U.S. patent number 3,661,483 [Application Number 04/848,625] was granted by the patent office on 1972-05-09 for apparatus for controlling the flow of liquid.
Invention is credited to Robert N. Bose.
United States Patent |
3,661,483 |
Bose |
May 9, 1972 |
APPARATUS FOR CONTROLLING THE FLOW OF LIQUID
Abstract
The intermittent flow of carbon dioxide liquid from a high
pressure reservoir to a low pressure use area is controlled by a
flow restricting orifice disposed in the supply line and a simple
control valve located in the line downstream of the orifice. An
additional source of pressurized fluid maintains the pressure
between the orifice and the valve above the triple point of carbon
dioxide to prevent solidification of the carbon dioxide upstream of
the valve. In a cyclical blow molding operation wherein liquid
carbon dioxide is used to chill the freshly molded parts, the
pressure of the fluid used to expand the parison is maintained
above the triple point of carbon dioxide to prevent solidification
of the carbon dioxide. Additionally, a predetermined amount of
carbon dioxide is permitted to vaporize in the line upstream of the
orifice during the off cycle in the molding operation thereby
providing the necessary time delay between the application of the
parison expanding gas and the injection of the liquid carbon
dioxide into the molded part.
Inventors: |
Bose; Robert N. (Wheaton,
IL) |
Family
ID: |
25303826 |
Appl.
No.: |
04/848,625 |
Filed: |
August 8, 1969 |
Current U.S.
Class: |
425/161; 264/28;
425/156; 425/536; 425/526; 62/384; 425/155; 425/160 |
Current CPC
Class: |
B29C
49/66 (20130101); B29C 2035/1658 (20130101); B29C
2035/165 (20130101) |
Current International
Class: |
B29C
49/64 (20060101); B29C 49/66 (20060101); B29C
35/16 (20060101); B29C 35/00 (20060101); B29c
005/06 () |
Field of
Search: |
;18/5BA,5BC,5BH,5BN,3HM,DIG.9 ;62/384,331 ;264/28 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
R Bose, "Carbon Dioxide as an Internal Coolant in Blow Molding,"
1-70, SPE Journal, Vol. 26 pages 29-31. .
Mackey et al., Engineering Thermadynamics, page 288, July
1957..
|
Primary Examiner: Overholser; J. Spencer
Assistant Examiner: Safran; David S.
Claims
What is claimed is:
1. Molding apparatus for molding a plastic part and for using
liquid carbon dioxide to cool said part after molding,
comprising
a mold having a mold surface against which plastic is formed into
the shape of said part,
a pressurized tank containing carbon dioxide in the liquid state,
supply line means connected between said mold and said tank for
carrying liquid carbon dioxide to said mold,
a valve connected in said line,
metering means having a small metering orifice therein connected in
said line upstream of said valve,
means for maintaining the pressure and temperature in said line
between said orifice and said valve above the pressure and
temperature of carbon dioxide at the triple point to prevent
solidification of carbon dioxide in said line upstream of said
valve,
means for vaporizing a portion of the carbon dioxide in said line
immediately upstream of said orifice when said valve is closed to
interrupt the flow of carbon dioxide in said line,
whereby, upon opening of said valve the vaporized carbon dioxide
upstream of said orifice first flows through said orifice to said
mold followed by liquid carbon dioxide from said tank.
2. Molding apparatus for molding a plastic part and for using
liquid carbon dioxide to cool said part after molding,
comprising
a mold having a mold surface against which plastic is formed into
the shape of said part,
a pressurized tank containing carbon dioxide in the liquid
state,
a supply line connected between said mold and said tank for
carrying carbon dioxide to said mold,
a valve connected in said line,
metering means having a small metering orifice therein connected in
said line upstream of said valve,
another line connected between a location in said supply line
between said orifice and said valve and a source of gas at a
pressure substantially less than that upstream of said orifice but
greater than the triple point of the carbon dioxide contained in
said supply line between said orifice and said valve,
means for vaporizing a portion of the carbon dioxide in said line
immediately upstream of said orifice when said valve is closed to
interrupt the flow of carbon dioxide in said line,
whereby, upon opening of said valve the vaporized carbon dioxide
upstream of said orifice first flows through said orifice to said
mold followed by liquid carbon dioxide from said tank.
