Note: Descriptions are shown in the official language in which they were submitted.
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At the present time, the application of vitreous,
porcelain enamel in dry powder form is carried out by
pro~ecting a cloud of the dry, powdered enamel from a
slight distance, generally about 200 mm., from the
objects to be enamelled which are principally objects
of sheet steel .
In order to improve uniformity of deposition, an
electrostatic field is created in the cloud of powdered
material, so that the particles receive a negative
electrostatic charge, while the conducting objects to
be coated are grounded, and thus have a relatlvepos~ive p~n- ;.
tial. There ensues an attraction of the negatively
charged particles by the conducting objects to be
coated, which assume a positive potential with respect
to said particles .
As for electrostatic powder application, in the
currently employed process, various means are used; ~-~
generally by aerating the powder~ with projection being
ensured by one or several spray gun which function by
compressed air .
The electrostatic field is created by a conti- .
nuous current generator which charges the electrodes
negatively in order to create the electrostatic field~
Generally, the field can be regulated between 60,000
and 100,000 volts, and the electrodes are positioned
at the place from which the powder is projected, that is
about 2.00 mm from the objectsO More specifically, when
the powder is projected by a pneumatic spray gun, the
electrode is placed at the center of the spray gun's
nozzle .
The application of vitreous enamel by the techni-
que in general use at the present time, and which has
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just been described, allows the deposit of a layer of
dry material which has an average thickness of 0.20 mm~
on the surface of metallic objects, and which, after
firing or fusing, gives an average coating thickness
of 0.14 mm.
It will be noted that, in spite of the use of an
electrostatic ~ield which directs the particles of
powdered enamel to the conducting object to be coated,
only part of the cloud of particles e~fectively reaches
the object; the deposit efficiency being in the range
of 30 to 40~ (this is the ratio between the quantity
of material actually deposited on the object, and the
quantity of material pro~ected. The portion (70 to 60%)
of enamel which is not deposited is recovered by means
of different kinds of apparatus, mainly cyclone sepa-
rators and filters, with the recovered powder being
recycled toward tne spray gun, for purposes of reuti-
lization. While it is true that the loss of powdered
material is relatively limited, due to this recycling,
nevertheless, the efficiency of the various kinds of
apparatus used for recovery, such as cyclone separators
and filters, is not 100%; moreover the recycled powder
is somewhat contaminated during the recovery and recy-
cling. Thus it would be advantageous to increase the
ef~iciency of the projection, and this is being done
at the present time by various means, notably :
- improvement of the devices for projecting powder~
- the arrangement and struct-ure of the electrodes
which will electrostatically charge the particles,
- improvement of the enamel powders by increasing
their capacity to receive an electrostatic charge O
Despite all these efforts, the efficiency is rare-
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ly greater than 40%.
This invention consists of reinforcing the electrostatic fieldcreated by the electrode or electrodes placed in immediate contact with the
enamel powder at the time of projection by means of an intense directional
electrostatic field, capable of directing the suspended particles in the air -~
toward the objects, with this intense directional electrostatic fieLt being
produced principally by field emitters, each of which has the form of the
antenna of a television set placed at the focal point of a parabo~ic reflector,
and which emit an intense electrostatic field, with these emitters being given
the same charge as the electrode or electrodes.
In accordance with the present invention there is provided in a
device for applying coating particles to a metallic, electrically grounded --
object comprising means for supporting the object, said device having a first
means for projecting the particles towards said object, said first means in-
cluding means for electrostatically charging said particles at a high poten-
tial and initially projecting same towards said metallic object, the improve-
ment of at least one supplementary electrostatic field emitter having an int - ; -
tense directional electrostatic field for re-directing said charged initially
directed particles towards said object, said emitter being composed of a rod ~ ;
member placed at the foca~ point of a metallic concave reflector and being
mechanically and physically disassociated from said first means.
Thus one succeeds in implementing, in a very intense way, the
phenomenon called wrap-around, which allows the particles that do not come
directly in front of the frontal part of the object to be attracted by it
and to be deposited on the lateral or upper or lower surfaces, and even to go
around the object completely and~ in some cases, to be deposited on the far
surface.
This wrap-around phenomenon is very important since it allows the -
powder to be deposited on all parts of a metallic object and not only on the
parts that directly face the projecting apparatus.
It is the application of this phenomenon that permits the conception
of simple and automated devices for coating objects that have edges or sur-
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faces at right angles to the principal surface to be coated. F~rmerly,devices capable of complicated maneuvers were necessary to project the powder
directly onto such secondary surfaces residing in a different plane, or it :~
was necessary
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to forego automation for coating these surfaces, and
pro~ect the powder with the help of a manually operated
projection apparatus O
The appropriately situated, supplementary field
emitters ensure that the contours of the cloud are
thrown in the direction of the ob~ect to be coated,
and thus ensure greater efficiency in the deposit of
the particles on the ob~ects and a better coverage of
the edges, and rlght angle surfaces, fully utilizing
the wrap-around phenomenon .
