This application is a non-provisional application claiming the benefit
under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 60/456,247
filed March 21, 2003 and U.S. Provisional Patent Application No. 60/479,908 filed
June 20, 2003.
FIELD OF THE INVENTION
The present invention relates generally to an injection molding apparatus
and, in particular, to an improved bushing for a gating valve pin.
BACKGROUND OF INVENTION
A common problem associated with valve gated hot runner injection
molding systems is the leaking of molten plastic that can occur between the valve
pin and the manifold plate. There are many different valve runner or bushing designs
that have attempted to stop leakage from occurring, examples of which can be seen
in U.S. Patent Nos. 4,740,151 issued April 26, 1988; 5,696,793 issued December 9,
1997; and 5,849,343 issued December 15, 1998; and United States Patent Application
No. US 2002/0106419 A1 published August 8, 2002.
Existing valve pin bushings tend to have a high thermal mass concentrated
around the valve pin and the manifold plate by having a larger disk head arranged
to bear against a manifold, which can result in a hot area next to the valve pin
prone to leakage in some applications. Thus, there remains a need for valve pin
bushing that is less prone to leakage and which is economical to produce and use.
SUMMARY OF THE INVENTION
The present invention provides a valve pin bushing having a reduced
thermal mass closer to the valve pin and manifold plate in order to reduce leakage.
In particular, the valve pin bushing of the present invention draws less heat from
the hot manifold than it transfers to the cooler back plate, such that the overall
temperature of the valve pin bushing is less than that of the manifold. As such,
leaking melt material will become more viscous and/or harden within or near the
valve pin bushing rather than leak out from the injection molding apparatus.
According to one aspect of the invention, there is provided an injection
molding apparatus that includes a heated manifold having a manifold surface, a back
plate having a back plate surface disposed adjacent and parallel to the manifold
surface, and a valve pin bushing disposed between the manifold and the back plate.
The valve pin bushing including a head portion with a manifold contacting surface
and an opposing back plate contacting surface. The back plate contacting surface
has a first surface area that is larger than a second surface area of the manifold
contacting surface, thus drawing more heat into the back plate than from the manifold
to cool the valve pin bushing. The manifold may also have a positioning pin which
fits within a positioning groove on the valve pin bushing for correct alignment
of the valve pin.
In other aspects of the invention, the valve pin bushing may also
include a head portion having a flange and a central portion extending from a back
end of the head portion. A lip may extend from the central portion, with another
surface contacting the manifold. The central potion may be spaced away from the
flange to form an air space between the flange and the central portion near the
manifold. For example, the central portion may taper away from the flange, such
as having a frusto-conical configuration. Alternatively, the back end may have a
surface parallel to the manifold, but not touching it, with the central portion
extending from the back end and being spaced away from the flange. The valve pin
bushing may include a tubular member extending from the central portion in the same
direction as the flange (opposite from the back end) and into a bore in the manifold,
which may form part of a melt channel in the manifold, by being curved or angled.
In other aspects of the invention, the valve pin bushing may also
include a sealing portion joined to the flange and the tubular member, so that the
flange, the sealing portion and the central portion define a closed space. The sealing
portion may be separate from the other parts of the valve pin bushing, or it may
be formed integrally with either the flange or the tubular member. The closed space
may form a vacuum (created by vacuum brazing the parts together) or may be filled
with air. The sealing portion may include at least one groove to reduce the surface
area in contact with the manifold and to trap leaking melt material. When the back
plate contacting surface is circular, then preferably the manifold contacting surface
is annular. However, the back plate contacting surface may be a shape other than
circular. In another embodiment, the valve pin bushing may have a plurality of flanges
extending from the back end of the head portion.
According to another aspect of the invention, there is provided, a
valve pin bushing having a head portion and a tubular member, where the tubular
member extends from the head portion. The head portion includes a flange and a central
portion extending from a back end thereof. The head portion has a back end with
a back plate contacting surface. The flange has a manifold contacting surface. The
back plate contacting surface has a first surface area that is larger than a second
surface area of the manifold contacting surface. The tubular member further extends
from the central portion of the head portion in the same direction as the flange
(i.e., opposites the back end of the head portion). Further, the head portion and
the tubular member define a channel through the valve pin bushing for a valve pin
to be inserted.
