particularly intended to solve the additional problems posed in this context by the electrostatic application of water-soluble paints or certain metallized paints, which are relatively conductive.

A paint spraying installation, in a production unit as large as an automobile manufacturing plant, for example, generally comprises several very long closed-loop paint circulation circuits (these circuits can cross an entire part from the factory) which establish the link between large paint tanks and the different projection booths. It is therefore necessary to provide such a circuit by color and another similar circuit for the solvent or the cleaning product. For obvious safety reasons, these circuits are connected to earth.

Furthermore, in a paint spray booth thus supplied, the objects to be painted, in this case the automobile bodies, in the example envisaged, are carried by means of conveying through the cabin, in which there are electrostatic projection means capable of operating in a certain "activity zone" inside the cabin.

These projection means can be "bowls" rotating at high speed, or pneumatic or hydrostatic spraying. One of the usual problems to solve in this type of installation is that of the color change between two consecutive objects. Indeed, in the automobile industry, in particular, there is no question of painting the bodies in series, according to the color. The most frequent case, on the contrary, is that where the color must practically be changed after each bodywork. This implies being able to implement rinsing and drying cycles of the projection means, which are extremely rapid. For example, a color change can take place every minute or so and the time allowed for carrying out all the operations necessary for the color change is of the order of ten seconds.

In known conventional installations, all the coating product circulation circuits are connected, as well as a compressed air circuit and a cleaning product circuit, through controlled isolation valves, to a manifold, one of which common output branch is connected to the projector. This known arrangement will be referred to hereinafter as "coating product changing unit" or, more simply, "color changing unit". Conventionally, to change color, it is necessary to close the valve of the coating product circuit used, a certain time (calculated) before the end of the spraying phase in progress, then open the compressed air valve to push the remaining product to the projector. A cleaning cycle is then carried out comprising a succession of injections of cleaning product and compressed air until the conduits are clean and dry. Finally, another valve from another coating product circuit is open to fill the manifold. and ducts until a little new color coating comes out of the projector. A new paint projection phase can then begin.

When the installation has only a small number of coating products of different colors, for example three or four, the collector can be placed fairly close to the projector. On the other hand, when there are too many different coating products (there can be up to twenty or more) this solution is no longer practicable and the color change unit must then be placed away from the spotlights. When the objects to be coated are bulky, and this is the case with automobile bodies, the projection means are subject to large displacements parallel to the largest dimension of these objects, in particular in the case of robots, for example five or six meters. In this case, the color change unit is very far from the projector (s), which considerably increases the volumes of conduits to be cleaned, and therefore the time of the color change sequences. Therefore, with each change of color, the amounts of coating product and cleaning product lost are significant, of the order of several hundred cubic centimeters.

In the case of an electrostatic installation, all these problems relating to color change are further accentuated when it is desired to use coating products with low resistivity, such as for example water-based paints, while retaining the advantages of '' an electrostatic projection. In this case, the projector is often brought to a high voltage and it is advisable to avoid the short circuit between this projector and the circuits of circulation of coating product connected to the ground. To deal with the specific problem of color change with a low resistivity coating product, French patent N ° 2572662 proposes to fill an intermediate reservoir with the right amount of paint necessary for each application. The arrangement is such that this intermediate reservoir is sometimes worn at ground potential when it is filled, and sometimes at high voltage, when it powers the projector (s). This intermediate tank is unique for all shades, so that each color change requires cleaning of the tank but also of all the conduits which are connected to it.

In addition, in this type of installation, it is relatively difficult to adjust the quantity of coating product to be introduced into the intermediate tank. The quantity must, in fact, be sufficient for the object to be painted in full. However, any excess is lost on rinsing, which leads to a reduction in the overall deposition yield and can cause all or part of the gains provided by the electrostatic application to be lost. The invention solves these problems.

In this spirit, the invention therefore essentially relates to a coating product spraying installation of the type comprising a coating product changing unit, means for supplying rinsing product, at least one distribution circuit, downstream of said unit and supplying at least one projector ensuring the spraying of said product, as well as an intermediate tank, forming part of this distribution circuit, characterized in that said intermediate tank consists of a section of conduit of said distribution circuit and in that that controlled connection means are arranged to push said coating product, in the spraying phase, from said rinsing product.

The fact of having transformed the intermediate tank into a conduit has many advantages.
- The intermediate tank, thanks to its new shape, is much easier to clean, which requires less rinse aid and therefore saves time.
- By "pushing" the coating product with the solvent or rinsing product, over the entire length of the intermediate tank, all the conduits located upstream and the intermediate tank itself are already starting to be cleaned, during the spraying phase of said coating product.
- Thanks to one or more flow sensors judiciously placed in the installation, it is possible to very precisely control the quantity of product injected in each cycle as well as the spraying of this product.

For electrostatic application at least one insulating conduit is provided between the parts connected to earth and the parts connected to high voltage. It is then possible to maintain an air circulation in such an insulating duct, to complete the drying and to avoid any short-circuit phenomenon attributable in particular to a possible ionization of the humid air in the pipes.

According to another improvement, at least part of such aforesaid insulating conduit is shaped as a serpentine, preferably oriented so that its axis is substantially horizontal. This prevents the formation of a continuous film of liquid inside the conduit. The electrical "path" is thus cut at each turn and the liquid droplets are "trapped", pending their complete evaporation, in the substantially horizontal parts of the coil.

On the other hand, the coating product changing unit is earthed, for the reasons stated above. If the installation is suitable for an application of said coating product by electrostatic means, said distribution circuit is then sequentially connected to a high voltage applied to the electrostatic projector. In this case, the installation is further characterized in that said controlled connection means are arranged between, on the one hand, said section of conduit and on the other hand, said unit and means for supplying rinse aid. isolated from the earth, so as to be able to push said coating product, in the electrostatic projection phase, from rinsing product coming from these isolated supply means.

