U.S. patent application number 16/711763 was filed with the patent office on 2020-04-16 for injection mold with thermoelectric elements.
The applicant listed for this patent is SABIC Global Technologies B.V.. Invention is credited to Shipu Cao, Xin Kong, Qingya Shen, Yan Wei.
Application Number | 20200114561 16/711763 |
Document ID | / |
Family ID | 52824511 |
Filed Date | 2020-04-16 |
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United States Patent
Application |
20200114561 |
Kind Code |
A1 |
Wei; Yan ; et al. |
April 16, 2020 |
INJECTION MOLD WITH THERMOELECTRIC ELEMENTS
Abstract
In some embodiments, an injection molding apparatus comprises: a
first mold section comprising a first molding surface, wherein the
first mold section is configured for attachment to a presser; a
second mold section and disposed opposite the first mold section, a
thermoelectric device disposed in one of the first and second mold
sections and in thermal communication with at least one of the
first and second mold surfaces; an electrical control system
disposed in electrical communication with the thermoelectric
device; the presser in mechanical communication with the first mold
section and configured to move at least one of the first and second
mold sections toward the other to define a molding space; and an
injector for introducing a material to be molded into the molding
space.
Inventors: |
Wei; Yan; (Kunshan, CN)
; Cao; Shipu; (Shanghai, CN) ; Shen; Qingya;
(Kunshan City, CN) ; Kong; Xin; (Shanghai,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SABIC Global Technologies B.V. |
Bergen op Zoom |
|
NL |
|
|
Family ID: |
52824511 |
Appl. No.: |
16/711763 |
Filed: |
December 12, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15126930 |
Sep 16, 2016 |
10549465 |
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PCT/IB2015/052026 |
Mar 19, 2015 |
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16711763 |
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61955596 |
Mar 19, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 2045/7368 20130101;
B29K 2909/02 20130101; B29C 33/02 20130101; B29C 33/38 20130101;
B29C 45/7331 20130101; B29C 45/73 20130101 |
International
Class: |
B29C 45/73 20060101
B29C045/73; B29C 33/02 20060101 B29C033/02 |
Claims
1. An injection molding apparatus comprising: a first mold section
comprising a first molding surface, wherein the first mold section
is configured for attachment to a presser; a second mold section
comprising a second molding surface and disposed opposite the first
mold section, wherein the first and second molding surfaces face
one another; a thermoelectric device disposed in one of the first
and second mold sections and in thermal communication with at least
one of the first and second mold surfaces; an electrical control
system disposed in electrical communication with the thermoelectric
device; the presser in mechanical communication with the first mold
section and configured to move at least one of the first and second
mold sections toward the other to define a molding space; and an
injector for introducing a material to be molded into the molding
space; and a heat transfer fluid disposed in at least one of the
first and second mold sections and in thermal communication with at
least one of the first and second mold surfaces, wherein the
thermoelectric device and the heat transfer fluid are configured to
simultaneously exchange different thermal energies with at least
one of the first and second molding surfaces, and wherein the
thermoelectric device and the heat transfer fluid are configured to
keep a portion of material in the molding space in a non-solid
state for a period of time while another portion of material in the
molding space is in a solid state.
2. The injection molding apparatus of claim 1, wherein the presser
is configured to move the first mold section toward the second mold
section, and wherein the second mold section is stationary.
3. The injection molding apparatus of claim 1, wherein the presser
moves both the first and second mold sections together.
4. The injection molding apparatus of claim 1, wherein the
electrical control system is configured to reverse a direction of
an electric current flow through the thermoelectric device.
5. The injection molding apparatus of claim 1, wherein at least one
of the first and second mold sections comprise a heat exchange
fluid passage disposed in thermal communication with at least one
of the first and second molding surfaces.
6. The injection molding apparatus of claim 1, wherein at least one
of the first and second mold sections comprise a heat exchange
fluid passage and a metal material, and wherein the metal material
is disposed in thermal communication with the thermoelectric device
and the heat exchange fluid passage.
7. The injection molding apparatus of claim 1, wherein at least one
of the first and second mold sections comprise a metal material,
and wherein the metal material is disposed in thermal communication
with the thermoelectric device and the molding surface.
8. The injection molding apparatus of claim 1, wherein at least one
of the first and second mold sections further comprises a cavity
therein, and wherein the thermoelectric device is disposed in the
cavity.
9. The injection molding apparatus of claim 1, wherein the first
mold section comprises a thermoelectric device disposed therein and
in thermal communication with the first mold surface and the second
mold section comprises a thermoelectric device disposed therein and
in thermal communication with the second mold surface.
10. The injection molding apparatus of claim 1, wherein the
electrical control system comprises a power source, a power
controller, a controller, or a combination of at least one of the
foregoing.
11. The injection molding apparatus of claim 1, wherein the
thermoelectric device comprises metals, ceramics, semiconductors,
nanostructured super-lattices, quantum wells, nano-materials,
single crystal silicon nanowires, or a combination comprising at
least one of the foregoing.
12. The injection molding apparatus of claim 1, wherein the
thermoelectric device operates to maintain less than or equal to a
5% reduction in a total flow area within the injection molding
apparatus.
13. A method of injection molding using the injection molding
apparatus of claim 1, comprising: forming a molding space between
the first mold section and the second mold section by pressing
together using a presser; heating at least one of the first mold
section and the second mold section with the thermoelectric device
by flowing an electric current through the thermoelectric device in
a first direction; introducing a material to be molded into the
molding space; simultaneously heating a portion of the material in
the molding space while cooling another portion of the material in
the molding space, wherein a portion of material in the molding
space is kept in a non-solid state for a period of time while
another portion of material in the molding space is in a solid
state; cooling the material to be molded to form a molded part; and
exiting the part from the part forming mold cavity.
