Process and apparatus for cleaning a paint supply device in a painting installation

ES 2 250 554 T3

DESCRIPTION

Procedure and device in a painting installation for cleaning a paint transport duct.

The invention relates to a method according to the preamble of claim 1 and to a device according to the preamble of claim 8.

Such a method and device are known from US-A-5863352. It discloses a method and a device with a color feed path, through which a coating color can be fed from one of several color reservoirs to a coating robot. When changing from one color to another color, the color feed path is cleaned of residues of the first color, by the following procedural steps: Washing and blowing of the first color with gas, eg nitrogen or air; diluent wash; washing and blowing off residues of the diluent, also with gas, for example nitrogen or air; new wash with diluent, new wash and blow with gas; feeding the new color for the next spray coating cycle. A device for a similar procedure is also shown in US-A-5330101.

Methods and devices of this type are applied especially in combination with painting devices in the form of automatic robot painting machines which are used in many ways, for example in the automotive industry for painting bodywork parts. Due to customer behavior, current production requirements (eg "just in time") and the ever-increasing multitude of colors, especially in the automotive field, such a painting device often has to be adapted to paints of another color or paints of different characteristics, being common, for example, up to 80 paint changes per day. Therefore, modern painting devices are not only equipped with powerful first color changing and dosing facilities that allow a selection between up to 30 different paints, but also washing and cleaning units, by means of which it is guaranteed that after a paint change do not reach the surface of the piece undesirable remains of the paint used previously.

The known methods and devices of the genres mentioned at the beginning provide for a cleaning phase between two work phases carried out with different paints. This consists, substantially, in that a transport conduit that transports the paint from a selected reserve tank of a color or paint change unit, to an application apparatus (for example, atomization unit or the like), is treated with a generally liquid cleaning agent circulating through it. To do this, the cleaning agent is forced to pass under pressure through the transport line with the help of compressed air, either in the same direction in which the paint flows (document DE2043789C3) or in the opposite direction to the paint flow. (document DE9110650U1). In both cases, the cleaning agent must be removed from the conveying line before starting the next work phase. The cleaning effect can be increased in such a way that a ball or other body generally referred to as a "devil" moves back and forth within the conveying conduit (EP0888825A2).

A problem that occurs in these types of procedures and devices for cleaning transport lines is that many of the liquid paints used today, and especially their hardeners, are extremely sensitive to oxygen. Even the smallest paint chips react to the air with the formation of lumps or solid pieces that, despite being small, are visible on a smooth painted surface, making the affected part practically unusable. To ensure that these types of lumps, the formation of which is unavoidable due to the compressed air used during the cleaning step, are safely removed from the cleaning chute before the new paint reaches the application unit, on the one hand, it is requires the use of relatively large amounts of cleaning agent. On the other hand, during the entire pause between two phases of work carried out with different paints, it is necessary to leave cleaning agent free of air or oxygen in the transport duct to avoid during this time also the formation of very small harmful air bubbles and, therefore, of paint lumps. The consequence of this is that at the beginning of a new phase of work or at the beginning of a new painting step, not only the cleaning agent itself but also a certain minimum amount of the paint that comes behind, must be expelled through the cleaning device. application and transfer to a collection container, before the actual painting job can be started, to ensure that no residual amounts of cleaning agents, which generally contain a solvent, reach the surface of the part to be painted.

The amounts of paint and cleaning agent lost in this way during each cleaning phase are considerable and are a significant cost factor. In addition, paint and cleaning agent have to be disposed of as special waste, which continues to increase costs and burden the environment. All this is independent of whether the cleaning procedure is carried out with the help of a so-called devil or not.

With this background, the invention is based on the technical problem of configuring the procedure and the device of the kind indicated at the beginning, in such a way that during the cleaning steps smaller amounts of paint and cleaning agents are produced that have to be removed, largely avoiding the danger of lump formation from paint residue.

The characterizing part of claims 1 and 8 serves to solve this problem.

