Note: Descriptions are shown in the official language in which they were submitted.
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This is a divisional of Canadian Patent Applic~tion
Serial No. 224,322, filed 10 April, 1975.
This invention relates to apparatus for electrostatically coating work-
pieces and, more particularly, to such apparatus whPrein heating and cooling
means are so disposed as to fuse particles at a first zone while preventing
fusion at a proximate second zone in heat-conductive contact therewith.
Of the various ways in which coatings of heat fusible resinous materials
are produced upon various workpieces, those in which the material is applied in
particulate or powdered form are often found to be the must effective and satis-factory. Such techniques are used to produce coatings upon a wide variety of
workpieces, including continuous lengths of wire and strip stock as well as indi- ~ ~-
I vidual objects which are often of a complex configuration, as would make coating
by other techniques difficult or impossible. For example, attempts have been
made to insulate the slots of rotors and stators for electric motors by depo~it- t -;-
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ing the resin in powdered form, which has proven particulariy difficult due tothe presence of reentrant surfaces which must be covered.
A common method of producing coatings of thermoplastic particulate -
materials is to utilize heat from the workpiece to cause softening and fusion
of the particles upon contact. Thus, it has long been the practice to heat the
article and to then submerge it in a bed (desirably fluidized) of the particulate
material so as to produce a coating upon all exposed surfaces, and as far as is
known prior attempts to produce coatings from powdPrPd resins upon electric
motor components have employed this technique. However, the fnherent drawbacks
are quite apparent, and include the need for masking of portions of the workp~ece
which are to remain free from the coating material and/or the need to handle
or direct the resin in such a manner that contact will be avoided. Not only
are such precautions time-c~nsuming, but frequently they are difficult if not
imposslble to achieve in practire. Moreover, since the snlount of material
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deposited usin~ such a method ~s dependent upon the intensity of heat avalldb1e
from the workpiece and/or the durat~on o~ exposure, un1fonm thicknesses are
oftentimes most difficult to obtaln.
It is also well known that electrostat~c forces may be 'uttlized to
cause attraction and adhesion of particles of thermoplastic materials to a
wide range of workpieces, which may thereafter be heated to melt the resin
and produce the final unified coating. This approach has many advantages
including uniformity of coverage, ease of access to undercut or reentrant sur-
faces, coating thickness control, etc. Nevertheless, the production of
preferential deposits upon selected areas of the object has typically relted
upon the use of mechanical or air masking techniques which are not entirely
satisfactory under certain circumstances, such as when it is necessary to obtaind virtually clean surface closely adjacent to one that is to be relatively
thickly covered.
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Accordingly, it is an object of the present invention to provtde
novel apparatus for the production of a unified, adherent coating of a heat
fusible resin upon a limited portion of a workpiece.
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A more specific object of the invention is to provide such apparatus
for electrostatically coating the workpiece and for effecting the removal of
the resinous material from selected portions thereof which are to be uncoated.
An even more specific object is to provtde such apparatus by which
a generally cylindrical article having reentrant surface portions may be coated
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with an adherent deposit upon the reentrant surface portions thereof.
Another object of the invention is to provide such apparatus by
which such coatings may be produced quickly, easily and economically, and tn
an automatic and continuous manner.
~i A further object is to provide a novel precuring devtce which ts
adapted to set the coating at one zone of a workpiece while simultaneously matn-taining the particulate form of the resin at a second zone to factlitate tts
complete removal therefrom.
It has now been found that the foregoing and related ob~ects of the
invention are readily attatned in an apparatus compris1ng, tn combtnation, a
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chassis, means on the chassis for producing a cloud of electrostatically
charged solid particles of resinous material, a precuring unit on the chassis,
and means for carrying the workpiece along a travel path through~the cloud-
producing means and precuring unit. The precuring unit includes means for
heating a first zone of a workpiece to be coated, and means for simultaneously
cooling a second zone thereof, the zones of the workpiece being in heat con-
ductive contact with one another. The heating and cooling means are so disposed
as to enable heating of the first zone of the workpiece to a relatively high
- temperature above ambient while the second zone thereof is simultaneously
maintained at a relatively low temperature substantially below the relatively
high temperature. Exposure of the workpiece to the charged particles from the
cloud-producing means, with the workpiece charged effectively opposite to the
particles, causes a layer of particles to deposit thereon. In the precuring
unit, the heating means at least partially fuses and coheres the particles at
the first zone of the workpiece and the cooling means substantially prevents
fusion and coherence of particles at the second zone thereof, removal of the
particles from the second zone thereby being facilitated.
In preferred embodiments of the invention, the heating and cooling -
means of the precuring unit extend along substantially the same length of the
travel path, and the cooling means comprises an element having a cooled support
surface upon which the second zone of the workpiece rests in heat transfer
contact during movement through the unit. The cooling means may additionally
include an overlying element having a cooled lower surface extending substan-
tially parallel to and in spaced alignment over the support surface to provide
a convective cooling effect upon the second zone of the workpiece during pass-
age therebeneath. In such a case, the conveyor may include an upstanding
element for supporting the article with the first and second zones of the article
lying on opposite sides thereof, and the conveyor element may cooperate with
the underly~ng element of the cooling means to provide a shield against heat
flow by radiation and convection to the second zone of the article,
The apparatus preferably includes cleaning means positioned on thè
chassis along the travel path downstream of the precuring unlt for effecting
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the removal of part~cles of resinous material from the second zone of the
workpiece. Most desirably, ~t also includes post heating means positioned
along the travel path downstream of the cleaning means. The p~st heat~ng means
is adapted to fully heat the workpiece so as to unify and produce from the
remaining particles of resinous material an adherent coating on the first zone
thereof.
The apparatus may be particularly adapted for produc~ng a coating
upon a generally cylindrical article having a central portion prov~ding the
first zone thereof and end portions extending axially from either side of the
central portion together providing the second zone of the article. In such an
instance, the cooling means of the precuring unit desirably comprises two ele-
ments, each having a cooled surface extending along an opposite side of the
travel path and being adapted to support and cool one of the end portions of
the article during movement thereof along the travel path through the unit.