14. The method of claim 13, wherein cooling the material to be
molded comprises: flowing a heat transfer fluid through a heat
transfer passage formed in at least one of the first mold section
and the second mold section, flowing an electric current through
the thermoelectric device in a second direction opposite the first
direction, or a combination comprising at least one of the
foregoing.
15. The method of claim 13, wherein cooling the material to be
molded comprises flowing an electric current through the
thermoelectric device in a second direction opposite the first
direction.
16. The method of claim 13, wherein the material to be molded is a
plastic material.
17. An injection molding apparatus comprising: a first mold section
comprising a first molding surface, wherein the first mold section
is configured for attachment to a presser; a second mold section
comprising a second molding surface and disposed opposite the first
mold section, wherein the first and second molding surfaces face
one another; a first thermoelectric device disposed in the first
mold section and in thermal communication with the first mold
surface; a second thermoelectric device disposed in the second mold
section and in thermal communication with the second mold surface;
an electrical control system disposed in electrical communication
with both the first and second thermoelectric devices; the presser
in mechanical communication with the first mold section and
configured to move the first mold section toward the second mold
section to define a molding space, wherein the second molding
surface is stationary; an injector for introducing a material to be
molded into the molding space; and a heat transfer fluid disposed
in at least one of the first and second mold sections and in
thermal communication with at least one of the first and second
mold surfaces, wherein the thermoelectric devices and the heat
transfer fluid are configured to simultaneously exchange different
thermal energies with at least one of the first and second mold
surfaces, and wherein the thermoelectric device and the heat
transfer fluid are configured to keep a portion of material in the
molding space in a non-solid state for a period of time while
another portion of material in the molding space is in a solid
state.
18. The injection molding apparatus of claim 17, wherein at least
one of the first and second mold sections comprise a heat exchange
fluid passage disposed in thermal communication with at least one
of the first and second molding surfaces.
19. The injection molding apparatus of claim 17, wherein the
electrical control system is configured to reverse a direction of
an electric current flow through at least one of the first and
second thermoelectric devices.
20. The injection molding apparatus of claim 17, wherein at least
one of the first and second thermoelectric devices operates to
maintain less than or equal to a 5% reduction in a total flow area
within the injection molding apparatus.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 15/126,930 which is a 371 of International Application No
PCT/IB2015/052026, filed Mar. 19, 2015, which claims the benefit of
Provisional Application No. 61/955,596, filed Mar. 19, 2014, both
of which are incorporated by reference in their entirety
herein.
BACKGROUND
[0002] In injection molding, granular molding material can be fed
by gravity from a hopper into a heated barrel. The granules can be
slowly advanced by a screw, which can aid in melting the molding
material due to frictional heat cause by shear forces within the
material. The molding material can be forced into a heated chamber,
where it can be melted. The melted molding material can be forced
through an injector that rests against the mold such that the
material can enter the mold through a gate and runner system to a
mold cavity. The mold can be kept cold by circulating a heat
transfer fluid through the mold walls adjacent the cavity so the
molding material solidifies as the mold is filled.
[0003] The mold can have a number of important sections. Molten
material, called the melt, can enter the mold through a sprue, or
channel, formed in the mold, e.g., along a mold surface or through
the mold section. A sprue bushing can be tightly sealed against the
injector of the injection device. A channel can be called a runner.
The runner can connect to the sprue. The runner can guide the melt
to the part forming mold cavity. The location at which the molten
material enters the part forming mold cavity is called the gate.
The amount of resin required to fill the sprue, runner, and part
forming mold cavity, or cavities, of a mold is sometimes known as a
"shot". Hot melt can cool as it flows to the part forming mold
cavity, as it flows along and/or within the mold sections. Thermal
energy removed from the melt can travel to an ancillary cooling
system. An ancillary cooling system can include a fluid heat
exchange circuit in thermal communication with a mold section. An
ancillary cooling system can include a fluid heat exchange circuit
in fluid communication with a mold section. An ancillary cooling
system can include a fluid heat exchange circuit in fluid
communication and thermal communication with a mold section. As the
melt cools, the inner section of the melt, farther from cool mold
walls, can continue to flow and fill the mold cavity. The injector
can pressurize the melt to eliminate gas bubbles. The injector can
force the cooling melt against the mold cavity walls. The injector
pressure can be maintained while the part solidifies. The injector
pressure can be increased while the part solidifies. The injector
pressure can be decreased while the part solidifies.
[0004] Challenges in injection molding can arise from controlling
the temperature of a mold during each phase of the process and in
every area that the plastic contacts. If a mold temperature is not
controlled properly then a variety of part defects can result. If a
mold temperature is not uniformly controlled then a variety of part
defects can result. A temperature control system for a molding
operation can be complex and can be capital intensive. A
temperature control system for a molding operation can have
significant customization to a particular mold design. A
temperature control system for a molding operation can be
inefficient. Thus there is a need in the art for a mold design that
can improve control of mold temperatures, improve efficiency, and
can reduce capital cost.
SUMMARY
[0005] The present inventors have recognized, among other things,
that a problem to be solved can include efficient control of mold
temperatures in an injection molding apparatus. The present subject
matter can help provide a solution to this problem, such as by
providing a thermoelectric device which can heat or cool a mold
surface based on the direction of current flow through the device.
Thermoelectric devices can reduce the heat loss of a temperature
control system such as by localizing the temperature control
function to a mold section.