The invention has the essential advantage that by applying an inert gas instead of compressed air there is no longer the danger that traces of liquid paint will turn into solid lumps during the cleaning phases. In this way, cleaning steps can be designed more simply overall and performed with smaller amounts of cleaning agents. Finally, by means of the invention a considerable reduction in the amounts of paint and cleaning agents to be removed can be achieved, thus contributing to the reduction of loads on the environment.

Other advantageous features of the invention appear from the dependent claims.

ES 2 250 554 T3

In the following, the invention is described in detail with the aid of an exemplary embodiment which is represented in the attached drawing in the form of a schematic flow diagram.

The attached drawing shows, first of all, a conventional device for changing and dosing color or paint of a suitable painting device, for example, for painting bodywork parts. A transport conduit 1 for paint at a first end 1a serves for connection to a paint reservoir 2, being connected, in terms of flow, at a second end 1b with an application apparatus 3. The application device 3 contains an application element 4 that can be constituted, for example, by a spray gun, an atomizer or another element known per se for the application by gun, spraying or other type of application of paint in a jet 5. All other parts of the application apparatus 3 of little importance to the invention have been omitted for ease of use.

Preferably, the reserve tank 2 is connected, by means of an annular conduit having an advance path 6 and a return path 7, to a paint or color change unit 8 known per se. To this is connected, preferably outside the reserve tank 2, at least one additional reserve tank 9, for which purpose another annular conduit is provided which also has an advance path 10 and a return path 11. In both annular conduits a controllable valve 12 or 14 is respectively connected connecting the corresponding advance path 6, 10 with the corresponding return path 7, 11 or, via a corresponding connection point 15, 16, with the first end 1a of the transport chute 1. If the advance path 6, 10 is connected to the corresponding return path 7, 11, a liquid paint located in the corresponding reservoir 2, 9 circulates with a preselected pressure (eg approx. 4 bar) through the conduit corresponding void. On the other hand, if the valve 12, 14 connects the advance path 6, 10 with the corresponding connection point 15 or 16, the paint is made to pass under pressure from the reserve tank 2, 9 corresponding to the transport conduit 1 being transported towards the applicator 3.

The reservoirs 2 and 9 are configured, for example, as pressure tanks or as membrane or piston tanks, from which, as is usual in painting devices of the type described, the paint is pumped into the annular conduit 6, 7 or 10, 11. Therefore, in the following, the reservoirs 2, 9 are generally referred to as "paint feeds".

For the exact metering of the paint, for example, a metering unit 17 is used. In the exemplary embodiment, this comprises a paint pressure regulator 18 and a metering pump 19 configured, for example, as a gear-driven pump. motor, which are connected one behind the other in the transport line 1. The pressure before the dosing pump 19 can be measured by means of a pressure sensor 20, while to measure the pressure with which the paint is fed to the application apparatus 3, another pressure sensor 21 arranged behind the dosing pump 19 serves in the direction of circulation. According to which of the two valves

12, 14 is open towards the conveying duct 1, therefore the paint is fed from the reservoir 2, 9 to the application apparatus 3. In addition, a bypass duct 22 can be connected to the conveying duct 1 extending parallel to the metering pump 19, in order, when applying certain types of paint, to pass a part of the paint, instead of through the slow-running metering pump 19, through the bypass conduit 22.

Devices of the type described are generally known to the skilled person and do not require further description. Therefore, to avoid repetition, reference is made to the documents mentioned at the beginning (documents DE9110650U1, DE2043789C3, EP0888825A2) for the purpose of the publication of the present invention.

According to the invention, the device described has a washing unit 23 that works with an inert gas, preferably nitrogen, to clean the transport conduit 1. The washing unit 23 is connected, by means of a conduit 24, either directly or through a valve not shown of the application apparatus 3, with the second end 1b of the transport conduit 1, in such a way that in a position of said valve, the paint fed by the transport conduit 1 comes out in the form of the jet 5 of the application apparatus 3, while in another position of the valve, the conduit 24 is connected with respect to the flow with the conveying conduit 1. Normally, however, the applicator element 4 has a passage freely connected with the conduits 1, 24, with which a spray nozzle or the like is connected. When it is not painting, it is closed with a needle that for a painting procedure is extracted from the nozzle to release the jet 5.