The heating means thereof may comprise a heating element extending along the
travel path and lying generally between the cooled surfaces to heat the central
portion of the article during movement through the unit.
The precuring unit may include a base providing at least in part the
cooling means thereof. The base may have an elongated channel extending therein
along the travel path through which at least the lower portion of the conveyor
passes, the surfaces of the base defining the channel being cooled to provide
a cooling effect thereabout. Preferably, the heating means employed comprises
a heating element supported by a cover member which is moveably mounted upon
the chassis for displacement from a normal position over the travel path to a
position outwardly therefrom. When the cooling means includes an overlying
element having a cooled lower surface, such an element may be supported by the
cover member and disposed as hereinbefore described when the cover member is
ln closed position.
In especially preferred embod~ments of the invention the cloud pro-
ducing means employed in the apparatus includes an electrostatlc cloud chamber.
Such a chamber may comprise a receptacle having means for produclng a fluidized
bed of charged part~cles including a gas-permeable plate extending thereacross
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in a generally horizontal intermediate plane and space above the
bottom wall of the receptacle to define a plenum ohamber there-
below. The receptacle also has electrode means extending there-
across to electrostatically charge particles of solid resinous
material passing proximate thereto. Most desirably, the apparatus
will include a particulate material reservoir having feed means
communicating with the cloud chamber. In such a case, the elec-
trode means may span a lesser area than the gas-permeable plate
to provide an electrode-free vertical corridor within the receptacle
through which particles of the resinous material may pass without
acquiring a significant charge. A device for sensing the level of
the bed of particles within the receptacle, in response to which
the feed means conveys resinous material from the reservoir to the
chamber when the bed level falls below a preselected height, may
also be provided. The sensing device is positioned within the
vertical corridor over the horizontal porous plate, to thereby
minimize the effect of electrostatic charging upon the sensed level
; of the bed. The electrode employed may be a generally planar,
grid-like structure disposed adjacent the upper surface of the gas-
permeable plate, and electrode and plate may be substantially
coextensive except at one area of the plate over which the electrode
does not extend, thereby providing the electrode-free vertical
corridor.
Figure 1 is a plan view of apparatus embodying the present
invention;
Figure 2 is a side elevational view thereof
Figure 3 is a side elevatiQnal view of the coating process
unit of the apparatus of Figures 1 and 2, drawn to an enlarged
scale and with housing portions removed to expose internal features
thereof;
'~' Figure 4 i8 a perspective view of an armature rotor for
which the illustrated apparatus is particularly adapted;
Figure 5 is a fragmentary perspective view of the forward
end of the coating process unit including the load zone and a
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portion of the electrostatic coating station, drawn to a scale
enlarged from that of Figure 3;
Figure 6, which appears on the second sheet of drawings,
is an enlarged sectional view alon~ line 6-6 of Figure 3 illus-
trating the support and positional control structure provided at
the load zone and showing an armature rotor carried on the forward
conveyor for movement therethrough;
Figure 7 is an end view of the electrostatic coating station
along line 7-7 in Figure 3 with portions of the housings broken
away to illustrate the internal features thereof and drawn to a
greatly enlarged scale;
; Figure 8 is a side elevational view of the sensing device
employed in the cloud-coating unit of the electrostatic coating
station;
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-~ Figure 9 is a fragmentary end view along line 9-9 in Figure
3 showing the powder removal zone of the apparatus with the contact
belt unit thereof in its normal operating position, drawn to a
greatly enlarged scale and having portions in vertical section to
illustrate the construction thereof; .
Figure 10 is a front view of the powder removal zone at an
acute angle to the upper surface of the deck, drawn to a slightly
diminished scale from that of Figure 9 and showing the contact belt
unit in its raised position;
Figure 11, which appears on the fifth sheet of drawings,
- is a fragmentary end view of the powder removal zone along line
11-11 of Figure 3, drawn to the scale of Figure 9;
Figure 12 is a fragmentary,plan view of the shaft cleaning
units provided within the powder removal zone, drawn to a scale
enlarged from that of Figure 10 and with the hold-down brackets
removed to expose the vacuum slots thereof;
Figure 13 is a side elevational view of the vacuum nozzle
and associated parts employed with each of the units of Figure 12:
Figure 14 is an enlarged sectional view along line 14-14 in
Figure 3 showing the precuring unit of the apparatus with an
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armature rotor passing therethrough, and in phantom line showing
the raised position of the cover assembly;
Figure 15, which appears on the second sheet of drawings,
is a perspective view of the air knife assembly at the powder
recovery zone of Figure 3, drawn to a greatly enlarged scale;
Figure 16, which appears on the third sheet of drawings,
is a fragmentary perspective view to a greatly enlarged scale of
the intermediate conveyor employed in the apparatus; and
Figure 17, which appears on the third sheet of drawings, is
a fragmentary perspective view of one band of the endmost conveyor
of the apparatus, drawn to the scale of Figure 16.
Turning now in detail to the appended drawings, therein
illustrated is an armature slot-coating system embodying the
present invention and details of the various units and zones
thereof. Figures 1 and 2 illustrate the overall layout of the
system, the heart of which is the "coating process unit", so
designated on the drawing. Auxiliary to the coating process unit
is an oven and a cooling unit, and main control and oven control
facilities are furnished. Also included in the system to enable
a desirable mode of operation is a powderrecovery and feed unit
and a powder replenishment unit. As will be appreciated from
Figure 2, the workpieces are loaded at an infeed zone at the left-
hand end of the coating process unit from which they pass serially
through an electrostatic coating zone, a powder removal zone, a
precure zone, and a powder recovery zone; they then pass into the
oven and finally through the cooling unit. Excess powder from the
electrostatic coating zone is recovered in the powder recovery and
feed unit and is returned through an appropriate conduit to the
coating unit on a substantially continuous basis, and additional
powder is furnished from the powder replenishing unit as needed.
An electric interface access channel runs along the rear of the
coating process unit to provide power at the various zones thereof.
