U.S. patent number RE38,396 [Application Number 09/922,594] was granted by the patent office on 2004-01-27 for method of making injection molding cooled thread split inserts.
Invention is credited to Jobst Ulrich Gellert.
United States Patent |
RE38,396 |
Gellert |
January 27, 2004 |
Method of making injection molding cooled thread split inserts
Abstract
A method of making pairs of thread splits inserts used to
injection mold bottle preforms. Machining a hollow outer part of
the pair of thread split inserts with an opening therethrough and
outer portions of two cooling conduits extending from the opening
therethrough to respective inlets and outlets. Making an inner part
of the pair of thread split inserts by injection molding a ceramic
core with the required shape and investment casting the inner part
around the ceramic core. The outer surface of the inner part having
grooves to partially form inner portions of the two cooling fluid
conduits. Then machining the cast inner part to fit in the opening
through the outer part. Mounting the outer part around the inner
part with the inner and outer portions of the two cooling fluid
conduits aligned. Applying brazing material between the inner and
outer parts and heating them in a vacuum furnace to integrally
braze them together. Finally, cutting the integral inner and outer
parts in half to form the pair of thread split inserts with each of
the thread split inserts having one of the cooling fluid conduits
therein.
Inventors: |
Gellert; Jobst Ulrich
(Georgetown, Ontario, CA) |
Family
ID: |
30118642 |
Appl.
No.: |
09/922,594 |
Filed: |
August 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
134952 |
Aug 17, 1998 |
05930882 |
Aug 3, 1999 |
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Foreign Application Priority Data
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Jul 29, 1998 [CA] |
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2244511 |
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Current U.S.
Class: |
29/411; 228/171;
29/415; 29/416; 29/527.6; 425/526; 425/533; 425/548 |
Current CPC
Class: |
B23P
15/007 (20130101); B23P 15/24 (20130101); B29C
33/04 (20130101); B29C 45/7312 (20130101); B29C
45/33 (20130101); B29C 2033/042 (20130101); Y10T
29/49794 (20150115); Y10T 29/49796 (20150115); Y10T
29/49989 (20150115); Y10T 29/49787 (20150115) |
Current International
Class: |
B23P
15/00 (20060101); B23P 017/00 () |
Field of
Search: |
;29/411,527.5,527.6,415,416 ;425/526,533,547,548 ;228/171 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Tanaka Kisaburo, "Manufacture of Mold," 3/90, Patent Abstract of
Japan vol. 015, No. 061..
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Primary Examiner: Echols; P. W.
Attorney, Agent or Firm: Sterne, Kessler, Goldstein &
Fox P.L.L.C.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed is defined as follows:
1. A method of making a pair of .[.thread.]. split inserts used in
injection molding elongated hollow .[.bottle.]. preforms, each
preform having a neck portion with an outer surface .[.forming a
ring collar and threads extending between an open end and the ring
collar.]. , each .[.thread.]. split insert having .[.a front end, a
rear end and.]. first and second .[.flat.]. inner aligned faces
extending on opposite sides of a curved inner surface, the
.[.thread.]. split inserts to be mounted together in a mold with
the respective .[.flat.]. inner faces of the .[.thread.]. split
inserts abutting, wherein the curved inner surfaces of the
.[.thread.]. split inserts combine to form an opening therethrough
shaped to mold the outer surface of the neck portion of the
preform, .[.the curved inner surfaces of the thread split inserts
each have a semicircular groove to form the ring collar and a
threaded portion extending between the semicircular groove and the
rear end to form the threads,.]. comprising the steps of.[.; (a)
injection molding a ceramic core having a predetermined shape, (b)
casting wax around the ceramic core in the shape of an inner part
of the pair of thread split inserts, (c) investment.]. .Iadd.: (a)
.Iaddend.casting a suitable metal in a mold .[.to replace the wax
around the ceramic core.]. to form a hollow inner part of the pair
of .[.thread.]. split inserts extending around a central
longitudinal axis, said inner part having .[.a generally
cylindrical.]. outer surface with grooves therein to partially form
inner portions of two cooling fluid conduits, each cooling fluid
conduit to extend around the curved inner surface of one of the
.[.thread.]. split inserts.[., (d) machining the cast inner part to
make the outer surface a predetermined size, (e).]. .Iadd.; (b)
.Iaddend.making a hollow outer part of the pair of .[.thread.].
