Molding device having a ring-gating and hole forming valve gate pin

In order to facilitate the formation of a plastic member with an aperture in a central portion thereof, a ring gating valve arrangement is provided with a multi-piston servo arrangement which enables a specially configured pin to be stepwisely reciprocated back and forth within a molding device. The pin is formed with a land at one end which is dimensioned and shaped to produce the required aperture. The pin further features a channel structure which includes an annular recess adapted to permit plastic to flow into the center of the mold cavity area when the pin is thrust to a predetermined location. After the cavity is filled with hot plastic, the pin is retracted to a position wherein the annular recess is located within a removable gate bushing and the shaped land is pulled up until it is appropriately located in the mold cavity area. As the injected plastic cools and solidifies, the shaped land acts as the aperture molding pin and forms a clean aperture in the molded part. After solidification, the pin is retracted and the mold is opened to permit the molded part to be ejected.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a ring gating technique and more 
specifically to an improved ring gating technique and apparatus which 
enables the formation of molded plastic products which have a clean 
through hole and which exhibit even stress and minimal flow marks. 
2. Description of the Prior Art 
Known mold gate systems are common in design and mode of operation. That is 
to say, hot plastic material is usually distributed through a hot manifold 
to a heated nozzle assembly. A valve gate pin within the heated nozzle is 
either hydraulically, pneumatically or mechanically retracted from a gate 
orifice in the mold cavity and hot plastic is injected therethrough into 
the mold cavity. After the cavity is filled, the valve gate pin is 
returned to its closed position wherein it seats against the gate orifice 
to cut-off the flow of plastic. 
However, when the mold is opened and the plastic part is ejected, 
inevitably a "gate pin mark" impression can be seen on the surface of the 
part at the location where the plastic was injected. 
The desired position for the injection mold gating of circular or square 
parts is usually in the center of the part. When a through hole is 
required to be formed at the center of the part, the gating must be offset 
from the center and use made of hot tip, cold runner, or gate valve 
techniques. However, these techniques tend to result in uneven filling, 
create molded-in part stress and a produce a weld line which originates at 
the core pin which forms the hole. Viz., as shown in FIGS. 1 and 2 the hot 
plastic flow (f) which is injected via a heated probe or conventional 
valve gate 1, enters a mold cavity 2 at a location or gate point (p) and 
separates (as indicated by the bold arrows) into two flows which pass 
around on either side of the projection or pin 3 which is used to form the 
required opening. When the two flow fronts meet on the other side of the 
pin, the undesirable weld line (w) is created. 
Alternatively, instead of using the above mentioned offset injection 
technique, the part may be centrally gated in the area of the hole which 
is formed, using hot or cold multi-tipped edge gating in the manner 
illustrated in FIGS. 3 and 4. However, this technique results in a less 
than perfect surface at each gate point and also produces flow lines in 
the molded part originating between the individual gate locations. Viz., 
as illustrated in FIG. 4, a number of flow or weld lines are created by 
the multiple flows of plastic which result from injection by way of a 
sprue 4 having multiple sub-gates. Viz., as shown, in the case wherein the 
sprue has three sub-gates, three separate flows are produced within the 
mold cavity. Upon the flow fronts meeting one another, three flow or weld 
lines are produced. 
A more laborious and less desirable technique of producing the above type 
of perforate part involves molding the part without the hole and then 
forming the opening using a separate drilling or punching operation. While 
this generally solves the flow line problem, it introduces the need for a 
number of additional operations to be performed and thus increases the 
cost of the article. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to enable plastic to be injected 
by way of "ring gating" into a mold cavity using a modified gate 
technology which enables the formation of a molded part exhibiting even 
stress, a clean through hole and no flow marks. 
This technique finds application in single or multiple cavity plastic molds 
designed to produce molded parts with through holes in or near the center 
of the same and which can be filled through the use of a single injection 
point within the cavity. 
