Mold for use in a gas-assisted injection molding system and ejector pin subsystem including a blocking pin assembly for use therein

A mold for use in a gas-assisted injection molding system includes an ejector pin subsystem including a blocking pin assembly which not only blocks the flow of molten plastic through a secondary runner but also helps to eject solid plastic from the mold. The mold also includes an adjustable overflow pin assembly and a conically-shaped spill cavity flow-coupled by the secondary runner to an article-defining cavity of the mold. The blocking pin assembly together with the adjustable overflow pin assembly are mounted on an ejector plate to move therewith between extended and retracted positions of the ejector plate. The blocking pin assembly includes a blocking pin which is slidably fit within a mold half to move between an extended blocking position to block the flow of molten plastic through the secondary runner and a retracted position to allow the flow of molten plastic through the secondary runner and into the spill cavity. The blocking pin assembly includes a hydraulic cylinder for slidably mounting and moving the blocking pin relative to the ejector plate. The blocking pin has an end surface which partially defines the secondary runner in its retracted position and partially defines the article-defining cavity in its extended blocking position. The adjustable overflow pin assembly and the blocking pin assembly, as well as the other ejector pins mounted on the ejector plate, eject plastic from the article-defining cavity, the spill cavity, and the secondary runner in the extended position of the ejector plate.

TECHNICAL FIELD 
This invention relates to molds and ejector pin subsystems for use therein 
and, in particular, to molds for use in gas-assisted injection molding 
systems and ejector pin subsystems including blocking pin assemblies for 
use therein. 
BACKGROUND ART 
U.S. Pat. No. 5,098,637 discloses a method and system for injection molding 
hollow plastic articles with pressurized gas which provides for 
displacement by the gas of a portion of plastic from the mold cavity into 
a flow-coupled spill cavity. The volume of the spill cavity may be varied 
to control the quantity of displaced plastic such as by a lead screw. 
U.S. Pat. No. 5,607,640 (i.e. '640 patent) discloses in FIGS. 1-4 thereof, 
the use of a spill cavity with a blocking pin and shims to control the 
volume of plastic going into the spill cavity. The pin is in its up 
position to block plastic flow from the article-defining cavity, through a 
runner and into the spill cavity. Subsequently, the pin moves to its down 
position to allow plastic to go to the spill cavity by pressurized gas. In 
the remainder of the '640 patent, a method and system are disclosed where 
the volume of the spill cavity is allowed to increase in a controlled 
fashion to a final volume based on the amount of plastic injected into the 
mold cavity. The volume of the spill cavity increases during a step of 
displacing the plastic into the spill cavity. In this way, the method and 
system eliminate the need for a shut-off or blocking pin. In two disclosed 
embodiments, pistons are utilized to purge or displace plastic from the 
spill cavity. 
European Patent Document No. 393,315 discloses a spill subgate with a 
blocking hydraulic pin. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a mold for use in a 
gas-assisted injection molding system and ejector pin subsystem for use 
therein wherein the subsystem includes an ejector plate and a blocking pin 
assembly mounted on the ejector plate to move therewith and wherein the 
assembly includes a blocking pin slidably fit within the mold to not only 
block the flow of molten plastic within a secondary runner in the mold but 
also to cooperate with the rest of the subsystem to eject solidified 
plastic from an article-defining cavity, a spill cavity and the secondary 
runner. This is a practical design which is not only relatively 
inexpensive but also is simple in operation and for servicing. 
In carrying out the above object and other objects of the present 
invention, a mold for use in a gas-assisted injection molding system is 
provided. The mold includes a first mold half and a second mold half. The 
first and second mold halves are movable relative to each other between an 
open position and a closed position. The first and second mold halves 
define an article-defining cavity, a spill cavity, and a secondary runner 
for flow coupling the spill cavity to the article-defining cavity. The 
mold also includes an ejector pin subsystem including an ejector plate 
supported to move relative to the second mold half between extended and 
retracted positions and a blocking pin assembly mounted on the ejector 
plate to move therewith. The blocking pin assembly includes a blocking pin 
slidably fit within the second mold half to move relative to the ejector 
plate between an extended blocking position to block the flow of molten 
plastic through the secondary runner and a retracted position to allow the 
flow of molten plastic through the secondary runner and into the spill 
cavity. The ejector pin subsystem also includes at least one ejector pin 
also mounted on the ejector plate and slidably fit within the second mold 
half to move with the ejector plate relative to the second mold half in an 
open position of the mold. The at least one ejector pin and the blocking 
pin eject plastic from the article-defining cavity, the spill cavity, and 
the secondary runner in the extended position of the ejector plate. 
Preferably, the blocking pin assembly includes a cylinder for slidably 
mounting and moving the blocking pin relative to the ejector plate. 
Preferably, the cylinder is a hydraulic cylinder. 
Also, preferably, the blocking pin has an end surface which partially 
defines the secondary runner in its retracted position and partially 
defines the article-defining cavity in its extended blocking position. 