3. Molding apparatus according to claim 2 wherein said source of
gas comprises
a pressure regulator connected to the upper portion of said
pressurized tank.
4. Molding apparatus according to claim 2 wherein said means for
vaporizing comprises
a short length of uninsulated tubing connected upstream of said
orifice in proximity thereto.
5. Molding apparatus for molding a plastic part and for using
liquid carbon dioxide to cool said part after molding,
comprising
a mold surface against which plastic is formed into the shape of
said part,
a pressurized tank containing carbon dioxide in the liquid
state,
a supply line connected between said mold and said tank for
carrying carbon dioxide to said mold,
a valve connected in said line,
metering means having a small continually open metering orifice
therein connected in said line upstream of said valve,
means for maintaining the pressure and temperature in said line
between said orifice and said valve above the pressure and
temperature of carbon dioxide at the triple point to prevent
solidification of carbon dioxide in said line upstream of said
valve,
means for vaporizing a portion of the carbon dioxide in said line
immediately upstream of said orifice when said valve is closed to
interrupt the flow of carbon dioxide in said line,
said means for vaporizing comprising a short length of uninsulated
tubing connected upstream of said orifice in proximity thereto,
whereby, upon opening of said valve the vaporized carbon dioxide
upstream of said orifice first flows through said orifice to said
mold followed by liquid carbon dioxide from said tank.
6. Molding apparatus according to claim 2 wherein said valve
comprises
a cylinder,
a piston valve member axially slidable in said cylinder between
valve open and closed positions,
a tubular needle carried by said piston and forming the outlet for
said valve for insertion of said needle through an aperture in said
mold when said piston is moved to the valve open position.
7. Molding apparatus according to claim 4 wherein said valve
comprises
a cylinder,
a piston valve member axially slidable in said cylinder between
valve open and closed positions,
a tubular needle carried by said piston and forming the outlet for
said valve for insertion of said needle through an aperture in said
mold when said piston is moved to the valve open position.
8. Blow molding apparatus comprising
a mold having a mold cavity therein and a hole extending through a
wall thereof to said cavity,
a valve including a reciprocable valve member having an outlet port
therein,
a tube mounted on said valve member over said outlet port for
reciprocation in said hole between a first position wherein the
distal end of said tube is retracted from said cavity and a second
position wherein said distal end is disposed in said cavity,
a fluid supply line connected to an inlet port in said valve
member,
said inlet and outlet ports being mutually disconnected when said
valve member is positioned to locate said tube in said first
position and being mutually interconnected when said valve member
is positioned to locate 300 in said second position,
a source of liquid carbon dioxide connected to said fluid supply
line,
a small orifice connected between said fluid supply line and said
source of liquid carbon dioxide,
a source of pressurized gas connected to said fluid supply line to
supply gas to said supply line downstream of said orifice at a
pressure exceeding the triple point of the carbon dioxide in the
supply line downstream of said orifice, but less than the pressure
upstream of said orifice,
a check valve connected between said supply line and said source of
pressurized gas to prevent the flow of carbon dioxide from said
orifice to said source of pressurized gas, and
means for vaporizing the carbon dioxide in a predetermined length
of the line between said orifice and said source of liquid carbon
dioxide when said valve is closed so that when said valve is opened
the vaporized carbon dioxide first flows through said orifice to
said supply line and is then followed by liquid carbon dioxide,
whereby said pressurized gas and said vaporized carbon dioxide
first flow through said valve into said cavity and is thereafter
followed by liquid carbon dioxide which solidifies in said mold to
cool a plastic part contained therein.
9. Blow molding apparatus according to claim 8 wherein said
pressurized gas is carbon dioxide at a pressure exceeding 75
p.s.i., said liquid carbon dioxide is at a pressure of about 300
p.s.i., and said orifice has a diameter of about 0.020 inch.
