AU486015B2 - Electrostatic powder coating installation - Google Patents

Description

70.8~04 /74 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 1,274,029 there is disclosed to the art an installation of this type. The arrangc~ment 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 7if 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 in creasing clogging-of the filter'by excess powder the operation of

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70.804/74 .e suction device internally of the cabin is reduced, resulting

a reduction of the desirable negative pressure prevailing in

ie cabin. Secondly, the filter of the prior art installation

not capable of solving the problem of reclaiming the excess

wder,-in any event not in a really satisfactory manner.

Yet if the greatest possible attention is not paid'

the problem of reclaiming the excess powder material which has

)t remained adhering to the articles then the electrostatic

wder coating technique considerably loses in terms of the

:onomies of the process.

With a different construction of prior art installation

exemplified in the German patent publication 2,153,395 there

paid attention to the problem of reclaiming the excess powder.

ith this installation the cabin floor is formed by a conveyor

ind which extends out of the internal space of the cabin through

pair of rollers operating as a seal and into a collecting con-

liner.

With this last-mentioned state-of-the-art installation

ie excess powder material is intended to deposit upon the con-

Byor band owing to its own weight and is then conducted by the

)nveyor band into the collecting container. On the other hand,

Lth this installation there is not provided any suction device

lich maintains the internal space of the cabin at a negative

cessure. If it is assumed, however, that such suction device

3 a general rule is a component of a coating installation then

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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 satis-

factorily fulfilled at the expense of the other.

Henc, it is a primary object of the present invention

to provide an improved snstruction of electrostatic powder

coating installation which is associated with the afore-

mentioned drawbacks and limitations o e prior art proposals.

Another and more specific object of the presenr. in- -venn-as-- he-prision-o f-a-new-and_ improved construct ion-

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Hence, it is desirable to provide an improved

)nstruction of electrostatic powder coating installation ich is not associated with the aforementioned drawbacks

id limitations of.the prior art proposals. More specifically it is desirable to provide a

aw and improved construction of installation of the previously

antioned type which satisfies both requirements, namely, on

-eone hand cleaning of the installation and, on the other

and, that of reclaiming the excess powder material. The present invention provides an electrostatic

owder coating installation comprising a booth having an

nternal compartment and intended to receive articles to be

oated, a suction device operatively connected with the nternal compartment of said booth said suction device having of n inlet; a horizontal filter band defining with a section

ts upper face the floor of the internal compartment of said

ooth and confronting with its opposite face within said

ection the inlet of said suction device, a cleaning device

peratively associated with said filter band, means for moving

aid cleaning device and filter band relatively to one another,

Lcollecting container, said cleaning device removing excess

)owder which has deposited upon said upper face of said filter

)andand delivering such to said collecting container for -e-use of the excess powder.

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ef installaticn of the pgeviouzly -rontt-ioned-ype-wh-i-h-sat-afies

both r uirements, namely, on the one hand cleaning of the in-

stallation d, on the other hand, that of reclaiming the excess

powder material.

Now in order to lement these and still further objects

of the invention, which will be me more readily apparent as

the description proceeds, the propos apparatus construction of

the invention is manifested by the feature that a cleaning de-

vice is associated with the filter and movable lative thereto, this cleaning device removing from the filter any ex ss powder which has deposited thereon and delivering such to a conv tional -clleting Containor.--

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 installatio 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 side- or lengthwise edges of the

filter band, can serve to guide the filter band through the cabin

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and at the same time prevent any fluttering thereof under the action of the suction device, which again ensures for an un- listurbed deposition of the excess powder material upon the filter )and.

3REIF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects

,ther than those set forth above, will become apparent when con- ;ideration is given to the following detailed description thereof uch description makes reference to the annexed drawings wherein:

Figure 1 is a schematic cross-sectional view through a

owder coating installation operating according to a throughpass

echnique;

Figure 2 is a schematic fragmentary sectional view of

he arrangement shown in Figure 1, taken substantially along the ine II-II thereof;

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

Figure 4 is a variant construction of cleaning device

iich follows the discharge end of the filter band;

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804 /74

Figure 5 illustrates a further variant construction

of cleaning device which follows the discharge end of the filter

band; and

Figure 6 is schematic plan view of the floor of the

cabin of the arrangement of Figure*1 revealing the shape of 'the

guides for the filter band.

