U.S. patent application number 09/900083 was filed with the patent office on 2003-01-09 for method and apparatus for injection molding articles.
This patent application is currently assigned to Husky Injection Molding, Ltd.. Invention is credited to Niewels, Joachim Johannes.
Application Number | 20030008034 09/900083 |
Document ID | / |
Family ID | 25411944 |
Filed Date | 2003-01-09 |
United States Patent
Application |
20030008034 |
Kind Code |
A1 |
Niewels, Joachim Johannes |
January 9, 2003 |
Method and apparatus for injection molding articles
Abstract
An injection molding system having an improved valve gate
arrangement that provides molded articles with improved vestige and
or surface quality.
Inventors: |
Niewels, Joachim Johannes;
(Thornton, CA) |
Correspondence
Address: |
HUSKY INJECTION MOLDING SYSTEMS, INC
288 NORTH ROAD
MILTON
VT
05468
US
|
Assignee: |
Husky Injection Molding,
Ltd.
500 Queen Street South
Bolton
CA
|
Family ID: |
25411944 |
Appl. No.: |
09/900083 |
Filed: |
July 6, 2001 |
Current U.S.
Class: |
425/549 ;
425/533; 425/564 |
Current CPC
Class: |
B29C 45/278 20130101;
B29C 2045/2879 20130101; B29C 45/2806 20130101; B29C 45/2711
20130101 |
Class at
Publication: |
425/549 ;
425/564; 425/533 |
International
Class: |
B29C 045/23 |
Claims
What is claimed is:
1. An apparatus for injection molding at least one article, said
apparatus having at least one mold cavity and a supply of flowable
material communicated to said mold cavity through at least one
injection nozzle, comprising: a movable valve member having a
predetermined cross-sectional area to selectably start and stop the
communication of said flowable material through a nozzle gate in
each said nozzle, and; a vestige adjacent said nozzle gate
protruding from a surface of said article, wherein said vestige has
a cross-sectional area greater than said cross-sectional area of
said valve member.
2. The apparatus in accordance with claim 1 wherein said article is
a preform.
3. The apparatus in accordance with claim 2 wherein said preform is
made from PET.
4. The apparatus in accordance with claim 1 wherein said mold
cavity is formed between a cavity plate and a mold core.
5. The apparatus in accordance with claim 4 wherein said mold core
is selectably movable to an open and closed position.
6. The apparatus in accordance with claim 4 wherein said nozzle
gate is located in said cavity plate.
7. The apparatus in accordance with claim 4 wherein said nozzle
gate is located in an insert located in said cavity plate.
8. The apparatus in accordance with claim 7 wherein said insert is
replaceable.
9. The apparatus in accordance with claim 1 wherein said injection
nozzle comprises: an elongated nozzle bushing having a melt
passageway therein, said nozzle bushing placed in a cavity of a
cavity plate in alignment with said mold cavity, a nozzle tip
affixed to said nozzle bushing for the communication of a flowable
material from said nozzle bushing to said mold cavity, a heater in
thermal communication with said injection nozzle.
10. The apparatus in accordance with claim 1 wherein said valve
member is cylindrical.
11. The apparatus in accordance with claim 1 wherein said valve
member has a reduced diameter portion in sealing communication with
said nozzle gate.
12. The apparatus in accordance with claim 1 wherein said valve
member has at least one longitudinal recess on the surface of said
valve member to allow for the communication of said flowable
material.
13. An apparatus for injection molding at least one article
comprising: a source of flowable material in fluid communication
with at least one injection nozzle, said injection nozzle having an
outlet in alignment with a mold cavity for the formation of said
article therein; a movable valve member for selectably starting and
stopping the communication of said flowable material through said
outlet; said article having a vestige adjacent said valve member,
wherein the cross-sectional area of said valve member is less than
said vestige.
14. The apparatus in accordance with claim 13 wherein said article
is a preform.
15. The apparatus in accordance with claim 14 wherein said preform
is made from PET.
16. The apparatus in accordance with claim 13 wherein said mold
cavity is formed between a cavity plate and a mold core.
