Note: Descriptions are shown in the official language in which they were submitted.
5 ~
The present invention concerns an electrostatic coating
apparatus used for coating an electroconductive paint such as
an aqueous paint, a slurry paint or a metallic paint by using
an electrostatic coating apparatus applied with a high
voltage .
When an electroconductive paint such as an aqueous paint
is used in an electrostatic coating machine applied with a
high voltage, it is necessary to electrically insulate paint
supply systems from the electrostatic coating machine for
preventing current leakage caused by the high voltage.
Accordingly, in a multi-color electrostatic coating apparatus
used for coating car bodies under color-change of paints of
so many different colors, which may include several tens of
tones, insulation means have to be applied to all of paint
supply pipelines or paint reservoirs on every color of paint,
which has been troublesome and expensive.
In view of the above, in the electrostatic coating for
car bodies, manufacturers such as automobile manufacturers
hesitate to use aqueous paints at present although aqueous
paints may be preferable for use, because they cause less
pollution of air, because they contain less volatile organic
compounds than do organic solvent-based coating compositions.
Instead, electrically insulative resin paints that require a
great amount of deleterious organic solvents continue to be
used predominantly.
However, social movements for environmental protection
- 1 -
~ ~) 3 ~ ~ 5 ~
-
have been raised world-world in recent years and it has been
advocated to more stringently regulate and thereby restrict
the use of organic solvents that release environmental
pollutants such as hydrocarbons also in the field of coating
industry.
The present invention provides a technique capable of
saving troublesome installation for insulation means to paint
supply systems such as pipelines for supplying a conductive
paint, for example, and aqueous paint or paint- reservoirs in
a case where electrostatic coating is applied by using an
electrostatic coating machine operated under a high voltage.
More particularly, the present invention provides an
electrostatic coating apparatus for coating an
electroconductive paint comprising an electrostatic coating
machine applied with a high voltage, a paint supply pipeline
for supplying an electroconductive paint and a reciprocal
pump disposed between the electrostatic coating machine and
the paint supply pipeline and adapted such that the
electroconductive paint introduced from the input port is
discharged at predetermined flow rate from the output port of
the reciprocal pump and supplied at a predetermined amount to
the electrostatic coating machine. The input port of the
reciprocal pump is detachably connected to the paint supply
pipeline.
In the apparatus of the present invention, the paint
supply pipeline is connected to the input port of the
-- 2
2 ~
reciprocal pump and the conductive paint is introduced from
the paint supply pipeline to the inside of the reciprocal
pump before starting a coating operation in a state where a
high voltage is not yet applied to the electrostatic coating
machine. Subsequently, when a predetermined amount of the
coating paint is filled in the reciprocal pump, the paint
supply pipeline is detached from the input port of the
reciprocal pump.
Coating is started with a predetermined high voltage
being applied to the electrostatic coating machine, and the
conductive paint filled in the reciprocal pump is discharged
at a predetermined flow rate from the output port and
supplied at a constant amount to the electrostatic coating
machine.
In this state, since the electrostatic coating machine
and the paint supply pipeline are separated and electrically
insulated from each other, the high voltage applied to the
electrostatic coating machine does not leak to the paint
supply systems such as the paint supply pipeline and the
paint reservoir.
Accordingly, troublesome installation of insulation
means to the paint supply systems is not necessary.
The present invention also provides an electrostatic
coating apparatus for coating an electroconductive paint
comprising an electrostatic coating machine applied with a
-- 3
~, .
7~311 ~54
high voltage, a paint charge pipe connected to the
electrostatic coating machine and capable of charging a
required amount of an electroconductive paint, a paint supply
pipeline detachably connected with the paint charge pipe for
charging the electroconductive paint into the paint charge
pipe, a cleaning liquid supply pipeline connected to the
paint supply pipeline for supplying a cleaning liquid and, in
turn, discharging the electroconductive paint filled in the
paint charge pipe at a predetermined flow rate in accordance
with the amount of the paint discharged from the
electrostatic coating machine and a cleaning liquid reservoir
disposed in an electrically insulated state for supplying the
cleaning liquid to the paint supply pipeline.