With specific reference now to Figure 3, the coating process
unit of the system is depicted in greater detail. It includes a
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frame 10 on which are rotatably supported three conveyor
drive sprockets, generally designated by the numerals 11,
12 and 13 respectively from left to right in the Figure,
and idler wheels 14 are positioned between adjacent
sprockets. A forward endless conveyor, generally designated
by the numeral 16, runs about sprockets 11 and 12 and the
idler wheel 14 therebetween; a center endless conveyor,
which is generally designated 18, runs about sprockets 12
and 13 and about the idler wheel 14 positioned between
them, and a rearward endless conveyor, which is generally
designated 20 and is fragmentarily illustrated, runs
about the righthand sprocket 13 and a cooperating
sprocket which is not illustrated and is positioned
adjacent the end of the cooling unit shown in
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Figures 1 and 2. A drive pul1ey 22 operates the powder removal unit and is
driven by the electric motor 24 which is supported wlthin the frame 10. A
second motor 25 is connected to sprocket 13, thereby synchronously driving
all conveyors 16,18, 20 since they are coupled by the sprockets 11, 12, 13.
Although the invention is not to be construed as limited to coating
of any particular workpiece, and may be feasible for coating selected portions
of objects which are elongated or of "continuous" length, the system illus-
trated is especially suited for the coating of armature rotors of the type
generally designated by the numeral 26 in Figure 4, and is intended prlnci-
pally for that purpose. The rotor 26 is of conventional configuration and
includes a ylindrical core portion 28 having spaced about its circumference
four axially extending, reentrant winding slots 30. Extending from opposite
ends of the core portion 28 are simple and crank-type shafts 32, 34 respective-
ly, and the shaft 34 has a spring clip 35 engaged upon it adjacent the end
of the core portion 28.
As will be appreciated, the slots 30 of the rotor 26 are designed
to receive wire windings, making lt necessary to provide the slots 30 and the
;l opposite end faces 37 of the core portion 28 with a layer of insulating materlal
to enable magnetic poles to be defined thereon. It is also important that the
outer circumferential surface of the core portion 28 and the shafts 32, 34
be free from insulating material; the present system is unique in enabling the
rapid and facile production of coated rotors having teposits of insulating
material which are present only at selected locations and are of substantially
un~fonm th~ckness.
Figure 5 ~llustrates in greater detail the loading zone of the
coatlng process un~t, whereat a narrow rectangular opening 38 is provided
thrwgh the deck 36 of the frame 10 to accommodate the edge of drive sprocket
11. As can be seen, the forward conveyor 16 is comprised of two lndependent
flexlble and contlnuous parallel bands, generally designated by the numerals
44 and 45, and the drive sprocket 11 consists of a pair of parallel sprocket
wheels 40 mounted on a common shaft for concurrent rotation. Each of the
sprocket wheels 40 has about lts circumferential edge a mult~plic~ty of small
rectangular teeth 42; the belt portlon 46 of each of the bands 44, 45 ls
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provided with a multipl1c~ty of rectangular apertures 48 wh~ch are spaced
along the length thereof, the apertures 48 meshing with the rectangular teeth
42 of the respective sprocket wheels 40 as the bands pass thereover along their
travel path. Extending at a right angle from the inner edge of the belt por-
tion 46 of each of the bands 44, 45 are a multiplicity of carr~er tabs 50, 50'
respectively, and each tab 50, 50' has beve11ed shoulders 51 leading into the
shaft slots 52, 52' therebetween. As will be appreciated, the slots 52, 52'
are dimensioned to receive the shafts of the armature rotor 26, and the tabs
50' are slightly narrower than the tabs 50 to render the slots 52' somewhat
wider than the slots 52, thereby enabling close-fitting engagement of shafts
32, 34, notwithstanding their different diameters. It will be evident that
the bevelled shoulders 51 facilitate insertion and removal of the shafts of
the armature rotors 26 into and from the slots 52.
; As can most readily be seen by additional reference to Figure 6,
one of a pair of elongated rectangular curb blocks 54 extends along each side
of the upper flight of the conveyor 16, with the curb blocks 54 being secured
to the deck 36 by bolts 56 (fastened in an appropriate manner, not illustrated).Coextensive with each of the curb blocks 54 is a guide rail 58 which is secured
upon the upper surface of the associated curb block 54 by a number of bolts
, 20 60 spaced along the length thereof. A shallow recess 61 is provided along
the upper surface adjacent the inner edge of each of the curb blocks 54 enabl~ng- the belt portion 46 of the conveyor bands 44, 45 to pass between the curb
blocks 54 and the bottom surface of the guide rails 58. The guide rails 58
have inner surfaces which extend downwardly and then at an angle inwardly to
provide guide surfaces 62 sloping downwardly toward the travel path. The guide
~s surfaces 62 define therebetween a trough which is dimensioned so that armature - -
' rotors 26 carried by the conveyor 16 extend thereacross with little free space
ad~acent the ends, thus ensuring that the rotors 26 remain accurately positionedi across the conveyor 16 and centrally pos~t~oned on the axis of the travel path
! 30 of the unlt.
Extending forwardly from ad~acent the ends of the curb blocks 54
; , ~s a support extension 64 wh~ch underl~es the conveyor 16 and prov~des support
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therefor as the bands 44, 45 disengage from the sprocket wheels 40. Supported
above the extension 64 is a loading platform portion 66 from which extend
rean~ardly a pair of thin support rails 68 which are secured in a parallel
relationship against the inner faces of the curb blocks 54. The loading plat-
form 66 is provided to facilitate loading and seating of the rotors 26 in the
slots 52 of the conveyor 16, and the support rails 68 provide underlying
support for the shafts 32, 34 as the rotors 26 proceed along the travel path,
it being appreciated that the shafts ride upon the upper edges of the support
rails 68 rather than resting at the bottom of the slots 52. As a result,
- 10 the conveyor 16 serves only to drive the rotors 26 fon~ardly through the sys-
tem, with contact upon the rails 68 causing them to rotate as they are conveyed.From the load zone, the annature rotors 26 are conveyed to the
electrostatic coating station illustrated in detail in Figure 7, which is
comprised of a hood, a powder feed stack, and an electrostatic coating chamber,
` generally designated by the numerals 72, 74 and 76 respectively. The elec-
; trostatic coating chamber 76 consists of an upwardly opening enclosure 78
secured against the bottom surface of the deck 36 and having a bottom wall
opening through which air is charged from a pressurized source 79 thereof. A
horlzontal porous ceramic partition 80 divides the enclosure 78 into a lower
air plenum chamber 82 and an upper cloud chamber 84. The partition 80 supports
an overlying grid-type electrode 86 connected to a diagrammatically illustrated
high voltage source 88 and extending partially across the enclosure 78 to
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-I provide an electrode-free area 85 between its inner edge 87 and the sidewall
89, through which extends an imaginary vertical corridor.
