EP2046504B1 - Powder pump with vacuum filling - Google Patents

Abstract

A powder supply system for a powder-coating installation, especially a parts painting installation using electrostatic powder, according to the invention, comprises a tank (2) designed to contain the powder, means (4, 5, 6) for feeding powder into the tank (2), means (15, 14) for injecting compressed air into the bottom of the tank (2) in order to fluidize the powder, and an exit pipe (8) in which the powder is entrained by the air from the tank (2), this pipe (8) being connected to at least one powder using device situated at a distance, in particular a spray gun (9). The system also includes means (16, 17, 18, 19) for reducing the pressure in the tank (2) below that of the feed means (4, 5, 6) in order to fill the tank (2) with powder.

Description

The present invention relates to a powder supply equipment for a powder coating plant, in particular a parts painting installation using electrostatic powder, as well as a powder supply method of a powder coating plant.

A powder coating plant, equipped with powder sprayers, usually has a conveyor for scrolling the parts to be painted in front of sprayers. Each piece, according to its size and shape, requires appropriate adjustment of the powder flow rate projected by the sprayers. These therefore require to be supplied from a remote point by a regulated and adjustable powder flow rate, the powder being fluidized and transported by air under pressure. It is therefore advisable to dose the powder flow, to mix it with compressed air, and to drive the powder air mixture by transporting it to the powder coating plant, to feed the sprayer (s) or "guns" of this installation.

A powder supply equipment for such an installation is generally made on the principle of a venturi pump, with the effect of driving the powder by air.

The pump. With a venturi drawing the powder in a tank placed at atmospheric pressure, this results in a limitation of the powder flow rate as a function of the length of the pipe between the pump and the powder coating plant, the length of this pipe being about ten fifteen meters following the desired powder flow. In any case, such a system does not make it possible to transport sufficient quantities of powder over a considerable distance, in particular greater than twenty meters, while requiring a high driving speed, the speed of the air in the pipe to be at least of the order of eight to ten meters per second.

Moreover, the amount of air important here implemented is detrimental to the performance of the powder deposit, that is to say the ratio between the amount of powder deposited and the amount of powder sprayed. Indeed, the air transport of the powder tends to blow the powder already deposited on the piece to be painted.

In addition, such a system tends to melt the powder by its friction in the venturi pump, and the melted powder particles then agglomerate, and they cause defects in the projected paint. The powder also creates an undesirable abrasion effect in the mixing device.

As a result, other equipment has been proposed to solve the problems mentioned above.

• un réservoir, prévu pour contenir de la poudre,
• des moyens d'amenée de poudre à l'intérieur du réservoir,
• des moyens d'injection d'air comprimé dans la partie basse du réservoir, pour fluidiser la poudre, et
• au moins un tuyau de départ de la poudre entraînée par l'air, depuis le réservoir, ce tuyau étant relié à au moins un dispositif d'utilisation de la poudre situé à distance, en particulier un pulvérisateur.

In particular, it is known to use equipment comprising:

• a reservoir, intended to contain powder,
• powder supply means inside the reservoir,
• compressed air injection means in the lower part of the tank, for fluidizing the powder, and
• at least one starting pipe of the powder driven by the air, from the tank, this pipe being connected to at least one device for using the powder located at a distance, in particular a sprayer.

Such type of equipment, known in particular EP1454675 , in accordance with the preamble of claim 1, and FR2872067 , makes it easier to control the flow of powder applied and to reduce the amount of air used, which in particular reduces the blowing effect.

In addition, the mixing speed is lower in the equipment, which prevents the powder from melting.

In known equipment of this type, the means for feeding the powder into the tank from a filling tank operate by gravity, or by using a pump to drive the powder, these means being associated with a valve.

These provisions cause powder compressions at the valve, and therefore polymerization and agglomeration of the powder at the valve, the agglomerations of powder then causing defects during the application of the powder on a piece to be painted .

