Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2019~i~8
CLEANING METHOD AND SYSTEM USING A SOLVENT
BACKGROUND OF THE INVENTION
The present invention relates to a cleaning method
and system for cleaning an article with a solvent, and
particularly but not exclusively relates to a cleaning
method and system for cleaning an article, such as a
metallic mold, a porous sintered metal and an integrated
circuit substrate, using an organic solvent such as Freon
(Tradename), trichloroethylene and the like substance.
Heretofore, cleaning systems using an organic
solvent, such as Freon and trichloroethylene, are widely
used for removing soil adhered to such an article to be
cleaned. For cleaning the article, an airtight cleaning
tank in which the article is to be placed is evacuated by
a vacuum pump so that an organic solvent can easily soak
to fine irregular surfaces and fine cavities of the
article, and then the organic solvent is supplied from a
solvent storing tank into the cleaning tank through a
solvent supply pipe. After supplied, the organic solvent
is oscillated by means of an ultrasonic oscillator or is
agitated by agitating blades to remove soil, such as an
oil, adhered to the surfaces of the article. When the
article is not cleaned by a single operation, the organic
solvent is discharged from the cleaning tank, which is
then evacuated by the vacuum pump again. Thereafter, the
organic solvent is reintroduced into the cleaning tank
and then the article undergoes the cleaning operation.
After accomplishing the cleaning, a solenoid valve of a
drain pipe which connects the cleaning tank to the
storage tank is opened and a draining pump, installed in
the drain pipe, is activated to discharge the liquid
organic solvent from the cleaning tank into the storage
tank. Then, the article is taken out from the cleaning
tank.
In the conventional cleaning system, leakage of part
of vapor of the organic solvent to the atmosphere is
'I
2 201~S~8
inevitable in supplying and discharging of the organic
solvent, and this can results in pollution of the
environment. More specifically, the conventional
cleaning system has a suction and exhaust pipe mounted to
the top of the cleaning tank for communication to the
atmosphere, and in addition a gas mixture of air and
vapor of the organic solvent is present in an upper space
of the storage tank. When the volume of the upper space
of the storage tank is reduced by introducing the liquid
organic solvent into the storage tank after the cleaning,
the gas mixture in the upper space is discharged to the
atmosphere through the suction and exhaust pipe, thus
contaminating the environment. Particularly, leakage of
Freon which is widely used as an organic solvent for
cleaning should be as little as possible since it is
rep~rted that it will destroy the ozone layer, resulting
in destruction of the global environment.
Accordingly, it is an object of the present
invention to prov-ide a cleaning method and system in
which in cleaning, leakage of the solvent to the
atmosphere is prevented with efficient use thereof,
whereby the problem to prevent pollution of the
environment with the solvent is solved.
SUMMARY OF THE INVENTION
With this and other objects in view, one aspect of
the present invention is directed to a cleaning method
using a solvent. A cleaning tank is closed after an
article to be cleaned is placed within the cleaning tank.
The solvent is supplied to the cleaning tank from a
solvent storage tank. The article is cleaned with the
supplied solvent. After the cleaning, the solvent is
discharged in liquid state from the cleaning tank while
vapor of the solvent which remains in the cleaning tank
is discharged to a condenser to condense the vapor. The
condensed solvent is returned from the condenser into the
solvent storage tank. After the liquid solvent and the
vapor solvent are discharged from the cleaning tank, the
~a ~ ~ 5 7 ~
cleaned article is taken out of the cleaning tank.
Before the cleaning tank is opened to take out the
cleaned article, air is introduced into the cleaning
tank during at least a last part of the vapor solvent
discharging step.
According to another aspect of the present
invention, there is provided a cleaning system using a
solvent, including: a tubular cleaning tank including
a cleaning tank body having an upper open end and a
closed bottom wall of a downwardly concave shape to
which an ultrasonic oscillator is secured, the cleaning
tank body being adapted to receive an article to be
cleaned, and a closure for sealingly closing the upper
open end of the cleaning tank body; a storage tank for
storing the solvent, the storage tank having an upper
space filled with vapor of the solvent when the solvent
is stored; a solvent supplying mechanism connecting the
storage tank to the cleaning tank for supplying the
solvent from the storage tank to the cleaning tank for
cleaning the article; and a solvent distiller,
communicating with both the cleaning tank and the
storage tank for distilling the solvent from the
cleaning tank and returning the distilled solvent to
the storage tank.
In another aspect the invention resides in a
method of cleaning articles with a solvent while
preventing discharge of solvent vapor to the
environment, comprising the steps of:
closing a cleaning tank after an article to be
cleaned is placed within the cleaning tank;
supplying the solvent into the cleaning tank from
a solvent storage tank which is isolated from said
cleaning tank and is communicatively connected to a
solvent condenser;
cleaning the article to be cleaned with the
-
~0 1!~57~
3a
solvent supplied into the cleaning tank;
after the cleaning step, discharging the solvent
in liquid state from the cleaning tank into the solvent
storage tank to raise the liquid solvent level in the
solvent storage tank thereby to force solvent vapor
above the level into said solvent condenser so as to
condense the solvent vapor in the condenser and then to
return the condensed solvent back into the solvent
storage tank;
after the cleaning step, discharging vapor of the
solvent which remains in the cleaning tank into said
solvent condenser and condensing the
returning the condensed solvent, which is derived
from within said cleaning tank, from the condenser into
the solvent storage tank; and
after the liquid solvent discharging step and the
vapor solvent discharging step, sealing off the
cleaning tank from the solvent storage tank and the
condenser, than re-opening the cleaning tank and taking
out the cleaned article.
