EP1188484A1 - Electrostatic powder coating device - Google Patents

Abstract

The electrostatic powder coating both for metal strip lengths has a chamber (1) for coating continuously supplied strip lengths in an electrostatic field provided by a movable wall (7,8) inside the chamber. the wall has actuators to move it along the feed path. A powder chamber is defined by the strip, the wall and a part of the chamber with a powder feed.

Description

The present invention relates to an application device in continuous coating powder on an oblong substrate having two opposite sides and parallel side edges, this device comprising a deposit enclosure having an inlet opening and an outlet opening allowing continuous scrolling of the substrate in the enclosure, a feeding device allowing to introduce the aforementioned powder into the enclosure, and means for creating in the enclosure at least one electric field making it possible to apply the coating powder on at least one of the faces of the substrate in scrolling.

It is currently very common to apply paint to metal strips, mainly steel and aluminum strips, scrolling continuously. When this paint is liquid, the application is carried out using machines fitted with rollers.

However, for various ecological reasons, economic or qualitative, we increasingly want to replace the liquid paints with 100% dry extract paints, i.e. solvent free. Powder coatings and crosslinked paints under UV radiation or under electron beams are the main representatives of such paintings.

Generally, the known line for powder coatings uses electrostatic headlights operating on the corona principle or tribo.

The disadvantages of using such projectors are all first due to their low flow rate, of the order of 100 to 500 g / min, which requires the simultaneous use of a large number of such projectors to obtain an economically justified return. However, line speeds using this process generally do not exceed step 30 m / min. In addition, the use of these projectors often poses problems of homogeneity of distribution of the powder on the surface to to paint.

US A-4,795,339 and US A-5,279,863 describe apparatus for forming a coating on a conductive substrate and electrostatic processes using a powdery substance.

These known processes and devices have the great disadvantage that the supply of the deposit enclosure by powdered substances is very complicated to regulate and maintain point requiring inter alia the use of an overpressure at the inlet and a depression at the outlet of the depository, in addition to expensive pumping facilities. This can lead to training of very heterogeneous coating layers giving products of poor quality which is not suitable for most applications.

There are also known devices for applying, by through an electrostatic process, a coating powder on a metal strip, scrolling from bottom to top in an enclosure. In US-A-4,188,413, the powder applied comes from a fluidized bed located in the lower part of the enclosure. In EP-A-0956909, the powder is introduced at the top of the enclosure so that it moves essentially by gravity along the face (s) of the substrate to coated. In this latest patent, the means to create a field consist of conductive wires arranged parallel to the face of the strip to be coated, transverse to the direction of the scrolling of it.

• toute la poudre qui se trouve dans une zone située à l'extérieur de celle où la bande se trouve aura tendance à se déposer sur la partie de la bande la plus proche, c'est-à-dire la rive,
• la partie des fils conducteurs qui se trouve dans une zone située à l'extérieur de la bande va donner lieu à une augmentation locale du champ électrique. Ce champ va se concentrer sur les rives et va y induire un dépôt de poudre supérieur.

In all of these prior patents, the powder in a box of greater width than that of the strip and the possible presence of conductive wires of greater length than the width of the strip will cause a greater deposit of powder on the lateral edges of the strip (the banks) for two reasons:

• all the powder which is in an area outside of that where the strip is located will tend to deposit on the nearest part of the strip, that is to say the bank,
• the part of the conducting wires which is in an area outside the strip will give rise to a local increase in the electric field. This field will concentrate on the banks and will induce a higher powder deposit there.

On the other hand, the strips to be coated can frequently have different widths and therefore it is not economically defensible to provide a special enclosure for each width of bandaged.

The object of the present invention is to develop a device continuously applying a coating powder to a substrate oblong scrolling which overcomes these problems with a simple way. Advantageously, this device must simultaneously allow high speed applications, for example throughput 12 kg / min and more for a belt speed of 100 m / min for example.

To solve this problem, provision has been made, according to the invention, for a device as indicated at the beginning, which further comprises at least one movable wall arranged inside the enclosure, means for displacement of said at least one movable wall allowing a arrangement thereof in an adjusted position perpendicular to the substrate, along at least one of its lateral edges, and at least one dusting compartment which is delimited by the substrate, said at minus a movable wall in the adjusted position and part of the enclosure and wherein said feeding apparatus introduces said powder of coating.