Description
The present invention generally relates to a method and apparatus
for controlling the flow of carbon dioxide or other volatile liquid
between a high pressure reservoir wherein it is maintained in a
liquid state and a low pressure use area at which it changes into
the solid state, and if further relates to a new and improved
method of molding plastic articles using carbon dioxide.
For many years blow-molded plastic articles have been chilled
immediately after molding by injecting a small amount of liquid
carbon dioxide into the cavity in the freshly molded part. Since
the pressure in the cavity is well below the triple point of carbon
dioxide the liquid carbon dioxide changes from the liquid to the
solid state within the part thereby quickly chilling the part and
thus accelerating the molding cycle. A more complete description of
this prior art system may be had by reference to U.S. Pat. No.
3,065,501--Gasmire.
While this accelerated cooling system has been successfully and
widely used, some problems have arisen in connection with the
feeding of a precisely controlled amount of liquid carbon dioxide
into the freshly molded part and in accurately controlling the time
in the molding cycle when the carbon dioxide is injected into the
part. Relatively complex installations including electric timers
and expensive control valves have been used in these systems but
even then freeze-ups in the lines have not been uncommon and
variations in the amount of carbon dioxide fed to the parts
occur.
In order to increase the use of carbon dioxide and other volatile
cooling liquids, not only in the plastic blow-molding field, but in
the plastics industry at large as well as for other uses, it is an
object of this invention to provide a new and improved method and
apparatus for accurately metering the flow of a pressurized
volatile liquid, such as liquid carbon dioxide, to a low pressure
use area.
Another object of this invention is to provide a new and improved
method and means for controlling the flow of liquid carbon dioxide
to a freshly molded part.
A further object of this invention is to provide a new and improved
method and apparatus for blow-molding plastic articles.
Briefly, the above and further objects may be realized in
accordance with the present invention by supplying liquid carbon
dioxide through a small, flow restricting orifice upstream of a
control valve and always maintaining the pressure between the
orifice and valve above the triple point of carbon dioxide to
thereby prevent the carbon dioxide from changing into a solid state
upstream of the valve. Where a time delay between the opening of
the control valve and the passage of liquid carbon dioxide
therethrough is desired, means is provided upstream of the orifice
to vaporize a predetermined amount of carbon dioxide in the line so
that when the control valve opens, the carbon dioxide vapor must
first pass the orifice before the liquid carbon dioxide can feed
therethrough. Hence, an adjustable predetermined time delay is
achieved without the use of timers or the like.
Further objects and advantages and a better understanding of the
present invention may be had by reference to the following detailed
description taken in connection with the accompanying drawings,
wherein:
FIG. 1 is partly schematic diagram showing the use of the present
invention in a blow molding system;
FIG. 2 is a partly schematic diagram of a multiple cavity blow
molding system embodying the present invention; and
FIG. 3 is a partly schematic diagram of an injection molding system
embodying the present invention.
Referring now to the drawings, and particularly to FIG. 1 thereof,
there is shown a portion of a blow molding system which includes a
pair of mold halves 10 and 11 which define therebetween a cavity 12
in the shape of the article to be molded therein. In the
illustrated embodiment of the invention, the article 12 is a
bottle. A vapor and liquid injection device 14 is mounted by
suitable means, not shown, adjacent the mold part 11 and is used to
inject a pressurized fluid into a hot tubular parison located
within the mold cavity in order to inflate the parison against the
wall of the cavity 12.
The manner in which the hot plastic parison is extruded and the
mold parts 10 and 11 are brought together over it to seal off the
top and bottom ends thereof is well known in the art. Once,
however, the parison has been positioned within the mold cavity 12,
the injection device 14 is actuated to insert a tubular needle 16
into the cavity within the parison and then a pressurized gas flows
through the needle 16 into the parison thereby to expand it against
the walls of the cavity. Pressure thereafter continues to build up
within the molded article and ruptures it at the location of a vent
line 18 in the mold half 10 which opens to the atmosphere and
reduces the pressure in the article. Almost immediately thereafter
a metered quantity of liquid carbon dioxide feeds through the
needle 16 and upon entering the cavity in the freshly molded
article it vaporizes and then changes into the solid state thereby
absorbing a substantial amount of heat from the molded article and
thus quickly chilling it. Thereafter, the injection device 14 is
operated to withdraw the needle 16 from the article, and the mold
parts 10 and 11 are opened to permit removal of the molded
part.