In a further aspect the invention resides in a
cleaning system using solvent, comprising:
a cleaning tank including a cleaning tank body
having an upper open end and a closed bottom, the
cleaning tank body being adapted to receive an article
to be cleaned, and a closure for sealingly closing the
upper open end;
a storage tank for storing a solvent, the storage
tank having an upper space filled with vapor of the
solvent when the solvent is stored, said upper space
being connected to a vapor supplying means for passing
vapor of the solvent to the upper space, the vapor
supplying means including a heater for heating and
supplied vapor;
solvent supplying means connecting the storage
5 ~ ~
3b
tank to the cleaning tank for supplying the solvent
from the storage tank to the cleaning tank for cleaning
the article;
solvent discharging means for discharging the
solvent in liquid state from the cleaning tank;
a solvent distiller, communicating with both the
cleaning tank and the storage tank, for distilling the
solvent from the cleaning tank and returning the
distilled solvent to the storage tank;
a pressure sensor for sensing pressure in the
cleaning tank to provide a pressure signal representing
the pressure in the cleaning tank; and
a controller for controlling, in response to the
pressure signal, the relative rates of the discharge of
the liquid solvent and the supply of the solvent vapor
for maintaining the pressure in the cleaning tank
negative.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a diagrammatic view, in vertical
section, illustrating a cleaning system according to
the present invention;
FIG. 2 is a diagrammatic vertical sectional view
of a modified form of the cleaning system in FIG. 1;
FIG. 3 is a diagrammatic view, in vertical
section, of a modified form of the cleaning tank of
FIG. 1;
FIGS. 4 and 5 are diagrammatic vertical sections
of modified forms of combined storage tank and
distiller;
FIG. 6 is a diagrammatic view, in vertical
section, showing a vapor supplying unit for supplying
vapor of a solvent to the storage tank of FIG. 2;
4 20~7~
FIG. 7 iS a diagrammatic view, in vertical section,
illustrating a vapor supplying unit for supplying vapor
of the solvent to the cleaning tank;
FIGS. 8 and 9 are enlarged diagrammatic views, in
vertical section, showing modified forms of a second
condenser of the distiller in FIG. 2, respectively;
FIGS. 10 and 11 are diagrammatic vertical sectional
views of modified forms of the distiller in FIG. 1,
respectively:
FIG. 12 is a diagrammatic view showing a controlling
system for preventing pressure in the cleaning tank of
FIG. 2 from becoming negative;
FIG. 13 is a vertical section of a cleaning tank
body of a conventional cleaning tank;
FIG. 14 is a vertical section of a cleaning tank
body used in a mode of the present invention;
FIG. 15 is a diagrammatic view of a modified form of
the cleaning system in FIG. 2, with essential elements in
vertical section;
FIG. 16 is an enlarged diagrammatic view of a unit
for preventing condensation of water in the distiller of
the present invention, with essential elements in
vertical section;
FIG. 17 is an enlarged diagrammatic view of a
modified form of the distiller in FIG. 16, with essential
elements in vertical section;
FIG. 18 is an enlarged diagrammatic view, in
vertical section, of a modified form of the distiller of
FIG. l;
FIG. 19 is a diagrammatic view, partly in section,
of a system for preventing bumping of the liquid organic
solvent in the vapor generator;
FIG. 20 is a diagrammatic view illustrating a
further modified form of the cleaning system;
FIG. 21 shows a partial view of an improvement of
the system of FIG. 20; and
2~3~78
FIG. 22 is a partial view of a still further
improved cleaning system.
- DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described with
reference to the accompanying drawings, in which like
reference numerals indicate corresponding parts
throughout several embodiments thereof and descriptions
thereof are omitted after once given.
Referring now to FIG. 1, reference numeral
designates a cleaning tank with an open upper end, which
is closed with a closure 12 in an airtight manner. The
cleaning tank 1 is provided at its bottom with ultrasonic
oscillators 11 for oscillating a liquid organic solvent
in it to efficiently clean an article 2 to be cleaned
which is immersed in the solvent.
Located at a higher lever than the cleaning tank 1
is a solvent storing tank 3, which is connected at its
conical bottom to a middle portion of the cleaning tank 1
through a supply pipe 4 including a solenoid valve 5. By
opening the solenoid valve 5, a liquid organic solvent in
the storage tank 3 gravitates into the cleaning tank 1
through the supply pipe 4. The storage tank 3 is
communicated at its upper portion to an intermediate
portion of a distiller 14 (or a trough 21 of a condenser
16) through a connecting pipe 13 so that the organic
solvent in liquid and gas state is sent from the
distiller 14 to the storage tank 3 for filling a top
space 10 of the storage tank 3 with gas of the organic
solvent.
The cleaning tank 1 communicates at its bottom
portion with an upper portion of the storage tank 3
through a drain pipe 6 which is provided with a solenoid
valve 7 and a liquid transfer pump 8. When the solenoid
valve 7 is opened, the organic solvent in the cleaning
tank 1 is returned to the storage tank 3 by actuating the
liquid transfer pump 8.
6 2 0 ~ 7 8
The distiller 14 has an evaporator 15 disposed at
its lower portion and the condenser 16 arranged at its
upper portion. The evaporator 15 is provided with a
tubular casing 17 having a closed bottom for storing the
organic solvent in liquid state and has a heater 18
mounted within a bottom portion of the casing 17 for
evaporating the liquid organic solvent. The condenser 16
has a tubular casing 19 closed at its upper open end with
a closure 12. In the casing-l9, a cooler 20 in the shape
of a coil is arranged in the vicinity of the inner wall
thereof for condensing vapor of the organic solvent. The
evaporator casing 17 is smaller in horizontal cross-
sectional area than the condenser casing 19. The
evaporator casing 17 passes through the bottom of the
condenser casing 19 so that the upper end thereof
projects from the bottom. The projected upper end of the
evaporator casing 17 and the bottom portion of the
condenser casing 19 define an annular condensed organic
solvent trough 21. The cooler 20 is located immediately
above the annular condensed organic solvent trough 21 so
that the organic solvent which is condensed by contacting
the cooler 20 drops into the condensed organic solvent
trough 21.
The cleaning tank 1 communicates at its upper
portion to an intermediate portion of the evaporator 15
through a vapor discharge pipe 24, which is provided with
a solenoid valve 22 and a vacuum pump 23. A vapor
organic solvent in the upper portion of the cleaning tank
1 is pumped by the vacuum pump 23 to the distiller 14
where it is condensed. In FIG. 1, reference numeral 25
indicates an air suction pipe to introduce air into the
upper portion of the cleaning tank 1, and 26 designates a
solenoid valve disposed in the air suction pipe 25.
In cleaning the article 2 to be cleaned, the closure
12 of the cleaning tank 1 is opened, and the article 2 is
placed into the cleaning tank 1. Then the closure 12 is
closed. Subsequently, the solenoid valve 5 is opened to
7 2UI~378
send the organic solvent in the storage tank 3 through
the feed pipe 4 to the cleaning tank 1, where the article
- 2 to be cleaned is subjected to ultrasonic cleaning by
actuating the ultrasonic oscillators 11. After
completion of the cleaning, the liquid transfer pump 8 is
actuated with the solenoid valve 7 opened for returning
the liquid organic solvent to the storage tank 3 through
the drain pipe 6. As the liquid solvent returns to the
storage tank 3, the level of the liquid solvent within
the storage tank 3 rises, so that the volume of a vapor
solvent space 10 in the upper portion of the storage tank
3 is reduced. This results in that vapor of the solvent
filled in the vapor solvent space 10 is forcedly sent
through the connecting pipe 13 to the trough 21, through
which the vapor solvent enters the condenser 16 of the
distiller 14. In the condenser 16, the vapor solvent is
cooled and condensed by the cooler 20 arranged along the
inner wall of the casing 19 of the condenser 16. The
resulting liquid solvent is received in the trough 21 and
then returned to the storage tank 3 through the
connecting pipe 13.
After the whole liquid solvent in the cleaning tank
1 is returned to the storage tank 3, the solenoid valve
22 is opened and the vacuum pump 23 is activated, so that
vapor of the solvent remaining in the cleaning tank 1 is
discharged to the evaporator 15 of the distiller 14
through the vapor discharge pipe 24. The vapor solvent
thus returned to the evaporator 15 flows upwards together
with solvent vapor already existing in the evaporator lS
into the condenser 16, where it is liquefied by the
cooler 20 and then trapped in the condensed solvent
trough 21, from which it is returned to the storage tank
3 through the connecting pipe 13.
