Note: Descriptions are shown in the official language in which they were submitted.
1~5~S58
The present invention relates generally to the coat-
ing of a work piece with an electrophoretic coating material.
The preeent invention has particular applicatlon in the coat-
ing of lnternal and external sur~aces of containers, such as
cans, and other ob~ects, such as heat exchangers, radiators,
drums, automobile wheels, automobile oil filter caps and the
like.
Electrophoresis generally concerns the movement of
ionic particles within an aqueous system in response to elec-
trical charges imparted to such system. Negatively chargedparticles or ions in such an aqueous solution (i.e., an anodic
coating) migrate in response to such electrical potential to
any positively charged conductor which may be immersed in the
solution for deposit thereon. Positively charged particles or
ions (i.e., cathodic coating materials) likewise migrate and
are deposited upon a negatively charged conductor within the
coating bath.
Typically, an electrical potential in the range of
approximately 100 to 500 volts has been used for electropho-
retlc coating. The thickness, and hence durability, of suchelectrophoretically deposited coating layer is dependent upon
a number of factors, including, inter alia, the voltage used,
the separation between the anode and cathode, the length Or
tlme coating is permitted to continue, the pH of the coating
solution, the characteristics of the coating polymer used and
the conductivity of the particular material then belng coated~ -
During coating, after some coating particles havè been depos-
ited upon the C~nductive surface being coated, there is a
gradual reduction in the conductivity thereof and the work
piece belng coated becomeæ increasingly insulated. When the
thicknes~ of the electrophoretic~lly deposited coating layer
--1--
lCI SasS5~
becomes su~flciently thick for a given system, the previously
conductive surface becomes insulated to the extent that no
further substantlal electrodeposition wlll occurO Slmilarly,
if some portion of the surface of the work piece to be coated
has been previously coated with an insulating coating, further
electrodeposition on that coated surface will occur only with
hlgher voltages, clo~er proximity of electrodes, more conduc-
tive coating materials, longer coating times or other changes
to the system.
Various of the above techniques of electrophoretic
coating have been used heretofore in the art. Those tech-
niques have had a number of disadvantages associated there-
with. In many such prior art electrophoretic coating tech-
niques, it has been necessary to immerse the work piece into a
coating bath, which has neces~itated large capital outlays for
the often spacious tanks required to accommodate the w~rk
piece therein. Also, such immersion techniques have been
found to require an excessive amount of time and extra:mechan-
ical equipment to accomplish such dipping or immersion.
A further serious disa~vantage of such pri~r art
immersion techniques is the necessary result that both the
internal and external surfaces of the work piece to be coated
must be done simultaneously. This is especially undesirable
when, as is often the case, either the exterior surface or the
interior surface thereof should not or does not need to be
coated, or when different types of coating are required for the
interior and exterior surfaces. The waste involved and lack
of product flexibility constitute in many cases debilitatlng
disadvantages so severe that other, e~en more expensive, tech-
nique~ may become necessary.
Another technique used heretofore has been the elec-
--2--
105455~ ~
trodeposition of coating materials on sheet metal prior to lts
being fabricated into a particular coated bOdy. Such tech-
nique~ have resulted in exposed and/or uncoated breaks in the
coating, which have occurred during the various fabrication
steps, such as stamping, welding, heating, etc. Such unpro-
tected areas may be especially undes~rable in the container
industry, or in other industries where bare metal will con-
stitute a safety hazar or economic loss.
Yet another prior art technique, that of electro-
static spraying, has been used for various commercial coating
operations. A number of further disadvantage~ have also re-
sulted from the use of those techniques. Such spray techniques
have required difficult ad~ustments and excessive maintenance
problems. Further, in electrostatic spraying techniques a
relatively thick coating has been required to insure complete
coverage of the surface to be coated. Yet iurther, spraying
techniques have been espècially difficult to utilize where the
coating of an iriegular and/or interior surface has been re-
quired.