In this modified apparatus, the reciprocal pump used in
the above-mentioned apparatus is replaced with the paint
charge pipe and the electroconductive paint charged in the
pipe is forced out by the cleaning liquid supplied at a
predetermined amount to the electrostatic coating machine for
cleaning the inside of the electrostatic coating machine.
After completion of the coating, since the inside of the
paint charge pipe connected to the electrostatic coating
machine has already been cleaned, there is no further
requirement for cleaning the inside the cleaning time can be
shortened.
If cleaning liquid supply pipe is detachably connected
to the paint charge pipe like that in the paint supply pipe,
there is no requirement for electrically insulating the
cleaning liquid reservoir.
-- 4
~ a ~
Further features of the present invention will become
apparent by reading the following descriptions of the
preferred embodiments according to the present invention with
reference to the appended drawings, wherein:
FIG. 1 is a front elevational view illustrating a
preferred embodiment of an electrostatic coating apparatus
according to the present invention;
FIG. 2 is a cross-sectional view for a reciprocal pump
used in the apparatus shown in FIG. l;
FIG. 3 is a front elevational view illustrating another
embodiment of the electrostatic coating apparatus according
to the present invention;
FIG. 4 schematically illustrates a still further
embodiment of the electrostatic coating apparatus according
to the present invention; and
FIG. 5 and 6 are, respectively, a front elevational view
and a top plan view illustrating detailed structures for a
portion of the apparatus shown in FIG. 4.
The present invention will now be described by way of
its preferred embodiments with reference to the drawings.
Structure of the First Embodiment
FIG. 1 is a front elevational view illustrating a
preferred embodiment of the electrostatic coating apparatus
according to the present invention and FIG. 2 is a cross-
sectional view for a reciprocal pump used in the apparatus.
- 5 -
A'
~3~ ~54
In this first embodiment, an electrostatic coating
machine 1 applied with a high DC voltage of about 80-120 KV
is supported on an electrically insulative support 2. In
adjacency with electrostatic coating machine 1, a reciprocal
pump 3 is disposed, in which an electroconductive paint such
as an aqueous paint (hereinafter simply referred to as a
conductive paint) is introduced from an input port 4 and
discharged from an output port 5 at a predetermined flow
rate.
The reciprocal pump 3 is fixed in an electrically
insulated state, to a bracket 6 attached to a housing for the
electrostatic coating machine. The reciprocal pump 3
comprises a cylinder 7 having the output port 5 disposed on
its top end, and a tubular piston rod 9 having a annular
piston 8 disposed on its top end and the input port 4
disposed at its rear end, with the top end of the piston rod
9 being opened in the cylinder 7.
The input port 4 has a female coupler 11 formed at its
connection port for detachably connecting a paint supply pipe
10 for a conductive paint.
The output port 5 has a valve device 15 that switchingly
connects the output port 5 to a paint hose 12 for supplying
the conductive paint discharged from the inside of the
cylinder 7 by the piston 8 of the reciprocal pump 3 to the
electrostatic coating machine 1, or to a drain pipe 14 for
- 6 -
, .
7~ 4
draining the conductive paint remaining in the cylinder 7 to
a liquid waste pipe 13 after the completion of the coating by
means of cleaning air or cleaning liquid supplied from the
paint supply pipe 10.
s
The valve device 15 is adapted such that a pipe 16 used
exclusively for cleaning is connected with the paint hose 12
when the output port 5 is connected with the drain pipe 14.
The drain pipe 14 and the cleaning pipe 16 are secured
to the bracket 6 one above the other and in parallel with the
piston rod 9 of the reciprocal pump 3. The top ends of the
pipes 14 and 16 have a female coupler 17 as a connection port
for detachably connecting the liquid waste pipe 13 and a
female coupler 19 as a connection port for detachably
connecting a cleaning liquid supply pipe 18 respectively for
alternately supplying a cleaning air at low pressure and a
cleaning liquid at low pressure.
Behind the cylinder 7 or the reciprocal pump 3, there
are disposed a driving device 21 that transmits a reciprocal
driving power to the piston rod 9 of the cylinder 7 by way of
an insulative shaft 20, and double-action-type air cylinder
22 that advances and retracts the top end of its piston rod
23 to and from the rear end of the piston rod 9.