When a pressure sensor detects that the pressure in
the cleaning tank 1 reaches a predetermined vacuum level,
it provides an electric signal representing the pressure
level to a controller, which in response to this signal
~0~78
closes the solenoid valve 22, deactivates the vacuum pump
23 and opens the solenoid valve 26 to introduce air into
the cleaning tank 1 through the suction pipe 25 to raise
pressure in the cleaning tank 1. When the pressure in
S the cleaning tank 1 reaches atmospheric pressure, the
closure 12 of the cleaning tank 1 is opened to take out
the cleaned article 2.
To regenerate the solvent which has become
contaminated by repeated use, the liquid solvent in the
storage tank 3 may be sent to the evaporator 15 of the
distiller 14 through a regeneration pipe 27 indicated by
the dot-and-dash line in FIG. 1.
Although in this embodiment the evaporator 15 and
the condenser 16 are integrally combined to constitute
the distiller 14, they may be formed separately. In FIG.
1, the condenser casing 19 is built in an airtight manner
and in this case pressure therein must be kept within a
predetermined range by regulating both the power supply
to the heater 18 and the supply of the coolant to the
cooler 20. The condenser casing 19 may be made
communicative with the atmosphere through a communicating
pipe (not shown) which is connected to a top portion
thereof, in which case the power supply to the heater 18
and the supply of the coolant to the cooler 20 must be
also controlled so that the vapor of the solvent may not
be discharged from the condenser 16 to the atmosphere
through the communicating pipe.
With such a construction, the cleaning system of
this embodiment prevents vapor of the solvent from being
released to the atmosphere and hence provides a
significant advantage in protecting the environment.
A modified form of the cleaning system is
illustrated in FIG. 2, in which there is provided a vapor
supplying unit which includes an evaporator 34, having a
heater 33 for evaporating a liquid organic solvent in it,
and a vapor supplying pipe 36 having a solenoid valve 35.
The vapor supplying pipe 36 connects an upper portion of
9 201~78
the evaporator 34 to an upper portion of the cleaning
tank 1 for sending organic solvent vapor in the upper
- portion of the evaporator 34 to the cleaning tank 1 by
opening the solenoid valve 35. The condenser 16
communicates at its closure 12, which closes the open
upper end of the condenser casing 19, with an activated
carbon filter 29 through exhaust pipe 30. The exhaust
pipe 30 is provided with a secondary condenser 32 having
a cooler 31. In this modification, the vapor discharge
pipe 24 is divided at a position downstream of the vacuum
pump 23 into a first branch pipe 40 leading to the
evaporator 15 and a second branch pipe 41 communicating
with the filter 29. The first and second branch pipes 40
and 41 are provided with solenoid valves 42 and 43,
respectively.
In operation of the modified system, after the
article 2 to be cleaned is placed in the cleaning tank 1
as shown in FIG. 2, the vacuum pump 23 is actuated with
the solenoid valve 22 opened so that the cleaning tank 1
is evacuated. In this case, the first solenoid valve 42
is closed while the second solenoid valve 43 is opened.
Thus, vapor which is drawn from the cleaning tank 1 is
introduced through the second branch pipe 41 into the
activated carbon filter 29, where a small amount of the
residual solvent which has been used in the previous
cleaning operation and remaining in the evacuated vapor
is absorbed in the activated carbon filter 29. The
resulting filtered vapor is discharged into the
atmosphere, and hence release of the solvent into the
atmosphere is prevented. After the evacuation of the
cleaning tank 1, the solenoid valve 5 is opened to supply
the solvent from the storage tank 3 into the cleaning
tank 1. The supply of the solvent is efficiently and
rapidly performed under the effect of the vacuum suction
as well as the effect of gravity. After the cleaning
tank 1 is supplied with a sufficient amount of the
--~ 2 ~ ~L 9 ë~ 7 ~3
solvent, the cleaning of the article 2 to be cleaned is
carried out by energizing the ultrasonic oscillators 11.
To increase the efficiency of the cleaning of the
article 2, the liquid supply pipe 4 may be connected, as
shown in FIG. 3, to a shower nozzle 45 which is mounted
to the inner surface of the closure 12 for spraying the
organic solvent to the article 2. In addition, an
agitator or a circulating pump (both members not shown)
may be mounted within the cleaning tank 1 to circulate
the organic solvent. However, when the article 2 to be
cleaned is weak against physical damages, it may be
merely immersed in the organic solvent in cleaning tank 1
without undergoing any additional operation including
ultrasonic oscillation.
After cleaning with the liquid solvent, the liquid
transfer pump 8 is activated at a low speed to gradually
return the liquid solvent to the storage tank 3. At the
same time, the heater 33 of the evaporator 34 is actuated
with the solenoid valve 35 opened, so that vapor of the
sol~vent at a relatively high temperature is supplied from
the evaporator 34 to the cleaning tank 1.
This results in that as part of the article 2 to be
cleaned is placed above the level of the solvent and
exposed to the solvent vapor, the solvent vapor is
condensed by contact with the exposed part of the article
2. Thus, the article 2 to be cleaned is subjected to the
so called vapor cleaning in which the surfaces thereof
undergoes finish cleaning by the clean condensed solvent.
During the vapor cleaning, part of the article 2 to be
cleaned is exposed to the vapor solvent and the rest is
immersed in the liquid solvent, and hence the difference
in temperature between the article 2 and the vapor
solvent is kept sufficient to condense the vapor, thereby
providing a sufficient amount of condensed solvent to the
exposed surfaces of the article 2 to be cleaned.
In contrast to this, when the vapor cleaning is
performed with the whole article 2 placed above the
-
11 2019~78
liquid solvent, the temperature of the article rises as
the solvent vapor is condensed, so that the temperature
difference between them is reduced with resultant
considerable decrease in the efficiency of condensation
of the vapor. This decreases the efficiency of the vapor
cleaning. When the vapor cleaning is carried out with
part of the article 2 immersed in the liquid solvent as
in this modified form, the immersed part of the article 2
is cooled with the liquid solvent, thereby sufficiently
keeping the temperature difference between the article 2
and the solvent vapor to efficiently condense the vapor
by contact with the exposed surfaces of the article.
~ uring the vapor cleaning, the liquid solvent in the
cleaning tank 1 may be sent back to the storage tank 3 by
raising the pressure of the vapor solvent. In this case
the liquid transfer pump 8 may be omitted. By raising
the pressure in the cleaning tank 1 during the vapor
cleaning, the amount of the condensate increases, so that
the efficiency of the vapor cleaning is further
increased.
The transportation of the solvent between the
cleaning tank 1 and the storage tank 3 may be made only
by means of pumps. How to transport the solvent is
determined in view of the physical nature of the article
2 to be cleaned, the scale of the equipment, and other
factors.
After the whole amount of the organic solvent is
returned to the storage tank 3 during the vapor cleaning,
the organic solvent vapor remaining in the cleaning tank
1 is returned to the distiller 14 through the discharge
pipe 24 and then through the first branch pipe 40 for
condensation. To do so, the vacuum pump 23 is activated
with the solenoid valves 22 and 42 opened and the
solenoid valve 43 closed. When the pressure in the
cleaning tank 1 drops to a predetermined vacuum level,
the controller closes the solenoid valve 22 and
deactivates the vacuum pump 23. At the same time, the
12 20~9578
controller opens the solenoid valve 26 to suck air into
the cleaning tank 1 through the suction pipe 25. This
raises the pressure in the cleaning tank 1 to atmospheric
pressure, at which the closure 12 is opened to take out
the article 2 cleaned.
