Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Rota~Atomlz~ Coater
Backqround of the Irlventioll
This inVentiOrl relates to coa tin-J apparatus and more
particularly to an improved rotary a~omizing coater for
depositing pairlt and similar materia] on a work piece.
One type of commercial coating apparatus for paint,
and the like, comprises a rotar~ clisc or bell and an air
motor Eor driving the disc or bell at a high speed. Paint
deliverecl to the surface of the rapidly rotatin~J disc or
bell is thrown off in small E~articles throu~h centrifucJal
force. The surface of the bell is charcJed to a high
voltage relative to the work piece so as to electro-
statically charc3e the paint particles. The atomized
charged paint particles are directed at and coat the work
piece through a combination of the charge on the paint
particles and, preferably, also a surrounding stream of
air discharged from -the coater.
In one common commercial app:lication of coaters of
this type, the coaters are mounted alon~ the path of a
conveyor which carries the work pieces past the coaters.
The delivery of paint to the rotary atomizing coa-ter is
turned on and off throu~h a suitable valve as work pieces
enter and leave the coating area so as to minimize waste.
When the paint flow is shut off, the air motor driven bell
~5 tends to accelerate to a speed considerably higher than
its normal operating speed due to the removal of the
paint load. The hiyher rotational speed of the bell
produces a finer particle size in the atomized paint. Con~
sequently, the particle size clecreases as the paint ~low
is terminated and the initial paint particle size is
smaller than normal when paint flow is first initiated~
Adjus-tments in the paint flow rate also chan~e the load
on the atomizin~ bell and, consequentl~, affects the speed
of the bell which in turn afEects the particle size.
Hiclher bell speeds resultin(J from a :lower t:han norlna.l,
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paint Elow rate rnay result ill.su~h a fine particle size
that the pdint particl~s dry belore they reach the work
piece. The fineness of tile atomization affects the
color shadincJ, the surrace appearallc~, the transfer
efficiency or perc~ntage of paint deposi-tedon the work
sur~ace, the wrap-around and the edc~e coverage o~ the work
piece. Optimizing the particle size can rnaximize the
transfer effici.ency, give goocl ed~e covcrage with accept-
able paint buildup on the edge of a panel, and control
the wrap-around on -the back of a panel. The coverage
will be adversely affected by chanc3~s in the speed of
the atomizer bell as the palnt flow is triggered on and Of ~A
The air motor used for driving khe high speed atomiza-
tion bell in a rotary atomizer coater is often an air driven
turbine. It is known in the prior art that a govexnor
may be built into an air turbine for limiting;the maximum
speed of the turbine ou-tput ~haft. Such a governor is
illustrated, ~or example, in United States patent
3,708,2~0. Mowever, this and other prior art does not
use a governor in an air turbine which drives a rotary
atomizer in order to maintain an o~timum paint particle
size while the load on the atomization bell changes.
Su~nary of the Invention
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According to the present invention, a yovernor is
provided for a rotary atomizer driven by an air turbine
so as to optirmize paint particle size through~varying
loads. In one preferred embodiment, the air turbine
generally comprises a hollow shaft on which a turbine
wheel is mounted. Compressed air is supplied from a
suitable source througll a rotating seal and the hollow
shaft to the turbine wheel for drivinc3 the turbine.
valve located within the turbine shaft rnodulates the air
~low to the turbine wheel in rcsponse l:o the turbine
speed to maintain a more unlForrn turbi.ne~ speed durinc3
changes ln loadinc3 on the rotary atornizer~ ~n atomi.zat:ion
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bell or disc is mounted on an ~nd ~f -the ~lrbine ~h.~ft
Paint is suppliecl to a chamb~r wi-thin the bell ~nd such
paint is discharged froTn thc bell through centrifugal
force as the bell is ~apidly rotatecl. The bell is ~naintained
at a hiqh electrical po-tential so as to electros-ta-tica~:ly
charge the paint pàrticles dischar~ed from the bell. In
addition, air is discharged in a pattern around the ~ell
and towards the work surface so as to control the pattern
of the discharged paint particles. Through the use of
the governor for controlling the speed of the atomization
bell, the uniformity of the paint par-ticles is greatly
increased even though the flow rate of the paint is
varied.