split inserts of a suitable metal having a predetermined shape with
an opening therethrough having an inner surface which fits around
the outer surface of the inner part and outer portions of the two
cooling conduits extending from the opening therethrough to
respective inlets and outlets.[., (f).]. .Iadd.(c)
.Iaddend.mounting the outer part around the inner part with the
inner and outer portions of the two cooling fluid conduits
aligned.[., applying brazing material between the inner part and
the outer part, and heating the assembled inner part and outer part
in a vacuum furnace to integrally braze the inner part and the
outer part together,.]. and .[.(g).]. .Iadd.(d) .Iaddend.cutting
the .[.integral.]. inner and outer parts .[.in half along the
central longitudinal axis.]. to form the pair of .[.thread.]. split
inserts, each of the .[.thread.]. split inserts having one of the
cooling fluid conduits therein.
2. .[.A.]. .Iadd.The .Iaddend.method of making a pair of
.[.thread.]. split inserts as claimed in claim 1.Iadd.,
.Iaddend.wherein the outer part of the pair of .[.thread.]. split
inserts is made by machining.
3. .[.A.]. .Iadd.The .Iaddend.method of making a pair of
.[.thread.]. split inserts as claimed in claim 2.Iadd.,
.Iaddend.wherein the .[.integrally brazed.]. inner and outer parts
of the .[.thread.]. split inserts are cut in half by an electrical
discharge machine.
4. .[.A.]. .Iadd.The .Iaddend.method of making a pair of
.[.thread.]. split inserts as claimed in claim 3.Iadd.,
.Iaddend.further comprising .Iadd.the step of: (e)
.Iaddend.machining the .[.brazed.]. inner and outer parts of the
.[.thread.]. split inserts to provide the .[.thread.]. split
inserts with a desired finish and shape..Iadd.
5. A method of making a pair of split inserts for use in injection
molding, comprising the steps of: (a) casting a hollow inner part;
(b) machining a hollow outer part; (c) integrally brazing the
hollow inner part and the hollow outer part together; and (d)
cutting the integral hollow inner and outer parts to form the pair
of split inserts. .Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates a method of making pairs of cooled thread
split inserts used to injection mold bottle preforms.
As seen in the applicant's U.S. Pat. No. 5,599,567 which issued
Feb. 4, 1997, it is well known to use a pair of thread split
inserts in a mold to form the threaded neck portion of a PET
bottled preform. The neck portion of the preform also has a ring
collar which is used to eject the preform from the mold. The thread
split inserts have conduits through which cooling fluid is
circulated to cool the neck portion of the preform prior to
ejection.
In the past, thread split inserts have been made by machining steel
upper and lower parts and then integrally brazing them together.
This method has the disadvantage that both parts must be machined
to provide cooling fluid conduits and threads and this is time
consuming and therefore relatively costly.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to at least
partially overcome the disadvantages of the prior art by providing
a method of making cooled thread split inserts wherein an inner
part which fits in an outer part is made by casting rather than
machining.