[0006] In some embodiments, an injection molding apparatus can
comprise: a first mold section comprising a first molding surface,
wherein the first mold section is configured for attachment to a
presser; a second mold section comprising a second molding surface
and disposed opposite the first mold section, wherein the first and
second molding surfaces face one another; a thermoelectric device
disposed in one of the first and second mold sections and in
thermal communication with at least one of the first and second
mold surfaces; an electrical control system disposed in electrical
communication with the thermoelectric device; the presser in
mechanical communication with the first mold section and configured
to move at least one of the first and second mold sections toward
the other to define a molding space; and an injector for
introducing a material to be molded into the molding space.
[0007] In some embodiments, a method of injection molding can
comprise: forming a molding space between two mold sections;
heating at least one of the mold sections with a thermoelectric
device by flowing an electric current through the thermoelectric
device in a first direction; introducing a material to be molded
into the molding space; cooling the material to be molded to form a
molded part; exiting the part from the part forming mold
cavity.
[0008] In some embodiments, an injection molding apparatus can
comprise: a first mold section comprising a first molding surface,
wherein the first mold section is configured for attachment to a
presser; a second mold section comprising a second molding surface
and disposed opposite the first mold section, wherein the first and
second molding surfaces face one another; a first thermoelectric
device disposed in the first mold section and in thermal
communication with the first mold surface; a second thermoelectric
device disposed in the second mold section and in thermal
communication with the second mold surface; an electrical control
system disposed in electrical communication with both the first and
second thermoelectric devices; the presser in mechanical
communication with the first mold section and configured to move
the first mold section toward the second mold section to define a
molding space, wherein the second molding surface is stationary;
and an injector for introducing a material to be molded into the
molding space.
[0009] This summary is intended to provide a summary of subject
matter of the present patent application. It is not intended to
provide an exclusive or exhaustive explanation of the invention.
The detailed description is included to provide further information
about the present patent application.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Refer now to the figures, which are exemplary embodiments,
and wherein the like elements are numbered alike.
[0011] FIG. 1 is an illustration of a side view of a partially open
injection molding apparatus with thermoelectric devices.
[0012] FIG. 2 is an illustration of a side view of a closed
injection molding apparatus with thermoelectric devices.
[0013] FIG. 3 is an illustration of a thermoelectric device.
[0014] FIG. 4 is an illustration of a side view of an open
injection molding apparatus with a thermoelectric device.
[0015] The figures are exemplary only and are not drawn to a
particular scale.
DETAILED DESCRIPTION
[0016] Disclosed herein are molds, such as ceramic molds, including
thermoelectric devices. The devices can control the surface
temperatures within the mold cavity. The devices can actively
control the temperature, such as through the use of feedback. They
can also passively control the surface temperatures. Controlling
the mold temperatures in a precise fashion can improve part quality
(e.g., dimensional consistency from part to part). Rapid control of
mold temperature can contribute to shorter cycle times.
[0017] In molding plastic parts, two or more mold sections, each
having a detachable or integral molding surface, can be pressed
together to define a molding space, including a part forming mold
cavity and an injection passage, or channel. A molten plastic
material can be introduced into one or more part forming mold
cavities through the injection passage, which is sometimes called a
runner. In the runner molten plastic can run along surfaces of the
passage as it makes its way through to the part forming mold
cavity. During the introduction stage of the molding process the
plastic is in a fluid phase. As the plastic flows through the
passage it touches the passage walls in the runner(s) and cools.
Portions of the flow, adjacent the passage walls solidify and
narrow the flow area within the passage. This can restrict the flow
of remaining plastic material entering the mold cavity. To overcome
this reduction in flow area, the injection pressure can be
increased to continue to push molten plastic into the mold. This
can lead to high injection pressure. In an example, the injection
pressure can rise from 5000 kiloPascals to 17000 kiloPascals when
the melt passes the runner and enters the mold cavity.
[0018] As molten plastic touches the molding surfaces it transfers
heat into the mold sections. A mold section can include cooling
channels or passages to allow a heat transfer fluid to circulate
through the mold section to maintain the molding surface at a
desired temperature. In a heat exchange circuit of this type,
thermal energy from the mold section can be transferred into a heat
transfer fluid. The heat transfer fluid can transfer thermal energy
to a second heat transfer fluid in a separate heat exchanger. The
temperature profile across the molding surface can be difficult to
adjust using fluid based heat exchange of this type, at least
because the fluid flow through each passage can have a fixed
relationship to the total fluid flow. To address this shortcoming,
heat exchange circuits can be complicated.
[0019] Complicated circuits can include valves, orifices, pumps,
temperature sensors, controllers, and the like as well as intricate
or convoluted flow paths within the mold sections. These circuits
can be designed to distribute the heat transfer fluid in a way that
desirably controls the molding surface temperatures, e.g.,
temperatures along the surfaces of the part forming mold cavity,
and injection channel(s). Thus the heat transfer fluid can be used
to maintain a desired temperature distribution throughout the mold
section, particularly along the surfaces of the part forming mold
cavity. These circuits can be efficiently sized and designed to
precisely achieve the desired molding surface temperatures, but can
be expensive to the design and manufacture.
[0020] Some examples maintain molding surfaces nearly isothermal.
Such an approach can rely on large fluid flows, secondary heat
exchangers, and other approaches that add cost, and can decrease
cycle time.
[0021] These heat transfer methods work well with pliable metal
mold sections because the heat transfer circuits can be easily
formed into metal sections using conventional techniques,
including, but not limited to, machining, drilling, stamping,
pressing, and the like, and because metal mold sections can provide
high heat conduction between the melt and the heat transfer
fluid.
