Note: Descriptions are shown in the official language in which they were submitted.
09
MEANS AND METHOD FOR ELECTROSTATICALLY APPLYING
POWDER CO~TING TO AN ~RTICLE
Technical Field
My invention relates to the coating of pipes and
other articles with a layer of plastic to provide protection
from rusting, salt deposition, paraffin deposition, corro-
sion by chemical agents, etc. and to create a smoothesurface which in the case of pipes can minimize resistance
from friction of substances being transported through them,
and in the case of other articles can serve a variety of
purposes, including aestheticO In the field at this time,
most of such coating is done either by applying liquid
coating by spraying or dipping objects and then drying them,
or by dry powder coating applied by the fluidized bed or
electrostatic methods using high voltage electrostatic
generators and spraying nozzles.
Background Art
Typically, pipes and articles which are to be so
coated must receive even coating on all surfaces. If they
are coated by the use of liquid plastic which is then dried,
they are usually either dipped or sprayed with several layers
which takes a lot of time, and neither of which methods
yields uniform complete coating. If they are coated by a
powder by the fluidized bed or electrostatic methods, the
technical problem is how best to get an even layer of powder
on all surfaces. To make this economically feasible, a
process should consume as little energy as possible, coat as
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many articles as possible with one run, and waste as little
of the coating agent as possible.
The prior art includes several patents which
achieved certain but not all of the desired results, and
which were not as energy-efficient or versatile as my
invention. German Patent No. 1910487 uses dry powder to
coat objects which are suspended in a working chamber and
sprayed with powder by an electrostatic gun, the powder being
transported from location to location by four blowers, with
unused powder recovered by two precipitators. U.S. Patent
No. 3918401 applies powder coating to pipes by charging the
particles of powder by means of an electrostatic generator
and then, by means of blowers, directing the charged particles
at the object to be coated. This process is repeated from
beginning to end for each object to be coated. If more than
one object is to be coated, working parts must be duplicated
for simultaneous operation to the extent that it would be
just as practical to operate several apparati, each coating
one object at a time, side by side. U.S. Patent No. 3976031
also applies powder coating to objects by the electrostatic
method. The powder is propelled into the vicinity of the
object to be coated by a fan, and is at that point charged
by a generator, so that it coats the part of the object exposed
to the powder. U.S. Patent No. 3982050 teaches coating
objects with powder, which must be used at high levels of
concentration upon pre-heated objects. The possibilities
of this patent are only for coating the inner surfaces of
pipes of small diameter. U.S. Patent No. 3946125 is also a
method of coating the inner surfaces of metal pipes, and is
used for one pipe at a time per Ullit; this patent teaches
heating the pipe, then introducing the powder so that it
fuses to the surface it touches.
~isclosure of Invention
In accordance with the present invention, I provide
an apparatus comprising a main closed circuit which may have
branches in series or in parallel in which the articles to
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be coated are placed. Plastic powder is introduced into the
main circuit and is circulated and accelerated to a high
speed by a fan, whexeby it acquires a high electrostatic
charge. When the working chambers (the branches containing
the articles to be coated) are placed in communication with
the main circuit by opening valves, the charged particles
thereupon flow through the branch circuits and cling to the
articles to be coated. When the desired thickness of coating
has been achieved, the branches are cut off from the main
circuit by closing valves and the coated articles can then
be heated to cure the coating. No static generator is used.
My apparatus possesses the advantage over the prior art
devices in that it eliminates the necessity for using costly
electrostatic generators. And because the process can take
place in an enclosed structure, there need be no loss of the
coating agent and no contamination of the surrounding atmos-
phere, which is a distinct improvement over certain prior
art devices in which coating had to take place in a booth.
Another advantage of my invention is that all surfaces of
articles of any size and shape may be evenly coated with a
desired thickness of coating without rotating or moving those
articles or repeating the process over and over.
Brie Description of the Drawings
The details of my invention will be described in
connection with the accompanying drawings.
Figure 1 is a schematic elevational view showing an
example of the prior art apparati for applying electro-
statically charged particles of coating to an article. It
does not represent any one of the cited prior art patents
but rather a general design employing the art they teach.
Figure 2 is a schematic elevational view showing a
first embodiment of the invention in which coating takes
place in a booth or open space.
Figure 3 is a schematic plan showing a second
embodiment of the invention in which coating takes place in
closed branches.
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Figure 4 is a schematic plan showing a third
embodiment of the invention which provides a universal
fixture to allow pipes of different diameters to be placed
into circuit branches for coating of their inner surfaces.
Figure 5 is a schematic plan showing another type
of universal fixture allowing pipes of different diameters
and lengths to be placed into branch circuits for coating
of their inner surfaces.
Best Mode for Carrying Out Invention
. . . _ . . . _
In accordance with Figure 2, air blower or fan 1
is stationed in a circuit which is the acceleration conduit 2.