` Within the corridor, supported upon the depending bracket 92, is
, a pneumatically operated fluidic sensing device comprised (as seen in Figure
! 8) of a body 90 with a wire actuating finger 94 extending therefrom; one appro-
priate device is sold by Norgren Fluidics of L1ttleton, Colorado under the
name FEATHERFLEX SFS-OlO-OOO. On the outer end of the wire finger 94 is a
float sphere 96 which may be fabricated of a foamed polystyrene or comparable
lightweight material, and pneumatic control lines 98 extend from the body 90
dnd are connected to control means (not illustr;lted),
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The feed stac~ /4 consists of a slfter box 100 having a screen 102
horizontally positioned across the central portion thereof and having a recycle
feed conduit 104 and a replenish conduit 106 leading thereinto. As will be
appreciated, the conduit 104 extends from the powder recovery and feed unit
and the conduit 106 extends from the powder replenishment unit, both shown
- in Figures 1 and 2. The conduits 104, 106 deliver thermoplast~c resin powder
103 into the upper portion of the sifter box 100 from which lt passes through
the screen 102 and the opening 108 in the deck 36 w~th lumps and foreign
matter being removed by the screen 102. The powder 103 then falls upon the
porous partition 80 where it becomes fluidized by air passing upwardly from
the plenum chamber 82 in a conventional manner. The fluidized powder 103
exerts an upward force upon the float sphere 96 of the fluidic sensing device;
` when the quantity of powder 103 above the partition 80 ~s insufficient to urge
the sphere 96 (and hence the actuating finger 94) upwardly to the necessary
extent, a signal from the sensor causes the control means (not illustrated)
to deliver an additional quantity of powder 103 through the condult 106 from
the powder replenish unit, thereby correcting the deficiency.
The hood 72 1s positioned over an elongated slot 110 in the deck 36
along which the parallel guide rails 68 extend. It is secured to the deck by
bolts 112 and has a tunnel portion 114 with an end wall 116 forming a partial
closure therefor and defining a tunnel opening 115 at each end thereof. A
stack portion 118 extends upwardly from the tunnel portion 114 of the hood 72, ~ i
and has a takeoff conduit 120 which is attached to a suitable vacuum source
3 and enables excess powder to be removed from the coating station. Such powder
¦ ~s returned to the recovery and feed unit for ultimate recycle through the
3 condult 104 leading to the feed stack 74. An elongated baffle plate 122
~s lnclined downwardly from each sidewall of the tunnel portion 114 toward
the travel path of the un~t, and the plates 122 cooperate wlth the carrler
tabs S0, 50' to confine powder 103 whlch passes upwardly through the slot 110
to the central port10n of the rotors 26 passing thereover.
As wlll be apprec~ated, the powder 103 employed for the coat~ng
operatlon ls of such a nature that lt is capable of acquirlng an electrostat~c
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charge as the particles pass through the grid electrode 86. The rotors 26
are maintained at ground potential (such as by grounding the conveyor 17
with whlch they are in contact) during passage over the slot 110, thus causing
attract~on and adherence of charged powder particles to the surfaces of the
rotors 26, with the electrostatic effect ensuring that all exposed surfaces,
` ~ncluding winding slots 30, are coated. Due to the charge on the powder
particles, it is important that the fluidic sensing device be positioned over
the electrode-free area 85 of the horizontal partition 80. In this region
charging of particles is minimized, as a result of which the attractive force
10 from the grounded rotors 26 is quite insignificant and particles thereat are
elevated only by the buoyant effect of the pressurized air. Otherwise, the
; . electrostatic force on the particles would lead to an inaccurate indication
of the quantity of powder present in the system, rendering control of the
-~ automatic replenishment system virtually ineffective.
Since the armature rotors 26 must be substantially free of insulat-
ing material on the circumferential surface of the core portion 28 and along
the shafts 32, 34, and since in the coating step powder deposits upon all
exposed surfaces, the method and apparatus of the invention require that -
means be provided for removing powder from selected surfaces of the rotor 26
20 where it is unwanted. To that end, the illustrated apparatus is provided
with a powder removal station which includes the contact belt unit, generally
designated by the numeral 124, and shown in Figures 3, 9 and 10. The contact ~;
belt unit 124 includes an elongated forward frame member 126 from which extend
rearwardly triangular mounting brackets 128 which are pivotally supported upon
posts 130 projecting upwardly from the deck 36. In this manner, the unit 124
j is hingedly-supported for ready displacement from the position over the deck
36 shown in Figure 9 to its open position in Flgure 10. Affixed in a central
,~ location behind the forward frame member 126 is a pinion block 131 which, in
tùrn, has a gear tra~n block 132 mounted behind it. A short central shaft 134
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3D is journaled at its ends by approprlate means to extend transversely through
the forward frame member 126, the pinlon block 131, and the gear train block
132, and it has a dr~ve gear 136 affixed on lt with1n the gear traln block
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132. The shaft 134 also has a drive pinion 138 affixed to it in
front of the gear 136, with the pinion 138 residing generally
within the pinion block 131. A lower shaft 140 is journaled at
its ends and extends transversely between the pinion block 131
and the gear train block 132; on it is affixed, in meshing engage-
ment with the drive gear 136, an upper transfer gear 142. The
transfer gear 142 communicates through a deck opening 143 with a
lower transfer gear 144 which is supported upon a shaft 146 posi-
tioned and appropriately journaled (by means not shown) below the
deck 36. As can be seen in Figure 3, the lower transfer gear 144
meshingly engages a gear 148 which is affixed to the shaft on
: which the drive pulley 22 is supported. In this manner, power is
delivered from the motor 24 through the drive pulley 22 and the
train of gears 148, 144, 142 ultimately to the drive gear 136 for
the contact belt unit 124. As can be seen, pivoting the unit 124
upwardly about the posts 130 simply disengages the gears 142 and
144, discontinuing operation of the unit 124 and permitting access
to the normally covered portion thereunder. ~ '.
