Vat Device For The Treatment Of Articles In A Fluidified Medium

Abstract

Vat device for the treatment of articles in a fluidified medium, adapted to perform the coating of various articles with a view to carrying out any appropriate surface treatment comprising an open-top vat having at least one substantially horizontal spraying pipe provided in the upper portion of the vat in proximity to a wall thereof, the said spraying pipe ejecting into the vat a thin and substantially horizontal layer of fluidified powder.

Description

The present invention has essentially for its object a vat device for the treatment of articles in a fluidified medium, adapted for instance to form a coating on various articles by means of a powder suspended in a fluidified medium, in view of any appropriate surface treatment. For instance, it is known that articles are coated by way of electrostatic deposition of a powder, by applying different potentials to the powder and the articles. The powder may be suspended in a fluidified medium in a tunnel in which the articles are displaced by a conveyor. The powder-coated articles may thereafter be subjected to the treatment desired, for instance a baking treatment in a furnace if the powder-coating obtained is to be baked.

Of course, such plants are extremely complicated and expensive. More particularly, serious problems arise in connection with the passing of the conveyor through the tunnel which must be isolated as sealingly as possible from the external medium.

The present invention is directed at a simplified and relatively inexpensive device permitting small or large-scale treatment of articles of any shape and dimensions.

The device according to the invention is in fact a vat device for the treatment of articles in a fluidified medium, which is characterized in that it is constituted by an open-top vat comprising at least one substantially horizontal spraying pipe provided in the upper portion of the vat in proximity to a wall of the latter, the said spraying pipe ejecting the fluidified powder into the vat.

Advantageously, the vat is substantially in the shape of a right-angled parallelepiped and is provided with two said spraying pipes arranged in substantially confronting relationship on two mutually opposite walls of the vat, and the upper portion of the vat is provided with a gutter-shaped powder-sucking channel preventing overflow losses, the said gutter-shaped channel being associated with a sucking and recovering device.

In order that the fluidified bed may be readily maintained in suspension in the vat, the latter is advantageously provided with an additional, inclined and porous bottom-wall, through which is blown a flow of conveying fluid forming a fluidified bottom, which flows into a channel arranged lower and in which the powder is fluidified and driven towards the said spraying pipes by means of directed injections of conveying fluid into supply ducts provided with Venturi devices or the like.

Owing to the device of the invention, the construction of which is simple, it is possible to treat intermittently (or continuously if desired) a great variety of articles of any shape, without any loss of powder and under altogether satisfactory conditions as to the results obtained and the hygiene conditions during work. Indeed, whether the vat device is used or not, there is never any loss of powder nor any efflux from the vat. Since the latter is open at its top, the articles to be treated can be simply introduced into the vat and withdrawn therefrom when suitably coated.

The invention will appear more clearly from the following description, made with reference to the appended drawing illustrating only by way of example, one form of embodiment of the invention.

According to the form of embodiment illustrated, a plant according to the invention is formed of a vat device for the treatment of articles in a fluidified medium, comprising an open-top vat 1 substantially in the shape of a right-angled parallelepiped having four lateral faces 2, 3, 4 and 5 and a bottom 6. Two spraying pipes 7, 8 are provided in the top of the vat in proximity to, respectively, the walls 4 and 2. The pipes 7 and 8 eject the fluidified powder into the vat as diagrammatized in the drawing.

At 9 there is seen a reservoir containing the powder 10 to be sprayed. The reservoir 9 feeds a fluidification channel 11 in which the powder is fluidified by means of an injection of a conveying fluid, such as air, supplied at 12 under a porous wall 13 forming an additional bottom wall of the channel 11.

The powder thus suspended in the channel 11 is sucked into the spraying-pipe supply ducts 14 and 17, by means of air injections into the ducts 16, 17 arranged in coaxial relationship to the ducts 14, 15, according to the well-known Venturi principle. Secondary air may also be supplied through ducts 18, 19 at the inlet of the spraying pipes 7, 8, so as to permit a more accurate regulation of the flow and density of the fluidified bed formed in the vat 1.