The device 14 includes a body portion 20 which is bored at 22 to
slidably receive a rodlike valve body 24 to which the needle is
suitably affixed by means of a fitting 26 threaded onto the end of
the valve member 24. As shown, the valve member 24 is provided with
a longitudinal bore 28 which is counterbored at 30 to receive the
rear end of the needle 16. The needle 16 is provided with an
annular bead 32 which is received in a generally complementary
groove in the fitting 26 so that when the fitting 26 is threaded
onto the end of the rod, the needle 16 is held firmly in place
thereon.
The valve member 24 is further provided with a transverse feed hole
34 which communicates with the longitudinal bore 28. With the valve
member 24 in the illustrated position, the hole 34 is aligned with
a hole 36 in the valve body 20 through which the parison expanding
fluid as well as the liquid coolant are supplied.
As described hereinabove, the needle 16 and thus the valve member
24 to which it is affixed reciprocates back and forth through the
bore 22 in the valve body 20 during a complete blow molding cycle.
To this end, the rear end of the valve member 24 is provided with a
longitudinally extending blind hole 38 which slidably receives a
guide rod 40 fixed to a plug 42. As shown, the plug 42 is tightly
fitted in the end of a tubular tail piece 44 which is secured to
the valve housing 20 by a suitable threaded fitting 46. The rear
end of the valve member 24 is press fitted into a piston-like
sealing member 48 which is provided with a pair of annular grooves
receiving suitable annular sealing gaskets 50 and 52.
When pressurized fluid is applied through a fitting 54 on the plug
42, it passes through a suitable hole in the plug 42 to the right
side of the piston 48 to force it and the valve rod 24 to the
leftward position as viewed in FIG. 1. Similarly, when pressurized
fluid is supplied through a fitting 56 and drilled holes 58 to the
left side of the piston 48, the piston 48 together with the valve
rod 24 move to the right until the right-hand end of the piston 48
engages the plug 42. In this latter position, the needle 16 has
been withdrawn completely from the molded article although it still
remains within the mold part 11.
In order to reciprocate the valve rod 24 during the molding
operation, a four-way valve 60 driven by a timer 62 is connected
between a source 64 of pressurized air, such for example as shop
air, and a pair of lines 66 and 68 which respectively connect
between the valve 60 and the fittings 54 and 56. A vent line 70 is
also connected to the valve 60. Therefore, in one position of the
valve 60 the source of air is connected to the line 66 while the
vent 70 is connected to the line 68, and in the other position the
source of air is connected to the line 68 while the vent 70 is
connected to the line 66. It may thus be seen that the valve rod 24
and the needle 16 move back and forth within the valve body 20
between a forward injecting position wherein the needle 16 extends
into the mold cavity and the passageway 34 is aligned with the
passageway 36, and a retracted position wherein the needle 16 is
withdrawn from the mold cavity and the passageway 34 is out of
alignment with the passageway 36. In this latter position, the
valve rod 24 closes over the rear end of the passageway 36.
In order to supply the pressurized gas and liquid to the hole 36
from which it is controllably fed to the mold cavity, a tubular
fitting 74 is threaded into a counterbore in the hole 36 and a
T-fitting 76 is threaded to the other end thereof. A threaded
fitting 78 connects a line 80 to the T-fitting and a fitting 82
connects another line 84 to the T-fitting. The line 80 supplies the
gas which is used to expand the parison within the mold cavity and
to control the supply of liquid CO.sub.2 to the mold cavity.
