Hot runner assembly with internally cooled, axially mounted electric actuator

Abstract

To provide an injection molding device.SOLUTION: A hot runner injection molding device that facilitates a use of electric actuator in a compact design includes: a hot runner manifold that defines a resin flow path for conveying a resin to a nozzle that acts as a conduit for introducing liquid resin into a mold cavity; a valve pin configured for linear movement along a longitudinal axis of the nozzle in order to control flow of the liquid resin through the nozzle; and an electric actuator having a body housing an electric motor. The electric actuator body includes a flow passage for circulating a coolant.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This application claims priority to U.S. Application No. 16 / 599,564, filed October 11, 2019, which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates to a hot runner injection molding apparatus having an electric actuator configured to circulate a cooling fluid within the body of the actuator, facilitating mounting the actuator in close proximity to a hot runner manifold while preventing overheating of the actuator's electric motor, and more particularly to such an apparatus in which the actuator can be axially assembled onto the hot runner manifold with substantially no lateral clearance, allowing multiple actuators to be assembled onto the manifold in close proximity to one another. [Background technology]

[0003] U.S. Patent Nos. 9,492,960 and 9,937,648 disclose an apparatus for controlling fluid flow to a mold, the apparatus including a manifold, a valve pin having a pin axis, a pin connector, and a stem, the valve pin being movable between an open position and an closed position relative to a gate. The electric actuator includes an electric motor having a motor housing that houses a drive gear and a drive shaft having a drive axis, the transmission includes a gear shaft, the drive gear and the transmission gear are drivably interconnected and arranged such that the drive axis and the gear axis are mounted and disposed non-coaxially relative to each other, and one or the other of the motor housing or the transmission housing is removably attached to a top clamping or mounting plate mounted upstream of the manifold and fixedly interconnected to the mold.

[0004] U.S. Patent No. 6,294,122 discloses an injection molding machine with an apparatus for controlling the movement of a pin including a plastic melt flow path having an output end for delivering molten plastic injected into the flow path under pressure into a mold cavity, wherein the pin comprises an elongated rod having an axis and an end, the pin is slidably mounted within the flow path for movement along its axis within the flow path, and an electrically driven motor is drivingly interconnected to an actuation mechanism, wherein the actuation mechanism is drivingly interconnected to the end of the pin and the motor is controllably drivable to drive the pin for movement along its axis within the flow path.

[0005] EP 2679374 A1 discloses an apparatus for injection molding of plastic materials, the apparatus comprising a hot runner, at least one injector including a nozzle mover inside which a valve pin is driven by a rotary electric motor, and an associated transmission including a screw and nut assembly for converting rotation of the shaft of the electric motor into translation of the valve pin, at least two of the valve pins, the rotary electric motor, and the screw and nut assembly being set parallel to each other.

[0006] In a hot runner injection molding system, liquid resin (molten plastic) is maintained in a molten state within channels defined in a heated manifold. The channels transport the molten plastic material from the injection molding machine to one or more nozzles, which deliver the molten plastic to at least one mold cavity through a gate defined at the interface between the nozzle and the mold cavity. After the mold cavity is filled, only the mold cavity is cooled to allow removal of the solid molded part. The resin in the manifold channels and nozzles is maintained at a temperature sufficient to keep the plastic in a liquid state, thus reducing cycle time and waste compared to cold runner injection molding systems, in which the resin-delivery channels are defined within the mold plate.

[0007] Because electric actuators are susceptible to degradation and failure when exposed to the high temperatures required in hot runner manifolds, hydraulic or pneumatic actuators are typically employed in hot runner injection molding machines to control the flow of molten resin into a mold cavity (or cavities). In these hot runner injection molding machines employing electric actuators, the electric actuators are positioned remotely from the manifold and / or provided with external cooling means (e.g., a cooling plate between the manifold and the actuator), further adding significant complexity and expense compared to more traditionally used pneumatic or hydraulic actuators.