Also, preferably, the at least one ejector pin moves within the spill 
cavity to eject plastic from the spill cavity and the secondary runner in 
the extended position of the ejector plate. 
Still, preferably, the molten plastic flows in a first direction through 
the secondary runner to reach the spill cavity and wherein the blocking 
pin moves in the secondary runner in a second direction substantially 
opposite the first direction during movement of the blocking pin from its 
retracted position to its extended blocking position. 
Still further in carrying out the above object and other objects of the 
present invention, in a mold having a first mold half and a second mold 
half wherein the first and second mold halves move relative to each other 
between an open position and a closed position and wherein the first and 
second mold halves defined an article-defining cavity, a spill cavity, and 
a secondary runner for flow coupling the spill cavity to the 
article-defining cavity, an ejector pin subsystem is provided. The ejector 
pin subsystem includes an ejector plate supported to move relative to the 
second mold half between extended and retracted positions thereof. The 
ejector pin subsystem also includes a blocking pin assembly mounted on the 
ejector plate to move therewith. The blocking pin assembly includes a 
blocking pin slidably fit within the second mold half to move relative to 
the ejector plate between an extended blocking position to block the flow 
of molten plastic through the secondary runner and a retracted position to 
allow the flow of molten plastic through the secondary runner and into the 
spill cavity. The ejector pin subsystem further includes at least one 
ejector pin also mounted on the ejector plate to move therewith and 
slidably fit within the second mold half to move with the ejector plate 
relative to the second mold half in the open position of the mold. The at 
least one ejector pin and the blocking pin eject plastic from the 
article-defining cavity, the spill cavity, and the secondary runner in the 
extended position of the ejector plate.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawing Figures, there is illustrated in FIG. 1 a 
mold, generally indicated at 10, for use in a gas-assisted injection 
molding system. The mold 10 includes a first mold half 12 and a second 
mold half 14. The first and second mold halves 12 and 14, respectively, 
are movable relative to each other between an open position and a closed 
position as shown in FIG. 1, wherein the first and second mold halves 12 
and 14 respectively define an article-defining cavity 16. 
The second mold half 14 includes a gas passageway 18 which extends from an 
exterior surface (not shown) of the second mold half 14 to an inner 
interior surface 20 of the second mold half 14 in fluid communication with 
the article-defining cavity 16. 
The second or stationary mold half 14 includes a sprue 22 for communicating 
thermoplastic material to a runner 24 which, in turn, communicates with 
the article-defining cavity 16 via a gate 26. A thermoplastic flow path is 
defined by the sprue 22, the runner 24 and the gate 26. Ejector pins 28 
extend through the first or movable mold half 12 and are connected to an 
ejector plate 29. The ejector plate 29 is supported to move relative to 
the first mold half 12 from a retracted position to an extended position 
to eject a completed part from the article-defining cavity 16 as well as 
the plastic in the runner 24 and the sprue 22. 
The mold 10 also includes a gas pin assembly, generally indicated at 30. 
The gas pin assembly 30 includes a one-piece housing 32. A base portion of 
the housing 32 is threadedly secured to the second mold half 14 at the 
interior surface 20 of the second mold half 14 so that the gas pin 
assembly 30 can be readily removed from the second mold half 14 in the 
open position of the mold 10. A rubber O-ring is typically provided about 
the base portion of the housing 32 to seal the housing 32 within the 
second mold half 14. 
Preferably, the housing 32 also includes a hexagonal head portion so that 
the assembly 30 can be readily removed from the second mold half 14 in the 
open position of the mold 10 by a conventional tool (not shown). 
The housing 32 includes an elongated aperture formed therein in 
communication with and aligned with the gas passageway 18 to permit the 
flow of gas therethrough. 
The base portion of the housing 32 is also internally threaded to 
threadedly secure therein a holding device in the form of a set screw 42 
which has a gas hole formed completely therethrough to permit the flow of 
gas therethrough. 
The gas pin assembly 30 also includes a porous insert 48 comprising a 
sintered material such as aluminum, copper, nickel, steel, bronze, 
porcelain, and brass which permits the flow of gas therethrough but 
prevents the passage of molten plastic therethrough. The insert 48 is held 
in position within the aperture by the set screw 42 at one end thereof and 
by flanges of the head portion at the opposite end thereof. 
The sintered material is preferably a bronze sintered material and can 
filter out foreign particles down to 20 microns. However, the micron size 
can be varied depending on the type of plastic utilized in the molding 
process. 
Further details of the gas pin assembly 30 can be found within the 
above-noted patent application entitled "Mold For Use In A Gas-Assisted 
Injection Molding System And Gas Pin Assembly For Use Therein". While the 
gas pin assembly 30 is illustrated as the particular mechanism for 
injecting pressurized gas into the article-defining cavity 16, other 
mechanism can be utilized to inject pressurized gas into the 
article-defining cavity 16 as illustrated and described in the prior art 
patents noted in the "Background Art" portion of this application. 