Accordingly, the line 80 connects to the top of a carbon dioxide
tank or reservoir 86 and includes a pressure regulating valve 88
which reduces the pressure to an adjustable predetermined level and
a check valve 90 which prevents the reverse flow of fluid in the
line 80.
In order to meter the liquid carbon dioxide which is supplied to
the mold cavity, a washerlike disk 92 having a small accurately
dimensioned orifice 94 therein is mounted in the T-fitting 76 and
is held in place by the fitting 82. The tube 84, which is
preferably plastic and may be formed of Teflon, is connected by a
suitable fitting 96 to a carbon dioxide loop 98 through which
liquid carbon dioxide is continually pumped at a predetermined
pressure by means of a pump 100 connected in the loop.
OPERATION
A typical blow molding operation begins with the valve rod 24 and
the needle 16 withdrawn from the mold cavity and with pressure from
the air source 64 connected to the left side of the piston 48
through the line 68. In this position, the valve rod 24 overlies
the passageway 36 to block the flow of carbon dioxide to the needle
16. The plastic parison is then extruded, and the mold parts 10 and
11 are brought together over the parison to occupy the position
illustrated in FIG. 1. During the time that the previously molded
part is being removed from the mold cavity and the parison is being
formed, the feeding of carbon dioxide liquid from the loop 98 and
the supply of carbon dioxide vapor from the line 80 is interrupted.
In order to prevent the carbon dioxide liquid from the line 84 and
the carbon dioxide vapor from the line 80 from changing to the
solid state within the T-fitting 76, the tube 74 and the valve 20,
the pressure in those lines must be maintained above the triple
point of carbon dioxide.
The triple point is that particular condition under which a
substance can be present in any or all phases (gaseous, liquid, or
solid). For carbon dioxide, this occurs on the Temperature-Entropy
Diagram at the condition of 75 p.s.i.a. and minus 70.degree. F. By
raising the pressue to say 300 p.s.i.a., the corresponding
temperature of saturated liquid CO.sub.2 would be 0.degree. F., the
standard storage conditions. If the pressure and temperature at the
triple point were kept constant and heat were added, the carbon
dioxide would turn directly to a saturated vapor. However, if the
pressure were reduced below 75 p.s.i.a., the carbon dioxide would
turn into a mixture of approximately 60 percent solid (dry ice) and
40 percent vapor. If heat were added, the solid carbon dioxide
would turn directly into the vapor phase. This phenomenon is known
as sublimation.
Since the triple point of carbon dioxide is approximately 75
p.s.i.a., the regulator 88 must be set such that the pressure
downstream of the orifice 94 and upstream of the valve 24 is never
less than 75 p.s.i.a. During the off duty cycle, therefore, since
the tube 84 is positioned in proximity to the molding machine which
is generally at an elevated temperature, the temperature of the
liquid therein will rise to the point where some of it vaporizes.
The extend to which the liquid will vaporize is dependent upon the
length of the tube 84, its proximity to a source of heat such as
the heaters of the machine, and to the time interval between the
closing and opening of the valve 24. All three of these factors can
be adjusted so that when the valve 24 is moved to the open position
there is a predetermined length or amount of carbon dioxide vapor
in the tube 84.
After the parison has been formed and the mold halves have been
brought together, the timer 62 then operates the valve 60 to
connect the air source 64 to the line 66 and to connect the line 66
to the vent 70 whereby the air pressure in the valve body 24 to the
leftwardmost position as illustrated in the drawing wherein the
valve is opened and the needle 16 pierces the wall of the hot
parison. The carbon dioxide vapor which is then at about 80 lbs.
p.s.i. feeds through the tube 80 and the tube 74 and through the
ports 34 and 28 of the valve 24 into the needle 16 to inflate the
parison against the walls of the mold cavity. At the same time that
the carbon dioxide vapor is feeding through the T-fitting 76 from
the line 80, carbon dioxide vapor is fed from the line 84 through
the restricting orifice 94 into the T-fitting 76 where it mixes
with the other carbon dioxide vapor and feeds through the needle 16
into the parison. Inasmuch as the pressure in the liquid loop 98 is
at about 300 p.s.i.a., or almost four times as great as the
pressure in the line 80, once the vapor in the line 84 has passed
through the orifice 94 it will be followed by liquid carbon dioxide
which remains in the liquid phase as it feeds through the tube 74,
the hole 36, the valve ports 34 and 28, and the passageway through
the needle 16 from which it enters the cavity in the molded part
which has by this time been completely formed. Since, as described
hereinbefore, the cavity in the molded article has been vented
through the line 18, and is at a pressure below the triple point of
CO.sub.2, the liquid CO.sub.2 quickly changes to the solid state.