DETAILED DE SCRIPTION OF THE PREFERRED EMBODIMENTS

Describing now the drawings, the exemplary illustrated

installation or apparatus 10 depicted in Figure 1 will be under-

stood to possess a cabin or compartment 11 in the form of a

lengthwise extending tunnel, the ceiling lla of which possesses

a lengthwise extending slot 12 through which piercingly extends

the suspension means, for instance in the form of hooks 13, of

a conveying device 15 which is guid ed above the cabin ceiling

lla in a hollow rail 14. The articles 16 which are to be coated

are suspended at the hooks 13. The one side wall 17 of the cabin 11 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 19 is connected in turn with a suitable voltag,

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 prefer-

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ibly being mounted in the pistol 19) and are then attracted to

'he relevant article 16 which is grounded via the hook 13 and

-emain adhering thereat.

The floor of the cabin 11 is constructed as a double-

iall structure, and specifically the wall confronting the interior

)r inside of the cabin 11 consists of a filter 24 supported upon

Lsupporting grid 49, for instance a wire grid, and which filter,

.s will be explained more fully hereinafter, can possess a band- haped configuration. Additionally,-the cabin 11 is operatively

!oupled with a suction device 25, the suction conduit 28 of which manates from the intermediate space 26 between the filter 24 and he bottom wall 27 of the cabin associated with such filter. The uction conduit or line 28 leads to a filter compartment 29

quipped with a heavy duty filter 30 and subjected to the action

f a powerful suction blower 31.

From what has been discussed above it should be

ecognized that the air sucked-up by the suction blower 31 enters

hrough the window 18 or through the inlet openings 32 leading

o the cabin 11, thereafter is conducted through the filter 24,

irough the suction conduit or line 28 and through the heavy duty

ilter 30. This air initially brings about that the portion fcoating material which does not arrive at the article 16 is

nmediately thinned and in this thinned condition arrives at the

Llter 24. At that location 90% to 95% of the aforementioned

)rtion of coating material is held back, whereas the air with

ie residual portion of coating material impinges at the heavy

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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 bee

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 coatin

material in order to maintain the coating operation within

economical limits whereas the permeability of the heavy duty filtE

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 Figure 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 11

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-1

guide rails 36 (Figure 1) of substantially U-shaped cross-

section in the direction of the arrow 24' along its length

through the cabin 11. It is to be observed that the conveyor or

conveying device 15 conducts the articles 16 through the cabin

Sl:in the direction of the arrow 15'. The filter 24 departs froU

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the interior of the cabin 11 at the height of the inlet opening

32, and at that location is deflected by a driven withdrawal

coller or roll 37, then is guided about two deflecting rollers 38.

Defore it is again wound-up at a receiving or take-up roller 39.

3etween-both of the deflecting rollers or rolls 38 there is pro-

tided, for instance, a blower nozzle 40 which easily blows througl

:he filter band 24 and thus frees the same of any deposited coat-

.ng material, which then collects at a catch or collecting con-

:ainer 41 which surrounds the withdrawal device.

With the embodiment shown in Figure 3 the filter 24 is

onstructed as an endless, revolving driven band, the upper run

f which confronts the inside of the cabin 11. This band is uided about two large deflecting rolls 42, 43, wherein the

eflecting roll 43 is constructed as a hollow perforated roller

r drum. Internally of this hollow perforated drum 43 there is

rranged a stationary, cylindrical sector-shaped body 44 at which

here is supported the hollow perforated drum 43. An air conduit 6 opens into the section 45 which is left free by the body 44,

o that air can be easily blown through the filter band 24 during

he time that it passes ab out the hollow perforated drum 43 and

aich filter band is freed from the adhering coating powder which

rien again drops into the collecting or catch container 41.