Inversion flooding has been suggested as a technique
for electrocoating of the interior surface of wide mouthed
containers. That process is suitable for columnar containers
and contemplates inverting the can and inserting upwardly and
into the can opening a mating prod with a diameter which
closely matc~es the internal diameter of the can. Electro- ;
deposition coating material is then force-pumped into the can
from the top of the prod so aæ to flood the constricted space
between the prod and the can from the top, down ~long the
sides, and out the bottom, thereby to coat the sur~ace. Such
a system is limited inherently to coating the interior of con-
tainers and, because of the force flooding in the constricted
-3-
'1054558
space unless the constrictions are uniform and continu~us thecoating thickness will vary and may be striped.
Accordingly, in view of the shortcomings of the
prior art, it is an ob~ect of the present invention to provide
method and apparatus for electrocoating wherein the problems
and disadvantages associated with the prior art may be materi-
ally reduced or avoided~
Accordingly, the present invention provides a method
for electrophoretically coating a surface of an electrically
conductive work piece having a selected linear dimension, com-
prising the steps of establishing said work piece at one elec-
trical potential, flowing an electrophoretlc coating ln a
linear stream corresponding to said selected linear dimension
and in close proximity to said surface of said work piece, im-
parting an electrical charge to sald linear stream, impinging
said charged linear stream`of electrophoretic coating onto
said surface o~ said work piece, and moving said work piece
and said charged linear stream of electrophoretic coatlng rela-
~ive to one another in a direction lateral to said linear di-
mehsion, thereby to electrophoretically deposit coating overthe entirety of said surface of said work piece.
The present invention al8o provides an apparatus for
electrophoretically coating a surface of an electri¢ally con-
ductive work piece having a selected linear dimension, said
apparatus comprising a reservoir for containing the electro-
phoretic coating material, means for mounting the work piece
to display the linear dimension thereof, nozzle mean~ for pro- :
viding a 11near stream of electrophoretic coating material
onto said linear dimension o~ said work piece, means for 8Up-
plying electrophoretic coating material from the reservoir to
the nozzle means, means for charging the linear stream of -
-4- : .
1~5~55~3
electrophoretic coating material relative to the work piece,
and means for moving said mounting means and said nozzle means
relative to one another in a direction later~l to said linear
stream, whereby an entire surface of the work piece on said
mounting means may be coatedO
In accordance with the invention a work piece may be
coated selectively and uniformly on the interior or exterior
surfaces thereo~.
The invention will now be described with re~erence
to accompanying drawings, in which
Figure 1 is a schematic plan view of apparatus used
in coating the exterior surface of a work piece, showing an
epdless conveyor strand reeved about sprockets and.carrying
work pieces in the form of can bodies thereon through coating,
rinsing and curing stations;
Figure 2 is a slighly enlarged portion of the plan
view of Figure 1 with the can body and work piece holder re-
moved and shQwing rack and pinion and chain means for rotating
work pieces during coating, rinsing and curing of the exterior
surface the.reof;
Figure 3 is a slightly enlarged elevational-view of
the structure for moving the work piece holder means along the
endless conveyor strand and for rotation thereof, as shown in
Figure 2;
Figure 4 is an enlarged elevational view of the
coating Or the exterior surface of a work piece, showing means
for disposing the structure into an electrical circul~t rela- ~ .
tionship, including alsD an application nozzle~electrodeg an
auxiliary ele~trode, and means for rotating during coating;
Fi~ure 5 is ~ plan view of the structure.shown in
~igure 4, :~
-5- : :
~ . .
~:
. - . . , . - , .. . .. . .. . . . . .. ... . .
. . . ; . . ' , . . ' . ' ' " , ' . ', . ' ` ' . ' ' " " ' ' '; .; ' ' .