[0008] Despite these commonly recognized drawbacks of electric actuators, there are advantages, such as the ability to more precisely control the movement and positioning of the valve pin, which can have associated benefits in terms of part quality and production efficiency as well. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent No. 9,492,960 [Patent Document 2] U.S. Patent No. 9,937,648 [Patent Document 3] U.S. Patent No. 6,294,122 [Patent Document 4] European Patent Application Publication No. 2679374 Summary of the Invention [Means for solving the problem]

[0010] The present disclosure addresses the need for utilizing electric actuators to control the position and movement of valve pins in hot runner injection molding apparatuses while providing a more compact apparatus that protects the actuators from overheating and does not require the use of a separate cooling plate or remote mounting of the actuators. The apparatus includes a hot runner manifold having a resin passage for conveying liquid resin from an injection molding machine toward a mold cavity, a nozzle for conveying the liquid resin from an outlet end of the resin passage to an inlet of the mold cavity, a valve pin configured for linear movement along a longitudinal axis of the nozzle to control the flow of liquid resin through the nozzle and into the mold cavity, and a direct-cooled electric actuator having an electric motor and a linear drive shaft, both housed within a body of the electric actuator, and the valve pin coupled directly or indirectly to the drive shaft such that linear movement of the drive shaft results in colinear movement of the valve pin.

[0011] A direct cooled electric actuator can be mounted in the space between the hot runner manifold and the upper mounting plate.

[0012] In one aspect of the present disclosure, a directly cooled electric actuator is directly and removably mounted to a support (e.g., stainless steel or titanium) that has a relatively high resistance to conductive heat transfer.

[0013] In certain embodiments, a directly cooled electric actuator includes a linear drive shaft and a transmission mechanism within the body of the actuator that converts rotational movement of the electric motor into translational movement of the drive shaft.

[0014] In certain aspects of the present disclosure, the linear drive shaft has an internally threaded bore extending along the length of the shaft, and the actuator body and / or housing has openings at both ends (e.g., top and bottom) to allow access to both ends of the threaded bore. With this arrangement, the upper end of the valve pin can extend upward into the internally threaded bore to engage an externally threaded valve pin nut. An externally threaded lock nut can be tightened against the valve pin nut on the opposite side of the valve pin to lock the position of the valve pin relative to the linear drive shaft.

[0015] The disclosed arrangement allows the actuators to be assembled onto the manifold along and coincident with the longitudinal axes of the nozzles and valve pins without requiring movement of the actuators laterally (i.e., radially) from the axis, thereby making it possible to design hot runner injection molding systems (i.e., apparatus) having multiple nozzles, valve pins, and actuators closer together than would otherwise be possible.

[0016] This arrangement allows the upper end of the valve pin (or valve pin extension) to be positioned within the drive shaft and thus within the body of the actuator, facilitating a vertically compact design. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is an elevational cross-section of an apparatus according to the present disclosure. [Figure 2] FIG. 2 is an enlarged view of the actuator and a portion of the hot runner manifold on which the actuator is supported. [Figure 3] FIG. 10 is a perspective view of the actuator support and mechanism for securing the valve pin to the linear drive shaft. [Figure 4] FIG. 10 is an enlarged cross-sectional view of an alternative embodiment in which the valve pin is indirectly coupled to the actuator drive shaft via a valve pin extension. DETAILED DESCRIPTION OF THE INVENTION

[0018] FIG. 1 shows a hot runner assembly 10 for use in delivering liquid resin (typically a molten thermoplastic composition) from an injection molding machine (not shown) to a mold cavity 12 defined by mold plates 14, 16. The resin flows from the injection molding machine into a channel 18 disposed within a sprue bushing 20 heated by an electrical resistance heating element 22 and is distributed through manifold channels 24 defined in a heated (or heatable) manifold 26. The heated manifold is equipped with an electrical resistance heating element 28 capable of maintaining the resin at a desired temperature to facilitate flow. From the manifold channels 24, the resin flows into an annular space 30 defined between an inner wall 32 of a nozzle 34 and a valve pin 36, which is linearly movable within the nozzle 34 along the vertical longitudinal axis of the nozzle between an open position (shown for the nozzle on the left in FIG. 1 ) and a closed position (shown for the nozzle on the right in FIG. 1 ). When the valve pin 36 is in the open position, the liquid resin flows into the mold cavity 12. The nozzle 34 is maintained at a temperature sufficient to keep the resin in a liquid (flowable) state by an electrical resistance heating element 38. The nozzle 34 may be provided with external threads 40 on the inlet end of the nozzle that engage internal threads of a bore through the bottom of the manifold 26 to provide a fluid-tight seal. The mold may define a single cavity or multiple cavities, and each cavity may be supplied with resin from a single nozzle or multiple nozzles.

