PROCESS FOR GAS ASSISTED AND WATER ASSISTED INJECTION MOLDING

PROCESSUS DE MOULAGE PAR INJECTION AU GAZ ET A L'EAU

English Abstract

A liquid and gas assisted injection molding apparatus comprising a source of
liquid coolant,
a source of compressed gas, a source of heated viscous plastic, a mold cavity
means for controllably
injecting said plastic into said cavity, means for controllably injecting said
compressed gas into said
cavity, means for controllably injecting said liquid coolant into said cavity,
and means for selectively
controlling the injection of said plastic, gas and liquid coolant.

Claims

WHAT IS CLAIMED IS:
1. A liquid and gas assisted injection molding apparatus comprising;
a source of liquid coolant;
a source of compressed gas;
a source of heated viscous plastic;
a mold cavity;
means for controllably injecting said liquid coolant into said cavity;
means for controllably injecting said compressed gas into said cavity;
means for controllably injecting said plastic into said cavity; and
means for selectively controlling the injection of said liquid coolant, gas
and plastic.
2. An apparatus for controlling the injection molding of plastic articles
comprising;
an inlet communicating with a source of non-compressible fluid;
an inlet communicating with a source of compressible fluid;
at least one outlet communicating with a mold cavity;
a remotely operated valve connecting said inlet for non-compressible fluid
with said
outlet;
a remotely operated valve connecting said inlet for compressible fluid with
said
outlet; and
an electronic programmable controller electronically operably connected to
said
remotely operated valves.
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3. A method of molding a plastic article comprising the steps of:
injecting a heated viscous plastic into a closed mold cavity;
injecting a gaseous fluid during the injection of said plastic to create a
fluid space
within the article and to urge the plastic to fill out the mold;
injecting into said fluid space a non-compressible fluid to increase the
pressure within
the fluid space and to increase the cooling rate of said plastic;
venting said non-compressible fluid from said cavity; and
injecting additional gaseous fluid into said fluid space after at least some
of said non-
compressible fluid is vented.
4. A method of injection molding plastic parts comprising:
injecting viscous plastic into a closed mold cavity; and
injecting a non-gaseous fluid into said mold cavity.
5. The method of claim 4 wherein said non-gaseous fluid is injected before the
injection
of said viscous plastic has been completed.
6. The method of claim 4 further comprising:
maintaining the non-gaseous fluid in the mold cavity while the viscous plastic
hardens
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7. The method of claim 6 further comprising venting the non-gaseous fluid
prior to
complete hardening of the viscous plastic.
8. The method of claim 4 wherein the volume of viscous plastic and non-gaseous
fluid
injected is substantially equal to the volume of said mold cavity.
9. The method of claim 4 further comprising injecting a gaseous fluid into
said mold
cavity.
10. The method of claim 9 wherein said gaseous fluid is injected prior to said
non-
gaseous fluid.
11. The method of claim 10 wherein said gaseous fluid is injected before the
injection
of said viscous plastic has been completed.
12. The method of claim 9 wherein said non-gaseous fluid is vented prior to
the injection
of gaseous fluid.
13. The method of claim 10 wherein additional gaseous fluid is injected after
at least
some of the non-gaseous fluid is vented.
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Description

CA 02348128 2001-05-16
PROCESS FOR GAS AS ISTED AND WATER ASSI TED IN TECTION MOLDIN
Continuation of Provisional Application
Serial No. 60/142,01 - Filed: Julv is 1999
Backt round of the Invention
Gas injection molding of plastic has long been known in the industry. During
gas assisted
injection molding molten plastic is forced into an enclosed mold, and gas is
injected into the mold
within the plastic material. The gas will raise the internal pressure and
create an expanding gas
pocket which will force the cooling plastic to the extreme recesses of the
mold, giving a better fill-
out of the mold surface and reducing the sag of the plastic from the mold
surface as the plastic
shrinks during cooling, thus producing a better finished surface.
There are two main methods of injecting gas into the mold cavity. The first is
directly
injecting the gas mold into the cavity, known as i~-article. The second is
injecting the gas into a
channel leading into the mold, which is known as in-runner. The injection of
gas from molten into
the cavities generally is preferred over the channel method.
Gas assisted injection molding uses some plastics that have a long cycle time
i.e. cooling
time in the mold. However, these plastics are still used in order to get
specific shaped parts as
needed. However, it should be noted that in the current art the use of TPO
resin will only allow the
outside of the part to cool while in the mold itself. The inside of the molded
part remains hot and
makes for a difficult molding cycle and/or ruined molded parts. Therefore,
there is a need in the art
for a process that will reduce the temperature of the molded product on the
inside while cooling the
outside at a precise time internal and temperature to allow for a smooth
finished plastic product.


CA 02348128 2001-05-16
Brief Description of the Drawing
Fig. 1 is a diagrammatic representation of a control system for carrying out
the claimed
invention.
Description of the Preferred Embodiment
The present invention is a process for a combination of gas assisted and water
assisted
molding operation for a plastic injection molding system 10 as shown in
attached Figure 1. The
system 10 generally includes a gas unit 12, a water unit 16, and the mold unit
14. The gas supply
unit 12 is connected via a valve 18 to the mold unit 14. The water assist unit
16 is connected via a
valve 20 and valve 22 to the mold unit 14.
In operation the sequence of the molding process is as follow: First an
injection gas assisted
molded operation is started by opening valve 18 to allow the gas to assist in
the initial molding of
the plastic within the mold 14. After a predetermined amount of time valve 18,
which connects the
gas unit 12 to the mold 14 is closed and valve 20 which connects the water
assist unit 16 to the mold
14 is opened in order to inject water into the plastic being molded. The
introduction of this water
will cool the part being molded down to a predetermined temperature in a
predetermined time frame.
Once the part is sufficiently cooled using the water injection system, valve
20 will be closed. After
valve 20 has been closed and the part being molded is sufficiently cooled,
valve 22 will be open to
drain the water from the mold 14. Once the water is fully drained from the
mold, valve 22 is closed
and the mold unit is opened up exposing the part with a smooth finish that has
been made with a
shorter cycle time than the original gas only assisted unit.
Alternatively, the process can be operated utilizing a liquid such as water
alone. Instead of
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CA 02348128 2001-05-16
injecting gas to assist the molding process, a liquid can be injected to
increase the pressure within
the mold and force the plastic to fill out the mold and create a void, the
liquid will also then act to
facilitate the cooling of the plastic.
It should be noted that the valves can be operated either mechanically,
electronically or by
any other means commonly known. It should also be noted that a variety of
coolants may be used
but water is the preferred coolant.
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Representative Drawing