The piston rod 23 has a holder 25 formed at its top end
for holding the end of the paint supply pipe 10 for
selectively supplying an aqueous paint of each of a plurality
-- 7
of colors, or cleaning air at a high pressure and a cleaning
liquid at a high pressure from a color-change valve device
24. The holder 25 has a male coupler 26 that engages or
discharges to or from the female coupler ll disposed on the
S input port 4 in order to detachably connect the paint supply
pipe 10 with the input port 4 of the reciprocal pump 3.
Air cylinders 27 and 28 each of an identical type are
disposed in parallel with the air cylinder 22 for advancing
and retracting the top ends of their piston rods 29 and 30 to
and from the female coupler 17 as a connection port on the
side of the drain pipe 14 and the female coupler 19 as the
connection port on the side of the exclusive cleaning pipe
16, respectively.
The air cylinder 27 has a holder 31 disposed on its
piston rod 29, for holding the end of the liquid waste pipe
13. A male coupler 32 is disposed on the holder 31, for
engaging and disengaging the liquid waste pipe 13 to and from
20 the drain pipe 14.
The air cylinder 28 has a holder 33 disposed on its
piston rod 30, for holding the end of the cleaning liquid
supply pipe 18. A male coupler 34 is disposed on the holder
25 33, for engaging and disengaging the cleaning liquid supply
pipe 18 to and from the exclusive cleaning pipe 16.
-- 8
~ ~ 3 ~
Operation of the First Embodiment
The operation of the apparatus of this embodiment, thus
constituted, will be explained below.
S Before starting an electrostatic coating operation, the
driving device 21 is at first actuated to extend the piston
rod 9 toward the rear of the cylinder 7 in the reciprocal
pump 3. Then the air cylinder 22 is actuated to extend the
piston rod 23 toward the piston rod 9 and engage the male
coupler 26 disposed at the top end of the piston rod 23 with
the female coupler 11 disposed at the rear end of the piston
rod 9, to thereby connect the paint supply 10 to the input
port 4 of the reciprocal pump 3.
Then, an aqueous paint of a desired color is selected,
by operating the color-change valve device 24, and the
aqueous paint thus selected is introduced from the paint
supply pipe 10 through the inlet port 4 into the cylinder 7
of the reciprocal pump 3.
When a predetermined amount of the aqueous paint has
been charged into the cylinder, the air cylinder 22 is
actuated again to contract the piston rod 23 in the direction
aparting from the piston rod 9 of the cylinder 7, thereby
detaching the male coupler 26 of the piston rod 23 from the
female coupler 11 on the side of the input port 4.
The female coupler 11 has a structure like that of a
check valve, i.e., opening the connection port on the side of
_ 9 _
h
the input port 4 when it engages the male coupler 26, while
closing the connection port when it disengages from the male
coupler 26. After detaching the paint supply pipe 10 from
the reciprocal pump 3, a predetermined high voltage is
applied to the electrostatic coating machine 1. At the same
time, the driving device 21 is actuated to contract the
piston rod 9 of the cylinder 7 and drive the aqueous paint
charged in the cylinder 7 out of the output port 5 by the
piston 8 disposed at the top end of the piston rod 9 and
supply it through the paint hose 12 to the electrostatic
coating machine 1, thereby starting the electrostatic
coating.
In this state, since the electrostatic coating machine 1
lS is separated and electrically insulated from the paint supply
systems including the paint supply pipe 10, the liquid waste
pipe 13 and the cleaning liquid supply pipe 18, there is no
worry at all that the high voltage applied to the
electrostatic coating machine 1 could cause current leakage
to the latter.
Accordingly, troublesome installation of electrical
insulation means to all of the paint supply systems in a
multi-colored electrostatic coating apparatus for supplying
2S aqueous paints of respective colors is not required.
When the electrostatic coating has been completed after
discharging the aqueous paint from the inside of the cylinder
7, application of the high voltage to the electrostatic
-- 10 --
CA 020311~4 1998-06-01
coating machine 1 is interrupted and the driving device 21 is
actuated to extend the piston rod 9 of the cylinder 7
rearwardly. At the same time, the air cylinder 22 is
actuated to extend the piston rod 23, and the female coupler
11 disposed on the rear end of the piston rod 9 is engaged -
with the male coupler 26 disposed at the top end of the
piston rod 23 to connect the paint supply pipe 10 again to
the input port 4 of the reciprocal pump 3.