A belt pulley shaft 150 is journaled in the forward frame
member 126 and pinion block 131 on either side of the central
shaft 134, and a pulley pinion (not exposed but identical to
pulley pinions 152 to be discussed hereinafter) is affixed to the
inner end of each of the shafts 150 and is in meshing engagement
. with the drive pinion 138. (It will be understood that the
pulley pinion on shaft 150 to the left shaft 134 in Figure 10 lies
behind pinion 138, as viewed in Figure 9, and that the pulleys and
, belt assembly at the left side of Figure 9 are shown along a sec-
tion line somewhat forward of line 9-9). To the opposite ends of
the pulley shafts 150 are affixed belt pulleys 154. Spaced to
either side of the central pinion block 131 is an auxiliary pinion
block 156 in which is contained a pair of belt pulley shafts 150
and a transfer pinion shaft 134 therebetween. The inner ends of
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the pulley shafts 150 have affixed to them pulley pinions 152 (as
can be seen in the left-hand auxiliary pinion block 156 in Figure
10) and the transfer pinion shaft 134 has affixed to its inner end
a transfer pinion 158 in meshing engagement with each of the pulley
pinions 152 on either side thereof. Adjacent each end of the forward
frame member 126 is a rectangular bearing block 162 in which is
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journaled, by appropr~at~means, a belt pulley shaft 150. A belt pulley 154
of the type previously referred to is secured on the outer end of each belt
pulley shaft supported in either the auxiliary pinion blocks 156 or the bearing
blocks 162.
The eight pulleys 154 function as four sets w~th adjacent pairs of
pulleys supporting a belt assembly cons~sting of an underlying support e1ement
164 and an outwardly exposed contact element 166. The contact element is of
foamed polyurethene or a comparable mater~al provid~ng a cellular outer surface.Such a structure enables the contact element 166 to pick up powder from the
surface of the core portion 28 simply by contact therewith, with no wiping or
brushing action being necessary or desirable. The support element 164 may
be a timing belt (i.e., having transversely extending ridges about its inner
surface) with the pulleys 154 being provided with corresponding ridges and -~
grooves, or square teeth, to cooperate therewith. Drive power is transferred -~
from the motor 24, through the gears 148, 144, 142, 136, to the pinion 138
within the central pinion block 131, and to the innermost belt pulleys 154.
Due to the interconnection through the pulley pinions 152 and transfer pinion
158 within each of the auxiliary pinion blocks 156, the belt assemblies on
the outer sets of pulleys 154 are simultaneously driven, with all belt assem- --
blies rotating at precisely the same rate and in the same direction.
As is seen in Figure 9, a central sprocket wheel 40' having rec- -
tangular circumferential teeth 42 is supported on a con~non shaft (not shown)
' with two outside sprocket wheels 40. The outside wheels 40 correspond to the ~ -
sprocket wheels bearing the same numeral which constitute drive sprocket 11,
and the three commonly supported wheels 40,40' provide the intermediate drive
sprocket 12. Endless conveyor 18 has the construction lllustrated in Figure
~! 16 and passes about the central sprocket wheel 40'. The conveyor 18 consists
of a central band 176 having carrier tabs 178,178~ extending at right angles
from the side margins thereof. The tabs 178~ are slightly narrower than the
tabs 178, again to render the slots 180~ therebetween slightly wider than the
slots 180 between the tabs 178 to snugly receive the shafts 34,32 of the rotor
26, respectively. The following edges of each of the tabs 178,178~ have
_ 15 _
:~''. . ,., ' ~ ~ ' '
1 Oti4;~jO
bevelled shoulders 51 to facil~tate entry of the shafts 32,34 thereinto;
however, it will be noted that the forward edges of the tabs 178,178' are
not bevelled, and the reason therefore will be explained directly.
As can be seen in Figure 10 a transfer of the rotors 26 occurs
with~n the powder removal zone with the rotors 26 shifting from the forward
conveyor 16 to the intermediate conveyor 78. Engagement of both conveyors
16,18 on different sprocket whee1s 40,40' of the common drive sprocket 12
and the construction employed permits conveyor 18 to pass between the bands
44,45 of the conveyor 16. At the point of common tangency of the conveyors
~ 10 16,18 to sprocket 12 the respective slots 52,180 thereof are substantially
- aligned, causing the shafts 32,34 of the rotors 26 to momentarily reside in
slots of both conveyors simultaneously. As the bands 44,45 of the forward
conveyor 16 pass downwardly about the sprocket 12, the upper corners of the
tabs 180,180' of the intermediate conveyor 18 engage behind the shafts 32,34
~ . . -
to smoothly and effectively carry them out of the slots 52 with the bevelled i
shoulders 51 at the following edges of the tabs 50,50' facilitating w~thdrawal.
Thereafter, the rotors 26 are propelled through the system by the center con- -
veyor 18.
Assuming movement to be in a left to right dîrection, contact of
the ends of the shafts 32,34 upon the support rails 68 causes rotation of the
rotors 26 in a clockwise direction, If the motor 25 also drives the belt -
assemblies of the contact belt unit 124 in a clockwise direction, the direction
of rotation of the rotors 26 will reverse upon encountering the lower fl~ght
of element 166 at the entrance of the unit 124 ~the relationship at contact
being as depicted in Figure 9). Such contact causes a significant proportion
of the powder on the outer circumferential surface of the cylindrical core
portion 28 of the rotors 26 to be displaced therefrom and to fall into the
powder recovery hopper 184, which is positloned at an appropriate locatlon
beneath the deck 36 (as may be seen in Figure 3). The hopper 184 ~s connected
l 30 to the powder recovery and feed unit through a vacuum system (not ~llustrated~
i by a conduit 186. Most of the rema~ning powder on the surface of the core
port1On 28 is picked up by the contact element 166 of the belt asse~bly, as
" ` ' .