105455~
Figure 6 is a schematic elevational view showing ap-
paratus for coating the interior of a work piece including an
insulated application nozzle/electrode means ~or disposing
such work piece lnto electrical circuit relationship with the
nozzle/electrodej means for rotating either the container or
the nozzle during coating, and a coating reservoir with asso-
ciated chilling means, filtering means, and pumping means;
Figure 7 is an enlarged transverse cross-sectional
view o~ a work piece, such ~s a containër9 as shown in Figure
6, and taken along line 7-7 o~ Figure 8, with an electrically
charged coating nozzle disposed therein, ~urther showing the
expansion portion of a nozzle embodiment and an insulating
ring for preventing electrical short circuiting of said charged
application nozzle;
Figure 8 is an enlarged longitudinal cross-sectional
view of a work piece with an electrically charged coating de-
livery nozzle disposed in the interior thereof, the particular
nozzle having an expansion at the distal end thereof to insure
more complete bottom surface coverage, slots or per~orations
therein for more uniform coating delivery, insulating rings to
prevent accidental electrieal shDrt circ~lting, and insulator
means between such nozzle and the reservoir, with arrows indi-
cating the direction of flow of such electrophoretic coating
material;
Figure 9 is an enlarged longitudinal cross-sectional -~
view pf another form of nozzle for coating the interior of a
work piece, such as an extruded beer can with beaded bottom
portion, illustrating a wedge-shaped nozzle for assuring uni-
form application of coating material to sueh beadR o~ the con- :
30 tainer bottom and showing a non-eonductive mesh covering for ~
the application nozzle openings to promote laminar flow and to :
-6-
, ~ -, - .. ~ ,... . .. , : .. :
- ..... . .. ~ . . . -
1~545S8
prevent bubbling;
Figure 10 is an enlarged longitudinal cross-sectional
view showing coating of the exterior surface of a rotating work
piece by use of a stationary non-charged nozzle having a
wedge-shaped top portion and having a separate electrode in
the form of a conductive grid or mesh and also showing inside
the work piece a schematic view of a vacuum operated work
piece holder;
Figure 11 is an end view taken along line 11~11 of
Figure 10;
... . ..
Figure 12 is an enlarged longitudinal cross-section-
al view showing coating of the exterior surface of a station-
ary work piece by means of a rotating application nozzle;
Figure 13 is a transverse cross-sectional view
taken along line 13-13 of Figure 12;
Figure 14 is an enlarged longitudinal cross-section-
al view showing coating of the~interior surface of a station-
ary work piece by a rotating application nozzle and also show-
ing a vacuum operated work piece holder for gripping an ex-
terior surface;
Figure 15 is a transverse cross-sectional view
taken along line 15-15 of Figure 14; and
Figure 16 is an enlarged achematic elevational view
showing coating of the exterior surface of a contoured work
piece, such as an automobile wheel, by means of a stationary
application nozzle and/or electrode having a surface matching
the contours of the work piece, and means for rotating such
work piece, whereby uniform application of coating material :
may be achieved.
In its preferred form the method of electrophoretic
coat1n~ of the present lnvention is carried out by me~ns o~
'
' :
,.
- . . .
1~4558
the coating structure set forth generally in Figure 1 hereofO
With specific reference to Figure 1, the coating apparatus lO
cQmprises a coating chamber 11 feedlng serially into a pair of
side-by-side rinsing chambers 12, 13 and a drying chamber 14,
such chambers being separated by walls 17 each having openings
16 therein for movement therethrough of a can body CB for
coating, rinsing, and curing thereof respectively in such
chambers.
The path of movement of can body CB is along a gen-
erally circular path beginning at entrance opening 18 to coat-
ing chamber 11 and exiting at opening 20 of drying chamber 14.
Such circular movement during processing is provided by means
of an endless conveyor strand 21 being reeved preferably about
spaced sprockets 22 and a pair of smaller intermediate sprock-
ets 22 disposed respectively near entrance 18 and exit 20.
Endless strand 21 may preferably be in the form of a link
chain having mandrels 19 disposed in spaced relationship there-
along for support and rotation of the can body CB to be coated.
An a~xillary electrode as shown in Figure 4 may be disposed in
said coating chamber 11 adjacent such can bodies CB~
Although the conveyor system of Figure 1 is shown in
a horizontal configuration it is understood that other con-
figurations, such as for example a vertical configuration, may
be utilized and such modifications are intended to be included
with the scope of the present invention.