17. The apparatus in accordance with claim 16 wherein said mold
core is selectably movable to an open and closed position.
18. The apparatus in accordance with claim 16 wherein said nozzle
gate is located in said cavity plate.
19. The apparatus in accordance with claim 16 wherein said nozzle
gate is located in an insert located in said cavity plate.
20. The apparatus in accordance with claim 19 wherein said insert
is replaceable.
21. The apparatus in accordance with claim 13 wherein said
injection nozzle comprises: an elongated nozzle bushing having a
melt passageway therein, said nozzle bushing placed in a cavity of
a cavity plate in alignment with said mold cavity, a nozzle tip
affixed to said nozzle bushing for the communication of a flowable
material from said nozzle bushing to said mold cavity, a heater in
thermal communication with said injection nozzle.
22. The apparatus in accordance with claim 13 wherein said valve
member is cylindrical.
23. The apparatus in accordance with claim 13 wherein said valve
member has a reduced diameter portion in sealing communication with
said nozzle gate.
24. The apparatus in accordance with claim 13 wherein said valve
member has at least one longitudinal recess on the surface of said
valve member.
25. In an injection molding system, a manifold subsystem for the
communication of a flowable material, comprising: a manifold
structure having at least one melt passageway in fluid
communication with at least one injection nozzle; a cavity plate in
spaced-apart alignment with a mold core for the formation of a
cavity therebetween, said nozzle being in fluid communication with
said cavity through a nozzle gate for the formation of a molded
article therein, an insert having a passageway therethrough in
fluid communication between said nozzle and said nozzle gate, a
movable valve member for selectably stopping and starting the
communication of said flowable material to said cavity, and said
nozzle gate adjacent a vestige protruding from said molded article,
wherein said vestige cross-sectional area adjacent said valve
member is larger than the cross-sectional area of said valve member
that contacts said molded article.
26. The apparatus in accordance with claim 25 wherein said molded
article is a preform.
27. The apparatus in accordance with claim 26 wherein said preform
is made from PET.
28. The apparatus in accordance with claim 25 wherein said mold
core is selectably movable to an open and closed position.
29. The apparatus in accordance with claim 25 wherein said nozzle
gate is located in said cavity plate.
30. The apparatus in accordance with claim 25 wherein said nozzle
gate is located in an insert located in said cavity plate.
31. The apparatus in accordance with claim 30 wherein said insert
is replaceable.
32. The apparatus in accordance with claim 25 wherein said
injection nozzle comprises: an elongated nozzle bushing having a
melt passageway therein, said nozzle bushing placed in a cavity of
a cavity plate in alignment with said mold cavity, a nozzle tip
affixed to said nozzle bushing for the communication of said
flowable material from said nozzle bushing to said mold cavity, a
heater in thermal communication with said injection nozzle.
33. The apparatus in accordance with claim 25 wherein said valve
member is cylindrical.
34. The apparatus in accordance with claim 25 wherein said valve
member has a reduced diameter portion in sealing communication with
said nozzle gate.
35. The apparatus in accordance with claim 25 wherein said valve
member has at least one longitudinal recess on the surface of said
valve member to allow for the communication of said flowable
material.
36. In an injection molding system for the formation of a molded
article, a gate insert comprising: a body having a passageway
formed therein, said passageway located between an injection nozzle
assembly and a mold cavity for the communication of a fluid to said
mold cavity, an orifice portion of said passageway in sealing
communication with a movable valve member such that when said valve
member is adjacent said orifice portion the flow of said fluid to
said cavity is prevented, a raised portion protruding from said
molded article in thermal communication with said gate insert and
said valve member thereby cooling the outer periphery of said
raised portion faster than the interior of said raised portion.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to injection molding systems. More
specifically, the present invention relates to a valve gating
system found in injection molding systems.
[0003] 2. Summary of the Prior Art
[0004] Injection molding nozzles are well known and are used to
inject materials, such as plastic, into the cavity of a mold. For
example, such nozzles receive molten material, such as plastic,
from an injection molding machine and direct the same into a mold
cavity through a passage called a gate. When an injection operation
is complete, and prior to opening the mold cavity to eject the
molded part, the transfer of molten material through the gate must
be stopped. Generally, two methods exist for stopping the transfer
of molten material through the gate, namely: thermal, or open,
gating; and valve gating.