In fact, the usual rinsing product for water-soluble paints is water containing a certain proportion of an alcohol; it is therefore necessary to have a certain volume of rinse aid in an electrically isolable tank from the ground, so that the spotlight (s) are not earthed by the column of paint and rinse aid. The presence of a tank carried periodically at high voltage and which may not find a place in the cabinets where the elements at high voltage of the projector are locked can, in certain cases, become a drawback. This is why a variant according to the invention proposes an installation of coating product according to the basic definition set out above, for the application of said product electrostatically, where said coating product changing unit is connected to the earth, and where the distribution circuit is, at least in the projection phase, connected to a high voltage applied to at least one electrostatic projector, characterized in that, the rinsing product being chosen with high resistivity, a flow sensor connected to the earth is arranged upstream of the distribution circuit, and a guard pipe is inserted between this flow sensor and said reservoir section with a length and a section such that, filled with said high resistivity rinse aid, it is capable of divert only a small part of the current consumed by the projector to said earth flow sensor.

It is understood that the guard pipe will consist of a tube of section as small as possible taking into account the admissible pressure drops, into which the rinsing liquid will be injected following the quantity of coating product required. Due to the small cross-section of the guard line, and the speed of progression of the rinse aid, most of the rinse will be obtained in the front parts of the rinse aid column, and the diffusion of the remains of the rinse aid coating upstream of this column will be minimal; thus, when the flow sensor has signaled that the paint advancement front reaches the headlamp, an insulating column of rinse aid will have formed in the guard pipe, and will limit the bypass of electric current from the headlamp raised to high voltage at an acceptable value, despite the significant conductivity of the coating product in the reservoir section.

It will be noted that, according to this arrangement, the controlled connection means can be confused with the set of controlled valves of the product change unit, all the circuits which are located upstream of the grounded flow sensor being protected against current shifts from the projector (s).

The coating product and the insulating rinse aid can be propelled by a positive displacement pump, preferably geared, immediately upstream of the flow sensor, and here earthed. This propulsion can be ensured by an overpressure of the supplies of coating and rinsing products, in cooperation with a rinsable pressure regulator known per se, disposed between the reservoir section and the projector (s).

Preferably, a purge circuit is mounted as a bypass on the distribution circuit immediately upstream of the projector (s), this purge circuit comprising a valve controlled near the distribution circuit, and an electrical isolation pipe opening into a collector. mass purge.

In a preferred arrangement, an isolated, controlled connection circuit is arranged between the guard line and the reservoir section, and capable of switching this reservoir section between the guard line and a rinsing circuit, and bypassing the guard line on a purge manifold, isolation pipes being arranged between the controlled connection circuit and the flushing circuit, and the purge manifold, respectively.

Thanks to this arrangement, it is possible, part to perform a rinsing and a blowing of the guard line between the filling of the tank section and the delivery of the coating product to the projector, and on the other hand to start the supply of coating product (in the guard line ) before the end of the tank section rinsing and blowing. Flushing the guard pipe just after filling the tank section ensures in particular that the guard pipe will not form an electrical leakage path from the high-voltage source to earth, due to the deposition of metallic paint or water-soluble paint on its inner wall.

It is possible to split the distribution circuit and the guard pipe so as to connect one or the other of the two distribution circuits alternately to the coating product change unit via the flow sensor, and to a flushing circuit, also earthed.

One can thus rinse and dry one circuit while the other is used for projection.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the description which follows, of several installations in accordance with its principle, given solely by way of example and made with reference to the accompanying drawings wherein:
- Figure 1 is a block diagram of a first embodiment of a paint spraying installation according to the invention;
- Figure 2 is a diagram of a variant of the embodiment of Figure 1;
- Figure 3 is a block diagram of another embodiment of a paint spraying installation according to the invention and allowing to obtain even shorter color change cycles;
- Figure 4 is a block diagram similar to that of Figure 1, with improvements aimed at improving the insulation between the parts brought to high voltage and those connected to earth;
FIG. 5 schematically represents another installation according to the invention, with a coating product propulsion pump;
Figure 6 is a variant of Figure 5, with a connection circuit between the guard pipe and tank section;
Figures 7 and 8 correspond to Figures 5 and 6, respectively, with replacement of the pump propulsion by a pressurization propulsion;
Figure 9 is a development of the installation of Figure 6, with a duplication of the distribution circuits.

Referring more particularly to FIG. 1, the painting projection installation shown comprises a color changing unit 11 and a distribution circuit 12 extending between said color changing unit 11 and at least one electrostatic projector 13 fitted with a needle valve 14 controlling the passage of the paint. This projector, connected to a high voltage source 13 a adjustable and / or interruptible is placed in a projection booth, not shown, in which transit objects to be painted in different colors. The distribution circuit 12 is therefore supplied by the color changing unit 11 which selects the desired shade. The distribution circuit 12, for its part, supplies a certain amount of paint of the selected shade, predetermined as a function of the size of the object to be painted, to the projector 13. During the paint projection phase, the projector is brought to high voltage; the conventional high voltage source is not shown. As mentioned previously, the paint used is conductive (water-soluble paint or metallic paint) and the distribution circuit 12 is brought to high voltage at the same time as the projector. In known manner, the color changing unit 11 comprises a set of selection solenoid valves 11A, making it possible to put its output collector 15 in communication with one of the following circuits:
- either one of the paint circulation circuits 16A, 16B, 16C, each circuit 16 corresponding to a given color,
- Or a circuit for circulating rinse aid 17; for a water-soluble paint, it is water possibly added with alcohol,
- either a compressed air supply circuit 18.

The outlet of the collector 15 is connected to the distribution circuit 12 by isolation means comprising a conduit made of insulating material, here called the first isolation conduit 20, a controlled valve 21 and purging means 22. The downstream end of the insulation conduit 20 is connected to the distribution circuit 12 via the valve 21 and to the purge means 22 via a controlled valve 25, via a portion of insulating conduit 24. The installation also includes purge means 26 connected via a valve 27, to the distribution circuit 12 at the downstream end thereof, that is to say in the vicinity of the projector 13. A pressure regulator 29, rinsable, of a known type, is connected to the downstream end of the circuit 12, that is to say as close as possible to the projector 13. A flow sensor 30, which will be described in detail below, is also inserted into circuit 12 near its upstream end. A cleaning unit 35 is connected by a valve 36 to the purge means 26, the connection being made in the vicinity of the valve 27 so as to be able to clean and dry the portion of conduit 28 connecting this valve 27 to the means of the purge 26. The purge means 22 and 26 are connected to the earth.