To this end, in one of its aspects, the invention provides a method
of making a pair of thread split inserts used in injection molding
elongated hollow bottle preforms. Each preform has a neck portion
with an outer surface forming a ring collar and threads extending
between an open end and the ring collar. Each thread split insert
has a front end, a rear end and first and second flat inner aligned
faces extending on opposite sides of a curved inner surface. The
thread split inserts are mounted together in a mold with the
respective flat inner faces of the thread split inserts abutting,
wherein the curved inner surfaces of the thread split inserts
combine to form an opening therethrough shaped to mold the outer
surface of the neck portion of the preform. The curved inner
surfaces of the thread split inserts each have a semicircular
groove to form the ring collar and a threaded portion extending
between the semicircular groove and the rear end to form the
threads. The method comprises the steps of injection molding a
ceramic core having a predetermined shape and then casting wax
around the ceramic core in the shape of an inner part of the pair
of thread split inserts. Then investment casting a suitable metal
in a mold to replace the wax around the ceramic core to form a
hollow inner part of the pair of thread split inserts extending
around a central longitudinal axis. The inner part has a generally
cylindrical outer surface with grooves therein to partially form
inner portions of two cooling fluid conduits. Each cooling fluid
conduit extends around the curved inner surface of one of the
thread split inserts. Then machining the cast inner part to make
the outer surface a predetermined size. Making a hollow outer part
of the pair of thread split inserts of a suitable metal having a
predetermined shape with an opening therethrough having an inner
surface which fits around the outer surface of the inner part and
outer portions of the two cooling conduits extending from the
opening therethrough to respective inlets and outlets. Mounting the
outer part around the inner part with the inner and outer portions
of the two cooling fluid conduits aligned. Then applying brazing
material between the inner part the outer part and heating the
assembled inner part and outer part in a vacuum furnace to
integrally braze the inner part and the outer part together.
Cutting the integral inner and outer parts in half along the
central longitudinal axis to form the pair of thread split inserts,
with each of the thread split inserts having one of the cooling
fluid conduits therein.
Further objects and advantages of the invention will appear from
the following description taken together with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view showing a bottle preform and a pair of
thread split inserts made according to a preferred embodiment of
the invention,
FIG. 2 is a sectional view of a ceramic core,
FIG. 3 is a sectional view taken along 3--3 in FIG. 2,
FIG. 4 is a sectional view of a wax mold having a cavity in the
shape of an inner part of a pair of thread split inserts,
FIG. 5 is a sectional view showing the wax covered by ceramic
coatings during investment casting,
FIG. 6 is a sectional view showing the cast inner part,
FIG. 7 is a sectional view showing the inner part after
machining,
FIG. 8 is a sectional view of a machined outer part of the pair of
thread split inserts,
FIG. 9 is a bottom view of the outer part seen in FIG. 8,
FIG. 10 is a sectional view of the outer part mounted around the
inner part ready for brazing in a vacuum furnace,
FIG. 11 is a plan view of the parts shown in FIG. 10,
FIG. 12 is a plan view of the integrally brazed two parts cut in
half to form the pair of thread split inserts,
FIG. 13 is a sectional view of the completed pair of thread split
inserts in FIG. 12 after grinding the outer surfaces, and
FIG. 14 is a schematic view showing the configuration of the
cooling fluid conduit in each of the pair of thread split
inserts.
DETAILED DESCRIPTION OF THE INVENTION
Reference is first made to FIG. 1 which shows a bottle preform 10
and a pair of thread split inserts 12, 14 made according to a
preferred embodiment of the invention. As can be seen, the bottle
preform 10 is hollow and is elongated to a selected length. The
bottle preform 10 has a neck portion 16 with an outer surface 18
forming a ring collar 20 and threads 22 extending between an open
end 24 and the ring collar 20. The bottle preform 10 is injection
molded of polyethylene terephthalate (PET) according to a
conventional injection molding cycle in a conventional mold.
Each thread split insert 12, 14 has a front end 26, a rear end 28
and flat inner aligned faces 30, 32 extending on opposite sides of
a curved inner surface 34. During molding of the bottled preforms
10, the thread split inserts 12, 14 are mounted in a mold with the
respective flat inner faces 30, 32 of the thread split inserts 12,
14 abutting, whereby as seen in FIG. 13 the curved inner surfaces
34 of the thread split inserts 12, 14 combine to form an opening 35
therethrough shaped to mold the outer surface 18 of the neck
portion 16 of the preform 10. The curved inner surfaces 34 of the
thread split inserts 12, 14 each have a semi-circular groove 36 to
form the ring collar 20 and a threaded portion 38 extending between
the semi-circular groove 36 and the rear end 28 to form the threads
22.