In the case of successively coating the aqueous paint of
a color identical with that in the preceding coating process,
the aqueous paint of that color is again supplied from the
color-change valve device 24.
In the case of coating an aqueous paint of a color
different from that in the preceding coating process, the
ouL~u~ port 5 of the reciprocal pump 3 is connected
switchingly from the side of the paint hose 12 to the side of
the drain pipe 14 by the operation of the valve device 15
and, at the same time, the paint hose 12 is connected
switchingly to the exclusive cleaning pipe 16.
Further, the air cylinders 27 and 28 are actuated to
extend the respective piston rods 29 and 30 and engage the
male couplers 32 and 34 formed on the top ends thereof, with
the female coupler 17 on the side of the drain pipe 14 and
the female coupler 19 on the side of the excluding cleaning
pipe 16 respectively, thereby connecting the liquid waste
-- 11 --
~ ~ 3 ~ ~'Ff~
pipe 13 with the drain pipe 14 and connecting the cleaning
liquid supply pipe 18 with the exclusive cleaning pipe 16.
In this state, cleaning air at a high pressure and a
cleaning liquid at a high pressure are supplied alternately
from the color-change valve device 24 through the paint
supply pipe 10 to instantaneously drain the aqueous paint
remaining in the cylinder 7 of the reciprocal pump 3 from the
drain pipe 14 through the liquid waste pipe 13 to the liquid
waste reservoir 35, to clean the inside of the paint supply
pipe 10 and the inside of the cylinder 7. At the same time,
the aqueous paint remaining in the paint hose 12 or
electrostatic coating machine 1 is discharged from the
coating machine 1 by the cleaning air at a low pressure and
by the cleaning liquid at a low pressure alternately supplied
from the cleaning liquid supply pipe 18 through the exclusive
cleaning pipe 16, to clean the inside of the hose 12 and
machine 1.
In this way, the paint remaining in the cylinder 7 of
the reciprocal pump 3 of a large volume is removed by
cleaning with the cleaning air and the cleaning liquid each
supplied at a high pressure, while the paint remaining in the
electrostatic coating machine 1 of a relatively small volume
is removed by cleaning with the cleaning air and the cleaning
liquid each supplied at a low pressure. Accordingly, the
cleaning time can be shortened remarkably and color-change of
paint can be conducted rapidly. In addition, vigorous
- 12 -
s ~ :
scattering of the paint removed from the inside of the
electrostatic coating machine 1 which would otherwise occur
and contaminate the periphery of the apparatus can be
eliminated.
s
Structure of the Second Embodiment
FIG. 3 shows a front elevational view illustrating
another embodiment of the electrostatic coating apparatus
according to the present invention.
In this embodiment, a paint charge pipe 40 is used
instead of the reciprocal pump 3 of the previous embodiment
shown in FIGS. 1 and 2, and the conductive paint charged into
the pipe 40 is driven out by cleaning liquid.
The paint charge pipe 40 capable of containing a
required amount of a conductive paint is connected to an
electrostatic coating machine 1 to be applied with a high
voltage and the pipe 40 has a female coupler 41 and a
connector 42 formed at its rear end, in which flow channels
for both of them are switched alternately by valve 43.
The paint supply pipe 10 and the paint charge pipe 40
are so adapted that they are detachably connected by engaging
and disengaging the male coupler 26 disposed at the top end
of the piston rod 23 shown in FIG. 1 to and from the female
coupler 41 disposed on the rear end of the paint charge
pipe 40.
- 13 -
A cleaning liquid supply pipe 46 is communicated to the
connector 42 by way of a gear pump 45 for supplying a
cleaning liquid stored in a cleaning liquid reservoir 44 at a
predetermined flow rate to the inside of the paint charge
pipe 40 in accordance with the amount of the paint charge
pipe 40 in accordance with the amount of the paint discharged
from the electrostatic coating machine.
The cleaning liquid reservoir 44 is supported on an
electrically insulative ceramic insulator 47.
Operation of the Second Embodiment
At first, the paint supply pipe 10 is connected to the
paint charge pipe 40 and the conductive paint is supplied to
the inside of the pipe 40.
When a predetermined amount of the paint has been
charged in the paint charge pipe 40, the paint supply pipe 10
is disconnected from the pipe 40 and, subsequently, a
predetermined high voltage is applied to the electrostatic
coating machine 1.