The cleaning unit 35 comprises controlled connection means able to put successively in communication with the valve 36, either the rinsing product circulation circuit 17, or a compressed air distribution circuit 18. The conduit 37 connecting the cleaning unit 35 at valve 36 is made of material insulating, the cleaning unit 35 being earthed.

It should be noted, at this stage of the description, that all the conduits, which connect the various constituent elements of the installation, are advantageously made of insulating material. Some of them, such as for example the conduit 20 mentioned above, whose specific function is to allow electrical insulation between two important parts of the installation when one of them is brought to high voltage, are more specifically called "insulation conduits". The length of such an insulation pipe is calculated so that it has sufficient resistance to high voltage, once it has been cleaned with rinse aid and dried internally with water. 'pressurized air.

An intermediate tank 41, which can be rinsed off, is part of the distribution circuit 12 and, according to an important characteristic of the invention, this intermediate tank consists of a section of conduit of length AB of this distribution circuit 12. Of course, this section duct is made of insulating material, and its length is determined according to the volume of paint required to completely cover an object. The circuit 12 is also connected, by means of controlled connection means, on the one hand to the color changing unit 11 and on the other hand, to means for supplying rinse aid 40, isolated of the earth. In the example of FIG. 1, said controlled connection means comprise the valve 21 already mentioned, and a controlled valve 45, inserted between the upstream end of the circuit 12 and an outlet conduit 42 of a tank 44 containing said rinse aid. This tank 44 is electrically isolated from the ground. It is substantially sealed and pressurized, so that one can (thanks to the pressure prevailing in the tank) "push" paint in the circuit 12, during the spraying phase, from rinsing product coming from the tank isolated 44 and discharged into the conduit 42 under the action of the pressure prevailing in the tank 44. To do this, the reservoir 44 is connected to a supply and pressurization unit 46 capable of delivering rinsing product coming from a circuit 47 (to complete the level in the reservoir 44) and compressed air coming from a circuit 48. The compressed air serves both to establish the pressure in the tank 44 and to dry the insulating conduit 49 connecting the unit 46 to the tank, after a refreshing phase of the latter. These upgrades are made when the tank 44 is not brought to high voltage; it is then temporarily depressurized to allow the air to flow and the duct 49 to dry out. In the example shown, the rinse aid reservoir is kept pressurized at a high pressure (of the order of 15 bars) to be able to push the paint despite the length of the section of conduit 41 forming the intermediate reservoir. Under these conditions, the regularity of the projection, as the "length" of paint decreases, is ensured by the pressure regulator 29. The sequencing of all the valves and units which have just been described, as well as piloting the pressure regulator 29 are operated under the control of a computer, not shown. Many commercially available computers can provide this function. Its programming is within the reach of the skilled person. This computer essentially receives information representative of the liquid flow rate (paint or rinsing product), which flows in the circuit 12. This information is produced from the signal delivered by the flow sensor 30.

The operation of the installation of Figure 1 is as follows.

When filling, the high voltage is set to zero and the color change unit 11 is controlled to select one of the paints. This flows towards the projector, the valves 21 and 27 being open. When the quantity necessary to paint an object is engaged between the collector 15 of the change-over unit color and circuit 12, the valve corresponding to the paint selected in unit 11 is closed and that of circuit 17 is opened simultaneously. From this moment, the paint is pushed by rinse aid coming from circuit 17. The lengths of conduits are calculated so that, when the paint reaches the projector (point B) the "limit" between the rinse aid and the paint, is located at A, that is to say at a point located downstream of the valve 21 and (preferably) downstream of the flow sensor 30.

The valve 27 is closed and the valves 25 and 45 are opened. This ensures continuity of the pushing fluid (that is to say the rinsing product) between the pressurized reservoir 44 and the distribution circuit 12. The product rinsing, which then comes from the reservoir 44, is directed for a short time to the purging means 22 through the valve 25.

Once this continuity has been ensured, all the valves are closed and the valve 25 is opened again. The insulation pipe 20 and the pipe 24 are then cleaned and dried using rinse aid and air. tablet from the color changing unit. At the same time, the pipes 28 and 37 are cleaned and dried from the cleaning unit 35 and the pipe 49 from the unit 46.

The high voltage is then established and painting begins by opening the valve 45. The flow is constantly monitored and regulated from the flow sensor 30 and the pressure regulator 29, via the computer.

The invention therefore makes it possible to clean the distribution circuit 12, the flow sensor 30 and the various valves immediately after the passage of the paint, since the latter is pushed by rinsing product. To this saving of time, there is added that which results from the fact that the shape of the intermediate reservoir 41, that is to say the section of conduit of length AB, is that which is most easily and quickly cleaned.

The flow sensor 30 is brought to high voltage during the projection phase; it must therefore be able to develop a signal that can be used despite the presence of this high voltage. Several solutions are possible. Preferably, a sensor with a mechanical structure similar to that of a gear pump will be used. The sensor is traversed by the liquid which drives rotating gear wheels. These can therefore easily be used to develop a variable frequency signal as a function of the flow rate, thanks to an appropriate transducer placed opposite a toothed wheel. This transducer can for example be of variable reluctance. Isolation can be ensured by a transformation into light pulses and a transfer by optical fiber.

