U.S. patent number 3,837,573 [Application Number 05/335,522] was granted by the patent office on 1974-09-24 for apparatus for electrified spraying.
Invention is credited to William C. Wagner.
United States Patent |
3,837,573 |
Wagner |
September 24, 1974 |
APPARATUS FOR ELECTRIFIED SPRAYING
Abstract
Apparatus for electrified spraying operation and including a
power supply with a flow operated switch and an integral assembly
with an elongated electrode mounted with an end adjacent to and
outside of spray from a spray gun. The electrode is adjustable in
position from 0.25 to 1.50 inches from the spray orifice and has a
pointed distal end portion extending perpendicularly to the
direction of flow of the spray, a sloped portion extending from
said end portion laterally and forwardly, and a looped portion for
resiliently maintaining the position of the pointed end, with the
electrode having an insulating coating over its greater part but
with its pointed end bare.
Inventors: |
Wagner; William C. (Wenham,
MA) |
Family
ID: |
26924905 |
Appl.
No.: |
05/335,522 |
Filed: |
February 26, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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231210 |
Mar 2, 1972 |
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Current U.S.
Class: |
239/705; 118/621;
239/707; 427/483 |
Current CPC
Class: |
B05B
5/10 (20130101); B05B 5/0533 (20130101); B05B
5/03 (20130101) |
Current International
Class: |
B05B
5/053 (20060101); B05B 5/10 (20060101); B05B
5/025 (20060101); B05B 5/03 (20060101); B05B
5/08 (20060101); B05b 007/08 (); B05b 005/02 () |
Field of
Search: |
;239/3,4,15
;117/17,93.4R ;118/621 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,099,829 |
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Mar 1955 |
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FR |
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1,157,214 |
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Dec 1957 |
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FR |
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865,763 |
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Apr 1961 |
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GB |
|
Primary Examiner: Ward, Jr.; Robert S.
Parent Case Text
This application is a continuation-in-part of copending application
Ser. No. 231,210, filed Mar. 2, 1972, and entitled "Apparatus For
Electrified Spraying"now abandoned.
Claims
What is claimed is:
1. In a spray gun for producing an atomized spray in a pattern
forward of said gun, said gun including a body with first passages
therethrough for supply of material to form said spray, said gun
including second passages for emission of jets of air impinging on
said spray to effect a fan-shaped spray pattern and defining at the
positions of impingement of said air on said spray a zone of second
stage atomization, an orifice in said body for the issue of said
material from said gun, and an elongated electrode adapted for
connection to electrification means for electrifying particles of
said spray,
that improvement in which said electrode is supported at a proximal
end by said body and supports a distal end portion having a sharply
pointed distal end in a position spaced adjacent a flat portion of
said fan-shaped spray pattern pointed at said zone of second stage
atomization between about 0.25 and 1.50 inches forward of said
orifice, said pointed distal end adjacent to and outside of said
spray pattern and pointed generally perpendicular to the direction
of flow of said spray.
2. Apparatus as claimed in claim 1, said improvement including
adjusting means supported by said body for adjusting said pointed
distal end along the direction of spray motion in its said position
forward of said orifice.
3. Apparatus as claimed in claim 2 in which said position of said
pointed distal end is between about 0.25 and 0.875 inches forward
of said orifice.
4. Apparatus as claimed in claim 2, said adjusting means including
a hollow tube supported on said body with a portion of said
electrode fitting therewithin and frictionally engaged thereto to
permit sliding motion between said tube and said electrode
portion.
5. Apparatus as claimed in claim 4 in which said position of said
pointed distal end is between about 0.25 and 0.875 inches forward
of said orifice.
6. Apparatus as claimed in claim 1, said electrode including
contiguous to said distal end portion a sloped portion extending
from said end portion laterally and forwardly.
7. Apparatus as claimed in claim 1, said electrode including a
looped portion for resiliently maintaining the position of said
pointed distal end.
8. Apparatus as claimed in claim 1, said electrode having an
insulating coating around a major portion thereof, said distal end
being bare.
9. Apparatus as claimed in claim 1, said pointed distal end being
positioned to be in one said jet pointed at said zone of second
stage atomization.