The mobile wall (s) of the enclosure allow them get as close as possible to the moving strip, which reduces the area where the powder is not located opposite the face of the strip to be coated. This arrangement of the movable wall (s) further allows the means for creating an electric field, which may for example be conductive wires, do not exceed the width of the strip. In one single operation, these two effects are achieved, since the walls mobiles which approach the strip to form a compartment powder coating of limited volume simultaneously mask the parts unnecessary threads.

According to an advantageous embodiment of the invention, the means for creating at least one electric field include at minus one electrode which is located in each compartment of dusting facing one side of the substrate to be coated and at least one connector which is located outside the powder compartment and to which one of said at least one electrode is connected so that a high continuous voltage can be applied to it relative to the substrate. In this way, the area where the powder is deposited, i.e. the powder compartment, and the area where the connections are carried out, are clearly separated from each other, from so as to isolate the two functions "deposition" and "current supply" and so leave the electrical connection area perfectly clean and powder-free.

According to an improved embodiment of realization of the invention, each movable wall has through holes allowing sliding of the movable wall along the wires.

According to a preferred embodiment of the invention, the enclosure has the entrance opening at a lower part and the outlet opening at an upper part as well as an opening powder feed at the top of each powder compartment for introducing powder into it from the gravity feeder along at least one of the faces of the substrate on which this powder must be applied. Advantageously, the powder supply is thus limited to the one or more dusting compartments and this feeding takes place by gravity. The powder can fall freely, only in the area necessary for the bandwidth to be treated, in the form of a homogeneous and uniform current of powdery particles along the or faces of the substrate running through the enclosure in a parallel direction and reverse to the downdraft of this powder.

Other embodiments of the device according to the invention are indicated in the appended claims.

Other details and particularities of the invention will emerge from the description of nonlimiting exemplary embodiments, given below with reference to the accompanying drawings.

FIG. 1 represents a view in vertical section through a embodiment of a deposit enclosure according to the invention, according to the line I-I of figure 2.

Figure 2 shows a sectional view along line II-II of Figure 1.

Figures 3 and 4 show views similar to Figure 2 of two alternative embodiments of the device according to the invention.

Figures 5 and 6 show in more detail the means for fixing and connecting the conductive wires of the device according to Figures 1 and 2.

FIG. 7 represents means of rapid wire fixing driver.

In the various drawings, identical or analogous elements have the same references.

There is shown in Figures 1 and 2 a following device the invention which comprises a deposit enclosure 1 in which scrolls continuously an oblong substrate, in this case a metal strip 2. This substrate has two opposite faces 3 and 4 and lateral edges parallels 5 and 6. This substrate can be of variable width and by example be a ribbon a few tens of mm wide or a strip of 1250 mm or more.

The enclosure has an entrance opening at its bottom and an outlet opening at its top and the metal strip 2 scrolls from bottom to top, preferably at high speed.

In the example illustrated, a powder supply device 45, shown schematically in dashed lines, is located at top of the enclosure so that the powder can be introduced into the enclosure, from above.

The enclosure is, in the embodiment of Figures 1 and 2, subdivided into three compartments of variable volumes by two walls mobile 7 and 8. In length, each of these walls extends perpendicular to the strip 2, from the upper wall 9 to the bottom wall 10, that is to say between the outlet opening and the tape entry opening. In depth, each of these walls mobile 7 and 8 extends from the front wall 11 to the rear wall 12. Each of the movable walls 7 and 8 can be actuated by means 13 and 14, which in the example illustrated are pushers which can be operated by hand or by machine. These pushers therefore allow the movable walls 7 and 8 to be moved into position each adjusted along one of the side edges 5 and 6 of the strip in scrolling. They can be adjusted at a distance of 1 to 10 mm from them, preferably 3 mm.

As is shown in particular in FIG. 2, in the adjusted position, the movable walls 7 and 8, the strip 2 to be coated and the front wall 11 form in the enclosure a compartment isolated from the rest of the enclosure and which will be called the dusting compartment 15. It is in this alone compartment that the powder introduced by the feeding device 6 descends by gravity.