The bottle preform 10 has an elongated cylindrical portion 40 and
may include a slightly tapered portion 42 extending from the neck
portion 16. As is well known, the cylindrical portion 40 and
tapered portion 42 are later enlarged by stretching and then blow
molding to form a beverage bottle. After the preform 10 is
stretch-blow molded and the resulting bottle is filled with a
suitable beverage, a removable threaded cap (not shown) is screwed
on to the threads 22 to close the bottle. The ring collar 20 is
used in the stretch-blow molding process, but is also used to
assist in ejecting the preform 10.
Reference will now be made to the rest of the drawings in
describing the method of making the pair of thread split inserts
12, 14 by casting a hollow inner part 44, machining a hollow outer
part 46, integrally brazing the hollow inner part 44 and the hollow
outer part 46 together, and then cutting the integral hollow inner
and outer parts 44, 46 in half to form the pair of thread split
inserts 12, 14.
Reference will first be made to FIGS. 2-7 to describe how the
hollow inner part 44 is made by a conventional lost wax or
investment casting process. First, as seen in FIGS. 2 and 3, a
hollow core 48 is injection molded of a suitable material such as
ceramic. As seen in FIG. 3, the ceramic core 48 is made with an
outer surface 49 shaped to form the inner surfaces 34 of the thread
split inserts 12, 14. The ceramic core 48 also has a locating ridge
50 on its inner surface 52 and is generally cylindrical, but has
two flat sections 54 which are long enough to allow the integral
thread split inserts 12, 14 to be circular after some material is
lost when they are cut in half. As seen in FIG. 4, the hollow
ceramic core 48 is then placed on a mounting pin 56 extending
upwardly from a bottom plate 58 of a wax mold 60. The locating
ridge 50 fits in a groove (not shown) on the mounting pin 56 to
ensure the ceramic core 48 is properly oriented. The wax mold 60
has a top plate 62 and two inserts 64, 66 which slide inwardly
together to form a cavity 68 extending between them around the
hollow ceramic core 48. After the mold 60 is closed, screws 70 are
inserted to hold the plates 58, 62 and the inserts 64, 66 together
during molding. A resilient O-ring 72 extending around the mounting
pin 56 ensures the ceramic core 48 is positioned at the top of the
mold 60. The sliding inserts 64, 66 are made having inner surfaces
74, 76 shaped with a configuration of interconnected ridges 78
extending therefrom to provide the hollow inner part 44 of the pair
of thread split inserts 12, 14 with a generally cylindrical outer
surface 80 with the same configuration of interconnected grooves 82
therein to form inner portions 84 of two cooling fluid conduits
extending around the curved inner surface 34 of the thread split
inserts 12, 14. Molten wax is then injected into the cavity 68
through a large casting gate 86. After the wax has cooled and
solidified, the mold 60 is opened leaving a wax part 88 having the
same shape as the hollow inner part 44 of the pair of thread split
inserts 12, 14 extending around the ceramic core 48.
As seen in FIG. 5, the wax part 88 is dipped repeatedly in a bath
(not shown) of ceramic material which hardens to form an outer
shell 90 of several layers 92 of ceramic material. The coated wax
part 88 is then heated in an autoclave to remove the wax and the
empty shell 90 is then filled with a suitable molten material such
as steel through the gate 86. After cooling, the outer shell 90 and
the ceramic core 48 are removed leaving the hollow raw cast inner
part 44 of the pair of thread split inserts 12, 14 extending around
a central longitudinal axis 96 as seen in FIG. 6. As can be seen,
the cast hollow inner part 44 has the generally cylindrical outer
surface 80 with the grooves 82 therein to partially form the inner
portions 84 of the two cooling conduits. It also has a central
opening 98 with the same shape as the ceramic inner core 48. This
process of, making the raw cast inner part 44 is a conventional
lost wax or investment casting process. Although only one hollow
inner part 44 is shown for ease of illustration, normally the wax
parts 88 and the hollow inner parts 44 are made in interconnected
arrangements or trees to expedite the process. The raw cast inner
part 44 seen in FIG. 6 is then mounted on spindles 100 as seen in
FIG. 7 and machined to make the outer surface 80 a predetermined
size and to form tapered end portions 102.