[0005] In thermal gating, the gate is an open aperture through
which molten material passes during an injection operation. The
gate is rapidly cooled at the end of the injection portion of the
cycle, when the injection pressure is removed, to "freeze" the
injected material into a plug. This plug remains in the gate to
prevent drool of molten material from the gate when the mold is
open for the ejection of the molded part. In the next injection
portion of the cycle, the cooling applied to the gate is removed
and hot molten material from the injection molding machine pushes
the plug into the mold cavity, where it melts and mixes with the
newly provided molten material.
[0006] In valve gating, the opening and closing of the gate is
independent of injection pressure and/or cooling and is achieved
mechanically with a valve stem. This stem can be moved between an
open position, wherein flow of molten materials through the gate is
permitted, and a closed position wherein the gate is closed by
entry of the valve stem into the gate which establishes a seal,
preventing molten materials from passing through the gate. Valve
gating is well known and examples of such systems are shown in U.S.
Pat. Nos. 2,878,515; 3,023,458; and 3,530,539, each being
incorporated herein by reference.
[0007] Generally, for situations that require improved aesthetics,
valve gating is preferable to thermal gating because it can reduce
the undesired gate vestige which results on the finished molded
part. However, there are problems with valve gating systems.
[0008] Specifically, the valve stem and gate each have a
complementary sealing portion which are brought into contact to
seal the gate. Typically there is a 0.001"-0.002" diametrical
clearance between the valve stem and the gate sealing portion. As
the valve stem is moved into alignment with the sealing portion of
the gate to effect sealing, a slight misalignment of the stem with
the gate will cause the stem to strike the gate sealing portion.
Over time, this will cause the gate area to wear and become
misshapen. Now that the gate sealing area is worn, the stem no
longer stops the flow of molten material and a small amount of
molten material will migrate between the stem and the worn gate
sealing area. This leakage adversely impacts the vestige quality
because as the mold is opened, the now solidified material between
the gate and the valve stem will cause a tear or blemish to form
along the vestige of the part, and in extreme cases, the tearing
can propagate to the surface of the molded article or preform.
[0009] Following the injection cycle, typically the mold halves
will open and the molded article in a somewhat solidified state
will be removed from the area of the stem/gate area. Due to the
entrapped molten material between the worn gate area and the stem,
the molded article will not break away cleanly when the mold is
opened, but rather will tear away from the gate area, which results
in a blemished vestige on the molded article.
[0010] Referring to FIGS. 1 and 2 this phenomenon can be clearly
seen. As well known in the art, a nozzle assembly 10 is comprised
of an elongated nozzle bushing 12 with a nozzle tip 16 affixed
co-axially therein. Optionally, an insulator 14 is affixed to a
proximal end of the nozzle tip 16 thereby thermally insulating the
heated nozzle assembly 10 from the cooled cavity plate 34. A
movable valve member 18 extends co-axially in the nozzle assembly
10 and is selectably positioned in or out of a passageway/gate area
22. A melt channel 20 surrounds the valve member 18 and runs the
length of the nozzle assembly 10 to communicate a flowable material
to a mold cavity 28. When the valve member 18 is placed in a fully
closed position (as shown in FIG. 1), a sealing portion 25 in the
cavity plate 34 sealingly surrounds the valve member 18 to shut off
the flow of material to the mold cavity 28. As shown in FIG. 1, a
face portion 21 of valve member 18 defines the entire top of the
vestige 26 of the molded article. A chamfer 36 is typically
provided along the face of the valve member 18 to help guide the
valve member into the gate area and reduce wear of the valve member
and cavity plate 34.
[0011] Due to the close fit of the valve member 18 to the sealing
portion 25, any misalignment that exists between their respective
interfaces will cause the valve member 18 to strike the surface of
the sealing portion 25 which will ultimately lead to a
deterioration of the seal portion 25 and/or the valve member
18.