The embodiment of FIG. 2 is very similar to that of FIG. 1. The analogous elements bear the same reference numbers and will not be described again. The sequencing is the same. On the other hand, the pressure regulator 29 is eliminated, while a volumetric pump 50, rinsable, is inserted in the distribution circuit 12, preferably in the vicinity of the flow sensor 30, that is to say near the upstream end of the distribution circuit 12. Preferably, the flushable pump 50 is a gear pump. Under these conditions, the pressure of the compressed air in the circuit 48 and therefore in the reservoir 44 can be much lower (of the order of a few bars) since it is only used for feeding the pump 50. filling, therefore the color change, is nevertheless faster and the product is not subjected to strong pressure variations. It only "rises" in pressure when it is going to be sprayed.

The embodiment of Figure 3 further reduces the time of color change operations. In general, the distribution circuit, described with reference to FIG. 1, is replaced by two distribution circuits 12 a , 12 b so as to be able to clean and fill a distribution circuit during the spraying of the paint previously engaged in the other distribution channel.

On the other hand, in the example of FIG. 3, the color changing unit 11 remains unique, as are the means for supplying rinse aid 40, isolated from the ground. Each distribution channel 12, 12b therefore comprises a pipe section forming intermediate tank 41 a, 41 b, rinsable and means for controlled connection are arranged to alternately connect each of these duct sections at the color changing unit 11 and to the means for supplying rinse aid 40, respectively.

In the diagram of Figure 3, elements similar to those of Figure 1 have the same reference numerals. In addition, similar elements belonging to or specifically connected to a distribution circuit 12 a or 12 b , bear an index a or b respectively.

Thus, the insulated reservoir 44, connected as previously to a supply and pressurization unit 46, communicates with the two circuits 12 a and 12 b via (in particular) two valves 45 a , 45 b controlled, respectively. A first flow sensor 60 is inserted between the outlet of the reservoir 44 and the two common inlets of the two valves 45 a , 45 b . The color changing unit 11 also communicates with the two circuits 12 a and 12 b via (in particular) two controlled valves 64 a , 64 b , while a second flow sensor 61 is inserted between the output of the unit 11 and the two common inlets of the two valves 64 a , 64 b . The pressure regulator 29 is here inserted immediately upstream of the projector 13 or of a group of such projectors. This projector is here common to the two distribution circuits 12 a , 12 b . The purge means 26 are connected immediately upstream of this regulator via a controlled valve 62.

With regard to the distribution circuit 12 a , between the valve 45 a and the flow sensor 61 on the one hand, and the pressure regulator 29 on the other hand, the following elements are encountered successively:

The output of the flow sensor 61, associated with the color changing unit is connected by the valve 64 a to a first isolation conduit 20 a extending between the valve 64 a and an inlet of a three-way valve tracks 66 a (of the type with two inputs and one output). Said first conduit insulation 20 therefore plays the same role as the conduit 20 which is described with reference to Figure 1. A three-way valve 65 has two inputs and an output, has one of its inputs connected at the outlet of the valve 45 a and its other inlet connected to a cleaning unit 68 a similar to the unit 35 of the installation of FIG. 1.

The output of the valve 65 a is connected to the other inlet of the valve 66 a via a second insulating duct 70 a.

The output of the valve 66 a is connected to purge means 22 is controlled via a valve 25 and a conduit section 41a forming the intermediate tank circuit 12 has, via a valve 74 a.

The intermediate reservoir 41 a of length AB, therefore extends here between the valve 74 a and a valve 27 a . The downstream end of the section of conduit of length AB is also connected to purging means 78 a via a controlled valve 79 a . The output of the valve 27 a is connected to the pressure regulator 29 via a third insulating duct 82 a and a valve 83 is commanded, in the vicinity of said regulator. The cleaning unit 35 a is connected to the outlet of the valve 27 a via a controlled valve 36 a . All these circuits and valves are easily rinsable.

It will be understood, at this stage of the description, that all connecting means (valves) and said insulating ducts 20 a, 70 a and 82 a are arranged to selectively isolate the electrical point of view, the distribution circuit 12 a corresponding (and consequently the rinsable tank 41 a ) of the color changing unit, the cleaning unit and the other distribution circuit 12 b , respectively.

It also appears that the arrangement is such that each isolation duct, defined above, is connected, by means of controlled valves, upstream to cleaning means and downstream to purging means. A distinction is thus made between the cleaning means of the color change unit 11 and the purge means 22 a for treating the insulation conduit 20 a , the cleaning unit 68 a and the purge means 22 a for treating the conduit has insulation 70 and the cleaning unit 35 a and the purging means 26 for processing the insulation 82 leads. Of course, these cleaning units and purging means are automatically electrically isolated at each cleaning phase by the rinsing and drying operations of the insulating conduits which terminate therein, as explained with reference to the embodiment of FIG. 1. It the same is true of the means 46 relative to the rinse aid reservoir 44.

The distribution circuit 12 b is strictly identical to the circuit 12 a and the corresponding elements have the same numerical references with the index b instead of a . A distinction is thus made between controlled valves 45 b , 64 b , 25 b , 74 b , 79 b , 27 b , 36 b and 83 b , three-way controlled valves 65 b and 66 b , cleaning means 68 b and 35 b , the purge means 22 b and 78 b , the insulation conduits 20 b , 70 b and 82 b and, of course, the insulating conduit forming an intermediate reservoir 41 b . All these elements are interconnected in the same way so that the circuit 12b does not need to be described again.

As in the case of the installation in FIG. 1, the computer controls all of the valves as well as the pressure regulator 29; it receives signals developed from the two flow sensors 60 and 61. It should be noted that the isolation conduits 82 a and 82 b , which have the function only of "holding" the high voltage once rinsed and dry, have smaller sections than other conduits. The quantity of product contained in these conduits is therefore small compared to that which is contained in the section 41 a or 41 b forming the rinsable tank. By moreover, the conduits 82 a , 82 b and the valves and cleaning means which relate thereto can be omitted if two independent projectors 13 and two groups of such projectors are provided.

The operation is as follows.