Referring now to Figures 2 and 3, the mandrels 19
are supported upon a rotating shaft 24 having fixed thereon a
pinion 26 meshing with a curved rack 27 for providing rotation
to such shaft 24 of mandrel 19 and, consequently, to can body
CB. Such rotation of can bodies CB occurs by reason of the
fact that prlor to entering the coating chamber 11, the can : ~ -
-8- :
1(~54558
bodies CB are placed upoh and supported by mandrels 19 about
an axial axis of such can bodies. A wear plate 28 may be pro- :
vided ad~acent said endless strand 21 for urging pinion gear
26 into engagement with rack 27. By reason of the movement of
endle~s strand 21 along rack 27 and the meshing of pinion 26
therewith, the can bodies CB supportéd by such mandrels 19 are
caused to rotate and move through the coatin~ chamber 11 and
rinsing chambers 12 and 13 while rotatingO Although the man-
drel rotational speed may be ad~usted depending on the physical
characteristics o~ the particular coating material used and
the voltage applied, suitable rotational speeds have been
found to be in the range of approximately 60-400 R~PoMo This
speed of rotation has been found to permit the can body CB to
make at least one.complete revolution, and possibly to make
two such revolutions, during coating application. Such can
bodies CB may be placed on mandrels 19 manually or by other
apparatus means (not shown). Likewise, apparatus (not ~h~wn)
may be provided for removing such can bodies CB from mandrels
19 after theIr exit at opening 20.
AIternatively, a star drive conveyor mechanism of a
type well-known in the art may be used for transmitting such
work pieces through the coating, rinsing and curing stations.
Referring now particularly to Figures 4 and 5, which ~. :
show one embodiment of the coating of an exterior surface by
rotating the work piece while moving through coating chamber
11, as set forth hereinabove. ~ can body CB is rotated by .
means of mandrel 19 during coating. Liquid elec~rophoretic
coating material is supplied t~ the exterior surface 40 of : :
such can body CB through application nozzle 29, disposed equi~
30 distant said can body CB and is connected to a supply pipe 31 .
drawing such coating material from a reservoir disposed there-
_g_
....
.. . . . . ..
1~54558
beneath. Such reservoir (not shown) also serves to collect
excess coating material flowing from such exterior surface 40
of can body CB to prevent waste thereof.
The supply nozzle 29 may include a supply arm 32 ex-
tending over the bottom of exterior surface 40 of inverted can
body CB. Where the coating material used is anodic, shaft 24
for turning mandrel 19 is provided with concentric electrical-
ly conductive anode means 35 with the nozzle 29 belng connect-
ed to the cathod side of the anodic-cath~dic circuit. (For a
cathodic coating material, not shown, the application nozzle
would become the anode and the ob~ect to be coated would be
the cathode.) An auxiliary cathode 33 may be provided oppo-
site said supply nozzle 29 to improve the uniformity of the
flow and distribution of the electrophoretic coating material.
The nozzles 29 are provided with a ~ultiplicity of small open-
ings 30 to improve uniformity of flow distribution of such
coating material. The distance between such openings 30 and
the exterior'surface 40 of such body are preferably in the
range of approx'imately 2 to 15 millimeters.
Rinsing of excess electrophoret~c material is pro-
vided in ri~sing chambers 12 and 13, each of which is supplied
from supply pipe 37 connected to nozzle 36J as set ~orth in
Figure 1.- Such excess material ~ay thus be returned to the
reservoir. Deionized water is used for such rinsing. In a
preferred embodiment, rinse water is supplied as permeate ~rom
an ultrafiltration system. The rinse water may be recycled to
provide a closed, non~polluting system. Such coated and rinsed
can body CB then moves through curing or drying chamber 14 in
a path past heater elements 39 provided for curing such rinsed
coating. No rotational movement need be provided during cur-
ing. When cured, such coated containers may be removed from
-10-
~054558
mandrel 19 by automated means (not shown).
Figures 6-9 illustrate method and apparatus for
coating the interior surface 50 of a can body or container CB.