In brief, the above object is achieved by a ring gating valve arrangement 
which includes a multi-piston servo arrangement which enables a specially 
configured pin to be stepwisely reciprocated back and forth within a 
molding device. The pin is formed with a land at one end which is 
dimensioned and shaped to produce the required aperture. The pin further 
features a channel structure which includes an annular channel adapted to 
permit plastic to flow into the center of the mold cavity area when the 
pin is thrust to a predetermined location. After the cavity is filled with 
hot plastic, the pin is moved to a position wherein the annular channel is 
located within a gate bushing and thus cuts off the supply of plastic 
while the shaped land assumes a position wherein it is appropriately 
located in the mold cavity area. As the injected plastic cools and 
solidifies, the shaped land acts as the aperture molding pin and forms a 
clean aperture in the molded part. After solidification, the pin is 
retracted and the mold is opened to permit the molded part to be ejected. 
Thus, some of the more prominent features of the invention are provided in 
that: 
1) the gate pin is axially movable to a position wherein a gate orifice is 
open and plastic is permitted to flow into the molding cavity; 
2) the gate pin is axially movable to a position wherein the plastic flow 
is cut-off; 
3) a portion of the gate pin is used as a molding pin which forms the 
aperture in the part being molded; 
4) the gate pin is connected with an actuating device which allows the pin 
to be selectively moved axially between the positions wherein injection 
and molding can take place. 
More specifically, a first aspect of the present invention is provided in a 
molding device which features: means defining a cavity in which a part can 
be molded; a reciprocal pin; a land formed at a location proximate an end 
of the pin, the land being so shaped and sized so that when the pin 
assumes a first predetermined position, the land cooperates with the 
cavity defining means in a manner wherein it acts as a molding pin and 
forms an aperture in a part which is formed by injecting a flow of molten 
material into the cavity; channel means formed on the pin, the channel 
means allowing a flow of the molten material to enter the cavity when the 
pin assumes a second predetermined position; and servo means operatively 
connected with the pin for selectively moving the pin between the first 
and second predetermined positions. 
A second aspect of the present invention is provided in a molding device 
which features: an axially displaceable pin; a first bushing disposed on a 
first side of a cavity which is defined between first and second 
structural elements which are relatively movable with respect to one 
another, the first bushing being disposed in the first structural member 
and adapted to guide the pin into the cavity; a second bushing adapted to 
receive the pin after it has been displaced by a predetermined amount 
through the cavity, the second bushing being disposed with the second 
structural member and on a second side of the cavity; channel means 
cooperating with the first bushing for permitting fluid communication 
between a supply conduit and the cavity when the pin has been displaced by 
a first predetermined amount; and a shaped portion which is formed on the 
pin and which is disposed in the cavity to act as a molding pin when the 
pin has been displaced by a second predetermined amount and wherein the 
communication between the supply conduit and the cavity is cut-off.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 5 to 8 show details of a preferred embodiment of the present 
invention. FIG. 8 is a sectional view of gated mold wherein the valve gate 
pin and actuating pistons are removed for illustrative clarity. In this 
arrangement, a piston chamber 100, pressure port 101 and bushing 102 are 
modified as compared with the normal valve gate mold design and 
characterizes the construction of the illustrated embodiment. 
In this arrangement, a heated material distribution manifold 104 is 
thermally isolated from the rest of the mold by standoffs 106 and a nozzle 
body 108. A material supply channel 110 which extends through the manifold 
104 conveys heated plastic material to the nozzle body 108. In this 
instance, the nozzle body 108 is heated by an electric heating coil or the 
like type of heating device 112. A thermocouple 114 is used to sense the 
temperature of the nozzle body 108 and to generate a temperature 
indicative signal by way of which the amount of heat produced by the 
heater 112 can be suitably regulated by a control circuit (not shown). 
A removable gate bushing 116 is secured in the illustrated position in a 
mold cavity by a retainer 118. This bushing 116 directs the flow of 
plastic material into a mold part cavity area 120 which is defined between 
a mold cavity 122 and a mold core 124. 