The present invention aims to solve this technical problem, that is to say to reduce the agglomerations of powder due to the supply means.

For this purpose, the present invention relates to an equipment of the aforementioned type, characterized in that the equipment comprises means for depressurizing the reservoir relative to the supply means for filling the reservoir with powder.

These arrangements make it possible to suck up the powder in the tank from the vacuum feed means, during a filling phase, then to eliminate the vacuum during a spraying phase, and not to closing the supply means by a valve only when the depression is removed.

As a result, the valve does not stress the powder, which prevents the formation of agglomerates.

Preferably, the feed means comprise a powder supply duct and a powder supply valve intended to close this duct, the powder supply valve being associated with cleaning means of the valve when it is open.

These provisions make it possible to prevent residual powder from being blocked at the valve and to generate a residual agglomerate by compression when closing the valve.

Advantageously, the supply duct comprises at least one substantially horizontal section at which the powder supply valve is disposed.

These provisions make it possible to avoid the compression of the powder by gravity.

Preferably, the means for depressurizing the reservoir relative to the supply means comprise a venturi device, associated with means for separating the air and the powder.

Advantageously, the means for separating the powder and the air comprise a cyclone.

Preferably, the means for separating the powder and the air comprise a filter.

Advantageously, the means for depressurizing the reservoir relative to the supply means comprise a valve for cutting the air flow downstream of the depression means.

Preferably, the compressed air injection means comprise a blowing nozzle, effecting a fluidization of the powder, located opposite the end of the pipe during spraying.

These arrangements allow local fluidization of the powder at the end of the pipe. The powdering rate in the outlet pipe is increased, this powdering flow having a better homogeneity compared to the devices of the prior art. It is thus possible to increase the pressure in the tank to increase the flow rate while maintaining a fluidized powder feed homogeneously.

According to one embodiment, the equipment comprises means for moving the pipe for starting the powder between a first position in which the powder present in the reservoir can penetrate the pipe, and a second cleaning position, in which the pipe is sealed away from the interior of the tank.

Advantageously, in the second position, the pipe is positioned against an air blast nozzle for cleaning the pipe.

These arrangements allow automatic cleaning of the pipe and avoid a "puff" effect at the beginning of a spraying phase, this effect being due to residual powder from the previous spraying phase remaining in the pipe.

Advantageously, the same air blowing nozzle makes it possible to clean the pipe in the low position of the pipe and to achieve a fluidization of the powder near the end of the pipe when the latter is in the high position.

These provisions make it possible to simplify the structure of the equipment by using the same nozzle for two different functions.

Preferably, the equipment comprises a permanent exhaust for regulating the pressure in the tank.

Advantageously, the air injection means comprise at least one proportional valve for regulating the pressure in the reservoir.

• une phase de remplissage d'un réservoir de poudre à partir de moyens d'amenée de poudre, et
• une phase de pulvérisation dans laquelle la poudre est fluidisée, et le réservoir est vidé par un tuyau de départ vers au moins un dispositif d'utilisation de la poudre situé à distance, en particulier un pulvérisateur,

le réservoir étant mis en dépression par rapport aux moyens d'amenée pendant au moins une partie de la phase de remplissage.The present invention also relates to a powder supply method of a powder coating plant, in particular a painting installation of parts using electrostatic powder comprising:

• a filling phase of a powder tank from powder supply means, and
• a spraying phase in which the powder is fluidized, and the reservoir is emptied by a starting pipe to at least one device for using the powder located at a distance, in particular a sprayer,

the reservoir being depressed relative to the supply means during at least part of the filling phase.

Advantageously, a fluidization rate of compressed air is maintained in the reservoir during the filling phase.

These provisions make it possible to avoid a delay in the powdering rate during the start of the spraying phase.

Preferably, the feed means comprise a powder supply valve for closing off a feed pipe for the powder, the powder supply valve being cleaned, and then closed at the end of the filling phase.