10. Apparatus as claimed in claim 9 in which said position of said
pointed distal end is between about 0.25 and 0.875 inches forward
of said orifice.
11. Apparatus as claimed in claim 10, said pointed distal end being
pointed at the portion of said zone of second stage atomization
adjacent said orifice.
12. In apparatus for converting a spray gun for electrified
spraying operation, said spray gun having an orifice adapted for
issuing atomized spray from said gun, said gun also having passages
for emission of jets of air impinging on said spray to effect a
fan-shaped spray pattern and defining at the positions of
impingement of said air on said spray a zone of second stage
atomization, said apparatus comprising an integral assembly
including a jig, an elongated electrode mounted on said jig for
positioning an end thereof adjacent to spray from said spray gun
when said assembly is attached to said gun, an electric cable
affixed to said jig and connected to said electrode to pass current
from said cable to said electrode, and means mounted on said jig
for affixing said assembly to and removing said assembly from said
gun,
that improvement in which said electrode is supported at a proximal
end by said jig and supports a distal end portion having a sharply
pointed distal end adjacent to and outside of said spray pattern
adjacent a flat portion thereof and pointed generally perpendicular
to the direction of flow thereof and in which adjusting means is
supported by said jig for adjusting the position of said pointed
distal end along the direction of spray motion to a distance
between about 0.25 and 1.50 inches forward of said orifice pointed
at said zone of second stage atomization adjacent said flat portion
of said spray pattern.
13. Apparatus as claimed in claim 12 including a power supply for
supplying an electrical output for electrifying said electrode,
said power supply including means for connecting said output to
said cable and a switch connected to control said output, a conduit
connected to said gun for supplying said gun with an operating
fluid, said switch being a fluid-flow responsive switch and
including means for connecting said switch to said conduit to make
said switch responsive to flow in said conduit.
14. Apparatus as claimed in claim 12 in which said distance is
between about 0.25 and 0.875 inches forward of said orifice.
15. Apparatus as claimed in claim 12, said adjusting means
including a hollow tube affixed to said jig with a portion of said
electrode fitting therewithin and frictionally engaged thereto to
permit sliding motion between said tube and said electrode
portion.
16. Apparatus as claimed in claim 12, said electrode including
contiguous to said distal end portion a sloped portion extending
from said end portion laterally and forwardly.
17. Apparatus as claimed in claim 12, said electrode including a
looped portion for resiliently maintaining the position of said
pointed distal end.
18. Apparatus as claimed in claim 12, said electrode having an
insulating coating around a major portion thereof, said distal end
being bare.
19. Apparatus as claimed in claim 12, including a resistor mounted
on said jig and connected to said cable and said electrode to pass
current from said cable to said electrode.
20. Apparatus as claimed in claim 12, said jig being of ring-like
form and of a size to be radially spaced from said gun when said
assembly is attached to said gun.
21. Apparatus as claimed in claim 12, said cable including a
metallic shield, and including an electrical connector mounted on
said jig to establish grounding contact between said shield and
said gun when said assembly is affixed to a metal gun.
22. Apparatus as claimed in claim 13 said power supply including
means for varying the voltage of said electrical output.
Description
BACKGROUND OF THE INVENTION
This invention relates to the spraying of coating materials and
particularly to electrifying sprays.
Spray guns are frequently used to apply paint or other coating to
ware. In this technique the paint is admitted continuously to a
spray gun through a hose. The gun comminutes the paint into
particles which are directed towards the ware to be coated. Some
spray guns effect the comminution by emitting the paint at high
pressure from an orifice, this technique often being referred to as
pressure atomizing. Other spray guns operate by emitting the paint
at lower pressure or by siphon from an orifice while directing at
the emerging paint a high speed stream of air from one or more
separate nearby orifices, this technique being often called air
atomizing.
It is recognized that in certain circumstances it is advantageous
to electrify the spray particles. When this is done the
trajectories of the electrified particles are modified by electric
forces with the result that the coating material is more
effectively applied to the ware.
SUMMARY OF THE INVENTION
Objects of this invention include providing an improved electrified
spray gun and providing apparatus for converting a spray gun for
electrified operation.