An optional wide section 3 is positioned in the path of
particles being blown from the fan, and by its shape, to wit,
tapered outwardly in the direction of the flow of particles,
it increases the turbulence of particles in the flow of air
and therefore builds higher electrostatic charge. A branch
conduit 4 communicates with a combination valve and spray
nozzle 5. During operation, a quantity of powder is
introduced into the conduit 2 and with the valve 5 in
closed position, the blower is operated to continuously cycle
the powder at high velocity, whereby upon contacting the
inner surface of the conduit 2 and among themselves the
particles acquire a high electrostatic charge in the absence
of any mechan:ical chaxging means. When sufficient charge
has been accumulated, the valve 5 is opened and the powder
is allowed to travel to the vicinity of the article 6. This
structure eliminates the necessity of the presence of a
powder tank with mechanical agitator and a costly electro-
static generator 78 (see Figure l~. As in the prior artdevice shown in Figure l, my apparatus in Figure 2 is used
in conjunction with a spray booth or similar enclosure to
reduce pollution and coating agent losses. Therefore my
invention as demonstrated by this Figure 2 configuration
teaches the basic invention of the main closed circuit
providing a stream of electrostatically charged particles,
which have been charged merely circulating them by means of
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a blower, said stream of charged particles thereupon
efficiently and thoroughly coating an article with an even
layer of film.
To completely eliminate coating agent losses and
pollution of the surrounding area, a coated article is placed
in a branch circuit conduit. Figure 3 is a schematic plan
showing a plurality of such branch circuit conduits. This
embodiment includes a blower element 7, a main conduit
element 8 including members 9, 10, 11 and 12; an optional
wide section 13 tapering outwardly in the direction of flow
of the particles to increase turbulence and cause the electro-
static charge to build up more readily. The main conduit 8
also includes valves 14 and 15 for flexibility in putting
branch circuits into communication with the main circuit
and regulation of gas flow in the branch circuits. The
conduit 8 selectively communicates with a first branch circuit
_ including valves 17 and 18 and members 19, 20 and 21._ _ _
Member 21 includes a selectively openable chamber 22 re-
taining an article to be coated 23, said article having an
optional suitable grounding connection 24. A second branch
25 selectively communicates with the main conduit 8 and
branch circuits, and includes two valves 26 and 27 and
members 28, 29 and 30. Member 30 has an openable chamber 31
enclosing a second article to be coated 32, said article
having an optional ground connection 33. A third branch 34
selectively communicates with the main conduit 8 and branch
circuits, includes two valves 35 and 36 and members 37, 38
and 39. Member 39 has an openable chamber 40 enclosing an
article or articles 41 for coating, the article~s) having an
optional grounding connection 42. A fourth branch circuit
43 selectively communicates with the main conduit 8, and
branch circuits, and includes two valves 44 and 45 and
members 46, 47 and 48. Member 47 has an openable chamber 49
enclosing an article or articles 50 for coating, the article(s)
having an optional grounding connection 51. In the operation
of this embodiment, the branch circuits 16, 25, 34 and 43
are used selectively either in series or in parallel, or in
combination, depending on different conditions and the
coating quality requirements.
Operation in Series
_
After sufficient charge in the plastic powder has
built up in the main conduit 8 while valves 14 and 15 are
open and the other valves are closed, due to the powder's
circulation by the blower 7, the valves 36, 35 and 18 are
opened and remain open until the articles 41 and 23 have
acquired coating of the desired thickness. By throttling
valves 36 and 14, the required powder concentration is
obtained. The valves 36 and 18 are then closed and the
articles 41 and 23 are heated to effect curing of the powder
deposited, using suitable means (not shown) such as inductive
heater or the like.
Operation in Parallel
While the branch circuits 16 and 34 are cut off
from the main conduit 8, valves 26, 27, 44 and 45 are opened,
and without discontinuing operation of the blower 7, the
articles 32 and 50 may be coated and the deposited powder
cured in a similar manner after the valves 26, 27, 44 and
and _ are closed.
Operation in Combination
_ . . .
While plastic powder is circulating inside the
main circuit 8, all valves are opened and all articles are
coated simultaneously, some in the parallel working
chambers and others in those in series. By throttling
certain valves, each article can be coated at the optimum
flow rate and powder concentration.
Referring to Figure 4, a universal fixture con-
structed in accordance with my invention allows pipes of
different diameters to be placed into branch circuits for
coating their inner surfaces. This embodiment includes a
blower element 54, a main circuit element 55 including
members 56, 57, 58 and 59. The circuit 55 also includes
a valve 60. The branch circuit 61 communicates with the
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main circuit 55 and includes valves 62 and 63 and members
64, 65, 66 and 67, which are rigid. The universal fixture
which comprises two funnel-like members 52 and 53 which are
slidably adjustable on the segments of members 66 and 67,
two springs 68 and 69 and two flanges which are permanently
attached to the members 66 and 67. As seen in Figure 4, a
wide variety of diameters of pipes can be accommodated by
sliding the funnel-like members 52 and 53 away from each
other for purposes of loading, and sliding them together
to engage members 52 and 53 with the article 72 prior to
commencement of the coating operation. The springs 68
and 69 insure air-tight connection between the members 52
and 53 and the article 72.
Referring to Figure 5, another type of universal
fixture is shown which allows pipes of different diameters
and different lengths to be placed into branch circuits for
coating of their inner surfaces. The universal fixture
includes two funnel-like members 73 and 74 and two or more
hinged bolts 75 and 76 with nuts which are attached to a
member 74. Because the universal fixture is attached to
members of a branch circuit which are flexible, a wide
variety of pipes, in length and diameter, can be accommodated
by moving members 73 and 74 away from each other for purposes
of loading, and bringing them together to engage them with
the article 77 to be coated, prior to commencement of the
coating operation. The hinged bolts and nuts 75 and 76
provide air tight connection between the members 73 and
74 and the article 77.
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