In this state, the valve 43 is switched to close the
flow channel on the side of the female coupler 41 and opens
the flow channel on the side of the connector 42. At the
same time, the gear pump 45 disposed at the midpoint of the
cleaning liquid supply pipe is actuated to supply the
cleaning liquid in the cleaning liquid reservoir 44 into the
paint charge pipe 40 at a predetermined flow rate in
- 14 -
accordance with the amount of the paint discharged from the
electrostatic coating machine 1.
Thus, the conductive paint charged in the paint
discharge pipe 40 is driven out at the predetermined flow
rate in accordance with the flow rate of the cleaning liquid
supplied into the pipe 40 and then supplied to the
electrostatic coating machine 1.
In this embodiment, since the inside of the paint charge
pipe 40 has already been cleaned upon completion of the
coating, it is possible to shorten the cleaning time and to
conduct rapid color-change.
Further, since the electrostatic coating can be
conducted in a state in which the electrostatic coating
machine 1 applied with the high voltage is electrically
insulated from the paint supply pipe 10 also in this
embodiment, installation of electric insulation means to the
paint supply systems for the conductive paint is not required
but the insulation means may be disposed only to the cleaning
liquid reservoir 44 and the cleaning liquid supply pipe 46.
As a further modified embodiment, if a female coupler is
disposed instead of the connector 42 and a male coupler is
disposed on the top end of the cleaning liquid supply pipe
46, so that the cleaning liquid supply pipe 46 is detachably
connected to the paint charge pipe 40 in the same manner as
- 15 -
k
in the paint supply 10, application of the insulation means
to the cleaning liquid supply system can be saved.
Structure of the Third Embodiment
FIG. 4 is a flow sheet illustrating a further embodiment
of the electrostatic coating apparatus according to the
present invention, and FIGS. 5 and 6 are, respectively, a
front elevational view and a plan view illustrating a
detailed construction for each of them.
In the third embodiment, an electrostatic coating
machine 1 is connected by way of a paint hose 12 with a
manifold 51 of a color-change valve device 50 having a
plurality of color-change valves CCVl-CCV5.
Tubular insulative supports 52a-52c are arranged in
parallel with the insulative support 2 for the electrostatic
coating machine 1, each of the cylinders 7 for the reciprocal
pumps 3a-3c is attached to each of the ends of the supports,
each of insulative shafts 53 serves as a piston rod for each
of the cylinders 7 and is inserted through the inside of each
support, and each of hydraulic cylinders 54a-54c for
reciprocating each of the insulative shafts 53 is attached to
the rear end of each shaft. Proximity switches 55 and 56 are
disposed for outputting start/stop signals for each of the
hydraulic cylinders 54a-54c.
Further, air valves 57a-57c which are turned on and off
by air signals are attached to the top end of the insulative
- 16 -
~ ,
supports 52a-52c respectively. Each of the valves is
connected at its exit to the input port 4 for each of the
cylinders 7 for the reciprocal pumps 3a-3c and has a female
coupler 58 disposed at its inlet as a connection port on side
of the input port 4.
The output port 5 for each of the cylinders 7 of the
reciprocal pumps 3a-3c is connected to each of the color-
change valves CCV1-CCV3 of the color-change valve device 50
disposed in an electrically insulated state.
An air valve 57d, which is turned on and off by air
signals, is attached at the top end of the insulative support
52c in adjacent with the air valve 57c. The valve 57d is
connected at its exit by way of an exclusive cleaning pipe
59, to the color-change valve CCV4 and has a female coupler
disposed at its inlet as a connection port on the side of the
exclusive cleaning pipe 59.
Double-action type cylinders 61a-61c are disposed at the
rear ends of the insulative supports 52a-52c, respectively,
and air valves 63a-63c which are turned on and off by air
signals are disposed on the top ends of the piston rods 62,
respectively. Each of the air valves 63a-63c is connected at
its inlet with each of paint supply pipes lOa-lOc for
supplying conductive paint of respective colors and has a
male coupler 64 connected at its exit, to be detachably
connected to a female coupler 58 as a connection port on the
side of the input port 4 for each of the reciprocal pump
3a-3c.
