Valve gating arrangement for an insulated runner

A valve gating arrangement for an injection molding system having an insulated manner and a heated torpedo across from a gate. The valve gating arrangement includes a valve member sidably received within a passage extending through the torpedo. The valve member terminates at one end with a pin reciprocally movable into and out of the gate. An actuator is connected to the valve member to effect the reciprocal movement.

FIELD OF THE INVENTION
 This invention relates generally to plastic injection molding systems. More
 specifically, this invention relates to insulated runner systems and in
 particular, to the commencement and cessation of melt flow at a gate
 associated with such runner systems.
 BACKGROUND OF THE INVENTION
 There are two basic types of hot runner molds, namely, insulated runner
 molds and true hot runner molds. In an insulated runner mold, an unheated
 runner extends between a machine nozzle and a mold cavity. In use, molten
 plastic ("melt") flows from the nozzle through the runner into a space
 defined between respective mold faces of a mold cavity and a mold core to
 form a part. During use, a portion of the plastic solidifies adjacent the
 runner walls and acts as an insulator for a molten core of plastic, hence
 the term "insulated runner".
 Immediately adjacent the mold face of the mold cavity is an aperture
 referred to as a "gate" through which melt exits the insulated runner to
 form the part. It is of course necessary to interrupt flow through the
 gate for mold opening and stripping portions of an injection molding
 cycle. In insulated runner systems, melt is generally allowed to "freeze"
 in the gate prior to mold opening. Early systems would re-open the gate by
 pushing the frozen "slug" of plastic into the next part by incoming melt
 which would also melt the slug.
 More recently developed systems use a nozzle heater, generally referred to
 by persons skilled in such devices as a "torpedo" to better control melt
 temperature adjacent the gate. The torpedo is situated in an area referred
 to as a "runner drop" at a gate end of the insulated runner. The use of a
 heated torpedo allows longer cycle times by extending the critical time in
 which freezing could occur which would require "restarting" of the molding
 process.
 A drawback to insulated runner systems is the presence of a "vestige" on
 the part in the vicinity of the gate and "stringing" which result from
 melt in the gate adhering to the part during mold opening. In order to
 produce more acceptable gate vestiges, the gate should ideally be
 closeable other than by a slug of plastic after injection and before mold
 separation. Various arrangements have been devised to date. Each has its
 drawbacks.
 U.S. Pat. No. 3,159,878 to Scott teaches an insulated runner mold that uses
 a moveable core plug in the mold to keep the gate closed until sufficient
 pressure has built up inside the runner to overcome the closing force of
 the plug thereby "blasting open" the gate to rapidly fill a thin wall
 container mold.
 U.S. Pat. No. 5,037,598 to Akselrud teaches a moveable heated torpedo in an
 insulated runner drop that acts as a gate valve. However, to open the gate
 the torpedo is advanced toward the gate to melt the cold slug therein and
 thereafter the torpedo is retracted to allow melt to flow. When the mold
 is filled the gate remains open and freezes off, it is not closed by
 advancing the torpedo.
 Both these approaches produce gate vestiges on the part the size of which
 are a function of gate diameter. The larger the diameter the larger the
 vestige. Large gate diameters promote good flow and rapid filling of the
 mold cavity when high viscosity, or filled resins are being processed. In
 contrast smaller gate diameters, which give smaller vestiges, make filling
 slower and more difficult for filled resins and for making thin walled
 parts.
 It is an object of the present invention to provide a valve gated insulated
 runner to enable maximization of gate opening while substantially
 eliminating the gate vestige to produce a substantially blemish free part
 in any application.
 SUMMARY OF THE INVENTION
 A valve gating arrangement for an injection molding system having an
 insulated runner terminating in a gate through which melt is dischargeable
 into a space defined between a mold core and a mold cavity. The valve
 gating arrangement includes a fixed torpedo having a heated tip and a
 passage extending longitudinally therethrough. The heated tip extends into
 the insulated runner adjacent the gate. A valve member with a valve stem
 is slidably received in the passage. The valve member has a pin reaching
 from the valve stem into the gate. The valve member is reciprocally
 slidable between a closed configuration and an open configuration. In the
 closed configuration the pin extends into the gate to block melt flow. In
 the open configuration the pin is withdrawn from the gate to permit melt
 flow therethrough. An actuator is connected to the valve member for moving
 the valve member between the open and closed configurations.
 The actuator may be a pneumatically operable piston.
 A thermocouple may be provided in the heated tip to monitor melt
 temperature in the vicinity of the gate.