It has been discovered that efficient charging of sprayed particles
can be achieved by an ionizing electrode without a separate
collector electrode, provided the discharge electrode is pointed at
the spray at a point where the particles have been atomized
substantially to their smallest size and prior to dispersal to a
degree at which charging efficiency is significantly reduced. In
air atomizing, employing second stage atomization, the electrode is
pointed at the zone of second stage atomization. In pressure
atomizing the electrode is pointed at the spray in a zone, similar
to the second stage atomization zone, in which the particles have
broken to substantially their smallest size but before significant
dispersal.
In general the invention features the improvement in electrified
spray guns wherein an electrode is supported at a proximal end on
the body of the gun and supports a sharply pointed distal end in a
position forward of the spray orifice and adjacent to and outside
of the spray pattern pointed generally perpendicular to the
direction of spray flow. The electrode is positioned from 0.25 to
1.50 inches forward of the spray orifice, preferably between 0.25
and 0.875 inches forward thereof, at the second stage atomization
zone of an air atomizing sprayer with the electrode in the air
stream. A preferred embodiment additionally features an adjustable
electrode, a sloped portion extending from said end portion
laterally and forwardly, and a looped portion for resiliently
maintaining the position of the pointed end, with the electrode
having an insulating coating over its greater part but with its
pointed end bare.
The invention features in a preferred embodiment an integral
assembly including a jig, an elongated electrode mounted on the jig
to be positioned with an end adjacent to spray from the spray gun
when the assembly is attached to the gun, an electric cable affixed
to the jig and connected to the electrode to pass current from the
cable to the electrode, and means mounted on the jig for affixing
the assembly to and removing the assembly from the gun, and a power
supply for supplying an electrical output for electrifying the
electrode, the power supply including means for connecting the
output to the cable, and a switch connected to control the output.
A specific embodiment features a fluid-flow responsive switch
controlling the electrical power supply, adjusting means for
adjusting the electrode in its position relative to the spray,
means for varying the voltage of the electrical power supply, and a
current limiting resistor mounted on the jig.
In another aspect the invention features, in a preferred
embodiment, a power supply with circuitry for providing electric
power for electrifying a spray comprising in combination first
circuit portion including a flow-responsive switch operatively
connected to a flow channel to close when fluid flows in the
channel and to open when fluid does not flow in the channel, the
flow-responsive switch being connected in series to receive power
from power mains and provide switched power to a first terminal, a
variable output transformer connected to draw power from the first
terminal, and providing a controllable voltage to a second
terminal, a voltmeter connected to indicate the voltage across of
the second terminal, a step-up transformer connected to draw power
from said second terminal and provide an output across a pair of
ungrounded terminals, a circuit loop comprising two diodes and two
capacitors connected in a loop with the diodes head to tail, the
loop connected to the ungrounded terminals at a first junction
between the diodes and at a second junction between the capacitors,
each of the capacitors having a resistor connected in parallel
thereto, the loop having a ground connection at a third junction
between a capacitor and a diode, the diode being connected to
deliver current to the third junction, a negative voltage output
terminal connected through a current limiting resistor to a fourth
junction of the loop, a diode of the loop being connected to draw
current from the fourth junction.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows partly in perspective view and partly schematically
apparatus according to the invention in operation.
FIG. 2 shows at enlarged scale a front view of the spray gun and
conversion assembly shown in FIG. 1, some parts being cut away to
reveal interior parts.
FIG. 3 shows in partial longitudinal section the front portion of
the gun and conversion assembly shown in FIG. 1, the section being
that designated 3--3 of FIG. 2.
FIG. 4 shows a circuit schematic drawing of the power supply shown
in FIG. 1.
DESCRIPTION OF PREFERRED EMBODIMENT
Apparatus 10 according to the invention is shown in FI. 1. The
apparatus includes air atomizing spray gun 12 which is shown
applying a coating of paint to ware 14. Paint from paint reservoir
16 is supplied to gun 12 through paint line 18. Compressed air, the
operating fluid in this type of gun, for atomizing the paint is
supplied to gun 12 through operating fluid conduit 20,
flow-responsive switch 24 of electrical supply 26, and operating
fluid conduit 28 from air plenum 22 supplied by compressor 30.
Trigger 21 controls the flow of both paint and air through gun 12.