Thus, each spraying pipe is supplied through two successive Venturi devices such as 32, 33 fed with conveying air through the conduits 17, 19.

The spraying pipes 7, 8 may be of any known type, for instance of the type provided with orifices, etc . . . .

In order to prevent the powder from accumulating at the bottom of the vat, the latter is advantageously provided with an additional, porous bottom-wall 20 inclined towards the channel 11, a flow of conveying air being injected between the vat bottom 6 and the wall 20. A fluidified bed is thus maintained at the bottom of the vat, so that the powder moving down by gravity from the spraying pipes 7, 8 forms in the vat a fluidified bed, the lower layer of which flows towards the channel 11 as shown by the arrows 21. The bottom 20 thus forms an aeroslide for the powder. It also forms a protecting grate stopping any object having casually fallen into the vat.

In order to prevent powder overflows from the vat 1, the latter is provided at its top with a gutter-shaped channel 22 arranged all around the vat and provided with an opening or slit 23 opening into the interior of the vat. A negative pressure is created in the channel 22 by means of a sucking device 24 connected to the channel 22 through a duct 25. The powder sucked into the channel 22 by the device 24 is recovered at 26 in a filter, or it may be conveyed back into the vat 1 through a duct 27, after being, if desired, freed from dust.

When it is desired to coat an article 28 by means of the powder suspended in the vat 1, it is sufficient to pass the said article between the spraying pipes 7 and 8 and to introduce it into the vat. The spraying pipes are so designed as to admit a uniform flow of powder distributed equally over the whole length. They are provided with an electrostatic charge electrode 31 connected to a high-voltage generator 30. The powder sprayed by the pipes 7, 8 forms a screen of electrostatically charged powder through which passes the articles 28 to be coated, the latter being connected to earth through the medium of a holder system, a handling means or a rod 29. The articles 28 may also be heated, so that the powder may adhere thereto spontaneously.

The design of such a device is therefore very simple and very practical in use.

Of course, the invention is by no means limited to the form of embodiment described and illustrated, which has been given by way of example only. The invention comprises all the technical equivalents to the means described as well as their combinations should the latter be carried out according to its spirit and within the scope of the following claims.

Thus, for instance, a vibrating sieve-grate may advantageously be provided on the upper beam of the channel 11.

Likewise, the sucking slit 23 of the gutter-shaped channel 22 may be arranged lower than the location shown in the drawing, for instance below the spraying pipes 7, 8, so that a negative pressure may be created in the whole of the vat.

The bottom 20 of the vat may also be constituted by one or several inclined metal sheets to which vibrations are imparted to ensure the flowing of the powder towards the channel 11.

Claims

What is claimed is:

1. Vat device for surface treatment of articles in a fluidized medium, comprising a container having at least one horizontal spray pipe adjacent the upper end portion of the container and in proximity to a side wall thereof, said container being formed at its bottom portion with a channel, means for supplying powder to said channel, fluid supply means for supplying a fluid within said channel to fluidize said powder therein, conduit means interconnecting said spray device with said channel, and drive means cooperating with said conduit means for driving said fluidized powder from said channel to said spray pipe through said conduit means.

2. A device according to claim 1, comprising a powder reservoir from which the powder falls into the said channel.

3. A device according to claim 1, wherein said drive means comprises a source of air injected into supply ducts, said air by Venturi effect driving said fluidized powder to said spray pipe.

4. A device according to claim 1, wherein said channel is defined at its upper end by an inclined porous wall through which powder from the spray pipe may pass should such powder reach said porous wall.

5. A device according to claim 1, wherein said container is substantially in the shape of a right-angled parallelpiped structure, two spray pipes being provided in substantially confronting relation, each being disposed adjacent a side wall of the container.

6. A device according to claim 5, comprising a gutter-shaped powder-sucking channel at the upper bounds of the container which is open for preventing overflow, suction means for removing excess powder through said sucking channel, and a recovering device connected to said suction means for recovering said excess powder.

7. Treatment vat device according to claim 6, wherein the said gutter-shaped channel is provided in the upper portion of the vat.

8. Treatment vat device according to claim 5, wherein the said spraying pipes are connected to a high-voltage generator.