The mold 10 also includes a conically-shaped spill cavity 50 and a 
secondary runner, generally indicated at 52, for flow coupling the spill 
cavity 50 to the article-defining cavity 16. The secondary runner 52 
includes a vertically extending portion 53, an angled portion 54 and a 
horizontally-extending portion 56 through which molten plastic flows from 
the article-defining cavity 16 to the conically-shaped spill cavity 50 
upon the injection of pressurized gas into the article-defining cavity 16. 
The mold 10 of the present invention also includes an adjustable overflow 
pin assembly, generally indicated at 58. The pin assembly 58 includes a 
pin 60 slidably fit within the mold half 12 and connected to the ejector 
plate 29 to move relative to the mold half 12 in an open position of the 
mold 10 upon movement of the ejector plate 29 relative to the mold half 12 
between extended and retracted positions thereof. 
The pin assembly 58 also includes a conical stack of annular shims 62 which 
are removably secured to the ejector pin 60 by means of a threaded 
fastener such as a screw, generally indicated at 64, which extends through 
the shims 62 and into an internally threaded hole 66 formed in an end face 
or surface 68 of the ejector pin 60. The screw 64 has a head portion 65 
which is in abutting engagement with the uppermost shim 62. The top 
surface of the head portion 65 is flush with the top surface of this shim 
62. 
The shims 62 move with the ejector pin 60 within the conically-shaped spill 
cavity 50 during movement of the ejector plate 29 from its retracted 
position to its extended position so that the assembly 58 ejects plastic 
from the spill cavity 50. The conical stack of shims 62 has an outer 
surface taper approximately in the range of 2.degree. to 8.degree. and is 
preferably approximately 5.degree.. In this way, the shims 62 form a tight 
fit with the spill cavity 50 which has a corresponding taper to its 
interior surface. The annular shims 62 form the tight fit within the spill 
cavity 50 in the retracted position of the ejector plate 29. 
Two or more annular shims 62 define the stack of annular shims 62. The 
number of annular shims 62 is dependent upon how much molten plastic need 
be removed from the article-defining cavity 16 to define the desired 
hollow plastic part formed within the article-defining cavity 16. 
The mold 10 also includes a blocking pin assembly, generally indicated at 
70, also mounted on the ejector plate 29 to move therewith. The blocking 
pin assembly 70 includes a blocking pin 72 which is also slidably fit 
within the mold half 12 to move relative to the ejector plate 29 to an 
extended plastic blocking position within the vertically extending portion 
53 of the secondary runner 52 to block the flow of molten plastic through 
the secondary runner 52 as shown in FIG. 1. 
The pin 72 is retractable within the portion 53 of the secondary runner 52 
to a retracted position by a hydraulic cylinder 76 which is also mounted 
on the ejector plate 29 to move therewith. In the retracted position of 
the blocking pin 72 within the portion 53 of the secondary runner 52, 
molten plastic is allowed to flow from the article-defining cavity 16 into 
the secondary runner 52 and then into the article-defining cavity 50. The 
blocking pin 72 has an end surface or face 78 which partially defines the 
runner 52 in the retracted position of the blocking pin 72 and which 
partially defines the article-defining cavity 16 in the extended position 
of the blocking pin 72. 
Referring now to FIG. 2, there is illustrated in block diagram flow chart 
form various process steps implemented by a gas-assisted injected molding 
system including the mold 10 of the present invention. 
At block 80, an injection molding cycle begins wherein the mold 10 is 
closed and the hydraulic or blocking pin 72 is extended within the 
vertically extending portion 53 of the secondary runner 52 to block the 
secondary runner 52 as illustrated in FIG. 1. 
At block 82, the article-defining cavity 16 is substantially filled with 
plastic. 
At block 84, pressurized gas is injected into the article-defining cavity 
16 and the hydraulic pin 72 is retracted substantially simultaneously with 
the injection of pressurized gas. 
At block 86, excess plastic displaced by the pressurized gas within the 
article-defining cavity 16 travels through the secondary runner 52 and 
into the adjustable overflow or spill cavity 50. 
At block 88, the molten plastic within the article-defining cavity 16, 
within the secondary runner 52 and within the spill cavity 50 is allowed 
to cool and the pressurized gas is exhausted from the article-defining 
cavity 16. 
At block 90, the mold 10 is opened. 
At block 92, the ejector plate 29 which carries the hydraulic cylinder 76, 
the ejector pin 60, and the other ejector pins 28 is extended toward the 
mold half 14 and the pins 72 and 28 and the shims 62 eject plastic from 
the sprue 22 and runner 24, the plastic article from the article-defining 
cavity 16, plastic from the secondary runner 52, and plastic from the 
overflow or spill cavity 50. 
At block 94, the ejector plate 29 is retracted by moving it relative to the 
mold half 12 to the position shown in FIG. 1. 
At block 96, the mold 10 is closed and the pin 72 is extended to block the 
portion 53 of the secondary runner 52 to await the beginning of another 
injection molding cycle. 
While the best mode for carrying out the invention has been described in 
detail, those familiar with the art to which this invention relates will 
recognize various alternative designs and embodiments for practicing the 
invention as defined by the following claims.