- 16 -
. ........... .
. .
,.. .
~LO~;4'~
previously described, with any add~tional powder be~ng removed by the successivebelt cleaning effects in the sam~ manner. As will be apprec~ated, since the
rotors 26 are supported for free rotation, after contact with the contact ele-
ment 166 they turn at precisely the same speed under the influence thereof.
This prevents relative wiping or brushing action between the element 166 and
the rotors 26, such as would tend to cause uneven deposits to be produced at
the edges of the slots 30. The nozzles 170 and associated vacuum conduits 172
are adjustably supported in the b~furcated end portions of the nozzle support
arms 168 with the nozzles 170 lying closely ad~acent the contact elements 1~6.
In this way, the powder picked up by the elements 166 is withdrawn from the
cells thereof and is conveyed to the recovery portions of the system for re-
cycle.
Positioned within the powder removal zone near the forward end
of the second belt assembly of the unit 124 is a pair of vacuum blocks 188,
which are secured to the deck 36 along the sides of the travel path. As can
best be seen in Figure 12, each of these blocks has a face plate 190,190'
secured upon its upper surface and of an elongated vacuum channel 192 extend-
ing lengthwise therein. As can be seen with additional reference to Figures
3 and 13, a vacuum nozzle 194 of generally oval cross section is secured
against the lower surface of each of the vacuum blocks 188, each nozzle 194
having a circular throat portion 196 about which is pos~tioned an annular
mounting collar 200 by which it is secured against the associated vacuum block
188 (by means not shown). Secured over the throat portion 196 of each nozzle
194 is a vacuum hose 198 which is connected to a vacuum source (not shown) -
and ultimately to the powder recovery and feed unit illustrated in Figures 1
. .
and 2.
The face plates 190,190' on the vacuum blocks 188 are provided with
elongated slots 202;202', each of which extends in a generally angular relation-ship outwardly from the travel path. ~hese slots 202,202' register over the
channels 192 in the blocks 188 and serve to define a flow passage for air under
the influence of vacuum drawn through the condults 198. As the armature rotors
- 26 travel between the vacuum blocks 188 with the shafts 32,34 thereof in roll-
ing contact upon the face plates 190,190' respect~vely, the vacuum effect
_ 17 -
, . , . ~
, . '-~ . .
10f~4;~0
from below thoroughly cleans the shafts 32,34 of any powder which may have
become deposited thereon. Normally, powder will be present in the shafts 32,
34 as a result of the initial electrostatic coating operation and/or due to
displacement from the circumference of the cylindrical core portion 28 during
powder removal by the first belt assembly in the contact belt unit 124. The
divergent disposition of the slots 202,202' will cause particles of powder to
be removed first from the portions of the shafts 32,34 adjacent the core por-
tion 28 and progressively outwardly therealong. It will be appreciated that
the nonlinear and nonuniform configuration of the slot 202' is necessitated
10 by the configuration of the crank shaft 34 which passes thereover. As can be
seen in Figures 9 and 10, a hold-down bracket 201 is secured to each of the
vacuum blocks 188. Each bracket 201 includes a pressure plate element 203
which overlies the slot 202,202' of the associated block 188 and serves to
engage the tops of the shafts 32,34 as they are conveyed thereunder, thereby
forcing the shafts against the face plates 190,190' to ensure efficient powder
removal therefrom.
After travelling past the vacuum blocks 188, the armature cores 26
are conveyed beneath the third of the series of belt-cleaning assemblies while -being supported upon parallel side rails 182. The fourth contact belt effect
20 is similar in design to the first three, with the exception that it is pro-
vided with contact belt assemblies for the shafts 32,34 as well as for the
cylindrical core portion 28 of the rotors 26. The construction of this portion
of the contact belt unit 12i is most clearly illustrated in Figure 11, wherein
i ~t can be seen that a set of three belt pulleys 154 are mounted on a co~fon
shaft 150 for simultaneous rotation. Each of the pulleys has a belt assembly
consisting of a support belt 164 and a contact belt 166 constructed as herein-
before described, and it will be appreciated that the belts extend between
two of such sets of three belt pulleys 154 (as can be seen in Figure 10).
From the contact belt unit 124, the armature rotors 26 pass ~nto
30 a precuring unit, generally designated by the numeral 204 and shown in
;i~ Flgures 3 and 14. With specific reference to the latter figure, it can be
seen that the precuring unit 204 conslsts of a cover assembly, generally
- 18 _
' ~.., ' ' ' '' '. . . ~. .
~i. ~ , :
, . .
1 O~i 4'~
des~gnated by the numera1 206, whicll has affixed thereto a pair of angle
brackets 208, only one of which is visible in Figure 14. The brackets 238
are secured at one end to the cover assembly 206 by appropriate bolts 210,
and the opposite ends thereof are pivotally supported upon posts 212 which
are mounted upon the deck 36 of the machine. Also secured to the cover
assembly 206 is a right angle contact arm 214 which has an element extending
over the end of a spring-loaded plunger assembly 216. In normal operation
the cover assembly 206 will be maintained in the position illustrated in fu11
line in Figure 14 by fluid pressure means acting against the upward force of
the plunger assembly 216. If the machine stops or if some emergency situation
occurs, the fluid pressure force is disrupted, permitting the plunger assembly
216 to immediately raise the cover assembly 206 to the position shown in
phantom line.
The cover 218 of the cover assembly 206 is elongated (as can be
seen in Figure 3) and is of inverted, generally U-shaped configuration (as
is shown in Figure 14). It has a number of layers 220 of insulating material
lining the top wall thereof, which are secured, along with a metal sheet
reflector 222 and a pair of elongated angular baffle plates 224, to the cover - -
218 by appropriate bolts 226. Heating elements 228, which may be CALROD units,
extend longitudinally within the cover 218 and are supported therein by a
number of inserts 230, which are spaced along the length of the cover 218
and have pairs of apertures 231 to receive and support the heating elements
228. The baffle plates 224 are constructed with inclined walls 232 which
slope downwardly and inwardly toward one another and toward the travel path;
the walls serve to support the inserts 230 as well as their primary function
of reflecting and concentrating heat from the elements 228 upon the central
portion of the travel path.