The nature of the cleaning device associated with the

Lthdrawal device for the filter band 24 is of course dependent

)on the properties of the filter band 24 itself as well as the

iture of the coating material which is used. In Figure 4, for

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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 Figure 5 there is provided a wide mouth-blower 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 Figure 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

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cabin 11 can be realized by a high-voltage alternating-current

field which releases any coating material which still adheres

co the filter band 24 and propels such into the collecting con- tainer 41. The cleaning of the filter band, i.e. the reclaiming

3f the excess coating material by means of a high-voltage alter-

iating-current field (also known in the art as an "electrostatic

find") in contrast to the heretofore discussed cleaning devices )ossesses the advantage that even in the case of extremely fine

jrain coating materials (with particle or gra-in sizes of a few

iicrons) there is not present any danger of dust turbulence, for .nstance the component 40' of Figure 5 can be constituted as an

!lectrostatic repulsion electrode, for instance a Masuda-type

epulsion electrode. Useful as the filter material in the implest case is a reinforced cellulose web or fleece or however

fabric or textile structure formed of synthetic fibers or

sbestos.

In any event the described installation permits chang-

ng-over from one coating material to another without any prob-

ems because the location at which there begins the reclaiming

f the excess coating material is arranged at the direct neighbor

3od of the articles to be coated, that is to say, in the cabin

i, and not as was the case for the conventional installations

irst at the neighborhood of the suction blower.

Although with the illustrated exemplary embodiments

ie filter band can be drawn through the cabin it is to be under

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stood that it is of course readily possible to also provide a

cleaning device which can be moved relative to the cabin and whic

continuously wipes across the filter band which in this case is

stationary. This cleaning device ensures not only for the re-

claiming orreobtaining of the excess powder which has been depositId

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

Figure 2, can be paid-off a supply roller and during each change

of the employed coating material can be further advanced 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 followin3

claims. -A ODIG

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Claims (1)

1. 804/74

   E CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

   An electrostatic powder coating installation

   mprising a booth having an internal compartment and intended receive articles to be coated, a suction device operatively

   nnected with the internal compartment of said booth said

   ction device having an inlet; a horizontal filter band fining with a section of its upper face the floor of the

   ternal compartment of said booth and confronting with its

   Dosite face within said section the inlet of said suction iice, a cleaning device operatively associated with said

   Lter band, means for moving said cleaning device and filter

   id relatively to one another, a collecting container, said

   aning device removing excess powder which has deposited )n said upper face of said filter band and delivering such

   said collecting container for re-use of the excess powder.

   The installation as defined in claim i, comprising

   tns for advancing the'filter band through the booth and for

   'ing such past the cleaning device. The installation as defined in claim 2, further luding conveying means for conveying the articles to be

   ted through the internal compartment of the booth, the

   ancing direction of the filter band being opposite to the veying direction of the conveying means for the articles.

   Theinstallation as defined in claim 2, wherein

   d filter band comprises an endless revolving filter band ing a run confronting the internal compartment of the

   th. The installation as defined in claim 2, wherein

   filter band has lengthwise extending edges, and two guide

   is of substantially U-shaped cross-sectional configuration

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   engaging with the lengthwise extending edges of the filter band.*

   6. The installation as defined in claim 5, wherein

   said guide rails have legs confronting the internal compart-

   ment of the booth, the width of said legs decreasing in the

   advancing direction of the filter band.

   7. An electrostatic powder coating installation

   substantially as hereinbefore described with reference to

   the accompanying drawings.

   DATED THIS 28TH DAY OF JULY, 1977. GEMA AG APPARATEBAU By Its Patent Attorneys:

   CLEMENT HACK'& CO.

   Fellows Institute of Patent Attorneys of Australia.

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   31

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   26 49

   Fig.3 241 28 49

   344

   S128 49 (2B2

   Fig.3 788

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