[0022] Apart from formability and heat transfer, another important
property, which can be considered in selecting a material of
construction for the mold sections, is the useful life of the mold
section. Soft metals (e.g., aluminum) can be used in relatively
short-lived manufacturing operations, but can be ill-suited for
long term manufacturing use due to their comparatively low wear
resistance in comparison to hardened steel. Similarly, hardened
steel can have inferior wear resistance and ductility (leading to
issues with long term dimensional control of molded parts) in
comparison to ceramic materials.
[0023] The useful life of a molding surface can be determined by
its ability to maintain the shape of the finished part within
dimensional requirements of the part. Through repeated thermal
cycling, and use, as in surface-to-surface contact and pressing,
metal molding surfaces can wear and can eventually result in
out-of-tolerance parts, i.e., parts which do not conform to the
established dimensional tolerances of the molded part. Ceramic
materials can offer superior hardness and abrasion resistance in
comparison to metals, properties that can be attributed to the
microstructure of the ceramic material. These properties can
contribute to superior durability and excellent wear resistance,
which result in longer useful service life for molding surfaces
made of ceramics in comparison to molding surfaces made of
metal.
[0024] Ceramics offer high rigidity, or stiffness (i.e., Young's
modulus), in comparison to metals which can reduce deflection
and/or deformation when a ceramic is under load. This property
contributes to ceramics ability to maintain close dimensional
tolerances over a long time, and enables the ability to mold thin
cross sections and intricate shapes.
[0025] Another property of ceramics which can be exploited for
molding operations is the wide variety of surface finishes not
available with metals.
[0026] However, despite these beneficial properties, ceramics do
not conduct heat well, and due at least in part to the high
hardness and abrasion resistance it can be difficult and/or
expensive to form heat transfer circuits in ceramic mold sections.
Because of these properties, ceramics have not seen wide scale
adoption in molding operations, despite their other advantages over
metals such as superior wear resistance, dimensional control, and
variety of surface finish. To overcome these drawbacks a ceramic
mold section can include a thermoelectric device which can be used
to control temperatures throughout the mold section.
[0027] In some thermoelectric devices, when direct current (DC)
passes through a circuit of heterogeneous conductors, heat can be
released or absorbed at the conductors' junctions. The amount of
heat released or absorbed is proportional to the current that
passes through the conductors. Whether a junction is "hot" or
"cold" depends on the direction of the current flow, i.e., the
polarity of the circuit. This phenomenon is used in thermocouples,
where the temperature gradient drives a current flow through the
device and the resulting voltage difference can be correlated to a
temperature at a junction.
[0028] Thermoelectric devices as used herein refer to devices
capable of converting a voltage gradient into a temperature
gradient and vice versa. Thermoelectric devices can include
interface between dissimilar materials. These dissimilar materials
can include metals, ceramics, semiconductors, and any materials
which demonstrate the Peltier effect (the presence of heating or
cooling at an electrified junction of two different conductors).
Thermoelectric devices can include nano-materials, such as
nanostructured super-lattices, quantum wells, and single crystal
silicon nanowires. Thermoelectric devices which operate using
thermo-tunneling fall within the present scope.
[0029] A mold section can include a thermoelectric device disposed
in thermal communication with the molding surface which can contact
the melt during the molding process.
[0030] A thermoelectric device can be used to form the molding
surface, or face, of the mold section which can contact the melt
during molding. Alternatively, a thermoelectric device can be
inserted in the mold sections, in cavities, where it can be in
thermal communication with the mold section and molding surfaces
which can contact the melt during molding (i.e. the walls of a part
forming mold cavity and injection passage). In this way, a
thermoelectric device can be disposed and/or configured in a way to
provide heating and cooling to the melt. Thermoelectric devices can
be stacked, one on top of another, adjacent to another, and/or
affixed to another, or otherwise configured in thermal
communication with one another to multiply the cooling and/or
heating effect.
[0031] Thermoelectric devices can be placed within a ceramic mold
section, in thermal communication with only selected portions of
the molding surface, to provide discrete temperature control to a
localized section of the molding surface. In this way, volumes
and/or areas of the melt can be cooled and/or heated in a desired
order, more or less rapidly, to a different temperature, and/or at
a different rate than other volumes and/or areas of the melt.
[0032] Cavities for holding thermoelectric device inserts can be
formed in ceramic mold sections from any side of the mold section,
including the molding surface of the section. In particular,
thermoelectric devices disposed in cavities formed in the mold
section can be easily accessed for routine maintenance and/or
overhaul, as in repair or replacement. Thermoelectric devices can
be located within the volume of the mold section, as in a distance
closer or further from the melt, to affect the temperature at a
location of the mold section and/or the rate that thermal energy is
transferred between the thermoelectric device and the melt.
[0033] A ceramic mold section can be formed with metal inserts.
These metal inserts can provide a heat transfer pathway between
areas/volumes of the mold section. These pathways can be used to
transfer thermal energy between volumes or areas of the mold
section, for example, between a molding surface, thermoelectric
device disposed in the mold section, and/or a heat transfer fluid
passage within the mold section.
[0034] Hybrid mold sections, of ceramic and metal, can
advantageously combine features of each material. The metal inserts
can provide defined heat flow pathways within the ceramic mold
section. While the ceramic portions can provide high hardness and
abrasion resistance, particularly to the molding surface or other
contacting parts within the mold apparatus, such that the mold
apparatus can meet the part tolerance requirements for a longer
service life in comparison to a mold apparatus with equivalent
metal portions.