Air plenum 22 is also connected to supply reservoir 32 with
compressed air to propel paint through line 18. Electrifying
conversion assembly 40 is affixed to the front portion of gun 12.
Electrical supply 26 draws power from conventional power mains
through plug 41 and supplies power to assembly 40 through cable 42.
The flow of power to cable 42 is controlled by flow sensitive
switch 24. An atomized spray of electrified paint particles is
propelled from the front of gun 12 through space 44 to ware 14. The
forward portion 56 of gun 12 as shown in detail in FIGS. 2 and 3,
includes central paint orifice 57 supplied by paint passage 58,
concentric, annular air orifice 59 supplied by air passages 61, and
side air orifices 63 on air horns 65. Containment orifices 67 in
line with air horns 65 and angular converging orifices 69,
90.degree. from orifice 67, are also provided on the forward
portion 56 of gun 12 and are supplied by passages 61. Orifices 69
are directed at a converging angle to the axis of orifice 57. The
rearward portions of gun 12 are conventional, and since they are
well known to those skilled in the spraying equipment art they need
not be further described here. When gun 12 is in operation, paint
issues from orifice 57 and is initially broken up in zone 70 by the
influence of an air jet issuing from orifice 59, zone 70 sometimes
being referred to as the zone of first stage atomization. The paint
is then further broken up in zone 72 by the influence of air
issuing from orifices 69, zone 72 sometimes being referred to as
the zone of second stage atomization. The second stage atomization
zone is defined by the zone of impingement of air from orifices 69
on the spray of paint. The air from orifices 63 contributes to
second stage atomization and also shapes the spray into a fan
pattern with a plane generally perpendicular to that of the paper
as viewed in FIG. 3.
Converter assembly 40, shown in detail in FIGS. 2 and 3, includes
jig 46 made of electrically non-conductive material such as nylon.
Jig 46 has a generally ring-like form and fits in a generally
concentric spaced relation around the front portion of body 48 and
gun 12. The spacing between jig 46 and body 48 permits necessary
airflow along the forward portion 56 of gun 12. Cinch screws 50,
52, and 54, of which at least screw 50 is metallic, are threaded
through jig 46 and permit assembly 40, including jig 46 and all
components mounted thereon, to be attached as an integral unit to
gun 12. Conductive metallic friction tube 60 is mounted on jig 46,
extending forwards therefrom. Electrode 62 has a shank portion 64
that fits within and frictionally engages tube 60 so that, while
generally supported in the tube, the electrode may be slid forward
or backward, tube 60 and electrode shank 64 together comprising
adjusting means for the electrode 62, Electrode 62 has a sharply
pointed distal end 79 positioned forward of paint orifice 58
opposite to the second stage atomization zone 72 and advantageously
in a jet from an orifice 63. The adjusting means permits adjustment
of pointed distal end 79 forward of orifice 57 to maintain its
position opposite the second stage atomization zone and for
optimizing the position thereof at such zone, the position of
distal end 79 being adjustable between about 0.25 and 1.50 inches
forward of orifice 57 and preferably between about 0.25 and 0.875
inches forward thereof. Electrode 62 has a distal end portion 80
extending and directing pointed distal end 79 perpendicularly to
the direction of flow of the spray, this orientation having been
found to give the best results in coating ware. A sloped portion 82
extends laterally and forwardly from portion 80. The end portions
80 and 82 are attached to shank portion 64 through a resilient
looped portion 84. The major portion of electrode 62, but not end
79, which is left bare, is covered with an insulating coating 86,
which minimizes the chance of inadvertant contact by operating
persons with the electrode. Tube 60 is similarly covered. Cable 42
is secured to jig 46. Resistor 88 (100 megohms in preferred
embodiment) is mounted on jig 56 in cavity 90 with one terminal
connected to the bottom of tube 60 and the other terminal connected
to the central conductor 86 of cable 42. The resistor 88 is placed
close to the electrode to minimize the effective capacitance of the
cable 42 that can discharge without the limiting effect of the
resistor. Conductive link 92 is electrically connected between
ground shield 94 of cable 42 and screw 50 so that an electrical
path is maintained from the ground shield through link 92 and screw
50 to the body 48 of the spray gun.