According to yet another aspect of the invention, there is provided
a method for inhibiting leakage of melt material from a valve gated injection molding
apparatus. This method includes the step of providing a valve pin bushing having
a valve pin channel and a head portion between a manifold and a back plate of an
injection molding apparatus, wherein less surface area of the head portion contacts
the manifold than the back plate. This method includes lowering the temperature
of leaking melt by drawing heat away from the melt and into the back plate through
the valve pin bushing until the melt hardens and forms a seal preventing additional
melt from leaking from the injection molding apparatus.
Other aspects and features of the present invention will become apparent
to those ordinarily skilled in the art upon review of the following description
of specific embodiments of the invention in conjunction with the accompanying Figures.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1A is a sectional view of a portion of an injection molding
system showing a valve pin bushing according to an embodiment of the invention.
Figure 1B is a top view of the valve pin bushing of Figure 1A.
Figure 2 is a perspective view of a valve pin bushing according to
an embodiment of the present invention.
Figure 3 is a perspective sectional view of the valve pin bushing
of Figure 2.
Figure 4 is perspective sectional view of a valve pin bushing according
to a further embodiment of the invention.
Figure 5 is a perspective sectional view of a valve pin bushing according
to a further embodiment of the invention.
Figure 6 is a perspective sectional view of a valve pin bushing according
to a further embodiment of the invention.
Figure 7 is a sectional view of a portion of an injection molding
apparatus showing a valve pin bushing according to a further embodiment of the invention.
Figure 8 is a perspective sectional view of a valve pin bushing according
to a further embodiment of the invention.
Figure 9 is a perspective sectional view of a valve pin bushing according
to a further embodiment of the invention.
Like numerals are used to refer to similar components throughout the
DETAILED DESCRIPTION OF THE INVENTION
Figure 1A shows a portion of a valve gated injection molding apparatus
10 according to an embodiment of the present invention. The injection molding apparatus
10 includes a melt distribution manifold 14 through which a manifold melt passage
12 extends for flow of a pressurized melt stream of moldable material. The manifold
14 is heated by an integral heater 24. The apparatus 10 includes a nozzle 16 to
convey the pressurized melt stream through a central nozzle bore, or nozzle melt
passage 34, from the manifold melt passage 12 to a cavity 26 in a mold 28. The nozzle
16 is located in a nozzle well in a cavity plate 20 through which cooling conduits
30 are provided for a cooling fluid such as water. The manifold 14 is located between
a back plate 22 and the nozzle 16, with an insulating air space 32 provided between
a manifold surface 14a of manifold 14 and a back plate surface 22a of back plate
22. Cooling conduits 30 are also provided through the back plate 22. Although only
one nozzle 16 and manifold melt passage 12 is shown in Figure 1A, the apparatus
10 will typically include a number of such nozzles and melt passages. As can be
seen in Figure 1A, a forward end of the manifold bore 42 forms part of the manifold
melt passage 12, and more particularly, it defines an outlet that is substantially
transverse to the rest of the manifold melt passage 12.
The nozzle melt passage 34 communicates with the mold cavity 26 through
a gate 36. An elongated valve pin 38 extends through axially aligned bores 40 and
42 in the back plate 22 and the manifold 14, respectively, and centrally through
the aligned nozzle melt passage 34. As known in the art, the valve pin 38 reciprocates
axially within the manifold bore 42 and has a tapered forward end 44 that cooperates
with gate 36 for controlling the flow of the melt stream into cavity 26. A pneumatic
or other type of actuator (not shown) acts on a back end 46 of the valve pin 38
for reciprocating the pin axially forward and backward between open and closed positions
relative to gate 36.