The washing unit 23 has a source of inert gas 28 and a source of cleaning liquid 29. The source of inert gas 28 consists, for example, of a conventional nitrogen cylinder, from which, when a valve is opened, causes gaseous nitrogen to pass under pressure to a conduit 30 connected to conduit 24 through a connection 31. Instead, the source of cleaning liquid 29 is composed, for example, of a reservoir, from which a cleaning liquid can be forced into a conduit 32 connected to conduit 24 through a connection. In line 30, in the inert gas flow direction (arrow and), a pressure regulator 34, a pressure sensor 35, a controllable valve 36, configured for example as a two-way valve, and a check valve 37 which prevents the backflow of undesirable media in the opposite direction to the arrow y. The components 34 to 37 form here not only a means for the connection of the inert gas source 28 to the transport conduit 1, but at the same time also a means for filling the transport conduit 1 with inert gas, as explained in more detail further go ahead. A pressure regulator 38, a pressure sensor 39, a non-return valve 40 and a controllable valve are connected one behind the other in a corresponding manner in the line 32 in the direction of flow of the cleaning liquid (arrow w). 41, whereby cleaning liquid can be introduced into conduit 24 via connection 33. Also here, check valve 40 prevents undesirable back currents. As described further3

ES 2 250 554 T3 te, components 30 to 41 further form a means for forming a foam mixture.

The source of cleaning liquid 29 can comprise, like the reserve tanks 2, 9, a pressure tank or a tank with a pump system. The desired pressure can then be adjusted with pressure regulator 38 and monitored with pressure sensor 39.

The first end 1a of the transport conduit 1 opens, according to the attached drawing, through a controllable outlet valve 42, into a collecting tank 43. The arrangement is preferably made in such a way that the connection points 15 and 16 , seen from the outlet valve 42, are located behind it in the direction of flow (arrow x), being connected, through pipe sections 44, 45 as short as possible, with the valves 12, 14. Directly behind the last connection point 15, seen in the direction of flow, a sensor 46 configured in the manner of a proximity switch or the like, for example capacitive or inductive, is further arranged, the function of which is described later.

The mode of operation of the described painting device and of the washing unit 23 according to the invention is substantially as follows.

During the usual work phase, initially, the valves 12, 14, 36, 41 and 42 are closed. By opening one of the valves 12, 14, then it is selected which paint should be emitted during the work phase through the application apparatus 3. Valve 22 is open or closed, depending on the paint used. Assuming that the valve 12 is open, the liquid paint leaves the reservoir 2 in the dosage set by the pressure regulator 18 and the dosing pump 19 and monitored by the pressure sensors 20, 21, circulating to the application apparatus 3 , so that it can be operated in the usual way by means of the automatic or manual opening and closing of its outlet nozzle. This operating mode remains unchanged, as long as the paint from the reserve tank 2 is being used.

If it is desired to switch to the use of the paint coming from the reserve tank 9, first of all, a cleaning phase is foreseen for the transport duct 1. To do this, with the application apparatus 3 being closed, the valve 36 is opened. the washing unit 23, whereby the inert gas arrives from the inert gas source 28, through the conduits 30 and 24 and the application apparatus 3 or directly, to the second end 1b of the transport conduit 1. The pressure of the inert gas that can be read from the sensor 35 is determined by the setting of the pressure regulator 34. The pressure of the inert gas (eg 10 bar) is chosen such that the paint in the transport line 1 is pressed against the usual transport direction (arrow x), returning in the direction of the reserve tank 2 or its annular conduit. Due to the short length of conduit 44, the return transport of the paint can be done almost completely.

The sensor 46 monitors this procedure by emitting a signal as soon as the boundary surface between the paint and the inert gas is passed. This signal can be used, through a control device not shown, preferably automatic, to close valve 12 and open outlet valve 42. As a consequence, the small amount of paint still in front of the inert gas column becomes now pass under pressure through the end of the transport conduit 1 to the collecting tank 43. Consequently, only a small amount of paint is produced which has to be removed.