Cooling channels 126, which are formed in the mold cavity 122, the mold 
core 124 and structural member 128 through which the nozzle body extends, 
have a cooling medium pumped therethrough. 
FIG. 6 shows a valve gate pin and piston assembly 130 which form a vital 
part of this embodiment. It should be noted that while the piston 132 and 
most of the pin 134 are generally fixed in shape and dimensions, the shape 
and size of a land 134a formed immediately adjacent the end of the pin 134 
can be varied in accordance with the size and shape of the aperture which 
is to be formed. A second land 134b is selected to act as a valve member 
and is dimensioned to close in the mouth or port of the gate bushing 116 
and thus act as a valve member. FIG. 7 shows the manner in which the pin 
134 is formed with a plurality of flutes 134c along a major portion of its 
length. 
It should be noted that typical prior art pins are solid in this area. 
It should also be noted that an annular recess 134d is formed about the 
periphery of the pin 134 at a location proximate the end thereof. This 
recess 134d is formed so as to fluidly communicate with the channels 
defined by the fluting 134c. The reason for this construction will become 
more apparent as a discussion of the operation of the embodiment is made 
with reference to FIGS. 10 to 17. 
The bushing 102 which is set in a through bore formed in the mold core 124, 
is axially aligned with the removable gate bushing 112 and arranged to 
slidably receive the end of the pin 134 during the molding process. 
FIG. 8 shows a piston 140 which cooperates with the valve gate pin and 
piston assembly. As will be appreciated, the piston 140 has a short piston 
rod 142 on which sealing rings or the like type of means are disposed. The 
diameter of the piston 140 is greater than that of the piston 132. 
FIG. 9 shows the pin and piston assembly 130 and piston 140 installed in 
the mold system. In this figure, the pistons 132, 140 are illustrated in 
what shall be referred to as "intermediate" positions. As will be 
appreciated from this figure, the gate pin and piston assembly 130 are 
disposed such that the piston 132 is received in a cylindrical bore formed 
in a structural member 146, while the pin portion 134 extends through 
elongate bores 146a, 104a (see FIG. 5) into an elongate stepped bore 148. 
The cylindrical bore 144 is closed by a structural member 150 in which a 
stepped bore 150a is formed. This stepped bore 150a is formed such that 
the smaller diameter portion thereof fluidly communicates the chamber 
which is defined between the bore 144 and the structural member 150. 
Piston 140 is disposed in the stepped bore 150a so that the short piston 
rod 142 which extends from the lower face thereof, extends through the 
smaller portion of the stepped bore 150a and is permitted to be 
projectable into the chamber in which piston 132 is disposed. The sealing 
rings on the rod 142 engage the walls of the smaller diameter portion of 
the stepped bore 150a thus establishing an effective pressure seal between 
the bores 144, 150a in which the pistons 132, 140 are disposed. 
A port 152 fluidly communicates with the lower section of the cylindrical 
bore 144 while a port 154, which is formed in the structural member 150 is 
arranged to communicate with the upper end of the bore 144 and the lower 
end of the stepped bore 150a. The upper end of the stepped bore 150a is 
closed by a cap member 156 in which port 101 is formed. This port 101 
fluidly communicates with the upper portion of the chamber defined in the 
stepped bore 150a by the cap member 156. 
The ports 101, 152 and 154 are communicated with a source (S) of fluid 
under pressure by way of a valve arrangement (V). This valve arrangement 
(V) enables the ports 101, 152 and 154 to be selectively communicated with 
the source of pressurized fluid or with the atmosphere. 
OPERATION 
The operation of the device described above will now be given with 
reference to FIGS. 10 to 17. 
FIG. 10 shows the situation wherein molten plastic (indicated by the dark 
shaded areas) has been supplied into the supply channel 110 and into the 
annular space defined between the pin 134 and the wall of the elongate 
stepped bore 148, by a molding machine (M). Note that the molding machine 
is schematically illustrated in block diagram form for simplicity. 