In the variant embodiment shown in FIG. 3, the two movable walls 16 and 17 extend in length in the same way as walls 7 and 8 of the example in FIG. 2, but, in depth, they extend from the front wall 11 to a distance approximately corresponding to the front face of strip 2. This allows adjustment of the rear edge of the movable walls just along edges 5 and 6 of the strip at a distance for example from 5 to 30 mm, in particular about 20 mm from the front face 4 thereof. We thus obtains a powder compartment 15 isolated from the rest of the enclosure.

In the variant embodiment shown in FIG. 4, the movable wall 7 is arranged in the same manner as in FIG. 2. In face is a fixed wall 18. The strip 2 is here adjusted laterally on the fixed wall 18 so that its lateral edge 6 always scrolls the along this wall, whatever the width of the strip. Wall mobile 7 is then adjusted according to the position of edge 5 of the bandaged. In this exemplary embodiment, the strip passes approximately at the middle of the enclosure and two powder compartments are thus obtained 15 and 19. This arrangement is advantageous when it is desired apply a coating powder on both sides of the strip to at the same time, in a single pass.

In the examples illustrated in FIGS. 1 to 4, means to create an electric field are provided in each compartment of powdering. These are electrodes formed by a series of wires conductors 20 and 21 respectively. These conductive wires extend parallel to strip 2 and transverse to its direction of scroll and are distributed successively between the entrance opening and the tape exit opening 2.

At one end of each thread, on the right in the figures 1 to 4, the conductive wire is connected to a connector 22 which is located in outside the dusting compartment and that is itself electrically connected to a direct current source 23 for example by cables 24. Band 2 is also connected so current to the current source 23 for example by a cable 25 with an earth connection 26. A high direct voltage can thus be applied to the conductive wires 20 and 21 relative to the strip 2, which thus causes the particles of coating powder to adhere to the sides of the strips by an electrostatic effect known per se.

The movable and fixed walls of the enclosure are advantageously made of an electrically insulating material so as not to influence the electric field formed between the electrodes and the substrate in scrolling.

In Figures 5 to 7, there is shown in more detail the means for fixing and connecting the conducting wires 20 or 21. In the example shown, these wires are fixed at each end to a cylindrical sleeve of conductive material 27, for example of aluminum, on the connector side (figure 6) and to a cylindrical socket in insulating material 28 on the opposite side.

In the example illustrated, the ends of the wires have a terminal thickening, for example by crimping in a ball conductive metal 29 (see Figure 7). A hook 30 of form corresponding can then be provided for example at the ends of the sockets 27 and 28 and thus allow rapid replacement of the wires. In indeed, damaged or broken wires must be replaced so that the installation does not remain stopped for a period economically expensive.

As can be seen in the figures, the sockets 27 and 28 are threaded into an outer sleeve 31 and respectively 32 which is fixedly supported in the enclosure by fixed walls 33, 34 and respectively 35, 36, and this outside the compartment powdering.

Between the outer sleeve 31 and respectively 32 and the sleeve corresponding 27 and 28 respectively, is arranged so as to ability to slide an internal sleeve 37 on the corresponding socket and respectively 38 which is fixedly connected to a movable wall corresponding 7 and respectively 8.

These movable walls each have, for the electrodes, through holes 39 and respectively 40 which allow the sliding of the movable walls 7, 8 along the conductive wires 20 when they are actuated by pushers 13 and 14.

The socket 27 of the connector 22 can be fixed to the sleeve external 31 for example by a thread.

The socket 28 is on the contrary advantageously mounted in the outer sleeve 32 so that it can slide inside this one. Between the flange 41 closing the external sleeve 32 and a stop 42 mounted at the end of the socket 28 opposite the compartment dusting, provision has been made in the embodiment illustrated in the figure 4, a return spring 43 which pulls the socket 28 and therefore the wire 20 towards the right in the drawing.

Over time and for various reasons, the threads drivers relax. They are no longer rigorously straight and parallel to the moving strip. By the use of springs judiciously calculated according to the resistance of the wires, these can be kept stretched constantly. For example, for tungsten wires 100 µm in diameter and having a breaking limit weighing 1.5 kg, a spring having an recall constant of approximately 1 kg.