[0012] At the end of the injection cycle, the valve member 18 is
moved into its closed position as previously described and the mold
cavity is held in a closed position with a core 30 for a
predetermined cycle time to allow the molten material to cool and
solidify, thereby forming the molded article. Once the molded
article has been allowed to cool to a sufficient level, the core 30
with the molded article thereon is moved in the direction as
denoted by arrow A, and the vestige 26 is pulled away from the face
portion 21 of the valve member 18. If enough wear exists between
the valve member 18 and the sealing portion 25, a small amount of
molten material will migrate therein, and as the mold core 30 and
the molded article 27 are moved to an open position, a peeled edge
38 will form on the vestige 26 of the molded article 27.
[0013] Also, as the valve member 18 is in the flow of molten
material when the gate is open, it can become quite hot. When the
gate is closed by the valve member 18, the hot tip of the valve
member 18 can be difficult to cool as the mold cavity 28 is cooled
and this can result in a need for increased cycle times to permit
the necessary cooling, and/or can result in undesirable
characteristics in the molded article 27. Specifically, as the
material in the mold cavity 28 adjacent the valve member 18 is
cooled less efficiently due to the hot tip, parts molded from
thermally sensitive materials such as PET can suffer from an
enlarged area of crystallinity 40 or other undesired
characteristics. In addition, since the entire top surface of the
vestige 26 is in contact with the face portion 21 of the hot valve
member 18, the molten material adjacent the face portion 21 remains
somewhat molten and stringing and an uneven edge forms when the
mold is opened.
[0014] Therefore there is a need for an improved injection-molding
machine with a valve gate system that reduces or obviates some or
all of the drawbacks of the prior art.
SUMMARY OF THE INVENTION
[0015] The primary objective of the present invention is to provide
an improved injection molding system with a valve gating system
that reduces or obviates the drawbacks of the prior art.
[0016] Another object of the present invention is to provide an
insert that interfaces with a valve member in an injection molding
system that reduces or eliminates the formation of peeled edges
along a vestige of a molded article.
[0017] Yet another object of the present invention is to provide a
gate insert in the mold plate adjacent the valve member that may be
easily replaced.
[0018] The foregoing objects are achieved by providing a mold
cavity with a vestige cross-sectional area that is larger than the
cross-sectional area of the valve member so that the periphery of
the vestige is cooled quicker than the interior portion of the
vestige. In another preferred embodiment, a replaceable insert is
provided to help guide the valve member into a sealing position
with the gate. Replacement of this insert can easily be performed
whenever the wear of the insert reaches a predetermined and
unacceptable level.
[0019] Further objections and advantages of the present invention
will appear hereinbelow.
BREIF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a simplified cross-sectional view of an injection
molding nozzle in accordance with the prior art;
[0021] FIG. 2 is a partial cross-sectional view of a molded article
in accordance with the prior art;
[0022] FIGS. 3 and 3a are simplified cross-sectional views of
exemplicative embodiments in accordance with the present
invention;
[0023] FIGS. 4a and 4b are partial cross-sectional views of
alternate exemplicative embodiments in accordance with the present
invention;
[0024] FIG. 5 is a simplified partial cross-sectional view of a
molded article.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Referring now to FIG. 3, an injection molding nozzle
assembly 10 in accordance with the present invention is located in
a cavity plate 34 for the communication of a flowable material to a
mold cavity 28 for the formation of a molded article therein.
Cavity plate 34 is provided with a plurality of cooling passageways
32 therein for the communication of a cooling fluid for the removal
of heat from the cavity plate to cool and solidify the flowable
material in the mold cavity 28.