If it is assumed that one of the circuits, for example the circuit, 12 b , has just been filled with paint and that said first insulation conduit 20 b has been cleaned and dried via the valves 66 b , 25 b and the purge means 22 b , in a manner analogous to what has been described with reference to FIG. 1, the circuit 12 b is therefore ready to paint, the paint being located between the closed valves 74 b and 27 b . This situation is reached during the projection phase using the distribution circuit 12 a , therefore without loss of time. The circuit 12 b is then isolated from the high voltage by the conduits 70 b , 20 a and 82 b which have been previously cleaned and dried. Before re-establishing the high voltage in circuit 12 b and starting to paint from this circuit, it is necessary to wait for the end of the projection phase in progress, implementing the distribution circuit 12 a , in order to be able to isolate it electrically . Simply clean and dry the insulation 70 and led to the isolation 82 leads. From this moment, the continuity of the rinsing product between the reservoir 44 and the distribution circuit 12 b can be established via the valves 45 b , 65 b , 66 b and 25 b , up to the purge means 22 b . The paint spraying phase can then begin by closing the valve 25 b and opening the valves 74 b , 27 b and 83 b . During this time, a paint of another color is injected into the circuit 12 a and the cycle is ended by cleaning and drying the conduit 20 a .

Of course, a variant similar to that of FIG. 2 can perfectly well be envisaged. It suffices, for example, to remove the pressure regulator 29 and to insert a positive displacement pump 90, which can be flushed, preferably a gear pump between the reservoir 44 and the pressure sensor. flow 60. The reservoir 44 then no longer needs to be pressurized at a high pressure.

Finally, it should be noted that with an installation of the kind described above, the fact of using a paint and a conductive solvent or rinsing product can become advantageous by making it possible to simplify the structure of the electrostatic spray 13, that is to say to lighten it, which can be very appreciable when such a projector is carried by a multi-axis robot. Indeed, it then becomes perfectly possible to apply the high voltage to another element than the projector and in particular to the reservoir 44.

The installation of Figure 4 is derived from that of Figure 1; the analogous elements bear the same numerical references increased by 200. The installation will therefore not be described again in all its details.

It will simply be specified that the downstream end of the insulation conduit 220 is connected to the distribution circuit 212 by means of the valve 221 and to the purging means 222 by means of a controlled valve 225, via a portion of insulating conduit 224. The installation also includes purge means 226 connected via a valve 227, to the distribution circuit 212 at the downstream end thereof, that is to say in the vicinity of the headlamp 213. A rinsable pressure regulator 229 of a known type is connected to the downstream end of the circuit 212, that is to say as close as possible to the headlamp 213. A flow sensor 230, which will be described in detail below, is also inserted into the circuit 212 in the vicinity of its upstream end. A cleaning unit 235 is connected by a valve 236 to the purge means 226, the connection being made in the vicinity of the valve 227 so as to be able to clean and dry the portion of insulating conduit 228 connecting this valve 227 to the purge means 226 The purge means 222 and 226 are connected to the ground.

The cleaning unit 235 comprises controlled connection means able to successively put in communication with the valve 236, either the rinsing product circulation circuit 217, or the compressed air distribution circuit 218. The conduit 237 connecting the cleaning unit 235 to the valve 236 is an insulating conduit, the unit 235 being grounded.

On the other hand, according to one of the aspects of this variant, the sequencing is such that during at least part of a coating product projection phase (that is to say while the circuit 212 is connected at high voltage) air circulation can be maintained in certain insulating conduits, in particular here said insulating conduit 220 and insulating conduits 224, 237, 228 and 249. This air circulation can be established for conduits 220 and 240 from the supply circuit 218 via the color change block and the valve 225 left open for this purpose. For the conduits 237 and 228, the air circulation can be established from the distribution circuit 218 via the unit 235 and the valve 236 left open for this purpose. For the duct 249, the air circulation can be established from the distribution circuit 248 via the unit 246, possibly creating a slight air leak at the level of the reservoir 244.

In addition, the rinsable insulating conduits 220, 224, 237 and 249 are at least partly shaped as a serpentine, preferably oriented substantially horizontally, for the reasons indicated above.

The operation of the installation is as follows.

When filling, the high voltage 213 a is set to zero and the color change unit 111 is controlled to select one of the paints. This flows towards the projector, the valves 221 and 227 being open. When the quantity necessary to paint an object is engaged between the collector 215 of the color changing unit and the circuit 212, the valve corresponding to the paint selected in the unit 211 is closed and that of the circuit 217 is opened simultaneously. From this moment, the painting is thrust by rinse aid coming from circuit 217. The lengths of conduits are calculated so that, when the paint reaches the projector (point B) the "limit" between the rinse aid and the paint, is located at A, c ' that is to say at a point located downstream of the valve 221 and (preferably) downstream of the flow sensor 230.

The valve 227 is closed and the valves 225 and 245 are opened. This ensures continuity of the pushing fluid (that is to say the rinsing product) between the pressurized reservoir 244 and the distribution circuit 212. The product rinsing, which then comes from the reservoir 244, is directed for a short time to the purging means 222 through the valve 225.

Once this continuity has been ensured, all the valves are closed and the valve 225 is opened again. We then proceed to clean and dry the insulation pipe 220 and pipe 224 from rinsing product and air. tablet from the color changing unit. At the same time, cleaning and then drying of the conduits 228 and 237 is carried out from the cleaning unit 235 and from the conduit 249 from the unit 246.

The high voltage is then established and painting begins by opening the valve 245. The flow is constantly monitored and regulated from the flow sensor 230 and the pressure regulator 229, via the computer. The air circulation is maintained in the aforementioned insulating conduits.

Of course, the improvements described with reference to FIG. 4 are not limited to the installation specifically described. In particular, the installations of FIGS. 2 and 3 can be completed in accordance with FIG. 4. In particular, FIG. 3 shows an installation comprising two distribution circuits in parallel, operating alternately. This installation therefore comprises a greater number of insulating conduits and in particular of insulating conduits as defined, between the color changing unit and each of the circuits of distribution, between the distribution circuits themselves and also between each of the distribution circuits and the projectors.

It is clear that all these conduits can be "blown" in the presence of high voltage and / or be shaped into coils.