At this stage, the same air or fluid pressure is supplied to the ports 101 
and 152. This induces the pistons 132, and 140 to move to their respective 
first restricted positions. Viz., as the pressures applied are equal, the 
piston 140 is moved to the bottom of the stepped bore 150a in which it is 
reciprocally disposed and conditioned to assume a position wherein the 
short piston rod 142, which extends from the lower surface thereof, 
projects into bore 144, engages the top of the piston 132, and displaces 
it downwardly by a predetermined distance against oppositely acting the 
pressure being supplied via port 152. 
FIG. 11 (no molten plastic material is illustrated for clarity) illustrates 
the situation wherein the pistons 132 and 140 are moved to their 
respective "projected" positions. This is achieved by venting the ports 
152 and 101 to the atmosphere and applying a fluid pressure to the port 
154. Under these conditions, the pistons 132 and 140 are moved to their 
second respective restricted positions. Viz., as shown, the piston 132 is 
driven to the bottom of the bore 144 while the piston 140 is moved to the 
top of the stepped bore 150a. In this state, the pistons 132, 140 assume a 
maximally separated condition. The pin 134 is displaced downwardly and is 
guided into the core block 124 and is guidingly received in the bushing 
102. 
Next, with the pin 134 maintained in this position (FIGS. 12 and 13), the 
molding machine injects molten plastic under pressure down along the 
fluting and into the molded part cavity area 120 by way of the annular 
recess 134d formed near the lower end of the pin. 
After the cavity 120 is completely filled in the manner illustrated in FIG. 
13, the port 154 is vented to the atmosphere and fluid pressure is 
supplied to the ports 101 and 152. This moves the pistons 132 and 140 back 
to their respective "intermediate" positions and induces the land 134b 
provided at the lower end of the pin 134, to be positioned in a central 
portion of the cavity in the manner illustrated in FIG. 14. In this 
position, the land 134b acts as a molding pin. 
Cooling media which flows through the coolant conduits 126 cools the cavity 
122 and the core 124 and induces the plastic in the cavity area 120 to 
solidify about the land 134b and thus bring about the formation of a clean 
hole in the center of the molded part. Further, as the pin 134 has been 
retracted to the degree that fluid communication between the annular space 
or recess 134d and the cavity 120 is cut-off, the opening through which 
the plastic was injected into the cavity is completely eliminated and no 
unsightly marks result at the site where the plastic was injected into the 
cavity. 
As shown in FIG. 15, after the plastic has solidified in the cavity area 
120, the ports 101 and 154 are vented to the atmosphere while pressure 
continues to be supplied to the port 152. As a result, the pistons 132 and 
140 are moved to their "retracted" positions. This results in the pin 134 
being removed from the cavity area 120 leaving a cleanly formed opening in 
the molded part. 
FIG. 16 shows the situation wherein the moving side of the mold arrangement 
is lowered away from the upper stationary section. FIG. 17 shows the 
situation after the plastic part is ejected from the core by way of a 
conventional technique. 
Following the ejection, the mold halves (viz., the mold core 124 and the 
mold cavity 122) are moved back into engagement with one another and fluid 
pressure is supplied to the port 101 while the pressure is maintained at 
the port 152. The port 154 is vented to the atmosphere. Under these 
conditions, the pistons 132, 140 are returned to their "intermediate" 
positions (viz., the positions illustrated in FIG. 9) in readiness for the 
next molding cycle. 
While the present invention has been disclosed with reference to only a 
single embodiment, it will be realized that many changes and/or 
modifications can be made thereto without departing from the scope of the 
present invention. For example, the invention is not limited to the use of 
pistons and this servo arrangement can be replace with any other suitable 
mechanism. Viz., a crank or cam actuated type servo could readily be used 
in place of the dual piston arrangement disclosed in detail above.