Moreover, the fact that they have the same poten-
tial as the primary electrodes avoids disturbances and i.
turbulence phenomena on the cloud .
In any case, the invention will be understood :~:
easily with the help of the description that ~ollows,
as well as the attached drawings, which are, of course,
given primarily for guidance O
Figure 1 portrays, in lateral view, a device pro-
vided with the improvements of the invention, for ap-
plying a powdered, dry vitreous enamel to metallic
ob;ects .
Figure 2 is a top view of the same device .
According to the invention, and particularly ac-
cording to the embodiment which should be given prefe- -
rence, for example, for the purpose of realizing a
device ~or applying a dry, powdered vitreous enamel to
metallic ob~ects, one should proceed as follows, or in
an a~alogous manner .
First, in accordance with the well-known technique,
a metallic object 1, such as a steel sheet, is electri-
cally grounded as at 2; ob~ect 1 is supported by means
of cables 4, for example, suspended from an upper rail 3,
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electrically connected to electrical ground 2.
Metallic object 1 can be composed of an object of
any form and dimensions, as well as a plate, and may even
have bent edges, due to ~he improvements of the invention.
It need not be steel, but can also be cast-iron and other
metals, particularly aluminum and copper.
The powder is projected on to object 1, after
having been aerated by means of a spray gun 6, which works
hy compressed air, and which has in its center an electrode
7, charged with a high potential, which can be between
60,000 and 100,000 volts, continuous current, negative
polarity, by means of a high tension generator 8, to which
it is connected by a conductor 9. Spray guns of this kind
are well known to the art. As for the powder, it can be
composed of any suitable vitreous enamel powder. For
example, a powder of the kind described in United States
Patent No 3,928,668 issued December 23, 1975 "Electrostatic
Deposition of Dr~ Ceramic Powders" may be used, which
powder has been pre-coated with an organopolysiloxane.
One can also use an enamel having the following
camposition in parts by weight :
SiQ2 3Q to 50
R2 ~ lQ to 30
Na20 3 to 15
K2Q 5 to 10
Ti02 10 to 25
P2Q5 Q to 10
F2 to lQ
These two types of enamel are ~n no way limiting.
Qne envisions, in the well-known manner, of course,
means of shifting spray gun 6 with respect to plate 1.
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Thus~ in Figure 1 are illustrated, in unbroken and
broken lines, respectively, the two extreme positions
(with regard to height of spray gun 6, namely, posi- ~-
tions 6a and 6b. In Figure 2, 6c represents a cloud
of powder in suspension in the air and pro~ected by
spray gun 6
m e system that has ~ust been described is of
the well-known kind .
In accordance with the invention, two supplemen-
tary electrostatic field emitters 10 are foreseen on
each side of spray gun 6. These two emitters are
parabolic an d are directed toward ob~ect 1 . Each
emitter 10 is advantageously composed of a television
set antenna 11 placed at the focal point of a parabo-
lic reflector 12, and emits an intense electrostatic
field. A conductor 13 puts each emitter 10 (mounted on
a support 14 by means of an insulating bar 15 born by
a rod 16) at the same potentlal as electrode 7 or
;~ spray gun 6. As a result, the emitters 10 are brought
A to the same potential as electrode 7, a potential
comprised between 60,000 and 10,000 volts, continuous
current, negative polarity .
Other supplementary field emitters can be placed
at will under and over ob~ect 1, depending on the
direction one is trying to give to the powder cloud 6c,
particularly if ob~ect 1 includes lower and/or upper
edges .
The method and the device of the ~nvention permit,
a~ong others, application to porcelain enamelled house-
hold articl~s such as cookware, parts of electric ovens,
washing machines, and refrigeratorsO They are ~lso
applicable to enamelled pannels for building façades.
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While part o~ a television antenna provides a
convenient means of achieving supplementary field
emitter member 11, it is obvious that the design and
dimensions of member 11 may be varied extensively to
accommodate varying processing requirements, and any
variety of branched or straight rod-like members will
serve equally well .
It is to be understood, of course, that the
particular embodiment illustrated in ~igures 1 and
2, and the kinds of ob~ects to be enamelled, as well
as the enamel composition disclosed~are merely exempla-
ry and may be modlfied extensively ~without departing
from the princlple of this invention.
Although the preferred embodiment illustrated
above discloses a parabolic reflector, it ls to be
understood that this particular shape is but exemplary
and, depending upon the parameters of a given coating
operation, the reflector may assume any one of myriad
shapes, so long as it is of a generally concave nature
and is capable of reflecting and directing the field
emitted from member 11 .
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