In this modified cleaning system, the level of the
solvent vapor in the condenser 16, that is, the level of
the interface between the solvent vapor and the air in
the condenser 16 varies in response to introducing and
stopping of the solvent vapor through the first branch
pipe 40. The larger the variation in the level of the
solvent vapor in the condenser 16, the easier the
discharging of the gas mixture including the solvent
vapor into the exhaust pipe 30. This variation of the
level may be reduced by appropriately adjusting the power
supply to the heater 18 and the supply of the coolant to
the cooler 20, whereby discharge of the solvent vapor
through the exhaust pipe 30 may be made as small as
possible.
In the cleaning system in FIG. 2, the secondary
condenser 32 including the cooler 31 fairly reduces the
amount of the solvent vapor exhausted through the exhaust
pipe 30, and the activated carbon filter 29 absorbs a
small amount of solvent vapor which is inevitably
exhausted without being condensed by the second condenser
32.
A modified form of the secondary condenser 32 of
FIG. 2 is illustrated in FIG. 8, in which a trap pipe 45
branches off from the exhaust pipe 30 upstream of the
secondary condenser 32 and communicates with the
evaporator 15. With such a construction, the trap pipe
which returns the condensate from the secondary
condenser 32 to the evaporator 15 is independent from the
exhaust pipe 30 which exhausts the gas mixture from the
primary condenser 16, and hence both the discharge of the
gas mixture from the primary condenser 16 and the return
13 201~ ~7 ~
flow of the condensate to the evaporator 15 are
efficiently and smoothly performed.
When the distiller 14 is of a sealed type to which
no exhaust pipe 30 is furnished, pressure in the
distiller 14 is regulated by adjusting the power supply
to the heater 18 and the supply of the coolant to the
cooler 20 so that the pressure is not excessively high or
low.
As illustrated in FIG. 9, the condenser 16 may be
provided with a suction pipe 47 and an exhaust pipe 30.
The suction pipe 47 has a check valve 48 which admits air
into the condenser 16 while the exhaust pipe 30 is
provided with a check valve 49 which allows a gas to flow
to the atmosphere.
15Although the storage tank 3 and the distiller 14 may
be provided independently as in FIG. 2, the upper portion
of the storage tank 3 may, as shown in FIG. 4,
communicate with the upper portion of the evaporator
casing 17. As illustrated in FIG. 5, a plurality of
storage tanks 3 may be connected in series, and the
liquid supply pipe 4 may be connected to the downstream
storage tank or lowermost storage tank 3.
In the cleaning system of FIG. 2, the upper space of
the evaporator 15 of the distiller 14 and the upper space
of the storage tank 3 are communicated to fill the latter
with the solvent vapor. As illustrated in FIG. 6, the
upper space of the storage tank 3 may communicate with an
evaporator 34A for supplying vapor of the solvent to it.
The evaporator 34A may be also used as the evaporator 34
for supplying vapor of the solvent to the cleaning tank
1. In the storage tank 3 of FIG. 4, the upper space
thereof is supplied with the solvent vapor from the
evaporator 17 and hence it does not need any evaporator
34A.
35Although in FIG. 2, the upper space of the cleaning
tank 1 is supplied with the solvent vapor from the
evaporator 34, the supply of the solvent vapor may be
14 2 ~ 7 ~
carried out by communicating, as shown in FIG. 7, the
upper space of the cleaning tank 1 with the upper space
of the evaporator 15 of the distiller 14 through a pipe
51 with a solenoid valve 50.
In the cleaning system of FIG. 2, the vacuum pump 23
serves to discharge both air and solvent vapor from the
cleaning tank 1 but two vacuum pumps may be provided to
respective independent lines communicating with the
cleaning tank 3, one serving as an air exhausting vacuum
pump and the other as a solvent vapor exhausting vacuum
pump.
In place of the distiller 14 in FIGS. 1 and 2, a
distiller shown in FIG. 10 may be adopted, in which the
condenser 16 is smaller in diameter than the evaporator
and is built in the latter. Alternatively, the
evaporator 15 and the condenser 16 may be separately and
independently arranged as illustrated in FIG. 11. In
these modified distillers 14, the liquid solvent in the
storage tank 3 may be sent to the evaporator 15 through
the pipe 27 as in FIG. 2 for regenerating the solvent
which has been contaminated by repeated use.
In the preceding cleaning systems of the present
invention, pressure in the cleaning tank 1 can exceed
atmospheric pressure, that is, it can become positive as
the cleaning operation progresses, thereby causing
leakage of vapor of the solvent. When an organic solvent
such as Freon (Tradename) is used as the solvent, a
clamping mechanism is thus needed to clamp the closure 12
against the packing, which is provided to the upper open
end of the cleaning tank body for sealing. Such a
clamping mechanism makes the cleaning tank 1 rather
complicated. In addition, poor airtightness of the
closure 12 due to loose clamping or damage of the packing
can cause leakage of vapor of the organic solvent from
the cleaning tank 1 to the atmosphere, which may cause
destruction of the ozone layer.
- ' 2 ~ 7 8
Also in the case where a cleaning liquid other than
the organic solvent is used and highly infectious
bacteria adhere to an article to be cleaned, the
airtightness of the closure 12 must be sufficiently high
and another problem of contamination of the environment
can occur.
FIG. 12 illustrates a control system which overcomes
the problem above mentioned. The control system is
provided with a controller 54 which is connected to a
pressure sensor 53 which provides a pressure detection
signal representing the pressure of the vapor organic
solvent at the upper portion of the cleaning tank 1. In
response to the pressure detection signal, the controller
54 controls at leàst one of the heater 33 of the vapor
supply unit 34 and the liquid transfer pump 8 so that the
discharge of the liquid solvent from the cleaning tank 1
exceeds the supply of the vapor solvent into it thereby
to keep the pressure in the upper space of the cleaning
tank 1 always negative.
In this modified form, the supply of the vapor
organic solvent is regulated by controlling the power
supply to the heater 33 of the vapor supply unit 34 but
it may be adjusted by a flow-passage-area-variable
solenoid valve 55 provided in the pipe 36. The flow
passage area of the solenoid valve 55 is controlled by
the controller 54 in response to the pressure detection
signal. In this modification, the control of the power
supply to the heater 33 is not necessary for regulating
the supply of the vapor solvent but it saves useless
power consumption. Such a flow-passage-area-variable
solenoid valve may be used as the solenoid valve 7 which
communicates with the liquid transfer pump 8 for
regulating the discharge of the cleaning liquid from the
cleaning tank 1.
To positively prevent leakage of the vapor of the
cleaning liquid, it is preferable to operate the vacuum
pump 23 (FIG. 2) of the vapor discharge pipe 24 to keep
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16 20~78
the pressure in the cleaning tank 1 negative during the
cleaning of the article 2 to be cleaned with the cleaning
liquid.