By the reaction of the sensor 46, the valve 41 of the washing unit 23 can be opened at the same time. In this way, the cleaning agent or liquid solvent circulates from the reservoir 29 to the conduit 32 which then, in an adjusted quantity via pressure regulator 38 and controlled by sensor 39, it reaches conduit 24 through connection point 33. By suitable adjustment of the pressures and conveying speeds, the cleaning liquid and the inert gas are preferably made to form a cleaning or washing agent in the form of a foam mixture, which, as before the pure inert gas, remains pressed backwards through the transport conduit 1 until finally the front of the foam mix column reaches the collecting tank 43.

During this process, the element 4 of the application apparatus 3 can also be briefly opened and thus cleared of paint. With the corresponding pressure of the inert gas, the washing unit 23 works like a high pressure cleaner and therefore extremely efficient and fast. In addition, the foam mixture can be adjusted in different ways depending on the paint used , and you can always achieve an optimal wash.

Shortly after the sensor 46 has recognized the boundary surface between the inert gas and the foam mixture and emitted a corresponding signal, the valve 41 closes for the cleaning liquid. Optionally, the cleaning phase can also be terminated via a preset run time, from the start of the cleaning agent supply or from the response of the sensor 46. This has the consequence that only inert gas is now passed back through the transport conduit 1, whereby the cleaning agent still located in it is forced to pass under pressure in its entirety to the collecting tank 43. The completion of this The procedure is indicated, in turn, by the sensor 46 or determined by a preselected execution time.

A short time later, the entire transport line 1 is filled exclusively with inert gas, after which the valve 42 is closed and this state is maintained until the next working phase begins, for example the valve 14 is opened instead of the valve 12 and valve 36 closing. In this way, it is ensured that during the time between the end of the cleaning procedure itself and the start of the next working phase, the inert gas is in the transport conduit 1 with such pressure that entry is safely avoided. air or oxygen due to uncontrollable leaks.

According to a preferred embodiment, after filling the transport line 1 with inert gas, up to a pressure of, for example, 1 bar, selected by the pressure regulator 34, the valve 36 is also closed, whereby the transport line 1 is closed everywhere. Subsequently, the pressure prevailing in the conveying line 1 is continuously monitored with the help of the pressure sensors 20, 21. If a component is leaking or if any medium enters the conveying line 1 uncontrollably from the outside, it is detected with the help of pressure sensors 20, 21 resulting in

ES 2 250 554 T3 to the generation of an alarm signal, a disconnection signal for the entire device, or the like. Valve 22 is preferably open.

After the closing of the valve 36 and the opening of the valve 14, which occurs at the latest with the start of the next working phase, the element 4 of the application device 3 can be reopened if necessary In this way, the new paint fed, in the first place, causes the column of inert gas located in the transport conduit 1 to be expelled from it. The sensor 46 that signals the influx of paint can be used to specify a breakthrough time resulting from the length of the conveying duct 1 before starting the painting job itself, if it is desired to avoid applying the inert gas by spraying onto the piece to be painted. However, since it is an inert gas, it generally does not matter if element 4 is directed, immediately after the release of the paint through valve 14, to the surface of the corresponding part by applying a little inert gas on the surface of the the piece to be painted.

During the normal operation of the described painting device, possible errors of the transport pipe 1 can be checked, with the help of the pressure of the paint located in the transport pipe 1, in the same way as described above in relation to inert gas. For this, for example, after a previously set time (for example, 10 s) from the end of the last paint intake by the applicator 3, the corresponding valve 12, 14 is closed, the pressure of the Paint currently located in the conveying line 1 is specified as the theoretical pressure and is monitored by the pressure sensors 20, 21. In the event of an undesirable increase or decrease in said pressure, with the help of the automatic control device, in turn, an alarm or disconnection signal or the like is generated. Also in this case, the valve 22 is preferably open. If it is subsequently repainted, the corresponding valve 12, 14 is reopened and valve 22 is closed again.