Power supply 26, the wiring diagram for which is shown in FIG. 4,
includes main switch 102 connected to the power line and fuse 104
connected in series with switch 102 to provide fused switched power
at terminal 106. Light 108 indicates excitation of terminal 106.
Flow responsive switch 110 and current limiting resistors 112 are
series connected from terminal 106 to supply operationally switched
power to terminal 114. Switch 24 is connected (in a piping rather
than an electrical sense) to conduits 20 and 28, and operates to
close its electrical contacts when flow occurs from conduit 28 to
conduit 20, and open them when there is no such flow. Light 116
indicates excitation of terminal 114. Adjustable autotransformer
118 is connected to terminal 114 to provide adjustable voltage
output to terminal 120. Meter 122 indicates the voltage present on
terminal 120. Step-up transformer 124 is connected to terminal 120
to provide a high voltage output across terminals 126 and 128. The
voltage across terminals 126-128 may be adjusted by manipulating
transformer 118 to any value less than 10 KV. Circuit loop 130,
made up of diodes 132 and 134 and capacitors 138 and 136 connected
serially in a loop with the diodes head to tail, is connected
across terminals 126 and 128, terminal 126 being at the junction
between capacitors and terminal 128 being at the junction between
diodes. The diodes are connected to draw current from junction 142
and to deliver current to junction 140. Resistors 144 and 146 are
connected in parallel across capacitors 138 and 136 respectively.
Junction 140 is grounded and junction 142 is connected through
limiting resistor 148 to output terminal 150 connecting with and
supplying a high voltage of negative polarity to the center
conductor of cable 42, the outer conductor of which is
grounded.
In operation, conversion assembly 40 is affixed to gun 12 by
placing it around the forward portion of the gun and advancing
screws 50, 52, and 54 to lock jig 46 to body 48 of the gun. The
assembly should be oriented so that electrode 62 opposes the flat
side of the spray if there is such. Operating fluid conduits 20 and
28 are connected so as to pass air through switch 24 on its way
from the air supply plenum to the gun. Gun 12 is then put in a
spraying condition, and with visual inspection the position of tip
79 of electrode 62 is adjusted by sliding the electrode shank 64 in
tube 60 so that the electrode tip is outside the spray opposite the
second stage atomization zone and in a jet from an orifice 63. In
no event should the electrode be closer to orifice 57 than about
0.25 inches to avoid shorting the system. Preferably, the electrode
is from 0.25 to 0.875 inches forward of the orifice at the second
stage atomization zone where the particles of paint are smallest
but before they have dispersed to the point where electrification
efficiencies are reduced. Ordinarily the electrode position will be
adjacent that portion of the second stage atomization zone closest
to orifice 57, but in some instances greater distances, as much as
1.5 inches from orifice 57, may be used, such greater distances
having been found useful in siphon feed systems. After this
adjustment the power supply is connected to the line and switched
on. It may be noted that prior to actuation of the gun by
depressing trigger 21 air does not flow, so that switch 110 is open
and no electrical output is delivered to cable 42 by the power
supply. Upon depression of trigger 21 by an operator, valves are
opened in the gun to permit the flow of paint and air and a spray
is formed in region 44. (Usually in an air atomizing gun the valves
are arranged so that the air begins to flow slightly before the
paint.) The flowing air causes switch 110 to close, applying power
to terminal 114 with the result that a negative voltage in the
kilovolt range is applied through cable 42 to electrode 62. When
thus electrified, electrode end 79 discharges electrons which
become attached to particles of the spray giving them a net
negative charge. Electric forces arising from the charges on the
particles modify the spray particle trajectories to increase the
coverage of the ware. The electrode, being positioned wholly
outside the spray collects little of the sprayed material and such
as does collect from stray drops is blown away from end 79 along
sloped portion 82 so that the point remains clean and any material
impinging on the electrode finally drops off the electrode from a
region out of the air blast and is not carried to the ware. The
space between assembly 40 and gun body 48 permits a flow of air
therethrough induced by the spray motion. It has been found that
this airflow is beneficial to the electrification of the spray and
improves operation of the apparatus.
The voltage control of transformer 118 and the position of
electrode 62 can be readily adjusted to obtain optimum coating
results and to accommodate to the properties of various paints and
other coating materials.
* * * * *