In a modified embodiment of the invention, the air
modulating va]ve is located in the air supply hose. The
speed of the turbine shaft is sensed electricall, mag-
netically or optically and is ~upplied to a microprocessor
which genera-tes .1 control signa] for modulating the valve
to maint~jn a constant turbine speed.
Accordingly, it is an ohject of the invention to
provide an improved rotary atomizing coater.
Ano-ther object of the inven-tion is -to provide a
rotary atomizing coater driven by an air turbine in which
the uni~ormity of the coating is maintained even though
the flow rate of the coating material to the rotary atom--
izer is increased or decreased.
Other objects and advarltages of the invention will
become apparent from the following detailed description,
with reference being made to the accornpanying drawing.
~rief Descri~tion of the Drawin~
J`he singl~ figure i~ a siclc elevational view in
partial section of a rotary atomizing coater constructed
in accordance with the present inventioll.
Detailed Descriptiol~
Turning now to the sing]e ~i3ure, a rotary atomizing
coater 10 is shown construet:e(3 in accordance with the
presen-t inven-~ion. The coater 10 ge~nerally co~nprises
an air turbine 11 which drives an atomization bell 12
The air turbine 11 dri~es the bell 12 at hiyh ro~ational
speeds, for example, in the rancle of 10,000 r.p.m. to
~0,000 r.p.m. or more. The air turbine 11 ineludes an
internal governor for maintainincJ substanti~llly constant
the spped at which the bell 12 is rotatecl r even though
the load on the bell 12 may change due to changes in the
lQ paint ~low rate or ehailges i~ the paint cdensity when, for
example, the paint color is changed. The ~ubstantially
eonstant speed is a function of the turbine air 5~1pply
pres~ure.
Th~ air turbine 11 inclucles a main housing 5ection 13
which has a generally circular cros.s section and mounts a
tuhular exten5ion 14. A shaft 15 is nlount~d within the
housing section 13 and tubular extension 14 and is sup-
ported by a plurality of bearings 16. The shaft 15 has
an end 17 which mount~ t.he atomization bell 12 and has a
hollow end 18 which is coupled throuyh a suitable rotary
seal (not shown) to a compressed air hose :L9. The hollow
shaft ~nd 18 de~ines an interior chamber 20 which cor~uni-
cat~s throuc3h side openings 21 to the interior 22 of a
turbine wheel 23. Compressed air normally f]ows from the
air hose :L9 -throught the interior shaft chamber 20, the
openinc3s 21 and the turbine wheel chamber 22 to radially
directecl openings 24 on the turbine wheel 23 and thence
the air is vented through rear openings 25 in the main
housincJ section 13. The air flowing through the turbine
~heel 23 causes the turbine wheel 23 to rotate the shat
15 at a high rate of speed which is dependent~upon the
load on the shaft 15, the air flow rate and the alr pressure.