The present invention is directed towards a valve pin bushing 50 that
is located in the air space 32 between back plate surface 22a and manifold surface
14a. Valve pin bushing 50 has a central bore 52 that is aligned with back plate
bore 40, manifold bore 42 and nozzle melt passage 34, through which the valve pin
38 extends. Bolts 54 may extend through the valve pin bushing 50 and manifold 14
into an upper end of nozzle 16 to secure the nozzle and valve pin bushing 50 in
this alignment. Further, manifold 14 may include a locating pin 97 that fits with
locating groove 97a (seen in Figure 1B) in valve pin bushing 50 to ensure proper
alignment of bores 42 and 52.
Figures 1A, 1B, 2 and 3 show one embodiment of the present invention.
In this embodiment, valve pin bushing 50 includes a tubular member 56, through which
bore 52 extends. A length of tubular member 56 extends a predetermined distance
into a back end of the manifold bore 42. A leading surface 58 of the tubular member
56 may be chamfered or angled and defines part of the manifold melt passage 12.
In one embodiment, valve pin bushing 50 has a head portion 66 with
a back end 62. The head portion 66 includes a central portion 57 and an outer support
flange 64, which is an annular wall. Flange 64 may be integrally formed with central
portion 57 at a back end 62 of head portion 66. In this embodiment, head portion
66 has a frusto-conical shaped central portion 57. A shoulder 68 is provided around
a forward end of the support flange 64. Further, flange 64 defines a manifold contacting
surface 63 of head portion 66 for bearing against manifold surface 14a of manifold
14. Back end 62 of the head portion 66 defines a circular substantially planar back
plate contacting surface 70 for bearing against back plate surface 22a of back plate
The frusto-conical central portion 57 of head portion 66 tapers inwards
as the distance from back end 62 increases, such that an air space 72 is defined
by an inner surface of the support flange 64, an outer surface of the central portion
57 and manifold surface 14a. Air space 72 increases in area nearer manifold surface
Central portion 57 of head portion 66 includes a resilient lip 74
for engaging manifold surface 14a near manifold bore 42. As shown in Figures 1A
and 3, a bolt passage 76 may be provided through the head portion 66 for bolts 54.
More than one bolt passage 76 may be provided. As known in the art, rings 73 may
be providing along bore 52 to allow venting of gases during operation of the injection
Valve pin bushing 50 functions as a retaining and sealing bushing
for helping to retain the valve pin in central alignment with the gate 36 and to
prevent, or reduce the amount of, melt stream material leaking from manifold bore
42. Valve pin bushing 50 also maintains a bearing pressure on manifold 14 to retain
its location. Flange 64 of valve pin bushing 50 is configured such that a relatively
small surface area of manifold contacting surface 63 of head portion 66 is in contact
with hot manifold 14, while at the same time a relatively larger surface area of
back plate contacting surface 70 of back end 62 is in contact with the cooler back
plate 22. Additionally, the mass of central portion 57 of head portion 66 is less
in the vicinity of the manifold 14, where valve pin 38 is at its hottest, and greater
near cooler back plate 22.
During operation of the apparatus 10, the air in air space 72 insulates
head portion 66 of the valve pin bushing 50 from the heat of manifold 14. The surface
area between back plate contacting surface 70 and back plate surface 22a provides
a relatively large surface area for heat exchange between valve pin bushing 50 and
back plate 22, permitting heat that has been picked up by valve pin bushing 50 through
its contact with valve pin 38, leaking melt and manifold 14 to dissipate into back
plate 22. Outer support flange 64 and the inner lip 74 are dimensioned and have
sufficient spring-like resiliency to permit relative motion between back plate 22
and the manifold 14 due to relative thermal expansion, but at the same time maintain
a sealing pressure between back plate 22 and manifold 14.
Valve pin bushing 50 may be a unitary structure formed from steel
or other heat conducting metal. Non-limiting examples of possible materials from
which valve pin bushing 50 can be made from include, among other things, stainless
steel, tooling steel such as H13, and various ceramic materials.