Reference is now made to FIGS. 8 and 9 which show the hollow outer
part 46 which is machined of a suitable material such as tool
steel. As can be seen, the hollow outer part 46 is made with four
retaining bolt holes 104 as well as a central opening 106 extending
therethrough with an inner surface 108. The inner surface 108 is
made to fit around the outer surface 80 of the hollow inner part
44. The hollow outer part 46 is also machined to have outer
portions 110 of two cooling fluid conduits which are made to align
respectively with the inner portions 84 of the two cooling fluid
conduits in the outer surface 80 of the inner part 84.
Nickel brazing paste 94 is applied to the inner portions 84 of the
cooling conduits and the hollow inner part 44 is inserted into the
central opening 106 through the hollow outer part 46 to form the
pair of thread split inserts 12, 14. As can be seen in FIGS. 10 and
11, this completes the inner portions 84 of the cooling conduits in
the hollow inner part 44 which are aligned with the corresponding
outer portions 110 of the cooling conduits in the hollow outer part
46. This produces the two cooling conduits 112 through which
cooling water flows from inlets 114 to outlets 116 on the front end
26. Nickel brazing material is inserted into circular groove 118
and the assembled hollow inner and hollow outer parts 44, 46 are
gradually heated in a vacuum furnace (not shown) to a temperature
of approximately 1925.degree. F. which is above the melting point
of the nickel alloy. As the furnace is heated, it is evacuated to a
relatively high vacuum to remove substantially all of the oxygen
and then partially backfilled with an inert gas such as argon or
nitrogen. When the melting point of the nickel is reached, it melts
and flows by capillary action between the hollow inner part 44 and
the hollow outer part 46 to integrally braze them together to form
the pair of thread split inserts 12, 14. Brazing them together this
way in the vacuum furnace provides a metallurgical bonding between
them to maximize their strength and prevent leakage of the cooling
water from the cooling conduits 112.
After removal of the integral pair of thread split inserts 12, 14
from the vacuum furnace, they are cut in half along the
longitudinal axis 96 in an electrical wire-cut machine to form the
two separate thread split inserts 12, 14 shown in FIG. 12. As
shown, they are cut in the correct plane to have one of the cooling
conduits 112 in each of the thread split inserts 12, 14. The pair
of thread split inserts 12, 14 are then machined to provide a good
outer finish and the tapered portions 120, 122 at their front and
rear ends 26, 28. During molding the pair of thread split inserts
12, 14 are secured tightly together by the tapered flange portions
120, 122 being engaged by the rest of the mold (not shown). In this
position, the matching flat inner surfaces 30, 32 abut and the
curved inner surfaces 34 of the pair of thread split inserts 12, 14
combine to form the opening 35 therethrough shaped to mold the
outer surface 18 of the neck portion 16 of the preform 10. Of
course, during molding an elongated cylindrical core (not shown)
extends through this opening 35 to form the inner surface 124 of
the preform 10.
In use in a multi-cavity mold, a number of pairs of thread split
inserts 12, 14 made according to the invention are mounted in a
conventional mold. A supply of cooling water or other suitable
cooling fluid is connected to the inlet 116 of the cooling fluid
conduit 112 in each thread split insert 12, 14 to circulate through
each cooling fluid conduit 112. Pressurized melt from a molding
machine is then injected into the cavity in the opening 35 through
each pair of thread split inserts 12, 14 according to a
predetermined injection cycle. After the cavities are full,
injection pressure is held momentarily to pack and then released.
After a short cooling period, the mold is opened to eject each
preform 10. This is done by the preform 10 first being ejected from
the core and the two thread split inserts 12, 14 then separated to
drop the preform 10 onto a conveyor belt or cooling plate. Of
course, this requires that the two thread split inserts 12, 14 be
separated enough to release the ring collar 20 and threads 22 of
the preform 10. After ejection, the mold is closed and injection
pressure is reapplied to refill the cavity and the injection cycle
is repeated continuously.
While the description of the method of making the pair of thread
split inserts 12, 14 has been given, with respect to a preferred
embodiment, it will be evident that various other modifications are
possible without departing from the scope of the invention as
understood by those skilled in the art and as defined in the
following claims.
* * * * *