Electrical ground connection for powder painting apparatus

Apparatus for electrostatically applying a coating to articles in a chamber includes nozzles for discharging a fluid stream of coating composition, usually a dry powder, into the chamber. An electrical charge is applied to the individual particles of the coating composition. An endless conveyor supports suspended racks on which the articles to be coated are supported. Electrically grounded conductive strips having a projecting edges electrically ground each of the racks they move through the chamber. The strips have a thin flat profile with a laterally projecting edge to frictionally engage the racks moving through the chamber. Preferably the edge is vertically inclined so that the point on the racks contacted by the edge continually varies as the racks are conveyed, thus insuring a scraping action and good electrical contact between the grounding strip and the rack.

FIELD OF THE INVENTION 
This invention relates to equipment for solventless painting. More 
specifically, the invention relates to equipment for painting using 
electrically charged powders deposited onto electrically charged grounded 
surfaces which are provided with a system for improved electrical 
grounding of the same. 
BACKGROUND OF THE INVENTION 
Environmental concerns regarding evaporation into the atmosphere of various 
solvents during conventional painting procedures have given rise to 
development of electrostatic painting procedures which entirely eliminate 
the use of solvents. Such painting is typically conducted in a chamber 
which is provided with numerous nozzles for discharging a powder spray 
against the electrically-grounded articles being coated. The nozzles are 
provided with means to apply an electrical charge to the individual 
pigmented particles which then are electrostatically attracted to the 
grounded articles. Also provided in the chamber is a track, usually along 
the ceiling of the chamber, through which a conveyor system is mounted. 
Individual racks are suspended from the conveyor to, in turn, support the 
articles which are to be coated. Additionally, flexibility may be added to 
the supporting racks by using upper and lower portions of more than one 
part, which may flex relative to each other. All of the resultant joints 
formed between connecting parts form regions through which electrical 
conductivity is reduced. Thus, the parts being coated are often not 
adequately grounded with the result that the coating of powdered paint 
material is not uniform. 
SUMMARY OF THE INVENTION 
It is a principal object of the invention to provide an improved grounding 
system for solventless electrostatic powder painting systems. In 
accordance with one aspect of the invention, a grounding device is formed 
by a series of contact strips which successively are engaged by a rack for 
objects being electrostatically painted as they are conveyed through a 
painting booth. 
In accordance with a further aspect of the invention, each of the 
rack-contacting strips is provided with thin, sharp laterally projecting 
edges for making positive electrical contact with article-supporting 
racks. In accordance with a further aspect of the invention, it is 
preferred that the rack-engaging strips have contact edges which are 
inclined so that the surface of the rack engaging the strip is 
continuously subjected to a scraping motion, thereby optimizing contact 
between the racks and the ground strips. 
Another advantage of the present invention relates to the fact that each 
product-containing rack is grounded directly to the grounding strip thus 
bypassing the need for any electrical circuit to pass through a series of 
electrical contacts through the rack supports. 
Briefly, the invention provides apparatus for electrostatically applying a 
coating to articles in a chamber which includes nozzles for discharging a 
fluid stream of coating composition, usually a dry powder, into the 
chamber. An electrical charge is applied to the individual particles of 
the coating composition. An endless conveyor supports suspended racks on 
which the articles to be coated, in turn, are supported. Electrically 
grounded conductive strips having a projecting edges electrically ground 
each of the racks they move through the chamber. The strips have a thin 
flat profile with a laterally projecting edge to frictionally engage the 
racks moving through the chamber. Preferably the edge is vertically 
inclined so that the point on the racks contacted by the edge continually 
varies as the racks are conveyed, thus insuring a scraping action and good 
electrical contact between the grounding strip and the rack. 
Further objects and advantages of the invention will be apparent from the 
following detailed description, the claims and the accompanying drawings.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring more particularly to the drawings, there is seen in FIG. 1 the 
overall apparatus 10 of this invention. Apparatus 10 includes an enclosed 
chamber 12 wherein electrostatic painting is carried out. Apparatus 10 
also includes a rack system 14 which is suspended through an opening 15 in 
the ceiling of chamber 12. 