- 17 -
CA 020311~4 1998-06-01
Further, the air valve 63d has a cleaning liquid supply
pipe 65 connected at its inlet for supplying a cleaning
liquid, and a male coupler 64' connected at its exit, to be
detachably connected with a female coupler 60 as a connection
port on the side of the exclusive cleaning pipe 59.
A cleaning air supply pipe 66 is directly connected with
the color-change valve CCVs.
Switching valves 67a-67c are disposed for supplying a
hydraulic fluid or oil to a hydraulically operated cylinders
54a-54c and so adapted that they send a hydraulic fluid in a
hydraulic fluid reservoir 71 to each of the hydraulic
cylinders 54a-54c through each pair of pipes 72 and 73, as
well as return the hydraulic fluid discharged from each of
the hydraulic cylinders 54a-54c to the inside of the
hydraulic fluid reservoir 71. In this case, the hydraulic
fluid is cyclically supplied at a predetermined flow rate by
a gear pump 68, regulators 69 and 70 in accordance with the
amount of a paint discharged from the electrostatic coating
machine 1.
Further, there are also provided air valves 74a-74d
for supplying driving air to the air cylinders 61a-61d, and
air valves 75a-75m (except 7si) that output air signals A-C
for switching valves 67a-67c and air signals D-M (except I)
for turning on and off the air valves 57a-57d, and 63a-63d
and the color-change valves CCVl-CCV5.
- 18 -
7~
Operation of the Third Embodiment
At first, driving air is supplied from the air valve 74a
to the air cylinder 61a for extending the piston rod 62 of
the cylinder, and the male coupler 64 attached to the top end
of the piston rod 62 is engaged with the female coupler 58 on
the side of the input port 4 of the reciprocal pump 3a.
In the case of coating a conductive paint supplied from
the paint supply pipe 10a, an air signal D is outputted from
the air valve 75d to the air valves 57a and 63a for turning
both of the air valves 57a and 63a on, thereby connecting the
input port 4 of the reciprocal pump 3a with the paint supply
pipe 10a.
Then, an air signal A is outputted from the air valve
75a to the switching valve 67a for switching the valve 67a
such that the hydraulic fluid in the hydraulic fluid
reservoir 71 is sent through the pipe 73 to the hydraulic
fluid cylinder 54a.
Thus, the cylinder 7 of the reciprocal pump 3a connected
through the insulative shaft 53 to the hydraulic cylinder 54a
is interlocked to suck and introduce the conductive paint
into the inside of the cylinder 7.
In this case, conductive paints each of different color
are also introduced previously from the paint supply pipes
10b and 10c in the same way into the cylinders 7 for the
other reciprocal pump 3b and 3c, respectively.
-- 19 --
A
7 ~ 4
Then, when a predetermined amount of the paint just
sufficient for the coating is charged in the cylinder 7 of
the reciprocal pump 3a, the proximity switch 55 is actuated,
and the switch signal causes the air signal A to output from
the air valve 75a to the air valve 67a for switching the
valve 67a to interrupt~driving for the cylinder 7. At the
same time, the air signal D is outputted from the air valve
75d for turning the air valves 57a and 63a off. Further,
driving air is supplied from the air valve 74a to the air
cylinder 61a for contracting its piston rod 62.
This disengages the paint supply pipe lOa from the input
port 4 of the reciprocal pump 3a again, and the pipe is
electrically insulated from the reciprocal pump 3a.
Further, the cylinder 7 of the reciprocal pump 3a is
also electrically insulated from the hydraulic cylinder S4a
by means of the insulative support 52a and the insulative
shaft 53 inserted into the inside thereof.
In this state, a high voltage is applied to the
electrostatic coating machine 1, an air signal A is outputted
from the air valve 75a to the switching valve 67a for
switching the valve 75a to the switching valve 67a for
switching the valve 67a such that the hydraulic fluid in the
hydraulic fluid reservoir 71 is sent through the pipe 72 to
the hydraulic cylinder 54a. At the same time, an air signal
H is outputted from the air valve 75h for turning the color-
change valve CCVl on, thereby discharging the conductive
- 20 -
A
paint introduced into the cylinder 7 of the reciprocal pump
3a from the output port 5 by the power of the hydraulic
cylinder 54a and supplying the paint at a constant flow rate
to the electrostatic coating machine 1. Thus, there is no
worry that the high voltage applied to the electrostatic
coating machine 1 coul~d cause current leakage to the paint
supply systems such as the paint supply pipe lOa and
troublesome installation of electric insulation means is no
more required.