[0026] The nozzle assembly 10, as well known in the art, is
comprised of an elongated nozzle bushing 12 with a nozzle tip 16
affixed to a proximal end of the nozzle bushing. In a preferred
embodiment, the nozzle tip 16 is threaded to the nozzle bushing 12,
but any such suitable means could be used. Typically, a heater 17
is wrapped around the nozzle assembly 10 to maintain the flowable
material in a viscous state. In the preferred embodiment an
optional insulator 14 is located between the nozzle tip 16 and the
cooled cavity plate 34 to reduce the transfer of heat from the hot
nozzle tip 16 to the cooled cavity plate 34. Located co-axially in
the nozzle assembly 10 is a movable valve member 18 that extends
adjacent a vestige 26 of the mold cavity 28. In a preferred
embodiment, the valve member 18 is a slender elongated cylindrical
piece that is moved up and down to an open and closed position
respectively. When the valve member 18 is in the open position as
shown by phantom line 50, the flowable material in melt channel 20
is allowed to enter the mold cavity 28. When placed in the closed
position, as shown in FIG. 1, the valve member 18 is in sealing
communication with a sealing portion 25 thereby stopping the flow
of material to the mold cavity 28.
[0027] In one preferred embodiment, an insert 42 with a passageway
41 formed therein is placed in a cavity 44 located in the cavity
plate 34 in alignment with the valve member 18. In this
arrangement, the sealing portion 25 is located in this replaceable
insert 42 to allow for easy maintenance when leakage around the
valve member 18 starts to occur.
[0028] The insert 42 may optionally provide a first chamfer 46 to
help guide the valve member 18 when it first enters the passageway
41 and a second chamfer 48 to help guide the valve member further
into the sealing portion 25. These chamfers act to reduce wear on
both the valve member 18 and the insert 42 and prolong the useable
life of both components.
[0029] Vestige 26, as shown in the figures, has a cross-sectional
area larger than the face portion 21 of the valve member 18. As
such, a portion 23 of the vestige 26 is in thermal communication
with the insert 42. Given that the insert 42 is placed in the
cooled cavity plate 34, the insert 42 will cool portion 23 faster
than the portion in contact with face portion 21 of the hot valve
member 18. This differential cooling action will allow portion 23
to solidify before the area adjacent face portion 21. When core 30
is retracted to remove the molded article from the mold cavity 28,
this now solidified portion 23 will tend to breakaway more cleanly
than the prior art. In addition, due to the location of the sealing
portion 25 being internal and displaced from the outer surface of
the finished vestige 26, any tearing that may occur when the mold
is opened is reduced or eliminated because the tear is not on the
surface of the vestige/preform as in the prior art.
[0030] As shown in FIG. 5, this clean break will result in a more
uniform and flat vestige 26 than previously seen. In addition, a
reduced area of crystallinity 40 will form inside the molded
article 27 due to the improved cooling of the vestige 26.
[0031] Referring to FIG. 3A, an alternative embodiment in
accordance with the present invention is shown which is identical
to the embodiment in FIG. 3 except for the removal of the insert
42. As shown in FIG. 3A, the sealing portion 25 is now located in
the cavity plate 34. Cooling of portion 23 will still occur quicker
than in the remainder of the vestige 26, which will allow for a
substantially clean break when mold core 30 is retracted.
[0032] FIGS. 4a and 4b (where like features have like numerals)
show alternative embodiments of the insert 42 and the valve member
18. As shown in FIG. 4a, the valve member 18 has a chamfer 54 near
the vestige 26. A reduced diameter section of the valve member is
in sealing communication with the sealing portion 25 when in the
closed position. At least one elongated recess 56 is formed in the
surface of the valve member 18 which allows the flowable material
to be forced up along the valve member 18 as the valve member is
brought to the closed position. Chamfers 46 and 48 help guide the
valve member 18 as it enters the passageway 41 and seats in the
sealing portion 25. FIG. 4b shows the valve member 18 as one
continuous cylinder down to the chamfer at the very bottom. The
passageway 41 in the insert 42 is also a uniform diameter for most
of its length, except for the lead in chamfer 46. In this
embodiment, the sealing portion 25 can be longer and provide a
longer lasting seal. The recess 56 allows the flowable material to
flow up out of passageway 41 as the valve member 18 is brought to a
closed position.
[0033] It is to be understood that the invention is not limited to
the illustrations described herein, which are deemed to illustrate
the best modes of carrying out the invention, and which are
susceptible to modification of form, size, arrangement of parts and
details of operation. The invention is intended to encompass all
such modifications, which are within its spirit and scope as
defined by the claims.
* * * * *