In one embodiment, lip 74 provides a seal to prevent melt stream material
that makes its way up the manifold bore 42 outside of tubular member 56 from leaking
into air space 72 or further into air space 32. The lip 74 extends outwards and
downward from forward end 59 of central portion 57 to engage the surface of manifold
14 around the back end of manifold bore 42. The lip 74 may taper as it extends outward
such that only a small area of lip 74 contacts the manifold 14. In another embodiment
the lip 74 may be replaced by a sealing ring of the type typically used in high
The seal between the tubular member 56 and the wall of the manifold
bore 42 can be enhanced in some applications by melt stream material that works
its way up the manifold bore 42 around the outside of tubular member 56 and hardens
nearer the cooler side of valve pin bushing 50 closer to back end 62. Further, melt
stream material that leaks between the valve pin 38 and the wall of the bore 52
will harden as the temperature of the valve pin bushing 50 cools toward the colder
back plate 22. Since the valve pin bushing 50 is designed to limit the contact with
the manifold 14 but retain substantial contact with the cooler back plate, heat
is pulled faster from the leaking melt towards the back end 62 of the valve pin
bushing 50 than from the manifold 14 causing the melt to cool and become more viscous
or even harden. By its configuration, the valve pin bushing of the present invention
provides a colder contact area around the valve pin and reduces the potential for
melt stream leakage.
In another embodiment, lip 74 may be omitted, and instead valve pin
bushing 50 may have a tighter tolerance between the tubular member 56 and the manifold
bore 42 in order to prevent leakage. By way of example, Figure 4 shows a valve pin
bushing 80 according to another embodiment of the present invention, which is substantially
similar to valve pin bushing 50 except for differences that will be apparent from
the Figures and the present description. Unlike valve pin bushing 50, valve pin
bushing 80 does not include an inner sealing lip 74 and does not include an enlarged
shoulder 68 as part of flange 64, which further reduces the contact surface area
of manifold contacting surface 63a.
In another embodiment, back plate contacting surface 70 may be contoured
to provide a desired heat transfer profile between the back end 62 of head portion
66 and back plate 22. By way of example, in valve pin bushing 80 of Figure 4, a
groove or recess 82 is provided in back plate contacting surface 70 to reduce the
direct surface area between back end 62 and back plate 22, such that less heat will
be exchanged between back end 62 and the back plate 22.
In another embodiment, the valve pin bushing may be formed from more
than one component, rather than being a unitary structure. For example, back end
62 of a valve pin bushing of the present invention could be formed independently
of flange 64, with the two portions connected together by a removable connection,
such as a threaded connection, or by a permanent connection, such as brazing, welding,
use of an adhesive, or other method apparent to one skilled in the art. Such a configuration
facilitates the use of different materials having different thermal and other physical
characteristics such that various portions can each be formed from different materials
each having the characteristics best suited for the different functions carried
out by such portions.
It will be appreciated that a valve pin bushing of the present invention
could be modified in a number of ways without departing from the scope of the invention.
Flange 64 may include one or more openings or cutouts therein to reduce contact
between the manifold contacting surface 63 and the manifold surface 14a, thus reducing
heat conduction from the hot manifold 14 to the valve disk 50. For example, figure
5 shows a valve pin bushing 85 that is similar to the embodiment shown in Figure
4 except that rather than flange 64, valve pin bushing 85 includes a plurality of
flanges 69, or legs, spaced apart along a perimeter of head portion 66. Each flange
69 has a first end 69a integrally connected to head portion 66 and a second end
69b having a manifold contacting surface 65 that contacts manifold surface 14a of
manifold 14. As such, having a plurality of manifold contacting surfaces 65 further
reduces the contact surface area between manifold 14 and head portion 66. The embodiment
of Figure 5 may be further modified by the addition of fewer or greater number of
flanges 69. Further, flanges 64/69 in a valve pin bushing of the present invention
may be modified in other ways as would be apparent to one skilled in the art provided
that a contact surface area between flanges 64/69 and manifold 14 is less than a
contact surface between back end 62 of a valve pin bushing of the present invention
and back plate 22.
