US3902455A - Electrostatic powder coating installation - Google Patents

Abstract

An electrostatic powder coating installation incorporating a cabin serving to house the articles to be coated, the internal space of the cabin being connected with a suction device. Further, there is provided a filter which bounds with one face or side thereof a part of the internal space of the cabin and with its other side or face confronts the inlet of the suction device. A cleaning device is operatively associated with the filter and movable relative thereto, this cleaning device removing from the filter the excess powder deposited upon the filter and delivering such to a collecting container.

Description

United States Patent [1 1 Lehmann et al.

[451 Sept. 2, 1975 ELECTROSTATIC POWDER COATING INSTALLATION [75] Inventors: Ernst Lehmann; Robert Prinzing,

both of St. GalLSwitzerland [30] Foreign Application Priority Data July 19, 1973 Switzerland 10568/73 [52] US. Cl 118/630; 98/115 SB; 1l8/DIG. 7; 118/312; 118/326 [51] Int. Cl. B05B 15/04; BOSB 5/02; BOSC 11/16 [58], Field of Search l18/D1G. 7, 630, 634, 629, ll8/312, 326; 98/115 SB 3,395,972 8/1968 Hardison 98/115 SB 3,690,298 9/1972 Venturi.....

3,744,450 7/1973 Hardy 118/326 FOREIGN PATENTS OR APPLICATIONS 1,020,591 2/1966 United Kingdom 98/115 SB Primary ExaminerMervin Stein Assistant ExaminerDouglas Salser Attorney, Agent, or Firm-Werner W. Kleeman [5 7] 7 ABSTRACT An electrostatic powder coating installation incorporating a cabin serving to house the articles to be coated, the internal space of the cabin being connected with a suction device. Further, there is provided a filter which bounds with one face or side thereof a part of the internal space of the cabin and with its other side or face confronts the inlet of the suction device. A cleaning device is operatively associated with the filter and movable relative thereto, this cleaning device removing from the filter the excess powder deposited upon the filter and delivering such to a collecting container.

ELECTROSTATIC POWDER COATING INSTALLATION BACKGROUND OF THE INVENTION The present invention relates to a new and improved construction of electrostatic powder coating installation of the type equipped with a cabin intended to house the articles to be coated, the internal space of the cabin being connected with a suction device, and there being further provided a filter which delimits by means of one face or side thereof a portion of the internal space of the cabin and the other face of such filter confronting the inlet of the suction device.

In French Patent No. 1,274,029 there is disclosed to the art an installation of this type. The arrangement of the filter as part of the cabin inner wall is justified by virtue of the fact that in this way it is possible to considerably reduce the downtimes of the installation when there is carried out a change in the coating material. This is so because with such change in the coating material the entire installation must be thoroughly cleaned. Now if the filter forms part of the cabin wall then the cleaning work is reduced to the interior of the cabin and to the change of the filter, whereas the pipe conduits which lead to the suction device need not be cleaned or only in a very superficial manner.

However, with the use of a stationary filter of the prior art installation and which forms a part of the cabin inner wall no really great advantages are realized. Firstly, with increasing clogging of the filter by excess powder the operation of the suction device internally of the cabin is reduced, resulting in a reduction of the desirable negative pressure prevailing in the cabin. Secondly, the filter of the prior art installation is not capable of solving the problem of reclaiming the excess powder, in any event not in a really satisfactory manner.

Yet if the greatest possible attention is not paid to the problem of reclaiming the excess powder material which has not remained adhering to the articles then theelectrostatic powder coating technique considerably looses in terms of the economies of the process.

With a different construction of prior art installation as exemplified in the German patent publication No. 2,153,395 there is paid attention to the problem of reclaiming the excess powder. With this installation the cabin floor is formed by a conveyor band which extends out of the internal space of the cabin through a pair of rollers operating as a seal and into a collecting container.

With this last-mentioned state-of-the-art installation the excess powder material is intended to deposit upon the conveyor band owing to its own weight and is then conducted by the conveyor band into the collecting container. On the other hand, with this installation there is not provided any suction device which maintains the internal space of the cabin at a negative pressure. If it is assumed, however, that such suction device as a general rule is a component of a coating installation then with the last-mentioned installation the inlet opening of the suction device must be arranged at a side wall or at the ceiling of the cabin, since the floor is formed by the conveyor band. This however has the result that an air current or air flow forms in the cabin which at least partially disturbs the proper deposition of the excess powder material due to its inherent weight. Furthermore, this has the result that it is so to speak almost impossible to avoid contamination of the suction device by the powder material, unless in this instance there would also be installed a filter which again must be specially cleaned when changing the coating material.