For access and 14 includes a number of individual racks 16 which are 
adapted to support and convey individual articles 17 which are being 
painted. Attachment means such as eyelets or hooks 18 are provided for the 
purpose of supporting a variety of shapes of articles 17. In some cases, 
racks 16 may be configured to conveniently support an article to be 
painted of a given shape or configuration. 
As best seen in FIG. 2, the upper end of rack 16 is provided by a hook 20 
adapted to be supported by a bracket 22 which is in turn integral with a 
conveyor chain 24. Conveyor chain 24 is preferably of an endless type 
driven by conventional conveying means such as an electric motor (not 
shown). 
Also provided within chamber 12 are a plurality on each side of the chamber 
of discharge nozzles 30 of conventional construction and configuration. It 
will be noted that the nozzles 30 are provided at different elevations and 
angular disposition relative to the racks 16 so that all surfaces of 
articles 17 will be uniformly coated. Nozzles 30 are provided with 
conventional electrical supply including switches 32. Thus, the dry paint 
particles expelled by nozzles 30 are provided with a positive electrical 
charge whereas the rack 16 and thus the articles 17 being coated are being 
electrically grounded. 
Referring again to FIG. 2, it will be appreciated that if electrical 
grounding of articles 17 is provided as in conventional manner through the 
conveying chain 24, bracket 22, hook 20 and loops 18, that a great number 
of electrical connections are involved. If any of these electrical 
connections do not provide an adequate flow of electrons, the articles 17 
will not be appropriately grounded or negatively charged. Thus, the 
electrostatically-charged paint particles discharged through nozzles 30 
will not adequately cling to the articles 17 in the prior art. Referring 
to FIGS. 2-9, or, the improved grounding system of this invention is shown 
in detail. It will be noted that the grounding system of this invention 
includes a number of grounding strips 40 which may be formed of an 
appropriate conductive material such as copper or brass. Each strip 40 has 
a base or attachment portion 42 at one end which is provided with holes 43 
to facilitate attachment of strips 40 to an electrically grounded surface 
by means of rivets or screws. Integral with and attachment sections 42 are 
a main body portion 44. Body portion 44 is somewhat flexible so that the 
grounding strips 40 can pivot as contacted by racks 16. The strips 40 will 
also exert some spring force against the racks 16. Each strip 40 has a 
distal end section 46 opposite from attachment and 42 which is folded over 
preferably at 90 degrees relative to body portion 44. End portion 46 thus 
presents a sharp edge 48 against which a vertical portion of racks 16 
slides as it moves through the chamber 12. As seen in FIG. 7-9, each strip 
40 is attached to a grounded supporting surface 50. Supporting surface 50 
is attached to an electrical ground by means of an appropriate ground wire 
52. Also as seen in FIG. 7-9, as rack 16 travels generally in the 
direction of the arrows shown in the figures, strips 40 are free to flex 
slightly toward ground surface 50, thus assuring good pressure against the 
contact surface of rack 16. Also note that due to the inclined, angular 
surface presented by edge 48 there will be continual scraping action 
against the vertical shaft of rack 16 as it advances through chamber 12. 
As seen in FIG. 9, vertical shaft portion of the rack 16 engages another 
of the strips 40 just as soon as it leaves, contact with the preceding 
strip. The continuous grounding of the strips is thus assured. 
Supporting surface 50 should also be formed of a highly 
electrically-conductive material. It may be formed, for example, from an 
aluminum beam. It will thus be apparent, referring again to FIG. 2, that 
the grounding strips effectively electrically ground each of the racks 16. 
Thus, the connections presenting potential problems are limited to the 
electrical path between supporting loops 18 and article 17. 
While certain preferred embodiments of the invention have been shown for 
purposes of illustration it will be understood that the true scope of the 
invention is determined by the appended claims including structures 
equivalent thereto.