[0035] Thermoelectric devices can be disposed in a mold section in
thermal communication with a heat transfer fluid passage to allow
for cooling or heating the thermoelectric device and/or of a single
side of the thermoelectric device. A heat transfer fluid can be
used in conjunction (together) with a thermoelectric device in a
molding operation, such that both a thermoelectric device and a
heat transfer fluid can exchange thermal energy with the molding
surfaces (and melt) simultaneously. In this case, the exchange of
thermal energy can be different for the thermoelectric device and
the heat transfer fluid, for example, the thermoelectric device can
heat while the heat transfer fluid cools the melt, or portions of
the melt, and vice versa.
[0036] During the melt introduction stage a thermoelectric device
can act to keep the mold section and/or molding surface adiabatic,
or nearly adiabatic, where no, or very little, thermal energy is
transferred from the melt to the molding surface. In this way, a
thermoelectric device can serve to keep the melt in a liquid,
molten or flowable state, to ensure the entire mold cavity is
filled with material to be molded. In other words, a thermoelectric
device can be used to reduce the amount of the melt which
solidifies on the molding surface, thereby reducing the amount of
flow area blocked by solidified melt, and reducing the pressure
required to fill the entire volume of the part forming mold
cavity.
[0037] For example, during the melt introduction phase a
thermoelectric device can be operated with a first polarity (i.e.,
direction of current flow) to generate heat at a thermoelectric
device junction, called the "hot" junction. The "hot" junction can
be in thermal communication with a molding surface. In this way the
thermoelectric device can transfer thermal energy into the flow
passages of the mold, including the sprue, runner, gate, and part
forming mold cavity, and can keep the melt flowing, (e.g., as in a
molten, liquid, or flowable state) reducing the occurrence of melt
solidification along a molding surface. Thus the flow area
available for the melt, e.g., sprue, runners, gate, and part
forming cavity, can be free of blockage or obstruction due to
solidified material. In other words, the heating can keep the melt
flowing, particularly within the flow passage(s) and along molding
surfaces. Because the melt can flow more freely during melt
introduction, due to greater flow area and reduction in the amount
of material which solidifies, the injection pressure can be reduced
without introducing part defects. Lowering the injection pressure
can reduce operating cost by reducing energy consumption of
pressing related equipment (e.g. hydraulic pump, motor, pneumatic
pump, and the like). Lowering the injection pressure can reduce
capital cost by reducing the design pressure of the mold sections,
pressers, injectors, and other parts of the molding apparatus.
Lowering the injection pressure can increase the useful life or a
mold apparatus by reducing the wear on molding surfaces per
cycle.
[0038] Once melt introduction is complete a thermoelectric device
can be operated with a second polarity (i.e., second direction of
current flow), opposite the first polarity, to reverse the
temperature gradient across the thermoelectric device. Thus cooling
the previously "hot" junction and, simultaneously, heating the
previously "cold" junction. In this way, the temperature of the
previously "hot" junction, which can be in thermal communication
with molding surfaces, starts to cool and in turn cools the molding
surfaces. This can draw thermal energy out of the mold and out of
the material to be molded (i.e., the melt).
[0039] A thermoelectric device can improve thermal control by
providing direct, local, control of molding surface temperatures,
rapid response time, and narrow temperature operating ranges,
without complicated and comparatively slow fluid controls (valves,
pumps, heaters, fans, and the like). The use of a thermoelectric
device within ceramic mold sections can be further advantaged by
ceramics lack of electrical conductivity. Unlike metal, mold
sections made of ceramic will not short out thermoelectric devices
and therefore the use of thermoelectric devices within ceramic mold
sections does not cause undue complexity to the mold design or to
the design of the thermoelectric device.
[0040] A thermoelectric device can be disposed in electrical
communication with an electrical control system. The electrical
control system can provide power and regulation of the electric
current flowing to and/or through the thermoelectric device. The
electrical control system can, generally, include a power source,
power conditioner, and controller, as well as wiring to conduct
power, communication, sensor, and/or control signals. The
electrical control system can, more specifically, include a power
transformer, alternating current (AC) power source, AC/DC
converter, DC power source, voltage converter, power regulator,
current regulator, voltage regulator, feedback signals (e.g.,
temperature, pressure, material flow, current, voltage, power, and
the like), and a microprocessor, controller, programmable logic
controller, or other type of logic controller.
[0041] Feedback signals can originate from a direct measurement
device (e.g., a thermocouple, voltmeter, mass flow meter, volume
flow meter, current clamp, and the like) or can originate from a
calculated parameter or property (e.g., enthalpy, viscosity,
density, and the like). Feedback signals can be used to improve the
accuracy, response time and ultimately the efficiency of the
thermoelectric device, and can be used in the electrical control
system to control the amount and/or direction of electric current
flow through the thermoelectric device.
[0042] Temperature measurement devices can include a thermocouple,
thermistor, resistance thermometer, UV sensor, and other
temperature measuring devices.
[0043] A controller can be used to drive the error between a
desired temperature (i.e., temperature set point) and a
thermoelectric device junction temperature, molding surface
temperature, or temperatures indicative thereof, or any desired
control temperature, to zero. The controller can use any suitable
control algorithm to drive the error between the set point and the
actual measured parameter to zero, for example, the algorithm can
include proportional error, integral error, differential error, or
a combination including at least one of the foregoing, as in, for
example, a proportional-integral-differential (PID) control
algorithm. The controller can use any type of intelligent control
techniques, including, for example, neural networks, Bayesian
probability, fuzzy logic, machine learning, and evolutionary
computation. Alternatively, the electrical control system can be
manually controlled.