Hence from what has been discussed above it should be apparent that with the heretofore known prior art technology the cleaning possibility of the installation on the one hand and the possibility of reclaiming excess powder material on the other hand constitute two requirements wherein one only can be satisfactorily fulfilled at the expense of the other.

SUMMARY OF THE INVENTION Hence, it is a primary object of the present invention to provide an improved construction of electrostatic powder coating installation which is not associated with the aforementioned drawbacks and limitations of the prior art proposals.

Another and more specific object of the present invention aims at the provision of a new and improved construction of installation of the previously mentioned type which satisfies both requirements, namely, on the one hand cleaning of the installation and, on the other hand, that of reclaiming the excess powder material.

Now in order to implement these and still further ob jects of the invention, which will become more readily apparent as the description proceeds, the proposed apparatus construction of the invention is manifested by the features that a cleaning device is associated with the filter and movable relative thereto, this cleaning device removing from the filter any excess powder which has deposited thereon and delivering such to a conventional collecting container.

It is preferred to construct the filter as an essentially horizontal filter band forming the floor of the inner space of the cabin, and which filter band can be drawn by a drive through the cabin and moved past the cleaning device. If the installation is equipped with a conveyor device by means of which the articles or objects to be coated, hereinafter simply referred to as the articles, are conveyed through the cabin, then it is advantageous if the throughpass direction of the filter band is opposite to the conveying direction of the articles. The filter band can be constructed as an endless revolving filter band, the one run of which confronts the internal space of the cabin. Two guide rails of substantially U- shaped cross-section, and which engage by means of their legs the sideor lengthwise edges of the filter band, can serve to guide the filter band through the cabin and at the same time prevent any fluttering thereof under the action of the suction device, which again ensures for an undisturbed deposition of the excess powder material upon the filter band,

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIG. 1 is a schematic crosssectional view through a powder coating installation operating according to a throughpass technique;

FIG. 2 is a schematic fragmentary sectional view of the arrangement shown in FIG. 1, taken substantially along the line II-II thereof;

FIG. 3 is a longitudinal sectional view similar to the showing of FIG. 2 through an embodiment wherein the filter band is constituted by an endless revolving band;

FIG. 4 is a variant construction of cleaning device which follows the discharge end of the filter band;

FIG. 5 illustrates a further variant construction of cleaning device which follows the discharge end of the filter band; and

FIG. 6 is schematic plan view of the floor of the cabin of the arrangement of FIG. 1 revealing the shape of the guides for the filter band.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, the exemplary illustrated installation or apparatus 10 depicted in FIG. 1 will be understood to possess a cabin or compartment 11 in the form of a lengthwise extending tunnel, the ceiling Ilu of which possesses a lengthwise extending slot I2 through which piercingly extends the suspension means, for instance in the form of hooks 13, of a conveying device 15 which is guided above the cabin ceiling Ila in a hollow rail 14. The articles 16 which areto be coated are suspended at the hooks 13. The one side wall 17 of the cabin 1] possesses one or a number of windows 18 or equivalent structure through which extends the mouth of a coating pistol or gun 19. The coating pistol I9 is connected in turn with a suitable voltage source 20 and also with a supply container 21 in which there is generated a suspension of the coating powder in air by means of a blower 22, this suspension being delivered to each coating gun 19 through the agency of a hose 23. At the latest upon discharge from the gun 19 the powder particles are electrostatically charged (the high-voltage source needed for this purpose preferably being mounted in the pistol l9) and are then attracted to the relevant article 16 which is grounded via the hook l3 and remain adhering thereat.

The floor of the cabin I1 is constructed as a doublewall structure. and specifically the wall confronting the interior or inside of the cabin 11 consists of a filter 24 supported upon a supporting grid 49, for instance a wire grid. and which filter, as will be explained more fully hereinafter, can possess a band-shaped configuration. Additionally, the cabin II is operatively coupled with a suction device 25, the suction conduit 28 of which emanates from the intermediate space 26 between the filter 24 and the bottom wall 27 of the cabin associated with such filter. The suction conduit or line 28 leads to a filter compartment 29 equipped with a heavy duty filter 30 and subjected to the action of a powerful suction blower 31.