Figures 5 to 9 show another development of the invention and the structural elements similar to those of Figures 1 to 3 bear the same reference numerals.

According to the embodiment chosen and shown in FIG. 5, a gear pump 50, of the so-called rinsable type, is disposed at the outlet of a coating product changing unit 11, generally electrically connected to earth (ground). electrically connected to ground, which flows into a distribution circuit 12, via a flow sensor 30, of a type derived from a gear pump. At the end of the distribution circuit 12 is connected an electrostatic type projector 13, with a needle valve 14 for controlling the admission of paint into the projector. This projector 13, of the rotating head or pneumatic or hydrostatic spray type, is simple or multiple depending on the applications; it is connected to a high voltage source 13 a , interruptible.

Just upstream of the sprayer 13, the distribution circuit 12 comprises a bypass a purge circuit, comprising a controlled valve 27 in the immediate vicinity of the circuit 12, an isolation conduit 28, and a purge manifold 26, connected to earth .

Isolation pipes or insulation pipes are referred to here as above, pipes made of insulating material the length of which is sufficient to withstand the high voltage after having been rinsed and dried internally with compressed air.

The distribution circuit 12 comprises a reservoir section 41, the length and the passage section of which are determined to define a volume at least equal to that of the quantity of paint required for an object (i.e. around 0.3 liters for a car body). As an indication, one can use tubes whose internal diameter is of the order of 4 to 6 mm; the length of the reservoir section is then 25 to 10 meters.

Between the flow sensor 30 and the reservoir section 41, a guard pipe 112 is arranged, with a diameter smaller than that of the reservoir section. A high resistivity rinse aid (> 10⁶Ω.m) was chosen. The cross-section of the guard pipe, and the length have been determined so that the resistance of the filling liquid column is sufficient so that the bypass current in the liquid column in response to the high voltage is negligible compared to the own consumption of the projector. For example, a guard pipe 1 m long and 2 mm in inside diameter offers, filled with a flushing liquid with a resistivity of 10⁶Ω.m, a resistance of 3.2 x 10¹¹ Ω. Under a high voltage of 50 kV, the through current will be of the order of 0.16 µA.

The operation of the device according to FIG. 5 can be described as follows:

At the end of projection of a paint of determined color, the high voltage 13 a is cut, and the needle 14 of the projector 13 closes; at this time, the entire distribution circuit 12 is filled with rinse aid, as will be explained below. The purge valve 27 opens, while the valve of the color change unit 11 which controls the admission of rinse aid closes and the compressed air intake valve opens. The compressed air drives the rinse aid through the pump 50, the flow sensor 30, the guard line 112, the reservoir section 41, the controlled valve 27 open, and the isolation conduit 28, in the manifold. purge 26; an additional compressed air flush evaporates the remaining rinse aid and dries all the elements of the circuit.

At this time, in the product change unit 11, the valve corresponding to the coating product intended for the incoming painting object opens. Pump 50 delivers the coating product to the distribution circuit, through the flow sensor 30. When the latter has measured the volume of coating product necessary for spraying (possibly taking into account the volume still upstream of the sensor 30 in the pump 50 and its connection to the unit 11), this unit is controlled to interrupt the supply of coating product and to replace it with rinsing product which pushes, under the impulse of the pump 50, the coating product towards the downstream end of the distribution circuit 12. When the flow sensor 30 has recorded a volume of product delivered such that the front edge of the coating product is at the height of the purge bypass, the valve 27 closes. At this moment the coating product is entirely contained in the reservoir section 41, while the rinsing product fills the pump 50, the flow sensor 30 and the guard line 112; between the coating product and the clean rinsing product, an interface X has been located located in the reservoir section near its upstream end, this interface consisting of a mixture of coating product and rinsing product. This interface, the limits of which are not straightforward, of course, occupies a short length of the reservoir section.

When the valve 27 is closed, the needle 14 of the projector 13 opens, and the projection begins with the establishment of the high voltage 13 a . Although the coating product is conductive, the guard line 112 filled with insulating flushing liquid, and the dry insulation conduit 28 form an isolation break towards the ground, while the reservoir section, over the length occupied by the coating product, is substantially at the potential of high voltage 13 a .

During the spraying of the coating product, the pump 50 delivers rinse aid into the distribution circuit, and the interface X progresses from upstream to downstream of the tank section, thereby ensuring that the tank section is rinsed. The isolation break provided by the guard line 112 is reinforced by the formation of a column of rinsing product in the reservoir section 41, upstream of the interface X.

At the end of the cycle, the automatic control system ends the projection.

At this moment the interface X has reached the level of the purge bypass. The high voltage 13 a is cut, the needle 14 closes while the valve 27 opens. The installation returned to the departure stage envisaged above.

The installation represented in FIG. 6 differs from that in FIG. 5 in that, between the guard line 112 and the reservoir section 41, a controlled connection circuit is inserted, isolated from the earth (from the ground) and composed of a line 100 on which the guard line 112 and the tank section 41 are stuck and three controlled valves arranged on the line 100, namely a valve 121 between the tappings of the guard line 112 and the tank section 41, a valve 125 between the connection of the guard pipe 112 and a first pipe end extended by an isolation pipe 129 opening into a drain manifold 122, and a valve 145 between the connection of the reservoir section 41 and the second end of the line 100, connected to a rinsing circuit or cleaning unit 135 through an insulation conduit 128. The complementary set of valves 121 and 145 switches the inlet of the reservoir section between the line on guard 112 and the cleaning unit 135, while the opening of valve 125 diverts the guard pipe 112 towards the purge manifold 122.

With this arrangement according to FIG. 2, it is possible, when the coating product has been completely delivered to the reservoir section 41, close the valve 121 and open the valve 125 in order to rinse the pump 50, the flow sensor 30 and the guard pipe by purging the rinse towards the manifold 122, and dry the circuit with compressed air, then re-establish communication between the guard line 112 and the reservoir section 41 to send insulating rinsing product to the reservoir section 41 to supply the projector 13. In addition, at the end of projection, the valve 121 is closed and the valve 145 is opened , to perform the cleaning of the reservoir section 41 from the cleaning unit 135. It will be noted that it is possible to supply the cleaning unit 135 with rinsing product different from the insulating rinsing product used in the unit coating product change 11.