[0044] Molds as disclosed herein can be used to mold many different
types of molding materials, including metal, glass, thermoplastic
polymer, thermoset polymer, and combinations comprising at least
one of the foregoing. The molding materials can include polymeric
materials. Some examples of polymeric materials include
thermoplastic materials such as polybutylene terephthalate (PBT);
polyetherimides (PEI); acrylonitrile-butadiene-styrene (ABS);
polycarbonate (PC); polycarbonate/PBT blends; polycarbonate/ABS
blends; co-polycarbonate-polyesters; blends of
polycarbonate/polyethylene terephthalate (PET)/PBT; as well as
combinations comprising at least one of the foregoing. The polymer
material can include additives, such as impact modifier,
ultraviolet light absorber, pigment, or a combination of one of the
foregoing. The molding materials can include reinforcing materials,
such as glass, carbon, basalt, aramid, or combination comprising at
least one of the foregoing. Reinforcing materials can include cut,
chopped, strand fibers, or a combination comprising at least one of
the foregoing. For example, the material can be PC/PBT, a
polyolefin (e.g., polypropylene such as glass filled polypropylene,
long glass fiber polypropylene, etc.) as well as combinations
comprising at least one of the foregoing.
[0045] In the molding operation the mold sections can be closed
while a shot (amount of molding material needed to fill the
passages and part forming mold cavity) of melt is prepared for
injection (e.g., heated and moved into an injector). During this
pre-injection phase, a thermoelectric device can be operated by an
electronic control system with a first polarity so as to heat the
junctions of the thermoelectric device which are in thermal
communication with a molding surface. The amount of electric
current flowing through the thermoelectric device can be
controlled, such that the hot junctions of the thermoelectric
device are at a temperature greater than or equal to the glass
transition temperature of the material to be molded, to keep the
material flowing during introduction.
[0046] As a shot of melt is introduced into the mold cavity, a
thermoelectric device can continue to operate with a first polarity
i.e., heating a molding surface, or maintaining the temperature of
the molding surface, to keep a majority of the melt in a non-solid
state, to reduce the amount of solidification, and keep the molding
space substantially free from restriction/obstruction due to
solidification. In this case, substantially free means that a
thermoelectric device can operate to maintain less than or equal to
5% reduction in total flow area, for example, 0.1% to 2%, or, 0.1%
to 1% reduction in total flow area in a melt injection passage.
[0047] Once the shot is introduced into the mold, and the part
forming mold cavity is filled with material, the injector maintains
a pressure of the melt within the molding space as the melt
solidifies into the form of the molded part; this stage is referred
to as solidification. During solidification the flow of electric
current from the electrical control system through the
thermoelectric device can be reversed, such that the thermoelectric
device can be operated with a second polarity (opposite the first
polarity). In this way, the junctions of the thermoelectric device
which were hot during melt introduction phase can start to cool.
These junctions, in thermal communication with a molding surface
and contacting the melt, can remove thermal energy from the melt
during the solidification process.
[0048] During any stage of the molding operation, a heat exchange
fluid circuit can be operated to exchange thermal energy between a
thermoelectric device, a mold section, including a molding surface,
or other components of the molding apparatus, and the heat transfer
fluid.
[0049] The temperature of the molding surface in contact with the
melt can be lowered below the glass transition temperature of the
material to be molded. A thermoelectric device and/or a fluid heat
exchange circuit can operate, together or separately, to cool the
melt during solidification. Once the temperature of the melt has
dropped below the glass transition temperature of the material to
be molded the mold can be opened and the molded part can be exited,
i.e., removed or ejected, from the mold cavity.
[0050] After exiting the mold, the molded part can cool to room
temperature and/or undergo further processing. Once the molded part
has been formed, the part can be further processed, or
finish-processed, to form a finished part. Finish-processing
operations can include removing material from the part, and/or
reforming the part chemically, mechanically, and/or thermally, for
example, post-consolidation processing can include abrasive
blasting, breaking, buffing, burnishing, cutting, drilling,
etching, eroding, grinding, indenting, machining, marking,
polishing, sanding, scoring, shaping, threading, trimming,
tumbling, vibrating, and/or otherwise creating surface treatments,
or a combination including at least one of the foregoing.
Finish-processing operations can also include adding material to
the part, for example, overmolding, remolding, back-molding, adding
(i.e., applying) coatings, as in sealers, glazes, paints,
functional layers, markings, and/or other surface additives to the
part, or a combination of at least one of the foregoing. Types of
coatings can include abrasion resistant, adhesive, antimicrobial,
catalytic, decorative, electrically or thermally conductive,
electrically or thermally non-conductive, light sensitive,
non-adhesive, optical, primers, ultra-violet protective,
waterproof, or a combination comprising at least one of the
foregoing.
[0051] FIG. 1 shows an illustration of an injection molding
apparatus 10 having thermoelectric devices 30 disposed therein. Two
mold sections 20 are attached to platens 18, which are attached to
a pressing device. The pressing device can be hydraulic, pneumatic,
electric, mechanical, and the like and can act to bring the platens
18 together to form a molding space, including a part forming mold
cavity 22 between the mold sections 20. The mold sections 20
include heat exchange fluid passages 28, or channels. The channels
can be disposed in fluid communication with a heat exchange
circuit. The channels can be disposed in thermal communication with
a heat exchange circuit. The channels can be disposed in fluid and
thermal communication with a heat exchange circuit. A heat exchange
circuit can include a separate heat exchanger for transferring
thermal energy between the heat transfer fluids.
[0052] Two thermoelectric devices 30 are disposed in electrical
communication with an electrical control system 40. The electrical
control system 40 uses a controller 50 to interpret temperature
measurements from temperature sensors 46 and control the delivery
of current (i.e., power) from a power source 42, through the power
controller 48, and to the thermoelectric devices 30.