Advantageously, the depression of the tank relative to the supply means is eliminated before proceeding with the cleaning of the powder supply valve.

Preferably, the powder feed pipe is moved between a first position during the spraying phase, wherein the powder in the reservoir can enter the pipe, and a second position during the filling phase, in which the pipe is sealed from the interior of the tank.

Advantageously, cleaning the pipe by blowing air in the second position.

• La figure 1 est une vue schématique de principe d'un équipement selon l'invention.
• La figure 2 est une vue en coupe d'un réservoir selon l'invention, le tube de départ étant en position basse.
• La figure 3 est un diagramme représentant le fonctionnement des organes de l'équipement pendant les phases du procédé.

In any case, the invention will be better understood with the aid of the description which follows, with reference to the appended schematic drawing, representing by way of nonlimiting example, an embodiment of an equipment according to the invention.

• The figure 1 is a schematic view of a principle of an equipment according to the invention.
• The figure 2 is a sectional view of a tank according to the invention, the starting tube being in the low position.
• The figure 3 is a diagram showing the operation of the equipment components during the process phases.

As shown on the figures 1 and 2 , a powder supply equipment for a powder coating plant according to the invention comprises a reservoir 2, provided to contain powder. The equipment comprises means for measuring the quantity of powder in the tank 2, constituted for example by weighing means 3 of the mass of the tank 2.

The equipment also comprises means for feeding powder into the tank. These feed means comprise a supply line 4 to the tank 2 and a supply valve 5 intended to close the feed pipe 4 of the powder. The supply valve is of the sleeve valve type.

The feed duct 4 is connected downstream to unrepresented loading means, in particular to a filling tank.

The supply duct 4 is arranged substantially horizontally, and the powder supply valve 5 is disposed at a horizontal section of this duct, which avoids any compaction of powder by gravity at the valve 5.

At its downstream end, the supply duct 4 is extended by a bend 6 which opens into the upper wall of the tank. An air inlet 7 is provided at the bend 6, in the axis of the supply duct, facing it. This pressurized air inlet, which makes it possible to propel air upstream of the supply channel 4, constitutes a means for cleaning the powder supply valve 5 in the open position.

The equipment also comprises a starting pipe 8 of the powder driven by the air, from the tank 2, this pipe being connected to a sprayer 9 located at a distance.

The equipment further comprises compressed air injection means in the lower part of the tank, for fluidizing the powder. The reservoir comprises a porous element 10 defining a first upper compartment 12 containing the powder and a second lower compartment 13 of the reservoir 2 containing compressed air, the air injection means comprise a first air intake 14 located in below the porous element 10 and a nozzle 15 whose opening is located below the end of the powder starting pipe, and above the porous element 10.

According to a feature of the invention, the equipment comprises means for depressurizing the reservoir relative to the supply means. The means for depressurizing the reservoir relative to the supply means comprise a venturi device 16, whose suction intake 17 is positioned in the center of a cyclone 18 for separating the air and the powder. The cyclone 18 opens at the end of its conical portion in the upper wall of the tank 2. A filter 19 is positioned on the suction port 17, to complete the separation of air and powder.

The venturi device 16 is powered by a proportional vacuum valve 20 to adjust the suction flow and thus the vacuum produced.

The depressurizing means comprise a valve 22, of the sleeve valve type, for cutting the flow rate in the depression means.

At the outlet of the venturi device 16 is positioned a permanent exhaust 23 making it possible to reduce the pressure in the tank 2. The air injection means comprise proportional valves 24, 25 which also make it possible to regulate the pressure in the chamber. reservoir 2. An unrepresented pressure sensor placed in the reservoir makes it possible to obtain a pressure measurement and to implement the pressure regulation.

The equipment further comprises means 26 for moving the powder starting pipe 8 between a first high position in which the powder in the reservoir can enter the pipe, and a second low cleaning position, shown in FIG. figure 2 in which the pipe 8 is positioned against the blowing nozzle 15 of the air injection means, thereby cleaning the pipe 8.