At this time the timer 62 operates the valve 60 to connect the air
source 64 to the line 68 and to connect the line 66 to the vent 70
whereby the valve body 24 moves to the right to its closed position
and the needle 16 is withdrawn from the mold cavity. The rapid
chilling brought about by the injection of liquid carbon dioxide
into the molded part has by this time caused the molded part to set
sufficiently so that it can be withdrawn from the mold without
distortion.
In this illustrated embodiment of the invention, the parison is
blown by the injection therein of carbon dioxide vapor, but it will
be understood that if desired dry air may be used for this purpose
in place of the carbon dioxide vapor and such dry air may be used
to control the flow of liquid carbon dioxide through the orifice
94. However, as in the case of the carbon dioxide vapor it must be
maintained at the pressure exceeding the triple point of carbon
dioxide to prevent the formation of solid carbon dioxide within the
orifice 94 and the associated parts of the supply line of the valve
24.
It will be understood that the various times, temperatures, and
pressures required will depend upon the particular machine with
which the invention is used, the size and shape of the article
being molded as well as the plastic from which the article is
molded. As an example, however, a 12-ounce beer bottle formed of
polyvinylchloride has been satisfactorily blow molded in an
11-second cycle using a 2-second time delay between the initial
blowing of the parison and the injection of liquid carbon dioxide
into the molded article. Moreover, a 2-second injection of the
liquid carbon dioxide is sufficient to adequately cool the bottle
to permit its removal from the mold without damage thus leaving an
off-cycle of 7 seconds during which the carbon dioxide liquid in
the line 84 may vaporize. For this purpose, the tube 84 was a
one-eighth-inch Teflon tube approximately 18 inches long, the
pressure regulator 88 was set at 80 p.s.i., and the diameter of the
orifice 94 was 0.020 inch.
Referring to FIG. 2, there is shown a multiple cavity mold 105
defining a plurality of mold cavities 106 which are fed by a single
blow pin assembly 108 from which air enters the mold cavities
through a plurality of flexible hoses 110. The mold 105 is cooled
by means of water passing through cooling ducts 112 suitably
embedded within the parts of the mold member 105. Dry air is
supplied from a pressure source 114 through a reducing regulator
115 wherein the air pressure is dropped to a value approximating
but exceeding the triple point of carbon dioxide. The air then
passes through a solenoid controlled valve 116 and a check valve
117 to a T-fitting 118 from which it feeds through a tube 119 to
the blow pin assembly 108. Carbon dioxide liquid is supplied to the
fitting 118 through a solenoid controlled valve 120 from a standard
liquid carbon dioxide loop 122 having a pressure of about 300
p.s.i. The solenoid valve 116 is under the control of a blow timer
124 which determines the time during the molding cycle when the
pressurized air is supplied to the blow pin assembly 108 to expand
the parisons. When the valve 116 is opened to inflate the parisons
the timer 124 initiates operation of a carbon dioxide delay timer
126 which after a predetermined time opens the valve 120 whereby
the loop 122 is connected through a restricting orifice 128 to the
T-fitting 118 whereby carbon dioxide liquid is carried by the air
to the blow pin assembly 108 from which it is injected into the
cavities in the freshly molded parts. The length of time during
which the liquid carbon dioxide is injected into the parts is
controlled by an injection timer 130 which is actuated when the
timer 126 energizes the solenoid valve 120 and which times out a
predetermined time such, for example, as 2 seconds whereupon it
closes the solenoid valve 120. It will be apparent that since the
pressure in the T-fitting 118 is maintained above the triple point
of carbon dioxide, the liquid carbon dioxide does not solidify. The
time, at which the change of phase from the liquid to the solid
state of the carbon dioxide actually occurs, is controlled by a
variable pressure relief valve 132 in a timer controlled solenoid
dump valve 134. If desired, the flow of the liquid carbon dioxide
through the restricted orifice 128 may be controlled by the
delaying action of vaporized carbon dioxide gas, as described
herein in connection with FIG. 1, or by the conventional solenoid
control valve 14 and the two timers 126 and 130 as shown in FIG. 2.