From what has been discussed above it should be recognized that the air sucked-up by the suction blower 31 enters through the window 18 or through the inlet openings 32 leading to the cabin ll, thereafter is conducted through the filter 24, through the suction conduit or line 28 and through the heavy duty filter 30. This air initially brings about that the portion of coating material which does not arrive at the article 16 is immediately thinned and in this thinned condition arrives at the filter 24. At that location 90% to 95% of the aforementioned portion of coating material is held back, whereas the air with the residual portion of coating material impinges at the heavy duty filter 30. At this filter there occurs'an extensive cleaning of the air to a degree which permits expelling of the air into the surroundings without any problem. Further, from what has been discussed above it is here mentioned that the permeability of the filter 24 with regard to the employed coating material only need be chosen such that there can be reclaimed sufficient coating material in order to maintain the coating operation within economical limits whereas the permeability of the heavy duty filter 30 depends upon the permissible residual contamination of the air blown-out by the suction blower 31.

Although it is basically possible to provide as the filter 24 individual, easily exchangeable sheets of a filter material, according to a preferred constructional embodiment of the proposed installation or apparatus it is advantageous to employ a band-shaped filter material 24 which can be moved through the cabin 11.

In FIG; 2 such embodiment of the invention has been schematically illustrated. In this case a supply of filter material of a width corresponding to the width of the cabin I1 is drawn-off a supply roll 33 and is guided about a dancer roll 34 and a deflecting roll or roller 35 before it is guided at the guide rails 36 (FIG. 1 of substantially U-shaped cross-section in the direction of the arrow 24' along its length through the cabin II. It is to be observed that the conveyor or conveying device 15 conducts the articles 16 through the cabin 11 in the direction of the arrow 15. The filter 24 departs from the interior of the cabin 11 at the height of the inlet opening 32, and at that location is'defl'ected by a driven withdrawal roller or roll 37, then is guided about two deflecting rollers 38, before it is again wound-up at a receiving or take-up roller 39. Between both of the deflecting rollers or rolls 38 there is provided, for instance, a blower nozzle 40 which easily blows through the filter band 24 and thus frees the same of any deposited coating material, which then collects at a catch or collecting container 41 which surrounds the withdrawal device,

With the embodiment shown in FIG. 3 the filter 24 is constructed as an endless, revolving driven band, the upper run of which confronts the inside of the cabin 11. This band is guided about two large deflecting rolls 42, 43, wherein the deflecting roll 43 is constructed as a hollow perforated roller or drum. Internally of this hollow perforated drum 43 there is arranged a stationary, cylindrical sector-shaped body 44 at which there is supported the hollow perforated drum 43. An air conduit 46 opens into the section which is left free by the body 44, so that air can be easily blown through the filter band 24 during the time that it passes about the hollow perforated drum 43 and such filter band is freed from the adhering coating powder which then again drops into the collecting or catch container 41.

The nature of the cleaning device associated with the withdrawal device for the filter band 24 is of course dependent upon the properties of the filter band 24 itself as well as the nature of the coating material which is used. In FIG. 4, for instance, cleaning of the filter band 24 occurs between both of the deflecting rolls or rollers 38 by means of an oppositely rotating and driven brush roller 47 which wipes across the entire width of the filter band 24. In FIG. 5 there is provided a wide mouthblower nozzle 40' at one side or face of the filter band 24, whereas at the other side or face of such filter band there is arranged a rotating beater roller 48 which subjects the throughpassing filter band 24 to a beating action which favors the release of the coating material adhering to the filter band 24.

In FIG. 6 there is illustrated a plan view of the side of the cabin floor which confronts the inside of the cabin 11, and from which it will be recognized that the width of the legs 36a of the guide rails 36 and which engage over the side edges of the filter band 24 decrease in the throughpass direction 24 of the filter band. Consequently, there is achieved the result that the excess coating material which deposits upon the filter band 24 cannot penetrate between the legs 36a of the guide rails 36 and possibly plasticize at that location and block the filter band 24.