The speed of the air turbine 11 is controlled by a
goverrlor 2~ which i~ located within the shaft eham~er 20
for controllincJ a:ir flow from Ihe air hose ].9 to the
turbine wheel cllamber 22. 'rhe (~overnor 28 inclucles a
piston 29 whictl slides wlthin ~lle ctlamber 20 iiltO and out
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~4~4S
of ~n~Jayement with a valve seat 30. The piston 2g ha~ a
valve surface 31 which, when abul:tin~3 the valve seat 30,
blocks air flow from the air hose :L9 to the turbi.ne
wheel 23. A spring 32 urges the piston 29 against the
valve seat 30 to block air flow in the turbine 23. At
the same time, the compresse~ alr within the chamber Z0
acts upon a face 33 on the piston 29 to move the piston
29 against the spring 32, there~y opening the passageway
from the chamber 20 to the turbine wheel interior chamber
22. A hole 34 extends through the piston 29 to allow a
restrict(_d ~low o~ the compressed ai.r within -the chamber
20 throu~h the pi.ston 29 -to a chamber 35 located between
the piStOIl 29 and an insert 36~ ~s wi].1 be shown below,
the chamber 35 may be vented to the atmosphere or may be
plugged, ~ependincJ upon -the action o~ the governor re-
quired to mai.ntain a constant shaft speed. When the
chamber 35 i.s vented to the atmosphere, the compressed
air in the cham~er 20 applies a signifi.cantly higher force
to the piston face 30 than appears at a face 37 on an
opposite e~d of the piston 29. The difference in ~orce is
sufficient to compress the spring 32, thereb~ openin~ the
air flow passages from the chamber 20 into the turbi.ne
wheel interior 22. On the other hand, i.f the chamber 35
is not vented -to the atmosphere, the compressed air will
~low through the piston hole 34 to pressurize the chambex
~5 a-t the same pressure as the chamber 20. Since the
~orces applied by the compressed air on the faces 33 and
37 o~ the piston 29 axe identical, the sprinc~ 32 acts to
move the piston 29 into contact with the valve seat 30
to block the flow of air from the chamber 20 to the turbine
wheel interior 22, thereby stop~)in-J the turbine. sy
modulating the posltion of the pi.ston 29, the flow o~ air
from the chamber 20 to the turbine wheel intexior 22 i.s
modulate~] to control the speed at which the shaf-t 15 l.s
3~ rotated.
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~ centrifugally actuatecl ~all valve 40 controls the
air pressure within the chanlber 35. A valve seat: 41 i5
formed between a passage 42 in the insert 36 which com-
municates ~Jlth the chamber 35 and a passaye 43 which is
vented to atmospnere through an annular region between
the shaft 15 and the tubular extension 14. A tubular
plug 49 retains a ball 45 adjacellt the valve seat 41
while leavi.ng clearance for the l~all 45 to move into and
out of contact with the seat ~31. The ball 45 is located
so that at all times its center is positioned to the side
of the a~is of the shaft 15 toward the seat 41. Conse-
quently, as the shaft 15 is rotatec3 at an increasing
speed, centrifu~al force urcJes the ball 45 a~ain~t the
seat 41 with an increasing force.
1~ In operation, at slow speeds of the turbine wheel
23 the compressed air from the hose 19 is allowed to flow
throuqh the piston hole 34, the chamber 35, the passage
42 and the passage 43 and thence is vented to the atrrlos-
pnere~ Co3~sequently, the chamber 35 will have a pressure
near or at atmospheric pressure ancl the pressure on the
piston face 33 will move the piston 29 to allow an
unrestricted air flow from the charnher 20 to the turbine
wheel interior 22. As the speed of the shaftll~ increases,
the ball 45 is folced more ti~htly against thé seat 41 and
the pressure within the charnber 35 increases. The air
pressure within the chamber 35 act.s against the piston ~ace
37 to offset the air pressure ac-ting on the piston
face 33. ~t some increasing turbine speed, the increasing
pressure within -the chamber 35 alony with the pressure
of the spring 32 moves the piston 29 to progressively
close the air flow passages frorn the chamber 20 to
the turbine wheel int~rio3- 22. At this point, the
r3peed of the sha~t 15 i~ co3ltrc)lled at n cons~ant level
Thus, when load is removed fro~n atornization bbl]. 12 and
the sha~t 15 tends to accelerclte, the piston 29 will mo~e
to further c]ose thr air ~low passage and govern the speed
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of the shaf-t 15. The yovernor con-trolled speed is a
function of the turbin~ air suppl~ pre~sure.