Supported along each side of the cover 218 at the lower edges thereof
is one of a pair of configured cooling blocks 234, which may be constructed
- 30 of aluminum or another suitable material having a high heat transfer coefficient.
It will be appreciated that these cooling blocks are elongated and extend along - -
substantially the entire length of the cover 218. The cooling blocks 234
- 19 -
,
.
i C~i4;~5 O
have inner upstand~ng elements 235 wh~ch are configured to def~ne behind
them circular recesses 236, in whi~h are supported cooling tube portions 238
Small, downwardly opening U-shaped channels 240 are defined along the lower
inner edges of the upstanding elements 235, and a depending ridge 242 is
provided on each of the cooling blocks 234 adjacent the lower outer edge
thereof.
The ridges 242 of the cooling blocks 234 are recelved in narrow,
upwardly opening U-shaped channels 244 defined in the upper surface of the
base of the precuring unit 204, the base being general1y designated by the
numeral 246. A relatively large, upwardly opening U-shaped channel 250 ex-
tends axially in the base 246 along its entire length to define the travel
path therethrough. The underside of the base 246 has a U-shaped channel 248
of a similar size running along its length, with the opposed relationship of
the channels creating a relatively thin floor portion 252 therebetween. A
rectangular base block 254 is seated in the downwardly opening channel 248
and is welded in place with its upper surface spaced a short distance downwardlyfrom the lower surface of the floor portion 252 to define a shallow water
channel 256 therebetween. Upwardly opening U-shaped slots 258 are formed in
the upper surface of the block and along the entire length thereof between
the central channel 250 and each of the relatively narrow channels 244, and
each of the slots 258 has a cover strip 260 engaged over its open end to there-
by define closed conduits therewithin.
At each end (only one end being shown) the base 246 is provided with
a transverse bore 262 which communicates with the opposite ends of the shallow
water channel 256.- To facilitate manufacture, the bores 262 are simply drilled
inwardly from the side of the base 246, with plugs 264 being inserted after-
ward to close the ends. Extending upwardly and inwardly from the opposite
ends of the bores 262 are short connecting channels 266 (only two of the four
of wh~ch are seen because only one end of the base 246 is illustrated), one of
which communicates wlth each of the U-shaped slots 258 at one end thereof.
Finally, an inlet port 268 communicates from the lower surface of the base
246 with the transverse bore 262, and lt will be appreciated that the other
- 20 -
~f ~ .. . . . . .
1064250
end of the base 246 has a s~milar port 268 commun1cat1ng with the assoc1ated
bore 262 provided thereat.
In operation, the precure unit 204 heats the cylindrical core por-
tion 28 of each of the armature rotors 26 while simultaneously cooling the
shafts 32,34 thereof. Heat is generated by the elements 228, with the reflector222 and the baffle plates 224 effective1y directing the heat 1nwardly toward
the core portion 28 and concentrat1ng it thereat. The s1multaneous cool1ng
effect is provided by passing water through the base 246 and the conf19ured
cooling blocks 234. With respect to the base`246, water passes inwardly
through illustrated port 268, transversely across the block in the bore 262,
and thence along the length of the base 246 within the shallow water channel
256 and the U-shaped slots 258 to pass outwardly through the transverse bore
and port not illustrated. In this manner, a cooling effect is transmitted
through the thin floor portion 252 to cool the central band 176 of the con-
veyor 18 and the surrounding area. Water passing through the slots 258 serves
not only to cool the sides of the conveyor 18, but has the primary function
of producing a cooling effect through the cover strips 260. The shafts 32,34
of the anmature rotors 26 contact these strips 260 directly, so that the cool-
~ng water passing therebeneath very effectively lowers the temperature of
those portions. The configured blocks 234 are cooled by water passing into
one of the cooling tube portions 23 and out of the other, the portions 238
being parts of a continuous conduit. As a result, the horizontal part 237
of each of the blocks 234 is cooled and cooperates with the base 246 to e ff ect-
~velymaintain the shafts 32,34 at a relat1vely low temperature. ~he upper
ends of the carrier tabs 178, 178' of the conveyor 18 extend into the down-
wardly opening U-shaped channels 240 adjacent the lower inner edges of the
blocks 234, and are cooled thereby. In addit1On, the engagement of the de-
pend1ng ridges 242 1n the upwardly open1ng channels 244 1ncreases the effect-
i ~veness of cool~ng by un~fy1ng the cover 218 and base 246 of the precure un~t
204. A low temperature shell 1s thereby deflned about the travel path through
the precur1ng un1t 204, except 1n the 11m1ted area thereabove at which the
heat~ng effect ~s concentrated. Accord1ngly, the unlt 204 very effect~vely
- ~ - 21 .
,: - .: :. ., : .
.. . . .
106425()
cools parts of the rotors 26 which lie outwardly of the cylindrical core
portion 28, while the portion 28 is heated to a relatively elevated tempera-
ture. As a result, only resin on the core portion 28 is melted and fused,
with any powder remaining on the shafts 32,34 being maintained in a solid
particulate state. Th~s permits removal of unwanted powder from the shafts
32,34 while simultaneously producing a relatively adherent coating in the
slots 30 of the core portion 28, the circumferential surface of the core por-
tion 28 having been freed from powder by the action of the belt assemblies in
the contact belt unit 124.
Turning now in detail to Figure 15, therein illustrated is an air
knife assembly, generally designated by the numeral 270, which is positioned
immediately downstream from the precure unit 204, as can be seen in Figure 3.
The air knife assembly 270 consists of a pair of spaced, inverted U-shape
bridge members 272 which have mounted thereon a pair of spaced air manifold
bars 274. The manifold bars 274 are adjustable (by means not shown) to vary ~-~
their spacing and angular attitude relative to one another, and each of them
has a number of flattened nozzles or air knives 276 extending downwardly there-
from toward the deck 36 of the machine. In general alignment under each of
the manifold bars 274 is an upwardly opening elongated trough 278 which
is connected to a vacuum source (not shown) through vacuum conduits 280 attachedto the lower ends thereof. As will be appreciated, armature rotors 26 pass - -
from the precuring unit 204 beneath the bridge members 272 of the air knife
assembly 270 with their shafts 32,34 extending outwardly over the troughs 278.