This arrangement reduces the risk of traces of water-soluble or metallized paint remaining on the inner wall of the guard line 112, which the rinsing product would not have removed completely from the start of its injection. In addition, the rinse aid supplied by the cleaning unit 135 can be chosen to be more effective or less costly than the insulating rinse aid used to push the coating product, this rinse aid supplied by the cleaning unit 135 not being enslaved to be insulating.

The arrangements shown in Figures 7 and 8 repeat the arrangements of Figures 5 and 6 respectively, for the most part. However, these arrangements do not include a pump 50, and the insulating rinse aid supplied by the product change unit 11 in FIG. 8, and by the cleaning unit 35 in FIG. 7 is supplied under high pressure, around fifteen bars. At the end of the reservoir section 41 is disposed a known rinsable pressure regulator 29 which makes it possible to adapt the pressure of the coating product to the circumstances.

It will be noted that, according to FIG. 7, the flow sensor 30 is supplied by a connection circuit controlled by three valves 21, 25 and 45, connected to a unit for changing the coating product 11 and to a cleaning unit 35. The rinse aid supplied by the cleaning unit 35 is insulating, and pushes the coating product in the distribution circuit. It is thus possible to rinse the coating product changing unit 11 while the cleaning unit 35 ensures the coating product progression during the spraying phase.

The installation shown in FIG. 9 comprises, in parallel, two distribution circuits 12 a and 12 b similar to the distribution circuit 12 in FIG. 6, between a coating product change unit 11 followed by a pump 50 and a flow sensor 30, and a projector 13 (or a group of projectors) with its high voltage source 13 a . The two distribution circuits 12 a and 12 b operate alternately, one circuit being in the projection phase while the other is in the cleaning phase.

To do this, there is between the output of the flow sensor 30 and the input of each of the two guard pipes 112 a and 112 b two valves 165 a and 165 b respectively with complementary operation, and between the ends of each of the sections tanks 41 a and 41 b and the needle valve 14 13, two valves 83 a and 83 b , respectively, operating in synchronism with the valves 165 a and 165 b . In addition there are two controlled valves 185 a and 185 b , connecting a cleaning unit 168 to the respective inputs of the guard pipes 112 a and 112 b . These valves 185 a and 185 b are controlled at the same time as the valves 165 b and 165 a so that when a distribution circuit 12 a or 12 b is supplied from the coating product change unit 11, the other circuit 12 b or 12 a is connected to the cleaning circuit 168.

However, the cleaning circuit 168 is provided essentially for cleaning and drying the guard pipes 112 a and 112 b , while the cleaning and drying of the tank sections 41 a and 41 b are carried out from the cleaning units 135 a and 135 b respectively.

It will be noted that the correct operation of the installation according to FIG. 9 imposes in all points the use of insulating rinses, since the rinsing of the elements of the distribution circuits 12 a and 12 b is carried out with the projector 13 at high voltage.

It will be appreciated that the sequencing of operations, and in particular the commands of the various valves, is regulated by a pilot microprocessor, the programming of which, outside the scope of the present invention, gives the process great flexibility. It will be possible to order certain operations on the distribution circuit 12 a or 12 b during cleaning in synchronism with operating stages on the distribution circuit 12 b or 12 a in the projection phase, to minimize interference. May for example execute preliminary rinses the circuit cleaning phase during filling of the reservoir section of the circuit by spraying phase, the filling is running with the high voltage source 13 is turned off.

Claims (29)