[0053] The thermoelectric devices 30 are in thermal communications
with a molding surface 23 and the heat transfer fluid passages 28.
A metal insert 27 can be disposed between a section of a
thermoelectric device 30 and the heat exchange fluid passages 28 to
provide a specific heat transfer pathway to augment the exchange of
thermal energy between the thermoelectric device 30 and the heat
exchange fluid.
[0054] FIG. 2 shows an illustration of a side view of an injection
molding apparatus 10 having molding surfaces 23 of mold sections 20
pressed together to form a molding space 25 (region enclosed with
dotted lines). The molding space is defined by two part forming
mold cavities 22, a sprue 26, two runners 29, and two gates 24
which are formed between the molding surfaces 23 of the
corresponding mold sections 20. A sprue bushing 14 is disposed
between the sprue 26 and the injector 12. As the melt is injected
from the injector 12 it flows through the sprue 26, through the
runners 29, through the gates 24, and into the part forming mold
cavities 22. Thermoelectric devices 30 can be used to heat the
molding material during melt introduction and cool the molding
material into a solid part during solidification.
[0055] FIG. 3 shows and illustration of a type of thermoelectric
device 30. In this case, the thermoelectric device 30 is a
semiconductor device having N-type semiconductors 38 and P-type
semiconductors 39.
[0056] N-type and P-type semiconductors refer to extrinsic
semiconductors which have been doped to impart different electrical
properties. The N-type semiconductor has larger electron
concentration than hole concentration (electron hole, absence of a
negative-mass electron, or absence of an electron near the top
valence band), whereas the opposite is true with P-type
semiconductors which have a larger hole concentration than electron
concentration.
[0057] In FIG. 3 the direction of electric current flow 44 is shown
to be generally, from electrical connection 36 to electrical
connection 37. When electric current flows along this path, the
electrical connection 36 is the negative pole, and the electrical
connection 37 is the positive pole. In this case, current flows
from P-type to N-type semiconductors in junctions 33 adjacent to
the top surface 31 and from N-type to P-type semiconductors in
junctions 34 adjacent to the bottom surface 32. Current flowing
from P-type to N-type semiconductors releases thermal energy,
whereas current flowing from N-type to P-type semiconductors
absorbs thermal energy. Thus, in this configuration the current
flow will result in "hot" junctions 33 adjacent to the top surface
31 which will become hot, and "cold" junctions 34 adjacent to the
bottom surface 32 which will become cold.
[0058] The "hot" and "cold" junctions can be reversed by reversing
the direction of current flow through the thermoelectric device,
e.g., by flowing current from electrical connection 37 to
electrical connection 36. This is because when the current flow is
reversed, current will flow from N-type to P-type semiconductors in
junctions 33 adjacent to the top surface 31, and from P-type to
N-type semiconductors in junctions 34 adjacent the bottom surface
32.
[0059] FIG. 4 shows an illustration of a side view of an injection
molding apparatus 10 having molding surfaces 23 (represented by
dotted lines) of mold sections 20 spaced apart from one another. A
presser 16 can be disposed in mechanical communication with a first
mold section 20 and can be configured to move at least one of the
first and second mold sections 20 toward the other to define a
molding space 25. The molding space 25 is defined by the molding
surfaces 23 of the corresponding mold sections 20 once the mold
sections are brought together. An injector 12 is positioned next to
a channel through a mold section 20 for introducing molding
material to the mold. As the melt is injected from the injector 12
it flows into the molding space 25. A thermoelectric device 30 can
be used to heat a molding surface 23 during melt introduction and
cool the molding surface 23 during solidification. An electrical
control system 40 can be disposed in electrical communication with
the thermoelectric device 30.
Embodiment 1
[0060] An injection molding apparatus comprising: a first mold
section comprising a first molding surface, wherein the first mold
section is configured for attachment to a presser; a second mold
section comprising a second molding surface and disposed opposite
the first mold section, wherein the first and second molding
surfaces face one another; a thermoelectric device disposed in one
of the first and second mold sections and in thermal communication
with at least one of the first and second mold surfaces; an
electrical control system disposed in electrical communication with
the thermoelectric device; the presser in mechanical communication
with the first mold section and configured to move at least one of
the first and second mold sections toward the other to define a
molding space; and an injector for introducing a material to be
molded into the molding space.
Embodiment 2
[0061] The injection molding apparatus of Embodiment 1, wherein the
presser is configured to move the first mold section toward the
second mold section, and wherein the second mold section is
stationary.
Embodiment 3
[0062] The injection molding apparatus of Embodiment 1, wherein the
presser moves both the first and second mold sections together.
Embodiment 4
[0063] The injection molding apparatus of any one of Embodiments
1-3, wherein both the first and second mold sections are formed
from a ceramic material.
Embodiment 5
[0064] The injection molding apparatus of any one of Embodiments
1-4, wherein the electrical control system is configured to reverse
a direction of an electric current flow through the thermoelectric
device.
Embodiment 6
[0065] The injection molding apparatus of any one of Embodiments
1-5, wherein at least one of the first and second mold sections
comprise a heat exchange fluid passage disposed in thermal
communication at least one of the first and second molding
surfaces.
Embodiment 7
[0066] The injection molding apparatus of any one of Embodiments
1-6, wherein at least one of the first and second mold sections
comprise a heat exchange fluid passage and a metal material, and
wherein the metal material is disposed in thermal communication
with the thermoelectric device and the heat exchange fluid
passage.