Subsequently, when the coating with the paint supplied
from the paint supply pipe lOa has been completed, the color-
change valve CCV1 is turned off by the air signal H from the
air valve 75h and the color-change valve CCVs is turned on by
an air signal M from the air valve 75m to drive the paint
remaining in the manifold 51 of the color-change valve device
50, the paint hose 12 and the electrostatic coating machine 1
out of the coating machine 1 by pressurized air supplied
through the cleaning air supply pipe 66. Then, the
application of the high voltage to the coating machine 1 is
interrupted.
Then, an air signal G is outputted from the air valve
75g to the air valves 57d and 63d for turning both of the
valves to on, and driving air is supplied from the air valve
74d to the air cylinder 61d for extending the piston rod 62
of the air cylinder 61d, to engage the male coupler 64'
disposed at the top end of the piston rod 62 with the female
coupler 60 and connect the cleaning liquid supply pipe 65~0 with the exclusive cleaning pipe 59.
- 21 -
Next, the color-change valve CCV4 is turned on by the
air signal L from the air valve 751 and the inside of the
manifold 51, the inside of paint hose 21 and the inside of
the electrostatic coating machine 1 are cleaned with the
cleaning liquid supplied from the cleaning liquid supply pipe
65 through the exclusiye cleaning line 59. Subsequently,
pressurized air is again supplied from the cleaning air
supply pipe 66 to drive out the cleaning liquid remaining in
the path from the inside of the manifold 51 to the inside of
the electrostatic coating machine 1.
After the cleaning has been completed by repeating the
above-mentioned procedures for several times, an air signal G
is outputted from the air valve 75g for turning the air
valves 57d and 63d off, and driving air is supplied from the
air valve 74d to the air cylinder 61d for contracting the
piston rod 62 thereof, by which the cleaning liquid supply
pipe 65 is disengaged from the exclusive cleaning pipe 59 to
electrically insulate both of them from each other.
Accordingly, when the high voltage is applied again to
the electrostatic coating machine 1 for starting the coating
after the cleaning has been completed, there is no worry that
the high voltage could cause current leakage to the cleaning
liquid supply systems including the cleaning liquid supply
pipe 65 and the like.
- 22 -
f~ Jd ~
In this embodiment, if the cleaning air supply pipe 66
is made of electrically insulative material, there is no
worry for the current leakage due to the high voltage, even
if it is directly connected with the color-change valve
device 50.
Further, since there is no requirement to clean the
inside of each of the cylinders 7 of the reciprocal pumps
3a-3c upon color-change, the time required for color-change
can be shortened remarkably, by the remarkable shortening of
the cleaning time.
Although each of the cylinders 7 of the reciprocal pumps
3a-3c for supplying the conductive paint at a predetermined
amount to the electrostatic coating machine 1 is driven by
respective of the hydraulic cylinders 54a-54c in this
embodiment, the cylinder may be driven also by an air motor
or the like by adapting the insulative shaft 53 as the piston
rod for the cylinder 7 such that the shaft is moved by a
screw-feed mechanism that converts the rotational movement
into a linear reciprocal movement into a linear reciprocal
movement.
Further, the reciprocal pumps 3a-3c are not limited only
to the hydraulic cylinders but they may be constituted, for
example, as diaphragm pumps. As has been described above
according to the present invention, troublesome installation
of insulation means to the paint supply systems is not
necessary, even when an electroconductive paint such as an
- 23 -
~,~,
aqueous paint is used in electrostatic coating machine
applied with a high voltage.
Furthermore, since the multi-color electrostatic coating
apparatus according to the present invention is adapted such
that installation of insulation means can be saved, not only
for the paint supply systems for paints of respective colors,
but also for the cleaning liquid supply system and also such
that the cleaning time upon color-changeable can be shortened
remarkably, it is possible to positively promote the change
of coating material for electrostatic coating from insulative
resin paints requiring a great amount of deleterious organic
solvents, to aqueous paints free from public pollution, which
can provide high usefulness in view of the environmental
protection.
- 24 -