Advantageously, the end of the starting pipe 8 located in the reservoir is made of a material limiting the polymerization of the powder, in particular a polyamide material.

With such equipment, a powder supply method of a powder coating plant can be implemented, which comprises a phase of filling the powder tank from the powder supply means, and a phase of spraying in wherein the powder is fluidized, and the reservoir is emptied by the starting pipe to at least one remote sprayer.

• Courbe A : le débit dans la première arrivée 14 d'injection d'air pour la fluidisation, commandé par la vanne proportionnelle 24,
• Courbe B : l'état de fermeture ou d'ouverture de la vanne manchon 22 permettant de couper le débit dans les moyens de dépression ; la valeur 1 indique une vanne fermée, la valeur 0 indique une vanne ouverte.
• Courbe C : l'état de fermeture ou d'ouverture de la vanne manchon 5 d'alimentation en poudre ; la valeur 1 indique une vanne fermée, la valeur 0 indique une vanne ouverte.
• Courbe D : le débit dans l'arrivée d'air du dispositif à venturi 16 des moyens de mise en dépression, commandé par la vanne proportionnelle 20.
• Courbe E : la masse de poudre dans le réservoir.
• Courbe F : le débit d'air au niveau de l'entrée d'air 7 constituant le moyen de nettoyage de la vanne d'alimentation en poudre 5.
• Courbe G : le débit dans la buse 14 d'injection d'air pour la fluidisation et pour le nettoyage du tuyau 8
• Courbe H : la position verticale du tuyau de départ de poudre 8 ; la valeur 1 indique une position haute, la valeur 0 indique une position basse.

We will now detail the filling phases of the equipment and spray with reference to the figure 3 , on which are represented the following curves, as a function of time t:

• Curve A: the flow rate in the first air injection inlet 14 for the fluidization, controlled by the proportional valve 24,
• Curve B: the state of closure or opening of the sleeve valve 22 to cut the flow rate in the depression means; the value 1 indicates a closed valve, the value 0 indicates an open valve.
• Curve C: the state of closure or opening of the powder supply sleeve valve; the value 1 indicates a closed valve, the value 0 indicates an open valve.
• Curve D: the flow rate in the air inlet of the venturi device 16 of the vacuuming means, controlled by the proportional valve 20.
• Curve E: the mass of powder in the tank.
• Curve F: the air flow at the air inlet 7 constituting the cleaning means of the powder supply valve 5.
• Curve G: the flow rate in the air injection nozzle 14 for fluidization and for cleaning the pipe 8
• Curve H: the vertical position of the powder starting pipe 8; the value 1 indicates a high position, the value 0 indicates a low position.

• A : le débit dans la première arrivée 14 d'injection d'air pour la fluidisation est à une valeur maximale dAmin ;
• B : la vanne manchon 22 est fermée,
• C : la vanne manchon 5 d'alimentation de poudre est fermée,
• D : le débit d'air dans le dispositif à venturi est nul,
• E : la masse de poudre est à une valeur basse mmin,
• F : le débit d'air au niveau de l'entrée d'air constituant le moyen de nettoyage de la vanne d'alimentation en poudre 5 est nul,
• G : le débit de la buse 14 d'injection d'air pour la fluidisation et pour le nettoyage du tuyau 8 est à une valeur basse dGmax, permettant de réaliser la fluidisation locale de la poudre au niveau de l'extrémité du tuyau de départ.
• H : le tuyau 8 est en position haute.

During a filling phase, initially, the equipment is in the following configuration, corresponding to the end-of-spray configuration:

• A: the flow rate in the first air injection inlet 14 for the fluidization is at a maximum value dAmin;
• B: the sleeve valve 22 is closed,
• C: the powder supply sleeve valve 5 is closed,
• D: the air flow in the venturi device is zero,
• E: the mass of powder is at a low value mmin,
• F: the air flow at the air inlet constituting the cleaning means of the powder supply valve 5 is zero,
• G: the flow rate of the air injection nozzle 14 for the fluidization and for the cleaning of the pipe 8 is at a low value dGmax, making it possible to carry out the local fluidization of the powder at the end of the starting pipe .
• H: the pipe 8 is in the up position.