It should be readily apparent that it is possible to further modify the described installation in that there can be applied a high-voltage alternating-current to the side walls of the cabin 11 by means of which it is possible to prevent coating of such side walls by excess coating material. Furthermore, the cleaning of the filter band 24 after the departure out of the cabin 11 can be realized by a high-voltage alternating-current field which releases any coating material which still adheres to the filter band 24 and propels such into the collecting container 41. The cleaning of the filter band, i.e. the reclaiming of the excess coating material by means of a high-voltage alternating-current field (also known in the art as an electrostatic wind) in contrast to the heretofore discussed cleaning devices possesses the advantage that even in the case of extremely fine grain coating materials (with particle or grain sizes of a few microns) there is not present any danger of dust turbulence. for instance the component 40' of FIG. 5 can be constituted as an electrostatic repulsion electrode, for instance a Masuda-type repulsion electrode. Useful as the filter material in the simplest case is a reinforced cellulose web or fleece or however a fabric or textile structure formed of synthetic fibers or asbestos.

In any event the described installation permits changing-over from one coating material to another without any problems because the location at which there begins the reclaiming of the excess coating material is arranged at the direct neighborhood of the articles to be coated, that is to say, in the cabin 11, and not as was the case for the conventional installations first at the neighborhood of the suction blower.

Although with the illustrated exemplary embodiments the filter band can be drawn through the cabin it is to be understood that it is of course readily possible to also provide a cleaning device which can be moved relative to the cabin and which continuously wipes across the filter band which in this case is stationary. This cleaning device ensures not only for the reclaiming or reobtaining of the excess powder which has been deposited upon the filter band but also the maintenance of an essentially uniform permeability of the filter, so that the negative pressure in the cabin is maintained over longer periods of time. In this case the filter band, similar to the exemplary embodiment of FIG. 2, can be paid-off a supply roller and during each change of the employed coating material can be further ad vanced in increments or steps, whereby then the previously used section of the filter band can be thrown away. In this way the cleaning operation is also considerably simplified.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereot but may be otherwise variously embodied and practiced within the scope of the following claims. ACCORD- INGLY,

What is claimed is:

I. An electrostatic powder coating installation comprising a cabin having an internal compartment and intended to receive the articles to be coated, a suction device operatively connected with the internal compartment of said cabin, said suction device having an inlet, a filter having a first face bounding part of the internal compartment of said cabin and another face confronting the inlet of said suction device, a cleaning device operatively associated with said filter, said cleaning device and filter being relatively movable with respect to one another, a collecting container, said cleaning device removing excess powder which has deposited upon said filter and delivering such to said collecting container, said filter comprising a substantially horizontal filter band forming the floor of the internal compartment of the cabin, drive means for advancing the filter band through the cabin and for moving such past the cleaning device, said filter band having lengthwise extending edges, two guide rails of substantially U-shaped cross-sectional configuration engaging with the lengthwise extending edges of the filter band. said guide rails having legs confronting the interior of the cabin and the width of which decreases in the throughpass direction of the filter band.

2. The installation as defined in claim I, further including conveying means for conveying the articles to be coated through the internal compartment of the cabin, the throughpass direction of the filter band being opposite to the conveying direction of the conveying means for the articles.

3. The installation as defined in claim 1, wherein said filter comprises an endless revolving filter band having a run confronting the internal compartment of the cabin.

Claims (3)

1. An electrostatic powder coating installation comprising a cabin having an internal compartment and intended to receive the articles to be coated, a suction device operatively connected with the internal compartment of said cabin, said suction device having an inlet, a filter having a first face bounding part of the internal compartment of said cabin and another face confronting the inlet of said suction device, a cleaning device operatively associated with said filter, said cleaning device and filter being relatively movable with respect to one another, a collecting container, said cleaning device removing excess powder which has deposited upon said filter and delivering such to said collecting container, said filter comprising a substantially horizontal filter band forming the floor of the internal compartment of the cabin, drive means for advancing the filter band through the cabin and for moving such past the cleaning device, said filter band having lengthwise extending edges, two guide rails of substantially U-shaped cross-sectional configuration engaging with the lengthwise extending edges of the filter band, said guide rails having legs confronting the interioR of the cabin and the width of which decreases in the throughpass direction of the filter band.

2. The installation as defined in claim 1, further including conveying means for conveying the articles to be coated through the internal compartment of the cabin, the throughpass direction of the filter band being opposite to the conveying direction of the conveying means for the articles.

3. The installation as defined in claim 1, wherein said filter comprises an endless revolving filter band having a run confronting the internal compartment of the cabin.

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