The stop 42 can for example be located opposite a detector presence of this stop, which bears the reference 44. In the event of wire break, the stop 42 is deflected to the right by the spring 43, this which is then detected by the detector 44 which is arranged so as to be able to transmit a signal corresponding to the general command, not shown, of the device. This signal has the effect of cutting automatically the power supply of the installation, and possibly also the powder feed.

Indeed, any wire that breaks during the use of the installation may come into contact with the tape and cause a short circuit or even an electric arc. This bow could be a source of ignition which would ignite the powder which is present in the form a cloud in the powder compartment.

It should be understood that the present invention is in no way limited to the embodiments described above and that well modifications can be made without departing from the appended claims.

We can for example consider a scrolling of the strip horizontally or obliquely. We can also provide a food in powder form from the bottom or from the sides, with in particular systems blowers or fluidized bed.

Claims (13)

Device for continuously applying a coating powder on an oblong substrate (2) having two opposite faces (3, 4) and parallel lateral edges (5, 6), comprising a deposition enclosure (1) having an inlet opening and an outlet opening allowing continuous movement of the substrate in the enclosure, a supply device (45) enabling the above-mentioned powder to be introduced into the enclosure, and means for creating in the enclosure at least one electric field making it possible to apply the coating powder on at least one of the faces (3, 4) of the moving substrate (2), characterized in that it further comprises at least one movable wall (7, 8, 16, 17) disposed inside the enclosure (1), displacement means (13, 14) of said at least one movable wall allowing an arrangement thereof in the adjusted position perpendicular to the substrate (2), along at least one of its lateral edges (5, 6), and at least one dusting compartment (15, 19) which is delimited by the substrate (2), said at least one movable wall (7, 8, 16, 17) in adjusted position and part of the enclosure (1) and wherein said supply apparatus (45) introduces said coating powder. Device according to claim 1, characterized in that each powder compartment (15) is delimited by the substrate (2), by two movable walls (7, 8, 16, 17), each in the adjusted position along one of the lateral edges (5, 6) of the substrate, and by a part of the enclosure (1). Device according to either of claims 1 and 2, characterized in that said at least one movable wall (7, 8) extends, between said inlet opening and said outlet opening, of a wall fixed (11) of the enclosure to another fixed wall (12) thereof. Device according to either of claims 1 and 2, characterized in that said at least one movable wall (16, 17) extends, between said inlet opening and said outlet opening, of a wall fixed (11) of the enclosure to one of said lateral edges (5, 6) of the substrate. Device according to any one of claims 1 to 4, characterized in that said at least one movable wall (7, 8, 16, 17) and said part of the enclosure are made of an electrically insulating material. Device according to any one of Claims 1 to 5, characterized in that the means for creating at least one electric field comprise at least one electrode which is located in each powdering compartment (15, 19) opposite a face ( 3, 4) of the substrate to be coated and at least one connector (22) which is situated outside the powder compartment and to which one of said at least one electrode is connected so that a high direct voltage can be applied to it relative to the substrate. Device according to claim 6, characterized in that each dusting compartment (15, 19) comprises several successive electrodes distributed between the inlet opening and the outlet opening. Device according to Claim 7, characterized in that the above-mentioned electrodes consist of a series of conductive wires (20, 21) which extend parallel to the substrate, transversely to its travel, in each powder compartment at a certain distance from it. one of the other. Device according to claim 8, characterized in that each movable wall (7, 8, 16, 17) has through holes (39, 40) allowing the movable wall to slide along the wires. Device according to either of Claims 9 and 10, characterized in that it comprises a device for rapid replacement (29, 30) of the conducting wires. Device according to any one of Claims 8 to 10, characterized in that it comprises means exerting constant traction (41-43) on the conducting wires. Device according to any one of Claims 8 to 11, characterized in that it comprises a wire break detector (44) which automatically cuts off the electrical supply. Device according to any one of Claims 1 to 10, characterized in that the enclosure (1) has the inlet opening at a lower part and the outlet opening at an upper part as well as an opening for powder feed at an upper part of each powder compartment (15, 19) allowing the powder to be introduced into it from the feed device (45) by gravity along at least one of the faces (3 , 4) of the substrate on which this powder is to be applied.

Images