The filling phase takes place as follows.

At a first instant t1, the flow rate in the first air injection inlet 14 for the fluidization, controlled by the proportional valve 24, goes to a minimum value dAmin, the sleeve valve 22 making it possible to cut the flow rate in the flow means. depression is open allowing the establishment of a flow rate in the means of depression, the flow rate of the nozzle 14 of air injection is set to a high value dGmax, allowing perform the cleaning of the powder starting pipe 8, this pipe being moved to the low position.

At a second instant t2, the powder supply sleeve valve 5 is opened, and the flow rate in the air inlet of the venturi device 16 of the vacuuming means, controlled by the proportional valve 20, changes to a level haur dDmax.

Under these conditions, the reservoir 2 is in depression with respect to the supply means, and the powder is sucked towards the reservoir 2. The mass of powder in the reservoir increases. The pipe 8 is positioned against the air blast nozzle 15 to clean it.

When the desired mass of powder mmax is reached, at a third instant t3, the sleeve valve 22 for cutting the flow rate in the vacuum means is closed, the flow rate in the air inlet of the venturi device 16 means of Depression, controlled by the proportional valve 20 is cut, and the flow rate of the air injection nozzle 14 for fluidization and cleaning of the pipe 8 drops to a low value dGmin sufficient for fluidization.

At a fourth time t4, the flow rate in the air inlet of the venturi device 16 of the depressurizing means, controlled by the proportional valve 20 is restored to a value dDmax, while the valve 22 is closed, which allows creating an overpressure to clean the filter 19, without creating depression in the tank; the air flow at the air inlet constituting the cleaning means of the powder supply valve 5 goes to a level dFmax, which makes it possible to clean the valve 5 which is open.

It should be noted that the increase of the air flow at the air inlet constituting the cleaning means of the powder supply valve 5 and the increase of the flow rate in the air inlet of the Venturi device 16 depression means can be desynchronized. In addition, several pulses on the flow in the air inlet of the venturi device 16 may be provided to complete the cleaning of the filter.

At a fifth instant t5, the powder supply sleeve valve 5 is closed, the flow rate in the air inlet of the venturi device 16 of the depressurizing means, controlled by the proportional valve 20 is cut, the flow rate air at the air inlet constituting the cleaning means of the powder supply valve 5 is cut.

Under these conditions, the supply means are isolated from the reservoir, and the depression means no longer work. The filling phase is completed, and the valve 5 of the supply means, the powder starting pipe 8 and the filter 19 of the vacuum means have been cleaned.

At a sixth time t6, the spraying phase starts, the starting pipe being moved to the high position in which the powder present in the tank 2 can enter the pipe 8, and the flow rate in the first injection inlet 14 of air for fluidization increasing to a high value dAmax.

It goes without saying that the invention is not limited to the preferred embodiment described above, by way of non-limiting example; on the contrary, it embraces all variants.

Claims (19)

1. Item of equipment for supplying powder to a powder-coating installation, in particular an installation for painting components using electrostatic powder, comprising:

   - a reservoir (2), provided for containing the powder,

   - means (4, 5, 6) for conveying powder inside the reservoir (2),

   - means (15, 14) for injecting compressed air into the lower portion of the reservoir (2), in order to fluidise the powder,