The inert gas in the inert gas source 28, especially if it is nitrogen, is preferably kept at a certain minimum temperature, which, for example, is equal to or greater than 10 ° C or 20 ° C. In this way, it is ensured that the paints used do not cool down to temperatures below, for example, 5 ° C, at which some paints may be destroyed.

In painting devices in which more than one application device 3 is connected to the transport duct 1, it may be advisable to choose a higher paint pressure in the annular ducts 6, 7 or 10, 11 (for example, 15 to 20 bar ). In this case, to the valves 12, 14, preferably, other valves or the like are pre-connected which, during the cleaning phases, reduce or regulate the pressure in the annular conduits 6, 7 or 10, 11 to a value sufficiently lower than the pressure of the Inert gas (eg 10 bar) to ensure the desired recovery of the paint during the cleaning phases. After the paint has been pressed into the annular passage 6, 7 or 10, 11, the necessary transport pressure is re-established.

The invention has numerous advantages. In the first place, by applying an inert gas that does not react with the types of paint used and the final filling of the transport conduit 1 with the inert gas, it is ensured that the remains of paint that remain in the transport conduit 1 are not transform into annoying lumps or the like. This is valid for the total duration of a cleaning phase carried out between two work phases. Furthermore, in this way it can be avoided that at the beginning of a working phase, a quantity of paint exiting the application apparatus 3 has to be introduced into the collecting container in order to reliably prevent the application of cleaning agent on the surface of the paint. the piece, that is to say that applying the invention, the new paint that comes out can be used directly and without producing waste. It is also advantageous that a cleaning foam consisting of the cleaning liquid and the inert gas can be used during the cleaning process, whereby the required amounts of cleaning liquid are considerably reduced. Both measures contribute significantly to cost reduction by correspondingly reducing the cost of special waste disposal. Since there is no longer any danger of lumps or the like forming from paint residues, the intensity of the cleaning work to be carried out can be reduced. Apart from this, after a working phase, the paint still present in the conveying line 1 can be almost completely recovered.

Likewise, it is advantageous that with the described method, not only the transport line 1 itself is cleaned without problems, but also all its fittings, valves, etc. (for example, 16, 18, 19, 20, 21, 22), which especially in facilities that work with devils is not easily possible, because devils generally cannot pass through faucets or the like. Finally, all the described processes can easily be controlled automatically, whereby the invention can be applied especially advantageously in automatic robot painting machines.

The invention is not limited to the exemplary embodiment described, which can be varied in many ways. This especially refers to the quantity of different types of paint, provided in certain cases, which can be selected with the help of the color change unit 8. Instead of paints of different colors, it is also possible to choose paints or types of paints with different characteristics, for example ordinary paints, in addition to paints for so-called metallic coatings. It is clear that instead of paints it is also possible to transport other liquids, especially colors, through the transport line 1, and that the name "paint" in the context of the present invention refers to all liquids of this type, suitable for coatings. Furthermore, the different steps during the cleaning phases can be carried out in another order and / or in another direction and / or with other time cycles. For example, it would be possible to remove the cleaning medium again after the recovery of the paint column remaining in the transport duct 1, in the direction of transport of the paint (arrow x), for example, by providing a second source of inert gas arranged at the first end 1a of the transport conduit

1. Furthermore, preferably not a nitrogen pump is used as the inert gas source 28, but a commercially available nitrogen generator, which generates, for example, nitrogen from air with a

ES 2 250 554 T3 pressure up to 15 bar. Furthermore, the transport conduit 1 can contain other suitable components, for example, a very fine filter that only allows particles to pass up to a size slightly larger than the pigment size of the paints used. In addition, the valves 12, 14 of the color change unit 8 can be reunited with the outlet valve 42 forming a compact block to further reduce or omit the conduit sections altogether.

44, 45. Likewise, it is clear that the invention should not only cover the device described for cleaning a paint transport duct 1, but also a complete painting device equipped with such a device. Finally, it is understood that the different characteristics can also be applied in other combinations than those represented and described.