The conventional cleaning tank is built by welding a
flat plate 60 to the bottom of a cleaning tank body as
shown in FIG. 13. As the flat plate 60, a rather thick
plate, a steel plate about 5 mm thick for example, is
used to withstand pressure when the cleaning tank 1 is
evacuated. However, such a thick plate makes it
difficult to transmit oscillation of the ultrasonic
oscillators 11 to the cleaning liquid of the organic
solvent in the cleaning tank 1, thus decreasing the
e~ficiency of thé cleaning of the article 2 to be
cleaned. To avoid the decrease in the efficiency, the
ultrasonic oscillators 11 must be large sized.
The cleaning tank illustrated in FIG. 14 solves this
problem. The cleaning tank body of the cleaning tank 1
is in the shape of a hollow cylinder with a closed bottom
and is composed of a hollow cylindrical wall portion 61
and a bottom portion 62 welded at its upper open end to
the lower open end of the wall portion 61. Although not
shown, the wall portion 61 is provided at its inner wall
with a cleaning liquid supply port directed in a
tangential direction of the wall portion 61. In
addition, the bottom portion 62 has a cleaning liquid
drain port (also not shown) formed through the center of
its bottom, the cleaning liquid drain port communicating
with the supply port through a pipe with or without a
filter. By circulating the cleaning liquid, it may be
moved spirally in the cleaning tank 1 about the center
thereof. The cleaning tank body is used with a closure
on the upper end thereof and an ultrasonic oscillators
arranged on the bottom thereof as illustrated in FIG. 1.
The bottom portion 62 has a downwardly convex bottom, and
the ultrasonic oscillators are mounted directly to the
outer surface of the downwardly convex bottom or
indirectly to it through a mounting plate (not shown).
-
17 20 ~ 9~7~
For this purpose, the ultrasonic oscillators or the
mounting plate has a shape complementary to the convex
shape of the bottom.
The cleaning tank body is curved outwards at the
bottom and hence has a sufficient strength against
pressure even if the bottom portion is made thinner than
the bottom plate 60 of the ordinary cleaning body. The
bottom of the bottom portion 62 may have a bowl shape or
a semispherical shape. According to design calculation
by the inventors, the bottom portion 62 having a
thickness 1.5 mm is sufficient to withstand pressure due
to evacuation of the cleaning tank 1 for the cleaning
tank body having a circumferential wall portion 61 with
an inner diameter 300 mm and the bottom with a curvature
radius 450 mm.
In the cleaning system of FIG. 2, before the
cleaning operation is commenced with the closure 12
closed, the vacuum pump 23 is actuated to evacuate the
cleaning tank 1 so that the article 2 to be cleaned is
fully soaked with the organic solvent. However, a small
amount of air necessarily remains in the cleaning tank 1
because of the capacity of the vacuum pump 23. When
under such a condition, the organic solvent is introduced
into the cleaning tank 1 through the pipe 4, the
remaining air is trapped in the upper space of the
cleaning tank 1, and hence the pressure in the upper
space increases by the partial pressure of the residual
air. When a cleaning tank 1 is used in which the
pressure becomes positive by introducing the solvent,
such as Freon or the like substance, rather complicated
accompanying equipment is needed as described before. To
keep the upper space of the cleaning tank 1 at relatively
low pressure the proportion of the volume of the upper
space over the total volume of the cleaning tank 1 may be
made large. However, this reduces the volume of the
space where the liquid solvent is contained for cleaning,
that is, the total volume of the cleaning tank 1 minus
18 2 ~ 7 8
the volume of the upper space. Thus, the cleaning tank 1
has a smaller upper limit of the volume of the article 2
to be cleaned or it must be made larger for a given
volume of the article 2 to be cleaned.
This problem is solved by the following two methods,
in both of which the cleaning operation is carried out
under negative pressure in the cleaning tank 1 produced
by operating the vacuum pump 23. According to the first
method, the closure 12 is opened, the article 2 to be
cleaned is placed in the cleaning tank 1 and then the
closure 12 is closed in an airtight manner. Thereafter,
the organic solvent is supplied from the storage tank 3
to the cleaning tank 1 through the pipe 4, and in this
condition, the vacuum pump 23 is continually actuated to
evacuate air remaining in the upper space-of the cleaning
tank 1.
In the second method, the vacuum pump 23 is operated
before the solvent is sent to the cleaning tank 1. The
air which is evacuated by the vacuum pump 23 is directly
discharged to the atmosphere without passing through the
distiller 14. When air is evacuated from the cleaning
tank 1 to some extent, the liquid solvent is sent to the
cleaning tank 1, and both the residual air and a vapor
produced due to evaporation of the solvent are passed to
the distiller 14.
According to these methods, the solvent vapor is
continuously supplied to the upper space of the cleaning
tank 1 by evaporating the liquid solvent in the tank 1,
and no air is supplied. Thus, the proportion of air in
the gas mixture in the upper space gradually decreases
and finally the upper space is filled with only the
solvent vapor. It is easy to keep the upper space below
1 atm. (negative pressure) since the pressure of the
solvent vapor in the upper space does not exceed 1 atm.
if the temperature of the cleaning tank 1 is kept below a
predetermined temperature. The solvent vapor in the gas
mixture which is sent by the vacuum pump 23 to the
19 201~i7~
distiller 14 through the pipes 24 and 40 is condensed by
the cooler 20 and the condensate is recovered by the
storage tank 3 as previously described.
In the cleaning system in FIG. 2, the solvent vapor
which remains in the cleaning tank 1 is drawn out by
operating the vacuum pump 23 but the capacity of the
vacuum pump 23 necessarily raises a problem in that a
small amount of the solvent vapor still remains in the
cleaning tank 1. If under such a condition air is sucked
into the cleaning tank 1 though the suction pipe 25 to
raise the pressure in it to an atmospheric pressure, and
if the closure 12 is then opened to take out the article
2 cleaned, the residual solvent vapor will be released
into the atmosphere. The use of a vacuum pump having a
higher capacity can fairly reduces the amount of the~
vapor solvent discharged to the atmosphere, but it raises
the equipment cost and is not practical.
This problem is according to the present invention
solved by the following two methods. According to the
first method, after the cleaning, the liquid solvent is
discharged from the cleaning tank 1 as previously
described, and then the vacuum pump 23 is operated while
air is being introduced into the cleaning tank 1 through
the suction pipe 25. This operation enables the residual
vapor solvent to be almost completely discharged from the
cleaning tank 1 through the pipe 24.
In the second method, before air is sucked through
the suction pipe 25, the vacuum pump 23 is operated to
discharge the residual vapor solvent from the cleaning
tank 1. After the residual vapor solvent is exhausted to
the limit of the capacity of the vacuum pump 23, an
appropriate amount of air is sucked into the cleaning
tank 1 through the suction pipe 25 to produce a gas
mixture made of the residual solvent vapor and air.
Then, the gas mixture is exhausted by the vacuum pump 23.
In these methods, air is continuously supplied by
opening the solenoid valve 26 through the suction pipe 25
2~)19~37g
but no vapor solvent is supplied. Thus, the proportion
of the vapor in the gas mixture in the cleaning tank 1
~ gradually decreases and eventually, only air constitutes
the gas in the cleaning tank 1. The solvent vapor in the
gas mixture which is sent to the distiller 14 by the
vacuum pump 23 through the pipes 24 and 40 is condensed
by the cooler 20 located at the upper portion of the
distiller 14 and is then recovered by the storage tank 3.