Air is charged under pressure into the manifold bars 274 through the air con-
, duits 282 and is blown at high velocity upon the shafts 32,34 through the air
¦~ knives 276 as the rotors 26 travel through the assembly 270. Due to the dis-
~ crete form in which the particles are maintained as a result from the cooling
j effects of the precuring unit 204, the air from the knives 276 effectively
dislodges any particles present on the shafts 32,34 and propels them into the
troughs 278. In this manner, the shafts are thoroughly cleaned prior to entry
of the rotor 26 into the oven, w1th the excess powder being returned to the
system through the conduits 280.
; - 22 -
1064250
Uncoated armature rotors 26 are loaded in success~ve pairs of
slots 52,52' of the conveyor bands 44,45 at the infeed station of the appara- -
tus, and enter the oven with at least partially fused and cohered coatings
of resin in the slots 30 and on the end faces 37 thereof. The circumferential
surfaces of the cylindrical core portions 28 of the rotors 26 are virtually
devoid of arW powder particles. This is accomplished by the contact belt
el~nents 166, which effectively r~nove all powder depos~ted thereon w~thout ! '
caus~ng significant amounts of the resin to be reToved or built up at the
edges of the slots 30, which is achieved due to the absence of any wiping
10 effect.
The shafts 32,34 are preliminarily cleaned in the belt contact unit
124 by passage over the slotted face plates 190, 190' of the vacuum blocks
188, and by the contact elements 166 of the fourth set of belt assenbl~es,
as illustrated in Figure 11. However, ~t should be appreciated that either
or both of these effects might be eliminated, with reliance being placed
entlrely upon the action in the precuring unit 204 to pennit powder removal,
but preferably both the contact belt unit 124 and also the precuring unit 204
will be provided as illustrated. From the precuring unit 204 the rotors 26 - -~
are carried to the air knife assembly 270 for a final cleaning, through tbe
20 oven for complete fusion, and finally to the cooling unit for solidification
of the resin.
Subsequent to the air knife assembly 270 and ahead of the oven is
~, a second transfer point which occurs over the rearmost drive sprocket 13.
Since the transfer is quite comparable to that which occurs over the sprocket
12, a detailed explanation is not believed to be necessary. However, as
illustrated in Figure 16, the construction of the conveyor 20 to which the
cores are transferred at this point is somewhat different from any described
previously. More particularly, the conveyor 20 consists of a p~ir of spaced
chain assemblies, generally descr~bed by the numeral 283 ~only one being shown
30 in Figure 16) which, at the point of transfer, lie to either side of the
conveyor 18. Each of the chaln assemblles 283 includes an endless sprocket
cha~n 292 on which is mounted a multiplicity of U-shaped cradles 284. Each
-- 23 --
:............. , , .; ~ ,,
1~tj4~jO
of the cradles 284 has in ~ts inner wall 288 an upwardly open~ng U-shaped
socket 286 in which the shafts of the rotors are received. The cradles 284
have a depending flange element 290 secured thereto, and the flange elements
constitute part of the sprocket chain 292 while affording the means of attach-
ment thereto. As will also be appreciated, drive sprocket 13 will consist of
a pair of sprocket wheels similar to those employed for the drive sprocket 12,
one wheel being used to support and drive each of the chain assemblies 283.
The particular fusible resin used may vary greatly; however, of
the types of materials which are suitable, thermoplastics, and particularly . .synthetic thermoplastic resins, are preferred. Exemplary of such thermo-
plastic resins are vinylidenes and vinyls (e. g., polystyrene and polyvinyl
chloride), the olefins (e.g., polyethylene, polypropylene and copolymers
thereof), the cellulosics, polyamides (e.g., nylons), etc.
As will be appreciated by those skilled in the art, many changes
may be made in the illustrated apparatus without departing from the concept
of the invention hereof. For example, heating may be by any appropriate ~ ~ -
means, and may employ convection, conduction, infrared, induction, or like
effects. Similarly, cooling may be accomplished in any appropriate manner,
such as by the use of cooled air or other fluid, conventional refrigeration,
etc. The proper electrical circuitry will also be readily apparent and of
the type conventionally employed in the electrostatic coating and electro-
mechanical arts. It should be appreciated that, although good practice and
safe operating procedures will normally dictate electrical grounding of the
;I apparatus and of the workpiece by contact therewith, no special provis~on
need normally be made for ground~ng of the workpiece to ensure adequate -!~ electrostatic attraction and adhesion. The high voltage charging of the
particles will usually suffice to establish an adequate potential relative
to the workpiece, regardless of the measures taken with respect to the latter;
however, independent connections may be made to the workp~ece lf so desired.
As used herein, the terms Hpartial fusion~ and "coherence~ are
tntended to connote a state in which the ~ndiv~dual parttcles of the res~n
have been affected by heat sufftc~ently to at least loosely ~oin them together,
.
- 24 -
, .......... . .
10~4;~
so as to resist separation. In such a condition indivldual particles may be
discernible, whereas upon complete fusion or melting the particles are no
longer identifiable as such. Due to the variety of resinous materials that
may be employed in the practice of the invention, it is not possible to place
specific values upon the temperatures involved for fusion or melting without
unduly limiting the scope thereof. Moreover, the conditions of operation that
are appropriate in each instance will be readily apparent to those skilled in
the art in view of the foregoing detailed information.
Thus it can be seen that the present invention provides novel appara-
tus for the production of a unified, adherent coating of a heat fusible resin
upon a limited portion of a workpiece. More specifically, it provides such
apparatus for electrostatically coating the workpiece and for effecting the
removal of the resinous material from selected portions thereof which are to
be uncoated, and the apparatus are particularly adapted for coating reentrant
surface portions of generally cylindrical articles. The coatings are produced
quickly, easily and economically, and on the automatic and continuous basis
if so desired. A novel precuring device is also provided which is adapted to
set the coating at one zone of a workpiece while simultaneously maintaining
the particulate form of the resin at a second zone to facilitate its complete
20removal therefrom.
- 25 -
.,; , . :
.".. . :