   - at least one pipe (8) for discharging the powder carried by air, from the reservoir (2), this pipe (8) being connected to at least one remote device for using the powder, in particular a spraying device (9),

   characterised in that
   the item of equipment further comprises means (16, 17, 18, 19) for reducing the pressure of the reservoir (2) with respect to the conveying means (4, 5, 6) for filling the reservoir (2) with powder.
2. Item of equipment according to claim 1, wherein the
   conveying means (4, 5, 6) comprise a powder conveying conduit (4) and a powder supply valve (5) which is intended to block this conduit (4), the powder supply valve (5) being associated with means for cleaning the valve when it is open.
3. Item of equipment according to claim 2, wherein
   the conveying conduit (4) comprises at least one section which is substantially horizontal and in the region of which the powder supply valve (5) is arranged.
4. Item of equipment according to either claim 1 or claim 2, wherein the means (16, 17, 18, 19) for reducing the pressure of the reservoir (2) with respect to the conveying means (4, 5, 6) comprise a Venturi device (16) which is associated with means (18, 19) for separating the air and the powder.
5. Item of equipment according to claim 4, wherein the means for separating the powder and the air comprise a cyclone (18).
6. Item of equipment according to either claim 4 or claim 5, wherein the means for separating the powder and the air comprise a filter (19).
7. Item of equipment according to any one of claims 1 to 6, wherein the means (16, 17, 18, 19) for reducing the pressure of the reservoir (2) with respect to the conveying means (4, 5, 6) comprise a valve (22) which allows the flow of air to be stopped downstream of the pressure reduction means.
8. Item of equipment according to any one of claims 1 to 7, wherein the means for injecting compressed air comprise a blowing nozzle (15), which fluidises the powder and which is located opposite the end of the pipe (8) during the spraying operation.
9. Item of equipment according to any one of claims 1 to 8, comprising means (26) for moving the powder discharge pipe (8) between a first position in which the powder in the reservoir (2) is able to enter the pipe (8), and a second position in which the inside of the pipe (8) is separated in a fluid-tight manner from the inner space of the reservoir (2).
10. Item of equipment according to claim 9, wherein, in the second position, the pipe (8) is positioned against an air blowing nozzle (15) which allows the pipe (8) to be cleaned.
11. Item of equipment according to claim 8 and according to claim 10, wherein the same air blowing nozzle (15) allows the pipe (8) to be cleaned when the pipe (8) is in the lower position and allows the powder to be fluidised in the region of the end of the pipe (8) when it is in the upper position.
12. Item of equipment according to any one of claims 1 to 11, comprising a permanent outlet (23) which allows the pressure in the reservoir (2) to be adjusted.
13. Item of equipment according to any one of claims 1 to 12, wherein the air injection means comprise at least one proportional valve (24, 25) which allows the pressure in the reservoir (2) to be adjusted.
14. Method for supplying powder to a powder-coating installation, in particular an installation for painting components using electrostatic powder comprising:

    - a phase for filling a powder reservoir (2) from powder conveying means (4, 5, 6), and

    - a spraying phase in which the powder is fluidised, and the reservoir (2) is emptied via a discharge pipe (8) to at least one remote device for using the powder, in particular a spraying device (9),

    the reservoir (2) being placed in a state of reduced pressure with respect to the conveying means (4, 5, 6) for at least part of the filling phase.
15. Method according to claim 14, wherein a flow (dAmin) for fluidisation of compressed air is maintained in the reservoir (2) during the filling phase.
16. Method according to either claim 15 or claim 16,
    wherein the conveying means comprise a powder supply valve (5) which is intended to block a powder conveying pipe (4), and in which the powder supply valve (5) is cleaned, then closed at the end of the filling phase.
17. Method according to claim 16, wherein the reduced pressure state of the reservoir with respect to the conveying means is neutralised before the powder supply valve is cleaned.
18. Method according to any one of claims 15 to 17, wherein the powder discharge pipe (8) is moved between a first position during the spraying phase, in which the powder in the reservoir (2) is able to enter the pipe (8), and a second position of during the filling phase, in which the pipe (8) is separated in a fluid-tight manner from the inner space of the reservoir (2).
19. Method according to claim 18, wherein the pipe is cleaned by means of air being blown in the second position.

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