With such a construction, in addition to the fact that
the organic solvent vapor is heavier than air, the
introduction of air into the cleaning tank 1 does not
cause the vapor solvent to leak to the atmosphere during
the operation of the vacuum pump 23.
FIG. 15 illustrates a modified form of the cleaning
system of FIG. 2. In this modified system, the drain.
pipe 6 which sends the liquid solvent from the cleaning
tank l to the storage tank 3 is omitted, and instead a
drain pipe 6A is provided for passing the liquid solvent
from the cleaning tank 1 to the distiller 14, where the
liquid solvent is distilled and then returned as a
regenerated solvent to the storage tank 3 as described
hereinbefore.
In the cleaning systems of FIGS. 2 and 15, after
compietion of the cleaning of the article 2, the liquid
solvent is sent from the cleaning tank 1 to the distiller
14, where it is evaporated by the heater 18 and then
condensed in the cooler 20. This causes a drop in
pressure in the distiller 14, so that air is sucked into
the distiller 14 through the pipe 30. Vapor in the air
sucked condenses into water droplets by passing the
secondary cooler 31 or by contact with the cooler 20 of
the distiller 14. Water droplets thus produced are mixed
~ with the solvent and sent to the storage tank 3 where it
is stored. Thus, the solvent which is to be supplied to
the cleaning tank 1 is deteriorated by the mixed water.
FIG. 16 shows a distiller 14 including a moisture
removing unit for preventing such deterioration of the
,
21 20~9~7~
solvent. The moisture removing unit includes a sealed
container 65, which contains the liquid solvent 66. The
sealed container 65 is provided at its bottom portion
with an evaporator 67 which constitutes part of a
refrigerator 64. The evaporator 67 cools the solvent in
the sealed container 65 to about -20~C for freezing water
in a very short time. The reference numeral 68 indicates
a suction pipe having one end open to the atmosphere and
the other end connected to a porous member 69 immersed in
the solvent in the sealed container 65. The porous
member 69 may be a perforated pipe or a member made of a
porous material. The sealed container 65 is connected at
its upper space 70 to the upper closed space 71 of the
condenser 16 through a communicating pipe 30. The
communicating pipe 30 is provided with a check valve 72
which allows a gas to pass through it only from the
sealed container 65 toward the upper closed space 71 of
the condenser 16. A release pipe 74 is connected at one
end thereof to the closure 12 of the condenser 16 for
releasing part of the gas in the closed space 71 when the
pressure in the closed space 71 rises. The release pipe
74 is provided with a secondary cooler 75 adjacent to the
one end for cooling the gas including the solvent vapor
to condense the solvent vapor to recover it. Another
check valve 76 is furnished to the release pipe 76
between the secondary cooler 75 and the other end
thereof. The other end of the release pipe 74 may be
opened to the atmosphere with or without an activated
carbon filter for filtering the solvent vapor.
When pressure in the closed space 71 of this
modified distiller 14 drops due to condensation of the
solvent vapor in the closed space 71 with the cooler 20,
; air is sucked into the closed container 65 through the
suction pipe 68 due to a drop in pressure in the upper
space 70. The air thus sucked is introduced into the
solvent 66 in the sealed container 65 in the form of fine
air bubbles through the porous member 69. The air is
,.
' 22
201~ ~ 78
sufficiently cooled by passing through the solvent 66, so
that water vapor in the air is frozen into ice, which is
caused to remain in the sealed container 65. Thus, air
in the upper space 70 of the sealed container 65 contains
a negligible amount of water vapor and is dry. This air
is passed through the check valve 72 into the closed
space 71 of the upper portion of the condenser 16, and
pressure in the closed space 71 accordingly rises to the
atmospheric pressure. As air in the closed space 71 is
hence extremely dried, little vapor in the air is
condensed by the cooler 20, with the result that little
water is mixed into the solvent which flows down into the
trough 21. Thus, practically there is no possibility of
the solvent being deteriorated by water mixed.
When pressure in the closed space 71 increases, it
is caused to drop to the atmospheric pressure by
discharging the gas mixture in the closed space 71 to the
atmosphere through the release pipe 74. While the
pressure in the closed space 71 is decreased in such a
- 20 manner, little organic vapor is discharged to the
atmosphere through the release pipe 74 since the solvent
which is contained in the gas mixture is trapped by
condensation with both the primary cooler 20 and the
secondary cooler 75.
A modified form of the distiller 14 of FIG. 16 is
illustrated in FIG. 17, in which the release pipe 74 is
communicated at the other end with a second moisture
removing apparatus which is identical in structure to the
first moisture removing apparatus except that the check
valve 72A has a release direction in which a gas is only
allowed to pass, and which is opposite to the release
direction of the check valve 72 of the first moisture
removing unit. In this modified form, when the pressure
in the closed space 71 rises, it is caused to drop by
passing the gas mixture in the closed space 71 through
the release pipe 74 into the second sealed container 65,
from which it is discharged through a pipe 68 to the
;
)
23 2 0 ~ rl 8
,
atmosphere. During this operation little solvent vapor
is discharged to the atmosphere. A major part of the
'~ solvent vapor in the gas mixture is trapped in the trough
.- 21 by condensation by means of the cooler 20 disposed in
the closed space 71. The remaining part of the solvent
vapor, which is not trapped by the cooler 20, is
condensed during passing through the cryogenic solvent in
the second sealed container 65 and is trapped in it.
The first and second moisture removing units may be
arranged within a common sealed container.
Referring to FIG. 18, another measure to prevent
degradation of the organic solvent due to condensation of
water droplets caused by a pressure drop in the distiller
14 will be descri~ed. In this modified distiller 14, a
pair of dehumidifiers 80A and 80B communicate through a
check valve 72 to the closed space 71 of the condenser 16
in parallel with each other. Each of the dehumidifiers
80A and 80B is charged with a regenerable drying agent,
such as silica gel and molecular sieve. The
dehumidifiers 80A and 80B communicate with the atmosphere
through suction pipes 81A and 81B, respectively, and are
further connected to the check valve 72 through
respective discharge pipes 82A and 82B. The discharge
pipes 82A and 82B are provided with solenoid valves 83A
and 83B, respectively. The dehumidifiers 80A and 80B are
communicated to a hot air producing heater 86 through
respective regenerating hot air supply pipe 84A and 84B
each including a solenoid valve 85A or 85B. The closed
space 71 of the condenser 16 is connected to a secondary
cooler 32 through a check valve 87.
When in such an arrangement, the solenoid valve 83a
of one dehumidifier 80a is opened with the solenoid valve
83b closed of the other dehumidifier 80b, air is sucked
into the closed space 71 through the dehumidifier 80a to
compensate for a pressure drop in the closed space 71 due
to condensation of the organic solvent. During this
operation, the solenoid valve 85a is closed while the
~ - 24 '~0~9~3~
solenoid valve 85b is opened. Thus, hot air which is
heated by the heater 86 is sent to the dehumidifier 80b
to regenerate the drying agent in it by evaporating
moisture, which is then discharged to the atmosphere
through the pipe 81b. When the drying agent in the
dehumidifier 80a becomes wet by the dehumidifying
operation, a controller opens the solenoid valves 83b and
85a and closes the solenoid valve 83a and 85b for
regeneration thereof. Thus, air is also sucked into the
closed space 71 through the second dehumidifier 80b to
compensate for the pressure drop in the closed space 71
while the first dehumidifier 80a undergoes regeneration.