It will be seen, however, that in many cases a substantial savings
in the initial and operating costs can be achieved by elimination
of the valve 120 and the two timers 126 and 130 by replacing the
same with a simple flexible tube of the proper length whereby the
same valve which controls the supply of air to the blow pin
assembly also controls the supply of liquid carbon dioxide as
described in connection with FIG. 1.
During the injection or compression molding of certain plastic
parts, the limiting factor in controlling the total cycle time is
the length of time necessary to remove heat from the freshly molded
plastic part in order to partially set it and prevent its
distortion after removal from the mold. With reference to FIG. 3, a
pair of molds 140 and 141 define therebetween a mold cavity 142 in
which an article 143 is injection molded or compression molded. The
mold members 140 and 141 are cooled by circulating water through
passageways therein. It is sometimes desirable, however, to
selectively cool small portions of the mold or to have one side of
the mold cavity remain warmer than the other in order to allow
plastic flow over a larger area or to prevent internal stresses
from setting up during the injection or compression cycle. In
accordance with the present invention, rapid and localized cooling
can be achieved by supplying a precisely metered quantity of liquid
carbon dioxide to a passageway 145 in the mold member 141. At the
time the rapid and localized cooling is desired, a vapor timer 147
opens a solenoid valve 148 which supplies carbon dioxide vapor at a
pressure at about 80 p.s.i. from a pressure regulator 150 through a
check valve 152 to the downstream side of a small orifice 154 as
well as to the cooling chamber 145 in the mold 141. When the
pressure at the downstream side of the restricted orifice 154 at a
value exceeds the triple point of carbon dioxide, operation of a
CO.sub.2 timer 156 is initiated by a pressure switch 157 to open a
solenoid valve 158 whereby liquid carbon dioxide is fed through the
orifice 154 and is carried by the CO.sub.2 vapor into the cooling
chamber 145 wherein it changes phase and later sublimates to absorb
heat from the mold at the location of the chamber 145. After the
timer 156 times out a preset time interval as required for the
particular part being molded and the desired localized cooling, the
valve 158 is closed.
A solenoid operated valve 162 connects the chamber 145 to the
atmosphere and is controlled by a dump timer 164 which opens the
valve 162 so that the pressure in the chamber is at about
atmospheric pressure and the liquid CO.sub.2, which was fed
thereto, flashes to the solid state at a temperature of minus
110.degree. F. As a safety precaution, a pressure relief valve 166
is provided and as an added safety feature a pressure sensitive
switch 168 is connected to the discharge side of the cooling
chamber 145 and by-passes the dump timer to open the dump valve 162
at pressures in excess of about 300 p.s.i.a.
It may thus be seen that in a system of FIG. 3 the restricted
orifice 154 meters the liquid carbon dioxide into the vapor stream
which carries it to the area of use which is above the triple point
pressure until the valve 162 opens, whereupon the liquid carbon
dioxide flashes to the solid state to rapidly cool the workpiece.
In this system it may be seen that the vapor pressure from the
carbon dioxide tank, as reducibly controlled by the regulator 150,
controls the flow of liquid carbon dioxide to the area of use and
no additional source of pressurized gas such as shop air is
required in this system.
While the present invention has been described in connection with a
particular embodiment thereof it will be understood that many
changes and modifications may be made without departing from the
true spirit and the scope of the present invention. It is intended,
therefore, to cover all such changes and modifications in the
appended claims.
* * * * *