Such apparatus generally designated as apparatus 49 includes a
coating nozzle 51, serving as the electrophoretic coating ma-
terial delivery tube and also as the cathode in an anodic-
cathodic relationship with the container, where anodic coating
material is used. Such can body or container CB is supported
by and rotationally driven about the axial axis thereof by
mandrel means 52 connected to a rotational drive unit (not
shown). Alternatlvely rotational movement may be applied to
nozzle 51, with can body CB remaining stationary. Such man-
drel means 52 may be connected to the container CB by means of
a collar 53 fitting over the bottom exkerior surface 54 of -
such container CB. Alternatively, a vacuum operated work piece
holder may be used, as shown in Flgure 14. The power supply
69 utilized typically delivers between approximately 50 and 350
volts. The coating nozzle 51 is insulated from the coating
reservoir 56 by means of an insulator 57. Coating material 58
i8 delivered to the coating nozzle 51 by means of a pump means
59 from coating res~rvoir 56 into which snorkel means 61 is
disposed. After flowing over lnterior surface 50 of the con-
tainer CB, excess coating material flows back into reservoir ;
56. Arrows in Figures 6-9 illustrate the path of movement of
such coating material 58 from the coating reservoir 56,
through snorkel 61, through pre-pump conduit means 62 to pump
59, through post-pump conduit means 63 to nozzle 51, onto the
charged interior surface 50 of container CB, with the excess
returning to reservoir 56. In a preferred embodiment a chiller
64 and a filter means 65 may be connected to such reservolr 56
for chilling and filtering such coating material.
--11--
~054558
Figures 7, 8 and 9 show in greater detail the shape,
disposition, and component parts of coating application nozzle
51. In Figure 8 for example, such nozzle 51 at a distal end
51a thereof has an expansion portion 66 to insure more complete
coverage of the interior bottom surface 50A of such container
CB. Insulating rings 67 are provided spaced along such nozzle
51 to prevent accidental electrical short circulting of the
cathodic nozzle 51 with the anodic container CB. In general,
the application nozzle 51 is ad~ustably disposed at a distance
of approximately two to fifteen millimeters from the container
interior surface 50. Disposed at intervals along such applica-
tion nozzle are slots or perforations 68 for supplemental
coating delivery, which slots 68 aid in producing unlformity
of the coating.
The embodiment shown in Figure 9 differs from that
of Figure 8 in the shape of nozzle 51, which is wedge-shaped
to provide u~i~orm application of coating material 58-into
beads 60 at the bottom of can body CB, which may be for ex-
ample an extrude~ beer can. Also provided is a non-cond~ctive
mesh 67a covering openings 68 of nozzle 51 to insulate nozzle
51 from can body CB, to promote laminar flow, and to prevent
bubbling of the coating material. Preferably, the application
nozzle 51 i8 ad~ustably disposed at a distance of approximate-
ly two tb fifteen millimeters from the container interior sur-
face 50. Apparatus in accordance with the present invention
should preferably have the open end thereof tilted slightly
downwardly from the horizontal to permit excess coating mater-
ial to flow back into the bath as illustrated by arrow A in
Figure 9.
The apparatus set forth ln Figures ~-9 ~or coating the
interior surface 50 of a rotating container CB by a ætationary
-12-
~'
.. . - .. . - - . . .. . , ,, . . . ,. ~ .
- . .. :, ... : : , , .
1~545S8
nozzle 51 may be utilized with an endless chain driving means
in con~unction with the rack and pinion drive for coating an
e~terior surface as set forth in Figure 1, and the principles
set forth therein are equally applicable to such apparatus for
coating interior surfaces.
Referring now to Figures 10 and 11, the coating of
the exterior surface 70 of a rotating work piece CB by means
of a stationary nozzle 71 similar in principle to that shown
in Figures 4 and 5 is shownO The stationary and uncharged
nozzle 71 has a wedge-shaped top portion 72 which is contoured
to correspond to the contours of exterior surface 70 of the
work piece CB, which may be a beer can as shown. The nozzle
71 contains coating openings 73 ad~acent work plece CB for
flowing a uniform coating over such work piece CB as shown by
arrows. A similarly shaped electrode grid 74 is disposed inter-
mediate said nozzle 71 and the work piece CB to provide elec-
trical current to the electrocoating material as it flows from
nozzle 71 onto work piece CB. A non-conductive mesh 75 covers
grid 74 for preventing accidental short circuiting between
work piece CB and grid 74 and also to promote laminar flow and
to reduce bubbling. Grid 74 has a wedge-shaped portion dis-
posed proximate to the exterior surface of the closed end of
the container C~ being coated and serves to insure the same
dwell coating time for any polnt on the closed end of exterior
surface 76 of work piece CB for a given rotation, to permit
uniform electrocoating thereof. Figure 10 also schematically
shows can holder means generally designated as 78. A vacuum
cup 80 engages the interior bottom surface 81 of the work
piece CB and is supplied with vacuum by means of a vacuum line
82. The can holder means 78 also holds the work piece CB in
; place by means of spring 83 abutting against interior side
13
'
1~54558
surface 84 and is supported on either side by spring supports
85, 85 connected to and projecting from vacuum line 82.