[0019] The position and speed of movement of the valve pin 36 are controlled by an actuator 100. The actuator 100 includes a body and / or housing of an electric motor 101 and converts rotational movement of the electric motor into linear movement (up and down in FIG. 2 ) of a drive shaft 102, which illustratively has an elongated, internally threaded bore 104. Rotation of the motor 101, generally about an axis 105, can be connected to the linear movement of the drive shaft 102, such as by providing a threaded structure on the rotor of the electric motor 101 that engages external threads on the drive shaft 102. The extent of travel of the drive shaft 102 can be limited to the limits of the body of the actuator 100. The bore 104 has a central axis 105 that coincides with the central axis of the pin 36 and the nozzle 34. The body and / or housing of the actuator 100 has a bottom opening 107 and a top opening 109 that provide access to the threaded bore 104, allowing an externally threaded valve pin nut 106 to be threaded into the bore 104. A lock nut 108 can be threaded into the bore 104 through the top opening and adjusted to lock the position of the nut 106 and valve pin 36. The lower end of the nut 106 has an inwardly protruding semicircular rim 111 that engages a circumferential groove 112 at the upper end of the valve pin 36 to secure the valve pin 36 to the nut 106. An opening in the rim allows the valve pin 36 to be inserted into the nut 106. The threaded connection between the valve pin nut 106 and the drive shaft 102 can be replaced with a fixed or other connection between the shaft 102 and the nut 106, thereby eliminating the possibility of manually adjusting the valve pin position (as described below).

[0020] The nut 106 has a tool head engagement structure 114 that can be engaged by a tool such as a hex wrench to allow manual adjustment of the position of the nut 106 and pin 36. Similarly, the lock nut 108 has a tool head engagement structure 116 to allow a tool such as a hex wrench to be used to tighten the lock nut 108 against the valve pin nut 106. In the illustrated embodiment, the engagement structures 114 and 116 are hexagonal sockets; however, other shapes or tool engagement means are possible. The top plate 64 can be provided with an opening or bore 117 to allow access to the tool engagement structures (e.g., sockets 114, 116) to allow manual adjustment of the valve pin position without removing the plate 64 or disassembling the hot runner assembly 10.

[0021] Electrical connectors 118, 120 are provided for powering and controlling the electric motor and for receiving signals from an encoder which operates to track drive shaft position.

[0022] A coolant inlet port 122 and a coolant outlet port 124 are provided to allow coolant (e.g., chilled water or oil) to be circulated through the body and / or housing of the actuator to protect the motor from deterioration or failure caused by overheating.

[0023] The actuator 100 may be supported on an insulating support member 126. The support 126 may, and preferably does, have a relatively low thermal conductivity. Preferred materials for the member 126 are stainless steel and titanium, or other materials with thermal conductivities equal to or less than that of titanium. The support 126 may be removably secured to the manifold 26 with screws or bolts (not shown), or the like.

[0024] When assembled, the upper end of the valve pin 36 extends through openings in the manifold 26 and support 126 and the body or housing of the actuator 100 into the bore 104 to provide a vertically compact design for the device 10 .

[0025] An anti-rotation plate or guide 130 can be removably secured to the support 126 with bolts 132. The plate 130 has an opening 134 for passing the valve pin 36. The opening 134 has a shape configured to engage a cross-section of the valve pin 36, which has a non-circular profile, to prevent rotation of the pin about the longitudinal axis of the pin 36 and nozzle 34. In the illustrated embodiment, the non-circular profile includes two opposing flat or planar surfaces 136 (one of which is shown in FIG. 3 ). While the flat surfaces 136 are engaged by a straight edge of the opening 134 in the illustrated embodiment, other anti-rotation means can be provided, such as splines, grooves, and other structures capable of preventing rotation of the valve pin 36.