The embodiment of Figure 5 also illustrates that a leading surface
55 of tubular member 56 may be curved rather than angled to proved a substantially
rheological bend for the melt stream to flow more smoothly though manifold melt
Figure 6 shows another alternative to the embodiments disclosed above.
In particular, Figure 6 shows a valve pin bushing 90 similar to valve pin bushing
80 of Figure 4 except that instead of back end 62 being circular, back end 61 of
valve pin bushing 90 is square. Flange 75 extends from back end 61 forming a square
shaped perimeter. As such, the general shape of the present invention need not be
limited to either of the circular or square embodiments, but may be a variety of
shapes as would be apparent to one of ordinary skill in the art. Central portion
57 of Figure 2 may have a configuration other than frusto-conical and still have
a mass that decreased towards manifold 14. For example, in Figure 6, a central portion
67 is a reverse square pyramid shape, rather than a frusto-conical shape. As such,
other shapes apparent to one skilled in the art would also be suitable.
Further, although a tapered central portion, as in central portions
57, 67 of Figures 2 and 6, is preferred because heat will be drawn toward the area
of the valve pin bushing having the larger mass to equalize the heat transfer within
the valve pin bushing, other embodiment will function similarly to the preferred
embodiment. For example, Figure 7 shows an injection molding apparatus 11 similar
to that of Figure 1, except that the valve pin bushing 95 positioned between back
plate 22 and manifold 14 does not have a tapered central portion 76. Instead, head
portion 66 has a thicker back end 62, which has a generally flat outer surface 62a,
which is parallel to but not contacting manifold surface 14a. Central portion 76
extends from back end 62, such that it has an outer surface 76a which is perpendicular
to outer surface 62a of back end 62. As such, an air space 72 is defined by flange
64, back end 62, central portion 76 and manifold 14. In the example shown in Figure
7, central portion 76 has a similar cross-sectional diameter as tubular member 56,
however central portion 76 may have several different cross-sectional shapes.
Valve pin bushing 95 works substantially the same as the other valve
pin bushings of the present invention. Heat is absorbed from the manifold 14 and
transferred to the colder back plate 22 at a faster rate than it is absorbed because
the contact surface area between the manifold 14 and flange 64 is less than the
contact surface area between back end 62 of head portion 66 and back plate 22. As
such, valve pin bushing 95 cools to a temperature lower than manifold 14, causing
leaking melt stream 78 to become more viscous or to harden forming a seal to avoid
leaking melt material.
Figure 8 illustrates yet another embodiment of the present invention.
In particular, Figure 8 illustrates a valve pin bushing 100, which is similar to
valve pin bushing 50 of Figures 2 and 3, except that valve pin bushing 100 lacks
lip 74. Also, valve pin bushing 100 includes a first member 51 that includes the
elements of valve pin bushing 50 (i.e., head portion 66 and tubular member 56) and
a sealing portion 53 that forms an internal sealed hollow chamber 71. Sealing portion
53 is a substantially planar, circular disk that seals off the leading end of chamber
71. Sealing portion 53 includes a central opening 74a forming an inner edge having
a circumference that sealingly engages an outer wall 56a of tubular member 56, and
has an outer peripheral edge 79 that sealingly engages flange 64. A step 87 is provided
around the inner edge of the forward end of flange 64 for receiving the outer edge
79 of the sealing portion 53.
In one embodiment, the sealing portion 53 is a pressure disk and includes
spaced apart inner and outer grooves 81 and 82 facing the manifold 14. As best seen
in Figure 8, the grooves 81 and 82 are separated by a first ridge 84 that bears
against the manifold 14. The outer groove 82 terminates at a second ridge 86 that
also bears against the manifold 14. The inner groove 81 can function to catch melt
escaping from around the manifold bore 42, which hardens as it gets further from
the heat of the bore 42 and which is also prevented from going further by first
ridge 84. The outer groove 82 acts to catch any melt passing first ridge 84, with
the second ridge 86, together with shoulder 68, acting as a further seal against
melt leakage. Grooves 81, 82 can also reduce heat transfer from the hot manifold
to first member 51, and increase the resilience of the sealing portion 53 to resist
breaking of the seal between the sealing portion 53 and first member 51. In various
embodiments, more or less than two grooves 81, 82, are provided in the manifold
facing surface of sealing portion 53, and in another embodiment, such surface is
flat with no grooves provided therein. Further, in another embodiment, ridges 84
and 86 are replaced by seal rings of the type typically used in high temperature
The surface 63 of flange 64 although in contact with sealing portion
53, does not increase the surface area of contact with manifold 14. Thus, valve
pin bushing 100 operates in the same manner as valve pin bushing 50.