Power supply 69 is shown connected to grid 74`and to
work piece CB through its conductive connection~with a slip
ring 86 having brushes 87 abutting on vacuum line 82 to provide
electrical current thereto through electrically conductive
spring supports 85, 85 and spring 83. Electrical current is
then applied to work piece CB through its contact'with spring
83. As indicated by arrow R, can holder 78 provides rotation
to the work piece CB by rotation means (not shown).
Figures 12 and 13 illustrate apparatus for coating
the exterior surface 90 of a stationary work piece CB by rotat-
ing an electrically charged application nozzle/electrode 91.
Nozzle 91 may completely enclose the portion of work piece CB ~-
to be coatedg such that, during rotation, the coating material ~ -
~lowed over surface 90 will be centrifugally urged against
6uch exterior surface 90 and not be wasted. After coating,
the excess coating drains back into the bath as illustrated by
arrow A.
Flow openings 93 are provided in nozzle 91 from
coating channels 94 therein. Although openings 93 only need
be provided over one side and one-half of the bottom of nozzle
72, a symmetrical arrangement such as shown in Figure 13 is
preferred for balance during rotation.
Coupling 95, which transmits coatlng material to
nozzle 91, is rotat~onallg disposed on electrically charged
coating supply tube 96. Rotational means (not shown) are co~-
nected to coupling 95 and provide rotation thereto and t~
nozzle 91 thereby as illustrated by arrow R. Power supply in
the form of a rectifier 69 provides~electrical curre'nt to
nozzle 91 and also to work piece CB through vacuum line 82 of
-14- ~ '
. . .
lOS4~58
can holder 78. The details of can holder 78 and the electric-
al connection provided thereby are similar to those described
hereinabove in connection with Figure 10.
As also disclosed hereinabove, the particular direc-
tion of the current applied depends upon whether anodic or
cathodic coating is to be used. A~ter rotational coating,
nozzle 91 and work piece CB may be separated by removal of
either, such as for example by reciprocating movement.
Figures 14 and 15 illustrate embodiments of the
present invention for coating the interior surface 50 o~ a
stationary work piece CB by means of a rotating application
nozzle/electrode. Rotating application nozzle/electrode, gen-
erally designated as 101, comprises an interior coating tube
102 opening into one or more coating channels 103, 103. As
shown by arrows, coating material flows through grid 104,
which is connected to power supply 69 to also serve as an
electrode. Pre~erably, a non-conductive mesh 105 covers grid
104 to prevent accidental contact between nozzle 101 and work
piece CB. As with the embodiment shoNn in Figure 9, nozzle
101 may have wedge-shaped terminal pqrtions 106, 106 to match
more closely the contours of a beaded bottom can, such as a
beer can, for uniformity of electrocoating deposition.
Figures 14 and 15 also depict schematically the
structure of an eIectrically conductive can holder generally
designated as 107. A vacuum cup 108, ~upplied by a vacuum -
line 109 eng~ges a portion of the bottom exterior surface 110
of work piece CB to hold it securely. A non-conductive collar
111 concentrically disposed with respect to the vacuum line
109 engages a portion of the exterior wall surface 112 of the
work piece CB to supplement the support provided py vacuum cup
108. An electrically conductive bottom plate 100 is disposed
~' ~
1~5455B
within holder 107 to provide electrical current to the work
piece CB.