Embodiment 8
[0067] The injection molding apparatus of any one of Embodiments
1-7, wherein at least one of the first and second mold sections
comprise a metal material, and wherein the metal material is
disposed in thermal communication with the thermoelectric device
and the molding surface.
Embodiment 9
[0068] The injection molding apparatus of any one of Embodiments
1-8, wherein at least one of the first and second mold sections
further comprises a cavity therein, and wherein the thermoelectric
device is disposed in the cavity.
Embodiment 10
[0069] The injection molding apparatus of any one of Embodiments
1-8, wherein the first mold section comprises a thermoelectric
device disposed therein and in thermal communication with the first
mold surface and the second mold section comprises a thermoelectric
device disposed therein and in thermal communication with the
second mold surface.
Embodiment 11
[0070] The injection molding apparatus of any one of Embodiments
1-10, wherein the electrical control system comprises a power
source, a power conditioner, a controller, or a combination of at
least one of the foregoing.
Embodiment 12
[0071] The injection molding apparatus of any one of Embodiments
1-11, wherein the thermoelectric device comprises metals, ceramics,
semiconductors, nanostructured super-lattices, quantum wells,
nano-materials, single crystal silicon nanowires, or a combination
comprising at least one of the foregoing.
Embodiment 13
[0072] A method of injection molding comprising: forming a molding
space between two mold sections; heating at least one of the mold
sections with a thermoelectric device by flowing an electric
current through the thermoelectric device in a first direction;
introducing a material to be molded into the molding space; cooling
the material to be molded to form a molded part; exiting the part
from the part forming mold cavity.
Embodiment 14
[0073] A method of injection molding using the apparatus of any of
Embodiments 1-12, comprising: heating at least one of the mold
sections with a thermoelectric device by flowing an electric
current through the thermoelectric device in a first direction;
introducing a material to be molded into the molding space; cooling
the material to be molded to form a molded part; exiting the part
from the part forming mold cavity.
Embodiment 15
[0074] The method of any one of Embodiments 13-14, wherein cooling
the material to be molded comprises: flowing a heat transfer fluid
through a heat transfer passage formed in at least one of the mold
sections, flowing an electric current through the thermoelectric
device in a second direction opposite the first direction, or a
combination comprising at least one of the foregoing.
Embodiment 16
[0075] The method of any one of Embodiments 13-15, wherein cooling
the material to be molded comprises flowing an electric current
through the thermoelectric device in a second direction opposite
the first direction.
Embodiment 17
[0076] The method of any one of Embodiments 13-16, wherein the
material to be molded is a plastic material.
Embodiment 18
[0077] An injection molding apparatus comprising: a first mold
section comprising a first molding surface, wherein the first mold
section is configured for attachment to a presser; a second mold
section comprising a second molding surface and disposed opposite
the first mold section, wherein the first and second molding
surfaces face one another; a first thermoelectric device disposed
in the first mold section and in thermal communication with the
first mold surface; a second thermoelectric device disposed in the
second mold section and in thermal communication with the second
mold surface; an electrical control system disposed in electrical
communication with both the first and second thermoelectric
devices; the presser in mechanical communication with the first
mold section and configured to move the first mold section toward
the second mold section to define a molding space, wherein the
second molding surface is stationary; and an injector for
introducing a material to be molded into the molding space.
Embodiment 19
[0078] The injection molding apparatus of Embodiment 18 wherein
both the first and second mold section is formed from a ceramic
material.
Embodiment 20
[0079] The injection molding apparatus of any one of Embodiments
18-19, wherein at least one of the first and second mold sections
comprise a heat exchange fluid passage disposed in thermal
communication with at least one of the first and second molding
surfaces.
Embodiment 21
[0080] The injection molding apparatus of any one of Embodiments
18-20 wherein the electrical control system is configured to
reverse a direction of an electric current flow through at least
one of the first and second thermoelectric devices.
[0081] In general, the invention may alternately comprise, consist
of, or consist essentially of, any appropriate components herein
disclosed. The invention may additionally, or alternatively, be
formulated so as to be devoid, or substantially free, of any
components, materials, ingredients, adjuvants or species used in
the prior art compositions or that are otherwise not necessary to
the achievement of the function and/or objectives of the present
invention.
[0082] All ranges disclosed herein are inclusive of the endpoints,
and the endpoints are independently combinable with each other
(e.g., ranges of "up to 25 wt. %, or, more specifically, 5 wt. % to
20 wt. %", is inclusive of the endpoints and all intermediate
values of the ranges of "5 wt. % to 25 wt. %," etc.). "Combination"
is inclusive of blends, mixtures, alloys, reaction products, and
the like. Furthermore, the terms "first," "second," and the like,
herein do not denote any order, quantity, or importance, but rather
are used to denote one element from another. The terms "a" and "an"
and "the" herein do not denote a limitation of quantity, and are to
be construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by context. The
suffix "(s)" as used herein is intended to include both the
singular and the plural of the term that it modifies, thereby
including one or more of that term (e.g., the film(s) includes one
or more films). Reference throughout the specification to "one
embodiment", "some embodiments", "some embodiments", and so forth,
means that a particular element (e.g., feature, structure, and/or
characteristic) described in connection with the embodiment is
included in at least one embodiment described herein, and may or
may not be present in other embodiments. In addition, it is to be
understood that the described elements may be combined in any
suitable manner in the various embodiments.
[0083] While particular embodiments have been described,
alternatives, modifications, variations, improvements, and
substantial equivalents that are or may be presently unforeseen may
arise to applicants or others skilled in the art. Accordingly, the
appended claims as filed and as they may be amended are intended to
embrace all such alternatives, modifications variations,
improvements, and substantial equivalents.
* * * * *