[0026] The manifold 26 and actuator 100 are located in a space generally bounded by the upper mold plate 64 and the middle mold plate 66 .

[0027] The assembly 10 may also include various lower support elements 68, dowels 70, and upper support elements 72 to facilitate proper alignment and spacing of the components of the assembly.

[0028] The pin seals 138 prevent liquid resin from leaking upwardly from the passages 24 of the manifold 26 .

[0029] The disclosed device allows the valve pin to be adjusted from the back side of the actuator (opposite the valve pin or valve pin extension side) using a special tool / wrench or the like.

[0030] The disclosed device can allow for axial coupling and decoupling of a cooled actuator to a valve pin.

[0031] The valve pin can be suspended within the height of the actuator.

[0032] The disclosed apparatus can also allow a cooled actuator to be mounted axially to the valve pin on an insulating support that directly contacts the hot runner manifold, where the support can protrude along the corners of the actuator.

[0033] FIG. 4 is an alternative arrangement in which the valve pin 36 is indirectly coupled to the drive shaft 102 (rather than directly as shown in FIGS. 1 and 2) by a valve pin extension 140.

[0034] The actuator 100 can be installed and coupled to the valve pin 36 axially, i.e., without moving the actuator laterally away from the axis 105. This can be achieved by first positioning the valve pin through the manifold and into the associated nozzle so that the upper end of the valve pin protrudes upward from the top of the manifold (i.e., the surface opposite the surface from which the nozzle extends). The support 126 can then be attached (e.g., with a screw) to the manifold, and an anti-rotation plate 130 can be positioned around the valve pin 36 and secured to the support with a bolt 132. Next, the nut 106 can be positioned onto the head (top end) of the valve pin 36. The actuator 100 is then positioned so that the bore of the drive shaft 110 is axially aligned with the valve pin. The tool-engaging structure of the nut 106 can then be accessed with a tool that rotates the nut 106 and threaded nut 108 through the top opening 109 of the actuator 100 into the threaded bore 104 of the drive shaft 102 .

[0035] The above description is intended to be illustrative, not limiting. The scope of the invention should be determined with reference to the appended claims, along with their full scope of equivalents. It is anticipated and intended that future developments will occur in the art, and that the disclosed devices, kits, and methods will be incorporated into such future embodiments. Accordingly, the present invention is capable of modification and variation, and is limited only by the scope of the following claims.

Claims

[Claim 1] 1. An injection molding apparatus comprising: a manifold defining a resin flow path for conveying liquid resin from the injection molding machine toward the mold cavity; a nozzle for conveying liquid resin from the resin channel to the mold cavity; a valve pin configured for linear movement along a longitudinal axis of the nozzle to control the flow of liquid resin through the nozzle; an electric actuator having a body containing an electric motor and a linear drive shaft having a bore, both the electric motor and the linear drive shaft being housed within the body of the electric actuator, the valve pin being directly or indirectly coupled to the drive shaft within the bore so that linear movement of the drive shaft causes co-linear movement of the valve pin, the bore through the drive shaft being internally threaded, the valve pin being directly or indirectly coupled to the drive shaft via an externally threaded valve pin nut threadably engaged with the internally threaded bore, the valve pin nut having tool head engagement structure for manually positioning the valve pin and valve pin nut relative to the drive shaft, and the device threadably engaging the internally threaded bore and the valve pin nut. an externally threaded lock nut located adjacent a side of the valve pin nut opposite a valve pin, the lock nut having a tool head engaging structure for manually tightening the lock nut against the valve pin nut; the electric actuator is mounted on a support attached to the manifold, and an anti-rotation plate located between a bottom of the support and the electric actuator and removably attached to the bottom of the support, the anti-rotation plate having an opening for allowing the valve pin to pass therethrough, the opening having a shape configured to engage with a cross-section of the valve pin having a non-circular profile to prevent rotation of the pin about the longitudinal axis of the nozzle.

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