The end 17 o:E the shaft 15 e~tcnds through and
projects from a ~ani~old 48. The atomizati.on~bell 12
is mounted on the projec-tin~J sha.Et end 17. ~ paint
hose ~9 .is connected to deliver paint ~hrouyh a pas-
sage 50 in the manifold 48 and thence through an ori-
~ice 51 to an annular ~hamber 52 formed on the back of
~ the atomization bell ~ . As the hell 12 rotates at a
high speed the paint within the cha~er 52 is thrown
rad.ially outwardly and flows along a conical surEace
55. The paint continues to Elow outwardly along the
surface 55 until it is thrown from an outer edge 56 on
the bell 12 in the form of sma.l.]. particles The size
of the discharged particles is de-termined by various
factors including the rotatlonal speed of the bell 12,
the flow rate of the paint and the properties of the
paint.
~ir is supplied to the manifold 48 through a fit-
ting (not shown) similar to 49. ~ passage similar to
the passage 50 connects the air supply fit-ting to an
annular chamber 59 located in a m~nifold face 60. A
plurality of openings 61 extend through the manifold
face 60 and communicate with the chamber 59. The
opening5 61 are uniforml~ spaced around the shaft
and cause an ~ir flow which 5urrounds the bell 12 for
directing the paint particles thrown off from khe
bell 12 toward~ the work piece.
To prevent paint or solvent from entering the
turbine 11 or the bearing 16 an annular slinger 62
is positioned on the shaft 15. The slin~er 62 ro-
tates with the shaft 15 and prevents liquid from
creeping along the shaf-t 15. The slinger includes
a lip 63 which overlaps a fixed annular seal 65. The
seal 64 is threaded i.n-to the tubular exten.C;ion 1~ and
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does not rotate with the sllaft 15. In cross~section,the seal 6~ has a cup shaped or hooked lip 65 located
radiallyinward ~rom the slinger ].ip f~3. I;'low of any
liquid coming into cont~ct wit]l t:hc 51i ncJer 63 will
be thrown off onto the manifold 48 and ~7ill drain
through a hole 57. Th~ liquid would have to follow
a torturou5 path to continue along the sha:Et 15.
Teflon or polytetrafluroethylene annular seal 66 has
a close running fit to the shaft 15. This serves to
further restrict any possible Eluid flow alony the
axial length of shaft 15. Thus, the slinger 62, the
seal 64 and the seal 66 prevent the flow of liquid
along the shaft 15 into the ai.r -turbine ll and the
bearing 16.
In accordance with the present invention, the air
turbine which drives the atomization bell for the
rotary a-tomizing coater is yoverned to rnaintain a
fai.rly constant speed for the atomi.æation bell
throughout varying paint loads on the atomiæation
bell. The governor 2a for regulating the turbine shaft
speed has been described as being located within the
turbine shaft 15. In a modified embodiment of the
invention, an air flow con-trol valve may be located
extern~l to the coater 10, for example, within the
~5 air supply hose 19, rather than within thc turbine
shaft 15.. A conventional electrical, magnetic or
optical sensor may be connected to gencrate a signal
indicative of the speed of tile air turbine shaft.
This signal is applied to a microprocessor which in
turn generates a signal for modulatirlg the air con-
trol valve to regulate the tur~ine speed. Still
another method of achieviny an approximately constant
rotational speed for the air turbine f or uni f orm
atomi~ation with varying paint flow is by measuring
the paint flow rate. The pai.nt flow rate then is
. . .
co~pared in a look up tahl~ with previou~1~ measured
paint flo~ rate data versu.s alr flow rate data. The
relationsh:ip be-tween the paint, flow rate, turbine air
supply pressure and turbine speed are stored in a
microprocessor. The microprocessor selects the pro-
per turbine air supply pressure to produce the desired
rotational speed and, accordingly, actuates an ~ir
flow control valve.
Various modifications and changes may be made in
the above described preferred ernbodimellts of the in-
vention without departing from the splrit and the
scope of the following claims. For example, onl~ an
exemplary governor mounted withill the air turbine has
been described. Other yovernor desiyns are recognized
lS in the ,air turbine art,