Figure 16 shows the electrophoretic coating of a
work piece WP having a surface 113 having an axis of symmetry,
such as for example an automobile wheelO Electrical current
is applied in one polarity from power supply rec~ifier 69 to
application nozzle and/or electrode 114 and in the opposite
polarity to a conductive work piece holder 115 and thereby to
work piece WP. Nozzle 114 is disposed to be co-extensive with
the longitudinal linear dimension of surface 113 and is shaped
to conform to any contours in surface 113 of work piece WP,
such that each nozzle opening 116 is proximate to and substan-
tial}y equidistant from surface 113 for uniformitylof applica-
tion of coating material.
Nozzle 114 may alternatively be made of a flexible
conductive material to be ad~ustable for various different
contoured surraces and can preferably be readily ad~usted for
a different such contoured surface merely by first pressing it
firmly against the surface to be coated and then disposing the
matching nozzle a selectedJ proximate dis*ance from the sur-
face.
A linear stream 117 of electrophoretic coating is ~ :
applied to surface 113 co-extensive wlth the longitudinal
linear dimension thereof and relative movement is provided be~
tween the linear stream 117 and the ~ork piece surface. Such
relative motion i8 lateral to the linear dimension and circum-
ferential to and about the axis Or symmetry of the work piece : .
surface 113. Although such relative movement may be accom~
plished by moving either the work piece WP or the linear stream
117, in the example shown in Figure 16 work piece WP is ro-
tated by means o~ a holder 115, which may also serve as a
-16- :
~54SS8
reciprocator connecting means f~r separating the work piece
from the application nozzle after coa~ing. Alternatively,
nozzle 114 may be mounted for reciprocating movement by means
not shown.
Although the selected linear dlmension of the work
piece is illustrated as being rectilinear in Figures 1-9 and
11-15 and partially rectilinear in other embodiments illus-
trated herein, it is within the contemplation of the present
invention that such selected linear dimension may also be par-
tially or totally curvilinear For example, where the select-
ed linear dimension of the work piece is curvilinear such as
for example in cylindrical tubing, the nozzle for flowing the
coating could be disposed annularly or semi-annularly with
respect to the surface to be coated and either the noZzle or
the work piece moved axially (laterally) with respect to the
circumferential (linear) dimension for coating the entirety
of the surface.
In the above described prefçrred embodiments the
distance between the anode and cathode can vary between 2 and
15 millimeters with a preferred separation of 4 to 5`~milli-
meters. The speed of rotatlon of the work piece or the elec-
trode may range from 60 R.P.M. to 400 R.P.M.; however, the
preferred range is 120 to 240 R.P M.
The flow o~ coating can vary from one quart to 5
gallons per minute per application nozzle. There is no ab-
so~ute optimum as the flow rate must be determined for each
~pecific work piece to be coated and will vary with the size
and shape thereof.
The coating voltage can range from 50 to 350 volts.
However, the preferred voltage will va~y with the size and
shape of the work piece and the formulation of the coating.
-17-
. ~ . .. . ..
. .
1~54558
However, 150 to 180 volts is generally satisfactory.
Coating temperature can range from 60 to 140F., butthe most practical range is 70 to 90F. The vlscosity of the
coating is not critical, but is most usually close to that of
water. The percent solids of the coating can be varied be-
tween 7 and 15~, but the preferred operating range is approx-
imately 12~.
~ oating time will vary considerably depending upon
voltage, paint temperature, type of substrate, and film thick-
ness desired; however, it is desirable to keep the coatingtime as low as possible. Practical operating ranges will vary
from 0.1 second to 10 seconds, with coating times of between
0.3 second and 3 seconds, usually being the most practical.
A typical example of apparatus ln accordance with
the present invention for coating the interior of aluminum
containers, as shown in Figures 6-9, would be designed to coat
300 cans per minute using a coating time of 0.5 seconds and a
voltage of 180 volts. The paint temperature would be 80F. - ~-
90F. and the percent solids of the paint would be 12~ to 14%.
The speed of rotation of the can would be 240 R.P.M. and the
flow rate of the paint would be 3/4ths of a gallon per minute ;
per application nozzle. Distance from the elect~ode to the
container would be 4 millimeters. Following the coating pro-
cess, the can would be rinsed to remove exceæs coating material
and baked in an oven at any desired temperature to e~fect sat-
isfactory cure o~ the coating.
-18-