1- Installation for spraying coating product of the type comprising a coating product changing unit (11), means for supplying rinsing product, at least one distribution circuit (12) downstream of said unit and supplying at least one projector ensuring the spraying of said product, as well as an intermediate tank (41) forming part of this distribution circuit, characterized in that said intermediate tank (41) is constituted by a section of conduit of said distribution circuit and in that controlled connection means are arranged to push said coating product, in the spraying phase, from said rinsing product. 2- Installation according to claim 1, for the application of said coating product electrostatically, wherein said coating product changing unit is connected to the ground and wherein said distribution circuit (12) is sequentially connected to a high voltage applied to at least one electrostatic headlight (13), characterized in that said controlled connection means are arranged between, on the one hand, said section of conduit and, on the other hand, said unit (11) and means supply of rinse aid (40), isolated from the ground, so as to be able to push said coating product, in the electrostatic spraying phase, from rinse aid coming from these isolated supply means (40). 3- Installation according to claim 2, characterized in that said means for supplying rinsing product comprises a reservoir (44) electrically isolated from the ground, containing said rinsing product. 4- Installation according to claim 3, characterized in that said tank (44) is sealed and pressurized by being connected to a source of compressed air (48). 5- Installation according to one of claims 2 to 4, wherein said coating product changing unit comprises a circuit for rinsing product circulation (17) and a compressed air supply circuit (18), characterized in that this unit is connected to said section of conduit forming an intermediate reservoir (41) by isolation means comprising a first rinsable isolation conduit (20). 6- Installation according to one of the preceding claims, characterized in that a flow sensor (30) is inserted in said conduit of said distribution circuit, upstream of the section forming said intermediate tank (41). 7- Installation according to one of claims 4 to 6, characterized in that said rinse product reservoir (44) is kept pressurized at a high pressure and that a pressure regulator (29), rinsable, known per se, is inserted into said distribution circuit (12) in the vicinity of said electrostatic projector (13). 8- Installation according to one of claims 4 to 6, characterized in that said rinse aid reservoir (44) is kept pressurized at a low pressure and that a pump (50), preferably a gear pump, is inserted into said distribution circuit, upstream of said section of conduit forming said intermediate reservoir (41). 9- Installation according to one of claims 2 to 5, characterized in that it comprises two distribution circuits (12 a , 12 b ) each comprising a section of conduit forming an intermediate tank (41 a , 41 b ) above and in that controlled connection means are arranged for alternately connecting each of the sections of conduit forming intermediate reservoirs to a coating product change unit (11) above and to said rinse aid supply means, respectively. 10- Installation according to claim 9, characterized in that each distribution circuit comprises a three-way valve (66 a , 66 b ) or the like, with two inlets, one of the inlets being connected to said means for supplying rinse aid (40), the other inlet being connected to said unit for color change (11) and its outlet being connected to said section of conduit forming a rinsable reservoir (41 a , 41 b ). 11- An installation according to claim 10, characterized in that each distribution circuit comprises insulation means comprising a first insulating conduit (20, 20b) above, inserted between an input of said three-way valve (66 a , 66 b ) and said unit (11) and a second isolation conduit (70 a , 70 b ), inserted between the other inlet of said three-way valve and said means for supplying rinse aid (40 ) isolated from the earth. 12- Installation according to claim 11, wherein the projector (s) (13) are alternately supplied by the two distribution circuits, characterized in that the isolation means of each distribution circuit each comprise a third conduit insulation (82 a , 82 b ), rinsable, inserted downstream of said section of conduit forming a rinsable tank. 13- Installation according to one of claims 9 to 12, characterized in that a first flow sensor (60) is inserted between said means for supplying rinse aid and the distribution circuits and in that a second flow sensor (61) is inserted between said unit (11) and the distribution circuits. 14- Installation according to one of claims 9 to 13, wherein said rinsing product supply means comprise an insulated, sealed and pressurized tank (44), characterized in that said rinsing tank is kept pressurized to a high pressure and that a pressure regulator (29), rinsable, known per se, is inserted in the vicinity of the electrostatic projector (s). 15- Installation according to one of claims 9 to 13, in which the said rinsing product supply means comprise a sealed and pressurized isolated tank (44), characterized in that the said rinsing tank is kept pressurized at a low pressure and that a pump (90), preferably a gear pump is inserted between said insulated tank and the two distribution circuits (12 a , 12 b ). 16. Installation for spraying coating product according to one of the preceding claims, comprising at least one insulating conduit (220, 224, 228, 237, 249) connected to a distribution circuit (212) capable of being connected to a high voltage, characterized in that it comprises means (218, 225, 236, 248) for blowing air into said insulating conduit for at least part of the time during which said high voltage is applied to the distribution circuit. 17- Installation for spraying coating product according to claim 16, characterized in that at least part of the insulating conduit (220, 224, 237, 249) is shaped as a serpentine. 18- Installation for spraying coating product according to one of claims 1 to 15, comprising at least one insulating conduit (220, 224, 237, 228, 249) connected to a distribution circuit (212) capable of being connected at a high voltage, characterized in that at least a part of said insulating conduit is shaped as a coil. 19- Installation according to claim 17 or 18, characterized in that said coil is oriented substantially horizontally. 20- Installation according to one of claims 16 to 19, characterized in that a said insulation pipe is an insulation pipe (220) of said distribution circuit (212). 21- Installation according to one of claims 16 to 20, characterized in that an aforementioned insulating conduit (249) is established between a rinse aid tank (244) electrically isolated from the earth and from the means for filling this tank. 22- Installation according to one of claims 16 to 21, characterized in that an aforementioned insulating conduit (237) is established in an arrangement for cleaning the purge means (226). 23. Installation for spraying coating product according to claim 1, for the application of said product electrostatically, where said coating product changing unit (11) is connected to the ground, and where the distribution circuit (12 ) is, during the projection phase at least, connected to a high voltage (13 a ) applied to at least one electrostatic projector (13), characterized in that, the rinsing product being chosen with high resistivity, a flow sensor ( 30) connected to earth is disposed upstream of the distribution circuit (12), and a guard pipe (112) is inserted between this flow sensor (30) and said reservoir section (41) with a length and a section such that, filled with said high resistivity rinsing product, it is likely to drift towards said flow sensor (30) to the ground only a minimal part of the current consumed by the projector (13). 24- Installation according to claim 23, characterized in that a pump (50), preferably geared, is arranged immediately upstream of said flow sensor (30). 25- Installation according to claim 23, characterized in that said rinsing product is admitted under high pressure, and a pressure regulator (29) rinsable and known per se is disposed between said reservoir section (41) and the projector (13) . 26- Installation according to one of claims 23 to 25, characterized in that a purge circuit is mounted in diversion on the distribution circuit (12) immediately upstream of said projector (13), this purge circuit comprising a valve controlled (27) near the circuit (12), and an electrical isolation conduit (28) emerging in a drain manifold (26) to ground. 27- Installation according to one of claims 23 to 26, characterized in that a controlled, isolated connection circuit (100) is disposed between the guard pipe (112) and the reservoir section (41), and capable of switching this reservoir section between the guard pipe (112) and a rinsing circuit (135), and to bypass the guard pipe (112) on a purge manifold (122), isolation pipes (128, 129) being disposed between the controlled connection circuit and the flushing circuit (135) and the purge manifold (122) respectively. 28- Installation according to claim 27, characterized in that the controlled connection circuit comprises a pipe (100) between the isolation conduits and on which the guard pipe (112) and the reservoir pipe (41) are stuck, and three valves (121, 125, 145), disposed on the pipe (100) respectively between the guard pipe (112) and the reservoir section (41), the guard pipe and the purge manifold (122), and the tank section and the rinsing circuit (135). 29- Installation according to one of claims 23 to 28, characterized in that it comprises two distribution circuits (12 a , 12 b ) each with a reservoir section (41 a , 41 b ) and a guard pipe (112 a , 112 b ), and controlled connection means (165 a , 165 b ; 185 a , 185 b ) arranged to alternately connect one and the other of the distribution circuits (12 a , 12 b ) to a unit for changing the coating material (11), via a flow sensor (30) to the ground, and to a flushing circuit (168), also to the ground, respectively.

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