Further, as seen in Figure 8, a peripheral lift edge 88 is provided
around a back end 62 of valve pin bushing 100 to provide an edge for attaching a
lift tool for inserting and removing valve pin bushing 100 from the injection molding
apparatus 10. However, lift edge 88 may omitted or replaced with tapped holes 94
(shown in phantom in Figure 8) provided through back plate contacting surface 70.
The sealing portion 53 may be formed from the same or different materials
as the remainder of valve pin bushing 100. In an embodiment of the present invention
where sealing portion 53 is formed from a different material, the materials may
have different thermal and/or other physical characteristics. For example, first
portion 51, including head portion 66 and tubular portion 56 through which valve
pin 38 reciprocates, can be formed from a harder material to accommodate wear from
valve pin 38, while sealing portion 53 may be formed from a more flexible material.
It will be appreciated that a vacuum space is generally a very good
insulator. Thus, vacuum brazing may be used to join sealing portion 53 together
with first portion 51, resulting in chamber 71 being a vacuum chamber. In a vacuum
brazing process to form valve pin bushing 100, brazing alloy or material is pre-positioned,
at the joints between sealing portion 53 and first portion 51 (i.e., where sealing
portion 53 meets flange 64 and tubular portion 56), and the valve pin bushing 100
is placed in a brazing oven that is evacuated of air. A sufficient gap is left between
sealing portion 53 and first portion 51 so that air can escape from the chamber
71 as the furnace is evacuated prior to sealing of the joint. Once the brazing furnace
is evacuated sufficiently to result in a desired negative pressure within chamber
71, the furnace temperature is increased and the brazing material seals the joints
between the sealing portion 53 and first portion 51. In various embodiments, sealing
portion 53 may be joined to first member 51 by means other than vacuum brazing,
such as by traditional brazing, welding, using adhesives or by another method apparent
to one skilled in the art. In other various embodiments, the chamber 71 is not a
vacuum chamber, but is filled with air, or other insulating material.
Figure 9 shows a valve pin bushing 110 according to another embodiment
of the present invention. Valve pin bushing 110 is substantially similar in construction,
function, and manufacture to valve pin bushing 100, with the exception of differences
that will be apparent from the Figures and the following description. The valve
pin bushing 110 is formed from a first member 51a and a second member 60 that collectively
define internal vacuum chamber 71. However, unlike valve pin bushing 100, first
member 51a includes only central portion 57 and tubular member 56. Thus, back end
62a is split between first member 51a and second member 60. In addition, the second
member 60 integrally includes support flange 64, along with manifold engaging shoulder
68 and lift edge 88. As with valve pin bushing 100, the first and second members
51a and 60 may be formed from the same materials or formed from different materials.
Further, first and second members 51a and 60 may be joined by methods similar to
those described above for valve pin bushing 100, such as vacuum brazing. In yet
another embodiment, sealing portion 53 may be an integral piece formed with tubular
member 56 and central portion 57, such that flange 64 may be subsequently joined
to back end 62a and sealing portion 53 using one of the methods discussed above
with respect to Figure 8 to form chamber 71, such as vacuum brazing.
As will be apparent to those skilled in the art in light of the foregoing
disclosure, many alterations and modifications are possible in the practice of this
invention without departing from the claimed scope thereof. Accordingly, the scope
of the invention is to be construed in accordance with the substance defined by
the following claims.