DESCRIPTION OF PREFERRED EMBODIMENTS
 FIGS. 1A and 1B are illustrative of a conventional insulated runner mold
 arrangement generally indicated by reference 10 in FIG. 1A. An insulated
 runner 12 has an inlet 14 and is illustrated as supplying two gates 16,
 each of which supplies melt for the molding of respective parts 18.
 Although two gates 16 and parts 18 are illustrated, persons skilled in
 such arrangements will appreciate that other numbers are feasible.
 A heated torpedo 20 extends into a runner drop 22 adjacent each gate 16.
 The torpedo 20 has a a heater 24 adjacent a tip 26 which provides heat in
 an amount sufficient to permit melt flow. This arrangement, which is
 discussed in the background above, relies on melt solidification rather
 than valve gating to interrupt melt flow.
 FIGS. 2A and 2B illustrate an arrangement in which a movable torpedo 30 is
 utilized for valve gating. Insofar as the structure illustrated in FIGS.
 2A and 2B is similar to the structure illustrated in FIGS. 1A and 1B,
 similar reference numerals have been used and the above description
 applies.
 The torpedo 30 has a tip 32 heated by a heater 34. Electrical leads 36
 extend from the heater 34 along an inside of the torpedo 34 and exit the
 torpedo 30 to the right as illustrated. The electrical leads 36 provide
 power to the heater 34.
 The torpedo 30 is slidably mounted in a bushing 38 to allow axial movement
 of the torpedo 34. A double acting pneumatically actuatable piston 40 is
 connected to the torpedo 30 to cause axial movement of the torpedo 30 as
 indicated by the arrows at reference 42. The movement of the torpedo 30 by
 the piston 40 causes the tip 32 of the torpedo 30 to move into and out of
 the gate 16 to respectively close and open the gate 16.
 Although the FIGS. 2A and 2B arrangement does provide a good vestige it
 does have certain drawbacks. Firstly, it has a relatively large diameter
 as it must act both as a heater and as a valve. Secondly, as the torpedo
 30 is hot, it is prone to back leakage between it and the bushing 38.
 Finally, the electrical leads 36 move with each back and forth cycle of
 the torpedo 30 thereby giving rise to frequent electrical failures.
 A valve gating arrangement according to the present invention is generally
 indicated by reference 50 in FIG. 3. The valve gating arrangement 50
 includes a torpedo 52 having a heated tip 54 extending into an insulated
 runner 56 in a runner drop 58 adjacent a gate 60. A passage 62 extends
 longitudinally through the torpedo 52.
 The torpedo is fixed in that it is securely mounted to a mold base 64 so as
 to be immovable relative to the gate 60. Electrical leads 66 extend from
 the heated tip 54 providing electrical current to a tip heater 55 in the
 tip 54.
 A valve member 70 has a stem 72 slidably received in the passage 62. The
 valve member 70 has a pin 74 which reaches from the valve stem 72 in the
 passage 62 toward the gate 60. Although the pin 74 is illustrated as being
 of reduced diameter this may not always be the case as the diameter of the
 pin 74 will depend on the breadth of the gate 60.
 The valve member 70 is reciprocally slidable in the direction of arrows 76
 between a closed configuration illustrated at the bottom of FIG. 3 and an
 open configuration illustrated at the top of FIG. 3. In the closed
 configuration the pin 74 extends into the gate 60 to block the gate 60. In
 the open configuration the pin 74 is withdrawn from the gate 60 to allow
 melt to flow through the gate 60.
 An actuator such as a pneumatically actuatable piston 80 is connected to
 the valve member 70 to move the valve member 70 between the closed and
 open configurations. The valve member 70 is illustrated as having an
 actuator end 82 of the valve stem 72 distal the pin 74 connected to the
 piston 80.
 In order to provide enhanced control of melt temperature, a thermocouple 84
 may be provided in the heated tip 54 to monitor the temperature of the tip
 54. Thermocouple leads 86 extend from the thermocouple 84 out of the
 torpedo 52.
 As the torpedo 52 is fixed, the electrical leads 66 and the thermocouple
 leads 86 do not move back and forth as in the arrangement illustrated in
 FIGS. 2A and 2B above. Hence the reliability of the thermocouple 82 and
 the heater 55 are enhanced as lead failure is less likely.
 As the torpedo 52 is fixed, it can be properly sealed to eliminate melt
 seepage to which the movable torpedo arrangement illustrated in FIGS. 2A
 and 2B is prone.
 In the valve gating arrangement of the present invention, the valve member
 70 is relatively slender and lightweight compared to the size and weight
 of a typical torpedo such as the torpedo 30 in FIGS. 2A and 2B thereby
 significantly reducing the reciprocating mass to be moved in and out of
 the gate 60.
 The above description is intended in an illustrative rather than a
 restrictive sense. Variations may be apparent to persons skilled in
 injection molding apparatus without departing from the spirit and scope of
 the invention as defined by the claims set out below.