The switching between the first and second dehumidifiers
80a and 80b by means of the solenoid valves 83a, 83b, 85a
and 85b is automatically performed by counting the number
of cleaning or by a timer incorporated into the
controller.
With such a construction, air to be introduced into
the closed space 71 through the suction pipe 30 for
increasing the pressure in the closed space 71 is
dehumidified on the way and always becomes dry. Thus,
little water vapor in the air sucked condenses by the
cooler 20 and hence little water is mixed into the
solvent liquid which flows down into the trough 21.
Thus, degradation of the solvent by contamination of
water is prevented.
In the cleaning systems of FIGS. 2 and 15, after
cleaning of the article 2 to be cleaned, the liquid
solvent is discharged from the cleaning tank 1. Then,
solvent vapor is supplied to the cleaning tank 1 from the
vapor supplying unit 34 for vapor cleaning. In this
case, there is a fear that abrupt boiling or bumping of
the liquid solvent takes place in the vapor supplying
unit 34 because of a considerable pressure drop in the
cleaning tank 1. The pressure drop in the cleaning tank
1 is produced by discharging the liquid solvent from it
with the liquid transfer pump 8 and eventually the
'~ 0 ~ 9 i~
pressure in the cleaning tank 1 drops to a vapor pressure
at the temperature of the liquid solvent. If in this
event, the vapor supplying unit 34 is made equal in
pressure to the cleaning tank 1 by opening the solenoid
valve 35 (the pressure in the vapor supplying unit 34 is
lowered), the pressure in the vapor supplying unit 34
becomes lower than the vapor pressure of the solvent at
the temperature thereof. This causes bumping of the
liquid solvent in the vapor supplying unit 34, which
bumping produces droplets of the liquid solvent. Thus,
there is a possibility of such droplets of the solvent
being sent to the cleaning tank 1. If these droplets
come into contact with an article 2 to be cleaned in the
cleaning tank 1 during the vapor cleaning, the droplets-
contacted portions of the article will fail to undergothe vapor cleaning, thus deteriorating the effect of the
vapor cleaning.
This problem is solved by means of a bumping
preventing system shown in FIG. 19, in which after
cleaning of the article 2, the liquid solvent is
discharged from the cleaning tank 1 to the storage tank
by actuating the liquid transfer pump 8 in the same
manner as in the preceding embodiments. In this stage of
the cleaning, the temperature T2 of the liquid solvent in
the cleaning tank 1 is raised slightly above the
temperature T4 of the liquid solvent in the vapor
generator 34. More specifically, an output signal of a
temperature sensor 90, which detects the temperature T2
of the liquid solvent in the cleaning tank 1, and an
output signal of a temperature sensor 91, which detects
the temperature T4 of the liquid solvent in the vapor
generator 34, are inputted to a controller 92 for
controlling power supply to the heater 33 of the vapor
generator 34. The controller 92 compares the inputted
signals and according to the outcome of the comparison,
controls the power supply to the heater 33 so that the
temperature T2 is slightly higher than the temperature
26 2 ~ 3 ~ ~
T4. In this condition, the valve 35 of the pipe 36 is
opened to send the solvent vapor from the vapor generator
34 to the cleaning tank 1. When pressure in the vapor
~ generator 34 becomes equal to the pressure in the
S cleaning tank 1, the former is not lower than the vapor
pressure of the liquid solvent in the vapor generator 34
at the temperature T4. Thus, the bumping of the liquid
solvent in the vapor generator 34 does not take place and
hence there is no possibility of droplets of the solvent
10 which are produced by the bumping being sent to the
cleaning tank 1 through the pipe 36.
After the supply of the vapor solvent from the vapor
generator 34 to the cleaning tank 1 is started in such a
manner, the controller 92 increases the power supply to
the heater 33 to raise the temperature of vapor of the
solvent to be sent to the cleaning tank 1. Thus, the
temperature difference between the solvent vapor which is
sent to the cleaning tank 1 and the surfaces of the
article to be cleaned becomes larger, so that the amount
of condensation of the solvent vapor on the surfaces of
the article to be cleaned increases for enhancing the
effect of the vapor cleaning. While the temperature T4
of the liquid solvent in the vapor generator 34 is raised
by the heater 33, the valve 35 is opened, and hence
pressure in the vapor generator 34 does not become lower
than the vapor pressure. Thus, there is no possibility
of occurrence of the bumping of the solvent.
FIG. 20 shows a further modified form of the
cleaning system according to the present invention. In
this figure, the same reference numerals as used in the
preceding embodiments designate the same or equivalent
elements or parts. The cleaning tank 1 is connected to a
solvent supply pipe 4 with a solenoid valve 5 and to a
drain pipe 6 with a solenoid valve 7 and a liquid
transfer pump 8.
According to this modified form, the cleaning tank 1
; and the distiller 14 are connected by way of a vapor
27 20~578
discharge pipe 24 having a hermetically sealed container
100. The container 100 has therein a cooler pipe 101 for
cooling the solvent vapor sent into the container 100
from the cleaning tank 1 through the vapor discharge pipe
24. The pipe 24 has a solenoid valve 22 and a three-way
solenoid valve 102.
The sealed container 100 is connected at its upper
portion with the condenser 16 through a connecting pipe
103 having a solenoid valve I04, so that it is possible
to send the solvent vapor from within the condenser 16
into the container 100. The container 100 is also
connected at its bottom portion with the evaporator 15
through another connecting pipe 105 having a solenoid
valve 106, so that liquid solvent in the container 100
may be sent into the evaporator 15.
The three-way valve 102 is connected to a suction
pipe 108 of a vacuum pump 23 and its delivery pipe 109
~ opens into the sealed container 100.
When cleaning an article in the cleaning tank 1, the
article is put into the tank 1 to be subjected to
ultrasonic cleaning by the oscillators 11. After
completion of the cleaning, the liquid transfer.pump 8 is
actuated to return the used liquid solvent to the storage
tank 3 (not shown) through the drain pipe 6. After the
entire liquid solvent has been sent to the storage tank,
the vacuum pump 23 is operated to draw vapor solvent out
of the cleaning tank 1.
In this case, the valve 22 in the vapor discha~ge
pipe 24 is first closed to shut off the communication
between the cleaning tank 1 and the sealed container 100,
while the valve 104 is opened to allow the solvent vapor
within the condenser 16 to flow into the container 100
through the connecting pipe 103. The three-way valve 102
is changed over to a state in which the suction pipe 108
does not communicate with the vapor discharge pipe 24.
With the solvent vapor introduced into the container
100 as above, the valves 104 and 106 are closed and
-
~ 28 2019578
coolant or refrigerant is passed through the cooler pipe
101 to cool and condense the solvent vapor in the
container 100. As a result, the pressure within the
~ container 100 is reduced.
Thereafter, with the valves 104 and 106 closed, the
valve 22 is opened so that the reduced pressure within
the container 100 causes the vapor solvent remaining in
the cleaning tank 1 to flow into the sealed container
100 .
The inducing flow of the vapor solvent into the
container 100 occurs only for a short time so that the
pressure in the cleaning tank 1 drops abruptly, whereby
bumping or rapid boiling of the liquid solvent adhering
to the article to be cleaned occurs to blow off dirt or
stain on the article with consequent cleaning of the
article.
The vapor solvent sucked into the container 100 is
cooled by the cooler pipe 101 and condenses into liquid
solvent, so that even with the sucked solvent in the
container 100 the pressure therein will increase only
~ slightly whereby flow of the vapor solvent from within
the cleaning tank 1 into the container 100 continues with
~ resultant pressure reduction in the cleaning tank 1.
When the pressure reduction in the cleaning tank 1
in the above stated manner is not sufficient, the three-
way valve 102 is changed over to a position in which the
vapor discharge pipe 24 communicates with the suction
pipe 108, and the vacuum pump 23 is put into operation.
Then, the vapor solvent in the cleaning tank 1 is sent
into the container 100 through the vapor discharge pipe
24, the suction pipe 108, the vacuum pump 23 and the
delivery pipe 109, and the vapor solvent condenses in the
container 100. While the vapor solvent is sent from the
cleaning tank 1 into the container 100, the pressure in
the container 100 is maintained considerably low due to
the operation of the cooler pipe 101, so that the
pressure difference between the cleaning tank 1 and the
' ' 29 20~57~
container 100 is small and therefore it is possible to
make the degree of vacuum in the cleaning tank
sufficiently high. This means that the vacuum pump 23
need not be of high performance in order to obtain high
degree of vacuum in the cleaning tank 1. It will be
noted that this modified form of the cleaning system is
advantageous in this respect.
In the cleaning system shown in FIG. 20, liquid
solvent accumulated in the bottom of the container 100 is
sent into the distiller 14 by opening the valve 106.
When the liquid ,solvent is thus taken out of the
, container 100 through the pipe 105, the vapor solvent
existing in the distiller 14 tends to be sucked into the
container 100 having a vacuum therein through the pipe
105. The interior volume of the container 100 under
vacuum is large enough to cause abrupt pressure drop in
the cleaning tank 1. Therefore, the amount of vapor
solvent sucked from the distiller 14 into the container
100 when the valve 106 is opened is also large enough.
For this reason, the opening of the valve 106 tends to
cause much amount of flow from the distiller 14 into the
container 1 within a short period of time with resultant
pressure drop within the distiller 14 and with consequent
sucking of atmospheric air through the exhaust pipe 30
into the distiller 14 to make up the pressure drop.
The thus sucked atmospheric air within the distiller
14 is pushed back through the exhaust pipe 30 by solvent
vapor generated by the operation of the heater 18, and at
this time the solvent vapor in the distiller 14 is
released through the exhaust pipe 30 into the atmosphere.
The released solvent vapor can be arrested by a filter
29, but some solvent vapor may be released to the
atmosphere or the filter 29 may deteriorate soon.
These problems are eliminated by a modification
shown in FIG. 21. In this modification, the bottom of
the hermetically sealed container 100 is connected to an
auxiliary sealed container 111 via a connecting pipe 112
.
2 0 ~ 7 8
having a solenoid valve 113. The auxiliary container 111
has a capacity considerably smaller than that of the
container 100. The auxiliary container 111 is connected
-. at its bottom with a pipe 114 having a solenoid valve 115
and leading into a bottom part of the evaporator 15. The
auxiliary container 111 is further connected at its upper
part with a pipe 116 having a solenoid valve 117 and
leading into the evaporator 15.
The liquid solvent accumulated in the bottom of the
sealed container 100 is delivered to the distiller 14
through the auxiliary container 111. More specifically,
when liquid solvent is accumulated in the container 100,
the valve 113 is opened with the valves 22, 104, 115 and
117 closed. Then, the liquid solvent in the container
100 flows down gravitationally into the auxiliary
container 111 via the pipe 112. At the same time, vapor
solvent existing in the auxiliary container 111 is sucked
upwards into the container 100 under vacuum.
Thereafter, the valve 113 is closed and instead the
valve 115 is opened, so that the liquid solvent in the
auxiliary container 111 flows down the pipe 114 into the
evaporator 15. At this time, some amount of vapor
solvent existing in the evaporator 15 is sucked into the
auxiliary container 111. However, the amount of vapor
solvent sucked is small since the auxiliary cintainer 111
is of small capacity.
When the operation of the cleaning system is
started, the valves 22 and 117 are closed and the valves
104, 113 and 115 are opened so that the container 100 and
the auxiliary container 111 are filled with vapor
solvent. Since the vapor solvent is heavier than the
air, whèn the valves 104, 113 and 115 are opened as
above, the vapor solvent in the distiller 14 flows from
below into the auxiliary container 111 and then into the
container 100 to expel air which has existed in these
containers 100 and 111, through the pipe 103 into the
upper part of the distiller 14. Therefore, an exchange
.
-
31 20~;37~
of air and vapor solvent is carried out between the
containers 100 and 111 and the distiller 14. This
exchange takes place slowly due to the difference in
specific weight between the air and the vapor solvent,
and the amount of the vapor solvent consumed does not
considerably exceed the amount of vapor solvent produced
by the heating of the heater 18. Therefore, the position
of the boundary surface between the vapor solvent and the
air in the distiller 14 does not change largely, so that
the amount of the solvent which leaks out of the cleaning
system can be suppressed to a minimum.
In the cleaning systems described with reference to
FIGS. 1, 2 and 15, the vacuum pump 23 is operated to draw
vapor solvent remaining in the cleaning tank 1 after
completion of the cleaning operation. It is however
unavoidable that a very small amount of the vapor solvent
remains in the cleaning tank 1. Therefore, when the
closure 12 is opened to take the cleaned article 2 out of
the tank 1 after increasing the pressure in the tank 1 to
the atmospheric pressure by drawing air into the tank 1
through the air suction pipe 25, the amount of the vapor
solvent remaining in the tank 1 will escape to the
atmosphere. It is possible to reduce the amount of the
escaping vapor solvent by increasing the capacity of the
vacuum pump 23, but there is a limit to the reduction of
the amount.
FIG. 22 shows an improved form of the cleaning
system. As shown, the system includes a connection pipe
120 communicatively connecting the condenser 16 and the
upper part of the cleaning tank 1. The connection pipe
120 may be connected to the air suction pipe 25 as shown
and has a solenoid valve 121 and a cooler 122 through
which coolant or refrigerant may be caused to flow.
In this improved system, air existing in the upper
space of the distiller 14 is sucked into the cleaning
tank 1. By thus avoiding the introduction of atmospheric
air into the cleaning tank 1, the entire amount of gases
32 201~78
contained in the interior of the cleaning system does not
increase. Therefore, the gases in the interior of the
distiller 14 are not forced towards the filter 22 so that
it is possible to reduce the amount of the vapor solvent
(heavier than air) which is released to the atmosphere
from the distiller 14. The cooler 122 functions to cool
- and condense the vapor solvent flowing through the
connection pipe 120 for recovering the solvent into the
distiller 14, thereby reducing the amount of the solvent
flowing into the cleaning tank 1 through the connection
pipe 120.
: 30
